Impact of Pre-Finishing Process on Comfort Characteristics ...7) D. Gorjanc.pdf · Impact of Pre-Finishing Process on Comfort Characteristics of Stretchable Cotton Fabric . ... The

Journal of Engineered Fibers and Fabrics 57 http://www.jeffjournal.org Volume 10, Issue 3 – 2015

Impact of Pre-Finishing Process on Comfort Characteristics of Stretchable Cotton Fabric

Dunja Sajn Gorjanc, Matejka Bizjak

Faculty of Natural Sciences and Engineering, Department of Textiles, Ljubljana, Slovenia SLOVENIA

Correspondence to:

Dunja Sajn Gorjanc email: [email protected] ABSTRACT The comfort characteristics of fabrics (especially thermal insulation and permeability properties) are closely associated with the changes in their structural parameters. The reaction of a stretchable fabric, either after the finishing process or after a mechanical deformation, is higher than the reaction of conventional fabrics. The reaction after the finishing process is usually expressed in terms of density, thickness or mass increase, and in dimensional changes. The structural changes influence thermal insulation and water vapor permeability properties, which are the most important properties associated with the comfort of textiles. This paper focuses on the impact of the pre-finishing process on the comfort characteristics of pure cotton fabrics and of cotton fabrics with elastane in the weft direction in plain and twill weave. The results indicate that after the pre-finishing process (scouring/bleaching) for the analyzed fabrics, water vapor resistance and thermal resistance decrease. These decreases occur due to the structural changes inside the fabrics (warp yarn density and mass increase, whereas thickness decreases). Keywords: pre-finishing process, thermal and water vapor resistance, stretchable cotton fabrics INTRODUCTION The pre-finishing processes for cotton fabrics before the bleaching and dyeing consist of removing the warp yarn starches and scouring the material in an alkaline bath or by using new environment-friendly enzymatic scouring. All of the mentioned processes are wet processes that utilize chemicals and high temperatures (depending upon the treatment, enzymatic treatments are processed at lower temperatures). During the finishing (scouring and bleaching), the structural changes in the fabric appear after applying a finishing agent [1–5] and high temperature. The

changes in the fabric structure cause changes in fabric density, thickness and mass, which usually results in dimensional changes that depend upon the raw material of the fabric and on the level of dimensional stability. Stretchable fabrics are dimensionally unstable, compared with conventional fabrics [5–7, 8]. The main comfort characteristics of fabrics are thermal insulation and water vapor permeability. A considerable number of research studies have been conducted on the comfort characteristics of fabrics over the past two decades. [9–21] This research paper concentrates on the impact of the pre-finishing process on the comfort characteristics of a stretchable cotton fabric. The results indicate that the thermal resistance and water vapor resistance of pure cotton and cotton/elastane fabrics decrease after the scouring/bleaching. FINISHING PROCESS OF WOVEN COTTON FABRIC The finishing process is a textile wet process and begins after a gray fabric is produced using a loom. The finishing process improves the fabric appearance (luster and whiteness), fabric handle (fullness, softness etc) and its wearing qualities. The fabric that leaves the loom passes through three steps: pre-treatment (preparation), coloration (dyeing or printing) and finishing. Finishing is the last step before the fabric end use. [22] This paper focuses on the pre-treatment (preparation) of a pure cotton fabric and of a cotton/spandex mixture in the weft direction. In this study, the pre-treatment includes sizing, scouring and bleaching processes. Wet processing improves the appearance, durability and usefulness of a fabric.

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The first wet process for a woven cotton fabric is produced using a loom and consists of starching. The process involves reducing the size material from warp yarns before the bleaching and dyeing. If starch is used for sizing, it is normally removed with enzymes and scouring. Furthermore, the scouring of cotton fabrics is a process that aims to improve the absorbency and whiteness of textile materials by removing the non-cellulosic natural matter from fibers (i.e., fats, waxes, pectines, proteins and waxy materials), which are responsible for the hydrophobic properties of bleached raw cotton. Conventional scouring is performed at T = 90°C in a NaOH solution for 45–60 minutes. The conditions depend upon the properties of the fabric being scoured. [22, 23] Bleaching is the step that follows scouring in textile processing. The grayness of cotton is a consequence of natural pigments and the matter present in fibers. Currently, the most commonly employed bleaching agent is hydrogen peroxide, which is dosed in excess to the fibers [22]. Hydrogen peroxide is suitable for most fibers and this chemical can be used in a wide range of machines under different conditions. The reaction products are non-toxic and non-dangerous; however, hydrogen peroxide is a highly corrosive compound and degrades to oxygen and water. On the other hand, hydrogen peroxide is damaging to the fiber since this compound is used in strongly alkaline media and requires high temperature for effective bleaching [5, 6]. In this study, the bleaching process was performed in the presence of caustic soda (NaOH, 50%), hydrogen peroxide (H2O2, 35%) and the stabilizer TANEX RENA (Sybron/Tanatex) at T = 40°C. Subsequently, the fabric was processed in a steam-machine at T = 102°C for 13 minutes. The primary focus of this study was to determine the influence of pre-treatments that utilize chemicals and very high temperatures on the structural changes (yarn density, thickness and mass), and comfort of the final pure cotton woven fabric and mixed cotton/elastane fabric in the weft direction (core-spun yarn).

COMFORT PROPERTIES OF WOVEN FABRIC A woven fabric provides a barrier between the human body and the environment. Due to the different temperatures of the human body (mean temperature T = 36°C) and the environment, which depends on the temperature zones of different parts of the Earth, fabrics require suitable heat conduction and water vapor permeability. The heat conduction and water vapor permeability of a fabric are the main factors that depend on the fabric raw material, the structural properties and the type of finishing used for the fabric. The heat conduction and water vapor properties influence the comfort of the wearer [15]. The thermal protection provided by a woven fabric is the most important property for comfort. The cloth covers approximately 90% of the human body and is sewn using a woven or knitted fabric that is produced on looms or knitting machines from yarns that are spun from fibers. The first parameter that affects the thermal properties of the fabric is the raw material (chemical composition of fibers). The fibers that are incorporated (spun) into yarn with different spinning technologies (ring, open-end, air-jet etc) have different arrangements in the yarn, which impact the interaction between the fibers and the air that surrounds the fibers in the yarn. Consequently, these fiber arrangements affect thermal comfort. Moreover, a woven fabric produced from warp and weft yarns with different weave types influences the number of air gaps between warp and weft yarns, and the mass, thickness and density of the yarn. In addition to the raw material, the aforementioned structural parameters of the woven fabric, which are closely related to the selected raw material, affect the thermal properties of the woven fabric and, in consequence, the comfort of the wearer of the sewn cloth from the previously mentioned fabric. [8, 10, 11] The second parameter which is important for user comfort is the transfer of perspiration (water vapor transport) from the body to the environment. A woven fabric is a barrier that affects the rate of evaporation. Although the woven fabric consists of warp and weft yarns using different types of weave constructions (structural parameters), i.e., different raw materials (chemical composition of fibers) and different types of yarn (ring spun, rotor, air-yet), the most important aspect in this study is the hydrophobic or hydrophilic nature of fibers and thus their ability to absorb water vapor.


In addition, the water vapor transport through the openings (pores) in a woven fabric occurs through the inter-yarn voids and depends on the type of weave. This property is essential for providing user comfort. The gradient between the water vapor pressure next to the skin and microclimate around the human body is of extreme importance. The barrier provided by the woven fabric affects the rate of diffusion, which depends upon the difference between the water vapor pressures of both the skin and environment. [12–14, 17, 20] This study primarily addresses the influence of the pre-treatment of gray cotton and cotton/elastane woven fabrics on the thermal resistance and water vapor resistance of these fabrics, two important properties for ensuring cloth comfort. MATERIALS AND METHODS Materials In this study, two different yarns were chosen: a 100% cotton rotor or OE-yarn with the fineness of 20 tex and a cotton/elastane core-spun yarn composed of 6.2% of elastane multifilament yarn with the fineness of 44 dtex in the core. The woven fabrics with the yarn density in the warp direction of 22 yarns/cm, width of 160 cm and two different densities in the weft direction, i.e., 17 and 20 yarns/cm, were produced on a Picanol OMNI loom. The first group of fabrics was woven from 100% cotton, OE-yarn (in both directions); the second group of fabrics was woven from 100% cotton, OE-yarn in the warp direction; and the raw material for the weft yarn was cotton/elastane core-spun yarn. The woven fabrics were produced in two basic weaves: plain weave P 1/1 and twill weave T 3/1 S. The investigated fabrics were analyzed using the ImageJ program (public domain image analysis program, The National Institutes of Health, USA) to

calculate the percentage of the area opening, A0 (Table I). The images of investigated fabrics (gray and scoured/bleached fabrics) are shown in Table II. The photos of fabrics were taken with a Leica microscope with 16× zoom. The photos were treated with the LASEZ program. The basic properties of the gray fabrics and bleached fabrics are listed in Table I. Pre-treatment (Finishing) Starching (Goller machine) The gray woven fabrics (produced with looms) were starched with the enzymatic agent TEXSTY ET – m (3 g/L) and the wetting and washing agent TANATERGE CSU (1 g/L) at T = 20°C with impregnating rollers and then in an impregnating tube (V = 600 L) at T = 40°C. After the starching, the fabrics were processed in a steamer at T = 100°C for approximately 8 minutes and washed using a counter-flow system in three tubes, with the first and second tubes at T = 95°C, and the third tube at a lower temperature of T = 80°C. After the washing in the third tube, the starching effect was tested with an iodine solution. The color of the iodine solution must remain unchanged (i.e., brown/yellow). Scouring and bleaching (Goller machine) The fabrics were initially scoured using caustic soda (NaOH 50%, 30 g/L) and eco-stabilizer (TANEX RENA, 56 g/L). The scoured fabrics were bleached in the presence of hydrogen peroxide (H2O2, 35%, 1000 mL/L) at T = 40°C in an alkaline medium, pH = 10. After the bleaching, the fabrics were processed in a steamer at T = 102°C for approximately 13 minutes and washed using a counter-flow system in three tubes, with the first and second tubes at T = 95°C, and the third tube at a lower temperature of T = 80°C.


TABLE I. Basic properties of analyzed fabrics.

Fabric Raw material

Yarn density, Mass, Thickness,

Weave

Area opening

g/ yarn cm–1 M/gm-2 h/ mm A0/ %

Warp Weft Gray fabrics

1 G Cotton 22 17 88.2 0.312

Plain

12.9

2 G Cotton 22 21 95.8 0.33 12.3

3 G Co/EL 24 17 92.2 0.187 12.8

4 G Co/EL 25 21 99 0.197 10.6

5 G Cotton 23 18 86 0.302 Twill 10.8

6 G Cotton 22 20 91 0.306 T 3/1 S 9.8

7 G Co/EL 25 17 94.8 0.348 5.9

8 G Co/EL 25 21 104.6 0.399 4.4

Scoured and bleached fabrics

1 B Cotton 24 17 86.8 0.174

Plain

12.1

2 B Cotton 24 20 94 0.169 11.8

3 B Co/EL 28 18 101.8 0.209 7.1

4 B Co/EL 28 21 107.2 0.197 4.6

5 B Cotton 24.7 18 86 0.224 Twill 9.1

6 B Cotton 24 20 93 0.253 T 3/1 S 7.9

7 B Cotton/EL 31.5 17 106.6 0.331 3.2

8 B Cotton/EL 29 21 111 0.347 1.6


TABLE II. Images of investigated fabrics taken with Leica microscope with 16× zoom.

Fabric Gray fabric Scoured and bleached fabric

1

2

3

4

5

6

7

8


METHODS The comfort properties, thermal resistance (Rct) and water vapor resistance (Ret) were determined using the Permetest method (Skin model), which is similar to the ISO Standard 11092 [24, 25]. The Permetest method is based on the ‘sweating hot plate’ method and has been frequently used over the last few years [24, 25]. With the Permetest method, the tested fabric with the diameter of 80 mm is positioned at the distance of 1–1.5 mm from the wetted area to measure the water vapor resistance. To measure the thermal resistance, the temperature is set to T = 35°C. The heat flow without the sample is measured first, qwithout sample (W/m2), and then the heat flow in the measuring head with the placed sample, qwith sample (W/m2). To calibrate the measurements, the calibration constant C was calculated by measuring the heat flow in the measuring head for the Permetest reference sample with known water vapor resistance (Ret = 2.36 m2Pa/W) and with known thermal resistance (Rct = 0.0184 m2K/W). Finally, the water vapor resistance of the analyzed sample was calculated according to Eq. (1).

(1)

where Ret is the water vapor resistance in m2Pa/W, C is the calibration constant of the reference sample, H is the air humidity (60% in this experiment), qwith

sample is the heat flow for the measurement with the sample in W/m2, and qwithout sample is the heat flow for measurement without the sample in W/m2. The equation used to calculate the thermal resistance Rct is similar to the equation used to calculate water vapor resistance. The difference between the two equations is in the temperature, which is by 10 degrees higher (T = 35°C) than the temperature used in the measuring water vapor resistance. The thermal resistance is calculated according to Eq. (2).

(2)

where Rct is the thermal resistance in m2K/W, C is the calibration constant of the reference sample, 10 is the temperature difference ∆T = 10 K, qwith sample is the heat flow for the measurement with the sample in

W/m2, and qwithout sample is the heat flow for the measurement without the sample in W/m2. The impact of the pre-finishing process (scouring and bleaching) on the comfort properties of analyzed fabrics (water vapor resistance and thermal resistance) was tested using the analysis of variance (ANOVA) to determine the significance of water vapor resistance and thermal resistance before (gray fabrics) and after the scouring and bleaching (fabrics bleached with a Goller machine). The basis of a one-factor ANOVA is represented by the partitioning of the sums of squares into between-class (SSb) and within-class (SSw). This technique enables all of the classes to be compared with each other simultaneously, rather than individually. This method also assumes that the samples are normally distributed. The one-factor analysis is calculated in three steps. The sums of squares are first determined for all of the samples, and then for the within-class and between-class cases. For each stage, the degrees of freedom (df) are determined as well, where df is the number of independent ‘pieces of information’ involved in the estimate of a parameter. These calculations are used with the Fisher statistics to analyze the null hypothesis. The null hypothesis states that there are no differences between the means of different classes, suggesting that the variance of the within-class samples should be identical to that of the between-class samples. If F ≥ 1, then the differences are likely to exist between the class means. These results are then tested for statistical significance or p-value, where the p-value is the probability that a variate assumes a value greater than or equal to the value observed strictly by chance. If the p-value is low (e.g., p ≤ 0.05 or p ≤ 5%), then the null hypothesis is rejected, indicating that differences exist between the classes and that these differences are statistically significant. If the p-value is greater than 0.05 (e.g., p ≥ 0.05 or p ≥ 5%), then the null hypothesis is accepted, indicating that the differences between classes are accidental [26]. ANOVA was performed using the SPSS Statistics software. RESULTS AND DISCUSSION Water Vapor Resistance The water vapor resistance of pure gray cotton fabrics and stretchable cotton fabrics with elastane in the weft direction before and after the scouring and bleaching is presented in Table III.


TABLE III. Water vapor resistance (WVR) results.

WVR,

Temp., Ret (m2Pa/W)

T (°C)

1 G Cotton Plain 0 5.06 0.605

2 G Cotton Plain 0 5.06 0.624

3 G Cotton/EL Plain 6.2 5.06 0.608

4 G Cotton/EL Plain 6.2 5.06 0.691

5 G Cotton Twill T 3/1 S 0 5.06 0.493

6 G Cotton Twill T 3/1 S 0 5.06 0.583

7 G Cotton/EL Twill T 3/1 S 6.2 5.06 0.867

8 G Cotton/EL Twill T 3/1 S 6.2 5.06 0.918

1 B Cotton Plain 0 56 4.96 0.56

2 B Cotton Plain 0 56 4.96 0.586

3 B Cotton/EL Plain 6.2 56 4.96 0.554

4 B Cotton/EL Plain 6.2 56 4.96 0.627

5 B Cotton Twill T 3/1 S 0 56 4.96 0.46

6 B Cotton Twill T 3/1 S 0 56 4.96 0.546

7 B Cotton/EL Twill T 3/1 S 6.2 56 4.96 0.766

8 B Cotton/EL Twill T 3/1 S 6.2 56 4.96 0.831

20

20

20

20

20

20 60


20

20

20

20 60

20 60

20 60

20 60

20 60

20 60

Conditions

Air hum., H (%)Const, C (m2Pa/W)

Gray fabrics

20 60

Fabric Raw Weave

Pct

of elastane

(%)

The water vapor resistance results for the gray and scoured/bleached fabrics show that the highest water vapor resistance was found for the fabrics with elastane in the weft direction and in twill weave (7 G, 8 G, 7 B and 8 B). This result holds for both groups of analyzed fabrics, the gray and scoured/bleached fabrics, and it occurred due to the construction of fabrics. Twill weaves obtained higher densities in the weaving process than plain weaves. The cotton/elastane core-spun yarn in the weft direction influenced a larger increase in the density in the warp direction for this fabric compared to the density of a pure cotton fabric. The density of warp yarns of fabrics (7 B and 8 B) was the highest (31.5 and 29 yarns/cm). This density increase influences the water vapor resistance changes. The water vapor resistance results show that the water vapor resistance of gray fabrics (taken from looms) was by approximately 6–11.6% higher than the water vapor resistance of scoured/bleached fabrics (Table III).

This difference was the highest (by 11.6% higher) for the fabrics with twill weave and elastane in weft. The reason for such a result was attributed to the yarn density of warp yarns, which increased from 25 yarns/cm (gray fabrics with elastane in twill weave, 7 and 8 G) to 29–31.5 yarns/cm (scoured/bleached fabric with elastane in twill weave, 7 and 8 B). This increase was the highest yarn density increase of analyzed fabrics after the pre-treatment (scouring and bleaching), and resulted in the highest difference in water vapor resistance between the gray and scoured/bleached fabrics. The statistical analysis (ANOVA) showed that the differences between the water vapor resistance between both groups, gray fabrics and scoured/bleached fabrics, were statistically significant (p-value = 0.04) in the case of fabrics with twill weave and elastane (7 G, 8 G – gray fabrics compared to 7 B, 8 B – scoured/bleached fabrics). The differences in the water vapor resistance between the gray and scoured/bleached fabrics of other analyzed fabrics (between gray fabrics 1–6 G and scoured/bleached fabrics 1–6 B) were not statistically significant (p-value = 0.102).


Although the differences in the water vapor resistance between the gray fabrics and scoured/bleached fabrics (1–6 G and 1–6 B) are not statistically significant, the water vapor resistance values of gray fabrics (1–8 G) were by approximately 6–10% higher than the water vapor resistance values of scoured/bleached fabrics (1–8 B). Why were the water vapor resistance values of gray fabrics higher than those of scoured/bleached fabrics? As indicated by the structural parameters (Table I), the warp density of gray fabrics increased from 22 to 25yarns/cm, whereas the warp density of scoured/bleached fabrics increased from 28 to 31.5 yarns/cm, especially for the fabrics with elastane. Despite the increase in water vapor resistance being expected, as the yarn density of scoured/bleached fabrics increased compared to that of gray fabrics (with lower yarn density), the results show the opposite trend, i.e., the water vapor resistance decreased. The analysis of the images of investigated fabrics (Table II), using the program Image J to calculate the area opening, showed the lowest area opening for twill weave fabrics 7 and 8 B with elastane in the weft direction (area opening = 1.6% and 3.2%). Other analyzed fabrics had a higher area opening. The images taken with a Leica microscope (Table II) showed an increasing number of pores or micro-pores for the twill weave fabrics with elastane (7 B and 8 B, area opening = 3.2% and 1.6%), compared to the fabrics (7 G and 8 G, area opening = 5.9% and 4.4%) where the number of micro-pores was lower. This result answers the question why the water vapor resistance of scoured/bleached fabrics was lower than the water vapor resistance of gray fabrics. After the wet processing at a high temperature, the fibers in the yarn appeared to relax. This observation means that the fibers in the yarn tried to find a new position with the lowest energy level, which resulted

in the increase in yarn density. The yarn density increase was considerable in the fabrics with elastane (3, 4, 7 and 8). These fabrics also had a higher level of elasticity and a larger relaxation level, compared to pure cotton fabrics (1, 2, 5 and 6). The yarn density increase caused the number of warp and weft interlacing points to increase and led to an increase in the quantity of pores or micro-pores. The increase in the number of pores influenced the increase in water vapor permeability; otherwise, the water vapor resistance decreased. The fact remains that for all of the analyzed fabrics, the result is only statistically significant for the fabrics which were able to reach high densities (twill weave) and exhibited increased elasticity (fabrics with elastane). The fabrics investigated in this study were 7 G, 8 G, 7 B and 8 B. In the case of other analyzed fabrics (comparing water vapor resistance results of gray and scoured/bleached fabrics), the difference between the water vapor resistance levels remained; however, this difference was minor. In this study, the water vapor resistance of fabrics with the yarn density in weft of 17 yarns/cm (1, 3, 5 and 7) and of fabrics with the yarn density of 20 yarns/cm (2, 4, 6 and 8) was compared. A statistical analysis showed that the water vapor resistance increased by increasing weft yarn density by 3 yarns/cm. The statistical analysis also showed that the water vapor increase was insignificant (p-value = 0.12). This result indicates that the differences in the water resistance levels were minor and were not significant. Thermal Resistance Table IV presents the thermal resistance results for pure gray cotton fabrics and stretchable cotton fabrics with elastane in the weft direction after the scouring and bleaching.


TABLE IV. Thermal resistance (TR) results.

TR with

T = 30°C,

Rct (m2K/W)

1 G Cotton 21 0.53 0.0128

2 G Cotton 21 0.53 0.0145

3 G Cotton/EL Weft 21 0.53 0.0121

4 G Cotton/EL Weft 21 0.53 0.0126

5 G Cotton 21 0.41 0.0126

6 G Cotton 21 0.41 0.0174

7 G Cotton/EL Weft 21 0.41 0.0161

8 G Cotton/EL Weft 21 0.41 0.0182

1 B Cotton 22 0.69 0.0124

2 B Cotton 22 0.69 0.0143

3 B Cotton/EL Weft 22 0.69 0.0114

4 B Cotton/EL Weft 20.5 0.53 0.0121

5 B Cotton 20.5 0.53 0.0118

6 B Cotton 20.5 0.53 0.0161

7 B Cotton/EL Weft 20.5 0.53 0.0151

8 B Cotton/EL Weft 20.5 0.53 0.018

Twill T 3/1 S 56

Twill T 3/1 S 56

Plain 56

Twill T 3/1 S 56

Twill T 3/1 S 56


Plain 55

Plain 55

Plain 55

Twill T 3/1 S 56

Twill T 3/1 S 56

Twill T 3/1 S 56

Plain 56

Plain 56

Twill T 3/1 S 56

Gray fabrics

Plain 56

Plain 56

Fabric Raw Weave

Dir.

Conditions

Temp.

T (°C)

of

elast.

Air hum. H (%) ConstC (m2K/W)

The results from the analysis of fabrics shows that the highest thermal resistance occurred for the fabrics with twill weave and elastane in the weft direction (8 G, 8 B, Rct = 0.0180 m2K/W). The reason for this result is similar to the water vapor resistance results and lies in the construction of the fabric. The twill weave achieved higher densities during the weaving process than the plain weave. The presence of elastane in the weft direction potentiated the yarn density increase in the warp direction, which influenced the thermal resistance increase. For example, fabric 6 (twill weave without elastane, warp yarn density 24 yarns/cm) had the thermal resistance of 0.012 m2K/W and fabric 8 (twill weave with elastane, warp yarn density 29 yarns/cm) the thermal resistance of 0.018 m2K/W. The structural parameters (mass, thickness, and yarn density – the number of air-gaps between warp and weft yarns) are strongly related to the thermal resistance.

The thermal resistance results show that the thermal resistance of fabrics with twill weave and elastane in the weft direction had much higher warp density (31.5 yarns/cm) and was higher than the thermal resistance of fabrics with plain weave (28 yarns/cm) and of fabrics without elastane in twill and plain weave (24 yarns/cm). The statistical analysis shows that the differences in the thermal resistance for the plain weave fabrics (1–4) and twill weave fabrics (5–8), as well as the differences between the fabrics with elastane (3 and 4 – plain weave, and 7 and 8 – twill weave) and without elastane (1 and 2 – plain weave, and 5 and 6 – twill weave) were accidental and statistically insignificant (p-value = 0.11). Nevertheless, these minor differences remained. The answer to the question why there were differences in the thermal resistance of the fabrics with two different weaves (plain and twill) and of the fabrics with or without elastane in the weft direction very low is that the


change in the structure was too small to influence the larger thermal resistance changes. Specifically, the warp density increased when comparing the plain weave fabrics (1–4) and the twill weave fabrics (5–8), and the fabrics with elastane (3 and 4 – plain weave, and 7 and 8 – twill weave) or without elastane (1 and 2 – plain weave, and 5 and 6 – twill weave). For example, the density increased from 24 to 31.5 yarns/cm. The thermal resistance results of the two compared groups of analyzed fabrics, gray fabrics (1–8 G) and scoured/bleached fabrics (1–8 B), show that the thermal resistance of gray fabrics (taken from looms) were by approximately 3–6% higher than the thermal resistance of scoured/bleached fabrics (Table IV). The statistical analysis (ANOVA) shows that the differences in the thermal resistance between both groups, gray and scoured/bleached fabrics, were statistically insignificant and accidental (p-value = 0.1) for all of the analyzed fabrics (1–8 G in comparison with 1–8 B). Although the differences in the thermal resistance between both groups, gray and scoured/bleached fabrics, were statistically insignificant, the question remains why the thermal resistance decreased by approximately 3–6% after the scouring/bleaching wet process when the warp density increased (from 24 yarns/cm to 31.5 yarns/cm). The answer to this question lies in the scouring/bleaching process. The wet process improved the fabric appearance (luster, smoothness, fabric handle etc). After the wet process, a pre-orientation of fibers in the yarn occurred, which resulted in the increase in yarn density, and in a more compact and stable structure. The fabric surface was after scouring/bleaching smooth and had lower thickness (Table I). The thickness of scoured/bleached fabrics (1–8 B) increased from 0.174 to 0.347 mm and these values were lower than the thickness of gray fabrics (1–8 G), which increased from 0.312 to 0.399 mm. Due to the decrease in thickness, the thermal resistance after the scouring/bleaching decreased, the above mentioned decrease being, as stated before, statistically insignificant. In the present study, the thermal resistance of fabrics with the yarn density in the weft direction of 17 yarns/cm (1, 3, 5 and 7) and fabrics with the yarn

density of 20 yarns/cm (2, 4, 6 and 8) were compared. The fabrics with higher yarn density in the weft direction (20 yarns/cm) had higher thermal resistance than the fabrics with lower yarn density in the weft direction (17 yarns/cm). The statistical analysis shows that the thermal resistance increased, the increase in density by 3 yarns/cm being accidental (p-value = 0.1). This result indicates that the differences in the thermal resistance were minor and not important. CONCLUSION From the research on the impact of the pre-finishing process on the comfort characteristics of a stretchable cotton fabric, the following conclusions can be drawn: – The scouring/bleaching process decreased the

water vapor resistance for all of the analyzed fabrics, while a significant decrease was calculated only for the fabrics with elastane in twill weave (7 B and 8 B) due to the considerably higher warp density increase (from 24 to 31.5 yarns/cm) compared to other fabrics.

– The decrease in the water vapor resistance (knowing that warp density increases) after the scouring/bleaching was a result of the increasing number of pores or micro-pores with increasing warp density.

– The decrease in the thermal resistance after the scouring/bleaching was unexpected as simultaneous increases in the warp density and the number of air-gaps ensure higher thermal resistance. The reason for this unexpected result lies in the pre-orientation of fibers in the yarn, which resulted in a decrease in thickness in the scoured/bleached fabrics and influenced the thermal resistance decrease after the scouring/bleaching.

– The stretchable fabrics with the twill weave (in comparison with other analyzed fabrics) offered the highest water vapor and thermal resistance.

– The increase in the weft density (from 17 to 20 yarns/cm) increased the water vapor and thermal resistance; however, the increase was very low and hence insignificant.

From the above conclusions, the scouring/bleaching process clearly influences the unexpected decrease in the water vapor and thermal resistance. The decrease in the water vapor resistance and thermal resistance is statistically insignificant and accidental (water vapor resistance decrease for twill weave fabrics with elastane in weft is statistically significant), whereas the water vapor and thermal resistance clearly decrease. After the scouring/bleaching, structural changes appear (warp density increase, mass increase


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AUTHORS’ ADDRESSES Dunja Sajn Gorjanc Matejka Bizjak Faculty of Natural Sciences and Engineering, Department of Textiles Askerceva 12 Ljubljana, Slovenia 1000 SLOVENIA

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