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ABSTRACT
ZUBAIR, MUHAMMAD. A Diagnostic Expert System for the Coloration of Textile Fiber Blends.
(Under the direction of Dr. Renzo Shamey).
Materials based on fiber blends are among the most common textile products and they are
projected to continue to expand. The coloration of textile fiber blends, however, is challenging
when compared to single fiber materials. This is due to differences in the dyeing behavior of the
fiber components of the blend. The colorant class and application conditions required for one fiber
may damage or not be suitable for the other component in the blend. Th colorants may cross-stain
the fiber they are not designed for, and moreover there is a possibility of physical and chemical
interaction between different colorant classes and chemicals used during the process. These issues
increase the complexity of the coloration of fiber blends. With an increasing demand for the right-
first-time dyeing approach to reduce costs and remain competitive, the need to producing dyed
materials that are free of faults and possess suitable levels of quality, at an affordable cost, is more
apparent.
Troubleshooting problems in the coloration of blends is a difficult task considering the
large numbers of factors involved. The determination of the exact cause of the problem can be
very difficult. Dyehouses usually utilize human experts to troubleshoot problems. Such experts are
often able to considerably reduce the number of probable causes involved. In some cases, however,
the determination of the actual cause of the problem requires a detailed analysis. Over the years
the availability of human expertise in the domain of textile coloration has declined considerably
and experts have become rather scarce.
An Expert System is a computer program that can be used to mimic the knowledge and
experience of human experts in troubleshooting problems in various domains. The goal of the
present study is to develop a functional knowledge-based expert system for troubleshooting
problems in the coloration of fiber blends (DEXPERT-B). The system was developed in three
phases; Phase I involved the identification of common blends and knowledge acquisition. Phase
II covered the design and development of the system and in Phase III testing and evaluation of the
system were performed.
Polyester/cellulosic (PES/CELL) blends are among the most common and widely used
fiber blends in textiles. This blend type was identified and selected based on trade statistics and
published literature. The most common problems in the coloration of these blends in different
material forms (e.g. yarn, knitted and woven fabrics) with various colorants classes (pigment,
disperse, reactive, direct, vat and sulfur dyes), utilizing different coloration process (batch, semi-
continuous and continuous), methods (one bath, two bath) and corresponding coloration machines
was reviewed in detail. This was achieved through a survey of technical literature and interviews
with practical dyers. Based on the knowledge base gathered, an electronic survey comprising
common coloration faults and their potential causes in the PES/CELL blends was developed. The
survey was employed to acquire specialized knowledge from coloration experts. The experts’
responses were analyzed and used to complement the knowledge base. The expert system shell
was developed using wxCLIPS which is the modified version of the C Language Integrated
Production System (CLIPS) to provide a custom GUI functionality.
The system was verified, validated and evaluated using human experts. Several faulty dyed
samples were obtained from production mill and used for the assessment of the comparative
performance of human experts and expert system in identification of the type and root causes of
faults. The test results showed good performance of the expert system when compared to human
experts. This system is developed for use in actual production settings for the diagnosis of common
coloration problems in the PES/CELL blends. With the aid of the expert system the number of
probable causes for a particular problem can be isolated and reduced considerably. The developed
system has a potential utility for use as an educational and training tool for novice and practical
dyers. DEXPERT-B can help practical dyers in a quick resolution of problems by identifying
causes and recommending solutions to problems which can help improve the efficiency of the
coloration of PES/CELL blends.
© Copyright 2020 by Muhammad Zubair
All Rights Reserved
A Diagnostic Expert System for the Coloration of Textile Fiber Blends
by
Muhammad Zubair
A dissertation submitted to the Graduate Faculty of
North Carolina State University
in partial fulfillment of the
requirements for the degree of
Doctor of Philosophy
Fiber and Polymer Science
Raleigh, North Carolina
2020
APPROVED BY:
_______________________________ _______________________________
Dr. Renzo Shamey Dr. Jeffrey Joines
Chair of Advisory Committee
_______________________________ _______________________________
Dr. George Hodge Dr. Peter Bloomfield
ii
DEDICATION
To my lovely wife and our son playing in heaven.
iii
BIOGRAPHY
Muhammad Zubair was born in Karachi, Pakistan, the largest metropolitan city and
financial hub of the country. He completed his Bachelor and Masters in Textile Engineering from
NED University of Engineering & Technology (NEDUET), Karachi in 2007 and 2009
respectively. He worked for one year in a dyehouse where he was involved in troubleshooting and
R&D. Later, he joined NEDUET as Lecturer where he was responsible for both advising and
teaching undergraduate students. In 2011, he was selected for Fulbright scholarship for Ph.D. at
North Carolina State University, Wilson College of Textiles.
His main research interests include sustainable processes in textile coloration, color
evaluation, and color management.
iv
ACKNOWLEDGMENTS
I express my sincere gratitude to Dr. Renzo Shamey for the invaluable guidance,
mentorship, encouragement, support and regular technical feedback he has given me throughout
this work and introducing me to the fascinating world of color; and Dr. Jeff Joines for his guidance
and great support in developing my programming skills.
I would also like to thank Dr. George Hodge and Dr. Peter Bloomfield for their valuable
suggestions.
I am extremely grateful to the US Department of State and Institute of International
Education (IIE) for awarding me Fulbright scholarship. I would also like to extend my gratitude
to Graduate School, Department of Textile Engineering Chemistry and Science (TECS) and Dr.
Renzo Shamey for their financial support.
I am very thankful to Mr. Jeff Krauss for his help and insightful discussions during dyeing
experiments and Mr. Brian Davis for help in producing knitting samples. I am also grateful to Mr.
Atiq-ur-Rehman and Mr. Idrees Shaikh for providing faulty dyed samples, Ms. Cheryl Smyre
(Parkdale Mills), Mr. Bryan Dill (Archroma), Mr. Mike Cheek (Huntsman), and Mr. Julian
Metcalfe (Dystar) for providing required materials for dyeing experiment. In addition, I would also
like to thank all dyeing experts who took part in the survey and assessment of faulty dyed samples.
Special thanks to my friends in Raleigh and Karachi: Zohaib, Ali, Owais, Raza and
Maqbool bhai for making my time memorable and helping me in difficult times.
Finally, I would like to thank my wife and parents for their patience, understanding,
motivation, and encouragement.
v
TABLE OF CONTENTS
LIST OF TABLES ......................................................................................................................... ix
LIST OF FIGURES .......................................................................................................................xv
CHAPTER 1 INTRODUCTION ..................................................................................................1
1.1 Background ......................................................................................................................... 1
1.2 Statement of the problem and goals .................................................................................... 2
1.3 Research methodology ........................................................................................................ 6
CHAPTER 2 TEXTILE FIBER BLENDS ...................................................................................8
2.1 Introduction ......................................................................................................................... 8
2.2 History of blends ................................................................................................................. 8
2.2.1 Blends of natural fibers ............................................................................................. 9
2.2.2 Blends of manufactured fibers .................................................................................. 9
2.3 Global fiber market and blends ......................................................................................... 12
2.4 Purpose of blending .......................................................................................................... 19
2.5 Types of fiber blends ........................................................................................................ 20
2.6 Properties of blended yarns and fabrics ............................................................................ 23
2.6.1 Compatibility of fibers in the blend ........................................................................ 24
2.6.2 Effect of blend ratio ................................................................................................ 26
2.6.3 Blending and resultant properties ........................................................................... 28
2.7 Polyester/cellulosic blends ................................................................................................ 31
2.8 Other common blends ....................................................................................................... 35
2.8.1 Polyester/wool blends ............................................................................................. 35
2.8.2 Polyamide/cellulosic blends.................................................................................... 35
2.8.3 Elastane blends........................................................................................................ 36
2.8.4 Microfiber blends .................................................................................................... 36
2.9 Application classes of fiber blends ................................................................................... 37
2.9.1 Intimate yarn blends ................................................................................................ 37
2.9.2 Bulked yarns ........................................................................................................... 37
2.9.3 Composite yarns...................................................................................................... 37
2.9.4 Structurally blended yarns ...................................................................................... 37
2.9.5 Structurally designed hawsers ................................................................................. 38
2.9.6 Structurally blended fabrics .................................................................................... 38
2.9.7 Filling material blends ............................................................................................ 38
2.9.8 Biomaterial blends .................................................................................................. 39
2.9.9 Static controlling blends ......................................................................................... 39
2.9.10 Apparel blends ........................................................................................................ 39
2.10 Manufacturing/production of blended textiles .................................................................. 39
2.10.1 Fiber distribution in blended yarns ......................................................................... 41
CHAPTER 3 COLORATION OF TEXTILE FIBER BLENDS ...............................................43
3.1 Introduction ....................................................................................................................... 43
3.2 Classification of blends according to their dyeing behavior ............................................. 43
3.3 Color effects produced on blends ..................................................................................... 45
3.4 Factors affecting the dyeing of fiber blends ..................................................................... 48
vi
3.5 Challenges in the coloration of fiber blends ..................................................................... 48
3.5.1 Cross-staining of the fiber by the dye intended for the other fiber type ................. 49
3.5.2 Fastness problems ................................................................................................... 50
3.5.3 Interaction between dye classes and dyebath auxiliaries ........................................ 51
3.5.4 Dye stability at high temperature and pH conditions .............................................. 52
3.5.5 Effect of additional processing required to fix the dye class .................................. 53
3.5.6 Effective liquor ratio and blend ratio ...................................................................... 53
3.5.7 Distribution of single dye and fiber saturation differences ..................................... 54
3.5.8 Obtaining solid shade in the blend by matching shade of an individual fiber type 55
3.5.9 Fiber damage and/or yellowing .............................................................................. 56
3.6 Coloration of polyester/cellulosic blends .......................................................................... 56
3.7 Pigment coloration ............................................................................................................ 59
3.7.1 Pigment preparations .............................................................................................. 62
3.7.2 Binders .................................................................................................................... 66
3.7.3 Auxiliaries ............................................................................................................... 71
3.7.4 Combined pigment coloration and finishing ........................................................... 75
3.7.5 Application method ................................................................................................. 75
3.7.6 Equipment ............................................................................................................... 79
3.8 Dyeing of polyester/cellulosic blends using a two-dye system ........................................ 79
3.8.1 Dye classes used for polyester/cellulosic blends .................................................... 79
3.8.2 Batch dyeing of polyester/cellulosic blends ........................................................... 93
3.8.3 Continuous dyeing of polyester/cellulosic blends .................................................. 99
CHAPTER 4 PRACTICAL PROBLEMS IN THE COLORATION OF TEXTILE FIBER
BLENDS ............................................................................................................................106
4.1 Introduction ..................................................................................................................... 106
4.2 Troubleshooting faults in coloration ............................................................................... 109
4.3 Dyeing problems arising from the fiber .......................................................................... 115
4.4 Problems arising from yarn formation ............................................................................ 137
4.4.1 Faults caused by spun yarns .................................................................................. 139
4.4.2 Faults due to filament yarns .................................................................................. 153
4.4.3 Problems due to the winding process.................................................................... 160
4.4.4 Problems due to conditioning ............................................................................... 172
4.5 Problems arising from fabric formation .......................................................................... 173
4.5.1 Yarn preparation for fabric formation ................................................................... 173
4.5.2 Weaving faults ...................................................................................................... 179
4.5.3 Knitting faults ....................................................................................................... 191
4.6 Problems caused by water ............................................................................................... 206
4.7 Problems caused due to pretreatment ............................................................................. 219
4.7.1 Problems caused during singeing.......................................................................... 223
4.7.2 Problems caused during desizing .......................................................................... 230
4.7.3 Problems caused during scouring ......................................................................... 239
4.7.4 Problems caused during bleaching ........................................................................ 244
4.7.5 Problems caused during weight reduction ............................................................ 256
4.7.6 Problems caused during mercerization and causticization ................................... 256
4.7.7 Problems caused during heat setting ..................................................................... 265
4.8 Problems in coloration .................................................................................................... 270
vii
4.8.1 Reproducibility in the dyeing of fiber blends ....................................................... 271
4.8.2 Problems caused in batch dyeing machines .......................................................... 274
4.8.3 Problems caused in continuous dyeing machines ................................................. 301
4.9 Problems in pigment coloration ...................................................................................... 326
4.9.1 Fastness of pigment colored fabrics ...................................................................... 330
4.10 Problems in the dyeing of polyester/cellulosic blends .................................................... 345
4.10.1 Disperse/reactive system ....................................................................................... 347
4.10.2 Disperse/direct system .......................................................................................... 374
4.10.3 Disperse/vat system .............................................................................................. 378
4.10.4 Disperse/sulfur system .......................................................................................... 388
CHAPTER 5 EFFECT OF BLEND RATIO ON DYEING PROPERTIES OF
POLYESTER-COTTON BLENDED FABRICS ........................................................................392
5.1 Introduction ..................................................................................................................... 392
5.2 Experimental ................................................................................................................... 395
5.2.1 Materials ............................................................................................................... 395
5.2.2 Methods................................................................................................................. 398
5.2.3 Evaluation methods ............................................................................................... 403
5.3 Results and discussion .................................................................................................... 404
5.3.1 Amount of dye required to match a target color ................................................... 404
5.3.2 Light fastness ........................................................................................................ 410
5.3.3 Crocking fastness .................................................................................................. 412
5.3.4 Washing fastness ................................................................................................... 415
5.3.5 Water fastness ....................................................................................................... 421
5.4 Conclusions ..................................................................................................................... 426
CHAPTER 6 DESIGN AND DEVELOPMENT OF AN EXPERT SYSTEM .......................428
6.1 Experts and expert systems ............................................................................................. 428
6.2 Benefits of expert systems .............................................................................................. 430
6.3 Domains of expert system ............................................................................................... 430
6.4 Application of expert systems in the textile industry ...................................................... 431
6.5 Components of an expert system .................................................................................... 435
6.6 Knowledge base .............................................................................................................. 436
6.6.1 Selection of most common coloration faults ........................................................ 438
6.6.2 Identification of common causes of coloration problems in PES/CELL blends .. 449
6.6.3 Knowledge acquisition.......................................................................................... 469
6.6.4 Analysis of expert responses ................................................................................. 472
6.7 Construction of a diagnostic expert system for dyeing of fiber blends (DEXPERT-B) . 479
6.7.1 Expert system building tool .................................................................................. 481
6.7.2 Knowledge representation .................................................................................... 482
6.8 Inference engine .............................................................................................................. 484
6.8.1 Effect of blend ratio .............................................................................................. 491
6.9 User interface .................................................................................................................. 494
6.9.1 Material function ................................................................................................... 495
6.9.2 Coloration function ............................................................................................... 496
6.9.3 Symptom function ................................................................................................. 497
6.9.4 Explanation function ............................................................................................. 501
6.10 Using the designed expert system ................................................................................... 502
viii
CHAPTER 7 TESTING AND EVALUATION OF AN EXPERT SYSTEM .........................504
7.1 Testing of the expert system ........................................................................................... 504
7.1.1 Verification ........................................................................................................... 505
7.1.2 Validation .............................................................................................................. 506
7.2 Evaluation of the expert system ...................................................................................... 514
CHAPTER 8 CONCLUSIONS AND FUTURE WORK ........................................................520
8.1 Conclusions ..................................................................................................................... 520
8.2 Recommendations for future work ................................................................................. 522
REFERENCES ............................................................................................................................525
APPENDICES ............................................................................................................................546
Mean expert responses for symptoms and their causes. ................................ 547
Questions related to various causes for diagnosis of symptom(s). ................ 563
DEXPERT-B installation guide..................................................................... 575
Analysis of the expert responses of the faulty colored samples. ................... 576
ix
LIST OF TABLES
Table 2.1: Global fiber use for the year 2013. ............................................................................13
Table 2.2: Summary of common textile fiber blends and their potential applications. ..............22
Table 2.3: Primary and secondary properties of textile fibers. ...................................................24
Table 3.1: Classification of binary blends according to their dyeing properties [9]. .................44
Table 3.2: Color effects in binary blends [9]. .............................................................................46
Table 3.3: Methods for dyeing of fiber blends. ..........................................................................47
Table 3.4: Effect of blend ratio on effective liquor ratios in the dyeing of blends. ....................54
Table 3.5: Characteristics of colorants for polyester/cellulosic blends. .....................................57
Table 3.6: Comparison of one bath and two bath methods used for dyeing of PES/CELL
blends. ........................................................................................................................59
Table 3.7: Advantages and limitations of pigment coloration. ...................................................60
Table 3.8: Comonomer types and polymer properties. ...............................................................70
Table 3.9: Factors affecting staining of cellulose by disperse dyes. ..........................................87
Table 3.10: Dyeing properties of reactive and disperse dyes [136]. ..........................................104
Table 4.1: Typical finished fabric quality levels [139]. ............................................................106
Table 4.2: Dyeing costs associated with not meeting the specifications. .................................107
Table 4.3: Classification of faults. ............................................................................................109
Table 4.4: Relationship between fiber properties and spun yarn characteristics. .....................116
Table 4.5: Factors affecting the dyeing behavior of cotton. .....................................................119
Table 4.6: Dyeing problems attributed to fiber. .......................................................................128
Table 4.7: Yarn classification. ..................................................................................................137
Table 4.8: Effect of different spinning operations on yarn properties. .....................................140
Table 4.9: Influence of yarn parameters on fabric properties ...................................................151
Table 4.10: Common problems related to spun yarns. ...............................................................152
x
Table 4.11: Effect of texturizing process parameters on yarn properties. ..................................155
Table 4.12: Problems due to filament yarn faults. ......................................................................159
Table 4.13: Types of winding systems. ......................................................................................165
Table 4.14: Problems caused by the winding process. ...............................................................169
Table 4.15: Objectives of the yarn preparation processes and associated fabric defects. ..........176
Table 4.16: Problems in woven fabrics their causes and countermeasures. ...............................181
Table 4.17: Causes and remedies of frequent problems in knitted fabrics. ................................194
Table 4.18: Sources of water and their constituents. ..................................................................206
Table 4.19: Requirements of water for textile processing units. ................................................207
Table 4.20: Problems in wet processing associated with water impurities. ...............................212
Table 4.21: Requirements to be fulfilled by pretreatment. .........................................................220
Table 4.22: Possible steps in the preparation of blended materials. ...........................................222
Table 4.23: Problems caused during singeing, its causes and remedial measures. ....................224
Table 4.24: Sizing agents and their removal processes. .............................................................231
Table 4.25: Problems caused during desizing, its causes and remedial measures. ....................233
Table 4.26: Problems caused during scouring, its causes and remedial measures. ....................241
Table 4.27: Bleaching agents and their suitability for different fibers. ......................................244
Table 4.28: Problems caused during bleaching, its causes and remedial measures. ..................247
Table 4.29: Problems in mercerization and causticization and possible solutions. ....................259
Table 4.30: Problems caused during heat setting, its causes and remedial measures. ...............267
Table 4.31: Main objectives of the dyeing process. ...................................................................270
Table 4.32: Important factors affecting reproducibility in the batch dyeing of fiber blends. .....272
Table 4.33: Dyehouse factors and associated tolerances. ...........................................................272
Table 4.34: Factors affecting continuous dyeing of PES/CELL blends by the continuous
method. ....................................................................................................................273
Table 4.35: Important characteristics of different batch dyeing machines. .................................275
xi
Table 4.36: Dyeing faults due to package dyeing machine. .......................................................278
Table 4.37: Dyeing problems related to batch dyeing machines and their countermeasures. ....287
Table 4.38: Different sequences used in the dyeing of blends by semi-continuous and
continuous process. ..................................................................................................302
Table 4.39: Migration in intermediate drying and associated faults. .........................................306
Table 4.40: Suitability of thermofixation conditions for different synthetic fibers. ...................309
Table 4.41: Dyeing problems in continuous dyeing machines and their countermeasures. .......311
Table 4.42: Pigment dyeing components and their corresponding effect on dyed fabric. .........328
Table 4.43: Problems in pigment coloration and possible solutions. .........................................334
Table 4.44: Problems and their possible solutions in the dyeing of polyester/cellulose
blends using a disperse/reactive system. .................................................................348
Table 4.45: Problems and their possible solutions in the dyeing of polyester/cellulose
blends with disperse and direct dyes. ......................................................................375
Table 4.46: Problems and their possible solutions in the dyeing of polyester/cellulose
blends using disperse/vat system. ............................................................................379
Table 4.47: Dyeing problems associated with disperse/sulfur system. ......................................388
Table 5.1: Properties of yarns and fabric codes. .......................................................................395
Table 5.2: List of chemicals and auxiliaries. ............................................................................396
Table 5.3: Properties of disperse dyes used in the study. .........................................................396
Table 5.4: Characteristics of reactive dyes used in the study. ..................................................397
Table 5.5: CIE whiteness and tint indices of fabrics after pretreatment. ..................................398
Table 5.6: Dye combinations used to match target colors using different dyeing methods. ....399
Table 5.7: Total amounts of dye required to match the target colors in fabrics of different
blend ratio using different dyeing methods. ............................................................405
Table 5.8: The effective liquor ratio for each fiber in the blend at a bath liquor ratio of
20. ............................................................................................................................406
Table 5.9: Light fastness results of polyester, cotton and their blends dyed in different
shade depths. ............................................................................................................411
xii
Table 5.10: Dry crocking fastness of fabrics of different colors and blend ratio dyed by
different dyeing methods. ........................................................................................413
Table 5.11: Wet crocking fastness results of polyester, cotton and their blends. .......................414
Table 5.12: Wash fastness properties of dyed polyester, cotton and polyester/cotton
fabrics. .....................................................................................................................416
Table 5.13: Water fastness of dyed polyester/cotton fabrics with different blend contents. ......422
Table 6.1: Characteristics of experts. .......................................................................................428
Table 6.2: Human expert versus the expert system. .................................................................429
Table 6.3: Categories of expert systems. ..................................................................................431
Table 6.4: Summary of the expert systems developed for textiles. ..........................................433
Table 6.5: Categorized list of possible causes associated with symptoms in the coloration
of polyester/cellulosic materials. .............................................................................462
Table 6.6: Sorting of causes into different categories based on their origin, ...........................469
Table 6.7: An example of different analytical methods that can be applied to aggregate
expert responses in two different scenarios (E=Expert). .........................................474
Table 6.8: List of causes associated with the reproducibility symptom after being
prioritized based on the weighted CFs obtained from experts (E represents
expert). .....................................................................................................................475
Table 6.9: Analysis of causes according to category and commonness. ..................................479
Table 6.10: Possible causes for S15 and weighted average CF. .................................................488
Table 6.11: Possible causes for S16 and weighted average CF. .................................................488
Table 6.12: Causes for S17 and weighted average CF. ..............................................................489
Table 6.13: The new salience values of the all the cause asserted for S15-S17. .........................490
Table 6.14: Mostly likey causes for S1 reproducibility with existing and new salience
values as the blend ratio is increased. ......................................................................493
Table 7.1: Expert responses and expert system’s knowledge base for presence of holes
and tears (S15). ........................................................................................................507
Table 7.2: Responses from human experts and the expert system for poor color yield
(S4). .........................................................................................................................509
xiii
Table 7.3: Responses from human experts and the expert system for widthwise shade
variation in pigment coloration (S10). .....................................................................512
Table 7.4: Evaluation results of the expert system. ..................................................................515
Table 7.5: Comparison of diagnosis of faulty colored samples, human vs expert system. ......517
Table 7.6: Diagnosis results of human experts and DEXPERT-B. ..........................................518
Table A.1: Mean responses of experts for symptoms and their causes related to dyes. ............547
Table A.2: Mean response of experts for symptoms and their causes related to pigments .......558
Table B. 1: Questions to user related to various causes for diagnosis. ......................................563
Table D.1: Expert responses and expert system’s knowledge base for reproducibility (S1). ...576
Table D.2: Expert responses and expert system’s knowledge base for unlevelness (S2). ........582
Table D.3: Expert responses and expert system’s knowledge base for streaks (S3). ................588
Table D.4: Expert responses and expert system’s knowledge base for shade change (S5). .....591
Table D.5: Expert responses and expert system’s knowledge base for inadequate washing
fastness (S6). ............................................................................................................595
Table D.6: Expert responses and expert system’s knowledge base for dark stains or spots
(S7). .........................................................................................................................598
Table D.7: Expert responses and expert system’s knowledge base for light stains or sports
(S8). .........................................................................................................................601
Table D.8: Expert responses and expert system’s knowledge base for lengthwise shade
variation (S9). ..........................................................................................................603
Table D.9: Expert responses and expert system’s knowledge base for shade variation
within layers (S11). .................................................................................................606
Table D.10: Expert responses and expert system’s knowledge base for two sidedness
(S12). .......................................................................................................................610
Table D.11: Expert responses and expert system’s knowledge base for reduced strength
(S13). .......................................................................................................................611
Table D.12: Expert responses and expert system’s knowledge base for irregular surface
appearance (S14). ....................................................................................................612
Table D.13: Expert responses and expert system’s knowledge base for poor hand (S16). .........614
xiv
Table D.14: Expert responses and expert system’s knowledge base for poor dimensional
stability (S17). .........................................................................................................615
xv
LIST OF FIGURES
Figure 2.1: World fiber production for the year 2013. .................................................................14
Figure 2.2: Global consumption of textile fibers by end-use. ......................................................15
Figure 2.3: Cotton content in the cotton yarn-world average. .....................................................16
Figure 2.4: Material distribution of yarn blends in the short-staple spinning system. .................17
Figure 2.5: Share of major fiber blends in dyeing processes. ......................................................18
Figure 2.6: Stress-stain curves of Pima cotton, regular and high tenacity polyester fibers
used in blended yarns [49]. ........................................................................................26
Figure 2.7: Effect of polyester levels in PES/CO blends on abrasion resistance and
wrinkle recovery properties of fabric [51]. ................................................................27
Figure 2.8: Properties of different fibers in the blend [54]. .........................................................29
Figure 2.9: Property spectrum of different fiber blends with optimum blend proportions
[54]. ...........................................................................................................................31
Figure 2.10: Variation in yarn strength of PES/CO as a function of polyester content [8]. ..........32
Figure 2.11: Variation in moisture regain properties of PES/CO fabrics with polyester
content [60]. ...............................................................................................................33
Figure 2.12: Fiber distribution in the blended yarns produced by sliver and flock blending
methods [74]. .............................................................................................................42
Figure 3.1: Staining of different fibers by disperse dyes during the dyeing process [80]. ..........50
Figure 3.2: Continuous pigment coloration process. ...................................................................61
Figure 3.3: Binder film formation and fixation mechanism. .......................................................67
Figure 3.4: Relationship between curing temperature and time. .................................................78
Figure 3.5: Batch dyeing system for polyester/cellulosics blends. ..............................................94
Figure 4.1: Fault investigation process in a dyehouse. ..............................................................111
Figure 4.2: Cause and effect model for investigating faults in the dyed fabric. ........................115
Figure 4.3: Factors influencing the spinning process of polyacrylonitrile fibers. .....................124
Figure 4.4: Steps involved in woven and knitted fabric production. .........................................175
xvi
Figure 4.5: Aspects of fabric quality. .........................................................................................180
Figure 4.6: Fabric quality assurance. .........................................................................................180
Figure 4.7: Continuous dyeing range for PES/CELL blends. ....................................................302
Figure 4.8: Schematic representation of migration types during intermediate drying (G
represents the direction of fabric movement). .........................................................305
Figure 4.9: Binder to pigment ratio and fastness properties. .....................................................331
Figure 4.10: Pigment coloration fixation conditions. ..................................................................333
Figure 5.1: Clearing mechanism of disperse dye stain [383]. ....................................................394
Figure 5.2: Simulations of Pantone colors used as target colors. ..............................................399
Figure 5.3: Dyeing profiles of different dyeing methods used. .................................................402
Figure 5.4: The effect of liquor ratio on the relative strength of cotton dyed with reactive
dyes (Liquor ratio of 20 is taken as the reference). .................................................409
Figure 5.5: The effect of liquor ratio on the relative strength of polyester dyed with
disperse dyes (Liquor ratio of 20 is taken as reference). .........................................410
Figure 5.6: Color change ratings for the navy blue color dyed fabrics after the washing
test. ...........................................................................................................................420
Figure 5.7: Nylon staining results for the navy blue color dyed fabrics. ...................................420
Figure 5.8: Cotton staining results of the navy blue color dyed fabrics. ...................................421
Figure 5.9: Grey scale rating for staining of nylon for the brown color after water fastness
test. ...........................................................................................................................425
Figure 5.10: Grey scale rating for staining of cotton for the brown color after water fastness
test. ...........................................................................................................................426
Figure 6.1: Components of an expert system [16]. ....................................................................436
Figure 6.2: Schematic of developing knowledgebase by a knowledge engineer. ......................437
Figure 6.3: A list of common faults in the coloration of polyester/cellulosic blends. ...............438
Figure 6.4: An example of reproducibility issues where the reproduced color from a new
dyed batch in not consistent with the original shade. ..............................................439
Figure 6.5: An example of unlevelness. .....................................................................................440
xvii
Figure 6.6: An example of bands in fabric. ................................................................................440
Figure 6.7: An example of low color yield (on the right) compared to the standard (left). .......441
Figure 6.8: An example of shade change. ....................................................................................441
Figure 6.9: An example of a dyed sample and a stained multifiber strip after the washing
test. ...........................................................................................................................442
Figure 6.10: An example of dark stains. ......................................................................................442
Figure 6.11: An example of light stains. ......................................................................................443
Figure 6.12: An example of lengthwise shade variation. .............................................................444
Figure 6.13: An example of widthwise shade variation (note the fabric is folded on itself). ......444
Figure 6.14: An example of shade variation within layers in a yarn package. ............................445
Figure 6.15: An example of two sidedness. .................................................................................445
Figure 6.16: An example of fabric with reduced strength. ..........................................................446
Figure 6.17: An example of crease marks. ..................................................................................447
Figure 6.18: An example of holes (left) and tears (right). ...........................................................447
Figure 6.19: an example of fabric with a poor hand. ...................................................................448
Figure 6.20: A symbolic representation of poor dimensional stability of the fabric. ..................448
Figure 6.21: A symbolic representation of the coating of rollers during pigment coloration. ....449
Figure 6.22: Cause and effect diagram for faults in the dyeing of fiber blends. ..........................451
Figure 6.23: Possible causes originating from the measurement. ................................................453
Figure 6.24: Possible causes originating from the machinery. ....................................................454
Figure 6.25: Possible causes originating from the materials. ......................................................457
Figure 6.26: Possible causes originating from method. ...............................................................458
Figure 6.27: Possible causes originating from the environment. .................................................459
Figure 6.28: Possible causes originating from human-related factors. ........................................461
Figure 6.29: A screenshot of the electronic survey distributed to experts in spreadsheet
format ......................................................................................................................471
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Figure 6.30: System architecture of DEXPET-B. ........................................................................481
Figure 6.31: Knowledge representation in DEXPERT-B in the form of rules. ...........................484
Figure 6.32: The main screen for the DEXPERT-B system. .......................................................495
Figure 6.33: Interface for the selection of material related information. .....................................496
Figure 6.34: Interface for the selection of the coloration process in DEXPET-B. ......................497
Figure 6.35: The user interface containing images of the faulty dyed PES/CELL yarns. ...........498
Figure 6.36: The user interface containing images of the faulty dyed PES/CELL knitted
fabric. .......................................................................................................................499
Figure 6.37: The user interface containing images of the faulty dyed polyester/cotton
woven fabric. ...........................................................................................................499
Figure 6.38: Diagnosis interface for woven fabric dyed by batch process using one bath
process in a jet dyeing machine. ..............................................................................500
Figure 6.39: An example of the diagnosis function with a question prompt based on the
selected symptom. ...................................................................................................501
Figure 6.40: Example of explanation function for DEXPET-B. ..................................................502
Figure 6.41: An example of the use of DEPXET-B system for diagnosis. .................................503
1
CHAPTER 1 INTRODUCTION
1.1 Background
Textiles and clothing constitute one of the basic necessities of human beings and are among the
most important trade commodities. They are often colored to increase their aesthetic appeal, as
color is one of the primary factors that directly influences the sale of the product. The world of
fashion may not be conceivable in the absence of color. Another reason to impart color to textiles
is for a functional purpose such as for camouflage. The process of imparting color to textiles is
very old [1, 2]. Approximately 75-80% of textile products comprise colored materials [3]. The
coloration is therefore considered as one of the most important processes in the textile industry.
The process of imparting color to the substrate using either dyes or pigments is known as
coloration. This can be achieved through a process of dyeing or printing. Dyeing involves a
uniform application of color while printing deals with localized color application. During the
dyeing process, the uniform adsorption and distribution of dyes inside the fiber takes place. This
excludes pigments, which are generally attached to the fiber surface with the help of binders or via
a process known as spun dyeing. The main objective of the dyeing process is to obtain a correct
shade that matches a target color, with a uniform distribution of the colorant, and whenever
possible, in the first attempt. However, dyeing is a complex process that involves many variables
such as fibers, water, dyes, chemicals, operators, machinery and process parameters. Any
variations in raw materials and in conditions during the dyeing process may lead to a faulty dyeing.
From the viewpoint of a consumer, the product should be free of faults and must be adequately
resistant to various conditions during use. The consumer requirements are often described in the
form of specifications. These requirements are met by the dyers through proper selection and
application of dyes, understanding of fiber properties and process control during each
manufacturing step involved in the production of textiles [1-5].
The importance of product quality is continuously increasing in the textile industry.
Consumer demands have increased while expectations for no increases in cost remain. Therefore,
for textile producers and retailers it is essential to determine and understand the factors that
influence the product quality and ultimately the value of the end product. With global sourcing,
retailers are establishing quality management systems in order to reduce the costs associated with
poor quality products. The cost of production comprises of direct and indirect costs. Direct costs
2
include raw material, machines, labor, storage, loans, customs duty, etc. Although direct costs can
be controlled up to some extent, since they depend upon external factors, it is the indirect cost that,
if controlled properly, gives an edge to the manufacturer or retailers over its competitors in today's
highly competitive market. Indirect costs are influenced by the reliability, right-first-time
production, just in time delivery, and goodwill, etc. It is therefore essential to understand the
concept of quality in terms of producing goods that meet the customer specifications at minimal
cost whenever possible. When a textile material is processed through different processing stages,
its value is increased; it is, therefore, essential to remove the causes of potential defects in the
material as early as possible. Sub-standard finished products incur high losses to retailers and
manufacturers. Therefore, in order to obtain high-quality products that meet the demands of the
end-user, the correct process parameters and specifications of raw material, yarn, fabric, and
finished fabric, must be selected and integrated into the retailer's supply chain operations and
strategy. This level of control leads to the desired product without the low-quality claims at the
end of the textile supply chain [6].
Today's textile market incorporates a significant amount of fiber blends. Blends are textile
materials which are the mixture of physically or chemically different fibrous polymers. Textile
materials can be fibers, filaments, yarns or fabrics such as bicomponent fibers, filament mixtures,
core-spun yarns, uniformly blended staple yarns and fabrics made from them. They also include
union fabrics which are produced by using different types of yarns in the fabric. Fibers are blended
for various reasons which include enhancement of performance properties, reduction of the price
of raw material and to obtain novel color effects. Blended textiles are widely used in apparel, home
textiles and carpets [7-9]. Although there are no reported figures about the use of fiber blends, it
is estimated that textile fiber blends account for 30-40% of textile products worldwide.
1.2 Statement of the problem and goals
According to Murphy's Law, anything that has a tendency to go wrong will go wrong. This also
holds true for the dyeing process where problems do occur, even if the process is properly
controlled, and the plant is efficiently managed. In addition, problems occur not only in new
processes but also in well-established processes. They may be in the form of processing faults or
consumer complaints. There are many causes of such problems. Some are due to faulty raw
materials, machine malfunctions, human errors and inappropriate use of textile goods against their
3
intended use [10, 11]. For troubleshooting purposes, it may be beneficial to have a sample of the
original substrate either in the dyed or undyed form so that the required investigation is carried
out. These samples are generally available from the quality control department. Troubleshooting
the processing defects involves some detective work to obtain information about processing details
and quality control records pertaining to the defective batch. With respect to consumer complaints,
the information obtained from the consumer must also be checked. The production site should also
be visited to determine potential problem spots. This is usually followed by appropriate laboratory
tests to investigate the causes of problems and eliminate them in a systematic manner. The sample
size, time limit, and economic considerations limit the number of tests that can be carried out.
Proper laboratory investigations require specific instruments and methods to determine the root
cause of the symptom. This necessitates a specialized laboratory setup [10].
Troubleshooting often requires much experience to investigate the causes of the defects.
This is usually performed by senior personnel or an expert who has spent years in handling such
types of problems, has a working knowledge about the process, machines, substrate, and dyestuff
characteristics, and specializes in such type of work. An expert based on experience recognizes
the causes of a problem and may suggest specific tests. The economic implications of the specific
problem determine the amount of time and expense spent on troubleshooting. It can be concluded
that effective troubleshooting requires experience and skill, and the technique is time-consuming
and may need specialized laboratory methods and equipment [10, 11].
In a dyehouse, the expert has to deal with questions arising from different sectors, which
may include measures to improve processes, causes of defects, facts, and data. Additional
information may thus be required to supplement their expertise. An expert, therefore, must possess
three qualities: factual knowledge, awareness of cause and effect relationships and systems, and
the ability to analytically answer questions which arise in day to day situations. Factual knowledge
refers to a comprehensive understanding of textile processes, products, and machinery. An expert
must also be able to deduce important causes based on the current situations and be able to suggest
measures for success. This is known as know-how relationships. Lastly, systematic thinking refers
to the analysis of the complex system as a whole. This makes problem-solving easier and more
effective [12].
4
The main problems and challenges with human experts and troubleshooting are [13]:
▪ A dyeing plant normally works seven days a week without any stoppages, a dyeing
expert, on the other hand, is only available on a working day. The problems may arise
during night and holidays and these are generally not resolved until the expert becomes
available. This results in delays and sometimes the production of faulty materials.
▪ The expert's knowledge is limited to themselves; if they quit, retire or die that expertise
is lost.
▪ The performance of a human expert is not the same at all times, as it depends on many
factors such as fatigue or stress. Also, experts do not always provide explanations for
resolving the problem as they may be too tired, unwilling or unable to do this. This also
limits the learning/training of new people joining the dyehouse.
▪ The current availability of dyeing experts is limited, as many experts have retired over
the recent decades, and cost constraints due to economic and competitive reasons limit
their availability. Dyeing plants have senior personnel who are responsible for
troubleshooting problems, but they may have limited experience and may not be
considered as experts.
▪ Dyeing plants often lack a proper system for documenting problems and their causes,
which limits the retrieval of information when required.
▪ Some of the troubleshooting involves routine practices. In these cases, a human expert
has to dedicate expertise to overcome routine matters. This leads to a loss of expert
time which could be spent on more important or difficult problems; and
▪ Human experts sometimes do make mistakes due to fatigue or stress, and there is
generally no second opinion available.
An expert system may resolve all the above-mentioned problems and challenges. An expert
system is a computer program, which can be installed on a computer. This makes expertise
available at all times without disrupting the work of individuals involved in dyeing and is not
confined to a person. Problems can be resolved as soon as they occur, and this results in time and
cost savings. Some routine tasks which require human expertise can also be easily performed by
the expert system. The performance of an expert system remains consistent at all times and it can
provide necessary explanations to overcome the dyeing problems. It can also be used as a training
5
tool. The expert system combines the knowledge from multiple experts, technical literature and
books, i.e. it combines theoretical knowledge, practices, and specialized knowledge. The combined
expertise usually exceeds that of a single human expert. It also increases the reliability of a human
expert by providing a second opinion and in cases where there are conflicts among multiple
experts. Depending on the design, the problems and their causes can be saved and retrieved when
required. This can help the dyehouse in identifying the recurrence of the problems when
monitoring the performance of personnel and machinery. This results in improving the efficiency
of the dyehouse. An expert system also provides a systematic troubleshooting approach which
avoids duplication of efforts for resolving problems and may provide cost and time savings [13].
Textile materials comprising of textile fiber blends are widely produced. It can be estimated
that at least 1/3 of all textile material dyed today consists of blends [14]. This signifies the
importance of blends. Almost all the troubleshooting expert systems that have been developed so
far are based on single fiber types. The development of an expert system for troubleshooting
problems in the dyeing of fiber blends would thus be beneficial for dyehouse managers, dyers,
management and training purposes as it would cover this important area.
The final properties of the blend are not the sum of individual properties of fibers making
up the blend and neither to its proportion to the concentration of constituent fibers in the blend
[15]. There are certain challenges and problems in coloration which are specific to fiber blends.
These include differences in the dyeing behavior of individual fibers, the requirement of different
dyeing conditions, cross-staining, interaction effects between different colorant classes and
coloration chemicals. All these behaviors make the coloration of blends different than the
individual fibers in the blends.
The primary aim of this research is to design and develop an expert system for
troubleshooting problems in the coloration of commercially important fiber blends. The diagnostic
expert system provides the dyer with the most likely cause(s) of common problems that occur
during the coloration of fiber blends in yarn, knitted or woven materials. The identification of the
cause(s) will help the dyer in resolving the problem in a timely manner and would likely
recommend a method to prevent the recurrence of the problem. The specific goals of this research
are:
▪ Development of a database of the most common faults and their causes in the coloration
of commercially important fiber blends (specifically polyester/cellulose);
6
▪ Design and development of a functional diagnostic expert system for dyeing of fiber
blends; and
▪ Validation and verification of the expert system.
A diagnostic expert system for coloration of textile fiber blends, DEXPERT-B was built
using wxCLIPS, a modified version of the CLIPS with functionality to provide a customized
graphical user interface (GUI). CLIPS is an acronym for C Language Integrated Production
System. CLIPS is an expert system programming language and available as an open source. It is a
rule-based language that is specifically used for developing an expert system [13, 16].
The rule-based expert system was developed in a Windows environment. The expert
system consists of two components: the knowledge base and the inference engine. The knowledge
base and the inference engine were coded in CLIPS. The GUI serves as the user interface for the
expert system. Two types of information are obtained from the user. The first deals with problem-
based knowledge, which contains background information about the fiber type, blend ratios,
material form, colorants used and the coloration process. The second set of information deals with
the problem-specific components, which involve facts about the problem through a series of
questions. The information is passed on to the expert system first to trigger the specific module.
The problem-specific component is then used to provide answers to the user queries. The inference
engine uses the knowledge base and the user-provided information to draw conclusions.
1.3 Research methodology
The DEXPERT-B system was developed in three phases. Phase I resulted in the identification of
the most common fiber blends and their practical coloration problems along with the possible
causes. The commercially significant fiber blends were identified through published reports, fiber,
dyes and machinery manufacturers and experts. A detailed survey of technical literature (reference
books, dissertation, and theses, technical reports and journals) was carried out to collect, organize
and analyze the potential faults and their possible causes in the coloration of fiber blends. Several
dyers were also interviewed to determine the nature of practical coloration problems in the dyeing
of these blends. A technical survey comprising of practical dyeing problems along with potential
causes was sent to dyeing experts to obtain their responses. Phase II resulted in the development
of a diagnostic expert system for the coloration of textile fiber blends (DEXPERT-B). The
7
responses obtained from experts were analyzed and coded in the form of rules in the expert system
language (CLIPS). The questions used for inference purposes were created based on the causes.
Phase III concluded the study by validation and verification of the developed expert system in
Phase II. This was achieved by testing the expert system against the known causes to check its
validity, evaluation of the expert system against the unknown causes and comparing its
performance against human experts. The final testing and debugging completed Phase III.
The findings of this study provide an important contribution to troubleshooting problems
in the coloration of polyester/cellulosic blends. It can not only help the dyer in finding the probable
causes for particular problems but will also help to find the root causes of the problem and correct
them at the source.
The dissertation is divided into eight chapters, which depending upon the requirement of
the subject matter are made up of sections. Chapter 2 deals with an in-depth review of textile fiber
blends. Reasons for blending fibers and their manufacturing are covered. Furthermore, the
optimum properties of fiber blends and common blend ratios are also included. The global fiber
market in the context of fiber blends is also discussed. Chapter 3 presents in a readily
comprehensible manner the dyeing processes for common blends. The coloration process is
discussed in the context of both pigment and dyes commonly applied for the coloration of blends.
The color effects that can be produced on different blend types are covered. Chapter 4 is concerned
with the commonly encountered problems in the coloration of blends discussed in chapters 2 and
3. The problems that occur in yarns, knitted and woven fabrics that are made up of fiber blends are
reviewed. The basic philosophy behind the troubleshooting of faults is also covered. The problems
are divided according to their origin. The common problems along with their causes and probable
solutions are summarized. Chapter 5 presents the effect of blend ratio on the coloration of
polyester/cotton blends. The dyeing method and the effect of different blend ratios are discussed.
The fastness results obtained are presented in detail. Chapter 6 deals with the development of
DEXPERT-B. The factors that lead to a problem in the dyeing of blends are presented in the form
of a cause and effect diagram. The most common faults along with their definitions are presented.
The strategy used to create the expert system, combining expert responses and inference engines
is covered. Chapter 7 is concerned with the validation and verification strategies used for the
testing of the DEXPERT-B. Chapter 8 is devoted to the conclusion and future work. The summary
of the results of this study is presented along with the recommendations for future work.
8
CHAPTER 2 TEXTILE FIBER BLENDS
2.1 Introduction
Today's textile market is predominantly based on blends. Fiber blends are materials produced by
mixing two or more fiber types. Their high popularity is due to unique properties and performance
characteristics that can be achieved in the case of blends. Each textile fiber, weather natural or
synthetic, has specific properties. Materials based on single fibers may not satisfy the specific
requirements of a given end-use. In such cases, two or more fibers are combined in such a way
that optimum properties are obtained according to the required end-use by enhancing a particular
product characteristic [17, 18]. The fiber blends comprise any textile materials either in the form
of fibers or filaments, yarns, and fabrics that contain a premeditated combination of chemically or
physically different fibrous polymers. This covers bicomponent fibers, filament mixtures, core-
spun yarns, the intimate blending of fibers during spinning, combination yarns, and union fabrics,
to name a few. The number of possible blends and blend levels are very large but noticeably a
small number of blends are commercially used. The most common and traditional type of blends
consist of two physically or chemically different fibrous polymers such as polyester/cotton and
polyester/wool. The use of blends consisting of three or four fibers is also popular especially in
apparel due to the unique nature of properties that can be obtained by such combinations, a good
example is polyester/cotton/elastane [7].
2.2 History of blends
Fiber blends have been in use for a long time and their use continues to grow [19]. Many
explanations can be found for the use of textiles made of more than one fiber type. The main reason
was likely the shortage of good quality fibers in large quantities. Silk, for example, is expensive
and its application was mainly reserved for dignitaries. To overcome this problem, silk was often
blended with different fibers. Another reason for the use of fiber blends in fabrics was the
possibility of creating specific designs by using two different fibers. This, however, was not widely
done until the twentieth century mainly due to technical difficulties [20].
Historically fiber blends were used for different purposes. The early blends consisted of
natural fibers as they were the only available fiber type at that time. With the development of
9
manufactured fibers at the beginning of the 19th century, blends of natural and manufactured fibers,
as well as blends of manufactured fibers themselves, appeared in the market.
2.2.1 Blends of natural fibers
Historically, natural fiber blends were used as separate warp and weft yarns and in some cases,
mixtures of fibers were used to make yarn. Paracas textiles showed the use of llama and other hair
fibers of different colors [19, 20]. In Ptolemaic textiles, Coptic textiles, and in textiles of early
New England, wool and linen blends have been found with generally wool being used as warp and
linen as weft yarns [19, 20]. These fabrics were known as linsey-woolsey and were made of
handspun linen and wool. These finely woven fabrics were moth-resistant and were used for
apparel and household purposes. Silk and wool blends have also been found in Regensburg fabrics
and silk and cotton in Hyderabad textiles. Other examples of historic blends include oriental yarns
consisting of silk and gold or silver and central Asian fabrics with linen or hemp warps and wool
weft. Blends of silk and wool are still common in Persian handwoven carpets. Soft fabrics
comprised of silk mixed with cotton or linen were woven by Phoenicians. Watertight tent fabrics
made of wool mixed with camel hair or goat hairs were found in Tunisian and Peruvian textiles.
Mixtures of cotton and bast fibers were used in the fabrics found in Nigeria. Decorative fabrics of
cotton and silk were woven in India. In England, for some time after 1720, the printing of pure
cotton fabrics was forbidden to protect the wool industry. Linen-cotton blends known as fustian
was used to evade the ban. In France, men's apparel consisting of wool-linen blends, women's
clothing containing silk warp and cotton weft and silk-wool blends for upholstery have also been
found [20-24].
2.2.2 Blends of manufactured fibers
Manufactured fiber blends emerged in the market soon after the appearance of manufactured
fibers. Rayon fiber, also known as artificial silk, was introduced in the market in 1892 [21]. Dress
materials made of rayon warp and cotton weft emerged shortly thereafter. One of the advantages
of these blends is the possibility of producing various cross-dyed effects. Other common blends
of rayon fibers included those with casein fibers, flax, nylon, and wool. Blends of rayon staple
fiber were also popular. The appearance of acetate fibers in the 1920s created a possibility of
producing three-component blends consisting of natural fibers, rayon, and acetate. Blends of
10
acetate and rayon can be used to generate a cross-dyeing effect, while the acetate fiber component
in the blend is used to improve the crease resistance property of the fabric. Another common blend
involved acetate and wool blends. These blends were used for the production of tropical suiting,
flannels and blouse fabrics. The acetate component in the blend reduced the fabric shrinkage,
improved the pleating and permanent fabric creases and created a possibility of cross-dyeing.
During World War I, rayon was blended with wool in order to develop new compositions. This
was partly due to the limited availability of wool and the long-distance shipment from a limited
number of wool growing regions. German army defeat in the USSR has been linked with the
inadequacy of rayon/woolen blends [19]. Some examples of rayon blends during this period are as
follows. Staple viscose fibers of coarser denier were blended with low crossbred wool, mohair,
and goat hairs. Fabrics made of 50/50 blends of rayon staple and casein fibers were produced that
exhibited the wooly handle. Casein fibers were blended with wool and rayon in felts. A modified
rayon fiber, Rayolanda-X, with an affinity for acid dyes was also used to give two-tone effects in
dyed blends. Three-component blends were also produced. In the early 1950s, due to the rising
prices of wool different blends of wool were experimentally produced to retain wool in the yarn
while reducing the amount of wool used [21, 22]. Examples of wool blends during this period
include wool and nylon, for excellent wearing qualities and wool-like hand, production of rayon
or acetate with wool for piece dyeing to obtain heather look and wool and Rayolanda-X for the
tone on tone effect [25]. Common blends used in hosiery were wool-rayon, wool-nylon and wool-
acetate-nylon [21, 22].
Nylon was commercially produced in 1939 and its high strength and good abrasion
resistance properties made it a prime blend component with weaker fibers to improve the yarn
properties. Nylon was successfully blended with wool. For example in the case of military textiles,
product life and light exposure were increased, while the weight of the product was reduced for
the same performance. Nylon/cotton blends, however, exhibited serious property problems. Blends
containing less than 50% nylon showed lower strength than cotton alone due to the lower modulus
of the nylon fibers. To counter this problem a new nylon, Dupont 420, was engineered that had the
same stress-strain curve as that of cotton up to the breaking point [21]. The US army has researched
the fiber blends as part of its wool conservation program. After the World War II, the quantity of
wool in the US was insufficient to meet domestic demand and this led to an aggressive wool
11
conservation program by the US army. The US Army adopted the first synthetic fiber nylon in
1951 as a blending fiber with wool [19].
Acrylic staple fibers became available in 1952. They were blended with other fibers or the
modified acrylic fiber. Hi-bulk acrylic fiber, a modified acrylic fiber, which shrinks on heating
was blended with acrylic fibers to make a lofty yarn. Acrylic fibers were also blended with nylon
or polyester in socks and with polyester in woven fabrics to improve the wrinkle recovery
properties. Blending of acrylic fibers with wool, angora, and silk was also done to improve physical
performance and to reduce cost. Modacrylic staple fibers were introduced in 1950. Blending with
modacrylic fibers was done due to its flame resistance properties. Polyester was blended with
modacrylic fibers to improve its abrasion resistance properties [21].
Polyester fibers were commercially available in the fifties and due to the excellent
properties of this fiber type, it was immediately used for blending with other fibers. One of the
earliest blends produced was polyester-wool. These blends have excellent wrinkle-resistance and
crease retention properties. The visual and tactile aesthetics of wool fabrics were also retained.
These blends continued to develop through the 1960s and their production became routine. The
most successful blend is probably polyester-cotton blends. One of the reasons for developing these
blends was the good wrinkle resistant properties of the polyester component in the blend. In the
late fifties and during sixties blends were developed that exhibited wash and wear properties. This
was achieved due to the development of durable press finishes [26]. Polyester has an advantage
compared to nylon in these blends as the properties of the polyester match better with the cotton
fiber. Due to excellent properties that can be achieved, these blends have become the most
commonly used blend types over the years [21].
Spandex fiber has high elongation properties and can be used in blends. After their
introduction in the market in the 1960s, they were blended with cotton, polyester, nylon, and
viscose to impart elastic properties to the fabric [21, 22]. Before the production of spandex, natural
rubber was used as an elastomeric fiber in apparel fabrics. Rubber yarn had many problems such
as it needed to cover with the outer layer of textile for protection during processing, low retractive
force, poor abrasion resistance, low heat settability, poor resistance against aging, low yarn
modulus and tenacity. Many of these problems were overcome by spandex fiber and thus it soon
replaced the rubber yarn and provided new ways for its use in apparel fabrics [27].
12
Many different combinations and blend proportions have been tried but only a few fibers
in a small number of combinations are commonly used nowadays [21].
2.3 Global fiber market and blends
Textiles and clothing comprise one of the most important trade commodities. In 2013, they were
the fifth largest merchandise exported in the world and showed the second-highest growth of 8%
in merchandise trade, four times higher than the average world export growth rate which amounted
to US$766 billion [28, 29]. One of the important indicators of textile and clothing industry trade
as a whole is the world fiber demand. Approximately 196.3 billion pounds (90 million tons) of
fibers were produced in 2013 which was increased by 4% compared to 2012. These figures can
also be considered as reasonable estimations of usage in recent years since the data collection and
reporting often lags by several years. Manufactured fibers accounted for the largest share (72%)
in global fiber production. The share of natural fibers was 28%. For the manufactured fibers
consisting of synthetic and regenerated cellulose fibers, the share was approximately 66% and 5%
respectively. Polyester fibers dominate overall fibers production worldwide with a share of about
52% while cotton was the second highest with a share of 27% [30-33]. The consumption of
manufactured fibers continues to expand (was 30% in 1980) while the share of the cotton is on a
decline. The second time ever the market share of cotton reached below 30% was in 2013.
Polyester fibers, on the other hand, showed an upward trend in their consumption and the share
lost by cotton was occupied mainly by polyester [34]. The main reasons for the substitution of the
natural fibers with manufactured fibers are due to the following [35]:
▪ Almost unlimited availability (not dependent on cultivation area and other factors);
▪ Not dependent on weather/climate;
▪ Cheap and cost-efficient;
▪ Large range of end-use; and
▪ Can be recycled (environmentally friendly).
Table 2.1 shows the global fiber production and share for the year 2013 [30]. The world
fiber use is differentiated according to the material (individual fibers) and fiber type (filament &
staple). Filaments account for approximately 2/3rd while staple fibers share is about 1/3rd of
manufactured fiber production respectively [35]. Figure 2.1a shows the consumption of textile
13
fibers according to their use in different industry segments along with the recycled fibers. Short
staple fibers comprising of cotton, cellulose and synthetic staple fiber have the highest share
followed by the filaments. The share of wool fibers (long-staple fibers) was approximately 2%.
Mill consumption of textile fibers which mainly utilize short-staple fibers is shown in Figure 2.1b.
Cotton fiber has the highest consumption of 47% followed by polyester with 27%. Nylon fibers
have the lowest share of 0.2% [36]. Figure 2.1c shows the production of manufactured fibers by
fiber type in the form of staple fibers and filaments [30].
Table 2.1: Global fiber use for the year 2013.
Fiber type Filament yarns Staple & Tow Total % Share
Natural fibers 55,710 28.4%
Cotton 52,395 26.7%
Wool 2,471 1.3%
Linen 540 0.3%
Silk 304 0.2%
Man-made fibers 90,261.9 50,328.7 14,0591 71.6%
Cellulosics 878.1 9,705.8 10,583.8 5.4%
Synthetics 8,9383.8 40,622.9 13,0007 66.2%
Polyester 69,032.4 33,844.3 102,916.7 52.4%
Nylon 9,200.7 369.3 9,569.9 4.9%
Olefin 9,587 1,451 11,039 5.6%
Acrylic 4,311.8 4,311.8 2.2%
Others 1,563.7 606.5 2,1702.2 1.1%
Total 196,301 100%
14
(a) World fiber type distribution [36].
(b) World textile fiber mill consumption by material distribution [36].
(c) World textile fiber mill consumption by fiber type [36].
Figure 2.1: World fiber production for the year 2013.
Cotton: 23,534; 47 %
Polyester: 13,553; 27 %
Recyling fiber: 6,309; 13 %
Polypropylene: 1,024; 2 %
Cellulosic: 4,178; 9 %
Acrylic: 934; 2%
Polyamide: 132; 0.3%
Manufactured Cellulosics Synthetic Polyester Nylon Acrylic0
20
40
60
80
100
% S
har
e
Filaments
Staple & Tow
15
World textile fiber consumption for the year 2013, according to the application is shown
in Figure 2.2. According to the end-use, textile products can be divided into four main segments
viz.: apparel, home textiles, carpets and rugs, and industrial and other products. The apparel sector
had the highest market share of 45% (42 million tons) followed by industrial and other products
with 34.7 million tons used with a share of 38%. Home textiles accounted for 9% of the fiber used
with 8.5 million tons while carpet and rugs accounted for 8% of world fiber use with 7 million
tons [37].
Figure 2.2: Global consumption of textile fibers by end-use.
World yarn production of all fibers was 100.4 million tons in 2012. The share of cotton
yarn was 46.3 million tons while the share of manufactured fiber production was 54.2 million tons.
The production of yarn classified as cotton (with 50% or more cotton) compared with cotton mill
use indicates that the increase in cotton yarn production was due to the increased use of other fibers
in blends. Before 2011, the amount of cotton spun into the yarn exceeded the amount of yarn
classified as cotton yarn. This is due to the use of cotton in blends with other fibers with less than
50% content. The average cotton content in cotton yarn was declined from 99% in 2002 to 51% in
2012 as shown in Figure 2.3 [34]. This indicates that a small portion of yarn types use cotton in
their blends and most cotton yarns include blends of cotton and other fibers with at least 50%
cotton portion [34].
Apparel: 45%
Industrial and others: 38%
Home textiles: 9%
Carpets and rugs: 8%
16
Figure 2.3: Cotton content in the cotton yarn-world average.
Spinning plants have increased the proportion of synthetic fibers, especially in blends due
to the high cotton prices in recent years. The ratio of the blends will continue to remain at such a
high-level [36]. Approximately 58% of all short-staple spun yarns produced nowadays is a blended
yarn. Figure 2.4 shows the distribution of blended yarn produced worldwide on short-staple
spinning systems. The distribution is given in the form of the main portion of the blend e.g.
CO/PES refers to a cotton-polyester blended yarn with CO as the main portion inside the blend.
The same is the case for the other blend types shown. Cellulosic fibers (CEL) include viscose,
Modal, and Tencel. The blended yarn produced can be divided into three broad categories based
on the main component as CO blend, CEL blend, and PES blend. CO blend has the highest share
of the market with approximately about 60%, CEL blend accounts for 21% and PES blend for 19%
of the short-staple blended yarn produced worldwide. No information about the exact blend ratio
and blended yarn produced on the long-staple spinning system is available. Based on the
information available it can be inferred that PES/CO blends comprise the largest produced blends
and PES/CEL are the second-largest blends available.
99%
51%
0%
20%
40%
60%
80%
100%
2001 2006 2011
17
Figure 2.4: Material distribution of yarn blends in the short-staple spinning system.
PES/CO blend is the major blend used currently and will remain the significant type due
to the unique characteristics of individual fibers used in the blend. Polyester consumption will
continue to increase by 3.6%, while the predicted growth rate of cotton is 2% per annum for the
next ten years [38, 39]. The cotton production is limited due to allocated growing regions, loss of
soil fertility, pollution, water availability, product yield and increasing food demand. With the
increase in fiber demand, cotton will not be able to cover the required demands, and this will cause
the so-called cotton gap. It was predicted that some part of this gap would be covered by increased
consumption of polyester fibers and partly by cellulosic fibers [40]. The best substitute for filling
this gap is cellulosic fibers due to having similar properties to those of cotton. One-third of textile
fibers based on the end-use are required to have specific properties such as absorbency and
moisture management which only cellulose-based fibers can provide [40-42]. With the increase in
the production and demand for polyester fibers and the limited production of cotton fibers, the use
of PES/CEL blends will continue to increase and this blend will maintain its popularity.
Unfortunately, information concerning the consumption of other fibers in the blend is not readily
available. It is estimated that approximately 55-60% of the polyester fibers are used in blends with
cotton and wool, out of which 40-45% is used for blends with cotton [3, 43]. Approximately 40%
of polyamide fibers are used in blends. About 50% of polyacrylonitrile fibers are also used in
blends with wool [3].
Fabric blends can be produced by two methods: yarns of different materials are combined
within the fabric structure, or intimately blended yarns are processed into fabric [36]. Similar to
cotton yarn designation, cotton fabrics are specified in the same manner i.e. fabrics with a cotton
CO/PES: 46%
PES/CO: 14%
PES/CELL: 5%
CELL/PES: 9%
CO/CELL: 14%
CELL/CO: 12%
18
component of at least 50% are termed as cotton fabric in the trade. According to the world textile
demand, an increased blending of cotton yarn is done in fabric production. This is evident from
the increased proportion of cotton yarn used in the production of synthetic fabrics. This implies
that cotton yarns are blended with other yarn types to produce blended fabrics [34].
Up to date information about the use of blended fabrics in dyeing is sadly not available.
However, it is estimated that 30-40% of the material dyed today comprise fiber blends and PES/CO
and PES/CEL blend are the largest blended fabric type in the dyeing process. Figure 2.5 shows the
estimates of the use of blended fabrics in the batch and continuous dyeing processes. The most
common blend types used are PES/CEL, PA/CEL, and PAN/CEL [44].
(a) Exhaust (including Cold Pad Batch)
(b) Continuous process
Figure 2.5: Share of major fiber blends in dyeing processes.
PES/CEL: 72%
Others: 3%
PAN/CEL: 4%
PA/CEL: 21%
2006
PES/CEL: 70%
Others: 3%
PAN/CEL: 5%
PA/CEL: 23%
2010
PES/CEL: 90%
Others: 4%PAN/CEL:6%
2006
PES/CEL: 89%
Others: 3%PAN/CEL:8%
2010
19
2.4 Purpose of blending
There are many reasons which are responsible for producing fiber blends.
▪ Economy
Expensive fibers are blended with cheaper ones to reduce cost. Expensive wool was
blended with viscose for cost reasons in the past. With the rising cost of cotton, the
polyester proportion in the polyester/cotton blend is increased due to economic reasons.
The cheaper fiber, however, should not have too much adverse effect on the properties
of the expensive fiber in the blend [8, 9, 18]. A similar approach was also used to blend
economical fibers with a luxury fiber such as silk and linen to produce
polyester/viscose/silk or polyester/viscose/silk blends for women’s apparel [7].
▪ Durability
A weaker fiber with a soft hand can be blended with a strong and durable fiber to
improve the useful life of the weaker fiber [8, 9]. This increases the resiliency and
durability of the resultant blend [45]
▪ Physical properties
One of the most important reasons for producing blends is the wide range of combined
physical properties that can only be achievable in blends. Two fibers with different
properties such as moisture regain, tenacity, elongation and initial modulus can be
combined to produce a blend that has the combined properties of both fibers. This may
be required to obtain uniquely desirable performance properties. The weaknesses of
one fiber, for instance, can be balanced with the strength of another. The most obvious
and common example is polyester/cotton. Polyester fibers have high tenacity, abrasion
resistance, and dimensional stability but low moisture regain. They can be blended with
cotton which has high absorbency, reduced pilling and comfort but low tenacity [7-9,
45, 46]. The properties that can be enhanced include abrasion resistance, strength,
absorbency (comfort), bulk and warmth, hand, dimensional stability, and wrinkle
resistance [18]. Most blends that are utilized today optimize the physical properties of
their component fibers and are usually a combination of natural fibers with a synthetic
fiber [45].
▪ Color
20
Different aesthetic color effects can be created using fiber blends. This leads to the
development of novel garments, color designs [8, 9] and multi-colored fabrics [18].
Different color effects such as tone in tone and cross-dyeing can be obtained by
combining regular dyeable fibers with differential dyeable fibers of the same material
type or by combining two different fiber types [7].
▪ Appearance
Yarns of different luster, crimp or denier can be combined to produce an attractive
appearance, visual effect, and tactile qualities. Although both yarns are dyed uniformly
with the same color, they still differ in appearance [8, 9, 18, 45]. For example, a small
amount of viscose provides luster to the cotton [46].
▪ Improved processing and uniformity
Fiber blends improve the productivity of yarn manufacturing, fabric manufacturing and
wet processing operations or increase the uniformity of the product. This type of
blending is called self-blending which is done in natural fibers that have variations in
diameter and length [18, 46, 47].
2.5 Types of fiber blends
The fiber combinations which provide optimum end-use properties and improve processability in
the blend are as follows [17, 48]:
▪ Manufactured fibers with natural fibers
Examples: Polyester with nylon, wool, cotton, viscose, modal, lyocell or linen; nylon
with wool or cotton; acrylic with wool or cotton; viscose, modal or lyocell with wool
or cotton
▪ Manufactured fibers with one another
Examples: Nylon 6 with viscose, nylon 66 or polyester; polyester with acrylic, elastane
or viscose
▪ Natural fibers with one another
Examples: cotton with wool or linen, wool with ramie; mohair with silk
21
With the technical advancements and for fashion reasons new fiber blends are constantly
being developed. The prevailing blends may vanish from the market and sometimes find their way
back to the market later [17].
The fiber blends made up of staple fibers or filaments may consist of similar or different
fibrous polymers with distinct chemical and physical properties. These include, but are not limited
to [17]:
▪ Fiber combinations having different morphology such as fineness, cross-section, and
crimp;
▪ Fibers having different physical properties involving shrinkage (normal/high
shrinkage), elastic modulus, flat/textured, luster (bright/matte); and
▪ Differences in the dye sites or the presence of different dye groups to obtain differential
dyeing effects.
When discussing blends, it is important to distinguish between the intimate blends, union
and combination yarns. When two or more fiber types are mixed intimately to produce a yarn, the
resulting mixture is known as an intimate blend. In intimate blends, different fibers are arranged
next to each other. Combinations yarns are produced by twisting of single yarns of different fibers.
Each ply in the yarn has different fibers as compared to the other ply, though their use is relatively
limited. The mixture or union fabrics are produced when yarns made from one fiber type are
combined with yarns produced from another fiber type. The usual arrangement consists of
lengthwise yarn of one fiber type and widthwise yarn of another fiber type. Other arrangements
are also possible in which yarns of different fiber types are used side by side or intimately blended
yarns of two fibers are used in on direction and yarns made of third fiber type are used in the other
fabric direction. Historically blended fabrics were produced in the union form as discussed in
section 2.2. Currently, union fabrics are produced to achieve various color effects that are difficult
and costly to produce by yarn dyeing of single fiber type. Another example of these fabrics is the
stretch denim in which textured polyester yarn is used in the widthwise direction with cotton yarn
in the lengthwise direction [46, 49].
Table 2.2 gives a summary of the most commonly used blend types, along with typical
blend ratios and end uses [17, 48].
22
Table 2.2: Summary of common textile fiber blends and their potential applications.
Blend components Blend proportions End use
Polyester/cotton 50/50, 65/35, (67/33) Underclothing, shirts, blouses,
nightwear, clothing, poplin coats
Polyester/viscose 70/30, 50/50 Work- and sportswear
Polyester/linen 65/35, 80/20 Leisurewear, clothing
Polyester/silk 70/30, 75/25, 80/20, 85/15 Leisurewear, clothing
Polyester/wool 55/45, 70/30 Suits, trousers, costumes, dresses,
coats, jerseys, pullovers, uniforms
Polyester/acrylic 50/50, 60/40, 65/35, 70/30 Leisurewear, clothing, women's
slack, pullovers, jerseys, tableware
Polyamide/cotton 10-50/90-50 Dress wear leisure shirts
Acrylic/wool 55/45, 70/30, 60/40 Jerseys, clothing, pullover, socks,
blanket, floor covering
Acrylic/viscose
Acrylic/cotton 55/45, 70/30 Jerseys, clothing
Acrylic/linen 55/45, 80/20 Leisurewear, knitted goods
Wool/polyamide 75/25, 80/20, 85/15 Uniforms, socks, hand knitting
yarns, woven carpets
Wool/viscose
Wool/cotton 50/50, 70/30 Suits, jackets, sports coats
Polyester/acrylic/wool 55/15/30, 30/40/30 Jerseys, clothing, pullovers.
Polyester/acrylic/cellulose Household textiles
Nylon/cotton/elastane Elastane 10-20% Knitted underwear
Staple combinations of
high shrinkage acrylic or
high shrinkage polyester
30-40% of high shrinkage
component
Jerseys, clothing, pullovers, hand
knitting yarns, trousers, clothing,
jackets
23
2.6 Properties of blended yarns and fabrics
For any textile fiber to be commercially successful, it must possess both primary and secondary
properties. Primary properties include certain essential fiber properties which enable them to be
converted to acceptable textiles. Secondary properties refer to those properties that improve
consumer satisfaction with the end-product made from the fiber. The fibers that exhibit high values
in all these properties do not exist in practice due to tradeoffs employed to achieve higher
performance in certain properties. The primary and secondary properties of different commercially
successful fibers are shown in the form of ratings. It can be seen that fibers can have lower values
in certain fiber properties. Consider the example of wool and acrylic fibers. The wool fibers have
good electrical conductivity and wicking properties but poor crease recovery and laundering
properties. The acrylic fiber on the other hand has good crease recovery and laundering properties
but poor electrical conductivity and wicking properties [46, 50].
Blending is an effective method of enhancing the positive and reducing the negative
properties of each fiber. This is commonly practiced in the case of natural fibers where the fibers
belonging to the same fiber category are blended before spinning to produce uniform properties in
the spun yarn. In the case of fiber blends, this is achieved by mixing different fibers such as
polyester and cotton where the positive properties of each fiber mask the negative properties of
other fiber and the resultant blend has excellent properties. However, it is important to know that
blending cannot enhance the properties of the blended material above the maximum levels
observed in the similarly constructed material produced from only of the fiber types found in the
blend [49]. For example, the strength of polyester/cotton blended yarn cannot be greater than the
strength of the yarn made from 100% polyester. However, polyester/cotton yarn is stronger than
100% cotton yarn. Similarly, if blending is not done properly, the blended fabric may even have
lower strength than a fabric produced entirely from the lower strength fibers. As shown in Table
2.3 synthetic fibers such as polyester and nylon having higher strength, abrasion resistance,
durability, and lower shrinkage are blended with natural fibers that have good moisture absorption,
comfort and exhibit no static generation. However, two properties of the resultant blends are
greatly affected which are pilling and flame retardancy. Pilling is not observed in the case of all
cotton fabrics but can be seen in blends made of polyester/cotton [47]. The burning time of the
polyester/cotton blend is lower than all cotton fabrics. The all-cotton fabrics were found to be less
flammable as compared to polyester/cotton fabrics of similar fabric types [65].
24
Table 2.3: Primary and secondary properties of textile fibers.
2.6.1 Compatibility of fibers in the blend
The fiber type used in a blend must be selected or produced according to the other fiber in the
blend. Special fiber variants have been developed by the manufacturers to obtain the required
properties in the blend. Specially developed viscose and polyester fibers are available in the market
for blending with cotton [50]. Each fiber in in the blend should be compatible otherwise the
properties of the blended yarn will be inferior when compared to the individual fibers in the blend.
Each fiber type in the blend must behave similarly under stress for the successful production of
yarn and to ensure adequate yarn strength during use [49]. The blended yarn is a composite
structure. The gauge length used during strength measurement has a strong influence on the yarn
strength and depends on the closeness and strength of the surrounding fibers [49]. It has been found
that predicted strength of a blend is often lower than experimental value. The fibers in the blend
must also have similar initial modulus and elongation at break [49]. When the strain level in the
25
yarn reaches the level of rupture of the less extensible component in the blend, that component
fails and this may lead to the rupture of the whole yarn [19].
Consider the example of producing polyester/cotton yarns by blending Pima cotton with
either the modified regular tenacity or high tenacity polyester fibers. The stress strains of these
fibers are given in Figure 2.6 [49]. The Pima cotton has an initial modulus and considerable force
is required to break the fibers. The cotton fibers break at 3.5 g/denier at 10% elongation. In the
case of modified regular tenacity polyester, fiber breaks at 4.8 g/denier at elongation of 45-55%.
Although regular tenacity polyester fibers are stronger than cotton but their contribution to the
strength of the blended yarn is minimal as they are in the elongation phase when the cotton fibers
start breaking at around 10% elongation. However, the high tenacity polyester contributes more to
the strength of the blended yarn because it has similar elongation properties thus increasing the
strength of the blended yarn [49].
It has been found that certain fiber types are not suitable for blends. In the case of 50/50
nylon/cotton blends the strength of the blend is less than the strength of 100% cotton yarn due to
significant differences in the extension properties of the two fibers. As nylon has considerably
higher extensibility than cotton, the cotton fibers in the blend break when the nylon fibers are still
within this extension region [50]. In the case of polyester/cotton or nylon/cotton yarn, the earlier
rupture takes place in the 7-10% extension range. The failure of one fiber in the blend does not
cause yarn extension to drop severely. In some cases, the blended yarn continues to extend even
up to the breaking extension of the most extensible component. The lateral pressure in the yarn
tends to grip the broken fiber segments of the less extensible fiber and thus aid in their reduced
level contribution to yarn strength. This phenomenon is affected by twist levels, blend ratio and
arrangement of components in the blended yarns. In polyester/cotton yarn, if the polyester
percentage is lower the extension percentage is found to be close to the cotton level, the failure
propagation tends to concentrate, and yarns would break at the lower extension levels. The effect
is more noticeable in highly twisted yarns, cotton-rich yarns, and yarns with cotton clustering [19].
26
Figure 2.6: Stress-stain curves of Pima cotton, regular and high tenacity polyester fibers used in
blended yarns [49].
2.6.2 Effect of blend ratio
Blends can be produced in many ratios, but certain blend levels are more dominant than others.
The required end use properties can be achieved by adjusting the ratios of each fiber in the blend.
Much research has been done by the fiber manufacturers to determine the necessary proportion of
each fiber to achieve desired properties. Only a specific blend ratio can produce the required
enhancement of properties. It is difficult to generalize the blend ratios, however, as they vary with
the fiber type, fabric construction and the desired end use [47]. Certain properties of the blend will
result in insignificant changes if the proportion of the fiber responsible for the effect (based on the
key fiber) is not significant [46, 49]. In general, it can be said that if the proportion of the key fiber
is less than 10%, the blend will not show any noticeable changes in its properties. The actual effect
of increasing the level above 10% depends on the properties of the key fiber and the component
fiber in the blend. For example, 15% nylon in nylon/wool blends improves the strength of the
blend but in the case of nylon/rayon blends, 60% nylon is required to show a significant change in
strength. In the case of wool/acrylic blends, 50% acrylic fiber is blended for use in a woven fabric
and 75% for knitted fabric production to improve the stability. If the blend proportion of the key
27
fiber is increased above 20%, the blend begins to show some noticeable differences in hand,
appearance and other properties. At around 50% level, the properties of the key fiber show a
significant effect on the properties of the resultant blend and this effect will continue with
increasing the proportion of the fiber [47]. The abrasion resistance of the PES/CO blend show
improvement if the polyester content is at least 20% in the blend. To obtain a significant
improvement the polyester content should be around 50%. Similarly wrinkle recovery properties
of the blend are increased gradually with increasing the polyester content of the blend with
prominent changes occurring at 50% polyester level. In order to obtain wrinkle free fabric without
resin treatment the PES/CO blend ratio should be 67/33. The effect of changing polyester levels
in PES/CO blends on abrasion resistance and crease recovery angle is shown in Figure 2.7 [49-
51].
Figure 2.7: Effect of polyester levels in PES/CO blends on abrasion resistance and wrinkle
recovery properties of fabric [51].
At around 90% the properties of the key fiber overtake the influence of the other component
in the blend [50]. Extensive research has been performed by fiber manufacturers to determine
what blend ratio is suitable for different applications. This is one of the primary reasons for
availability of certain blend ratios in practice. For example, PES/CO in 50/50 ratio is mostly
recommend for light to medium weight fabrics while 65/35 PES/CO is recommend for suit weight
materials [46]. The resultant properties of the blends do not necessarily correspond to the
28
percentage of each fiber in the blends as many properties of the fibers are not additive in nature
[46].
2.6.3 Blending and resultant properties
Several studies have been conducted to evaluate the benefit of fiber blends and their effect on
fabric appearance, tailorability, drapeability and handling, shape retention, shrinkage, and comfort
[19]. Dupont carried out extensive studies on the implications of combining hydrophobic synthetic
fibers with hydrophilic natural fibers. The blends of polyester, nylon and acrylic with wool and
viscose have been studied and impressive results were obtained. Their results can be summarized
as follows [15, 52]:
▪ Fabric strength and abrasion resistance are increased as the proportion of the synthetic
fiber component are increased.
▪ Dimensional stability with respect to humidity effects increases.
▪ Moisture content is reduced in wool synthetic blends as synthetic proportion is
increased.
▪ Crease recovery of polyester containing blended fabrics is increased as polyester
content is increased.
▪ Swelling induced shrinkage of polyester containing blends is reduced.
The polyester fibers when blended with other fibers enhance the crease recovery, press
retention, laundering stability, strength, abrasion resistance and wash and wear performance. The
main problems associated with polyester are static generation and pilling. The acrylic fibers in the
blend enhances the bulk, dimensional stability, press retention and melt resistance properties.
Acrylic has good crease recovery properties though this is lower than that of polyester and wool
fibers. The static generation and pilling properties of acrylic are lower compared to polyester
fibers. Nylon fibers have good dimensional stability, strength, and abrasion resistance. A smaller
proportion of the nylon in a blend increases the abrasion resistance but a significant proportion of
nylon is required to improve the strength. The improvement is strength is usually achieved if the
stress-strain characteristics of the component fibers in the blend are similar to nylon. If the stress-
strain properties are different the blend may have lower strength. The properties of different fibers
in the blends are schematically represented in Figure 2.8 [15, 52-54].
29
Figure 2.8: Properties of different fibers in the blend [54].
If properly blended, polyester/wool blends represent an excellent balance of properties that
cannot be achieved otherwise. The blend ratio that provides the best results is 65% polyester and
35% wool. This blend has outstanding aesthetic properties, wrinkle resistance, press retention,
dimensional stability, strength and abrasion resistance characteristics. The static generation is also
found to be lower. The 65/35 blend ratio also provides practically minimum wash and wear
properties for the worsted type suiting [54].
Viscose blended with polyester reduces the static generation and pilling. The blend ratio
that provides optimum properties is 70% polyester and 30 % viscose. The blend has good wash
and wear properties [53, 54].
Polyester/acrylic blends at 50/50 blend level provide superior properties. The polyester in
the blend enhances the strength and abrasion resistance of the blended fabric. The polyester and
acrylic fibers in the blend provide press retention and laundering stability. The acrylic fiber
improves the hand and add bulk to the blend. The pilling tendency is also reduced. However, this
blend is prone to static buildup due to hydrophobic nature of both fibers [53, 54].
The presence of viscose fiber in acrylic/viscose blends reduces static generation. The blend
containing as low as 15% viscose provides lower levels of static generation. The blends containing
approximately 25% rayon provides comparable results as compared to 100% viscose in terms of
static propensity. The blend level that provides optimum properties is 75% acrylic and 25% viscose
[53, 54].
In nylon/acrylic blends, nylon improves the abrasion resistance thus enhancing the
durability. The blend containing 25% nylon increases the abrasion resistance significantly higher
than that for the 100% worsted wool fabrics. To achieve significant increases in the strength of the
Aesthetics Texture
Liveliness
Bulk
Wear-care
properties
Crease recovery – 65% R.H.
Crease recovery – 90% R.H.
Crease retention – 65% R.H.
Crease retention – Wet
Stability – Laundering
Durability
Strength – Tear
Abrasion resistance
Garment
performance
Static resistance
Melt resistance
Polyester Acrylic Nylon Viscose Wool
Key
Outstanding
Excellent
Moderate
Poor
30
blend, approximately 40% nylon is required. The blend ratio that provides the best combination of
properties is 75% acrylic and 25% nylon [53, 54].
For nylon and viscose blends, the optimum properties are obtained when blend contains
40% rayon and 60% viscose. The resultant blend has superior strength, abrasion resistance, static
resistance and melt resistance properties. However, wash and wear properties, wrinkle recovery
and press retention properties are inferior to polyester/rayon blends. For worsted type suiting
polyester/viscose blend with 70/30 blend ratio provides superior properties than nylon/viscose
blend [53, 54].
The combined property spectrum of different blends with optimum blend ratio is shown in
Figure 2.9 . The vertical rectangle represents the blend compositions with optimum wash and wear
properties [54]. A simple rule of mixtures, according to which the resultant properties of the blend
is the weighted average of the individual fiber properties according to their proportion in the blend
may not accurately predict the properties of the blend. This may be attributed to following reasons
[55]:
▪ The properties of the two fibers may be incompatible with each other under certain
conditions.
▪ There is an interaction effect between two fiber components in the blend where the
behavior of one fiber component is affected by the other component.
▪ The blend is not exactly uniform in terms of fiber distribution and contains regions
exhibiting properties different than the average properties of the blend.
31
Polyester-wool Polyester-viscose
Aesthetics
Texture
Liveliness
Bulk
Wear-care
properties
Crease recovery – 65% R.H.
Crease recovery – 90% R.H.
Crease retention – 65% R.H.
Crease retention – Wet
Stability – Laundering
Durability
Strength – Tear
Abrasion resistance
Garment
performance
Static resistance
Melt resistance
% polyester % polyester
Polyester-acrylic Wool-acrylic
Aesthetics
Texture
Liveliness
Bulk
Wear-care
properties
Crease recovery – 65% R.H.
Crease recovery – 90% R.H.
Crease retention – 65% R.H.
Crease retention – Wet
Stability – Laundering
Durability
Strength – Tear
Abrasion resistance
Garment
performance
Static resistance
Melt resistance
% polyester % acrylic
Nylon-acrylic Viscose-nylon
Aesthetics
Texture
Liveliness
Bulk
Wear-care
properties
Crease recovery – 65% R.H.
Crease recovery – 90% R.H.
Crease retention – 65% R.H.
Crease retention – Wet
Stability – Laundering
Durability
Strength – Tear
Abrasion resistance
Garment
performance
Static resistance
Melt resistance
% acrylic % nylon
Figure 2.9: Property spectrum of different fiber blends with optimum blend proportions [54].
2.7 Polyester/cellulosic blends
Polyester/cellulosic (PES/CELL) blends occupy an important place in textile materials and are the
most commonly produced blend in the market. The primary reason for their success is their
excellent performance properties and low cost. Cotton and other cellulosic fibers have been used
in textiles for centuries and with the introduction of polyester they were blended in different
proportions. These blends became extremely popular since their introduction in the early 1960s
[56, 57]. The polyester fiber is more commonly blended with cotton and viscose compared to wool.
This may be attributed to the ease of processing, effective removal of disperse dye stains (clearing),
32
and a multitude of applications in the case of cotton. A wide range of dyed and finished effects
thus can be produced [9].
PES/CELL are available in different blend ratios such as 80/20, 67/33, 50/50, 55/45, and
20/80. Some blend ratios are more popular than others such as 50/50 and 67/33 (65/35). The
polyester provides easy care properties while the cotton contributes comfort properties in the blend
[58]. A small percentage of polyester fiber in the blend improves abrasion resistance but does not
provide a significant benefit in strength as shown in Figure 2.10 [8, 59]. With higher percentage
of polyester fibers in the blend the strength is improved and is better than the 100% cotton yarn.
Polyester contributes to the high crease recovery and durable press while cotton improves the
moisture absorbency properties of PES/CELL blends. Since cotton has a higher moisture regain
than polyester it absorbs moisture and provides comfort in garments made of PES/CELL blends
[59]. The moisture regain properties of PES/CO blend decreases with increase in the polyester
content of the blend as shown in Figure 2.11 [60].
Figure 2.10: Variation in yarn strength of PES/CO as a function of polyester content [8].
33
Figure 2.11: Variation in moisture regain properties of PES/CO fabrics with polyester content
[60].
While polyester was available in the market in the very early 1950s, commercial blends of
polyester/cotton did not become available until the late 1950s. Initially polyester was blended with
wool [61]. Over the years polyester fibers were blended with almost every fiber available in the
market due to economic reasons or to achieve other attractive properties and effects. However,
only a few blends have survived in the market [56, 57].
The most common PES/CELL blend is polyester/cotton, but polyester/viscose is also used
depending upon the application. They are blended in different ratios depending on the end-use
[57]. Other cellulosic fibers such as Modal, Lyocell and linen are also blended with polyester.
These blends offer a perfect break-even of contrasting physical properties of natural and synthetic
fibers. They are used in a multitude of applications in the form of yarn, wovens, and knits with
different colored and finished effects [9].
In yarns, they are used in sewing threads and slub yarns for apparel. The application of
woven PES/CELL blends includes shirting, sheeting, outerwear, and workwear. The most common
blends are the staple PES/CO blend with the 65/35 blend ratio and the PES/CO of 50/50 ratio.
These blends are made in different constructions and are mostly dyed by continuous methods. The
common knitted constructions of PES/CELL blends are fleece knits, interlocks, and jerseys which
are used in sportswear, T-shirts, and dress wear. The presence of polyester in the blend improves
34
the elastic recovery of knit goods [62]. These fabrics are generally dyed by a batch process on jet
dyeing machines due to their lower dimensional stability. Jets offer shorter dyeing cycles, lower
liquor ratio, high turbulence, and strong washing conditions. If the fabric is not prone to creasing
during dyeing in jets, presetting can often be avoided [9].
Polyester/cotton is the most important blend. The fabric ranges from lightweight poplin
shirting to heavy drill workwear. The most important shortcoming of the woven blended fabrics
in the late 1950s was their inability to retain creases in garment form. This was overcome with the
development of durable press finish with deferred curing option i.e., where the reaction of the
finish with the cotton component of the blend in the constructed garment takes place once the
creases have set in. This finish, when applied to cotton alone in the early 1960s, resulted in the
loss of strength and abrasion resistance. In the case of blends, polyester provides durability and
crease resistance and thus this problem was overcome. This finish type is further optimized by
improvements in finish formulations, fiber blending, and garment curing methods [9]. Woven
polyester/cotton blends are used in a broad spectrum of apparel due to their performance and
aesthetics reasons. They are produced in large quantities and often their price is determined by
commercial factors instead of their characteristics. [63]
Polyester/viscose has become a vital blend for apparel substituting polyester to a larger
extent in the late 1980s and early 1990s. The main reasons for their popularity include the superior
comfort and the physical and chemical finishes that can make these fabrics unrecognizable from
the starting material. This makes them suitable for a diverse range of applications [64]. Regular or
crimped viscose types can be used with polyester in blends. Crimped viscose, a specialized type
of viscose, can be made by chemical crimping during the regeneration process. This produces
filaments with asymmetric cross-sections that leads to helical curves in the filaments, thus forming
crimped fibers. The crimped fiber is blended with polyester in 65/35 ratio which has become a
popular blend for production of apparels [65]. Other important regenerated cellulosic fibers that
are often blended with polyester are Modal and Lyocell. Their applications include lightweight
tropical suiting, fashionwear, raincoats, leisure clothing, and sportswear. Due to their higher luster
and softness, they are more suitable than cotton for blends used in knitwear [9]. Modal in the blend
improves the dimensional stability and shape retention of the knitted goods [62]. Polyester rich
blends with modal are of interest for rainwear, and for lightweight constructions as summer
clothing [9].
35
Polyester/linen can be used as an alternative to polyester/cotton in luxury applications due
to the characteristic nature of the linen texture. It is used in high-quality fashion articles, tableware,
and bed linen [9].
Conventional polyester is generally used in blends. The fiber type used is generally fine
and round with no profiles. The length and diameter of polyester fibers should be adapted based
on cotton spinning system used. For the cotton system, the length and diameter should be similar
to cotton fibers. Initially, the polyester fibers known as the first-generation had a cut length
between 38-40 mm and fineness of 1.7 dtex. The fiber finishes and crimps levels were optimized
to match the cotton spinning systems. Polyester fibers of 0.7-1.3 dtex are currently used [66]. For
yarns up to 30 Ne, 1.7 dtex is suitable and for yarns of Ne 20, 2.6 dtex are generally used.
Commonly produced blended fabrics contain polyester/cotton warp and weft yarns at 65:35 or
50:50 blend ratio. Texturized or flat polyester may also be used in the weft to produce a blended
fabric with either blended or cotton warp yarns [57].
2.8 Other common blends
2.8.1 Polyester/wool blends
Wool fiber is often blended with polyester in various ratios mainly due to cost but also to provide
good properties. These blends are mainly used in apparel applications such as dresses, suits, skirts,
blouses, etc. Polyester/wool is the most popular blend due to its lightweight, good strength,
drapability, easy washability, and lower cost compared to 100% wool materials. The wool
contributes warmth, resiliency while polyester provides strength, abrasion resistance, and lower
cost. Typical blend ratios are 55/45, 65/35, and 50/50 [67, 68]. The polyester fibers are
technologically modified to make them suitable for blending with wool. They are completely
preshrunk before blending and have stronger crimp and lower strength. They have a lower degree
of stretching and higher affinity for disperse dyes than other polyester types [68].
2.8.2 Polyamide/cellulosic blends
Nylon is often blended with cellulosic fibers to improve durability. The blending of nylon with
cellulose improves the strength and abrasion resistance while maintaining comfort properties of
cellulosic fibers in the resultant blends [46]. These blends find their use in the sportswear market.
Cotton or viscose fibers can be blended with nylon [69]. The blended material comprise of either
36
intimately blended yarns or different warp and weft yarns to form union mixtures. The blend ratio
varies greatly and the nylon content in the blend may be in the range of 10-50%. These are typically
used for shirting and blouse material, ladies’ garments and work clothing. The union blends of
polyamide/cellulose consist of texturized polyamide yarn in warp and cotton or viscose yarn in
weft [70].
2.8.3 Elastane blends
Textile materials containing elastane yarns are widely used for production of clothing material for
lingerie, swimwear, sportswear, outerwear and hosiery products. Elastane yarns have very high
elastic stretch (550-600%) properties. They are blended with both natural (cotton, regenerated
cellulosic fibers) and synthetic fibers (polyester, polyamides) in a wide range of proportions (5-
35%). Elastane yarns are processed into woven, warp and weft knitted fabrics in different forms.
These include bare route, covered, twisted, core-spun and air-intermingled. The presence of
elastane in the material provides extensibility, elasticity, comfort and ability to retain shape after
extension. The selection of material containing elastane yarns depends on whether the material is
used in stretched form or in the loose state [71, 72].
2.8.4 Microfiber blends
These blended fabrics, made from standard diameter fibers and microfibers or filaments, were first
introduced in the late 1980s and early 1990s. The main reason for the development of microfiber
containing fabrics was to obtain finer and richer look without a characteristic synthetic shine and
good drapability as compared to blends made from standard diameter fibers. Microfibers are
classified as having a diameter of 1 denier or less, but the microfibers used in the production of
blended fabrics are slightly coarser. Polyester microfibers are blended with wool for tailored
clothing. The polyester microfiber component varies from 5-65% by weight. The standard
polyester used for worsted blends has a denier of 3.5. The microfibers currently employed have a
diameter in the range of 1.5-1.9 denier. The polyester fibers may be finer than the wool fiber
depending on the wool type [8, 49]. Polyester microfibers are also blended with viscose having
50/50 ratio to produce a casual shirt. Nylon microfibers are successfully blended with cotton, wool
and elastane for a variety of garment types [8]. Polyester/nylon microfiber blends are also produced
37
by conjugate spinning. They are used in imitation suede, silk-like fabrics, active sportswear, ultra-
high-density fabrics and high-tech cleaning cloths [73].
2.9 Application classes of fiber blends
Fiber blends found their use in a variety of applications. They are used in apparel workwear
clothing, military textiles and clothing, industrial fabrics, cords, ropes, geotextiles, medical
textiles, and home textiles [19].
2.9.1 Intimate yarn blends
These can be classified as parameter or structural blends. Parameter blends are mixtures of fibers
that vary in mechanical or chemical properties, in diameter, length or cross-section. Structural
blends contain fibers or yarns of different properties placed at particular locations in yarn or fabric
to target distinct product property [19].
2.9.2 Bulked yarns
These yarns have greater voluminosity because of mechanical or chemical treatments. In the case
of staple fibers, different shrinkage levels are blended to increase bulk since high shrink fibers in
subsequent wet and heat treatments contract. Fibers are converted to top and then blended in the
pin drafting process, thus any blend ratio can be achieved. A high shrink level of 40-60% is
generally used. This is very common in acrylic fibers. Bulky yarns containing 50% high shrink
polyester, 20% normal polyester and 20% natural fibers are also available for knitwear. Bulky
yarns containing 50% high shrink polyester and 50% normal polyester are also used [19].
2.9.3 Composite yarns
These yarns consist of both staple fibers and filaments of the same or different types. Core spun
yarns, with filament core and staple sheath and wrap spun yarn with staple core and filament wrap
are the examples of composite yarns [19].
2.9.4 Structurally blended yarns
These types of yarns are produced under conditions that facilitate preferential migration of fiber
or filaments in the yarn. One of the components is migrated to the core while the other fiber moves
38
to the surface of the yarn. The process control requires proper selection of fiber types based on
their stress-strain properties, differences in fiber diameter or staple length. The proper allocation
of fibers to the core and the surface is complete after a rope making process where fiber migration
is suppressed [19].
2.9.5 Structurally designed hawsers
The hawser structure contains filaments of different physical and chemical properties restricted to
specific locations. This is possible due to the special rope making equipment. A
polyester/polypropylene rope is used extensively in the utility and marine industry. For ocean
tugs, polyester hawsers made of different types of polyester yarns are used to compensate for the
cyclic loading incurred during use. They are made of high tenacity polyester in the core with a
different elongation to rupture as compared to the sheath braid. These two fiber arrangements
according to individual stress-strain characteristics compensate for the local strain [19].
2.9.6 Structurally blended fabrics
They are mostly used in technical fabrics such as paper maker felts. Such fabrics are made by
covering the base structure of filament yarns with the staple batting. This is done by needle
punching to reduce porosity and provide a smooth surface for contact with the processed paper.
Woven fabrics containing different warp and weft yarns are typical examples of the structural
blend. Warp yarns differ in fiber content and processing history from weft yarns. An example of
such structure is the geotextile lining materials used in oil containment booms. They are made of
two different yarns as this structure requires higher strength in one direction and higher elongation
in the other [19].
2.9.7 Filling material blends
Polyester fibers are widely used as filling materials in pillows, sleeping bags, quilted covers, and
furniture padding. The fiber can be a hollow type which provides more insulation per unit weight
or blended product. These blended products may contain fibers or filaments of the bicomponent
type that can be bonded together at the contact points to provide structural support or microfibers
to provide thermal conductivity like down and feathers [19].
39
2.9.8 Biomaterial blends
These are the type of structural blends found in prosthetic devices in which polyester is blended
with bioabsorbable polyglycolides. The polyester maintains the integrity of the implant [19].
2.9.9 Static controlling blends
The main problem associated with hydrophobic fibers is static charge generation. This may cause
many problems such as fabric clinging, and discharge of unpleasant sparks when walking on
carpets. To resolve this problem in carpets steel fiber was cut to staple fiber length and blended
with nylon or polyester pile yarn. Fibers containing conductive carbon are also used to overcome
this problem. One approach to incorporate carbon is the use of a bicomponent fiber. These
conductive yarns are woven into fabric in special locations to dissipate the charge. These materials
are also an example of structural blends where incorporating specific fiber provides specific
functions in the material [19].
2.9.10 Apparel blends
The garment itself may be a blend of different materials to provide different properties and
functions. Different fibers and fabric structures are used for outerwear clothes, linings, and
trimmings. The layered design of functional clothing, used by the army and in sports for protection
against cold, contains blended materials. Each layer has a different function to perform, the base
layer is responsible for moisture management, the insulating layer traps and stores warm air, and
the outer layers protect against wind, water, tear and abrasion and allowing water vapors to pass
through [19].
2.10 Manufacturing/production of blended textiles
Blending is a complex and expensive process but the resultant combination of properties of the
blend are permanent [47]. There are different ways the blending of fibers can occur depending
upon the fiber components. Obtaining a perfect blend ratio distribution is impossible to achieve as
local blend varies across and along the yarn. Blend constancy is important for uniformity of color
although heather effects can also be produced by blending different stock dyed fibers [19]. The
following methods can be used to produce blends [17, 18]:
▪ Staple fibers can be combined in flock or sliver form;
40
▪ Staple and/or filament yarns can be combined utilizing twisting, plying or entangling;
and
▪ Yarns made of individual fibers are combined during the fabric manufacturing.
The first method is usually performed during opening, carding, drawing; combing, sliver,
ring and rotor spinning. The second method involves plying yarns and core-spun yarns. In the third
method filament yarns and staple yarns may be employed to produce the blend [18].
Intimate blending involves the mixing of fibers in stock form. This blending method
provides a uniform distribution of fibers across the yarn cross-section and along its length. It can
occur in the early stages of processing such as during the opening stage. Several bales of fiber are
laid near the bale picker and each bale is fed alternatively. In another method, sandwich blending
is carried out, where the precise amount of each fiber is spread over the preceding layer to form
the sandwich. Vertical sections are then removed from the sandwich and fed to the picker. The
fibers can be mixed before being fed to the carding machine. This requires separate cleaning stages
as natural fibers may require more cleaning stages [19, 47]. This is carried out by blending hoppers.
Each fiber after the cleaning stage is fed into the hopper. The individual hoppers precisely feed
each fiber into the mixing belt. Precise blend ratios can be obtained by this method [47].
Blending can also be done later at the blending draw frame. This provides the advantage
of proper cleaning at the carding stage as settings can be optimized for a particular fiber type. It is
also more suitable for fibers that have different physical properties. The fibers can be processed
separately until the carding or combing stage depending upon the yarn type. In the case of
polyester/cotton blends, the carded or combed cotton slivers and carded polyester slivers are used.
In the case of wool and synthetic fiber blends spun on the worsted system, the blending can be
done in different ways. They can be blended before recombing or before drawing stages. The
synthetic fibers are used in the form of tops produced from tow to top conversion processes [19].
The blending process can also be done on the roving and spinning stage. The fiber strands
are combined to reduce linear density and increase the amount of twist to achieve the required yarn
linear density and twist level. This is mostly used for blending colors to produce novel color
effects [47].
41
In another method of blending at the spinning stage, core spun yarns are produced. A core
yarn consists of staple fiber covered with filament or staple fiber core, generally of a different
material [19].
2.10.1 Fiber distribution in blended yarns
In blended yarns, if the fibers are randomly distributed there is an equal chance of fiber to settle at
a given radius in the yarn’s cross-section. This does not imply that fibers will remain in a set radial
ring all the time. The control of the fiber placement in the blended yarn is an important control
parameter. In ring spun yarns, fibers are arranged in the form of helices. The helices are nearly
concentric yet migrate from the yarn surface to the core and back to the surface. It has been found
that in the yarns made of two fiber types fibers show preferential distribution. One fiber component
tends to prefer the core or central region while the other tends to reside in the outer radial rings
[19]. The short, coarser fibers in the blend tend to migrate to the outside edge of the yarn while the
shorter, fine fibers migrate to the center of the yarn [47]. This type of distribution has both
favorable and unfavorable implications. If the fiber present in the outer layers has a higher dye
affinity than the other component, then this distribution is favorable in piece dyeing. During the
spinning of polyester/cellulosic blends, the cellulose fibers tend to migrate to the surface of the
yarn creating a blended yarn with more cellulosic fibers on the surface than the whole yarn.
Viscose fibers show more migration than cotton and this effect is more prominent at higher
humidity levels in spinning. However, if the shade correction is required then the fiber present in
the outer layer will pick up more dye than the one present in the core [19]. This migration may
result in a more prominent effect if shading is done in a cellulosic component to match the target
[57]. For high fabric durability, it is desirable to have the fiber with higher abrasion resistance on
the surface of the yarn. The concentration of hydrophilic fibers on the surface improves the hand
and comfort of the fabric [19].
The earlier the fibers are blended during spinning, the better is the arrangement of the fiber
in the blends. The longitudinal and radial distribution of the fibers in the blended yarns is shown
in Figure 2.12. The fibers blended in flock form are more uniformly distributed than the ones
blended in sliver form [47, 74].
42
Figure 2.12: Fiber distribution in the blended yarns produced by sliver and flock blending
methods [74].
43
CHAPTER 3 COLORATION OF TEXTILE FIBER BLENDS
3.1 Introduction
The dyeing of textile materials is an old art. As blends of two or more fibers entered into the market
the dyer has to go through new learning experiences to deal with new problems and challenges
that are created. There has been an increasing pressure on the dyer to reduce dyeing cost by right
first time dyeing methods along with low water and energy consumption, reduced effluent costs
keeping higher fastness properties [75]. With the increasing popularity of the blends, special
attention is required in the dyeing due to differences in the dyeing characteristics of each fiber
component in the blend. Each fiber component in the blend can be dyed either separately or
simultaneously. The main criteria that decide the dyeing method is the cost and the required
fastness properties. Both dyes and pigments can be used in the dyeing of blends [9, 76].
3.2 Classification of blends according to their dyeing behavior
Blends are usually classified in terms of the fiber type in a blend. This classification is not useful
for dyeing purposes as it is based on a particular fiber type in the blend. The useful classification
may take into consideration the dyeing behavior of the fiber component in the blend. The blends
can be classified into four substantive groups based on the classes of dyes used to obtain dyeings
in full depth. This is known as the ABCD classification. This classification of fibers based on their
ability to obtain full depths in dyeing is useful as many challenges in the dyeing of blends become
more prominent under these conditions. Fibers can be dyed with acid dyes in full depth. These
include wool, silk, elastane, and acid-dyeable fiber variants. B for fiber dyed with basic dyes in
full depths such as acrylic and modacrylic fibers and basic dyeable polyester and nylon fibers. C
fibers can be dyed with cellulosic dyes in full depths. This comprises of cotton, viscose, modal,
lyocell and linen fibers. D for fibers dyed with disperse dyes in full depth such as cellulose acetate,
triacetate, and polyester fibers [7, 9, 77]. The classification of binary blends according to this
method is given in Table 3.1.
44
Table 3.1: Classification of binary blends according to their dyeing properties [9].
AA blends
Wool/silk
Nylon/wool
Nylon/silk
Wool/polyurethane
Nylon/polyurethane
AB blends
Wool/acrylic
Silk/acrylic
Nylon/acrylic
Elastane/acrylic
Wool/modacrylic
Nylon/modacrylic
AC blends
Wool/cotton
Nylon/cotton
Elastane/cotton
Wool/viscose
Silk/viscose
Nylon/linen
CB blends
Cotton/acrylic
Viscose/acrylic
Cotton/modacrylic
Viscose/modacrylic
CC blends
Cotton/viscose
Cotton/modal fiber
Cotton/linen
Linen/viscose
DA blends
Polyester/wool
Polyester/silk
Polyester/nylon
DB blends
Polyester/acrylic
Polyester/modacrylic
Normal/basic-dyeable polyester
DC blends
Polyester/cotton
Polyester/viscose
Polyester/modal
Polyester/linen
DD blends
Cellulose triacetate/polyester
Normal/deep-dye polyester
45
3.3 Color effects produced on blends
The various color effect can be produced during the dyeing of blends [7, 9]. These are as
follows:
▪ Solid or union
All components of the blend are dyed as close as possible to the same, hue, depth and
brightness. Binary blend, a blend of two or more fibers, are often dyed to achieve this
effect. The underlying reason is due to their design criteria. These blends are produced
to achieve economics, durability and desired physical properties and not for achieving
multicolored designs. Fiber components in the blend determine the extent to which
solid dyeing can be achieved. The solid effect is difficult to achieve in blends of
polyester with cellulose acetate in which both components can be dyed with disperse
dyes. For polyester/nylon or polyester/acrylic, this effect can be achieved by shading
with acid or basic dyes. In blends of nylon with wool, elastane or cellulosic fibers,
reserving or blocking agents can be used to achieve this effect.
▪ Reserve or resist
One of the fiber components in the blend remains undyed. Cross-staining is the major
problem in this type of dyeing effect. This problem is more common in fiber blends
with different dyeing properties such as disperse dyeable synthetic fiber blended with
natural fibers. It is also difficult to achieve reserve effect in acid dyeable fibers blended
with wool. The problem leads to poor fastness properties. Proper section of dye and
dye conditions or use of resist agent or reduction clearing treatment may help in
minimizing the degree of cross-staining.
▪ Shadow or cross stain or two-tone or tone-in-tone
All the fiber components in the blend have the same hue but different depths. This color
effect is in between solid and reserve effects. This effect is best achieved when paler
depth is between one-third and one-half of the deep-dyed fiber component. This effect
can easily be achieved in blends with all components of the fiber can be dyed with the
same dye class as compared to the blend requiring different dye classes.
▪ Contrast or cross dye
In this type of dyeing effect, fiber components in the blend are dyed with the same
depths but contrasting hues. This color effect cannot be achieved on blends where fiber
46
components have similar dyeing properties such as blends of cellulosic fibers with one
another, polyester fibers with one another and blends of nylon, wool or elastane blends
with themselves. Blended fabrics comprising of acid-dyeable with basic-dyeable
synthetic yarns showed the best contrast effect. For blends that are more prone to cross-
staining only partial contrast effect are possible.
The different color effects that can be achievable in binary blends are shown in Table 3.2.
Table 3.2: Color effects in binary blends [9].
Blend type
(example)
Color effect
Solid Reserve Shadow Contrast
AA (nylon/wool) Use of
auxiliaries
Neither
component
Easily
controlled
Not
possible
AB (nylon/acrylic) Easily
controlled Acrylic reserve
Seldom
required
Wide range
available
AC (nylon/cellulosic) Easily
controlled
Cellulosic
reserve
Seldom
required
Wide range
available
CB (cellulosic/acrylic) Easily
controlled
Either
component
Seldom
required
Wide range
available
CC (cotton/viscose) Dyeing
conditions
Neither
component
Viscose
deeper Not possible
DA (polyester/wool) Dyeing
conditions
Polyester
reserve
Seldom
required
Limited range
DB (polyester/acrylic) Easily
controlled
Polyester
reserve Acrylic deeper
Limited
range
DC
(polyester/cellulosic)
Easily
controlled
Either
component
Seldom
required
Wide range
available
DD
(triacetate/polyester)
Dyeing
conditions
Polyester
reserve
Easily
controlled
Not
possible
47
Due to economic reasons, it is desirable to have a dyeing time of blend less than the sum
of dyeing time required to dye individual components in the blends keeping high-quality levels
and operational flexibility. The process of dye blend can be classified into conservative or rapid,
depending on how the fiber blend materials are dyed. During the conservative process, the
individual fiber components in the blend are dyed separately. On the other hand, the rapid process
involves the elimination of some process steps involved in a conservative process thereby
achieving short process timings [7].
Dyeing methods can also be classified based on the number of dye classes and dyebaths
used to dye fiber blends. A fiber blend can be dyed with a single dye class in which one dye is
distributed between two fiber components in the blend. This is only possible if both fibers have
the same dyeing properties. Solid and shadow effects can be obtained with this method, but reserve
and contrast effects are not possible. Fiber blend materials can also be dyed with two separate dye
classes using appropriate dyeing conditions according to fiber and dye class. Because of the
separate dyeing process, the cross-staining can be eliminated. This method can achieve solid,
reserve shadow and contrast color effects. Due to economic reasons and flexibility, different
dyeing methods have been developed. These are one-bath and two-stage methods. In one bath
method, separate dye classes are used for each component in which both components are dyed at
the same time. The two-stage method involves the dyeing of individual fiber components using
separate dye classes in succession. Table 3.3 shows the classification of dyeing methods [9].
Table 3.3: Methods for dyeing of fiber blends.
Methods Dyebaths Dye classes Stages
Single-class One One One
One-bath One Two simultaneously One
Two-stage One Two in sequence Two
Two-bath Two Two Two
48
3.4 Factors affecting the dyeing of fiber blends
Important points that need to be considered in the dyeing of blends are [18, 78]:
▪ Effect of pretreatment on the individual fibers in the blend.
This can include desizing, scouring, bleaching, etc. The effect of any of the chemicals
used on all of the fibers in the blend must be established before processing
▪ Fastness properties required
Wet fastness is the most common challenge dyeing of blends
▪ Dyestuff cross-staining properties
Many dyes that are used to dye one fiber may stain the other fiber(s) in the blend. In
some cases, a selection of non-staining dyes will be available.
▪ Dyes and auxiliaries' compatibility and their chemical/physical effect
There might be chemical and/or physical interaction between dyes and chemicals used
for dyeing of each fiber. The compatibility problems such as perception or blocking
should be considered.
▪ Dyeing method
Dye procedure is determined by dye selection. The limitation of the dyeing procedure
is determined by the properties of the specific fibers in the blend.
▪ Effect of finishing processes on the dyed material.
This includes the effect of chemical and or mechanical finishing on the dyed materials.
3.5 Challenges in the coloration of fiber blends
The main challenges associated with the coloration of fiber blends are [7, 9, 77, 79]:
▪ Cross-staining of the fiber by the dye intended for the other fiber type;
▪ Fastness problems;
▪ Interaction between dye classes or between a dye and dyebath auxiliaries;
▪ Dye stability at high temperature and in different pH conditions;
▪ Effect of additional processing required to fix each dye class on a respective fiber
component on the other fiber component in the blend;
▪ Effect of second fiber component in the blend on increasing the liquor ratio
significantly;
49
▪ Problems in obtaining solid shade in the same fiber type due to differences in saturation
limits of the component fibers;
▪ Obtaining solid shade in the blend by matching shade of an individual fiber type; and
▪ Fiber damage and/or yellowing.
3.5.1 Cross-staining of the fiber by the dye intended for the other fiber type
Cross-staining is a serious problem in the dyeing of fiber blends especially containing fiber
components having different dyeing properties. This is generally observed in the blends of natural
fibers with synthetic fibers. The synthetic fibers which are only dyed with disperse dyes are more
prone to this problem [9]. The staining tendency of different fibers with disperse dyes are shown
in Figure 3.1. Elastane and wool fibers are much strongly stained by disperse dyes due to the
hydrophobic nature of these fibers as compared to cotton and viscose fibers [80]. The wool cuticle
is hydrophobic that allows disperse dyes to heavily stain the wool component. The mechanism of
wool staining consists of hydrogen bonding, dipolar and van der Waals interaction between
disperse dye molecules and sorption of the aggregated particles of the disperse dyes on the cuticle
of the wool fiber [9].
Cross-staining also important if a reserve effect is required. It is very difficult to achieve
reserve effect on acid dyeable fiber blends such blends of wool, nylon or elastane blends. The
nylon fibers give poor reserve effect with polyester, cellulosic and acetate fibers. Acrylic fibers
are difficult to reserve with disperse dyeable polyester fibers. In the case of blends containing deep
dyeable and normal dyeable variants, it is impossible to reserve a deep dyeable component. The
reserve effect is usually easy to achieve in blends of acrylic or polyester fibers with cellulosic
fibers and in synthetic fiber blends containing acid dyeable and basic dyeable fiber types [9].
The following approaches can be used to minimize cross-staining [9]:
▪ Selection of dyes with high affinity for the fiber to be dyed with that dye class and
lower affinity for other fiber components in the blend.
▪ Using dyebath conditions that allow maximum exhaustion of the dyes to the intended
fiber to be dyed with that dye class.
▪ To achieve reserve effect on one fiber, special colorless dyebath additives may be
added that preferentially absorbed to the fiber to be reserved and resist the sorption of
dyes.
50
▪ Depending upon the dye class a clearing treatment may be performed to remove the
dye stain that may involve desorption of dye by washing with detergent or dye
destruction either by reduction or oxidation treatments.
Figure 3.1: Staining of different fibers by disperse dyes during the dyeing process [80].
3.5.2 Fastness problems
The fastness properties of the fiber blends are generally inferior as compared to single fiber
materials. They may be attributed to the cross-staining of the fiber by dye class used for the dyeing
of the other fiber component. The stain has poor fastness properties [9]. Since some fibers such as
wool, acrylic, and elastance can be damaged at higher dyeing temperature used for disperse dyeing
of polyester component, the dyeing temperature is reduced to minimize this problem. This
aggravated the staining problem in two ways. Firstly, the staining of disperse dyes is excessive at
lower dyeing temperature. Secondly, the dye selection may be limited to lower energy disperse
dyes that may give lower fastness properties [9, 77, 81, 82].
Fiber blended with polyester
Low
High
Cotton
Viscose
Acrylic
Polyamide
Wool
Elastane
Deg
ree
of
dis
per
se
dye
stai
n
51
The disperse dyes have a tendency to desorb from the polyester and stain the cellulose
component of the blends during subsequent dyeing of the cellulosic fiber. This results in additional
staining of cellulose. However, this problem is limited to low energy disperse dyes in comparison
to several medium and high energy they didn’t exhibit this behavior [83]. The polyester/cellulosic
blends are often resin finish to improve the crease recovery and pilling properties. At high resin
finishing temperature (> 150 oC) disperse dye may migrate from the interior of the fiber to the
fiber surface at high temperature. This phenomenon is known as thermomigration. This
deteriorates the fastness properties of the blends and causes more staining of adjacent nylon during
the fastness tests [9, 79, 83].
3.5.3 Interaction between dye classes and dyebath auxiliaries
Polyester/cellulosic blends can be dyed either by one or two bath process using disperse and
reactive dyes. During one bath process, both dyes are fixed simultaneously. Dye selection is
important especially for one bath process due to the risk of interaction between the two dye classes.
These interactions lead to a loss in color yield or dye precipitation. The two dye classes may react
with each other to form a covalent bond. Other types of interactions may be between reactive dyes
and dispersing agent or instability of the dispersion system under the alkaline conditions [9].
It has been found that during the one bath thermosol process, disperse containing phenol
and amino groups may react with reactive dyes containing highly reactive monochlorotriazine
groups to form a covalent bond. The bond form found to be unstable and easily decomposed by
alkaline hydrolysis [84]. This problem can be avoided by selecting reactive dyes of low reactivity
or disperse dyes that do not have amino or phenolic acid groups. Using reactive dyes of low
reactivity allows a wider range of disperse dyes can be selected. Another approach is to control
the pH of the pad liquor to minimize problems of a chemical reaction by using the two-stage, pad-
dry-thermosol-chemical-pad steam process. The two-stage process allows a broader range of dye
selection. During this process, both disperse ad reactive dyes are padded first under neutral pH
conditions. The pad bath usually contains an anti-migrating agent along with a mild oxidizing
agent (sodium meta-nitrobenzenesulphonate) to avoid reductive decomposition of certain azo
reactive dyes. The disperse dyes are fixed by the thermosol process. The fabric is then padded with
alkali and salt followed by steaming to fix the reactive dyes. The rinsing and washing complete
the process [9].
52
The disperse dye dispersions are not stable under high quantities of salt used in dyeing with
reactive and disperse dyes to promote dye exhaustion. This may cause dye aggregation and
prevents the leveling and migration of disperse dyes. Since powder and grain type disperse
contains more dispersing agent than liquid dyes, they exhibit more stability as compared to liquid
dyes [79].
In polyester/acrylic blends the presence of anionic dispersing agents may interact with
basic dyes or cationic retarding agents used for the dyeing of acrylic fibers. Different approaches
may be used to minimize this problem. The use of nonionic emulsifier and anionic retarder may
help in reducing the interaction. The anionic dispersing agent must be avoided if possible.
However, the alternate products maybe not as effective in their performance as compared to actual
products. The anionic dispersing agents already present in the disperse dye formulation cannot be
excluded [9, 77].
The anionic dispersing agent present in the vat dyes is incompatible with the basic dyes
and cationic retarding agents during one bath dyeing of cellulose/acrylic blends. The basic dyes
are also chemically unstable under strongly alkaline conditions required for the vat dyes. This
limits the application of the vat/basic dye system to be applied by two bath process [9].
3.5.4 Dye stability at high temperature and pH conditions
The dyes selected in the dyeing of blends must be stable under the dye bath conditions (pH and
temperature) employed for other fiber components of the blend. During one-bath, dyeing of
polyester/cellulosic blends using disperse and vat dyes, the stability of vat dye dispersion is
important under disperse dye conditions. The vat dyes in the oxidized form are chemically stable
under high temperature conditions employed in the dyeing of a polyester component with disperse
dyes, However, dyeing carried out for a longer duration at high temperature may cause instability
of the vat dye dispersion. It is recommended during batchwise dyeing to add vat dyes at a lower
temperature after high temperature dyeing of polyester component The direct dyes applied along
with disperse dyes in one bath process should be soluble and stable under slightly acidic and high
temperature conditions employed for disperse dyeing. Not all direct dyes are stable under these
conditions. This is also applicable to th one bath and reverse two bath dyeing with reactive dyes.
Some reactive dyes may not be stable at high temperature and slightly acidic pH conditions
employed for disperse dyeing. The high temperature and slightly acidic conditions cause acidic
53
hydrolysis of reactive dyes leading to a depth of shade. This effect is more prominent in highly
reactive dyes compared to dyes of medium reactivity. Some disperse dyes are very sensitive to
alkaline pH conditions employed during reactive dyeing. The color yield of disperse dyes tend to
be lower under alkaline conditions [56, 79].
3.5.5 Effect of additional processing required to fix the dye class
In the dyeing of polyester/cellulosic blends, the disperse dyes once diffused into the interior of
polyester fibers are usually resistant to subsequent chemical and physical treatments. This is due
to the hydrophobic nature of the polyester fibers which prevents the penetration of many
chemicals. The disperse dyes, however, are susceptible to physical and chemical interactions when
they are present in the dyebath. The direct and reactive dyes applied to cellulosic fibers are
susceptible to damage whether they are present in the dyebath or on the fiber. The reduction
clearing process performed to remove the disperse dye stain and surface disperse dye will also
destroy the reactive and direct dyes. The alkaline conditions required to fix the reactive only
destroy the surface disperse dyes. The disperse dyes present in the fiber interior are not affected
[79].
3.5.6 Effective liquor ratio and blend ratio
Liquor ratio directly influences the reproducibility and economics of the batch dyeing process. The
effective liquor available for the dyeing each fiber component in the blend depends on the blend
ratio. The effect of the blend ratio on the effective liquor ratio is shown in Table 3.4 [79].
At a liquor ratio of 10:1, the effective liquor ratio available for a blend ratio of 50/50 is
20:1 for each fiber component. When the blend ratio is increased to 80/20 the effective liquor is
changed to 12:1 for fiber 1 and 50:1 for fiber 2. This causes a significant change in the effective
liquor ratio for fiber 2. It is well known that at higher liquor ratio the exhaustion and fixation of
the dyes are lower compared to lower liquor ratio. This requires more quantity of dye to match a
given shade at a high liquor ratio compared to a lower liquor ratio. Therefore, to achieve good
color yield and fixation values, the dyes having high substantivity should be selected. This ensures
an efficient, inexpensive and reproducible dyeing process [79].
54
Table 3.4: Effect of blend ratio on effective liquor ratios in the dyeing of blends.
Effective liquor ratio
Blend ratio 50/50 65/35 80/20
Liquor ratio Fiber 1 Fiber 2 Fiber 1 Fiber 2 Fiber 1 Fiber 2
5:1 10:1 10:1 8:1 14:1 6:1 25:1
10:1 20:1 20:1 15:1 29:1 12:1 50:1
15:1 30:1 30:1 23:1 43:1 20:1 75:1
20:1 40:1 40:1 31:1 57:1 25:1 100:1
3.5.7 Distribution of single dye and fiber saturation differences
During the dyeing of blends, a single dye may be distributed between the fiber component. This
distribution is determined by differences in the dyeing properties of the fiber components in the
blends, dyeing conditions, depth of shade, blend ratio and the dye structure. The dye distribution
that may be unequal in an early stage of dyeing is leveled out by the transfer of the dye from the
fiber component that initially absorbs a high quantity of the dye to the fiber that has a high affinity
for the dye. In the long run, more dye is absorbed by the fiber component that dye has more affinity
as compared to the fiber component that has lower affinity although it absorbs more dye at the
early stage of the dyeing process [9].
Nylon/wool blends are dyed by a single class of anionic dyes. These include acid and metal-
complex dyes. To achieve solidity of shades in these blends the dye selection is important. The
dye selected should have similar dye rates and exhaustion properties. Both fibers are dyed under
acidic conditions where both fibers acquire a positive charge. The dye rates of nylon and wool are
different from each other. The nylon shows a higher rate of dyeing in lower shade depths at 60-80
oC. The nylon fiber is more hydrophobic as compared to wool, so it attracts dyes containing a
lower number of sulfonated groups. The wool fibers exhibit more attraction for dyes which are
hydrophilic in nature. The saturation concentration in the wool is much higher than nylon. This
effect is more prominent in dark shades where wool absorbs more dye as compared to nylon.
Depending upon the dyeing conditions and at some intermediate depth, both fibers are dyed to the
same depth although nylon has higher dye uptake. This critical depth depends on the dye type.
55
Above the critical depth, the dye distribution greatly favors the wool as compared to nylon in
nylon/wool blends [9].
The cellulosic blends such as cotton/viscose or cotton/modal require proper control of
dyeing temperature and salt concentration. The viscose and modal fibers are dye darker with direct
dyes as compared to cotton. In general, it is difficult to obtain solidity of shade with direct or
reactive dyes as compared to vat or sulfur dyes. The lower temperature may also be used to ensure
solidity [9].
3.5.8 Obtaining solid shade in the blend by matching shade of an individual fiber type
One of the main challenges that a dyer has to deal with in case of blends is the solidity of shade.
The shade required to be balanced in depth and tone in each fiber component. The required degree
of solidity varies with a product, for example, dyed woven blend fabrics require excellent solidity
while carpet yarns lower solidity levels are acceptable to provide characteristic broken appearance
or difficulty in achieving solid shade due to surface features [9].
The distribution of the fiber in the blend influence the overall solidity of shade. The
blending process must be controlled. If the fiber clumps are not properly opened up and mixed,
they may give an unlevel or hazy appearance [9]. The blend ratios should be controlled to avoid
difficulties in producing uniform appearance [77]. Since the scattering properties of different fiber
types in the blends are different due to differences in fiber denier, shape, and luster, the depth of
shade in one fiber may be kept higher than the other to achieve shade solidity. In
polyester/cellulosic blends, the cellulosic component of the blend is usually dyed darker than
polyester component to achieve a uniform appearance.
Another factor that may affect the solidity of shade is staining. In polyester/wool blends,
wool is heavily stained by disperse dyes. This becomes more critical due to lower temperature
employed in the dyeing of these blends as wool may be damaged at higher dyeing temperature.
The carriers employed to obtain good penetration on the polyester component at lower
temperatures minimize this problem. The addition of a wool protecting agent also minimizes the
wool staining during prolonged dyeing [9, 85]. Some vat dyes employed in the dyeing of
polyester/cellulosic blends stained the polyester component under thermofixation conditions
employed for disperse dyes during the one-bath process [7, 9, 79].
56
3.5.9 Fiber damage and/or yellowing
The cotton component of the polyester/cellulose blend may degrade at the higher temperature
required for the fixation of disperse dyes by a thermosol process. The actual effect depends on
different factors such as treatment temperature and time, pH and additives present in the dye liquor.
The degradation increases rapidly above 150 oC. The degradation and yellowing effect are more
severe under alkaline conditions at a higher temperature. The presence of a dispersing agent
usually causes browning of cellulose at higher thermofixation temperature [56, 79].
The wool, acrylic and elastane fibers blended with polyester are damaged at higher dyeing
temperature employed for the dyeing of a polyester component with disperse dyes. To avoid
yellowing or strength the dyeing is, therefore, is carried out at 100-105 oC to minimize this damage.
During dyeing of polyester/wool blends wool protective agents may be used to minimize the
damage. This also allows dyeing to be carried out higher temperature (120 oC) [9, 77, 81, 82].
3.6 Coloration of polyester/cellulosic blends
Polyester/cellulosic blends are the most important and commonly dyed fiber blends. They are
available in different blend ratios, but 50/50 and 65/35 combinations are most common. The
polyester and cellulosic fibers exhibit different dyeability characteristics and therefore dyed with
different dye class and require different dyeing conditions [58]. The polyester is dyed only by
disperse dyes while cellulose portion can be colored by various dye classes such as direct, reactive,
vat and sulfur dyes. The selection of dyes and dyeing methods depends upon hue, depth of shade
and required fastness properties [9, 18, 57, 86, 87]. Table 3.5 shows the features and challenges
associated with colorants used for these blends [56, 83, 87]. The commonly used dye systems are
disperse/direct, disperse/reactive and disperse/vat. The disperse/reactive dye system is the most
popular due to brilliant hues, the possibility of achieving dark shades along with excellent fastness
properties [57].
57
Table 3.5: Characteristics of colorants for polyester/cellulosic blends.
Dye
systems Colorants Advantages Challenges
Two-
dye
process
Disperse/
direct
▪ Economy
▪ Shortest process time.
▪ Excellent reproducibility
through proper dye
selection
▪ Lower water, chemicals
and energy
consumption. Shades are
easy to correct
▪ High exhaustion levels.
▪ Lower quantities of salt
required
▪ Moderate wet fastness
in pale/medium shades
▪ Staining on cellulose
portion by disperse
dyes
▪ Limited selection of
direct dyes for one bath
process
Color
matching
is
dependent
on a blend
ratio
Disperse/
vat
▪ Excellent light and wet
fastness
▪ Shorter one-bath dyeing
process
▪ Heavy depth of shade
▪ Dull shade
▪ Proper control is
required in jet dyeing
Disperse/
reactive
▪ Brilliant shades
▪ Good reproducibility,
Colorfastness
▪ Lower fixation
temperature of reactive
dyes
▪ Staining on cellulose
portion by disperse
dyes
▪ Large quantity of salt
required
▪ High wastewater load
▪ Decomposition of
disperse dyes due to
alkaline conditions in
one bath process which
reduce color yield.
58
Table 3.5 (continued).
Dye
systems Colorants Advantages Challenges
Dye
systems
▪ Decomposition of
disperse dyes due to
alkaline conditions in
one bath process which
reduces color yield.
▪ Re-staining by wash
water
▪ Lower color yield for
one bath process (about
60%).
Pigment Pigment-
binder
system
▪ Economy
▪ Workability
▪ Poor rubbing fastness in heavy
shades
▪ Poor hand
These blends are dyed by both batch and continuous processes using either a one-bath or a
two-bath method depending on the lot size, availability of equipment, blend type and suitability
and process economics [18, 56, 57, 85]. Table 3.6 shows the comparison of one and two bath
dyeing methods used for dyeing [87]. Polyester/cellulosic yarns and knit fabrics are generally dyed
by a batch process. Package dyeing is more commonly used for yarns while the jet is common for
knitted and woven fabrics. Some fabrics are also dyed on beam dyeing. The majority of the woven
fabric is dyed by a continuous method using pad-thermosol, pad-steam and pad-batch ranges [9,
57].
The selection of suitable dyeing process and a particular dye class depends on [68]:
▪ Economy;
▪ Availability of equipment;
▪ Batch size;
▪ Shade and brilliancy required;
▪ Depth of shade;
59
▪ Required color effect;
▪ Type of polyester and cellulosic fiber; and
▪ Blend ratio.
Table 3.6: Comparison of one bath and two bath methods used for dyeing of PES/CELL blends.
One bath Two bath
▪ Shorter process
▪ Lower consumption of energy and water
▪ Selection of disperse dye is important as
reduction clearing is not possible
▪ Longer process
▪ Flexibility in machinery use
▪ Reduction clearing can be performed
depending upon the fastness requirement
The standard two-bath dyeing process of these blends has a long cycle time and higher
cost. Furthermore, the standard process employs a reduction clearing that uses hydrosulfite. This
creates environmental challenges. With increasing brand focus towards environment and
sustainability, the production process aims to minimize water and energy consumption along with
minimum environmental impact [88]. This is usually achieved by the one-bath method.
Although the dyeing of polyester-cellulosic blends is more challenging, requires a longer
process, more utilities, and energy they are sold at lower price owing to lower cost of polyester.
This creates a challenge for the dyer to have a balance between profit and performance. The
selection of dyes for both fibers is a prerequisite to achieving good fastness properties and shorter
dyeing process [88]. The selection of dye combinations largely determined by the end-use
requirements.
3.7 Pigment coloration
Pigment coloration involves the application of dyeing liquor by usual dyeing methods such that
the dyeing liquor consists of pigments as a coloring component and binder. Unlike dyes which are
fiber substantive, pigments are anchored to the substrate with the help of binders, which attach
itself to the fiber and traps the pigment particles. Other than pigments and binder, auxiliaries
depending on the requirements are also used. These include processing aids and fastness and hand
60
feel improver e.g. wetting agents, defoamer, anti-migrating agents, softeners, etc. [89, 90].
Pigments can be applied by both batch and continuous methods. The batch method is usually used
for garments to create wash-down effects. Fabrics made of single fiber or blends are largely colored
by the continuous method. Continuous pigment coloration is a well-established field and accounts
for 10% of the total pigment used in textile applications. The main application areas include home
textiles, bed linen, upholstery fabrics, and leisurewear. Polyester/cotton blend is the most
commonly dyed fiber blends by this method. In home textiles, they provide fastness properties
equivalent to that of vat dyes with wash fastness and adequate handle to meet the quality
requirements. Therefore, they have almost entirely replaced vat dyes resulting in time and cost-
saving [90, 91]. Generally, coloration with pigments is limited to the pale shades. The advantages
and limitations of pigment coloration are given in Table 3.7 [89, 91-95].
Table 3.7: Advantages and limitations of pigment coloration.
Advantages Limitations
Coloristic
▪ Reproducible and safe process.
▪ Faults can be easily detected.
▪ Good to excellent fastness and fabric
quality meeting market demands, excellent
lightfastness.
▪ Application is not fiber specific
Ecology
▪ Low amount of wastewater, as washing is
not required
Economy
▪ Simple application process and fixation
conditions.
▪ Can be combined with finishing, saving
time, cost, and energy
Limited shade depth
▪ Limited buildup of shade (e.g. due to high
penetration into the fabric)
▪ Large amount of binder is required for
deeper shades results in poor fabric hand
feel
▪ Special binders are required for achieving a
high depth of shade
Wet fastness profile
▪ Limited washing fastness in heavy shades.
▪ Limited results in brush wash testing, due
to the cracking of binder film
▪ Poor rubbing fastness in heavy shades
Running properties
▪ Can buildup on rollers
61
Table 3.7 (continued).
Advantages Limitations
▪ Low capital investment, no requirement of
complicated machinery
▪ Economical process and short delivery
times
▪ Low requirement of time, energy and
personnel resources
Economy
▪ For heavy shades, special binder & a large
amount of pigment are needed, increasing
the cost of the process.
Hand
▪ Dyed materials can have poor hand if
binder and softener are not properly
selected. This effect is more prominent in
thin or very heavy substrates
The fabric, appropriately prepared, is padded with a pigment coloration liquor and then
dried. To reduce the tendency of migration, the fabric is generally passed through pre-dryer before
the drying and curing process. The dyed fabric is usually fixed in a separate operation at a high
temperature. The fixation time and temperature depend on the type of binder used and the nature
of the substrate. After fixation, the dyed fabric does not need any wet after treatment e.g. washing
[89]. The standard pigment coloration process is shown in Figure 3.2 [96].
Figure 3.2: Continuous pigment coloration process.
Pad
Dry
Cure
▪ at room temperature (25-30ºC)
▪ Pick-up 60-70%
▪ at 100-120ºC
▪ In a hot-flue or in a pin stenter frame
(preferably infra red-dryer)
▪ at 140-150ºC – 5 min or 170ºC – 2 min or
185-200ºC – 1 min
62
The pigment coloration liquor normally consists of [92, 94, 97]:
▪ Pigment preparations;
▪ Binder; and
▪ Auxiliaries.
- Additives; and
- Surfactants.
Pigment preparations are the coloring agents and can be either inorganic or organic. The
pigments are restrained to the substrate with the help of binders which are film-forming substances
and tie themselves with the fiber and trap the pigments inside the film formed during the fixation
process. To improve the application properties and hand feel of a fabric, auxiliaries are also a part
of pigment coloration formulation. These include additives and surfactants. Additives are required
to improve the handle and compensate for the loss of softness due to the binder. These include
softening and smoothing agents. Surfactants are used as emulsifiers, wetting agents, stabilizers and
foam suppressants. These are added to ensure the rapid wetting of fabric during padding, improve
the stability of liquor and to avoid roller deposits. Generally, a specially formulated surfactant
auxiliary capable of performing all these functions is used. For foaming problems, anti-foaming
agents are also used [89, 97].
Product selection for pigment coloration must take into consideration the following aspects
[92]:
▪ Compatibility of products;
▪ Stability of liquor under high shear forces of padding; and
▪ Presence of dispersing agents in pigment formulation that promote wetting.
3.7.1 Pigment preparations
Pigments are class of colorants, can be chromatic or achromatic and are insoluble in the medium
in which are applied. This does not imply the pigments are insoluble in all solvent types, it refers
to the fact that they are insoluble in water or lipophilic media. There are certain solvents in which
some pigments are partially or completely soluble e.g. a chlorinated hydrocarbon such as
perchloroethylene which is used in dry-cleaning. They belong to almost all classes of dyes, based
on their chemical constitution. Pigments, unlike dyes, do not contain water-soluble or fiber reactive
63
chemical groups. Therefore, they have no affinity and can be applied irrespective of fiber type.
They need a binder to attach them to the fiber surface with good fastness properties [89, 91-94].
To acheive right first time coloration, and to meet fastness and ecological requirements,
there are certain physical and chemical properties of the pigments that have to meet during
synthesis and formulation, i.e. influenced by the manufacturer, these are [91]:
▪ Particle size and particle size distribution;
▪ Crystal shape;
▪ Conductivity;
▪ pH;
▪ Viscosity;
▪ Storage stability of pigments;
▪ Re-dispersibility;
▪ Shade (purity) and color strength;
▪ Suitability and stability of pigments under different application conditions;
▪ Formaldehyde free; and
▪ Ecological and toxicological compliance.
These physical and chemical properties, if adjusted optimally, resulted in, high brilliance,
high color yield, flexibility in usage, high reproducibility, ecological safely and user-friendly
handling in color kitchens and production. Quality assurance of pigment preparations start from
the synthesis of the pigments and include the dispersion and milling steps to maintain batch to
batch reproducibility [91]. The auxiliaries used in milling and dispersing pigments to produce
pigment preparations includes [91]:
▪ Dispersing agent;
▪ Wetting agent;
▪ Preservatives;
▪ Anti-frost agents;
▪ Water retention agents; and
▪ pH regulators.
64
3.7.1.1 Application properties
Modern pigment preparations used in pigment coloration have to meet the following application
properties [98]:
▪ Coloration properties
Pigments are available as fine dispersions and they give more color value as they
remain on the fabric surface. In order to show uniform buildup across the whole
spectrum in light to dark shades and good color value by pigments, the particle size and
its distribution are the key factors. An ideal particle size would in between 0.1 and 0.5
µm and a maximum size of < 1 µm. The particular size of around 0.5 µm is considered
good [94, 98, 99]. Pigment preparations should remain stable for a long time and
without agglomerates formation. Additionally, if the product is stabilized sufficiently,
this will result in excellent brilliancy and optimum build-up. This, in turn, provides that
a lower amount of pigments is required to achieve the required shade. Therefore, the
binder amount will be less and ultimately cost is reduced and a soft handle is achieved.
Fewer coarse particles in the pigment system will result in good fastness properties due
to the fact that larger particles are difficult to fix to the fabric and reduce fastness [94,
98].
▪ Handling properties
For ease of use in the color kitchen, pigment preparations should have low viscosity,
which should be between 50 and max. 500 mPas. For some inorganic pigments, to
ensure product stability, high viscosity is up to 1000 mPas is required. Too low
viscosity may result in increased sedimentation and/or agglomeration, which can result
in shade fluctuations if the pigment system inside the drum is not properly mixed. Too
high viscosity may cause dosing or filtration problems. During normal use, slight
skinning of pigments preparations might form. This should be readily and completely
redispersable to prevent the risk of specking and pin-holing. Another important factor
related to the handling of pigment preparations is the presence of toxic substances or
irritants [94, 98].
▪ Reproducibility/application reliability
For pigment coloration, these properties are dependent on storage stability, tendency to
sediment out and viscosity of pigment system. This affects the dosage and re-
65
dispersibility and may cause pin-holing and specking. For an optimum application of
pigments, there should be good compatibility between pigment formulations and
additives and commercial products used to prepare dye liquors [98].
3.7.1.2 Performance and processing properties
Performance properties
Colorfastness of pigment dyed fabric may be affected by the following factors: the substrate, pre-
treatment, application process, pigments, binder, other auxiliaries (softener, etc.), drying and
fixation conditions. Pigment-specific properties are highly variable and vary between different
chemical classes of pigments or even the same class if the constituents of pigment preparations are
different. Fastness properties also depend on substrate properties (fiber type, yarn type,
construction, etc.), pretreatment, padding, drying and curing conditions.
Pigments are selected according to fastness requirements such as fastness to light,
weathering, the light at elevated temperature, solvents, dry cleaning, PVA, dry heat fixation [93,
98].
Processing properties
These include stability to heat and specific conditions or chemicals used during the process. If the
fixation of pigments is carried out above the recommended temperature of 150 oC for technical or
economic reasons or because of current production practice, heat stability is an important property
that needs to be considered. For fixation of pigment dyed substrate on stenter generally, fixation
temperatures are raised to reduce the reaction/drying time for getting production speeds. The
pigments which are not heat stable at high temperatures show a marked change in shade. This is
more common in commercially available yellow, orange and red shades. The structure of the
pigment is the principal factor. At higher temperatures and a lower concentration of pigments, the
change in shade is more prominent. Therefore, pigments for this case need to be selected with care.
For improving reproducibility and process reliability, heat stability can be the first property that
can be considered. Generally, pigment for a particular substrate, fastness properties, and
application conditions are selected with the help of a manufacturer's pattern card [98].
66
3.7.2 Binders
The binders are film-forming high molecular weight polymers. They are present in homogeneous
form as dissolved or finely dispersed state. On heating, evaporation of a solvent or dispersing
medium takes place and polymer chains connect together to form a thin and coherent film that is
attached to the fiber. Pigment particles are enclosed by this several microns thick film. Since the
only connection between the pigments and the fiber is a binder so it greatly influences the fastness
properties. The fastness properties, such as rubbing, washing, and dry-cleaning, depend largely on
binder [89].
In order to meet the properties required from a binder, careful selection and combination
of the different monomers and control polymerization methods are of greater importance. Reactive
groups can be incorporated into the binder molecules which on heating form crosslinks with binder
chains and improve the resistance against the actions of physical and chemical agents [89].
The binders used in pigment coloration nowadays are made up of synthetic polymers.
Common types used are derivatives of acrylic acid, mostly their esters, butadiene, and vinyl
acetate. Commercially used binders are available both in the form of solutions and aqueous
dispersion, later being commonly used. In aqueous dispersion, water-insoluble high molecular
weight macromolecules in the form of 0.1-0.5 µm droplets are dispersed in the encompassing
aqueous medium. The dispersion has a low viscosity although having high solids content. The
polymer chains in the dispersion need only a small number of solubilizing groups, an advantage
as compared to a true solution. Accordingly, it is not required to make them inoperative either by
blocking them through chemical means after binder application or through inactivation by
crosslinking. The use of solution-based binders is limited [89].
The binder film formation is a two-step process. In the first step, water is removed from
the binder and the dye solution through vaporization and capillary action of fiber and dispersion is
removed. The binder and pigment coagulate to form an unstable gel-like layer. In the next step,
the gel layer merges under simultaneous deformation to form a film which has no elasticity and is
attached loosely to the substrate. During the curing process, cross-linking of binder film took place
making a film elastic and strongly attached to the substrate. The cross-linking reaction is a
condensation process which takes place in acidic conditions (pH < 4) to create a networked
structure. Hot air is the best fixation medium. The curing process is generally carried out at 150
oC for 5 min or at 175 oC for 45-60 sec. Wet steam and superheated (HT) steam is not suitable as
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a fixation medium in which low fixation yield is achieved due to hydrolysis [100]. Figure 3.3
shows the film formation and fixation process in a pigment coloration process [101].
Figure 3.3: Binder film formation and fixation mechanism.
3.7.2.1 Binder selection
Binder is the main component of the pigment coloration system and a significant number of
problems associated with pigment coloration are related to binders. The binder has to fulfill many
properties, both during application as well after it is anchored to the substrate. The list of required
properties is very long and often balancing them is not possible. The quality of dyed fabric in terms
of its handle and fastness properties is determined by the quality of the binder. A binder for
successful pigment coloration system should have to fulfill the following requirements [93-95, 99,
100]:
▪ High pigment binding ability;
▪ Resistance against acids and alkalies;
▪ Wash resistance;
▪ Abrasion resistance;
▪ Dry cleaning fastness;
▪ Resistance against swelling;
▪ Lightfastness;
After drying (still polymers)
Incomplete fixation (too short time, low temperature, or incompatible additives)
Completed fixation
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▪ Resistance to aging, weather, and heat;
▪ Should not be thermoplastic, as it affects the heat related fastness properties;
▪ Dry and wet rubbing fastness;
▪ Chlorine resistance;
▪ Soft handle (no or little effect on fabric handle);
▪ Compatibility with auxiliaries;
▪ Inhibit the migration of pigment particles during the drying and curing process;
▪ Smooth running properties (no buildup on padders, guide rollers and drying cylinders
and easy removal from machine components); and
▪ Film formation.
The most important characteristic is the film formation. The binder film must be [89, 94,
95, 99, 100]:
▪ Colorless and clear;
▪ Of uniform thickness and smooth;
▪ Neither too soft nor too harsh;
▪ Flexible;
▪ Have good substrate adhesion without being tacky;
▪ Resistant to physical and chemical agents after fixation;
▪ Coat and effectively bond to the pigment;
▪ Good adherence to the fiber;
▪ Not pre-polymerize during normal heating condition; and
▪ Transparent so that color and brilliance of pigments are not masked.
To produce a binder with required properties, several different monomers need to be
combined to produce a copolymer as homopolymers would not produce usable binders [89, 102].
Each monomer depending on its chemical structure give specific characteristics to the binder film
[102]. A copolymer is produced from these monomers represent the best possible compromise of
their properties [100]. For example, a copolymer can be formulated that gives necessary, uniform
film hardness from two comonomer types, one whose homopolymer yields hard and brittle films,
69
e.g. styrene, methyl methyacrylate and other types whose homopolymer produce very soft but
tacky films e.g. butadiene, butyl acrylate [89].
Comonomers are selected based on the following properties of the binder film [100, 102]:
▪ Flexibility (softness and elasticity).
▪ Strength and toughness;
▪ Durability (cohesion and adhesion);
▪ Surface tack;
▪ Adhesion;
▪ Water resistance;
▪ Solvent resistance;
▪ Resistance to hydrolysis;
▪ Thermoplasticity;
▪ Ease of fixation;
▪ Stability to light; and
▪ Resistance to aging.
The chemical composition of comonomers and their properties are given in Table 3.8 [100,
102-104]. The softness of the film is directly related to glass transition temperature (Tg), lower the
Tg, greater the softness of the film [100]. The main criteria for monomer selection are the soft
handle and good wet fastness properties. Additionally, the binder is the decisive cost factor in
pigment coloration so monomers are also selected according to the cost [103, 104].
The polymers apart from basic components usually contain cross-linking agents--
monomers that provide reactive groups [104]. On curing, polycondensation of linear groups into
the three-dimensional network takes place, thereby improving the fastness, temperature stability
and permanency of binder effects. The cross-linking monomers can be subdivided into two
categories based on their reaction mechanism. The first type, known as foreign crosslinking type
consists of monomers that have groups that can be reacted with bifunctional compounds e.g.
acrylamide and methyl acrylamide have free amide groups that can be cross-linked with
condensation products of urea or melamine. This type of cross-linking is essential for if the
functional group of binders cannot react themselves. The second type, known as self cross-linking
type consists of monomers such as methylol acrylamide and methylolmethacrylamide or their
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ethers. The reactive groups present are capable of reacting themselves. The cross-linking reaction
takes place at high temperature and under acidic conditions. For binder application under alkaline
conditions monomers containing epoxy or chlorohydrin groups are used [89, 100, 104]. Cross-
linking of binder molecules influence the viscoelastic and swelling properties of the binder film.
The later one affects the washing and solvent fastness. As the degree of cross-linking is increased
the elasticity of the film is reduced i.e. film hardness increases but swelling resistance is increased.
The balance needs to be maintained between the greatest possible swelling resistance and lowest
possible cross-linking [100].
Table 3.8: Comonomer types and polymer properties.
Basic components
Film characteristics
Tg (oC) Tacky Harshness Swells in
Water Solvent
CH2=CH-CO-OCH3
methyl acrylate 5 - medium no somewhat
CH2=CH-CO-OC2H5
ethyl acrylate -27 + soft no somewhat
CH2=CH-CO-OC4H9
N-butyl acrylate -57 ++ very soft no yes
H2C CH
styrene
95 -- very harsh no yes
CH2=CH-C≡N
acrylonitrile 105 -- very harsh no no
CH2=CH-CH-CH2
butadiene -86 ++ very soft no yes
71
The most commonly used binders types are [89, 100]:
▪ The first class is the most commonly used type. They are formed from acrylate esters
and styrene but also from vinyl ester copolymer and have good fastness to aging and
running properties. They show good stability to an electrolyte and but inferior fastness
to dry-cleaning. The film is non-tacky and produces soft handle in combination with
silicone softeners.
▪ The second class consists of acrylonitrile along with acrylic esters. They have good
fastness to aging and dry-cleaning but not stable to electrolytes. In general, they
produce unsatisfactory handle.
▪ The third type is based on butadiene. They have an extremely soft handle but have poor
dry-cleaning fastness and resistance against the light. This is due to the presence of
double bonds which under the action of light or/and heat makes binder film brittle and
decolorized. Dry-cleaning fastness can be improved by the incorporation of
acrylonitrile. They have marginal stability against electrolyte but show excellent
running properties.
3.7.3 Auxiliaries
Auxiliaries are generally used to correct or control the problems that might occur during the
pigment coloration process. They generally have a specific function to perform but can affect
different properties at the same time. The role of auxiliaries is also dependent on the coloration
system. It is very important to understand the properties of the auxiliaries as well as the coloration
system so that appropriate auxiliaries can be selected [102].
3.7.3.1 Anti-migrating agent/migration inhibitors
In continuous coloration, pigments tend to migrate during the drying step. This is due to the
migration of dye liquor towards the hotter regions of the fabric. The migration process is
uncontrolled and random in nature and will cause uneven coloration that leads to shade variation.
The effect can be in the form of either patchiness or an undesirable two-sided effect. To prevent
this problem, migration inhibitors are used. Chemically they are either anionic which includes
polyacrylates and polyacrylamides or nonionic which consists of polyethoxylates. Polyethoxylates
consist of block copolymers consisting of poly (oxyethylene) and poly(oxypropylene) segments.
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Their mechanism of action is based on coagulation. At the start of the drying process, it physically
absorbs the pigment and attaches it strongly with the substrate thereby inhibiting migration. By
doing this, it also maintains the soft handle of the substrate. It also improves the hydrophilic
properties of the fabric which favors the uniform application of coloration liquor by padding.
Magnesium chloride or diammonium phosphate promotes the effect of migration inhibitors [95,
100, 105]. Migration inhibitor used should not make the fabric handle stiff, because the fabric is
not washed after the coloration or combined coloration and finishing process. Conventional
migration inhibitors e.g. alginates are not suitable [92].
3.7.3.2 Dispersing agent/emulsifier
The main function of the dispersing agent is to maintain the stable dispersion in the pigment
coloration system, prevent roller deposits and wet the fabric [97]. The pigment coloration system
usually contains the dispersing agents from pigment preparations and binders. Pigments
preparations contain up to 25% commonly of anionic or nonionic types. Binders also contain the
same type and the amount is 2-5% depending upon the solid content of the binder [89]. Emulsifiers
are also added directly to the pigment coloration system to prevent roller deposits [106]. When
pigment coloration components are mixed together there is a local exchange of surfactants until a
dynamic equilibrium is achieved. Therefore, compatibility is of prime importance. Also, they must
function properly in the mixture as they work individually. In practice, this aspect is not usually
given much attention. Unstable pigment coloration liquor or poor running properties can result
from mixing incompatible products or poor selection of emulsifier type as they are not able to meet
the requirement because of the structure. It also needs to be considered that emulsifier because of
its proportion in the system influence the film formation which ultimately affects the brilliance
and fastness properties. For each g of binder around 0.5 g of a dispersing agent is present in the
coloration liquor and both components are non-volatile. The emulsion breakage point, film
formation and nature of the film formed are affected by the type of dispersing agent and changes
in the concentration during and curing process. Therefore, manufacturers make sure that the
compatibility of the pigments, binders, and auxiliaries used in their ranges [89].
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3.7.3.3 Catalyst
The catalyst is generally added to accelerate the crosslinking reaction and maybe acid or basic
depends upon the system. They provide the catalytic effect by lowering or raising the pH when the
temperature is increased during the fixation process. The appropriate pH and high temperature
conditions are necessary for a high degree of polymerization of the binder. They are generally
ammonium salts such as ammonium sulfate, phosphate, and nitrate which generate mineral acid
during curing conditions. Metal salts such as magnesium chloride may also be used. The amount
of catalyst should be properly used, otherwise, it may cause tendering of the fabric due to the
excess generation of acid. For lower fixation temperatures (< 120 oC) free acids such as phosphoric
or tartaric acid may be used however if crosslinkers are present in the system problems related to
stability might occur due to rapid reaction [89, 99].
3.7.3.4 Crosslinkers/fixing agents
A pigment coloration system may contain a fixing agent depending on the fastness requirement
[106]. The term crosslinker is also used for these products. They improve the crosslinking of binder
film which enhances the rubbing, washing and dry-cleaning fastness. The disadvantage of this
improvement in crosslinking is the firmer handle. Crosslinkers are substances that have at least
two reactive groups per molecule. The most commonly used are low molecular weight nitrogen
based formaldehyde products e.g. dimethylolurea or dimethylolethyleneurea, hexamethoxymethyl
melamine or their ethers, hydroxymethyl urethane compounds and urea-formaldehyde products.
The addition of crosslinker is dependent on the type of crosslinking component present in the
binder. They are needed if the binder has no self-crosslinking groups present. But they can also be
used with the binder having self-crosslinking groups and markedly improve the fastness properties.
The crosslinking reaction is a condensation reaction and requires elevated temperature and a
catalyst to increase the rate of reaction between the binder and the crosslinkers. The selection of
crosslinker is dependent on the existent curing temperature, time and pH conditions. If a very
reactive crosslinker is used it may cause premature crosslinking and hinder the binder film
formation process [89, 103].
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3.7.3.5 Hand modifiers
The main drawback associated with pigment coloration is the stiffening effect of binder film on
the hand feel. One of the prime reasons for this effect is the restricted relative mobility of the fibers
due to their mutual adhesion by the binder. The stiffening can be restricted up to a certain extent
by ensuring the correct amount of binder required. The hardness of binder film can be controlled
by the proper selection of monomer types and crosslinking agents and the degree of crosslinking.
The relative movement of molecules in the binder film determines its hardening effect. Strongly
polar groups or hydrogen bond forming groups can restrict the mobility of binder chain. To
increase the interchain mobility, low molecular weight compounds known as plasticizers are added
in binder formulation. These compounds increase the distance between the binder chains through
swelling. This imparts softness due to greater interchain mobility. Mostly these compounds are a
long chain with aliphatic groups and their amount in binder formulation depends upon the level of
effect required, usually up to around 30% based on solid content. The addition of a plasticizer is
accompanied by the drawback that swollen film is prone to attack by the mechanical agents. To
counteract this effect balance in the fastness properties and softness of binder film is obtained by
selecting the appropriate type and quantity of plasticizer fit for the particular binder. The handle
of binder film can also be improved by a formulation of soft binder types i.e. selecting of monomer
types that give soft hand such as butadiene and acrylates. In the case of soft binders, the steric
hindrance of binder chains is small at room temperature and therefore have a low glass transition
temperature. However, binder film of this type is tacky and in certain substrates give a sticky or
soapy handle [89]. This problem can be overcome by incorporating silicone base softeners which
improves the dry handle. There is no swelling of binder film as silicone softeners have no
interaction with the binder, therefore no negative influence on the fastness properties. These
softeners compensate for the film brittleness and therefore increase the dry rubbing fastness [89,
103].
3.7.3.6 Defoaming agent
To counteract the foam formation due to the entrapment of air which can result in coloration defect,
defoamers are used in pigment coloration. They act by increasing the surface tension of the
coloration liquor so that foam formation is suppressed. The main requirement of the defoamer is
its suitability in the pigment coloration system [89]. They are generally based on an emulsion of
75
silicone oils [102, 106]. Alkoxylate based defoaming agents are also used for combined pigment
coloration and finishing [97].
3.7.4 Combined pigment coloration and finishing
Coloration with pigments have an advantage, as compared to conventional coloration methods,
that coloration and finishing can be done in the same bath. This is contrary to a normal processing
method in which coloration is followed by finishing. This one bath procedure is now an established
process and has several advantages like savings in cost, in equipment, and also in time, labor and
water [92]. The depth is generally limited to light to medium shades (5 g/L to 10 g/L). Two types
of finishing are most common: soft finishing or resin finishing. In the case of soft finishing, silicone
or polyethylene based softeners are used alone or in combination. Compatibility with the pigment
coloration system should be considered in selecting softeners. The use of cationic softeners with
pigment preparations containing anionic emulsifiers may cause finishing spots [93]. In the case
of resin finishing, cross-linking agent and catalyst are used. In general selection of a cross-linking
agent is based on the same requirements as those for resin finishing without pigment coloration.
The effect of resin finishing on the lightfastness of dyed fabric needs no longer to be considered.
Modified DMDHEU is used as a crosslinker and magnesium chloride is commonly used as a
catalyst. In order to compensate for the harsh handle and loss in strength due to resin finishing
softening agents and additives are used [92, 97]. Product compatibility and bath stability is an
important factor in the selection of products. Special auxiliaries based on ethoxylation product on
curing of cross-linking agent may degrade certain pigments and result in loss of depth of shade
[92].
3.7.5 Application method
Pigment coloration and combined pigment coloration and finishing involve the following
operations [92]:
▪ Padding;
▪ Drying; and
▪ Curing
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3.7.5.1 Padding
The aim of the padding process is the even and uniform distribution of the pigments over the fabric.
It must be ensured that coloration padders and guide rollers are clean, because droplets may cause
stains on the fabrics resulting in a faulty fabric. In order to ensure the uniform application of
pigments, the surface of padders must be even and smooth and pad rollers must apply pressure
evenly i.e. wet pickup of the fabric should be constant along the length and width. High pressures
should be used so that fabric pick-up is kept as low as possible to minimize the effect of migration
[92, 100]. The dye bath must be agitated continuously to avoid settling of pigments. Depending
upon availability, air exposure should be given to fabric after the padding process. This improves
the penetration of pigment. The penetration of dye liquor is also influenced by the good
pretreatment of the fabric [95, 100]. The wetting agent may be added in the dye bath to increase
the penetration of liquor into the fabric [93].
3.7.5.2 Drying
After the dye liquor has been applied to the fabric, drying is generally carried out in infra-red pre-
dryer. They are arranged in parallel such that fabric passed through them and get dried from both
sides. One of the important aspects need to be considered is migration. Migration should be
avoided as much as possible to ensure level/uniform coloration. Level coloration depends on
penetration and migration. The migration process begins with the drying step. As the fabric surface
is dried, the liquor from the inside of the fabric moves to the dried surface causing the pigment to
move to the surface and accumulate. This results in poor penetration. Migration continues until the
interruption of the liquid phase due to the non-availability of migration-active surface water. The
threshold values are dependent upon fiber type and are about 25% for cotton fibers and 5-10% for
synthetic fibers [92, 100]. Water in the liquid phase is only responsible for the migration problem,
so the following steps may be taken to overcome or reduce the severity of the problem [92, 95,
100]:
▪ Keep the wet pick-up low as possible (e.g. by high squeeze off, or installation of
vacuum suction slot after padder).
▪ Short liquor trough with a short dip to reduce the wet pick-up.
77
▪ Long-air passage of 30-60 seconds. The migration active surface is converted to
migration-neutral swelling water during this time. When water evaporates during
drying, no migration occurs.
▪ Gentle drying, reduction of fan speed and keep the maximum temperature to 120 oC in
the first two drying zones.
▪ In stenter, run the first chamber with air circulation. This primarily results in heating
up of fabric instead of drying. Also, the migration inhibitor effect will be developed
before the drying starts. IR dryer used for drying serves the same purpose.
▪ Use an anti-migrating agent. On heating, it precipitates in its solution causing viscosity
increase or coagulate depending on the type. This effect controls the pigments from
migration.
The migration of pigments is also influenced by the type of heat supply. A hot flue is most
suitable for uniform and mild drying and curing conditions. The air circulation should be uniform
and tension on the fabric should be kept minimum as possible. This includes the even distribution
of airflow of the top and bottom to minimize the face-back problem. Temperature variation should
be controlled along the sides to prevent width-wise shade variation. Guide rollers in the starting
section should be Teflon coated to avoid binder deposits [92, 93].
Stenters can also be used for both drying and curing process. Pins found to more suitable
as compared to clips as its possible with proper adjustment of overfeed, shrinkage can be
minimized. Selvage dark pin marks can be avoided by proper temperature control [92].
3.7.5.3 Curing
Optimum fastness is achieved when pigment dyed fabric is fixed in the hot air. The temperature
should not exceed 170 oC. The fixation process can be carried out on hot flue machines or stenters.
In hot flue machines, the time and temperature required are dependent on the binder or
reactivity of the cross-linking agent. Optimum fixation is achieved by curing for 4-5 min at 150
oC. Fixation time can be reduced at higher temperatures. A general rule of thumb is, with 10 oC
increase in temperature, fixation time is reduced by 1 min [92, 107]. The relationship between
curing time and temperature is shown in Figure 3.4. The temperature and time correspond to the
binder condensation reaction [101].
78
Dry and fixation can be carried out simultaneously on stenter. This process is known as
flash curing and is carried out at an elevated temperature, e.g. 160-200 oC. This method is less
reliable as compared to performing drying and curing separately. Fixation is carried out when a
fabric is dried, so the exact moment at which fabric is dried is difficult to determine. This results
in uncontrollable fixation time and therefore affects the fastness properties. This method is only
recommended for dryers having large fabric capacity [107]. The machine speed is dependent on
the type of binder, type of fiber, fabric weave and in case of combined coloration and finishing
cross-linking agent and catalyst used need to be considered. It must be taken into consideration
that an increase in the curing rate may have a processing risk such as temperature fluctuations
within stenter, non-uniformity in liquor pickup, machine stoppages and varying heating up times
of the textile materials [92].
Figure 3.4: Relationship between curing temperature and time.
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3.7.6 Equipment
Pigment coloration can be carried out on a variety of equipment [93]:
▪ Padder - stenter
It minimizes the equipment cost. But it has some disadvantages such as limited
migration control, limited shade range, clip buildup. These problems can be controlled
by the proper selection of binders and anti-migrating agent.
▪ Padder - drying cylinder - stenter
This machine configuration can be found in old finishing departments. It offers a full
range of color and migration control. Deposits on the drying cylinder are very excessive
in this case.
▪ Padder - pre-dryer - drying cylinder - stenter
It offers better migration control and minimizes the roller build-up.
▪ Padder - vacuum slot - pre-dryer - stenter
Vacuum slot allows the low pick up which minimize the migration problem. The
unbound moisture on the fabric surface is removed. It also minimizes the roller buildup
and improves the appearance of the dyed fabric.
3.8 Dyeing of polyester/cellulosic blends using a two-dye system
3.8.1 Dye classes used for polyester/cellulosic blends
3.8.1.1 Disperse dyes
Disperse dyes are used to dye polyester filament and staple fibers. Disperse dyes on polyester
generally give adequate light and wet fastness properties. As polyester is extremely crystalline and
has hydrophobic nature, dyes are generally protected from the chemical attack. Some disperse dyes
are sensitive to heavy metals ions (iron and copper), reducing agents and alkaline conditions. They
are applied under acidic conditions (pH 4-5) and sequestering and mild oxidizing agents may be
used depending on the sensitivity of certain dyes [9]. Different chemistries of disperse dyes are
available such as aminoazobenzene, anthraquinone, nitrodiphenylamine, styryl (methine),
quinophthalone, aminoketone, and benzodifuranone derivatives [75]. Almost all chemical classes
of disperse dyes can be used for the dyeing of polyester/cellulosic blends [9]. The dyeing
requirements for dyeing polyester in polyester/cellulosic blends are often different than that of
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100% polyester. They are generally required to higher thermomigration properties as
polyester/cellulosic blends are often resin finished [79].
Disperse dyes are partially soluble in water and usually dispersed as a fine, uniform and
stable suspension. For good dispersion smaller particle size is essential. Disperse dye already
contains dispersing agent and sometimes additional dispersing agents may be added during the
dyeing process. The dispersing agent is added to improve dye dispersion, improve dye solubility
and prevent it from breakage due to a variety of factors such as higher dyeing temperature, water
impurities, and dyebath chemicals. The agglomeration of dye is also prevented. Optimum
quantities must be added as an extra dispersing agent may create problems in dye exhaustion. Both
nonionic and anionic type dispersing agents are available but anionic are preferred due to their
high-temperature stability [108]. They must be compatible with the dyes being used. The disperse
dye usually contains dispersing agent one-third of its weight, therefore, the additional dispersing
agent must be added during dyeing when essentially needed especially in light to medium shades
[109].
The polyester portion in the blend can be dyed by different methods [85, 110]. These are
as follows:
▪ Carrier or atmospheric dyeing;
▪ High temperature (HT) dyeing (also known as high pressure dyeing); and
▪ Thermosol dyeing.
The carrier and HT dyeing methods are batch processes while Thermosol is a continuous
process. In the batch dyeing process, commercially available disperse dyes along with auxiliaries
are dispersed in a dyeing machine containing water and polyester. The temperature of the dyeing
system is raised to 100 oC (for carrier dyeing) or 130 oC for (high-temperature dyeing) and is held
for required dyeing duration. The dyeing system is then cooled and the substrate is removed from
the machine [109]. The carrier dyeing as the name implies uses carriers for the dyeing of polyester.
The carriers are swelling agents which permit the dyeing of polyester to be carried out at 100 oC
(atmospheric pressure). Several problems such as lower dye built up on fiber, environmental issues
related to the carriers and odor development during dyeing have significantly declined the use of
carrier dyeing method for polyester/cellulosic blends [85, 110]. The blends containing the sensitive
fiber that can be damaged at higher temperature such as wool and acrylic employs carrier dyeing
81
up to a certain extent. Polyester/cellulosic blended fabrics are usually performed by high-
temperature jet or overflow dyeing machines under pressure 2 to 2.5 times higher than atmospheric
pressure) at 130-135 oC [75, 85, 110]. The beam dyeing machines may also be used. The use of
winch and jig is limited due to the economy and steam consumption. A good selection of disperse
dye is required to ensure uniform dyeing [67]. The selection of disperse dyes depends on [111]:
▪ Stable dispersion under dyeing temperature in the presence of dyebath chemicals;
▪ Good leveling behavior;
▪ Higher exhaustion values;
▪ No buildup or shade change after 20 minutes at 120 oC; and
▪ Compatibility of dyes in combination shades.
Batch dyeing of polyester fibers from the dye liquor occurs in three distinct stages termed
as exhaustion, diffusion, and migration. In the initial stages of dyeing at a lower temperature (<
60 oC) dye is present in a dispersed state. With the increase in temperature, some disperse dye
dissolves in the aqueous medium and absorbed onto the fiber surface. This drives more dye to
become soluble [111]. The rate of exhaustion depends on the substrate, concentration, and
solubility of the dye. The rate of dye exhaustion should be controlled to ensure uniform dye
distribution throughout the substrate. The temperature ramp rate during the dyeing process is the
key factor that determines the dyeing rate. This rate needs to be carefully controlled during the
initial dyeing phase, especially after the glass transition temperature (greater than 75 oC). For
polyester dyeing with disperse dyes, there is a temperature range where there is maximum
exhaustion rate (between 80 oC and 120 oC) depending on the dye type. This temperature range is
termed as the critical dyeing temperature, ∆Tcrit. Slow diffusing dyes have higher ∆Tcrit while
rapidly diffusing dyes have lower ∆Tcrit. The actual value depends on temperature ramp rate, dye
amount, liquor flow rate, liquor ratio, substrate type. The temperature is increased slowly in the
∆Tcrit region to control the exhaustion rate that allows level dyeing. The temperature is then
increased from just above the ∆Tcrit to the maximum dyeing temperature at a higher rate possible
[9, 112]. The rate of dyeing depends on following factors [108]:
▪ Fiber crystallinity and degree of orientation;
▪ Molecular weight of the dye;
▪ Dye particle size and its distribution;
82
▪ Dye solubility; and
▪ Dye concentration in the bath.
The dyeing of polyester fibers is carried out at temperatures (dyeing temperature: T) which
is above the glass transition temperature (Tg). Generally, dyeing of polyester can be carried out at
130-135 oC known as high-temperature dyeing or can be done at 100 oC using carriers that act as
plasticizers and lowers the Tg. As the temperature is increased to dyeing temperature and more dye
is diffused into the fiber interior. Dyeing is continued at this temperature for a certain duration to
permit complete diffusion. Dye diffusion into the fibers is determined by Williams, Landell, and
Ferry equation. During this phase, migration also takes place which enhances uniformity and
penetration in tight structures. At the end of the dyeing process, the dye is uniformly distributed
throughout the fiber. The rate of diffusion depends on the substrate, the molecular weight of the
dye and temperature. The migration rate is based on dye properties and temperature [75, 111].
In all dye systems used for coloration of polyester/cellulosic blends, the leveling agents are
seldom required as compared to the dyeing of polyester alone. During the starting phase of batch
and continuous processes, the cellulosic portion of the blend owing to its high hydrophilicity
absorbs a majority of the disperse dye. With an increase in temperature to the final dyeing or fixing
temperature the dye gradually and subsequently migrates towards the polyester. Thus it can be said
that the cellulose is acting as a leveling/retarding agent for disperse dyes [86]. For certain disperse
dyes and lighter shades leveling agents are still used [9]. The leveling agents should have the
following characteristics [111]:
▪ Satisfactory leveling properties.
▪ Easy to remove from the substrate.
▪ Little or no foaming.
▪ Little or no effect on dye yield.
▪ Easy to handle.
The continuous dyeing of the polyester portion of the blend is carried out by a thermosol
process. This process comprises padding of dye liquor, Infrared pre-drying, drying and
thermofixation (thermosol process) [9, 113, 114]. The fabric is padded with a disperse dye,
dispersing agent, non-ionic wetting agent and a migration inhibitor. The disperse dye is in the form
83
of fine dispersion and the pH of the bath is maintained at 5-6 generally with acetic acid. The
migration inhibitor used is anionic polyelectrolyte. This includes sodium alginate, polyacrylamide,
polyacrylates, polyvinyl alcohol, and carboxymethylcellulose [9, 115]. They agglomerate the dye
particles that lead to the enlargement of particle size. Thus the movement of larger dye particles to
the surface is restricted during the drying phase [9, 116-118]. On the other hand, they should allow
the dye transfer to take place during the thermofixation process. The polyacrylamides are preferred
over alginates because of this property. Both liquid and powder types of the dyes can be used. The
liquid brands make the preparation of dye liquor easier, give less migration during drying, are less
prone to staining of the cellulosic component of the blend and produce high color yields. However,
they may settle down during storage which requires agitation before use, also during storage of
used container water may evaporate or solids may deposit at the surface leading to strength
variations [9, 115].
Before thermofixation step disperse dye is present in an aggregated state along with wetting
and dispersing in the matrix of antimigrating agent. The dye is converted from aggregated to the
monomolecular form during the thermofixation and migrates to the fiber surface. The dye is then
diffused to the interior of the fibers. The suitability of disperse dye for the thermofixation method
should be checked by plotting its time-temperature curve. Not all disperse dyes have the same
fixation profile. For trichromatic shades, the dye selected should have a similar fixation profile
[113, 115]. Suitable disperse dye can be grouped into two categories, the first requires fixation at
200-210 oC and the second produces reproducible results at 210-200 oC. Selecting the dyes should
be based on the fastness properties that can be obtained using the chosen dyeing route on the blend
as a whole and the cost [115].
The behavior of disperse dyes in the thermofixation process depends on [115]:
▪ Pad liquor pH;
▪ Concentration of the dye;
▪ Dispersion behavior of the dye;
▪ Fixation temperature; and
▪ Fixation time.
During impregnation, most of the dye liquor is absorbed the hydrophilic portion of the
blend as compared to hydrophobic polyester fibers. More dye is present on the cellulose portion
84
than where it is required [114]. The staining of cellulose may take place by disperse dyes during
drying and the theormofixation stages. This depends on the drying unit, fabric construction, and
pad liquor composition. A good dispersion system allows the transfer of disperse dye from
cellulosic fibers to the polyester during the drying and the thermofixation stage [9, 114]. This is
carried out through the vapor phase where dye sublimes off of the cotton to the polyester. Many
factors affect this transfer such as the surface area of dye particles, the morphology of dye particles,
morphology and surface area of cellulose, and substantivity of dye towards the cellulose. Dye that
cannot sublime shows poor transfer to the polyester [114]
Disperse dyes can be classified into three classes depending upon the molecular weight and
sublimation properties. These are low energy, medium energy, and high energy. These classes
determine the dyeing temperature and thermomigration properties of disperse dyes. Low energy
disperse dyes have a molecular weight less than 300 and they are applied in lighter shades due to
their good leveling properties [9]. Medium energy dyes have a molecular weight between 300-
400. High energy disperse dyes have a molecular weight in the range of 550-650. These dyes
require high energy for dye diffusion into polyester fibers and therefore can be raised at a higher
temperature gradient. They also have a higher critical temperature zone than for most disperse
dyes [75]. These dyes are designed to have extra solubilizing groups to improve their dyeing
properties and slightly better solubility as compared to medium energy dyes. If the fabric is not
subjected to high temperature 160-170 oC, good thermomigration properties are seldom required.
The fastness to cold water or perspiration is inferior as compared to medium energy dyes because
of color migration in aqueous medium [109].
Over the years many developments have been done in polyester dyeing and disperse dyes
[75]:
▪ Dye selection having a similar compatible strike rate for rapid dyeing;
▪ Application methods to ensure proper dye penetration and avoid ring dyeing;
▪ Use of granular, pearl and liquid disperse dyes;
▪ Alkali-clearable dyes that do not require reducing agents;
▪ Development of novel chromophores that gives excellent thermomigration and wet
colorfastness;
▪ Alkali-stable disperse dyes that are stable up to pH 8.5-9.5; and
▪ Development of high brilliance disperse dyes.
85
There are some fastness issues associated with the dyeing of weight-reduced and
microfibers. It is difficult to achieve level dyeing and desirable fastness properties in the dyeing
of polyester/cellulosic blends containing polyester microfiber variant. These problems are due to
[9]:
▪ Polyester microfilament yarns of 0.6 denier or less cannot be dyed on package or beam
because of inadequate liquor circulation due to the high density of the wet substrate.
▪ Microfiber requires much more disperse dye than conventional polyester to achieve the
same visual depth. Due to the smaller proportion of microcrystalline material in
microfilament structure, absorb dye forms larger aggregates in the amorphous regions.
This leads to reduced tinctorial power.
▪ The rate of dyeing is much faster in microfibers as compared to conventional polyester
fibers. Starting dyeing at very high temperature, using a higher ramp rate above 90 oC,
differences in the rate of dyes used and insufficient fabric agitation at slow speeds leads
to uneven dyeing.
▪ Inferior lightfastness, washing and rubbing fastness as compared to standard polyester.
High-temperature treatment after dyeing often magnifies these issues. Scouring of
unfixed dye is more difficult and reduction clearing is always recommended.
By modifying dyeing procedures and proper dye selection these challenges can be dealt
with. It is suggested to select dyes with similar dyeing rates, higher fastness properties, star the
dyeing process at low temperature and use slower ramp rates. Jet or overflow dyeing machines are
recommended with small fabric lengths to promote agitation. Over the years new disperse dyes
have also been developed to overcome these problems. Azo dyes containing diester groups and
some azothiophene based dyes that become soluble under mild alkaline conditions give good
results in the dyeing of polyester microfiber/cellulose blends. They offer numerous advantages
such as minimal or no cross-staining of cellulose, ability to combine clearing step in reactive
dyeing, no need for reducing agent to remove disperse dye stain and desirable fastness properties
after post dyeing heat treatment [9].
Alkaline dyeing of polyester offers numerous advantages such as less oligomer problem,
less requirement for reduction clearing and soft and smooth hand of the substrate. This also
provides an option to combine high-temperature scouring/bleaching of cotton with a disperse
86
dyeing of polyester saving time and energy costs [75]. Oligomers are low molecular weight
substances and polyester fiber contains between 1.3 and 1.7% by weight mainly composed of the
cyclic trimer. During high-temperature dyeing, they move from the fiber into the dye bath. They
remain in solution until the dyebath temperature is lowered below 110-115 oC. They crystallize
and form deposits on fabric and in various zones of the machine. The latter may cause problems
in liquor flow in the machine. Nonionic residues in the fabric and dye remaining in the bath at high
temperature may combine with oligomers. Oligomer controlling products may be added to increase
oligomer solubility and prevent redeposition [109].
One of the important criteria that determine the selection of disperse dyes, for both exhaust
and continuous dyeing of polyester/cellulosic blends, is their affinity for cellulose. The cellulosic
component of the blend is stained by disperse dyes. Staining leads to reduced light and wet
fastnesses. For continuous dyeing rapid clearing and sensitivity of staining to the thermofixation
conditions are essential factors to consider [9, 111]. Different factors that may influence staining
are summarized in Table 3.9 [9, 111]. The migration of disperse dye from cellulose to the polyester
is promoted by prolonged boiling. Also, cellulose damage is minimum at boiling temperature. At
the end of the dyeing cycle, some disperse dye remains in the dye bath. As the dye bath is cooled
this dye will redeposit onto the fabric surface. Therefore, it is recommended to drain the dyebath
at higher temperatures [9]. Lignin present in linen fibers has more tendency to get stained by
disperse dyes [9].
The removal of unfixed disperse dyes on polyester and stain on the cellulose component is
essential to ensure the highest fastness properties. Different methods can be used to remove the
disperse dye stain depending on the chemistry of disperse dye. These methods include soaping
with detergent or reduction clearing or in some cases oxidative bleaching. Reduction clearing is
the most common and effective method to remove any surface and residual dyes on the polyester
and the staining on the component fiber in the blend. It cannot be used when the cellulose portion
of the blend is already dyed with direct or reactive dyes. In vat and sulfur dyes the reduction stage
can be combined with reduction clearing. Standard reduction clearing procedure is carried out
usually for 20 minutes at 70 oC using sodium hydrosulfite, caustic soda and non-ionic detergent
depending upon the depth of shade [9, 79].
87
Table 3.9: Factors affecting staining of cellulose by disperse dyes.
Favors staining Reduce staining
▪ Lower dyebath pH
▪ High affinity of disperse dyes for cellulose.
▪ Poor dispersion stability
▪ Slow cooling of disperse dyebath
▪ Non-ionic chemicals
▪ Carriers
▪ Lignin (linen)
▪ Disperse dye having less substantivity
for cellulose
▪ Draining of dyebath at a higher
temperature
▪ Use of leveling agents
The disperse dyes may migrate to the surface of polyester fiber during soaping treatment
at a boil. This treatment is necessary for the dyeing of the cellulosic component with reactive, vat,
or sulfur dyes. Some disperse dye may remain on the surface even reduction clearing treatment is
given after soaping. This leads to inadequate wash fastness properties. Selecting disperse dyes
which have a minimum or no tendency to migrate to fiber surface at boil during soaping mitigate
this problem [9]. Some dye movement may take place during post-heat treatment after dyeing
carried out a temperature higher than the dyeing temperature. This leads to deterioration in fastness
[109]. High energy disperse dyes are preferred where the fabric has to undergo subsequent high-
temperature treatment such as durable press finishing [9, 109]. The additional reduction clearing
process performed after disperse dyeing is not beneficial for lower energy disperse dyes as these
dyes tend to move from the interior of the fiber to the outer surface during post-heat treatment.
Reduction clearing though improves the fastness but in subsequent heat treatment deteriorates the
fastness [109].
3.8.1.2 Reactive dyes
These dyes form a covalent bond with the fibers containing hydroxyl, amino or mercapto groups.
Cellulosic, proteins and polyamide fibers can be dyed with reactive dyes. They have excellent
fastness properties and produce brighter shades [7, 64]. Reactive dyes are characterized by having
a reactive group attached directly or through a bridge to the chromophore. The reactive group is
responsible for forming a bond between the fiber and the dye. Over the years several reactive
88
groups have been introduced having different reactivities and can be classified into two broad
categories based on their mechanism of reaction with the fibers [119]. These include addition and
substitution type reactive dyes. The reactive dyes based on their reactivity can be classified into
three groups [79]:
▪ Group 1: High reactivity dyes
Examples: Dichlorotriazine, dichloroquinoxaline, fluorodichloropyrimidine and
fluorotriazine.
▪ Group 2: Medium reactivity dyes
Examples: Vinyl sulphone
▪ Group 3: Low reactivity dyes
Examples: Monochlorotriazine and tricholorpyrimidine.
The dyeing temperature in the batch process depends on the reactivity. High reactivity dyes
require lower temperature (40 oC) while low reactivity dyes require higher dyeing temperature (80
oC). The medium energy dyes require moderate dyeing temperature (60 oC) for fixation. In the
case of continuous dyeing, this is controlled by changing the alkalinity where strong alkali is used
for low reactive dyes while weak alkali is used for high reactivity dyes while keeping the fixation
conditions the same. It is important to note the reactive dye may contain more than one reactive
group to improve the dye fixation and application temperature. In some cases, a dye may contain
3 reactive groups. The dye molecular design is matched with the nature of the reactive group. High
reactivity dyes generally have smaller dye molecules while low reactive dyes have large
molecules. The mismatch dye molecular design gives leveling and wash-off problems. The dyes
having lower substantivity are easier to wash-off compared to one having higher substantivity.
This factor is more important in continuous dyeing. Furthermore, highly substantive dyes give
tailing problem. Therefore, low to medium energy dyes should be used in a continuous process
whole high substantivity dyes should be used for a batch process [79].
Reactive dyes can be applied to polyester/cellulose blends by a variety of routes. These
include batch, semi-continuous and continuous process. The suitability of a reactive group for a
particular route and fastness properties requires determines their selection. The reactive dye
selection is important to ensure good fastness properties and level dyeing [56].
89
The batch dyeing of reactive dyes involves three steps that include exhaustion, fixation,
and soaping. Exhaustion stages require a large quantity of salt to promote dye exhaustion. This
phase is dependent on the substantivity of the dye. Different reactive systems have different levels
of substantivity but substantivity levels tend to be of the same order within a given type of reactive
system. The dye is exhausted into the substrate under neutral dyebath conditions. When alkali is
added to the dyebath, secondary exhaustion takes place along with the fixation of the dye with the
cellulose. For good level dyeing in highly reactive dyes, the difference between the initial
exhaustion and alkali exhaustion should be smaller. The soaping process is done to remove the
hydrolyzed dye. This makes the batch dyeing process quite lengthy [7, 79].
Pad-batch is an economical route used mainly for dark shades. The fabric is padded with
reactive dyes and alkali and the batched for 3-24 hours while rotating slowly. The fixation time
depends on the depth of shade, padding temperature, alkali system and batching temperature [113].
The reactive dyes can be applied by a continuous process through variety of routes which
are [113]:
▪ Pad-dry-thermofix;
▪ Pad-dry (Econtrol);
▪ Pad-steam (pad- chemical pad steam);
▪ Pad-dry-steam; and
▪ Pad-dry-chemical pad steam
The pad-dry-chemical pad steam and pad-dry-thermofix are most commonly routes used
for polyester/cellulosic blends. In a continuous dyeing process, the reactive dyes must fulfill the
following requirements [120]:
▪ Similar affinity factors of dyes used in combination shade including shading elements
(low tailing, high reproducibility);
▪ Good dye bath stability (low tendency for hydrolysis);
▪ High reactivity (especially for pad batch so that fixation is not affected by variations in
batching temperatures);
▪ Higher lightfastness; and
▪ Good wash-off behavior.
90
In the dyeing of polyester/cellulosic blends with reactive dyes following points need to be
considered:
▪ The reactive dyes do not exhibit any cross-staining effects on the polyester fibers. The
only exception is phthalocyanine-based dyes (turquoise blues and greens) that may
show a very small amount of staining [79].
▪ The reactive dye system may undergo interaction between disperse dye system during
dyeing. Highly reactive dyes may form a covalent bond with disperse dyes. This
problem is more likely to be seen when the disperse and reactive dyes are present in
the same bath. The use of two bath process is recommended [79].
▪ Reactive dyes require a large quantity of salt for dye exhaustion. This salt can interfere
with the disperse dye dispersion system. The use of two bath process or lower quantity
of salt is recommended [79].
▪ The reactive dyes require alkaline conditions for their fixation. Many disperse dyes are
not stable under these conditions. The use of one-bath two stage or two bath process is
recommended. The alkaline bath can serve as a wash-off bath for disperse dyes
depending on the chemical groups present [79].
▪ The reactive dyes are sensitive to change in liquor ratio. The effective liquor for the
cellulose component is higher than the bath liquor. The reactive dyes with lower
substantivity give lower color yield than high substantivity dyes in higher liquor ratios
[79].
The real challenge in dyeing with reactive dyes is the removal of unfixed hydrolyzed
reactive dye. The washing off process is critical and requires a large quantity of water and higher
washing temperature for effective dye removal. The washing off process involves rinsing followed
by soaping at high temperature. Initial rinse reduces the salt and alkali concentration. Lowering
the salt reduces the dye substantivity and makes the removal of unfixed dye easier. The favorable
conditions are a high number of bath changes, higher liquor ratio, and strong mechanical action.
Reactive dyes containing vinyl sulphone groups may hydrolyze at higher pH and temperature
conditions. The soaping process is carried out near the boil (95 oC). It removes the unfixed
hydrolyzed dye form the fiber interior. The favorable conditions are high bath temperature, low
amount of unfixed dyes, lower electrolyte concentration, higher liquor ratio, a high number of bath
91
changes and lower substantivity of the dye. The cold reactive dyes having lower substantivity may
cause less problem during washing. [61, 87, 113].
3.8.1.3 Direct dyes
These dyes are still used to dye of cellulose portion of the blend because of their shorter dyeing
cycle, lower cost, good dye compatibility, and acceptable fastness properties in lower depth.
However, they have limited fastness properties and produce dull shades. The strengths and
weaknesses are given in Table 3.5. Their application process is simple. They require salt for their
exhaustion. Direct dyes are normally applied to polyester/cellulosic blends by a batch process only
[61].
In the early 1980s, Sandoz presently Archorma launched a reactant fixable series of direct
dyes called Indosols. These are specialized direct dyes that can be fixed with specialized cationic
fixing agents giving good washing fastness properties. Most of them are pre-metalized copper
complex dyes. A new series of reactive fixable direct dyes called Optisols were introduced in the
1990s that do not contain metal [9, 64, 121]. These ranges are later combined and now called
Indosols [122]. The high-temperature stability of these dyes makes them suitable for one-bath one
stage dyeing of polyester/cellulosic blends. For the production of black, alkaline pH is required to
maintain solubility, one bath two-stage is therefore required [64, 122].
Disperse/direct system is usually restricted to the cheaper product segment that requires
relatively low fastness properties. This also provided leverage for disperse dye selection based on
their staining tendency for the cellulosic component. This system is commonly used for dyeing of
polyester blends containing viscose and other regenerated cellulosic fibers. These blends are used
as a suiting material where high wet fastness is not required. The aftertreatment with cationic fixing
agents along with resin finishing give direct dyeing adequate wet fastness properties [9, 56, 57, 64,
83, 87]. Shade change after this treatment, however, may be observed [83].
The solid color effect is usually achieved on blended staple yarns. Direct dyes give a good
reserve on a polyester component. This enables one bath bleaching and direct dyeing to be
performed. The polyester/cotton blended fabric can be scoured and bleached followed by dyeing
with selected disperse and direct dyes in the same bath [123].
Reactant fixable direct dyes can be used for dyeing of cotton portion in wool/cotton,
cellulosic/polyamide and cellulosic/acrylic blends by one bath one stage method with good
92
fastness properties. The acidic conditions required for dyeing of wool, nylon and acrylic fibers
complement the use of these dyes [9, 122].
3.8.1.4 Vat dyes
Cellulose fibers can be dyed with vat dyes by both batch and continuous processes. Batch dyeing
usually involves package, jet or overflow dyeing machines. The factors that may affect the dyeing
of cellulose portion with vat dyes are given below.
The presence of oxygen inside the machine can create problems during vat dyes assuming
that the machine is airtight, and no air can enter the machine once the process is started. There is
a higher contact between the dye liquor and the entrapped air because of the turbulence effect in
jet dyeing machines. This entrapped air can cause decomposition of hydrosulfite and therefore
cause problems in the reduction of vat dyes. Also, the decomposition products are acidic in nature,
so an extra amount of caustic is required for their neutralization. As a rule of thumb, 1 cm3 of air
requires 2 liters of caustic soda (36 oBé) and 1.7 kilograms of sodium hydrosulfite. Sufficient
quantities of caustic and hydrosulfite must, therefore, be used at the start of the dyeing process.
Additions during the dyeing process may cause problems. The actual quantity required depends
upon the machine and remains fixed for that machine under a particular set of conditions [57].
The important points to consider in deciding whether the jet or overflow dyeing machine
is suitable is given below [57]:
▪ The presence of large enough expansion tank so that complete dyeing liquor can be
prepared in it before it enters the machine.
▪ The rinsing system in the machine. The material should be rinsed, and liquor should be
drained while it is moving inside the machine and should not be stationary.
▪ The entrance of rinsing water in the machine. Water should either be entered through a
jet or through the inner walls of the machine and should not be fed from one side of the
machine.
The presence of alkaline earth metals in the material to be dyed should be avoided. The
dyeing process used can either be one bath two stage or two bath process. Dye selection is critical
to obtain good results. Certain vat dyes are sensitive to over reduction so either glucose or sodium
93
nitrate must be used [57]. The final rising and oxidation are critical for vat dyeing. Initial rinsing
helps in the removal of unexhausted leuco dye and chemicals [57].
Selection of vat dyes for jet dyeing depends on the following factors [57]:
▪ Less desorption tendency;
▪ Better leveling characteristics;
▪ Easily oxidized; and
▪ Higher exhaustion rate.
Sodium dithionite (hydro) is very sensitive to atmospheric oxygen in air and temperature.
Due to the exothermic nature of decomposition, it accelerates with a rise in temperature. The stock
solution is kept at a lower temperature and covered to prevent air. The stock solution with higher
hydro to caustic ratio is prepared separately and diluted with a caustic solution to bring it to a 1:1
ratio before it is fed into the trough. The volume of a trough is important as it affects the
decomposition of hydro [61]. Oxidation can be done either with hydrogen peroxide and sodium
metanitrobenzene sulphonate. Sometimes two oxidation steps are required for dye which has slow
oxidation rates or difficult to oxidize [57].
The reduction clearing step can be combined with the reduction step of vat and dyes used
to dye the cellulose component of the blend. For the two-bath dyeing process using
disperse/reactive system, the reduction clearing process is done as a separate step after disperse
dyeing to achieve excellent fastness properties [9]. In the case of vat dyes, oxidation and washing
of dyed materials are performed. For other dye classes such as reactive, direct and disperse,
washing off of unfixed dyes are carried out [61].
3.8.2 Batch dyeing of polyester/cellulosic blends
Figure 3.5 shows the commonly used dye system for batch dyeing of polyester/cellulosic blends
along with their color fastness properties and dyeing times [87]. The disperse/reactive although it
provides good fastness properties required much longer dyeing time than the disperse/direct and
disperse/vat system. The disperse/vat system is usually restricted to high end products that require
excellent fastness properties which are not usually achievable with disperse/reactive system. The
high cost of the vat dyes restricts their application to specialized products only [87].
94
Figure 3.5: Batch dyeing system for polyester/cellulosics blends.
3.8.2.1 Disperse/reactive system
PES/CELL blends can be dyed by batch process using a variety of methods. These methods are
described as follows.
Two bath method:
This is the traditional and standard method of dyeing PES/CELL blends. It allows optimum
fixation conditions for reactive and disperse dyes that provide good color yield and excellent
fastness properties. The polyester and cellulosic portions of the blends are dyed in two separate
baths. The Polyester is dyed first at 130-135 oC for 30-60 minutes followed by reduction clearing.
The cellulose portion of the blend may be stained by disperse dye thus affecting the reproducibility,
washing, and crock fastness. Reduction clearing is employed to remove the stain using sodium
hydrosulfite and alkali. The dyeing is then rinsed, and the cellulose portion is dyed with reactive
dyes for 45-60 minutes at 60 or 80 oC depending upon the reactive dye. This is followed by soaping
and washing to remove the hydrolyzed dye. This method gives excellent fastness properties.
However, the process is very time-consuming and consumes higher water and energy. The total
dyeing time required is around 9-10 hours [7, 87, 111]. No special disperse and reactive dye
selection is required for this method as all the dyes that are used for batch dyeing process are
suitable [87].
disperse/reactive
highColour Fastness
Dyei
ng
pro
cess
tim
e(h
ou
rs)
2
disperse/
4 direct
6
8
10
12
disperse/
vat
moderate
95
The two-bath method can be modified to reduce the dyeing time to 7-8 hours. This is
achieved by omitting the reduction clearing process. The polyester is dyed first with disperse dyes
and the dyebath is dropped. The dyeing with reactive dyes is then carried out in a separate bath
followed by rinsing and soaping. The reactive bath also serves as an alkaline clearing bath for
disperse dyes. This method is preferred for package dyeing and in cases where the stock tank is
not available [87].
Reverse two-bath method:
In this method, cellulose is dyed first with reactive dyes followed by dyeing of polyester with
disperse dyes. The higher temperature of disperse dyeing (130 oC) will serve to remove the unfixed
reactive dye. The separate washing and soaping are thus eliminated. However, not all reactive dyes
are suitable due to the saponification of dye fiber linkage under high temperature (130 oC) and
acidic conditions (pH 4.5-5). The reactive dyes which are most suspectable to this form ester bonds
(substitution type) with a hydroxyl group of the cellulose. Suitable buffer such as monosodium
phosphate can be used to prevent this problem [111]. Since reactive dyes are destroyed by
reduction clearing so this process cannot be performed. The disperse dyes must be selected that
show minimum staining of the cellulosic component. This process is shorter than two bath process
and saves water and time thus allowing more productivity. The total dyeing time is reduced to
about 7 hours [7, 87].
Type of alkali used for reactive dyeing should be such that it would not create effervesce
when pH is reduced for disperse dyeing so bicarbonates cannot be used. This necessitates the use
of either caustic soda, trisodium phosphate or sodium silicate. Scarlet and red colors can be easily
dyed with this method. For tertiary shades that require shading are dyed by conventional methods
as the cellulose portion is the one in which shade is adjusted according to target color [57].
One bath two stage method:
This method is very popular due to the shorter process. The Glauber's salt is added first at 60 oC
followed by the addition of dyebath auxiliaries. The dyebath pH is adjusted to pH 4.5-5.5 with
acetic acid. Disperse and reactive dyes are then added, and the temperature is raised to 130-135
oC. The dyeing is carried out at 15-30 minutes. The temperature is then dropped to 80 oC and pH
is adjusted with alkali to dye the cellulosic component with reactive dyes for 45-60 min. This is
96
followed by rinsing and soaping [64, 87]. The disperse dye selection is important as disperse dye
dispersion may not be stable under a large quantity of salt. The reactive dyes selected must be
stable under acidic conditions at a higher temperature. Since no reduction clearing is possible the
disperse dye should not stain the cellulose component and must be easy to wash-off. This requires
specialized disperse dyes which can be saponified at 80 oC with soda ash [7, 64].
In the modified one bath two stage process, the disperse dye is added first to dye the
polyester component under acidic conditions at 130-135 oC for 15-60 minutes. The dye bath
temperature is then dropped to 90 oC and salt is added. The temperature is then further reduced to
the dyeing temperature and reactive dyes are added. The dyeing process is carried at 80 oC or 60
oC depending on the reactive dye for 30-45 min. This is followed by rinsing and soaping. This
process allows common or Glauber’s slat to be used [87]
One bath method:
Reactive and disperse dyes can be applied to polyester/cellulosic blend by one bath method. The
bath pH is adjusted to 9-9.5 and the dyeing temperature is raised to 130-135 oC with simultaneous
fixation of both reactive and disperse dyes. The process is simple and less time consuming as
compared to the conventional two-bath process. Not all reactive and disperse dyes are suitable for
this method. Therefore, proper dye selection of reactive and disperse dyes are required as dye yield
is effected at compromised pH [7, 64].
3.8.2.2 Disperse/direct system
This is the simplest of two dye system used for the dyeing of polyester/cellulosic blends. The
dyeing is the shortest of all the dye systems currently applied and but the fastness properties are
moderate especially in dark shades as shown in Figure 3.5 [85, 87]. As compared to
disperse/reactive system many advantages can be obtained with this system. These are
significantly reduced dyeing times, less quantity of salt is required, less labor-intensive due to one
bath one stage process and uniform dyeing. The main disadvantage associated is the restricted
range of brighter shades as compared to reactive dyes [69, 122].
The disperse and direct dyes can be applied to polyester/cellulosic blends by one bath or
two bath process [57]. One bath provides a cheaper and simpler process [9]. Considerable savings
in water, steam, electricity, and labor along with increased productivity is obtained [124].
97
One bath method:
Dyeing by one bath is performed by either one or two-stage methods. In one bath one step process
all dyebath chemicals and dyes are added and bath temperature is increased to 130 oC. The dyebath
pH is maintained at 5-5.5 with acetic acid. The bath is then cooled to 80 oC for the exhaustion of
direct dyes and dyeing is continued until target depth is achieved. For some black direct dyes (C.I.
Direct Black 22) the pH needs to be adjusted to 9-9.5. Direct dyebath serves as a soaping bath for
clearing of disperse dyes. This is followed by cold rinsing and after treatment. The dyeing time
required varies from 3 to 4.5 hours [7, 9, 87, 125].
One bath two stage method:
During this method high temperature stable direct dyes are added along with the disperse dyes.
The polyester is dyed first at high temperature (130 oC). The temperature is then reduced to 80 oC
and electrolyte is added. The dyeing process is then carried out for direct dyeing. The traditional
reduction clearing process is not suitable due to the instability of direct dyes [86]. The cycle time
is slightly longer requiring 3.5-5 hours. The process is suitable for package dyeing in dyeing
difficult shades and processes requiring a large quantity of salt (longer liquor ratios). The dye
selection is important as all direct dyes are not suitable for one bath process [7, 9, 125]. The dyes
used are mainly self-leveling or salt controllable disazo multisulphonated dyes [9]. Staining of
cellulose by disperse dyes is not problematic for lighter to medium shade depths. However, for
darker shades, special approaches may be used to destroy the disperse dye stain. In the first
approach, silicone-based chemicals are used in resin finishing that liberates hydrogen. In the other
approach, the mild reducing agent is used and treatment is performed 70 oC under alkaline
conditions after cationic after-treatment [69].
Two bath method:
In the traditional two-bath method, the polyester and cellulosic portion are dyed separately with
intermediate reduction clearing. The polyester is dyed at 130 oC followed by reduction clearing to
remove the disperse dye stain. This is followed by neutralization. Direct dyeing of cellulosic
component is then carried out at 90 oC. For pale shades, the reduction clearing process can be
omitted. The two-bath process provides better fastness due to the intermediate reduction clearing
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step. A large selection of direct dyes is available and moderate to good fastness can be achieved.
This method, however, requires longer cycle time [7, 9, 85].
The cellulosic component dyed with selected direct dyes can be post-treated to obtain
adequate fastness properties. Cationic fixing agents or resin finishing can be employed [125]. The
fastness of disperse dye may be affected by resin finishing and must be checked [86]. Leveling
and dispersing agents are seldom used. It is recommended that they should be electrolyte stable
especially for one bath process [75].
3.8.2.3 Disperse/vat system
The batch dyeing with disperse/vat system is usually carried out for package dyeing of yarns. They
can be applied by both one bath and two bath methods. The main advantage of this system is that
the reduction bath requires for vat dyeing also perform reduction clearing of disperse dyes [85].
In one bath method, both disperse and vat dyes are simultaneously applied from the same
bath. The disperse dyes are fixed in the first stage in the acidic medium followed by reduction and
oxidation of vat dyes in the second stage. The vat dyes should be in a fine state of dispersion to be
suitable. The IK type vat dyes are not preferred as they required a lower temperature of 30 oC after
vatting for fixation. The vat and disperse dyes are applied along with the dispersing and wetting
agent. The dye bath pH is maintained at 4-5. The temperature of the dyebath is increased to 130
oC. The heating rate needs to be carefully controlled and should be in the range of 1.5-2 oC/min to
avoid unlevelness. The dyeing is performed for 60-90 mins depending on the depth of shade
required on the polyester component. This also causes pre-pigmentation of the cellulose
component with the vat dyes. The temperature is then reduced to 80 oC and sodium hydrosulfite
and caustic soda are added for the reduction of vat dyes. The reduction of vat dyes and reduction
clearing of disperse dyes occur simultaneously. The dyeing is continued for 30-45 minutes. To
prevent the over-reduction of some vat dyes, sodium nitrite is added. The fabric is then rinsed
followed by oxidation and soaping. The oxidation is carried out using hydrogen peroxide at 50 oC
for 10-15 minutes. The soaping is usually performed at a boil for 10-15 min using detergent [7,
81, 85].
The two-bath dyeing method is used for dark shades. Disperse dyes are applied first, the
dyeing temperature is then reduced, and vat dyes are added. The reduction bath for vat dyes served
99
as a reduction clearing bath for disperse dyes. The method provides better vat dye stability and
fastness properties than one-bath method [7, 87].
3.8.2.4 Disperse/sulfur system
The use of this system is limited for the dyeing of certain dark shades such as dark browns, navy
blue, and blacks [7, 85]. The main drawbacks associated with this system are [85]:
▪ Damage of polyester component due to large quantities of reducing agent at high
temperature;
▪ Long dyeing process;
▪ Damage of cotton component due to residual sulfur; and
▪ Environmental problems due to a reducing agent.
They can be dyed by both one bath dyeing and two bath dyeing methods similar to vat dyes [7].
3.8.3 Continuous dyeing of polyester/cellulosic blends
The continuous dyeing is the most common method of dyeing woven polyester/cellulosic blends.
Due to differences in the dyeing properties of each fiber in the blend two dye system is usually
used. The disperse/reactive and disperse/vat combinations are the most common dye system
applied to these blends by continuous process [9].
3.8.3.1 Disperse/vat system
Earlier dye system used for the coloration of polyester/cellulosic blends was based on disperse and
vat dyes. The continuous chemical pad-steam dye range was developed in 1944 for dyeing with
vat dyes preliminary to fulfill the demand to dye large quantities of uniforms to uniform shade [61,
126]. To ensure trouble-free pad-steam process it was recommended to consider the following
factors [126]:
▪ The temperature of the pad liquor, as high temperature may lead to instability of dyes
and chemicals.
▪ The distance between the padder exit and steamer inlet. The reducing agent may
prematurely decompose due to exposure to air.
100
▪ The presence of air in the steamer. This may cause the decomposition of the reducing
agent.
▪ Steamer roof and inlet heating to prevent condensation drops.
The thermosol process which was introduced for polyester dyeing with disperse dyes in
the 1950s was subsequently applied to polyester/cotton blend [61, 127, 128]. It was suggested to
consider the following points in the dyeing of polyester/cotton blends [127]:
▪ It is better to dye the polyester portion first with disperse dye as shade control is easier.
▪ In the dyeing of disperse/vat system, the economical process at that time, some vat dyes
tend to fix into the polyester during the thermosol process. Thus, creating problems in
shade matching.
▪ Due to shrinkage problems of fabric during disperse dyeing, it was suggested to heat
set on the stenter before the thermosol process.
▪ Disperse dye gave less color yield during thermofixation due to alkali in the dye pad.
In initial studies carried out for dyeing of polyester/cotton blends, it was recommended to
use vat dyes by the pad-steam process for pale shades, disperse dyes by a thermosol process for
medium shades and vat-disperse combination for dark shades. The fabric was dyed first with
disperse dyes by pad-dry-thermosol process and then vat dyes are applied by the pad-dry-chemical-
pad-steam process [129, 130]. A more economical approach was later used to apply both disperse
and vat dyes from the same bath. The selected vat and disperse dyes were padded together along
with the anti-migrating agent followed by infrared drying. The thermofixation process is carried
out at 200-210 oC for 60-90 seconds. The fabric is then chemically pad with hydro and caustic
followed by steaming at 105 oC for 25-40 seconds. The fabric is then oxidized, soaped and dried
[130-132]. This approach had problems as some of the vat dyes were fixed to the polyester portion
of blend this creating a shade matching problem [127]. To counteract this problem, it was
suggested to keep the thermosling temperature around 190 oC. At this temperature, the diffusion
of vat dyes in the polyester was found to be lower. Although the fixation of disperse dye was also
lower at that temperature but shade matching problems were avoided. At higher temperatures
during thermofixation, some vat dyes may aggregate and cause dulling of shade and specky
dyeing. To rectify this problem, it was recommended to carry out the chemical pad-steam process
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at 107 oC. Furthermore, to avoid migration, approximately half of the applied pad liquor (30-40%)
needed to remove by infrared drying [133]. As the disperse dyes require reduction clearing to
achieve good fastness properties, the reducing pad-steam method used to convert vat dyes into
their leuco form was also utilized for the clearing of the disperse dyes on the polyester surface
[128]. The advantage of this process was good fastness properties, dark shades can be dyed easily,
availability of a wide selection of dyes and the possibility of producing a cross-dyeing effect. The
limitations were dull shades and crock fastness problems in dark shades [130-133].
In the early 1960s, selected vat dyes from the Indanthrene range were selected and marked
as Polyestren. They can give the same depth of shade on polyester/cotton but there was a limit on
the color depth that can be achieved. For dark colors, a mixture of vat and disperse dyes were
required [134]. In the 1960s the largest and well-established dye system used for continuous dyeing
of polyester/cotton blend was based on disperse/vat combination. Although reactive dyes were
available but at a higher cost of dyeing dark shades with disperse/reactive system, disperse/vat
system was recommended. Different configurations of padder were used. Pre-drying was carried
out using either can driers or infrared chambers. For thermofixation, gas-fired ovens with top and
bottom rollers were used [131].
Disperse/vat dyes are currently applied to polyester/cellulosic blends by a pad-dry-
thermosol-chemical pad-steam process. Light to dark shades with excellent fastness level is
obtained by this process. Both disperse dyes and vat dyes are applied from the same pad liquor
under acidic conditions (pH 5.5 with acetic acid) along with wetting agent and anti-migrating
agent. In the first stage, disperse dyes are fixed by thermofixation at 200-220 oC. In the second
stage, pad-steam development of vat dyes is performed where vat dyes are first reduced and then
oxidized to complete the fixation process. The fabric is padded with hydro and alkali and is then
steamed for 60 seconds at 102-105 oC using saturated steam. The alkali and hydro in the steamer
destroy the unfixed disperse dye. The water seal and first two washing units kept at 40 oC remove
the caustic to lower the fabric pH before the oxidation process. Oxidation is then performed in
subsequent washing units at 60 oC by feeding peroxide and occasionally acetic acid. The pH is
kept at or below 9 to avoid the problem of greener and duller shade of indanthrone blue dyes due
to higher pH in the oxidation process. The removal of caustic is more problematic in heavier
fabrics and it is found that in a typical vertical washing unit caustic removal is more at the sides as
compared to the fabric center. This may cause width wise shade variation. Proper feeding of
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chemicals across the width can help to solve this issue. The remaining units are for soaping and
washing off at 95 oC. After washing fabric is dried on drying cylinders [61, 113].
3.8.3.2 Disperse/reactive system
In the late 1950s and earlier 1960s, the continuous dyeing of polyester/cotton blend was mostly
carried out by disperse/vat system. With the introduction of reactive dyes, disperse/reactive dyes
have become common [61, 130]. The continuous dyeing with disperse/direct dyes can be carried
out by both one and two bath methods. During the two-bath process, the disperse dyes are fixed
on a polyester component by thermofixation. This is followed by an intermediate reduction
clearing process. The reactive dye fixation is then achieved on the cellulose component by pad-
dry chemical pad-steam process.
For one bath process, either one bath two stage or one bath one stage methods can be used:
▪ In one bath two stage method, the fabric is padded with disperse and reactive dyes. The
disperse dyes are fixed by thermofixation. The fabric then padded with alkali followed
by steaming to fix the reactive dye [85, 113].
▪ During one bath one stage method, the fabric is padded with disperse and reactive dyes
along with alkali followed by simultaneous fixation of both dyes [85, 113].
Two bath method:
During the two bath the disperse and reactive dyes are applied in two separate stages. The reduction
clearing process is optional and can be performed depending upon the fastness requirement and
depth of shade. This method is very time consuming is restricted to dark shades where excellent
fastness properties are required. The first stage involves the dyeing of the polyester component
with disperse dyes by the pad-thermosol process. The process involves padding, drying, and
thermosol treatment. During the second stage, the cellulose component of the blend is dyed. The
dyeing of cellulose component can be carried out by a various method that includes pad-thermofix,
pad-steam, pad-dry-chemical pad-steam or pad-moist (Econtrol) process. The dye material is then
rinsed and soaped at boil [135].
During the pad-thermofix process, the fabric is padded with reactive dyes along with urea,
alkali and anti-migrating agent. The fabric is then dried and thermofixed at for 1 minute at 150 C.
The exact duration and temperature of fixation depend on the type of reactive dye used. The main
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disadvantage associated with this process is the excessive urea fumes. These fumes cause white
resist marks on fabric requiring frequent cleaning of the machine. Not all reactive dyes are suitable
for this method [135].
Pad-moist or Econtrol is a specialized process that requires specialized thermosol unit to
carry out fixation of reactive dyes at 120-130 oC in 25-30% relative humidity. The thermosol unit
is supplied with a steam injection unit to maintain the required relative humidity inside the
thermosol unit. This process is environmentally friendly and requires fewer chemicals and no urea.
This method provides good color yield and fastness properties [135].
Pad-dry-chemical pad-steam is a classical continuous method with reactive dyes. The
process gives excellent fastness properties and bright shades. This process is not suitable for
shorter runs and requires large quantities of salt [135].
One bath two stage method:
The application of disperse/reactive dyes is carried out by pad-thermosol-chemical pad-steam
process. This is an economical and energy saving process as compared to two bath process. This
process is mainly used for medium to dark shades. The process gives good dye yields and good
appearance of the fabric [113].
During this process, the fabric is padded with disperse and reactive dyes along with anti-
migrating agent, wetting agent, mild oxidizing agent and dispersing agent under slightly acidic
conditions (pH 5.5 with acetic acid). The fabric is then pre-dried using an infrared dryer followed
by drying at 110-130 oC. The thermofixation of disperse dyes is carried out at 200-220 oC for 60-
90 seconds. In the second stage, the fabric is padded with salt, sodium hydroxide and sodium
bicarbonate followed by steaming at 102-105 oC for 60 seconds using saturated steam. The
steaming process under alkaline conditions also serves to clear the disperse dye. The fabric is then
rinsed, soaped and neutralized followed by drying [113].
One bath one stage method:
This is an economical and environmental method for dyeing PES/CELL blends. Several attempts
have been carried by dye manufacturers to develop a suitable one-bath method. As reactive dyes
can be fixed with pad-thermofix process, the one-bath process was attempted to use thermosol
phase for fixation of both disperse and reactive dyes to PES/CELL blends. The main challenge
104
associated with a suitable one-bath method is differences in dyeing conditions required for disperse
and reactive dyes as shown in Table 3.10 [136].
The one step theromosol process is recommended for the dyeing of mercerized PES/CO
woven and PES/CV blends with at least 50% polyester. Good pad liquor stability and
reproducibility acan be obtained in this process. The fastness properties are inferior as compared
to one bath two stage. This method is restricted to pale to medium depths. This process is shorter
and economical. However, the dye selection is limited due to compromised fixation conditions
[85, 113].
Table 3.10: Dyeing properties of reactive and disperse dyes [136].
Reactive dyes Disperse dyes
Applied to cellulose Applied to disperse
Alkali required to fix the dye Sensitive to alkali (reduction in color yield)
pH 10.8-13.5 pH 4-6
Sensitive to reduction Reductive clearing is necessary to achieve
excellent fastness properties
Fixation of damp goods (moist conditions) Fixation of dry goods
Cotton yellows at elevated temperature Fixation at elevated temperature (200-200 oC)
The fabric is padded with disperse and reactive dyes followed by simultaneous
thermofixation of both dyes under milder alkaline conditions [85, 113]. The dye liquor consists of
wetting agent, ant-migrating agent, urea, dicyandiamide, and sodium bicarbonate. The reactive and
disperse may interact with each other and dyebath auxiliaries such as urea and dispersing agent.
The dicyandiamide is added in especially in dark shades. The use of dicyandiamide creates a
challenge because of its availability and lower solubility. Since cotton may yellow at high
temperature and under alkaline conditions borax may be added in the dye bath. The liquor
temperature is kept at 20-30 oC. The pickup is usually set at 60-65% followed by infrared drying
to 50% residual moisture before the final drying is carried out at 110-130 oC. Thermofixation is
carried out at 210-220 oC for 60 seconds. The fabric is then washed by a special wash-off process
to optimum fastness properties. During washing the fabric is soaped at boil under alkaline
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conditions first followed by soaping without alkaline. The fabric is then rinsed, neutralized and
dried [113, 136].
Recently Dystar in collaboration with Monforts developed a new one-bath process known
as Econtrol T-CA. This process is based on the already established Econtrol process used for
reactive dyes [136]. The main advantages associated with this process are [136]:
▪ Good degree of fixation of reactive dyes as compared to the standard process;
▪ Good color yield of diperse dyes;
▪ No yellowing of cellulosic fibers;
▪ Good fastness properties that meet the customer requirements without reduction
clearing;
▪ Wide range of shades; and
▪ All necessary dyebath chemicals and dyes can be applied from one-bath.
Only specialized reactive dyes with medium to high reactivity and disperse dyes are
suitable by this process. These dyes provide excellent color yields under the Econtrol T-CA
fixation conditions. The shades up to 30 g/l can be produced with good fastness properties. The
fabric is padded with reactive and disperse dyes along with wetting agent and anti-migrating agent.
Sodium carbonate along with the buffer is used to maintain alkaline conditions. The fabric after
infra-red pre-drying is dried at 110-130 oC under 25-30% humidity. This is followed by thermosol
treatment at 190-215 oC for 60-100 seconds. The fabric is then rinsed and soaped at the boil to
achieve good fastness properties [136].
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CHAPTER 4 PRACTICAL PROBLEMS IN THE COLORATION
OF TEXTILE FIBER BLENDS
4.1 Introduction
Fiber blends have been dyed for a long time and despite many developments in the process,
including dyes, chemicals, and machinery there are still challenges and problems in their dyeing
process [57]. In addition, although the dyeing process is properly controlled and required
procedures are properly implemented and the plant is efficiently managed issues still arise [10, 11,
137]. The occurrence of faults in the dyeing process is an ongoing concern for all those who run a
dyehouse. The nature of faults may vary from one dyehouse to another. It is the attitude and
approach towards process control and eradicating defects that differentiates one dyehouse from
another [138].
The estimates of fabric quality levels produced in typical dyehouse are given in Table 4.1
[139]. The finished fabric produced by a dyehouse can be grouped as whites, dyed and printed
material. These are just estimates and vary with the material type being processed. A fabric with
minor faults may still be marketable at reduced cost depending upon the severity of the fault. Major
faults, on the other hand, are often sold at a lower tier quality [140]. Due to the increased demand
to maintain product quality standards, the importance of recognizing faults and a means to resolve
such issues is increased. The product quality level that may have been considered salable a few
years ago may not be acceptable by consumers today [141].
Table 4.1: Typical finished fabric quality levels [139].
Finished fabric Fresh % Minor fault % Major fault%
White 95-98 2-3 up to 3
Dyed 92-94 4-5 up to 5
Printed 85-90 5-8 up to 10
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In the current global competitive environment, there is added pressure on the dyehouse to
make the dyeing processes more competitive [142]. To meet the customer's requirements and make
a profit, low fault levels and high-quality productions are required [141]. The profitability of
dyeing blends, like any other dyeing process, is based on three parameters: quantity, quality, and
cost [64]. This necessitates a review of the process as well as cost reductions wherever possible
[142]. To make any dyehouse profitable the reprocessing and amount of faulty materials must be
minimized. The use of appropriate processing techniques can avoid the generation of faulty
materials. This can result in savings due to reduced reprocessing and increased production of new
materials [143].
Over the years, the textile industry had achieved drastically higher productivity gains
mainly by reducing processing times. However, the lots that are processed under increased time
constraints can lead to complaints either due to not meeting the requirements or having insufficient
quality. Generally, companies maintain a record of costs associated with customer complaints and
waste at the final inspection stage. However, the costs that may incur due to reprocessing and
laboratory trials associated with fault identification and rectification are often not recorded. These
costs influence the final turnover (profit) of the company. Table 4.2 shows the dyeing process costs
associated with not meeting the target [144]. Faulty articles cost the same to produce as the right
quality articles but have a lower market value. To repair such faulty products requires certain
procedures that incur cost and may also have a lesser chance to meet the required target [138]. To
achieve optimum profits, the production and reprocessing costs should be minimized [145]. The
key steps in this direction are the process reproducibility and the reduction of dyeing times [142].
Table 4.2: Dyeing costs associated with not meeting the specifications.
Process Cost Productivity Profit
Blind dyeing 100 100 100
Small addition 110 80 48
Large addition 135 64 -45
Strip and redye 206 48 -375
108
To make the operation of dyehouse profitable, it is important to set certain targets. The key
performance indicators of dyehouse are given below [143]:
▪ Dyeings match the target shade within a given tolerance range and are uniform.
▪ High levels of right-first-time dyeing without any additions (> 95%).
▪ Minimum percentage of rejects attributed to different processing operations (< 2.5%).
▪ Shortest possible processing time (< 4 hours)
▪ Proper monitoring of the water and energy consumption and nature and quantity of
effluent production (efforts to reduce water and energy consumption and effluent
production).
▪ Meeting production targets (total quantity and ratio of products).
▪ A proper definition of responsibilities and management structure.
Since a dyehouse involves highly technical operations having a good laboratory is
necessary to provide technical services and training facilities for production personnel. Good plant
layout and production planning are essential to obtain good workflow and avoid bottlenecks.
Future changes in demands and product diversification must be considered when the plant is being
set up. With the increasing pressure due to cost and environmental reasons older machines may be
replaced with new machines whenever possible. Regular audits of the plant are also necessary to
monitor water and energy consumption. This provides the possibility of reducing processing costs.
The standard procedures that are documented in manuals must be made available to all production
personnel [143].
The first prerequisite to eradicate faults is management commitment which then trickles
down to the entire team. Some signs that show a lack of management commitment include lack of
resources, unrealistic product requirements, and poor communication between marketing and
manufacturing [138]. In any dyehouse not meeting the targets may be attributed to [138, 143]:
▪ Shortage of resources;
▪ Lack of knowledge;
▪ Scarcity of skills;
▪ Improper attitudes; and
▪ Lack of management commitment.
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4.2 Troubleshooting faults in coloration
In order to troubleshoot faults it is important to first define faults so that the concerned personnel
have the same understanding of what constitutes a fault. A fault is an imperfection that may negate
or reduce the value or serviceability of the product. It may be something undesirable or an
imperfection or a deficiency [100, 141, 146].
Several approaches that can be used to classify faults are given in Table 4.3. In terms of
diagnosis, the most useful approach is to classify faults based on their origin. Thus, the processing
stage/or stages responsible for generating faults can be identified accordingly [100, 114].
Table 4.3: Classification of faults.
Types Description
Major and minor [100]
Minor faults have a slight effect on meeting the intended
requirements and can be corrected.
Major faults make the product unfit for the intended end-use.
Visible and hidden
[100, 146]
Visible faults are immediately recognizable while the hidden fault
can only be detected during use or through testing.
Aesthetic and
functional [146]
Aesthetic faults are deviations from the target specification in
terms of appearance, hand, and other visible differences.
Functional faults are related to not meeting the required end-use
properties.
Origin based [17, 100,
114]
The faults are identified based on the process stage responsible for
the fault, e.g., weaving faults, spinning faults.
Many faults in fabrics are only visible after the dyeing process. The slight variations in
intensity or hue can easily be detected and can adversely affect the aesthetics of the dyed materials
[114, 138]. In order to produce a satisfactory high-quality product at a competitive price, faults
must be eliminated. There is always a cost associated with a fault when the product does not meet
the intended requirement [100, 138]. The faults also include quality concerns raised during the
preceding processes and provide an improvement opportunity in the coloration process. Faults,
110
depending on their severity, either can be reworked or result in selling the product as seconds. The
reworking process will increase the cost of the product [141].
The troubleshooting process can be considered analogous to the criminal investigation
process [147-150]. An expert acting as a detective is responsible for determining the root cause of
the fault. The level of expertise associated with troubleshooting faults varies among experts. A
dyehouse expert, however, must possess the necessary skills to troubleshoot and eradicate the
defect. This requires proper understanding and knowledge of the process and raw materials
involved. Proper troubleshooting requires a proper approach to solving the problem more
effectively and efficiently [141, 149, 150]. A successful troubleshooter possesses three attributes
that include high curiosity, diversified experienced background, and good communication skills.
Having high curiosity inclines a troubleshooter to explore causes of faults. Having a broad
background allows effective determination of the cause and effect relationship and possessing
good communication skills leads to the organization of thoughts, asking questions and hearing
answers objectively [137]. It is important to note that two faults that may have a similar appearance
can be caused by different sources and in different ways. Thus, each fault should be investigated
based on its own characteristics and specific circumstances. A fault that is produced in one mill
may not necessarily be exactly reproduced in a different mill [138, 151]. However, fundamental
knowledge and techniques can be applied to mill specific faults [138].
The systematic investigation process requires at least four steps. Firstly, the data is gathered
through visual evaluation and a series of questions and answers specifically related to the fault.
This includes specific details about the current and preceding processing stages, chemicals and
process parameters used, time and shift when this fault occurs and fault trend. Secondly, a
hypothesis is developed using a list of probable causes related to the fault. Thirdly, experiments
may be performed to test the hypothesis. This requires laboratory analyses of the fault and attempts
are made to synthesize the fault based on the probable causes. This serves as a verification of the
causes. Lastly, the results obtained after analyses are interpreted to determine the exact cause of
the fault [137, 146-148, 152].
Figure 4.1 shows a typical troubleshooting process for a dyeing fault. The main goal of a
troubleshooting process is to investigate the causes of faults, determine their solutions and steps
taken to avoid them in the future. The nature and cause of the faults must be properly investigated
[143].
111
Figure 4.1: Fault investigation process in a dyehouse.
The visual assessment of faulty fabric is done to determine the relationship between fabric
appearance and causes of the defect [152, 153]. Assessment is carried out to ascertain [153]:
▪ Nature of the fault’s appearance - periodic or sudden, size, directionality, start and
endpoint location;
▪ The actual appearance of the fabric - color change, differences or changes in fabric,
yarn differences as compared to the non-faulty area.
Common faults can easily be traced by a careful investigation. The source of coloration
faults can be traced to preceding processing stages or even to raw material [147]. Other
investigations to narrow down the origin of defects may only be possible after visual assessments
[153]. Although the probable cause of faults can be large in number, the likely sources can be
shortlisted through the process of elimination. To prevent fault from happening again, it is
important to determine the exact cause of the issue [147, 152]. If the appearance of the fault is not
direction biased, it may be attributed to the pretreatment or dyeing processes. If further
investigation is required, the fabric may be stripped and redyed. If the fault reappears it may be
attributed to yarn or fabric related issues [153]. The faults confronted in a dyehouse can be
analyzed from three dimensions [140]:
Detective work
Processing details
Quality control records pertaining to the defective batch
Visit of production site
Expert or senior personnel
Experience
Working knowledge
Specialization
Specialized laboratory
Specific instruments and methods
Time
Cost
fastness
RFT Practical dyeing know-how
compatibility
shade constancy
DYEHOUSE EXPERT
112
▪ Faults produced in the dyehouse;
▪ Faults identified in the dyehouse due to causes from preceding steps; and
▪ Faults from preceding stages but can be covered-up in the dyehouse.
Troubleshooting faults is multifaceted for many reasons. Firstly, current industrial
coloration processes include many processing elements, such as preparing dye recipes, dyeing
process, and washing off, which can introduce faults. Process inputs such as fabric or yarn, water,
dyes, and chemicals can also introduce faults. Another problem with faults is that often they are
only observed after several succeeding operations and many do not appear in the same process
step where they were created [141].
Generally, the dyed fabric is inspected for any faults in folding or cut for sewing. This
implies faults in the fabric may not be observed until the final stages of processing. This strategy
lacks the target of preventing defects from occurring in the first place. A yarn fault, for example,
may not be observed when the yarn is dyed but may be detected when the yarns are converted into
fabric. Additionally, faults can occur within the product development cycle that starts with
laboratory dyeing and goes through bulk dyeing in a plant. Each stage may introduce faults and
their removal at the initial stages does not guarantee fault free processing at the later stages[138,
141].
Moreover, a fault may occur randomly from time to time. Also, the same type of fault may
have many causes and their occurrence may be different from the others. As mentioned earlier,
faults can occur due to a variety of reasons and may be classified according to their origin [143].
Faults may originate from fiber, yarn, fabric, water, preparation, dyes, dyeing methods, or
machines. Faults can be machine-related and may be attributed to the inherent design limitations
and capability of devices [141]. For instance, the following examples illustrate different origins of
unlevelness [143]:
▪ If only observed on one type of fabric, the cause may be associated with the particular
fabric or it’s pretreatment.
▪ If seen only on one machine the likelihood may be a machine related fault.
▪ With a particular processing method or dye, the fault is likely caused by an inadequate
processing method or wrong dye selection.
113
▪ If only noted among material from a given shift, the case may be associated with the
personnel involved.
All these factors make the troubleshooting process quite complex in nature. A formally
structured troubleshooting system protocol will give a more accurate, rapid and cost-effective
solution to a problem as compared to a random unstructured or empirical approach that is more
resource and time-intensive. Determining a true cause may require testing a number of possible
causes. It is quite possible that if the dyehouse expert is analyzing the other causes to solve the
problem, the actual conditions which have caused the problem might have changed accidentally
or by chance. Thus, the effort required to solve the problem may be duplicated. The problem may
not be completely resolved and may reoccur in the future. Formal problem-solving methods are
cost-effective and efficient as compared to random hit and trial methods [141].
A troubleshooting protocol is a reactive program that is used when faults occur in the
process and need to be eliminated. In order to prevent a fault from occurring in the future, a
proactive program is required in which information obtained from the troubleshooting system can
be used. So, the latter system complements the former method [141]. The most effective
troubleshooting strategy is one that will not let faults to happen in the first place [11].
Troubleshooting protocols may consist of the following elements [141]:
▪ Standard operating procedure for problem-solving;
▪ Identification of faults in the process and key process elements;
▪ Practical knowledge and fundamental understanding of the process. Identification of
key process parameters. Consideration of actual workplace conditions is equally
important. This is the key element for the determination of cause and ultimately fault
elimination;
▪ Use of statistical techniques for identification of key factors, design of experiment and
data analysis; and
▪ An accessible computer database for data storage and workplace-specific problems and
experiences.
Controls in every stage of processing are required to prevent the occurrence of faults and
stopping them from going further until the issues are resolved. Thus, in order to reduce faulty
114
products, the responsible causes must be removed [138]. A proper diagnosis is the key to prevent
the reoccurrence of faults [140]. In that regard, there are four key areas to consider [138]:
▪ Recognition of specific faults and their causes;
▪ Preventing defects that occur in a dye house;
▪ Detecting defects from earlier stages; and
▪ Regulating variations in raw materials.
As indicated variations in a dyed product may be due to process or raw material variations
including the substrate. In order to control any process, it is important to ensure all the raw
materials remain constant in terms of their properties. This must be controlled first as processing
factors can be optimized. Hence, in order to optimize and control any process to produce defect-
free products the raw materials must be controlled first. Raw materials include substrate and
chemicals used in processing. For a substrate, it is important to know the defect levels from prior
processes and any residues that the substrate may contain from previous processes. It is important
to know the test methods to identify these residues and how to remove them. Residues may include
sizing reagents, knitting oils, alkali, surfactants, metal impurities, spinning oils, etc. The impurities
present in the chemicals and quality variations must also be determined. Dyes and other special
chemicals should be selected according to some prescreening criteria. Every lot of chemicals and
dyes received by the dyehouse should be tested [138].
The equipment selected for processing should be based on end-use requirements of the
product and fabric properties. Not all substrates can be processed on all equipment types and their
compatibility must be checked. The equipment should be properly maintained, and its limitations
should be known. Controlling the process requires a thorough understanding of the process. The
critical factors related to a process must be identified. Products requiring special care and controls
should be identified and required precautions must be properly implemented [138].
The relationship between the dyeing faults and the potential sources can be very complex.
This requires a deep understanding of each process involved in the manufacturing of the product.
The dyeing of blended materials can be done either in yarn, fabric or garment form. The raw
materials and preceding manufacturing stages standout as possible sources of faults as shown in
Figure 4.2 [17, 100, 114].
115
Figure 4.2: Cause and effect model for investigating faults in the dyed fabric.
4.3 Dyeing problems arising from the fiber
The fiber is a basic component of any textile product and plays a significant role in the making
and properties of a product as shown in in Table 4.4 [6, 154, 155]. The fiber characteristics are
selected based on the fabric requirements and differences between them can be a major source of
faults in a product [6]. Fibers can be natural or manufactured and are used to make a variety of
products, each with different properties. The dyeing properties of a substrate is influenced by the
chemical structure and molecular arrangement of the polymer molecules making up the fiber,
treatment conditions during growth or manufacturing, subsequent processing stages, yarn and
fabric formation, as well as preparation [114, 156]. Fibers can be natural or manufactured and are
used to make a variety of products, each with different properties. The dyeing properties of a
substrate is influenced by the chemical structure and molecular arrangement of the polymer
molecules making up the fiber, treatment conditions during growth or manufacturing, subsequent
processing stages, yarn and fabric formation, as well as preparation [157].
Raw material
Spinning
Winding
Warping and sizing
TEXTILEFABRIC
Make-upcutting
Finished goods
Weaving
Knitting Preparation
Coloration
Finishing
Direct effect
Indirect effect
116
Table 4.4: Relationship between fiber properties and spun yarn characteristics.
Fiber Properties
Yarn quality characteristics
Even
nes
s
Th
ick
pla
ces
Th
in p
lace
s
Nep
s
Hair
ines
s
Str
ength
Elo
ngati
on
Ap
pea
ran
ce
Dyea
bil
ity
Micronaire/fineness/diameter/ diameter
variability D D D D D D D D D
Maturity D D D D N D D D D
Length/length variability D D D D D D D D N
Short fiber content D D D D D D D D N
Strength N N N N N D D N N
Elongation N N N N N D D N N
Nep content I N N D N N N D D
Dust, trash content, vegetable matter I D I D N D D I N
Contamination/dark and medullated fibers N N N N N N N D D
Color/color deviation within lot N N N N N N N D D
UV value/UV deviation within lot N N N N N N N I N
D: direct relationship, I: indirect relationship, N: no relationship
The differences in dyeing properties of a substrate may be due to the variations in fiber
structure either due to the inherent properties of particular fiber, or changes occurring during
processing or the dyeing process. The chemical composition and structure of the fiber is often the
deciding factor determining the suitability of a dye for dyeing that fiber. The physical forces of
attraction and chemical reactions between fiber and dye determine the dye retention in the fiber.
However, due to the geometrical structure of fiber, the movement of the dye molecules to the
interior of the fiber can be restricted despite the attraction between the dye and the polymer. The
following factors affect the dyeing properties of textile materials [114]:
▪ The differences in the chemical structure of the fibers;
▪ The physical structure of fiber;
117
▪ Effect of pre-dyeing processes on fiber structure; and
▪ Fiber properties affected during the dyeing process.
The penetration of the dye inside the fiber is greatly influenced by the interaction between
the fiber and dyebath medium. Hydrophilic fibers that swell in water are best dyed with ionic dyes
while nonionic dyes are best suited for hydrophobic fibers. Some fibers that fall in between these
two categories can be dyed by both non-ionic and ionic dyes. The fiber swelling during dyeing
directly depends upon the molecular orientation or crystallinity [114].
The internal structure of fibers can be categorized into two broad areas. The area where the
polymeric molecules are arranged in a systematic order is termed as the crystalline region and the
area where there is no order is called the amorphous region. Textile fibers contain both amorphous
and crystalline regions. The ratio of these two regions affects the dyeability of the fiber [156]. The
relative proportion of these regions influences dyeing properties. Amorphous regions are more
accessible to dyes and liquids compared to crystalline regions [114, 156]. The degree of
crystallinity is affected by a variety of factors depending upon whether it is a natural or
manufactured fiber. For natural fibers, it depends on conditions during growth and in the case of
manufactured fibers, extrusion, and subsequent drawing and heat setting affect the crystallinity of
the material. Dyeing processes also affect the fiber structure, as the dyed or stripped fabric dye to
different extents compared to the undyed fabric. The fiber dyeability and the result of dyeing are
affected by the internal structure of the fiber since it controls the penetration and distribution of
dye molecules inside the fiber [156]. The fiber swelling during dyeing directly depends upon the
molecular orientation or crystallinity. This either changes the availability of functional groups or
their interaction with the dye. The physical properties of the fiber are also affected by the degree
of crystallinity [114].
The dyeing properties of natural fibers such as the nature of functional groups and the
permeability of dyes are difficult to control as they are often determined during fiber growth [114].
The dyeability of cotton fibers depends on a multitude of factors such as the area of growth, color,
natural fluorescence level, weathering history, maturity, and heating history. Table 4.5 shows the
factors along with their effect on dyeing behavior [158]. Cotton fiber contains different types of
impurities which can be classified as physical and natural contaminants. The amount of non-
cellulosic substances in cotton varies considerably from 3-12% depending on various factors such
118
as variety, growth area, environmental factors, maturity level, and agronomic factors. These
impurities include proteins, waxes, and minerals which may impart color and interfere in the
dyeing process. It is important to note that natural constituents such as neps and seed coat
fragments may also be considered as contaminants considering their effect on the quality of end
products. Every effort should be made to reduce the external impurities present in the fabric. The
metal constituents in cotton fiber can cause a serious problem in preparation, dyeing, and finishing
if present in large quantities. Metals may be introduced from different sources such as soil
conditions, and harvesting aids [158, 159].
Fiber maturity is one of the most important quality parameters. It has a strong effect on
processing behavior and dyeing properties. Matured fibers have fully developed cell walls in
contrast to immature fibers which have thinner cell walls. This may be caused by insects, plant
disease, drought, bad weather, and premature harvesting. The dye uptake of immature fibers is
lower than that on mature fibers. After dyeing, these fibers may appear as white or light-colored
specks on cotton or cotton blend fabrics. Areas of fabric may have a lighter color which can cause
shade variation if the distribution of immature fiber is not uniform. These fibers can cause several
other problems such as nep formation, fiber breakage, poor fabric appearance, low yarn strength
and increased yarn breakage [6, 160-163]. Several preventive actions need to be taken at the
spinning stage to minimize or avoid these problems. These include selecting bales with low
immature fibers, measurement of the immature fiber content of every bale, proper blending at bale
laydown and controlled waste recycling [6]. If these controls are not employed, immature fibers
may appear in the fabric. The dyer may be able to deal with this problem, to some extent, by a
proper selection of dyes and through mercerization. It is important to note, however, that the
performance of dyes varies from class to class and based on the dyeing process employed [161-
163].
119
Table 4.5: Factors affecting the dyeing behavior of cotton.
Factors Implications
Area of growth Rain gown cotton fibers, compared to irrigated cotton, are dyed to more
fuller and more solid colors in appearance due to differences in fibers
reflectance characteristics. Thus, the ratio of these types must be controlled
carefully in cotton mixes. Some dyeing differences may be minimized by
mercerization.
Color
(yellowness and
grayness)
Varies depending on the variety, growth area, weathering, maturity, and
non-cellulose content and this may affect the final dye shade. It is difficult
to minimize significant color differences in raw cotton after scouring and
bleaching.
Fluorescence Variation in fluorescence affects dyeing characteristics and may result in
weft band formation in critical fabrics such as weft-faced fabrics.
Weathering Long weathering of cotton leads to yellower or grayer color and an increase
in carboxyl groups which can repel certain dyes such as direct dyes.
Mercerization may even out certain differences.
Heating history Excessively overheated cotton will dye lighter. This is attributed to an
increase in hydrogen bonding and carboxyl group formation (see above).
The former affects penetration while the latter repels certain dyes. Using
higher heat in ginning, over drying or uneven drying during preparation
affects the dyeing.
Maturity Immature cotton leads to lighter shades, undyed clumps of fibers, uneven
appearance, and inferior wash fastness. Mixing cotton of varying maturity
levels may cause weft bands. Maturity also affects nep formation and leads
to poor yarn appearance and uneven dyeing. The neps in combination with
trash particles appear as light or dark specks in dyed fabrics. The dyeing
behavior of ring-spun yarn is more affected by maturity variations than
rotor spun yarn.
120
Wool fibers are obtained from different sheep breeds and are available in different fiber
lengths and diameters. The raw wool consists of 25-70% impurities such as wool grease, suint,
dirt, and vegetable matter. Various processes are performed to remove these impurities. Wool
contains different types of amino acid side chains which vary in size and chemical nature. These
side chains contain acidic and basic groups and have a strong influence on the dyeing properties
of wool [164]. There are 170 different types of proteins found in wool which are not uniformly
distributed throughout the fiber [165]. Wool contains different types of cells knowns as cuticle,
cortex, and medulla. Cuticle cells are on the outside layer while the cortex is found in the inner
layer. The cortical cells are separated from each other by the cell membrane. Prolonged dyeing at
low pH damages this cell membrane and leads to lower abrasion resistance [164].
Wool fibers may exhibit unlevel dyeing due to the damage of the tip of the fiber during
growth (on sheep's back) because of exposure to sunlight and weather. The tip of the wool is dyed
differently than the rest of the fiber due to the differences in its affinity for dyes. The outer layer
(cuticle) of the wool fiber is hydrophobic and resists the penetration of hydrophilic dyes.
Photodegradation makes the outer layer hydrophilic due to partial removal of the epicuticle and
oxidation of cystine. The tips of the fibers undergo these changes to a larger extent which results
in a preferential adsorption of acid dyes known as tippy dyeing. The epicuticle may also be
damaged due to mechanical processing. It is difficult to differentiate tippy dyeing from fiber
damage during growth or from mechanical processing of the fiber. In either case if a single dye is
used, this may show up as a difference in the depth of shade of the tip as compared to the rest of
the fiber. In the case of dye mixtures, this fault may show up as dichroism [82, 149, 166].
Wool and silk fibers have small quantities of chromophores which is linked to their growth.
These chromophores give a creamy off white color to wool and silk fibers. The bleaching process
can be carried out to improve the whiteness of the wool fiber [167]. However, it is not possible to
generate a brilliant white look on these fibers by the commercial bleaching process. Careful
selection of wool fibers with finer diameters can improve the color of raw wool. The yellowing of
wool may occur due to some problems associated with growth such as bacterial damage, oxidation
of protein and increase in pH of suint during growth. These problems are more common in
crossbred types of wool as compared to Merino wool. Different grades of wool exhibit different
dyeability and dye penetration. Coarser or low-grade wools are more yellowish and more difficult
to dye in lighter or brighter shades as compared to high-grade wool types. Improper mixing of
121
different grades of wool will cause difficulties in obtaining a balanced shade in wool blended
materials [67].
The structure of manufactured fibers is affected by various stages involved in fiber
manufacturing and processing from extrusion to drawing or texturing, and all the way to the fabric
finishing stage. Therefore, variations in parameters during these processes lead to changes in fiber
properties. The dyeing behavior and the resulting shade of the fabric are greatly affected by these
processing conditions. The extrusion, drawing and texturing conditions are important to dyeing
and dimensional stability properties of fibers and issues can be seen after the fabric has been dyed
and finished [168, 169]. The iodine sorption test can be carried out to ascertain the differences in
the structure after different treatments [170].
The chemical structure of synthetic fibers is mainly determined during the polymerization
process. The dyeability of synthetic fibers is influenced by various factors during polymerization.
These are given below:
▪ Quality of monomers used - recycled vs virgin monomers
Recycled monomers influence the color, end group concentration and may form
polymer gels. These gels cause problems during fiber spinning and drawing and may
lead to faults in dyeing [168].
▪ The concentration of end groups in the polymer
This directly affects the dyeing behavior such as the rate of dye uptake and fiber
saturation values. These groups may vary from one manufacturer to another and from
source to source. The end group concentration varies by the changes in monomers’
concentration, temperature and polymerization times. Nylon and acrylic fibers’
dyeability is determined by the concentration of these groups [114]. For acrylic fibers,
the number of dye sites are inversely related to polymer’s molecular weight and the
extent of the low molecular weight composition of the fiber. For finer fibers more dye
sites are required to achieve the target shade, the molecular weight of the polymer may
thus be reduced to achieve this. Neutral copolymers are also added to increase the rate
of dyeing by increasing amorphous regions in the fiber [171]. The mixing of fibers with
differences in concentration of the end group leads to faulty dyeings. Different dye
variant fibers are also available which either have different dyeability (cationic dyeable
122
polyester and nylon) or differences in dyeability (ultradeep, deep, low dyeing types)
[114].
▪ Presence of byproducts of side reactions
Diethylene glycol formed during the polymerization of polyester influences the dyeing
properties of the fiber. Cyclic oligomers of polyester are problematic in dyeing [168].
▪ The use of polymers that are recycled during the spinning
This produces fibers with generally lower strength, color, and uneven dyeability.
Mixing such fibers with fibers produced from virgin polymer produces products with
uneven properties [168].
▪ Chemical changes in the polymer during spinning and processing
Nylon may oxidize and form cross-links. This leads to gel formation in fiber and causes
variability during dyeing. Solutions of polyacrylonitrile have a tendency to yellow. This
depends on temperature, residence time, and availability of oxygen or inert gases in the
surrounding atmosphere, solvent stability, comonomers, and impurities present in the
spinning solution [172].
Oligomers are lower molecular weight species formed during the polymerization process.
The commercially available polyester fiber contains cyclic oligomers that contain two or more
repeating units without an end group. The major proportion of oligomers consists of a trimer (1.5%
by mass) which is important in fiber processing as it tends to move to the fiber surface during
thermal treatment such as heat-setting and dyeing. Oligomers form a deposit on the fiber surface
and affect the fiber properties. Trimers are soluble in high-temperature dyebaths but recrystallize
on fiber surface or on machine components on cooling as white deposits [173-175]. Their presence
reduces the brilliance of dyeing and shade depth in dark shades [158]. The main problems
associated with oligomers include adverse spinning properties of yarns, reduced liquor flow during
package and beam dyeing, and agglomeration of dyes. Several approaches are suggested to deal
with oligomers during dyeing. The dyebath can be dropped at high temperatures without cooling.
The oligomers are released from the fiber at temperatures around 120 oC and at shorter dyeing
times. Non-ionic leveling agents may be added to prevent their redeposition. The reduction
clearing process can also remove oligomer deposits from the fiber surface [174]. The dyeing of
123
polyester can be carried out in an alkaline medium using alkali-stable disperse dyes and this
process can dissolve the majority of oligomers though saponification [176].
Manufactured fibers are produced by either dry, wet or melt spinning. The viscous liquid
(melt/dope) of fiber-forming polymer is extruded through a spinneret which is then solidified by
blowing air on filaments or passing them through a coagulation bath. This is followed by a spin
finish application [114, 168]. The spin finish should be easy to remove during fiber preparation to
prevent dyeing problems. Otherwise, unlevel dyeing of nylon and acrylic fibers with acid and
cationic dyes respectively, can occur due to emulsion formation. This also affects the thermal
migration of dyes [177].
The spun filaments should have a uniform diameter and are affected by various factors
such as variation in diameter of spinneret hole, poor quality of the viscous liquid, variations during
solidification, differences in liquid throughput, presence of gels, cross-linked polymers and mixing
of incompatible polymers. The partial blocking of spinneret holes would produce a fiber with a
small diameter and high orientation. The turbulence during the fiber solidification phase would
lead to short term unevenness in the fiber. Many of these faults are further enhanced during the
drawing process. The variations in the fiber diameter cannot be changed in later processing stages
and affects dyeing behavior. The final appearance of the final product is thus affected [114, 168].
Different stages and corresponding factors involved in the wet spinning of acrylic fibers
are shown in Figure 4.3 [178]. The wet spinning process is very complicated and involves a lot of
variables. During polymerization along with acrylic comonomers, one to two monomers are added
to modify the acrylic fiber properties such as its’ dyeability and flame retardancy. The control of
molecular weight and molecular weight distribution is essential not only to obtain the desired fiber
properties but to avoid problems during dope formation. The partially soluble gels of high
molecular weight may influence the preparation of homogenous dope required for spinning. The
molecular weight also influences the dope viscosity. The lower molecular weights are preferred
due to ease in the dope formation and enhanced dyeability keeping the required levels of fiber
strength [171]. To prepare the dope for spinning the polymer is dissolved in a solvent. The polymer
content in the dope is based on polymer solubility in a solvent and the spinning pressure. The
temperature control is essential to avoid gel formation in dope. In general, the wet spinning
spinnerets have a large number of capillaries and thin plate designs to operate at lower speeds thus
limiting the polymer molecular weight and polymer content of the dope. In coagulation, it is
124
essential to control the polymer content, flow rate, temperature, coagulant type and concentration
as they determine the fiber structure. The difference in fiber structure obtained from wet and dry
spinning is due to the differences in the initial fiber formation step. The interaction between the
solvent, coagulant and polymer composition generates a characteristic fiber structure in the
coagulation bath. All these factors need to be controlled properly as they influence the structure
and dyeing behavior of acrylic fibers [179]. The rate of dyeing of acrylic fibers is dependent on
the physical structure of the fiber. The dyeing rates of wet and dry spun fibers are different [180].
The wet spun fiber has a more open structure (voids) and a circular cross-sectional shape. This
results in lowering the glass transition temperature (Tg), a higher dyeing rate and a larger surface
area than the dry spun fiber counterpart which has a bean-shaped cross-section and relatively
closed structure [112]. The differences in voids in wet spun fibers lead to appearance and dyeing
problems [114, 168].
Figure 4.3: Factors influencing the spinning process of polyacrylonitrile fibers.
COAGULATION
POLYMER
DOPE
SPINNERET
Type and amount of comonomers
Molecular weight
Molecular weight distribution
Type of solvent
Polymer content
Temperature
Rheological behavior
Type of material
Hole geometry
Injection speed
Solvent concentration
Nature and quantity of the precpitant
Temperature
Coagulation
Spinline
Cross-sectional shape
Gel filament structure
Nozzle speed
Stretchability
SPIN BEHAVIOR
125
The drawing process improves the orientation of molecular chains which leads to an
increase in crystallinity. The relative increase in orientation and crystallinity is fiber dependent.
Polyester has a considerable degree of crystallinity compared to nylon 6,6 due to the orientation
of chains in the undrawn state. However, there are no significant structural differences between
the two fibers after the drawn state. Generally increasing the draw ratio leads to a decrease in the
rate of dye diffusion [114]. Variations in the draw ratio and differences in relaxation temperature
during or after stretching produce changes in the physical structure. Weft bars and streaky dyeing
may have their origin in the faulty drawing process. The combined effect of faulty spinning and
drawing will produce faulty filaments and large variations in properties. Slight overstretching or
under stretching of filaments causes different shrinkage and dyeing properties. This is due to
differences in the orientation of chains and crystallinity of the fiber. Improper drawing of the
filaments may occur due to slippage of filaments on the drawing gadgets, inappropriate spin finish
composition failing to keep the filaments together, inadequate lubrication, and unsuitable
temperature of drawing godets. The filaments which are not drawn fully may have a larger
diameter than normal fibers and dye darker than the rest [114, 168].
The diffusion of disperse dyes by polyester is dependent on both draw ratio and heat setting
temperature. The heat treatment affects the physical fiber structure as it affects the size and volume
of the voids. The heat setting and drawing process are correlated. The usual heat setting
temperature range is 170-200 oC. The fiber shows reduced dye uptake in this temperature region
compared to temperatures before and after this range where they exhibit higher dye uptake. The
change in fiber structure is not confined to very high temperatures. The treatment of acetate and
nylon 6,6 in a boiling solution, for example, also affects the diffusion behavior of the dyes [114].
Variations in yarn tension and temperature during heat setting may also lead to dyeing
problems. Differences in tension within and between yarns can cause permanent deformation of
polymer. The yarns on the outer layer of the package dye differently than those in the inner layer
due to their differential shrinkage. Tension variations may also cause differences in the heat setting
process [114].
Synthetic fibers are cut in length to match the length of the fiber(s) that they will be blended
with. In the case of blended yarn, the length of the fibers and their fineness determine the
irregularities in yarns and affect variations in yarn strength [181].
126
Fibers with similar chemical compositions may exhibit different dyeing behaviors due to
having different structures. For instance, cellulosic fibers have a similar chemical structure, but
they have differences in proportions of amorphous and crystalline regions, pore size of the fibers
and accessibility of their internal adsorption regions [114]. The dyeability of cellulosic fibers is
influenced by the following factors [182]:
▪ Fiber structure (skin/core);
▪ Orientation;
▪ Crystallinity;
▪ Fiber pore structure; and
▪ Inner fiber pore volume.
Regenerated cellulosic fibers are obtained from wood pulp. These include viscose, modal,
and lyocell fibers. Although they are chemically similar to cotton, they have different
morphological structures and hence differences in dyeing behaviors. They are made up of cellulose
II and have different degrees of crystallinity. Viscose fibers have the lowest crystallinity of all with
41% followed by modal 49% and lyocell 80% [183]. The differences in their morphological
structure may be due to different factors involved in their manufacture which are [184]:
▪ The ripeness of alkali cellulose;
▪ The ripeness of the viscose (degree of xanthation);
▪ Compositions of precipitation baths; and
▪ Draw ratio.
Important fiber properties that may affect the wet processing of regenerated cellulose fibers
include [182]:
▪ Wet tenacity and elongation;
▪ Wet modulus;
▪ Water retention capacity;
▪ Fiber swelling;
▪ Fibrillation; and
▪ Dyeing behavior.
127
Viscose rayon has a skin and core structure where the skin is highly ordered when
compared to the core. The skin and the core exhibit different degrees of dyeability [158]. An
adequate supply of dyes with suitable kinetic energy is required for adequate dye penetration [185].
Treatments involving fiber swelling may be performed to improve penetration [114]. The pore
volume of viscose is larger than that of cotton. Therefore, the dye uptake is more for viscose as
compared to cotton [186]. Viscose fibers exhibit the lowest wet tenacity and highest wet elongation
among cellulosic fibers. This necessitates extreme care in processing [182]. Due to the reductive
nature of viscose certain dyes may reduce during dyeing. This is due to either aldehyde content or
high sulfur content (as CS2Na2S) remaining from fiber manufacturing. The aldehyde may easily
reduce azo dyes under certain conditions. High sulfide levels in fully flooded machines may
destroy some dyes and affect the shade under acidic conditions. Sulfide contents as low as 10 mg/L
can be problematic for dyeing operations [64].
Modal fibers are modified forms of viscose fibers by making changes during the
coagulation process. They have near-circular cross-sections and more highly oriented crystalline
regions than viscose rayon [114]. Lyocell has a higher degree of crystallinity due to stretching
during manufacturing and also has a near-circular cross-section. They have a tendency to undergo
longitudinal splitting known as fibrillation under wet state due to weaker cohesion between
crystalline regions. This produces microfibers of 1-4 µm in diameter and imparts a peach-skin
characteristic to the fabric. This may cause pilling problems and a frosty appearance in medium to
heavy shades [158, 187]. Modal and viscose show good wet tenacity and lower wet elongation.
Compared to viscose they show better stability during wet processing [182, 188]. The color yield
of various regenerated cellulosic fibers obtained after dyeing with direct, vat and sulfur dyes,
compared to cotton follows the following decreasing order: viscose, lyocell and cotton [189].
When dyed with direct dyes, the modal fibers dye lighter than viscose, lyocell and cotton due to
having a lower affinity. With reactive dyes modal dyes darker than cotton but lighter than viscose
and lyocell. In order to produce a solid color effect (similar color tone and equal depth) in cellulosic
blends, the dye affinity for each of the fibers should be similar e.g. cotton/modal or lyocell/viscose
[182, 188].
Synthetic fibers such as polyester and acrylic show an increase in the rate of dye diffusion
around a particular temperature due to the increase in segmental mobility of polymer chains. This
temperature is known as the glass transition temperature (Tg). As dyeing temperature is increased,
128
the diffusion of dye into the fiber (rate of dyeing) increases exponentially. This requires a close
control of dyeing conditions to avoid unlevel dyeings [114]. In acrylic fibers, there is a high degree
of affinity between the dye molecules and the ionizable active groups in the fiber. This is in
combination with the fact that a higher rate of dyeing above Tg demands a proper control of dyeing
conditions to obtain a level dyeing. For instance, retarders are used in acrylic dyeing to control the
rate of dyeing. Cationic or anionic retarders may be used. The former works by competing with
the dye for the available dye sites in the fiber. The latter temporarily associates itself with the dye
limiting the amount of dye available for dyeing at any particular time [114]. Acrylic fibers that are
spun by dry or wet spinning methods differ in their dyeability [156]. The commonly used nylon
fibers are nylon 6 and nylon 6,6. Although they are similar, their structure, dyeability, dyeing rate,
and colorfastness are different. Nylon 6 has a more open structure, higher affinity for dyes, faster
dyeing rates and lower colorfastness. On the contrary, nylon 6,6 has a lower affinity for dyes,
slower dye strike rates, higher colorfastness, and more oriented fiber structure. It is also
recommended to heatset nylon 6 at a lower temperature than nylon 6,6 due to its’ lower heat
stability [190].
Common problems affecting the dyeing of fiber blends, their causes, and remedial
measures are summarized in Table 4.6.
Table 4.6: Dyeing problems attributed to fiber.
Problems Probable causes Remedial measures Ref.
Dark areas,
stains, or spots
▪ Oil and grease
contamination from
harvesters, gin presses, truck
or warehouse floors
Ensure the sorting of contaminated
fibers and proper handling of
material.
[159,
160,
162,
191,
192] ▪ Presence of vegetable matter
such as seed husks, leaf and
stem remnants due to:
- Improper scouring
conditions
The recipe and process parameters
(time and temperature) should be
followed.
129
Table 4.6 (Continued)
Problems Probable causes Remedial measures Ref.
- No scouring is given to
blends containing smaller
cotton components
Design process routes keeping into
consideration the actual
contamination level where a
scouring process may be required.
- Not enough removal in
opening and carding
stages due to choosing
inappropriate machine
settings (wide gaps) to
accommodate polyester in
an intimate blending
process
Use proper machine settings to
effectively remove trash without
damaging the fiber.
- Use of unbleached
backing fabric in
processes with a different
face and back
Use a backing fabric with a good
appearance.
▪ Presence of high quantities of
calcium and magnesium in
cotton may lower dye
solubility and lead to
precipitation
1. Use sequestering agents during
pretreatment and dyeing
processes.
2. The demineralization process
may be required depending upon
the severity of the problem.
▪ Undrawn filament due to
filament slippage during
drawing, inappropriate spin
finish and unsuitable
temperature of drawing
godets
1. Use a suitable spin finish
combination.
2. Check the drawing process for
slippage and required
temperature.
[114,
168]
130
Table 4.6 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Due to the presence of dark
wool fibers
Proper identification and sorting
system should be implemented in
the early stage of fiber processing
to remove dark wool fibers.
▪ Due to splinters generated
during polyester fiber
spinning, containing
irregularly drawn fibers
Check the spinning process for
faults.
[193]
▪ Fusion of fibers due to
damage caused by the
crimper
1. Check the settings of the
crimper.
2. Ensure proper feed of the tow.
▪ Agglomeration of disperse
dyes due to the presence of
oligomers
1. Drop the dyebath at a high
temperature.
2. Use a non-ionic reducing agent
during dyeing.
3. Dye polyester in an alkaline
medium depending on the
feasibility of the operation.
[174,
194]
Resist/colored
areas
▪ Presence of foreign matter
such as polypropylene or
polyethylene or jute
impurities in the fibers
▪ Melting of polypropylene
fibers during singeing and
drying and subsequent rolling
out to form a thin film
1. Avoid the use of plastic and jute
bags for storing and
transportation.
2. Inspection and removal of
foreign material during
spinning. Installation of foreign
fiber detector during fiber
opening and winding stages.
[100,
149,
159,
161,
162]
131
Table 4.6 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Insecticides and pesticides
used during cotton growth
Ensure proper washing of
substrate before the dyeing
process.
Pale spots/areas ▪ Presence of immature cotton
fibers in the material
Ensure proper blending and
measurement of immature fiber
content at bale laydown.
[6,
149,
159,
162,
163,
191,
192]
▪ Due to the presence of
medullated wool fibers.
These fibers have different
light reflecting properties and
take up less dye due to less
protein available to take up
the dye compared to the rest
of the wool fibers.
Ensure proper detection and
segregation of fibers at the early
stage of processing.
▪ Excessive overheating causes
cotton to dye lighter
The temperatures in ginning and
drying processes should be within
specified limits.
[159]
Shade change ▪ Using different cotton fibers
with differences in
weathering and maturity can
lead to color differences
Avoid mixing cotton from
different sources.
[159]
▪ The presence of sulfur
residues in viscose from
manufacturing
A peroxide bleach might be
recommended to remove sulfur.
Use a mild oxidizing agent during
dyeing.
[64,
185]
▪ The presence of aldehyde in
viscose from manufacturing
Use a mild oxidizing agent during
dyeing that should be stable under
dyebath conditions.
[64]
132
Table 4.6 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Deposit of polyester
oligomers on fiber reduces
brilliance and shade depth
1. Drop the dyebath at high
temperature.
2. Use a non-ionic wetting agent
during dyeing.
3. If possible, dye polyester in an
alkaline medium.
[174]
Unlevelness ▪ Damaged wool fiber tips
during growth because of
sunlight and weather
1. Use a leveling agent during
wool dyeing.
2. Select acid dyes with good
leveling properties.
[149,
166,
192]
▪ Variations in the degree of
polymerization, end group
content
Check the degree of
polymerization and end group
content before extrusion.
[82]
▪ Mixing fibers with different
end group concentrations.
Check the end group content of
polymers before extrusion and
avoid mixing polymers from
different sources.
[114]
▪ Use of recycled monomers
causes gel formation that
leads to problems in spinning
and drawing.
Avoid using recycled monomers
during polymerization or their
concentration should be kept as
low as possible.
[168]
▪ Mixing of virgin and recycled
polymers during extrusion
produces fibers with uneven
properties
Avoid mixing different polymer
types.
[168]
▪ Differences due to improper
extrusion, drawing and heat
setting
Check proper controls are
implemented during fiber spinning
and processing stages.
[82]
133
Table 4.6 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Variation in temperature
during extrusion, drawing or
heat setting process
Ensure uniformity of temperature
during extrusion, drawing and heat
setting.
[177,
195]
▪ Differences in voids in
acrylic fibers
Ensure uniformity of parameters in
the extrusion process.
[114,
168]
▪ Formation of emulsion due to
spin finish in the dyeing of
nylon and acrylic fibers.
1. Improper selection of spin finish
with poor removal properties.
2. Residual spin finish due to
inadequate pretreatment process.
▪ Instability of spin finish at
higher heat setting
temperature required for
nylon/elastane blends.
Use special spin formulations that
are stable and protect the nylon
from damage at a higher
temperature.
▪ Agglomeration of disperse
dyes due to the presence of
oligomers
▪ Reduced liquor flow in
package dyeing due to
oligomer deposits
1. Drop the dyebath at a high (e.g.
120 oC) temperature.
2. Use a non-ionic wetting agent
during dyeing.
3. Dyeing of polyester in an
alkaline medium depending
upon the possibility.
[174,
194]
▪ Differences in yarn tension
and temperature during heat
setting cause differential
shrinkage in a package
leading to unlevelness
Ensure uniformity of yarn tension
and temperature during heat
setting.
[114]
Stripes/bars ▪ Higher proportion of short
fiber content increases the
yarn hairiness, neps, and
Check and control short fiber
content for each bale lay down.
[100,
160,
162,
134
Table 4.6 (Continued)
Problems Probable causes Remedial measures Ref.
irregularity which may
appear in the form of stripes
163,
196,
197] ▪ Variation in micronaire,
fluorescence, and maturity of
cotton fibers cause horizontal
stripes in knitted fabrics
Control the micronaire, maturity,
and fluorescence of the fiber
within a mix and among mixes.
The variation in fluorescence
(measured in terms of UV) should
be < 10, micronaire should be <
0.2 within a mix.
▪ Variation in draw ratio and
temperature
Ensure uniformity of draw ratio
and temperature.
[114,
168]
▪ Differences in yarn tension
and temperature during heat
setting
Ensure uniformity of yarn tension
and temperature during heat
setting.
[114]
Inferior
colorfastness,
thermomigration
▪ Presence of spin finish
facilitates the movement of
disperse dyes to the fiber
surface
Ensure complete removal of spin
finish during pretreatment process.
[177]
Holes ▪ Presence of iron causes
catalytic damage of cellulose
due to rapid decomposition of
bleaching bath
1. Use sequestering agents during
pretreatment.
2. A demineralization process may
be required depending on the
severity of the issue.
[162,
198]
▪ Melting of polypropylene
fibers present in cotton
1. Avoid plastic and jute bags for
storing and transportation.
2. Inspect and remove foreign
material during spinning. Install
135
Table 4.6 (Continued)
Problems Probable causes Remedial measures Ref.
a foreign fiber detector in fiber
opening and winding stages.
Reduced
strength
▪ Wrong selection of cotton
variety. The fiber strength
depends on the source,
variety, fineness and growth
conditions
The selection should be based on
end-use requirements.
[159,
160,
162]
▪ Overheating of fiber during
ginning
The ginning should be carried out
at a lowest possible temperature (<
170 oC).
▪ Higher proportion of
immature and short fibers
Check each bale laydown for
immature and short fiber contents.
▪ Damage due to weathering The fiber strength should be
checked before purchasing cotton.
▪ Presence of metal impurities
(iron) in fiber cause catalytic
decomposition of hydrogen
peroxide and leads to fiber
damage
1. Use sequestering agents during
pretreatment.
2. A demineralization process may
be required depending on the
severity of the issue.
▪ Damage of wool fiber during
growth due to environmental
factors leads to fiber strength
loss or a decrease in fiber
diameter
Ensure proper blending of fibers.
The fibers should be checked for
strength and diameter before
processing.
[192]
▪ Damage due to chemical
treatments, excessive heating
and storage under hot and
humid conditions
1. Avoid storage in hot and humid
environments.
136
Table 4.6 (Continued)
Problems Probable causes Remedial measures Ref.
2. Avoid high temperature, low pH
conditions and long treatment
times during processing.
▪ Presence of very low
micronaire cotton leads to
weight loss during scouring
and bleaching
Check each bale laydown for
micronaire.
[159]
Poor appearance ▪ Frosty appearance and pilling
due to fibrillation of lyocell
fibers under wet conditions
Use lower alkalinity during
dyeing, reduce dyebath
temperature, and tension during
processing.
[158,
187]
▪ Excessive hairiness due to the
higher content of short fibers
Check each bale laydown for short
fiber content.
Whiteness
variation/lower
degree of
whiteness
▪ Insufficient bleaching action
due to the presence of metal
impurities such as iron in
cotton fibers
1. Use sequestering agents during
pretreatment.
2. A demineralization process may
be required depending on the
severity of the issue.
[159,
162]
▪ Creamy off-white color of
wool fibers due to damage
during growth, oxidation and
pH change which makes it
difficult to obtain brilliant
white
1. Use a bleaching process to
increase whiteness.
2. Consider the use of optical
blighters.
[167]
Creases or rope
marks
▪ High lateral swelling of
lyocell fibers causes
stiffening of fabric
1. Use high liquor temperature (>
50 oC).
2. Use lubricating agents in rope
processing.
[187,
199]
137
4.4 Problems arising from yarn formation
Yarn is a basic building block in a fabric which is composed of linear, ordered twisted or parallel
fiber strands. There are many types of yarn produced in the market depending on the required
physical properties and performance characteristics. Yarns can mainly be classified as continuous
filament or spun yarns. In the first type, multiple filaments are arranged side by side in parallel.
This type of yarn is made by extruding a polymer liquid through a spinneret which is then solidified
to form a continuous filament. Filament yarns can be further classified as monofilament, when the
yarn contains a single filament, or multifilament when the yarn consists of a group of filaments.
Multifilament yarns can be converted into bulky or stretched forms by a process known as
texturizing. The second type of yarn is known as spun yarns which are made from staple fibers of
natural or synthetic origin using a number of spinning stages such as opening, cleaning, blending,
drawing, combing and spinning. Spun yarns can be further classified based on the method of
spinning into ring-spun, rotor-spun or air-jet spun yarn and by the method of preparation into
carded, combed, woolen or worsted yarn. Structurally yarns can be single, plied, cable and
composite yarns [200]. The different yarn types are shown in Table 4.7 [181, 200].
Table 4.7: Yarn classification.
Division Group Subgroup Class
According to fiber
length
Continuous
filament
Continuous monofilament
yarn
Continuous
multifilament yarn
▪ Flat yarns
▪ Textured yarns
Spun yarns Short-staple spun yarn ▪ Carded yarn
▪ Combed yarn
Long-staple spun yarn ▪ Woolen yarn
▪ Semi-worsted yarn
▪ Worsted yarn
Conventional yarn ▪ Ring-spun yarn
▪ Compact yarn
138
Table 4.7 (Continued)
Division Group Subgroup Class
▪ Rotor spun yarn
Unconventional yarn
▪ Air-jet spun yarn
▪ Friction spun yarn
Fancy/effect yarn
▪ Slub yarn
▪ Fancy twisted yarn
According to fiber
content
Blended yarn
▪ Intimate blended yarn
▪ Drawframe blended
yarn
Composite yarn Core spun yarn
According to yarn
structure
▪ Single yarn
▪ Folded yarn
▪ Cabled yarn
In theory, yarns can be produced without any fault, but in practical mass production
conditions, faults do occur. A fault in the yarn is determined based on its end-use requirements
and performance. It does not include the normal variations present in the yarn. Yarn faults can be
attributed to one or more of the following reasons [157, 201, 202]:
▪ Raw material
Faulty raw material and an incorrect selection of raw material are major sources of
faults. There are many fiber properties that influence formation of faults in yarns such
as fiber length, length uniformity, short fiber content, fineness, maturity, strength,
elongation, trash, contamination, crimp, and finish. A determination of individual
values, as well as variation in these properties, is important as these values directly
influence the appearance, hand and performance characteristics of the yarn. Raw
material factors are covered in more detail in section 4.3. For blended yarns, this factor
is more critical because of the differences in the fiber properties of blend components.
139
▪ Machines
Incorrect machine settings, improper speeds, incompatible or damaged machine
elements affect the fiber processing and can lead to forming faulty yarns.
▪ People/practices
This includes operator negligence, unskilled or poor operator training, incorrect
material handling, poor machine maintenance, lack of machine and environmental
cleanliness and improper or no housekeeping practices.
▪ Ambient conditions
Temperature and humidity control is essential for proper fiber processing. The correct
conditions depend on the fiber type and process stage. Static generation, roller lapping,
and strength related problems may occur if conditions are not properly controlled.
Yarn faults can lead to problems during further processing in the following ways [157]:
1. End breakage rate in warp preparation (warping, sizing), weaving and knitting.
2. Fabric quality problems due to yarn faults.
3. Fabric faults due to yarn breakage in yarn preparation or fabric formation processes.
As yarns can be produced by different methods, their structure and properties vary from
each other. Therefore, the selection of yarn is important for a particular end-use. A wrong selection
of yarn leads to problems in subsequent processing and not meeting the target product
characteristics [203]. For example, yarn produced for weaving and knitting have different
properties due to the nature of these fabric formation processes.
4.4.1 Faults caused by spun yarns
Spun yarns are made by the process known as spinning in which a large quantity of individual
unordered fibers of relatively short length is converted into a very long ordered and linear product
known as yarn [204]. The spun yarn can be produced by two common spinning systems: short
staple or cotton system and long staple or wool system. The important characteristics of both
systems are the fiber length and diameter. The fiber type that needs to be processed in either of
these two systems must adhere to these requirements. Therefore, for the production of blended
yarn, the length and fineness of fibers are important. Synthetic fibers are cut in length to match the
140
spinning system and the length of the fiber they are blended with. For instance, waste material
from the production and processing of raw silk can be used to produce spun silk yarns. Depending
upon the fiber length, spun silk yarns can be produced either on cotton or worsted spinning
systems. Wool and silk fibers need to be scoured before the spinning process to remove their
natural impurities (e.g. waxes in wool, and sericin in silk) to make their processing easier [205].
Table 4.8: Effect of different spinning operations on yarn properties.
Fiber Properties
Yarn quality characteristics
Even
nes
s
Th
ick
pla
ces
Th
in p
lace
s
Nep
s
Hair
ines
s
Cou
nt
Str
ength
Elo
ngati
on
Ble
nd
reg
ula
rity
Bale lay-down D D D D D N D D N
Blowroom D D D D N N D D D
Card D D D D D D I I N
Drawframe I I I I N D I I D
Comber D D D D D N D D N
Roving frame I I I N I I I I N
Spinning machine I I I I I I I I D
Winding machine I I I D D N I D N
D: direct relationship, I: indirect relationship, N: no relationship
In yarn production, staple fibers go through a series of operations depending on the fiber
and yarn requirements. These include opening, cleaning, blending, aligning, uniting, equalizing,
attenuating, twisting and winding [204]. Yarn quality is dependent on each of these different
processing stages in spinning. Proper process control is essential in order to achieve the required
yarn quality levels. The influence of different spinning processes on quality characteristics of spun
yarn is shown in Table 4.8 [6]. It can be seen that the presence of neps in yarns, which influences
the dyeing of fabrics, is directly affected by bale lay-down, blowroom, card, comber, and the
141
winding machine. Similarly, blend regularity, which is denoted by the distribution of different
fiber types in the yarn and affects the color of the blend, is dependent on the blending process done
in blowroom, drawframe or spinning process. Thus, different stages of the spinning process
directly influence the properties of fabric formed from yarns [6].
Roller drafting is one of the most common sources of errors in yarn formation. Defective
or damaged machine parts such as rollers, aprons, guides, etc. lead to defects in the yarn. Fly fibers
from the atmosphere can spin into the yarn creating defects. Therefore, proper cleaning of the
spinning environment is essential for fault free yarn production. In the case of yarn blends, fiber
finish can accumulate on the balloon control rings, rings and travelers causing problems during
spinning [157].
Many yarn faults originate from inadequate fiber preparation for spinning such as carding.
For intimate blending, which is performed in the blowroom, compromised card settings need to be
used to adjust the fiber type in the blends. This may lead to various problems such as inadequate
removal of neps, improper cleaning, etc. Another factor is the increased production speed. If the
material that is fed to the spinning machine is already faulty, yarn production will be faulty [181].
The common faults found in spun yarns are: seldom occurring faults, incorrect yarn count, yarn
count variations, unevenness, periodicities, high levels of imperfections, excessive hairiness and
hairiness variation, yarn contamination including trash and dust, low tensile strength and
elongation, improper fiber blending, and melt spots or local fusion of yarn [6].
Seldom occurring faults
Random variations in a yarn cannot be controlled as it is difficult to achieve the same number of
fibers in the yarn’s cross-section at every moment, but it should be within close limits. These
variations are among frequent yarn faults and are not removed from the yarn. Seldom yarn faults
include large mass or diameter or length causing thick and thin places which are removed during
the yarn clearing process. These faults are classified as short thick places (0.2 cm to 1 cm) or N,
medium-thick places (1 cm to 8 cm) or S, and long thin places (> 8 cm) or L [6]. The possible
causes and countermeasures for their formation are:
▪ Improper functioning of drawframe auto-leveling system;
▪ High short fiber content in sliver or roving after combing operation. Optimization of
comber noil is required;
142
▪ Fly waste is spun into roving or yarn;
▪ Draft distribution is not proper in drawframe, roving frame, and spinning machine;
▪ Twist level is incorrect in roving;
▪ Tension problem in a roving frame;
▪ High unevenness in roving;
▪ Large fly fiber contamination on the spinning machine;
▪ Air-conditioning system is not working properly;
▪ Higher amount of yarn breaks which result in excessive fly generation and outlier
bobbins;
▪ Eccentric rollers in roving and spinning machines;
▪ Damaged or worn out aprons, worn out rings and travelers. Improper settings of aprons;
▪ Wrong selection of traveler;
▪ Static generation;
▪ False draft in spinning machine creel or draft distribution is not proper; and
▪ Too high winding speed and tension during the winding process.
Incorrect yarn count
Mixing of different yarn counts in the yarn lot can result in a poor fabric appearance, which will
depend on either mixed yarns being used in the length or widthwise direction of the fabric. The
use of different colors of bobbin tubes can prevent or minimize yarn count mix-up [6].
Yarn count variations
Variation in the yarn count exceeding the limits is also known as long-term mass variation. It may
result in uneven fabric appearance [6]. Possible reasons are:
▪ Missing fiber component or missing sliver at the draw frame for a short period of time;
▪ Use auto leveler or finisher drawframe;
▪ Unevenness or weight variations in rovings result in count variation within a bobbin;
▪ Incorrect trumpet hole diameter and cleanliness;
▪ Incorrect roller weights;
▪ Improper alignment of the spinning creel, dragging bobbin holder, blocked spinning
trumpet;
143
▪ False draft in spinning machine creel; and
▪ Mixing up of bobbins of different count. Use different colors for bobbin tubes to avoid
yarn count mix-up.
Uneven yarn
Random mass variations in yarns exceeding the limits will produce an irregular or uneven yarn
and result in a cloudy fabric appearance [6, 206]. Uneven yarns are caused by the following:
▪ Improper card maintenance;
▪ Improper functioning of the auto-leveling system in the finisher drawframe and
inadequate maintenance of the drafting system;
▪ Wrong setting for the roving traverse;
▪ Incorrect break drafts and roller settings. Improper roller weights;
▪ Wrong selection of the size of the apron. Inadequate quality or replacement schedule
of the aprons. Excessively worn out aprons. Improper apron spacing;
▪ Inadequate hardness, grinding schedule and minimum diameter of top rollers. Incorrect
position of top front rollers;
▪ Improper roller chatter and dimensions of spacers;
▪ Cutting of top roller due to improper operator training;
▪ Yarn diameter differences;
▪ High balloon tension and centering of a pigtail;
▪ Worn rings;
▪ Periodic mass variation from card, drawframe or roving;
▪ Thermal fiber damage due to excessive spinning speed;
▪ Dust accumulation in rotors;
▪ Damaged rotor groove surface or rotor cover; and
▪ Damaged wire or lapping on the opening roller.
Periodicities
These faults are repeated at the same interval and are extremely disturbing. They can be related to
yarn mass and can cause a pattern in the fabric [6]. The important factors associated with this type
of fault are [6, 155]:
144
▪ Incorrect settings of the comber piecing process;
▪ Eccentricity or fault of front rollers or opening roller of the spinning machine;
▪ Contaminated front roller (honeydew etc.);
▪ Symmetrical yarn tension variation with reversal movement of the spinning package;
▪ Asymmetrical yarn tension variations with reversal movement of spinning package;
▪ Dust or dirt in the rotor groove of the rotor spinning machine;
▪ Opening roller damage, or asymmetrically supported rollers in the rotor spinning
machine; and
▪ Defective joint in the apron of the ring spinning machine.
High levels of imperfections
This refers to yarns consisting of too many thick and thin places, neps and may result in a poor
quality fabric. These faults are caused either due to raw material or processing during the spinning
process. Thick places, thin places, and neps are classified as imperfections exceeding -30% or
+35% or +140% of the mean yarn cross-sectional size. Table 4.4 shows the raw material factors,
which include length uniformity, short fiber content (SFC), high micronaire variations and high
level of neps [6].
The main reasons for thick and thin places in yarn due to processing are [6, 207]:
▪ High SFC after the combing process;
▪ Accumulation of lint or fly on roving;
▪ Accumulation of lint on drafting roller, blow in lint and bad operation of overhead
cleaner in ring spinning frame;
▪ Wrong roving traverse, apron and cot conditions, apron spacing, out of position top
roller, roller spacing, incorrect hardness and bad surface of top cots, eccentric or
damaged front rollers, incorrect break draft and main draft settings of the drafting
system of ring spinning frame;
▪ High balloon tensions and loaded travelers in ring spinning;
▪ Use of too coarse fibers;
▪ Improper air conditions, wrong settings or improper working of the air conditioning
system; and
145
▪ Incorrect oiling or oil concentration during long-staple spinning or spin finish for
synthetic fibers.
Neps in a yarn are caused by [6]:
▪ High nep levels in roving;
▪ Deteriorated apron, the opening of a tensor pin;
▪ Damaged or worn out ring and traveler, improper setting of traveler clearers and
deteriorated balloon control ring.
Excessive hairiness and hairiness variation
A yarn with a large number of protruding fibers may cause pilling and reduce abrasion resistance
of fabric. However, high hairiness may be desirable when requiring a softer yarn hand. The high
hairiness of yarns is strongly correlated to the pilling of fabrics, which is the formation of small
entanglements of fibers on the fabric surface due to wear. Knitted fabrics are more prone to pilling
due to high hairiness of the knitting yarns which are produced with less twist compared to yarns
manufactured for the woven fabrics. Hairiness may also cause problems during the fabric
formation process. If hairiness variation is high it may affect the fabric appearance. Hairiness is
dependent on both fiber and process-related factors [6]. Fiber properties that have an influence on
yarn hairiness are fiber length, length uniformity and high short fiber content as shown in Table
4.4.
The main causes of hairiness due to processing are [208]:
▪ Low roving twist;
▪ Wrong selection and worn out or bad conditions of rings and ring travelers;
▪ Improper spinning tension during ring spinning;
▪ Low yarn twist;
▪ Spindle belt slippage;
▪ Damaged or improper centering of pigtail guides;
▪ Spindle and rings are not centered;
▪ Improper traveler changes or wrong traveler weights;
▪ Separator slap;
▪ Incorrect positioning or missing balloon control rings;
146
▪ Improper spindle speed and curve;
▪ Damaged rubber coverings;
▪ Variation in spinning atmospheric conditions; and
▪ High winding speed.
Yarn contamination
Any foreign matter, such as plastic, jute, or polypropylene, spun into the yarn is considered as
contamination. Contamination in natural fibers such as cotton is a major problem in the spinning
mill and has increased in recent years [6]. The major type of contamination found in cotton
includes organic matter such as leaves, feathers, paper, leather, etc., strings made of woven plastics
and cotton, fabrics made of cotton and strings made of jute/hessian [209]. They are embedded in
cotton during harvesting, ginning or the spinning process. They can be of different origin,
composition, color, and structure than the fibers in the yarn. They exist in the form or single fibers
as well as fiber bundles of variable length, but are generally limited to 10 cm in length [210]. ].
Early detection and removal of these contaminations is essential as later processing steps (e.g.
carding) open up and spread these foreign matters and may result in the production of many
contaminated yarn packages. Contaminations may cause several problems in processing such as
end breaks in warping, weaving, and knitting, non-uniform dyeing and a poor fabric appearance
[6]. Their appearance in fabrics depends on their length and thickness, as well as fabric type and
wet processing employed. Bleaching is the most critical step in wet processing for the removal of
contaminations [210]. Generally, contaminations are seen after finishing processes due to their
difference in dyeing affinity, fiber size or color and cause quality problems [157]. The approaches
used to eliminate the foreign matter in order to keep the defect levels within acceptable limits
include selection of fibers containing low contamination levels, use of manual labor to pick foreign
matter before the opening process, use of foreign material detector devices before the card and
foreign fiber clearer in winding [210]. Foreign matters may also be originally present in cotton
bales but may also be embedded into the fibers due to improper stripping down of bale during the
bay lay down process [157].
Some of the possible reasons and preventive actions in the spinning process to counteract
contamination issues are [6, 210]:
▪ Cotton with high contamination levels;
147
▪ Use of plastic bags for fiber waste collection and transportation;
▪ Use of manual labor and foreign fiber detector in the blowroom;
▪ Controlled recycling of the waste in the blowroom;
▪ Efficient carding, combing and blending at all drawframes;
▪ Optimization of comber setting for effect foreign fiber reduction; and
▪ Use of foreign fiber clearer in the winding.
Trash and dust
High content of trash and dust may lead to problems in spinning, weaving and knitting processes.
They may lead to weak places in rotor spun yarns and wear and tear and abrasion of metal parts
e.g. needle wear on a knitting machine, wear of yarn guide elements and accelerated wear of
production parts in the spinning process [6]. One of the main objectives of the spinning process is
the removal of impurities present in the fiber. Trash and dust content are significantly reduced after
the spinning process. The blowroom, carding, and combing are important spinning stages for the
removal of trash and dust from fibers. Improper functioning of these processes can lead to the
presence of a small amount of trash and dust in the yarn [157].
Low tensile strength and elongation
Yarn strength and elongation influence the selection of yarn for a particular end-use and therefore
are of prime importance [155]. If the yarn strength is low, it leads to low tensile, tear and bursting
strength in the fabric, which may be contrary to the requirements in the final product. It also causes
yarn breakages during warping and weaving and produces holes in knitted fabrics thereby reducing
process efficiency and increases costs [6, 155]. Dimensional properties of the fabric are directly
influenced by the elongation of the yarn [6]. Both yarn properties are influenced by raw material
selection and the spinning process as shown in Table 4.4 and Table 4.8 respectively. Raw material
causes are low fiber strength and elongation, high short fiber content and the use of coarse fibers
[202]. For blended yarns, length and fineness of the individual fibers determines the yarn
irregularity which influences the yarn strength variation. The mean strength of the blended yarn is
always less than the yarns of the same count made from individual fiber types. This is due to the
difference in the extensibility of the fibers used in the blends [181]. The relative humidity must be
taken into consideration as it affects the yarn strength properties especially for cellulosic fibers
148
and their blends. Low strength and elongation in yarns may be due to the following causes Low
strength and elongation in yarn having the following causes [202, 211]:
▪ Low yarn twist levels;
▪ Improper fiber blending (blend regularity and blend levels);
▪ Damaged roller drive system (periodic faults);
▪ High spinning tensions; and
▪ Thermal fiber damage due to very high spinning speed for processing synthetic fibers
or their blends.
One of the problems found only in air-jet spun yarns is known as weak yarn. This slightly
weaker yarn has less twist. This leads to a higher volume and hairiness. Such a yarn survives the
downstream processing but will create barré in the dyed fabric. The possible causes of weak yarn
formation are [212]:
▪ Partially blocked suction system at a spinning position; and
▪ Spin finish or oligomer or fiber wax deposits on ceramic spin tips.
Improper fiber blending
Blended yarns should have good longitudinal and lateral blending. Longitudinal blending refers to
the arrangement of blend components along the length of yarn whereas lateral blending indicates
the arrangement of the fiber components along the cross-section. It is impossible to maintain
constant values of longitudinal and lateral blending, but higher variations must be avoided. Fiber
properties such as fineness and length have an influence on the arrangement of fibers on the blends,
e.g. finer and longer fibers tend to concentrate in the center of the ring-spun yarns. Blending faults
may be due to systematic (with specific values in different measurements) and accidental errors
(different values in every measurement). Systematic errors in longitudinal blending lead to a
difference between fabric batches produced from these yarns [213]. Optimum blending is essential
for the production of a uniform appearance of the fabric after dyeing and in achieving a particular
color effect. This also holds true for the production of mélange yarns in which dyed fibers are
mixed to produce the yarn [6, 181]. Low blending irregularity is also required for uniform physical
properties of the yarn [181].
149
Problems in fiber blending may be caused by:
▪ Use of drawframe blending for critical blend ratios;
▪ Mixing of fiber waste collected from card and drawframe; and
▪ Missing or broken sliver at drawframe feed.
In the case of core-spun yarns, the core should be properly centered and covered by the
outer fiber sheath as the most important properties of this yarn type are stretch and recovery [6].
Two types of fault can be found in core-spun yarns: core voids and sheath voids [214].
Core voids can be further classified as short core voids in which short sections of yarn have
nowhere to stretch due to broken core after spinning and long core voids which are characterized
by long portions of yarn without a core. The possible reasons for short core voids are [214]:
▪ Poor alignment of core yarn with roving, especially for finer yarns;
▪ Over drafting of core yarn;
▪ Improper lubrication or worn out rings;
▪ Use of heavy travelers; and
▪ Excessive traveler speed.
Long core voids are caused due to [214]:
▪ Over drafting of core yarn;
▪ Guide with a rough surface or sharp edges;
▪ Insufficient feed roller contact; and
▪ Missing yarn tubes.
In sheath void, a certain length of core yarn is without or contains partial covering. This is
caused due to [214]:
▪ Roving breakage during drafting;
▪ Worn aprons and roller coverings;
▪ Uneven roving or high spinning drafts and speeds; and
▪ Improper alignment of core yarn and roving at the front roller.
150
Melt spots or local fusion of yarn
This type of defect occurs for yarns made-from man-made fibers such as PES and PA or their
blends due to their thermoplastic nature. The friction between the fibers and part of the machinery
can result in the generation of excessive local heat, which causes melt spots or local fusion [193,
211]. Such changes in fiber may lead to a reduction of yarn strength and elongation, generation of
fiber particles, increase in yarn breakage and dust generation during winding, yarn unevenness and
dyeability variation [206].
The main causes are [193, 211]:
▪ Excessive speeds at the balloon control ring, traveler and ring;
▪ Incorrect hardness of roller coverings; and
▪ Running of carding and drawframe at excessive speed.
The yarn produced after a spinning process has a direct effect on fabric properties. Table
4.9 shows the correlation between yarn and fabric characteristics [6, 154, 202]. Yarn failure during
the weaving or knitting process may result in production of off quality fabrics. The cost of repairing
yarn faults is far less if repairs occur before the fabric formation. Most of the quality related
problems during the fabric formation process are related to errors occurring during the spinning or
yarn preparation processes. Maintaining high yarn quality along with the package quality are very
important to producing fault free fabrics [215].
151
Table 4.9: Influence of yarn parameters on fabric properties
Fabric Properties
Yarn quality characteristics
Even
nes
s
Th
ick
pla
ces
Th
in p
lace
s
Nep
s
Hair
ines
s
Hair
ines
s vari
ati
on
Dia
met
er
Dia
met
er v
ari
ati
on
Sh
ap
e
Den
sity
Tra
sh a
nd
du
st
Fore
ign
mate
ria
l
Str
ength
Elo
ngati
on
Tw
ist
Ble
nd
reg
ula
rity
Appearance D D D D D D D D D D D D D D
Dimensional stability D D D
Thickness D D D D D
Hand/Drape D D D D D D D D
Pilling D D D
Warp and weft
breakage rate D D D D D D D D D
Holes, knitting D D D D D D D
Spirability D
Dyeability/color
intensity, fastness D D D D D D D D D D D D
Wash and wear
properties D D D D
Strength D D D D D D
Elongation D D D D
D: direct relationship
Table 4.10 gives the common type of problems found in dyed and finished fabrics
attributed to yarn defects. These defects are caused due to raw material, machinery or improper
procedures. Some of the problems cause issues in the fabric formation process.
152
Table 4.10: Common problems related to spun yarns.
Problems Probable causes Ref.
Uneven/poor/
cloudy fabric
appearance
▪ Seldom occurring thin and thick places. [6]
▪ Imperfections (thick and thin places, neps). [6, 216]
▪ Excessive yarn hairiness, hairiness variation. [6, 216]
▪ Yarn contamination. [6]
▪ Yarn mixing (uneven yarn, mass variation, combed and
carded, imperfections).
[6]
▪ Improper lateral blending and short-term longitudinal
blending.
[149, 213]
▪ Melt spots/thermal damage in yarn. [206]
Horizontal
line/stripes/barré
▪ Seldom occurring thin places. [6]
▪ Long term mass variation. [6]
▪ Excessive yarn hairiness and hairiness variation. [6]
▪ Short term longitudinal blending problems (accidental
errors).
[6, 213,
216]
▪ Yarn mixing (different counts, twist direction, periodic
mass variation).
[6]
▪ Periodic mass variation (e.g. Moiré). [6]
▪ Twist variation. [6, 212]
▪ Surface damage of yarn caused during spinning causing
fusing of fibers.
[193]
Vertical streaks ▪ Long term mass variation. [216]
▪ Yarn mixing (different counts, periodic mass variation). [6]
▪ Periodic mass variation. [6]
▪ Long term longitudinal blending problems (accidental
errors).
[213]
Holes, yarn
breakage
▪ Seldom occurring thin places. [6]
▪ Neps in yarn. [181]
▪ Low yarn strength. [216]
153
Table 4.10 (Continued)
Problems Probable causes Ref.
▪ Yarn contamination. [6]
Pilling/abrasion ▪ Excessive yarn hairiness, hairiness variation. [6]
Poor dye uptake ▪ Yarn contamination. [6]
▪ Neps in yarn. [181]
Variation in
dyeability
▪ Melt spots/thermal damage in yarn. [193,
206]
Dimensional
stability
▪ Low elongation. [6]
▪ Low tensile strength. [6]
Fluff ▪ Excessive yarn hairiness. [216]
Abrasion of
machine parts
▪ Trash and dust. [6]
4.4.2 Faults due to filament yarns
Filament yarns are used to produce union fabrics, in which two or more yarns of different fiber
types are combined to produce a fabric. Filament yarns depending upon the type may consist of
one or more filaments. Filaments can either be natural, such as silk, or manufactured such as
polyester, nylon, viscose, etc.
4.4.2.1 Faults in manufactured filament yarn
Manufactured filaments are produced either by melt, wet or dry spinning depending upon the fiber
type. The extruded filaments are then partially drawn during the spinning process. These partially
drawn filaments are further stretched to their desired draw ratio to produce filament yarns in a
continuous or separate processing step. Filament yarns for textile applications are used as either
flat yarns or textured yarns. Flat yarns are generally produced by drawing the partially drawn
filaments directly after the spinning process. Textured yarns are produced through a process known
as texturizing in which flat filaments are converted into stretchy or bulky yarns. Texturizing is a
modification process to create bulk, stretch or texture in filament yarns [200, 217]. This gives them
the desired warmth, hand, natural texture, extensibility and appearance to use them in textile
154
applications. The process of modification is carried out by thermal, mechanical or chemical
transformation of the individual filaments and their spatial arrangement in the yarn bundle keeping
the continuity of original filaments [218]. Different types of texturizing processes used depend on
the desired yarn characteristics such as false-twist, stuffer-box, knife-edge crimping, knit-de-knit,
air-jet, intermingling, etc. The most common type is the false twist texturing [218, 219]. The
important factors affecting the quality of textured yarns are yarn tension (before spindle (T1), after
spindle (T2) and winding (T3)), draw ratio, primary heater temperature, twist insertion (D/Y ratio),
second heater temperature, overfeed and package build [219]. These process variables must be
controlled properly according to yarn and fiber type to ensure a problem-free yarn production. The
most common faults that occur in manufactured filament yarns include variation in polymer
morphology, tight spots, broken filaments, bulk variation, intermingling faults, surging, package
build and density problems, and mass variations. The relationship between different texturizing
process parameters and various yarn properties during the texturizing process is given in Table
4.11 [219].
155
Table 4.11: Effect of texturizing process parameters on yarn properties.
156
Variation in polymer morphology
Polymer morphology differences during texturizing lead to differences in dye uptake, tenacity,
elongation, and dimensional stability. Hence, thermal and mechanical stress histories of the
filaments during texturizing are of prime importance. Differences in dye uptake in the textured
yarn are generally observed as both within or among packages. Dyeability variation within a
package is generally due to the variation in the raw material. The difference in dyeability between
packages is commonly due to the texturizing process. Correct machine settings should be used
especially during a material change over. The tension and temperature should be uniform during
processing within and in between machines. The storage of raw materials for texturizing also
influences the dyeing behavior and crimp of filaments and varies with the age of raw material.
Therefore, long storage of raw material should be avoided. The raw materials should be
acclimatized to atmospheric conditions for 1-2 days before being used. The yarn strength and
dyeing behavior are often used as indicators of variation in polymer morphology since low and
high strength yarns show differences in their dyeing behavior. During the twisting and untwisting
process filament migration takes place. If core filaments are drawn and heated differently than the
outer filaments the filament migration due to twisting may result in dyeability variation.
Depending upon the variation in polymer morphology, the dyeing defect may appear as random
defects in the form of dark flashes and streaks and periodic defects such as moiré and barré [157,
218-222]. The main reasons for structural variations are [218-221]:
▪ Damaged yarn transportation devices;
▪ Dirty primary heaters;
▪ Faulty yarn feeding;
▪ Wearing off of twisting disk;
▪ Improper contact of the cooling plate;
▪ Variation in yarn cooling;
▪ Melting of filaments due to contact with the secondary heater walls;
▪ Application of coning oil to the package intended for yarn dyeing;
▪ Variation in draw ratio;
▪ Differences in the primary heater temperature; and
▪ Improper atmospheric conditions.
157
Tight spots
These are regions of highly twisted yarn compared to the rest of the yarn and hence do not have
the same bulk. The length and frequency of this fault are highly variable. Non-steady state
functioning of the texturing machine and differences in yarn structure along the thread line should
be avoided. The underlying reason for tight spots is the use of too high torque or too low yarn
tension. Tight spots of more than one per 20 m of yarn are considered unacceptable. This type of
fault appears as dark bands in fabrics [218, 220, 223]. They can be detected by inspecting the yarn
or by using a knitted sleeve or via on-line monitoring [219].
Broken filaments
This problem is due to many causes, such as variation in properties of raw material, mechanical
damage in the yarn path and incorrect settings of the texturizing machine. Yarns containing fine
filaments exhibits this problem more often compared to coarse filament yarns [219].
Bulk variation
These variations occur either along the yarn length or from one package to another. These are
caused due to high throughput speeds, low draw ratio, and incorrect rate of twist insertion [219].
Intermingling faults
These faults comprise two broad groups. The first group includes intermingling properties such as
intermingling knot frequency and strength, and the second group comprises of irregularity. Thus,
a proper selection of intermingling jet and its operating parameters should be made. The jets should
be clean and replaced after a certain period. The irregularity is seen as the presence of long and
short gaps without interlace [219].
Surging
This is the thread line instability during the texturing process and observed as the untextured
appearance of the yarn. This problem occurs as the texturing speed increases. Surging is caused
by the raw material properties and parameters of the texturizing machine. This problem can be
overcome by increasing the draw ratio, reducing throughput speed and increasing the D/Y ratio
(ratio of speeds between friction discs and throughput speed of yarn) [219].
158
Package build and density problems
Package density is important in order to obtain level dyeings. Incorrect package density, either too
soft or too hard, and variation within and in between packages are common causes of dyeing
problems [219]. This problem is discussed in more detail in section 4.4.3.
Package structure faults are caused due to improper winding parameters such as winding
angle, traverse length, take-up tension, and package density. Poor housekeeping and incorrect
handling procedures may also cause package faults. The most common faults are bulging,
webbing, overthrown ends, ridges, saddling, shouldering, no-tail package and dirty or damaged
packages [219].
Mass variations
Short to medium mass variations (length: 0.01 to 50 m) are caused during texturizing. These
variations can be periodic or non-periodic depending upon their occurrence. The main reasons for
such variations are differences in drawing, twisting and defective traversing mechanisms during
winding [224]. Some coloration problems due to mass variations include barré in knits, warp
streaks or weft bands in woven fabrics [225].
4.4.2.2 Faults in natural filament yarn
Natural raw silk yarn is a continuous filament yarn made up of a number of individual silk
filaments. It is obtained by the process of reeling in which filaments from several silk cocoons
(approx. 7-8) are combined to produce a raw silk yarn (approx. size 20/22 den). They are then re-
reeled and twisted, depending upon the requirements, to produce 2 or 3-ply yarns [205]. Common
faults found in raw silk yarns include uneven yarns, cleanness, and neatness.
Uneven yarn
The silk filament produced by the silkworm is not uniform. Moreover, the number of filaments in
the cross-section of the yarns vary, which reduces the evenness of the yarn. Evenness values of
raw silk are considerably higher than the synthetic filament yarns of the same count. It depends on
the number of fibrils removed from the cocoons and finished cocoon replacement during the
reeling process. Periodic unevenness in the yarn is attributed to a new cocoon added during the
reeling process [205].
159
Cleanness/defects
These are the randomly occurring thick and thin places in yarn and are defined per 100m. Thick
place refers to mean mass > +35% of the mean mass of silk yarn while for the thin place the
threshold is -40% of the mean value. They are mainly caused by operator performance and skills
and also by cocoon unwinding process. These defects may lead to yarn breakage, stoppages and
poor fabric appearance [205].
Neatness/impurities
These include frequently occurring thick places of shorter length (< 4 mm) having mean mass >
140% of the mean mass of silk yarn. These impurities are caused by the reeling process. Damaged
yarn guides also cause this type of impurities. They may cause poor fabric appearance and dark
spots due to more adsorption [205].
A summary of the problems caused by filament yarns due to yarn faults in downstream
processing is given in Table 4.12.
Table 4.12: Problems due to filament yarn faults.
Problems Probable causes Ref.
Manufactured filament yarn
Dark flashes/dark dye
defects
▪ Variations in polymer morphology [222]
Streaks/bars in woven
fabric or barré in knits
▪ Variations in polymer morphology [218-220]
▪ Mass variations [222, 225,
226]
▪ Yarn mixing (different deniers, number
of filaments, twists)
[226]
▪ Intermingling faults [226]
▪ Bulk variation [149]
Uneven/poor fabric
appearance
▪ Mass variations [226]
▪ Tight spots
160
Table 4.12 (Continued)
Problems Probable causes Ref.
▪ Broken filaments
▪ Bulk variations
▪ Intermingling faults
▪ Surging
Dimensional stability ▪ Variations in polymer morphology [226]
Crease formation in fabric ▪ Yarn mixing (number of filaments) [226]
▪ Intermingling faults [226]
Natural silk filament yarn
Poor fabric appearance ▪ Uneven yarn [205]
▪ Defects [205]
▪ Impurities [205]
Dark spots ▪ Impurities [205]
4.4.3 Problems due to the winding process
Winding is usually the last process stage in the yarn formation and the starting point for the
subsequent processing stages (weaving, knitting, and dyeing). The yarn winding process is used
in various stages of processing depending on product type [157, 181, 208, 227, 228]. The main
aim of the winding process is to collect a large quantity of yarn on the package suitable for use in
downstream processing [157, 181]. The winding step is dependent on spinning methods. In most
of the spinning systems, except ring spinning, such as open-end (rotor), air-jet spinning and
filament production, the winding step is integrated with the spinning process. The yarn is taken
directly from spinning for use in the knitting process or as weft in weaving or in the warping
process. The ring-spun yarn needs to go through a separate winding process due to package size
limitations which are normally carried out in a spinning mill [157, 181, 215, 227, 228].
The winding process must meet the following requirements:
▪ Creation of suitable package type meeting the requirements of downstream processing.
Yarn packages are created in various forms which depends on the intended application.
The main considerations for packages are shape and size, density, stability and
161
unwinding performance. Yarn packages for warping, weft, knitting, twisting, and
dyeing require different package shape, density and geometry. The common package
shapes are cheese (cylindrical) and cones. For cones, there are different types of cone
tapers depending on the end-use. The taper may be constant and known as a straight
ended package or accelerated taper with a concave end at the top and convex end at the
bottom called dished ends. For transport and storage, high package density is desirable
but for dye packages low and uniform package density is required for good and even
dye penetration. Yarn tension is the most important parameter for homogeneous
package structure and depends on the yarn and package parameters. The yarn tension
during the entire package buildup should be constant. The package should be free from
critical pattern zones to avoid sloughing-off during unwinding and unlevel dyeing. The
package should also be stable so that it can bear the stresses and retain the structure
during subsequent handling and processing. Also, the package must have a regular
structure for error-free unwinding at high speeds. Lastly, the package should be free
from any defects [157, 181, 227, 229].
▪ Removal of yarn faults with a low number of yarn joints as possible.
Spun or filament yarns contain different types of faults which must be removed in the
winding process. This process is known as clearing. In this process the yarn fault is
detected, and depending on the clearing limit, it is cut and yarn ends are then joined by
the splice. The main objectives of the clearing process are the detection and elimination
of seldom occurring yarn faults such as thick places, thin places, and foreign fibers.
Additionally, any quality problems throughout the whole yarn bobbins should be
detected and the off-quality should be separated and the operator should be alerted if
the process is out of control. Special attention is required for count change in the
machine. Yarn tension is an important fault detection, so it must be uniform. There
should be a proper fluff removal installed on the machine to remove the fly fibers [208,
230]. The selection of splicer type is important which depends on the type of yarn to
be processed. Important points related to splicing are retention of specific yarn
structure, quality, yarn appearance, elastic property and strength of the spliced joints
[229].
162
▪ Uniform application of lubricant (wax) depending upon the requirement such as
knitting.
Knitted yarns are waxed in order to reduce their coefficient of friction for better knitting
performance. The amount of wax applied should be sufficient and constant throughout
the whole yarn length and from package to package. This is essential to avoid yarn
breakage, fly generation and needle breakage during knitting [216, 227]. The quality
of waxing is dependent on the yarn to wax, roller contact pressure, rotation of wax
roller against the yarn, proper dimensions and quality of the wax (softness and melting
point) [227]. The amount of wax deposited is generally 0.5-1 g/kg of yarn. The
selection of wax grade for good running performance depends on fiber type, yarn
structure, count, moisture content, temperature and humidity during the winding area,
conditioning, storage and shipment [181].
The preparation of a suitable yarn package is an essential requirement for successful
package dyeing [231-233]. Many problems in yarn dyeing are due to inadequate winding of
packages. There can be two approaches for producing a correct package for yarn dyeing. In the
first type, a spun yarn package is produced on perforated cones which are produced directly by the
spinner. This eliminates the winding process but may cause problems during dyeing. Also, yarn
density is not controlled by the dyer. Texturized yarn packages are generally prepared on the
texturizing machine thereby reducing the need for an extra winding step. In the second approach,
which is the most common, yarn cones from spinning are rewound on perforated dye tubes [232].
Package rewinding has two main functions [234]:
▪ Package buildup according to end-use requirement. This includes package rewinding
for dyeing, after dyeing and sample packages.
▪ Adjustment of yarn quality.
The most important requirements to be fulfilled by a winding process for package dyeing
are [235]:
▪ Production of yarn packages on current dye tubes;
▪ Uniform package density, diameter, and format with as little variations as possible;
▪ Reproducibility of package qualities to ensure reproducible dyeings;
163
▪ Good package stability for resistance against mechanical stresses during the dyeing
process; and
▪ Flexibility in lot size.
Yarn package has an influence on the levelness, quality, and reproducibility of the dyeing
process [236]. There are many factors that affect the properties of yarn packages which are package
shape and size, dye tubes, type of winding system, winding angle, traverse ratio, yarn shrinkage,
yarn conditioning and length, and package density [231, 236, 237].
Package shape
Two package shapes are commonly used in yarn dyeing which include conical and cylindrical
packages. The cylindrical package is a preferred package shape used for dyeing. This package
shape gives a uniform liquor flow along the package axis, as well as optimum packing and sealing
between the packages in the dyeing machine. This leads to good dyeing levelness, maximized
machine loading and dye house cost savings [228, 232, 233, 238, 239]. Cones have a difference in
liquor penetration along the package axis, especially along the edges due to their shape.
Furthermore, they need expensive spacing devices which are difficult to obtain complete column
sealings and result in unsatisfactory pressing leading to dyeing problems. Also, the slippage of
cones may lead to channeling and unlevel dyeings. Residual dyestuff may also be deposited around
spacers [232, 233, 240].
Package size
Package diameter influences the uniform flow of dye liquor across the entire package [228].
Depending upon the machine and spindle, different package sizes are used [238]. Larger diameter
packages are preferred as they give more carrier capacity, with a lower tendency of leakage and
more uniform liquor flow. Therefore, they require less liquor flow rate [241]. Large diameter
packages give long flow channels in which the flow resistance is largely affected by the fiber
swelling, shrinkage or deposits as compared to short flow channels such as in small package
diameters. If this parameter is not properly controlled it may lead to package deformation, unlevel
dyeing and damage to spindle locks. Liquor flow must be controlled properly depending on the
package resistance characteristics. The diameter of a package must correspond to machine vessel
164
diameter as there is not a single package diameter which gives optimum machine capacity and
dyeing performance [242].
Dye tubes
There are different types of dye tubes with a broad range of designs and materials. Some common
types are inflexible, flexible, tapered, cylindrical, plastic, spring, steel, one-way or reusable [233,
235]. Tubes are made up of different materials such as plastics, aluminum alloys and stainless steel
[228]. The dye tubes must have a perfectly cylindrical body, axial stability, good temperature and
pressure stability and must be resistant to dye staining [228, 231]. Dyeing tubes are selected based
on cost, durability and staining behavior [233]. Depending on the winding process and dye tubes,
the packages are axially pressed. However, density variation might occur due to reverse flow and
errors in pressing. Also, it increases yarn hairiness due to the sliding of yarn and problems in
unwinding after winding [228].
Type of winding method
The winding process should produce a suitable package in terms of weight, diameter, traverse, and
density with good unwinding properties with a minimum waste generation [239]. There are three
common types of winding systems: random, precision and step precision winding. Table 4.13
shows the comparison between the different winding types [181, 231, 237, 243]. In random
winding, which is mainly used for spun yarns, the yarn is laid randomly which can result in forming
pattern zones if the anti-patterning device is not used. The package density, however, is uniform
due to a constant angle of winding over all diameters. Due to the random arrangement of yarn, a
yarn package having varying structure of cavities is produced. Precision winding is mainly used
for filament yarns in which the distance between adjacent yarns is controlled. The winding angle
decreases as package diameter increases keeping the winding ratio constant. This is accompanied
by a uniform increase in package density outwards. Higher package density can be achieved as
compared to random winding. The degree of package density increase can be controlled with the
help of parameters such as yarn distance, starting angle of winding or yarn tension according to
the end-use. There are more chances of producing a package with hard flanks. Lastly, step
precision winding combines constant winding angle of random winding and a constant winding
ratio of precision winding. Package structure can be controlled by the selection of any winding
165
parameter resulting in a wide range of end-use applications [181, 237, 238, 243]. For dye packages,
step precision is the most suitable type as it is free from pattern zones and the almost constant
winding angle produces a homogeneous package density [228]. Package density is affected by a
number of winding parameters that depend on the type of winding system used [238]. During the
winding process, some margin must be considered to take shrinkage or swelling into consideration
[244].
Table 4.13: Types of winding systems.
Characteristics Random winding Precision winding Step precision
winding
Arrangement of yarn
layers
Random Precise Precise
Winding angle Constant Decreasing Slightly reduced
Winding ratio Reducing Constant Reducing
Winding density High Low High
Package density Uniform Varies from inside
to outside
Uniform
Package stability Stable Fragile Stable
Critical pattern zone
(Ribboning)
Possible
(Anti-patterning
device required)
No No
Unwinding performance Poor (pattern zones) Good Good
Liquor flow
characteristics
Not optimum Good Good
Capital cost Low High Moderate
During yarn dyeing, yarn packages are pressed to increase the column density. When
packages are pressed, the package geometry must be such that pressing would not cause local
changes in the density. For some cylindrical packages where the package face is not flat and
rectangular, as in random and precision wound packages, higher pressing force is required to avoid
166
leakages due to uneven faces which may cause non-uniform flow due to high local densities in a
package. The maximum package density is around the package center and cavities may form
around the dye tube. Water and deposits may accumulate in these cavities and lead to unlevel
dyeing and problems in washing, soaping, cleaning, and drying. In contrast, packages produced by
step precision winding have flat faces and soft edges. They also don't require high pressing
pressure and uniformity in package density is maintained [236].
Winding angle
Many package characteristics such as package density, unwinding performance, sloughing-off,
hard package flanks are affected by the winding angle. For dyeing, a higher winding angle is used
to create an open structure and low winding density [228].
Traverse ratio and length
Traverse influences the package structure and thus it must be chosen in a way to result in an open
package structure and low density as required for dyeing. Hard flanks may be formed at the yarn
reversal points during winding and must be avoided in order to obtain a uniform dyeing. It also
results in the abrasion of package flanks with winding drums. To solve this problem either edges
are pressed after winding or rounded side flanks are created. Traverse stroke is gradually reduced
to produce rounded side flanks of the desired rounding radius [228].
Package density
Package density influences the liquor flow. A dye package should have a uniform package
structure and density, from the inner to the outer layers of the package and in-between packages
[231, 238, 243, 245]. The package should have an open construction to allow optimum liquor flow
and should be stable against the mechanical, hydrostatic and hydraulic forces during package
dyeing [238]. Package density determines the porosity of the package. Therefore, it affects the
liquor flow and dyeing behavior [246]. All packages in the same lot must have the same density
and diameter. The density variation should not be more than ± 2.5%. This is required for uniform
and similar liquor flow through entire packages inside the machine and for reducing within lot
variation. Uniform package geometry and density are essential to avoid channeling within and in
between yarn packages. This problem occurs due to the high liquor flow through areas of least
167
resistance compared to high-density areas. This leads to unlevel dyeing within and in-between
packages [231]. Soft wound packages may distort during dyeing and cause channeling. The
package distortion also causes problems in handling and rewinding [232, 233, 240]. Synthetic
fibers shrink during dyeing. Therefore, the package structure should allow yarn shrinkage without
yarn deformation and affecting the package flow [244].
The yarn package must also have uniform and symmetrical package flanks with the same
density as the remaining portions of the package and must be firm and stable as these affect the
package durability [157, 231]. Poor dye penetration (dead zones) may occur due to package flanks
despite a low density being used. To solve this problem package edges are broken by mechanical
deformation. This process leads to a damaged package build and affects the yarn winding due to
the movement of yarn layers. Package rounding during winding of dye packages may solve this
problem and there is no need for edging and rewinding processes [157, 181, 238, 243].
Yarn packages for dyeing are created with a constant diameter (volume). Package density
is affected by a number of winding parameters which depends on the type of winding system used.
The important parameters are winding speed, winding tension, angle of winding and cradle
pressure. Package density may be adjusted during the winding process by changing the traverse
and winding ratio. Cradle pressure controls the winding tension. The winding tension should be
kept below a certain limit to avoid damage to the yarn. The package should be free from critical
pattern zones (ribboning) and an uneven package density. Dye penetration is different in pattern
zones compared to the rest of the package and this results in unlevel dyeing [157, 181, 233, 238,
243, 247]. Despite proper control during winding, variations in packaging density occur.
Variations in yarn properties (count, twist, etc.) within the tolerance range during yarn
manufacturing may also lead to fluctuations in yarn compactness during winding. In practice, a
deviation in package density of ± 5-8% is considered normal while those around ± 3% are very
rare [247].
The flow resistance of the dye liquor through the yarn packages inside the dyeing machine
is indicated by the differential pressure which may determine the liquor throughput. The
differential pressure increases with an increase in package density. Yarn packages with higher
package densities in close proximity to dyeing tubes may lead to non-uniform dyeing. The radial
package density is altered due to a reduction in the coefficient of friction of yarn in the dye liquor
and chemicals in the dye liquor. The shearing force exerted by the dye liquor may cause yarn
168
slippage and change the liquor flow direction. The changes in the winding density in areas adjacent
to the dye tube lead to an increase in the differential pressure which is beyond the control of the
dyer [248]. Liquor throughput affects the movement of dyestuff to the fiber surface of yarn
assembly and ultimately influences the uniformity of dyeing. The aim of the dyer is to produce
level dyeings despite having some variations in package densities. For practical purposes, the dyer
has to take into consideration ± 10% variation in package density within and between packages.
It has been found that for yarn packages with varying winding densities within and in between
packages, the difference in dimensions of the package will not affect the dyeing results if liquor
throughput is controlled with a preselected differential pressure. Radial variations in package
density especially in the areas adjacent to the yarn tube may cause a high amount of dye liquor
flow. This is due to the high differential pressure and shearing forces operating in these zones. The
outside regions of the package, therefore, have a low amount of dye supply. This may lead to
lighter edges if the dye movements are slower than the diffusion rate of the fiber. Generally, this
is not the case as dyer considers the yarn type and dyestuff behavior. For synthetic yarns, this
problem can be overcome by controlling the heating rate. In the case of vat dyeing, where the
movement of dye is faster during the initial stage, the variations in density are compensated in the
end by the leveling stage. Therefore, the local variations in the liquor throughput have a minor
influence on the variation in dyeing results as compared to the radial difference in package density
which has a significant impact [247].
After yarn dyeing has been carried out, two procedures may be performed on the winding
machine which are known as 1:1 rewinding and peeling. In 1:1 rewinding, one feed package is
rewound to form a finished package to avoid color differences in the finished package due to the
deviations in several feed packages. Another operation performed in reference to the rewinding of
dye packages is termed as peeling. This is done to even out color differences within a dyed
package. Quality improvement of dye package exhibiting a difference in dye penetration from the
core to surface is achieved by unwinding the defined length of yarn from the start and or the end
of the package [234, 235].
Table 4.14 presents the problems caused in subsequent processing due to the winding
process and their solutions.
169
Table 4.14: Problems caused by the winding process.
Problems Probable causes Remedial measures Ref.
Problems in weaving and knitting
Yarn breakages during
the warping process
▪ Faulty yarn package The yarn packages should be
fault-free.
[249]
▪ Improper splicing The spliced joined strength
should be as close to yarn
strength as possible.
Drop stitches, holes or
cloth fall-out
▪ Insufficient waxing of
yarn
Ensure proper contact of waxing
roller and the yarn. The preferred
wax deposition ranges between
0.5-1 g/kg of yarn.
[181,
216]
▪ Faulty yarn package Check the yarn package after
winding. It should be free from
defects.
[249]
▪ Improper splicing The spliced joint should have at
least an average strength of 80%
of the yarn strength with low
strength CV%.
[181,
216]
Barré or horizontal
stripes in knitted
fabrics/weft stripes or
bars in woven fabrics
▪ Fluctuation in package
density leads to uneven
yarn tension during
unwinding.
The package should have uniform
density and yarn tension during
winding should be constant.
[216,
250-
252]
Problems in yarn dyeing
Channeling ▪ Uneven winding density The package density should be
uniform within the package.
[231,
253]
▪ Very low winding
density (soft package)
Use optimum package density
according to yarn count and fiber
type.
[231]
170
Table 4.14 (Continued)
Problems Probable causes Remedial measures Ref.
Leakage in package
column
▪ Poor stability of dye
tubes against
temperature and pressure
Select dye tubes which should be
stable against temperature,
mechanical, hydrostatic and
hydraulic forces.
[231]
Unlevelness
(Uneven dyeing)
▪ High package density Use optimum package density.
The yarn shrinkage factor should
be considered.
[231,
253]
▪ Uneven waxing of yarn Ensure proper contact of waxing
roller and the yarn.
[149]
Shade variation within
package layers
▪ Uneven package density The density should be uniform
within layers inside the package.
[231]
Pressure or luster
marks on inner yarn
layers
▪ Very high package
density
1. Use proper package densities
according to fiber type and
yarn count.
2. Cover the tube or cone with a
paper or PP woven sleeve.
[231]
Package deformation
and yarn abrasion
▪ Varying package
density, within and in
between packages
1. The package density should be
homogeneous.
2. Control the winding
parameters to produce yarn
packages with uniform and
reproducible densities.
[231]
▪ Non uniform winding of
packages
Ensure uniform package density
throughout. Use step precision
winding if possible.
▪ Improper coverage of
tube perforations
The winding process should
properly cover the tube
perforations with the yarn.
171
Table 4.14 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Use of damaged tubes Use defect free dye tubes.
▪ Poor temperature
stability of the dye tubes
leads to shrinkage and
deformation of dye tubes
Select dye tubes according to
their temperature stability.
▪ Edging process for
rounding of package
flanks
Use rounding during winding. [243]
Poor liquor
penetration in edges of
the package (dead
zones)
▪ Yarn reversal points
during package winding
Gradually reduce the traverse
length.
[228]
▪ Improper edging or
rounding of package
flanks
Perform proper edging or use
rounding during winding.
[243]
Swelled package
shoulders with a puffy
appearance
▪ Too soft package
winding
Use optimum package density. [254]
White or light streaks
of yarn on package
▪ Too soft package
winding
Use proper package density. [254]
Package yellowing ▪ Too high winding
density can lead to
partial over drying of
packages
Use the optimum winding
density.
[231]
Variation in moisture
content
▪ Differences in winding
density
Check the winding density. [231]
172
4.4.4 Problems due to conditioning
The spinning and winding process may generate stresses in the yarn. These stresses may cause
instability in the yarn which may have a tendency to untwist or form snarls and loops [100]. The
conditioning process is performed to stabilize the yarn. Different types of processes can be
performed which include relaxing, twist-setting, pre-shrinking, fixation and stabilization
depending upon the yarn and fiber type [255]. The main aim of the conditioning process is to
increase yarn strength and elongation, reduce snarling tendency and improve the performance of
yarn during downstream processing. The process is carried out in a closed pressure vessel with
vacuum and steam. Indirect or direct steam conditions may be used [100, 227]. The conditioning
temperature depends on the type of process and fiber type. For example, a minimum temperature
of 90 oC is required for wool while for synthetic fibers the temperatures of 110-140 oC are needed
[100]. For stabilization of blended yarn, the temperature must be selected according to fiber with
the least temperature stability without affecting the color and properties of the fiber [100]. Twist
setting is generally carried out below 100 oC (70 oC, max. 80 oC for polyester and their blends),
while pre-shrinking is carried out at temperatures above 100 oC (max. 115 oC for polyester and
their blends) [206].
Cotton yarns are conditioned after the spinning process to increase their moisture content
and enable the moisture to evenly distribute throughout the yarn package. The moisture content in
the yarn influences the physical properties of the fiber and yarn [227]. Very high and uneven
moisture distribution should be avoided as it may cause variations in yarn elongation when tension
is applied. The stretched areas in the yarn are fixed during drying. When yarn undergoes a wet
process the overstretched areas can contract and form tight regions. This type of fault is more
common in wool [149].
Waxed yarns should be not be steamed or conditioned at high-temperature conditions.
These conditions can cause the wax on the yarn to melt which may also penetrate into the yarn,
which would increase the coefficient of friction. Waxed yarns that needs to be processed by this
method should have high wax content in order to counteract this problem. Alternatively, waxes
with high-temperature stability should be utilized [181].
The important factors for conditioning include the penetration of vapor inside the package,
temperature, treatment time and steam type. In the production of large and high-density packages,
an even and uniform penetration of steam should be ensured. This is usually obtained by increasing
173
the treatment time. The steam penetrates from the surface of the package inwards at a variable rate.
It can also penetrate from the side of the yarn carrier if the carrier is perforated or deformed. Even
penetration can be obtained by using the intermediate vacuum during the first third of the treatment
time. Using very short or long treatment times, or variability in package density can result in
variation in fiber properties which leads to problems in further processing of yarn. The formation
of condensate inside the machine should also be avoided [100, 206, 255]. Storage time before
conditioning and package size should be similar for all packages in the lot [221]. The treatment
program (time and temperature) from one yarn lot to another should be constant to ensure obtaining
the same yarn properties.
The major problems caused by improper yarn conditioning comprise increased unwinding
tension, knitting needle breakages, variation in yarn frictional values, static generation, fly
generation, yarn breakages, improper yarn strength, reduced size pick-up, yarn snarling, tight
threads, shade variation, and streaks during dyeing [149, 157, 206, 256].
4.5 Problems arising from fabric formation
The textile fabric is a combination of fiber or yarn or both and can be produced by different
methods: weaving, knitting, braiding, tufting and non-woven manufacturing [215, 257]. The
selection of fabric for a particular application depends on the required performance and/or aesthetic
characteristics, keeping into consideration cost and price. The main application areas for fabric are
apparel, home furnishings and industrial [215]. Weaving and knitting constitute the major
applications typically used for apparel and home furnishings while non-wovens are mainly used
for industrial applications. Braiding and tufting use is limited to specific purposes [257]. The
majority of the fabric produced nowadays is by weaving and knitting, although non-wovens are
gaining importance.
4.5.1 Yarn preparation for fabric formation
Yarn is a basic building block of woven and knitted fabrics [215]. In order to produce quality
fabrics, the yarn must be presented in a form which is appropriate for the fabric formation process.
Yarn obtained after the spinning process in most cases cannot be used directly to produce a fabric.
The yarn preparation involves a series of processes that improve the properties of yarn to meet the
174
requirements of knitting or weaving processes [215, 258]. The preparation requirements for yarns
according to different fabric forming processes are [258]:
▪ Weaving yarns
a. Warp:
- Good yarn alignment (on weaver's beam);
- Good yarn strength (weaving tensions);
- Low hairiness;
- Good yarn smoothness; and
- Good elongation and flexibility.
b. Weft:
- Good yarn package for proper unwinding.
▪ Knitting yarns.
a. Warp knitting:
- Low yarn friction;
- Low fiber shedding; and
- Good yarn smoothness.
b. Weft knitting:
- Low yarn friction;
- Low fiber shedding;
- Good yarn smoothness; and
- Proper alignment of yarns with respect to needles.
175
Figure 4.4: Steps involved in woven and knitted fabric production.
The weft and warp yarns in the weaving process and yarns for the knitting process are
subject to different conditions, requirements and therefore preparations. The processes used are
also dependent on the yarn type [215, 216]. The steps involved in fabric manufacturing using
knitting and weaving processes are given in Figure 4.4 [215, 258]. As already discussed, the
winding process is normally carried out in a spinning mill. Section 4.4.3 covers the potential faults
that can arise from the winding process. Table 4.15 shows the common yarn preparation processes
and their objectives [215, 230, 258-260].
Yarn production
Weaving Knitting
Weft Warp Weft knit Warp knit
Winding
Quilling (Shuttle loom)
Winding
Warping
Sizing
Winding and Waxing
Warping
Drawing-in orTying-in
Winding and Waxing
Knit fabric
Knit fabric
Woven fabric
176
Table 4.15: Objectives of the yarn preparation processes and associated fabric defects.
Processes Objectives Fabric defects caused
Quilling ▪ Package formation (for
shuttle loom).
Knots, sloughing-off, coarser or finer weft,
foreign body.
Warping ▪ Preparation of even and
uniform sheet of yarn.
Knots, double ends, missing or broken ends,
mixed count, loose or slack ends, streaks.
Sizing ▪ Improvement in strength,
smoothness, elasticity,
lubrication and abrasion
resistance of yarn.
▪ Reduction of yarn
hairiness.
Missing ends, wrong pattern, bad selvages,
sticky ends, loose or slack ends, double ends,
missing or broken ends, lint balls, floats,
abraded ends, stiff warp, incomplete
desizing, wax deposits, hard size, streaks,
harsh hand.
Drawing-in or
tying in
▪ Setting up of yarn ends in
the weaving machine.
Wrong pattern, reed marks, streaks in the
warp direction.
The defects that are present in the woven or knitted fabric can be due to numerous reasons.
Some faults are attributed to the yarn preparation processes. The underlying reasons for such
defects are due to:
▪ Yarn related problems: yarn quality and mixing
The quality of the yarn used is a very important aspect of producing good quality
fabrics. Many defects during the knitting or weaving process are due to yarn alone. It
is important to check the incoming yarn for different yarn quality parameters, which
should be within the tolerance limits. These parameters and their values depend on
whether the yarn is intended for the knitting or weaving process and the yarn type (spun
or filament). Variation in parameters is equally important along with individual values.
Section 4.4 covers the quality of yarn and associated faults in more detail. Another
aspect of equal importance is the mixing of different yarn types (different fibers, blend
compositions, count, etc.) during the yarn preparation processes. A proper yarn
segregation system should be designed, and workers should be trained. If the yarn
mixing takes place it would be very difficult to identify them in the subsequent
177
processes until the fabric is dyed or printed. The chance of yarn mixing is very high in
the winding process, especially in the case of ring spinning process. The incoming yarn
bobbin should be checked for the presence of marks or tints. This is very important in
the case of blends when the mill is producing yarns with different blend ratios or fiber
components. If the bobbins are faulty or stained they must be separated otherwise faulty
fabrics may be created. For filament yarns, attention should be given to different yarn
manufacturers, lot numbers, yarn denier and number of filaments as dye uptake varies
from lot to lot and may result in the formation of weft bars in dyed fabrics [230].
▪ Wrong machine settings and parameters
Machinery related parameters constitute important factors in the production of quality
fabrics include machine settings and selection of process parameters. Proper machine
settings are essential for efficient machine operation. The fiber component in the yarn
has an influence on the processing behavior of the yarn and therefore needs proper
attention. The polyester component in the blend may generate static charges. The
polyester/cotton blended yarns are thus hairier and bulkier than the equivalent count
cotton yarns. These differences in properties must be considered for machine settings
as well as process parameters when blended yarns are processed in winding, warping
and sizing machines [230]. Filament yarns may be frayed or ruptured during high-speed
processes due to static charges and may thus cause defects during the weaving process
[252]. The following points are important in relation to yarn preparation machines for
fault-free fabric production in weaving and knitting:
- Warping:
Stoppages of yarn amounting to 0.1-0.2 per million meters are considered good for
the warping process. It has been found that yarn, package and machine settings
faults are equally responsible (33% each) for yarn breaks during the warping
process. The distance between a yarn package and the yarn guide element must be
optimized to obtain a uniform take up-speed [249]. Proper working of stop motion
is essential to avoid broken ends which may lead to lappers and migratory ends.
Machine speeds should be set according to material being processed. For blended
yarns which can generate static electricity the use of a static eliminator device is
recommended. The yarn tension should be uniform, otherwise, warp-way streaks
178
may occur. The average yarn running tension should be as low as possible, and
must not exceed 1/15th of the single yarn strength and should be uniform. Yarn
should be free from any fluff (lint accumulation) and the mixing of wrong ends
must be avoided [215, 230]. The yarn guide should not have sharp edges [261].
- Sizing:
The end goal of the sizing process is to eliminate or reduce warp breaks during the
weaving process. The size application should be uniform along the length and width
of the yarn. The yarn tension, stretch and size add-on need to be controlled properly
by correct machine settings and conditions to avoid abrasion, stretching, and
improper sizing of warp. The yarn spacing must be proper on the slasher box and
on the drying cylinders. Crossing and missing ends due to migration of ends must
be avoided. Size recipe is selected according to fiber type, blend ratio, yarn type,
fabric weave and construction and loom type. The anti-static agent is also used for
synthetic fibers. Blended yarn is more hairy, bulky and hydrophobic than cotton
yarns [215, 230, 262].
- Pirn winding:
The yarn tension should be uniform and slough-off of yarns must be avoided. The
mixing of yarn (wrong yarn) must also be avoided [215, 230].
▪ Operator related faults
The personnel involved in fabric formation processes such as machine operators,
supervisors, etc. are of equal importance for producing fault free fabrics. They should
be trained and made aware of the quality aspects, the importance of reducing defects
and machine downtimes [230]. Many defects such as wrong and broken ends are due
to the carelessness of the machine operators. The mixing of yarn packages during
clearing due to operator negligence is one of the common sources of warp streaks. Their
role is crucial in achieving the right-first-time production.
▪ Faults due to improper practices
Good housekeeping practices are important for improving quality. Blended yarn
accumulates dust and fluff due to static charge, so it need special attention. Yarn
packages and beams must be properly covered to avoid settling of dust and dirt. The
179
package movements in between processes should be done properly to avoid damaged
yarn packages or beams, rust marks and stains [230].
4.5.2 Weaving faults
The weaving process produces fabric by the interlacing of two sets of yarns that are perpendicular
to each other. The structure and appearance of the fabric are largely dependent on the weaving
pattern [215]. In todays’ weaving plants there are increasing requirements for performance,
productivity, and quality improvement. Some of the underlying reasons include market
competition, cost pressure, quick response, and market demand. The quality of the fabric is
measured in terms of two factors: fabric properties and the fabric defects as shown in Figure 4.5
[263, 264]. These aspects of fabric are dependent on a multitude of parameters extending from raw
material to the finished fabric and have complex interdependence between them. There are some
physical aspects of fabric that can be predetermined by the raw material, yarn type, density and
weave collectively known as style. But there is a large number of quality demands which are only
fulfilled by optimizing spinning, weaving and finishing process dependent factors. Figure 4.6
shows the flow chart of various factors that has an influence on fabric quality in fulfilling customer
requirements [263]. The interdependence of two areas of fabric quality on various factors is not
similar. The creation of fabric defect is more dependent on the weaving process as compared to
the fabric properties [263]. The properties of woven fabric are dependent on material
characteristics, properties, and structure of fiber and yarn and the structure and geometry of fabric
[215]. The weaving parameters need to be set properly and according to yarn type, blend
component, and fabric design in order to obtain the required fabric properties.
Today's most important quality criteria in the weaving mill is a cost-effective production
of acceptable fabrics free of defects [263]. A defective fabric sells at a lower price and therefore
results in lower profits [215, 230]. Fabric defects can be attributed to many reasons and can be
classified as yarn defects and process defects. Process defects arise from the processes involved in
the fabric formation process: winding, warping, sizing, drawing-in, weaving process, operator
related and due to improper material handling. The fabric defects are a combination of all such
defects [230]. The defects mending process is generally very costly and acceptable defects levels
are steadily declining [264]. The permissible number of stoppages that are considered acceptable
are 2 stoppages per 100,000 picks [249] or 1-2 non-repairable defects per 100 m length of fabric
180
[263, 264]. Along with the fabric quality, machine stoppages due to yarn breakages, fabric faults
and seconds must be avoided [215]. Ten weft breaks or 4 warp breaks correspond to 1% loss in
weaving machine efficiency in an 8 h shift [249]. It has been found that 20% of machine stoppages
are due to the weft and 80% are associated with warp yarns. The stoppages due to deficiencies in
warp can be subdivided into 20-30% due to yarn faults; 30-40% related to the weaving preparation
process and 30-40% associated with the weaving process [264]. A proper quality control system
is essential for controlling the production of defective fabrics which need to be kept at minimum
levels [215, 230].
Figure 4.5: Aspects of fabric quality.
Figure 4.6: Fabric quality assurance.
Fabric quality
Fabric defectsFabric properties
Textile physics(Styles)
AestheticsWeaving
technology (Processes)
Type of yarn Finishing
Fashion
Function
Fabric
Weave
Density
Yarn
Fabricconstruction
Pro-perties
Preparation
Finishing
Weaving
Process
Defects
FulfillmentConsumers'requirements
Secondaryrequirements
181
Fabric quality can be improved by minimizing yarn stress on warp and weft downtime
reduction and good housekeeping practices [215]. The primary and secondary weaving motions
should be properly timed. Defects will occur if the motions are not properly configured. These
include picking, shedding, beating, let-off, take-off, warp, and weft stop motion. In a shedding
process, healds with good surface properties must be selected to reduce friction. There should be
a proper cleaning system to avoid fluff and fly accumulation [230]. Segregation should be made if
colored yarns or different fiber types are processed under the same shed. The temperature and
relative humidity of the air has an influence on the weaving performance, so they must be
controlled properly. The temperature varies between 21 to 25 oC and the relative humidity levels
are dependent on the fiber type being processed which is between 50% for some synthetic fibers
to 80% for low grades of cotton. Humidity also reduces the generation of static, lint, dust and fly
[215].
The common woven fabric defects are given in Table 4.16. It can be seen than defects can
be attributed to yarn, yarn preparation and weaving processes. The fabric fault is described along
with their appearance in the fabric, following which causes and countermeasures are discussed.
Table 4.16: Problems in woven fabrics their causes and countermeasures.
Problems Description and probable causes Remedial measures Ref.
Faults in weft direction
Stripe/
streak/ bar/
thick place
Excessive weft density due to
compaction of yarns creates a
difference in shade or brightness.
Usually, extended along the full
fabric width.
[6,
215,
250-
252,
261]
▪ Irregular weft density Check weft density and ensure it
is uniform.
▪ Excessive yarn tension during the
preparatory process changes the
yarn reflectance properties
Ensure the yarn is not subjected
to excessive tension in the yarn
preparatory process.
182
Table 4.16 (Continued)
Problems Description and probable causes Remedial measures Ref.
▪ Due to the starting mark,
standing place, set mark or
uneven let-off or uneven take-up
1. The loom startup should be
proper.
2. Delay start, slight tensioning or
loosening of the warp
depending on the length of the
stoppage
3. Check the setting of the let-off,
take-up, shedding mechanisms.
▪ Uneven yarn tension during yarn
unwinding of packages
The yarn tension during
unwinding should be uniform.
Thin place Normally visible as a translucent
fault but in extreme cases only a
few weft yarns per cm. It usually
extends across the full width of the
fabric.
[6,
250,
251,
261]
▪ Insufficient weft yarn density. Check the setting of the let-off,
shedding, and take-up
mechanisms.
▪ Improper yarn tension. The warp tension needs to be
controlled.
▪ Faulty weft insertion system. Check the weft insertion system.
▪ It may also be caused by faults
such as standing place, starting
mark, pulling back place, and
repping.
Lashed-in/
pulled-in/
dragged-in/
Some part of weft yarn is
accidentally pulled into the shed
from the following pick. It varies
[6,
215,
250,
183
Table 4.16 (Continued)
Problems Description and probable causes Remedial measures Ref.
jerked-in
weft
widely depending upon the length,
thickness, and the number of yarns
drawn into the shed.
251,
261]
▪ Due to damaged pickers,
improper working of trimmers,
tuckers, and holders.
Ensure proper working of the
picking system and weft selvage
devices.
▪ Incorrect timing of picking. Adjust correct pick timings.
Extraneous
yarn/
sloughed-off
weft/ double
pick
Appears as a thick place of varying
thickness depending on the form
the yarn is incorporated and in
some cases as projecting loops.
[6,
250,
261]
▪ Individual unrelated lengths of
yarn in a single or doubled form
in the same shed are woven into
the fabric due to improper
setting or functioning of the weft
insertion system.
Check the settings the functioning
of weft insertion system.
Fly/ slub/
foreign body/
lump/ gout
Generally visible in the fabric as
contrasting color in the form of
lumpy thick place.
[6,
250,
261]
▪ Foreign substances such as
fibrous fly, dust or contaminants
are woven into the fabric
1. There should be a proper loom
cleaning system and
segregation of loom where
colored yarns are present.
2. Check the humidity system.
Broken
pick/missing
Missing weft yarn for whole or
part of the fabric. It appears as a
[6,
250,
184
Table 4.16 (Continued)
Problems Description and probable causes Remedial measures Ref.
pick/dropped
pick/ chapped
weft
bar with no weft present for whole
or part of the fabric width.
251,
261]
▪ Due to breakage, running out, or
premature release of the weft
1. Ensure correct settings and
proper working of yarn feeder
and picking system.
2. Yarn tension during pick
insertion should be kept at
minimum levels.
Short pick Weft yarn missing at the edge zone
of the fabric and the end of the
inserted pick is pulled back into
the shed. It appears as a broken
pick in the fabric edge zone and as
a slack pick in the remaining zone,
especially where the weft is
inserted.
[6,
250]
▪ Improper working of weft
insertion system
Ensure the weft inserting is
working properly and weft is
correctly inserted till the end.
Faults in the warp direction
Reed mark/
stripe/ crack
It appears as a narrow transparent
stripe running in the warp
direction.
. [6,
250,
261]
▪ Irregular lateral spacing of the
warp ends with intact weave
interlacing
1. Check the reed plan.
2. Warp yarns are stressed more
than intended, check the shed
and warp tension settings.
185
Table 4.16 (Continued)
Problems Description and probable causes Remedial measures Ref.
▪ Due to non-uniform reed dent
spacing, defective or damaged
reed
1. Check the reed surface
(damaged reed).
2. Use finer reed if possible
Temple
mark/ pin
mark
A slight disturbance in the edge
zone of the fabric in warp direction
occurring periodically or full
length.
It appears either in the form locally
distorted warp threads or small thin
stripes or holes are created near the
selvage.
[6,
250,
251,
261,
265]
▪ Improper selection of temples 1. Correct selection of temples.
2. Use temples with cylinders
having a differential
arrangement of the rings in
spiral form.
▪ Damaged or worn out temples Replace worn out or damaged
temples.
Drawing-in
fault/ double
end/
misdraw/
wrong draft
Appearance depends on the type of
weave. It is in the form of two
parallel warp ends with equal
interlacing sequence in plain
weave and narrow warp-way stripe
differing in construction in other
weaves. In some cases, extra warp
ends are drawn in resulting in
incorrect warp density.
[6,
250]
186
Table 4.16 (Continued)
Problems Description and probable causes Remedial measures Ref.
▪ Incorrect sequence of drawing-in
through heald eye resulting in a
recurring incorrect interlacing
warp ends
Incorrect drawing-in or wrong
drawing-in-draft or reed plan.
Warp break/
missing end/
end out
▪ Warp end is missing over a
certain length of fabric. It is
present as a narrow transparent
stripe with incorrect construction
running along the warp direction
and insufficient warp density of
varying lengths.
[6,
250,
251,
261]
▪ Lower yarn strength 1. Check the yarn quality. The
yarn should have enough
strength and extensibility to
bear the weaving tensions.
2. Check the sizing process.
▪ Yarn abrasion from the guide
element
Yarn guide elements, reed
surface, and heald eye should
have a smooth surface.
▪ Faulty warp stop motion Check the warp stop motion
which should be free from any
lint or broken wires.
▪ Carelessness of the operator in
the tying of broken ends
Proper attention should be given
by the operator to repair broken
ends.
Direction independent faults
Poor
appearance
Fabric variations in large areas in
appearance, structure or
187
Table 4.16 (Continued)
Problems Description and probable causes Remedial measures Ref.
characteristics. The severity of the
fault varies depending on the form
and may be in fabric or along the
selvages.
[250,
259,
266]
▪ Abrasion caused by an emery
roller
Check the surface of the emery
roller or surfaces coming in
contact with the fabric.
▪ Incorrect tension in the left off
and take-up system
The let-off and take-up motion
should be fault-free.
▪ Incorrect working of the
shedding process
Check the shedding process.
▪ Faulty yarn The yarn should be uniform and
defect-free.
Stain/soiling/
oil/ rust
stain/fog
mark
Local discoloration in the fabric,
which may be periodic if the fabric
layers are pressed to each other.
[250,
251,
259,
261] ▪ Oil spots caused by the weaving
loom.
1. The machine should be
properly clean and the
lubrication system should be
working properly. Avoid
spilling and dripping.
2. Use stain remover.
▪ Discoloration caused by rust and
soiling during transport and
storage.
▪ Streaks due to rubbing.
The fabric should be transported
properly, and contacts rusty or
dirty areas should be avoided.
▪ Carelessness of the operators. Ensure proper yarn handling and
storage.
188
Table 4.16 (Continued)
Problems Description and probable causes Remedial measures Ref.
Yarn defect Usually, appear as an indistinct
changes in yarn thickness or shade
difference.
For mixed yarns, it can be seen as
wide stripes. It can occur both in
warp and weft directions.
[6,
250,
251]
▪ Fault in the yarn
(thick/thin/slub/knot/
unevenness/foreign fiber/
soiling/gassing mark)
Check the yarn quality. The yarn
should be free from defects.
▪ Mixing of incorrect yarn (wrong
yarn).
Good housekeeping is essential to
avoid yarn and lot mixing.
▪ Differences in blend
composition or using yarn from
different lots.
Blend ratio variation should be
within the tolerance limit (< 7%
for 67/33 PES/CO).
▪ Manufactured fiber coming from
different lots show variation in
dye pick-up if used side by side.
Use yarns from the same lot type
in case of manufactured yarns.
Snag/pick-
out mark/
pulling-back
place/ hang
pick
Appears as lumpy fault with
locally displaced lines of weft and
the faulty warp is either broken or
highly tensioned.
[250,
267]
▪ Rough or knotted warp end
causes one or more pick to snag
on and get jammed or displaced.
1. Use flat knot for broken warp
yarns.
2. Check the surface of the emery
roller
Interlacing
fault/
Usually appears as a compact and
distinct fault
[250,
261]
189
Table 4.16 (Continued)
Problems Description and probable causes Remedial measures Ref.
disturbed
place/ broken
pattern
▪ Faulty interlacing of several
adjacent warp and weft yarns
▪ Wrong drawing of yarns,
incorrect pick insertion in a shed
and faulty shedding
Check the settings of the picking
and shedding mechanism.
Snarl/looped
yarn
Appears as a short thick place with
projecting loops.
It may also occur at irregular
intervals in the center of the fabric.
[6,
250,
251,
259,
261] ▪ Yarn twisted around itself in
short lengths thereby resulting in
loops that are woven in.
1. Use optimum twist levels in
yarn.
2. Setting of yarn improves the
twist setting for high twist
yarns.
3. Use appropriate humidity in the
shed.
▪ Loosely woven yarns Ensure proper setting of weft
feeders and picking mechanism to
control yarn tension.
▪ Due to defective weft-fork Set the correct shedding timing
Hole/tear/cut Several adjacent weft and warp
yarns are broken or cut and vary
widely in size and form.
Check the surface of emery roller,
cloth roll and front rest.
[250,
259,
261]
▪ Wrong selection of temple Select the temple according to the
fabric type.
▪ Due to sharp edges on loom
parts
1. Ensure the machine surface is
smooth and free of sharp
objects.
190
Table 4.16 (Continued)
Problems Description and probable causes Remedial measures Ref.
2. Proper attention should be
given during fabric transport.
Slack yarn/
pick/ end/
cockled yarn
▪ Yarn with insufficient tension
during warping and sizing
(warp) or winding (weft)
process.
Check the warp or weft tension
during warping, sizing or winding
process.
[6,
250,
259]
▪ Longer length of yarn is woven
in and yarn appears bulky. This
results in a change in fabric
structure.
1. Ensure the correct working of
the let-off, picking, and take-up
system.
2. The warp tension should be
uniform over the entire warp
width.
Tight yarn/
fiddle string
▪ Yarn with excessive tension or
having less crimp.
Check the yarn tension. The
tension of warp ends in the beam
should be proper.
[6,
250]
▪ Shorter length is woven into the
fabric resulting in slightly
disturbed structure. It is often
difficult to detect but occurs
commonly.
Check the picking, let-off and
take-up system.
Float/
stitching/
undershot
▪ Yarn with defective interlacing
at one or more successive points
resulting in a portion of yarn
remaining free on the fabric
surface.
Ensure warp stop motion is
working properly and the broken
pick should be repaired.
[250-
252,
259,
261]
▪ Due to entanglement of warp
ends due to breakage, knots with
long tails, fluff or foreign matter,
1. Keep the leasing rod near the
heald shaft.
191
Table 4.16 (Continued)
Problems Description and probable causes Remedial measures Ref.
improper working of warp stop
motion.
2. Special attention should be
given during the preparation of
yarn for weaving.
▪ Due to frayed filaments,
improper sizing, and improper
shedding.
1. For PES-CO yarn, wax the ends
after sizing.
2. Proper yarn tension and
checking of guide elements’
roughness is required.
▪ Sticking of ends due to static
charge.
Check the humidity level in the
weaving shed.
Warp end-
repair/ shuttle
trap mark/
smash
Broken and tied warp yarns with
ends projecting or woven in as a
narrow thick place in the weft
direction.
[250,
251,
261]
▪ Improper knotting of broken
yarn. The broke yarn is missing.
The broken yarn end should be
correctly knotted.
▪ Slack ends in a certain portion
obstruct the movement of the
picking system.
In shuttle loom, check the timing
of shedding, shuttle in boxes,
shuttle balance, picking system,
pirn transfer and proper startup of
loom after a stoppage.
4.5.3 Knitting faults
Knitting is a fabric construction technique in which one or a set of straight yarns are formed into
columns of vertically intermeshed loops. The fabric is made up of a cohesive structure of
intermeshed loops. The loop structure provides stretch, comfort recovery and dimensional
flexibility which is normally associated with the knitted fabrics. The knitting process can be
divided into two categories based on the yarn presentation and processing known as weft knitting
192
and warp knitting. In weft knitting, yarn is fed horizontally to the knitting zone and the same yarn
feeds all knitting needles of one knitting course. In warp knitting the set of yarns, aligned
longitudinally, are interloped with another. Several yarns are presented to all the needles and
collective needle movement produces a loop row simultaneously [216, 257, 268, 269].
Knitters and finishers usually specify knitted fabrics in terms of stitch density, which is the
total number of loops in a measured area of fabric, which in turn is related to loop length. They
are usually measured as courses per inch (or cm) or wales per inch (or cm) respectively [216, 257,
268-270]. A difference in loop length within fabric produces appearance related defects such as
horizontal stripes [270]. As loop length increases, the wale density and fabric width stability
decreases. Another term commonly used for knitted fabrics is run-in, in weft knitting, which is the
amount of yarn required to produce one complete course of fabric, that determine the aesthetics
and performance of the knitted fabric [268].
The acceptability of the knitted fabric by a customer is dependent on its quality, which
includes fabric properties and defects. In order to meet the customer's required specifications and
reduce faults, an effective process and quality control is essential. This includes systematic and
continuous monitoring and control of the yarn supply, knitting process and the end product [203,
270]. Important quality aspects are loop length, GSM (g/m2), stitch density, fabric width, yarn
count, fabric construction and defects [270].
The faults in the knitted fabric may be due to various reasons, some common causes are
given below [203, 216, 270].
▪ Yarn faults and package defects
Any fault in the yarn could result in producing a faulty fabric. The important points that
need to be considered are the appropriate selection of yarn type, count, storage and
quality aspects. The yarn count selection is generally based on machine gauge [216,
270]. Yarn related problems are covered in more detail in section 4.4, 4.4.3 and 4.5.1.
Proper yarn storage is essential for good knitting behavior. Yarns should have
sufficient moisture for easy processing. The storage conditions should be as close to
knitting conditions as possible. Storage under extreme conditions and large temperature
fluctuations must be avoided. Elastic yarn storage is critical in order to obtain the
required fabric properties such as stretch recovery and modulus repeatably. If the
193
temperature is high, wax migration might occur. Under cold conditions, condensation
may occur [216, 271].
▪ Yarn feeding and yarn feed regulator
Monitoring and regulation of yarn feeding is an important aspect in knitted fabric
production. Improper feeding of yarn leads to tension variation which may cause yarn
breakage [216, 270].
▪ Machine settings and pattern faults
Control of machine settings is important for producing quality fabrics in which several
factors must be balanced in order to achieve optimal settings. Optimum settings are
calculated each time for a given yarn type and structure. A balanced relationship must
be set between yarn tension before and after the feeder, yarn drawing-in at the cylinder
and dial, the height of dial and fabric take-up tension. Important settings that need to
be considered include the minimum yarn tension during a feed, low fabric take-up
tension, the right setting of dial and cylinder needles, and the optimum spacing between
dial and cylinder [216, 270]. The correct machine settings mainly depend on yarn and
article to be made.
▪ Machine state and maintenance
Maintenance includes proper lubrication, repair of machine defects, and replacement
of broken and defective parts. For example, a bent needle can cause improper needle
movement which leads to an increase in yarn tension. This may cause a variation in
loop length or even needle or yarn breakage [270].
The important points in relation to machine’s state are: horizontal and vibration-
free installation, proper yarn transport and tension system from bobbin to the knitting
zone, defect-free surface of yarn guide paths, proper selection and routine replacement
of knitting elements, appropriate drive system between needle dial and cylinder,
centering of needle beds, right fabric take-off, and the wind-on tension system. For
example, the improver setting of the yarn feeder can cause dropped stitches [216].
▪ Plant climatic conditions
The knitting plant should be air-conditioned in order to produce good quality knitted
fabrics [216, 270]. Appropriate conditions can avoid yarn drying during processing,
reduce the number of yarn breaks (which leads to holes) and improve the surface
194
structure of the knitted fabric. The optimum conditions are a relative humidity of
55±10% at a temperature of 25 ± 3 oC [216].
▪ Machine cleanliness and fluff
A proper fluff removal system is essential in the knitting plant as it may produce defects
in the knitted fabric such as colored fly fibers. There must be a proper separation in the
plant where different colored yarns or fiber types are processed, otherwise, there is a
chance of fly accumulation on the knitted fabric which leads to defects in later
processing. The fly agglomerates from the cams and residual wax from yarn guide
elements should also be removed [216].
Table 4.17 gives a description of frequent faults in knitted fabrics, their causes and how to
eliminate them. After the determination of the cause, the remedy of the faults can be provided. The
faults given in the table mainly occur during the knitting process and are observed in gray fabrics.
Table 4.17: Causes and remedies of frequent problems in knitted fabrics.
Problems Description and probable causes Remedial measures Ref.
Cracks or
holes
▪ Incorrect relation between dial
loop and cylinder
Use optimal settings according to
yarn type and pattern.
[203,
216,
272-
275]
▪ Bad setting of the yarn feeder or
stitch cams
Use optimal settings according to
yarn type and pattern.
▪ Weak places in yarn lead to
breakages during loop
formation
1. Check the quality of the yarn.
2. Use yarn with optimal
properties for the knitting
process. ▪ Thick and thin places, too low
yarn strength and high trash
content cause the yarn to break
▪ Knots or splice in yarn cause the
yarn to sit tightly in the last
stitch and lead to breakage
Use flat knots. Check the quality
of the yarn.
195
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
▪ Uneven yarn removal from a
package or a faulty package
Avoid using a faulty package.
▪ Improper machine elements or
position of the cones
Placement of the yarn package
should be as required.
▪ Too high yarn running tension Check the yarn feeding system
and reduce the tension settings.
▪ Too dry yarn due to insufficient
waxing or oiling
1. The knitting plant should
have optimum humidity to
ensure problem-free running
of yarn.
2. The yarn should be properly
waxed or oiled during the
spinning process.
▪ Defective guide elements, the
surface is edgy or not uniform
1. Replace the guide elements.
2. Use elements with good
surface properties.
▪ Fabric movement is improper
and it is pulled strongly or
intermittently
Check the fabric take-up
system.
▪ Incorrect yarn size for machine
gauge
Use proper yarn size according
to machine gauge or needle
hook.
▪ Excessive yarn hairiness
resulting in increased yarn
tension and lint shedding
Check the quality of the yarn.
▪ Improper setting of stitch cams Use the right settings for
stitching cams. ▪ Cams set too low
196
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
▪ Wrong sinking ratio between rib
and cylinder cam
Use the right sinking ratio.
▪ Too high machine speed Run the machine at the speed
recommended by the
manufacturer and according to
yarn type and pattern.
▪ Damaged needles 1. Replace the damaged needles.
2. Implement and follow a
routine checking system for
needles.
Dropped
stitches
▪ Bad setting of the yarn feeder,
yarn is being fed at improver
angle
Check the yarn feeding system. [216,
272,
273,
275] ▪ Wrong threading-in of yarn
feeder
The yarn should be properly
threaded through the dial bore
and cylinder needles.
▪ Dial and cylinder loop lengths
are not properly related. The
loop jumps out of the needle
hook.
Use correct dial and loop
cylinder lengths.
▪ Bad take-up, the already formed
loop comes out before the next
course.
Check the take-up system.
▪ Too dry or stiff yarn which
jumps out of the needle hook
when laid-in.
1. Re-adjust the yarn feeder or
increase yarn tension.
2. Check humidity levels of the
plant and waxing/oiling of
yarn.
197
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
▪ Yarn tension is insufficient.
Yarn is not easily caught by the
needle hook.
Tension compensation should
be as close as possible to the
knitting zone.
▪ Defective needle (bent latch,
hook)
Replace defective needles.
▪ Knitting pattern not properly
designed. Same take-off tension
on all loops and all yarn types
cannot be maintained.
Ensure optimal design of
knitting patterns according to
machine type.
▪ Thick and thin places in yarn Check the quality of the yarn.
▪ Yarn with excessive hairiness Use yarn with low hairiness.
▪ Too high yarn twist level
causing the yarn to kink, which
changes the yarn tension and
diameter.
Use optimal twist levels in yarn.
Cloth fall-out
or runners
Yarn is not stitched by several
adjacent needles. Occurs after a
dropped stitch. The yarn from the
hooks of the subsequent needles is
removed due to the impact of an
empty needle with a closed latch
with yarn feeder. Yarn breakage
without any immediate
connection.
[216,
272,
274,
275]
▪ Too stiff or brittle yarn Check the humidification
system. Ensure proper
lubrication of yarn
(waxing/oiling).
198
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
▪ Excessive tendency of yarn to
curl
Too high twist levels in yarn.
The twist level in the yarn
should be optimum.
▪ Thick places or knots in the
yarn
Use flat knots. Check the quality
of the yarn.
▪ Too high incoming yarn tension Check the yarn path.
▪ Too low yarn tension during
running.
Check the yarn tension is set
correctly.
▪ Wrong yarn feed and
adjustment
Ensure the right setting for yarn
feeding and adjustment.
▪ Improper setting of the cam
sinking ratio
Use the right setting of the cam
sinking ratio.
▪ Incorrect setting distance
between dial and cylinder
Set the right distance between
the dial and cylinder.
▪ Improper take-off Ensure the fabric take-off
system is working properly.
▪ Defective needle or sinker
elements
Replace the defective needle or
sinker elements.
▪ Improper adjustment or worn
cleaning brushes
Select the right adjustment or
replace the brushes if required.
▪ Machine vibration The machine must be installed
properly and without any
vibrations.
Snagging or
Snags
▪ Specific sensitivity of the
filament yarns
Use yarns with a coarser dpf,
less crimp elasticity, and higher
twist.
[216,
274]
▪ Mechanical strain during the
knitting process due to damage
Avoid rough surfaces on the
knitting machine and ensure the
199
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
to fabric take-off or spreader,
damage to lap rod.
take-off system is in a proper
working condition.
Tuck or double
stitches or
bunch-ups
▪ Insufficient sliding ability of the
yarn due to a high coefficient of
friction. The spinning oils or
waxes are not applied properly.
Ensure proper application of
spinning oils and waxes. Check
the humidity levels of the plant.
[216,
274]
▪ Thick places in yarn Check yarn quality.
▪ Too high dial setting. Dial
needle is not able to support the
fabric and thus pulled up.
Use an optimal dial setting.
▪ Too small needle clearance. The
old loops are not brought safely
behind the latch and remain on
the spoon.
Use optimal needle clearance.
▪ Incorrect setting of course
density. Too tight loops. These
loops are not removed from the
needles.
Check the settings, use correct
settings.
▪ Too weak fabric take-up. It has
a one sided drag or is not
continuous
Must be readjusted to ensure
uniform and continuous fabric
drag.
▪ Damaged needles Replace the damaged needles.
The needles must be replaced
regularly.
Vertical lines
or longitudinal
streaks
▪ Wrong selection of yarn count
according to gauge. Yarn is too
fine for machine gauge.
Select the yarn count according
to machine gauge. For coarse
density check the machine
settings.
[203,
216,
272,
200
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
▪ Incorrect course density/stitch
size
Check the machine settings. 274-
276]
▪ Broken or bent or dirty needles
and needle elements.
Replace the damaged needles.
Implement a proper needle
replacement plan.
▪ Heavily running needles Ensure needle movements is
uniform and smooth. The
needles should be of the same
type.
▪ Dial and cylinder needle
misalignment lead to rubbing of
needles.
Check the alignment of dial and
cylinder needles. Ensure the
correct setting of needles.
▪ Improper setting of yarn guides Check the yarn guides settings
and must be adjusted correctly.
▪ Machine vibration Check machine placement,
installation should be horizontal
and vibration-free.
▪ Spreader abrasion/creasing Check the settings and surface
of the spreader.
▪ Improperly set spacers on take-
up
Spacers must be adjusted
correctly.
▪ Too narrow spreading at take-up
causing folds
Use optimum spreading.
▪ Wrong or mixed needles Select needles according to yarn
count and type. Use same needle
type for same yarn count.
201
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
Barré or
horizontal
stripes
▪ Yarn irregularities or
differences in cross-section.
Fabric’s irregular stripes or
fuzzy appearance is mainly due
to yarn.
Check the yarn quality. The
defects must be within tolerance
limits.
[196,
203,
216,
272,
274-
276] ▪ Yarn running-in tension is not
constant.
Check the settings of the yarn
feeding system, there should be
no hindrance in yarn delivery.
▪ Wrong yarn-size, color, blend
level, twist direction
The yarn package should be
properly numbered and
segregated. Check the quality of
the yarn. Spinning related fault.
▪ Mixing of yarns (a) of different
spinning, raw material or
production batches (b) with
different fiber properties, (c)
from different production types.
Yarn packages should be
properly segregated.
▪ Oiling or waxing of yarn is not
even.
Check the incoming yarn
quality.
▪ Differences in yarn bulkiness,
crimp, and strength
The yarn quality should be
checked regularly.
▪ Fluctuations in bobbin hardness Inspect the yarn packages before
installation.
▪ Deflector in dial cam brought
into a tuck position. The
deflector not completely
switched off. The needle can
The knitting machine must be in
a properly working condition.
202
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
still grip the yarn and form a
tuck loop.
▪ Improper setting of yarn feeder Ensure the correct setting of
stitch size and that yarn
consumption on feeders is
uniform.
▪ Couliering not constant at all
feeders
The yarn drawing-in ratio
between dial and cylinder must
be constant.
▪ Jerks in fabric take-up Ensure that fabric take-up is
uniform and working properly.
▪ Different stitch settings (stitch
lengths)
Check the stitch settings and
ensure they are correct.
▪ Dirt, lint or yarn fragments in
needle elements or faulty needle
selection
The knitting elements must be
cleaned on regular intervals and
needle selection should be
according to yarn type.
▪ Rib dial or needle cylinder
skewness
Check the machine settings.
▪ Differences in sinking depths The sinking depth should be set
correctly.
▪ Machine vibration The machine installation should
be vibration-free.
Soil stripes ▪ Stripes in the direction of wales
are due to the knitting machine.
Mostly, they are called needle
stripes. They are due to the
individual replacement of
The needles should be replaced
at regular intervals and machine
lubrication should be working
properly without leaks or
drippings.
[216,
275]
203
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
needles or defective working of
oiling or greasing device.
▪ Stripes in course direction can
be caused by:
- Soiled places in the yarn
The yarn should be clean and
must be stored in a proper place.
- Standing course due to
machine stoppage
Keep equipment clean all the
time.
- Oil lines Ensure the machine lubrication
system is working properly and
there should be no leaks or
drippings. Oiling quantity
readjustment.
Color fly ▪ Natural remnants present in the
fiber. In the case of wool, hairs
with natural dark colors,
vegetable and food residue,
bast, etc.
It is impossible to completely
avoid these residues and a
certain amount must be
tolerated.
[216]
▪ During different stages from the
spinning process, a color fly can
be embedded in the yarn.
Individual colors during yarn
production must be carefully
separated.
▪ Knitting plant processing a large
number of colors or producing
color jacquards along with
single-colored fabrics with close
machine spacing.
There should be a proper fluff
removal system and colored
articles should be knitted
separately.
Distorted
stitches or
▪ Due to the bad setting of a
knitting machine, mainly
Check the machine settings. The
sinking depth must be adjusted
204
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
skittery
appearance
unequal sinking depths between
dial and cylinder needles. The
heads of stitches in wales are
not round but tilted to either
side. They result in disordered
fabric appearance and most
disturbing in single colored
goods. The fabric appearance is
skittery.
correctly according to article
type.
[203,
216,
274]
▪ Faulty yarn (short term
variations in yarn count, crimp,
thick and thin places)
Check the incoming yarn
quality. The defects should be
within tolerance limits.
Foreign yarn ▪ Worker carelessness Train workers to recognize
different yarn types.
[275]
▪ Presence of the same yarn type
having the same color on the
same creel
Rigorous yarn sorting and
storage system.
Elastomeric
yarn
misplacement
▪ Defective elastic yarn feeder Check the yarn feeding system
and knitting elements.
[275]
▪ Improper setting of elastic roll-
guide
Resetting of elastic roll-guide.
Side crease ▪ High pressure applied by take-
down rolls on the tubular fabric
causing permanent fiber
deformation (e.g. elastane).
Use of take-down rolls with
movable side rubber rings.
[275]
▪ The tubular grey fabric is stored
for a long time
Keep the storage of grey fabric
as short as possible.
205
Table 4.17 (Continued)
Problems Description and probable causes Remedial measures Ref.
▪ Take-down devices not properly
selected
Use of open width take-down
devices.
Spirality Wales follow a spiral bath around
the tube axis, caused due to yarn
or weft knitting machine.
[6,
203]
▪ High number of feeders in the
knitting machine. Due to more
course inclination, increasing
spirality
1. Use a lower number of
feeders if possible.
2. Do tight knitting when
possible.
▪ Uneven working of take-down
equipment leading to uneven
tensioning, spreading and
winding of fabric.
Ensure proper working of fabric
take down equipment.
▪ The yarn used has only one
direction of the twist.
1. The direction of twist is
dependent on the machine
rotation direction. Increase
knitting tightness.
2. The use of ply yarn instead of
single yarn reduces the
spirality.
3. The s- and z-twist yarn must
be alternately fed to feeders.
▪ Very high twist level in yarns The yarn used should have
lower twist values (twist factor).
▪ Unbalanced twist ratio in a plied
yarn
Ensure the twist ratio is
balanced.
206
4.6 Problems caused by water
Water is one of the most important and widely used ingredients of a dyehouse and performs
different functions such as wetting, removal of dirt, fiber swelling and solubility of dyes and
chemicals. It is used in the plant either in boilers (steam supply) or in different wet processing
operations such as desizing, scouring, bleaching, mercerizing and dyeing, etc. There is no common
standard of water required for different applications and it depends on its intended use [277-281].
Many problems in wet processing are caused by the inadequate quality of water. The physical
properties and chemical composition of water need to be monitored on a regular basis. The
important water quality parameters are temperature, pH, suspended solids, and dissolved
substances [100, 278, 281]. Table 4.18 gives the different types of water sources and substances
present in them [277, 278, 281]. It is important to note that the quality of water varies depending
on the source, location, and season [280, 281].
Table 4.18: Sources of water and their constituents.
Sources Color and constituents
Well water Clear; with Ca, Mg, Fe salts and may contain CO2
Swamp water Clear or colored, acidic pH, tannins or other organic residues
Surface water Turbid, with Ca, Mg and other metal salts depending on the
area characteristics and rainfall, variable compositions
Municipal water Generally constant in content. Clear, may contain Ca, Mg and
Fe salts. It also contains treatment chemicals such as chlorine,
alum, copper sulfate, acids, and alkalis.
Water supply for the textile wet processing unit should have a minimum set of requirements
to be considered fit for use in different wet processing operations such as pretreatment, dyeing,
printing, and finishing. The important parameters and the corresponding limits are given in Table
4.19 [231, 282, 283]. In order to meet these standards, water might be treated before it is supplied
to wet processing operations [231].
207
Table 4.19: Requirements of water for textile processing units.
Parameters Tolerances
- Water hardness Total max: 5 dH (17.85 mg/l)
- Suspended solids < 1 mg/l
- Organic load (KMnO4 absorption) < 20 mg/l
- Filterable solids < 50 mg/l
- Solid residues from evaporation < 500 mg/l
- Iron (Fe) < 0.1 mg/l
- Manganese (Mn) < 0.02 mg/l
- Copper (Cu) < 0.005 mg/l
- Nitrate (NO2-) < 50 mg/l
- Nitrite (NO3-) < 5 mg/l
- Chlorine < 1 mg/l
- pH 7-8
- Odor Odorless.
- Color Colorless.
- Free CO2 As close to 0 as possible.
- NaHCO3 Daily monitoring for dyebath pH adjustment.
Different sources of water often have considerable variations in temperature. Ground and
surface water are more prone to this variation compared to a municipal water supply. The pH also
varies depending upon the source. The soft water may be acidic with a pH of ~5 and hard water
may be alkaline in nature approximately around pH 8. The acidic conditions are attributed to the
organic and inorganic acids (in air-free water), sulfuric acid (swamp water) and silicic acid. This
may damage machinery components and cause various problems during processing [100]. Water
may contain a variety of dissolved substances. These substances change the equilibrium of H and
OH ions present in water thereby affecting the pH of water. The pH shift may affect the solubility
of different soluble substances. Water containing a high content of oxygen may interfere with the
processes involving reduction. This also affects pipes and boilers. Deaeration of boiler feed and
208
addition of oxygen scavengers can help in controlling the problems. The carbonic acid in different
states may also be present such as CaCO3, Ca(HCO3)2 and CO2. On heating, bicarbonates are
converted into gas while carbonates are partially precipitated. The free carbonic acid content, in
the form of CO2, increases with an increase in temperature [100].
The water for wet processing should be colorless, clear and free of suspended matters.
Water turbidity is due to suspended particles that can be organic and inorganic. These particles
consist of finely divided vegetable matter, microorganisms, clays, silica, calcium carbonate [282,
284]. The suspended matters may deposit on the cross points of the fabric surface. In yarn or beam
dyeing, the package or beam may act as a filter for water used in the process. Any residue present
in the water will concentrate on the package and result in staining [284]. The suspended matter
may have an acidic character or might be reductive in nature. They may cause dark-colored
precipitation in dyeing from soaps, auxiliaries and dyes, stains like deposits and dully cloudy
dyeings. Also, precipitation in boilers may also be caused. The condensate water may be
contaminated with lubricants that contain oils and grease. This leads to spot-like stains, faulty
dyeing, and many problems in boiler operation [100]. To remove these suspended matters
mechanical or chemical (coagulants) purification may be used. This procedure is followed by
filtration [282, 284].
Another substance found in the municipal water supply is chlorine. Chlorine is highly
reactive and oxidizing in nature. Low levels of chlorine in a dyebath even at low temperatures may
cause dye degradation thus affecting the shade and reproducibility. The chlorine levels in water
may vary depending upon the season. Proper monitoring of dyehouse water is thus essential. The
water supply coming to the laboratory should also be monitored for chlorine and other impurities.
One approach to solve this problem is to select dyes that are stable to chlorine, but this is not
always possible due to shade, fastness requirements and cost. During dyeing, reducing agents may
be added such as sodium thiosulfate or sodium bisulfite where the former is better as its excess
amount does not typically affect dyes. The sequence of adding dyebath chemicals is critical and
reducing agents should be added before dyes [281, 285, 286].
Depending on the source water may also contain different matters in a soluble or insoluble
form such as alkaline and alkaline earth, and heavy metal salts. The common heavy metals found
are iron (Fe), copper (Cu), manganese (Mn), nickel (Ni), Zinc (Zn) or cobalt (Co) with small traces
of aluminum (Al). Alkaline earth salts commonly found are calcium (Ca), and magnesium (Mg).
209
These salts exist in the form of chlorides, sulfates, and carbonates. These metals may interfere with
various processes [277, 281, 283, 286, 287]. In some cases, the presence of alkaline and alkaline
earth salts is favorable. The degradation of starch size by enzymes is favored by calcium salts due
to their activating and stabilizing effect on the enzyme [286, 287]. The presence of magnesium
ions in the bleach liquor has a stabilizing effect along with organic stabilizers [286, 287].
The presence of transition metal ions may cause the following problems:
▪ The presence of Cu and Zn ions deactivates the enzyme and makes sizes insoluble [280,
286, 288].
▪ The presence of Fe, Cu and Mn strongly affect the stability of the bleaching bath. The
catalytic damage leads to pinhole damage and strength loss. The substrate may have a
lower degree of whiteness and yellowing due to oxycellulose formation [277, 280, 283,
286, 289].
▪ Stains on the substrate may be formed due to Fe and Cu deposits [280].
▪ Reduced absorbency, luster and process efficiency may be observed due to the
formation of metal oxides during mercerization [280, 289].
▪ Some anionic dyes may chelate metal ions and cause the shade to become duller [290].
▪ Insoluble complexes or precipitate dyes, especially reds, may be formed that cause
shade change, unlevelness, dull shades, and reduce dye diffusion and result in poor
fastness [280, 290-292].
▪ Bronzing of shades may occur in the case of sulfur dyes [290].
The alkaline and alkaline earth salts lead to many problems which are given below:
▪ The solubility characteristics of different sizes in water containing alkaline and alkaline
earth salts are not the same and vary depending on their chemical structure. The
removal of anionic sizing agents is strongly affected. The sizing agents that may be
affected are polyacrylates, polyester, polyvinyl alcohol, and polyvinyl acetate. The
desizing of polyvinyl alcohol is strongly affected by the presence of sodium chloride
in washing liquor [287].
▪ During alkaline scouring, Ca and Mg ions depend on the alkali form calcium hydroxide,
magnesium hydroxide, calcium carbonate, and magnesium carbonate. These salts have
poor water solubility and may deposit on the scoured yarns or fabric. These deposits
210
affect fabric hand, sewability, knittability, water absorbency, and dirt removal [283,
289].
▪ The products formed by saponification of natural waxes, fats, and oils may be
precipitated in hard water and form sticky deposits on the fabric that lead to spots,
uneven absorbency, and uneven dyeing. It also reduces the efficiency of scouring,
bleaching, mercerizing, and soaping [280, 283, 286, 288].
▪ Poor stability of the stabilizer in peroxide bleaching should be considered. Some
stabilizers are strongly affected as compared to others thus affecting the whiteness and
strength of the material. Stabilizers based on polyhydroxy carboxylic acid show poor
stabilizing effects as compared to those based on soda glass, magnesium sulfate system
[293].
▪ The solubility of surfactants due to the formation of complexes with alkaline and
alkaline earth salts may be reduced. This may cause improper removal of surfactants
during pretreatment. Anionic surfactants may form deposits on fiber surface during
washing [288, 294].
▪ Sodium bicarbonate may be introduced from the ion-exchange method where zeolite
resin absorbs alkaline earth metals ions and replaces it with Na ions. The heating
process during dyeing converts sodium bicarbonate to sodium carbonate. This provides
alkali in the dyeing process before alkali is added in the process. The change in the bath
pH causes premature hydrolysis and early fixation before the migration of reactive
dyes. This leads to unlevel dyeing, lower dye yield, and poor reproducibility [283, 295,
296]. Sodium bicarbonate also has a buffering effect and affects dyebath exhaustion.
The required dyebath pH value may not be reached [297].
▪ The Ca and Mg ions reduce the solubility of dyes and lead to aggregation which may
precipitate on the fiber. The dye in this form cannot migrate or diffuse into the substrate.
This causes low color yields, uneven dyeing, stains, shade change, and machine
deposits. Turquoise and blue dyes are more sensitive to this problem. The crock
(rubbing) fastness is also reduced [280, 290, 292, 296].
▪ Due to the above-mentioned problem, the substantivity of the dyes is increased. Mg
ions have stronger influence as compared to Ca ions due to their higher aqueous
211
solubility. The sensitivity of dye to be affected by hard water depends on its
substantivity. Highly substantive dyes are more affected [283, 298].
▪ The leuco form of the vat and sulfur dyes are very sensitive to Ca and Mg ions and
form insoluble salts. This leads to poor color yield, unlevelness, and poor rub fastness
[290, 292].
▪ Disperse dyes may agglomerate due to the formation of Ca salt with an anionic
dispersing agent present in the disperse dyes [292].
▪ Dull shades and harsh hand may be observed due to the deposits of insoluble Ca and
Mg carbonates on the substrate [277, 283].
▪ Ca ions can result in poor removal of the dye during the rinsing and soaping thus
affecting wet fastness. Nonionic detergents should be used for washing. The
electrolytic effect of anionic detergent affects wash off behavior of reactive dyes
thereby affecting wet fastness properties [277, 283, 296, 298].
▪ Spots on substrate and loss in color yield depend upon the concentration of magnesium
or calcium where the former has a more detrimental effect. Alkali precipitates the
calcium and Mg salts dissolved in water. These precipitates absorb dye and lead to
incomplete utilization of dyebath. Redyeing may be required to achieve the target depth
[298, 299].
The problems mentioned earlier can be minimized using two approaches. The first
approach involves monitoring water supply on a regular basis and the treatment of water to make
it fit for the required process. Sever water treatment methods such as filtration and ion exchange
method can be employed to achieve this objective. In the second approach special chemical known
as a sequestering agent is added during preparation and dyeing processes. Their function is to
suppress the functionality or reaction of polyvalent cations without removing them from the
solution. They achieve this function by forming a complex with a metal ion. There are different
classes of sequestering agents used in different wet processing stages. These are polyphosphonic
acids, amino polycarboxylic acids, polyphosphates, hydro carboxylic acids, polymeric carboxylic
acids. It is important to know that not one type of sequestering agent is suitable for all applications
as they differ in their functionality and properties. The sequestrants differ in terms of their
sequestering power, specific metal sequestering, the effect of temperature and pH on sequestering
212
power and specific metal sequestering, sequestering capacities, stability to oxidation or hydrolysis
and their effect on dyes [278, 290, 292, 300].
It can be concluded that successful wet processing greatly depends on the quality of the
water. It strongly influences the solubility of chemicals and dyes, stability of the system, removal
of impurities, and wash off of unfixed dyes. Several problems in preparation, dyeing, and finishing
that may be caused due to inadequate quality of water along with their possible solutions are shown
in Table 4.20.
Table 4.20: Problems in wet processing associated with water impurities.
Problems Probable causes Remedial measures Ref.
Incomplete
desizing
▪ Deactivation of the enzyme by Cu
and Zn ions
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents
during desizing.
[277,
286,
287] ▪ Insolubility of the sizing materials
due to Ca and Mg ions
Incomplete
removal of
impurities
during
preparation
▪ Reduced activity of the detergent
(cleaning efficiency) due to Ca and
Mg
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents
during preparation.
[277,
286]
▪ Reduction of water sorption due to
Ca and Mg deposits
Decreased
absorbency
▪ Deposits of insoluble Ca/Mg
carbonates/ hydroxides on fabric
formed during scouring due to Ca
and Mg ions
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents
during preparation and
dyeing.
[277,
280,
283,
301]
▪ Formation of insoluble metal oxides
due to the presence of Fe and Cu
Low luster ▪ Formation of insoluble metal oxides
due to the presence of Fe
Use sequestering agents
during mercerization.
[277]
▪ Fe in water due to the bad condition
of water tanks/pipes
Check water tanks and pipes
for rust and clean them.
[301]
213
Table 4.20 (Continued)
Problems Probable causes Remedial measures Ref.
Low degree of
whiteness
▪ Catalytic decomposition of bleach
baths due to Fe and Cu
1. Use magnetic filters in
water lines.
2. Use sequestering agents
during preparation.
3. The demineralization
process may be carried
out depending upon the
severity of the problem.
[277,
279,
280,
282,
283,
286,
301]
▪ Low stability of the bleaching process
due to interaction with Ca ions
▪ Formation of oxycellulose due to Fe
and Cu
▪ Fe in water due to the bad condition of
water tanks/pipes
Check water tanks and
pipes for rust and clean
them.
[301]
Variation in
whiteness
▪ Presence of alkaline earth metals in
fabrics that over stabilizes peroxide
Perform demineralization
of fabric before bleaching.
[301]
Fabric
damage/loss in
strength/
pinhole
formation
▪ Catalytic damage during bleaching due
to Fe and Cu
1. Use magnetic filters in
water lines.
2. Use sequestering agents
during preparation.
3. The demineralization
process may be carried
out depending upon the
severity of the problem.
[277,
282,
283,
286,
301]
▪ Fe in water due to the bad condition of
water tanks/pipes
Check water tanks and
pipes for rust and clean
them.
[301]
Deposits on
fabric
▪ Deposits of suspended matter onto the
cross points of the fabric surface or on
package surface
1. Regularly monitor water
and ensure appropriate
treatment before use.
[280,
282,
294]
214
Table 4.20 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Incomplete removal of anionic and
nonionic surfactants due to the
formation of complexes with Ca and
Mg ions
2. Use sequestering agents
during preparation and
dyeing.
▪ Deposits on the substrate due to the
formation of insoluble Ca and Mg
salts.
Poor
reproducibility
▪ Presence of bicarbonate that converts
into carbonate on heating and
increases dyebath pH
Use acetic acid to partially
eliminate the bicarbonate.
Adjust the pH to 5.5-6.5.
[283,
288,
295-
297] ▪ Buffering effect of sodium bicarbonate
that causes poor dye exhaustion
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents
during preparation and
dyeing.
3. The demineralization
process may be carried
out depending upon the
severity of the problem.
▪ Formation of dye-metal complex or
dye precipitation due to Fe and Cu
▪ Reduced solubility of dye due to the
presence of Ca and Mg ions
▪ Dye aggregation caused by Ca and Mg
ions
▪ White precipitates of Ca and Mg on
the substrate
▪ Degradation of dyes due to chlorine 1. Select dyes that are
stable to chlorine.
2. Use reducing agents
such as sodium
thiosulfate or sodium
bisulfite in the dyebath.
[285,
286]
215
Table 4.20 (Continued)
Problems Probable causes Remedial measures Ref.
Shade change ▪ Chelation of Cu, Fe, and Mn by
anionic dyes resulting in dull or
change in shade
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents
during preparation.
[277,
280,
282,
286,
290-
292,
296]
▪ Formation of insoluble complexes or
precipitation of dyes due to Fe, Cu,
and Mn
▪ Reduced solubility of dye due to the
presence of Ca and Mg ions
▪ Deposits on the substrate due to the
formation of insoluble Ca and Mg salts
▪ Fe in water due to the bad condition of
water tanks/pipes
Check water tanks and
pipes for rust and clean
them.
[301]
▪ Buffering effect of sodium bicarbonate
that causes poor dye exhaustion
Use acetic acid to partially
eliminate the bicarbonate.
Adjust the pH to 5.5-6.5.
[297]
▪ Degradation of dyes due to chlorine 1. Select dyes that are
stable to chlorine.
2. Use reducing agents
such as sodium
thiosulfate or sodium
bisulfite in the dyebath.
[285,
286]
Poor color
yield
▪ Low dye diffusion due to the
formation of insoluble complexes or
precipitation of dyes due to Fe, Cu,
and Mn
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents
during preparation and
dyeing.
[277,
283,
285,
286,
295,
297]
▪ Reduced solubility of dye due to the
presence of Ca and Mg ions
216
Table 4.20 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Deposits on the substrate due to the
formation of insoluble Ca and Mg salts
▪ Formation of dye metal-complex
resulting in a change of shade
▪ Presence of bicarbonate that converts
into carbonate on heating and
increases dyebath pH causing dye
hydrolysis
Use acetic acid to partially
eliminate the bicarbonate.
Adjust the pH to 5.5-6.5.
▪ Buffering effect of sodium bicarbonate
that causes poor dye exhaustion
▪ Degradation of dyes due to chlorine 1. Select dyes that are
stable to chlorine.
2. Use reducing agents
such as sodium
thiosulfate or sodium
bisulfite in the dyebath.
Unlevelness ▪ Formation of insoluble complexes or
precipitation of dyes due to Fe, Cu,
and Mn
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents
during preparation.
[100,
277,
280,
282-
284,
286,
295,
296]
▪ Low diffusion or migration of dye due
to dye precipitation caused by Ca and
Mg ions
▪ Increased substantivity of the dye due
to the presence of Mg and Ca ions
▪ Precipitation of scouring products and
soap by Ca and Mg ions which form
sticky deposits on to the substrate
217
Table 4.20 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Deposits of suspended matter onto the
cross points of the fabric surface or on
package surface
▪ Increased rate of dyeing due to large
quantities of sulfates
▪ Deposits on the substrate due to the
formation of insoluble Ca and Mg salts
▪ Presence of bicarbonate that converts
into carbonate on heating and
increases dyebath pH causing
premature fixation
Use acetic acid to partially
eliminate the bicarbonate.
Adjust the pH to 5.5-6.5.
[297]
▪ Poor reduction of vat and sulfur dyes
due to the higher content of dissolved
oxygen in the water
Use higher quantities of
reducing agent.
[100]
▪ Fe in water due to the bad condition of
water tanks/pipes
Check water tanks and
pipes for rust and clean
them.
[301]
Spots or stains ▪ Formation of insoluble complexes or
precipitation of dyes due to Fe, Cu,
and Mn
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents
during dyeing.
[277,
280,
282-
284,
286,
292,
296,
298]
▪ Reduction in dye solubility leads to
dye precipitation caused by Ca and Mg
ions
▪ Increased substantivity of the dye due
to the presence of Mg and Ca ions
▪ Agglomeration of disperse dyes due to
the formation of Ca salt with an
anionic dispersing agent
218
Table 4.20 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Precipitation of scouring products and
soap by Ca and Mg ions which form
sticky deposits on the substrate
▪ Deposits of suspended matter onto the
cross points of the fabric surface or on
package surface
▪ Deposits of metal salts on the substrate
▪ Emulsion breakage due to the presence
of Ca and Mg ions
▪ Deposits on the substrate due to the
formation of insoluble Ca and Mg salts
[149]
Inadequate
fastness
▪ Poor removal of unfixed dye due to the
presence of Ca and Mg ions
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents
during preparation.
[277,
283,
286,
296,
298,
299]
▪ Lower solubility or precipitation of
dye caused by Fe, Cu, Ca and Mg ions
Poor hand ▪ Deposits on the substrate due to the
formation of insoluble Ca and Mg salts
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents
during preparation.
[282,
283]
▪ Precipitation of scouring products and
soap by Ca and Mg ions which form
sticky deposits on the substrate
Poor
dimensional
stability
▪ Presence of metals ions may cause a
loss in the activity of resins, additives,
catalysts and wetting agents
1. Regularly monitor water
and ensure appropriate
treatment before use.
2. Use sequestering agents.
[277,
286]
219
4.7 Problems caused due to pretreatment
Preparation is one of the important stages in textile processing as good and thorough prepared
fabric largely determines the efficiency and reproducibility of the coloration and finishing
processes. It is recommended that the quality of prepared fabrics should not be compromised by
the cost savings approach, a challenge constantly faced by a dyehouse along with increased
productivity [61, 302, 303]. Approximately 70% of the dyeing faults can be traced back to
inadequate preparation [304]. Many problems of inadequate pretreatment are only visible after the
coloration and finishing process [67, 305]. To achieve trouble-free preparation following specific
areas need to be monitored and assessed on a regular basis, these are [305]:
▪ Greige substrate (yarn/fabric).
▪ Chemicals and auxiliaries.
▪ Water.
▪ Preparation process and control variables.
▪ Pretreated fabric.
The blended yarns and fabrics contain different types of impurities that may hinder the
coloration process [9, 61]. These include size, fats, waxes, proteins, ash, metal salts, vegetable
matter, proteins, spin finishes, weaving and knitting oils, dirt, and colored substances. The main
goal of the preparation step is to remove impurities and contaminations for the successful
application of dyes and pigments. In addition, chemical and physical modification of the fibers
may also be performed [303, 306, 307]. To meet these goals, it is important to know the different
substances present in the substrate such as types (mineral oils, silicone oils, etc.) and amount of
oils, type and amount of inorganic impurities. By having this knowledge correct pretreatment steps
can be selected, and correct chemical products may be chosen to deal with these substances [308].
The quality of chemicals and auxiliaries should not be taken for granted. This is not true
always and can cause problems during pretreatment. The strength and activity of the product may
vary from lot to lot due to small variations in the manufacturing process, improper dilution or
decomposition of the product. The concentration of chemicals used in pretreatment is set based on
their strength and activity. If the product has lower strength and activity it may lead to inadequate
pretreatment. It is important to analyze each lot of chemicals and auxiliaries before use. This is
usually performed in a laboratory. The chemicals and auxiliaries should also be tested for
220
functionality under actual conditions encountered in a process they will be used. The standards
methods are available that can be used for analysis [305]. The chemicals should also be analyzed
for impurities that may create problems during preparation e.g. iron content in caustic [138].
Table 4.21: Requirements to be fulfilled by pretreatment.
Chemical Physical (mechanical)
▪ Thoroughness and consistency of effects,
levelness.
▪ High absorbency.
▪ Higher degree of whiteness.
▪ Complete removal of size.
▪ Absolute absence of husks/vegetable
matter.
▪ Reduction of impurities and contaminants
to very low levels.
▪ Minimum or no damage to the material.
▪ Neutral pH.
▪ High dye-absorbing power (high color
yield).
▪ Complete removal of processing
chemicals (surfactants, bleaching agents
and caustic).
▪ Good dimensional stability.
▪ Absence of wrinkles and creases.
▪ Constant residual moisture content.
Uniformity is the key to preparation. Inconsistent pretreatment is more problematic than
insufficient absorbency, whiteness or mote removal. Many problems in dyeing and finishing
originates from preparation, these include unlevelness, spots, shade variations, holes and lower
strength [9, 64, 94, 308]. Table 4.21 enlists the requirements that need to be met by the preparation
step to avoid problems in subsequent processing [63, 302, 303, 309]. These are the requirements
for a substrate based on cotton and cotton blends and may vary whether the prepared substrate
needs to be dyed, printed or finished white. For example, a fabric that is to be dyed in the dark
221
shade does not require a very high degree of whiteness. Similarly, the needs of dyer using pigment
coloration on polyester/cotton blend can be different from that of dyer who is dyeing
polyester/cotton blend with disperse and reactive dyes [310]. The fabric pH is also critical as it
may directly influence the dyeing process [93, 94]. For blends, hydrophobic fibers tend to absorb
less liquor hence associated fibers in the blend such as cellulosic fibers should have high
absorbency [133]. Additionally, all acid, alkali, chlorine and peroxide residues should be
completely removed.
The pretreatment stage is constantly faced with a challenge of varying substrate qualities
but must have to meet the quality requirements in time and without reprocessing. The blends add
to this problem as impurities level and sensitivity of the individual fibers in the blend to different
pretreatment steps need to be considered [68].
The pretreatment involves several steps, depending on the material composition, one or
several pretreatments may be necessary. The pretreatment of synthetic materials is simple and
involves washing and setting [68]. The bleaching process is optional and may be employed where
higher whiteness is desired. Table 4.22 shows the possible steps involved in the preparation of
fiber blends. As shown due to differences in the nature of the material involved not all steps are
required [311, 312]. Each fiber in the blend has different properties that must be taken into
consideration during their processing by selecting the appropriate process sequence [67]. These
steps can be carried out by either batch or continuous process depending upon the availability of
machines and material suitability [9]. Woven materials are generally processed by the continuous
method while knitted fabrics are more suitable by batch methods [63]. The different processes
carried out in the preparation of woven polyester/cotton blend fabrics include singeing, enzymatic
desizing, alkaline scouring and bleaching, mercerizing and heat setting. Different fabric types are
prepared by this route and include home textiles, shirting, light suiting, rainwear, workwear, and
uniforms. Most of these treatments only remove surface impurities from the polyester component
in the blend as little penetration is achieved by the alkaline solution [9, 63]. However, the surface
saponification and reduction in denier may take place under highly alkaline and higher temperature
conditions that may be employed during scouring and mercerization of cotton based materials. The
concentration of alkali and process conditions must be adjusted accordingly [68]. The regenerated
cellulosic fibers differ in their wet stability and alkali resistance. Although they can be pretreated
222
similarly, special care must be given to viscose which has a lower wet strength and alkali stability
than lyocell and modal [311, 312].
Table 4.22: Possible steps in the preparation of blended materials.
Pretreatment process Fiber blends
PES/Co PES/CV PES/Wo Co/PA EL blend
Singeing x x x x
Desizing x x x x
Demineralization x x
Acid treatment x x
Washing x
Scouring x x x x
Combined scouring and
bleaching x
x
Crabbing x
Bleaching x x x x
Mercerizing x
Causticizing x x
Heat setting x x x x
PES=Polyester, Co=Cotton, CV=Viscose, Wo=Wool, PA=Polyamide, EL=Elastane
x: represents pretreatment process performed for the particular blend
223
4.7.1 Problems caused during singeing
The fabrics made of staple blends are singed to remove protruding fibers to produce a smooth and
clean surface and reduce the possibility of skittery appearance and pilling tendency. Singeing can
be performed on yarn, knitted and woven fabrics [9, 63, 64, 149, 168, 313].
Gas singeing is the commonly used singeing technique used nowadays that uses a flame to
burn the protruding fibers without damaging the firmly bounded fibers in the fabric. Before
singeing, the fabric is passed through a brushing and cleaning system for removal of dust and
loosening of surface fibers [68, 314]. The fibers due to their inherent nature show two distinct
behaviors when exposed to gas flames exothermic and endothermic. The former continues to burn
once ignited and the later requires continuous supply to burn. Cotton, wool, and viscose exhibit
exothermic nature while polyester and nylon show endothermic behavior respectively. The
polyester fiber melts at 250-260 oC and ignites at 480-500 oC. To burn the polyester and prevent
melting which cayuse bead formation, energy must be supplied in shock form. This creates a real
challenge in the singeing blends composed of fibers having different burning behaviors. The most
sensitive fiber in the blend determines the singeing process. The balance needs to obtained between
the thoroughness of singeing and over singeing [313-317].
The factors affecting singeing are [63, 168, 313, 314]:
▪ Flame intensity;
▪ Angle of contact between flame and fabric (singeing position);
▪ Fabric or singeing speed; and
▪ Distance between burner and fabric.
In modern singeing machines to prevent fiber damage fabric temperature is continuously
monitored. If the fabric temperature is increased beyond the threshold value the flame intensity is
reduced. The blends of polyester with wool and cotton can be heated up to 150 oC without any
damage [313, 318]. The singeing machine usually has an impregnation unit following singeing
operation on economic grounds that may be used for the application of desizing or bleaching liquor
depending upon the process [67, 314].
It is recommended to singe fabric after dyeing if the fabric is to be dyed by a batch process.
This is due to the formation of beads of molten fibers due to the insufficient supply of energy that
causes the synthetic fiber to melt instead of burning. The fiber beads absorb more dye as compared
224
to the rest of the fiber. This may cause dark spots and unlevelness depending on the severity [133,
253, 313, 316, 317]. This problem is generally not observed in thermosol dyeing. These fabrics
can, therefore, be singed before dyeing. For fabrics singed after dyeing, the dye selection is critical
to avoid unlevel dyeing [67].
Table 4.23: Problems caused during singeing, its causes and remedial measures.
Problems Probable causes Remedial measures Ref.
Uneven
singeing
▪ Incorrect singeing position Use correct singeing position
according to fiber blend and fabric
construction.
[313]
▪ Inadequate flame intensity Use correct flame intensity according
to fiber blend and fabric construction.
[313]
▪ Variation in flame height 1. Ensure the flame height is constant.
2. Clean the burner regularly.
3. Check burner for clogged areas.
[149]
▪ Incorrect or variation in
fabric speed
Correct fabric speed to provide
adequate flame contact time.
[149]
▪ Too high moisture content
in the fabric
Ensure the residual moisture content of
the fabric according to fiber type and
blend ratio (moisture regain).
[67,
149]
▪ Presence of raise and
depressed areas in fabric
1. Ensure the fabric is smooth and
properly open before it enters the
singeing zone.
2. Check the proper working of the
expander and edge guiders.
[149]
▪ Presence of creases in the
fabric
The entry should have an expander
roller to ensure crease-free entry.
[67,
149]
225
Table 4.23 (Continued)
Problems Probable causes Remedial measures Ref.
Uneven
singeing
across the
fabric width
▪ Uneven flame height or
intensity across the fabric
width
1. Ensure the flame height and
intensity is the same across the
fabric width.
2. Clean the burner regularly.
3. Check burner for clogged areas.
[313,
315,
319]
▪ Fluctuation in the moisture
content of the fabric along
the width
1. Ensure the residual moisture
content of the fabric is uniform.
2. The fabric should be stored and
transported properly.
▪ Inadequate setting of the
guide rollers
Ensure guide rollers are properly
aligned.
▪ Uneven smoke evacuation
over the burners
Check the exhaust system is working
properly.
Uneven
singeing
across the
fabric length
▪ Differences in the fuel
mixture supply to the burner
Ensure a uniform supply of the fuel
mixture to the burner.
[313]
▪ Fluctuation in the flame
outlet of the burner
Ensure the flame intensity remains
the same throughout the process.
▪ Variations in the fabric
speed
Use constant fabric speed according
to fiber type and fabric construction.
▪ Fluctuation in the moisture
content of the fabric along
the length
1. Ensure the residual moisture
content of the fabric is uniform.
2. The fabric should be stored and
transported properly.
Horizontal
stripes or
bands
▪ Eccentric or improper
alignment of the rollers
Ensure guide rollers are properly
aligned and centric according to
burner position.
[313]
▪ Sudden increase in fabric
tension
Ensure the compensators and guide
rollers are working properly
226
Table 4.23 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Redeposition of beads on the
fabrics collected on the
guide roller
Clean the guide rollers regularly. [315]
Vertical
stripes or
bands
▪ Partial blockage of burner
outlet
Clean the clogged burner outlet. [313,
320,
321]
▪ Fluctuation in flame outlet
of the burner
Ensure the flame intensity remains
the same throughout the process.
[321]
▪ Presence of creases in the
fabric
The entry should have an expander
roller to ensure crease-free entry.
▪ Incorrect stitching of fabric
ends leading to the
formation of creases.
Check the fabric ends are properly
stitched without any creases
[322]
▪ Selvage curling Ensure the proper adjustment and
functioning of the edge guiders.
Poor hand ▪ Long contact time between
flame and fabric
Check the fabric speed and flame
intensity. It should be selected
according to the fabric weight and
blend ratio.
[168,
313,
318]
▪ Using higher flame intensity Use correct flame intensity according
to fiber blend and fabric
construction.
▪ Long contact time between
flame and fabric due to
slower fabric speed
Increase fabric speed to provide
appropriate contact time between the
flame and fabric.
▪ Deep penetration of the
flame into the fabric
Adjust the distance between the
fabric and the burner. It should be 6-
8 mm.
[149]
227
Table 4.23 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Inappropriate singeing
position
Use an appropriate singeing position.
▪ Deformation of synthetic
fibers under tension
immediately after singeing
Ensure cooling of the fiber
immediately after singeing.
[149]
▪ Cooling system of the guide
rollers in the singeing zone
is not working properly.
Ensure the water circulation system
for cooling of the guide roller is
working properly.
▪ Thermal damage of the size
(PVA) causes it to become
hardened and difficult to
remove during desizing.
1. Check the fabric speed and flame
intensity. The contact time should
be as low as possible.
2. Perform singeing after desizing for
heat-sensitive size, if possible.
[67,
149]
Reduction in
strength
▪ Long contact time between
flame and fabric due to
slower fabric speed
Increase fabric speed to provide
appropriate contact time between the
flame and fabric.
[168,
313]
▪ High flame intensity Use correct flame intensity according
to fiber blend and fabric
construction.
[149]
▪ Deep penetration of the
flame into the fabric
Adjust the distance between the
fabric and the burner. It should be 6-
8 mm
[149]
▪ Inappropriate singeing
position
Use correct singeing position
according to fiber blend and fabric
construction.
[149]
Dark spots ▪ Formation of beads due to
insufficient supply of energy
that dye darker.
1. Use high-energy non-luminous
flame.
[68,
133,
253,
228
Table 4.23 (Continued)
Problems Probable causes Remedial measures Ref.
2. Use correct flame intensity,
singeing position and fabric speed
according to fiber blend and fabric
construction.
3. Avoid grey singeing. Singe fabric
after dyeing for fabrics to be dyed
by a batch process.
313,
316-
318]
▪ Redeposition of the burned-
out fiber on the fabric
surface
1. Ensure proper brushing of the
fabric before and after the
singeing process.
2. Exhaust blower system should in
proper working order.
[323]
Dark areas ▪ Damage/melting of synthetic
fibers during singeing that
dye darker
1. Use high-energy non-luminous
flame.
2. Use correct flame intensity,
singeing position and fabric speed
according to fiber blend and fabric
construction.
3. Correct fabric speed to provide
adequate flame contact time.
[149]
Unleveleness ▪ Insufficient supply of energy
that causes beads formation
1. Use high-energy non-luminous
flame.
2. Use correct flame intensity,
singeing position and fabric speed
according to fiber blend and fabric
construction.
[318]
229
Table 4.23 (Continued)
Problems Probable causes Remedial measures Ref.
3. Avoid grey singeing. Singe fabric
after dyeing for fabrics to be dyed
by a batch process.
▪ Morphological changes in
synthetic fibers due to high
temperature in singeing that
dye differently than
unchanged areas.
Check the fabric speed and flame
intensity. It should be selected
according to the fabric construction
and blend ratio.
[68,
318]
▪ Dark dyeing of protruding
fibers compared to the base
fibers due to unenven
singeing
1. Ensure the singeing is uniform by
proper selection of flame intensity,
singeing machine and fabric speed.
2. Ensure the fabric is dry and have
uniform residual moisture.
Poor color
yield
▪ Presence of protruding fibers
due to improper singeing
gives a lighter perception
1. Ensure the singeing is uniform by
proper selection of flame intensity,
singeing machine and fabric speed.
2. Ensure the fabric is dry and have
uniform residual moisture.
[319]
Streaks/ bar ▪ Damage of a large number
of polyester fibers during
singeing that dye lighter by
continuous dyeing
1. Use high-energy non-luminous
flame.
2. Use correct flame intensity,
singeing position and fabric speed
according to fiber blend and fabric
construction.
[149]
▪ Damage of synthetic fibers
during singeing that dye
darker by batch dyeing
Two
sidedness
▪ Uneven singeing of the face
and back of fabric due to
Ensure the same settings for both of
the singeing burners.
[317]
230
Table 4.23 (Continued)
Problems Probable causes Remedial measures Ref.
differences in settings of the
two singeing burners
Light areas ▪ Thermal damage of the size
(PVA) causes it to become
hardened and difficult to
remove during desizing.
1. Check the singeing speed and
flame intensity. The contact should
be as low as possible.
2. Perform singeing after desizing for
heat-sensitive size, if possible.
[67,
149]
Pilling ▪ Improper singeing of fabric.
The protruding fibers may
lead to pill formation
Use correct flame intensity, singeing
position and fabric speed according
to fiber blend and fabric
construction.
[317,
320]
Poor
appearance
▪ Due to uneven singeing and
may be random or
directional depending on the
severity
Use correct flame intensity, singeing
position and fabric speed according
to fiber blend and fabric
construction.
[67,
149]
4.7.2 Problems caused during desizing
Desizing process is carried out to remove sizing chemicals from woven fabrics. For cellulosic
fibers, it also aims to perform some precleaning with initial swelling. This is required for uniform
bleaching, even dyeing, and soft hand [100, 324]. A typical size mixture may contain film-forming
compounds (size), softeners, plasticizers, and antiseptics. For effective size removal, it is important
to know the type of size used on warp yarns. This is essential to avoid problems in subsequent
processes as weavers regularly change sizing formulation to optimize the weaving process without
notification to the dyer [64, 325, 326]. Often the size used is a mixture of different size, the desizing
recipe should be adjusted based on the most difficult size to remove [306, 326].
231
Table 4.24: Sizing agents and their removal processes.
Size Removal
mechanism Chemicals Process Precautions
Native starch Enzymatic α-amylase CPB, Pad
steam,
Immersion
Aged or
crystalizes starch
difficult to
dissolve Alkaline
Oxidative
Persulphate,
peroxide
CPB
Acidic Oxalic, sulfuric or
hydrochloric acid
CPB
Tapioca starch Alkaline
Oxidative
Persulphate,
peroxide
CPB Oxidative and
acidic
decomposition
only
Acidic Oxalic, sulfuric or
hydrochloric acid
CPB
CMC Swelling Detergents Wash off (all
process)
Rapid increase in
viscosity after
dissolving
PAC Swelling
(alkaline)
Detergents Wash off (all
process)
Sensitive to acid
PVA Swelling
(neutral)
Detergents Wash off (all
process)
Sensitive to alkali
and heat
PES Dispersion Detergents Wash off (all
process)
Sensitive to
electrolytes and
alkali
Fatty substances
& additives
Emulsification Detergents Wash off (all
process)
Table 4.24 shows the different types of size and their corresponding removal methods.
Batch, semi-continuous (CPB) and the continuous process can be employed. The starch and starch-
based size can easily be removed by enzymatic or oxidative methods usually by pad-batch process
232
immediately following singeing. Most of the synthetic size is soluble in water but they are difficult
to remove due to film formation. Singeing and heat setting of the sized fabric (especially containing
PVA) can make their removal more challenging if the size is exposed to very high temperature or
for long duration [303, 306, 307, 324-329]. They are generally removed by hot water though they
are more sensitive to pH as compared to natural size and may coagulate creating problems in their
removal [64, 306, 325, 329]. The factors affecting size removal are [327, 328]:
▪ Viscosity of the size in solution;
▪ Ease of dissolution of the size film on the fiber;
▪ Concentration of applied size;
▪ Drying and storage conditions;
▪ Nature and amount of size auxiliaries (paraffin, tallow, waxes, fungicides);
▪ Fabric construction;
▪ Selection of desizing chemicals;
▪ Method and nature of washing-off; and
▪ Washing temperature and pH.
The residual size can cause different problems in subsequent processes. These include
resist areas, poor wettability, reduction in dye yield, precipitation in dyebath, the formation of
creases and poor hand. The origin of these problems can be classified into two groups as sizing
and process problems. The first problem has origin in sizing process. Larger quantities of waxes
and lubricants that are difficult to emulsify, higher size content, over drying of sized yarns, and
variations in drying temperature are some of the challenges. Process problems include poor wetting
and lower pickup, less swelling of size, variation in dwell time, deactivation of enzyme, drying of
edges during dwelling and ineffective washing [100, 317, 326, 329]. The problems in subsequent
processes attributed to desizing along with their causes and remedial measures are given in Table
4.25.
233
Table 4.25: Problems caused during desizing, its causes and remedial measures.
Problems Probable causes Remedial measures Ref.
Incomplete
removal of
size
▪ Variation in bath pH or
incorrect bath pH
1. Check the bath pH before the
start of the process.
2. Monitor the water pH regularly.
3. Ensure the post-cleaning after
singeing is working properly.
Singeing dust may fluctuate the
bath pH.
[67,
149,
305-
307,
324,
328,
329]
▪ Variation in
bath/impregnation
temperature
Ensure the bath temperature is
followed according to the process
guidelines and must be constant
throughout the process.
▪ Lower liquor pickup 1. Reduce the padder pressure.
2. Use wetting and aerating agent.
▪ Variation in dwell/treatment
time and temperature
The batching and treatment should
be constant according to the
process guidelines.
▪ Use of live steam for heating
of bath leads to the
deactivation of an enzyme
Avoid direct heating of the bath.
Use indirect steam heating if
possible.
▪ Poor quality of the wetting
agent
Check the stability of the wetting
under desizing conditions
(temperature and pH).
▪ Poor compatibility of wetting
agents with other chemicals
in the desize bath
Check the computability of
wetting agents with the desize bath
chemicals in the lab before bulk
processing.
234
Table 4.25 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Poor quality of water 1. Monitor the quality of water
regularly.
2. Use a sequestering agent.
▪ Presence of contaminants in
the bath (peroxide etc)
Ensure proper cleaning of the
machine after the change in the
process.
▪ Wrong washing pH Use the correct washing bath pH
according to the type of sizing
agents. The synthetic sizing agents
are sensitive to pH variation and
may coagulate.
▪ Wrong washing temperature Use correct washing bath
temperature according to the type
of sizing agents. High washing is
temperature is preferred for
washing of the size and degraded
size fragments.
▪ Hardening of size from
previous heat treatment
(singeing and/or heat setting).
1. Check the fabric speed and
flame intensity. The contact time
should be as low as possible.
2. Perform singeing after desizing
for heat-sensitive size, if
possible.
3. Avoid heat setting of fabric
containing PVA size.
Incomplete
removal of
▪ Variation in liquor pickup
along the fabric width
Check the padder pressure across
the fabric width.
[128,
305]
235
Table 4.25 (Continued)
Problems Probable causes Remedial measures Ref.
size across the
width
Incomplete
removal of
size along the
length
▪ Variation in liquor pickup
along the length
Ensure the padder pressure remains
consistent throughout the padding
process.
[128,
305]
Uneven
removal of
size
▪ Poor quality of the wetting
agent
Check the stability of the wetting
under desizing conditions
(temperature and pH).
[305]
▪ Incorrect selection of wetting
agent having a lower cloud
point than the process
temperature
Check the stability of the wetting
under desizing conditions
(temperature and pH).
▪ Uneven pickup of the
desizing chemicals due to
lower bath levels
Ensure the level sensor is working
properly.
▪ Variation in treatment/dwell
temperature
Follow the treatment/dwell time
procedures according to the
manufacturer’s recommendation.
▪ Variation in the washing
process (pH, temperature and
time)
Follow the wash process according
to the manufacturer’s
recommendation.
▪ Presence of water or
condensation drops in the
fabric
Ensure the fabric should be dry and
free of any moisture drops.
Unlevelness ▪ Incomplete removal of size Check desizing conditions. Ensure
required time, temperature and pH
[100]
236
Table 4.25 (Continued)
Problems Probable causes Remedial measures Ref.
according to size type must be
followed.
▪ Wrong selection of detergent Select detergent with good wetting
and emulsifying properties.
[309]
Resist areas ▪ Incomplete removal of size Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[100,
317]
▪ Coagulated PVA or PES size Ensure the required pH is
maintained during desizing to
avoid coagulation.
[100,
329]
▪ Inadequate removal of oils,
grease, and waxes due to
wrong selection of detergent
Select detergent with good wetting
and emulsifying properties.
[309]
Light
stains/areas
▪ Incomplete removal of oil
stains from the fabric
Use special surfactant intended for
oil stain removal. The fabric
should not be allowed to dry before
washing off.
[67,
100]
▪ Inadequate removal of size. Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[100]
Dark stains ▪ Incomplete removal of grease
stains from the weaving
process containing graphite
residues
Use a surfactant with good oil
emulsifying properties.
[100]
237
Table 4.25 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Incomplete removal of rust
stains from transport and
storage
Select the complexing agent
according to its ability to remove
rust. Perform demineralization if
required.
[100,
149]
Size stains ▪ Coagulated PVA or PES size Ensure the required pH is
maintained during desizing to
avoid coagulation.
[100,
329]
▪ More pickup of the dye by
the residual size
Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[325]
Lower color
yield
▪ Reduction in dye pickup due
to lower absorbency caused
by residual size
Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[67,
100,
326,
329]
▪ Reaction of reactive dyes
with the residual size
Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
▪ Presence of hydrolyzed starch
that may act as a reducing
agent
Use a mild oxidizing agent during
dyeing.
Insufficient/
reduced
absorbency
▪ Presence of residual size. Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[100,
309,
326]
▪ Wrong selection of surfactant Select surfactant with good wetting
and emulsifying properties.
238
Table 4.25 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Setting of tint due to salt used
in enzymatic desizing
Check the tint used in fabrics.
Avoid using salt in the fabric
containing tint.
[150]
Creases ▪ Inadequate size removal Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[100]
▪ Incorrect stitching of fabric
ends leading to the formation
of creases
Ensure proper stitching of the
fabric ends with the correct thread
type.
[322]
Streaks ▪ Incomplete removal of the
size from the warp yarns
Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[149,
150]
Poor hand ▪ Inadequate size removal Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[100,
326]
Luster
differences.
▪ Presence of residual size Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[150]
Inadequate
fastness
▪ Holding up of dye on the
fiber surface due to the
presence of residual size
Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[326]
239
Table 4.25 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Thermomigration of the
disperse dyes to the residual
size.
Check desizing conditions. Ensure
required time, temperature and pH
according to size type must be
followed.
[67]
Insufficient
removal of
metal ions
▪ Incorrect selection of a
sequestering agent
Select the sequestering agent based
on its chelation power for metal
ions under desizing conditions.
[309]
4.7.3 Problems caused during scouring
Natural fibers contain many natural impurities such as fats, waxes, protein, pectin, seed husks,
alkaline earth, and heavy metals. Manufactured fibers and yarns during processing are treated with
spin finishes and lubricating agents to enhance their running behavior in spinning, knitting or
weaving processes. These substances inhibit rapid wetting, absorbency, and absorption of dyes
and chemicals. The scouring process is carried out to remove impurities found in textile materials.
In cotton containing fabrics, softening and swelling of seed husks also take place. This is essential
for a good appearance. Several mechanisms that may take place during scouring are saponification,
emulsification, solubilization, hydrolysis, and dissolution. Along with caustic or sodas ash, several
other auxiliaries like surfactants and sequestering agents are required [149, 277, 278, 297, 303,
305, 317, 327].
Incomplete removal of oils, waxes, size leads to resist areas in the dyed fabric. The
redeposition of impurities during the preparation process may also cause this problem. These are
only visible after the dyeing process and therefore difficult to resolve [305, 317]. It is
recommended the check the residual oils, waxes, and spin finish levels in the fabric containing a
higher proportion of synthetic fibers. Many spin finishes used are a combination of products of
varying melting points. The different combinations of anionic and nonionic scouring agents may
be required for their proper removal. The spin finish in some cases may contain nonionic surfactant
that can cause foaming with scouring surfactants. Severe foaming can lead to pump cavitation,
rope tangling, and stoppages. The best solution is to drain the bath immediately and does not
240
immediately add defoamer as it makes the situation worse instead of making it better due to the
formation of hard scum that is difficult to remove [297]. The cloud point of these surfactants is
lower than the temperature typically encountered in disperse dyeing. If they are not removed
properly during scouring, they may precipitate cause instability of dye dispersion which leads to
poor colorfastness [109]. If the foaming is less it may be advisable to add defoamer [297].
A typical scouring recipe for cotton blends consists of caustic soda or soda ash, surfactant
and sequestering agent [301]. The amount of chemicals is reduced as compared to 100% cotton
based on the proportion of manufactured fibers in the blend [312]. The surfactant should be stable
under alkaline conditions. Not all surfactant types are stable hence penetration of alkali for
saponification inside the fiber is hindered. The emulsification of wax is also affected due to poor
detergency and dispersing properties [301]. Both exhaust and continuous methods are available
for scouring. The batch process can be done on winches or jets using anionic detergents and soda
ash at 70-80 oC [9, 305]. The continuous process is usually performed wet on wet on continuous
pad-steam range. J-box type system is not suitable for polyester/cotton blends due to the formation
of the crease by the thermoplastic polyester component [317]. The parameters affecting the
scouring process are given as follows [63, 303, 305]:
▪ Chemical concentrations (caustic soda, soda ash);
▪ Type and concentration of auxiliaries;
▪ Stability and computability of surfactants;
▪ Wet pickup;
▪ Liquor levels;
▪ Liquor feed rates;
▪ Reaction time;
▪ Treatment temperature;
▪ Exclusion of air;
▪ Water flow rates;
▪ Washing temperature;
▪ Final pH;
▪ Degree of drying;
▪ Moisture content of incoming fabric; and
▪ Residual size level of incoming fabric.
241
The scouring process in addition to the removal of impurities also helps in the relaxation
of fabric. The fabric shrinks due to residual stresses from previous processes. Uneven shrinkage
due to differences in heat history, variation in yarn twist and count may cause puckering. In rope
processing on jets, attention should be given on the possibility of crease formation [81].
After the scouring process, the fabric should be tested for wetting out the behavior of fabric
to ascertain the thoroughness of scouring. A water drop test can be used as a measure. The
polyester/cotton usually have less absorbency than cotton fabrics. This test is more applicable if
the polyester portion in the blend is less than 50%. The fabric should be tested systematically at
different points along the width (side – center – side) and length [305]. The main problems
associated with the scouring process along with probable causes and suggested corrections are
given in Table 4.26.
Table 4.26: Problems caused during scouring, its causes and remedial measures.
Problems Probable causes Remedial measures Ref.
Inadequate
scouring or
absorbency or
removal of
impurities.
▪ Inadequate impregnation
temperature.
Ensure proper heating of
impregnation liquor.
[305,
323]
▪ Lower liquor pickup. Use a wetting agent.
▪ Higher levels of residual
moisture in the fabric
causing dilution of
chemicals.
Ensure the residual moisture of the
fabric as low as possible in the wet-
on-wet application.
▪ Inadequate
steaming/treatment time.
Main proper steaming/treatment time
depending upon blend ratio and
fabric type.
▪ Inadequate washing
temperature
Check the temperature settings for
the washing chamber.
▪ Inadequate concentration
of chemicals
Use the proper concentration of
scouring chemicals (alkali and
detergent).
242
Table 4.26 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Poor quality of surfactant Check the stability of the wetting
under scouring conditions.
▪ Incorrect selection of
surfactant having a lower
cloud point than the
process temperature
Select anionic surfactant or use
non-ionic surfactant with a higher
cloud point.
Uneven scouring
or absorbency or
removal of
impurities across
the width.
▪ Variation in liquor pickup
along the fabric width
Check the padder pressure is
uniform across the width.
[305]
Uneven scouring
or absorbency or
removal of
impurities across
the length.
▪ Variation in chemical feed
rates to the impregnation
trough
Ensure the dosing system is
working properly. Ensure the
concentration bath by titration.
[305]
▪ Variations in the moisture
content of the incoming
fabric
Check the squeeze pressure of the
washing unit. The pressure should
be constant to maintain similar wet
pickup levels.
Nonuniform
scouring or
absorbency or
removal of
impurities
▪ Incorrect selection of
detergent having a lower
cloud point than the
process temperature
Select anionic detergent or use
non-ionic surfactants with a higher
cloud point.
[305]
▪ Poor quality of surfactant Select surfactant with good
wetting and emulsifying
properties.
▪ Incorrect selection of
sequestering agents for
Select sequestering with good Ca
and Mg complexing properties.
243
Table 4.26 (Continued)
Problems Probable causes Remedial measures Ref.
sequestering Ca and Mg
ions
▪ Uneven distribution of the
chemicals in the
impregnation trough
Check the liquor distribution
system is working properly.
▪ Presence of water or
condensation drops in the
fabric
Ensure the fabric should either be
dry or should have a uniform
moisture level.
▪ Variation in the washing
process (temperature and
time)
Ensure the required dwell time and
the temperature is maintained
during the washing process.
▪ Nonuniform removal of
size
Check the desizing conditions.
Spots ▪ Incomplete removal of fats,
waxes and knitting and
weaving oils
Ensure optimum scouring
conditions for the effective
removal of fats, waxes, and oils.
[67]
Reduced strength ▪ Damage of wool
component due to strong
alkali used in scouring.
Use mild alkali such as soda ash
for scouring of blended fabrics
containing wool.
[67]
▪ Damage of cellulose due to
atmospheric oxygen and
alkali
Ensure the steam level is properly
maintained inside the steamer.
Maintain slight overpressure.
[70]
▪ Too high concentration of
scouring chemicals or too
long treatment/steaming
time causing higher weight
loss
Use a proper concentration of
chemicals as per the blend ratio.
Maintain required
treatment/steaming time.
[323]
244
4.7.4 Problems caused during bleaching
Bleaching is carried out to destroy the natural and acquired coloring matter in the fiber and bring
it to a white state. Natural fibers contain natural colored pigments that are destroyed by the
bleaching process. This is accompanied by the removal of residual size, fats and waxes and in the
case of cotton seed husks are also removed. In comparison to natural fibers, manufactured fibers
contain no natural coloring matter and impurities (pectin, seed husks). For most cases scouring
process is enough but in some cases where higher whiteness is required bleaching may be required
[277, 278, 305, 317, 327].
There are two types of bleaching system, oxidative and reductive. Oxidative bleaching
includes peroxide, hypochlorite, chlorite and peracetic acid. In a reductive system either
hydrosulfite, sulphoxylates may be used. It is important to note that one type of bleaching agent
that is suitable for one fiber may not be appropriate for other fibers as shown in Table 4.27. The
polyester fibers cannot be bleached with hydrogen peroxide hence the degree of whiteness and
final shade of white after preparation depends on inherent whiteness and luster of the polyester
fiber. Alternatively, sodium chlorite can be used for polyester bleaching but due to environmental
reasons, this process cannot be used [63]. The bleaching process is necessary for blended fabrics
containing cellulose fibers. Nylon containing fabrics may also need bleaching if fabric turns yellow
during the setting process [133].
Table 4.27: Bleaching agents and their suitability for different fibers.
Bleaching agent Fibers
Co PES PA PAN EL
Hydrogen peroxide I N P N I
Sodium dithionite N N I N I
Sulfoxylate formaldehyde N N I N I
Sodium hypochlorite I N D D D
Sodium chlorite I I N I D
Peracetic acid N D N D D
I=Important, N=Not important, D=no effect, damaging, P=only with fiber protection
245
Hydrogen peroxide is the most commonly used bleaching agent for 100% cotton and cotton
blends. A hydrogen peroxide bleach bath consists of caustic soda, stabilizer, surfactant, and
sequestering agent. The concentration of chemicals is adjusted according to the proportion of the
cotton component in the blend. Hydrogen peroxide is a strong oxidizing agent that is activated by
alkali that increases pH that generates bleaching species. To control the process stabilizers are
added that can either be organic and inorganic. They create an equilibrium between activation and
stabilization of the bleaching system. However, this equilibrium is shifted by the presence of
catalysts (heavy metals) that increases the rate of activation leading to overoxidation of cellulose.
Heavy metals such as iron, copper, nickel and magnesium ions along with their oxides and salts
are responsible for catalytic damage during bleaching. The most common among all these is iron.
There are different sources of iron during the bleaching process. It may be present in water or
fabric from abraded metal and grease stains. The rust particle and iron chips may be spun in yarns
or embedded during fabric manufacturing. The caustic may also contain iron contaminants. The
raw cotton may also have iron and manganese. The presence of iron may cause spontaneous
decomposition of hydrogen peroxide producing free radicals that cause a breakdown of fiber
chains. This lowers the degree of polymerization and fiber strength and may lead to tears and holes
depending upon the severity. The presence of air in the machine or steamer may cause the
formation of oxycellulose under alkaline conditions. The oxidized portion of the cellulose is dyed
lighter as compared to undamaged areas producing uneven dyeing. The amount of peroxide
available for bleaching is also reduced due to reaction with catalysts. This lowers the degree of
whiteness. To prevent this problem two approaches may be used. In the first approach, the fabric
is treated with oxalic or hydrochloric acid before bleaching. This process is known as
demineralization. In the second approach sequestering agents are added in the bleaching bath [149,
303, 305].
The process can be done by the batch, semi-continuous and continuous method [9, 63,
149]. The batch process can be performed on winches or jets [9]. Cold pad-batch bleaching can be
used as an economical alternative process to increase production rate and quality of
polyester/cotton knit goods [330]. The continuous process is generally a wet-on-wet process. The
fabric containing desizing chemicals is first washed to remove the degraded size followed by
impregnation with caustic soda and detergent. The fabric is then fed to steamer where the action
of steam and caustic break down the impurities and cotton seeds. The steaming is an important
246
process. The temperature should not vary within the steamer. Widthwise variation may occur due
to temperature differences in the steamer [100]. The fabric is then washed to remove the degraded
impurities. The scoured fabric is then immediately impregnated with bleaching liquor containing
hydrogen peroxide, caustic soda, stabilizer, sequestering agent and surfactant. The fabric is then
steamed to break down colored and residual impurities. Washing and drying complete the process.
In the last washing, chamber fabric is neutralized [63, 317]. The factors affecting the process are
chemical concentrations, wet pickup, liquor levels, chemical flow rates, dwell times and
temperature, final pH, water flow rates and degree of drying [63].
The crease marks are developed when the tightly woven heavyweight fabric is creased in
a swollen state and stored for some time. They may be developed inside steamer when the fabric
is pleated during the continuous scouring and bleaching process. After the continuous dyeing, they
may show up as irregular dark dyed line-shaped marks. They may depend on the size and intensity
referred to as crow’s feet. These marks appear due to the crushing of the swelled fibers when they
are folded and compressed in the crease areas. When the fibers are deswelled and stretched in the
wash box the cracks are developed. The severity of the problem can be reduced by using a special
chemical that improves the elasticity and flexibility of the fibers [149]. After the scouring and
bleaching process, the fabric should be tested for residual size, pH, wetting out, and residual
peroxide. Residual hydrogen peroxide interferes with the dyeing process [297].
The final drying of fabric before dyeing is of critical importance. Both over-drying and
under-drying should be prevented. The fabrics with different moisture regain exhibit variations in
dye uptake especially in continuous dyeing. Over-dried fabric batches, other than increasing the
cost of drying, also lead to uneven conditioning of top layers and edges as compared to the center
and inside. This may cause dyeing problems and affects reproducibility. To prevent this problem
the drying stage should be equipped with an automatic residual moisture control system [317].
The scouring and bleaching can be combined in one stage called the Solo-Matic process
depending on blend ratio and fabric type. The fabric containing higher proportions of cotton,
higher weight (gsm) and requires higher whiteness usually requires separate scouring and
bleaching stages.
After bleaching the substrate should be checked for whiteness and fiber damage. The
whiteness is measured using the whiteness index (WI) along the fabric length and across the fabric
width and should be uniform. The fiber damage should be kept minimum. There is a maximum
247
whiteness that can be obtained keeping the fiber damage to a minimum [305]. Table 4.28
summarize the problems that occur during the bleaching process and their associated causes and
corrective actions.
Table 4.28: Problems caused during bleaching, its causes and remedial measures.
Problems Probable causes Remedial measures Ref.
Lower
whiteness
▪ Lower concentration of
bleaching chemicals
Adjust the recipe according to the
blend ratio of the material. Ensure
required bath concentration by
titration or proper flow rates.
[305]
▪ Inadequate setting of pH
during the bleaching process
Check/monitor the pH of the bath
regularly.
▪ Lower liquor pickup Use a wetting agent or lower padder
pressure.
▪ Inadequate
treatment/steaming time and
temperature
Ensure proper steaming time
according to fabric type and blend
ratio. The fabric with high thread
count requires more time for
treatment than fabric having lower
thread counts.
▪ Incomplete removal of tint 1. Check the tint for its sensitivity
to pH.
2. Follow tint manufacturer
recommendation for effective tint
removal.
3. Check the bleaching recipe.
[150]
▪ Poor stabilization of
peroxide
1. Select a suitable stabilizer.
2. Use the optimum quantity of
stabilizer based on the bleaching
agent concentration.
[301,
305]
248
Table 4.28 (Continued)
Problems Probable causes Remedial measures Ref.
▪ 3. The residual peroxide after the
bleaching process should be at
least 15%.
▪ Higher content of Fe and Ca
in fabric interfering with
peroxide.
Perform a demineralization
process.
[301]
▪ Presence of residual alkali in
a fabric that causes
yellowing during drying.
1. Wash at a higher temperature
to remove residual alkali.
2. Finish the fabric in slightly
acidic pH 5.5-6.
3. Keep fabric away from nitrous
oxide.
4. Provide enough dwell time to
fabric for proper
neutralization.
[301,
309]
▪ Loss in whiteness/yellowing
of fabric after storage due to
poor working practice and
storage conditions.
1. Finish the fabric in slightly
acidic pH 5.5-6.
2. Keep fabric away from nitrous
oxide.
3. Use wrapping sheet without of
butylated hydroxy toluene
(BHT).
4. Do not store goods in
excessive light.
[301]
▪ Poor storage conditions. Avoid storing the fabric in a hot
and humid environment.
249
Table 4.28 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Local drying marks due to
delay in hydro extraction
and drying.
Dry the hydro extracted fabric as
early as possible.
[301]
▪ Inadequate selection of
bleaching method
(especially for elastane
containing fabrics)
Perform reductive pre-scour with
hydrosulfite at 75-80 oC to
improve the whiteness of elastane
followed by peroxide bleaching.
[301]
Variation in
whiteness
▪ Variations in liquor pickup
along the fabric width
Check the padder/doctor blade
settings.
[305]
▪ Variations in chemical
concentration of the
impregnation uni
Periodically check the
concentration of chemicals.
[323]
▪ Variations in the
treatment/steaming
temperature
Ensure proper steaming time
according to fabric type and blend
ratio. The fabric with high thread
count requires more time for
treatment than fabric having lower
thread counts.
Unlevelness ▪ Instability of the dye
dispersion system due to
incomplete removal of
spinning lubricants
Ensure proper removal of spinning
lubricants by using detergents
with good emulsifying properties.
[109]
▪ Inadequate or uneven dye
penetration due to
incomplete removal of spin
finishes, oils, fats, and waxes
[100,
150,
253]
250
Table 4.28 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Production of oxycellulose
due to catalytic damage that
dye lighter than undamaged
areas
1. Check the incoming water
quality and iron deposits in
fabric.
2. Perform a demineralization
process before bleaching for
fabric with high iron content.
3. Use a sequestering agent with
good iron binding capacity.
[149]
▪ Alkali residues in the fabric Neutralize the fabric. The fabric
pH should be neutral.
[253]
Oil stains ▪ Oxidation of knitting oils on
prolonged storage depending
on the quality of knitting oil
1. Use a special scouring agent to
remove oxidized oil marks.
2. Perform lab trials do determine
optimum recipe and process
conditions.
[301]
▪ Incomplete removal of oil
stains from the fabric
Use special surfactant intended for
oil stain removal. The fabric
should not be allowed to dry
before washing off.
▪ Improper handling and
housekeeping of fabric rolls
during processing
Ensure proper housekeeping.
Ensure clean machines and clean
working methods.
[301]
Inadequate
wash fastness
▪ Incomplete removal of
spinning lubricants causing
instability of dye dispersion
system
Ensure proper removal of spinning
lubricants by using detergents
with good emulsifying properties.
[109]
251
Table 4.28 (Continued)
Problems Probable causes Remedial measures Ref.
Poor
reproducibility
▪ Residual peroxide from the
bleaching process destroys
the dyes
Ensure the residual peroxide
levels after bleaching. Ensure
proper washing of fabric after
bleaching.
▪ Lower whiteness due to
decomposition of peroxide
caused by Ca and Fe
Use a sequestering agent. [100]
▪ Alkali residues in the fabric Neutralize the fabric. The fabric
pH should be neutral.
[253]
Poor color
yield
▪ Residual peroxide from the
bleaching process destroys
the dyes
1. Check washing parameters
(water flow, temperature).
2. Check peroxide level in the
fabric after bleaching before
rinsing through titration.
3. Use catalase enzyme in washing
for removing peroxide.
[301]
▪ Uneven dye penetration due
to incomplete removal of
spin finishes, oils, fats, and
waxes
Ensure the required concentration
of scouring chemicals, treatment
time and temperature.
[100,
150]
▪ Residual alkali due to
improper neutralization
Neutralize the fabric. The fabric
pH should be neutral.
[194]
Widthwise
shade variation
▪ Temperature differences in a
steamer
Check the steam pressure.
Maintain a slight overpressure
inside the steamer.
[100]
▪ Variation in liquor pickup
during chemical application
Check the padder pressure/doctor
blade settings.
[128]
252
Table 4.28 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Alkali residues in the fabric Neutralize the fabric. The fabric
pH should be neutral.
[253]
▪ Variation in residual
moisture of the fabric across
the width
Prevent over drying of the fabric.
Install the residual moisture
control system.
[317]
Lengthwise
shade variation
▪ Variation in residual
moisture of the fabric across
the length.
Prevent over drying of the fabric
Install the residual moisture
control system.
[317]
Dark stains,
patches
▪ Direct contact of
concentrated alkali with
fabric in the saturator
causing localized swelling of
unmercerized cotton
1. Ensure proper dilution of alkali
before feeding into the
saturator.
2. Ensure the careful addition of
alkali.
[323]
▪ Inadequate removal of motes
(seed husks)
1. Check the pH of the bleaching
bath. It should be between 10.2-
10.7.
2. Ensure the optimum
stabilization of the peroxide.
3. Check the scouring process. The
seed husks should be softened
in scouring.
[149,
305]
▪ Alkali residues in the fabric Neutralize the fabric. The fabric
pH should be neutral.
[253]
▪ Foaming caused by residual
surfactants in the fabric
1. Ensure the substrate is properly
washed.
2. Use defoamer during dyeing.
[253]
Lower strength ▪ Catalytic damage due to the
presence of iron
1. Perform demineralization
process.
[100,
149]
253
Table 4.28 (Continued)
Problems Probable causes Remedial measures Ref.
2. Use a sequestering agent with
good iron binding capacity.
▪ Formation of oxycellulose
due to the presence of air
Ensure slight overpressure in the
steamer.
[323]
▪ Wool fiber damage due to
higher alkali content and
temperature
Adjust the concentration of the
bath according to the blend ratio
and the sensitivity of the fiber in
the blend.
[150]
Light areas or
patches
▪ Problems in dye penetration
as fats, waxes, spin finishes,
and mineral oil are not
properly removed
1. Use a scouring agent with good
emulsification and detergency.
2. Use a suitable wetting agent
which good stability under
alkaline conditions.
3. Avoid heat setting in a gray
stage.
[100,
149,
253,
317]
▪ Production of oxycellulose
due to catalytic damage or
presence of air that dye
lighter than undamaged
areas
1. Perform demineralization
process.
2. Use a sequestering agent with
good iron binding capacity.
[149,
305]
Crease marks ▪ Due to crease formation
inside the steamer during the
scouring and bleaching
process
Use a lubricating agent. [149]
▪ Distortion of weft due to the
application of too much
vacuum in the wash box
Check the vacuum settings
according to the fabric type.
[317]
254
Table 4.28 (Continued)
Problems Probable causes Remedial measures Ref.
leading to the formation of
creases
▪ Incorrect stitching of fabric
ends leading to the
formation of creases
Ensure fabric ends are properly
aligned when stitched.
[322]
Holes ▪ Catalytic damage due to the
presence of Fe in bleaching
bath
▪ Presence of heavy metals
(Fe, Cu) in the fabric, water,
and caustic soda
1. Use magnetic filters in
water/steam lines.
2. Use sequestering agents during
preparation.
3. Perform a demineralization
process.
[100,
149]
Streaks
(longitudinal
stripes)
▪ Incomplete removal of spin
finishes
Use detergent with good
emulsifying properties.
[149]
Poor hand ▪ Over drying of the fabric Prevent over drying of the fabric.
Install the residual moisture
control system.
[317]
▪ Catalytic damage due to Fe 1. Use a sequestering agent with
good iron binding power in
bleaching.
2. Perform demineralization
process.
[301]
Loss of elastic
properties
▪ Use of strongly acidic or
alkaline conditions during
processing
Avoid processing of elastane
blends in strongly acidic (pH < 4)
and strongly alkaline (pH > 10.5).
[301]
Poor
dimensional
▪ Insufficient relaxation of the
substrate
Ensure the tension in the substrate
is minimum during the washing
process.
[253]
255
Table 4.28 (Continued)
Problems Probable causes Remedial measures Ref.
stability
(shrinkage)
Entanglement
of fabrics.
▪ Ballooning of fabric as air is
entrapped due to densely
sewn seam and tightly knit
fabric structure
1. Cut a vertical slit of 10-15cm
near the joint to allow air to
escape.
2. Use a larger diameter nozzle.
3. Use a deaerating and
penetration agents.
4. Use a chain stitch or butt stitch
to join the rope pieces.
[297,
301]
▪ Due to foaming caused by
lubricants used in knitting or
surfactants used in scouring
and bleaching
1. Use non-silicone based
antifoaming agent.
2. Check the filter and clean it
before the start of the process.
[301]
Poor
appearance
▪ Pilling due to the rubbing of
fabric surface with each
other or machine parts
1. Singe the fabric to remove the
protruding fibers.
2. Run the machine at optimum
speed.
3. Check the machine lining is
smooth.
4. Use a lubricating agent.
[301]
▪ Fluff formation on the fabric
surface due to poor running
of fabric, the action of alkali
and low quality wetting
agent
Use a lubricating agent. [301]
▪ Longer duration of running
due to reprocessing
Use a lubricating agent.
[301]
256
Table 4.28 (Continued)
Problems Probable causes Remedial measures Ref.
Insufficient
absorbency
▪ Poor quality of surfactant
that has low stability under
alkaline conditions
Use a good quality surfactant
having good stability under
alkaline conditions.
[301]
▪ Redeposition of oil and
waxes
Use a higher rinsing temperature
(> 80 oC).
[301]
Alkaline pH ▪ Buffering action of sodium
acetate formed by acetic acid
that prevents penetration of
acid inside the fiber core
Use specialized products for
neutralization.
[301]
4.7.5 Problems caused during weight reduction
The fabrics containing polyester filaments are treated with hot caustic solutions to hydrolyze the
fiber surface causing weight loss. The weight loss is controlled by the concentration of caustic and
treatment temperature. The alkali cleaves the ester linkages in polyester fibers to water soluble
terephthalate salts and ethylene glycol. The weight loss occurring at the fiber surface leads to the
reduction of the fiber denier. The surface of the polyester fibers is removed layer by layer. This
process improves slight hydrophilicity and imparts silk-like hand to the material and the stiffness
is greatly reduced. The propensity of the fabric to develop crack marks is also reduced. The factors
affecting the process are treatment temperature, the concentration of sodium hydroxide, treatment
time and type of accelerator. Insufficient weight reduction due to inadequate concentration of
caustic, treatment time and temperature leads to crack marks during dyeing. On the other hand,
too much weight reduction leads to a reduction in the strength of the material. The process needs
to be controlled to achieve the required degree of weight loss [331, 332].
4.7.6 Problems caused during mercerization and causticization
Mercerization is an optional process and generally performed for all cotton-based fabrics to
enhance dye uptake, luster, tear strength, dimensional stability. It also improves appearance by
coverage of immature cotton fibers due to the leveling of structural differences. The fiber swelling
257
takes place and the internal structure of the cellulose is modified. The percentage of micropores
responsible for dye adsorption is also increased. The wetting agent may be required to improve the
penetration of caustic soda into the substrate. The treatment can be carried out under cold or hot
conditions. [9, 63, 133, 168, 333].
A typical mercerization process consists of an impregnation zone, dwelling zone,
stabilization, and a washing zone. It can be performed by both dry-on-wet and wet-on-wet process.
In the impregnation zone, the caustic soda solution (28-30 oBé) is applied to the fabric followed
by the dwelling zone where some reaction time is provided. For good results, the good circulation
of the caustic soda solution is essential. During impregnation, if the space between the rollers is
not completely filled with caustic, it may cause stripes in a fabric that may be seen after the dyeing
process. The caustic should not be sprayed directly on to the fabric. This may also cause stripes in
the fabric. In a stabilization zone, the concentration of caustic is reduced to 6-8 oBé. This is
important to provide dimensional stability to the fabric and prevent shrinkage in the washing zone.
After caustic treatment, the fabric is washed to remove the caustic soda from the substrate. The
fabric is then neutralized followed by drying. Fabric pH control is critical to obtain reproducible
dyeing results. It should be uniform both along the length and width of the fabric [317]. During
continuous processing, the neutralization process is carried out in the first half of the last wash box
divided into two zones. The fabric, based on the fabric content of the washer, approximately has
10 sec of reaction time for neutralization. This time may be suitable for light to medium weight
fabrics but for heavier fabrics, this time is insufficient to achieve complete neutralization. It is
recommended to use to complete washing box for neutralization to achieve the required results
[309].
The factors controlling the mercerization effect are [63, 305, 317, 334]:
▪ Origin and degree of maturity of cotton;
▪ Cellulose content;
▪ Concentration of caustic soda in the impregnation section (min. 28 oBé) and on the
fabric (220-240 g 100% NaOH per kg substrate);
▪ Wet pickup;
▪ Temperature (hot: 60-65 oC, cold: 18-20 oC);
▪ Reaction time (hot: 25-30 sec, cold: 45-60 sec);
▪ Tension (rollers or stenter); and
258
▪ Removal of caustic (caustic in wash water, water flow rates, temperature, final pH).
Polyester/cotton blends having a high proportion of cotton can be mercerized to improve
the properties of cotton. This process has little or no effect on polyester. The absorbency of
polyester/cotton blend is low as compared to cotton. This is because the blended fabrics have not
been given the usual thorough scouring and bleaching treatment of all cotton fabrics. The wetting
agents are therefore required to improve the penetration of caustic in the blended fabric. The
operating conditions required for cotton can be followed for the mercerization of polyester/cotton
blends. The mercerization of the cotton/regenerated cellulosic blend is only beneficial provided
that the blend proportion of the regenerated cellulosic fibers does not exceed 50%. The regenerated
cellulosic fibers are swelled by the action of caustic. Special precautions must be followed as
different regenerated cellulosic fibers different in their wet strength and alkali stability. The lyocell
and modal fibers have higher wet strength and alkali resistance compared to viscose. Improper
conditions for the mercerization of cotton/regenerated cellulosic blends leads to the stiff, brittle
and weaker fabric. The use of a wetting agent is essential due to the higher absorbency of
regenerated cellulose fibers as compared to cotton. The cotton/modal and cotton/lyocell blend can
be mercerized using a caustic solution of 28 oBé at 30 oC to obtain maximum swelling. The reaction
time should be kept minimum (30-60 sec) but kept as long as possible to achieve the uniform and
even penetration of caustic. The overstretching of fabric should be avoided. During stabilization,
the concentration of caustic should be reduced to 6 oBé as fast as possible at a higher temperature.
This is followed by washing and neutralization [100, 312, 334-336].
Blends containing viscose are not generally mercerized due to lower wet tenacity and
greater sensitivity to alkali. Fabric containing regenerated cellulose fibers are treated with caustic
soda solution without tension to achieve high color yields. This process is known as causticization.
The improvement in dyeability may be attributed to the easy dye diffusion and a higher degree of
dye fixation. The caustic soda modifies the internal structure of regenerated cellulose fibers. The
concentration of caustic soda is more important than treatment time in the causticization process.
The fabric is treated with a 6-8 oBé caustic soda solution for 30-60 sec at room temperature without
tension followed by a rinsing process [9, 184, 333, 337, 338].
Barium activity number is the test used to ascertain the degree of mercerization. For
complete mercerization, the number should be greater than 125. The test should be performed
259
along several places in the fabric to check for non-uniformity [305]. Uneven mercerization effects
are caused by many reasons such as uneven distribution and or wetting of caustic, uneven moisture
levels in fabric, uneven squeezing or rinse off caustic and creases in the fabric. Table 4.29 enlists
the problems in the mercerization and causticization process and possible solutions to resolve these
problems.
Table 4.29: Problems in mercerization and causticization and possible solutions.
Problems Probable causes Remedial measures Ref.
Lower degree
of
mercerization
(Barium
activity
number) or
lower color
yield
▪ Lower concentration of
caustic on fabric
1. Check the concentration of caustic
on fabric by titration. It should be
220g 100% NaOH per kg substrate.
2. Lower machine speed to provide
adequate time to achieve required
caustic concentration on fabric.
[305,
334]
▪ Inadequate reaction time Reduce the fabric speed. The reaction
time should be 25-30 sec for hot or
45-60 sec for cold mercerization.
▪ Low concentration of
process caustic lye
Check the concentration of caustic
lye in the impregnation zone, it
should be 28 oBé.
▪ Improper selection of a
wetting agent
Select a wetting agent that is stable
under higher alkaline conditions.
▪ Inadequate application of
caustic during impregnation
1. Use a good quality of wetting
agent.
2. Provide enough time by adjusting
machine speed for the proper
application of caustic.
260
Table 4.29 (Continued)
Problems Probable causes Remedial measures Ref.
Variation in
the degree of
mercerization
along the
length
▪ Dilution in the
concentration of caustic due
to increase in water content
of the fabric
1. Check the water content of the
infeed fabric, it should remain the
same.
2. Use a higher concentration of
caustic lye (35-40 oBé).
[305]
▪ Increase in temperature of
the process due to the
reaction between water and
caustic
Check the water content of the infeed
fabric, it should remain the same.
Uneven
mercerization
▪ Uneven distribution of
caustic in the impregnation
zone
Ensure the caustic distribution is
working properly and the same levels
are maintained in the impregnation
zone.
[305]
▪ Improper penetration of
caustic in the fabric due to
poor wetting agent
Select a wetting agent with good
stability under alkaline conditions.
▪ Uneven squeezing of
caustic after impregnation
Check the padder uniform. It should
be uniform.
▪ Presence of creases in the
fabric
Ensure fabric should be free of
creases when it enters the
mercerizing range.
Insufficient
dimensional
stability
(shrinkage)
▪ Lower concentration of
caustic on fabric
Check the concentration of caustic on
fabric by titration. It should be 220g
100% NaOH per kg substrate.
[253,
305,
334]
▪ Low concentration of
process caustic lye
Check the concentration of caustic
lye in the impregnation zone, it
should be 28 oBé.
261
Table 4.29 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Too low temperature of
caustic soda solution
Use higher caustic temperature. The
best dimensional stability is obtained
at 60 oC.
▪ Not enough washing water
in stabilization
Use an adequate amount of water, it
should be at least 4 L/kg of substrate.
▪ Too low washing
temperature in stabilization
The temperature during stabilization
should be 90-95 oC.
▪ Non-functional stenter
spray system
Check the operation of the spray
system.
Selvage center
differences or
widthwise
shade variation
▪ Very high stretching on
stenter
Use optimum stretch settings on
stenter. Best results are obtained
when stretched width is equal to the
final width.
[323,
334]
▪ Inadequate removal of
caustic from selvage areas
Check the working of the selvage
extraction device.
Lower luster ▪ Lower concentration of
caustic on fabric
Check the concentration of caustic on
fabric by titration. It should be 220g
100% NaOH per kg substrate.
[323,
334]
▪ Inadequate reaction time.
Lower dwell time
Reduce machine speed. The reaction
time should be 25-30 sec for hot or
45-60 sec for cold mercerization.
▪ Low concentration of
process caustic lye
Check the concentration of caustic
lye in the impregnation zone, it
should be 28 oBé.
▪ Inadequate stretching of a
substrate during
mercerization
Use optimum stretch settings on
stenter. The stretched width should be
equal to the final width.
262
Table 4.29 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Higher concentration of
residual alkali after
stabilization
1. Use an adequate amount of water,
it should be at least 4 L/kg of
substrate.
2. The temperature during
stabilization should be 90-95 oC.
3. Check the operation of the spray
system.
Creases ▪ Distortion of weft due to
excessive pressure during
chain mercerization leading
to the formation of creases
Use optimum stretch settings on
stenter. Best results are obtained
when stretched width is equal to the
final width.
[317]
▪ Incorrect stitching of fabric
ends leading to the
formation of creases
Ensure fabric ends are properly
aligned when stitched.
[322]
Lower
whiteness
▪ Presence of residual alkali
in a fabric that causes
yellowing during drying
1. Wash at a higher temperature to
remove residual alkali.
2. Finish the fabric in slightly acidic
pH 5.5-6.
3. Keep fabric away from nitrous
oxide fumes.
4. Provide enough dwell time to
fabric for proper neutralization.
[301,
309]
Two sidedness ▪ Differential mercerization
due to superimposed layers
of fabric
Restrict the mercerization of
superimposed layers of fabric to
thinner fabrics.
[194]
Alkaline or
variation in
fabric pH
▪ Insufficient or variation in
water flow rate in the wash
boxes
Control and monitor the washer water
flow rates according to the fabric
[317,
334]
263
Table 4.29 (Continued)
Problems Probable causes Remedial measures Ref.
weight, speed, and concentration of
caustic soda.
▪ Incorrect setting of liquor
counterflow in the wash
boxes
Use correct settings of counterflow.
▪ Use of too low or variation
in washing temperature
The washing temperature should be
90-95 oC.
▪ Wrong pH adjustment
during neutralization
process
Control and monitor the dosage of
acid in the neutralization chamber.
Set pH at approximately 5.5
depending on fabric weight.
▪ Inadequate time is given for
the neutralization process
Ensure enough time is given to
achieve the core neutralization of
fabric. Use the second last washing
chamber for neutralization.
[309]
▪ Incomplete removal of
caustic along the selvages
during stabilization
Check working of selvage extraction
device.
▪ Inadequate neutralization of
fabric due to the formation
of sodium acetate buffer in
the fiber
Use a specialized mixture of organic
acid for neutralization.
[305,
309]
▪ Use of a very higher
concentration of caustic
during impregnation
Check the concentration of caustic lye
in the impregnation zone, it should be
28 oBé.
Light or dark
streaks/bars
▪ Uneven mercerization 1. Check the concentration of caustic
on fabric by titration. It should be
220g 100% NaOH per kg substrate.
[323]
264
Table 4.29 (Continued)
Problems Probable causes Remedial measures Ref.
2. The reaction time should be 25-30
sec for hot or 45-60 sec for cold
mercerization.
▪ Incomplete filling of space
between rollers during
impregnation zones
The space between rollers should be
completely filled with caustic.
[149]
▪ Direct spraying of caustic
on to the fabric
The caustic should not be sprayed
directly on to the fabric.
▪ Incomplete removal of
caustic after mercerization
Ensure proper washing of the fabric
during mercerization.
▪ Machine stoppage Avoid frequent machine stoppages. [323]
Shade change ▪ Presence of higher
concentration of iron in
fabric carried over from the
residual caustic
1. Check the iron content of the
caustic. Install filters in the caustic
infeed.
2. Ensure proper washing of the
fabric.
3. Use sequestering agent during
dying having good iron binding
capacity at a higher temperature.
[301]
Dark patches ▪ Drying of improperly
neutralized/residual alkali
1. Ensure proper washing and
neutralization.
2. Remercerize using a higher
concentration of caustic.
[194,
301]
Poor color
yield
▪ Residual alkali due to
improper neutralization
Neutralize the fabric. The fabric pH
should be neutral.
[194]
Torn selvages
or clip cuts or
clip miss
▪ Over stretching of the
fabric
1. Avoid overstretching of fabric.
2. Select grey width in accordance
with the finished width.
[194]
265
Table 4.29 (Continued)
Problems Probable causes Remedial measures Ref.
3. Increase the reed spacing and use
coarser reed during weaving.
▪ Too tight grip or improper
grip due to inadequate
maintenance
Ensure proper maintenance of the
stenter clips on regular basis.
[194]
▪ Bursting of fabric selvages
due to alkali sensitivity of
regenerated cellulosic fibers
1. Check the caustic concentration.
Use lower caustic concentration.
2. Ensure proper tension control.
Avoid too high tension.
[194]
Reduced
strength
▪ Improper control during
caustiziation
1. Avoid using a higher concentration
of caustic. Viscose fibers are
sensitive to higher alkali
concentrations.
2. Ensure proper washing of fabric for
effective alkali removal.
[323]
4.7.7 Problems caused during heat setting
Heat setting is carried out to remove the tendency of the substrates containing synthetic fibers to
shrink and form creases during heat treatment. This is obtained by stabilization of structure by
removing stresses in fibers and fabric. The blends containing 65% or more polyester must be heat
set to obtain uniform dyeing results. Heat setting also improves crease recovery, dimensional
stability, and pilling resistance [9, 63, 64, 68, 168, 339]. The fabric becomes a little stiffer after the
heat setting process so higher temperatures should be avoided. At higher temperature, the damage
and yellowing of fiber may take place. The preferred approach is to use the minimum best possible
temperature that provides required dimensional stability [168, 339]. As a general rule of thumb,
the heat setting temperature should be 10 oC higher than the temperature at which maximum
stability is required [339, 340]. The fabrics containing texturized polyester yarns should not be
266
heat set above 160-170 oC. Above this temperature range (180-200 oC) the fabric loses its extension
and recovery and aesthetic qualities [81, 109].
The heat setting process may be carried out at different stages during wet processing. It is
usually performed after the scouring and bleaching process [83, 168]. Heat setting before dyeing
prevents creasing and fabric shrinkage during the dyeing process. Although, some shrinkage
margin must be also be given. The medium to heavy weight fabrics should be heat set before
dyeing [339]. If done after dyeing it removes the creases that might be introduced during dyeing
and stabilize the fabric at its finished width. All the blended fabrics to be dyed by thermosol process
need to be heat set before dyeing [9, 168, 339].
Heat setting under hot air is the most commonly used method for the setting of polyester
blends. This process is carried out, on stenter for open width fabrics and special heat setting
machine for tubular fabrics, at temperatures greater than usually encountered in dyeing [9, 63, 64,
340]. The temperature is set based on the ratio of polyester component, substrate weight and
structure, energy classification of disperse dyes and whether carried out before and after dyeing
[317]. The polyester/cellulosic blended fabrics are usually heat set at 195-205 oC for 30 seconds
[83, 168]. The polyester/wool blends should be heat set at 185 oC for 30 seconds [67]. Heat setting
on stenter provides dimensional control of fabric in a longitudinal and horizontal direction [168].
For elastane containing fabrics, the fabric should be relaxed before heat setting to reduce
residual stresses. The heat setting temperature and dwell time should be set keeping into
consideration the percentage and kind of elastic yarn in the fabric. The shrinkage behavior,
stretchability, recovery capacity, and residual elasticity must be considered.
A consistent moisture level in the fabric is essential for uniform drying and heat setting.
Uniformity of treatment is critical to avoid dyeability variations. A small variation in temperature
can induce variations in fiber morphology and drastically affect the dyeing rate. The temperature
across the fabric width, lengthwise in heat setting bays, upper and lower part of the heat setting
bay should be kept uniform [317]. Thermopaper can be used to check temperature along with
routine calibration checks of temperature sensors [339]. Residual size and oil stains if present may
get fixed into the fabric during heat setting and therefore difficult to remove [9, 64, 168]. Table
4.30 shows the heat setting problems along with their causes and corresponding corrective
measures.
267
Table 4.30: Problems caused during heat setting, its causes and remedial measures.
Problems Probable causes Remedial measures Ref.
Poor
dimensional
stability
(Shrinkage)
▪ Inadequate heat setting
conditions (temperature and
time)
1. Use optimum settings (time and
temperature) according to the fabric
blend ratio and setting process.
2. For cases where fabric is wet before
heat setting attention should be paid to
the drying time as it influences the
heat setting duration.
3. Ensure proper cooling of fabric after
steneter to stabilize the set structure.
[67,
194,
253,
320,
323]
▪ Inadequate overfeed Provide a desired overfeed depending
upon the blend ratio and fabric width.
[194,
323]
Differential
shrinkage
▪ Differences in setting
conditions
Ensure the same heat settings ae
maintained within a lot and between
lots.
[320]
▪ Omitting setting step from
one part of the batch
Ensure the lots are properly tagged and
following the processing route as
planned.
Poor hand ▪ Too high heat setting
temperature
The fabric should heat set according to
the most sensitive fiber in the blend and
required dimensional properties.
[168]
▪ Longer heat setting time For cases where fabric is wet before
heat setting attention should be paid to
the drying time as it influences the heat
setting duration.
Unlevelness ▪ Variations in heat setting
conditions (temperature and
time)
Ensure uniformity of heat setting
conditions along the length and width.
[168,
323]
268
Table 4.30 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Burnt-in or diffused
residual oils and grease
Avoid grey heat setting
Ensure the stenter sieves are cleaned
regularly.
[149]
▪ Irregular heat setting due to
variations in the moisture
content of the incoming
fabric
For cases where fabric is wet before
heat setting attention should be paid to
the drying time as it influences the heat
setting duration.
[67]
Dark stains ▪ Burnt-in or diffused
residual oils and grease
1. Avoid grey heat setting
2. Ensure the stenter sieves are cleaned
regularly.
[149]
▪ Localized variations in the
moisture content of the
fabric before heat setting
Ensure the padder pressure is uniform
before the heat setting process.
[149]
Streaks ▪ Overstretching of fabric
across the width
1. Avoid overstretching of fabric.
2. Select grey width in accordance to the
finished width.
3. Increase the reed spacing and use
coarser reed during weaving.
[341]
Widthwise
variation/
listing
▪ Fluctuations in temperature/
airflow rate across the
width of the fabric
Ensure the air velocity is uniform across
the stenter. Check the temperatures
using thermal paper.
[128,
168,
253]
Edge marks ▪ Unlevel dyeing of materials
along the selvages due to
clip/pin marks
Ensure the clips/pins are cooled when
they grab the new incoming fabric.
[194,
320]
Weft streaks ▪ Local overheating of fabric
during the machine
stoppage
Check the proper working of nozzle shut
off system on stenter.
[149]
269
Table 4.30 (Continued)
Problems Probable causes Remedial measures Ref.
Poor
appearance/
yellowing
▪ Too high heat setting
temperature
The fabric should heat set according to
the most sensitive fiber in the blend and
required dimensional properties.
[149,
320]
▪ Longer heat setting time For cases where fabric is wet before
heat setting attention should be paid to
the drying time as it influences the heat
setting duration.
▪ Setting of tint Avoid the heat setting of fabric during
the gray stage.
[150]
Luster
marks
▪ Excessive heat setting. Use optimum settings according to the
fabric.
[253]
Creases/
rope marks
▪ Improper heat setting Ensure proper heat setting. [253,
320]
Stich
distortion
▪ Inadequate heat setting
conditions (time and
temperature)
Use optimum settings according to the
fabric.
[253]
▪ Too high air circulation 1. Control air circulation according to
fabric type.
2. Use a perforated belt for material
transport if possible.
[68]
Pilling ▪ Improper heat setting Ensure proper heat setting. [253,
320]
Loss of
elastic
properties
▪ Higher tension and
temperature during
processing
The temperature should not more than
150 oC and tension should be kept lower
during the process.
[301]
Lengthwise
shade
variation
▪ Stoppage or slowing of
stenter
Avoid stopping or reducing machine
speed. Use j-scray for fabric change to
avoid fabric damage.
[326]
270
Table 4.30 (Continued)
Problems Probable causes Remedial measures Ref.
Torn
selvages or
clip cuts or
clip miss
▪ Over stretching of the
fabric
1. Avoid overstretching of fabric.
2. Select the grey width according to the
required finished width.
3. Increase the reed spacing and use
coarser reed during weaving.
[194]
▪ Too tight grip or improper
grip due to inadequate
maintenance
Ensure proper maintenance of the
stenter clips regularly.
[194]
Poor color
yield
▪ Use of too high heat setting
temperature or longer dwell
time leading to reduced
fiber swelling capacity
Use appropriate heat setting conditions
according to fiber type in the blend.
[342]
4.8 Problems in coloration
The objective of the coloration process is the uniform application of color to achieve shade and
colorfastness as enlisted in Table 4.31. The coloration process depends on the colorants (dyes or
pigments), material form and fiber blend. The coloration process produces the most visible results
in all the wet processing operations. Any variations in the previous processing stages may not be
evident under the material is dyed [1].
Table 4.31: Main objectives of the dyeing process.
▪ Dyeing fibers to desired shade.
▪ Obtain a uniform and level dyeing.
▪ Maintain required fastness properties according to the intended end-use.
▪ Prevent damage to the material (fiber, yarn, fabric).
▪ Maintain cost levels.
271
4.8.1 Reproducibility in the dyeing of fiber blends
High shade reproducibility or right first time (RFT) is the prerequisite to increase productivity and
reduce the cost of any dyehouse in today’s competitive market. This requires skill, attention to
detail and will to succeed. A dyeing process said to be reproducible if the required shade is matched
within specified limits at the end of the first process without any additions or reprocessing [61,
142]. These include but not limited to dye or chemical addition, extra run time, stripping and re-
dyeing, and shading.
In batch dyeing, RFT dyeing technique can also be termed as blind dyeing or no-addition
dyeing. The term blind dyeing refers to the dyeing process in which dyed substrate is only
examined for shade and levelness and found acceptable after it is out of the dyeing machine and
the next dyeing cycle is started. In contrast, in no addition dyeing, the substrate is examined in the
usual way for shade while in the machine, but it is found to be matched. Blind dyeing not only
reduces the dyeing time, as the assessment process is done after the substrate is offloaded from the
machine but also energy savings [142].
To achieve blind dyeing, excellent reproducibility is required. This can only be obtained
by identifying and controlling the variables involved in the dyeing process [142]. Table 4.32 lists
important factors that may affect the reproducibility in batch dyeing of fiber blends [77, 142].
It is important to note that no two dyehouse is the same and must determine their tolerances
for each of the variables. Some variables such as moisture content and weighting errors of both
substrate and the dye can be simulated in the laboratory by measuring the effect of these on the
color difference. These tolerances are critical in obtaining reproducible results. Table 4.33 lists
some of the factors along with their allowable variability as a guide for the dyehouse. These
tolerances indicate that reproducible results within a ΔEcmc < 1 would be obtained if the tolerances
are kept within the mentioned limits [142].
272
Table 4.32: Important factors affecting reproducibility in the batch dyeing of fiber blends.
▪ Water quality
▪ Blend ratio of material
▪ Dyeing characteristics of the substrate
▪ Substrate pretreatment
▪ Weight and moisture content of the
substrate
▪ Weighing of dyes and chemicals
▪ Dye and chemicals dispensing
▪ Dye selection for each fiber type
▪ Dye combinations for each fiber
▪ Compatibility between dye classes
▪ Cross-staining of each fiber type
▪ Water impurities
▪ Dye standardization
▪ Dye moisture content
▪ Dyeing weighing
▪ Dye dispensing
▪ Compatibility of auxiliaries
▪ Chemical weighing and dispensing
▪ Dyebath auxiliaries
▪ Liquor ratio with respect to each fiber type
▪ Machine flow and reversal or material
circulation rate
▪ Time/temperature profile
▪ Dye bath pH
▪ Shade assessment procedure
Table 4.33: Dyehouse factors and associated tolerances.
Factors Variability (%)
Moisture content of the dye ± 3.5
Moisture content of the substrate ± 0.5
Substrate weight ± 0.5
Weighing of dyes and chemicals < 0.5
Dyebath pH 0.35 units
Dyes standardization ± 2.5
To obtain high lab to bulk reproducibility in continuous dyeing, the tailing and reverse
tailing behavior of dyes must be considered. During bulk dyeing, the equilibrium shade on the
fabric is reached after several minutes. It is important to consider the relationship between the
laboratory padder, stock tank and pad liquor formulations. The dye produced in lab scale is
equivalent to the first few meters dyed in bulk and may give off-shade dyeing in bulk once
273
equilibrium is reached. The allowance factors can be calculated to quantify these differences so
that required adjustments in lab scale formulations and stock feed can be performed. This ensures
the matching of target shade once the pad liquor reaches equilibrium. The process variables that
may influence the continuous dyeing of polyester/cotton blends by pad-dry-chemical pad steam
process are listed in Table 4.34. They need to be controlled according to the dye type to ensure
excellent reproducibility, levelness, and fastness properties.
Table 4.34: Factors affecting continuous dyeing of PES/CELL blends by the continuous method.
Process stage Variables
Dye application ▪ Impurities level, absorbency, residual moisture
and temperature of fabric (material quality)
▪ Dye type and concentration (recipe quality)
▪ Chemicals concentration
▪ Liquor pick-up
▪ Liquor temperature
▪ Trough volume
Infrared pre-drying ▪ Intensity
▪ Levelness
▪ Residual moisture
Hotflue drying and
thermofixation
▪ Temperature
▪ Time
▪ Humidity
▪ Ventilation
Chemical application ▪ Chemicals concentration
▪ Salt quality
▪ Liquor pick-up
▪ Material temperature
▪ Liquor temperature
▪ Trough volume
Steaming ▪ Temperature
274
Table 4.34 (Continued)
Process stage Variables
▪ Time
▪ Steam quantity
▪ Steam quality
▪ Water lock
Wash-off ▪ Temperature
▪ Water quantity
▪ Dwell time (fabric speed)
▪ pH
▪ Water quality (impurities)
4.8.2 Problems caused in batch dyeing machines
Batch dyeing machines are commonly used for dyeing of various blended materials such as yarns
and fabrics. Yarns are dyed either in cones, cheeses or on beams [9]. For tabular or open width
knitted fabric, jet or overflow dyeing machines are most commonly used. The problem of creasing
at the edges of tubular fabrics favors the batch dyeing process [9, 57].
The batch dyeing machines can be classified into three types of machines based on the
movement of dye liquor and substrate. In the first type known as circulating liquor machine, the
substrate is stationary while the dye liquor is circulated. These machines include yarn package
dyeing and fabric beam dyeing machines. The second type is known as circulating goods machines
in which the substrate is moving. The winch and jig dyeing machines are the circulating good
machines. In the last type called circulating liquor and good machines, both substrate and dye
liquor is moving. Jet and overflow dyeing machines are of this type. Table 4.35 lists the
characteristics of different batch dyeing machines [233].
275
Table 4.35: Important characteristics of different batch dyeing machines.
Fabric dyeing Yarn dyeing
Winch or beck
▪ Versatile and less expensive
▪ High fabric tension
▪ Long cycle time
▪ Variations in temperature
▪ Large energy and water consumption.
▪ Requires carrier for polyester dyeing
Jet and soft flow
▪ Minimum tension of the fabric
▪ Short cycle
▪ Good leveling and barre coverage
▪ Can be used for fabrics containing
texturized yarns
▪ High temperature dyeing possible (130-
135 oC)
▪ Expensive
▪ Fabric weight limitations
▪ Foam formation
Jig
▪ Open width.
▪ High tension on the fabric
▪ Economical than jet dyeing
▪ Large quantity of fabric can be dyed
▪ Lower liquor ratios possible
▪ Mainly suitable for woven fabric
▪ Knitted fabrics, stretch woven fabric and
very light weight fabrics cannot be dyed
▪ Listing and ending problems
Beam*
▪ Open width processing of the fabric
▪ Rapid dyeing process
▪ Economical
▪ Large fabric quantity can be dyed.
▪ Minimum tension on the fabric.
▪ Requires light weight flat, plain fabrics
having open constructions.
▪ Uniform batching is critical for levelness.
Package
▪ Yarn wound on cheese or cones.
▪ High temperature dyeing possible (130-
135 oC)
▪ Lower liquor ratios possible.
▪ Special winding process to produce a
package for dyeing
▪ Uniformity in packing essential for
levelness
Hank dyeing
▪ Good bulk in yarn, yarns allow to shrink
▪ Expensive process
▪ High water and energy consumption
▪ Difficulty in achieving uniformity
▪ Special winding and reeling requirements
*Can also be used for yarn dyeing.
276
In circulating liquor machines, the uniform and strong circulation of liquor throughout the
material is required to obtain uniformity in dyeing. The turbulence during liquor flow should be
avoided. There must be no liquor flow through spaces between packages in yarn dyeing. The
perforations in the beam dyeing must also be completely covered with the textile material [68]. To
produce level dyeing, the initial dye uptake must be similar throughout the material. If the liquor
circulation rate is lower and higher dyeing rate is used they may lead to nonuniform dyeings. The
exhaustion rate should be restricted to a maximum of 2% per cycle to ensure uniform dyeing. The
machines should have an option to drain exhausted liquor under pressure [9]. During the dyeing
process, large changes in pressure must be avoided to prevent material damage and non-uniform
dyeing. This is often linked to shrinkage of the material during the dyeing process. The materials
must, therefore, be heat set before dyeing to have lower residual shrinkage [68].
4.8.2.1 Yarn dyeing
The blended yarns are usually dyed in package form. For yarns where high bulk is required skein
method can be used. To obtain level dyeing, the dye exhaustion needs to be controlled. The
difference in exhaustion at various points in the material leads to unlevelness. The exhaustion
depends on the concentration of dye on the fiber surface and in the bath. As the liquor pass through
the substrate, there is a change in the dye concentration which decreases as in the direction of
liquor flow. Therefore, the ratio of the rate of exhaustion to the rate of flow determines levelness.
During package dyeing of yarn if the liquor flow is not uniform across the whole package it may
cause unlevelness [343].
Numerous mechanical factors may affect the dyeing of yarn in package form[100, 231,
244]. These are as follows:
▪ Yarn package
These include package shape, size, dye tubes, winding method, winding angle, traverse
ratio and length, and package density [231]. These are covered in section 4.4.3.
▪ Number of dye packages per spindle
It is decided based on the uniform flow of liquor through each of the dye package. The
balance must be reached between the number of dye package and liquor supply. This
depends on the machine capacity, the liquor flow rate and flow properties of the
package [231]. The spindle loading is decided by:
277
- Carrier type (top and bottom plate or bottom plate only);
- Carrier inlet, tube diameter and type of spindle;
- Speed and pressure of liquor at the spindle inlet;
- Liquor flow rate;
- Number of material to liquor interchanges;
- Type of dye package (diameter, shape and inter package sealing); and
- Winding and pressed density of the yarn.
▪ Liquor flow rate
The optimum liquor flow rate is essential for level dyeing. The right liquor flow
conditions should be followed for each blend. The liquor throughput affects the
movement of dyestuff to the fiber surface of yarn assembly and ultimately uniformity
of dyeing. Using very high liquor flow may cause package deformation and yarn
damage. The actual flow rate depends on package winding density, fiber specific
gravity, liquor exchange factor, and liquor loss in the package column [231, 248]. The
yarn packages can be classified into three types based on the maximum flow rate it can
handle before deformation or channeling or other defects can occur. These are low flow
rate dyeable, medium flow rate dyeable and high flow rate dyeable packages. These
flow rate limits depend on the properties of yarn and the winding process [344].
▪ Liquor ratio and number of contact cycles
The liquor should be enough to ensure uniform wetting of dye packages. The use of a
very low liquor ratio may lead to dye unlevelness. Any additions made during the
dyeing process must be considered in the calculation of liquor ratio. The number of
times liquor passes through a material in a given time is known as contact time and it
is calculated based on liquor flow rate and liquor ratio [231].
▪ Differential pressure
The flow resistance of the dye liquor through the yarn packages inside the dyeing
machine is indicated by the differential pressure which may determine the liquor
throughput. This pressure can give an estimate of the liquor flow rate. The differential
pressure increases with an increase in winding density [248].
The faults related to the yarn dyeing machine are shown in Table 4.36.
278
Table 4.36: Dyeing faults due to package dyeing machine.
Problems Probable causes Remedial measures Ref.
Reproducibility ▪ Variation in the liquor ratio Ensure the liquor ratio is the same in
every batch.
[231]
▪ Variation in liquor flow
rates
Maintain the same liquor flow rates.
▪ Stoppages in between
process due to delays in
addition of dyes and
chemicals
Avoid any standing times. The dyes
and chemicals should be ready for
addition at the right time.
▪ Presence of air in the
machine
The air in the machine should be
neutralized by the addition of hydro
or displacement with nitrogen. 1.7
kg hydro and 1.7 L caustic 38 oBé is
required or each 1 m3 of air in the
system.
Unlevelness ▪ The temperature ramp rate is
higher in the critical dyeing
region
Use the correct dyeing program to
control the temperature ramp rate. It
should be kept between 1-1.5 oC/
min to ensure level dyeing.
[9,
253]
▪ Slower liquor circulation
rate leading to higher
exhaustion of the dye
Use the optimum circulation rate.
The maximum exhaustion should be
restricted to 2% per cycle.
[79]
▪ Improper liquor flow rate
due to package and carrier
leakage.
Check the carrier spacers. [231]
▪ Improper penetration of the
dye liquor due to the
oligomer deposits
Check the machine for oligomer
deposits and clean it regularly.
[67]
279
Table 4.36 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Too low liquor flow rate due
to higher package density
1. Increase the liquor flow rate.
2. Reduce the package density.
3. Use low temperature ramp rate.
[231]
▪ Too low liquor flow rate due
to leakage in package
column
Check column sealing and for
leakage.
▪ Too low liquor flow rate due
to high residual shrinkage
Check fibers for residual shrinkage
(maximum 5%).
▪ Differences in liquor flow
rates in coupled machines
1. Ensure the proper operation the
control valves and cross coupling
device.
2. Check both pumps are set for the
same flow rate.
▪ Differences in liquor levels
in coupled machines
1. Check the liquor level is same in
both kiers.
2. Load each carrier with same size
carrier and batch.
▪ Trapped air bubbles (air
pockets) in the material
causing problems in liquor
penetration
Ensure proper wetting and
deaerating of the package
[110,
149,
253]
▪ Incorrect addition of
chemicals (salt, hydro,
alkali) in the bath leading to
rapid exhaustion
Use metered dosing system for
optimum exhaustion of dyes.
Shade change ▪ Presence of air in the
machine
The air in the machine should be
neutralized by the addition of hydro
or displacement with nitrogen. 1.7
[231,
345]
280
Table 4.36 (Continued)
Problems Probable causes Remedial measures Ref.
kg hydro and 1.7 L caustic 38 oBé is
required or each 1 m3 of air in the
system.
Dark stains or
spots
▪ Improper cleaning of the
machine and preparation
tanks
Clean the machines, dye preparation
tanks and supply lines regularly.
[231]
Light spots ▪ Trapped air bubbles (air
pockets) in the material
leading to reserve areas
1. Ensure proper wetting and
deaerating of the package.
2. The temperature ramp rate should
be kept between 1-1.5 oC/ min.
[110,
149,
253]
Leakage in
package
column
▪ Use of inappropriate sealing
cap
The package column must be fitted
with a suitable and proper sealing
cap.
[231]
▪ Using too low pressing
density
The compression between 10-35%
should be used. The recommended
pressed densities are 420-460 g/l for
PES/Co and 420-500 g/l for
PES/Wo.
▪ Long height of the package
column
1. Reduce the height of the package
column.
2. Use of double carrier is better than
single carrier.
Shade variation
within package
layers
▪ Variation in pressed density Check the homogeneity of the
pressed density.
[231]
▪ Inappropriate liquor flow
times (in-out and out-in)
Change the liquor flow times.
▪ Use of incorrect flow rate Select the correct flow rate.
281
Table 4.36 (Continued)
Problems Probable causes Remedial measures Ref.
Pressure or
luster marks on
inner yarn
layers
▪ Using too high pressed
density
Reduce the package density. [231]
▪ Too high yarn shrinkage The residual yarn shrinkage should
be less than 5%.
Package
deformation
and yarn
abrasion
▪ Incorrect setting of spacers
leading to leakage
Correct fit the right type of
intermediate spacers.
[231]
▪ Use of too high flow rates Reduce the flow rate.
▪ Inappropriate circulation
times
Use correct liquor circulation times
as per material type.
▪ Incorrect wetting out of the
material due to the presence
of air
1. Ensure proper wetting out of
material and remove any air
from the package.
2. Set the flow converter in a
neutral position when filling for
liquor blow in both directions.
▪ Abrupt increase in the
differential pressure.
Slowly increase the differential
pressure.
Sloughing of
outer yarn
layers
▪ Abrupt increase in the
differential pressure
Slowly increase the differential
pressure.
[231]
▪ Inadequate wetting out of
the yarn package.
1. Add a wetting agent.
2. Set the flow converter in a
neutral position when filling for
liquor blow in both directions.
Swelled
package
shoulders with
a puffy
appearance
▪ Foaming caused by wetting
agent
Use a non-foaming wetting agent. [254]
▪ Foaming due to leakage in
the pump. The air can enter
the pumping chamber and
Ensure the pump is properly sealed.
282
Table 4.36 (Continued)
Problems Probable causes Remedial measures Ref.
produce foam with
circulating dye liquor
Poor color
yield
▪ Oligomer deposits leading to
reduced liquor flow
Check the machine for oligomer
deposits and clean it regularly.
[85]
▪ Presence of air in the
machine
The air in the machine should be
neutralized by the addition of hydro
or displacement with nitrogen. 1.7
kg hydro and 1.7 L caustic 38 oBé is
required or each 1 m3 of air in the
system.
[231,
345]
Poor hand ▪ Oligomer deposit on the
yarn surface
1. Drop the dyebath at high
temperature.
2. Use a non-ionic reducing agent
during dyeing.
3. Dyeing of polyester in alkaline
medium depending upon the
possibility.
[85]
4.8.2.2 Fabric dyeing
Various machines can be used to dye blended fabrics in rope and open width form. These include
jet, beam, jig, and winch.
In winch dyeing, the fabric is processed in the form of endless rope through a stationary
liquor with the help of winch reel. The dye liquor exchange in a bath with the liquid in the fabric
is low. This can be enhanced by increase winch speed, but it is accompanied by high stress in the
fabric. The use of a winch is limited [346].
During beam dyeing, the fabric is wound on a perforated metal cylinder and liquor is
circulated through the beam with the help of a pump. The uniform circulation through the whole
batch and across the complete width is required for uniform dyeing [68]. The variation in batching
283
density, too tight winding and improper location of selvages on the beam leads to problems. This
method of dyeing is only suitable for fabrics having enough permeability, uniform fabric
constructions and knit goods that can uniformly wind with appropriate tension on to a beam. As
the fabric has little or no chance of relaxation and shrinkage the fabric has a firmer and flatter hand
and high luster. This is suitable for certain polyester/cotton and polyester/linen fabrics [9, 110].
Jig dyeing is a circulating goods type dyeing machine where the fabric in open width form
is passed back and forth from one roll to another through an open dyebath. The lengthways fabric
tension should be kept minimum to avoid the extension of fabric under hot and wet conditions.
The jigs can be open where the fabric roll is exposed to the atmosphere or can be enclosed by
covers. The open type jigs may cause temperature variation of the roll especially the selvage areas.
This affects the rate of the dyeing and leads to a listing problem. The cooling of the roll reduces
the rate of dyeing thus creating problems in achieving dark shades. Since in jig dyeing the fabric
is passed back and forth from one roll to another, the dwell time in roll for fabric at each end of
the batch is much smaller than the center of the batch. This provides inadequate time for the
complete absorption of liquor to fiber interior before it meets the liquor again. This may cause the
fabric end to be dyed paler or of a different shade than the rest of the batch. This problem is known
as ending. To reduce the listing and ending problems, the temperature of the fabric batch and
dyeing bath temperature should be as close as possible. This is achieved by using hoods that reduce
heat loss and by heating the air space within the dyeing chamber to dyeing temperature [347].
During jig and beam dyeing of fabric, the following factors need to be controlled to avoid
unlevel dyeing due to batch related problems [68, 85]:
▪ Correct tension during batching;
▪ Adequate size of the batch; and
▪ Right amount of overlap.
The jet dyeing technology is well-established and most popular method of batch dyeing
blended fabrics in rope form. The jet of dyeing liquor created through venturi action is used to
move the fabric in the machine. A modified form of jet dyeing machine known as soft flow is very
common which consists of a winch reel along with the jet to transport the fabric. The fabric can be
dyed at higher temperature conditions and very liquor ratios can be used. For error free dyeing the
important factors to consider are rope speed, rate of rise of temperature, dwell time and rate of
284
cooling. Due to the high speed of fabric movement foaming may take place. This can be overcome
by using a suitable antifoaming agent. It is sometimes necessary to add a lubricant to minimized
friction and reduce the tendency for crease marks. The machine cleaning is essential to remove
dye deposits, if any, especially after dyeing of darks shades and to remove oligomer deposits. The
jet dyeing machine offers much more lengthwise relaxation of fabric than winch dyeing. The
problems associated with winches are fabric extension, crease marks and hydro-setting synthetic
fabrics in high temperature machines that cannot be rectified by post heat-setting [346].
Sensitive fabrics such as velvet and corduroy are not suitable for dyeing on jet dyeing
because of the possibility of crushing and creasing. The cooling rate of the dyebath up to around
80 oC should be kept lower to avoid creasing of the dyed fabric. For lightweight fabrics, there may
be a problem of the larger lengths to ensure economical machine loading. The jet or overflow
dyeing machine provides relaxed and tensionless conditions to fabrics. The dyed fabrics have
softer, bulkier and some luster. This is preferred for fabrics such as polyester/viscose knit goods
[9].
Most of the knitted fabrics are dyed by soft flow dyeing machines. The following machine
factors influence the batch dyeing process [297]:
▪ Chamber loading
The machine should not be overloaded otherwise the fabric will not float causing the
fabric to jam in front of the machine and create problems for a winch to lift the fabric.
The machine loading depends on construction, width, blend ratio, weight per unit meter
of the fabric.
▪ Rope cycle time
The rope circulation speed and rope length influence the rope cycle time. It should be
1-1.5 min for disperse, 1-2 min for vat, 2-3 min for reactive dyeing.
▪ Nozzle (jet) pressure and size
The size is based on fabric weight and must be ½ to ¾ occupied by fabric. Lower jet
pressure cause fabric to jam in front of the machine. Too high pressure cause
entanglement of the fabric at the winch and accumulate fabric at the back of the
machine.
285
▪ Liquor ratio
It is calculated from actual bath volume and fabric weight. The additions carried out
during the dyeing cycle with increase the liquor ratio. The heavier fabric requires more
liquor than light fabrics.
Of all the cellulosic fibers, the regenerated cellulosic fibers are more sensitive and therefore
requires more attention in dyeing as compared to cotton or linen. The dyeing properties of
regenerated cellulosic fibers depends on the dye class, dyeing process and fiber type and the origin
of the fiber. It is important to understand that not two regenerated cellulosic fibers are the same
[312]. The dyeing in rope form needs to consider the creasing tendency of these fibers. The heating
and cooling rate should be kept lower to avoid crease formation. It is recommended to add a
lubricating agent in all processing baths. The thicker and denser woven fabrics can form creases
during rope dyeing. The fabric speed should be set according to fabric construction and dye class.
For fabrics having open structure and knitted fabrics should use lower fabric speed to avoid
hairiness problems and longitudinal stretching of fabric [188].
The elastic recovery of cotton is lower compared to synthetic fibers. A lubricating agent is
required to avoid the formation of creases during rope processing in a batch dyeing machine. It is
important to note that not all lubricant agents are suitable for all fiber types due to differences in
fiber properties. The selection must be done keeping into consideration the fiber type being
processed [301]. During processing of fabrics containing flat polyester filaments if the fabric is
not moving at even speed at the required fabric speed it may be essential to increase the nozzle
pressure or use a smaller nozzle size. The cotton rich fabrics if the fabric is running smoothly the
nozzle pressure can be reduced.
In the dyeing of polyester containing blends by batch process, the dyer has to deal with the
problem of oligomers. Oligomers are low molecular weight polymers (trimers) formed as a
byproduct during polymerization of polyester fibers. Although they are present in small quantities,
they may cause serious problems in dyeing [67]. The degree of timer release to the fiber surface
depends on the various processing stages the fiber has gone through such as drawing, texturizing
and heat setting [85]. The oligomers during dyeing may lead to frosting, poor running of material
in subsequent processing and soiling of the machine. To avoid these problems, it is recommended
to follow multiple approaches such as discharging the liquor at high temperature, use of short
286
dyeing cycle, avoid carriers and reduction clearing [253]. Special auxiliaries are available that
helps in dispersing or dissolving of oligomers. The machine should be cleaned regularly to avoid
redeposition on the fabric [67, 233].
The machine malfunction may occur due to a variety of mechanical and electrical related
reasons. The common problems caused by these malfunctions are summarized below [297]:
▪ Water filling problem;
▪ Faulty pressure release system;
▪ Unsatisfactory heating and cooling rate;
▪ Boiling of liquor above 100 oC;
▪ Problems in adjusting differential pressure;
▪ Inadequate nozzle pressure;
▪ Problems in dyeing related to one chamber in a multi-chamber machine;
▪ Differences in liquor level between chambers;
▪ Faulty chemical tank pressure pump; and
▪ Liquor circulation pump not working.
It is recommended to check the residual oils present in the fabric before dyeing. Any oil
present in the fabric is removed from the fabric during dyeing and the actual fabric weight available
for dyeing is affected. Since the weight of the fabric is measured in the dry state before the start of
the dyeing process and determines the amount of the dyes, this reduction in fabric weight leads to
more dye in the dyebath than actually required. This cause matching problem and poor
reproducibility. The bath appearance after 5 minutes of fabric loading into the machines may help
in determining the residual oils present in the fabric. If the bath has a very pale or white milky
appearance and contains no or low foam it is safer to start the dyeing process. The bath needs to
be dropped if it has a white or pale creamy appearance and some foam. Lastly, if the appearance
of the bath is thick creamy and contains heavy foam and pump is cavitating it is recommended to
drain the machine and refill [297].
The main dyeing problems associated with batch dyeing machines are summarized in Table
4.37.
287
Table 4.37: Dyeing problems related to batch dyeing machines and their countermeasures.
Problems Probable causes Remedial measures Ref.
Reproducibility ▪ Variations in rope lengths in
batches
Use the same rope lengths to give
the same rope cycle time to each
batch.
[297]
▪ Variation in fabric length in
batches
Strictly follow the procedure to
measure the batch size.
Correlate the variation in length
and shade deviation from the target.
▪ Damaged or worn out Teflon
rollers of winches causing
different reel speeds.
1. Replace worn out Teflon rollers.
2. Avoid using low cost lubricating
agents based on acrylamide. Use
fatty acid based lubricant and
wetting agent.
[301]
▪ Use of different dyeing
programs
Use consistent dyeing conditions. [297,
301]
▪ Use of different liquor ratios. Use consistent dyeing conditions. [301]
▪ Fabric with variation in gsm
leading to differences in a
rope length
Ensure gsm of the fabric are the
same in different ropes and batches.
[301]
▪ Difference in the tightness
factors of the ropes
Ensure the fabric tightness factor is
similar for all ropes.
[301]
▪ Differences in liquor ratio Maintain the same liquor ratio.
Adjust the bath volume based on
fabric weight.
[297]
▪ Variation in liquor ratio due
to direct heating system
1. Use an indirect heating system
if possible.
2. Take into consideration change
in liquor level due to
condensation of steam.
288
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Differences in nozzle settings
from one chamber to another
Ensure the same nozzle settings. [297]
▪ Differences in winch speed
from one chamber to another
Check winch speeds, especially
after maintenance work.
[297]
▪ Blockage of nozzle gaps Check the filter. It should be
working properly.
▪ Differences in the timings of
the addition of chemicals
Ensure the operators add the
chemicals at the same time and
temperature.
[297]
▪ Differences in the number of
passages of fabric
Ensure in each batch the fabric
passes through nozzle the same
number of times.
[297]
▪ Presence of air in the
machine
The air in the machine should be
neutralized by the addition of hydro
or displacement with nitrogen. 1.7
kg hydro and 1.7 L caustic 38 oBé
is required or each 1 m3 of air in the
system.
[231]
Unlevelness ▪ Poor circulation of the fabric
due to interruptions, knots,
and overloading
Setup the machine carefully. The
fabric ends should be properly
joined.
[253]
▪ The temperature ramp rate is
higher in the critical dyeing
region
Use the correct dyeing program to
control the temperature ramp rate.
It should be kept between 1-1.5 oC/
min to ensure level dyeing.
[9,
253]
▪ Too slow or too fast rope
speed
Check rope speed. The rope cycle
time should be the same.
[297,
301]
289
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
Check the correct rope speed is
programmed for this rope length.
Recheck the correct
synchronization of motor speed.
▪ Variation in pressure head in
the tubes leading to a
reduction in speed of the rope
Increase the pump rate to increase
the pressure. The pressure should
be even in all tubes.
▪ Stoppage of the rope due to
damaged stitches during
running
Ensure the rope ends are stitched
properly with strong threads.
▪ Stoppage of certain portions
of fabric in the dyebath due
to entanglement and twisting
Avoid accumulation of the fabric in
the dyebath.
[301]
▪ Use of a low tension during
jig dyeing leading to the
formation of folds
Use optimum tension settings
according to fabric.
[67]
▪ Insufficient agitation of the
liquor in the dyebath
Use high fabric speed.
▪ Insufficient flow of liquor
through the fabric layers
during beam dyeing
Use high liquor flow rate.
Check winding of the fabric on the
beam.
[347]
▪ Variation in the flow of
liquor across the fabric due to
channeling caused by too
tight or too loose fabric
winding
Ensure the winding of the fabric is
uniform on the beam.
[347]
290
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Slower liquor circulation rate
leading to higher exhaustion
of the dye
Use the optimum circulation rate.
The maximum exhaustion should
be restricted to 2% per cycle.
[79]
▪ Variation in dyebath
temperature due to heat loss
1. Ensure the dyeing machine is
covered with lid.
2. Ensure the heating system is
working properly.
▪ Trapped air bubbles (air
pockets) in the material
causing problems in liquor
penetration
After beam loading, fill the
autoclave with water and circulate
the water alone without any
chemicals.
[110,
149,
253]
▪ Use of direct steam heating
causing the disperse dye
dispersion to break down
Avoid exposing disperse dye
solution to live steam heating. Use
indirect heating.
[348]
Poor color
yield
▪ Lower dyebath exhaustion
due to high residual moisture
in fabric before the dyeing
process
Check the last drying step in
pretreatment. The residual moisture
should be uniform and according to
the fiber type and blend ratio
(moisture regain).
[342]
▪ Reduction in fabric
temperature due to heat loss
in open jigs
Use closed jigs whenever possible.
▪ Cooling of selvages due to
heat loss in jig causing
differences in rate of dye
uptake
1. Use closed jigs with hoods to
avoid heat loss.
2. Ensure proper heating of the air
space inside the jig.
[347]
Shade change ▪ Use of different liquor ratios Use consistent dyeing conditions. [301]
291
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Presence of air in the
machine
The air in the machine should be
neutralized by the addition of hydro
or displacement with nitrogen. 1.7
kg hydro and 1.7 L caustic 38 oBé
is required or each 1 m3 of air in the
system.
[231]
Abrasion or
chafe mark,
Pilling of
fabrics
▪ Rubbing of fabric surface
caused by uneven or
damaged machine lining and
fabric guiding elements
The machine lining, fabric guiding
elements should be even.
[150,
346,
349]
▪ Mechanical friction due to
machine overloading
Avoid using very large batches.
Use a lubricant agent.
[67,
253]
▪ Stationary material in the
running machine (knots)
Ensure the fabric ends are properly
stitched before dyeing.
[253]
▪ Using very high machine
speed
Use optimum machine speed
according to the rope cycle time.
[253]
▪ Incorrect nozzle size and gap Use correct nozzle size and gap to
ensure proper opening of rope. The
cotton/lycra fabric requires a higher
flow.
[297]
Poor
appearance
▪ Longer duration of running
due to reprocessing.
Use a lubricating agent.
[301]
▪ Variation in fabric tension in
a jig during dyeing leading to
structure distortion
Ensure the tension is properly
adjusted according to the fabric.
[67]
Moire (wavy
appearance)
▪ Too tight batching on the
beam
1. Avoid tight winding of the
fabric on the beam.
[110,
194,
350]
292
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
poor
appearance
2. Avoid using too high
differential pressure.
3. Ensure the fabric has high
absorbency.
▪ Incorrect flow of liquor in
beam dyeing
1. Ensure the dye liquor circulation
as per the following sequence:
Inside-out: 5 minutes
Outside-in: 3 minutes
until temperature reaches 110 oC.
After that maintain inside-out.
2. Perform caustisizing or treat with
3-5 g/L carrier at 130 oC for 30
minutes.
[194]
Dimpling or
cockling of
fabric surface
▪ Using too low rope speed
during cooling
1. Use increased liquor ratio.
2. Run the machine at optimum
speed.
3. Use a large diameter nozzle.
[301]
▪ Too slow fabric speed during
the cooling phase
Use optimum machine speed
according to the rope cycle time.
[346]
▪ Dropping the bath at too high
temperature leading to shock
cooling of fabric (especially
viscose blends)
Avoid draining the bath at a very
high temperature.
[297]
Crush marks ▪ Running fabric at a very high
speed
1. Increase the liquor ratio.
2. Use a slower rate of cooling.
[297]
▪ Improper selection of nozzle
diameter
Use a suitable diameter nozzle
depending on the fabric.
[323]
293
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
Creases/ rope
marks
▪ Poor suitability of the dyeing
machine.
Select a dyeing machine based on
the fabric.
[253]
▪ Too heavy fabric batch.
machine overload
1. Avoid using very large batches.
2. Use a lubricant agent.
[253,
297]
▪ Using too low liquor ratio Use a sufficient quantity of the
liquor in the machine.
[297,
321]
▪ Too slow fabric speed 1. Use optimum machine speed
according to the rope cycle time.
2. Use a lubricant agent.
[75,
253,
321]
▪ Twisting of the rope
accompanied by weight or
pressure
Use a lubricating agent. [67,
301]
▪ Incorrect nozzle size and gap Use correct nozzle size and gap to
ensure proper opening of rope.
[110]
▪ Improper loading of the
fabric into the machine
1. Ensure proper loading of the
machine.
2. In the case of rope dyeing, the
length of each rope and the
number of ropes need to be
determined in advance.
3. Check the batch for creases. It
must be straightened to remove
creases and folds.
[67,
150,
253,
301]
▪ Too rapid rates of
temperature rise or cooling
Use optimum heating and cooling
rates.
[347]
▪ Dropping the bath at too high
temperature leading to shock
cooling of fabric
Avoid draining the bath at a very
high temperature.
[297]
294
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Improper opening of fabric in
jig during dyeing
Ensure the fabric is properly
opened and crease free during
running.
[194]
▪ Incorrect stitching of fabric
ends leading to the formation
of creases
The fabrics should be stitched with
ends properly aligned and using
correct stitching thread.
[322]
End-marks ▪ Storage of fabric rolls on
their ends
Store and transport the fabric
horizontally in suitable bags.
[301]
▪ Improper dyeing process
(heating, cooling)
Adjust the temperature program.
Use a lubricating agent.
[253]
Seam marks ▪ Incorrect flow direction of
liquor in beam dyeing.
Avoid liquor flow in both
directions (in-out and out-in) in the
early stages of dyeing. In the early
stages, in-out flow is preferred.
[85]
Light spots ▪ Trapped air bubbles in the
material leading to reserve
areas
Ensure proper wetting and
deaerating of the package.
The temperature ramp rate should
be kept between 1-1.5 oC/min.
[110,
149]
Pale areas ▪ Use of wrong dyeing
machine settings (heating,
pressure, speed)
Use the correct dyeing program to
control the temperature ramp rate.
It should be kept between 1-1.5
oC/min to ensure level dyeing.
[253]
Streaks/stripes/
bar/bands
▪ Chafe or rub marks caused by
uneven or damaged machine
lining and fabric guiding
elements appear as dark
streaks (if occur before
1. Inspect the machine surface
regularly.
2. Use a lubricating agent.
[149,
150,
321]
295
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
dyeing) and light streaks (if
occur after dyeing)
▪ Crush fiber surface that dyes
darker than undamaged areas
Avoid rope tangling and crushing
during dyeing.
[149]
▪ Uneven distribution of dye
liquor at the bottom of the
batch due to prolong machine
stoppage
1. Avoid stopping the machine for
longer period.
2. Avoid using very big batch sizes.
[67,
194,
321]
▪ Too high tension on fabric
during jigger dyeing
Ensure the fabric tension is
optimum by proper adjustment of
guide rollers and tensioning device.
[321,
323,
350]
▪ Improper nozzle selection in
jet dyeing
Select nozzle based on fabric
construction and type.
[321]
▪ Improper rinsing of dyed
fabric
Ensure washing conditions are
adequate (speed, temperature, water
quantity).
[321]
▪ Localized uneven squeeze by
tension bar on a jig
Ensure the surface of the tension
bar is uniform and is properly
aligned.
[321]
Lustrous
stripes
▪ Pressing carried out at a too
high temperature and
pressure
Check the machine's settings
(nozzle pressure, reel speed) to
avoid tangling of a fabric rope.
[320]
Holes ▪ Projecting sharp objects in
the dyeing machine causes
punctured holes or tears.
Check the presence of sharp objects
in the machine.
[150,
301]
Dark spots ▪ Dye deposits in the machine Ensure the machine is cleaned
properly before the dyeing process.
[253]
296
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Foaming caused by high
turbulence in the dyebath
Use a defoamer [317,
351]
▪ Foaming caused due to air
leak in the circulation system
Check the liquor circulation system
for any leaks
[317]
▪ Use of direct steam heating
causing the disperse dye
dispersion to break down
Avoid exposing disperse dye steam
to live steam heating. Use indirect
heating
[348]
Dark patches ▪ Dark dyeing of damaged
fiber portions due to higher
nozzle pressure (especially
viscose)
1. Load the fabric with a lubricating
agent.
2. Ensure proper piling and smooth
running of fabric.
[301]
Widthwise
shade
variation/
listing
▪ Inadequate circulation of
liquor within fabric rope
1. Avoid too tight ropes.
2. Use correct size of nozze
[346]
▪ Too rapid cooling of selvages
due to heat loss in jig causing
differences in rate of dye
uptake
1. Use enclosed dyeing machine if
possible, to avoid heat loss from
the sides.
2. Ensure proper heating of the air
space inside the jig.
3. Select dyes with which are less
sensitive to temperature
variations.
[150,
347]
▪ Uenven heating along the
width in jigger leading to
temperature variations
1. Ensure uniform heating the
dyeing liquor.
2. Circulate the liquor in the dyeing
trough.
[68,
323]
▪ Poor winding of fabric on the
beam or roller causing
1. Ensure proper winding of fabric
on the beam.
[110,
253]
297
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
uneven package density
across the width
2. Check the shrinkage of fibers in
the blend.
▪ Poor batching of the fabric
leading to a difference in
liquor pickup and cooling of
the selvages
Ensure the winding of the fabric is
edge to edge and tension should be
uniform.
[67]
Center selvage
variation
▪ Uneven overlapping of the
beam perforations
Ensure the fabric is properly rolled
on to the beam edge to edge with
no overlapping of selvages.
[67,
85]
▪ Tight batching on the beam Check the shrinkage of fibers in the
blend.
[110]
▪ Using too big batch size on a
jig
Avoid using too big batch size. [323]
Perforation
marks
▪ Incorrect rolling of the fabric
on the beam
The beam should be lapped with 5-
10 layers of loosely woven PP
material.
[67]
▪ One direction (in-out) flow of
liquor in beam dyeing
1. Ensure the dye liquor is flowing
in both directions (in-out and
out-in).
2. The beam should be lapped
with 5-10 layers of loosely
woven PP material.
[85]
Inadequate
fastness
▪ Improper rinsing of the
substrate due to lower water
pressure
The water supply pressure should
be 2-3 bar.
[297]
Rubbing
fastness
▪ Inadequate dye fixation
conditions (lower
Use appropriate dyeing fixation
conditions (time and temperature).
Perform reduction clearing.
[253]
298
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
temperature or shorter dyeing
time)
Two sidedness ▪ Slight difference in depth
between face and back of
fabric due to very high
tension or differences in
tension during batching
Ensure correct batching of fabric
with uniform tension.
[67,
323]
Tailing ▪ Insufficient flow of liquor
through the fabric layers
during beam dyeing
1. Check the fabric is not tightly
wound or use of oversized batch.
2. Use a pump with a larger liquor
flow rate.
3. Ensure the reverse circulation
system is working properly.
[67,
110]
▪ Variation in tension during
winding of the fabric on the
beam due to an increase in
the diameter of the batch
1. Ensure the fabric tension remains
the same in the batch during
winding.
2. Avoid using an oversized batch.
[110]
▪ Incorrect additions of the
dyes and chemicals
Ensure the dyes and chemicals are
added in a proper manner.
[323]
▪ End portions of the batch are
dyed differently than the
middle portions of the blend
on jig due to differences in
the speed of the fabric
Ensure the fabric speed remains the
same irrespective of batch size and
during loading and normal run.
[67]
▪ Denser winding of the pre-
runner cloth on the beam
affecting liquor flow
Use an adequate number of
windings of the pre-runner fabric.
The fabric should have open
structure.
[110]
299
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
▪ One direction (in-out) flow of
liquor in beam dyeing
Ensure the dye liquor circulation as
per the following sequence:
Inside-out: 5 minutes
Out-in 3 minutes
till the temperature reaches 110 oC.
After that maintain in-out.
[85,
194,
323,
350]
▪ Inadequate dwell time for
complete adsorption of dyes
during batch reversal in jig
Inherent jig problem. It cannot be
corrected.
[347]
▪ Variation in dye rate of fiber
due to variation in the
temperature
1. Use closed jigs with hoods to
avoid heat loss.
2. Ensure proper heating of the air
space inside the jig.
3. Use rubber rollers or metal
rollers with long leader cloth to
prevent heat loss.
[68,
346,
347]
▪ Use of wrong dye program
having a higher temperature
ramp rate in the critical
dyeing region
Use the correct dyeing program to
control the temperature ramp rate.
It should be kept between 1-1.5 oC/
min to ensure level dyeing
[9,
253]
Poor
dimensional
stability
(shrinkage)
▪ Lengthwise distortion caused
by the machine
Adjust machine settings according
to the substrate being processed.
[253]
Fabric/stitch
distortion
▪ Improper or too high tension
on the fabric
Adjust machine settings according
to the substrate being processed.
[253,
346]
▪ Incorrect seams Use straight seams. [253]
300
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Using too high fabric speed. Reduce the nozzle pressure and
winch speed.
[297]
Luster marks ▪ Physical change in fiber
caused by local pressure and
higher temperature
Avoid prolonged contact of
stationary material with the hot
machine.
[253]
Poor hand ▪ Wrong dyeing program
(temperature/time)
Select a suitable dyeing program. [253]
▪ Oligomer deposit on the
fabric surface
1. Drop the dyebath at high
temperature.
2. Use a non-ionic reducing agent
during dyeing.
3. Dyeing of polyester in alkaline
medium depending upon the
possibility.
[85]
Entanglement
of fabrics
▪ Lower jet pressure Adjust the jet pressure based on
fabric.
[297,
301]
▪ Overloading of the machine Avoid overloading the machine.
Calculate fabric weight based on
fabric gsm, rope length, tube
diameter.
[297,
301,
346]
▪ Too high jet pressure 1. Adjust the jet pressure based on
fabric.
2. Load the fabric at a warm
temperature.
[301]
▪ Ballooning of fabric as air is
entrapped due to densely
sewn seam and tightly knit
fabric structure.
1. Cut a vertical slit of 10-15 cm
near the joint to allow air to
escape.
2. Use a larger diameter nozzle.
[297,
301]
301
Table 4.37 (Continued)
Problems Probable causes Remedial measures Ref.
3. Use a deaerating and penetration
agents.
4. Use a chain stitch or butt stitch to
join the rope pieces.
4.8.3 Problems caused in continuous dyeing machines
The continuous dyeing is the most commonly used method of dyeing woven polyester/cotton
blends. Continuous dyeing usually involves long runs (> 5000 m) and gives high color yields,
reproducible results at lower costs as compared to batch methods. With increasing trends of shorter
trends put pressure on continuous dyeing to produce results at lower costs [9]. Different methods
can be used for the continuous dyeing of blends. The common procedure is to impregnate the
fabric using a padder with the dye solution or dispersion (depending upon the dye class). The fabric
containing dye liquor is then subjected to various treatments to fix the dyes. It can be obtained
either by chemical treatment or application of energy or a combination of both. The heat in the
form of steam or dry heat is usually used as a source of energy that creates required chemical
and/or physical changes. The fixation of the applied dye is thus achieved [352]. During semi-
continuous dyeing, the fabric is continuously impregnated with the dye liquor followed by a slower
fixation treatment. The dye liquor in the fabric gradually diffuses into the fiber interior and fixation
of dye is gradually achieved. The unfixed dye is then removed by rinsing and soaping. This is
followed by drying. Table 4.38 shows the common sequences used in semi-continuous and
continuous dyeing of blended fabrics [128].
302
Table 4.38: Different sequences used in the dyeing of blends by semi-continuous and continuous
process.
Process Type Dye class Blend
Pad-batch-beam Semi-continuous Disperse/reactive Polyester/cellulosic
Pad-batch-jet Semi-continuous Disperse/reactive Polyester/cellulosic
Pad-dry-thermofix-jig develop Semi-continuous Disperse/vat Polyester/cellulosic
Pad-dry-thermofix Continuous Disperse/reactive Polyester/cellulosic
Cellulosic/elastane
Disperse Polyester/elastane
Pad-dry-chemical pad-steam Continuous Reactive Cotton/viscose
Cotton/modal
Pad-dry-thermofix- chemical
pad-steam
Continuous Disperse/reactive Polyester/cellulosic
Disperse/vat Polyester/cellulosic
Disperse/sulfur Polyester/cellulosic
A typical continuous dye range for polyester/cellulosic blends depending upon the dyeing
method, as shown in Figure 4.7, consists of scray, a compensating device, padder, infrared dryer,
hot flue, cooling cylinders, scray, chemical padder, steamer, washing range, can dryers and finally
scray [61]. This range is designed for dyeing both the polyester and cellulosic components in the
blend in one pass through the range. The polyester is dyed by a pad-dry-thermosol process in the
first stage of the range. Latter stages of the range are used to dye cellulosic fibers using a pad-
steam process [353]. Typically in dyehouse, this range exists in two units: Pad-dry-thermosol and
pad-steam-wash-dry [61].
Figure 4.7: Continuous dyeing range for PES/CELL blends.
pad
hot flue dry wash-off I.R.
pre-dry chemical
pad steam
303
The padder is the critical unit in continuous dyeing and gets great attention from dyehouse
technicians [61, 353]. After creases, width-wise shade differences are the largest cause of customer
rejects [61]. The hardness of rubber covering depends on fiber and fabric construction and should
be the same for both padders [133]. The nip-width or contact zone of the padder needs to be the
same across the full working width of the padding rollers. This can be checked by a carbon paper
sandwich test or powder spray test. The width of impressions or rectangular band between different
points is recorded. When pressure is applied to the sides of the central mandrel, the pad rollers
may deflect causing more pickup at the center than at the edges. Different approaches used to
overcome this problem involves medication of the camber of the rubber bowl or using alternative
padder design (e.g., Kuesters swimming roller) [61, 353]. As fabric pick-up is affected by various
factors other than uniformity of the nip such as fabric running speed, variations in the fabric due
to preparation or weaving, continuous monitoring during production is important. This is usually
done by measuring the moisture of the fabric at the center as well as the sides. These sensors are
part of a closed-loop system. Any variation in the pickup detected by the sensors is sent to the
padder for automatic pressure adjustment. It is recommended to install such a system before and
after padder as variation in incoming moisture may cause shade differences [354, 355].
The correct stitching of fabric ends is essential to avoid stich marks in dyed fabric. If cotton
thread is used for dyeing it absorb more solution as compared to synthetic fibers and may cause
stich impression on fabric layers. It is recommended to stich polyester containing blends with
100% polyester thread to avoid this problem [67, 322].
For level dyeing, fabric running speed and the immersion length should be constant during
the padding process. The immersion length refers to the distance between the point of entry to the
pad liquor to the point where the fabric exits the liquor. The level control can be used as a measure
to control immersion length but may not be very accurate for small trough sizes. Small troughs are
preferred due to less wastage. Different trough designs are available depending on fabric
characteristics [61].
The important factors affecting the padding process are as follows [100].
▪ Fabric related:
- Uniform fabric width;
- Free of creases;
- Free of curled selvages;
304
- Consistent absorbency; and
- Uniform temperature.
- Homogeneous moisture content.
▪ Padder related:
- Defect-free roller covering;
- Uniform roller pressure across the width;
- Homogenous liquor temperature;
- Uniform liquor feed; and
- Consistent liquor level in the pad trough.
A common problem that may be encountered in the continuous dyeing attributed to padding
is tailing and listing. Tailing is the gradual decrease in dye concentration in the pad liquor leading
to variations in hue or depth along the fabric length of a dye lot. Tailing stops once the equilibrium
is reached between the dye moving towards the fabric and dye fed into the pad trough. Another
similar problem seen in the pad-dry-thermofix-chemical pad-steam process for polyester/cellulosic
blends is known as reverse tailing or chemical pad bleeding. The unfixed dye present on the dried
substrate desorbs into the chemical pad. This also causes shade variation along the fabric length.
This movement stops as the equilibrium is reached after several minutes. A large quantity of
electrolyte is added in the pad liquor to avoid this problem. Another approach is to add a small
quantity of the pad liquor into the chemical pad [128].
The padding liquor temperature is an important parameter as it affects the stability of the
dyes. An increase in temperature may cause instability and leads to tailing. It has been found that
an increase in temperature of pad liquor from 20 oC to 25 or 30 oC results in higher color depth
due to higher wet pickup. These temperature variations are due to the temperature differences
within the fabric rolls especially when big batching is done, or fabric may be over dried. It is
recommended to have a cooling roller before padding to avoid this problem also final drying
temperature should be controlled [353, 356]. It is recommended to pass the fabric through a skying
unit before drying. The skying units consist of a series of top and bottom roller that provides
adequate time for dye penetration [357].
The drying section aims to remove the moisture and leave the dye uniformly deposited on
the fabric. Drying is performed in two stages; firstly using infrared units for preliminary drying
305
and secondly utilizing hot flue to complete the drying [133]. During the drying process as the water
is evaporated the dye present in the fabric moves to the surface and this movement is known as
migration [118]. After impregnation and squeezing, the distribution of the dye liquor on the fabric
is nearly homogenous and is held in capillary pores. During drying, the water starts evaporating
from the fabric surface is substituted with water moved by capillary forces from the fabric interior.
The dye dissolved in water also carries to the fabric surface during this movement. The water
movement also occurs due to the concentration difference between the fabric surface and the
interior provided the capillaries contain water. The movement stops when the dye size becomes
large so that its movement is hindered (agglomeration due to anti migrating agent) or the coherence
of the water channel is broken (migration threshold). The migration stops on reaching the
migration threshold and varies considerably for different materials. Hydrophobic fibers contain
more water on the fabric surface as compared to hydrophilic fibers that have more swelling water.
A typical cotton fabric having a wet pickup of 75% has a migration threshold of 25% (2/3rd of the
water is evaporated). For other fibers the corresponding values are: viscose or lyocell 40%, wool
36%, polyester/cotton 20%, nylon 10%, polyester 5% [100, 118]. Fabrics with the smaller specific
surface area have lower migration threshold values [118].
Figure 4.8: Schematic representation of migration types during intermediate drying (G represents
the direction of fabric movement).
Depending upon the movement of the dyes in the fabric during drying, the migration can
be categorized as four types as shown in Figure 4.8. These are horizontal migration (A), selective
horizontal migration (B), vertical migration (C), and selective vertical migration (D) [358]. In
horizontal migration, the dye particles migrate over the fabric surface while vertical migration
involves the movement of the dye particles from the interior to the fabric surface. The selective
G
A B
C D
306
horizontal and vertical migration are the special case of horizontal and vertical migration that
involves movement of the dye particles of different class at different rates on the fabric surface
and from interior to the surface respectively. These are important specially in blends where
different classes of dyes are present in the substrate at the same time. Numerous faults may occur
in continuous dyeing due to migration, that is difficult to rectify, are described in Table 4.39 [9,
100, 118, 358].
Table 4.39: Migration in intermediate drying and associated faults.
Migration related faults Description
Unlevelness Faded or washout appearance of the portions of the dyed
fabric.
Tailing Variation in the shade or hue along the fabric length due to
variation in drying rate.
Listing Variation in the shade or hue along the width of the fabric.
Stripes or streaks Differences in rates of drying over the fabric surface,
uneven drying.
Frosting Dye migration from inside to the surface of the fabric.
Two-sidedness Shade difference between two sides of the fabric due to
differences in drying rate of two sides of the fabric, one side
being hotter than the other. Hotter side dye darker than
another side.
Dark selvages Selvage area dyes deeper as this region has a higher
temperature than the center of the fabric.
Light selvages Selvage area dye lighter as the fabric center has a higher
temperature than the side of the fabric.
Poor penetration Undyed zones in the fabric at the yarn crossover point and
interior of the fabric.
Infrared pre-drying prevents the migration of the dye by rapidly reducing the moisture
content of the fabric moisture to the migration threshold that is considered optimal to avoid dye
307
migration [353]. In radiation drying, the temperature difference between fabric interior and surface
is minimal as compared to convection and conduction radiation [128]. The infrared drying units
are either gas or electric fired. The radiant heat source has a temperature of around 800 oC and the
radiation peak is 3 µm. The infrared radiators are placed in superimposed rows on each side and
fabric is passed vertically. The unit is usually located just after the padder. For some fabrics, the
skying unit is required as mentioned earlier [9, 133, 354, 355].
The dyes used for both fibers in the blend must show low migration and have similar
migration behavior. Disperse dyes having the same color index numbers may contain different
dispersing agents and thus exhibit different migration behavior. The liquid dye shows fewer
problems as compared to powder to grain type [118]. Dyes having smaller particle size show
greater migration tendency. Similarly, coarse yarns and more dense fabrics exhibit more migration
problems. Polyester/cotton blends have more tendency to show migration as compared to cotton
fabrics [100]. It has been reported that migration increases with the increase in polyester content
of the blend [359].
The following points are important to control migration [9, 100, 118]:
▪ Lower pick-up (less surface or free water molecules);
▪ Skying between padding and drying (better swelling, penetration);
▪ Addition of electrolyte to increase dye affinity (but a risk of tailing);
▪ Infra-red pre-drying (residual moisture after pre-drying);
▪ Well balanced airflow in the dryer (rate of drying);
▪ Use of an anti-migrating agent (especially for disperse and vat dyes);
▪ Better dye selection (dyes with similar affinity/diffusion properties, physical form of
the dye, dye class and constitution); and
▪ Good pretreatment of the fabric (levelness).
It is possible to measure the fabric moisture exiting from the infrared unit which can be
used to regulate the infrared unit. The moisture detectors are installed just before the drying unit
and measure fabric residual moisture [360]. Modern infrared units, to conserve energy and prevent
fabric charring or fusion, are equipped with an option to shut the sides off based on fabric width
and rotation option which moves the infrared panels away from the fabric or heat shields which
move in front of radiation panels in the event of machine stoppage [361].
308
The hot flue is the most common unit employed for drying and thermofixation of dyed
fabrics. Drying is carried out at 100-120 oC. A typical dye range consists of two or three of these
units depending on the dyeing process, first one serving as a drying unit and remaining as a dye
fixation unit. It consists of a series of driven top rollers and free bottom rollers. Drying is achieved
through circulating hot air which is directed to the fabric through nozzles. The drying and fixation
rate is managed by the temperature of circulating air, airflow volume, and nozzle pressure. For
optimum results drying should be uniform over width and length of the fabric [9, 133, 361].
Stenters can be used for thermofixation of dyes but their use is limited due to lower production
rates. The main drawback associated with it is the machine speed as some time is required for the
fabric to heat up and reach the dye fixation temperature. Their main advantage is the ability to
control fabric shrinkage along the width. Shade variations may occur at selvages if the dyed fabric
comes in contact with the base of the pin plates [61, 128, 133].
During the thermofixation process, the fabric is heated in hot air to a higher temperature
to carry out the fixation of dyes for 30 to 60 seconds depending on the dye class [114]. It is
important to control the temperature across the width of the fabric and should not exceed ± 3 oC
[128]. Higher the fixation temperature shorter will be the thermofixation time. It is recommended
to use the highest possible fixation temperature possible. To avoid ring dyeing and fastness
problems, the temperature or dwell time or both should not be too low [115]. Excess temperature
and dwell must be avoided to prevent fiber damage during dyeing. It is essential to consider the
stability of fibers under thermofixation conditions. The stability depends on the exposed
temperature and treatment time. Table 4.40 shows the suitability of different fibers in different
thermofixation conditions. The diacetate fibers damage starts damaging at 80 oC at so it is not
suitable [133].
The steaming is an important process for the fixation of vat, sulfur or reactive dyes on
cellulosic fibers. The tight-strand roller steamers are used to provide required steaming conditions
(102 to 105 oC, 20 to 120 seconds, depending upon the dye class). The uniformly distributed dye
present on the fiber surface diffused into the fiber interior during treatment with saturated steam
[128]. For vat or sulfur dyes, the steamer should be free from air. This gives full development of
shade. This is achieved by a slight overpressure in the steamer [128, 362]. The temperature should
not vary within the steamer. Widthwise variation may occur due to temperature differences in the
steamer [100, 363]. For steamer, inlet and outlet zones are important. [362]. To prevent steam
309
condensation and dropping the entry and roof the steamer is heated. There is a water seal at the
exit to prevent air from entering into the steamer and is fed with a slight overflow [61].
Table 4.40: Suitability of thermofixation conditions for different synthetic fibers.
Fiber
Maximum allowable temperature
(oC) with a treatment time of
20 sec 60 sec
Diacetate Not suitable Not suitable
Triacetate 220 210
Polyamide 210 200
Polyester 220 220
Acrylic 170-180 160-170
The washing stage performs different tasks depending upon the dye class used. It can be
classified as dilution wash, fastness wash and reaction process. The dilution wash removes caustic,
salts and chemicals from the fabric. During rinsing wash also called diffusion wash the unfixed
dye is removed. In the reaction process, oxidation of vat and sulfur dyes and neutralization are
performed. A typical washing section consists of six to eight boxes. In each washbox the fabric is
passed through a series of top and bottom rollers. The bottom rollers are filled with the washing
liquor. The movement of the rollers creates turbulence inside the washing chamber. The agitation
and excessive turbulence during washing at high temperature (100 oC) lead to a creasing problem.
The nip between the roller surface and the fabric create a force that squeezes washing liquor from
the fabric. The multiple dip and nip in each washbox facilitate the removal of impurities. The
washing efficiency is enhanced by use of counterflow within each wash box. The bottom roller in
the wash box is separated by dividing the plate that facilities counterflow. The wash boxes are
interconnected with each other such that overflow from one washbox is feed to the other to save
the water consumption. In between washboxes intermediate squeezers are present to reduce the
carryover liquor from the previous washbox. This helps in reduction of contamination from one
washbox to another [61, 128, 353].
The washing process is affected by the following factors [128, 364]:
310
▪ Amount of unfixed dye;
▪ The time allowed for washing (fabric speed and wash box capacity);
▪ The temperature of the washing liquor;
▪ Quantity of water;
▪ Quality of the water (impurities);
▪ Agitation (mechanical action);
▪ The attraction of the unfixed dye for the fiber; and
▪ The chemicals used to facilitate washing.
The washing process can be considered as a two-phase process. During the first phase
unfixed dyes and chemicals removed from the fabric surface that facilitates the removal of the
unfixed dye from the fabric interior in the subsequent step. This phased in favored by a high
number of bath changes, larger water quantity, and high mechanical action. In the second phase,
soaping and hot rinsing is performed to remove the unfixed dye and chemical from the fabric
interior. This phase is facilitated by higher washing temperature, lower water hardness, larger
water quantity, a high number of bath changes, lower quantity of unfixed dye to be removed, lower
substantivity of the dye with high diffusion.
With short runs, high-quality standards and short delivery times require the dyeing process
to be controlled precisely. To increase machine utilization grouping of shades is a must along with
automatic controls for a padder, drying units, drying cylinders and water usage. The control
equipment is widely available to make the dyeing process more efficient. Proper maintenance is
essential for avoiding machine faults along with quick fault rectification is mandatory for
maximizing machine efficiency [365]. That being said, the quality of the workforce cannot be
overlooked. Sometimes it is seen that the sophisticated equipment is available in the dyehouse but
not been used as its goal was not properly known to the workforce or middle management. Also,
it might have developed problems over time which were not corrected. It is the responsibility of
the senior management to make proper use of talent and equipment available. Producing the right
quality product for the right cost is always a challenge for all management [61].
Table 4.41 summarize the dyeing problems caused in different sections of the continuous
dyeing machine along with their causes and remedial measures.
311
Table 4.41: Dyeing problems in continuous dyeing machines and their countermeasures.
Problems Probable causes Remedial measures Ref.
Reproducibility ▪ Dye hydrolysis Check the pad trough cooling
system is working properly.
[120]
▪ Differences in drying conditions Ensure uniformity of the drying
conditions by controlling the IR
intensity, airflow rates, and
temperature.
[120]
▪ Differences in fixation
temperatures during batching
(CPB dyeing)
1. Consider the actual
atmospheric condition during
batch fixation.
2. Ensure the same temperature
during fixation if possible or
adjust batching time
accordingly.
[120]
▪ Variation in fabric immersion
time
Ensure the fabric speed is
uniform to have the same
immersion time.
[120]
▪ Variation in dwell time during
fixation
Maintain the contestant machine
speed.
[128]
▪ Variation in dwell time during
aftertreatment
Maintain the contestant machine
speed.
[128]
▪ Presence of air in the steamer
that retards reduction
Maintain a slight overpressure in
the steamer.
[366,
367]
Unleveleness ▪ Dye migration during drying 1. Set low pickup as possible.
2. Select dyes with a low
tendency to migration.
3. Use a suitable anti migrating
agent.
[67,
367]
312
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Variation in nozzle pressure in
hot flue dryer
Check nozzle cleanliness and
air supply over.
▪ Uneven padder pressure due to
the accumulation of fluff on the
padder surface
1. Ensure proper singeing of the
fabric.
2. Give the fabric extra wash to
remove excess fluff.
3. Clean the padder surface
regularly.
[67]
▪ Incomplete removal of moisture
after drying
Check the IR intensity and
drying conditions (dwell time,
temperature).
[79]
Pale spots or
areas
▪ Light areas where yarns cross
due to poor penetration
1. Use a wetting agent.
2. Increase impregnation time.
3. Change the pressure of the
rollers.
[118,
253]
▪ Light areas in the fabric due to
heavy migration
1. Use dyes with low migration
behavior.
2. Use the optimum quantity of
the anti-migrating agent.
3. For cotton wovens, use a wet
steaming method.
[118,
253]
▪ Condensation droplets from
steamer roof, exhaust canopies,
and stationary steamer rollers
1. Regularly check dryer and
pad-steam units.
2. The roof of the dryer and the
steamer should be heated.
3. Increase the steam flow.
4. Carefully skip the roller in
the steamers. The top rollers
[128,
253,
317,
366]
313
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
must be in contact with the
fabric.
▪ Differences in residual moisture
of the fabric
Check the last drying step in
pretreatment. The residual
moisture should be uniform and
according to the fiber type and
blend ratio (moisture regain).
[342]
▪ Accumulation of lint on the
padder or guide rollers
Clean the padder and guide
rollers regularly.
[317]
Widthwise
shade
differences/
listing
Variation in padder pressure across
the width
1. Check the fabric pick-up
regularly.
2. Check the padder pressure
settings.
3. Ensure constant air pressure
at the padder controls.
[61,
149,
253,
367-
369]
▪ Differences in fabric moisture
entering the padder
Ensure the fabric moisture
levels are uniform. Check the
drying settings of the preceding
stage.
[355]
▪ Differences in fabric weight
across the width
1. Adjust the padder pressure to
compensate for fabric
differences.
2. Check the incoming fabric
quality for uniformity in
fabric weight.
[355]
▪ Variation in intensity of the
infrared predryer
Ensure the IR intensity is
uniform across the width and
both sides of the fabric.
[348,
363]
314
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Variation in the moisture content
of fabric during drying
Ensure the IR intensity is
uniform across the width and
both sides of the fabric.
[128]
▪ Variation in air velocities across
the width in hot flue dryer
Check nozzle cleanliness and
air supply over the entire width.
[67,
317,
361,
363]
▪ Dye migration during drying 1. Set low pickup as possible.
2. Select dyes with a low
tendency to migration.
3. Use a suitable anti-migrating
agent.
[85,
118,
253,
369]
▪ Variation in temperature during
fixation (thermosoling)
1. Check temperature over the
entire width using
thermopaper or temperature
sensors.
2. Select dyes with lower
sensitivity to temperature
differences.
[118,
253,
348,
370]
▪ Variation in steaming
temperature
Ensure the sufficient supply of
steam in the steamer.
[100,
363]
▪ One sided inflow of dyeing
liquor into the trough
1. Check the injection pipe.
2. Ensure the liquor feeding is
uniform across the dyeing
trough.
[253,
368]
▪ Zone formation in the trough Keep the liquor circulated in
pad trough.
[369]
315
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Uneven dye bath temperature 1. Check the cooling system for
variations.
2. Check the temperature
variations in the fabric.
[368]
▪ Uneven hardness of the padder Check the hardness and renew
rubber covering.
▪ Wear of the roller covering Inspect the padder on regular
basis and grind the rubber
covering if required.
[317,
348,
370]
▪ Differences in dye fixation due to
neutralization of alkali in fabric
edges during batching in CPB
process
Wrap the batch in plastic to
avoid contact with CO2 in the
air.
[7]
Variation in fabric tension across
the width
Ensure the compensator is
working properly and guide
rollers are properly aligned.
▪ Differences in vertical tension of
the fabric into the infrared drying
zone
Check alignment of the guide
rollers.
Shade change ▪ Migration in drying due to high
residual moisture
30-40% liquor should be
removed during infrared pre-
drying.
[133]
▪ Inadequate dye penetration 1. Use the skying unit before
infrared drying for adequate
dye penetration.
2. Check the incoming fabric
temperature.
[120,
357]
316
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Variation in pickup during
chemical pad leading differential
reduction of vat/sulfur dyes
Ensure the wet pick-up should
be uniform during the chemical
pad.
[366]
▪ Presence of air in the steamer
that retards reduction
Maintain the slight
overpressure in the steamer.
[366]
▪ Inadequate steam condition 1. Check the steam supply,
valves, and gauges regularly.
2. The steamer conditions
should be maintained
according to dye type:
Reactive: 102 oC, saturated
steam, 60-90 sec.
Vat: 102-105 oC, dry
saturated steam.
[128,
370]
▪ Long distance between the water
seal and washing unit leading to
over-oxidation of dyes
1. After steamer/water seal
fabric should have sufficient
quantities of hydro.
2. Ensure proper water flow in
the water seal for removal of
alkali.
[371]
Lengthwise
shade
variation/
Tailing
▪ Variations of moisture in the
fabric batch entering the padder
Ensure the fabric moisture
levels are uniform. Check the
drying settings of the preceding
stage.
[317,
369]
▪ Differences in temperature of
fabric throughout a batch
1. Check the fabric cooling
device is working properly.
2. Check the drying settings of
the preceding stage.
[317]
317
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Variation in fabric running speed Ensure the same fabric running
speed. Use j-scray for batch
change.
[61]
▪ Differences in fabric immersion
length
Ensure the same fabric running
speed and settings of the spacer
in the trough.
[61]
▪ Variation in dye trough level Monitor the trough level.
Ensure the level sensor is
working properly.
[194,
323]
▪ Settling of dye in the dyebath
(due to anti-migrating agent)
Keep the liquor circulated in
the stock tank and the pad
trough.
[118,
368]
▪ Variations in the air pressure
controlling the padder
1. Check the air supply for any
variations in pressure or
leaks.
2. Ensure same pressure
settings.
[317]
▪ Change in dyeing trough
temperature. High padding liquor
temperature causes instability of
disperse/reactive mixture
1. Check the cooling system for
variations.
2. Check the temperature
variations in the fabric.
[61,
120,
368]
▪ Longer immersion times Use smaller trough for smaller
immersion times.
[120,
323]
▪ Slower liquor turnover in the
trough
Use a smaller trough for faster
liquor turn over.
[120,
350]
▪ Dye migration during drying 1. Set low pickup as possible.
2. Select dyes with a low
tendency to migration.
[85,
118,
318
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
3. Use a suitable anti migrating
agent.
253,
369]
▪ Variation in infrared intensity
during pre-drying
Ensure the IR intensity is
uniform across the width and
both sides of the fabric.
▪ Variation in drying temperature Monitor the drying
temperature. It should be same
thought the process and across
the machine.
▪ Variations in fixation
temperature during streaming
and thermofixation
1. Monitor the thermofixation
temperature. It should be the
same thought the process and
across the machine.
2. Check the steam pressure.
[317]
▪ Marginal dwell times in the
fixation
Ensure optimum dwell times. [128,
317]
▪ Variations in the washing process
(water flow, time, temperature)
Ensure similar water flow
levels, dwell time and
temperature within a lot.
[128,
317]
▪ Differences in dye fixation due to
drying of outer fabric layers
during batching in CPB process.
Wrap the batch in plastic to
avoid drying.
[7]
▪ Improper rotation of batch during
CPB dyeing causing collection of
dye liquor at the lower portion of
the batch
Ensure the fabric batch is
rotating without any
interruption.
319
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
Two sidedness ▪ Uneven migration due to
variations in air flow or heating
on both sides of the fabric (faulty
drying equipment and process
control)
1. Check nozzle cleanliness,
temperature, and air supply.
2. Set low pickup possible.
3. Use the optimum quantity of
the anti-migrating agent%
4. Dye selection based on their
migration behavior.
5. Examine migration
parameters of disperse dyes.
[67,
118,
370]
▪ One sided contact of the guide
rollers
1. Check the entry of fabric.
Replace the guide roller, if
necessary.
2. Change the fabric direction.
[67,
368]
▪ Blocked guide rollers Fix the guide roller. [368]
▪ Contact of the material with the
edge of the dyebath
Install guide rollers. [368]
▪ One side feeding of dyeing liquor
at the fabric exit
Check the liquor feeding
system for uniformity.
[368]
▪ Differences in the hardness of
padders
Check hardness of the padders
is the same.
[133,
194]
▪ Differences in rates of drying of
two sides of the fabric
Check temperature and air
current in drying chambers.
[128,
133]
▪ The fabric is not guided
vertically to the padder
Replace the guide roller. [368]
Dark and light
edges
▪ Due to uneven drying across the
fabric width
Check nozzles and exhaust
settings.
[118]
▪ Improper distribution of dye
liquor across the dyeing trough
Check the liquor feeding
system for uniformity.
[253,
368]
320
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Poor liquor circulation in the
dyeing trough
Check the liquor circulation
system is working properly.
[368]
▪ Using a wider width padder for
the padding of narrower width
material
Use a suitable machine with a
smaller width padder.
[253,
368]
▪ Overstressed rollers due to
construction or hydraulics
problem
1. Check the pressure effect.
2. Replace rollers.
3. Check the hydraulic system.
[253,
368]
▪ Worn out padders or bent
padders due to higher loading.
1. Check the pressure effect.
Grind the padder rubber
covering.
2. Lower the padder pressure.
[253,
368]
▪ Curling of selvages during
padding
Ensure the proper adjustment
and functioning of the edge
guiders.
[323,
350]
Streaks/
stripes/ bar/
bands
▪ Light and dark bands caused by
uneven nozzle pressure
Check nozzle for evenness in
pressure.
[118]
▪ Chafe or rub marks caused by
uneven or damaged machine
lining and fabric guiding
elements appear as dark streaks
(if occur before dyeing) and light
streaks (if occur after dyeing)
Inspect the machine parts
coming in contact with the
fabric frequently.
[149,
150]
▪ Variation in tension in the dryer
and fixation unit
Check proper settings of
tensioning device and working
of guide rollers.
[253,
323]
▪ Jammed or slowly rotating guide
rollers inside the steamer
Check the steamer rollers for
proper working.
321
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Machine stoppage for a longer
period
Use j-scray for fabric change
when possible.
[194]
▪ Inadequate stitching Use proper stitching for fabric
ends. The stitches should be
parallel to weft yarns.
[321]
▪ Use of wrong stitching thread
that causes stitch marks during
batching of wet padded fabric
Use proper stitching thread as
per blend being processed.
[67,
322]
Holes ▪ Projecting objects in the dyeing
machine cause punctured holes
or tears
Inspect the machine parts
coming in contact with the
fabric regularly.
[150]
Creases ▪ Improper entry of the fabric in
the padder
The entry should have an
expander roller to ensure
crease-free entry.
[150,
253,
363]
▪ Improper batching of the fabric Ensure proper batching of the
fabric in the last preparatory
process.
[301]
▪ Excessive, insufficient or
variable tension during fabric run
Perform machine inspection
and maintenance regularly.
[128,
370]
▪ Improper alignment of the guide
rollers leading to variation in
tension on the fabric
1. Check the proper alignment
of guide rollers regularly.
2. Perform machine
maintenance regularly.
[128,
253,
317,
370]
▪ Incorrect setting of bow rollers Perform machine maintenance
on regular basis.
[317,
370]
▪ Differences in tension at the
padder or variation in pressure
across the padder
1. Ensure proper tension control
at the padder.
[370]
322
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
2. Check the padder pressure
for variation across the
width.
▪ Hard deposits of lint and loose
thread on rollers
Ensure routine machine
cleaning.
[128,
317,
370]
▪ Shrinkage of fabric during drying
and fixation units.
1. Heat set the fabric before
dyeing to finished width.
2. Check guide rollers.
[127,
253]
▪ Turbulence due to boiling in a
wash box
Check the steam settings in the
washbox. Avoid using live
steam.
[317]
▪ Distortion of weft due to the
application of too much vacuum
in the wash box leading to the
formation of creases
Use optimum settings
according to fabric construction
and weight.
[317]
▪ Selvage curling during padding
and thermofixation process
Ensure the proper adjustment
and functioning of the edge
guiders.
[194]
▪ Improper drying cylinder
temperature
Control the drying temperature
according to fabric type.
[370]
▪ Incorrect stitching of fabric ends
leading to formation of creases
Ensure fabric ends are properly
aligned when stitched.
[322]
Dark stains,
spots or specks
▪ Dents in the roller containing dye
deposits
Grind the rollers to produce a
smooth surface.
[368]
▪ Foaming spots due to excessive
foaming in the pad liquor
1. Avoid high turbulence in the
dyeing trough.
[253,
317]
323
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
2. Use chemicals with lower
foaming tendency.
3. Add defoamer.
▪ Foaming caused by an air leak in
the circulation system
Check the liquor circulation
system for any leaks.
[317]
▪ Incorrect preparation of the pad
liquor
1. Follow the standard
operating procedure of
preparing pad liquor.
2. Filter pad liquor before
feeding into the trough.
[367]
▪ Settling of dye in the dye trough Keep the liquor circulated in
the stock tank and the padding
trough.
[253]
▪ Transfer of dye deposit to the
fabric from the guide rollers
1. Clean the guide roller
regularly.
2. Avoid too dry conditions
during steaming.
[366]
Poor color
yield
▪ Inadequate dye penetration
during impregnation due to fabric
construction
1. Use the skying unit before
infrared drying for adequate
dye penetration.
2. Use wetting agent.
[120,
357,
366]
▪ Inadequate dye penetration
during impregnation due to high
fabric temperature
Check the incoming fabric
temperature. The fabric should
be cold before it enters the dye
bath.
▪ Inadequate dye penetration
during impregnation due to high
Check the last drying step in
pretreatment. The residual
moisture should be uniform and
324
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
residual moisture content of the
fabric
according to the fiber type and
blend ratio (moisture regain).
▪ Hydrolysis of dye due to increase
in dyebath temperature
1. Check the cooling system
for variations.
2. Check the temperature
variations in the fabric.
[120,
368]
▪ Ring dyeing of fiber caused by
poor penetration due to use of too
low thermofixation temperature
or short dwell time
Use appropriate thermofixation
conditions depending upon the
dye class and depth of shade.
[67]
▪ Incomplete fixation of the dyes
due to variation in temperature
and/or dwell time during
steaming/thermofixation
1. Use appropriate
thermofixation conditions
depending upon the dye
class and depth of shade.
2. The steamer conditions
should be maintained
according to dye type:
Reactive: 102 oC, saturated
steam, 60-90 sec.
Vat: 102-105 oC, dry
saturated steam
[79,
85]
▪ Presence of air in the steamer
that retards reduction
Maintain a slight overpressure
in the steamer.
[128,
366]
▪ Long distance between the
reducing bath nip to the steamer
entry slot leading to oxidation of
dithionate in the absorbed dye
liquor
Keep the passage time within 2
seconds.
[128]
325
Table 4.41 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Incomplete removal of moisture
after drying
Check the IR intensity and
drying conditions (dwell time,
temperature).
[79]
▪ Lower dye fixation due to
neutralization of alkali in the
fabric during batching in CPB
process
Wrap the batch in plastic to
avoid contact with CO2 in the
air.
[7]
▪ Using too high thermofixation
temperature or dwell time
Use appropriate thermofixation
conditions depending upon the
dye class and depth of shade.
[79,
85]
Inadequate
fastness
Inadequate
wash and
rubbing
fastness
▪ Inadequate theromofixation
conditions (lower temperature or
shorter dyeing time)
1. Use appropriate
thermofixation conditions
(time and temperature)
depending upon the dye class
and depth of shade.
2. Perform reduction clearing.
[79,
253]
Abrasion or
chafe mark
▪ Chafe or rub marks caused by
uneven or damaged machine
lining and fabric guiding
elements appear as dark streaks
(if occur before dyeing) and light
streaks (if occur after dyeing)
Inspect the fabric guide
elements regularly. Perform
routine maintenance of the
machine.
[149,
150]
Poor
dimensional
stability
(shrinkage)
▪ Lengthwise distortion caused by
the machine.
Adjust machine settings
according to the substrate being
processed.
[253]
326
4.9 Problems in pigment coloration
Coloration with pigments is a well-established process due to its simplicity, economics, and
environmental reasons. Pigments have no affinity for the fiber so they can be applied to all fibers
and fiber blends. The coloration procedure consists of padding, drying and curing steps similar to
the classical resin finishing process. Pigments are fixed to the fabric with the help of binders, by
film formation that physically traps the pigments [89, 91-95, 102].
There are three main elements of the pigment coloration process, which are [102]:
▪ Substrate: Fiber type and blend ratio, fabric structure, pretreatment;
▪ Coloration process: Padding, drying and curing process and equipment; and
▪ Dye liquor: Pigments, binder, auxiliaries (migration inhibitor, dispersing agents,
catalyst, fixer, softeners, defoamers, etc.).
Uniform and even pretreatment is key to good pigment coloration. The fabric must be free
of residual chemicals and should have neutral pH and be defect free. Many of the faults that occur
during pigment coloration are related to fiber, yarn, fabric or pretreatment [89, 92-94, 102].
The uniform application of the coloration liquor, even and gentle drying and curing along
with appropriate speed and temperature are key to successful pigment coloration. In addition, all
devices must be in proper working order [89, 92-94, 102, 372].
The coloration liquor should be properly formulated. The binder to pigment ratio and the
amount of auxiliaries should be optimally set. One of the important aspects that affect running and
fastness properties is product compatibility [89, 91-94, 102].
In order to produce a pigmented fabric that meets customer requirements proper process
control for fabric pretreatment, padding, drying and fixation process and dye bath formulation is
required. This also helps in the early identification and correction of problems [102].
Pigments are supplied as paste-like preparations in the form of fine dispersions by means
of surfactants. The particles are variably shaped and partially dependent on their chemical
constitution. The surfactants stabilize the particle form and size during the grinding process.
Pigment agglomeration in coloration liquor is also prevented by surfactants. The requirements
include the highest possible pigment amount, good flow properties and protection against crust
formation. High pigment concentrations result in minimum transport and warehouse cost while the
327
flow properties ensure ease during the dosing process. The last factor ensures the homogeneity and
therefore prevents speck formation [89].
The pigments are anchored to the substrate with the help of a binder. The binders are
synthetic polymers with a low degree of polymerization in their unfixed form. At higher
temperatures and in the presence of acidic conditions that are generated with the help of a catalyst,
the polymerization of binder chains takes place, making the binder linked to the substrate
simultaneously attaching the pigments [99]. The fastness properties are therefore mainly
dependent on the properties of the binder used [92]. They influence the hand and almost all fastness
properties of the pigmented fabric such as fastness to washing, wet scrubbing, rubbing (dry and
wet), abrasion, etc. The type and amount of binder and other auxiliaries used to affect the
achievable results. This aspect needs to be considered in the selection of binders and auxiliaries
[91, 94]. Commercially available binders are a mixture of co-polymers, softeners, thickeners, and
emulsifiers. The binders are formulated in such a way that they give optimum running, good
fastness properties and soft hand to the pigmented fabric [94]. The fastness properties of pigmented
fabrics are dependent on the adhesion of the binder to the substrate. The adhesion of the binder to
the fiber can be viewed from three aspects [100]:
▪ Physical bonding forces: which depend on the binder type and the quantity of the cross-
linker. The concentration of cross-linker has no influence on the fastness level of the
given binder type.
▪ Chemical bonding forces: they are only present if both the binder and the fiber possess
reactive functional groups. In the case of cellulosic fibers, the binder may react with
the hydroxyl groups on fiber thereby creating chemical bonding between the binder
and the fiber.
▪ Mechanical adhesion of the binder due to surface characteristics. Cotton fiber has high
mechanical adhesion with the binder due to the rough surface of the fiber.
The colorant and auxiliaries used in pigment coloration must be compatible with each
other. It is necessary to check for the compatibility before and during the coloration process.
Incompatible products lead to problems in the process. There are many factors that may affect the
compatibility of the products in the mixture; these include ionic characteristics, solubility,
emulsion stability, pH conditions, and temperature. Binder, pigments, softeners and the
328
formulation contain emulsifiers for product stabilization. The emulsion should be stable when
products are mixed during the coloration process and must be stable under the action of forces
involved during solution preparation and coloration process. Products should be selected in such
a way that their ionic characteristics are similar. When there is a change in the amount of the
products or old products is replaced with a new product due to non-availability, cost or ecological
reasons, compatibility should be checked in the laboratory before the changes are made in the bulk
process [373].
One of the common problems found in coloration with pigments is the agglomeration of
the binder on the pad rollers. These agglomerates can easily transfer during the application process
from the roller and deposit on the fabric in the form of dark areas. There are many factors that can
affect this problem such as shear forces due to pressure, hardness, width and diameter of the rollers,
roller speed, swelling and absorption properties of the substrate, dispersing agents, wetting agents
and chemical composition of the binder. Suitable products with good emulsifying properties such
as a mixture of alkoxylates may be used to avoid this problem [92, 97, 374].
During the coloration process, there are certain requirements that have to be met in order
to produce a successful product. These requirements are function-related based on end-use e.g.
fastness properties, and hand or application related e.g. foam inhibition, drying, and curing. The
colorant and auxiliaries used have the largest impact on both functional and application
requirements. Table 4.42 shows the components of the pigment coloration system and their
influence on different outcomes of the process. The properties of the individual component are
related to the particular effect for which they are responsible.
Table 4.42: Pigment dyeing components and their corresponding effect on dyed fabric.
Component Properties Effect
Pigment ▪ Particle size Agglomeration (dye spots), rubbing,
dry-cleaning fastness, color yield
▪ Particle shape Rubbing, wash fastness
▪ Heat resistance Shade variation, shade change
▪ Solubility Dry-cleaning
▪ Quantity Fastness, buildup
329
Table 4.42 (Continued)
Component Properties Effect
Binder ▪ Tg of the comonomers Softness
▪ Chemical resistance of
comonomer
Fastness properties
▪ Heat and light resistance of
comonomer
Lightfastness, shade change
▪ Adhesion and cohesion Rubbing, wash fastness
▪ Crosslinker Wash, rubbing fastness
▪ Amount of crosslinker Fastness, softness
▪ Quantity Fastness, softness, buildup
▪ Film formation Appearance, softness, color yield
Migration inhibitor ▪ Type and quantity Migration, appearance, shade
variation
Emulsifier ▪ Type and quantity Stable dispersion, prevent dye
spots and roller deposits
Softener ▪ Type and quantity Dry rubbing fastness, fabric
handle
Defoamer ▪ Type and quantity Prevention of dye spots
Padding ▪ Pressure Liquor pickup, migration
▪ Uniform application Side-to-side variation
▪ Liquor circulation Shade change
▪ Liquor feed Shade change
Drying ▪ Temperature and uniform
airflow
Migration, appearance
Fixation ▪ Time and temperature,
uniformity in airflow
Fastness properties, color yield,
handle, shade change
330
4.9.1 Fastness of pigment colored fabrics
The following factors affect the fastness properties of pigmented fabrics [372]:
▪ Binder quality;
▪ Amount of binder;
▪ Pigment quality;
▪ Fabric quality;
▪ Fixation method; and
▪ Fixation conditions.
4.9.1.1 Binder quality
Binder quality refers to the components making up the binder which include comonomers,
crosslinkers, plasticizers, and emulsifiers. This is an important factor which is mainly responsible
for achieving the required fastness. The hand of the pigmented fabric is largely dependent on the
binder used. Important factors affecting the hand are the comonomers, crosslinkers and the level
of crosslinking. Other factors affecting the hand feel is the type and amount of softener used. The
binder also influences the wash fastness. Resistance against wash fastness depends on the swelling
behavior of the binder film which is controlled by the amount and level of crosslinkers used in the
binder formulation. Rubbing fastness is partially influenced by the binder. The crosslinker present
in the binder is responsible for the wet rubbing fastness, and the softener is added in the formulation
to improve the dry rubbing fastness. The fastness to light and dry cleaning is least dependent on
the binder used and is largely based on the resistance of the comonomer against aging and solvent
respectively.
4.9.1.2 Amount of binder
To achieve the best fixation of pigments on the substrate, the optimum quantity of binder is
required in relation to the amount of pigment being used. A low amount of binder will result in
inferior fastness properties while a higher than the optimum amount will affect the hand of the
fabric and increase the cost of the coloration process [94]. The thickness of the pigment layer is
approximately 0.5 µm, depending on the particle size of pigments. The amount of binder should
be adequate to cover this layer of pigments. For a binder with a 40% solid content, for excellent
fastness properties, the binder to pigment ratio should be around 4:1. The minimum binder level
331
should be around 6%. The relationship between binder to pigment ratio and fastness properties are
shown in Figure 4.9 [375].
The binder to pigment ratio depends on the following [94]:
▪ Quality of the fabric;
▪ Binder efficiency;
▪ Pigment quality;
▪ Required fastness properties; and
▪ Hand of the fabric.
Figure 4.9: Binder to pigment ratio and fastness properties.
4.9.1.3 Pigment quality
Pigments are supplied in the form of a dispersion in water. They are insoluble in water, therefore
wash fastness is primarily dependent on the binder used. Rubbing fastness also depends on the
binder used but is also influenced by the particle form, size, and hardness of the pigment.
Lightfastness, on the other hand, is primarily dependent on the pigment used. Since pigments are
0
50
100
150
200
250
300
0 10 20 40 50 6030
High fastness Level
Good fastness Level
Low fastness Level
3:1
2.5 :1
0:1 2:1 3:1 4:1Fabric
Pigment 0.3-0.5 µBinder
Binder : Pigment Ratio
4:1
g/k
g o
f 40
% A
ctiv
e B
inder
Pigment Concentration (g/kg)
Binder : Pigment Ratio
0.5 µ
332
in the form of molecular aggregates, they have superior fastness compared to individual molecules.
The solubility of pigments in a solvent determines their fastness to dry-cleaning [89].
4.9.1.4 Fabric quality
This includes residual impurities such as sizing agent present, fabric pH, residual moisture, surface
appearance, and yarn type. Pretreatment should be uniform, and fabric should be free from defects.
Fiber type and blend ratio affect the fastness properties. Cotton fiber has a rough surface which
results in more adhesion of the binder as compared to polyester which has a smooth surface [100].
Therefore, rubbing fastness of the pigmented layer is superior to cotton rich blends as compared
to polyester rich blends.
4.9.1.5 Fixation method
Pigmented fabrics are generally fixed by the curing process. The curing process can be done on a
hot flue or a stenter. The curing time and temperature should be properly monitored to ensure
proper and even fixation. Hot air is the preferred method of fixation. High-temperature steamers
do not usually give the desired fixation levels and therefore result in inferior fastness properties.
4.9.1.6 Fixation conditions
Binder polymer chains are linked together through cross-links during the fixation process which
is carried out at elevated temperatures. Cross-linking helps in attaching the trapped pigments to
the substrate. Acidic conditions during curing are essential for the effective fixation of a binder.
The pH of the system should be alkaline before the curing process to avoid premature fixation of
binders. As the curing process commences the pH is gradually changed from alkaline to acidic
conditions resulting in the fixation of binder [94]. Figure 4.10 shows the factors responsible for
the fixation during pigment coloration of the fabric which affects the fastness properties of the
pigmented fabric. These include temperature, time and pH. Insufficient fixation time for a
particular temperature would result in poor fastness properties attained. The time and temperature
required for the fixation are inversely related. However, adjustments are also limited by the
machine, fiber and pigment’s thermal properties. The temperature cannot be increased over a
certain limit due to the chance of fiber damage or due to yellowing or sublimation of pigments.
Similarly, the time that can be given for curing is limited by production requirements and the
333
machine configuration [372]. The pH is also an important factor affecting the fixation process.
Generally, the fixation is performed at 150 oC for 4-5 min. The pH should be < 5 [101, 375].
Figure 4.10: Pigment coloration fixation conditions.
A summary of the faults that can occur during the pigment coloration process and the
possible solutions are given in Table 4.43.
To achieve successful pigment coloration, the following preventive measures must be
taken [94, 96]:
▪ The binder drums should be stored in a cool place to avoid the formation of a skin. The
binder must be filtered through a fine fabric before preparing the padding liquor. The
binder left off on the fabric should not be pressed or squeezed. This might cause some
polymer particles to escape and form a nucleus for further agglomeration in the liquor.
▪ Padding mangle should not be exposed to hot conditions. The location should not be
very close to other machines.
▪ The substrate should be uniformly dried and should not be hot before the padding
process.
▪ The fabric should have uniform absorbency and be free from the residual size and other
impurities.
▪ Filtering of padding liquor should be done before feeding it into the dyeing trough.
▪ When two or more pigments are used according to shade requirements, it may be
possible that one pigment may settle at a faster rate, hence the padding liquor should
be properly stirred before starting the process and there should be a proper liquor
circulation system.
▪ Padders should have the same uniform hardness and diameter.
Temperature
Fixation binder
Fixation pigment
Time pH
334
▪ The liquor pickup should be around ~ 60% (pick up depends on the fiber type
processed.). Lower pick up values are preferred as the tendency of pigment migration
is reduced.
▪ If there is a film formation on rollers, it should be cleaned immediately.
▪ Loosely, woven and open structures have a low tendency for migration as compared to
tightly woven and compact structures.
▪ Fabrics containing synthetic fiber should be heat-set before coloration. High
temperatures during fixation may cause yellowing.
▪ Fluorescent whitening agents are not recommended for use on substrates that are to be
to be pigmented, as FWAs tend to turn yellow during the curing process which will
impact the final shade of the goods.
▪ Shade matching should be done after the curing process, as there may be a tone change
for some pale shades during the curing process.
▪ All the guide rollers should be moving, as stationary rollers may cause accumulation
of the liquor on them and would drip resulting in dark patches or spots on the fabric.
Table 4.43: Problems in pigment coloration and possible solutions.
Problems Probable causes Remedial measures Ref.
Dark stains or
spots or areas
▪ Pigment preparations not
properly diluted
Dilute the pigments with a small
amount of cold water while stirring.
[92,
93,
100] ▪ Pigments not strained
properly
The diluted solution should be added
to the preparation tank through a filter
cloth or a fine sieve. A finer filter
must be employed if speckiness still
occurs.
▪ Crust formation in pigment
during storage
1. Select good quality pigments.
2. Ensure proper storage conditions.
3. Inverse the hold can often.
▪ Mix incompatibility 1. Colorants and auxiliaries should be
compatible with each other.
335
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Excessive foaming of the
padding liquor, pigments
may accumulate in the
foam and on drying cause
stains on the goods
Use defoamers to inhibit foam
formation.
▪ Poor pigment dispersion 1. Select good quality pigments.
2. Increase the amount of emulsifier.
▪ Pigments with very small
particle size may result in
agglomeration
Coating of the primary particles with
dispersing agents during
manufacturing.
▪ Transfer of film, formed on
the pad rollers, to the cloth
during the padding
Increase the amount of emulsifier to
prevent roller deposits.
Pale spots ▪ Moist parts in the fabric
before padding may cause
less liquor pick-up
Ensure that the fabric is uniformly
dried.
[92]
▪ Contact of condensate
water drops with unfixed
colorants
Avoid the formation of condensate in
all parts of the machine through
which the fabric passes before the
fixation
▪ Deposits of hardened resin
that resist pigment
penetration
Ensure the compatibility of chemicals
used in one step coloration and
finishing.
[149]
Unlevelness Instability of liquor due to: [92,
93,
96,
▪ Incompatibility of products Ensure the products used are
compatible with each other.
336
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
▪ High amounts of polyether-
based softening agents
used (more than 15 g/L)
Use the recommended concentration
of softening agents. Follow the
manufacturer’s recommendation.
100,
376]
▪ High temperature of bath
liquor caused by the heated
substrate entering the bath
may result in some
auxiliaries such as
ethoxylate based
antimigrating agents to
precipitate
1. The temperature of the bath liquor
must not increase over 40 oC.
2. Allow the liquor or the substrate to
cool, before processing.
3. Use cold water to prepare the
liquor.
4. Do not immediately use the fabric
for coloring after the stentering or
drying processes.
▪ Presence of Ca and Mg
ions in fabric affects
pigment dispersion
Fabric should be free from impurities
after pretreatment.
▪ Poor pigment penetration 1. Ensure uniform and proper
pretreatment of fabric.
2. Use a wetting agent to increase
pigment penetration.
3. Give airing time between padding
and drying.
▪ Pigment migration during
drying
1. Reduce the uptake of liquor by
increasing the padder pressure.
2. Provide adequate swelling time for
fabric.
3. Reduce the fan speed and keep the
maximum temperature to 120 oC.
337
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
4. Select appropriate anti-migrating
agents or increase the amount of
anti-migrating agent.
▪ Improper drying Airflow and temperature should be
uniform along the length and width of
the dryer.
▪ Cracking of the binder film Add a softener.
▪ Fabric imperfections like
knots, slubs, lint, etc
Ensure the fabric is properly
inspected and free from defects
before pretreatment.
Pin marks ▪ Due to colorant migration,
stenter pins may cause
marks along the selvages
1. Increase the amount of anti-
migrating agent.
2. Use low temperature for drying.
[92]
Coating of
rollers
▪ Due to agglomeration of
binder on the padder
because of shear forces
1. Increase the amount of emulsifier.
2. Select the appropriate emulsifier.
3. Coating of rollers is generally less
for hard rollers as compared to soft
rollers.
[92]
Streaks or
stripes
▪ Pale stripes along the
length of fabric may be due
to the rubbing of the
unfixed substrate against
the guide roller or a
machine part
Ensure all the machine parts which
come in contact with the fabric before
fixation are Teflon coated and
moving.
[92]
▪ Uneven drying may result
in dark longitudinal stripes
due to improper
Ensure the dryer air jets are properly
cleaned and the airflow is uniform.
338
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
functioning of the jets of
the dryer
▪ Fabric fault Ensure the fabric is properly
inspected and free from defects
before pretreatment.
Shade change ▪ Improper color selection.
Due to melting,
sublimation or destruction
of pigment under
application temperature
Use shade card to select appropriate
pigment type according to
requirements.
[92,
93,
96,
100]
▪ Polyester containing
fabrics are sometimes
darker in shade due to the
dissolution of pigments
like disperse dyes in the
polyester fiber during the
curing process
This fault is observed after the curing
process. Shade matching should be
done after the curing process.
▪ Pigment migration 1. Reduced the uptake of the liquor by
increasing the padder pressure.
2. Provide adequate swelling time for
fabric.
3. Reduce fan speed and keep the
maximum temperature to 120 oC in
the first two chambers of the
stenter.
4. Select appropriate anti-migrating
agents or increase their amount.
339
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Pale shade due to anti-
migrating agent. The
migration of pigment is
prevented so that the fabric
surface is lighter in shade
as compared to when
migration takes place and
pigment accumulates on
the surface.
Use the optimum amount of anti-
migrating agent.
▪ Sensitivity of some
pigments (reds and blues)
to reduction results in the
paler or changed shade
Avoid using chemicals having
reductive nature.
▪ pH variation or too high
pH
▪ Alkaline pH on fabric can
neutralize the padding
liquor so anti-migrating
agents can be blocked and
binder fixation slows
down.
The pH of the fabric should be neutral
or slightly acidic.
▪ Settlement of pigment due
to the improper stirring of
the liquor
Continuous agitation of the bath by a
circulation system.
▪ Improper bath preparation
procedure
Follow the mixing procedure as per
the manufacturer’s recommendation.
▪ Poor pretreatment of fabric. Ensure adequate and uniform
pretreatment of fabric.
340
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Comonomers making up
the binder. The resistance
of comonomer against heat.
Select a binder with good aging
resistance.
▪ Higher curing temperature
or time. Yellowing of fiber
may take place at high
temperatures or long curing
times.
Select the treatment time and
temperature according to the most
sensitive fiber in the blend.
Inadequate
fastness
1. Rubbing
fastness
▪ Poor fastness properties of
binder
Select a binder with good fastness
properties.
[90,
93,
100,
376]
▪ Insufficient curing or
improper curing conditions
Ensure proper curing time,
temperature and pH according to
manufacturer recommendations are
employed.
▪ Particle shape of the
pigmen
Pigments must be properly ground
during manufacturing. Sharped edge
crystals can easily scratch the binder
film under rubbing loads as compared
to round off shapes.
▪ Particle size of the
pigment. Difficulty for the
binder to cover large
pigment particles
Select good quality pigments. The
particle size should be between 0.1
and 0.5 µm.
▪ Fabric structure and
surface
Very smooth fiber surface e.g.
polyester has low adhesion to a
341
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
binder, compared to cotton which has
a rough surface.
There is a limit of maximum fastness
level achievable for a particular fiber.
Uneven fabric surface will deteriorate
the fastness. Use fabric which is free
from defects and protruding fibers.
(a) Dry
rubbing
fastness
▪ Due to the brittleness of the
binder film
Use a softener to reduce the
brittleness.
▪ Insufficient amount of
binder
Increase the amount of binder.
(b) Wet
rubbing
fastness
▪ Improper selection of
binder. Crosslinking agents
are incorporated in the
binder to enhance the
crosslinking of binder film.
Select binder that can meet the
fastness requirement.
2. Wash
fastness
▪ Binder selection. Select a binder that can meet the
fastness requirements.
[93]
▪ Inadequate curing The fabric should be properly cured
as per the recommended curing
conditions.
▪ Shade too heavy Do not use pigment for dark/deep
shades.
▪ Poor pretreatment.
Impurities present in the
fabric hinder the proper
fixation of the binder.
Ensure pretreatment is uniform and
even.
342
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Particle size of the
pigment. Difficulty for a
binder to cover large
pigment particles
Select good quality pigment. The
particle size should be between 0.1
and 0.5 µm.
3. Dry-
cleaning
fastness
▪ Pigment, due to their
solubility in the dry
cleaning solvents
Select recommended pigments. [93,
102]
▪ Binder selection. Due to
increased swelling of the
binder film under the
action of solvents
Select a binder with good fastness
against dry-cleaning solvents.
▪ Pigments with very small
particle size diffuse
through binder film
Select good quality pigments. The
particle size should be between 0.1
and 0.5 µm.
▪ Improper curing conditions Follow the recommended curing
conditions.
4.
Lightfastness
▪ Pigment selection
(selection of primaries for
making mixes)
Select recommended pigments. [93,
100,
102]
▪ Binder. Select binders with good fastness to
light.
▪ Calibration of lightfastness
tester.
Ensure the light fastness tester is in
proper working order.
Listing/ side-
to-side shade
variation/
▪ Uneven padder pressure
along the width.
Check the padder pressure along the
width.
[93]
▪ Temperature variation. 1. Check the temperature of the fabric
along the width.
343
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
width wise
shade variation
2. Ensure the filters and nozzles in
dryer and hotflue are cleaned and
airflow is uniform.
▪ Uneven fabric preparation. Ensure the uniform pretreatment of
the fabric.
▪ Formulation liquor feed is
not uniform.
The liquor should be fed uniformly
along the width of the dye trough.
▪ Thread-up. The machine should be properly
thread-up before the process.
Poor color
yield or build-
up
▪ Low quantity of the binder. Use binder amounts corresponding to
the amount of pigment.
[93,
100]
▪ Particle size of pigment
influences the yield and
brilliance. Large particles
have lower total surface
areas as compared to small
particles of the same mass.
Select good quality pigments. Particle
size should be between 0.1 and 0.5
µm.
▪ Excessive binder/pigment.
Higher concentrations of
pigments give poor build-
up due to the overlapping
of pigments on the
individual fiber.
Use pigments for medium to light
shades.
▪ Dry cans (no predryer). Use correct settings for a dry cans.
The temperature should be gradually
increased.
▪ Excessive pick-up Increase the pad pressure setting.
344
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Incompatible mix Ensure all the auxiliaries are
compatible with each other.
Tailing/
ending/
lengthwise
shade variation
▪ Inadequate agitation in the
mix tank
Ensure the bath is properly agitated
by a circulation system.
[93]
▪ Change in bath stability
over time either due to a
change in pH or
temperature
Monitor the bath pH and temperature
over time. This fault is also related to
fabric pretreatment.
▪ Variation in fabric
pretreatment
Ensure pretreatment is uniform and
fabric is cool when entering the bath.
▪ Mixing procedures Make sure a proper mixing procedure
is in place.
Poor hand ▪ Poor binder binder
selection. The composition
of the binder determines
the softness attained. The
softness of the binder film
is related to the Tg of the
comonomers and the level
of crosslinking
Select binder with good softness
properties.
[100]
▪ Improper softener selection Select a suitable softener.
▪ Too high curing
temperature. The substrate
depending on the fiber type
may be damaged at high
temperatures.
Select a curing temperature taking
into consideration the fiber type and
blend ratio.
345
Table 4.43 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Longer curing time Select a curing time in relation to
temperature. Follow manufacturer
recommendations.
▪ Fabric structure and yarn
count
Select a fabric according to hand
requirements. There is a limit to the
level of softness achievable on a
particular fabric type.
4.10 Problems in the dyeing of polyester/cellulosic blends
The polyester/cellulosic are the most common blend. The dyeing of these blends creates a
challenge as each fiber type is dyed with a different class of dyes that requires different process
conditions. These blends can be dyed by both exhaust, semi-continuous and continuous processes
using following colorant systems [9, 18, 56-58]:
▪ The two-dye system using dyes for polyester (disperse dyes) together with dyes for
cellulose (direct, reactive, vat or sulfur); and
▪ Pigment coloration using the pigment-binder system.
The typical dye combinations are disperse/reactive, disperse/direct and disperse/vat or
sulfur. The use of pigments is also becoming common for light shades due to excellent light
fastness, shorter and economical coloration process. Although pigments have excellent light
fastness and the coloration process is shorter and economical this system is restricted to light to
medium shades due to fastness and hand limitations. The important aspects and problems in
pigment coloration are covered in section 4.9.
The choice of dye classes for the dyeing of polyester/cellulosic blends depends on the
following factors [79, 377] :
▪ The attainable fastness standards in relation to different shade depths;
▪ The color space available in a particular dye class; and
346
▪ The total cost of the dyeing process.
The disperse dye is the only class available for the dyeing of polyester components. They
vary in their fastness properties depending on the dye chemistry and energy levels. The later
property determines their thermomigration behavior. This property is required to be higher in
PES/CELL blends as compared to 100% polyester materials. This restricts the choice of dyes to
medium and higher energy levels. Another problem associated with their application is the staining
of the cellulose component which affects the fastness properties. The stain needs to be removed to
achieve good fastness properties. This often requires a separate reduction clearing process,
especially in dark shades. This limits the attainable fastness levels and the choice of the dyeing
methods [79].
For the cellulose portion of the blend, a wide range of dye classes are available that include
vat, reactive, direct and sulfur dyes. The vat dyes have limited color space but can provide excellent
fastness properties. The dyes are usually expensive and limited to a special application that requires
excellent fastness properties. The reactive dyes can be applied by various methods and have a wide
range of color gamut available. The direct dyes and sulfur dyes are limited to applications that
require lower fastness levels. They are cheaper than reactive and vat dyes. The use of sulfur dyes
is usually restricted to dark shades.
The dye classes can be applied by various methods which include one-bath and two-bath
methods. In one-bath methods both dye classes used to dye each of the two fiber are applied to the
substrate at the same time but are fixed in two stages because of their differences in the
requirements for fixation. The fastness achieved is usually inferior as compared to the one-bath
process. In the two-bath process, each fiber is dyed separately. This also provides the possibility
of reduction clearing to remove the disperse dye stain. The machine occupation time varies
significantly from one dye method, it is important to select the process that provides the required
fastness levels with good reproducibility and shortest possible time [377].
The occurrence of faults in a dyehouse is inevitable due to a large number of variables
affecting the dyeing process. These vary from growth or manufacturing conditions of fiber to the
dyeing process [67, 108]. In comparison to dyeing single fiber, the dyeing of blends creates a
challenge because of the following [79]:
▪ Cross-staining of the fiber by the dye intended for the other fiber type;
347
▪ Interferences between dye classes or between a dye and dyebath auxiliaries;
▪ Effect of additional processing required to fix both dyes for cellulose and the dye for
polyester; and
▪ Effect of second fiber component in the blend on increasing the liquor ratio
significantly.
These effects vary based on the different dye classes uses. The disperse dye is more affected
by the chemical and physical interaction in the dye bath and before it is diffused. The disperse
once absorbed and diffused into the fiber is not affected much by the chemical and physical effects.
For the cellulosic component, the reactive and disperse dyes can be destroyed by reduction clearing
whether they have been absorbed by the cellulose. Some disperse dyes, on the other hand, are only
affected in the dyebath but are protected once present in the polyester fiber [79].
4.10.1 Disperse/reactive system
This is the most common dye system used for the dyeing of polyester/cellulosic materials. The
selection of disperse dyes and reactive dyes is critical depending upon the methods used for dyeing.
Following points need to be considered for proper dye selection [56]:
▪ Staining
The disperse dyes tend to stain the cellulosic fibers in the blend. This takes place during
dyeing, washing or fastness tests [56, 88]. This may cause poor wash fastness and dull
shade, especially in one bath process. It is important to select dyes that give low staining
and can easily wash off either in alkaline or higher temperature conditions and do not
require a reduction clearing step. The staining tendency adjacent fibers, especially
nylon, in wet fastness tests is critical for disperse dyes [9].
▪ Thermomigration
Thermomigration involves the movement of dye during post heat treatment operations
(finishing). Disperse dyes should have a minimum tendency to thermomigration at a
temperature above 140 oC. High energy dyes are suitable in such cases where high
temperatures are involved in a finishing stage (e.g. resin finishing).
348
▪ Reduction sensitivity
This causes a reduction in dye yield and poor reproducibility. Certain shades such as
bluish-red, blue and navy are more sensitive to reduction. In fully flooded machines
with an absence of air, the risk is even higher. The reductive chemicals come from
fibers such as wool, viscose, cotton. The dispersants based on sulfonated lignin also
have a reductive effect [88].
▪ Material suitability
The dyes that are suitable for single fiber type may not give satisfactory results in a
blend. It has been seen the some disperse dyes that show good fastness results on 100%
polyester would not give similar results in the polyester cellulosic blends. It is
important to consider this factor in dye selection [88].
▪ Stability under alkaline conditions
Generally, disperse dyes give optimum fixation under acidic conditions (pH < 5). The
disperse dyes may decompose under alkaline conditions and lose color yield. There are
some disperse dyes available that are stable up to pH of 8-9. This is important in the
case of one bath dyeing process.
Table 4.44 shows the most common problems that are faced in the dyeing of
polyester/cotton blends using disperse and reactive dyes along with their possible reasons and
corrections.
Table 4.44: Problems and their possible solutions in the dyeing of polyester/cellulose blends
using a disperse/reactive system.
Problems Probable causes Remedial measures Ref.
Reproducibility ▪ Sensitivity of dye to
hydrolysis, reduction, and
electrolyte
1. Careful selection of dyes
according to the dyeing method.
2. Proper control of dyebath pH.
3. Use dyes that are stable under
high electrolyte concentration.
[253,
301]
349
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Sensitivity of dye to metal
ions
Use a sequestering agent.
▪ Incompatibility of same
class dyes of the different
chemical constitutions
Select dyes having good
compatibility with each other.
▪ Improper dye buildup due to
dyebath chemicals such as a
retarding agent
Carry out lab trials to determine the
dye buildup with special chemicals
used in the dyebath.
▪ Too short dyeing time Ensure the dyeing time is sufficient
such that dye in the fiber is
uniformly distributed.
[57]
▪ Poor dye selection in
combination shade
Select dyes with a similar dyeing rate
(strike rates).
[75]
▪ Staining of cellulose portion
with disperse dyes
1. Select disperse dyes with lower
staining tendency on cellulose.
2. Perform reduction clearing.
[111]
▪ Hydrolysis of dye 1. Maintain the temperature of the
bath as cold as possible.
2. Use a dosing pump.
3. Use dyes with prolonged dyebath
stability.
[120]
▪ Inappropriate dye
combination
Select dyes have similar dyeing
behavior.
[253,
301]
▪ Variations in dye strengths 1. Check dye strength for each lot.
2. Establish correlation between
laboratory report and experience in
bulk.
[253,
301]
350
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Differences in the quality of
the chemicals
1. Test the strength of each lot.
2. Establish correlation between
laboratory report and experience in
bulk.
▪ Settling of liquid dyes Stir the dye container before use. [253]
▪ Effect of other blend
components on dye
exhaustion
Select dyes and processes based on
fiber type in the blend.
[253]
▪ Error is the weighing of
dyes and chemicals
1. Check the accuracy of the
weighing instruments.
2. Train the workers about the
importance of accuracy.
[317]
▪ Dye reduction due to
reductive chemicals in the
dyebath
Add mild oxidizing agent for dyes
sensitive to reduction.
[251]
Unlevelness ▪ Rapid addition of dyes and
chemicals (mainly alkali)
1. Follow the linear dosing of dyes
and chemicals.
2. Check the dyes and chemicals are
dissolved properly before addition.
3. Use a dosing system.
[297,
301]
▪ Rapid shift in pH Gradually change the dyebath pH. [345]
▪ Use of incorrect pH leading
to instability of disperse
dyeing system
Set the pH of the dyeing bath
according to disperse dye class. Not
all dyes gave optimum results in the
same pH range.
[67]
▪ Non-compatible dye
combination in combination
shade
1. Check the compatibility of dyes
used for combination shade.
[231,
348]
351
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
2. Use dyes form the same supplier
for combination shade.
▪ Poor dispersion stability of
the dye
Use dispersing agents for beam and
package dyeing.
[75]
▪ Dyeing leveling in light
shades and microfibers
Use a leveling agent for light shades
and finer fibers.
[75]
▪ Addition of dyes in the
dyebath at a very high
temperature
Avoid the addition of the dyes at a
very high temperature.
[347]
▪ Insufficient dyeing time to
allow migration of dye onto
the substrate
Ensure optimum dyeing time as per
dye manufacturer recommendations.
[347]
▪ Too much foam in the
dyebath
Use an antifoaming agent. [67,
253]
▪ Dye precipitation during the
dyeing process
Ensure proper dyeing conditions
(time, temperature, chemicals) as per
dye class.
[85,
149,
150,
253,
345]
▪ Inadequate mixing and
dissolution of dye with an
insufficient amount of water
or at incorrect temperature
or operator negligence
1. Use an adequate amount of water
to dissolve the dye.
2. Use filters to avoid undissolved
particles to enter the dyeing
chamber.
3. Use recommend temperature for
mixing the dyes.
[297,
301,
317]
352
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
4. Ensure the standard operating
procedure for mixing and
dissolving of the dye is followed.
▪ Non-compatibility of
different chemicals and
auxiliaries used
Auxiliaries should be compatible
with each other and different dyes
present in the system.
[86,
253]
▪ Unstable chemicals and
auxiliaries
Select chemicals and auxiliaries that
are stable under dyeing conditions.
[253]
▪ Migration of dye during pre-
drying due to substantivity
differences. The migration
of water soluble dyes is
inversely proportional to
substantivity
Use anti-migrating agents and
electrolyte in pad liquor.
[128]
▪ Using dyes of very high
reactivity leading to partial
fixation of dye during pre-
drying and competes with
migration
Check the reactivity of dyes
according to the application method
and dyeing conditions.
[128]
▪ Improper selection of
reactive dyes without
considering the exhaustion,
migration, and reactivity of
dyestuffs
1. Select dyes based on the dyeing
method. Not all dyes are suitable
for all dyeing process.
2. Modify the dye exhaustion curve.
[231,
345]
▪ Improper selection of
disperse dyes with poor
diffusion and migration
behavior
1. Select dyes with good diffusion
and muigration properties.
2. Modify the dye exhaustion curve.
[68,
231]
353
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Residual alkali in the fabric Add acetic acid in pad liquor to
maintain pH 5-6.
[253]
▪ Improper absorption of dyes
by very light or heavy gsm
fabrics
Use dyes with good leveling
properties.
[301]
▪ Lower diffusion or
migration of dye due to dye
aggregation caused by Ca
and Mg ions present in the
salt
Use a sequestering agent with good [301]
▪ Presence of dye residues
due to inadequate removal
of hydrolyzed dye
Treat the fabric with a good soaping
agent to remove dye residues.
[301]
▪ Using large quantities of salt
leading to dye aggregation
Use the salt quantity based on the
dye manufacturer’s recommendation.
[345]
▪ Using too high rate of
dyeing followed by poor
migration
Use a lower heating rate to avoid the
rapid exhaustion of dye into the fiber
surface.
[346]
▪ Using of very low liquor
ratio
Use optimum liquor low. Ensure
sufficient liquor is available for
proper movement of fabric inside the
machine.
▪ Use of salt of varying
quality and high levels of
impurities
1. Use Glauber’s salt, if possible.
2. Check the salt quality regularly.
[297]
▪ Using an excessive amount
of anti-migrating agent
Use the optimum amount of anti-
migrating agent.
[348]
354
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
causing a reversal of the
migration
▪ Break down of dye
dispersion due to excessive
amount of electrolyte (salt)
1. Check the disperse dye stability.
2. Avoid using an excess amount of
salt.
[7]
Dark stains or
spots
▪ Dye precipitation during the
dyeing process
Ensure proper dyeing conditions
(time, temperature, chemicals) as per
dye class.
[149,
150,
253,
317]
▪ Inadequate mixing and
dissolution of dye with an
insufficient amount of water
or at incorrect temperature
or operator negligence
1. Use an adequate amount of water
to dissolve the dye.
2. Use filters to avoid undissolved
particles to enter the dyeing
chamber.
3. Use recommend temperature for
mixing the dyes.
4. Ensure the standard operating
procedure for mixing and
dissolving of the dye is followed.
[297,
301,
317]
▪ Improper storage of the dye
leading to the formation of a
dried film on top
Use filters to avoid undissolved
particles to enter the dyeing
chamber.
Store the dye in a proper place and
mix it properly before use.
[348]
▪ Using too high temperature
during dye preparation
leading to breakage of the
dispersion
1. Avoid using hot water (> 50 oC) in
preparing disperse dye mixture.
2. Mixture should run slowly at all
times.
[348]
355
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Addition of dyes in the
dyebath at a very high
temperature
Add dyes at a lower temperature as
per the manufacturer’s
recommendations.
[347]
▪ Insufficient dyeing time to
allow migration of dye onto
the substrate
Provide enough dying time
depending the depth of shade and
dye class as per manufacturer’s
recommendations.
[347]
▪ Poor dispersion system
leading to filtration effect
during beam and package
dyeing
1. Follow manufacturer instructions
for dispersing dye in the bath. Use
a good dispersing agent that is
stable under application
conditions.
2. Use dyes form the same supplier
for combination shade to assure
that the dispersion system is the
same.
[253,
348]
▪ Dyes with poor dispersion
stability
1. Select dyes with good dispersion
stability.
2. Use dyes form the same supplier
for combination shade to assure
that dispersion system is the same.
[253,
348]
▪ Break down of dye
dispersion due to excessive
amount of dispersing agent
Use the optimum quantity of the
dispersing agent.
[67]
▪ Break down of dye
dispersion due to excessive
amount of electrolyte (salt)
1. Check disperse dye stability
against an excessive amount of
electrolyte.
2. Add salt after disperse dyeing.
[7, 68]
356
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
3. Use the two-bath process.
▪ Crystallization of dye due to
temperature variation in the
dyebath
Ensure proper liquor circulation. [253]
▪ Incompatibility of dyes used
in combination shades
Select dyes based on their dyeing
behavior in combination shade.
Follow manufacturer
recommendation for combination
shade.
[323]
▪ Incompatibility between
different classes of dyes
Check the dyes for computability
before using in the one-bath dyeing
process. Follow manufacturer
recommendation.
[128]
▪ Non-compatibility of
different chemicals and
auxiliaries used
Auxiliaries and chemicals should be
compatible with each other and
different dyes present in the system.
[85,
86,
253]
▪ Fluctuation in dye bath pH 1. Ensure the bath pH is kept uniform
during the whole dyeing process.
2. Check the incoming water for
bicarbonate.
[128]
▪ Unstable chemicals and
auxiliaries
Select chemicals and auxiliaries that
are stable under dyeing conditions.
[253]
▪ Using a too high
concentration of dyes
Check the solubility limit of the dyes
before preparing the dye liquor.
[323]
▪ Foaming caused by
dispersants in the dye
Use a silicone free defoamer.
357
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Foaming caused by excess
quantities of anti-migrating
agent
Use optimum quantities of anti-
migrating agent depending upon the
depth of shade.
[128]
▪ Foaming caused by excess
quantities of wetting agent
Use optimum quantities of wetting
agent.
[317]
▪ Use of silicone based
defoamers that breaks under
high turbulence and
temperature
Use a silicone free defoamer. [253,
351]
▪ Presence of oligomers in the
dyebath
1. Drop dye bath at a higher
temperature (> 120 oC).
2. Avoid longer dyeing times.
3. Use special auxiliaries.
[253]
▪ Contamination of substrate
by dyestuff dust
1. Avoid storing material near the
dye storage area.
2. Use low dusting/granular dyes.
[253]
▪ Contamination of substrate
by rust, oil, dust, etc
Ensure proper housekeeping.
Ensure clean machines and clean
working methods.
[253]
▪ Drying out of liquid dyes
due to inappropriate storage
Avoid drying out of dyes. [253]
▪ Residual alkali in the fabric Add acetic acid in pad liquor to
maintain pH 5-6.
[253]
▪ Foaming caused by residual
surfactants in the fabric
Use defoamer. [253]
▪ Improper addition of the
caustic
Do not add caustic directly into the
dyeing chamber. Dilute before
addition.
[301]
358
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Incorrect addition of the
dyes
Carefully add dye into the dyeing
chamber. Avoid direct contact of
dyes with the fabric without dilution.
▪ Very fast dye strike rate due
to dyes of high reactivity
Control the dye strike rate by
optimum process control.
[345]
▪ Use of short liquor ratio The quantity of water should be
enough to feed the pump and
movement of the fabric.
[345]
▪ Inadequate washing of
unfixed/hydrolyzed dyes
Use a good quality soaping agent to
remove the hydrolyzed dye and
prevent redeposition.
[345]
▪ Using large quantities of salt
leading to dye aggregation
Use the salt quantity based on the
dye manufacturer’s recommendation.
[345]
▪ Redeposition of disperse
vapors on the fabric due to
very high fixation
temperature
1. Follow the thermofixation
temperature as per the dye
manufacturer recommendation.
2. Avoid using too high
thermofixation temperature.
[317]
▪ Improper handling of dyes
in the vicinity of fabric or
machinery
The dyes should be handled carefully
and should not be stored near a
fabric storage area or dyeing
machine.
[128]
▪ Condensation of volatile
carriers on the roof that falls
back on the fabric
1. Select suitable carriers (non-steam
volatile carriers).
2. Use overhead heating in the
machine to prevent condensation.
[67,
253]
359
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Presence of the carrier stains
that dye deeper than the rest
of the fabric
Ensure proper measures for leveling
and removal of carrier stains.
[85]
▪ Crystallization of carrier on
the fabric on cooling of the
dye bath
1. Test the carrier for its
crystallization behavior. Select
carriers with a lower melting
point.
2. Drop the dye bath at a high
temperature.
[85]
▪ Transfer of film to the fabric
from the guide roller due to
an excessive amount of anti-
migrating agent
1. Use the optimum amount of anti-
migrating agent
2. Clean the guide roller regularly.
[348]
Light stains ▪ White deposits on the fabric
due to oligomer deposits.
1. Drop the dyebath at high
temperature.
2. Use a non-ionic reducing agent
during dyeing.
3. Dyeing of polyester in alkaline
medium depending upon the
possibility.
[67,
149]
Light
spots/areas
▪ Effect of strong vapors from
the surroundings (acids etc.)
1. Use of proper ventilation system.
2. Avoid contact with substances that
may damage the substrate.
[253]
▪ Poor stability of silicone
defoamer
Use a silicone-free dofoamer. [253]
▪ Fiber tips not dyed (e.g.
viscose)
Use a wet fixation method
(steaming)/
[253]
360
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Incorrect addition of acid Avoid direct contact of acid with the
substrate. Using a mixing tank.
[320]
▪ Precipitation of anti-
migrating agent
Check the stability of the anti-
migrating agent under pad liquor pH.
▪ Condensation of volatile
carriers on the roof that falls
back on the fabric
1. Select suitable carriers (non-steam
volatile carriers).
2. Use overhead heating in the
machine to prevent condensation.
[67,
253]
Shade change ▪ Incomplete dye diffusion
due to short dyeing time
Use appropriate dyeing conditions
according to material and depth of
shade.
[57,
253]
▪ Inadequate sublimation
fastness
Select dyes with good sublimation
fastness.
[253]
▪ Variation in exhaustion
rates of dyes
Select dyes with similar exhaustion
rates in a combination shade.
[150]
▪ Sensitivity of dyes to metal
ions
Use a sequestering agent. [253]
▪ Presence of alkali residues
in the substrate
Neutralize the substrate properly. [253]
▪ Higher pH during soaping
may hydrolyze the dye-fiber
bond of vinyl sulphone
based reactive dyes
Perform soaping under neutral
conditions.
[61,
301]
▪ Acidic hydrolysis of
reactive dye-cellulose fiber
bonds during acidic pH in
disperse dyeing
1. Adjust the pH of dyebath 6-6.5.
2. Select reactive dyes having stable
dye-fiber bond under acidic
conditions required for disperse
dyeing.
[7]
361
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Use of higher quantities of
dye fixative
Use optimum quantities of fixing
agent based on dye type and
concentration.
[301]
▪ Wrong selection of dye
fixative
Carry out laboratory trials before
dyeing in bulk.
[301]
▪ Browning of the cellulose
component at thermosoling
temperature under alkaline
condition
Avoid using too high temperature
during one-bath dyeing.
[79,
85]
▪ Browning of the cellulose
component at thermosoling
temperature caused by
dispersing agent
Use optimum quantities of a
dispersing agent.
[79]
▪ Gas fading of dyes due to
exposure to hot air during
thermofixation.
Select dyes with good stability
against gas fading.
[359]
▪ Destruction of reactive dyes
under higher temperature
Select dyes with good stability under
high temperature conditions.
[79]
▪ Staining of cellulose portion
with disperse dyes due to
dye properties
1. Select dyes with lower staining
tendency.
2. Select an appropriate blend dyeing
method.
3. Select disperse dyes with good
wash properties in an alkaline
medium.
4. Perform reduction clearing if
possible.
[79,
253]
362
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
Poor color
yield
▪ Hydrolysis of dye during
dyeing
1. Maintain the temperature of the
bath as cold as possible.
2. Use a dosing pump.
3. Use dyes with prolonged dyebath
stability.
[120]
▪ Higher pH during soaping
may hydrolyze the dye-fiber
bond of vinyl sulphone
based reactive dyes
Perform soaping under neutral
conditions.
[61,
301]
▪ Formation of sodium acetate
with acetic acid in the
presence of highly alkaline
fabrics
1. Ensure the fabric should be neutral
before dyeing.
2. Using a specialized product for pH
adjustment.
3. The pH of the dye bath should be
~5.5.
[348]
▪ Differences in a buildup of
dyes on different materials
Perform preliminary dyeing tests
before bulk dyeing.
[253]
▪ Reduction of dyes due to the
presence of reductive
substances in fabric or water
Use a mild oxidizing agent during
dyeing.
[301]
▪ Using dyes of low
substantivity
Select dyes with low-medium
substantivity.
[345]
▪ Using a low concentration
of electrolyte
Use the optimum quantity of
electrolyte.
[345]
▪ Low dyebath pH 1. Use the required quantity of
alkali/acid to achieve desired
dyebath pH (based on the reactive
group).
[85,
345]
363
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
2. Select reactive dyes that require
lower pH for fixation in one bath
process.
▪ Poor stability of reactive
dyes under higher dyeing
temperature required for
disperse dyeing
Select reactive dyes with good
stability under high temperature
conditions.
[79,
81]
▪ Physical or chemical
interaction of disperse and
reactive dyes in the dye bath
Check the compatibility of dyes in
the lab before using it in bulk. Select
dyes with minimum or no
interaction.
[79]
▪ Use of compromised pH
during one bath dyeing
Select dyes with good color yield in
compromised pH
▪ Improper weighing/
dispensing of dyes leading
to loss of dyes
Careful weighing/dispensing of the
dyes.
[345,
348]
▪ Dye reduction due to
reductive chemicals in the
dyebath
Add mild oxidizing agent for dyes
sensitive to reduction.
[251]
▪ Improper dye selection
having different fixation
profiles
Select dye combinations with a
similar fixation profile.
[370]
▪ Poor stability of disperse
dye under alkaline
conditions
1. Select disperse with good stability
under alkaline conditions.
2. Modify the dyeing method. Either
use one bath two stage or two bath
process.
[79,
81,
85]
364
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Acidic hydrolysis of
reactive dye-cellulose fiber
bonds during acidic pH in
disperse dyeing
1. Adjust the pH of dyebath 6-6.5.
2. Select reactive dyes having stable
dye-fiber bond under acidic
conditions required for disperse
dyeing.
[7, 85]
▪ Gas fading of dyes due to
exposure to hot air during
thermofixation
Select dyes with good stability
against gas fading.
[359]
Streaks/bars ▪ Deposition of dye in the
crease areas of fabric due to
poor dispersion
1. Select good dispersing agent.
2. Select dyes with good migration
properties.
3. The temperature should be raised
at a slower rate.
[67]
▪ Staining of the warp or weft
yarns of different fiber types
due to improper washing
1. Select dyes with minimum
staining tendency.
2. Use a good quality soaping agent
to remove the unfixed dye and
prevent redeposition.
Inadequate
fastness
1. Rubbing
fastness
▪ Redeposition of dye on to
the fabric on bath cooling.
Drop the dyebath under pressure
without cooling.
[79,
85]
▪ Staining of cellulose portion
with disperse dyes due to
dye properties
1. Select dyes with lower staining
tendency.
2. Select an appropriate blend dyeing
method.
[88,
111,
253]
365
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
3. Select disperse dyes with good
wash properties in an alkaline
medium.
4. Perform reduction clearing if
possible.
▪ Incomplete diffusion of dye Ensure dye is properly diffused by
the selection of optimum dyeing
conditions (time, temperature,
auxiliaries).
[345]
▪ Inadequate removal of
unfixed/ hydrolyzed dye
1. Use good quality soaping agent to
remove the hydrolyzed dye and
prevent redeposition.
2. Check washing parameters (water
flow, washing temperature and
time).
3. Use an adequate number of wash
cycles/baths.
[68,
301,
345]
▪ Break down of dye
dispersion due to excessive
amount of electrolyte (salt)
1. Check disperse dye stability
against an excessive amount of
electrolyte.
2. Add salt after disperse dyeing.
3. Use the two bath process.
[7, 68]
▪ Leveling agent not
completely removed from
the substrate after dyeing. A
small quantity of dye is
retained by the leveling
agent on the fiber surface.
1. Ensure proper washing of fabric
after dyeing.
2. Select a leveling agent with good
wash-off properties.
[111]
366
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Presence of oligomers on
the fiber surface
1. Drop the dyebath at high
temperature.
2. Use a non-ionic reducing agent
during dyeing.
3. Dyeing of polyester in alkaline
medium depending upon the
possibility.
[351]
▪ Nonionic softener
containing mineral oils used
in finishing
Use cationic polyethylene or
silicone-based softeners.
[83]
▪ Staining of cellulose portion
by disperse dyes due to the
presence of urea
1. Select an appropriate blend dyeing
method.
2. Select disperse dyes with good
wash properties in alkaline
medium.
3. Perform reduction clearing.
4. Lower the concentration or replace
urea.
[79]
▪ Lower fixation of disperse
dyes due to the presence of
urea
1. Select an appropriate blend dyeing
method.
2. Lower the concentration or replace
urea.
[79]
2. Wash and
water fastness
▪ Staining of cellulose portion
with disperse dyes due to
dye properties
1. Select dyes with lower staining
tendency.
2. Select an appropriate blend dyeing
method.
[79,
111,
253]
367
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
3. Select disperse dyes with good
wash properties in alkaline
medium.
4. Perform reduction clearing if
possible.
▪ Redeposition of dye on to
the fabric on bath cooling.
Drop the dyebath under pressure
without cooling.
[79,
85]
▪ Improper fixation of
dyestuff due to short dyeing
time or low dyeing
temperature or inappropriate
pH.
Check the fixation conditions (pH,
dyeing temperature and time).
[301]
▪ Inadequate washing of
unfixed/hydrolyzed dyes
1. Use good quality soaping agent to
remove the hydrolyzed dye and
prevent redeposition.
2. Check washing parameters (water
flow, washing temperature and
time).
3. Use an adequate number of wash
cycles/baths.
[301,
345,
370]
▪ Poor washing of surface
disperse dyes due to poor
washing behavior
1. Select disperse dyes with a good
wash off behavior in one bath
process.
2. Performed reduction clearing.
3. Check reduction clearing
conditions.
[85]
368
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Poor washing of surface
disperse dye due to
inadequate reduction
clearing
1. Maintain the required
concentration of caustic and hydro.
2. Keep the temperature at 80-90 oC
during the process.
▪ Using reactive dyes of too
high substantivity which are
difficult to wash-off
Select dyes with good wash-off
properties (low substantivity).
[345]
▪ Incomplete removal of
leveling agent after dyeing.
A small quantity of dye is
retained by the leveling
agent on the fiber surface.
1. Ensure proper washing of fabric
after dyeing.
2. Select leveling agent with good
wash-off properties.
[111]
▪ Inherent properties of the
dyes
1. Select dyes with good wash-off
properties.
2. Treat with a fixing agent after
reactive dyeing.
[75,
345]
▪ Low and certain medium
energy dyes exhibit lower
fastness properties
Use high energy disperse dyes. [83]
▪ Thermomigration of
disperse dyes at higher
temperature, > 170 oC (e.g.
resin finishing)
1. Use medium to high energy
disperse dyes.
2. Use the lowest drying/possible
curing time and temperature.
3. Perform reduction clearing of
material after dyeing.
[83,
88,
253]
▪ Nonionic softener
containing mineral oils used
in finishing
Use cationic polyethylene or
silicone-based softeners.
[83]
369
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Presence of spinning
lubricants in the substrate
Ensure scouring is done properly and
spinning lubricants should be
completely removed.
[109]
▪ Use of poor quality of salt
that contains Ca and Mg
ions leading to problems in
dye removal
1. Check the salt quality.
2. Use sequestering agent during
dyeing.
[301]
▪ Use of low energy disperse
dyes having poor
sublimation fastness during
thermosol process
Select disperse dye of medium to
high energy level for thermosol
process.
[348]
▪ Improper removal of
unfixed disperse dye due to
poor removal of surfactant.
The surfactant carries
unfixed dye to the final
drying
Select surfactants that are easy to
remove in the rinsing process.
[348]
▪ Staining of cellulose portion
by disperse dyes due to the
presence of urea
1. Select an appropriate blend dyeing
method.
2. Select disperse dyes with good
wash properties in an alkaline
medium.
3. Perform reduction clearing.
4. Lower the concentration or replace
urea.
[79]
▪ Lower fixation of disperse
dyes due to the presence of
urea
1. Select an appropriate blend dyeing
method.
[79]
370
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
2. Lower the concentration or replace
urea.
3.
Lightfastness
Inadequate removal of unfixed
dye from the fabric
Perform proper soaping of fabric.
Check the washing temperature.
[370]
Presence of carrier residues Perform reduction clearing. [253,
350]
Staining of cellulose portion
with disperse dyes due to dye
properties
1. Select dyes with lower staining
tendency.
2. Select an appropriate blend dyeing
method.
3. Select disperse dyes with good
wash properties in an alkaline
medium.
4. Perform reduction clearing if
possible.
[253]
▪ Redeposition of dye on to
the fabric on bath cooling
Drop the dyebath under pressure
without cooling.
[79,
85]
▪ Catalytic fading due to
inappropriate dye
combination
Carry out laboratory trials before
dyeing in bulk.
[253]
▪ Improper selection of dyes Select dyes based on shade and
dyeing method.
[301]
▪ Use of low energy disperse
dyes having poor
lightfastness fastness during
thermosol process
Select disperse dye of medium to
high energy level for thermosol
process.
[348]
371
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Use of cationic fixing agent Select after treatment agents with
minimum effect on lightfastness.
[301]
▪ Browning of the cellulose
component at thermosoling
temperature under alkaline
conditions having lower
fastness
Avoid using too high temperature
during one-bath dyeing.
[79,
85]
▪ Browning of the cellulose
component at thermosoling
temperature caused by the
dispersing agent
Use optimum quantities of a
dispersing agent.
[79]
▪ Staining of cellulose portion
by disperse dyes due to the
presence of urea
1. Select an appropriate blend dyeing
method.
2. Select disperse dyes with good
wash properties in alkaline
medium.
3. Perform reduction clearing.
4. Lower the concentration or replace
urea.
[79]
▪ Lower fixation of disperse
dyes due to the presence of
urea
1. Select an appropriate blend dyeing
method.
2. Lower the concentration or replace
urea.
[79]
Widthwise
shade
▪ Using disperse dyes which
are sensitive to temperature
variations
Select dyes with which are less
sensitive to temperature variations.
[347]
372
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
differences/
listing
▪ Inadequate concentration of
anti-migrating agent causing
migration
Use the optimum concentration of
the anti-migrating agent depending
on the depth of shade.
[118]
▪ Using dyes with poor
migration properties
1. Dye selection based on their
migration behavior.
2. Examine migration parameters of
disperse dyes.
Two sidedness ▪ Poor migration properties of
disperse dyes
1. Use the optimum quantity of the
anti-migrating agent.
2. Dye selection based on their
migration behavior.
3. Examine migration parameters of
disperse dyes.
[118]
▪ Differences in the
substantivity of the dyes in
the combination shade
Select dyes with similar
substantivity.
[128]
Lengthwise
shade variation
/tailing/ ending
▪ Higher substantivity of dyes 1. Select dyes having lower
substantivity.
2. Use small trough volume.
3. Rapid circulation of liquor from
pad trough to stock feed tank.
[128,
253]
▪ Sedimentation of dye 1. Keep the liquor in circulation.
2. Keep the trough temperature
below 35 oC.
[253]
▪ Dye hydrolysis. 1. Select dyes with good dye bath
stability.
[369]
373
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
2. Keep the trough temperature
below 35 oC.
▪ Unstable dye dispersion 1. Use dyes with good dispersion
stability.
2. Use dispersing agent during
dyeing.
[253]
▪ Different adsorption
behavior of the dye due to
inappropriate dye
combination
Select dyes have similar dyeing
behavior.
[253,
369]
▪ Poor migration of the dyes Select dyes with good migration
properties.
[301]
▪ Differences in the affinity of
the dyes for the fiber
1. Use dyes with similar affinities.
The affinity factor of the dye
should be as low as possible.
2. Use short liquor trough.
[120,
368]
▪ Bleeding of the dye form
padded and dried fabric in
the chemical padding trough
1. Use a high concentration of
electrolyte.
2. Use some quantity of dyeing
liquor in the chemical pad.
[128,
317]
▪ Differences in dye
concentrations from one dye
preparation tank to another
Ensure the concentration of the dye
preparation remains consistent.
Dark and light
edges
▪ Residual alkali in the fabric Add acetic acid in pad liquor to
maintain pH 5-6.
[253]
Pilling of
fabrics
▪ Increase in specific gravity
of bath by addition of salt
Use a lubricating agent.
[301]
374
Table 4.44 (Continued)
Problems Probable causes Remedial measures Ref.
and alkali leading to higher
fabric-to-fabric friction
▪ High fabric to fabric friction
especially fabrics with a
very sensitive surface
1. Use a lubricating agent.
2. Turn the fabric inside out.
[297]
Lower strength ▪ Fiber damage during drying
due to residual alkali after
dyeing (especially viscose
Ensure proper neutralization of the
fabric after dyeing.
[301]
Poor
appearance
▪ Improper color matching of
the shade on fibers in the
blend having differences in
depth and tone
1. Check the shade obtained on
polyester fiber by dissolving the
cotton component.
2. Keep the shade 10-20% deeper
after polyester dyeing.
[351]
4.10.2 Disperse/direct system
PES/CELL blends dyed with disperse and direct dyes often show unsatisfactory fastness. This is
usually attributed to the lower fastness properties of direct dyes as the washing fastness tests
performed on cotton dyed with direct dyes showed staining of cotton in the multifiber strip.
However, this statement is partially correct for PES/CELL blends. Poor selection of disperse dyes
are also responsible for lower fastness properties. The washing tests performed on the polyester
materials dyed with disperse dyes showed staining of nylon and acetate fibers in the multifiber
strip and for some dyes staining of cotton was also observed. As disperse dye tend to stain the
cellulose during dyeing, this led to unsatisfactory fastness properties. During the washing fastness
test, the dye present on the cellulose can easily stain the multifiber. The stain on the cellulose may
wash off during the washing fastness test and but stain the nylon fiber in the multifiber. For fabrics
subjected to resin finishing, the problem is further aggravated. The curing process during resin
finishing may cause the migration of dyes, known as thermomigration, from the inside to the
surface of the fiber. Thermomigration depends on time and temperature of curing, resin type,
375
softener type, depth of shade, and energy level of disperse dyes. Disperse dyes of low energy and
certain medium energy dyes have low fastness properties as compared to high energy dyes as they
show more migration as compared to high energy disperse dyes. The cationic softeners usually
exhibit the least problems as compared to nonionic softeners [83].
The important points needed to be considered during dyeing with disperse/direct dyes are
[9, 57]:
▪ Effect of salt on dyeing with disperse dyes; and
▪ Stability of direct dyes to the higher temperature and acidic pH used in dyeing with
disperse dyes.
As compared to reactive dyes, direct dyes required less quantity of salt around 10-15 g/l
depending upon the depth of shade. This may have less effect on the dispersion stability of disperse
dyes although the problem may observe in short liquor dyeing machines such as a beam or package
[86]. The salt may interfere with the exhaustion of the disperse dyes and may cause rubbing
fastness problems [57]. The leveling and dispersing agents used for disperse dyes generally do not
affect the direct dyeing process [86, 125]. Many direct dyes, however, are affected by the acidic
pH (4.5-5.5) and the high temperature (120-130 oC) and sequestering agents used for disperse
dyeing. Under these conditions, dyes must be adequately soluble and chemically stable [9, 69, 125,
378]. Some direct dyes may stain the polyester component and may cause fastness problems.
However, carriers and leveling agents minimize the direct dye staining [125].
The summary of the main problems associated with disperse/direct system is given in Table
4.45. Many problems listed in the disperse/reactive system are also applicable to disperse and
direct dyes.
Table 4.45: Problems and their possible solutions in the dyeing of polyester/cellulose blends with
disperse and direct dyes.
Problems Probable causes Remedial measures Ref.
Reproducibility ▪ Variation in soda ash content
of direct dyes.
Check bath pH when dye when the
alkali is added and should be
adjusted if required.
[64]
376
Table 4.45 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Partial destruction of
disperse dye due to the
interaction between free
copper in metal complex
direct dyes in one bath
process
Removal of copper from the
dyeing system by using
specialized complexing agents.
[69]
Unlevelness ▪ Variation in soda ash content
of direct dyes. For certain
direct that require alkaline
pH for their solubility,
higher than normal soda ash
content leads to a very high
pH. Also, lower than normal
soda ash may cause a lower
pH. The desired pH at the
later stage may not be
achieved when alkali is
added.
Check bath pH when dye when the
alkali is added and should be
adjusted if required.
[64]
▪ Decrease in the solubility of
direct dyes under acidic
conditions and high
temperature used for
polyester dyeing
Select dyes that are stable in one
bath dyeing. Follow
manufacturers' recommendations.
[79]
Shade change ▪ Partial destruction of
disperse dye due to the
interaction between free
copper in metal complex
direct dyes in one bath
1. Use of copper-free direct dyes if
possible.
2. Use of metal complex dyes
having no free copper.
[69]
377
Table 4.45 (Continued)
Problems Probable causes Remedial measures Ref.
process. Especially taken
place in fully flooded
machines
3. Removal of copper from the
dyeing system by using
specialized complexing agents.
▪ Variation in exhaustion rates
of dyes
Select dyes with similar
exhaustion rates in the
combination shade.
[150]
▪ Destruction of direct dyes
under high dyeing
temperature used for
polyester dyeing
1. Select direct dyes with good
stability at a higher temperature.
2. Use a mild oxidizing agent.
3. Use the two bath process.
[68]
▪ Destruction of direct dyes
under acidic conditions used
for polyester dyeing
Check the stability of direct dyes.
Select dyes which are stable under
acidic and high temperature
conditions used in disperse dyeing.
[79]
Poor color yield ▪ Destruction of direct dyes
under high dyeing
temperature used for
polyester dyeing
1. Select direct dyes with good
stability at a higher temperature.
2. Use a mild oxidizing agent.
3. Use the two bath process.
[68]
▪ Physical interaction of
disperse and direct dyes in
the dye bath
1. Check the interaction between
the dyes in the lab before
dyeing.
2. Select dyes that show no or
minimum interaction effect.
3. Use the two-bath process if
possible.
[79]
Stains ▪ Variation in soda ash content
of direct dyes makes dye
insoluble in the dyebath
Check bath pH when dye when the
alkali is added and should be
adjusted if required.
[64]
378
Table 4.45 (Continued)
Problems Probable causes Remedial measures Ref.
Dark stains ▪ Precipitated or undissolved
dye
Ensure proper dye solution
procedure as per dye manufacturer
recommendation.
[149,
150]
▪ Decrease in the solubility of
direct dyes under acidic
conditions and high
temperature used for
polyester dyeing
Select dyes that are stable in one
bath dyeing. Follow the
manufacturers' recommendations.
[79]
Inadequate
fastness
1. Rubbing
fastness
▪ Break down of dye
dispersion due to excessive
amount of electrolyte (salt)
1. Check disperse dye stability
against an excessive amount of
elecltrolyte.
2. Add salt after disperse dyeing.
3. Use the two bath process.
[7, 68]
2. Wash fastness ▪ Inherent dye property, due to
weak attachment with the
fiber through Vander wall
forces
1. Treat with a fixing agent after
direct dyeing.
2. Use reactant fixable direct dyes.
[69,
75]
4.10.3 Disperse/vat system
This system is mainly used in package dyeing of yarns, semi-continuous and continuous dyeing of
fabrics [85]. This system is used where excellent fastness properties are required. They can be
applied by a relatively simple one bath two-stage process. The reduction bath required for the
reduction of vat dyes may also serve as a reduction clearing bath for disperse dyes. The vat dye
tends to strongly stain the polyester component of the blend at thermofixation temperature during
the one bath continuous processes [85, 359]. However, this cross-staining does not affect the
fastness properties achieved in PES/CELL blends. The vat dyes have limited stability under the
379
higher temperature dyeing conditions required for polyester in the batch dyeing process. The vat
dye dispersion for longer duration at high temperature is not stable. It is therefore recommended
to add vat dyes in the cooling bath after dyeing of polyester [79].
Many problems that occur during disperse/reactive system are also applicable to
disperse/vat dyes. Table 4.46 shows the specific problems and their causes and preventive
measures
Table 4.46: Problems and their possible solutions in the dyeing of polyester/cellulose blends
using disperse/vat system.
Problems Probable causes Remedial measures Ref.
Unlevelness ▪ Rapid exhaustion of dye due
to a higher rate of rise
1. Gradually increase the
temperature to control the
exhaustion.
2. Use a leveling agent.
▪ Inadequate reduction of the
dye caused by variation in
alkalinity due to higher
quantities of hydro
Use the correct amount
caustic/hydro as per manufacturer
recommendations.
[67]
▪ Inadequate reduction of the
dye to lower concentration of
hydro/caustic
Use the correct amount
caustic/hydro as per manufacturer
recommendations.
[194,
345]
▪ Using vat dyes of high
substantivity leading to higher
exhaustion of dyes to the
substrate
1. Select dyes with lower
substantivity, if possible.
2. Use leveling agent.
[254]
▪ Use of lower dyeing
temperature
Using higher dyeing temperature as
possible to promote leveling.
[7]
▪ Poor dispersion of the vat
pigments in the bath
Use dispersing agents. [70,
150]
380
Table 4.46 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Poor selection of dyes for
combination shade using dyes
of extremely different groups
Dyes used in combination shade
should belong to the same group.
[67,
70]
▪ Incomplete oxidation of the
dye due to inadequate
concentration oxidizing
chemicals and residual alkali
in the fabric
1. Check the concentration of the
oxidizing agent, pH, temperature
and proper replenishment.
2. Ensure proper rinsing of fabric
before oxidation.
▪ Poor dispersion stability of vat
dyes under high dyeing
temperature and longer dyeing
time
Add vat dyes to the cold bath after
the high temperature dyeing of
polyester.
[79]
Dull shade ▪ Partial diffusion of dye during
steaming due to inadequate
reduction.
Using optimum quantities of
hydro/caustic
▪ Too high dye fixation
temperature during disperse
dyeing.
The fixation temperature should be
lower than 190 oC.
[133]
▪ Over-reduction of vat dyes
due to excess quantities of
hydro or excess
steaming/dyeing times or high
temperatrure
1. Add sodium nitrite during the
dyeing process.
2. Following manufacturer
recommendation for
hydro/caustic concentration and
temperature.
3. Use adequate dyeing/steaming
time depending on the depth of
shade.
[7,
67]
381
Table 4.46 (Continued)
Problems Probable causes Remedial measures Ref.
▪ The shade becomes duller of
indanthrone blue dyes due to
higher pH values in oxidation
The pH in the oxidation process
should be or below 9.
[61]
▪ Over-oxidation of dyes due to
strong oxidizing agent
Use a mild oxidizing agent (sodium
metanitrobenzenesulfonate) for
oxidation.
[7]
Shade change ▪ Improper reduction due to
inadequate concentrations of
the hydro and caustic
Check the concentration of
hydro/caustic. It should be
according to the dye concentration.
[359,
366]
▪ Greener shade of indanthrone
blue dyes due to higher pH
values in oxidation
Oxidation of vat dyes should be
carried out at or below pH 9.
[61,
67]
▪ Over-reduction of vat dyes
due to excess quantities of
hydro or excess
steaming/dyeing times or high
temperature
1. Add sodium nitrite during the
dyeing process.
2. Following manufacturer
recommendation for
hydro/caustic concentration and
temperature.
3. Use adequate dyeing/steaming
time depending on the depth of
shade.
[7]
▪ Variation in exhaustion rates
of dyes
Use dyes with similar exhaustion
rates in combination shade.
[150]
▪ Incomplete oxidation of the
dye due to inadequate
concentration oxidizing
chemicals and residual alkali
in the fabric
1. Check the concentration of the
oxidizing agent, pH, temperature
and proper replenishment.
2. Ensure proper rinsing of fabric
before oxidation.
[68,
345,
370]
382
Table 4.46 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Combination shade produced
by mixing dyes of extremely
different groups
Select dyes with same groups or
nearby groups. Do not use dyes of
extremely different groups.
[67]
▪ Oxidation of detergents used
for soaping at high
temperature for longer
duration cause oxidation of
vat dyes
1. Select detergents which are
stable at high temperature.
2. Avoid using too long dwell
times.
[67]
▪ Bleeding of dye due to high
rinsing temperature
The temperature of the rinsing bath
should not exceed 40 oC.
▪ Staining of polyester by vat
dyes at high thermofixation
temperature
1. Perform the two bath process, if
possible.
2. Select vat dyes with lower
staining properties for
polyester.
[79,
85]
▪ Gas fading of dyes due to
exposure to hot air during
thermofixation
Select dyes with good stability
against gas fading.
[359]
▪ Over-oxidation of dyes due to
strong oxidizing agent
Use a mild oxidizing agent (sodium
metanitrobenzenesulfonate) for
oxidation
[7]
Widthwise
shade
variation/
listing
▪ Differences in caustic removal
from sides and the center of
fabric during washing lead to
differences in oxidation
Ensure the caustic is properly
removed from the fabric before
oxidation.
[61]
▪ Variation in oxidation of the
selvages as compared to the
center
Avoid the exposure of selvages due
to air.
[67,
194]
383
Table 4.46 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Nonuniform reduction of the
dye across the width of the
fabric
Ensure the distribution of the
reducing agent and caustic is
uniform across the fabric width.
Lengthwise
shade
variation/
tailing/ending
▪ Bleeding of the dye form
padded and dried fabric in the
chemical padding trough
Use a high concentration of
electrolyte.
Use some quantity of dyeing liquor.
[317,
379]
▪ Bleeding of dye due to high
rinsing temperature
The temperature of the rinsing bath
should not exceed 40 oC.
▪ Poor dispersion of the vat
pigments in the bath
Use dispersing agents. [379]
▪ Settling of the dye in the
preparation tank and the
dyeing trough
1. Ensure proper agitation in
preparation tank and the dyeing
trough.
2. Use dispersing agent with good
dispersion properties.
[379]
Dark stains ▪ Precipitated or undissolved
dye
1. Use optimum temperature for dye
solution preparation.
2. Use dispersing agents.
[149,
150]
▪ Poor dispersion of the vat
pigments in the bath
Use dispersing agents. [150]
▪ Settling of the dye in the
preparation tank and the
dyeing trough
1. Ensure proper agitation in the
preparation tank and the dyeing
trough.
2. Use a dispersing agent with good
dispersion properties.
[379]
▪ Agglomeration and
sedimentation of vat dyes due
to anti-migrating agent
1. Use optimum quantities of anti-
migrating agent.
[371]
384
Table 4.46 (Continued)
Problems Probable causes Remedial measures Ref.
2. Control the dye bath pH. The pH
of 4 reduces or cancels the
agglomeration effect.
▪ Poor compatibility of the dyes
and the auxiliaries
Check the dyes and auxiliaries for
computability in the laboratory
before dyeing in the bulk.
[379]
▪ Variation in the alkalinity of
the bath due to higher
quantities of hydro leading to
precipitation of vat dyes
Use the correct amount
caustic/hydro as per manufacturer
recommendations.
[67]
▪ Reoxidation of leuco
compounds desorbed from the
fabric surface in particulate
form due to foaming caused
by excessive wetting agent or
turbulence of the dye liquor
Use a defoamer. [128]
▪ Premature or improper
localized oxidation of the dye
1. Maintain proper oxidation
conditions (chemical
concentration, pH and
temperature).
2. Rinse the fabric with sodium
bicarbonate before oxidation for
easy removal of caustic.
3. After steamer/water seal fabric
should have sufficient quantities
of hydro.
[323]
385
Table 4.46 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Formation of insoluble leuco
acid form in rinsing due to
inadequate pH
The pH must remain between 9-
10.5 during rinsing.
▪ Variation in the particle size
of the vat dyes. The large dye
particles may cause crystal
growth or form deposits on the
yarn surface or difficult to
reduce
1. Perform dye filtration test for
new lot.
2. Add dispersing agent to avoid
crystal growth.
3. Wound a woven PP fabric on the
dye tube.
[254,
379]
Poor color
yield
▪ Inadequate reduction of dye
due to the presence of air in
the water/dyeing machine
1. Remove air from the machine at
the start of the dyeing cycle.
2. Minimize the contact of reduced
fabric with air.
3. Use closed chamber machines.
[345]
▪ Inadequate reduction of dye
due to insufficient quantities
of hydro/caustic
Check that sufficient reduction
potential is maintained by
controlling the concentration of
hydro/caustic.
[345,
370]
▪ Premature oxidation of the
dye due to the presence of air
in the water/dyeing machine
1. Remove air from the machine at
the start of the dyeing cycle.
2. Minimize the contact of reduced
fabric with air.
3. Use closed chamber machines.
[345]
▪ Incomplete oxidation of the
dye due to inadequate
concentration oxidizing
chemicals and residual alkali
in the fabric
1. Check the concentration of the
oxidizing agent, pH, temperature
and proper replenishment.
2. Ensure proper rinsing of fabric
before oxidation.
[68,
345,
370]
386
Table 4.46 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Gas fading of dyes due to
exposure to hot air during
thermofixation
Select dyes with good stability
against gas fading.
[359]
Inadequate
fastness
1. Rubbing
fastness
▪ Partial diffusion of dye during
steaming due to inadequate
reduction
Using optimum quantities of
hydro/caustic
▪ Inadequate removal of unfixed
dye from the fabric
1. Perform thorough soaping of the
fabric.
2. Check the washing temperature.
[370]
▪ Insufficient quantities of
caustic in the dyebath
Add an adequate quantity of caustic
depending on the concentration and
class of vat dye used.
[254]
▪ Inadequate rinsing of the
fabric before oxidation
Ensure proper rinsing of the fabric
with an adequate amount of water
supply.
[345]
▪ Premature oxidation of the
dye due to the presence of air
in the water/dyeing machine
1. Remove air from the machine at
the start of the dyeing cycle.
2. Minimize the contact of reduced
fabric with air.
3. Use closed chamber machines.
[345]
▪ Inadequate oxidation of the
dye by using peroxide/
perborate and acetic acid
leading to the formation of vat
acid pigment
Replace acetic acid with sodium
bicarbonate for oxidation.
[194]
387
Table 4.46 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Incomplete oxidation of the
dye due to inadequate
concentration oxidizing
chemicals and residual alkali
in the fabric.
1. Check the concentration of the
oxidizing chemicals and proper
replenishment.
2. Ensure proper rinsing of fabric
before oxidation.
[345,
370]
2. Wash
fastness
▪ Inadequate removal of unfixed
dye from the fabric.
1. Perform thorough soaping of the
fabric.
2. Check the washing temperature.
[370]
▪ Inadequate rinsing of the
fabric before oxidation.
Ensure proper rinsing of the fabric
with adequate amount of water
supply.
[345]
▪ Premature oxidation of the
dye due to the presence of air
in the water/dyeing machine.
1. Remove air from the machine at
the start of the dyeing cycle.
2. Minimize the contact of reduced
fabric with air.
[345]
▪ Use of non-ionic soaping
agent having lower cloud
point temperature.
Use an anionic soaping agent. [254]
▪ Incomplete oxidation of the
dye due to inadequate
concentration oxidizing
chemicals and residual alkali
in the fabric.
1. Check the concentration of the
oxidizing chemicals and proper
replenishment.
2. Ensure proper rinsing of fabric
before oxidation.
[345,
370]
▪ Inadequate soaping
temperature or dwell time.
Use adequate soaping temperature
and dwell time.
[7]
▪ Inadequate removal of unfixed
dye from the fabric.
1. Perform thorough soaping of the
fabric.
2. Check washing temperature.
[370]
388
Table 4.46 (Continued)
Problems Probable causes Remedial measures Ref.
3.
Lightfastness
▪ Catalytic fading of vat dyes. Select dyes with good light fastness
in combination shades.
[7]
▪ Poor dye selection. Select dyes with good light fastness
in combination shades.
Poor
appearance
(haziness)
▪ Random concentration of a vat
dye on the fabric surface.
Strip and re-dye the fabric. [67]
Reduced
strength
▪ Photo tendering of cellulose
by some vat dyes.
Carefully select the dyes with a
lower tendency to phototendering.
[7]
4.10.4 Disperse/sulfur system
This combination is usually restricted to dull and dark shades such as black, navy, brown, olive
and green. They are generally used in low cost articles due to limited fastness properties. They can
be applied to PES/CELL blends by both bath and continuous dyeing methods. The sodium sulfide
used for the reduction of sulfur dyes has an adverse effect on the polyester, sodium hydrosulfide
is therefore preferred to minimize this problem [79, 380]. The use of disperse/sulfur system for the
dyeing of PES/CELL blends is very limited. The main problems related to disperse/sulfur system
and possible solutions are given in Table 4.47.
Table 4.47: Dyeing problems associated with disperse/sulfur system.
Problems Probable causes Remedial measures Ref.
Unlevelness ▪ Addition of the dyes in the bath
at a very high temperature.
Add dyes at a lower temperature.
Start the dyeing process at a lower
temperature.
[380]
▪ Higher temperature ramp rate. 1. Use slower ramp rate.
2. Increase liquor circulation rates
with higher ramp rates.
389
Table 4.47 (Continued)
Problems Probable causes Remedial measures Ref.
▪ Too quick addition of
electrolyte
Add electrolyte gradually during the
dyeing process.
▪ Inadequate rinsing before
oxidation leading to
precipitation of unfixed dye on
the fiber surface during the
acidic oxidation stage
Ensure proper rinsing conditions
(time, temperature and adequate
water supply)
Bronziness ▪ Premature oxidation of dye 1. Use the excess quantity of hydro.
2. Remove air from inside the
machine.
3. Strip to remove some of the
surface dye.
[345]
▪ Using too much concentration
of the dye
1. Use dyes with high tinctorial
strength.
2. Avoid using too high dye
amounts.
3. Strip to remove some of the
surface dye.
▪ Excess quantity of salt used
during dyeing.
Use the optimum quantity of the salt
based on the shade.
[150]
[345]
▪ Using poor quality or lower
quantity of sodium sulfide
leading to incomplete reduction
of the dye
1. Check the reduction potential of
the sodium sulfide.
2. Use the optimum quantity of
sodium sulfite based on the shade.
[345]
▪ Presence of free sulfur in the
dye bath
Use sodium sulfite along with
sodium sulfide for dissolving free
sulfur in the dye bath.
[323]
390
Table 4.47 (Continued)
Problems Probable causes Remedial measures Ref.
Tailing or
ending
▪ Addition of all dyes and
auxiliaries at the start of the
process
Add dyes and auxiliaries gradually
during the dyeing process.
[380]
▪ Beginning of the dyeing at a
very high temperature
Add dyes at a lower temperature.
Start the dyeing process at a lower
temperature
▪ Addition of electrolyte at the
start of the dyeing process
1. Don’t add electrolyte along with
the dye. Allow the dye to run with
the substrate for some time before
electrolyte is introduced.
2. Add electrolyte gradually in steps.
Acid
tendering
▪ Storage of fabric in warmer
and humid conditions leading
to the release of acid by some
sulfur dyes
1. Store the fabric at low
temperature and humidity.
2. Finish the fabric to slightly
alkaline pH after dyeing.
[345]
▪ Incomplete removal of sulfur
residues from the fabric
1. Ensure proper rinsing before
oxidation.
2. Thorough soaping of the dyed
fabric after oxidation.
3. Finish the fabric to slightly
alkaline pH after dyeing.
[345]
Dark stains ▪ Precipitated or undissolved dye Use a dispersing agent. [149,
150]
▪ Re-oxidation of leuco
compounds desorbed from the
fabric surface in particulate
form due to foaming caused by
Avoid using an excessive amount of
wetting agent and high turbulence.
[128]
391
Table 4.47 (Continued)
Problems Probable causes Remedial measures Ref.
excessive wetting agent or
turbulence of dye liquor
Lower
strength
▪ Adverse effect of sodium
sulfide on polyester
Use hydro as a reducing agent. [79]
392
CHAPTER 5 EFFECT OF BLEND RATIO ON DYEING
PROPERTIES OF POLYESTER-COTTON BLENDED FABRICS
5.1 Introduction
Polyester/cotton blends are the most important and commonly dyed fiber blends. Their profound
success is due to their excellent properties. Both single colorant and two colorants system can be
used to dye these blends. The single colorant system uses pigments which are attached to the
substrate (fiber) with the help of a binder. Although pigment coloration is economical but it is
mostly limited to light to medium shades due to inadequate fastness of the colored substrate and
harsh fabric hand at higher concentrations. The two colorant system involving separate dye classes
for each component of the blend is applicable at different depths of shade and for a wide range of
fastness properties depending upon the end use. Disperse dyes are used to dye the polyester
component only, but reactive, vat, direct and sulfur dyes can be applied to cotton. Although the
cotton portion of the blend can be dyed with different dyes reactive dyes exhibit a high level of
fastness properties and a wide shade range. The disperse/reactive system is, therefore, the most
common dye system used for the dyeing of polyester/cotton blends in most applications.
Different methods can be used to dye polyester/cotton blends using disperse and reactive
dyes. These include conventional two-bath, reverse two-bath and one-bath methods. The
conventional two bath method is recommended for medium to dark shades with good fastness
properties. A reduction clearing can be performed to provide good to excellent fastness properties.
The reverse two bath is the modified process in which cotton is dyed first followed by polyester.
The reduction clearing process is not suitable in this case as it may destroy the reactive dyes. Some
reactive dyes may not be stable under high temperature conditions and acidic pH employed in
disperse dyeing. The one bath process significantly reduces the dyeing times as both dye classes
are added together at the start of the dyeing process. Fixation is usually achieved in two stages. In
the first stage disperse dyes are fixed and the bath temperature is then reduced to fix the reactive
dyes. Good dye selection is important to achieve good fastness results and color yield [7, 9, 381].
393
Factors affecting the selection of the disperse dyes for polyester/cellulosic blends include
the required hue, depth of shade, level dyeing behavior, cross-staining, and fastness properties.
The dyes that may be suitable for dyeing of 100% polyester fibers may not give satisfactory
performance in the dyeing of blends. The migration properties of disperse dyes are generally
inferior on polyester/cellulosic blends compared to those on 100% polyester. Due to the
hydrophilic nature of the cellulosic fibers, the dyeing liquor movement is preferred in cellulosic
regions compared to the polyester which is more hydrophobic. This inhibits the migration of
disperse dyes to the polyester [86, 381].
The overall appearance of the dyed polyester/cotton blends need to be controlled to achieve
good union effects due to differences in the distribution of polyester and cotton fibers in the yarn
body and the reflectance properties of the polyester and cotton fibers. In the case of polyester rich
fiber blends such as polyester/cellulose with 67/33 blend ratio, it seems logical that the color
obtained on the polyester portion mainly determines the overall dyeing effect. However, due to the
migration of cellulosic fibers to the surface of the yarn during spinning, their color can have the
main contributing effect on the appearance of the yarn. It has been found that in the case of medium
to deep shades the color of the cellulosic component predominates while in case of light shades
the reverse is true. This makes shade corrections difficult for the polyester component of the blend.
The amount of dyes required to match a shade may also vary due to the differences in the
distribution of fibers [381].
During the dyeing of blends with disperse dyes, the dye is distributed between the two fiber
components while some also remains in the dyebath. Some disperse dyes may superficially attach
to cotton, forming stains, which can be heavy and result in poor washing fastness properties.
Therefore, often for the same type of dyes employed the polyester/cotton blends exhibit lower
washing fastness as compared to 100% cotton [87]. The superficially attached disperse dyes need
to be removed to obtain good fastness properties. Two approaches can be used to deal with this
problem. The first approach involves the use of disperse dyes with a minimum tendency to stain
the cotton which have good wash-off properties. This can be achieved by using alkali clearable
disperse dyes that have a lower tendency to stain cotton or dyes that do not require a conventional
reduction clearing process. They can be removed in the alkaline medium used for reactive dyeing.
The second approach employs the reduction clearing process for the removal of surface dye from
cotton and polyester fibers. This requires a two bath process where polyester is dyed first followed
394
by reduction clearing. The cotton is dyed in the second stage. The mechanism for the removal of
disperse dye is shown in Figure 5.1 [7, 9, 87, 381, 382].
Figure 5.1: Clearing mechanism of disperse dye stain [383].
One of the objectives of this study was to investigate the effect of different proportions of
polyester and cotton fibers in the blend on the dyeing behavior of polyester/cotton blend fabrics.
The following hypotheses, pertaining to batch dyeing by standard dyeing methods, were tested to
determine the effect of blend ratio on the dyeing properties of the polyester/cotton blends.
▪ The amount of dye required for dyeing of each fiber in the blend varies with the blend
proportion of each fiber in the blend. For example, by using approximately 50% of the
original amount of disperse and reactive dyes respectively on 50/50 PES/CO blend a
similar shade to that obtained on 100% polyester and 100% cotton can be produced.
▪ The two-bath method will yield better fastness properties as compared to reverse two
bath and one bath methods.
▪ The fastness properties of the polyester/cotton blends vary with the blend ratio.
Increasing the polyester component in the blend results in deteriorated wet fastness
properties in general especially for staining nylon in a multi-fiber strip during wash
fastness tests. In addition, as the cotton portion of the blend increases there will be a
decrease in the wet rubbing fastness.
TS S&W BD PES June 2008
Polyester/cellulose
blend
Dye
polyester
fibre
dye on fibre
surface
reduction/
alkali clear
Page 3/23Main menu
Dye inside the fiber and on
the surface
395
5.2 Experimental
5.2.1 Materials
Six knitted fabrics were used in this study. Single jersey knitted fabric samples were produced
from each of the yarns kindly supplied by Parkdale Mills. The count and the composition of the
yarns are given in Table 5.1.
Table 5.1: Properties of yarns and fabric codes.
Yarn count Fiber Composition Fabric codes
Ne 18/1 100% Cotton CT
Ne 20/1 100% Polyester PET
Ne 16/1 65% High tenacity polyester, 35% Cotton PC1
Ne 18/1 50% Cotton, 50% Polyester PC2
Ne 18/1 60% Cotton, 40% Polyester PC3
Ne 18/1 75% Cotton, 25% Polyester PC4
All the yarns used were knitting yarn that were waxed during spinning except the 65%
polyester/35% cotton yarn which was a weaving yarn and was waxed before knitting. The blended
yarns were produced by intimate blending and spun by rotor spinning. For all yarns, the cotton
fiber used was Memphis Eastern with an average length of 1.12 inches. Two types of polyester
fiber were used. For all yarn types except 65% polyester/35% cotton yarn, the polyester used had
a linear density of 1.2 deniers, with a cut length of 32mm, optically brightened, having a tenacity
of 6.2 grams/denier. For 65/35 blend ratio the high tenacity polyester was used having a linear
density of 1.2 deniers, 38 mm staple length and tenacity 6.9 grams/denier.
Table 5.2 shows the list of general chemicals and auxiliaries used. In order to dye the
polyester/cotton blends disperse and reactive dyes were obtained from Archroma (Foron,
Drimaren), Huntsman (Terasil, Novacron), and Dystar (Dianix, Procion, Remazol). The disperse
dyes used are presented in Table 5.3 while the reactive dyes are listed in Table 5.4.
396
Table 5.2: List of chemicals and auxiliaries.
Name Application Supplier
Sodium hydroxide (NaOH, 50%) Alkali for scouring and
bleaching
Brenntag
Hydrogen peroxide (H2O2, 35%) Bleaching agent Brenntag
Acetic acid (glacial) Acid for disperse dyeing and
neutralization
Brenntag
Clarite Max Stabilizer Huntsman
Invadine PBN Wetting agent Huntsman
Sodium sulfate (Glauber's salt) Electrolyte Brenntag
Sodium carbonate (Soda ash) Alkali for dyeing Trontox
Novadye NT9 Dispersing agent (A) Boehme Filatex
Sera Sperse M-IS Dispersing agent (B) Dystar
Sera Gal P-SDL Leveling agent Dystar
ApolloScour SRDS Surfactant Apollo Chemicals
Table 5.3: Properties of disperse dyes used in the study.
Dye name Color Index number Chemical Class Energy level
Foron Brilliant Yellow S-6GL Disperse Yellow 231 Azo High
Foron Rubine S-WF Not assigned Azo High
Foron Blue S-BGL Disperse Blue 73 Anthraquinone High
Foron Navy S-2GRL Disperse Blue 79:1 Azo High
Dianix Flavine XF Disperse Yellow 126 Pyrolidone High
Dianix Blue XF Disperse Blue 284 Azo thiophene Medium
Dianix Crimson SF Mix Benzodifuranone High
Dianix Yellow CC Disperse Yellow 241 Pyrolidone Medium
Dianix Rubine CC Mix Azo Medium
Dianix Blue CC Mix Azo Medium
397
Table 5.3 (Continued)
Dye name Color Index number Chemical Class Energy level
Dianix Red CC Disperse Red 343 Azo Medium
Terasil Yellow 4G Disperse Yellow 211 Pyridone Medium
Tersail Rubine 2GFL Disperse Red 167.1 Azo High
Terasil Blue 3RL-02 Disperse Blue 56 Anthraquinone Low
Terasil Brown 2RFL Disperse Orange 30 Azo High
Terasil Navy GRL-C Disperse Blue 79.1 Azo High
Table 5.4: Characteristics of reactive dyes used in the study.
Dye name Color Index number Reactive group
Drimaren Yellow CL-2R Reactive Yellow 145 MCT, VS
Drimaren Red HF-6BL Not assigned TFP, VS
Drimaren Blue HF-RL Not assigned TFP, VS
Procion Yellow H-EXL Not assigned 2 x MCT
Procion Dark Blue H-EXL Not assigned 2 x MCT
Procion Red H-E3B Reactive Red 120 2 x MCT
Remazol Yellow RR Mixture VS
Remazol Red RR Mixture VS, MCT
Remazol Blue RR Mixture VS
Remazol Black B Reactive Black 5 2 x VS
Novacron Yellow FN-2R Reactive Yellow 206 2 x FT
Novacron Ruby S-3B Mixture 2 x MCT, VS
Novacron Blue FN-R Reactive Blue 235 FT, VS
Novacron Orange W-3R Reactive Orange 131 2 x VS
Novacron Navy S-G Mixture 2 x VS + 2 x VS,
MCT
MCT:Monochlortriazine, VS: Vinyl suplhone, MFT: Monoflorotriazine, TFP:
Trifloropyrimidine, FT: Florotriazine
398
5.2.2 Methods
5.2.2.1 Knitting
The fabric samples were produced on a Shima Seiki flat knitting machine with a 14 gauge. The
fabric codes for different blend compositions are given in Table 5.1.
5.2.2.2 Pretreatment
The solomatic bleaching (combined scouring and bleaching) of the greige knitted fabrics was
carried out in a laboratory-scale Thies Jet Machine using a 15:1 liquor to goods ratio. The fabrics
were scoured and bleached using 2 g/L of NaOH, 4 g/L of H2O2, 2 g/L of stabilizer and 1 g/L of a
wetting agent at the boil for 1 hour. The fabrics were then rinsed twice and neutralized using 0.5
g/L acetic acid to adjust the fabric pH to 6-7. The fabrics were then centrifuged and dried. The
fabrics containing polyester, whole or in a blend, were heatset on a Mathis laboratory-scale stenter
at 200 oC for a dwell time of 2 minutes. The fabric absorbency was tested by a drop test after
pretreatment and was found to be less than 3 seconds for all fabrics. The CIE whiteness and tint
values of the fabrics after pretreatment are given in Table 5.5.
Table 5.5: CIE whiteness and tint indices of fabrics after pretreatment.
Fabric Whiteness Index Tint Index
CT 73.50 -0.95
PET 127.99 2.35
PC1 112.63 0.65
PC2 121.46 1.56
PC3 115.44 1.08
PC4 108.83 0.64
5.2.2.3 Dyeing
Disperse and reactive dyes were used to dye polyester and cotton components respectively. Three
colored chips, two dark and one light were selected from the Pantone book of color as target colors.
The selected chips were Pantone 462U (brown), Pantone 2768U (navy) and Pantone 468U (beige)
and are simulated in Figure 5.2. These target colors were matched on four polyester/cotton blended
399
fabrics, as well as on 100% cotton, and 100% polyester fabrics. The dyes were provided by
Archroma, Dystar, and Huntsman. The dyes were selected from the manufacturer's
recommendations based on the target color and their suitability for the batch dyeing method. The
dye combinations used to produce the target colors in different dyeing methods are given in Table
5.6. In the first step, the primaries were produced from each dye on CT and PET fabrics according
to the recommended dyeing method. The various dye concentrations used are 0.05, 0.1, 0.25, 0.5
and 1% owf. The Datacolor Match Textile software was used to generate recipes to match a target
color. The blended, as well as cotton and polyester fabrics, were then dyed based on generated
recipes according to different dyeing methods. The dyeings were corrected until a match with
DEcmc < 1.5 was obtained. Approximately 4-5 corrections were needed to match the color of the
dyed substrate for the target shades. The dyeings were then replicated on a larger sample. All
dyeings were carried out in a laboratory-scale Ahiba IR Pro dyeing machine. A liquor to goods
ratio of 20:1 was employed. A total of 90 samples (6 fabrics, 3 colors, 3 dyeing methods: two-bath
with 3 different dye combinations, reverse two-bath and one bath) were produced.
(a) Pantone 462U (b) Pantone 2768U (c) Pantone 468U
Figure 5.2: Simulations of Pantone colors used as target colors.
Table 5.6: Dye combinations used to match target colors using different dyeing methods.
Shade Supplier Dyeing
method Dye combinations
Brown Dystar C2B
PES: Yellow CC, Blue CC, Red CC
CO: Yellow RR, Red RR, Black B
Archroma C2B PES: Brilliant Yellow S-6G, Rubine S-WF Navy S-2GRL 200
CO: Yellow CL-2R, Red HF-6BL, Blue HF-RL
400
Table 5.6 (Continued)
Shade Supplier Dyeing
method Dye combinations
Huntsman C2B PES: Yellow 4G, Rubine 2GFL, Navy GRL-C
CO: Navy S-G, Ruby S-3B, Yellow FN-2R
Huntsman R2B PES: Yellow 4G, Rubine 2GFL, Blue 3RL-02
CO: Navy S-G, Ruby S-3B, Yellow FN-2R
Dystar 1B PES: Flavine XF, Blue XF, Crimson SF
CO: Red HE3B, Dark Blue HEXL, Yellow HEXL
Navy
Dystar C2B
PES: Yellow CC, Blue CC, Red CC
CO: Yellow RR, Red RR, Black B
Archroma C2B
PES: Brilliant Yellow S-6G, Rubine S-WF, Navy S-2GRL
200
CO: Yellow CL-2R, Red HF-6BL, Blue HF-RL
Huntsman C2B PES: Brown 2RFL, Rubine 2GFL, Navy GRL-C
CO: Navy S-G, Ruby S-3B, Orange W-3R
Huntsman R2B PES: Brown 2RFL, Rubine 2GFL, Blue 3RL-02
CO: Navy S-G, Ruby S-3B, Orange W-3R
Dystar 1B PES: Flavine XF, Blue XF, Crimson SF
CO: Red HE3B, Dark Blue HEXL, Yellow HEXL
Beige
Dystar C2B
PES: Yellow CC, Blue CC, Red CC
CO: Yellow RR, Blue RR
Archroma C2B PES: Brilliant Yellow S-6G, Rubine S-WF
CO: Yellow CL-2R, Red HF-6BL, Blue HF-RL
Huntsman C2B PES: Yellow 4G, Rubine 2GFL, Blue 3RL-02
CO: Blue FN-R, Ruby S-3B, Yellow FN-2R
Huntsman R2B PES: Yellow 4G, Rubine 2GFL, Blue 3RL-02
CO: Navy S-G, Ruby S-3B, Yellow FN-2R
Dystar 1B PES: Flavine XF, Blue XF, Crimson SF
CO: Red HE3B, Dark Blue HEXL, Yellow HEXL
PES: Polyester, CO: Cotton
401
The different dyeing methods used for the dyeing of polyester/cotton blended fabrics were
conventional two-bath (C2B), reverse two-bath (R2B) and one bath two-stage (1B). During the
C2B method, as shown in Figure 5.3a, the polyester portion is dyed first with disperse dyes at 130
oC for 45 minutes for navy and brown colors and 30 minutes for beige color using 0.5 g/L
dispersing agent. The heating rate of the dye bath was kept at 2 oC/min. The pH of the dye bath
was maintained at 5.5 with acetic acid. The reduction clearing process was then performed with 2
g/L hydro and 2 g/L caustic at 80 oC for 10 min. This was followed by rinsing and neutralization.
In the second bath, the cotton portion was dyed with reactive dyes using Glauber’s salt and soda
ash. The pH of the dye bath was 10.8. The amount of Glauber’s salt used depended on the depth
of shade. The dyeing was carried out at 60 oC for 60 minutes for the navy and brown colors and
45 minutes for the beige color. The dyed fabric was then soaped at 95 oC for 10 min using 1 g/L
surfactant to remove the unfixed reactive dye. The rinsing and neutralization completed the
process.
In the R2B method shown in Figure 5.3b, the cotton portion was dyed first followed by
polyester dyeing using the same chemicals and conditions used as in the C2B method except the
reduction clearing process was replaced with the rinsing and neutralization process as reactive
dyes are not stable under reduction clearing conditions. The polyester was then dyed with disperse
dyes. The soaping process was then used to remove the unfixed and hydrolyzed dyes.
The dyeing in the 1B method was carried out in two stages as shown in Figure 5.3c. Both
disperse and reactive disperse dyes were added together with a dispersing agent, leveling agent
and Glauber’s salt. The pH of the bath was maintained at ~ 4 with the help of acetic acid. The
temperature of the bath was then increased to 135 oC to dye the polyester portion. The temperature
gradient was kept at 1 oC/min in the critical dyeing region (65-135 oC). The disperse dyes used
were sensitive to dyeing conditions so different dispersing agent and leveling agent were used
according to manufacturer recommendations. The pH of the dyebath was also adjusted to be more
acidic as compared to the two-bath methods. The dyeing was continued for 45 minutes for the
navy and blue colors and 30 minutes for the beige color. The temperature was then dropped to 80
oC and soda ash was added to maintain a pH of ~ 11. The dyeing was then carried out for 60
minutes for the navy and brown and 45 minutes for the beige colors. The dyed fabrics were soaped
similarly as in the two-bath methods.
402
(a) Conventional two-bath dyeing method.
(b) Reverse two-bath dyeing method.
(c) One-bath two-stage dyeing method.
Figure 5.3: Dyeing profiles of different dyeing methods used.
The PET and CT fabrics were dyed according to the methods used for the dyeing of the
respective portion of the blend. The PET fabrics were reduction cleared while the CT fabrics were
2 oC/min
2 oC/min
130 oC, 30-45 min
80 oC, 10 min
60 oC, 45-60 min
95 oC, 10 min
0.5 g/L Dispersing agent (A)
Acetic acid, pH ~ 5.5Glauber's salt
Soda ash, pH ~ 11
1 g/L surfactant
Tem
per
atu
re,
oC
Time, min
Polyester Dyeing Reduction
clearingCotton dyeing SoapingRinsing &
Neutralizationn
Rinsing &
Neutralization
2 oC/min
2 oC/min
130 oC, 30-45 min
60 oC, 45-60 min
95 oC, 10 min
0.5 g/L Dispersing agent (A)
Acetic acid, pH ~ 5.5
Glauber's salt
Soda ash, pH ~ 11
1 g/L surfactant
Tem
per
atu
re,
oC
Time, min
Polyester DyeingCotton dyeing SoapingRinsing &
Neutralizationn
Rinsing &
Neutralization
95 oC, 10 min
1 g/L surfactant
Tem
per
ature
, oC
Time, min
Polyester Dyeing Cotton dyeing SoapingRinsing &
Neutralization
80 oC, 45-60 min
2 oC/min
1 oC/min
135 oC, 30-45 min
2 g/L Dispersing agent (B)
1 g/L Leveling agent
Acetic acid, pH ~ 4
Glauber's salt
Soda ash, pH ~ 1165
oC
403
soaped according to the different methods employed. In the 1B and R2B methods no reduction
clearing was performed. In such cases the PET fabric was soaped to match the same treatment.
5.2.3 Evaluation methods
5.2.3.1 Color strength
The colorimetric attributes of the fabrics were measured using a calibrated Datacolor 850
reflectance spectrophotometer with Tools® software. The color match predictions were computed
using Datacolor Match Textile software. The settings used for measurement were illuminant D65,
CIE 10o standard observer with specular and UV included. Three readings were taken at random
points of the samples and then averaged.
The color strength of the dyed samples was calculated using the Kubelka-Munk equation
given below:
𝐾
𝑆=
(1 − 𝑅)2
2𝑅 (5.1)
Where R is the reflectance of the samples at a wavelength of maximum absorbance. The relative
color strength of the samples is calculated by dividing the K/S value of the sample by the K/S
value of the reference. The relative strength value is reported in percentage.
5.2.3.2 Color fastness
Different fastness properties, e.g. light fastness, crocking fastness, washing fastness and water
fastness were evaluated for the dyed fabrics. These were selected based on the most commonly
used fastness tests for dyed polyester/cotton blended fabrics in the industry.
Color fastness to light was measured according to the AATCC TM 16.3, Option 3. The
strip of fabric, part of which was covered was placed in a light fastness tester and exposed to 40
hours of accelerated fading units (AFU). After the exposure, the color of the exposed and protected
portion of the samples were compared. The color change was then quantified using grey scale for
color change [384].
Crockfastness was determined using the AATCC TM 8. Both dry and wet rubbing fastness
assessments were carried out by using a digital crockmeter. The ratings were assigned to the
amount of color transferred to the white fabric [385].
404
The color fastness to washing was assessed using a Launder-o-meter according to the
AATCC TM 61. The settings used were according to option 2A (49 oC). A multifiber strip was
attached to each sample to evaluate staining. After the test, the color change of the test specimen
and the magnitude of staining of the multifiber strip were determined using the grey scale ratings
[386].
Color fastness to the water of the dyed samples was determined using a perspirometer
according to the AATCC TM 107 and the staining of the multifiber was recorded [387].
The greyscale ratings, from 1 to 5, were determined instrumentally using the AATCC
Evaluation Procedure 7 for change in color [388] and the AATACC Evaluation Procedure 12 for
staining [389]. The scale grades were then converted to step values. The grade of 5 implies no
color change or staining [390, 391].
5.3 Results and discussion
5.3.1 Amount of dye required to match a target color
The actual amounts of dyes used to generate a match are given in Table 5.7. The amount of dyes
required to match a given shade varied with the depth of shade and blend ratio of the fabric as
expected. The navy color required the largest dye amounts followed by brown and beige colors.
The results for dye concentrations showed that the dye amounts vary with the blend ratio of the
fiber in the blend. It is interesting to note that the dye amounts required to match the shade on a
blend were significantly higher compared to the blend ratio for all three colors. In some cases, the
disperse and reactive dye amounts required to match the respective portion of the blend were found
to be similar to those used to produce a match on 100% cotton and polyester fabrics.
405
Table 5.7: Total amounts of dye required to match the target colors in fabrics of different blend
ratio using different dyeing methods.
Color Fabric C2B-Dystar C2B-Archroma C2B-Huntsman R2B-Huntsman
D R D R D R D R
Brown
PET 0.212 0.228 0.262 0.304
PC1 0.321 0.584 0.351 0.790 0.409 0.501 0.463 0.519
PC2 0.257 0.820 0.305 1.215 0.324 0.732 0.416 0.779
PC3 0.194 0.948 0.229 1.414 0.255 0.873 0.325 0.896
PC4 0.091 1.141 0.124 1.559 0.134 0.887 0.173 0.914
CT 0.839 1.138 0.654 0.645
Navy
PET 0.254 0.329 0.349 0.465
PC1 0.386 0.550 0.565 0.783 0.539 0.649 0.719 0.641
PC2 0.321 0.820 0.581 1.316 0.453 0.946 0.623 0.949
PC3 0.214 0.975 0.511 1.821 0.332 1.075 0.457 1.195
PC4 0.104 1.109 0.239 2.061 0.150 1.108 0.231 1.113
CT 0.733 1.669 0.787 0.798
Beige
PET 0.014 0.015 0.015 0.015
PC1 0.021 0.045 0.020 0.039 0.023 0.027 0.025 0.046
PC2 0.019 0.082 0.021 0.055 0.021 0.044 0.023 0.058
PC3 0.013 0.103 0.017 0.072 0.017 0.053 0.018 0.062
PC4 0.007 0.105 0.009 0.080 0.008 0.053 0.009 0.057
CT 0.071 0.060 0.040 0.038
D: Disperse, R: Reactive
In blends, the amount of dyes required to produce the same color as on a single fiber is
usually adjusted according to the blend ratio of the fabric. For example as shown in Table 5.7, if
0.212 % owf disperse dye and 0.839 % owf reactive dyes were required to produce the same shade
on 100% polyester and 100% cotton fabrics respectively, the same shade can be matched on
polytester/cellulosic blends by adjusting the dye amount according to blend ratio. For 65/35
polyesyer/cotton blend (PC1) the adjusted disperse and reactive dye amount is expected to be
406
around 0.138% owf (65% of 0.212% owf total disperse dye) and 0.294% owf (35% of 0.8393%
owf of total reactive dye) respectively. This assumes that the fiber type used is the same and both
single fibers and fiber blend are processed under the same dyeing conditions. This behavior is not
exhibited by the dyes and dyeing methods used in this study. The amount of dyes required to match
the same shade on polyester/cotton blends were found to be approximately two times the
theoretical amounts based on the match obtained on all polyester and all cotton fabrics irrespective
of the color to be matched. The only exception is the one bath method that shows 3-5 times more
dye amounts than calculated based on the blend ratio. The use of higher dye amounts than expected
may be attributed to a loss in color yield of the reactive and disperse dyes with a change in the
blend ratio. Although in the case of continuous dyeing the amount of dyes required to match the
given shade may vary slightly as compared to the blend ratio, the results obtained by batch dyeing
in this study show higher amounts than in practical continuous dyeings [139].
Table 5.8: The effective liquor ratio for each fiber in the blend at a bath liquor ratio of 20.
Fabric Blend ratio Effective liquor ratio
PES CO PES CO
CT 100 20
PET 100 20
PC1 65 35 31 57
PC2 50 50 40 40
PC3 40 60 50 33
PC4 25 75 80 27
As the required pH was maintained according to dye type and the dyeing auxiliaries were
used based on g/L, the drop-in dye yield may be due to the change in the effective liquor available
for each fiber type in the blend as shown in Table 5.8. At a liquor ratio of 20, the effective liquor
ratio available for PES/CO 50/50 is 40 for cotton and for a polyester portion of the blend. For
PES/CO with a 25/75 ratio, this will increase to 80 for polyester and 27 for cotton. The increase in
liquor ratio may be attributed to the drop in the color yield thus requiring more dye to produce the
same color. Liquor ratio is one of the important aspects of the batch dyeing process. It can vary in
407
the dyeing process due to changes in the dye bath water level or variation in the fabric load. The
effect of variation in the liquor ratio is well known as it affects the reproducibility and economics
of the dyeing process [79].
It is well known that the exhaustion of dyes is reduced when the liquor ratio is increased.
To compensate for this more dye is required to match the given shade [392]. The relation between
equilibrium exhaustion (𝐸∞) of dye and liquor ratio (L) is given by Equation 5.3 [392]:
𝐾𝑒𝑓𝑓 =[𝐷]𝑓
[𝐷]𝑠 (5.2)
𝐸∞ =𝐾𝑒𝑓𝑓
[𝐾𝑒𝑓𝑓 + 𝐿] (5.3)
Where K is constant and depends on the dye isotherm. [𝐷]𝑓 and [𝐷]𝑠 are the concentration
of dye on the fiber and in dyebath at equilibrium. The effect of liquor ratio is commonly observed
in laboratory and production dyeing where the laboratory recipe (normally higher) needs to be
adjusted according to the liquor ratio used in the production (generally lower) [392]. In the case of
reactive dyes, the fixation efficiency (F) of the reactive dyes is the ratio of the rate of fixation and
the rate of hydrolysis. The higher the hydrolysis the lower will be the fixation. The F can be
described by the equation 5.4 [393] which is a modified version of the equation (5.3):
𝐹 =
Rate of exhaustion
Rate of hydrolysis=
𝑆[𝐷]𝐹√𝐷𝑘𝐹′
𝐿[𝐷]𝑆𝑘𝐻′ (5.4)
Where S is the surface area of the substrate, D is the diffusion coefficient of the dye in the
substrate and 𝑘𝐹′ and 𝑘𝐻
′ are the reaction constants for the dye fixation and hydrolysis respectively.
This implies if all the other factors remain constant, an increase in the liquor ratio will lower the
fixation efficiency of reactive dyes. The amount of dye required to achieve the given depth of
shade must thus be increased [393]. The reactive dyes with low substantivity are more sensitive to
variations in liquor ratio in comparison to dyes with high substantivity which are more robust
[144].
408
Several studies have been carried out to ascertain the effect of liquor ratio on the color
strength of dyeings using reactive and disperse dyes. It has been found that for reactive dyes that
an increase in liquor ratio lowers the exhaustion values of the dyes and the resultant depth of shade.
One study examined the effect of different liquor ratios from 15 to 50 on dyeings [394]. In another
study, it was reported that the color strength of the reactive dyes applied to mercerized fabrics was
significantly different when the liquor ratio was changed from 2 to 15 for deep shades. It was also
observed that at a lower liquor ratio the uptake was greater than at a higher liquor ratio [395]. It
has been claimed that reactive dyes containing bifunctional groups are less sensitive to liquor
variations [396]. In the case of package dyeing of polyester with disperse dyes, it was noted that
the increase in liquor ratio from 10 to 50 reduced the dyebath exhaustion. As a result, the resultant
shade depth was lower at higher liquor ratios. They also observed that combination shades, exhibit
different exhaustion rates. Therefore, the tone of the shade was also found to be different [397]. In
another study on polyester fabric a liquor ratio ranging from 6 to 12 was used. The color strength
and exhaustion rates were found to be different at different liquor ratios [398]. The influence of
liquor ratio on dyeing of cotton with reactive dyes and polyester with disperse dyes were studied
at various liquor ratios that are typically encountered in the dyeing of these materials. It has been
observed that a large change in liquor ratio leads to a significant change in the dye shade and this
behavior depends on the dye type, with some dyes exhibiting more change than the others [399].
To study the effect of liquor ratio, the same dye amounts that produced the match by the
C2B method, using dyes from Archroma as shown in Table 5.6, were applied on cotton and
polyester reference fabrics at different liquor ratios analogous to effective liquor ratios that may
be encountered in blends. The different liquor ratios used were 20, 25, 30, 40, 50, 60, 80 and 100.
The relative color yield obtained for three colors considering a liquor ratio of 20 was taken as the
reference, as shown in Figure 5.4 for reactive dyes and Figure 5.5 for disperse dyes. As can be
seen for reactive dyes the relative color yield is reduced to as low as 60% at a liquor ratio of 100
as compared to the reference liquor ratio of 20. The biggest drop is observed in the navy (63%),
followed by beige (74%) and brown (80%). Disperse dyes exhibited higher drops in yield in
comparison to reactive dyes. The beige color showed a drop in the relative color yield by 31%,
brown by 41%, and navy by 54%. This may explain why the actual dye amounts required to match
the same shade on blends are significantly greater than theoretically required. The DE*ab of the
samples corresponding to the effective liquor ratios of 30, 40, 50, 80 for polyester and 25, 30, 40,
409
60 for cotton were also measured using a liquor ratio of 20 as a reference. Polyester showed a large
color difference as compared to cotton and following the same trend as the relative color yield
discussed above. For polyester, DE*ab values were 3.4, 5.9, 8.9 and 10.9 for respective liquor to
goods ratios for the brown, 3.3, 5, 7.2, 11.1 for navy and 2.6, 3.7, 4, 6.6 for beige. In the case of
cotton, the brown showed color difference values of 0.6, 0.7, 2.1, 2.5, navy: 1.1, 1.3, 2.1, 4.3 and
beige: 1.3, 1.4, 1.4, 2.7. While the actual relative color yields may vary with different dye types,
they are likely to follow a similar trend.
Figure 5.4: The effect of liquor ratio on the relative strength of cotton dyed with reactive dyes
(Liquor ratio of 20 is taken as the reference).
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
20 25 30 40 50 60 80 100
Rel
ativ
e st
reng
th
Liquor ratio
Brown Navy Beige
410
Figure 5.5: The effect of liquor ratio on the relative strength of polyester dyed with disperse dyes
(Liquor ratio of 20 is taken as reference).
5.3.2 Light fastness
Dyed materials often fade when exposed to light for prolonged periods. The lightfastness of dyed
materials depends on many factors such as the type of dyes used, depth of shade, fabric surface,
and finishing treatment, among others. The lightfastness is mainly the property of colorant
molecule and therefore it is influenced by the selection of colorants [400]. If disperse dyes and
reactive dyes of good lightfastness are selected, good light fastness results are obtained. The dyes
selected in this study were based on the manufacturer’s recommendations to obtain good fastness
results under different dyeing methods. The disperse dyes Dianix XF/SF recommended by Dystar
for the 1B method are marketed as dyes with superior fastness properties. These dyes are based
on special chemistries indicated in Table 5.3 that enable them to provide good fastness properties
[382].
The light fastness results in the form of grey scale ratings of different dyed fabrics after
exposure to 40 AFUs are shown in Table 5.9. The CT fabric dyed with reactive dyes, in general,
showed more fading compared to PET fabric dyed with disperse dyes. With increasing the
polyester content in the blend, fading was reduced. The highest fading was observed for beige,
whereas navy and brown exhibited quite similar fading results. The fading for lighter colors was
found to be higher compared to dark colors due to the fact that smaller dye amounts are present
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
20 25 30 40 50 60 80 100
Rel
ativ
e st
reng
th
Liquor ratio
Brown Navy Beige
411
and exposed to light in the former substrate compared to darker colors where more dye molecules
are present. For the brown shade on average, the 2B method showed lower fading compared to
the R2B and 1B methods. The Archroma’s 2B method exhibited more fading as compared to other
dyeing methods used for the navy color. The light fastness results for navy color in ascending order
are Huntsman-R2B, Dystar-1B, Huntsman 2B, Dystar-2B and Archroma-2B. For the beige, a
slight change in the lightfastness ratings is observed in the case of blends depending upon the light
fastness obtained in CT and PET fabrics.
Table 5.9: Light fastness results of polyester, cotton and their blends dyed in different shade
depths.
Shade Supplier Dyeing
method
Fabrics
PET PC1 PC2 PC3 PC4 CT
Brown Dystar C2B 4.5 4.5 4 3.5 3.5 3.5
Archroma C2B 4 3.5 4 4 4 4
Huntsman C2B 4.5 4 4 3.5 3.5 3.5
Huntsman R2B 4.5 4 3.5 3 3 3
Dystar 1B 4 3.5 3.5 3.5 3.5 3.5
Navy Dystar C2B 4 3.5 3.5 3.5 3 3
Archroma C2B 3.5 3.5 3.5 3.5 4 4.5
Huntsman C2B 4.5 4 4 3.5 3.5 3.5
Huntsman R2B 4 4 3.5 3.5 3 3
Dystar 1B 4 4 3.5 3.5 3.5 4
Beige Dystar C2B 3.5 3.5 3.5 3 2.5 2.5
Archroma C2B 3.5 3.5 3.5 3.5 3 3
Huntsman C2B 3.5 3.5 3 3 3 2.5
Huntsman R2B 3.5 3.5 3.5 3.5 3 3
Dystar 1B 3.5 3.5 3.5 3.5 3 3
It can be seen that fading characteristics of the dyed fabric varies with the blend, but this
change was not found to be directly related with the change in blend ratio. In some cases, the
412
lightfastness was not changed much until the blend ratio was significantly changed. The dye
selection is critical to obtain good light fastness results on blends as the resultant fading of the
dyed material is influenced by both reactive and disperse dyes used.
5.3.3 Crocking fastness
Crocking fastness involves the transfer to colorant from the dyed material to another fabric surface
by rubbing. The crock fastness depends on many factors which include the dyed substrate, rubbing
cloth, the surface of the dyed substrate and rubbing cloth, dye class, depth of shade, dyeing method,
aftertreatment process and amount of moisture present when rubbing is performed. The dry
crocking fastness results after dyeing are shown in Table 5.10. In all fabrics, the dry rubbing
fastness ratings of 5 was obtained. The wet crocking results are presented in Table 5.11. The wet
rubbing fastness of all cotton fabric was found to be inferior for all polyester fabrics in brown and
navy colors. The fastness improves with the increase in the portion of the polyester component in
the blend. In the case of beige color, no color transfer to crocking cloth was observed i.e. rating of
5 was obtained. It can be concluded that for light shades good dry and wet crocking fastness was
obtained, independent of the dyeing method and blend ratio employed.
For the brown and navy colors, good wet crock fastness results were obtained for the C2B
method as compared to the R2B and 1B methods. This is due to the fact that in the 2B method a
separate reduction clearing treatment was given as compared to the R2B and 1B methods where
no reduction clearing was performed. The results obtained in the R2B method are generally lower
than the 2B methods due to mode of treatment of disperse dyes. The reactive dyes were washed-
off at the high temperature used for the dyeing of the polyester portion of the blend. Since reduction
clearing was not performed some disperse dye may have transferred during the wet crocking test.
For the 1B however, only one soaping process was given which may increase the chances of
residual dye remaining on the surface of the fiber thus resulting in some dye transfer to the crocking
cloth.
413
Table 5.10: Dry crocking fastness of fabrics of different colors and blend ratio dyed by different
dyeing methods.
Shade Supplier Dyeing
method PET PC1 PC2 PC3 PC4 CT
Brown
Dystar C2B 5 5 5 5 5 5
Archroma C2B 5 5 5 5 5 5
Huntsman C2B 5 5 5 5 5 5
Huntsman R2B 5 5 5 5 5 5
Dystar 1B 5 5 5 5 5 5
Navy
Dystar C2B 5 5 5 5 5 5
Archroma C2B 5 5 5 5 5 5
Huntsman C2B 5 5 5 5 5 5
Huntsman R2B 5 5 5 5 5 5
Dystar 1B 5 5 5 5 5 5
Beige
Dystar C2B 5 5 5 5 5 5
Archroma C2B 5 5 5 5 5 5
Huntsman C2B 5 5 5 5 5 5
Huntsman R2B 5 5 5 5 5 5
Dystar 1B 5 5 5 5 5 5
The problem of reduced wet rubbing fastness for darker colors in cotton fabrics is well
known. During the wet crocking test due to the abrasive action of crocking cloth on the dyed
substrate, small fiber particles from the dyed material are rubbed off from the fiber surface which
stain the crock cloth. As wet crocking test involves the use of a wet fabric the dye may bleed out
of the damaged fiber material and rub off on fiber particles. By selecting dyes with good fastness
properties, some improvements can be obtained. However, there is a limit to which this
improvement in crock fastness can be obtained. Since the amount of colorant rubbing off is
determined by the substrate, there is a limit to improving the wet crock fastness [401, 402]. If a
suitable dye selection is performed and good washing of dyed fabric is performed, poor crock
fastness results may be attributed to fiber damage. It has been observed that mercerized fabric
414
exhibits better wet crocking fastness than unmercerized fabric [402]. In the case of polyester fibers,
crock fastness depends on good dye selection and wash-off process. Dyes of high energy levels
exhibit high sublimation fastness and therefore they do not migrate to the surface of the fiber during
the finishing process at high temperatures. If a proper reduction clearing treatment is given to the
dyed fabric or dyes with good wash off properties that can be washed-off in alkaline conditions
without a reduction clearing are selected, good crock fastness can be obtained. It can be concluded
that lower wet crock fastness in polyester/cotton fabrics in dark shades is due to the cotton portion
of the blend. As the cotton portion of the blend decreases, an improvement in wet crocking fastness
is attained.
Table 5.11: Wet crocking fastness results of polyester, cotton and their blends.
Shade Supplier Dyeing
method PET PC1 PC2 PC3 PC4 CT
Brown
Dystar C2B 5 5 4.5 4.5 4.5 4
Archroma C2B 5 5 5 5 4.5 4
Huntsman C2B 5 5 5 4.5 4.5 4
Huntsman R2B 5 4.5 4.5 4.5 4.5 4
Dystar 1B 5 5 4.5 4.5 4.5 4
Navy
Dystar C2B 5 5 5 4.5 4.5 4
Archroma C2B 5 5 5 4.5 4.5 4
Huntsman C2B 5 4.5 4.5 4.5 4.5 4
Huntsman R2B 4.5 4.5 4.5 4.5 4.5 4
Dystar 1B 5 5 4.5 4.5 4.5 4
Beige
Dystar C2B 5 5 5 5 5 5
Archroma C2B 5 5 5 5 5 5
Huntsman C2B 5 5 5 5 5 5
Huntsman R2B 5 5 5 5 5 5
Dystar 1B 5 5 5 5 5 5
415
5.3.4 Washing fastness
Color fastness to washing is one of the important quality parameters in polyester/cotton dyed
materials. The test determines the change in color of the dyed substrate and staining of the
multifiber fabric in the washing process. Improper dye fixation or presence of unfixed dye on the
fiber surface at the end of the dyeing process reduces the wash fastness [383]. Table 5.12 and
Figure 5.6 show the color change and staining results after the washing test. Very good wash
fastness results were obtained for the beige color which is found to be independent of the blend
ratio and the dyeing method used. This may be attributed to the lower concentration of dyes present
on the substrate in this case, the use of dyes with good fastness properties and the reduction clearing
performed in the C2B methods. Good to moderate color change and staining ratings were obtained
for the brown and navy colors. The polyester and polyester rich fabrics in general exhibited better
results compared to the cotton and cotton rich fabrics in the 2B methods. This may be attributed
to the reduction clearing performed in the 2B methods as shown in Figure 5.1. Similar results were
obtained in the 1B method except the color change ratings were slightly worse for the PC2 fabric
for the brown and for the PC2 and PC3 fabrics for the navy shade when compared to the 2B
methods. The good results of the 1B method are due to the use of disperse dyes with good wash-
off properties which do not require a reduction clearing process. These dyes contain alkali soluble
groups which make them easy to wash off during the reactive dyeing of cotton [87, 382]. On the
other hand, interesting results were obtained in the R2B method. Cotton fabrics exhibited better
fastness properties compared to polyester and polyester/cotton blended fabrics. Since the cotton
portion was dyed first followed by polyester dyeing and since no reduction clearing was
performed, these results could be expected. The hydrolyzed and unfixed reactive dyes are removed
due to the high temperature conditions involved in the disperse dyeing section of the process. Since
no reduction clearing is possible in this method, the fastness properties are compromised due to
disperse dye stains present on cotton and dye residues on the polyester surface.
The nylon staining results for the navy color dyed by different dyeing methods are shown
in Figure 5.7. The staining of nylon and acetate fibers with disperse dyes in the wet fastness test is
well known. Good dye selection and the use of two bath method with a reduction clearing can
minimize the staining tendency [9, 383]. Increased staining of nylon was observed in blends due
to the disperse dyes present on cotton. The reverse 2B method showed more staining than other
methods. Figure 5.8 shows the cotton staining results of the navy dyed fabrics. Reactive dyes tend
416
to stain wool and cotton fabric during wet fastness tests. Unfixed and hydrolyzed reactive dyes
may also stain the cotton portion of the multifiber strip. The use of dyes with a high fixation yield
and good fastness properties along with adequate washing of unfixed dyes is essential to attain
good fastness results.
Table 5.12: Wash fastness properties of dyed polyester, cotton and polyester/cotton fabrics.
Color Supplier Dyeing
method Fabric
Shade
change
Staining
Wo PAN PES PA Co Ac
Brown
Dystar
C2B
PET 4.5 4.5 4.5 4.5 4 4.5 4.5
PC1 4.5 4.5 4.5 4.5 3.5 4.5 4
PC2 4.5 4.5 4.5 4.5 3.5 4.5 4.5
PC3 4.5 4.5 4.5 4.5 4 4 4.5
PC4 4 4 4.5 4.5 4.5 4 4.5
CT 4 4 4.5 4.5 4.5 4 4.5
Archroma
C2B
PET 4.5 4.5 4.5 4.5 4 4.5 4
PC1 4.5 4.5 4.5 4.5 3.5 4.5 4
PC2 4.5 4.5 4.5 4.5 4 4.5 4.5
PC3 4 4.5 4.5 4.5 4.5 4 4.5
PC4 4 4.5 4.5 4.5 4.5 4 4.5
CT 4 4 4.5 4.5 4.5 4 4.5
Huntsman
C2B
PET 4.5 4.5 4.5 4.5 4 4.5 4
PC1 4.5 4.5 4.5 4.5 3.5 4.5 4.5
PC2 4.5 4.5 4.5 4.5 4 4.5 4.5
PC3 4 4.5 4.5 4.5 4.5 4 4.5
PC4 4 4 4.5 4.5 4.5 4 4.5
CT 4 4.5 4.5 5 4.5 4 4.5
Huntsman
R2B
PET 4 4.5 4.5 4.5 4 4.5 4
PC1 4 4.5 4.5 4.5 4 4.5 4
PC2 4 4.5 4.5 4.5 3 4.5 4.5
417
Table 5.12 (Continued)
Color Supplier Dyeing
method Fabric
Shade
change
Staining
Wo PAN PES PA Co Ac
PC3 4.5 4.5 4.5 4.5 3.5 4.5 4.5
PC4 4.5 4.5 4.5 4.5 4 4.5 4.5
CT 4.5 4.5 4.5 4.5 4.5 4 4
Dystar
1B
PET 4.5 4.5 4.5 4 4 4.5 4
PC1 4.5 4.5 4.5 4.5 4 4.5 4.5
PC2 4 4.5 4.5 4.5 4.5 4 4.5
PC3 4 4.5 4.5 4.5 4.5 4 4.5
PC4 4 4.5 4.5 4.5 4.5 4 4.5
CT 4 4 4.5 4.5 4.5 4 4.5
Navy
Dystar
C2B
PET 4.5 4.5 4.5 4 4 4.5 4
PC1 4.5 4.5 4.5 4 4 4.5 4
PC2 4.5 4.5 4.5 4.5 3.5 4.5 4
PC3 4.5 4 4.5 4.5 4 4.5 4.5
PC4 4.5 4 4.5 4.5 4.5 4 4.5
CT 4 4 4.5 4.5 4.5 4 4.5
Archroma
C2B
PET 4.5 4.5 4.5 4.5 4 4.5 4
PC1 4.5 4.5 4.5 4.5 3.5 4.5 4
PC2 4.5 4.5 4.5 4.5 4 4.5 4.5
PC3 4.5 4.5 4.5 4.5 4.5 4 4.5
PC4 4 4.5 4.5 4.5 4.5 4 4.5
CT 4 4 4.5 4.5 4.5 4 4.5
Huntsman
C2B
PET 4.5 4.5 4.5 4.5 4 4.5 4
PC1 4.5 4.5 4.5 4.5 4 4.5 4.5
PC2 4.5 4.5 4.5 4.5 3.5 4.5 4.5
PC3 4.5 4.5 4.5 4.5 4 4 4.5
PC4 4.5 4 4.5 4.5 4.5 4 4.5
CT 4 4.5 5 5 4.5 4 4.5
418
Table 5.12 (Continued)
Color Supplier Dyeing
method Fabric
Shade
change
Staining
Wo PAN PES PA Co Ac
Huntsman
R2B
PET 4 4 4.5 4.5 4 4.5 4.5
PC1 4 4 4.5 4 3 4.5 3
PC2 4 3.5 4.5 4.5 3.5 4.5 4
PC3 4.5 4 4.5 4.5 3.5 4.5 3.5
PC4 4.5 4 4.5 4.5 4 4.5 4.5
CT 4.5 4 4.5 4.5 4.5 4.5 4.5
Dystar
1B
PET 4.5 4.5 4.5 4.5 4 4.5 4
PC1 4.5 4.5 4.5 4.5 4 4.5 4
PC2 4 4.5 4.5 4.5 3.5 4.5 4
PC3 4 4.5 4.5 4.5 3.5 4.5 4.5
PC4 4 4.5 4.5 4.5 4.5 4.5 4.5
CT 4 4 4.5 4.5 4.5 4 4.5
Beige
Dystar
C2B
PET 5 4.5 4.5 4.5 4.5 4.5 4.5
PC1 5 4.5 4.5 4.5 4.5 4.5 4.5
PC2 5 4.5 4.5 4.5 4.5 4.5 4.5
PC3 5 4.5 4.5 4.5 4.5 4.5 4.5
PC4 5 4.5 4.5 4.5 4.5 4.5 4.5
CT 5 4.5 4.5 4.5 4.5 4.5 4.5
Archroma
C2B
PET 5 4.5 4.5 4.5 4.5 4.5 4.5
PC1 5 4.5 4.5 4.5 4.5 4.5 4.5
PC2 5 4.5 4.5 4.5 4.5 4.5 4.5
PC3 5 4.5 4.5 4.5 4.5 4.5 4.5
PC4 5 4.5 4.5 4.5 4.5 4.5 4.5
CT 5 4.5 4.5 4.5 4.5 4.5 4.5
Huntsman
C2B
PET 5 4.5 4.5 4.5 4.5 4.5 4.5
PC1 5 4.5 4.5 4.5 4.5 4.5 4.5
PC2 5 4.5 4.5 4.5 4.5 4.5 4.5
419
Table 5.12 (Continued)
Color Supplier Dyeing
method Fabric
Shade
change
Staining
Wo PAN PES PA Co Ac
PC3 5 4.5 4.5 4.5 4.5 4.5 4.5
PC4 5 4.5 4.5 4.5 4.5 4.5 4.5
CT 5 4.5 4.5 4.5 4.5 4.5 4.5
Huntsman
R2B
PET 5 4.5 4.5 4.5 4.5 4.5 4.5
PC1 5 4.5 4.5 4.5 4.5 4.5 4.5
PC2 5 4.5 4.5 4.5 4.5 4.5 4.5
PC3 5 4.5 4.5 4.5 4.5 4.5 4.5
PC4 5 4.5 4.5 4.5 4.5 4.5 4.5
CT 5 4.5 4.5 4.5 4.5 4.5 4.5
Dystar
1B
PET 5 4.5 4.5 4.5 4.5 4.5 4.5
PC1 5 4.5 4.5 4.5 4.5 4.5 4.5
PC2 5 4.5 4.5 4.5 4.5 4.5 4.5
PC3 5 4.5 4.5 4.5 4.5 4.5 4.5
PC4 5 4.5 4.5 4.5 4.5 4.5 4.5
CT 5 4.5 4.5 4.5 4.5 4.5 4.5
420
Figure 5.6: Color change ratings for the navy blue color dyed fabrics after the washing test.
Figure 5.7: Nylon staining results for the navy blue color dyed fabrics.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
PES PC6535 PC5050 PC4060 PC2575 CO
Gre
y s
cale
rat
ing
Fiber proportion
Dystar-C2B
Archroma-C2B
Huntsman-C2B
Huntsman-R2B
Dystar-1B
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
PES PC6535 PC5050 PC4060 PC2575 CO
Gre
y s
cale
rat
ing
Fiber proportion
Dystar-C2B
Archroma-C2B
Huntsman-C2B
Hunstman-R2B
Dystar-1B
421
Figure 5.8: Cotton staining results of the navy blue color dyed fabrics.
5.3.5 Water fastness
Water fastness measures the transfer of color from a dyed fabric to the adjacent fiber when dipped
in water or under moist conditions. The two materials are in immediate contact with each other.
This test is a useful measure to assess the presence of loose color in the material. The staining
results of the multifiber fabric after the water fastness ratings of the dyed materials are given in
Table 5.13. Very good water fastness results were observed for the beige color with slight or no
staining of the multifiber fabric. All fibers in the multifiber fabric showed a rating of 4.5 for all
fabrics and dyeing methods used. The brown and navy colors showed moderate to good water
fastness ratings. As expected, the polyester and polyester rich fabrics showed staining of nylon in
the multifiber strip and in some cases, staining of polyester and acetate fibers was also observed
[9]. The staining of the nylon fiber component was found to be heavier in blends compared to
100% polyester fabric. The cotton and wool staining were observed in all fabrics which was
reduced as the polyester component of the blend was increased. Good results were obtained in the
C2B method as compared to the R2B method. Since no reduction was performed and thus disperse
dye stains were not properly removed in the R2B method, the nylon staining was found to be
heavier in the blend fabrics during the wash fastness test. The extra reduction clearing process
performed in the C2B method is designed to remove the loose surface disperse dyes thus improving
the fastness property of the dyed substrate. Good fastness results were obtained in the 1B method,
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
PES PC6535 PC5050 PC4060 PC2575 CO
Gre
y s
cale
rat
ing
Fiber proportion
Dystar-C2B
Archroma-C2B
Huntsman-C2B
Huntsman-R2B
Dystar-1B
422
which may be attributed to the use of dyes with very good fastness properties. These dyes do not
require reduction clearing and can be easily removed in the alkaline conditions employed for a
cotton dyeing portion of the blend [87, 382].
Table 5.13: Water fastness of dyed polyester/cotton fabrics with different blend contents.
Color Supplier Dyeing
method Fabric
Staining
Wo PAN PES PA Co Ac
Brown
Dystar
C2B
PET 4.5 4.5 4 4 4.5 4
PC1 4.5 4.5 4.5 3.5 4.5 4.5
PC2 4.5 4.5 4.5 3.5 4.5 4.5
PC3 4.5 4.5 4.5 4 4 4.5
PC4 4.5 4.5 4.5 4 4 4.5
CT 4 4.5 4.5 4.5 3.5 4.5
Archroma
C2B
PET 4.5 4.5 4.5 4 4.5 4
PC1 4.5 4.5 4.5 3.5 4.5 4.5
PC2 4.5 4.5 4.5 4 4.5 4.5
PC3 4.5 4.5 4.5 4 4 4.5
PC4 4.5 4.5 4.5 4.5 4 4.5
CT 4 4.5 4.5 4.5 3.5 4.5
Huntsman
C2B
PET 4.5 4.5 4.5 4 4.5 4
PC1 4.5 4.5 4.5 3.5 4.5 4
PC2 4.5 4.5 4.5 4 4.5 4.5
PC3 4.5 4.5 4.5 4 4 4.5
PC4 4.5 4.5 4.5 4.5 4 4.5
CT 4 4.5 4.5 4.5 3.5 4.5
Huntsman
R2B
PET 4.5 4.5 4.5 3.5 4.5 3.5
PC1 4.5 4.5 4.5 3 4.5 4
PC2 4.5 4.5 4.5 3 4.5 4
PC3 4.5 4.5 4.5 3.5 4 4.5
PC4 4.5 4.5 4.5 4 4 4.5
423
Table 5.13 (Continued)
Color Supplier Dyeing
method Fabric
Staining
Wo PAN PES PA Co Ac
CT 4 4.5 4.5 4.5 3.5 4.5
Dystar
1B
PET 4.5 4.5 4.5 4 4.5 4.5
PC1 4.5 4.5 4.5 4 4.5 4.5
PC2 4.5 4.5 4.5 3.5 4.5 4.5
PC3 4.5 4.5 4.5 3.5 4 4.5
PC4 4 4.5 4.5 4 3.5 4.5
CT 4 5 4.5 4.5 3 4.5
Navy
Dystar
C2B
PET 4.5 4.5 4.5 4 4.5 4
PC1 4.5 4.5 4.5 3.5 4.5 4
PC2 4.5 4.5 4.5 3.5 4.5 4.5
PC3 4.5 4.5 4.5 4 4.5 4.5
PC4 4.5 4.5 4.5 4.5 4 4.5
CT 4 4.5 4.5 4.5 3.5 4.5
Archroma
C2B
PET 4.5 4.5 4.5 3.5 4.5 4
PC1 4.5 4.5 4.5 3.5 4.5 4.5
PC2 4.5 4.5 4.5 4 4.5 4.5
PC3 4.5 4.5 4.5 4.5 4.5 4.5
PC4 4.5 4.5 4.5 4.5 4 4.5
CT 4 4.5 4.5 4.5 3 4.5
Huntsman
C2B
PET 4.5 4.5 4.5 3.5 4.5 4
PC1 4.5 4.5 4.5 3.5 4.5 4
PC2 4.5 4.5 4.5 4 4.5 4.5
PC3 4.5 4.5 4.5 4 4.5 4.5
PC4 4.5 4.5 4.5 4.5 4 4.5
CT 4.5 4.5 4.5 4.5 4 4.5
Huntsman
R2B
PET 4.5 4.5 4.5 3.5 4.5 3.5
PC1 4.5 4.5 4.5 3 4.5 4
424
Table 5.13 (Continued)
Color Supplier Dyeing
method Fabric
Staining
Wo PAN PES PA Co Ac
PC2 4.5 4.5 4.5 3 4.5 4
PC3 4.5 4.5 4.5 3.5 4.5 4.5
PC4 4.5 4.5 4.5 4 4 4.5
CT 4.5 4.5 4.5 4 4 4.5
Dystar
1B
PET 4.5 4.5 4.5 4 4.5 4.5
PC1 4.5 4.5 4.5 4 4.5 4.5
PC2 4.5 4.5 4.5 3.5 4.5 4.5
PC3 4.5 4.5 4.5 3.5 4.5 4.5
PC4 4.5 4.5 4.5 4 4.5 4.5
CT 4.5 4.5 4.5 4.5 4.5 4.5
Beige
Dystar
C2B
PET 4.5 4.5 4.5 4.5 4.5 4.5
PC1 4.5 4.5 4.5 4.5 4.5 4.5
PC2 4.5 4.5 4.5 4.5 4.5 4.5
PC3 4.5 4.5 4.5 4.5 4.5 4.5
PC4 4.5 4.5 4.5 4.5 4.5 4.5
CT 4.5 4.5 4.5 4.5 4.5 4.5
Archroma
C2B
PET 4.5 4.5 4.5 4.5 4.5 4.5
PC1 4.5 4.5 4.5 4.5 4.5 4.5
PC2 4.5 4.5 4.5 4.5 4.5 4.5
PC3 4.5 4.5 4.5 4.5 4.5 4.5
PC4 4.5 4.5 4.5 4.5 4.5 4.5
CT 4.5 4.5 4.5 4.5 4.5 4.5
Huntsman
C2B
PET 4.5 4.5 4.5 4.5 4.5 4.5
PC1 4.5 4.5 4.5 4.5 4.5 4.5
PC2 4.5 4.5 4.5 4.5 4.5 4.5
PC3 4.5 4.5 4.5 4.5 4.5 4.5
PC4 4.5 4.5 4.5 4.5 4.5 4.5
425
Table 5.13 (Continued)
Color Supplier Dyeing
method Fabric
Staining
Wo PAN PES PA Co Ac
CT 4.5 4.5 4.5 4.5 4.5 4.5
Huntsman
R2B
PET 4.5 4.5 4.5 4.5 4.5 4.5
PC1 4.5 4.5 4.5 4.5 4.5 4.5
PC2 4.5 4.5 4.5 4.5 4.5 4.5
PC3 4.5 4.5 4.5 4.5 4.5 4.5
PC4 4.5 4.5 4.5 4.5 4.5 4.5
CT 4.5 4.5 4.5 4.5 4.5 4.5
Dystar
1B
PET 4.5 4.5 4.5 4.5 4.5 4.5
PC1 4.5 4.5 4.5 4.5 4.5 4.5
PC2 4.5 4.5 4.5 4.5 4.5 4.5
PC3 4.5 4.5 4.5 4.5 4.5 4.5
PC4 4.5 4.5 4.5 4.5 4.5 4.5
CT 4.5 4.5 4.5 4.5 4.5 4.5
Figure 5.9: Grey scale rating for staining of nylon for the brown color after water fastness test.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
PES PC6535 PC5050 PC4060 PC2575 CO
Gre
y s
cale
rat
ing
Fiber proportion
Dystar-C2B
Archroma-C2B
Huntsman-C2B
Huntsman-R2B
Dystar-1B
426
Figure 5.10: Grey scale rating for staining of cotton for the brown color after water fastness test.
5.4 Conclusions
The dyeing properties of polyester/cotton fabrics at different blend ratios along with cotton as well
as polyester only fabrics, used as a reference, were examined. Three target colors, namely navy,
brown and beige were matched as typical examples of different shades encountered in practice. It
was found that the color yield of disperse and reactive dyes are reduced in blends compared to
when they are applied to polyester and cotton only fabrics respectively. This is attributed to a
change in the effective liquor to goods ratio available for each fiber in the blend which can vary
significantly.
It was found that the fastness properties of dyed material vary for different blend ratios and
in some cases nylon staining was found to be inferior for the reference polyester fabrics used in
this study. The actual variation in the light fastness of dyed substrates with a change in the blend
ratio was found to be dependent on the dye class used. When the light fastness of the dyed sample
was better for the cotton only reference fabric compared to the polyester only fabric, increasing
the proportion of the polyester component would lead to a reduction of the light fastness of the
blend. The light fastness did not vary much with a change in the dyeing method. Among the three
target shades examined, the lightfastness was found to be inferior for the beige as compared to
brown and navy colors due to a smaller amount of colorant present on that fabric which was
expected.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
PES PC6535 PC5050 PC4060 PC2575 CO
Gre
y s
cale
rat
ing
Fiber proportion
Dystar-C2B
Archroma-C2B
Huntsman-C2B
Huntsman-R2B
Dystar-1B
427
All the fabrics in this study exhibited very good dry crocking fastness properties. The wet
crocking was found to be inferior for cotton and cotton rich blends. The two-bath process exhibited
better crocking results than the reverse two-bath process due to employing a separate reduction
clearing step. The wet crock fastness of the substrates from the one bath process was also found to
be good due to the use of disperse dyes with good fastness properties.
Good water and washing fastness results were obtained for the beige color which showed
almost no dye transfer to the multifiber test strip. The staining of nylon was found to be worse for
blends compared to 100% polyester fabric. However, higher levels of cotton and wool staining
were observed as the cotton content of the blend was increased in fabrics. The reverse two-bath
process showed lower fastness properties compared to the two-bath process.
The color fastness requirements for polyester/cellulosic blends can vary greatly depending
upon their intended end-use. It is difficult to generalize trends obtained from the fastness results
obtained in this study. The fastness properties of the polyester depend on a large number of factors
which include the depth of shade, dye selection, dyeing methods used, blend ratio and post
treatments employed. Good dye selection and proper washing-off are essential to ensure good
fastness results. The fastness results obtained under one set of conditions and a dyeing method
may not be applicable to another dyeing method or for a change in the depth of shade. It can be
said, however, that the blending ratio has an influence on the fastness properties of the blends. The
results obtained from this study on 100% cotton and 100% polyester fabrics may not necessarily
be applicable to polyester/cotton blends.
428
CHAPTER 6 DESIGN AND DEVELOPMENT OF AN EXPERT
SYSTEM
6.1 Experts and expert systems
An expert is a person who is recognized as a reliable source of knowledge, technique or skill in a
specific domain and whose judgment is considered to be the authority by the public or people in a
particular area. Human experts acquire knowledge and skills based on research, experience,
occupation or education in a specialized area. Expertise consists of characteristics, skills, and
knowledge that distinguishes an expert from the others in the same domain and reason for their
superior performance [403, 404]. The characteristics of an expert are summarized in Table 6.1
[405]. These characteristics describe the ways in which experts are different from novices [405].
Table 6.1: Characteristics of experts.
Strengths Shortcomings
▪ Generating the best response fast and
accurately.
▪ Accurate detection and recognition ability.
▪ Ability to do qualitative analyses.
▪ More accurate self-monitoring skills to
detect errors and status of their
understanding.
▪ Ability to choose specific strategies.
▪ Opportunistic in using resources to solve
problems.
▪ Ability to retrieve domain knowledge in
minimal cognitive effort.
▪ Expertise is domain limited.
▪ Overly confident.
▪ Glossing over.
▪ Context-dependence within a domain.
▪ Inflexible.
▪ Inaccurate prediction, judgment, and advice
under uncertainty.
▪ Bias and functional fixedness.
429
Expert systems fall under the category of artificial intelligence, which is a branch of
computer science that deals with the design and development of programs that simulate the
reasoning of humans. The expert system mimics an expert’s cognitive activities to reduce the time
and money associated with complex problem-solving. A comparison of the expert system with the
human expert is given in Table 6.2 [16, 406, 407].
Table 6.2: Human expert versus the expert system.
Factors Human Expert Expert System
Availability Workday Always
Geographic constraints Local Anywhere
Security Irreplaceable Replaceable
Perishable/consumable Yes No
Performance Variable Consistent
Speed Variable Consistent
Cost High Reasonable
Ability to explain Depends Yes
Flexibility No Yes
Meta-knowledge Yes No
An expert system is a computer program that uses knowledge and inference procedures to
solve complex problems or give advice in a specific domain at a high level of expertise. The
purpose of developing an expert system is to make a computer system that can act similar to a
human expert in relevant respects. An expert system may be used as a direct replacement of a
human expert or can be used as an assistant to help in the decision-making process where it can be
directly used by an expert to increase their productivity. Alternatively, expert systems can help a
person to generate responses at a level of performance similar to that of an expert. Expert systems
are designed to solve the problem in a specific domain called problem domain like human experts.
The expertise of the expert system is derived from the knowledge it possesses, known as the
knowledge domain. In order to come up with a solution to the problem, expert systems make
inferences. The inference is based on information about the problem (facts) and a series of rules
430
which are either satisfied or not (knowledge base) [13, 16]. Expert systems are built by knowledge
engineers.
6.2 Benefits of expert systems
An expert system can provide several benefits which are given below [16]:
▪ Availability: The expert system is a computer program that is stored on a computer. It
is available at any time irrespective of geographic location.
▪ Reasonable cost: The cost of expertise per user is usually less for expert systems. Once
an expert system is developed it can be mass-produced.
▪ Permanent: The expertise provided by the expert system is not “typically” perishable
and can last for a long time.
▪ Multiple expertise: The expert system is usually developed by combining expertise
from multiple experts. Its’ performance may be better than a single expert.
▪ Reliability: Expert systems provide the second opinion and increase the confidence of
the decision. An expert can make a mistake due to fatigue or stress, whereas the same
level of reliable expertise can be provided by the expert system.
▪ Explanation: The expert system can have an explanation facility to provide reasons and
explanation for reaching a specific conclusion.
▪ Quick response: Since the expert system is available at all times, the response times
may be faster especially in emergency situations.
▪ Consistency: The expert system provides consistent responses at all times irrespective
of the time of the day or situation.
▪ Learning tool: The expert system can be used as a learning tool by novice users.
▪ Intelligent database: The expert system can be used to retrieve information from the
database in an intelligent manner. It can also store information related to a specific
problem and can be recalled when required.
6.3 Domains of expert system
Over the years various expert systems dealing with different problems have been developed. They
have been widely used in many areas to perform different tasks. They are used as a research tool
431
or to perform various business and industrial functions. The typical tasks performed by expert
systems range from inferring information to predicting, repairing, and monitoring system
behaviors. Table 6.3 shows the broad classes of expert systems based on their functionality [13,
16, 408].
Table 6.3: Categories of expert systems.
Type Areas
Interpretation Ascertain information about the situation from the given data.
Prediction Inferring likely outcome from given situations.
Diagnosis Determining the causes of the specific problem from observations.
Design Devising objects satisfying specific requirements.
Planning Design actions for a certain course.
Monitoring Comparing system behavior to predict flaws in the planned outcomes.
Debugging Providing probable solutions for a specific problem.
Repair Executing the plan to monitor the prescribed solution.
Instruction Determining causes and providing solutions to student behaviors.
Control Governing overall behavior of the system by interpretation,
formulation, and monitoring.
6.4 Application of expert systems in the textile industry
The use of expert systems in the textile industry is not new and many expert systems have been
developed in the past that cover an entire field of textiles such as fibers, spinning, weaving, knitting
and dyeing. The initial expert system applications were introduced in 1987 at ITMA held in Paris.
Examples of different expert systems developed for specific textile domains and their brief
descriptions are given in Table 6.4. The broad category in which these expert systems fall and the
year of their development are also given. Almost all of these systems have been developed keeping
into consideration a single fiber type.
The problems and issues mentioned about the human expert and the troubleshooting
process have motivated our group to develop a comprehensive expert system for the diagnosis of
432
faults in the coloration industry. Several expert systems have been developed by our group in the
past. These include an expert system for the diagnosis of problems in the coloration of cotton
(DEXPERT) [409], polyester (DEXPERT-P) [410], ink-jet printing (INKJETEXPERT) [411] and
protein fibers (Dexpert-PT) [412] for various types of textiles, including yarns, woven and knitted
constructions. All of these systems were developed by a rule-based approach using wxCLIPS, a
modified version of clips with GUI functionality.
DEXPERT was developed for troubleshooting problems in the dyeing of cotton yarn and
fabrics with direct, reactive, vat, sulfur and azoic dyes. The system is capable of diagnosing a total
of 132 faults comprising pretreatment and dyeing faults along with explanations and suggestions
for corrective and preventive actions [409].
An expert system for diagnosing problems in the coloration of polyester material was
developed in 2009. DEXPERT-P can troubleshoot issues in the dyeing of the polyester material in
yarn, knitted or woven fabrics with disperse dyes for different dyeing methods. A total of total 14
faults and 116 associated causes originating from fiber, yarn, fabric, pretreatment, dyestuff, water,
dyeing bath, auxiliary, machinery and post dyeing operations are identified and coded to build this
expert system [410].
In order to troubleshoot problems associated with ink-jet printing of cotton fabric an expert
system, INKJETEXPERT, was developed. This system examines 13 faults and 61 causes to
diagnose a wide range of problems in ink-jet printing process [411].
More recently, an expert system for troubleshooting problems in the dyeing of protein
fibers, Dexpert-PT, for fibers, yarns, fabrics or garments was developed. Twelve protein fibers
were covered in the system which include alpaca, camel, cashmere, guanaco, llama, mohair,
muskox, rabbit, silk, vicuna, wool, and yak. A list of 16 faults and their causes originated from
raw materials, yarn and fabric formation, pretreatment and water was created and incorporated into
the program [412].
433
Table 6.4: Summary of the expert systems developed for textiles.
Area Expert
system class Description Year Ref.
Fiber Classification Color grading of cotton. 1999 [413]
Spinning Monitoring
and planning
Evaluation of spinning technique, costing, and
prediction of yarn characteristics.
1990 [414]
Drafting Planning and
prognosis
Determination of optimum pin settings for gill
drafting.
1991 [415,
416]
Spinning Planning and
prognosis
Prediction of the characteristics of the yarn
based on fiber properties or vice versa.
1996 [417]
Filament
spinning
Diagnosis and
monitoring
On-line diagnosis of faults during the spinning
of filament yarns.
1996 [418]
Rotor
spinning
Planning and
prognosis
Selection of optimum machine settings and
rotor spinning machine parts according to end-
use (COROSULT), Schlafhorst.
1991 [419]
Weaving Diagnosis Identification of causes responsible for
excessive warp stops and end breaks in
weaving (WEBAS).
1985 [420]
Dyeing of
wool
Planning and
prognosis
Determination of fastness requirements,
processing rate, dye selection, and recipe in
the dyeing of wool (WOOLY), Sandoz.
1991 [421-
423]
Finishing Planning Optimization of textile finishing recipes and
their performance (TEXPERTO), Sandoz.
1992 [424]
Finishing Planning and
diagnosis
Process optimization and troubleshooting in
the dyeing of various fiber materials
(OPTIMIST), BASF.
1988 [423,
425]
Pretreatment Planning Recipe selection in the pretreatment of cotton
fabric (PREMATIC), Ciba-Geigy.
1988 [423,
426]
434
Table 6.4 (Continued)
Area Expert
system class
Description Year Ref.
Dyeing Planning Determination of dye recipe and behavior of dyes
according to fiber and dyebath variables (IGCS
Expert system).
1989 [427,
428]
Dye recipe Planning Generation of the dye recipe for continuous
dyeing of cotton and cotton/polyester by pad
steam method (BAFAREX), BASF.
1992 [429]
Exhaust
dyeing
Planning and
prognosis
Prediction of dyeing behavior of disperse dyes
and compatibility index for polyester.
Recommendation of process parameters.
2001 [430]
Exhaust
dyeing
Planning and
prognosis
Determination of optimized dyeing profile and
compatibility index for dyeing of polyamide with
acid dyes.
2002 [431]
Color
matching
Planning and
prognosis
Expert system for the generation of color
formulation for dyeing (SmartMatch), Datacolor.
1995 [432,
433]
Color
matching
Planning and
prognosis
Expert system for color matching in dyeing and
printing. Correct dye combinations based on
compatibility, fastness, environmental
considerations, and cost, (COLPOCA), Ciba.
2000 [434,
435]
Fluorescen
t whiteners
Planning and
prognosis
Selection of suitable fluorescent whitening agent
based on whiteness requirement, shade and
application method.
1991 [436]
Wet
processing
Diagnosis Expert system for the diagnosis of defects in
woven fabrics. Faults were divided into five main
fault categories, the system suggests tests and
investigations determine the precise cause of a
defect, (TESS), EMPA.
1992-
1998
[437-
439]
435
Table 6.4 (Continued)
Area Expert
system class
Description Year Ref.
Dyeing Planning and
prognosis
Expert system for optimizing dyeing process,
process recommendations, recipe calculations and
problem-solving, different modules for PES, PA,
PAN, WO, and CO fibers, (Optidye), Dystar.
1999 [440]
6.5 Components of an expert system
An expert system consists of different elements which are shown in Figure 6.1. They are briefly
described as follows [16]:
▪ Knowledge base: It contains the domain knowledge represented in the form of rules. In
a rule-based system knowledge base is also known as production memory.
▪ Inference engine: It draws conclusions from the knowledge base. It takes existing
information in the knowledge base and information provided by the end-user to reach
a conclusion. It determines which rules are satisfied, orders the satisfied rules and
executes the rules based on their priority. The prioritized list of rules created by the
inference engine is known as an agenda. The global database of facts is stored in the
working memory.
▪ User interface: It provides communication between the end-user and the expert system.
The end-user provides process and problem-specific information to the expert system
to get advice on how to solve the particular problem.
▪ Explanation facility: It provides justification and reasoning for the conclusion(s)
provided by the expert system.
▪ Knowledge acquisition: It allows the knowledge engineer to interact with the system
and make some changes or add new information into the system.
A rule-based expert system can use two different methods for inference which are as
follows [16]:
436
▪ Backward chaining system: This system assumes the likely hypothesis and then works
backward to collect the information and evidence (facts) required to support the
conclusion. Expert systems developed for planning often use a backward chaining
system.
▪ Forward chaining system: It gathers evidence and information (facts) to reach the
conclusion. Expert systems used for diagnosis are often based on a forward chaining
system.
Figure 6.1: Components of an expert system [16].
The main goal of the current project is to develop an expert system for troubleshooting
problems in the coloration of PES/CELL blends (DEXPERT-B). DEXPERT-B can help practical
and novice dyers obtain a quick resolution to common problems by identifying causes and
recommending associated solutions.
6.6 Knowledge base
Knowledge base (KB) is the major part of an expert system which contains a comprehensive
collection of domain knowledge. It contains data (facts) and rules that use those facts as the basis
of decision making. The knowledge base of an expert system is a combination of expertise and
KNOWLEDGE BASE
Rules
INFERENCE ENGINE
Agenda
WORKING MEMORY
facts
EXPLANATION SUBSYSTEM
USER INTERFACE
KNOWLEDGE ACQUISITION
PROCESS AND PROBLEM RELATED
INFORMATION
437
knowledge obtained from books, technical reports, journals, etc. The expertise contains the
symbolic representation of the expert’s factual and heuristic knowledge. It represents what the
expert has learned in schools and through many years of experience in their specialized field. The
person responsible for the development of KB is called knowledge engineer and the process is
called knowledge engineering. Knowledge engineering is a process of acquiring knowledge from
experts or other sources and coding it in the expert system. The process of knowledge engineering
continues until the system’s performance is found to be satisfactory in comparison to the expert’s
knowledge [16]. Figure 6.2 shows a schematic of building a knowledgebase.
Figure 6.2: Schematic of developing knowledgebase by a knowledge engineer.
The knowledge base for DEXPET-B was developed in three stages. The first stage led to
the development of a list of most common problems in the coloration of PES/CO. In the second
stage, the most common causes responsible for these faults were identified. A cause and effect
diagram was produced for the systematic arrangement of causes. In the third stage, an electronic
survey was created and distributed to experts to determine the relationship between the causes and
the problems in the form of certainty values. The certainty factors ranged from 0-10 where 0
represents no relationship between the cause and symptom and 10 represents the cause is the main
source of the problem. The responses collected from expert were analyzed to develop the
knowledge base.
438
6.6.1 Selection of most common coloration faults
The first task in the development of a knowledge base for DEXPERT-B was to determine and
categorize the frequent faults in the coloration of polyester/cellulosic blends. A list of potential
faults was generated through literature review and discussions with the dyeing personnel in
different companies. The list was modified based on the feedback from several dyeing experts and
dye manufacturers. The final list comprising 18 faults in coloration of PES/CELL blends is given
in Figure 6.3.
S1 Reproducibility
S2 Unlevelness
S3 Streaks, stripes or bands
S4 Poor color yield
S5 Change of shade
S6 Inadequate fastness
a. Inadequate rubbing fastness
b. Inadequate water fastness
c. Inadequate washing fastness
d. Inadequate light fastness
e. Inadequate dry-cleaning fastness
S7 Dark stains or spots
S8 Light stains or spots
S9 Lengthwise shade variation
S10 Widthwise shade variation
S11 Shade variation within layers
S12 Two sidedness
S13 Reduced strength
S14 Irregular surface appearance
S15 Holes or tears
S16 Poor hand
S17 Poor dimensional stability
S18 Coating of rollers
Figure 6.3: A list of common faults in the coloration of polyester/cellulosic blends.
439
The faults are briefly described in the following section.
6.6.1.1 Reproducibility
Reproducibility or “right-first-time” in a dyeing process refers to the production of dyed material
within the tolerance limits at the end of the first process without any additions or reprocessing [61,
142]. In simple terms, it is the consistency of the dyeing process to produce the target color in the
first attempt as depicted in Figure 6.4. This includes accuracy and reproducibility within a
laboratory (laboratory reproducibility), accurate transfer from laboratory and scale-up in bulk
production (laboratory to bulk reproducibility) and repeatability between bulk dyed batches dyed
to the same color (bulk to bulk reproducibility). There are many factors that may affect
reproducibility of dyeing which include substrate properties, dyeing liquor characteristics,
machine parameters and the properties of dyes.
Figure 6.4: An example of reproducibility issues where the reproduced color from a new dyed
batch in not consistent with the original shade.
6.6.1.2 Unlevelness
In the coloration of the textile materials uniform appearance of the colored material is the primary
requirement. Differences in shade depth over the entire dyed area, as shown in Figure 6.5, are
termed as unlevel dyeing. In yarn or fabric dyeing small differences in shade from different parts
of the material can exhibit unlevelness [82].
440
Figure 6.5: An example of unlevelness.
6.6.1.3 Streaks, stripes or bands
Streaks are lines that appear to be different in color and/or texture from the surround. Streaks
usually follow straight lines either parallel or perpendicular to the fabric length direction. Streaks
can occur as single or multiple lines. Multiple adjacent lines which are different from the
surrounding material are referred to as bands, as shown in Figure 6.6. Streaks are usually shorter
in length than bands.
Figure 6.6: An example of bands in fabric.
6.6.1.4 Poor color yield
Color yield refers to the depth of color obtained when the standard weight of colorant is applied to
a substrate under standard coloration conditions. It is related to the amount of colorant fixed on
441
the substrate based on the application amount. A poor color yield is obtained when the color of the
dyed material is lighter than the target based on the quantity of colorants used due to a number of
factors including low fixation. An example of poor color yield is shown in Figure 6.7. The image
on the left shows the color obtained under standard dyeing conditions. The image on the right
shows the poor color yield due to low dye fixation.
Figure 6.7: An example of low color yield (on the right) compared to the standard (left).
6.6.1.5 Shade change
This is also known as inconsistent shade or off shade. It refers to the color of the substrate not
exactly matching the target color, as shown in Figure 6.8.
Figure 6.8: An example of shade change.
442
6.6.1.6 Inadequate fastness
Color fastness refers to the resistance of the colored material to a change in its color or a transfer
of color to an adjacent material (staining) due to the action of various chemicals or because of
mechanical influences. Different types of color fastness are defined based on the end use
requirements. The important fastness types are rubbing fastness, water fastness, washing fastness,
light fastness, and dry-cleaning fastness. An example of a stained multifiber strip after the washing
fastness test is shown in Figure 6.99.
Figure 6.9: An example of a dyed sample and a stained multifiber strip after the washing test.
6.6.1.7 Dark stains or spots
These are small regions with a darker color than the adjacent material as shown in Figure 6.10.
They can be in the form of small dots or dark areas in the substrate.
Figure 6.10: An example of dark stains.
443
6.6.1.8 Light stains or spots
These are small regions with a lighter color than the adjacent material. Like dark stains, they can
be in the form of small light dots or light areas in the substrate (see for example Figure 6.111).
Figure 6.11: An example of light stains.
6.6.1.9 Lengthwise shade variation
Lengthwise shade variation refers to a difference in shade between the starting layers of the
substrate and the point where the final shade is achieved. This is also known as tailing and ending.
The term ending is more commonly used in batch dyeing. Ending refers to change in color from
one end of the fabric to the other end. An example of lengthwise shade variation is shown in Figure
6.122. The color appearance of the top fabric taken at the start of the roll is different than the
bottom fabric taken at the end of the roll. Both fabrics are from the same lot dyed with the same
colorants and coloration process.
444
Figure 6.12: An example of lengthwise shade variation.
6.6.1.10 Widthwise shade variation
This refers to a variation in shade across the substrate or gradation of shade from the selvage to
the center of the dyed substrate. This is also known as listing or side to side shade variation. Figure
6.133 shows an example of listing where the shade of the left side of the fabric is different than
the right side.
Figure 6.13: An example of widthwise shade variation (note the fabric is folded on itself).
445
6.6.1.11 Shade variation within layers
This refers to a variation in depth of shade between the inner, middle and outer layers of a yarn
package or a beam dyed fabric. Figure 6.14 shows an example of shade variation within the layers
of a yarn package.
Figure 6.14: An example of shade variation within layers in a yarn package.
6.6.1.12 Two sidedness
This is also known as the face and back problem in which the front side of the fabric has a different
color appearance than the backside of the fabric. Figure 6.15 shows an example of two sidedness.
The left side shows the front and the right side shows the back of the fabric.
Figure 6.15: An example of two sidedness.
446
6.6.1.13 Reduced strength
The strength of material demonstrates its ability to resist the action of external forces. It is related
to the durability of the material. The fabrics with reduced strength can easily be torn and would
not meet the common end-use use requirements of the material. An example of a fabric with
reduced strength is shown in Figure 6.16. It can be seen that due to a reduction in strength, the
fabric can easily be torn.
Figure 6.16: An example of fabric with reduced strength.
6.6.1.14 Irregular surface appearance
These are faults in which the surface of the substrate is distorted due to the action of mechanical
forces or friction. These include abrasion marks, creases (as shown in Figure 6.17), rope marks,
crush marks, fabric distortion, wavy fabric appearance, and perforation marks. These usually have
a different appearance compared to the substrate body.
In yarn packages, these may be evident in the form of package deformation, yarn
deformation or luster marks in yarn layers.
447
Figure 6.17: An example of crease marks.
6.6.1.15 Holes or tears
Holes are small punctures in the fabric where a portion of yarn may be broken or missing. A tear
is a large cut or puncture in the fabric. Examples of holes and tears are given in Figure 6.18. Pin
marks due to stentering fabrics also constitute an example of holes.
Figure 6.18: An example of holes (left) and tears (right).
6.6.1.16 Poor hand
This refers to a material which is harsh or rough to touch. An example of a poor hand is given in
Figure 6.19.
448
Figure 6.19: an example of fabric with a poor hand.
6.6.1.17 Poor dimensional stability
This is also known as shrinkage. It is the ability of the substrate to retain its dimensions when
exposed to certain conditions such as water, steam, washing, drying or other processes. A symbolic
representation of this problem is given in Figure 6.20.
Figure 6.20: A symbolic representation of poor dimensional stability of the fabric.
6.6.1.18 Coating of rollers
This problem is machine-oriented which is generally seen in pigment coloration. It refers to the
accumulation of binder film on the dye padder and guide rollers. A symbolic representation of this
problem is given in Figure 6.21.
449
Figure 6.21: A symbolic representation of the coating of rollers during pigment coloration.
6.6.2 Identification of common causes of coloration problems in PES/CELL blends
The coloration process is quite complex and affected by a very large number of factors. Proper
attention and control are required for the coloration process to be successful. Each variable in the
coloration process has a direct or indirect influence on the processing of material and may cause
problems if not properly controlled. Since the dyeing of fiber blends has more variables than single
fiber dyeing, there are more chances of producing faulty dyed materials [140].
The problems in the coloration of blends can be attributed to a number of causes ranging
from fiber harvesting or manufacturing, yarn, and fabric manufacturing to the preparation,
coloration process and conditions, machinery, water, and chemicals used. It can be seen that
coloration issues may originate from a large number of factors that are sometimes not in the control
of the dyer. It is also not feasible to control or standardize all the factors due to economical
limitations. Thus, it will be better to focus on important or key causes that are responsible for
deviation from achieving the required target. These key factors or causes can be determined using
the Pareto principle [441]. It is essential to have an in-depth knowledge of the properties of
materials, machines, processes, and dyestuffs to prevent or solve coloration problems [11]. Actual
conditions in the dyehouse should also be considered. Once the key factors or causes are identified
they can be standardized in order to achieve process control [441].
The cause-and-effect (CED) or fish-bone diagram is one of the important tools used for
quality control and process improvement along with other statistical tools. CED shows the
relationship between the problem and factors or causes that are considered to influence the
problem. These factors can be considered as bones of a fish or branches of a tree. A typical CED
consists of different parts which include the head, spine, and bones. The head represents the
450
problem under consideration and is positioned on the far-right side of the diagram. The spine of
the CED is represented with the horizontal arrow pointing towards the head. The direction of the
arrow and all the items that join the arrow represent the causes that may be responsible for the
problem described in the head. Several large bones feed into the spine using smaller arrows. They
represent the broad categories of probable causes. Broad categories are added using smaller arrows
from the left side and according to the order of the process. The categories are based on the
principle of 6Ms, though other categories can also be used. The 6Ms comprise machinery,
methodology, materials, man power, measurements, and Mother Nature (environment). Multiple
levels of smaller bones show sub-categories of the causes of the problem. The connection between
the smaller bones and larger bones show their relationship. The number of small bones keeps on
adding until the cause that can be acted on is reached. Once all causes have been accounted for,
they are ranked according to their influence on the outcome of the process based on their technical
significance. In order to avoid biases when creating the CED, the relevant people, including those
from other departments, should be consulted. Important points that need to be considered are
management-related causes, sampling and measurement errors, and the interaction effect between
these causes [441, 442].
A CED diagram was created to identify and organize possible causes of problems in the
coloration of PES/CELL blends in a structured format. Figure 6.22 shows the CED for the faults
or problems that occur in the dyeing of fiber blends. This diagram was created according to the
process described above. Several brainstorming sessions were conducted and technical
information was obtained from the literature survey to ascertain the causes that may affect the
coloration problems for the PES/CELL blends. A special symbol (*) was used to show the
interaction effect between the broad categories. The developed CED diagram is composed of six
major categories or large bones that are responsible for problems in the coloration of PES/CELL
blends: measurement, machine, materials, method, environment, and people. Each of these broad
categories is discussed as follows.
451
Figure 6.22: Cause and effect diagram for faults in the dyeing of fiber blends.
Dyes/
Pigments
Quality control
Material handling
Inspection
Color kitchen
Controls
Production
Ventilation
Problems in the Coloration of Fiber Blends
Water
Utilities
Auxiliaries/
Chemicals
Chemicalproperties
Work forcePersonnel
Contaminants
Laboratory
Storage
Substrate
Standard
Dyeing
Bath preparation
Inspection
Sampling
Maintenance
Process planning
Physiologicalissues
Attitude
Training
Culture
Experience
Attention
Qualification
Accuracy &repeatability
Dyeing
Control unit
MeasurementMaterialsEnvironment
MachineMethodPeople
People*
Method*
Machine*
Standard operating procedure (SOP)
Color assessment
Communication
Cleanliness
452
6.6.2.1 Measurement
Measurement covers the monitoring of the ‘coloration’ process. The success of the coloration
process is incomplete without a proper measurement system in place. The broad categories include
quality control and color assessment as shown in Figure 6.23. The quality controls cover various
parameters that are essential to control the proper running of the coloration equipment. Any
variations in these parameters may lead to coloration problems. Color evaluation includes various
factors such as instrumental and visual assessment of colored samples to ensure the conformance
of the colored material to the target shade. There are many factors that may affect the color
assessment of dyed materials such as the illumination conditions, viewing angle, sample size, the
distance between the sample and the observer, orientation of samples, instrument settings used and
type of assessment. Thus, these factors must be controlled for accuracy and reproducibility of the
results.
6.6.2.2 Machine
The PES/CO blends can be dyed by various processes such as batch, semi-continuous and
continuous. The type of process used depends on material form (yarn, knit, woven), fiber type,
size of dye lots and quality requirements of the dyed fabric. Based on the dyeing process, different
dyeing machines are used. The selection of different dyeing machines depends upon the dyeing
process, material suitability, dyeing conditions (atmospheric or high temperature), and open or
rope processing of the material.
In order to ensure proper running of the machines certain factors need to be controlled. For
example, in continuous dyeing uniformity of liquor pickup is a prerequisite for successful dyeing.
The liquor pickup is controlled with the help of padder roll pressure and speed. Any variations in
padder pressure may lead to widthwise shade variation. The temperature of the trough should be
controlled to avoid instability of the dye liquor that causes tailing and poor color yield. Similarly,
the temperature of the hot flue dryer and steamer should be controlled properly for efficient dye
fixation. For batch dyeing machines, such as the jet a proper control of heating rates and the
sequence of chemical additions including dyes are important to attain a level dyeing. Proper control
of the liquor ratio is required for reproducible dyeing results.
453
Other machines that may affect the outcome of the dyeing process include inspection related
machines such as light booths, inspection tables, and spectrophotometers. The role of a color
kitchen cannot be ignored as accuracy of weights and dye liquor preparation related problems are
originated from here. The machines should be properly maintained and routinely calibrated to
avoid problems. Various machine-related causes are shown in Figure 6.24.
Figure 6.23: Possible causes originating from the measurement.
.
Quality control
pH Pick-up
No. of measurements
Orientation
Type of assessment
Distance
ConductivityRedox
potentialFlow rate
ConcentrationOxygencontent
Temperature
Substrate
Liquor
Water
Entry
Exit
Moisture
Residual
Application
Exhaust
Accuracy &repeatability
Measurement
People*
Method*
Machine*
SpecularIncluded/Excluded
Aperture size
Std. Observer
Illumination*
Color assessment
InstrumentalVisual
Type
Pass/Fail
Whiteness
Matching
Fastness
Viewing angle
Sample size
Illumination*
Sample type
454
Figure 6.24: Possible causes originating from the machinery.
Liquor
Material handling
Inspection
Weighing Balance
Color kitchen
Automation
Spectrophotometer
System drift
Availability
Light cabinet
Illumination
Dispensing system
Laboratory
Cleanliness
Maintenance
Calibration
Accuracy
Calibration Accuracy
Preparationtanks
Machineconnections
Steam pipe
Availability
Watersupply
Linear
Progressive
Controls
Liquor ratio
Amountof water
Substrateweight
Fill level
Dye addition
Chemicals addition
Time
Amount
Rate
Rate
Amount
Time
Temperature
Heating rate
Cooling rate
Dyeing
Washing
Preparation
Dyes
Chemicals
Time
Drying Dyeing
Cleanliness
Vacuum
Fill
Filters
Drain
Substrate
Speed
Substratetension
Drying
Curing
Moisture
Steamcontent
Entry
Exit
Liquorpick-up
ExhaustHumidity
Residual
Washing
Curing
Dyeing
Degree of controls
Maintenance
Sensors
Automation level
Displays
Breakdowns
Delays in supply
Malfunctions
Availability
Infra-red Intensity
Liquor circulation
rate
Pressure
Padder
Nozzle
Substrate
Reel
Materialcirculation
rate
Vessel
Troughvolume
Liquor turnover rate
Continuous
Exhaust
SteamerThermosol
Water-lockRoof
Uniformity
Control unit
Software
Signals
Availability
Hardware
ControllersMaintenance
Calibration
Computers
Monitors
Alarms
Air flow
People*
Machine
Geometry
DirectionalSphere
Equipement
Illumination
Source
UV content
BenchtopHandheld
Type
Surround
CalibrationMaintenance
UV content
Yarn
Space
Fabric
Type
Package
Hank
Jet
Jigger WinchBeam
Air-flow
Over-flow
Soft-flowVertical
Horizontal
Tube
Continuous
Pad-Batch
Pad-SteamPad-Theromosol
Accuracy
455
6.6.2.3 Materials
Any variation in the coloration process may be attributed to two fundamental causes which are
variation in raw materials and processing. Various causes attributed to materials are shown in
Figure 6.25.
Raw materials include the substrate, water, dyes, and chemicals. Many problems in the
dyed substrate are due to defects present in the fabrics, yarn or fiber [443]. For example, the
presence of immature fibers may lead to the appearance of white spots in the fabric after dyeing.
The variation in fiber crystallinity and orientation due to variations in extrusion, heat setting, and
drawing conditions may cause unlevelness or streaks in the dyed fabric. The variation in blend
ratio causes reproducibility issues and off shades. Yarn mixing during weaving may appear as bars
in the dyed fabric. The presence of hard sizing agent may cause problems during desizing as it is
difficult to remove and leads to streaks or spots in the dyed fabric.
The pretreatment of fabric or yarn is critical for successful coloration. Many problems in
coloration originate from, or are due to, improper pretreatments. The pretreatment of PES/CELL
blends includes various operations such as singeing, desizing, scouring, bleaching, heat setting,
and mercerization. Any variations in process parameters of chemical concentrations can cause an
improper pretreatment. After pretreatment fabrics should have good absorbency, neutral pH, good
dimensional stability, minimum levels of residual impurities, and no deposits of residual peroxide.
The pretreatment conditions should be selected such that fibers are not damaged. This is critical
especially in PES/CELL blends due to differences in their sensitivities and impurity levels. The
process parameters and chemical concentrations are often adjusted according to the blend to
achieve optimum results.
The chemicals and auxiliaries are added to provide different functions such as controlling
dye strike and minimizing unlevelness, improving dye exhaustion, providing required chemicals
for dye fixation and increasing the color fastness of dyed materials. Auxiliaries include
electrolytes, wetting agents, alkalis, acids, oxidizing agents, reducing agents, leveling agents,
dispersing agents and others. They should be checked on a regular basis for their purity, chemical
and performance properties. Several problems in the coloration process may be attributed to the
wrong selection, high impurity levels and inadequate /low performance properties of the chemicals
and auxiliaries [443].
456
The PES/CELL blends can be dyed using dyes or pigments and with one or two colorants
systems. The one colorant system uses pigments that can be attached to both fibers in the blend
with the help of a binder. In the two colorant system separate dyes for each fiber in the blend are
used. The polyester portion of the blend is dyed with the disperse dyes while cellulose can be dyed
with direct, reactive, vat and sulfur dyes. Many factors should be considered in dye selection for
each fiber in the blend as the conditions required for dye class for each fiber are different. The dye
class use for each fiber should be compatible with each other under dyeing conditions. Some
reactive dyes may react with disperse dyes and cause instability issues. Some reactive and direct
dyes are not stable under high temperatures and acidic conditions used in disperse dyeing. Disperse
dye tends to stain the cellulose component of the blend which may cause fastness related problems.
In order to remove the disperse dye stain from the cellulose component of the blend a reduction
clearing is required. Direct and reactive dyes are not stable under these treatment conditions. This
forces the dyer to use either a longer two-bath process or skip the reduction clearing process to
shorten the dyeing time. Some requirements related to specific dye classes can be used as an
advantage such as reduction clearing step required for disperse dye stain removal can be combined
with the reduction step required for vat and sulfur dyes. The dyes should be checked for color
strength on a regular basis to adjust the dyeing formula if a change in the color strength of dyes in
a new lot is observed.
457
Figure 6.25: Possible causes originating from the materials.
Dyes/
Pigments
Amount
Blendregularity
Yarn mixing
Moisture content
Thermal damage/melt spots
Priodicities
Broken fllaments
Improper steam conditioning (twist setting, stabilization, pre-shrinking, heat-setting)
Splicing
Storage stablity
Particle size and its distribution
Dispersion
Heat stability
Reduction sensitivity
Metameric
Phototrophic StructureYarn denisty
Fixation behavior
Shape SizeDensityDye tube
StrucutrePattern zones
Hard flanks
Package
SpiralityDrop
stiches
Cloth fall-out
Bunch-ups
Pretreatment Fabric
AbsorbencyResidual alkalinity
Whiteness
Degree of mercerization
ImpuritiesDimensional
stability
OilsWaxesSeed
fragments
Spinfinishes
Sizing agent
Fiber degradation
Defect
Surfaceproperties
Residual H2O2
Hard sizeSize selection
Wax deposits
Stripe
Sizing
Thin place
Lashed-in weft
Extraneous thread Fly
Broken pick
Short pick
Appearance fault Stain Snag
Interlacing fault
Snarl Hole Slack thread
Tight thread
Float Warp end repair
Reed mark
Temple marking
Drawing-in fault
Warp end break
Crease
Tights spots
Bulk
Intermingling
Auxiliaries/
Chemicals
PurityPerformance
propertiesAmount
Chemicalproperties
pHIonic character
Viscosity
Color
CompatibilityI.D.
Supply
Effect of Moisture
Substrate
Fiber properties
Maturity
Ioniccharacter
TemperaturestabilityCrystallinity
pH stability
Fiber saturation value
Fineness
Orientation
Degree ofpolymerization
Glass transitiontemperature
Chemical stability
Degree of fibrillation
Winding
Weight
Standard
Hank
Ageing
Twist Lot size
Batch size
Numberof strands
Length
Blend components
Blendingmethod
Blend ratio
Chemicalproperties
Compatibility
Affinity
Fastness
Color
Reactivity
pH sensitivity
Sensitivity to metal ions
Hard water sensitivity
Ionic character
Staining
DiffusionSalt sensitivity
MigrationMolecular weight
DyesChemicals
PurityI.D.Moisturecontent
Dye Substitutes
Supply
Form
Solubility
Color
Materials
Variation inproperties
Dust & trash
Length
Neps
Short fibercontentStrength
Elongation
Oligomer
Winding System
Yarn tension
Construction
Width
Count variation
Irregularity
Seldom occuring faults
Imperfections
Density
Hairiness
Trash & Dust
Diameter
Strength
Elongation
Shape
Wax
Yarn
Number of end groups
Selection Amount
Contamination
Lot characteristics
Faulty package
458
6.6.2.4 Method
The method includes procedures to ensure consistent coloration results. The procedure covers the
dyeing process, bath preparation, inspection, sampling, process planning, and maintenance, as
depicted in Figure 6.26. These procedures are usually implemented in the form of the standard
operating procedure (SOP). An SOP is a standardized document that contains step by step
instructions to carry out a routine or a repetitive operation. SOP helps in performing the operation
more effectively and efficiently and allows the consistent implementation of a process and
procedure within an organization [444]. The SOPs can be developed using technical data sheets of
dyes and chemicals, machine manuals, and standardized testing methods.
Figure 6.26: Possible causes originating from method.
Addition sequence
People*
Dyeing
Bath preparation
Inspection
Sampling
Procedures
Machine*
Process
Color effect
Dyeing method
Dye selection
Sampling
Sample preparation
Maintenance
Preventive
Breakdown
Schedules
SOP
Procedures
Process
SOP
Weighing
Machine*
Lab recipe
Adjustments
AdditionsDyes &
Chemicals
Dilution
Filtration
Process planning
People*
Delays
Schedules
JobsequenceParameters
Measurement*
Process planning
Bottlenecks
Availability
Method
Standard operating procedure (SOP)
Specifications
People*
People*Measurements*
People*
SOP
Machine*
SOP
Conditioning
Test methods
Standards
Sample selection Identification
Handling
SOP
Sampling
AATCC
ISO
ASTM
Buyer
Others
Internal
Machine manual
Operation
Maintenance
Calibration
Dyes & chemicals technical data sheet
Storage
Handling
Reprocessing
Tolerances
Inspection
459
6.6.2.5 Environment
The environment includes several factors, shown in Figure 6.27, which are not usually under the
control of the dyer. These include working and storage conditions, utilities and water. The water
quality needs to be monitored on a regular basis to avoid problems in coloration. The water may
contain several impurities that may interfere with the coloration process. The impurities in water
other than the source may come from broken or rusted pipes, and improperly cleaned storage tanks.
A dyehouse is generally equipped with a water treatment plant such that water is made available
for coloration operation. For a good lab to bulk reproducibility, it is important to use the water of
the same quality in both cases.
Figure 6.27: Possible causes originating from the environment.
Production
Ventilation
Water
pH
Dissolved CO2
HardnessDissolvedsolids
Heavy metals
ChlorineSuspended
matterNitrate &
Nitrite
Iron
Copper
Manganese
Organicsubstances
ColorOdor
NaHCO3
Utilities
Impurities
Pressure
Electricity
Availability
Flow rate
AirSteam
Water
Air
Steam
Voltage fluctuation
AirSteam
Water
Electricity
Contaminants
Humidity
Laboratory
Temperature
Temperature
Humidity
Storage
Temperature
Humidity
Environment
Cleanliness
460
6.6.2.6 People
People are the most important resource of a dyehouse. They can serve in different functions that
include but are not limited to establishing and controlling processes and production, selection and
controlling of raw material supplies, defining and controlling product quality, plant maintenance,
operations supervision and carrying out the process efficiently and safely [445]. The most
recurring source of a problem in a dyehouse is a human error. The dyehouse personnel should be
well informed and have strong knowledge about the process so that human-related faults can be
avoided [11]. The human-related causes can be sub-divided into physiological issues, experience,
training, attention, qualification, attitude, communication and different types of workforce
personnel involved in the dyeing factory as shown in Figure 6.28. The physiological factors
include fatigue, health-related problems, age, and color vision deficiency. The personnel involved
in a dyehouse include production, inspection, color kitchen, maintenance, and management crew.
Several errors in the coloration process may be caused due to tiredness, distraction or loss of
concentration of people involved. Dyehouse personnel should have adequate training, knowledge
or experience to carry out their tasks effectively and efficiently. The mental and physical or
abnormal surrounding conditions, however, may still lead to stress or loss of concentration or
sensitivity thus causing human errors.
A lot of coloration problems can be prevented if proper attention is given to people
management. The selection of employees is a factor that influences the day to day running of the
dyehouse. A cooperative attitude is important for the successful operation of the dyehouse and can
be cultivated over time. The personnel involved in a production floor should be healthy to deal
with the physical and mental demands of the production environment. A structured payment
system is important for people's well-being and a good working environment. The attitude of the
people is important for the efficient working of the plant. Several factors that influence the attitude
include appreciation, job security, promotions, good wages, management loyalty, resolution of
problems in a timely manner and good working conditions. A proper training program is essential
to improve quality and productivity, promote a healthy and safe working environment, reduce the
learning time for new employees, reduce labor turnover and improve the quality of new and
existing employees [445].
461
Figure 6.28: Possible causes originating from human-related factors.
As shown there are several factors that may be responsible for the problems observed in
the coloration of PES/CELL blends. A detailed list of the potential causes of various problems in
the coloration of PES/CELL blends is given in Table 6.5. The list was developed to illustrate
important factors that may be considered by dyers on a daily basis and can be useful to ascertain
the root cause of problems. The causes of coloration problems may vary when the process and
machinery are different and this was considered in the development of the list. Potential causes
were segregated into 11 different categories based on their origin as shown in Table 6.6.
Work force
Inspection
Maintenance
Color KitchenManagment Production
Quality control
Laboratory
Personnel
Physiologicalissues
Gender
Color defeciency
Age
Acquired Inherited
Attitude
Training
Culture
Experience
Attention
Qualification
Health
People
Communication
462
Table 6.5: Categorized list of possible causes associated with symptoms in the coloration of
polyester/cellulosic materials.
Cause Category Description
C001 Bath
preparation
Errors in the weighing of colorants and chemicals
C002 Improper bath preparation procedure
C003 Too fast/quick addition of chemicals in the bath
C004 Too fast/quick addition of dyes in the bath
C005 Colorants Too high colorant concentration
C006 Wrong selection of dyeing method (1 bath, 2 bath)
C007 Poor dye selection for polyester component
C008 Poor dye selection for cellulose component
C009 Poor dye combinations for each fiber type
C010 Variation in colorant strength
C011 Incompatibility between dye classes
C012 Cross-staining of fiber
C013 Bleeding of unfixed dye into the bath/trough during development
C014 Poor pigment selection
C015 Crust formation in pigments during storage
C016 Poor pigment dispersion system
C017 Differences in pigment particle size and particle size distribution
C018 Poor disperse dye dispersion system
C019 Poor disperse dye dispersion stability
C020 Poor disperse dye diffusion properties
C021 Poor disperse dye leveling and migration properties
C022 Poor thermomigration property of disperse dye
C023 Too high substantivity of reactive/direct dyes
C024 Poor solubility of reactive/direct dyes
C025 Poor diffusion properties of reactive/direct dyes
C026 Poor migration properties of reactive/direct dyes
463
Table 6.5 (Continued)
Cause Category Description
C027 Poor stability of reactive/direct dyes under polyester dyeing
conditions
C028 High dye reactivity
C029 Too high substantivity of vat/sulfur dye in the leuco form
C030 Too low substantivity of vat/sulfur dye in the leuco form
C031 Poor diffusion properties of vat/sulfur dyes
C032 Poor leveling properties of vat/sulfur dyes
C033 Poor vat/sulfur dyes dispersion system
C034 Poor color matching of each fiber in the blend
C035 Auxiliaries Variations in strength and purity of dyebath chemicals
C036 Chemical or physical interaction between colorants and chemicals
C037 Poor selection of dyebath chemicals
C038 Formation of binder film on padder or rollers
C039 Agglomeration of binder
C040 Binder with poor fastness properties
C041 Brittleness (poor softness) of the binder film
C042 Insufficient amount of binder
C043 High amount of binder
C044 Poor resistance of binder against aging
C045 Binder with poor swelling resistance
C046 High amount of softener
C047 Improper softener selection
C048 Inappropriate electrolyte (salt) concentration
C049 Inappropriate concentration of dispersing agent
C050 Too low amount of lubricating agent
C051 Too high concentration of carriers
C052 Lower quantity of anti-migrating agent
C053 Precipitation of anti-migrating agent
464
Table 6.5 (Continued)
Cause Category Description
C054 Too high concentration of dye fixative
C055 Use of silicone based defoamer
C056 Pre and post
dyeing
operations
Too low concentration of reducing agent and/or alkali
C057 Presence of air in the machine
C058 Inappropriate rinsing temperature
C059 Inadequate water flow rates/liquor ratio during rinsing
C060 Inadequate number of rinse cycles/rinse baths
C061 Inappropriate pH during oxidation
C062 Insufficient concentration of oxidizing agent
C063 Inappropriate temperature during oxidation
C064 Inadequate reduction clearing temperature
C065 Inadequate reduction clearing time
C066 Inadequate concentration of hydro and caustic during reduction
clearing
C067 Inadequate soaping temperature
C068 Inadequate pH during soaping
C069 Inadequate soaping time
C070 Improper selection of detergent for soaping
C071 Inadequate water flow rates/liquor ratio during soaping
C072 Improper neutralization of substrate after dyeing
C073 Too high drying temperature
C074 Dyeing
machine
Improper storage and handling of substrate
C075 Machine stoppage for a longer duration
C076 Presence of dye deposits in the dye preparation tank and machine
C077 Presence of reductive chemicals in substrate, water or steam
C078 Excessive foaming in the dye bath/trough
C079 Non-uniform or damaged machine parts
C080 Excessive, insufficient or variable tension during fabric run
465
Table 6.5 (Continued)
Cause Category Description
C081 Longer duration of substrate run due to reprocessing
C082 Variations in dyeing program
C083 Rubbing of unfixed substrate against the guide roller/machine part
C084 Batch dyeing Too fast increase in the differential pressure
C085 Too low liquor flow rate
C086 Too high liquor flow rate
C087 Inappropriate liquor flow times (in-out and out-in)
C088 Too high pressing density
C089 Too low pressing density
C090 Leakage in package column
C091 Defective locking caps
C092 Too large batch size (machine overloading)
C093 Presence of oligomer and other deposits in the machine
C094 Presence of oligomer deposits on the substrate surface
C095 Trapped air pockets in the material during dyeing
C096 High temperature rise rate
C097 Inappropriate dyebath pH
C098 Use of too low liquor ratio
C099 Use of too high liquor ratio
C100 Too low dyeing temperature
C101 Too high dyeing temperature
C102 Too slow fabric/rope speed
C103 Too fast fabric/rope speed
C104 Too short dyeing time
C105 Too long dyeing time
C106 Shock cooling of fabric after completion of dyeing cycle
C107 Too low liquor flow rate
C108 Too high liquor flow rate
466
Table 6.5 (Continued)
Cause Category Description
C109 Incorrect liquor flow direction
C110 Incorrect overlap of fabric covering the beam perforations
C111 Uneven winding of fabric on the beam
C112 Variation in pressure head in the tubes
C113 Poor circulation or stoppage of fabric
C114 Incorrect nozzle size (diameter)
C115 Twisting or pressing of the rope at high temperature
C116 Inappropriate nozzle pressure
C117 Cooling of outer/inner fabric layers
C118 Cooling of selvages
C119 Variation in dyebath temperature
C120 Too tight or too loose fabric edges
C121 Continuous
dyeing
Deposits of fluff/lint on the padder surface and guide rollers
C122 Damaged, worn out or uneven padder surface
C123 Too high pad trough temperature
C124 Difference in the hardness of dye padders
C125 Too high wet pickup
C126 Too low wet pickup
C127 Improper distribution and circulation of dye liquor
C128 Uneven wet pickup
C129 Inadequate airing time between padding and drying
C130 Selvage curling during padding and thermofixation process
C131 Improper rotation of the fabric batch during batching
C132 Poor covering of fabric batch during batching
C133 Differences in fixation temperature or time during batching
C134 Variation in the intensity of the IR pre-dryer
C135 Non-uniform air velocity or flow
C136 Too high drying temperature
467
Table 6.5 (Continued)
Cause Category Description
C137 Too low thermofixation temperature
C138 Too high thermofixation temperature
C139 Too long thermofixation time
C140 Too short thermofixation time
C141 Temperature variation in the hotflue
C142 Contact of condensation drops with unfixed colorant
C143 Inadequate steaming temperature
C144 Inadequate steaming time
C145 Variation in temperature inside the steamer
C146 Too high water seal temperature
C147 High turbulence in the washbox
C148 Pretreatment Difference in the singeing of fabric’s face and back
C149 Fiber damage during singeing
C150 Incomplete singeing
C151 Incomplete removal of sizing agents and sizing wax
C152 Incomplete removal of oil, rust and grease stains
C153 Fiber damage during scouring and bleaching
C154 Too high weight loss during scouring
C155 Insufficient relaxation of the substrate during washing
C156 Localized swelling of fiber
C157 Incomplete removal of fats, waxes, spin finishes, and knitting oils
C158 Inadequate weight reduction of polyester
C159 Catalytic damage during bleaching
C160 Presence of residual peroxide in substrate
C161 Incomplete removal of motes (seed husks)
C162 Inadequate whiteness of substrate
C163 Improper heat setting of substrate
C164 Fiber damage during heat setting
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Table 6.5 (Continued)
Cause Category Description
C165 Physical damage of substrate (pin marks, cuts)
C166 Excessive overstretching of substrate on stenter
C167 Incomplete mercerization
C168 Differential mercerization due to superimposed layers of substrate
C169 Alkaline pH of substrate before dyeing
C170 Improper stitching of substrate ends
C171 Presence of insect residues in substrate
C172 Water Presence of Ca and Mg ions (hardness) in water
C173 Presence of heavy metals (Cu, Fe, Mn, Zn) in water
C174 Presence of suspended matter in water
C175 Presence of bicarbonate in water
C176 Presence of chlorine in water
C177 Fabric
manufacturing
Presence of holes, tears or cuts in greige substrate
C178 Presence of bands or stripes in greige substrate
C179 Fabric rolls from different knitting or weaving machines or batch or
factory
C180 Yarn mixing
C181 Variation in yarn tension during warping/sizing
C182 Winding Too high package density
C183 Too low package density
C184 Uneven package density
C185 Edging process for rounding of package flanks
C186 Improper rounding of package flanks
C187 Improper coverage of dye tube perforations
C188 Use of damaged dye tubes
C189 Poor temperature stability of dye tubes
C190 Yarn
manufacturing
Too many yarn imperfections
C191 Lower yarn strength and elongation
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Table 6.5 (Continued)
Cause Category Description
C192 Variation in blend ratio
C193 Foreign fiber contamination
C194 Fiber and
filament
Variations in crystallinity and orientation of fiber
C195 Variations in the degree of polymerization of fiber
C196 Presence of immature fibers
Table 6.6: Sorting of causes into different categories based on their origin,
No. Category Causes
A Bath preparation C1-C4
B Colorants C3-C34
C Auxiliaries C35-C55
D Pre and post dyeing operations C56-C73
E Dyeing machines C74-C83
F Batch dyeing C84-C120
G Continuous dyeing C121-C147
H Pretreatment C148-C171
I Water C172-C176
J Fabric manufacturing C177-C181
K Winding C182-C189
L Yarn manufacturing C190-C193
M Fiber and filament C194-C196
6.6.3 Knowledge acquisition
Knowledge acquisition involves the transfer and transformation of problem-solving expertise from
some knowledge source to a program. The sources of knowledge comprised human experts,
textbooks, scientific data, technical reports and other resources [446]. In order to develop a
relationship between the symptoms and various causes in the coloration of PES/CELL blends, an
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electronic survey was constructed. Electronic surveys are commonly used nowadays as a method
to collect information. The main advantages of using an electronic survey include [447]:
▪ Fast turnover time;
▪ Lower cost as no printing or postage is required;
▪ Wider reach to a large number of respondents which can lead to higher response rates;
▪ Variety of formats: email, web survey, and others;
▪ Many types of response formats such as dropdowns, radio buttons, input boxes;
▪ Instant and convenient data analysis since manual entry of data is not required;
▪ Easy to respond to by participants; and
▪ Flexibility in design.
The survey was designed in the form of a Microsoft Excel spreadsheet. A screenshot of the
survey is shown in Figure 6.29. The survey consisted of one excel spreadsheet containing 18
symptoms and 196 causes. The symptoms are represented in columns while the causes are
provided in the form of rows. Each cell in the excel sheet represented the interrelationship between
the causes and symptoms. A certainty factor (CF) was provided for each response from 0-10. The
CF of 10 indicates a very strong correlation between the cause and the symptom, while a CF of 0
denotes no correlation exists between the cause and the symptom. If the experts were not sure
about the relationship between the cause and the symptom they could select X. A cell that was left
blank was considered to indicate no relationship existed between the cause and the symptom.
As the coloration of PES/CELL blends can be achieved by both pigments and dyes, the
survey was distributed to experts with experience and expertise covering both coloration systems.
A total of 10 dyeing experts from the USA, South Korea, Italy, Germany, India, and Pakistan
participated in the study. Five experts were from pigment coloration domain and five had expertise
in the conventional dyeing domain. Experts’ responses were analyzed and coded into rules to
develop the knowledge base. The analysis of expert responses is covered in the next section.
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Figure 6.29: A screenshot of the electronic survey distributed to experts in spreadsheet format
472
A common challenge that was encountered when seeking responses from experts was
finding willing experts who could complete the work in a timely fashion. Although, some experts
provided a quick response many experts found it difficult to complete the survey due to their busy
schedules and could not respond in time. In addition, the task was found to be very time-consuming
according to some experts. It should be noted that the survey was carefully designed and broken
down into sections for easy completion. The experts who participated in this study were from
different sectors of the industry including dye manufacturing, as well as practical dyers and dyeing
consultants with a wide range of experience from 10-40 years. The weighted average responses
from experts are given in Appendix A.
6.6.4 Analysis of expert responses
It has been found that, usually, a single expert may not be enough to get suitable responses to
resolve a particular problem. It is important to recognize that experts other than having shared
expertise of the domain usually specialize in a sub-section of a domain [448]. For example, a
dyeing expert may have working experience and deep knowledge of different dyeing processes,
but they may have more expertise in the area of continuous dyeing. Experts may also differ in their
expertise level, with some having more expertise than others because of training, experience, and
intelligence. Using responses from different experts increases the reliability and confidence in the
knowledge base as compared to responses obtained from a single expert [449]. Therefore, the use
of multiple experts in the development of an expert system is recommended. This is useful in the
development of a high-quality practical expert system in a particular domain.
When dealing with multiple experts, three strategies can be used to develop a knowledge
base by a knowledge engineer. This can be achieved either by using experts individually, or
designating primary and secondary experts or by combining multiple responses [450]. The main
advantages associated with combining multiple experts’ responses are summarized as follows
[450]:
▪ The understanding of the knowledge domain is improved;
▪ The developed knowledge base will be more comprehensive and accurate;
▪ Broader domains can be combined; and
▪ Complex problems can be dealt with.
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Several strategies can be used to integrate responses depending on the nature of responses
obtained from multiple experts. The analytical approach is useful when dealing with numerical
values such as probabilities, weights, etc. The treatment of expert responses in such cases is
mathematical in nature [450, 451].
For the construction of this knowledge base the expert responses were obtained in the form
of certainty factors (CF). The certainty factors, ranging from 0-10, were used to interrelate the
symptoms with the causes. Certainty factors are useful because it is often very difficult to have
complete information to arrive at a solution to a problem with complete certainty. Often one
symptom may be due to multiple causes, in such cases, the cause with a higher CF has a higher
likelihood of being the correct cause as compared to the cause with a lower CF. To develop the
knowledge base for this study, CFs ranging from 0-10 were segregated and categorized into three
groups based on their values. Causes with high CF values (7-10) were listed as the most likely,
medium CF values (4-6) were considered likely and low CF (0-3) were categorized as the least
likely. In troubleshooting coloration problems, it seems logical to consider those causes first which
are more likely responsible for the problem under consideration to reduce the time and effort
required to reach a solution.
The combination of expert responses or aggregation into a single value can be challenging.
Since the data involved in this case were numerical in nature (CF), a variety of techniques could
be used to perform the mathematical aggregation. Different statistical techniques can be used to
calculate a single value based on the data. The most commonly used estimators for central tendency
are mean, median, mode and geometric mean. The mean gives equal weight to each expert
response. In this case the extreme value in the expert responses greatly influences the mean value.
This value may not be suitable especially in cases where extreme values are reported or where
values seem unreasonable. The median is the 50th percentile value. It is not influenced by extreme
values but by central values. The geometric mean is the average based on a logarithmic scale. It
can be useful for expert judgments in applications where small values are suitable to fit in a log
scale compared to the linear scale used by the mean. The mode uses the more frequent value in the
data set. The main problem associated with the mode is that a set can have multiple modes. Another
approach involves the use of weighted mean in which expert’s answer is assigned its own weight.
The main challenge is to determine a suitable weight for each expert which requires information
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about how experts reach a particular answer. However, this information is often difficult to obtain.
A simple approach involves assigning equal weights to the expert responses [452].
Table 6.7: An example of different analytical methods that can be applied to aggregate expert
responses in two different scenarios (E=Expert).
Scenario Cause Expert responses Analytical
method Result
E1 E2 E3 E4 E5
A C144: Inadequate
steaming time 8 6 5 8 8
Weighted mean 7
Median 8
Mode 8
B
C053: Precipitation
of anti-migrating
agent
10 8 0 0 0
Weighted mean 4
Median 0
Mode 0
The weighted average with equal weights was found to be a suitable method for
aggregating expert responses in a previous study involving the development of a diagnostic expert
system for the dyeing of protein fibers (Dexpert-PT) [412]. The same approach is used in this
study. Although the weighted mean may be affected by outlier responses experts CF responses are
likely affected by their expertise pertaining to a particular problem and can vary among experts.
The experts who participated in this study were from different sectors with many years of
experience and had different types of professional experience and education. The use of median
and mode which rely on the central value and the most frequently occurring value may result in
ignoring the highest rating provided by an expert and may change the rank of the cause. The use
of the weighted average is more reliable in this case as it gives equal weight to each expert’s
response. The example shown in Table 6.7 illustrates different analytical methods that can be used
to aggregate expert responses. The two scenarios with different expert responses are assessing the
causes of reproducibility (symptom 1) issues in the dyeing of PES/CELL blends by the continuous
method. It can be seen if the response varies widely from one expert to another the median and
475
mode may not provide a good aggregation response. The weighted mean on the hand appears to
provide a better approach as it covers the whole range of responses given by different experts.
All causes associated with reproducibility (symptom 1) in the case of pigment coloration
are shown in Table 6.8. The CF was calculated from 1-10 with fractions rounded off to the nearest
number using a weighted average method. The causes are prioritized based on high (CF 7-10),
medium (CF 4-6) and low (CF 0-3) values using the ranking approach. The cause with the largest
CF is assigned the highest priority among all causes and the associated rule is fired first during
diagnosis. All responses obtained from the experts were analyzed by the same method and
aggregated responses were used in the development of the expert system in this study.
Table 6.8: List of causes associated with the reproducibility symptom after being prioritized
based on the weighted CFs obtained from experts (E represents expert).
Cause Description E1 E2 E3 E4 E5 Weight High
CF
Medium
CF
Low
CF
C001
Errors in the weighing
of colorants and
chemicals
10 10 8 10 8 46 9
C135 Non-uniform air
velocity or flow 10 10 7 10 8 45 9
C137
Too low
thermofixation
temperature
9 7 9 10 8 43 9
C136 Too high drying
temperature 10 5 8 8 8 39 8
C005 Too high colorant
concentration 9 9 8 5 8 39 8
C002 Improper bath
preparation procedure 9 7 5 8 29 7
C140 Too short
thermofixation time 5 7 10 6 28 7
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Table 6.8 (Continued)
Cause Description E1 E2 E3 E4 E5 Weight High
CF
Medium
CF
Low
CF
C075 Machine stoppage for
a long duration 5 6 8 5 7 31 6
C128 Uneven wet pickup 5 10 8 0 8 31 6
C052 Low quantity of anti-
migrating agent 5 5 7 17 6
C127
Improper distribution
and circulation of dye
liquor
5 6 5 6 22 6
C078 Excessive foaming in
the dye bath/trough 5 5 6 16 5
C125 Too high wet pickup 5 6 5 16 5
C015
Crust formation in
pigments during
storage
5 5 5 6 21 5
C016 Poor pigment
dispersion system 5 5 5 15 5
C053 Precipitation of anti-
migrating agent 5 5 10 5
C134
Variation in the
intensity of the IR
pre-dryer
5 5 10 5
C141 Temperature variation
in the hotflue 0 10 5 5 20 5
C179
Fabric rolls from
different knitting or
weaving machines or
batch or factory
5 5 5 15 5
477
Table 6.8 (Continued)
Cause Description E1 E2 E3 E4 E5 Weight High
CF
Medium
CF
Low
CF
C162 Inadequate whiteness
of the substrate 2 7 5 14 5
C036
Chemical or physical
interaction between
colorants and
auxiliaries
5 0 7 12 4
C049
Inappropriate
concentration of
dispersing agent
5 0 7 12 4
C163 Improper heat setting
of substrate 5 2 5 5 2 19 4
C157
Incomplete removal
of fats, waxes, spin
finishes, and knitting
oils
2 5 4 0 5 16 3
C126 Too low wet pickup 3 4 2 9 3
C173
Presence of heavy
metals (Cu, Fe, Mn,
Zn) in water
2 3 5 3
C174 Presence of suspended
matter in water 2 3 5 3
C175 Presence of
bicarbonate in water 2 3 5 3
C176 Presence of chlorine
in water 2 3 5 3
C164 Fiber damage during
heat setting 2 2 1 2 5 12 2
478
Table 6.8 (Continued)
Cause Description E1 E2 E3 E4 E5 Weight High
CF
Medium
CF
Low
CF
C59 Catalytic damage
during bleaching 2 3 2 7 2
C157
Incomplete removal
of sizing agents and
sizing wax
2 2 0 5 9 2
C149 Fiber damage during
singeing 2 1 2 0 5 10 2
C172
Presence of Ca and
Mg ions (hardness) in
water
2 3 0 3 8 2
C014 Poor pigment
selection 0 0 5 5 2
C169
Alkaline pH of
substrate before
dyeing
2 2 0 2 6 2
C180 Yarn mixing 3 0 1 4 1
C166
Fiber damage during
scouring and
bleaching
2 0 2 1
There are many causes that may be responsible for a specific coloration problem. Similarly,
a single cause can lead to multiple problems. Therefore the commonness of causes among
symptoms along with their origin category was analyzed. The example given in Table 6.9 shows
the most likely causes selected by experts for unleveleness (S2) in continuous dyeing with
pigments. It can be seen that the cause C128: uneven wet pickup is also the most likely cause of
reproducibility (S1), streaks or stripes (S3), poor color yield (S4) and lengthwise shade variation
(S9).
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Table 6.9: Analysis of causes according to category and commonness.
Cause Description High
CF Category Commonness
C128 Uneven wet pickup 10 G S1, S3, S4, S9
C002 Improper bath preparation procedure 9 A S1, S5, S7, S9, S10,
S18
C039 Agglomeration of binder 8 C S4, S7-S8, S18
C125 Too high wet pickup 8 G S5, S10, S18
C005 Too high colorant concentration 7 B S1, S4, S6a, S7, S9,
S10, S18
C036 Chemical or physical interaction
between colorants and auxiliaries 7 C S7, S18
C135 Non-uniform air velocity or flow 7 G S1, S3, S10
C052 Low quantity of anti-migrating agent 7 C S4
C157 Incomplete removal of fats, waxes, spin
finishes and knitting oils 7 H S4
C134 Variation in the intensity of the IR pre-
dryer 7 G S5, S10
C151 Incomplete removal of sizing agents
and sizing wax 7 H S4
6.7 Construction of a diagnostic expert system for dyeing of fiber blends
(DEXPERT-B)
The functional knowledge-based expert system, DEXPEPRT-B has been developed to diagnose
problems in the coloration of fiber blends (DEXPERT-B). The system is designed to determine
the root cause(s) of the most common faults specifically in the coloration of PES/CELL blends
using pigments and dyes.
DEXPET-B has been organized with three components to perform its diagnosis. The
system architecture of DEXPERT-B is shown in Figure 6.30: System architecture of DEXPET-B.
480
. The direction of arrows indicates the path of flow of information.
▪ Component A- Interface: The system consists of four interfaces. The first interface is
designed to seek material related information from the end-user which includes fiber
types, blend ratio, and material form. The fiber types can be selected from the two
groups provided. Each group contains six fibers, polyester and five cellulosic fibers
namely cotton, viscose, modal, lyocell, and linen. Different combinations of polyester
with cellulosic fiber types can be selected in any order. Three material forms: yarn,
knitted fabric, and woven fabrics are provided. After the material selection is performed
the information about the coloration process is required from the end-user in the second
interface. The user selects the corresponding colorants according to fiber type, dyeing
process, method, and machines. The third interface enables the user to select the
corresponding coloration faults based on the selections made in the first two interfaces.
The material and coloration selections lead to the initial sorting of the symptoms. The
fourth and final interface shows the selected material, coloration process, and selected
symptoms by the end-user. This interface also interacts with the end-user to perform
diagnosis through a series of questions. The interface is shown in grey color.
▪ Component B- Inference: During this process, the facts inserted by the user in the first
component are evaluated and compared based on the rules coded in the knowledge
base. The material, coloration, and symptoms selected by the user (facts) are analyzed
and compared with the knowledge base containing rules for causes related to
symptoms. The rules satisfied by the analysis are prioritized and fired to initiate the
queries for diagnosis.
▪ Component C- Diagnose: This component asks appropriate questions from the user
through a dialog box based on the prioritized rules which are fired in Component B.
The system starts with the most likely causes for troubleshooting to facilitate a quick
resolution of the problem. The end-user is provided with an option to display all
possible suggested causes for the symptom. The system is also provided with an
explanation facility based on the causes selected by the user through an Explanation
button.
481
Figure 6.30: System architecture of DEXPET-B.
6.7.1 Expert system building tool
These include the programming language and the support package used to build the expert system.
Experts systems are often built from scratch using specialized expert system languages.
Specialized software products are available that provide the methodology and system tool that can
be used to build an expert system. The structure for coding the knowledge base and inference
engine is provided in such systems. These software products provide two basic functions. First,
they provide the development environment for building an expert system and second they support
a delivery system that allows the end-user to actually use the system [453].
482
The coloration expert system for fiber blends (DEPXERT-B) was developed using wxCLIPS
(version 1.64), a modified version of expert system tool CLIPS (version 6.0), developed to allow
portability and graphical user interface that can run under windows environment.
CLIPS is an acronym for C Language Integrated Production System. CLIPS is an expert
system programming language which is available as an open-source software. Its source code is
well documented. It was developed at NASA in the mid-1980s and was originally written in C.
CLIPS is a rule-based language that is specifically used for developing an expert system. A CLIPS
program consists of facts, knowledge-base, and an inference engine. Facts are data or information
and represent the current state of the problem. The knowledge base contains all the rules which
are fired based on facts. The inference engine works by matching facts against the rules, choosing
which rule to fire and executing the actions. It takes a decision based on rule matching and rule
priorities [13, 16].
In wxCLIPs, the structure of CLIPS is modified to include GUI functions. Essentially
wxCLIPS is a combination of CLIPS and wxWindows. The wxWindows enables GUI
functionality in the CLIPS. wxCLIPS is also available as an open-source software and was
developed by Julian Smart at the Artificial Intelligence Applications Institute, University of
Edinburgh, UK in the 1990s [454].
6.7.2 Knowledge representation
The knowledge representation step deals with steps involved in setting up methodology for storing
facts and rules in the knowledge base. It represents how knowledge is structured in a knowledge
base [453, 455]. The knowledge can be represented using standard sets of techniques. The
technique helps in making a program more efficient, easy to understand and easy to modify.
Different techniques can be used such as rules, semantic nets, frames, etc. The knowledge
representation based on rules uses IF condition THEN action statements. When the current
situation matches the IF part of a rule the action specified by THEN part of the rule is carried out.
These rules can be of different nature such as obtaining responses from the end-user, may cause a
particular set of rules to be tested and fired based on the end-user input or may instruct the system
to reach a conclusion based on the rules satisfied [453].
In rule-based expert systems also known as production systems, the knowledge domain is
represented in the form of rules. The rules are statements that define the relationships between the
483
facts. The information related to the current problem or situation (facts) is checked against the
rules. The rules whose IF portion are satisfied by the facts fire the action in the THEN portion of
the rule. The IF portion of rules in the system is compared with facts by a rule interpreter. Matching
of facts with the IF portion of the rule leads to the execution of that rule [453]. The IF statement
of the rule may consist of several conditions. These conditions are joined by connecting words
AND and OR, depending on the condition. The rule is then executed IF all conditions (AND) or
any of the (OR) conditions of the rule is satisfied [455].
A knowledge engineer must select a way for the reasoning to reach a conclusion in the
expert system based on the rules and facts stored in the knowledge base. To search for the solution
of a problem, a statement for a problem is required. An expert system should be designed in such
a way to take this problem and break it down into small sub-problems [455].
In CLIPS the rules are represented as follows:
(defrule <rule-name>
pattern-1 ... pattern-n ; Rule Properties; Left-Hand Side (LHS)
=>
action-1 ... action-m) ; Right-Hand Side (RHS)
The header of the rule consists of three parts. The rule must start with a defrule keyword
followed by the name of the rule. Then there are (zero or more) conditional elements which are
called patterns. Each pattern has one or more constraints intended to match the fields. CLIPS
attempts to match the pattern against the facts list. If the pattern of the rule matches all facts, the
rule is activated and placed on the agenda which is a collection of activated rules. CLIPS
automatically determines which rule to fire based on the priority called Salience [16].
The example given in Figure 6.31 illustrates how rules are coded in CLIPS for the
development of DEXPERT-B. In this example the user selected the lengthwise shade variation as
the symptom, woven fabric as the material type, pigment as colorant, and pad-thermosol process
as the dyeing method. When all the conditions of rules are matched, the rule is activated and the
system will insert “uneven pickup” as the mostly likely cause. Since the coloration problems are
usually due to multiple causes, as shown, the system needs to assess various possible causes and
identify them in the initial stage to diagnose the possible causes of the problem. In this case
continuous dyeing, bath preparation and colorant are the categories. The continuous dyeing
category is further divided into sub-categories padder, pre-drying and hotflue. The descriptions
484
under these sub-categories represent the most likely causes for the symptom which in this example
are uneven wet pickup, variation in the intensity of the IR pre-dryer and non-uniform air velocity
or flow respectively.
Figure 6.31: Knowledge representation in DEXPERT-B in the form of rules.
6.8 Inference engine
The collection of problem-solving processes is called the inference engine. The inference engine
can be a part of the coded language, or separately designed and implemented. The use of the latter
approach provides an option to organize the inference strategy [453]. Although the knowledge
base and inference engine complement each other they are separate and distinct parts of the expert
system. The knowledge base can be replaced with new rules and facts and the inference engine
can then be used for the new knowledge base [455].
An inference engine is a complex program. It consists of two main components: an
inference mechanism and control mechanism [455]. The inference mechanism contains the
reasoning approach used by the expert system to develop new facts based on existing or established
facts. It decides how to apply rules based on facts to infer a new knowledge. The control
mechanism decides the order for rule execution. It is a technique for controlling its reasoning
process. The two most common control strategies are backward chaining and forward chaining
[453, 455].
(defrule PC-pigment
(Lengthwise shade variation)
(Woven fabric)
(Pad-Thermosol)
=>
(assert (uneven wet pickup))
)
Lengthwise shade variation
Continuous dyeing
Padder
Uneven wet
pickup
Pre-drying
Variation in the
intensity of the IR pre-
dryer
Non-uniform air
velocity or flow
Hotflue
Bath preparation Colorant
485
The study of making valid inferences is called logic. An inference can be valid depending
on the conclusion it reaches based on the facts that are either true or false [16]. The knowledge can
be represented symbolically in the form of proposition logic. The proposition refers to statements
that can either be true or false. In propositional logic, it is checked whether a statement is true or
false by comparing it to known facts and rules that are available for manipulating these facts. The
conclusion can be reached by combining several propositions together. The propositions can be
combined using logical operators such as AND, OR, NOT, etc. The relationship between two or
more statements can be defined with the help of predicate logic [455].
In CLIPS the inference engine controls the overall execution of the rules. The working
memory may contain one or many facts at the same time. The facts in the working memory have
no interaction with each other. The inference engine compares each rule in the knowledge base
with the facts in the working memory. If the IF part of the rule is satisfied by the facts, then the
THEN action part of the rule is accomplished, and the rule is placed on the agenda. The rule may
contain multiple patterns and these patterns must be simultaneously matched to execute the rule.
A rule is said to be activated whose patterns are satisfied. An agenda may contain multiple
activated rules at the same time. The inference engine then decides which rule to fire. Rule based
expert systems are designed to prevent trivial loops. When the rules fire the list of actions is
executed in the THEN part of the rule. The inference works in a way that is known as recognize-
act cycles. The inference will repetitively perform the groups of tasks until certain termination
criteria is reached which causes execution to stop. This criterion is known as conflict resolution.
The inferences accomplish tasks based on the priority. The task with a high priority will be
executed first followed by a task with the second-highest priority until no activation is left in the
agenda. When the rule is satisfied it is put on the agenda. When the rule fires a new fact may be
obtained which is added to the working memory. The inference chains are obtained by firing rules
which determine how expert systems reach a conclusion. Conflicts may occur on the agenda while
activating different rules that have the same priority. In CLIPS the rules have the same default
priority unless assigned by the knowledge engineer [16].
Different strategies can be used to deal with conflict resolution in CLIPS using certainty
factors and salience. In real-world scenarios, human experts are often not completely sure of their
information. Sometimes they try to reach a conclusion based on the limited information available.
The expert system must be able to deal with uncertainty. One way for the expert system to deal
486
with uncertainty is by using certainty factors. The certainty factors (CF) represent uncertainty
numerically using some type of scale. The scales can be from 0 to 5, 0 to 100 or -1 to +1, etc. The
higher value of the scale represents the higher confidence in the answer while the lower value
shows lower confidence. In CLIPS the CF ranges from 0 to 1 [16, 455].
Another approach that can be used to deal with uncertainty is salience. Salience allows the
priority of the rules to be defined using a numerical value. The higher the salience value of
activated rule the higher will be its order on the agenda regardless of when it is activated. This
allows more important rules to stay on top of the agenda and be fired first. The salience can range
from -10,000 to 10,000. The rules with no explicitly defined salience are assigned a neutral salience
value of 0. This does not imply the rule has no salience value since 0 denotes the middle value of
the salience range. The salience allows the rules to be fired in a sequential order [16]. The salience
approach was used in developing DEXPERT-B.
CLIPS has seven conflict resolution strategies built in the system to determine the
execution order of the rules that have the same salience. These include depth, breadth, simplicity,
complexity, lex, mea, and random. The default strategy used by CLIPS is depth in which a newly
activated rule is placed above all the rules of the same salience [454].
The interface of the expert system in this study was designed to enable the end-user to
select more than one symptom, if desired. This is to address the practical possibility of having a
faulty dyed fabric that may exhibit more than one symptom. In an extreme case, a user may select
all displayed symptoms. This was made possible in the system by using a dynamic salience
approach. The other reason to adopt a dynamic salience was to rapidly fire the rules for the most
likely causes of all symptoms based on the selection by the end-user. The dynamic salience
approach was applied by separating the rules in the knowledge base with codes. The rules are
coded in a separate file and can be called when required. The dynamic salience applied in the
development of the system is based on the summation of weighted average values obtained from
the expert responses.
In the user interface designed for DEXPERT-B, the observer was provided with the option
to select the symptom from a list of symptoms based on the material and coloration process
selections. The survey consists of 18 symptoms and 196 possible causes. The causes in the
knowledge base were defined as single rules with salience values defined as global variables at the
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beginning of the ‘diagnose’ module. The default values were set to zero. The rules are saved in a
separate file. The structure of the rules is given below:
(defrule cause001
(declare (salience ?*salience001*))
(c001)
=>
(ask-question-update causes “question related to cause 1” YES “answer related to cause 1”)
)
……
(defrule cause196
(declare (salience ?*salience196*))
(c196)
=>
(ask-question-update causes “question related to cause 196” YES “answer related to cause 196”)
)
The following example illustrates the actual rule built into the expert system:
(defrule cause001)
(declare (salience ?*salience001*))
(c001)
(ask-question-update-causes "Were the colorants and chemicals weighed accurately?" NO "Errors
in the weighing of colorants and chemicals")
)
Consider a scenario where a user selects symptoms S15 (holes and tears), S16 (poor hand)
and S17 (poor dimensional stability) for a dyed PES/CELL woven fabric. The possible causes and
their weighted average expert responses are given in Table 6.10-
Table 6.12. The causes in bold represent common causes, C166 and C173, among
symptoms S15, S16, and S17.
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Table 6.10: Possible causes for S15 and weighted average CF.
Cause Description CF
C159 Catalytic damage during bleaching 8
C079 Non uniform or damaged machine parts 7
C165 Physical damage of substrate (pin marks, cuts) 7
C177 Presence of holes, tears or cuts in greige substrate 7
C153 Fiber damage during scouring and bleaching 5
C166 Excessive overstretching of substrate on stenter 4
C081 Longer duration of substrate run due to reprocessing 4
C193 Foreign fiber contamination 4
Table 6.11: Possible causes for S16 and weighted average CF.
Cause Description CF
C164 Fiber damage during heat setting 8
C081 Longer duration of substrate run due to reprocessing 7
C153 Fiber damage during scouring and bleaching 7
C151 Incomplete removal of sizing agents and sizing wax 6
C094 Presence of oligomer deposits on the substrate surface 5
C158 Inadequate weight reduction of polyester 5
Table 6.11 (Continued)
Cause Description CF
C159 Catalytic damage during bleaching 5
C073 Too high drying temperature 4
C138 Too high thermofixation temperature 4
C139 Too long thermofixation time 4
C154 Too high weight loss during scouring 4
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Table 6.12: Causes for S17 and weighted average CF.
Cause Description CF
C163 Improper heat setting of substrate 8
C166 Excessive overstretching of substrate on stenter 7
C080 Excessive, insufficient or variable tension during fabric run 6
C081 Longer duration of substrate run due to reprocessing 6
C153 Fiber damage during scouring and bleaching 6
C155 Insufficient relaxation of the substrate during washing 6
C180 Yarn mixing 5
C191 Lower yarn strength & elongation 5
C154 Too high weight loss during scouring 4
C164 Fiber damage during heat setting 4
Based on the selections, the system will run the following code to assert the causes. It can
be noted that default salience values of all causes are zero and when new causes are asserted their
specific salience value are added into the existing salience value. Symptom S15 is presented here
as an example.
(if (neq ?*factsymptom15* 0) then
(bind ?*salience159* (+ ?*salience159* 8))
(bind ?*salience079* (+ ?*salience079* 7))
(bind ?*salience165* (+ ?*salience165* 7))
(bind ?*salience177* (+ ?*salience177* 7))
(bind ?*salience153* (+ ?*salience153* 5))
(bind ?*salience193* (+ ?*salience193* 4))
;;;asserting likely and most likely causes
(bind ?*salience159* (assert (c159)))
(bind ?*salience079* (assert (c079)))
(bind ?*salience165* (assert (c165)))
(bind ?*salience177* (assert (c177)))
(bind ?*salience153* (assert (c153)))
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(bind ?*salience193* (assert (c193)))
Similarly causes related to S16 and S17 will be inserted into the system. As mentioned
earlier the system calls the related saliences and adds up their values. For example, the resultant
salience value for C153 would be 5+7+6=18. The resultant salience of a total of 22 causes is given
in Table 6.13. The number of questions that needs to be answered is increased to 22 questions in
this case and can be increased considerably if more causes are selected.
Table 6.13: The new salience values of the all the cause asserted for S15-S17.
Cause Description CF
C153 Fiber damage during scouring and bleaching 18
C081 Longer duration of substrate run due to reprocessing 17
C159 Catalytic damage during bleaching 13
C164 Fiber damage during heat setting 12
C166 Excessive overstretching of substrate on stenter 11
C163 Improper heat setting of substrate 8
C079 Non uniform or damaged machine parts 7
C165 Physical damage of substrate (pin marks, cuts) 7
C177 Presence of holes, tears or cuts in greige substrate 7
C080 Excessive, insufficient or variable tension during fabric run 6
C151 Incomplete removal of sizing agents and sizing wax 6
C155 Insufficient relaxation of the substrate during washing 6
C094 Presence of oligomer deposits on the substrate surface 5
C158 Inadequate weight reduction of polyester 5
C180 Yarn mixing 5
C191 Lower yarn strength & elongation 5
C073 Too high drying temperature 4
C138 Too high thermofixation temperature 4
C139 Too long thermofixation time 4
C154 Too high weight loss during scouring 4
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Table 6.13 (Continued)
Cause Description CF
C154 Too high weight loss during scouring 4
C193 Foreign fiber contamination 4
In scenarios like these where a user can select more than one symptom, the questions that
need to be answered by the end-user are increased considerably. To deal with such scenarios the
threshold salience values were defined at the beginning of each rule. Since salience values are
dynamic the threshold values should also be dynamic. With a constant value it is possible to disable
the rules that are required to be fired. The approach used to deal with such cases is based on the
principle of checking the maximum salience value of the selection and dividing it by 2. The system
considers this value as a threshold and compares the actual value of the salience with the threshold.
The rule is only fired if the actual value is greater than the threshold. This allows the end-user to
access the most likely causes and find the root cause of the symptom as quickly as possible. The
use of half of the maximum salience value as threshold allows the upper half of the most likely
rules to be fired. In cases where only one symptom is selected by the end-user the threshold values
allow all of the most likely rules to be fired. The new version of the rule is given below:
(defrule cause001
(declare (salience ?*salience001*))
(c001)
(test (> ?*salience001* (/ (max ?*salience001* ?*salience002* ….. ?*salience196*) 2)))
=>
(ask-question-update-causes " question related to cause 1" YES "answer related to cause ")
)
6.8.1 Effect of blend ratio
This study aims at troubleshooting coloration problems for PES/CELL blends. One important
factor that may determine the dyeing properties of the material is the blend ratio. These properties
may change when the blend ratio is changed. In general, the PES/CELL blends with different blend
ratios are processed in similar machinery and using the same processes. The process parameters
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and conditions are also usually kept the same for ease in processing. Specific changes required
based on the blend ratio are usually small and the process parameters and conditions are usually
optimized to cover a wide range of conditions. This is due to the fact that a change often requires
a long adjustment time and may not be practical or feasible due to production conditions. Thus, in
practical terms, there is almost no difference in process parameters and conditions for a 50/50
PES/CELL blend when compared to 65/35 or 35/65 blends. However, when the share of one fiber
is increased such it gets very close to the 100% fiber, the dyeing properties may change drastically.
For example, in PES/CELL blends with very high polyester content more precautions are required
for processing the polyester component as compared to the cotton component of the blend as PES
determines the main properties. Similar results may also be obtained for a PES/CELL blend with
a higher cotton component.
Thus, the effect of the blend ratio was incorporated in the system rules. For this, the fiber
groups were divided into three categories, namely polyester rich or PC1, polyester/cotton or PC2
and cotton rich or PC3. As the name implies this division is based on the blend ratio of the
respective portion of each fiber component in the material. The PES/CELL blends with a blend
ratio of 75/25 or above are placed in the PC1 group while the PES/CELL with a blend ratio of
25/75 or less is placed in the PC3 group. Blend ratios within the two are placed in the PC2 group.
This is in relation to the results reported in CHAPTER 5 where it was shown that blends with very
high ratio of one fiber exhibited properties similar to the 100% fiber. Table 6.14 shows the
aggregated responses of the most likely cause of causes of symptom 1 (reproducibility) of a fabric
dyed using disperse/reactive dyes by a batch process. The PC2 represents the aggregated responses
of experts obtained from a survey for a polyester/cellulosic blends. The causes that may affect
dyeing properties of the respective fiber in the blend are selected based on the importance of these
causes when 100% fiber is dyed. These are represented as P and C. The P and C represent causes
that are more important when processing 100% polyester and 100% cotton respectively. As the
portion of a fiber in the blend is increased, the causes become more important for the dyeing of
that specific fiber. As the rules in the expert system are fired based on their priority, the causes that
have a larger effect on the symptom should have a higher priority. To incorporate this strategy into
the design of rules in the expert system, the salience values of the causes that directly affect the
symptoms based on the given blend ratio are increased. As the causes in the most likely (CF 7-10)
category have a salience range of 4, the salience values of all causes that may affect the symptom
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based on the blend ratio of material are increased by 4. For example, if a cause C008 has a salience
of 8 in PC2, its new salience value in PC3 (higher cotton content) will be 12. This results in a
change in the firing sequence of causes as shown in columns PC1 and PC3 in Table 6.14 The
causes C007 and C008 have the same priority in PC2 but as the blend ratio is increased C007 has
a higher priority in PC1 and C008 will be fired first in PC3. This strategy was incorporated for all
symptoms during the development of rules in this expert system.
Table 6.14: Mostly likey causes for S1 reproducibility with existing and new salience values as
the blend ratio is increased.
Cause Description P C PC2 PC1 PC3
C001 Errors in the weighing of colorants and chemicals 9 13 13
C003 Too fast/quick addition of chemicals in the bath 8 12 12
C007 Poor dye selection for polyester component P 8 12 8
C008 Poor dye selection for cellulose component C 8 8 12
C082 Variations in dyeing program 8 12 12
C096 High temperature rise rate 8 12 12
C135 Non-uniform air velocity or flow 8 12 12
C087 Inappropriate liquor flow times (in-out and out-in) 7 11 11
C140 Too short thermofixation time 7 11 11
C097 Inappropriate dyebath pH 7 11 11
C179 Fabric rolls from different machines or batch or factory 7 11 11
C002 Improper bath preparation procedure 7 11 11
C004 Too fast/quick addition of dyes in the bath 7 11 11
C010 Variation in colorant strength 7 11 11
C011 Incompatibility between dye classes 7 11 11
C019 Poor disperse dye dispersion stability P 7 11 7
C027 Poor stability of reactive/direct dyes under polyester
dyeing conditions C 7 7 11
C034 Poor color matching of each fiber in the blend 7 11 11
C092 Too large batch size (machine overloading) 7 11 11
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Table 6.14 (Continued)
Cause Description P C PC2 PC1 PC3
C100 Too low dyeing temperature 7 11 11
C128 Uneven wet pickup 7 11 11
C133 Differences in fixation temperature or time during
batching C 7 11 11
C137 Too low thermofixation temperature 7 11 11
C143 Inadequate steaming temperature 7 11 11
C144 Inadequate steaming time 7 11 11
C145 Variation in steam pressure inside the steamer 7 11 11
C167 Incomplete mercerization C 7 7 11
C009 Poor dye combinations for each fiber type 7 11 11
C104 Too short dyeing time 7 11 11
C136 Too high drying temperature 7 11 11
C099 Use of too high liquor ratio 7 11 11
C109 Incorrect liquor flow direction 7 11 11
C184 Uneven package density 7 11 11
P: Causes having more effect on the symptom in polyester rich blends
C: Causes having more effect on the symptom in cotton rich blends
6.9 User interface
The user interface is one of the important components of an expert system and a prerequisite for
the success of the expert system. It allows communication between the expert system and the end-
user. The end-user is a person who consults the expert system to solve problems. The interaction
can be in the form of dialog boxes, command prompts, forms or other input methods. In the
development of the user interface, it is important to consider the needs of the user and the tasks
the system is expected to support [456]. The user interface serves two main aspects of the expert
system. The first aspect is a process and problem-specific information. This allows the user to
input the details about the problem and process in the expert system which are used to form the
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basis for the diagnosis. The second aspect is the explanation facility in which the expert system
provides a solution to the problem based on user input along with an explanation [16].
In the development of DEXPERT-B system, the knowledge acquisition from the end-user
includes the material information, and details about the coloration process and symptoms. The
output includes the possible causes of the selected symptoms and explanation pertaining to the
diagnosis. The user interaction starts with the first window of the system as shown in Figure 6.32.
It is a window that provides the end-user with some information about how to run the program
through the help menu and start the program.
Figure 6.32: The main screen for the DEXPERT-B system.
6.9.1 Material function
After the end-user starts the program, a new window appears which deals with the material
function. The material function window is shown in Figure 6.33, where the user is prompted to
provide information pertaining to the material. Three options are provided to the user for selection.
The first option is to select the fiber type from the list of fibers provided. Two dropdown menus
(Fiber 1 and Fiber 2) are provided and the user can select the fiber type in any order. The second
option needs information about the blend ratio of the material (Fiber 1 ratio and Fiber 2 ratio). For
this, a slider is provided and the blend ratio can be selected by moving the slider. The sliders are
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interlinked and changing the blend ratio for one fiber will automatically change the blend ratio of
the other fiber. The third option in the material window is the selection of the substrate type, where
the user can select either yarn, or knitted fabric or woven fabric. After making all selections the
user needs to click the Next button to move to the coloration interface window. If any of the
required information is missing a warning dialogue box appears which asks the user to provide the
missing information.
Figure 6.33: Interface for the selection of material related information.
6.9.2 Coloration function
The coloration function window is shown in Figure 6.34. The window is designed to attain
pertinent information from the user about the coloration process. The available options are mapped
based on the information provided in the material window. In this window, four options are
provided, namely, colorants for each fiber type, dyeing process, dyeing method used and the
machinery. All the options are interlinked, and the end-user is prompted to select the options in
order. Under the colorant option, the various colorants that are applicable to the fiber type are
provided. The colorant options are interlinked based on the knowledge about the coloration
process. For example, if the user selects pigment as the colorant for fiber 1 the system
automatically selects pigment as the colorant for fiber 2 also. The second option deals with the
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dyeing process. The user is prompted to select either a batch, semi-continuous or continuous
process. As some colorants are not applied or cannot be applied through certain dyeing processes
the user is prompted if a wrong selection is made. The third option prompts the user to select the
desired dyeing method, either 1-bath or 2-bath, for the application of colorants and for the dyeing
process selected. In the fourth section, the list box of appropriate coloration machines is
automatically populated based on the information provided by the user in the first three selections.
When multiple choices are available the user is prompted to select the desired machine. Once all
selections are made, the user can proceed to select symptom(s) by clicking the Continue button.
Figure 6.34: Interface for the selection of the coloration process in DEXPET-B.
6.9.3 Symptom function
In order for the expert system to generate accurate results, the end-user must be capable of mapping
the observed symptoms. To facilitate the end-user’s task in selection of the symptoms and to
improve the likelihood of correctly answering the diagnosis questions images showing various
dyeing problems were incorporated in the expert system’s interface. DEXPERT-B contains a total
of 18 faulty dyed sample images. These images are from real faults and were added to improve the
end-user's ability to better categorize and select the symptoms. This also serves as a basis for better
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and more accurate diagnosis of the problem by applying the reasoning process to the selected
symptom(s). Various interfaces for symptoms based on the material and coloration selection are
shown in Figure 6.35 to Figure 6.37.
An end-user can select a minimum of 1 symptom to a maximum of 18 symptoms
simultaneously. A user can only proceed to diagnosis if at least 1 symptom is selected. Changes in
the selection of symptoms images can be made by clicking the same image again to deselect the
image or by using the reset button provided in the symptom window which removes all selections.
Figure 6.35: The user interface containing images of the faulty dyed PES/CELL yarns.
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Figure 6.36: The user interface containing images of the faulty dyed PES/CELL knitted fabric.
Figure 6.37: The user interface containing images of the faulty dyed polyester/cotton woven
fabric.
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The interface window for the diagnosis provides two functionalities as shown in Figure
6.38. On the left side of the window, the information pertaining to the material, colorants used,
dyeing process, machine used, and selected symptoms is provided. In the example provided, the
user selects the polyester/cotton woven fabric dyed using disperse and reactive dyes by the one-
bath process in a jet dyeing machine. The right side of the window provides the diagnosis and the
most probable causes(s) of the symptoms. On pressing the diagnosis button a series of questions
are promoted pertaining to the causes that may be responsible for the symptom(s) under
consideration, as shown in Figure 6.39. Based on the end-user response to these questions the
probable causes responsible for the symptom will be shown under suggested (causes). The detailed
questions related to diagnoses are given in Appendix B. The end-user is also provided with an
option to view all possible causes responsible for the specific symptom(s).
Figure 6.38: Diagnosis interface for woven fabric dyed by batch process using one bath process
in a jet dyeing machine.
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Figure 6.39: An example of the diagnosis function with a question prompt based on the selected
symptom.
6.9.4 Explanation function
The expert system reaches the conclusion for the selected problem(s) by inference. An explanation
function provides reasoning for a particular cause(s) associated with the selected symptom(s).
Many expert systems provide this functionality so that the end-user understands the reasoning
process. In DEPXPERT-B this is implemented by using the “Explain” option after diagnosing the
symptom. Explanation option can be selected from the suggested causes(s) to obtain additional
details. The explanation provides the reason for how this cause is responsible for a particular
symptom(s) and thus providing a better understanding of the process and how to prevent them
from occurring in the future. An example of the explanation interface is given in Figure 6.40.
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Figure 6.40: Example of explanation function for DEXPET-B.
6.10 Using the designed expert system
DEXPERT-B can be run on any windows environment after installing the wxclips application.
The procedure for installation and running the software is given in Appendix C. Different options
are provided to facilitate the use of the program. The user is provided with the option to go back
and change their selections using the “Back” button. The user selections from the preceding
interface windows are shown and the end-user can make the required changes. A “Reset” button
is provided to reset all selections on a particular interface. A “home” button provides the
functionality if the end-user wishes to run the program again from the start. The help option is also
provided to guide the end-user on how to use the interface and select the provided options.
An example of polyester/cotton woven fabric, pigment colored using pad-thermosol
machine is given in Figure 6.41. The end-user selected dark stain or spots (S06) as a symptom. By
clicking the diagnose button the system initiates a series of questions related to specific selections.
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Figure 6.41: An example of the use of DEPXET-B system for diagnosis.
Step 1 Step 2
Step 3 Step 4
Step 5
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CHAPTER 7 TESTING AND EVALUATION OF AN EXPERT
SYSTEM
7.1 Testing of the expert system
Expert systems are computer programs designed to mimic human expert cognitive problem-
solving capabilities. Human experts acquire those capabilities that are garnered through training,
experience, and intelligence. During the development of an expert system, the focus is usually to
extract the knowledge and skills from the domain experts and compile them in the form of a
knowledge base. Expert systems tend to evolve over time. Once the expert system is developed, it
needs to be reviewed, analyzed and tested to ensure a quality system is produced. This whole
process is known as verification, validation, and testing. Verification involves checking the system
against a set of requirements. It is mainly concerned with the structure and form of the system. It
is a process of checking if the expert system is made correctly. The validation is a process of
checking for the correctness of the expert system. It determines if the right product is being made.
Validation is concerned with the behavior of the expert system. Testing involves the examination
of the expert system program by execution on a small dataset. The testing phase determines the
correctness of the expert system [457]. The quality of the expert can also be checked through
evaluation, which involves a testing system for its usability and usefulness [458].
Verification is a process of checking the expert system for its consistency, completeness,
accuracy, and correctness. It involves checking the knowledge base and inference engine. The
main aim is to remove errors in the system. The types of errors that occur in the expert system are
related to the knowledge representation scheme and methods of dealing with conflict resolution
during inference. Verification therefore involves checking the rules and codes for any errors and
making sure, they are correct [458]. This is mostly concerned with the structure or form of the
expert system. The verification process can be considered to be analogous to the paper activity
[16, 457].
Validation is a process to determine if the chain of correct inferences is responsible for
getting the right answer. It is concerned with the model of the expert system. It aims to determine
the quality of the decisions made by the expert system. It is independent of technology or software
used to implement the system. It involves checking the final product and determining if the output
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is meeting the required target. It is an activity that involves testing. Test cases are used to compare
the conclusions obtained from the experts and the expert system [16, 457, 458].
Evaluation deals with value of the expert system. The value of the system depends on its
acceptance by the end-user and its performance during use. During the evaluation phase the system
is assessed against different criteria such as user-friendliness and usefulness by a potential user.
An expert system that is already verified and validated may fail during evaluation if it is found to
have no value to the end-user or it is difficult to use or if it solves something that is rarely required
in practice [459].
7.1.1 Verification
The construction of an expert system is a programming task that involves coding of rules in the
knowledge base and the inference engine. During the verification process, the rules and their
structure are verified for anomalies. The verification checks the technical aspects of the expert
system that can be performed by the developer or knowledge engineer [458].
DEXPERT-B was verified during the development phase and after the complete
development of the final program. Verification of the system was performed using the following
approaches:
▪ Reviewing and proofreading the knowledge base and inference rules for syntax and
correct logic and making revisions if and when required. This involved checking the
system for consistency, completeness, and correctness [458].
▪ Checking the results obtained from the expert system using sample cases and
comparing it with the knowledge obtained from various sources during the knowledge
acquisition step. This is known as a domain dependent verification [458].
▪ Checking the system for anomalies which involves the unusual representation of
knowledge scheme. This is known as domain independent verification. Anomalies can
be of different types that include duplication, inconsistency, looping and
incompleteness [458, 460].
▪ Examining system for incorrect or incomplete input from the end-user. This involves
checking the working of the rules if incorrect input or combination is selected by the
end-user or required information is missing.
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7.1.2 Validation
The validation of DEXPERT-B was performed using actual faulty colored samples acquired from
Lucky Textile Mills in Pakistan and ACS Textile Mills in Bangladesh. The faulty dyed samples
were taken randomly from the dyed fabric rolls during the inspection process. The dyed fabric roll
was examined for faults during the inspection process and the faulty portion of the fabric was cut.
These faulty samples were then segregated based on the nature of the faults. They comprised
seventeen faulty PES/CELL samples that were colored either using pigments or dyes by batch and
continuous processes. These samples were examined by a number of coloration experts to obtain
their opinion pertaining to the root cause of faults in these samples. The samples presented to
experts for examination were ironed to remove creases. Five experts with a broad range of
experience in coloration and research took part in this validation phase. These responses were then
used to validate the knowledge base of DEXPERT-B.
Experts were provided with the categorized list of possible causes along with faulty colored
samples to suggest most likely causes responsible for the occurrence of each fault. The experts
were also provided the colorants and process related information. The responses obtained were
then analyzed to perform the validation process. During validation, the possible causes suggested
by the experts were compared to the knowledge base developed using expert responses and the
literature obtained during the knowledge acquisition phase of DEXPERT-B development.
Expert responses for the diagnosis for one of the symptoms “holes and tears” (S15) are
given in Table 7.1. The left side of the table shows the expert system knowledge base along with
the weighted average response. The right side of the table shows the responses from the individual
experts who participated in the validation stage. Expert responses were mostly consistent among
experts and most selected response was referred to catalytic damage during bleaching (C159) as
the most likely cause of the problem. This was also the most likely cause according to the expert
system knowledge base. The majority of the experts also selected a longer duration of substrate
run due to reprocessing (C081) as one the causes that may be responsible for the occurrence of
holes in the observed sample. No experts selected foreign fiber contamination (C193) as one of
the cause that may be responsible for the holes.
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Table 7.1: Expert responses and expert system’s knowledge base for presence of holes and tears (S15).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C159 Catalytic damage during bleaching 8 S13, S16 [100, 149, 303, 305,
323] x x x x x
C079 Non uniform or damaged machine parts 7 S3, S14 [149, 150] x x x
C165 Physical damage of substrate (pin marks, cuts) 7 [67, 194, 341] x x
C177 Presence of holes, tears or cuts in greige substrate 7 [203, 216, 250, 259,
261, 272-275] x
C153 Fiber damage during scouring and bleaching 5 S2, S13, S14,
S16, S17 [70] x x
C166 Excessive overstretching of substrate on stenter 4 S14, S15, S17 [194, 341] x x
C081 Longer duration of substrate run due to
reprocessing 4
S13, S14,
S16, S17 [301] x x x x
C193 Foreign fiber contamination 4 S7 [6, 157, 209, 210]
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
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Expert responses for the occurrence of poor color yield, symptom (S4), are shown in Table
7.2. According to the expert system knowledge base, poor color yield in the colored fabric may
occur due to multiple causes. In fact, a total of 30 causes with high and medium certainty factors
may be attributed to this symptom. According to the results obtained from human experts, most
agreed that the “presence of residual alkali/hydro after dyeing cycle” (C072) and “incomplete
mercerization (C167)” were the most probable causes of this symptom. According to the expert
system’s knowledge base, the most likely causes responsible for this symptom included too low
dyeing temperature (C100) which was also chosen by two experts (Expert B and E).
Experts’ responses together with the expert system knowledge base for the symptom S10
“widthwise share variation in pigment colored fabric” are given in Table 7.3. The experts were
very consistent in their response when selecting “uneven pickup” (C128) as the cause which is
also the second most likely cause according to the expert system’s database. Three experts
diagnosed additional possible causes whereas Experts C and D chose only two causes for the
symptom. The expert system, on the other hand, provided 11 likely causes for the symptom.
509
Table 7.2: Responses from human experts and the expert system for poor color yield (S4).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C100 Too low dyeing temperature 9 S1, S2, S6a-c, S11 [297, 301] x x
C048 Inappropriate electrolyte (salt)
concentration 7 S1, S2, S9, S11 [128, 317, 345] x x x
C027 Poor stability of reactive/direct dyes under
polyester dyeing conditions 7 S1, S2, S7
[64, 68, 79, 122,
253] x x x
C072 Presence of residual alkali/hydro after
dyeing cycle 7 S1, S2, S5, S8 [251, 253, 348] x x x
C011 Incompatibility between dye classes 7 S1-3, S5-7, S9,
S10, S11
[7, 9, 79, 92, 93, 100,
128, 253, 301] x x
C019 Poor disperse dye dispersion stability 7 S1, S2, S7, S9,
S10, S11
[7, 67, 68, 75, 79,
81, 85, 253] x x
C167 Incomplete mercerization 7 S1, S2, S3, S9,
S10
[9, 184, 253, 305,
333, 334, 337, 338]. x x x x
C097 Inappropriate dyebath pH 7 S1, S2, S5, S6a-c,
S9, S10, S13 [301] x x x
C018 Poor disperse dye dispersion system 6 S1, S2, S5, S7, S9,
S10, S11 [75, 253, 348] x x
510
Table 7.2 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C077 Presence of reductive chemicals in
substrate, water or steam 6 S1, S2, S5 [64, 251, 301] x x
C160 Presence of residual peroxide in substrate 6 S1, S2, S5, S8 [100, 150, 253,
301] x x x
C163 Improper heat setting of substrate 6 S1, S2, S3, S5, S9,
S10, S14, S17
[67, 83, 168, 194,
253, 320, 323] x x
C099 Use of too high liquor ratio 5 S1, S4, S5 [297] x x x
C001 Errors in the weighing of colorants and
chemicals 5 S1, S2, S5, S9
[77, 142, 317, 345,
348] x
C010 Variation in colorant strength 5 S1, S2, S5 [253, 301] x x
C024 Poor solubility of reactive/direct dyes 5 S1, S2, S5, S6b,
S6c, S7, S9-11
[9, 68, 75, 100, 111,
118, 231] x x
C035 Variations in strength and purity of
dyebath chemicals 5
S1, S2, S5, S6a-d,
S7 [79, 89, 103] x
C036 Chemical or physical interaction between
colorants and auxiliaries 5
S1-3, S5, S6a-d,
S7-11
[18, 78, 79, 86, 89,
103, 253] x x
C049 Inappropriate concentration of dispersing
agent 5
S1, S2, S5, S9,
S10,S11
[67, 89, 97, 106,
109] x x
511
Table 7.2 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C068 Inadequate pH during soaping 5 S6a-c [61, 85, 301, 345,
370] x
C082 Variations in dyeing program 5 S1, S2, S5 [9, 253, 297, 301] x
C151 Incomplete removal of sizing agents and
sizing wax 5
S1-3, S5, S7-10,
S16
[67, 149, 303, 305-
307, 324-329] x x
C157 Incomplete removal of fats, waxes, spin
finishes, and knitting oils 5 S1-3, S5, S8-10
[149, 277, 278, 297,
303, 305, 317, 327] x x
C028 High dye reactivity 5 S1, S2, S7-10 [9, 68, 100, 118,
128, 231] x x
C175 Presence of bicarbonate in water 5 S1, S2, S5 [283, 295-297] x x
C176 Presence of chlorine in water 4 S1, S2, S5, S11 [281, 285, 286] x x
C162 Inadequate whiteness of substrate 4 S1, S2, S5 [150, 301, 305,
309] x x
C172 Presence of Ca and Mg ions (hardness) in
water 4
S1, S2, S5, S6a-c,
S7, S11
[277, 280, 283, 290,
292, 296, 298, 299] x
C169 Alkaline pH of substrate before dyeing 4 S2, S9, S10 [301, 305, 309, 317,
334] x x
512
Table 7.2 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C173 Presence of heavy metals (Cu, Fe, Mn,
Zn) in water 4
S1, S2, S5, S7,
S13
[277, 280, 283, 286,
288-292] x x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
Table 7.3: Responses from human experts and the expert system for widthwise shade variation in pigment coloration (S10).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C134 Variation in the intensity of the IR
pre-dryer 9 S1-3, S5, S9, S12 [348, 363] x x x x
C128 Uneven wet pickup 9 S1-3, S9 [61, 100, 128, 133,
353] x x x x x
C135 Non-uniform air velocity or flow 8 S1-3, S5, S6a, S9, S12 [67, 317, 361, 363] x x x
C136 Too high drying temperature 7 S1-3, S5, S6a, S6e,
S9, S12 [85, 118, 253, 369] x x x
C052 Lower quantity of anti-migrating
agent 6 S1, S2, S3
[92, 95, 100, 105,
118, 130-132] x x x
513
Table 7.3 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C036 Chemical or physical interaction
between colorants and chemicals 5
S1-5, S6a, S6d, S6e,
S7-9, S16, S18
[18, 78, 79, 89, 103]
[86, 253] x x x
C053 Precipitation of anti-migrating agent 5 S1-5, S8, S9 [92, 95, 100, 105, 118,
130-132]
C141 Temperature variation in the hotflue 5 S1, S5, S6e, S9 [118, 253, 348, 370] x x x
C002 Improper bath preparation procedure 4 S1, S2, S5, S7, S9,
S18 [297, 301, 317] x
C005 Too high colorant concentration 4 S1-5, S6a, S7, S9,
S16, S18 [93, 100] x
C127 Improper distribution and circulation
of dye liquor 4 S1, S2, S5, S9, S12
[61, 100, 128, 133,
353] x x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
514
A detailed comparison of the remaining symptoms is given in Appendix D. The experts’
opinion pertaining to the most likely cause(s) of the symptoms tend to contain few causes when
compared to the expert system’s knowledge base. This may be due to the fact that the expert
system’s knowledge based was developed by aggregating responses from multiple sources based
on a wide range of scientific and technical knowledge and expertise.
The performance of individual experts was found to be below par as compared to
DEXPERT-B. In some cases the individual responses were found to be inconsistent with each
other. There may be many reasons that are responsible for these results. Individual experts often
have different expertise based on their training, experience, and intelligence and they usually
consider only a few most common causes based on their experience or observations. This is not
the case for expert systems where the knowledge base is developed by combining responses from
multiple experts and using causes reported in the technical and scientific literature. This provides
the expert system with the ability to generate a more comprehensive list of causes responsible for
a specific fault. While a list comprising multiple potential causes can be useful from an educational
perspective, it may also hinder the rapid identification of the root cause of a problem. Nonetheless,
expert systems can be useful tools since they often perform better than individual experts. They
can also be effective when in dealing with contradictions or differences in opinions among human
experts dealing with a particular problem.
In conclusion the performance of DEXPERT-B in troubleshooting a range of symptoms in
the dyeing of PES/CT blends was found to be better than that of individual experts tested in this
study. Therefore, it can be said that this system provides comprehensive and useful information
when attempting to determine the actual root causes of dyeing faults.
7.2 Evaluation of the expert system
The evaluation of an expert system is an important step. The process of evaluation includes the
determination of the appropriateness of the system against its requirements, to establish its
usefulness by the end-user and performance in the field [459, 461]. The main challenge associated
with the evaluation of the expert systems is to establish common evaluation criteria for its
usefulness and functionality as different domains may have different requirements and applications
of the expert system [461]. In general, for the evaluation of expert systems one may consider the
following points [459, 461]:
515
▪ User-friendliness and acceptance by the end-user;
▪ Correctness of the results and reasons provided by the system;
▪ Improvements in the practices of the domain where the system is designed to be used;
▪ Easiness in the learning of the system by the end-user;
▪ Training potential of the system;
▪ Manageability of the system by the organization where it is deployed;
▪ Practical use of the system in the actual work environment;
▪ Ability of a system to replace human experts in the decision-making process; and
▪ Financial impact.
The evaluation of DEXPERT-B was performed based on the criteria adopted in previous
studies used to develop a diagnostic expert system for the coloration of polyester [410] and protein
fibers [412]. The criteria chosen were usefulness, user-friendliness, response time, educational/
training value and overall performance. Five experts with a wide range of experience in the
coloration industry took part in the evaluation of the software using a Likert scale with five ratings
comprising, very poor, poor, fair, good and excellent. The results obtained from the expert
evaluations are given in Table 7.4.
Table 7.4: Evaluation results of the expert system.
Criteria Very poor Poor Fair Good Excellent
Usefulness 3/5 2/5
User-friendliness 2/5 3/5
Response time 2/5 3/5
Educational/ training value 1/5 1/5 3/5
Overall performance 4/5 1/5
The results showed overall positive results for the system. All experts found the system to
be useful and user-friendly with 40% giving it a rating of ‘Good’ and the remaining 60%
‘Excellent’. The response time was also found to be good to excellent. One out of five experts
chose a rating of ‘Fair’ for its educational/training value and suggested the development of a
516
mobile application as a preferable platform. In terms of the overall performance criterion, the
evaluators found the system to be good (80%) to excellent (20%). Many evaluators showed quite
an interest in the developed system and asked that the full version be made available for
deployment in their industry. The evaluators provided the following suggestions regarding the
system:
▪ Availability of the system in an easy to deploy platform, such as Windows applications.
▪ Availability of the system in a mobile application format.
▪ Availability of the system for other blends like elastane blends.
▪ Ability to store and taking printouts of the diagnosis results.
▪ Ability of the system to take pictures of the actual fault and storage of results in a
database.
The expert system was also evaluated for its diagnosis accuracy using the seventeen faulty
colored samples. The exact causes of all the faults were known in advance. Each faulty sample
was examined by five human coloration experts. To compare the responses from human experts
against those from the expert system and to avoid bias DEXPERT-B was run by a potential user
who was not aware of the actual causes of the symptoms. The results obtained are shown in Table
7.5. The average accuracy of experts was found to be 58% with the highest rate achieved by Expert
A (76%). The accuracy of DEXPERT-B was found to be 100%. The difference in the performance
of human experts and expert system is because the experts tend to consider only the more common
causes of symptoms based on their experience. The knowledge base of DEXPERT-B was more
comprehensive since it was developed by combining the expertise of multiple experts and
knowledge reported in the literature. Therefore, it is highly unlikely for the expert system to miss
the cause of the given symptom.
Table 7.6 shows the details of the faulty colored samples that were observed by human
experts along with their responses in comparison with DEXPERT-B. It can be seen that the
expert’s accuracy for diagnosis varied for each symptom. The highest fault diagnosis accuracy of
100% was obtained for three symptoms ‘widthwise shade variation’ (S11), ‘holes and tears’ (S12)
and ‘poor dimensional stability’ (S17). The lowest accuracy of 20% was obtained for ‘darks stains’
(S7) and ‘lengthwise shade variation’ (S9).
517
Table 7.5: Comparison of diagnosis of faulty colored samples, human vs expert system.
Details Expert A Expert B Expert C Expert D Expert E DEXPERT-B
Experience 20 15 20 35 30 -
Correct
diagnosis 12 8 11 10 7 17
Accuracy % 76% 48% 65% 59% 42% 100%
Table 7.6 shows the details of the faulty colored samples that were observed by human
experts along with their responses in comparison with DEXPERT-B. It can be seen that the
expert’s accuracy for diagnosis varied for each symptom. The highest fault diagnosis accuracy of
100% was obtained for three symptoms ‘widthwise shade variation’ (S11), ‘holes and tears’ (S12)
and ‘poor dimensional stability’ (S17). The lowest accuracy of 20% was obtained for ‘darks stains’
(S7) and ‘lengthwise shade variation’ (S9).
It can be seen that the expert’s ability to correctly diagnose the problem varies among
experts. Experts A, C, and D are directly involved in the production of dyed material whereas
experts C and D while having previously had industrial experience are no longer involved in a
production setting and conduct research-related activities. The experts who are involved in the
coloration process on a day to day basis are often better in diagnosing faults as compared to ones
who have coloration experience but are not currently involved in the production of colored
material. The experts who are currently working in the industry are more aware of the actual causes
of the problems because of dealing with these types of faults on a daily basis. The difference,
however, may also be due to differences in the educational background and the nature of the
experience of experts in production settings. The performance of DEXPERT-B, on the other hand,
was found to be significantly better than the human experts in the diagnosis of faulty colored
samples. Since the expert system has an explanation facility along with the diagnosis it is
considered to be more useful and helpful in determining the root causes of faults and providing
solutions to avoid or minimize their repeated occurrence.
518
Table 7.6: Diagnosis results of human experts and DEXPERT-B.
Symptom
Actual cause
Exp
ert
A
Exp
ert
B
Exp
ert
C
Exp
ert
D
Exp
ert
E
% c
orr
ect
DE
XP
ER
T-B
S1 Reproducibility C099 Use of too high liquor ratio x x 40% x
S2 Unlevelness C096 Higher temperature rise rate x x x 60% x
S3 Streaks, stripes or bands C135 Non-uniform air velocity or flow x x 40% x
S4 Poor color yield C072 Presence of residual alkali/hydro after
dyeing cycle x x x 60% x
S5 Shade change C192 Variation in blend ratio x x 40% x
S6 Inadequate washing
fastness C066
Inadequate concentration of hydro & caustic
during reduction clearing x x x x 80% x
S7 Dark stains or spots C156 Localized swelling of fiber x 20% x
S8 Light stains or spots C053 Precipitation of anti-migrating agent x x 40% x
S9 Lengthwise shade
variation C145
Variation in steam pressure inside the
steamer x 20% x
S10 Widthwise shade
variation C128 Uneven wet pickup x x x x x 100% x
S11 Shade variation within
layers
C107 Too low liquor flow rate x x x 60% x
S12 Two sidedness C134 Variation in the intensity of the IR pre-dryer x x x 60% x
519
Table 7.6 (Continued)
Symptom
Actual cause
Exp
ert
A
Exp
ert
B
Exp
ert
C
Exp
ert
D
Exp
ert
E
% c
orr
ect
DE
XP
ER
T-B
S13 Reduced strength C149 Fiber damage during singeing x x 40% x
S14 Irregular surface
appearance C122
Damaged, worn out or uneven padder
surface x x 40% x
S15 Holes or tears C159 Catalytic damage during bleaching x x x x x 100% x
S16 Poor hand C164 Fiber damage during heat setting x x x x 80% x
S17 Poor dimensional stability C166 Excessive overstretching of substrate on
stenter x x x x x 100% x
520
CHAPTER 8 CONCLUSIONS AND FUTURE WORK
8.1 Conclusions
The research work has provided a functional expert system that contains and utilizes expert
problem-solving knowledge to identify the specific causes of different problems in the coloration
of PES/CELL blends using dyes and pigments. The problem of troubleshooting is covered
holistically using knowledge from the experts and published literature. The system was developed
in three phases. In phase I common blends were identified and knowledge acquisition was carried
out. In phase II, the design and development of the system were performed. In phase III, the system
was tested and evaluated for its functionality and usefulness.
The first phase was divided into sub-phases (A and B). In sub-phase A, common blend
types were identified. This is necessary as there are many blend combinations available in the
market and a coverage of every blend type is not realistic nor practical. Through consultations with
fiber and yarn producers, and a study of the reported trade data, it was found that PES/CELL blends
represent the majority of the blends currently produced. Once the blend type was identified sub-
phase B was carried out which led to the development of a comprehensive knowledge base.
Selected manuscripts from scientific journals, textbooks, published reports and technical
information from dye manufacturers were used to develop a comprehensive list of common
coloration problems and their potential causes. A comprehensive cause and effect diagram was
created to systematically analyze problems in the coloration of PES/CELL blends. The list of
common coloration problems and their causes was finalized in consultation with the practical dyers
and machinery manufacturers. A final list of eighteen problems in the coloration of PES/CELL
was thus obtained. An electronic survey, based on the list of common dyeing problems and
potential causes, in the form of an excel spreadsheet was developed to determine the
interrelationship between the problems and causes. Several coloration experts from different
regions with a broad range of experience from 10-40 years participated in the electronic survey.
They were from different sectors of the industry including practical dyers, dye manufacturers, and
dyeing consultants. The experts were asked to provide the relationships between the causes and
coloration problems using certainty factors ranging from 0 (no correlation) and 10 (excellent
correlation). Additionally, they were also provided with an option to use X if they felt unsure about
the existence of a relationship. The responses obtained from different experts were analyzed and
521
evaluated. These were then incorporated in the knowledge base according to three categories: most
likely, likely and least likely causes of each symptom. Responses were aggregated using the
weighted average method.
During phase II, the comprehensive knowledge obtained in the previous phase was coded
in the form of rules using the CLIPS expert system tool. The system was designed in the form of
two modules covering both dyes and pigments that are used in the coloration of PES/CELL blends.
A modified version of CLIPS with GUI functionality, wxCLIPS, was used to code the knowledge
base. The inference engine was also developed to determine rule priority. Several practical
functionalities were also incorporated in the design and development phase. These included the
use of dynamic rules to calculate new values based on selected problems, the ability of the system
to deal with multiple problems at the same time and the incorporation of the effect of blend ratio
on the nature of coloration problems. The system was also provided with an explanation facility
based on the causes that are found to be responsible for a particular problem and which may change
based on the fiber type and blend ratio. Some other functionalities, related to the use of the
program, included the option for the user to return to their previous selections and replace them if
required, or to reset their selections in the current interface if errors are made, or to restart the
program for a new diagnosis. In the diagnosis screen, the end-user is provided with the material
and coloration related problem along with problems selected for diagnosis. The user is also
provided with the help option for guidance on how to use the program and definitions of some
terms used in the software to make the system user-friendly and easy to use.
In phase III, the system was tested and evaluated using a validation and verification
approach. During the verification phase, the system was checked for any errors or anomalies. In
the validation phase, the knowledge base of the system was authenticated by testing the
performance of the system against human experts using actual faulty dyed samples taken from
production facilities. The system was then evaluated for its usefulness using multiple criteria that
included usefulness, user-friendliness, response-time, educational/training value, and overall
performance.
To compare the performance of DEXPERT-B against human experts in diagnosing
problems, several faulty samples were obtained from production facilities that covered both
pigment and dye based coloration processes. The exact causes of the faults were known to
determine the accuracy of the designed system and compare its diagnosis ability against human
522
experts. The samples were then diagnosed and evaluated by five human experts as well as the
expert system. It was found that the expert system was able to correctly diagnose all faults whereas
in the case of human experts comparatively lower accuracy was obtained.
Since the system was developed by combining the expertise of several experts as well as
the reported literature, it outperformed individual experts. In fact the average accuracy for human
experts was found to be 58%. Troubleshooting is a complex process and may take considerable
time. It depends to a large extent on the level and type of expertise of the human expert which can
vary widely among individuals based on their experience and training. The expert system, on the
other hand, can provide a comprehensive knowledge base to determine the root causes of faults in
the coloration of material, in this case PES/CELL blends, in a relatively shorter period. Since the
system covers all major sectors that are involved in the production of material and may thus be
responsible for the development of a specific problem, the results obtained from an expert system
are likely more comprehensive and can be helpful in practical settings for different users.
8.2 Recommendations for future work
PES/CELL blends occupy a very important position in the textile industry due to their compatible
and enhanced properties. However, their coloration can be challenging due to the large number of
variables involved. The coloration of blends requires different dye classes due to differences in the
dyeing behavior of the two materials. Dyeing challenges include cross-staining of the fiber by the
dye intended for the other fiber type, interferences between dye classes and dye bath chemicals, as
well as the additional time required to fix both dyes for each component, in this case cellulose and
polyester. However, PES/CELL blends are sold at cheaper prices than 100% cotton. With
increasing labor and production costs and due to the exerted pressure to enhance profits, the need
to rapidly resolve coloration problems for blends is becoming increasingly evident.
The diagnostic expert system developed for the coloration of PES/CELL blends in this
study was designed to assist practical dyers and the personnel involved in the coloration of these
materials to quickly identify the root causes of problems and provide rapid solutions. This is
expected to help the industry by improving the shade reproducibility of blended products and by
reducing their coloration cost thus making their processing more competitive, environmentally
friendly and profitable.
Nonetheless, it is recommended to consider further work in the following areas:
523
▪ Expert systems are useful in diagnosing a problem in the complex coloration domain.
However, they have certain shortcomings which can result in making errors. The
systems should have the ability to adapt and adjust their response based on
consideration of the mistakes made.
▪ A feedback mechanism should be incorporated into the design and development of the
expert system.
▪ Neural networks or other inference techniques could be incorporated in the system to
improve the performance of the inference engine and make them more useful and
practical. In a rule-based system, the expert system may be unable to diagnose the fault
if the knowledge base does not have essential information about a particular fault i.e.
no specific rules are present in the knowledge base for an unknown fault. However,
this limitation can be overcome by using models of the process structure and functions
using an artificial neural network (ANN). ANN has an inherent property of learning
that maps a functional relationship between causes and symptoms. In case of an
unknown fault, the ANN can provide the closest possible cause(s) that may be
responsible for the particular fault.
▪ The system could include a built-in option to store all the diagnostic data for retrieval
and ease of access for future use.
▪ Furthermore, other modules for coloration of elastane containing fiber blends may also
be incorporated. Elastane is extensively used in blends and approximately 35-40% of
all apparel contains elastane due to its unique functional and fashion related properties.
▪ The newly developed expert system in this study can be combined with the existing
expert systems to create a comprehensive expert system for troubleshooting faults in
the coloration of textiles.
▪ Several additional modules such as denim finishing, conventional printing, and
finishing can be developed to increase the expertise domains in textile wet processing.
▪ The system was developed using wxCLIPS that has limited functionality in the
development of a user friendly GUI. JAVA, VB.net, or other suitable environments can
be incorporated to develop more user-friendly and easier to deploy systems. The main
challenge associated with using these environments is to allow information to be easily
exchanged by calling CLIPS functions from these environments. This requires writing
524
of interface functions. Clearly, knowledge engineer would also need good
programming skills along with coloration knowledge to allow complete language
mixing.
▪ A new expert system can be developed that uses a real-time image capturing facility to
diagnose root causes of problems for actual faulty dyed materials.
▪ Several faults’ accurate diagnosis requires laboratory analysis to reach the root cause
of the problem. The ability to add laboratory analysis during the troubleshooting
process can be helpful in making a more accurate diagnosis of the problem.
▪ The system should be developed as a web-based or mobile application to facilitate its
use and provide real-time functionality.
525
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546
APPENDICES
547
Mean expert responses for symptoms and their causes.
Table A.1: Mean responses of experts for symptoms and their causes related to dyes. C
au
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C001 9 4 0 5 4 0 0 0 0 2 0 5 0 0 0 0 0 0 0 0
C002 7 5 0 2 4 0 0 0 0 6 2 4 0 0 0 0 0 0 0 0
C003 8 9 3 0 0 0 0 0 0 3 0 6 2 7 0 3 0 0 0 0
C004 7 9 0 0 0 0 0 0 0 0 0 6 2 6 0 0 0 0 0 0
C005 2 2 2 0 0 5 5 5 0 4 0 2 0 0 0 0 0 0 0 0
C006 0 3 0 0 0 9 9 9 0 0 0 0 0 0 0 0 0 0 0 0
C007 8 3 0 0 0 9 9 9 9 0 0 0 0 0 0 0 0 0 0 0
C008 8 3 0 0 0 9 9 9 9 0 0 0 0 0 0 0 0 0 0 0
C009 7 8 0 0 6 0 0 0 5 0 0 5 5 4 3 0 0 0 0 0
C010 7 4 0 5 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C011 7 7 4 7 7 5 5 5 5 6 0 5 5 6 0 0 0 0 0 0
C012 3 2 0 0 3 9 9 9 4 0 0 0 0 0 3 0 0 0 0 0
C013 2 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0
C018 6 7 1 6 7 0 0 0 0 8 0 7 5 7 3 0 0 0 0 0
C019 7 7 0 7 0 0 0 0 0 8 0 4 4 5 0 0 0 0 0 0
C020 5 6 2 3 3 0 0 0 0 0 0 0 0 7 0 0 0 0 0 0
548
Table A.1 (Continued) C
au
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C021 6 6 2 0 5 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0
C022 0 0 0 0 0 9 9 9 0 0 0 0 0 0 0 0 0 0 0 0
C023 6 6 0 0 0 5 5 5 0 0 0 8 4 5 0 0 0 0 0 0
C024 6 7 0 5 7 3 4 4 0 8 0 5 5 7 0 0 0 0 0 0
C025 5 5 0 0 0 2 3 3 0 0 0 0 0 7 0 0 0 0 0 0
C026 6 6 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0
C027 7 4 0 7 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0
C028 5 6 0 5 0 0 0 0 0 5 0 7 4 0 0 0 0 0 0 0
C029 6 7 0 0 0 0 0 0 0 0 0 8 4 5 0 0 0 0 0 0
C030 4 4 0 0 0 0 0 0 0 0 0 2 3 5 0 0 0 0 0 0
C031 5 5 0 0 0 0 0 0 0 0 0 0 3 7 0 0 0 0 0 0
C032 6 6 0 0 5 0 0 0 0 0 0 0 3 6 0 0 0 0 0 0
C033 6 7 1 6 7 0 0 0 0 7 0 7 5 7 3 0 0 0 0 0
C034 7 0 0 0 8 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0
C035 5 5 0 5 4 4 4 4 4 5 0 2 0 0 3 0 0 0 0 0
C036 5 5 5 5 5 4 4 4 4 5 4 4 4 6 0 0 0 0 0 0
C037 5 5 4 0 4 4 4 4 4 5 4 5 5 4 3 0 4 0 0 0
549
Table A.1 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C048 5 4 2 7 0 3 3 3 0 0 0 4 3 7 3 0 0 0 0 0
C049 5 5 1 5 5 0 0 0 0 0 0 4 5 5 0 0 0 0 0 0
C050 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0
C051 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0 0
C052 5 6 7 0 4 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0
C053 5 5 5 0 5 0 0 0 0 0 6 4 4 0 0 0 0 0 0 0
C054 3 0 0 0 6 0 0 0 7 0 0 0 0 0 0 0 0 0 3 0
C055 0 0 0 0 0 1 1 1 0 7 0 0 0 0 0 0 0 0 0 0
C056 5 5 0 6 5 5 5 5 0 0 0 0 0 5 3 0 0 0 0 0
C057 5 5 0 5 4 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0
C058 5 0 0 0 3 4 4 4 0 0 0 2 3 0 0 0 0 0 0 0
C059 5 0 0 0 2 4 4 4 0 0 0 3 0 4 0 0 0 0 0 0
C060 5 3 2 0 3 6 6 6 0 0 0 3 3 0 0 0 0 0 0 0
C061 5 5 2 0 5 6 6 6 0 0 0 2 5 4 0 0 0 0 0 0
C062 5 5 0 6 5 5 5 5 0 0 0 5 5 4 0 0 0 0 0 0
C063 5 0 2 0 4 5 5 5 0 0 0 2 3 0 0 0 0 0 0 0
C064 3 3 2 2 2 8 8 8 0 0 0 2 0 0 0 0 0 0 0 0
C065 3 3 2 1 2 8 8 8 0 0 0 2 0 0 0 0 0 0 0 0
550
Table A.1 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C066 3 3 2 0 2 8 8 8 0 0 0 2 0 0 0 0 0 0 0 0
C067 3 3 2 0 4 8 8 8 0 0 0 5 5 4 0 0 3 0 0 0
C068 3 2 1 5 2 7 7 7 0 0 0 2 2 0 0 0 0 0 0 0
C069 3 3 3 2 5 8 8 8 0 0 0 0 3 0 0 0 0 0 0 0
C070 3 3 1 0 1 8 8 8 0 0 0 2 2 0 0 0 1 0 0 0
C071 3 3 2 1 4 7 7 7 0 0 0 5 5 4 2 0 2 0 0 0
C072 5 5 0 7 5 0 0 0 0 3 5 0 0 0 0 3 0 0 0 0
C073 0 0 0 2 3 1 1 0 1 0 1 0 0 0 0 2 0 4 3
C074 1 0 3 1 0 0 0 0 0 1 0 1 0 0 0 2 3 2 3 1
C075 2 0 6 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0
C076 0 2 1 0 0 0 0 0 0 6 0 0 0 0 0 0 2 0 0 0
C077 6 5 0 6 5 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0
C078 2 5 2 0 0 0 0 0 0 7 5 0 0 0 0 0 2 0 0 0
C079 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 6 7 0 0
C080 0 0 0 0 0 0 0 0 0 0 0 3 3 0 0 0 6 0 0 6
C081 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 6 4 7 6
C082 8 8 0 5 6 2 2 2 0 0 0 3 3 0 3 0 1 0 0 0
C083 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0
551
Table A.1 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C084 4 2 5 0 0 0 0 0 0 0 0 0 0 5 0 0 6 0 0 0
C085 5 6 0 4 0 0 0 0 0 0 0 0 0 8 0 0 0 0 0 0
C086 3 1 7 0 0 0 0 0 0 0 0 0 0 4 0 0 8 0 0 0
C087 7 8 5 4 5 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0
C088 4 7 6 4 2 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0
C089 2 2 3 2 2 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0
C090 6 7 3 3 4 0 0 0 0 0 0 0 0 7 0 0 2 0 0 0
C091 3 3 3 3 3 0 0 0 0 0 0 0 0 3 0 0 6 0 0 0
C092 7 7 5 0 2 0 0 0 0 0 0 2 3 7 2 0 7 0 3 1
C093 5 5 2 2 1 0 0 0 0 5 5 1 0 7 0 0 0 0 0 0
C094 3 2 1 1 1 0 0 0 0 5 5 1 0 0 0 0 1 0 5 0
C095 2 4 0 2 2 0 0 0 0 0 5 0 0 6 0 0 0 0 0 0
C096 8 9 5 0 3 0 0 0 0 0 0 5 0 8 0 0 8 0 0 0
C097 7 7 3 7 5 6 6 6 0 2 0 5 5 0 0 5 1 0 0 0
C098 2 6 4 0 2 0 0 0 0 4 0 3 0 6 2 0 4 1 3 3
C099 7 0 1 5 5 0 0 0 0 1 0 2 0 2 0 0 2 0 0 0
C100 7 6 2 9 0 6 6 6 0 0 0 3 3 8 3 0 3 0 0 0
C101 3 0 2 0 0 0 0 0 0 0 0 2 0 3 0 3 2 0 1 0
552
Table A.1 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C102 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0
C103 2 5 0 1 1 0 0 0 0 0 0 1 0 0 0 0 5 0 3 0
C104 7 6 3 2 4 6 6 6 0 3 0 2 3 8 3 0 2 0 1 0
C105 2 1 2 0 1 0 0 0 0 0 0 2 0 3 0 0 5 0 3 0
C106 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 0 2 0
C107 5 6 2 4 0 0 0 0 0 2 0 0 4 8 0 0 1 0 0 0
C108 2 5 2 1 0 0 0 0 0 0 0 0 0 4 0 0 8 0 0 0
C109 7 7 0 4 0 0 0 0 0 0 0 0 0 9 0 0 8 0 0 0
C110 3 0 0 0 0 0 0 0 0 0 0 0 7 6 0 0 7 0 0 0
C111 5 7 0 0 0 0 0 0 0 0 0 0 7 7 0 0 5 0 0 0
C112 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0
C113 6 5 0 0 0 0 0 0 0 0 0 4 0 0 0 0 9 0 0 0
C114 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0
C115 0 4 5 0 0 0 0 0 0 0 0 0 0 0 0 0 8 0 0 0
C116 3 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0
C117 5 5 0 6 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0
C118 2 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0
C119 6 0 2 0 0 0 0 0 0 0 0 5 5 0 0 0 0 0 0 0
553
Table A.1 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C120 1 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0
C121 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0
C122 1 3 2 0 0 0 0 0 0 2 0 0 2 0 0 0 6 3 0 0
C123 5 6 0 7 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0
C124 0 0 0 0 0 0 0 0 0 0 0 0 5 0 7 0 2 0 0 0
C125 5 7 0 0 0 0 0 0 0 0 0 5 5 0 0 0 0 0 0 0
C126 2 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C127 4 4 0 0 4 0 0 0 0 0 0 0 6 0 5 0 0 0 0 0
C128 7 7 7 0 0 0 0 0 0 0 0 7 9 0 0 0 1 0 0 0
C129 1 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C130 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0
C131 6 8 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0 0 0 0
C132 6 8 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0
C133 7 3 0 8 0 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0
C134 5 7 5 0 7 0 0 0 0 0 0 6 8 0 9 0 0 0 0 0
C135 8 7 7 0 6 0 0 0 0 0 0 5 8 0 9 0 0 0 0 0
C136 7 6 2 0 6 0 0 0 0 0 0 5 7 0 6 0 3 0 3 2
C137 7 0 0 9 5 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0
554
Table A.1 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C138 2 3 3 0 4 0 0 0 0 0 0 0 0 0 0 0 0 0 4 3
C139 1 0 2 3 2 0 0 0 0 0 0 0 0 0 0 0 1 0 4 3
C140 7 0 1 8 5 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0
C141 5 7 0 0 6 0 0 0 0 0 0 6 6 0 0 0 0 0 0 0
C142 0 0 0 0 0 0 0 0 0 0 8 0 0 0 0 0 0 0 0 0
C143 7 5 0 7 0 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0
C144 7 0 0 7 0 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0
C145 7 5 0 0 0 2 2 2 0 0 0 6 0 0 0 0 0 0 0 0
C146 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C147 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 0 0
C148 1 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 1 0
C149 1 7 0 0 0 0 0 0 0 5 0 0 0 0 0 7 0 2 3 2
C150 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C151 5 6 7 5 5 2 2 2 0 4 5 4 4 0 0 0 2 0 6 0
C152 0 3 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0
C153 1 4 2 0 2 0 0 0 0 0 0 1 0 2 0 7 4 5 7 6
C154 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 4 4
C155 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 6
555
Table A.1 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C156 0 3 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0 0
C157 5 6 6 5 5 0 0 0 0 0 5 4 4 3 0 0 0 0 0 0
C158 2 0 6 0 0 0 0 0 0 0 0 0 0 0 0 4 5 0 5 3
C159 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 3 8 5 3
C160 4 5 2 6 5 0 0 0 0 2 4 2 0 3 0 0 3 0 3 0
C161 0 0 0 0 0 0 0 0 0 7 0 0 0 0 0 0 0 0 0 0
C162 5 4 3 4 4 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0
C163 3 7 6 6 6 3 3 3 0 0 0 5 5 0 0 0 9 0 0 8
C164 2 0 0 0 2 0 0 0 0 0 0 0 0 0 0 8 0 2 8 4
C165 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 0 3
C166 0 1 2 2 1 0 0 0 0 1 0 2 0 2 0 3 4 4 3 7
C167 7 5 6 7 0 2 2 2 0 0 0 5 5 0 0 0 0 0 0 0
C168 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0
C169 2 4 0 4 0 0 0 0 0 0 0 4 4 0 0 0 0 0 0 0
C170 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C171 2 0 0 0 0 0 0 0 0 0 5 2 0 0 0 0 0 0 0 0
C172 6 5 3 4 5 4 4 4 0 5 0 2 0 4 0 0 0 0 2 0
C173 5 5 1 4 5 0 0 0 0 5 0 2 0 3 0 4 0 0 2 0
556
Table A.1 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C174 5 5 0 2 2 0 0 0 0 4 0 1 0 4 0 0 0 0 0 0
C175 5 7 0 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C176 5 5 2 4 5 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0
C177 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 7 0 0
C178 2 0 9 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0
C179 7 2 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0
C180 6 2 8 0 4 2 2 2 0 0 0 0 0 0 0 3 4 0 3 5
C181 0 0 7 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0
C182 5 8 7 1 4 0 0 0 0 2 0 0 0 8 0 0 1 0 0 0
C183 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 0 0 0
C184 7 6 5 2 5 0 0 0 0 3 0 0 0 7 0 0 5 0 0 0
C185 2 3 1 1 2 0 0 0 0 1 0 0 0 0 0 0 6 0 0 0
C186 1 6 1 0 1 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0
C187 1 4 1 2 3 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0
C188 1 4 1 2 2 0 0 0 0 1 0 0 0 0 0 0 5 0 0 0
C189 2 2 1 2 2 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0
C190 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0 3 4 0 0 0
C191 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 3 0 5
557
Table A.1 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06b
S06c
S06d
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
C192 6 0 5 0 7 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0
C193 1 2 2 2 2 0 0 0 0 4 0 0 0 0 0 3 0 4 0 0
C194 5 4 6 2 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0
C195 4 4 1 2 2 0 0 0 0 1 0 0 0 0 0 3 0 0 0 0
C196 1 4 0 2 2 0 0 0 0 0 4 0 0 0 0 3 0 0 0 0
558
Table A.2: Mean response of experts for symptoms and their causes related to pigments
Cau
se
S01
S02
S03
S04
S05
S06a
S06d
S06e
S07
S08
S09
S10
S12
S13
S14
S15
S16
S17
S18
C001 9 4 0 4 4 0 0 0 0 0 5 0 0 0 0 0 0 0 0
C002 7 9 0 2 7 0 0 0 8 3 4 4 0 0 0 0 2 0 5
C005 8 7 6 7 6 9 0 3 7 0 4 4 3 0 0 0 5 0 7
C014 2 3 3 5 4 6 9 9 0 0 2 0 0 0 0 0 0 0 0
C015 5 6 0 5 0 3 0 0 8 0 0 0 0 0 0 0 0 0 5
C016 5 6 0 5 0 3 0 0 7 0 0 0 0 0 0 0 0 0 5
C017 0 5 0 0 4 5 0 0 3 0 0 0 0 0 0 0 5 0 0
C036 4 7 5 5 6 6 5 5 8 5 6 5 0 0 0 0 5 0 7
C038 0 5 7 6 0 0 0 0 6 5 0 3 0 0 0 0 2 0 9
C039 0 8 5 7 0 5 0 0 9 6 0 3 0 0 0 0 3 0 9
C040 0 0 0 0 0 9 8 9 0 0 0 0 0 0 0 0 0 0 0
C041 0 3 0 0 0 4 0 0 3 3 0 0 0 0 0 0 9 0 6
C042 0 0 0 6 0 9 7 8 2 2 0 0 0 0 0 0 0 0 0
C043 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 9 0 6
C044 0 0 0 0 0 5 9 2 0 0 0 0 0 0 0 0 0 0 3
C045 0 0 0 0 0 5 0 1 0 0 0 0 0 0 0 0 0 0 3
C046 0 0 0 0 0 5 0 0 0 0 0 0 0 0 0 0 0 0 3
C047 0 2 3 1 0 9 0 0 0 2 0 3 0 0 0 0 6 0 3
559
Table A.2 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06d
S06e
S07
S08
S09
S10
S12
S13
S14
S15
S16
S17
S18
C049 4 6 0 0 5 5 0 0 4 0 0 0 0 0 0 0 0 0 9
C052 6 7 5 0 2 0 0 0 2 2 2 6 0 0 0 0 2 0 0
C053 5 4 5 5 5 1 0 0 0 7 5 5 0 0 0 0 2 0 7
C055 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0
C075 6 0 5 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0 0
C076 7 0 0 0 0 0 0 0 6 0 0 0 0 0 2 0 0 0 0
C077 0 5 0 0 2 5 5 0 0 3 0 0 0 0 0 0 0 0 0
C078 5 5 2 0 0 3 0 0 7 6 0 0 0 0 2 0 0 0 0
C079 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 7 0 0 0
C080 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 6 0
C081 0 0 0 0 0 0 0 0 0 0 0 0 0 6 6 4 0 6 0
C083 0 0 5 0 2 0 0 0 0 0 0 0 0 0 0 0 3 0 0
C121 0 2 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0
C122 0 0 0 0 0 0 0 0 4 0 0 0 0 0 6 3 0 0 0
C124 0 1 0 0 0 0 0 0 0 0 0 7 0 0 0 0 0 0
C125 5 8 5 0 8 4 0 3 0 3 5 2 0 0 0 0 3 0 6
C126 2 3 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0
C127 6 4 0 0 4 0 0 0 0 0 4 4 5 0 0 0 0 0 0
C128 6 10 8 0 3 3 0 3 0 2 8 9 0 0 1 0 0 0 1
560
Table A.2 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06d
S06e
S07
S08
S09
S10
S12
S13
S14
S15
S16
S17
S18
C129 0 3 0 0 2 3 0 0 0 0 0 0 0 0 0 0 0 0 0
C130 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0
C134 5 7 4 1 7 3 0 0 0 3 6 9 9 0 0 0 0 0 0
C135 9 7 7 2 6 5 0 0 0 0 5 8 9 0 0 0 1 0 1
C136 8 6 5 2 6 5 0 4 0 0 5 7 6 0 3 0 2 2 0
C137 9 0 0 0 6 9 0 7 0 0 0 0 0 0 0 0 0 0 0
C138 0 0 0 0 5 0 0 3 0 0 0 0 0 0 0 0 6 2 0
C139 0 0 0 0 2 0 0 3 0 0 0 0 0 0 1 0 2 2 0
C140 7 0 0 0 4 9 0 7 0 0 0 0 0 0 0 0 0 0 5
C141 5 3 0 3 6 1 0 5 0 0 6 5 0 0 0 0 2 0 1
C142 0 2 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0
C148 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0
C149 2 0 0 0 0 0 0 0 0 0 0 0 0 6 0 2 3 2 0
C150 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C151 2 7 5 5 6 5 3 5 3 2 2 2 0 0 2 0 5 0 0
C152 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 0
C153 1 0 0 0 0 0 0 0 0 0 0 0 0 7 7 5 2 6 0
C154 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 4 0
C155 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 6 0
561
Table A.2 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06d
S06e
S07
S08
S09
S10
S12
S13
S14
S15
S16
S17
S18
C157 3 7 3 4 5 3 3 3 2 2 2 2 0 0 0 0 0 0 0
C159 2 0 0 0 0 0 0 0 0 0 0 0 0 7 3 8 0 1 0
C161 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0
C162 5 4 3 2 3 0 3 1 0 0 2 2 0 0 0 0 0 0 0
C163 3 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 8 0
C164 2 0 0 0 0 0 0 0 0 0 0 0 0 8 0 2 7 4 0
C165 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 0 3 0
C166 0 0 0 0 0 0 0 0 0 0 0 0 0 3 4 4 0 7 0
C169 2 3 3 3 3 5 3 4 2 1 2 2 0 0 0 0 0 0 1
C172 2 3 0 0 2 4 1 1 0 0 0 0 0 0 0 0 0 0 1
C173 3 2 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0
C174 3 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C175 3 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C176 3 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C177 0 0 0 0 0 0 0 0 0 0 0 0 0 3 0 7 0 0 0
C178 0 0 4 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0
C179 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
C180 1 0 7 0 0 0 0 0 0 0 0 0 0 3 5 0 0 5 0
C181 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0
562
Table A.2 (Continued)
Cau
se
S01
S02
S03
S04
S05
S06a
S06d
S06e
S07
S08
S09
S10
S12
S13
S14
S15
S16
S17
S18
C190 0 3 0 0 0 2 0 0 0 0 0 0 0 3 4 0 0 0 0
C191 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 3 0 5 0
C192 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0
C193 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0
C195 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0
563
Questions related to various causes for diagnosis of symptom(s).
Table B. 1: Questions to user related to various causes for diagnosis.
Cause Description Question to the user
C001 Errors in the weighing of colorants and
chemicals Were the colorants and chemicals weighed accurately?
C002 Improper bath preparation procedure Was the bath prepared as per the colorant manufacturer’s recommended
procedure?
C003 Too fast/quick addition of chemicals in the
bath Were the chemicals added too quickly during the dyeing process?
C004 Too fast/quick addition of dyes in the bath Were the dyes added too quickly during the dyeing process?
C005 Too high colorant concentration Was the depth of shade too high?
C006 Wrong selection of dyeing method (1 bath, 2
bath)
Was the dyeing method selected according to the depth of shade and
fastness properties?
C007 Poor dye selection for polyester component Were the dyes selected correctly according to depth of shade, fastness
properties for polyester fiber in the blend?
C008 Poor dye selection for cellulose component Were the dyes selected correctly according to depth of shade, and
fastness properties for the cellulose fiber?
C009 Poor dye combinations for each fiber type Were the dyes selected in combination shade have similar dyeing
properties?
C010 Variation in colorant strength Were the colorants checked for their strength prior to their application?
C011 Incompatibility between dye classes Were the dye classes selected compatible to each other?
C012 Cross-staining of fiber Were the disperse dyes selected have lower staining tendency of the
cellulose component and good wash-off behavior?
C013 Bleeding of unfixed dye into the bath/trough
during development
Was there any change in the bath appearance before and after chemical
development?
C014 Poor pigment selection Were the pigments selected according to depth of shade, fastness and
application properties?
C015 Crust formation in pigments during storage Were the pigment cans stored properly and stirred prior to the coloration
process?
564
Table B.1 (Continued)
Cause Description Question to the user
C016 Poor pigment dispersion system Were the pigments evaluated for their dispersion properties?
C017 Differences in pigment particle size and
particle size distribution Were the particle size of pigments and their distribution uniform?
C018 Poor disperse dye dispersion system Were the disperse dyes tested for their dispersion properties?
C019 Poor disperse dye dispersion stability Were disperse dyes selected according to their stability under electrolyte
and alkaline pH?
C020 Poor disperse dye diffusion properties Were the disperse dye used have good diffusion properties?
C021 Poor disperse dye leveling and migration
properties Were the disperse dye used have good leveling and migration properties?
C022 Poor thermomigration property of disperse
dye
Were the disperse dyes of low or medium energy levels used in the
dyeing process?
C023 Too high substantivity of reactive/direct dyes Was the substantivity of dye too high?
C024 Poor solubility of reactive/direct dyes Was the solubility of dye good under the dyeing conditions?
C025 Poor diffusion properties of reactive/direct
dyes
Were the dyes with poor diffusion properties used for the dyeing of
cellulose component?
C026 Poor migration properties of reactive/direct
dyes
Were the dyes with poor migration properties used for the dyeing of
cellulose component?
C027 Poor stability of reactive/direct dyes under
polyester dyeing conditions
Were the dyes for cellulose component selected based on their stability
under acidic and high-temperature dyeing conditions used in polyester
dyeing?
C028 High dye reactivity Were the reactive dyes of high reactivity used in the dyeing process?
C029 Too high substantivity of vat/sulfur dye in the
leuco form Was the dye substantivity too high in the lueco form?
C030 Too low substantivity of vat/sulfur dye in the
leuco form Was the dye substantivity too low in the lueco form?
C031 Poor diffusion properties of vat/sulfur dyes Were the dyes with poor diffusion properties used for the dyeing of
cellulose component?
565
Table B.1 (Continued)
Cause Description Question to the user
C032 Poor leveling properties of vat/sulfur dyes Was the dye with poor leveling properties used for the dyeing of
cellulose component?
C033 Poor vat/sulfur dyes dispersion system Were the dyes used for cellulose component tested for their dispersion
properties?
C034 Poor color matching of each fiber in the
blend Is the appearance of the both fiber components look similar?
C035 Variations in strength and purity of dyebath
chemicals
Were the dyebath chemicals tested for their chemical properties prior to
their application?
C036 Chemical or physical interaction between
colorants and auxiliaries
Were the colorants and auxiliaries used have good compatibility with
each other?
C037 Poor selection of dyebath chemicals Were the dyebath chemicals selected based on their application and
performance properties for the coloration of blends?
C038 Formation of binder film on padder or rollers Was the binder evaluated for its agglomeration properties?
C039 Agglomeration of binder Was the binder stored and stirred properly before use?
C040 Binder with poor fastness properties Was the binder tested for its dispersion properties?
C041 Brittleness (poor softness) of the binder film Was the binder film evaluated for its softness?
C042 Insufficient amount of binder Was the amount of binder too low according to the depth of shade?
C043 High amount of binder Was the amount of binder too high according to the depth of shade?
C044 Poor resistance of binder against aging Was the heat stability of binder not good?
C045 Binder with poor swelling resistance Was the swelling resistance of binder not good?
C046 High amount of softener Was the amount of softener used too high?
C047 Improper softener selection Was the softener selected according to fabric hand and its effect on
coloration properties?
C048 Inappropriate electrolyte (salt) concentration Was the electrolyte concentration too low according to the depth of
shade?
C049 Inappropriate concentration of dispersing
agent
Was the dispersing agent concentration too low according to the depth of
the shade?
C050 Too low amount of lubricating agent Was the concentration of lubricating agent too low for a given substrate?
566
Table B.1 (Continued)
Cause Description Question to the user
C051 Too high concentration of carrier Was the carrier concentration too high as compared to the depth of
shade?
C052 Low quantity of anti-migrating agent Was the concentration anti-migrating agent too low according to the
depth of shade?
C053 Precipitation of anti-migrating agent Was the anti-migrating agent tested for its stability under the coloration
process conditions?
C054 Too high concentration of dye fixative Was the concentration of dye fixative used according to the depth of
shade?
C055 Use of silicone based defoamer Was the defoamer used based on silicone?
C056 Too low concentration of reducing agent
and/or alkali
Was the concentration of reducing agent and alkali too low according to
the dye recommendations?
C057 Presence of air in the machine Was there any air present in the machine before or during the dyeing
process?
C058 Inappropriate rinsing temperature Was the rinsing water temperature too high?
C059 Inadequate water flow rates/liquor ratio
during rinsing
Was the appropriate quantity of water/liquor used for the rinsing process
according to the depth of shade?
C060 Inadequate number of rinse cycles/rinse baths Was the required number of rinse cycles given to the dyed substrate
according to the depth of shade?
C061 Inappropriate pH during oxidation Was the pH acidic during the oxidizing process?
C062 Insufficient concentration of oxidizing agent Was the concentration of oxidizing agent too low?
C063 Inappropriate temperature during oxidation Was the temperature too high during oxidation?
C064 Inadequate reduction clearing temperature Was the temperature too low during reduction clearing (<70 C)?
C065 Inadequate reduction clearing time Was appropriate time given for reduction clearing according to the depth
of shade?
C066 Inadequate concentration of hydro and
caustic during reduction clearing
Was the concentration of hydro and caustic used for reduction clearing
according to the depth of shade?
C067 Inadequate soaping temperature Was the temperature during soaping too low?
C068 Inadequate pH during soaping Was the pH during soaping maintained based on dye stability?
567
Table B.1 (Continued)
Cause Description Question to the user
C069 Inadequate soaping time Was appropriate time given for soaping according to the depth of shade?
C070 Improper selection of detergent for soaping Was the detergent used evaluated for its dye wash-off properties?
C071 Inadequate water flow rates/liquor ratio
during soaping
Was the appropriate quantity of water/liquor used for the soaping process
according to the depth of shade?
C072 Presence of residual alkali/hydro after dyeing
cycle
Were there any residues of alkali/hydro present in the substrate after
reduction clearing process?
C073 Too high drying temperature after the dyeing
process Was the substrate dried at very high temperature after dyeing?
C074 Improper storage and handling of substrate Was the substrate stored under controlled conditions and transported
carefully?
C075 Machine stoppage for a long duration Was the machine stopped for a longer duration during the dyeing
process?
C076 Presence of dye deposits in the dye
preparation tank and machine
Were the dyeing machine and preparation tanks properly cleaned after
the dyeing process?
C077 Presence of reductive chemicals in substrate,
water or steam Were the dyes used sensitive to reduction?
C078 Excessive foaming in the dye bath/trough Was there a foam formation during the dyeing process?
C079 Non-uniform or damaged machine parts Was the surface of the dyeing machine and fabric guide elements non-
uniform or damaged?
C080 Excessive, insufficient or variable tension
during fabric run Was there a change in fabric tension during the dyeing process?
C081 Longer duration of substrate run due to
reprocessing Was the substrate reprocessed (pretreatment or dyeing)?
C082 Variations in dyeing program Were there any changes made in the dyeing program (time, heating and
cooling rates)?
C083 Rubbing of unfixed substrate against the
guide roller/machine part
Was the substrate rubbed with the guide roller or machine part before dye
fixation?
C084 Too fast increase in the differential pressure Was the differential pressure increased too quickly?
568
Table B.1 (Continued)
Cause Description Question to the user
C085 Too low liquor flow rate Was the liquor flow rate too low according to package density?
C086 Too high liquor flow rate Was the liquor flow rate too high according to package density?
C087 Inappropriate liquor flow times (in-out and
out-in)
Were there any differences in the duration of the liquor flow between in-
out and out-in?
C088 Too high pressing density Was the pressing density too high?
C089 Too low pressing density Was the pressing density too low?
C090 Leakage in dye package Was there any leakage in the dye package and package column?
C091 Defective locking caps Were the defective locking caps used during the dyeing process?
C092 Too large batch size (machine overloading) Was the batch size too large according to the machine capacity?
C093 Presence of oligomer and other deposits in
the machine Were there any oligomer deposits in the machine?
C094 Presence of oligomer deposits on the
substrate surface Is there any oligomer deposits present on the substrate?
C095 Trapped air pockets in the material during
dyeing
Were the air pockets removed from the material at the start of the dyeing
cycle?
C096 High temperature rise rate Was the dyebath temperature increased too rapidly?
C097 Inappropriate dyebath pH Was the pH maintained according to the dye class and fiber type?
C098 Use of too low liquor ratio Was the liquor ratio too low according to the substrate type and machine?
C099 Use of too high liquor ratio Was the liquor ratio too high?
C100 Too low dyeing temperature Was the dyeing temperature too low as compared to the recommended
dyeing temperature?
C101 Too high dyeing temperature Was the dyeing temperature too high as compared to the recommended
dyeing temperature?
C102 Too slow fabric/rope speed Was the fabric speed too slow during the dyeing process?
C103 Too fast fabric/rope speed Was the fabric speed too fast during the dyeing process?
C104 Too short dyeing time Was the dyeing duration too short based on the depth of shade and
substrate type?
569
Table B.1 (Continued)
Cause Description Question to the user
C105 Too long dyeing time Was the dyeing duration too long based on the depth of shade and
substrate type?
C106 Shock cooling of fabric after completion of
dyeing cycle Was the substrate cooled too rapidly after the dyeing process?
C107 Too low liquor flow rate Was the liquor flow rate too low?
C108 Too high liquor flow rate Was there any increase in the liquor ratio during the dyeing process?
C109 Incorrect liquor flow direction Were there any differences in the duration of the liquor flow between in-
out and out-in?
C110 Incorrect overlap of fabric covering the beam
perforations Were the beam perforations correctly overlapped with the fabric?
C111 Uneven winding of fabric on the beam Was the fabric wound uniformly on to the beam?
C112 Variation in pressure head in the tubes Were there any differences in pressure heads among the dyeing tubes?
C113 Poor circulation or stoppage of fabric Were there any interruptions in the fabric circulation during the dyeing
process?
C114 Incorrect nozzle size (diameter) Was the correct nozzle size used according to fabric weight per running
meter?
C115 Twisting or pressing of the rope at high
temperature Was there any twisting or pressing of the rope during the dyeing process?
C116 Inappropriate nozzle pressure Was the nozzle pressure set according to the required rope dwell time?
C117 Cooling of outer/inner fabric layers Were the top layers and inner layers of the fabric batch cooler due to heat
loss?
C118 Cooling of selvages Was there any variation in temperature across the fabric width due to heat
loss?
C119 Variation in dyebath temperature Was there any variation in the dyebath temperature during the process?
C120 Too tight or too loose fabric edges Was the fabric correctly wound without tension differences?
C121 Deposits of fluff/lint on the padder surface
and guide rollers Was there any lint or fluff deposits on the padder or guide rollers?
C122 Damaged, worn out or uneven padder surface Was the padder surface uniform and free of defects?
570
Table B.1 (Continued)
Cause Description Question to the user
C123 Too high pad trough temperature Was there an increase in the pad trough temperature during the dyeing
process?
C124 Difference in the hardness of dye padders Were there any differences in hardness of the dyeing padders?
C125 Too high wet pickup Was the fabric wet pickup too high?
C126 Too low wet pickup Was the fabric wet pickup too low?
C127 Improper distribution and circulation of dye
liquor Was the dye liquor circulation and distribution system working properly?
C128 Uneven wet pickup Were there any differences in wet pickup across the fabric?
C129 Inadequate airing time between padding and
drying Was the fabric not given adequate airing time after the padding process?
C130 Selvage curling during padding and
thermofixation process Were the edge guiders and fabric guiding elements not working properly?
C131 Improper rotation of the fabric batch during
batching
Were there any differences in the rotation of fabric batches during the
dyeing process?
C132 Poor covering of fabric batch during batching Was the fabric batch not covered properly with the plastic bag after dye
padding?
C133 Differences in fixation temperature or time
during batching
Was there any fluctuation in the temperature of the surroundings during
the batching process?
C134 Variation in the intensity of the IR pre-dryer Were there any variations in the intensity of IR pre-dryer?
C135 Non-uniform air velocity or flow Were there any variations in airflow in the hotflue dryer?
C136 Too high drying temperature Was the drying temperature too high as compared to the recommended
temperature?
C137 Too low thermofixation temperature Was the thermofixation temperature too low as compared to dye
recommendation?
C138 Too high thermofixation temperature Was the thermofixation temperature too high as compared to dye
recommendation?
C139 Too long thermofixation time Was the thermofixation time too long?
C140 Too short thermofixation time Was the thermofixation time too short for a given depth of shade?
571
Table B.1 (Continued)
Cause Description Question to the user
C141 Temperature variation in the hotflue Were there any differences in temperature in different regions of the
hotflue?
C142 Contact of condensation drops with unfixed
colorant Were the steamer roof and exhaust canopies properly heated?
C143 Inadequate steaming temperature Was the required steaming temperature maintained according to the dye
class used?
C144 Inadequate steaming time Was the steaming time sufficient according to the dye class and depth of
shade?
C145 Variation in steam pressure inside the
steamer Were there any variations in steam pressure inside the steamer?
C146 Too high steamer water seal temperature Was the temperature of the steamer water seal too high?
C147 High turbulence in the washbox Was there a high turbulence in the wash box due to steam?
C148 Difference in the singeing of fabric’s face
and back
Were there any differences in the appearance of the fabric's face and back
after singeing?
C149 Fiber damage during singeing Were the singeing conditions not selected according to the fiber type,
blend ratio, and fabric construction?
C150 Incomplete singeing Was the singeing position and flame intensity selected correctly?
C151 Incomplete removal of sizing agents and
sizing wax Was the degree of desizing of fabric too low?
C152 Incomplete removal of oil, rust and grease
stains
Are there any oil or grease stains present on the substrate that glows
under UV light?
C153 Fiber damage during scouring and bleaching Were the concentration of scouring and bleaching chemicals used
according to the fiber type and blend ratio?
C154 Too high weight loss during scouring Was the weight loss of substrate too high after the scouring process?
C155 Insufficient relaxation of the substrate during
washing
Was enough dwell time provided to substrate for relaxation during the
washing process?
C156 Localized swelling of fiber Was there any direct contact for concentrated alkali with the substrate?
572
Table B.1 (Continued)
Cause Description Question to the user
C157 Incomplete removal of fats, waxes, spin
finishes, and knitting oils Was the absorbency of fabric too low after scouring process?
C158 Inadequate weight reduction of polyester Was the fabric weight loss after the weight reduction process too low?
C159 Catalytic damage during bleaching Were there any pinholes present in the fabric after bleaching due to
chemical damage?
C160 Presence of residual peroxide in substrate Were there any residues of peroxide on the substrate left from the
bleaching process?
C161 Incomplete removal of motes (seed husks) Are there any broken seed particles present in the substrate?
C162 Inadequate whiteness of substrate Was there any variation in the whiteness across the fabric?
C163 Improper heat setting of substrate Were the heat setting conditions set properly according fiber type and
blend ratio?
C164 Fiber damage during heat setting Was the substrate exposed to too high temperature during heat setting?
C165 Physical damage of substrate (pin marks,
cuts)
Was the fabric physically damaged in the form of cuts and pin marks
during heat setting?
C166 Excessive overstretching of substrate on
stenter Was the fabric stretched too much on the stenter?
C167 Incomplete mercerization Was the degree of mercerization of substrate too low (<125) and varied
across the substrate?
C168 Differential mercerization due to
superimposed layers of substrate Was the fabric mercerized in the form of superimposed layers?
C169 Alkaline pH of substrate before dyeing Was the pH of the fabric alkaline after the preparation stage?
C170 Improper stitching of substrate ends Was the fabric ends properly stitched using correct thread?
C171 Presence of insect residues in substrate Were there any insect residues in the fabric?
C172 Presence of Ca and Mg ions (hardness) in
water Was the hardness of the dyeing water too high?
C173 Presence of heavy metals (Cu, Fe, Mn, Zn) in
water Were there high levels of heavy metals in the dyeing water?
C174 Presence of suspended matter in water Was the appearance of water used for dyeing water turbid?
573
Table B.1 (Continued)
Cause Description Question to the user
C175 Presence of bicarbonate in water Was the dyeing water monitored for bicarbonates level?
C176 Presence of chlorine in water Was there any presence of chlorine in the dyeing water?
C177 Presence of holes, tears or cuts in greige
substrate Were there any holes or cuts present in the greige substrate?
C178 Presence of bands or stripes in greige
substrate Were there any bands or stripes present in the greige substrate?
C179 Fabric rolls from different machines or batch
or factory Were the rolls used in the same lot obtained from different sources?
C180 Yarn mixing Do the fabric contains yarns which are different in appearance than
neighboring yarns?
C181 Variation in yarn tension during
warping/sizing
Do the fabric contains yarn which are loose or too tight as compared to
the neighboring yarns?
C182 Too high package density Was the yarn package density too high?
C183 Too low package density Was the yarn package density too low?
C184 Uneven package density Was there any variation in density within a package?
C185 Edging process for rounding of package
flanks Was the edging process used for the rounding of package flanks?
C186 Improper rounding of package flanks Were the package flanks rounded properly during the winding process?
C187 Improper coverage of dye tube perforations Were the dye tubes perforations not covered properly by the yarn?
C188 Use of damaged dye tubes Were the damaged tubes used during the dyeing process?
C189 Poor temperature stability of dye tubes Were the dye tubes used have poor temperature stability?
C190 Too many yarn imperfections Was the level of imperfections in the yarn too high?
C191 Lower yarn strength and elongation Were the yarns present in the griege fabric had lower strength and
elongation?
C192 Variation in blend ratio Are there any differences in the blend ratio of the substrate compared to
actual?
C193 Foreign fiber contamination Are there any foreign fibers present in the substrate?
574
Table B.1 (Continued)
Cause Description Question to the user
C194 Variations in crystallinity and orientation of
fiber
Are the fibers used in the substrate came from the different batch and had
differences in crystallinity and draw ratio?
C195 Variations in the degree of polymerization of
fiber
Are the fibers used in the substrate came from the different batch and had
differences in degree of polymerization?
C196 Presence of immature fibers Are there any immature fibers or neps present in the substrate?
575
DEXPERT-B installation guide
1. Open the DEXPERT-B folder.
2. Open the “wxclips” folder and double-click “wxclips.exe” file to run the application on your
computer.
Method 1
a. Once the wxclips application is open, the wxclips screen will appear on your computer.
b. Find the file named “0start” in the folder and drag it to wxclips icon.
c. The DEXPERT-B-Blends will run automatically.
Method 2
a. Once the installation is done, locate the wxClips program among the installed program on your
computer and double click the file to open the application.
b. Once the wxClips window is open, click on “File” tab and click on the dropdown menu functions
“load definitions”.
c. Locate the file “0Start” in the DEXPERT-B folder and open it
d. Once the file loads in the wxClips window, click on “Applications” tab, and then click on the
dropdown menu functions “start application”.
e. The DEXPERT-Blends will run promptly.
If you have any questions, please feel email: [email protected] for troubleshooting installation
and problems regarding the program.
576
Analysis of the expert responses of the faulty colored samples.
Table D.1: Expert responses and expert system’s knowledge base for reproducibility (S1).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C001 Errors in the weighing of colorants and
chemicals 9 S2, S4, S5, S9
[77, 142, 317, 345,
348] x x x
C003 Too fast/quick addition of chemicals in the
bath 8 S2, S9, S11 [297, 301, 345] x x x x
C007 Poor dye selection for polyester component 8 S6a-d
[9, 56, 57, 64, 67,
77, 83, 87, 125, 142,
161-163]
x x x
C008 Poor dye selection for cellulose component 8 S6a-d
[9, 56, 57, 64, 67,
77, 83, 87, 125, 142,
161-163]
x x x x
C082 Variations in dyeing program 8 S2, S4, S5 [9, 253, 297, 301] x x x x
C096 Higher temperature rise rate 8 S2, S3, S9, S11,
S14
[9, 112, 231, 253,
380] x x x x
C097 Inappropriate dyebath pH 7 S2, S4, S5, S6a-
c, S9, S10, S13 [301] x x x x
C002 Improper bath preparation procedure 7 S2, S5, S7, S9 [297, 301, 317] x x x x
577
Table D.1 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C179 Fabric rolls from different machines or batch or
factory 7 S9 [139] x x x x
C004 Too fast/quick addition of dyes in the bath 7 S2, S9, S11 [297, 301, 347] x x
C010 Variation in colorant strength 7 S2, S4, S5 [253, 301] x
C011 Incompatibility between dye classes 7 S2-S5, S6a-d,
S7, S9-11
[7, 9, 79, 92, 93, 100,
128, 253, 301] x x x x
C019 Poor disperse dye dispersion stability 7 S2, S4, S7, S9-
11
[7, 67, 68, 75, 79,
81, 85, 253] x x x
C027 Poor stability of reactive/direct dyes under
polyester dyeing conditions 7 S2, S4, S7
[64, 68, 79, 122,
253] x x x x
C034 Poor color matching of each fiber in the blend 7 S5 [139] x x
C092 Too large batch size (machine overloading) 7 S2, S3, S11,
S14 [67, 231, 253] x x x x
C100 Too low dyeing temperature 7 S2, S4, S6a-c,
S11 [297, 301] x x x x
C104 Too short dyeing time 7 S2, S5, S6a-c,
S11 [297, 301] x x x x
578
Table D.1 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C167 Incomplete mercerization 7 S2, S3, S4, S9,
S10
[9, 184, 253, 305,
333, 334, 337, 338] x x x x
C009 Poor dye combinations for each fiber type 7 S2, S5, S6d, S9-
11 [231, 345, 348] x x x x
C099 Use of too high liquor ratio 7 S4, S5 [297] x x
C109 Incorrect liquor flow direction 7 S2, S4, S11,
S14 [9, 68, 85, 110, 194] x x x
C180 Yarn mixing 6 S3, S5, S14,
S17 [215, 230, 258-260] x x
C021 Poor disperse dye leveling and migration
properties 6 S2 ,S5, S11
[9, 68, 75, 100, 111,
118, 231] x x
C023 Too high substantivity of reactive/direct dyes 6 S2, S6a-c, S9-
11 [128, 253, 345] x x
C024 Poor solubility of reactive/direct dyes 6 S2-5, S6b, S6c,
S7, S9-11
[9, 68, 75, 100, 111,
118, 231] x x
C026 Poor migration properties of reactive/direct
dyes 6 S2, S11
[9, 68, 100, 111,
118, 231, 345] x x x
C112 Variation in pressure head in the tubes 6 [297, 301] x x x
579
Table D.1 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C172 Presence of Ca and Mg ions (hardness) in
water 6
S2, S4, S5, S6a-
c, S7, S11
[277, 280, 283, 290,
292, 296, 298, 299] x x x
C192 Variation in blend ratio 6 S3, S5 [6, 181, 213]
C119 Variation in dyebath temperature 6 S9, S10 [68, 323] x x x
C018 Poor disperse dye dispersion system 6 S2, S4, S5, S7,
S9-11 [75, 253, 348] x x x
C077 Presence of reductive chemicals in substrate,
water or steam 6 S16 [64, 251, 301]
C113 Poor circulation or stoppage of fabric 6 S2, S9, S14 [253] x
C102 Too slow fabric/rope speed 5 S2, S14 [301, 346] x x x
C151 Incomplete removal of sizing agents and sizing
wax 5
S2-5, S7-10,
S16
[67, 149, 303, 305-
307, 324-329] x x x
C157 Incomplete removal of of fats, waxes, spin
finishes and knitting oils 5 S2-5, S8-10
[149, 277, 278, 297,
303, 305, 317, 327] x x x x
C093 Presence of oligomer and other substance
deposits in the machine 5 S2, S7, S8, S11
[67, 85, 173-175,
233, 253] x
C036 Chemical or physical interaction between
colorants and auxiliaries 5
S2-5, S6a-d,
S7-11
[18, 78, 79, 86, 89,
103, 253] x x x
580
Table D.1 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C020 Poor disperse dye diffusion properties 5 S2, S11 [9, 68, 75, 100, 111,
118, 231] x x
C025 Poor diffusion properties of reactive/direct
dyes 5 S2, S11
[9, 68, 75, 100, 111,
118, 231] x x
C028 High dye reactivity 5 S2, S4, S7, S9,
S10
[9, 68, 100, 118,
128, 231] x x x
C035 Variations in strength and purity of dyebath
chemicals 5
S2, S4, S5, S6a-
d, S7 [79, 89, 103] x x
C037 Poor selection of dyebath chemicals 5
S2, S3, S5, S6a-
d, S7, S8-11,
S14
[443] x x
C048 Inappropriate electrolyte (salt) concentration 5 S2, S4, S9, S11 [128, 317, 345] x x x
C049 Inappropriate concentration of dispersing agent 5 S2, S4, S5, S9,
S10, S11
[67, 89, 97, 106,
109]
C056 Too low concentration of reducing agent
and/or alkali 5
S2, S4, S5, S6a-
c, S11 [67, 194, 345, 370] x x
C072 Presence of residual alkali/hydro after dyeing
cycle 5 S2, S4, S5, S8 [251, 253, 348] x x x x x
581
Table D.1 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C085 Too low liquor flow rate 5 S2, S4, S11 [9, 68, 85, 110]
C163 Improper heat setting of substrate 5 S2-5, S9, S10,
S14, S17
[67, 83, 168, 194,
253, 320, 323] x x x
C173 Presence of heavy metals (Cu, Fe, Mn, Zn) in
water 5
S2, S4, S5, S7,
S13
[277, 280, 283, 286,
288-292] x x
C174 Presence of suspended matter in water 5 S2, S7, S11 [100, 282, 284] x x x
C175 Presence of bicarbonate in water 5 S2, S4, S5 [283, 295-297] x x
C176 Presence of chlorine in water 5 S2, S4, S5, S11 [281, 285, 286] x
C194 Variations in crystallinity & orientation of fiber 5 S2, S3 [114, 157, 168, 218-
222]
C107 Too low liquor flow rate 5 S2, S4, S10,
S11 [9, 68, 85, 110] x x
C162 Inadequate whiteness of substrate 5 S2, S4, S5 [150, 301, 305, 309] x x
C160 Presence of residual peroxide in substrate 4 S2, S4, S5, S8 [100, 150, 253, 301] x x x x x
C195 Variations in degree of polymerization of fiber 4 S2 [82, 114, 171]
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
582
Table D.2: Expert responses and expert system’s knowledge base for unlevelness (S2).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C003 Too fast/quick addition of chemicals in
the bath 9 S1, S9, S11 [297, 301, 345] x x x x
C004 Too fast/quick addition of dyes in the
bath 9 S1, S9, S11 [297, 301, 347] x x x x
C096 Higher temperature rise rate 9 S1, S3, S9, S11, S14 [9, 112, 231, 253,
380] x x x
C082 Variations in dyeing program 8 S1, S4, S5 [9, 253, 297, 301] x x x
C009 Poor dye combinations for each fiber
type 8 S1, S5, S6d, S9-11 [231, 345, 348] x x x
C018 Poor disperse dye dispersion system 7 S1, S4, S5, S7, S9-11 [75, 253, 348] x x x
C019 Poor disperse dye dispersion stability 7 S1, S4, S7, S9-11 [7, 67, 68, 75, 79, 81,
85, 253] x x x
C024 Poor solubility of reactive/direct dyes 7 S1, S4, S5, S6b, S6,
cS7-11
[9, 68, 75, 100, 111,
118, 231] x x x x
C011 Incompatibility between dye classes 7 S1, S3-5, S6a-d, S7, S9-
11
[7, 9, 79, 92, 93, 100,
128, 253, 301] x x x x x
C097 Inappropriate dyebath pH 7 S1, S4, S5, S6a-c, S9,
S10, S13 [301] x x
583
Table D.2 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C149 Fiber damage during singeing 7 S7, S13 [67, 149, 168, 313,
318] x x
C163 Improper heat setting of substrate 7 S1, S3, S4, S5, S9,
S10, S14, S17
[67, 83, 168, 194,
253, 320, 323] x x x
C175 Presence of bicarbonate in water 7 S1, S4, S5 [283, 295-297] x x
C092 Too large batch size (machine
overloading) 7 S1, S3, S11, S14 [67, 231, 253] x x
C157 Incomplete removal of fats, waxes, spin
finishes and knitting oils 6 S1, S3-5, S8-10
[149, 277, 278,
297, 303, 305, 317,
327]
x x x
C151 Incomplete removal of sizing agents and
sizing wax 6 S1, S3-5, S7-10, S16
[67, 149, 303, 305-
307, 324-329] x x x
C026 Poor migration properties of
reactive/direct dyes 6 S1, S11
[9, 68, 100, 111,
118, 231, 345] x x
C020 Poor disperse dye diffusion properties 6 S1, S11 [9, 68, 75, 100,
111, 118, 231] x x x
C021 Poor disperse dye leveling and migration
properties 6 S1, S5, S11
[9, 68, 75, 100,
111, 118, 231] x x
584
Table D.2 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C023 Too high substantivity of reactive/direct
dyes 6 S1, S6a-c, S9-11 [128, 253, 345] x x x
C098 Use of too low liquor ratio 6 S3, S7, S11, S14 [297, 301] x
C100 Too low dyeing temperature 6 S1, S4, S6a-c, S11 [297, 301]
C104 Too short dyeing time 6 S1, S2, S5, S6a-c, S11 [297, 301]
C028 High dye reactivity 6 S1, S4, S7, S9, S10 [9, 68, 100, 118,
128, 231] x
C049 Inappropriate concentration of dispersing
agent 5 S1, S4, S5, S9-11
[67, 89, 97, 106,
109] x x x
C078 Excessive foaming in the dye
bath/trough 5 S7, S8
[89, 97, 253, 254,
317, 346, 351] x x x x x
C172 Presence of Ca and Mg ions (hardness)
in water 5
S1, S4, S5, S6a-c, S7,
S11
[277, 280, 283,
290, 292, 296, 298,
299]
x x
C176 Presence of chlorine in water 5 S1, S4, S5, S11 [281, 285, 286] x x x
C002 Improper bath preparation procedure 5 S1, S5, S7, S9 [297, 301, 317] x x x
C025 Poor diffusion properties of
reactive/direct dyes 5 S1, S11
[9, 68, 75, 100,
111, 118, 231] x x x
585
Table D.2 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C035 Variations in strength and purity of
dyebath chemicals 5 S1, S4, S5S, 6a-d, S7 [79, 89, 103] x x
C036 Chemical or physical interaction
between colorants and chemicals 5
S1, S3-5, S6aS6a-d,
S7-11
[18, 78, 79, 86, 89,
103, 253] x x x x x
C037 Poor selection of dyebath chemicals 5 S1, S3, S5, S6aS6a-d,
S7-11, S14 [443] x x x
C072 Improper neutralization of substrate after
dyeing 5 S1, S4, S5, S8 [251, 253, 348]
C077 Presence of reductive chemicals in
substrate, water or steam 5 S1, S4, S5 [64, 251, 301] x x x x
C113 Poor circulation or stoppage of fabric 5 S1, S2, S9, S14 [253] x x x
C167 Incomplete mercerization 5 S1, S3, S4, S9, S10 [9, 184, 253, 305,
333, 334, 337, 338] x x x
C173 Presence of heavy metals (Cu, Fe, Mn,
Zn) in water 5 S1, S4, S5, S7, S13
[277, 280, 283,
286, 288-292] x x x
C174 Presence of suspended matter in water 5 S1, S7, S11 [100, 282, 284] x x
C160 Presence of residual peroxide in
substrate 5 S1, S4, S5, S8
[100, 150, 253,
301] x x x x
586
Table D.2 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C102 Too slow fabric/rope speed 5 S1, S14 [301, 346] x x x
C103 Too fast fabric/rope speed 5 S14 [253]
C048 Inappropriate electrolyte (salt)
concentration 4 S1, S4, S9, S11 [128, 317, 345] x x x x x
C095 Trapped air pockets in the material
during dyeing 4 S8, S11 [110, 149, 253]
C169 Alkaline pH of substrate before dyeing 4 S4, S9, S10 [301, 305, 309,
317, 334] x x
C194 Variations in crystallinity and orientation
of fiber 4 S1, S3
[114, 157, 168,
218-222] x x x x
C196 Presence of immature fibers 4 S8 [6, 160-163] x x x x
C027 Poor stability of reactive/direct dyes
under polyester dyeing conditions 4 S1, S4, S7
[64, 68, 79, 122,
253] x
C115 Twisting or pressing of the rope at high
temperature 4 S3, S14
[149, 297, 301,
323]
C195 Variations in the degree of
polymerization of fiber 4 S1 [82, 114, 171] x
587
Table D.2 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C153 Fiber damage during scouring and
bleaching 4 S13-17 [70] x x
C162 Inadequate whiteness of substrate 4 S1, S4, S5 [150, 301, 305,
309] x
C001 Errors in the weighing of colorants and
chemicals 4 S1, S4, S5, S9
[77, 142, 317, 345,
348]
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
588
Table D.3: Expert responses and expert system’s knowledge base for streaks (S3).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C178 Presence of bands or stripes in greige
substrate 9 S10
[6, 203, 215, 216, 250-
252, 261, 272, 274-276] x x x x x
C180 Yarn mixing 8 S1, S5, S14, S17 [215, 230, 258-260]
C128 Uneven wet pickup 7 S1, S2, S9, S10 [61, 100, 128, 133, 353] x x x x
C052 Lower quantity of anti-migrating agent 7 S1, S2, S5, S10 s x
C135 Non-uniform air velocity or flow 7 S1, S2, S5, S9,
S10, S12 [67, 317, 361, 363] x x
C151 Incomplete removal of sizing agents and
sizing wax 7
S1, S2, S4, S5,
S7-10, S16
[67, 149, 303, 305-307,
324-329] x x
C181 Variation in yarn tension during
warping/sizing 7 S14 [215, 230, 258-260] x x
C163 Improper heat setting of substrate 6 S1, S2-5, S9,
S10, S14, S17
[67, 83, 168, 194, 253,
320, 323] x x x
C158 Inadequate weight reduction of polyester 6 S13, S14, S16 [331, 332] x
C194 Variations in crystallinity & orientation
of fiber 6 S1, S2
[114, 157, 168, 218-
222] x
C075 Machine stoppage for a longer duration 6 S14 x x
589
Table D.3 (Continued)
Expert system’s knowledge base
Literature
Experts
Cause Description CF
Commonness
H M A B C D E
C157 Incomplete removal of fats, waxes, spin
finishes and knitting oils 6
S1, S2, S4, S5,
S8-10
[149, 277, 278, 297,
303, 305, 317, 327] x
C167 Incomplete mercerization 6 S1, S2, S4, S9,
S10
[9, 184, 253, 305, 333,
334, 337, 338] x x
C036 Chemical or physical interaction between
colorants and auxiliaries 5
S1, S2, S4, S5,
S6a-d, S7-11
[18, 78, 79, 86, 89, 103,
253] x x
C053 Precipitation of anti-migrating agent 5 S1, S2, S5, S8-10 [92, 95, 100, 105, 118,
130-132] x x
C079 Non uniform or damaged machine parts 5 S14, S15 [149, 150] x x x
C134 Variation in the intensity of the IR pre-
dryer 5
S1, S2, S5, S9,
S10, S12 [348, 363] x x
C170 Improper stitching of substrate ends 5 [67, 322]
C192 Variation in blend ratio 5 S1, S5 [6, 181, 213] x
C011 Incompatibility between dye classes 4 S1, S2, S4, S5,
S6a-d, S7, S9-11
[7, 9, 79, 92, 93, 100, 128,
253, 301] x
C083 Rubbing of unfixed substrate against the
guide roller/machine part 4 S14 [92, 149, 150]
C190 Too many yarn imperfections 4 S14 [6, 207, 216] x
590
Table D.3 (Continued)
Expert system’s knowledge base
Literature
Experts
Cause Description CF
Commonness
H M A B C D E
C037 Poor selection of dyebath chemicals 4 S1, S2, S5. S6a-
d, S711, S14 [443] x x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
591
Table D.4: Expert responses and expert system’s knowledge base for shade change (S5).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C034 Poor color matching of each fiber in the blend 8 S1 [139] x x x x x
C018 Poor disperse dye dispersion system 7 S1, S2, S4, S7, S9-
11 [75, 253, 348] x x x
C010 Variation in colorant strength 7 S1, S2, S4 [253, 301] x x x
C011 Incompatibility between dye classes 7 S1-4, S6a-d, S7,
S9-11
[7, 9, 79, 92, 93,
100, 128, 253, 301] x x x
C024 Poor solubility of reactive/direct dyes 7 S1, S2, S4, S6b,
S6c, S7, S9-11
[9, 68, 75, 100, 111,
118, 231] x x x
C192 Variation in blend ratio 7 S1S3 [6, 181, 213] x x
C163 Improper heat setting of substrate 6 S1-4, S9, S10, S14,
S17
[67, 83, 168, 194,
253, 320, 323] x x x
C009 Poor dye combinations for each fiber type 6 S1, S2, S6d, S9-11 [231, 345, 348] x x x x
C141 Temperature variation in the hotflue 6 S1, S2, S9, S10 [118, 253, 348, 370] x x x
C054 Too high concentration of dye fixative 6 S6d [301] x x x x
C077 Presence of reductive chemicals in substrate,
water or steam 5 S1, S2, S4 [64, 251, 301] x x x
C160 Presence of residual peroxide in substrate 5 S1, S2, S4, S8 [100, 150, 253, 301] x x x x
C176 Presence of chlorine in water 5 S1, S2, S4, S11 [281, 285, 286] x
592
Table D.4 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C021 Poor disperse dye leveling and migration
properties 5 S1, S2, S11
[9, 68, 75, 100, 111,
118, 231] x x
C036 Chemical or physical interaction between
colorants and auxiliaries 5
S1-4, S6a-d,
S7-11
[18, 78, 79, 86, 89,
103, 253] x x x
C049 Inappropriate concentration of dispersing
agent 5
S1, S2, S4, S9-
11
[67, 89, 97, 106,
109] x x x
C053 Precipitation of anti-migrating agent 5 S1, S2, S3, S8-
10
[92, 95, 100, 105,
118, 130-132] x
C069 Inadequate soaping time 5 S6a-c [85, 301, 345, 370] x
C072 Presence of residual alkali/hydro after
dyeing cycle 5 S1, S2, S4, S8 [251, 253, 348] x x
C097 Inappropriate dyebath pH 5
S1, S2, S4,
S6a-c, S9,
S10, S13
[301] x x x
C140 Too short thermofixation time 5 S1, S4, S6a-c [114, 115, 128, 133] x x x
C151 Incomplete removal of sizing agents and
sizing wax 5
S1-4, S7-10,
S16
[67, 149, 303, 305-
307, 324-329]
593
Table D.4 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C157 Incomplete removal of fats, waxes, spin
finishes and knitting oils 5 S1-4, S8-10
[149, 277, 278, 297,
303, 305, 317, 327] x x x
C173 Presence of heavy metals (Cu, Fe, Mn, Zn)
in water 5
S1, S2, S4, S7,
S13
[277, 280, 283, 286,
288-292] x x x
C175 Presence of bicarbonate in water 5 S1, S2, S4 [283, 295-297] x
C172 Presence of Ca and Mg ions (hardness) in
water 5
S1, S2, S4,
S6a-c, S7, S11
[277, 280, 283, 290,
292, 296, 298, 299] x x x
C180 Yarn mixing 4 S1, S3, S14,
S17 [215, 230, 258-260]
C067 Inadequate soaping temperature 4 S6a-c, S9-11 [85, 301, 345, 370] x
C002 Improper bath preparation procedure 4 S1, S2, S7, S9 [297, 301, 317]
C035 Variations in strength and purity of dyebath
chemicals 4
S1, S2, S4,
S6a-d, S7 [79, 89, 103] x x
C037 Poor selection of dyebath chemicals 4
S1, S2, S3,
S6a-d, S7-11,
S14
[443] x
C052 Lower quantity of anti-migrating agent 4 S1, S2, S3,
S10
[92, 95, 100, 105,
118, 130-132] x x
594
Table D.4 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C138 Too high thermofixation temperature 4 S16 [114, 115, 128, 133] x x
C162 Inadequate whiteness of substrate 4 S1, S2, S4 [150, 301, 305, 309] x
C001 Errors in the weighing of colorants and
chemicals 4 S1, S2, S4, S9
[77, 142, 317, 345,
348] x x
C071 Inadequate water flow rates/liquor ratio
during soaping 4 S6a-c, S9-11 [85, 301, 345, 370] x x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
595
Table D.5: Expert responses and expert system’s knowledge base for inadequate washing fastness (S6).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C007 Poor dye selection for polyester component 9 S1, S6b-d [9, 56, 57, 64, 67, 77, 83,
87, 125, 142, 161-163] x x x x x
C008 Poor dye selection for cellulose component 9 S1, S6-d [9, 56, 57, 64, 67, 77, 83,
87, 125, 142, 161-163] x x x x x
C012 Cross-staining of fiber 9 S6b-d [7, 9, 18, 77-79, 142] x x x x x
C022 Poor thermomigration property of disperse
dye 9 S6b, S6c
[9, 56, 79, 83, 88, 177,
253] x x x x x
C006 Wrong selection of dyeing method (1 bath,
2 bath) 9 S6b, S6c
[9, 56, 57, 64, 67, 83, 87,
125, 161-163] x x x x x
C069 Inadequate soaping time 8 S5, S6b, S6c [85, 301, 345, 370] x
C067 Inadequate soaping temperature 8 S5, S6b, S6c,
S9-S11 [85, 301, 345, 370] x x x x x
C070 Improper selection of detergent for soaping 8 S6b, S6c [85, 301, 345, 370] x x
C064 Inadequate reduction clearing temperature 8 S6b, S6c [9, 85, 109, 301, 345,
370] x x x x
C065 Inadequate reduction clearing time 8 S6b, S6c [9, 85, 109, 301, 345,
370] x x x
596
Table D.5 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C066 Inadequate concentration of hydro and
caustic during reduction clearing 8 S6b, S6c
[9, 85, 109, 301, 345,
370] x x x x
C068 Inadequate pH during soaping 7 S4. S6b, S6c [61, 85, 301, 345, 370] x x
C071 Inadequate water flow rates/liquor ratio
during soaping 7
S5, S6b, S6c,
S9-S11 [85, 301, 345, 370] x
C060 Inadequate number of rinse cycles/rinse
baths 6 S1, S6b, S6c [57, 61, 81] x x
C100 Too low dyeing temperature 6 S1, S2, S4,
S6b, S6c, S11 [297, 301] x x x
C097 Inappropriate dyebath pH 6
S1, S2, S4, S5,
S6b, S6c, S9,
S10, S13
[301] x
C104 Too short dyeing time 6 S1, S2, S5,
S6b, S6c, S11 [297, 301] x x
C011 Incompatibility between dye classes 5 S1-5, S6b-d,
S7, S9-11
[7, 9, 79, 92, 93, 100,
128, 253, 301] x x
C023 Too high substantivity of reactive/direct
dyes 5
S1, S2, S6b,
S6c, S9-11 [128, 253, 345] x
597
Table D.5 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C005 Too high colorant concentration 5 S6, bS6c, S7 [93, 100] x
C036 Chemical or physical interaction between
colorants and chemicals 4
S1-5, S6, S6b-
d, S7-11
[18, 78, 79, 86, 89, 103,
253] x
C037 Poor selection of dyebath chemicals 4
S1, S2, S3, S5,
S6b-d, S7-11,
S14
[443] x x x
C058 Inappropriate rinsing temperature 4 S1, S6, bS6c [61, 81] x x x x
C035 Variations in strength and purity of dyebath
chemicals 4
S1, S2, S4, S5,
S6b-d, S7 [79, 89, 103] x x x
C059 Inadequate water flow rates/liquor ratio
during rinsing 4
S1, S6b, S6c,
S11 [61, 81] x x x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
598
Table D.6: Expert responses and expert system’s knowledge base for dark stains or spots (S7).
Expert system’s knowledge base
Literature
Experts
Cause Description CF
Commonness
H M A B C D E
C018 Poor disperse dye dispersion system 8 S1, S2, S4, S5, S9-
S11 [75, 253, 348] x x x
C019 Poor disperse dye dispersion stability 8 S1, S2, S4, S9-11 [7, 67, 68, 75, 79, 81, 85,
253] x x
C024 Poor solubility of reactive/direct dyes 8 S1, S2, S4, S5, S6b,
S6c, S9-11
[9, 68, 75, 100, 111, 118,
231] x x x
C078 Excessive foaming in the dye
bath/trough 7 S2, S8
[89, 97, 253, 254, 317,
346, 351] x x x
C055 Use of silicone based defoamer 7 [253, 351] x x x x
C161 Incomplete removal of motes (seed
husks) 7 [149, 305] x x
C011 Incompatibility between dye classes 6 S1-5, S6a-d, S9-11 [7, 9, 79, 92, 93, 100, 128,
253, 301] x x x
C156 Localized swelling of fiber 6 [323] x
C076 Presence of dye deposits in the dye
preparation tank and machine 6 [231] x x x
C002 Improper bath preparation procedure 6 S1, S2, S5, S9 [297, 301, 317] x
599
Table D.6 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C035 Variations in strength and purity of
dyebath chemicals 5
S1, S2, S4, S5,
S6a-d [79, 89, 103] x x
C149 Fiber damage during singeing 5 S2, S13 [67, 149, 168, 313,
318] x x
C027 Poor stability of reactive/direct dyes
under polyester dyeing conditions 5 S1, S2, S4 [64, 68, 79, 122, 253] x x
C028 High dye reactivity 5 S1, S2. S4, S9,
S10
[9, 68, 100, 118, 128,
231] x x x
C036 Chemical or physical interaction
between colorants and auxiliaries 5
S1-5, S6a-d, S8-
11
[18, 78, 79, 86, 89,
103, 253] x x x
C037 Poor selection of dyebath chemicals 5 S1-3, S5, S6a-d,
S8-11, S14 [443] x x
C172 Presence of Ca and Mg ions
(hardness) in water 5
S1, S2, S4, S5,
S6a-c, S11
[277, 280, 283, 290,
292, 296, 298, 299] x x x
C173 Presence of heavy metals (Cu, Fe, Mn,
Zn) in water 5
S1, S2, S4, S5,
S13
[277, 280, 283, 286,
288-292] x x x
C193 Foreign fiber contamination 4 S15 [6, 157, 209, 210] x x
600
Table D.6 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C151 Incomplete removal of sizing agents
and sizing wax 4 S1-5, S8-10, S16
[67, 149, 303, 305-
307, 324-329] x x x
C005 Too high colorant concentration 4 S6a-c [93, 100] x x x
C174 Presence of suspended matter in water 4 S1, S2, S11 [100, 282, 284] x x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
601
Table D.7: Expert responses and expert system’s knowledge base for light stains or sports (S8).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C142 Contact of condensation drops with unfixed
colorant 8
[100, 128, 362,
363] x x x
C152 Incomplete removal of oil, and grease stains 6 [67, 100, 301] x x
C053 Precipitation of anti-migrating agent 6 S1-3, S5, S9,
S10 x x
C121 Deposits of fluff/lint on the padder surface and
guide rollers 6 [67, 317] x x
C078 Excessive foaming in the dye bath/trough 5 S2, S7 x x x
C151 Incomplete removal of sizing agents and sizing
wax 5
S1-5, S7, S9,
S10, S16
[67, 149, 303, 305-
307, 324-329] x x x x x
C157 Incomplete removal of fats, waxes, spin
finishes, and knitting oils 5 S1-5, S9, S10
[149, 277, 278, 297,
303, 305, 317, 327] x x x
C171 Presence of insect residues in substrate 5 [139] x x x
C160 Presence of residual peroxide in substrate 4 S1, S2, S4, S5 [100, 150, 253,
301] x x x x
C036 Chemical or physical interaction between
colorants and auxiliaries 4
S1-5, S6a-d, S7,
S9-11
[18, 78, 79, 86, 89,
103, 253] x x x
C196 Presence of immature fibers 4 S2 [6, 160-163] x x x
602
Table D.7 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C037 Poor selection of dyebath chemicals 4 S1-3, S5, S6a-d,
S7, S9-11, S14 [443] x x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
603
Table D.8: Expert responses and expert system’s knowledge base for lengthwise shade variation (S9).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C023 Too high substantivity of reactive dye 8 S1, S2, S6a-c, S10,
S11 [128, 253, 345] x x x x x
C028 High dye reactivity 7 S1, S2, S4, S7,
S10
[9, 68, 100, 118, 128,
231] x x x
C128 Uneven wet pickup 7 S1, S2, S3, S10 [61, 100, 128, 133, 353] x x x
C018 Poor disperse dye dispersion system 7 S1, S2, S4, S5, S7,
S10, S11
[7, 67, 68, 75, 79, 81,
85, 253] x x x
C141 Temperature variation in the hotflue 6 S1, S2, S5, S10 [118, 253, 348, 370] x x x
C134 Variation in the intensity of the IR pre-
dryer 6
S1, S2, S3, S5,
S10, S12 [348, 363] x x x
C145 Variation in steam pressure inside the
steamer 6 S1, S2 [100, 363] x
C179 Fabric rolls from different machines or
batch or factory 6 S1 [139] x x x
C013 Bleeding of unfixed dye into the
bath/trough during development 6 [128, 139] x x x x
C011 Incompatibility between dye classes 5 S1-5, S6a-d, S7,
S10, S11
[7, 9, 79, 92, 93, 100,
128, 253, 301] x x x x
604
Table D.8 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C135 Non-uniform air velocity or flow 5 S1, S2, S3, S5, S10,
S12 [67, 317, 361, 363] x
C125 Too high wet pickup 5 S1, S2, S10 [61, 100, 128, 133,
353] x x x
C001 Errors in the weighing of colorants and
chemicals 5 S1, S2, S4, S5
[77, 142, 317, 345,
348] x x
C009 Poor dye combinations for each fiber type 5 S1, S2, S5, S6d,
S10, S11 [231, 345, 348] x x x
C024 Poor solubility of reactive/direct dyes 5 S1, S2, S4, S5, S6-
c, S7, S10, S11 [231, 345, 348] x
C067 Inadequate soaping temperature 5 S5, S6a-c, S10, S11 [85, 301, 345, 370] x x x
C071 Inadequate water flow rates/liquor ratio
during soaping 5 S5, S6a-c, S10, S11 [85, 301, 345, 370] x x x
C163 Improper heat setting of substrate 5 S1-4, S5, S10, S14,
S17
[67, 83, 168, 194,
253, 320, 323] x x x
C037 Poor selection of dyebath chemicals 5 S1-3, S5, S6a-d, S7,
S8, S10, S11, S14 [443] x x x
605
Table D.8 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C136 Too high drying temperature 5 S1, S2, S5, S10,
S12 [85, 118, 253, 369] x x x
C019 Poor disperse dye dispersion stability 4 S1, S2, S4, S7, S10,
S11
[7, 67, 68, 75, 79,
81, 85, 253] x x
C049 Inappropriate concentration of dispersing
agent 4
S1, S2, S4, S5, S10,
S11
[67, 89, 97, 106,
109] x x x
C053 Precipitation of anti-migrating agent 4 S1, S2, S3, S5, S8,
S10
[92, 95, 100, 105,
118, 130-132] x
C157 Incomplete removal of fats, waxes, spin
finishes, and knitting oils 4 S1-4, S5, S8, S10
[149, 277, 278, 297,
303, 305, 317, 327] x x x
C169 Alkaline pH of substrate before dyeing 4 S2, S4, S10 [301, 305, 309, 317,
334] x x
C036 Chemical or physical interaction between
colorants and auxiliaries 4
S1-5, S6a-d, S7, S8,
S10, S11
[18, 78, 79, 86, 89,
103, 253] x x
C002 Improper bath preparation procedure 4 S1, S2, S5, S7 [297, 301, 317] x x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
606
Table D.9: Expert responses and expert system’s knowledge base for shade variation within layers (S11).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C109 Incorrect liquor flow direction 9 S1, S2, S4, S14 [9, 68, 85, 110,
194] x x x x x
C096 Higher temperature rise rate 8 S1-3, S9, S14 [9, 112, 231, 253,
380] x x x x
C104 Too short dyeing time 8 S1, S2, S5, S6a-c [297, 301] x x x
C107 Too low liquor flow rate 8 S1, S2, S4, S10 [9, 68, 85, 110] x x x
C100 Too low dyeing temperature 8 S1, S2, S4, S6a-c [297, 301] x x x
C018 Poor disperse dye dispersion system 7 S1, S2, S4, S5, S7,
S9, S10 [75, 253, 348] x x x
C020 Poor disperse dye diffusion properties 7 S1, S2 [9, 68, 75, 100,
111, 118, 231] x x x
C024 Poor solubility of reactive/direct dyes 7 S1, S2, S4, S5, S6b,
S6c, S7, S9, S10
[9, 68, 75, 100,
111, 118, 231] x x x
C025 Poor diffusion properties of reactive dyes 7 S1, S2 [9, 68, 75, 100,
111, 118, 231] x x x
C048 Inappropriate electrolyte (salt)
concentration 7 S1, S2, S4, S9 [128, 317, 345] x x x
607
Table D.9 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C092 Too large batch size (machine
overloading) 7 S1-3, S14 [67, 231, 253] x x x x x
C093 Presence of oligomer and other deposits
in the machine 7 S1, S2, S7, S8
[67, 85, 173-
175, 233, 253] x x x x
C111 Uneven winding of fabric on the beam 7 S1, S2, S10, S14 [9, 68, 85, 110] x x x x
C003 Too fast/quick addition of chemicals in
the bath 7 S1, S2, S9 [297, 301, 345] x x x x
C095 Trapped air pockets in the material
during dyeing 6 S2, S8 [110, 149, 253] x x
C098 Use of too low liquor ratio 6 S2, S3, S7, S14 [297, 301] x x x
C004 Too fast/quick addition of dyes in the
bath 6 S1, S2, S9 [297, 301, 347] x x
C011 Incompatibility between dye classes 6 S1-5, S6a-d, S7,
S9, S10
[7, 9, 79, 92, 93,
100, 128, 253,
301]
x x
C021 Poor disperse dye leveling and migration
properties 6 S1, S2, S5
[9, 68, 75, 100,
111, 118, 231] x x
608
Table D.9 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C026 Poor migration properties of
reactive/direct dyes 6 S1, S2
[9, 68, 100, 111,
118, 231, 345] x x x
C036 Chemical or physical interaction
between colorants and auxiliaries 6
S1-5, S6a-d, S7-
10
[18, 78, 79, 86,
89, 103, 253] x x x
C110 Incorrect overlap of fabric covering the
beam perforations 6 S10, S14 [9, 68, 85, 110] x x
C019 Poor disperse dye dispersion stability 5 S1, S2, S4, S7,
S9, S10
[7, 67, 68, 75,
79, 81, 85, 253] x x x
C023 Too high substantivity of reactive dyes 5 S1, S2, S6a, S6b,
S6c, S9, S10 [128, 253, 345] x x x
C049 Inappropriate concentration of dispersing
agent 5
S1, S2, S4, S5,
S9, S10
[67, 89, 97, 106,
109] x x
C176 Presence of chlorine in water 4 S1, S2, S4, S5 [281, 285, 286] x x x
C009 Poor dye combinations for each fiber
type 4
S1, S2, S5, S6d,
S9, S10 [231, 345, 348] x x
C037 Poor selection of dyebath chemicals 4 S1-3, S5, S6a-d,
S7-10, S14 [443] x x
609
Table D.9 (Continued)
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C067 Inadequate soaping temperature 4 S5, S6a-c, S9,
S10
[85, 301, 345,
370] x x
C172 Presence of Ca and Mg ions (hardness)
in water 4
S1, S2, S4, S5,
S6a-c, S7
[277, 280, 283,
290, 292, 296,
298, 299]
x x
C071 Inadequate water flow rates/liquor ratio
during soaping 4
S5, S6a-c, S9,
S10
[85, 301, 345,
370] x x
C108 Too high liquor flow rate 4 S2, S14 [9, 68, 85, 110] x x
C174 Presence of suspended matter in water 4 S1, S2, S7 [100, 282, 284] x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
610
Table D.10: Expert responses and expert system’s knowledge base for two sidedness (S12).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C134 Variation in the intensity of the IR pre-dryer 9 S1, S2, S3, S5,
S9, S10 [348, 363] x x x
C135 Non-uniform air velocity or flow 9 S1, S2, S3, S5,
S9, S10
[67, 317, 361,
363] x x x x
C124 Difference in the hardness of dye padders 7 S10 [133, 194] x x
C148 Difference in the singeing of fabric’s face and
back 6
[67, 149, 168,
313, 318] x
C136 Too high pre-drying temperature 6 S1, S2, S5, S9,
S10
[85, 118, 253,
369] x x x
C127 Improper distribution and circulation of dye
liquor 5 S1, S2, S5, S10
[61, 100, 128,
133, 353] x x
C168 Differential mercerization due to superimposed
layers of substrate 4 [194] x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
611
Table D.11: Expert responses and expert system’s knowledge base for reduced strength (S13).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C164 Fiber damage during heat setting 8 S16, S17 [67, 168, 323] x x x
C149 Fiber damage during singeing 7 S2, S7 [67, 149, 168,
313, 318] x x
C153 Fiber damage during scouring and bleaching 7 S2, S14-17 [70] x x x
C159 Catalytic damage during bleaching 7 S15, S16 [100, 149, 303,
305, 323] x x
C154 Too high weight loss during scouring 6 S16, S17 [323] x x x
C081 Longer duration of substrate run due to
reprocessing 6 S14-17 [301] x x x
C097 Inappropriate dyebath pH 5 S1, S2, S4, S5,
S6-c, S9, S10 [301] x x x
C173 Presence of heavy metals (Cu, Fe, Mn, Zn) in
water 4
S1, S2, S4, S5,
S7
[277, 280, 283,
286, 288-292] x x x
C191 Lower yarn strength and elongation 4 S17 [6, 155, 181, 202,
211] x
C158 Inadequate weight reduction of polyester 4 S3. S14, S16 [331, 332]
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
612
Table D.12: Expert responses and expert system’s knowledge base for irregular surface appearance (S14).
Expert system’s knowledge base
Literature Experts
Cause Literature CF
Commonness H M A B C D E
C163 Improper heat setting of substrate 9 S1-5, S9, S10,
S17
[67, 83, 168, 194, 253,
320, 323] x x x x
C122 Damaged, worn out or uneven padder
surface 6 [317, 348, 370] x x
C079 Non-uniform or damaged machine parts 6 S3, 15 [149, 150]
C081 Longer duration of substrate run due to
reprocessing 6 S13, S15-17 [301] x x x x x
C080 Excessive, insufficient or variable tension
during fabric run 6 S17
[67, 110, 128, 323,
370]
C158 Inadequate weight reduction of polyester 5 S3, S13, S16 [331, 332] x x
C075 Machine stoppage for a longer duration 5 S3 [67, 149, 194, 321,
323] x x x
C084 Rubbing of unfixed substrate against the
guide roller/machine part 4 S3 [9, 68, 85, 110, 231]
C130 Selvage curling during padding and
thermofixation process 4 [194]
C153 Fiber damage during scouring and bleaching 4 S2, S13, S15-17 [70] x x
C180 Yarn mixing 4 S1, S3, S5, S17 [215, 230, 258-260]
613
Table D.12 (Continued)
Expert system’s knowledge base
Literature
Experts
Cause Description CF
Commonness
H M A B C D E
C181 Variation in yarn tension during
warping/sizing 4 S3 [215, 230, 258-260] x x
C190 Too many yarn imperfections 4 S3 [6, 207, 216]
C166 Excessive overstretching of substrate on
stenter 4 S15, S17 [194, 341] x x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
614
Table D.13: Expert responses and expert system’s knowledge base for poor hand (S16).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C164 Fiber damage during heat setting 8 S13, S17 [67, 168, 323] x x x x
C081 Longer duration of substrate run due to
reprocessing 7 S13-17 [301] x x
C153 Fiber damage during scouring and bleaching 7 S2, S13-15,
S17 [70] x x x x
C151 Incomplete removal of sizing agents and sizing
wax 6 S1-5, S7-10
[67, 149, 303, 305-
307, 324-329] x x x
C094 Presence of oligomer deposits on the substrate
surface 5 S7, S8
[67, 85, 173-175, 233,
253] x x x x
C158 Inadequate weight reduction of polyester 5 S3, S13, S14 [331, 332] x
C159 Catalytic damage during bleaching 5 S13, S15 [100, 149, 303, 305,
323] x x
C073 Too high drying temperature 4 [301] x
C138 Too high thermofixation temperature 4 S5 [114, 115, 128, 133] x x
C139 Too long thermofixation time 4 [114, 115, 128, 133] x x
C154 Too high weight loss during scouring 4 S13, S17 [323] x x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
615
Table D.14: Expert responses and expert system’s knowledge base for poor dimensional stability (S17).
Expert system’s knowledge base
Literature Experts
Cause Description CF
Commonness H M A B C D E
C163 Improper heat setting of substrate 8 S1-5, S9, S10,
S14
[67, 83, 168, 194,
253, 320, 323] x x
C166 Excessive overstretching of substrate on
stenter 7 S14, S15
[9, 184, 253, 305,
333, 334, 337, 338] x x x x
C080 Excessive, insufficient or variable tension
during fabric run 6 S14
[67, 110, 128, 323,
370] x x x x x
C081 Longer duration of substrate run due to
reprocessing 6 S13-16 [301] x x
C153 Fiber damage during scouring and bleaching 6 S2, S13-16 [70] x x x x x
C155 Insufficient relaxation of the substrate during
washing 6 [253] x x x
C180 Yarn mixing 5 S1, S3, S5, S14 [215, 230, 258-260]
C191 Lower yarn strength & elongation 5 S13 [6, 155, 181, 202,
211] x x x x x
C154 Too high weight loss during scouring 4 S13, S16 [323] x
C164 Fiber damage during heat setting 4 S13, S16 [67, 168, 323] x
CF: Certainty factor, H: High, M: Medium, A-E: Experts 1-5, x: Expert selections
616