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STUDY OF THE RELATIONSHIP BETWEEN ULTRAVIOLET PROTECTIONAND KNITTED FABRIC STRUCTURE

CHAN YAN YI

BA (Hons) Scheme in Fashion and Textiles

(Fashion Technology Specialism)

INSTITUTE OF TEXTILES & CLOTHING From

THE HONG KONG POLYTECHNIC UNIVERSITY

2012


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STUDY OF THE RELATIONSHIP BETWEEN ULTRAVIOLET PROTECTION

AND KNITTED FABRIC STRUCTURE

A Thesis Submitted

in Partial Fulfilment of the Requirements

for the Degree of

Bachelor of Arts (Honours)

in

Fashion & Textiles

(Fashion Technology Specialism)

under the Supervision of

Dr. C.W. KAN

by

Yan Yi CHAN

Institute of Textiles & Clothing

The Hong Kong Polytechnic University

March 2012


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ACKNOWLEDGEMENTSI would like to express my sincere gratitude to my supervisor, Dr. C.W. Kan of the

Institute of Textiles & Clothing in the Hong Kong Polytechnic University, not only for

his kind guidance and invaluable advice, but also for his generous support and patience

throughout my preparation of the project work.

I would also like to express my appreciation to Mr. Stephen Chong. and Mr. Eddie Yim

for his constant and generous assistance to provide experimental support and guidance.

Special thanks should also be given to the technicians of the ITC laboratories including

Ms. Susan Liu and Mr. Zhou in knitting workshop who gave me generous guidance and

experimental advice on the laboratory work.


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CERTIFICATE OF ORIGINALITY

I hereby declare that this thesis is my own work and that, to the best of my knowledge

and belief, it reproduces no material previously published or written, nor material that

has been accepted for the award of any other degree or diploma, except where due

acknowledgement had been made in the text.

_____________________________________________________________(Signed)

______________________________________________________(Name of student)


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ABSTRACTOver the past few decades, the increasing number of worldwide skin cancer cases

raises the public concerns about ultraviolet light protection by means of textile clothing.

This study was aimed at studying the relationship between the lightweight knitted fabric

structures and Ultraviolet (UV) protection by analyzing various types of knitting

structures after the scouring process.

In this project, the effect of different kinds of the knitted fabric structure in relation

to the UV protection was studied. Different knitting structures were investigated which

included single jersey such as plain, pineapple, lacoste and other combinations of

different knitting stitches of knit, tuck and miss as well as double jersey fabrics of half

Milano, full Milano, half cardigan, full cardigan, 1x1 rib and interlock. The results

showed that double knit fabrics had better UV protection due to the heavier and thicker

nature.

The relationship with type of the stitch, fabric openness and UV protection was

studied as well as the effect of different weights, thicknesses, stitch density and bursting

strength of knitted fabric in UV protection was studied. It was found the type of stitches

and porosity affected the UPF significantly. Weight was the most important factor that

affected UPF while thickness and stitch density were not the leading factor in

determining UPF. The correlation between bursting strength and UPF was moderate.


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CONTENTSACKNOWLEDGEMENTSCERTIFICATE OF ORIGINALITYABSTRACTLIST OF TABLESLIST OF FIGRURESCHAPTER 1 INTRODUCTION ......................................................11.1 Background of Study ..................................................................... 11.2 Research objective ...................................................................... 31.3 Research methodology ................................................................... 31.4 Research significant ..................................................................... 41.5 Chapter Summary ........................................................................... 4CHAPTER 2 LITERATURE REVIEW .............................................62.1 Introduction on Ultraviolet radiation .................................................... 6

2.1.1 Three groups of UVR: UVA, UVB and UVC ..................................... 72.1.2 Effect of UVR on human health ........................................................ 8

2.2 Quantitative methods of assessing UV Protection of textiles ...................... 102.2.1 In vitro test method ...................................................................... 102.2.2 Determination of the Ultraviolet Protective Factor (UPF) ........................ 12

2.2.2.1Spectral transmittance ................................................................ 122.2.2.2Solar spectral irradiance ............................................................... 132.2.2.3Erythemal action spectrum ............................................................ 14

2.2.3 In vivo test method ....................................................................... 142.3 Characteristics of knitting elements and structures ................................. 15

2.3.1

Fundamentals elements of knitting .................................................... 152.3.1.1Knit stitch ................................................................................ 162.3.1.2Tuck stitch ............................................................................... 162.3.1.3Miss stitch ............................................................................... 172.3.1.4Course and Wale ....................................................................... 18

2.3.2 Knitting structures ........................................................................ 182.3.2.1Single knit ............................................................................... 182.3.2.2Double knit .............................................................................. 20


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2.3.2.2.1 Half Milano ............................................................. 212.3.2.2.2 Full Milano ............................................................. 212.3.2.2.3 Half Cardigan .......................................................... 222.3.2.2.4 Full Cardigan ........................................................... 232.3.2.2.5 1x1 Rib .................................................................. 242.3.2.2.6 Interlock ................................................................. 24

2.4 Summary of literature review .......................................................... 26CHAPTER 3 METHODOLOGY......................................................273.1 Introduction ............................................................................... 273.2 Fabric sample preparation .............................................................. 27

3.2.1 Yarn preparation ......................................................................... 273.2.2 Knitting fabric samples .................................................................. 293.2.3 Knitting structures ........................................................................ 303.2.4 Cotton scouring ........................................................................... 33

3.3 UV Transmission Test .................................................................. 353.3.1 Standardized Test Methods ............................................................. 363.3.2 Calculation of Ultraviolet Protective Factor (UPF) ................................ 373.3.3 Test procedures ........................................................................... 38

3.4 Test on other fabric parameters ....................................................... 393.4.1 Test on fabric weight per unit area .................................................... 393.4.2 Test on fabric thickness ................................................................. 403.4.3 Test on stitch density .................................................................... 403.4.4 Test on bursting strength ................................................................ 41

3.5 Summary of methodology .............................................................. 42CHAPTER 4 RESULT AND DISCUSSION ................................................434.1 Introduction ................................................................................. 434.2 General review of testing results ...................................................... 43

4.2.1 Single knit structure ...................................................................... 444.2.2

Double knit structure .................................................................... 474.3 Effect of knitting structure on UPF ................................................... 49


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4.3.1 Result on single knit structures ........................................................ 494.3.2 Discussion on single knit structures ................................................... 544.3.3 Result on double knit structures ....................................................... 564.3.4 Discussion on double knit structures .................................................. 604.3.5 Comparison on both knitting structures .............................................. 63

4.4 Effect of fabric weight, thickness and weight-to-thickness ratio on UPF ...... 664.4.1 Effect of fabric weight on UPF ........................................................ 67

4.4.1.1Relationship between fabric weight and UPF among individual structures .......... 674.4.1.2Relationship between mean fabric weight and mean UPF on different structures .. 72

4.4.2

Effect of fabric thickness on UPF ..................................................... 774.4.2.1Relationship between fabric thickness and UPF among individual structures ....... 774.4.2.2Relationship between mean fabric thickness and mean UPF on different structures 80

4.4.3 Effect of weight-to-thickness ratio on UPF ................................................. 854.4.3.1Relationship between weight-to-thickness ratio among individual structures ........ 854.4.3.2Relationship between mean weight-to-thickness ratio and mean UPF on different

structures ....................................................................................... 88

4.4.4 Conclusion on the effect of weight, thickness, W/T ratio in different knit structures 934.4.5 Comparison between the effect of weight, thickness and W/T ratio .................... 96

4.5 Effect of stitch density on UPF ........................................................ 984.5.1 Relationship between stitch density and UPF among individual structures ............ 994.5.2 Relationship between mean stitch density and mean UPF on different structures ... 102

4.6 Effect of bursting strength on UPF ................................................. 1084.6.1

Relationship between bursting strength and UPF among individual structures ....... 108

4.6.2 Relationship between mean bursting strength and mean UPF on different structures................................................................................................... 111

4.7 Summary of result and discussion ................................................... 118CHAPTER 5 CONCLUSION AND RECOMMENDATIONS ......................... 1195.1 Conclusion .............................................................................. 1195.2 Recommendation ...................................................................... 122REFERENCES .................................................................................. 125


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LIST OF TABLESTable Page

3.1 Typical fabric mass and yarn requirements to manufacture specific

garments

28

3.2 Specifications of the 10 types of 100% cotton yarns used 29

3.3 Notations and types of stitches of the 9 single knitting structures 31

3.4 Notations and types of stitches of the 6 double knitting structures 32

3.5 Recipe of the scouring bath 34

3.6 Rating system of UPF 37

4.1 Result of UV transmission tests of single knit structures 45

4.2 Result of mean UPFs and other physical properties of single knit fabric 47

4.3 Result of UV transmission tests of double knit structures 474.4 Result of mean UPFs and other physical properties of double knit

fabric

49

4.5 Result of mean UPFs of different cotton fibers in single knit structures 50

4.6 Result of mean UPFs of different yarn counts in single knit structures 51

4.7 Table of mean UPFs and type of stitches in single knit structures 53

4.8 Summary of maximum and minimum mean UPFs in single knit

structures

54

4.9 Result of mean UPFs of different cotton fibers in double knitstructures

57

4.10 Result of mean UPFs of different yarn count in double knit structures 58

4.11 Table of mean UPFs and type of stitches in double knit structures 59

4.12 Summary of maximum and minimum mean UPFs in double knit

structures

61

4.13 Table of the ratio of tuck or miss stitch to knit stitch of milanos and

cardigans

62

4.14 Table of mean UPFs of both single and double knit structures 64

4.15 Summary of maximum and minimum mean UPFs in single knit

structures

65

4.16 Interpretation of CorrelationCoefficient 67

4.17 Table of regression statistics of UPF against fabric weight 69

4.18 Table of the relationship between mean fabric weight and mean UPFs 72

4.19 Table of regression statistics of mean UPF against mean fabric weights 76

4.20 Table of regression statistics of UPF against fabric thickness 79

4.21 Table of the relationship between mean fabric thickness and mean

UPFs

80


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4.22 Table of regression statistics of mean UPF against mean fabric

thickness

84

4.23 Table of regression statistics of UPF against weight-to-thickness ratio 87

4.24 Table of the relationship between mean weight-to-thickness ratio and

mean UPF

88

4.25 Table of regression statistics of mean weight-to-thickness ratio against

mean UPF

92

4.26 Summary of the regression statistics of the effect within same knit

structures

93

4.27 Summary of the regression statistics of weight, thickness and W/T

ratio

96

4.28 Table of regression statistics of UPF against stitch density 101

4.29 Table of the relationship between mean weight-to-thickness ratio andmean UPF

103

4.30 Table of regression statistics of mean stitch density against mean UPF 107

4.31 Table of regression statistics of UPF against stitch density 110

4.32 Table of the relationship between mean weight-to-thickness ratio and

mean UPF

111

4.33 Table of the ratio of tuck stich to knit stitch of knit-and-tuck single knit 113

4.34 Table of regression statistics of mean bursting strength against mean

UPF

116


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LIST OF FIGURESFigures Page

2.1 Wavelength and energy level of electromagnetic spectrum 6

2.2 Statitics of non-melanoma skin cancer in Hong Kong 9

2.3 Illustration of total transmittance with an integrating sphere 11

2.4 Reflection, absorption and transmittion of UV radiation on textile

material

13

2.5 Diagram of a knit stitch on technical face 16

2.6 (a) Diagram of a knit stitch, (b) Photograph of backside of a plain

knitted

16

2.7 (a) Diagram of a miss stitch, (b) Photograph of backside of a plain

knitted

17

2.8 (a) Diagram of a wale, (b) Diagram of a course 18

2.9 Model of (a) front and (b) back views of plain knit 19

2.10 Model of (a) front and (b) back views of lacoste structure 19

2.11 Photograph of pineapple structure 20

2.12 Yarn path diagram of half Milano structure 21

2.13 Yarn path diagram of full Milano structure 21

2.14 Yarn path diagram of half cardigan structure 22

2.15 Model of (a) front and (b) back views of half cardigan structure 222.16 Yarn path diagram of full cardigan structure 23

2.17 Model of (a) front and (b) back views of full cardigan structure 23

2.18 Yarn path diagram of 1x1 rib structure 24

2.19 Model of (a) front and (b) back views of 1x1 structure) 24

2.20 Yarn path diagram of interlock structure 25

2.21 Model of interlock structure 25

3.1 Photograph of the Varian Cary 300 UV-visible spectrophotometer 35

3.2 Photograph of measuring the fabric weight 39

3.3 Photograph of measuring the stitch density 41

4.1 Graph of the average UPFs of each type of yarn used and mean UPF

of single knit structure.

45

4.2 Graph of the average UPFs of each type of yarn used and mean UPF

of double knit structures

48

4.3 Compound bar chart of mean UPFs of different cotton fibers in single

knit structures

50

4.4 Compound bar chart of mean UPFs of different yarn counts in single

knit structures

52


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4.5 Bar chart of mean UPFs of different single knit structures 53

4.6 Illustration of geometry of (a) knit stitch, (b) miss stitch and (c) tuck

stitch

55

4.7 Compound bar chart of mean UPFs of different cotton fibers in double

knit structures

57

4.8 Compound bar chart of mean UPFs of different yarn count in double

knit structures

58

4.9 Bar chart of mean UPFs of different double knit structures 60

4.10 Bar chart of mean UPFs of all knitting structures 64

4.11 Linear regression diagram of UPF against fabric weight of single knit 68

4.12 Linear regression diagram of UPF against fabric weight of double knit 69

4.13 Graph of mean fabric weights and mean UPFs in ascending order of

single knit structures

73

4.14 Graph of mean fabric weights and mean UPFs in ascending order of

double knit structures

75

4.15 Linear regression diagram between mean fabric weights and mean

UPF

76

4.16 Linear regression diagram of UPF against fabric thinckess of single

knit

78

4.17 Linear regression diagram of UPF against fabric thinckess of double

knit

78

4.18 Graph of mean fabric thickness and mean UPF in ascending order of


81

4.19 Graph of mean fabric thickness and mean UPF in ascending order of


82

4.20 Linear regression diagram between mean fabric thickness and mean

UPF

84

4.21 Linear regression diagram of UPF against W/T ratio of single knit 86

4.22 Linear regression diagram of UPF against W/T ratio of double knit 864.23 Graph of meanweight-to-thickness ratio and mean UPF in ascending

order of single knit structures

89

4.24 Graph of meanweight-to-thickness ratio and mean UPF in ascending

order of single knit structures

91

4.25 Linear regression diagram between mean W/T ratio and mean UPF 92

4.26 Compound bar chart of the correlation coefficient of weight of weight,

thickness and W/T ratio

94

4.27 Compound bar chart of the coefficient of determination of weight of

weight, thickness and W/T ratio

95


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4.28 Compound bar chart of the correlation coefficient of weight, thickness

and W/T ratio

97

4.29 Compound bar chart of the coefficient of determination of weight,

thickness and W/T ratio

98

4.30 Linear regression diagram of UPF against stitch density of single knit 100

4.31 Linear regression diagram of UPF against stitch density of double knit 100

4.32 Graph of meanstitch density and mean UPF in ascending order of


104

4.33 Graph of meanstitch density and mean UPF in ascending order of


106

4.34 Linear regression diagram between mean stitch density and mean UPF 107

4.35 Linear regression diagram of UPF against stitch density of single knit 109

4.36 Linear regression diagram of UPF against stitch density of double knit 1094.37 Graph of mean bursting strength and mean UPF in ascending order of


112

4.38 Graph of mean bursting strength and mean UPF in ascending order of


115

4.39 Linear regression diagram between mean bursting strength and mean

UPF

117


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1

CHAPTER 1INTRODUCTION

1.1 Background of StudyAmong the solar radiations, the sun emits ultraviolet radiation (UVR) which is an

electromagnetic radiation with a shorter wavelength but higher energy than that of visible

light. The electromagnetic spectrum of UVR is mainly classified into three classes

according to the wavelength which includes UVA, UVB and UVC. It is a unique and

important process for a human to be exposed to adequate amount of ultraviolet radiation

in sunlight as a natural source to trigger the production of vital nutrient, vitamin D3.

However, long-term exposure of ultraviolet light is harmful and carcinogenic to

human and leads to damage to skins, eyes, immune system (MacKie, 2000) and even

DNA damage as well as genetic mutations (Narayanan et al., 2010). Moreover, it is

proved that UVR from the Sun is the primary cause of skin cancer by the previous

researches (Saladi & Persaud, 2005; Narayanan et al., 2010)

The number of skin cancer cases found has been increasing around the world in the

recent years, including both non-melanoma and melanoma skin cancers. There are about

2 to 3 million non-melanoma skin cancers and 132,000 melanoma skin cancers found in

the globe annually (World Health Organization, 2011). The Skin Cancer Foundation

(2011) also points out that actually the possibilities of skin cancers of America is high


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one in every five Americans will develop skin cancer in their lifetime.

In terms of local health issue, the number of non-melanoma skin cancers found was

also increased according to the statistics from the Hong Kong Cancer Registry of

Hospital Authority. Non-melanoma skin cancer was ranked at eighth among the top ten

cancer cases found in Hong Kong in terms of incidence (Hong Kong Cancer Registry,

2011). The risk of UVR cannot be neglected since it brings bad impact to the health of

Hong Kong citizens and well as worldwide populations. Indeed, skin cancer is a

worth-concerning international problem and hence UV protection is very important for

mankind to prevent the harmful effect of overexposure under sunlight.

Apart from sunscreen and shading, wearing textile garments is also a practical

precaution to avoid the contact of skin and UVR so as to prevent the symptoms of sun

exposure like sunburn or even more serious diseases including and skin cancers.

Although it has been published that apparel textiles is recommended as a means of sun

protection (Gies et al., 1998), the supply of suitable clothing which offers simple and

effective UV protection is still inadequate. There is a worldwide consumer demand for

lightweight summer clothing which is comfortable to wear and offers good UV protection

(Pailthorpe, 1997). In summer times, there is a higher chance of UVR exposure in terms

of intensity and duration while light weight knitted garment is much more popular in that

season.


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3

1.2 Research objectiveThis project is aimed at investigating the ability of UV protection of light weight

knitted fabric in terms of knitting structure. The objectives of this study are summarized

as follows:i. To study the effect of different kinds of knitted fabric structures in relation to the UV

protection

ii. To study the relationship with type of the stitch, cover factor and UV protectioniii. To study the effect of different weights, thicknesses, stitch density and bursting

strength of knitted fabric with different structures in UV protection

1.3 Research methodologyIn this research study, different characteristics of light weight knitted cotton fabric

were examined for the relationship of UV protection. The dependent variable, the index

of UV protection Ultraviolet Protective Factor (UPF), was measured by

spectrophotometer, an integrating sphere and detector. Different fabric parameters were

tested to see if they were the independent variables to determine UVR transmission and

could be used to predict the UV protective capabilities of light weight cotton knitted

fabric.


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1.4 Research significantIt is known that textile clothing can provide substantial protection against UVR and is

able to reduce the harmful effect. Thus it is essential to understand the relationship of UV

protection ability and other parameters of textile clothing, especially the lightweight

knitted summer clothing. Quantifying the amount of UVR protection of textile materials

can have useful applications from manufacturing to daily use. However, studies and

research on the ability of UV protection and light weight knitted fabric are still

insufficient. This study can provide a comprehensive database to the manufacturers and

designers for considerations during the production of UV protective knitted fabric and

enhance the development of functional knitted garments for UV protection.

1.5 Chapter SummaryIn chapter 1, a general review on the background of the research was given. The

research objective, methodology and significant was also shown.

In chapter 2, introduction on UVR was told including the three classes of UVR and

the effect on UVR on human health. The two quantitative methods of assessing UV

protection of textiles, in vitro test and in vivo test were studied. Also, the characteristics

of different knitting elements (stitch, course and wale) were told. The construction

methods and properties on both single and double knitting structures were also studied.


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In chapter 3, the methodology of this research including how to prepare the fabric

samples and testing methods were given. The structures investigated in this research were

listed. The detail information of the materials, apparatus, equipments, testing procedures

used in the research was written down.

In chapter 4, the result of all tests including UV transmission, fabric weight,

thickness, stitch density and bursting strength were listed in tables. The data was also

grouped and plotted in different graphs for further analysis. Linear regression was used

to investigate the correlation between different fabric parameter and UPFs. The effects of

different fabric parameters on UPF were discussed with the aid of graphs and tables.

In chapter 5, conclusion on all results in this research was drawn and further

recommendations to enhance this research were suggested.


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6

CHAPTER 2LITERATURE REVIEW

2.1. Introduction on Ultraviolet radiationUltraviolet radiation (UVR) is one of the radiations among the electromagnetic

spectrum and the major source is the sun. According to figure 2.1, the sun emits

electromagnetic radiation which ranges from short wavelength but high energy Gamma

rays to long wavelength but low energy radio waves. Ultraviolet has a shorter wavelength

but higher energy level than visible light since wavelength is inversely proportional to

energy. UVR bring great influence to all living organisms and affect the biological

metabolism. Since the wavelength of UVR is beyond visible light, it is also not visible to

human eyes.

Figure 2.1 Wavelength and energy level of electromagnetic spectrum


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2.1.1. Three groups of UVR: UVA, UVB and UVCUltraviolet radiation is normally divided to three classes by wavelengths, which are

UVA, UVB and UVC. UVA is the ultraviolet radiation of wavelength from 315

nanometers (nm) to 400nm. UVB means the ultraviolet radiation with wavelength from

280nm to 315nm and UVC is the ultraviolet radiation of wavelength from 100nm to

280nm. (Akaydin, 2010; World Health Organization, 2011)

Approximately 9099% of the UVA reaches the surface of the earth and is not

filtered by the ozone layer (Narayanan et al., 2010). UVA has longer wavelength and

lower energy than the other UVR but it can penetrate into the skin deeper. Over

expousure of UVA also triggers premature ageing ofprotein fibres, elastin and collagen

of skin and is carcinogenic to the stem cells of the skin. (Benjamin & Ananthaswamy,

2007)

For UVB, only about 110% reaches the earths surface and is filtered by the

stratospheric ozone layer in the atmosphere. (Narayanan et al., 2010) The thickness of

ozone layer is not uniform and the concentration tends to increase toward the poles.

(Kullavanijaya & Lim, 2005) The intensity of UVB radiation varies from season, time

and location, however, ozone depletion has a significant effect on the increase amount of

UVB that reaches the earth. UVB has shorter wavelength and stronger energy than UVA

and is still able to penetrate the upper layers of the skin epidermis. Photoageing which


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means the degradation of exposed skin including wrinkling, loss of elasticity, and

accumulation of yellowish pigments is mainly caused by UVB (Juzeniene et al, 2011)

UVB radiation induces DNA damage, which causes inflammatory responses, formation

of tumor (Meeran et al., 2008) . UVB is the main cause of skin cancer and increase risk

on cataracts.

UVC is extremely dangerous but most of it is absorbed by the ozone layer in the

atmosphere and does not reach the surface of the earth normally but it can sill burn the

skin. (Narayanan et al., 2010) If it can arrive the surface of the earth, it would be the

most harmful radiation to eyes and skin (Palacin, 1997; Akaydin et al., 2009).

2.1.2. Effect of UVR on human healthThe intensity of UVR is reduced by clouds but not to the same extent of infrared. It

would diminish the feel of heat and leads to potential of overexposure of UVR. Exposure

to UVR may result in immunosuppression, genetic mutations and is harmful to different

human organs like eyes and especially the one with largest surface area, integumentary

system by erythema, sunburn, tanning, skin ageing and skin cancer (Keybus et al, 2006).

UVR also affect the eye and lead to pterygium and corneal degenerative changes.

(Balk, 2011) UVR also contributed to the development of cataracts, a disease that

develops clouding in the crystalline lens of the eye or in its envelope and can cause

blindness. It is suggested that wrap-around sunglasses should be wear to block both UVA


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9

and UVB radiation.

UVR can cause damage to all types of skin, both for light or dark brown skin.

Excessive exposures of UVR would cause cumulative damage to skin and hence UVR is

also the major etiologic agent of developing skin cancers. (Saladi, 2005) The

International Agency for Research on Cancer (1992) proved that UVR exposure would

lead to two types of dangerous cancer including non-melanoma skin cancer (NMSC) and

cutaneous malignant melanoma.

Figure 2.2 Statitics of non-melanoma skin cancer in Hong Kong

Source: Data complied by the Cancer Statistics Query System (CanSQS), Hong Kong

Cancer Registry

In addition, in terms of local health issue, the number of non-melanoma skin cancers

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

No. of cases 503 536 602 526 594 569 624 762 717 811

0

100

200

300

400

500

600

700

800

900

Nmboceo

Incidence of non-melanoma skin cancercases in Hong Kong from 2000 to 2009


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10

found was also increased from 2000 to 2009 according to the statistics from the Hong

Kong Cancer Registry (HKCR) of Hospital Authority (figure 2.2).It is obvious that the

risk of UVR induced skin cancers is hazardous to the health of Hong Kong citizens and

continuously growing.

In order to prevent skin cancer, it is suggested that protective clothing and hats

should be wear (Glanz et al, 2002) Therefore, it is necessary to understand the UV

protection ability of textile garments and even an emerging market exists and people have

demand for special UV protective clothing (Osterwalder et al, 2000).

2.2. Quantitative methods of assessing UV Protection of textilesIn general, there were two approaches of quantitative methods to assess the UV

protection ability of textile products. One approach is in vitro which is direct while

another approach, in vivo, is indirect. (Gambichler et al., 2001) Theoretically, both in

vitro method and in vivo method measure the relative ability of textile to protect against

minimal sunburn compared to skin that is not protected.

2.2.1. In vitro test methodAccording to the previous researches (Stanford et al., 1997; Hoffmann et al, 2001;

Algaba & Riva, 2002), in vitro approach is a direct method which measures the diffuse

UV transmittance through a fabric to determine the UV protection ability by the ration

Ultraviolet Protective Factor (UPF).


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In vitro test method is a spectrophotometry method which mainly involves several

equipments including a spectrophotometer, an integrating sphere, and a detector which

responds similarly to human skin as well as the aids of PC computes. A

spectrophotometer with an artificial UV light source, that matches the solar spectrum

closely, irradiates fabric sample with radiation of varying wavelength. The

spectrophotometric measurements are with wavelength of 5-nm interval from 290 to 400

nm. (Hoffmann et al., 2001)

As fabric scatters the light, an integrating sphere is used to collect photons of light

which are transmitted through the fabric sample and then measured by a photomultiplier

(Davis et al, 1997). According to researches of Moss (2000) and Mohan et al. (2000), the

integrating sphere is made of a highly reflective white matt material known as spectralon

which diffusely reflects over 96% of the light.

Figure 2.3 Illustration of total transmittance with an integrating sphere (Moss, 2000)

The sphere is able to collect all the input optics of the measurement system,


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including both the transmitted and the scattered UVR, and reflects the radiation round the

sphere until a proportion reaches the photodiode detector. The working principle of an

integrating sphere is shown on figure 2.3.

2.2.2. Determination of the Ultraviolet Protective Factor (UPF)Ultraviolet Protective Factor (UPF) is defined as the ratio of the average effective

UVR calculated for unprotected skin to the average effective UVR calculated for skin

protected by the test fabric (Hoffmann et al., 2001), i.e. the risk estimated of unprotected

skin is divided by that of protected skin.

Though the measurement of UV transmission is measured by instruments, Algaba

and Riva (2002) pointed out that three correction factors are influential to the

determination of the UPF. Thereore, the UVR exposure of fabric can be simulated much

closer to the real situation. The three correction factors taken into account in the

calculation of UPF were spectral transmittance (T), solar spectral irradiance (S) and

erythema action (E) spectra.

2.2.2.1.Spectral transmittanceWhen a UVR falls onto a textile material directly, three possibilities will be

happened which included reflection, absorption or transmission (figure 2.4), i.e. the

radiation will be reflected, absorbed by the textile or passed through it.


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Figure 2.4 Reflection, absorption and transmittion of UV radiation on textile material

(Alagaba & Riva, 2002)

For the transmission of UV radiation, the proportion of scattered radiation, that has

different angle from the incoming radiation and goes to different direction, is generally

much greater than the proportion of non-scattered one. However, no matter the radiation

in transmission is scattered or not, it is deleterious to the skin and should be taken into the

consideration of calculating the UPF.

Therefore, spectral transmittance of textile which represents the proportion of the

transmitted radiation throughout the entire wavelength ranges of UV radiation is taken as

a correction factor. In general, higher transmittance of the UVR through the fabric will

give a lower UPF.

2.2.2.2.Solar spectral irradianceSolar spectral irradiance is the amount of solar energy of the UVR which reaches the

surface of the earth for each wavelength. The proportion of UVR of different


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wavelengths which reaches the surface of the earth is not the same and depends on

several factors including latitude, altitude, ozone layer, season, time of day and weather

condition. (Algaba & Riva, 2002) Solar spectral irradiance is a representative of a

noonday solar spectrum (Menter & Hatch, 2003) and taken account in the consideration

of UPF.

2.2.2.3.Erythemal action spectrumErythemal (sunburn) action spectrum is a weighting spectrum of the action of UV

radiation on the skin for each wavelength.

The capacity of UVR which is lead to erythema in the human skin depends to a great

extent on the wavelength. It was known that UVR with lower wavelength and higher

energy is more harmful so that the effect of UVC is greater than that of UVB and then

UVA. (Algaba & Riva, 2002) Therefore, the UVR action on the skin is required to be

express bt weighting depending on its erythemal effect, i.e. more weight would be given

to the wavelength with more harmfulness and less weight would be given to the

wavelength of less harmful effect.

2.2.3. In vivo test methodIn vivo test method, the sun is used as the UV source and impracticable to test the

UV transmission through fabrics with the aid of human volunteers. Generally xenon arc

is used as solar simulations, with filters to absorb wavelengths below 290nm and to


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reduce visible and infrared radiation. (Hoffmann et al, 2001) The fabric sample is

produced to justperceptible erythema in UVR-irradiated test subjects with and without

the fabric in position. The result is determined by calculating the ratio of the erythemally

weighted solar UVR dose required to cause minimal erythema in a human rest subject

with the fabric sample in place to that measured with no fabric present. (International

Commission on Illumination, 2006) Sun Protection Factor (SPF) for the fabric is used as

the rating of in vivo test method. The SPF measures the protection provided by

sunscreens to the skin of a volunteer by taking the time used before the occurrence of

sunburn when exposed to an artificial sunlight source and compared with unprotected

skin levels. The meaning of UPF is interpreted in same way with SPF (Kim et al., 2004),

higher value of SPF means that the UV protection is better.. However, there are

limitations of in vivo test methods due to cost and impracticability.

2.3. Characteristics of knitting elements and structuresIn this research, different types of knitting structures were used to analyze the effect

on UV protection ability. The characteristics of different knitting elements and structures

are hence studied.

2.3.1. Fundamentals elements of knittingThe loop is the fundamental element of all knitted fabrics. It is a basic unit consisting

of a loop of yarn meshed at its base with previously formed basic units (stitches).


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2.3.1.1.Knit stitch

Figure 2.5 Diagram of a knit stitch on technical face

Knit stitch is the Basic stitch of majority of fabrics. A knit stitch on technical face has

V-shape appearance where the shanks are shown in figure 2.5 and the feet are below the

head of the preceding stitch.

2.3.1.2.Tuck stitch

(a) (b)

Figure 2.6 (a) Diagram of a knit stitch, (b) Photograph of backside of a plain knitted

(Kurbak & Kayacan, 2008)

Tuck stitch is formed by old stitch staying on needle in forming new stitch, i.e. a


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needle rises to take a new loop without casting off the old.(figure 2.6). It consists of a

held loop and a tuck loop, both of which are intermeshed in the same course. The yarn is

tucked into the structure by the needle, instead of being formed into a loop. It is an effect

created by stretched loop with a segment of yarn tucked behind it. And, there is an

important element of the tuck stitch, what gives a big difference to the Miss Stitch, is the

tucked yarn is placed behind the stretched face loop (Raz, 1993). Tuck stitch would lead

to the fabric become thicker, wider but less likely to elongate than knit stitch.

2.3.1.3.Miss stitch

(a) (b)

Figure 2.7 (a) Diagram of a miss stitch, (b) Photograph of backside of a plain knitted

fabric with a miss stitch (Kurbak & Kayacan, 2008)

Miss stitch (figure 2.7) is an effect created by the missing of knitted loop in the loop

formation sequence. The main elements of the stitch are included an enlarged knitted

loop and a straight element of yarn. A length of yarn not received by a needle and

connecting two loops of the same course that is not in adjacent wales. At the back side,

there is a long yarn floating across wale when miss stitch is formed. It is the result of a


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needle has not participated in one sequence of loop formation (Raz, 1993). Fabrics with

miss stitches would become narrower, thinner and more likely to elongate than knit

stitch.

2.3.1.4.Course and Wale

(a) (b)

Figure 2.8 (a) Diagram of a wale, (b) Diagram of a course

The definition of a course is a row of loops either across the width of a flat fabric or

around the circumference of a circular fabric (Savci et al., 2000) and the loops that are

inter-connected widthwise. Wale is a column of loops along the length of a fabric (Savci

et al., 2000) and the series of loops that intermesh in a vertical direction. Generally

speaking, wale is the vertical column of stitches while course is the horizontal row of

stitches.

2.3.2. Knitting structures2.3.2.1.Single knit

Single knit fabric or single jersey was the knitted fabric that produced by only one


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needle bed. The production speed is relatively faster than that of double knit fabric.

(a) (b)

Figure 2.9 Model of (a) front and (b) back views of plain knit (Kurbak & Ekmen, 2008)

Plain (figure 2.9) is simplest of single knitted structures and formed by the

inter-meshing of a number of loops from side to side and top to bottom. It is also known

as plain knit or stocking stitch. The characteristics of single jersey fabrics are single

sided, light-weighted. It has disadvantages of edges curl, difficult to handle due to

partially unstable, stitch distortion.

Other single knit structures are also common in different textile products including

lacoste and pineapple structure.

(a) (b)

Figure 2.10 Model of (a) front and (b) back views of lacoste structure (Alpyidiz &

Kurbak, 2006)


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Lacoste (Figure2.10) is a single knit structure formed by alternating tuck and knit

stitches creat the mesh-like fabric.

Figure 2.11 Photograph of pineapple structure

Structure in figure 2.11 has uneven in surface like the fruit pineapple and hence

named as pineapple structure. The strength of pineapple structure is low: when stretching,

the force received by the loops is not even and easily concentrated in the tighter loops.

Thus, the yarn is easily to be broken when external force applied.

2.3.2.2.Double knitTechnically, two set of needles are required to produce double knit fabrics while

each set of needles works individually to form loops on the particular side of fabric.

Double knit fabrics have more stable structure than single knit fabrics since loops are

formed on the both sides. Fabric weight and thickness will also be higher because there

are the face of fabric is double and the number of loops per unit area is higher.

Altogether, there are six types of double knit structure used in this study which are

half Milano, full Milano, half cardigan, full cardigan, 1x1 rib and interlock. The


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characteristics of each structure are discussed respectively.

2.3.2.2.1. Half Milano

Figure 2.12 Yarn path diagram of half Milano structure

Half Milano (figure 2.12) is knitted by two courses per repeat, with first course

knits on both front and back needles and the second course on front needles only. Half

milano is made of 1 rib course followed by 1 plain course which is always facing the face

side. Half Milano is hence an unbalanced structure and with different appearance on both

sides.

2.3.2.2.2. Full Milano

Figure 2.13 Yarn path diagram of full Milano structure

Full Milano (figure 2.13) structure is knitted in three courses per repeat. The first

course is a rib course and the second and third courses are knit courses in front and one


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knit in back plain courses. (Chiu & Lam, 2009) The second and third plain courses of full

milano reduce most of the width way elasticity and thus full Milano has better

dimensional stability than half milano.

2.3.2.2.3. Half Cardigan

Figure 2.14 Yarn path diagram of half cardigan structure

(a) (b)

Figure 2.15 Model of (a) front and (b) back views of half cardigan structure (Alpyidiz &

Kurbak, 2006)

Half cardigan (Figure 2.14-2.15) was knitted two courses per repeat, with one

course of 1x1 rib and the other course of all needles knit one side and all needles tuck of

the other side of the fabric. Half cardigan has high width and large amount of tuck loops

reduce side way contraction. The structure is not balance since the number of courses per

unit length is different on both sides of the fabric.


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2.3.2.2.4. Full Cardigan

Figure 2.16 Yarn path diagram of full cardigan structure

(a) (b)

Figure 2.17 Model of (a) front and (b) back views of full cardigan structure (Alpyidiz &

Kurbak, 2006)

Full cardigan (Figure 2.16-2.17) is knitted two courses per unit: one course of knit

stitches on face but tuck on back and then one course of tuck on the face but knit on the

back. (Chiu & Lam, 2009) The face and back views of the fabric with this structure are

the same and hence it is a balanced structure. The excessive tuck loops make the fabric

become bulk and heavy.


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2.3.2.2.5. 1x1 Rib

Figure 2.18 Yarn path diagram of 1x1 rib structure

(a) (b)

Figure 2.19 Model of (a) front and (b) back views of 1x1 structure (Kurbak, 2009)

In the rib structure (figure 2.18-2.19), the fabrics is produced by two sets of needles

where the needle heads were not directly facing each other with a zig-zag shape. The

horizontal agnitude between the opposite needles is just half of a needle space. The

sequence of technical face and technical back knit stitches is 1:1 along the course

direction, so that 1x1 is balanced and quite stable. Curling is not easy to be found on the

edge and the elasticity of horizontal direction is very high.

2.3.2.2.6. Interlock


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Figure 2.20 Yarn path diagram of interlock structure

Figure 2.21 Model of interlock structure

The knitting method of interlock structure (figure 2.20) can be regarded as knitting

two 1x1 rib concurrently since it requires two set of needles to complete one row by

knitting on opposite needles alternately. Therefore, interlock has a balanced structure

(figure 2.21) and will not curl easily. Both the technical face and back of interlock

structure are similar to plain knit.

Curling or stretching out is not easy to be occurred in interlock structure since this

stable structure was locked together on both sides. Thus, the reverse meshed loops were

not easily to be revealed. Generally, interlock fabrics have higher thickness and weight

but lower weight when compared to 1x1 rib structure. The handle of interlock fabric is

also good as the surface is smooth.


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2.4. Summary of literature reviewIn chapter 2, literature review was done on introducing the nature of

electromagnetic wave and ultraviolet radiation (UVR). The characteristics of three

classes of UVR were also introduced. The descending order of energy level is

UVC>UVB>UVC but UVA and UVB should be paid more attention since they are

able to reach the surface of the earth and lead to many hazardous effect on eyes and skin.

Moreover, the effect of UVR on human health was investigated, especially the effect on

skin cancer. Overexposure of UVR would bring potential risk of DNA damage and skin

cancer, thus, protective clothing is suggested to be wear.

Moreover, two different kinds of quantitative methods which are used to measure

the UV protection ability of textiles are studied, including in intro and in vivo method. In

vitro method is a more straight forward method and easy to be performed and UPF was

used as the rating of UVR transmission. The three major factors in calculating UPF was

discussed. Different knitting elements, single and double knit structures were studied. It

gave a better understanding on the formation method of particular knitting structures and

hence its characteristics.


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CHAPTER 3METHODOLOGY

3.1. IntroductionIn this chapter, the processes of producing the lightweight knitted cotton fabrics in

different structures and preparation of the testing samples will be shown. Experiments

conducted on the samples will also be described in details, including the equipments and

apparatus used, testing procedures as well as calculation methods.

Ten types of cotton yarns with different properties and yarn counts were knitted into

fifteen different knitting structures in this study, including nine single knit structures and

six double knit structures. The cotton knitted fabrics were followed by the scouring

process in order to remove the impurities in its raw state while the non-scoured parts

were also kept. Further tests were conducted in order to investigate the fabric parameters

and analyze how the change of knitting structure would affect the UPFs which represent

the UV protection abilities.

3.2. Fabric sample preparation3.2.1. Yarn preparation

Since this study was focused on the properties of knitting structures, only 100%

cotton, the most common yarn for summer knitted clothing, was selected for the

comparison of results. In total, ten different types of commercially manufactured cotton


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yarns were used in producing the sample fabrics.

According to the information of Australian textile industry (Bange, et al., 2009),

most common yarns produced from Australian Upland type cottons were from Ne 20 to

Ne 50 which were used to produce a wide range of reasonably high-end knitted fabrics.

In addition, the typical yarn requirement for producing knitted T-shirts and hosiery was

from Ne 20 to Ne 40. (Table 3.1)

Table 3.1 Typical fabric mass and yarn requirements to manufacture specific garments(Bange et al., 2009)

Garment Fabric Mass (gsm*) Yarn Count

Indirect system

(Ne)

Direct system (tex)

Jeans (woven) 200-400 6-10 60-100

Business shirt(woven)

< 100 40-120 5-15

T-shirts and hosiery

(knit)

120-180 20-40 15-30

Bed sheets (woven) 150-250 17-30 20-35

Towels (woven) >500 7-15 40-80

*gsm=grams per square meter

Therefore, the yarn counts of the selected yarns in this study were Ne 30, Ne 40, Ne

50 and Ne 60 since they were commonly used for producing casual summer knitted

garments. Further details and codes used to represent each specific yarn and were listed

in the Table 3.2.


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Table 3.2 Specifications of the 10 types of 100% cotton yarns usedCode Type of cotton fibers Yarn count

(Ne)

Ring spinning method

CH30 Combed Cotton 30 Conventional combing

CH40 Combed Cotton 40 Conventional combing

F30 Combed Supima Cotton 30 Conventional combing




MF30 Combed Supima Cotton ESTex 30 Torque-free




3.2.2. Knitting fabric samplesThe ten types of cotton yarns were knitted by a flat knitting machine, the STOLL

CMS 822 HP knit & wear tandem machine (Germany) with fourteen gauges, which

means there were fourteen needles per inch. This flat knitting machine was capable to

knit both single and double knit with two needles beds. It also had a maximum working

width of 213 cm or 84 inch so that large sizes of light weight knitted fabric was able to be

produced for UV transmission and other tests. The fabric samples were knitted into

fifteen different knitting structures respectively by weft knitting method. Altogether one

hundred and fifty kinds of knitted fabric samples were knitted in terms of yarns and

structures variations and acted as fundamental resources for examination of UPFs,

knitting structures and other fabric parameters.

In order to avoid the slackness of the knitted fabric become too serious in a


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fourteen-gauge flat knitting machine, especially on single knit structure, single yarn

would not be used in knitting the fabric samples. Instead, yarns with yarn count Ne 30

and 40 were knitted with two yarns together concurrently, while yarns with yarn count

Ne 50 and 60 were knitted with three yarns together. By this means, it was ensured that

the fabrics produced would have stable and firm constructions for the further

investigation.

3.2.3. Knitting structuresFor the nine single knit structures, three of them were general types including plain

knit (single jersey), pineapple and lacoste; while the other six of them were different

combinations of knit, tuck and miss stitches including 1) knit and tuck with ratio 1:1, 2)

knit and miss with ratio 1:1, 3) knit and tuck with ratio 2:2 along the wale direction, 4)

knit and miss with ratio 2:2 along the wale direction, 5) knit and tuck with ratio 2:2 along

the course direction and 6) knit and miss with ratio 2:2 along the course direction. The

notations of the nine single knitting structures which represent different types of loops

were shown in Table 3.3.


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Table 3.3 Notations and types of stitches of the 9 single knitting structures Knitting structure/ code Notation diagram Types of stitches

Plain Only knit stitches

Pineapple Knit and tuck stitches

Lacoste Knit and tuck stitches

KT11 Knit and tuck stitches with ratio 1:1

KM11 Knit and miss stitches with ratio 1:1

KT22W Knit and tuck stitches with ratio 2:2

along the wale direction

KM22W Knit and miss stitches with ratio 2:2

along the wale direction

KT22C Knit and tuck stitches with ratio 2:2

along the course direction


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Table 3.3 (continued)KM22C Knit and miss stitches with ratio 2:2

along the course direction

= knit stitch

= tuck stitch

= miss stitch

For the double knit, the six structures chosen were half Milano, full Milano, half

cardigan, full cardigan, 1x1 rib and interlock.

Table 3.4 Notations and types of stitches of the 6 double knitting structuresKnitting structure Notation diagram Types of stitches

Half Milano Knit and miss stitches

Full Milano Knit and miss stitches

Half Cardigan Knit and tuck stitches

Full Cardigan Knit and tuck stitches


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Table 3.4 (continued)1x1 Rib All knit stitches

Interlock All knit stitches

= knit stitch (technical face)

= knit stitch (technical back)

= tuck stitch = miss stitch

3.2.4. Cotton scouringScouring was an important process to remove the impurities, such as waxes, proteins,

oils and pectin, on the surface of cotton yarns or fibers during the manufacturing process.

(Karmakar, 1999) Scouring also allowed the cotton fabric to be prepared for further

treatment since absorbent textiles were produced for uniform dyeing or finishing.

(Polaina & MacCabe, 2007) Standard procedures of cotton scouring involved boiling of

alkaline solutions such as Sodium hydroxide (NaOH) under mild concentration and

detergent.

In this study, the scouring process was conducted in laboratory scale by a Batch type

washing machine and the procedures were followed by the of bath of Associated


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Professional Engineers Ltd. The recipe of the scouring bath was listed in the table 3.4.

For the sake of preventing the detached dirt back to the fabric surface, a builder Sodium

silicate (Na2SiO3) which acted as an anti-redeposition agent was also added into the

scouring bath.

For the scouring procedure, the knitted cotton fabrics were weighted by a balance

first and the total fabric weight (g) were obtained. The total volume (L) of liquor in

scouring was twentyfold of the total fabric weigh since the Liquor-to-goods Ratio is 20:1.

The volume of chemicals to be taken from stock solution is then calculated according to

the required concentration. The calculation process was listed as below:

Liquor-to-goods Ratio = 20:1

Total volume of liquor (L) = 20 Total fabric weight (g)

Table 3.5 Recipe of the scouring bathChemical Stock

Concentration

Required

concentration

Volume of chemicals to be

taken from stock solution

Sodium Hydroxide

(NaOH)

10% 20 g/L 20 Total volume of water

Sodium Silicate

(Na2SiO3)


Sodium Sulphite

(Na2SO3)


Detergent 10% 2 g/L 2 Total volume of water

Dilute Sulphuric

acid (H2SO4)

0.5% N/A Depends on the neutralization

process

After the calculation from table 3.5, suitable volume of sodium hydroxide, sodium


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silicate, sodium sulphite and detergent were added into the batch washing machine and

water were also added till the total liquor volume. All the cotton knitted fabrics were put

into the scouring bath at boil for 60 minutes. The volume of the bath was maintained by

frequent addition of hot water or steam throughout the whole process. Any part of fabrics

floating on the surface of the liquor should be avoided during boiling.

The knitted cotton fabrics were then rinsed thorouaghly with hot water first and then

cold water. The fabrics were neutralized with appropriate amount of cold dilute sulphuric

acid with the aid of pH test papers and then rinsed with cold running water again, until

they were free from acid. All of the fabric samples were squeezed gently to remove the

excess water and dried completely by a centrifuge and laying flat.

3.3. UV Transmission TestIn this study, in vitro approach was used to measure the cotton knitted fabric instead

of in vivo one since it was able to provide a simple method of rating the UV protective

abilities of fabrics by using relatively low-cost procedures.

Figure 3.1 Photograph of the Varian Cary 300 UV-visible spectrophotometer


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As literature review mentioned, the in vitro UV protection measurement system

used the spectrophotometer to measure the UVR transmittance through the fabric and

then personal computer (PC) was responsible for the calculation of UPFs which

depended on the requirement of the standard used. The spectrophotometer used in this

research was the Varian Cary 300 UV-visible spectrophotometer (Figure 3.1) which was

used for cost-effective laboratory based spectral measurements for research purpose.

This spectrophotometer was labeled as ultraviolet (UV) visible because it was

capable to analyze electromagnetic radiations both in the UV and visible regions.

3.3.1. Standardized Test MethodsIn textile clothing industry, more than one test standards can be applied for rating of

UPF. These standards are developed and set by different countries which include

Australian and New Zealand, United States, British, Canadian, etc. as well as other

multinational organizations such as Commission on Illumination and International

Organization for Standardization. The process of determination of the UVR transmission

through the fabric and the method of UPF calculation are given in these standards.

However, they have difference from each other in terms of erythemal action spectrum

used, wavelength range to be measured, and requirements on the fabric samples, etc.

In this study, the most common standard from Australia and New Zealand AS/NZS

4399:1996 (Gies, 2007) was used. In AS/NZS 4399 standard, the spectral measurement


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of UVR transmission is within the wavelength range from 290 to 400nm. The erythemal

action spectrum to be used is from CIE (1987).

Moreover, a classification system of UPF was developed by the standard AS/NZS

4399:1996. This system (Table 3.) can be used as the rating scheme for public to

understand the UV protective abilities not just by UPF but also descriptions. The table

3.6 is the UPF classification system.

Table 3.6 Rating system of UPF (Akgun et al., 2010)UV Protection

Category

UPF Fabric

Value

% of effective UVR

transmission

UPF ratings

Good UV

Protection

15 - 24 6.7 - 4.2 15, 20

Very Good UV

Protection

25 - 39 4.1 - 2.6 25, 30, 35

Excellent UVProtection

40-50, 50+ < or = 5.2 40, 45, 50, 50+

3.3.2. Calculation of Ultraviolet Protective Factor (UPF)Ultraviolet Protective Factor (UPF) was used in this study as a quantitative indicator

to represent the UV protective capabilities of textile fabrics from sunburn. Therefore, the

wavelength range in the standard only includes UVA and UVB.

UPF is defined as the ratio of risk estimates for unprotected skin (the erythemally

effective intensity without the fabric) to that for protected skin by the fabric (the intensity

with the fabric in position) and is calculated by the following equation (Gies et al., 2003;

Khazova et al, 2007):


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where S is the solar spectral irradiance (in Wm-2Nm-1),

E is the erythemal spectral effectiveness from CIE (1987),

T is the spectral transmission through the textile,

is the bandwidth (in nm), and

is the wavelength (in nm).

3.3.3. Test proceduresIn order to determine the UPF of a textile sample, at least four textile samples must

be taken from a garment while two in the machine direction and two in the cross-machine

direction. (Hoffmann et al., 2001)

The UV transmission test was done by the following testing procedures. First of all,

all samples were placed in the condition room of temperature 211C and relative

humidity of 652% for more than 24 hours. All the testing samples were cut into

swatches with 3cm 4 cm. The UV testing programmer in the computer was run and did

the calibration to set a baseline before doing the test. The samples were put into the clip

and then insert the clip into the spectrophotometer. The standard AS/NZS 4399 was

chosen and four scans were done per each sample where two times followed the machine

direction of the fabric and the other two times were turned 90 degree. After the scanning,


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the UPF and other relevant data would be calculated and a report would be generated

automatically by the software.

3.4. Test on other fabric parametersApart from the UV transmission, other fabric parameters including weight,

thickness, stitch density and bursting strength were also tested by the following methods.

Before all the testing on paramters, all the fabric samples were put into the condition

room of temperature 211C and relative humidity of 652% for more than 24 hours.

3.4.1. Test on fabric weight per unit area

Figure 3.2 Photograph of measuring the fabric weight

Fabric weight per unit area is defined as the areal mass of fabric in grams per area in

square metres (g/m2) (Savci et al., 2000) and was measure by the ASTM D3776-1996

(Standard Test Methods for Mass per Unit Area [Weight] of Fabric). The knitted fabric


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samples was placed on a flat surface and allowed to relax. The fabric sample was then put

on a insulating mat and cut the designated area by a circular die cutter of 100cm 2. The

fabric cut was then put in an electronic balance to measure the weight of the fabric (figure

3.2). The fabric weight per unit area was then calculated by multiplying the result by 100

since the unit used was gram per square meter.

3.4.2. Test on fabric thicknessFabric thickness was measured by the fabric thickness tester, Hans Baer AG

CH-Zurich Telex 57767. The fabric sample was placed on a flat surface to allow natural

relaxation before the test and the thickness tester was calibrated by setting zero without

fabric placed between the metal plates. Thickness of each sample was then tested by

placing it between the metal plates with a pressure of 10 g/cm2 for 4 times. Different

positions were used for measuring the same fabrics in order to take more samples.

3.4.3. Test on stitch densityCourse density is the number of visible loops per unit length measured along a wale

and the while the wale density is the number of visible loops per unit length measured

along a course (Savci et al., 2000) Stitch density is the multiple of course density and

wale density.


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Figure 3.3 Photograph of measuring the stitch density

Both the course density and wale density was measured by human observation .The

number of courses and wales were counted in a 1 inch length fixed area under a agnifying

glass with a aid a pointed metal needles. (Figure 3.3)

3.4.4. Test on bursting strengthThis bursting test was used to determine the force that must be exerted to cause a

fabric to burst from the inside. The bursting test was performed indiaphragm bursting

method by the bursting strength testers (Mullen type). This test takes a small tube of the

material and clamps it over a machine that slowly fills the material with oil. The machine

tested the resistance of textile fabrics to bursting by the pressure exerted by the oil.

Before the test, it was made sure that both the pointer in the meter was set zero and

no oil addition was performed. Fabric sample was then clamped above the diagram

firmly by the metal ring. Oil was added continuously and the diagram would go up due to

the increase in pressure. Once the fabric was burst and noticed by a significant pop

sound, the addition of oil was stopped immediately. The maximum pressure before


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bursting and pressure just after bursting were shown by the two pointers in the meter and

recorded. All the oil was then returned back to the original position after the test.

The actual bursting strength of the knitted fabric was then calculated by the

following equation: Bursting strength (psi) = Maximum pressure before bursting -

pressure just after bursting. For each fabric samples, the bursting test was done for five

times to obtain a more accurate value on average.

3.5. Summary of methodologyIn chapter 3, the methodology of this research was given including the preparation of

fabric samples. The materials used were three different types of cotton yarns with yarn

count from Ne30 to Ne60 and knitted by a 14 gauge knitted machine. The structures

investigated in this research were nine single knit structures including plain, pineapple,

lacoste, KT11, KM11, KT22W, KM22W, KT22C and KM22C as well as six double knit

structures including half Milano, full Milano, half cardigan, full cardigan, 1x1 rib and

interlock.

The detail procedure of scouring process of cotton knitted fabric was written. The

materials, apparatus, equipments, testing procedures of UV transmission test, fabric

weight, thickness, stitch density and bursting strength were also given in details. The

calculation methods of the UPF and other fabric parameters were also explained.


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CHAPTER 4RESULT AND DISCUSSION

4.1. IntroductionIn this study, fabric samples of fifteen different structures were investigated. The

structures chosen were divided into two groups: single knit structures which are plain,

pineapple, lacoste, KT11, KM11, KT22W, KM22W, KT22C, KM22C as well as double

knit structures which are half Milano, full Milano, half cardigan, full cardigan, 1x1 rib

and interlock. Ten different cotton yarns were used to knit fabric samples for a boarder

view while the yarns used could be classified into four different yarn count and three

different types of cotton fibers.

Different parameters of knitted fabrics are influential to the ration of UV protection

abilities of in vitro testing method which is called the Ultraviolet Protection Factor (UPF).

In this chapter, the experimental results were shown and the relationship between

different parameters and UPFs were analyzed. The testing was done on scoured knitted

fabrics only since scouring was a necessary process for treating cotton fabrics. 4.2. General review of testing results

In order to obtain a more objective result, some of the tests were conducted by more

than one time. The UVR transmission test was conducted by four times for each fabric

samples since both machine direction and cross-machine direction should be covered.


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The fabric thickness test was also conducted four times and also the bursting test was

repeated five times for each fabric samples in order to maximize the area of fabric

samples being tested. Therefore, for the test records which were taken in more than one

time, average value was required to be calculated first for each kind of fabric samples.

For example, the results of the four times of UV transmission tests were averaged in

terms of each yarn and each structure first. And then in order to have a general concept

of the test results in terms of knitting structure, mean values of UPF were calculated for

each structure but not yarn type and used in the comparison of the UV protection abilities

and other fabric parameters. The results of fabric thickness and bursting test would also

be averaged first which were same as that of UV transmission test result. However, data

of fabric weight and stitch density (cpi and wpi) were just record in one time, thus no

average value was required to be taken.

As the constructions of single knit fabrics and double knit fabrics had great

difference, the results were hence divided into two groups first for better analysis.

Further discussion and comparisons of the two groups of knit structures were then

elaborated and analyzed by graphs and charts.

4.2.1. Single knit structureThe averaged values of UV transmission tests for the ten types of yarn and nine types

of single knit structures were listed in Table 4.1. The mean UPFs for each single knit


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structure were also calculated.

Table 4.1 Result of UV transmission tests of single knit structuresYarn

Structure

CH

30

CH

40F30 F40 F50 F60

MF

30

MF

40

MF

50

MF

60

Mean

UPF

Plain 7.77 7.63 6.31 6.53 10.11 8.99 7.49 4.77 9.59 6.31 7.55

Pineapple 6.77 7.56 8.92 6.42 10.43 9.26 9.38 4.99 9.24 7.72 8.07

Lacoste 7.82 7.95 16.82 8.12 9.23 8.34 8.87 5.95 11.01 7.45 9.16

KT11 12.46 7.97 8.10 6.03 8.71 5.94 9.77 5.57 8.19 5.84 7.86

KM11 16.44 11.35 17.83 10.06 18.53 13.73 25.72 10.08 10.32 10.10 14.42

KT22W 8.29 5.33 6.96 4.47 6.11 5.28 7.86 4.97 8.52 5.09 6.29

KM22W 19.73 10.67 25.96 9.59 22.00 14.43 40.03 9.67 17.03 12.07 18.12

KT22C 10.52 6.24 9.56 7.25 9.20 5.96 10.43 9.67 8.56 6.28 8.37

KM22C 20.00 14.88 20.59 12.64 16.93 14.43 17.63 7.81 16.26 11.35 15.25

Figure 4.1 Graph of the average UPFs of each type of yarn used and mean UPF of single

knit structure

0

5

10

15

20

25

30

35

40

45

UPFvalues

Single Knit structures

Mean UPF

CH30

CH40

F30

F40

F50

F60

MF30

MF40MF50

MF60


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A graph (Figure 4.1) was plotted to show the average UPFs of each type of yarn

used and mean UPFs of each single knit structure. It was shown in Figure 4.1 that though

generally each type of yarn had similar trend, some of the yarn types had some

exceptional result, such as the unexpected high average UPF of lacoste structure of F30

yarn, the unexpected low average UPF for KM22C structure of MF40 yarn, etc. These

variations were due to the change of the nature and fabric parameters of yarn used.

However, in this research, only the effect of the knit structures would be investigated.

Thus, the mean value of UV transmisson test in terms of knit structure were be used in

for further data comparison and discussion instead of individual result of each yarn.

Among the fabric samples of single knit structures, the mean values of UPF and

other fabric parameters were varied in the ten different types of yarns. Thus, summary of

the results of single knit structures on UV transmission test and other physical tests was

listed in Table 4.2.


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Table 4.2 Result of mean UPFs and other physical properties of single knit fabricMean value

Single Knit

Structure

Fabric

Weight

(g/m2)

Fabric

Thickness

(mm)

UPF

cpi

(courses

per inch)

wpi

(Wales

per inch)

Bursting

strength

(psi)

Plain 152.95 0.99 7.55 29 21.5 54

Pineapple 159.46 1.21 8.07 29.5 18 49.4

Lacoste 157.06 1.34 9.16 32.4 15.8 53.7

KT11 146.53 1.11 7.86 19.4 15.7 57.6

KM11 181.64 1.31 14.42 20.9 26.9 79.2

KT22W 133.25 1.32 6.29 16.7 17.3 49.6

KM22W 191.32 1.43 18.12 22.7 27.2 75.9

KT22C 153.50 1.26 8.37 21.6 14.6 59.5

KM22C 177.11 1.34 15.25 20.9 27 90.6

psi=pound-force per square inch (lbf/in2)

4.2.2. Double knit structureThe averaged values of UV transmission tests for the ten types of yarn and six types

of double knit structures were listed in Table 4.3. The mean UPFs for each double knit

structure were also calculated.

Table 4.3 Result of UV transmission tests of double knit structuresYarn

Structure

CH

30

CH

40F30 F40 F50 F60

MF

30

MF

40

MF

50

MF

60

Mean

UPF

Half

Milano24.84 13.88 39.96 31.88 29.78 32.66 16.86 10.76 22.89 18.60 24.21

Full

Milano37.49 26.81 51.23 17.80 52.43 37.49 73.70 10.30 58.26 26.99 39.25

Half

Cardigan31.38 13.48 39.96 11.82 29.35 11.17 41.58 11.48 17.42 19.93 22.76

Full

Cardigan12.40 18.20 20.39 9.15 17.22 10.82 18.45 9.08 23.30 13.74 15.27

1x1 rib 15.99 16.22 46.78 17.85 11.83 13.87 23.15 8.71 21.86 23.70 20.00Interlock 128.63 53.01 133.36 76.27 139.43 125.35 129.23 62.38 164.67 73.34 108.57


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Figure 4.2 Graph of the average UPFs of each type of yarn used and mean UPF of


Another graph (figure 4.2) was also plotted to show the average UPFs of each type

of yarn and mean UPFs of each double knit structures. Similar to the result in single knit

structures, there were similar trends on the average UPFs of each double knit structures

with some variation due to the different natures of yarn. However, as mentioned in

section 4.2.1, further data comparison and discussion would be done according to the

mean UPFs in terms of different knitting structures instead of each individual yarn.

Apart from the UV transmission test, the mean values of other test results were also

varied in different yarns types for the double knit structures. Therefore, in Table 4.4,

summary of the test results on UV transmission test and other physical tests of double

0

20

40

60

80

100

120

140

160

180

Half

Milano

Full Milano Half

Cardigan

Full

Cardigan

1x1 rib Interlock

UPFvalues

Double Knit structures

Mean UPF

CH30

CH40

F30

F40

F50

F60

MF30

MF40

MF50

MF60


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knit fabric was shown.

Table 4.4 Result of mean UPFs and other physical properties of double knit fabricMean value

Double

Knit

Structure

Fabric

Weight

(g/m2)

Fabric

Thickness

(mm)

UPF

cpi

(courses

per inch)

wpi

(Wales

per inch)

Bursting

strength

(psi)

Half

Milano211.85 1.52 24.21 30 16.8 69.5

Full Milano 263.44 1.56 39.25 30.5 19 75

Half

Cardigan 232.06 1.6822.76

26.8 10.8 49.8

Full

Cardigan203.68 1.64 15.27 26.1 9.9 66.2

1x1 rib 197.95 1.46 20.00 30.6 13.6 52.1

Interlock 316.44 1.66 108.57 31.7 22.6 115.3

psi=pound-force per square inch (lbf/in2)

4.3. Effect of knitting structure on UPF4.3.1. Result on single knit structures

Since there were ten different types of yarns was used, the mean UPFs of single knit

structures in terms of different cotton fibers and different yarn counts were analyzed first.

The mean UPFs in terms of different cotton fibers were shown in Table 4.5.


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Table 4.5 Result of mean UPFs of different cotton fibers in single knit structuresYarn types

Structure

Combed Cotton

(CH Yarn)

Combed Supima

Cotton (F Yarn)

Combed Supima

Cotton ESTex (MF

Yarn)

Plain 7.70 7.99 7.04

Pineapple 7.17 8.76 7.84

Lacoste 7.89 10.63 8.32

KT11 10.22 7.20 7.34

KM11 13.90 15.04 14.06

KT22W 6.81 5.71 6.61

KM22W 15.20 18.00 19.70

KT22C 8.38 7.99 8.74

KM22C 17.44 16.15 13.26

Figure 4.3 Compound bar chart of mean UPFs of different cotton fibers in single knit

structures

In figure 4.3, the mean UPFs were shown for three types of cotton yarns used in the

0

2

4

6

8

10

12

14

16

18

20

MeanUP

F

Single knit structure

CH Yarn

F Yarn

MF Yarn


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research including Combed Cotton (CH yarn), Combed Supima Cotton (F yarn) and

Combed Supima Cotton ESTex (MF yarn). It was proved that KM22W was the most UV

protective structure for F yarn and combed MF yarn while KM22C was the most UV

protective structure for CH yarn. However, no matter which type of cotton yarn was

used, KT22W was the most ineffective structure in UV protection.

Table 4.6 Result of mean UPFs of different yarn counts in single knit structuresNe 30 Ne 40 Ne50 Ne 60

Plain 7.19 6.31 9.85 8.21

Pineapple 8.36 6.32 9.84 9.08

Lacoste 11.17 7.34 10.12 8.34

KT11 10.11 6.52 8.45 7.27

KM11 20.00 10.49 14.42 14.31

KT22W 7.70 4.92 7.31 5.60KM22W 28.57 9.98 19.52 17.04

KT22C 10.17 7.72 8.88 7.74

KM22C 19.40 11.78 16.59 14.14

Yarn

Structure


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Figure 4.4 Compound bar chart of mean UPFs of different yarn counts in single knit

structures

From figure4.4, the minimum mean UPF, the result of different yarn count was also

similar to that of cotton fibers. Thus, the mean UPF of KT22W was the lowest ones for

all yarn counts from Ne 30 to Ne60. And for the maximum one, the structure KM22W

has the highest mean UPF in the groups of yarn count Ne 30, Ne50 and Ne60 while

KM22C obtained the highest value of mean UPF in the group of yarn count Ne40.

0

5

10

15

20

25

30

35

MeanUPF

Single knit structure

Ne30

Ne40

Ne50

Ne60


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Table 4.7 Table of mean UPFs and type of stitches in single knit structuresStructure Types of stitches UPF

Plain Only knit 7.55

Pineapple Knit and tuck 8.07

Lacoste Knit and tuck 9.16

KT11 Knit and tuck 7.86

KM11 Knit and miss 14.42

KT22W Knit and tuck 6.29

KM22W Knit and miss 18.12

KT22C Knit and tuck 8.37

KM22C Knit and miss 15.25

Figure 4.5 Bar chart of mean UPFs of different single knit structures

From the figure 4.5, it was summarized that the structure KT22W had the lowest

mean UPF while KM22W had the greatest UPF. This result agreed with the previous

comparison in terms of yarn count and fiber type. Apart from the most powerful UV

protective structure KM22W, KM22C was also able to provide a good UV protection.

7.55 8.079.16

7.86

14.42

6.29

18.12

8.37

15.25

0

2

4

6

8

10

12

14

16

18

20

MeanUPF

Single Knit Structure


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Plain structure (single jersey) and KT11 were also not able to provide good UV

protection since the mean UPF is very low. And for the pineapple and lacoste structures,

they were also not able to as good protection as the knit-and-miss structure. The mean

UPF of lacoste is slighter higher than pineapple and plain structure.

4.3.2. Discussion on single knit structuresIn Table 4.7, it listed the summary of the single knit structures with maximum and

minimum values in different cotton fiber, yarn count and overall performance.

Table 4.8 Summary of maximum and minimum mean UPFs in single knit structuresMaximum

Mean UPF

Minimum

Mean UPF

Structure Type of stitches Structure Type of stitches

Cotton

Fiber

CH Yarn KM22C Knit and miss KT22W Knit and tuckF Yarn KM22W Knit and miss KT22W Knit and tuck

MF Yarn KM22W Knit and miss KT22W Knit and tuck

Yarn

count

Ne30 KM22W Knit and miss Plain Only knit

Ne40 KM22C Knit and miss KT22W Knit and tuck

Ne50 KM22W Knit and miss KT22W Knit and tuck

Ne60 KM22W Knit and miss KT22W Knit and tuck

Overall KM22W Knit and miss KT22W Knit and tuck

It was confirmed that the type of stitch would alter the geometry of the knitting

structure (Alpyildiz et al., 2009) and the effects had been illustrated on figure 4.6.As theloop stitches provided space and allow the yarn to move, it is known that knitted fabric is

more extensible then woven fabric. The alternation of the stitch type would affect knitted

Yarn

SingleKnit


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fabric in terms of not only extensibility but also other fabric parameters including fabric

openness and density. The appearance of tuck and miss stitch would bring great

difference to the fabric openness. The effect of stitch density (number of courses and

inches per unit area) on UPF would be further elaborated in section 4.4.

Figure 4.6 Illustration of geometry of (a) knit stitch, (b) miss stitch and (c) tuck stitch

(Alpyildiz et al., 2009)

Tuck stitch would increase the distance between each wale and the fabric width and

o

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float stitch