CHAPTER 3 MATERIALS AND METHODS

Transcription

1 41 CHAPTER 3 MATERIALS AND METHODS 3.1 INTRODUCTION The most important property in textiles that contribute to wearer comfort is stretch. Elastic fibers (spandex/lycra) are used to impart stretch and recovery to fabrics. To produce woven stretchable blouses that can adhere to the shape of the body better with comfortable fit and pressure, cotton core spun lycra, polyester lycra and silk/nylon lycra (hybrid yarn) were used as weft yarn. The study aimed to develop woven stretch fabrics for comfort fit sari blouse. Thermal comfort properties, low stress mechanical properties, total hand value, stretch properties, pressure comfort and fit analysis of these woven stretch fabrics for women s sari blouse are presented in the study. The influence of fabric specifications on low stress mechanical properties, total hand value, thermal comfort properties and stretch properties of developed woven stretch fabrics are discussed. The influence of fabric specifications, total hand value and stretch properties of cotton/cotton core spun lycra and silk/cotton core spun lycra fabrics on pressure comfort is also studied. Comparative study of pressure distribution of cotton core spun lycra fabrics and commercially available blouse materials are also presented in the study. The influences of fabric specifications, low stress mechanical property, total hand value and stretch properties on fit are also analyzed.

2 MATERIALS The flow diagram of materials and methods are shown in Figure 3.1. To fabricate woven stretchable blouse that can provide comfortable fit, cotton core spun lycra, polyester lycra, hybrid yarn (silk/nylon covered lycra) is incorporated in weft during weaving, which can stretch in width wise direction and conform to the contour of the human body. In this research work, cotton, silk, polyester yarns were used in warp and cotton core spun lycra, polyester lycra and hybrid yarns were used in weft to develop woven stretch fabrics for sari blouse. Totally twenty one samples were developed and sixty three woven stretch blouses were constructed Materials Chosen for Developing Woven Stretch Fabrics Two sets of fabrics were produced, one set with 50 s and 60 s, 100% cotton yarn in warp with 40 s, 50 s and 60 s cotton core spun lycra in weft and another set with 2/75Nm and 2/120Nm silk in warp with 40 s, 50 s and 60 s cotton core spun lycra yarn in weft. A total of twelve different (1 1) plain woven fabrics were produced. In addition, the respective control samples were developed with 60 s cotton yarn in warp with 60 s cotton in weft and another set with 2/75 Nm silk in warp with 60 s cotton in weft for comparing the results. The methodology for production of test fabrics is shown in Figure 3.1(a). The effect of yarn count on properties was analyzed and as the 60 s cotton yarn in warp with 60 s cotton core spun lycra yarn in weft gave best results, it was selected for further study. Further two sets of fabrics were produced, one set with cotton, silk and polyester in warp and 60 s cotton core spun lycra in weft and another set with cotton, silk and polyester in warp with polyester lycra yarn (61D) in weft as shown in Figure 3.1(b). A total of six woven stretch fabrics, cotton/cotton core spun Lycra, silk/ cotton core spun lycra, polyester/ cotton core spun lycra, cotton/polyester lycra, silk/polyester lycra and polyester/polyester lycra fabrics have been developed and studied.

3 (a) Methodology of Production of Test Fabrics 43

4 (b) Methodology of Cotton, Silk and Polyester Stretch Fabrics 44

5 45 (c) Methodology of Silk/Hybrid yarn Stretch Fabrics Figure 3.1 Flow Diagrams of Materials and Methods

6 46 An attempt was also made to develop silk/ lycra fabrics using silk lycra twisted yarn. To develop a silk/lycra twisted yarn, silk yarn of 22 denier and lycra yarn of 40 denier was tried using AGTEKS direct twist 2B machine. Due to higher elasticity property of lycra, the yarn stretched while being passed through a guide or tensioner, hence silk/lycra twisting could not be done (Reasons are discussed in Chapter 8). In yet another approach, woven stretch fabrics were developed using silk filament (20D) in warp with hybrid yarn (silk/ nylon covered lycra) of 69D in weft in three different weaves for women s sari blouse as shown in Figure 3.1(c) Selected Sari Blouse Materials Commercially Available in the Market Sari blouse materials commercially available in the market were used in the study for pressure comfort analysis and also for a comparative study of pressure distribution of cotton core spun lycra fabrics with blouse materials. All the fabrics were structured in plain weave. The blouse materials used were 2/2 full voil-100% cotton, 2/1 polyester/cotton union fabric, 100% polyester, polyester/nylon union fabric. 3.3 METHODS Development of Woven Stretch Fabrics for Sari Blouse Woven stretch fabrics of cotton/cotton core spun lycra and silk/cotton core spun lycra were woven using sulzer weaving machine. In weaving, warp preparation was normal except that adequate adjustments must be made in the loom sley to allow for fabric contraction which takes place between the reed width and finished width. The main precaution required in weaving of filling stretch fabrics involves tension control on the filling yarns during pick insertion. The processing sequence for cotton/cotton core spun

7 47 lycra fabric samples were desizing, scouring, dyeing and heat setting. The processing sequence for silk/cotton core spun lycra fabric samples were scouring, dyeing and heat setting. Woven stretch fabrics were developed with three different fibers namely cotton, silk and polyester yarns in warp with cotton core spun lycra and polyester/lycra doubled yarn in weft were woven using (Make Andal) power loom machine. Polyester yarn of 21denier and lycra of 40 denier were doubled using a TFO (Two for one twister, Make- Veejay Lakshmi Engineering work, RPM-900). Silk/nylon covered lycra (hybrid yarn) fabrics were produced by using raw silk of 22 denier. Raw silk was degummed and wound on a bobbin in a hank form. Initially, silk yarn has zero twist and was doubled to give 2 ply using a TFO (Two for one twister). The resultant silk yarn was in the form of a cheese (S-twist). The imported nylon covered lycra yarn was introduced in between two parallel cheeses of silk. Silk was twisted with nylon covered lycra yarn using a zari covering machine at 50 twists per inch using negative feed mechanism. The twist given is Z- twist to prevent the removal of silk yarn twist. The output was obtained in perforated plastic cones. Silk yarn of 20 denier was wound into a beam and silk/ nylon covered lycra (Hybrid yarn) as weft yarn is inserted by means of a pirn and the fabric was woven in a power loom. Silk/hybrid yarn stretch fabrics were woven in plain, crepe and sateen weave Testing for Physical Properties of the Fabrics Ends per inch and picks per inch of the fabrics were measured as per ASTM D using counting glass at 10 different places for each sample and an average was taken for further analysis. Fabric weight was found as per ASTM D by GSM cutter and electronic weighing

8 48 balance at different parts of the fabric samples. Beesley balance was used to measure the direct yarn count of the woven stretch fabric samples Testing Low Stress Mechanical Properties of Fabrics The KES-F (Kawabata Evaluation System) was used for measuring low-stress mechanical properties of core spun lycra fabrics (Kawabata & Niwa 1991). The tensile and shear properties were studied on KES-FB1. The tensile properties were measured by plotting the force extension curve between 0 and a maximum force of 500gf/cm and the recovery curve. Shear properties were measured by shearing a fabric sample parallel to its long axis, keeping a constant tension of 10g/cm the clamp. Bending property was measured on KES-FB2 by bending the fabric sample between the curvatures ±2.5 / cm. Compression properties were tested on the KES-FB3 (compression tester) by placing the sample between two plates and increasing the pressure while continuously monitoring the sample thickness to a maximum pressure of 50 gf/cm 2. The surface roughness and coefficient of friction are measured using KES-FB4 (surface tester). All the fabrics were conditioned at 65 ±2% and 27± 2 0 C before the measurement Primary and Total Hand Value Primary hand values (HV), Koshi (stiffness), Numeri (smoothness) and Fukurami (fullness and softness) were calculated by the software required for women s thin dress using the equation as follows: Y k = C 0 C ki X i (3.1) where Y k is the K th hand value such that, K=1 is stiffness, K=2 is smoothness and K=3 is fullness for women s thin dress. The term X i is the normalized i th (I = 1-16) mechanical parameter, normalized as

9 49 X i =(X i M i ) / i (3.2) where X i is the mechanical parameter measured by KES system. There are 16 parameters selected from tensile, bending, shear, surface and compression and structural properties of fabric (Kawabata, 1980). M i and i are the mean and standard deviation of X i. C 0 and C ki are constant coefficients for women s thin dress fabrics obtained from regression. Then the total hand value was determined by substituting Y k that are derived from Equation (3.1) into Equation (3.3) as follows: THV = C 0 + Z k (3.3) Where Z k =C k1 [Y k M k1 ]/ K1 +C k2 [Y k 2 -M k2 ]/ K2 (3.4) Where Z k is the K th primary hand value to THV; M k1 and K1 are population means and standard deviation of Y k ; M k2 and K2 are population means and standard deviations of Y 2 k and C 0, C k1, C k2 are the constant coefficients of the K th parameter Testing for Air Permeability (ASTM D 737) The air permeability of the woven stretch fabrics was obtained by FX 3300 Lab Air IV air permeability tester. This test method covers the measurement of the air permeability, the rate of air flow passing perpendicularly through a known area under a prescribed air pressure differential between the two surfaces of a material of textile fabrics. The air permeability of the woven stretch fabrics were analyzed in normal state and stretched state in order to simulate the behavior in blouses. The result of air permeability was recorded in term of cm 3.cm 2 /s. A 2 2 cm 2 area was marked on the fabric and the fabric was extended to 50% in weft direction so that the marked area is extended by the desired amount. The fabrics was held in hands on both sides of the area marked and extended in weft direction till the

10 50 marked area of 2cm reach 3cm. The fabric was extended to both sides while the fabric was kept under the marked area of the air permeability tester. The air flow was passed in that extended state and measurement was recorded Testing for Thermal Conductivity (ASTM C518) The thermal property was studied by using Lee s disc apparatus. This test is used to measure the speed at which the heat travels through a material through conduction. The transmission of heat occurs both by conduction through the fibre and the entrapped air any by radiation. The Figure 3.3 represents the simple form of Lee s disc which has been used for determining the thermal conductivity of core spun lycra fabrics. The sample is placed in between a steam chamber N and a brass disc M. The thermometers T 1 and T 2 are inserted into the holes in N and M to record the temperatures on the two sides of the sample. The heater is switch on to heat the brass disc and the temperatures of all disc increases in nonlinear relationships and at different rates with the time according to its position from the heat source. And the temperatures were recorded every (5 minutes) until reach to the equilibrium temperature of all disks. To find the rate at which heat is radiated by the disc M, it is brought directly into contact with the steam chamber after removing the fabric sample and its temperature T raise about 10 0 C above the steady temperature T 2. With a stop clock, the time is recorded for every one degree fall of temperature as it cools from (T 2 +5) 0 C to (T 2-5) 0 C. Similar calculations are made with the other readings and the average value of the rate fall of temperature R at T 0 2 C is found. Heat conducted by the specimen =K A (T 1 T 2 )/d (3.5) Heat lost by the disc=msr (2h+r) / (2h+2r) (3.6) At the steady state K A (T 1 T 2 )/d = MSR (2h+r) (2h+2r) (3.7) Thermal conductivity K= MSR.d (2h+r)/A (T 1 T 2 ) (2h+2r) (3.8)

11 51 where M-mass of the disk, S-specific heat capacity of the brass, d-thickness of the sample, R-rate of fall temperature due to heat, h-thickness of the brass disc, r-radius of the brass disc and A-surface area of the sample Testing for Water Vapour Permeability The water vapour permeability of the samples has been measured using the cup method, according to ASTM E96 (Procedure B) testing standard in normal and in stretched state (Saville 1999). A 2 2 cm 2 area was marked on the normal fabric and the fabric was extended to 50% in weft direction for testing the moisture vapour transmission of fabrics in stretched state. This method involves the determination of weight loss, with evaporation time (24 h) of water contained in a cup, the top of which is covered by the cover ring. A glass beaker of the height 75mm with the internal diameter of 50mm was chosen. The beaker was filled with water to a height of 55mm. In this method, the woven stretch fabric is placed in an airtight manner over the top of a cup in normal state and in another cup the fabric is stretched and secured in the same airtight manner by a strong rubber band. After mounting the fabric, the weight of the whole assembly was measured and after 24 hours, final weight of the assembly was recorded. The water vapour permeability (WVPTR) was calculated using the following equation: 24xM WVPTR (3.9) AxT Where M is the loss in mass (g); T, the time interval (h); and A, the internal area of the cup (m 2 ), A was calculated using the following relationship:

12 52 d2x10 6 A where d is the internal diameter of cup (mm) (3.10) Analysis of Fit Selection of subjects Three different figures namely slim, normal and stout were chosen as subjects for fit analysis and objective pressure test. To understand the measurements of women of different figures, a pilot study was carried out by taking the measurements of 50 women of different sizes for sari blouse sizing. From this work, figures were defined based on the height and bust circumference. Slim figure (size 12) -Tall women (158cm-162cm) with small bust (84cm-87cm); normal figure (size 16)-Tall women (160 cm-165cm) with medium bust (96cm-98cm) and stout figure (size 22)-short women (150cm- 155cm) with large bust (108cm-114cm). Women aged between 19 and 35, who met the desired size criteria of slim, normal and stout were selected as subjects to participate in fit analysis and objective pressure comfort evaluation. The subjects wore cloth bra of size 32B (slim figure), 36C (normal figure) and 40B (stout figure) under the blouse during the fit analysis and pressure comfort evaluation. The mean and standard deviation of subject s body measurements are shown in Table 3.1. Subjects were given orientation about the research purpose, methodology and fit evaluation scales before the conduct of subjective wear trial and objective pressure test.

13 53 Table 3.1 Body Measurements of the Subjects Slim figure Normal figure Stout figure Measurement Size 12 Mean Standard Size 16 Mean Standard Size 22 Mean Standard (cm) Deviation (cm) Deviation (cm) Deviation Height Bust circumference Upper Waist circumference Upper arm circumference Blouse length Shoulder to bust point Front neck depth Back neck depth Sleeve length Sleeve round Armhole circumference Back width Shoulder length Distance between bust points

14 Pattern design and garment construction The measurements required for drafting sari blouse are shown in Figure 3.2. A pattern with negative ease value is used for the construction of stretch garments. The pattern is cut to body dimensions smaller than the actual body. The optimization of ease reduction allowance for woven stretch fabrics based on percentage of stretch and subjective mean fit rating are discussed in chapter 4. The pattern drafting and construction sequence of sari blouse are given in Table 3.2. The pattern pieces were developed for three sizes and pattern drafting procedure, ease reduction allowance and the type of measurements required were confirmed after a series of sample garments have been fitted and adjusted on three different figures. A pattern consisting of front, back, midriff yoke and sleeve was drafted. Three darts were used in the cup area of front pattern to achieve correct shape. Two darts were used in the back waist. It is traditional to cut the blouse back and sleeve on straight grain oriented vertically, perpendicular to the hem as warp yarns hold the shape well and resist bagging and lycra yarn in weft, stretched well horizontally around the body. Midriff yoke (waist band) was cut on cross grain, as it reduces stretch horizontally and gives stability around the waist line, when a person moves or bends. A pattern layout is shown in Figure 3.3. Figure 3.2 Body Dimension

15 55 Figure 3.3 Pattern Layout Table 3.2 Drafting and Construction Sequence of Sari Blouse DRAFTING PROCEDURE FRONT BACK SLEEVE FRONT 0-1 ¼ the bust circumference 1-2 Length of the blouse Square down Front neck depth 0-5 ½ Neck width 0-6 ½ shoulder width 6-7 Armscye depth Join the points 3-8 ¼ waist circumference 3-9, 8-10 Height of the midriff yoke Curve the yoke (9-10) ¼ waist circumference + 5cm dart allowance /12 th of the Bust Circumference + 2.5cm 11-12, ½ Dart width, Dart length- 2cm below the bust point

16 56 Table 3.2 (Continued) 14 Midpoint of the centre front 14-15, ½ Dart width 17 Dart point at armscye 18-17, ½ Dart width Mark the bust point from the shoulder and draw the darts pointing towards the bust point. BACK ¼ the bust circumference Length of the blouse Square down 20, 21, 22 and ½ Neck width ½ Shoulder width Back neck depth Armscye depth ¼ Waist circumference + 2cm of dart allowance Join the points /12 th of the Bust Circumference + 1cm 29-30, ½ Dart width Join the dart points SLEEVE: A-B Armscye depth of the body taken while drawing body draft or armhole circumference. B-C Length of the sleeve Square down ABCD A-E, B-F G,H I-H, H-J Sleeve cap height or 1/8 th of bust Midpoints of AB and DC Draw the sleeve cap through K and shape the front and back armscye. ½ of sleeve open Join the points and draw the sleeves CONSTRUCTION PROCEDURE 1. Finish the darts at the armscye, centre front and waistline in the front bodice of the blouse. 2. Finish the midriff yoke. 3. Attach the midriff yoke to the front bodice on either side of the blouse 4. Finish the placket in the front with binding and facing. 5. Attach the shoulders of front and back bodice of the blouse. 6. Finish the hemline of the back bodice. 7. Finish the darts at the back bodice 8. Attach the side seams of the front and back bodice of the blouse 9. Finish the hemline of the sleeves 10. Attach the side seam of the sleeves 11. Attach the sleeve armscye to the bodice armscye. 12. Finish the neckline of the front and back (bias facing) and attach the fasteners.

17 Subjective wear trial Wearers perceived fit evaluation consisting of seven attributes were used to attain feedback from the subjects regarding wearing comfort and fit. Subjects were asked to express their agreement or disagreement on a five point response scale from 1(strongly disagree) to 5(strongly agree). Questions 1 to 4 inquire on wearing comfort, flexibility, tightness and freedom of movement. Questions 5 and 6 concentrated on donning and doffing the garment. Question no. 7 focused on garment fit. Each subject was asked to remain in the garment for 15 minutes. The subjects' perceptions of clothing fit were determined after 10 minutes. Each figure type consisting of five subjects expressed their perceived fit evaluation on a five point scale (Nam et al 2005) Visual fit evaluation Three subjects among the five under each figure type volunteered to participate in visual fit evaluation. Visual fit of the garment was evaluated by five judges (faculty members from Apparel and fashion design) on nine subjects (three figures*three subjects). The five judges evaluated the fit of blouses on each subject (while wearing). Blouse was segmented into 20 areas, 12 front parts, 6 back parts and 2 side parts as shown in Figure 3.4. Judges were given orientation on the fit evaluation scales and procedures. Evaluation was carried out for both right and left side of the subject (Nam et al 2005). Visual fit evaluation by judges was carried out in three sessions, each subject under each figure type (three subjects) in a session to improve the reliability of the judges ratings. Each judge was asked to assign their extent of agreement/disagreement towards the point of fit for all 20 areas using a five point scale with 5 representing strongly agree and 1 representing strongly disagree.

18 58 From the fit assessment carried out on cotton core spun lycra fabrics discussed in chapter 5, it is observed from the results of visual fit ratings by judges and fit assessment on ease linear index, number of folds and seam line deviation by judges using the standardized fit rating scale that there was good correlation between the visual fit assessment by judges at different areas of blouse and fit assessment on ease linear index measurement, number of folds and seam line deviation. Hence, the visual fit evaluation by judges was not been carried out further for the developed woven stretch fabrics discussed in chapter 7 and Front right shoulder 2.Front left shoulder 3. Right bust 4. Left bust 5. Front right waist 6. Front left waist 7. Back waist 8. Front right neckline 9. Front left neckline 10. Back neck line 11. Front right armscye 12. Front left armscye 13. Back right armscye 14. Back left armscye 15. Right side underarm 16. Left side underarm 17. Front right midriff 18. Front left midriff 19. Right mid back, 20. Left mid back Figure 3.4 Visual Fit Evaluation

19 Fit assessment on ease measurement, number of folds and seam line deviation by judges using the standardized fit rating scale The influence of fit attributes such as ease linear index value, number of folds and seam line deviation were measured on nine subjects by judges (3 figure*3 subjects* 5 judges) for each sample and ratings were assigned based on the developed fit rating scale. The standardization of fit rating scale on ease, number of folds and seam line deviation are discussed in Chapter 4. The linear index (LI) was calculated from the linear measurement (LM) of garment and body= (LM garment LM body)/lm body (Ng et al 1996). The bust circumference was measured on nine subjects (3 figures 3 subjects) without the garment (over the cloth bra) for obtaining the linear measurement of the body. The judges measured the bust circumference of the sample blouses on the subjects and calculated the linear index value. The linear index value obtained was correlated with the developed fit rating scale to assign the fit rating for ease. The judges counted the number of folds formed in the sample blouses at upper arm, armscye area of left and right arm, front and back neck, back waistline, front cup area, midriff yoke and side seam of left and right. The total number of folds found in the blouse on each subject was counted while wearing and as per the number of folds obtained, the ratings were correlated with the developed fit rating scale to assign the fit rating for number of folds. The picture of the folds formed in the blouses is shown in Figure 3.5. The length of seam line deviation from bodyline was measured by judges at the side seam, armscye, shoulder line and parallel position of sleeve of the blouses on each subject while wearing and the values obtained were correlated with the fit rating scale.

20 60 Figure 3.5 Picture of the Folds Formed in the Blouses Testing for Maximum Stretch, Recovery and Un-Recovered Elongation As lycra yarn was used in the weft direction, the assessments for stretch and recovery were carried out only in weft direction after conditioning specimens in a standard atmosphere (temperature 20±2 0 C, 65±2%). Stretch properties were determined according to BS EN :2005, to determine the elasticity of fabrics. The elastic properties of the samples were determined by the constant rate of loading. Sample strips from weft direction were hung with the load of 30N [6N/ cm width of specimen] to study the elastic property of fabrics. The samples were then removed and allowed to recover from stress. The immediate and delayed elastic recovery was measured at time intervals of 1 minute and 30 minutes respectively. The percentage of fabric stretch, recovered elongation and un-recovered elongation values were calculated from these measured outcomes, as follows Fabric stretch % = change in length/original length x 100 Fabric un-recovered elongation % = 100 recovery percentage Where, Recovered elongation % = change in length [removal of load] x 100 Original length

21 Pressure Comfort Evaluation Measuring instrument A new pressure measurement system with self-inflatable balloon, Kikuhime, (TT Medi Trade, Soleddet 15, DK 4180 Soro) was used to measure the interface pressure between body and the garment. This system uses two identical: oval-shaped measuring sensors, 30 x 38 mm, 3 mm thick when calibrated to 0 mmhg. The interface pressures were measured on the nine subjects (three subjects in each figure type) in standing position at different body locations (Jin et al 2008). The instrument composed of balloon sensor, a connecting tube and a measuring unit as shown in the Figure 3.6. Figure 3.6 Pressure Measuring Device Garment pressure experiment The Pressure distribution of woven stretch blouses and commercially available blouse materials were assessed objectively using kikuhime pressure sensors at different body locations in standing position. Three subjects under each figure type participated in pressure comfort evaluation of blouses. Eighteen pressure points were selected according to the characteristics of body structure and ergonomics principle (Jin et al 2008). These points can reflect the pressure comfort. The positions of pressure points

22 62 are shown in Figure 3.7. To measure the amount of pressure given by the blouse at different body location, pressure sensors were placed between the skin surface and inner layer of the garment. The interface pressures were measured after the subjects remained in standing position for 10 seconds. The test is repeated three times for each subject and an average pressure value obtained at each pressure test point is calculated for the study. Figure 3.7 Pressure Points Dynamic pressure measurement Pressure comfort was evaluated dynamically in four postures, bending, twisting, flexing the arms to 90 0 and flexing the arms to as shown in Figure 3.8. Among many pressure test points, the test points that produce the maximum objective garment pressure will make a determinant effect to the pressure comfort of these postures (Jin et al 2008). So, the

23 63 maximum pressure value obtained in standing position was chosen as pressure test points for dynamic pressure evaluation. Figure 3.8 Body Postures such as (a) Bending (b) Twisting (c) Flexing Arms to 90 and (d) Flexing Arms to 180