CHAPTER 3 MATERIALS AND METHODS

Transcription

1 60 CHAPTER 3 MATERIALS AND METHODS 3.1 INTRODUCTION In this Chapter, the materials and methods used in the experimental work are described. 3.2 MATERIALS The materials used are spun silk fibers and nylon multifilament yarns details of which are given in Table 3.1 Table 3.1 Details of spun silk and nylon multifilament S.No Materials Yarn linear density Mulberry spun silk 60 Nm 1 Tasar spun silk 60 Nm Eri spun silk 60 Nm 2 Nylon 6 multifilament 20 Denier 34 Denier 40 Denier 70 Denier

2 DESIGN OF THE EXPERIMENTS The experiments were designed to study: The effect of hollowness on the properties of mulberry, tasar and eri silk yarns and fabrics. Yarn production: Core spun yarns consisting of nylon as core material and spun silk in sheath were produced in the ring frame.the filament was fed into the nip of the front roller of the drafting system with optimum pretension. The roving produced from spun silk was fed in the usual way. Figures 3.1, 3.2. shows the method of core yarn production Gate Tensioner Disc Pre-tensioner Core Filament Staple feed Drafting Rollers Core Yarn delivery Figure 3.1 Hollow Yarn Preparation in Ring Spinning System

3 62 A special attachment was fabricated according to the design of the drafting system. The core yarn attachment consists of a metal bracket (E) bent according to the drafting zone. One end of the device is fitted on the roving traverse bar(b-rowing bar,c-rowing guide & H-core yarn guide). The other end of the plate (L) is fitted a porcelain guide to feed the core filament at a precise position behind the front roller nip. The gate tensioning unit (F) is fitted to the device to control the feed tension. the staple feed(d)passes through Three drafting rollers(a). The input tension of the core filament was adjusted by adding or removing dead weight(j-tension weight) according to the core denier. Figure 3.2 Hollow Yarn Preparation in Ring Spinning System

4 63 The filament was passed through the gate tensioned and pre tensioned before feeding into the front roller nip. The position of core yarn should be adjusted so that it can be placed in the center of the sheath material. The process flow chart of spun silk yarns given in Figure tex spun silk yarns were produced from mulberry, tasar and eri types. Process flow chart Systematic Diagram Silk waste Nylon multifilament yarn Blow Room Carding 4 passage pre combing Gill box 2 passage combing 7 passage pre combing Gill box Simplex Spinning Figure 3.3 Plan of Work

5 64 Core spun yarn Mulberry + Nylon multifilament yarn (den 20,34,40,70) Tasar + Nylon multifilament yarn (den 20,34,40,70) Eri + Nylon multifilament yarn (den 20,34,40,70) Yarn (Core yarn with nylon multifilament) Weaving Dissolving in 85% Formic Acid Dissolving in 85% Formic Acid Washing Washing Hollow yarns with Hollowness (0%, 11%, 17%, 22%, 32%) Hollow yarns in Fabric (0%, 11%, 17%, 22%, 32%) Testing of Yarns Testing of Fabrics Calculation of hollow percentage Handle and thermal properties using Kawabata evaluation system and Alambeta Tenacity and Elongation Figure 3.3 (Continued)

6 65 Compression Thermal conductivity (Lee s apparatus) Recovery Drape with Seams Twist Factor Abrasion Resistance Bending Regidity Wicking and Wetting Wicking Dyeability Dimensional stability Dimensional stability Bursting strength Flexural rigidity Figure 3.3 (Continued) A total of 15 yarns were produced by varying the linear density of the nylon multifilament yarns. Details of all the samples produced are given in Table 3.2. The control yarn in each case is one which has 100% spun silk. The fabric samples were treated with 85 % formic acid for about 45 minutes at room temperature and the fabrics were washed thoroughly twice in hot water and then in cold water to remove the traces of formic acid and core component. The percentage varied as the linear density of the nylon

7 66 multifilament became coarse. The effect of formic acid on silk was determined by measuring the tenacity of spun silk yarns before and after treating the spun silk yarns with 85% formic acid and the results indicate that there is not much difference in the tenacity (Appendix 1). 3.4 TESTING OF YARNS All the tests were conducted at 65% r.h ± 2% and 27º C ± 2º C after conditioning the samples for 48 hours. Details of yarn samples produced to study the effect of hollowness are given in Table 3.2. All the 15 yarn samples yarn samples were tested for 1. Flexural rigidity 2. Compressional energy 3. Tenacity 4. Elongation 5. Initial modulus 6. Work of rupture. 7. Elastic recovery 8. Twist factor 9. Dimensional stability The yarn samples were also tested for hollowness by a) Microscopic method b) Gravimetric method and c) Centrifuge technique

8 67 Table 3.2 Details of yarn samples produced to study the effect of hollowness S.No 1 Type of silk Nylon multifilament denier Hollowness (%) Yarn linear density Nm ----Tex Twist α M No of Samples Nil Mulberry Nil Tasar Nil Eri Grand Total 15 The measurement of hollowness in spun silk yarns is described in a separate Chapter. The yarn samples were tested for structural parameters like hollowness. Low stress mechanical and comfort properties of fabrics were studied for fabrics made from spun silk hollow yarns containing different hollowness Yarn Tenacity and Elongation Premier Uster Tensomaxx7000 was used for testing yarn tenacity and elongation. Testing was done in accordance with the ASTM standard 1425:1996. The parameters initial modulus and work of rapture were also obtained.

9 Initial Modulus The initial modulus, which is expressed in g/tex, is obtained by taking the slope of the stress strain curve Bending Rigidity Bending rigidity was determined by the loop test based on Carlene s (1950) method. The mean of five tests was taken. In this method, the yarn is made in the form of a loop, and it is distorted by adding a rider (Figure 3.4) Morton and Hearle (1997) Flexural rigidity is calculated from the following formula Flexural rigidity (mg.cm 2 ) = kwl 2 cos θ / tan θ (3.1) where, k is a constant the value of which is around W = applied load in grams L = circumferential length of in distorted ring in cm θ = 493d/L d = deflection of lower end of the ring under action of applied load. For greater sensitivity, a value of W is chosen such that θ lies between 40º and 50º. When W is in grams, L and d are in cm, the filament rigidity is derived in units of g.cm 2 and has the dimensions ML 3 T -2.

10 69 Figure 3.4 Flexural rigidity by loop ring method Compression Yarn compression was tested using Kawabata Compression tester. A single yarn was compressed at two different pressures, name by 0.5 and 50 gf/cm 2 and parameters LC, WC and RC were obtained for representing compression Elastic Recovery The elastic recovery of the hollow yarns was determined as per the method suggested by the Wilding (2007) Figures 3.5 and 3.6 shows details of the method followed. Recovery of yarn was determined by taking a yarn of length L 1 at zero stress. A stress of 0.18 g/tex was applied for a period of one minute, which extended the length of the yarn. The extended length is measured as L 2. When stress was removed, the yarn recovered back to a length of L 3.

11 70 Figure 3.5 Elastic Recovery Figure 3.6 Recovery curve (Wilding)

12 71 The recovery was measured using the formula, L 2 L 3 Recovery = 100 (3.2) L 2 - L 1 L 1 = Length of the yarn without tension. L 2 = Extension the yarn after subjected it to a stress. L 3 = Recovered length Dimensional Stability out as per ISI. This refers to the shrinkage of yarns in water.this test was carried Twist in the Hollow Yarn In order to measure the twist in the hollow yarn, the method outlined in ASTMD1423 was used. The essence of the method is to unwind the twist in a yarn until the fibers are parallel to the yarn axis and to count the number of turns. The twist tester has two jaws at a set distance apart.one of the jaws is fixed and the other is capable of being rotated. The rotating jaw has a counter attached to it to count the number, the whole turns and fractions of turn. Testing was started of with least one meter from the open end of the yarn as the open end of the yarn was free to untwist so that the level of twist might be lower in the region. As the yarn is being clamped in the instrument, it must be kept under a standard tension (0.5cN/tex) as the length of the yarn will be altered by too high too low a tension. The twist is removed by turning

13 72 the rotatable clamp until it is possible to insert a needle between the individual fibers at the non rotatable clamp end and to traverse the needle across to the rotatable clamp. The use of a magnifying lens may be required in order to test fine yarns. The twist direction and the mean turns per centimeter or per meter were reported. The mean of ten tests was considered Radial Packing Density The cross section of yarns produced with and without hollow studied by using microscope. The technique is based on the soft cross section developed by Ishtiaque et al (1988).In this, the yarn samples was given a coating of polyvinylacetate to prevent any to prevent any deformation of fibers while cutting the cross section on a microtome. The yarn was then dried and embedded in a mixture of molten wax and paraffin by pouring the mixture into a receptacle in the middle of which the yarn was positioned. The thickness of cross section was kept at 15 µm as this was found to provide a satisfactory view under microscope Measurement of cross sectional area of fibres and radial packing density of yarn A transport Perspex template on which concentrate circles are engraved is used for measuring the area of fibers in the yarn cross section. The total area of yarn cross section is divided into six zones of equal width and area of fibers in the individual zone is calculated Area of i st zone = 2π r i h (3.3) where, h = width of zone ; r i = mean radius of zone.

14 73 Since h is constant r i = [i-1/2]h (3.4) Area of zone = 2π h 2 [i-1/2] (3.5) Area occupied by the fibers in this zone = 2π h 2 [i-1/2] µ i (3.6) where, µ i = packing density of i st zone. The total area of fibers in yarn cross section, 2 se 2 r n I 1 i 1 µ n = Number of zones. 2 (3.7) Packing density of each zone = Total packing density Area of the zone (3.8) Total area of fibers in yarn cross section Packing density of yarn = Total area of yarn cross section (3.9) Fiber packing density of each one is define as the ratio of the area of fibers in the zone to the total area of the zone. A 1 A n (3.10) In order to compare the yarn produced with different modification the radial poison of each zone in the section was expressed as a fraction of the yarn radius (R). In these measurements, the radius of a zone was taken as the distance from the yarn axis to the point midway between the two boundaries of

15 74 the zone, and the yarn radius was considered to be the distance from the yarn axis to the point midway between the two boundaries of the outer most zone measured. Thus, in essence, the procedure followed is similar to the technique developed by Hickie and Chaikin (1974) for studying the packing density. 3.5 FABRIC PRODUCTION Fabrics were produced using the core yarns in warp and weft. These fabrics were subsequently washed and treated with 85% Formic acid for about 45 minutes at room temperature. The fabric constructional particulars are given in Table 3.3 and details of fabric samples produced to study the effect of hollowness are given in Table 3.4. Table 3.3 Constructional particulars of fabric made put of spun silk yarns Linear density of warp (Nm) 50 Linear density of weft (Nm) 47 Ends/cm 24 Picks/cm 24 Weave plain Dyeing of hollow silk fabrics was carried out using acid dyes and with the following recipe: a) Material to liquor ratio = 1:50 b) Acid Dye = X c) Glauber s salt = 20% d) Temperature = 85º C e) Time = 45-50min f) Acetic acid = 2% (owf) The material was rinsed and dried.

16 Table 3.4 Details of fabric samples S. No Types of silk with hollow percentage Ends/cm Picks/cm Weight (GSM) Thickness (mm) Mulberry Tasar Eri Mulberry Tasar Eri Mulberry Tasar Eri Mulberry Tasar Eri

17 76 In order to study low stress mechanical and comfort properties of fabrics, all the 12 spun silk yarns containing nylon multifilament in core were woven in semi automatic loom. 3.6 STANDARDIZATION OF NUMBER OF TESTS PER SAMPLE The number of tests to get minimum CV in the estimation of flexural rigidity was determined by conducting 10, tests each time. Table 3.5 gives the CV for different number of tests. Table 3.5 Values for varying numbers of tests for flexural rigidity of yarns S.No No of tests CV% It is apparent that the coefficient of variations stabilizes at N = 20 and it does not show any improvement with large number of tests. In view of this, 20 tests per sample were carried out for assessing the flexural rigidity of yarns.

18 77 The method of measuring fabric mechanical properties involves a complete fabric deformation recovery cycle for tensile, shear, bending and lateral compression properties. In all the cases the deformation recovery cycle is accompanied by a significant energy loss or hysteresis. From the view point of fabric objective measurement technology it is possible to measure either the entire deformation recovery behaviour as is the case for the KESF set of instruments (Kawabata et al 1980), or alternatively to measure what amounts to single point on the deformation curve which forms the basis of Fabric Assurance by Simple Testing (FAST) set of instruments (Ly et al 1988, Minazio 1995). The former approach is preferable for research and development work whilst the latter approach has the advantage of simplicity and is preferable for routine testing purposes. 3.7 FABRIC MECHANICAL PROPERTIES Although Kawabata introduced his KES-FB system and a method to evaluate fabric hand, this approach was extended to evaluate other fabric performance, such as tailorability and fabric softness Kawabata s Evaluation System for Fabric (KES-FB) Professor Kawabata developed the KES-FB system mainly for measurement of fabric hand value in the 1970 s (Kawabata and Niwa 1989).It was also designed to measure basic mechanical properties of non-woven, papers and other film-like materials. (KATO Tech Co -1) The purpose of developing this KES-FB system was to replace the traditional subjective method of evaluating fabric hand. The KES-FB system consists of four instruments to measure the following different properties given in Table 3.6.

19 78 KES-FB 1 for Tensile and Shearing KES-FB 2 for Bending KES-FB 3 for Compression KES-FB 4 for Surface Friction and Roughness. Both the tensile and shear property of fabrics are very important features in evaluating fabrics. Tensile indicates the recovery of deformation from strain, or the ability to recovery from stretching, when the applied force is removed. Shearing stiffness is the ease with which the fibers slide against each other resulting in soft/ pliable to stiff/ rigid structures. Lower values indicate less resistance to the shearing movement corresponding to a softer material having better drape. The combination of these two properties may sometimes be even more important than other mechanical properties to fabric evaluation. In all Kawabata systems an integrator, an automatic data processing system, is used. For most fabrics, tested results can be calculated and recorded by the computer software. Table 3.6 KESF system for fabric objective measurement Machine Block Use Characteristic Values Measured KES-F -1 Tensile and Shear testing LT,WT,RT,EMT,G, 2HG, 2HG5, KES-F -2 Pure bending testing B, 2HB KES-F -3 Compression testing LC,WC,RC,T KES-F -4 Surface testing MIU,MMD,SMD Tensile Test Using KES-FB-1 The principle of the instrument is to apply a constant tensile force to fabric in one direction and to measure the amount of stretch on the fabric. The stretching deformation can be considered as a kind of biaxial tensile

20 79 deformation. As shown in Figure 3.7 the sample is held by two chucks (A and B), and chuck B is on a movable drum connected to a torque detector. The fabric sample is clamped between chucks A and B and the distance between the chucks is 5cm. A torque meter is used to measure the tensile stress and by sensing the movement of chuck B, a potentiometer is used to measure the tensile strain. Stretching the sample when the tensile force reaches the preset value, it turns back and recovers to the beginning position. There are two tensile rate adjustments as 0.2mm/sec or 0.1mm/sec. This is done by changing the gears at the back of the instrument. The tensile force (F) and strain (ε) are recorded on the X-Y plotter. From the graph, LT, WT, RT, and EMT can be calculated. The sample size between the chucks is 20 cm x 5 cm. Figure 3.8 shows a typical tensile force strain curve which is similar for both warp and weft directions. Figure 3.7 Sample portion between chucks A and B WT F d (3.11) Em o where, WT: Tensile Energy or the work done while stretching the fabric until maximum force.

21 80 ε - tensile strain ε m - the strain at the upper limit load F m gf/cm F - tensile load as function of strain LT = WT (1/2) F m ε m (3.12) where, LT - Linearity WT RT% WT RT - Tensile Resilience (%); where, WT is the recovery work and calculated as Em o WT F d (3.13) where, F (ε) = tensile force during the recovering. Referring to Figure 3.8 hand calculation can be done as below, Figure 3.8 A Typical Force- Extension Tensile Curve of Fabric

22 81 LT : Linearity of load-extension curve Area (a) + (b) (WT) LT = (3.14) Area Δ ABC* 500gf/ cm EMT ΔABC = (3.15) WT : Tensile Energy WT = Area (a)+(b) WT = INT 5 RT : Tensile resilience B- INT RT= 100 (3.16) INT EMT : Tensile Strain at the point A on the curve Shear Test Using KES-FB-1 The shear test using the KES-FB-1 is shown in Figures 3.9 and A constant force is applied to the fabric by attaching a weight to the fabric end on clutch A side. By turning the clutch off, chuck B is freed and able to move. When the test starts, chuck B constantly slides to the side until there are 8 degrees of shear angle (standard condition), and chuck B returns to the original position. During the test, shear force is detected by a transducer and shear strain is detected by a potentiometer.

23 82 The shear angle can be adjusted between ±1 and ±8 degrees by presetting the potentiometer. It is advisable to do shear test before the tensile test because tensile deformation is greater than the shear deformation. Figure 3.9 Principle of Shear Property Test (KATO Tech Co-1) Figure 3.10 Initial Tension to Place Sample on Chucks

24 83 Figure 3.11 shows the shear deformation under a constant extension and Figure 3.12 illustrate the typical shear test force-shear angle curve. Figure 3.11 Shear Deformation Under a Constant Extension G - The slope measured between ø = 0.5 and 2.5º (gf/cm.degree) 2HG - Hysteresis of Fs at ø = 0.5º (gf/cm) 2HG5 - Hysteresis of Fs at ø = 5º (gf/cm) MEAN - Average of these values for positive and negative curves on warp and filling. Figure 3.12 A Typical Shear Test Force-Shear Angle Curve

25 84 Referring to Figure 3.13, hand calculation can be done as below. a b G 2gf / cm 2 2 (3.17) where, G = Shear stiffness. c d 2 HG 2gf / cm (3.18) 2 where, 2HG = Hysteresis of shear force at 0.5 of shear angle. e f G 2gf / cm (3.19) 2 where, 2HG 5 = Hysteresis of shear force at 5 of shear angle. Figure 3.13 Shear Hand Calculation Pure Bending Test Using KES-FB-2 Bending property is an important feature to evaluate fabrics. It is necessary to assess fabric hand as well as fabric drape. Pure bending test is a

26 85 component of the KES-FB system. It is used to determine fabric bending rigidity. Before the invention of the KES-FB pure bending test, Peirce s cantilever method was used to measure bending rigidity. The pure bending tester can be used to measure the bending property of thin film materials such as leather, rubber, film and yarn as well as fabrics (manual bending). The KES-FB pure bending method is a different method than the cantilever test because the sample is bent to a uniform curvature. It is also automatic and computerized, consisting of mechanical unit and electronic unit (KATO Tech Co-2). The fabric sample is mounted on the instrument. One chuck that holds one end of the sample is movable and the other is fixed. The moving of the sample edge by one of the chucks enables the measurement of bending properties. The Figure 3.14 shows the top view of the mounted sample on the instrument. Figure 3.15 illustrate the bending mechanism and Figure 3.16 shows the sample setting. Figure 3.14 Pure Bending Deformation cosk X (3.20) K sin K Y (3.21) K

27 86 C 1 cm and C K (3.22) 3. K(cm -1 ) = (3.23) B = slope between at K = 0.5 cm -1 and K = 1.5 cm -1 2HB = hysteresis at K = 0.5 cm -1 2HB 1.5 = hysteresis at K = 1.5 cm -1 X - digital output of voltmeter received from T terminal. M - BK ± HB where, M - Bending momentum per unit width (gf.cm/cm) K - Curvature (cm 1 ) B - Bending rigidity per unit width (gf.cm 2 / cm) Figure 3.15 Schematic Illustration of the Bending Mechanism

28 87 Figure 3.16 Setting of Sample To find B, bending rigidity, the average of the two slopes is taken. One value is when sample is bent with its face surface outside and the other is when sample bent with its face surface inside (Figure 3.17). This leads to Bf Bb B (3.25) 2 Similarly to finding bending rigidity, to find bending hysteresis, 2HB, and the average of the two hysteresis width at curvature ±1 is taken. Thus, 2HBf HB HB (3.26) 2 2 b

29 88 Figure 3.17 Bending Test Diagram Compression Test Using KES-FB-3 Compressional property of fabrics is another mechanical property of fabric that is necessary to evaluate fabrics. The KES-FB-3 is a component of the KES-FB series and is used for measuring the compressional property of fabrics as well as other materials such as nonwoven, leather, rubber and film. One advantage of the instrument is it can test fabrics with nonlinear compressional property. This is made possible by the installation of an integral circuit. It also can be used to measure the bending properties of a loop-shaped fabric and yarn. The sample should be under the upper-limit force and constant rate of compressional deformation. There are two types of maximum strokes. A standard stroke is 0mm to 5mm and a large stroke is 0mm to 50mm. The maximum applicable compressional force is 2500gf. First the upper-limit force and the distance of the plunger from the bottom plate should be set. Then the sample should be placed on the bottom plate. When the measurement starts, the plunger comes down at a constant rate and compresses the sample. As soon as the

30 89 compressional force reaches the upper limit force, the plunger starts to move up and it stops when it completes the recovery process (KATO Tech Co-3). The KES-FB-3 consists of two units, a mechanical unit and an electronic unit. The electronic unit consists of amplifier and integrator. The mechanical unit and the working mechanism of the KES-FB-3 are illustrated in Figures 3.18 and The fabric sample to be measured is placed on the sample plate. The plunger for compression moves down at the rate of 1mm/50sec (standard) to compress the sample. A potentiometer detects the displacement of the plunger. While the plunger compresses the fabric sample, the output voltage of the compressional force reaches the preset voltage and the synchronous motor reverses causing plunger to ascend. During the testing, pressure versus thickness is measured and recorded on the X-Y recorder. The resilience, compression energies, and linearity can be calculated according to the compression curve on an X-Y chart. Figure 3.20 shows an example of pressure thickness curve. Figure 3.18 Schematic Illustration of the Compression Tester

31 90 Figure 3.19 Initial Setting of Plunger Figure 3.20 An Example of Pressure Thickness Curve LC : Linearity of compression thickness curve Area a b WC LC Area ABC* (3.27)

32 91 50 gf/cm2 ( ABC (3.28) 2 10 * m WC : Compressional Energy WC = Area (a) + (b) WC = INT 0.1 RC: Compressional resilience B INT 100 RC (3.29) INT T o : Thickness value of X-axis at Pm=0.5gf/cm² T m : Thickness value of X-axis at Pm=50gf/cm² TO Tm EMC 100 (3.30) T o Surface Friction and Roughness Test Using KES-FB-4 As well as other properties previously explained, the surface test is also necessary to evaluate fabrics. Also the surface properties are closely related to the fabric hand. The KES-FB-4 measures the frictional coefficient (MIU), the mean deviation of the coefficient of friction (MMD) and geometrical roughness (SMD). The measurement is automated and the data processing is computerized so data can be read directly after the test.

33 92 As shown in Figure 3.21, the sample is fixed at a winding drum, chuck A, and a constant force is applied on the opposite end, chuck B, which gives a tension to the sample by pulling it down. During the testing, a winding drum moves the sample by turning at a constant speed (1mm/sec). To measure the friction, a contactor, which was designed to simulate the human finger surface, is placed on the fabric surface. By the rotation of the drum, the fabric moves, and the contactor senses the fabric surface. Contactor holder Contactor for friction detecting Sample Winding drum Frictional force transducer Weight for tension Chuck A Chuck B Tension device Figure 3.21 Principle of Surface Roughness Measurement To measure the geometrical roughness (SMD), a vertical contactor, which is at the top of the instrument, touches to the fabric with a constant force. While the fabric moves, the displacement of the contractor is detected by a transducer and the SMD value is calculated automatically. After the drum turns 3cm, it turns back to the starting position with the same speed (KATO Tech Co-4) surface frictional curve is illustrated in Figures 3.22 and 3.23 shows the surface roughness curve.

34 93 Figure 3.22 Surface Frictional Curve µ = frictional coefficient F = frictional force P = normal force (The force applied by the contractor pressing on the fabric sample.) F µ (3.31) P surface where, The µ value differs while roughness detector moving on the sample 1 Lmax µ o µdl (3.32) L max L - distance on fabric surface L max - the sweep length MMD - deviation of the frictional coefficient

35 94 Thus, 1 Lmax MMD µ µ dl (3.33) o L max Figure 3.23 Surface Roughness Curves where, L - distance on fabric surface L max - the sweep length SMD - Surface roughness To test surface geometrical roughness, SMD, the contactor moves vertically. If the vertical displacement of the contactor is Z, the surface roughness is the mean deviation of SMD of Z. 1 Lmax SMD Z Z dl (3.34) o L max

36 95 The parameters used by Kawabata are listed in Table 3. 7 Table 3.7 Parameters describing fabric mechanical and surface properties Shear Parameter symbol Description Unit Tensile Bending Compression EMT Fabric extension at 5N/cm width (%) LT Linearity of load extension curve None WT Energy in extending fabric to 5 N/cm width J/m 2 RT Tensile resilience (%) G Shear rigidity N/m 2HG Hysteresis at shear force at 8.7 mrad N/m 2HG5 Hysteresis at shear force at 87 mrad N/m B Bending rigidity µn.m 2HB Hysteresis of bending movement mn LC Linearity of compression-thickness curve None WC Energy in compressing fabric under 5 kpa J/m 2 RC Compression resilience (%) T o Fabric thickness at 50 Pa pressure mm T m Fabric thickness at 5 KPa pressure mm Weight W Mass per unit area g/m 2 Surface MIU Coefficient of friction None MMD Mean deviation of MIU None SMD Geometrical roughness µm Sample Preparation Test material for this study consists of 15 spun silk woven fabrics,. Since the relative humidity and the temperature of the testing environment can affect the test results, the fabric sample were conditioned at least 24 hours before testing under the standard relative humidity (RH) and temperature.

37 96 The standard Condition was: RH 65 ± 2 % T 70 ± 2 ºF For use in the Kawabata System, the fabric specimens were cut into the dimensions illustrated in Figure 3.24.Two specimens from each fabric were cut straightly along with warp and filling directions. Sample ID and the directions were marked on each sample clearly. For those fabric samples with very high stiffness, a 10 cm 10 cm specimen size was used. One of the specimens was tested on filling direction and the other was tested on warp direction. Since the compression property did not have directions, both specimens were tested for a repeat test. Figure 3.24 Sample Cut Straight and Marked

38 97 instrument Figures 3.25 to 3.28 show four testing units of the KES-FB Figure 3.25 KES-FB Bending testers Figure 3.26 KES-FB Compression tester

39 98 Figure 3.27 KES-FB Tensile tester Figure 3.28 KES-FB Surface tester 3.8 FABRIC COMFORT PROPERTIES Thermo-Physiological Comfort using Alambeta Instrument Alambeta instrument was developed by Technical University in Liberec and was used for measuring thermal conductivity, thermal resistance R, qmax, and thickness of fabric. All these are obtained between 3-5 minutes and the results evaluation, lasts less than 3-5 min. An objective measure of warm-cool feeling of fabrics, so called thermal absorptivity

40 99 b [Ws1/2/m2K] introduced by Hes (1987) was used. The principle of the Alambeta instrument is given in Figure H Figure 3.29 Principle of the Alambeta instrument The principle of first version of this instrument protected by several patents depends in the application of ultra thin heat flow sensor 4, which is attached to a metal block 2 with constant temperature which differs from the sample temperature. When the measurement starts, the measuring head 1 containing the mentioned heat flow sensor drops down and touches the planar measured sample 5, which is located on the instrument base 6 under the measuring head. In this moment, the surface temperature of the sample suddenly changes and the instrument computer registers the heat flow course. Simultaneously, a photoelectric sensor measures the sample thickness. All the data are then processed in the computer according to an original programme, which involves the mathematical model characterising the transient temperature field in thin slab subjected to different boundary conditions. To

41 100 simulate the real conditions of warm-cool feeling evaluation, the instrument measuring head is heated to 32ºC (see the heater 3 and the thermometer 8), which correspond to the average human skin temperature, while the fabric is kept at the room temperature 22ºC. Similarly, the time constant of the heat flow sensor, which measures directly the heat flow between the automatically moved measuring head and the fabrics, exhibits similar value (0,07 sec), as the human skin.. Thus, the full signal response is achieved within 0,2 sec. An important aspect of the warm-cool feeling evaluation is the change of this feeling when the textile product gets wet. Since the thermal conductivity and thermal capacity of water is much higher than those of the fiber polymer and the air entrapped in the textile structure, the warm-cool feeling of garments moistened by sweat can exceed The resulting thermal contact discomfort is generally known and this is measured. Hes introduced a parameter called thermal absorptiveness to evaluate the warmcool feeling. It was found that this parameter characterized perfection by the transient thermal feeling which one gets at the moment when one puts on an under garment, a shirt or other textile product. This is computed according to the following formula b = λρc, W s 1/2 m -2 k -1 (3.35) where, λ the thermal conductivity, ρ the fabric s density, and c the specific heat of the fabric. The heat flow passing between the textile samples and the measuring head during thermal contact is measured by a special thin sensor, whose thermal inertia is similar to that of human skin. The thermal contact sensation is strongly affected by the fabric s structure and composition. The thermal resistance, thermal conductivity and thermal absorptivity of the textured fabrics have been measured by means of the computer-controlled Alambeta device, which enables rapid measurement of

42 101 both the steady-state and transient-state thermal properties of any plain compressible non-metallic materials such as textile fabrics. The instrument directly measures the classical stationary thermal properties of fabrics such as the stationary heat flow density, thermal resistance and the fabric s thickness. The rest of the thermal parameters, such as thermal conductivity, thermal absorption and thermal diffusion are calculated on the basis of the measured properties using algorithms appropriate for the unstratified materials. The whole measurement procedure includes the measurement of thermal conductivity (λ), thermal resistance (R), peak heat flow density (qmax), sample thickness (h), thermal absorptivity (b). The thermal properties of the fabrics were measured by the Alambeta instrument according to standard ISO EN The measurements were repeated 5 times on randomly chosen parts of the fabrics, and average values and standard deviations were calculated Measurement of Thermal Conductivity by Lee s Disk Thermal Conductivity Apparatus The apparatus used was a modification of the standard Lee s disk method for the measurement of thermal conductivity by the absolute plane parallel plate technique. The fabric sample was kept between copper plates, and the power to the heater was switched on. A simple modified form of Lee s disc method was used for the determination of thermal conductivity of poor conductor (non-metals). A thick and circular brass disc C with a hole drilled in it to insert a sensitive thermometer T 2, is suspended in air from a heavy retort stand by means of three strings with top face quite horizontal. The specimen in the from of a

43 102 flat circular disc D of the same radius as that of C is sandwiched between C and bottom of hollow, cylindrical metal steel chamber A. A hole is drilled in the heavy bottom of a thick brass block B of a steam chamber to insert another thermometer T 1. The two thermometers T 1 and T 2 record the temperature of the top and bottom of the specimen disc D. The top surface of disc and bottom surface of block B are well nickel-polished and have a smearing glycerin to ensure good thermal contact between them Procedure The steam is passed through the chamber A and the temperature indicated by the thermometers T 1 and T 2 are recorded turn by turn until they become steady. In the steady state the rate of rate of heat flowing across the specimen disc D is equal to the rate at which the heat is radiated through the exposed surface of the lower disc C as the heat radiated by the curved surface of thin experimental disc D is negligibly small. Suppose X and Y be the steady state temperature recorded by thermometer T 1 and T 2, r the radius and X the thickness of experimental (ebonite) disc D and K its thermal conductivity, Heat conducted by the specimen = KA T 1 T2 (3.36) d Heat lost by the disc = MSR 2h r 2h 2r (3.37)

44 103 At steady state T T MSR 2h r KA 1 2 d 2h 2r (3.38) MSRd 2h r T * 2h 2r K (3.39) A T 1 2 where, K - Thermal Conductivity of material M - Mass of disc S - Specific heat of the material of the disc R - Rate of fall of temperature h - Thickness of the lower disc r - Radius of the lower disc d - Thickness of the specimen A - Area of cross section of the specimen To find out R, the rate of fall of temperature, the disc is removed and the brass block makes contract with the steam chamber. Brass disc is removed when its temperature is about 100C higher than T 2. It is placed over two knife edges and its temperature is observed by allowing it to cool. Then the time is noted at equal intervals of temperature (time in seconds). A graph is plotted between temperature and time. From the plotted graph the rate of fall of temperature is found. From the above formula, the thermal conductivity of the spun silk is calculated and the thermal insulation value is derived which is the reciprocal of thermal conductivity value.

45 Air Permeability The air permeability of the samples was measured by KES-F 8 AP instrument designed by Kato Tech.Co. Ltd, Japan. In the air permeability tester KES-F8- AP1 designed by Kato Tech. Co. Ltd., Japan, a constant rate of air flow is generated (i.e., 4x10-2 m/sec) and passed through the specimen. This leads to development of the pressure difference across the specimen Since the pressure difference has linear relation with air resistance the later can be calculated from the former. The instrument has a digital panel meter from which air resistance of the specimen can be read off directly. The specimen conditioned at 65 ± 2% relative humidity and 27 ± 2 C is mounted onto the instrument using the clamping mates. The area of the specimen is 6.28 sq.cm. The flow of specimen is maintained at a constant rate by the piston motion of the plunger mechanism. Air is sucked through the specimen for a period of five seconds and then discharged for the next five seconds. The air resistance (Pa.sec/m)is directly record from the digital panel meter. The inverse of this value gives air permeability in units of m/pa.sec Drape Coefficient Fabric drape response is an important property due to its influence on the appearance of clothing. Drape determines the adjustment of clothing to the human silhouette. Drape is defined as the extent to which a fabric will deform when it is allowed to hang under its own weight (British Standards Institution BS 5058: 1973). Drape coefficient of fabrics was measured using Cusic Type RC -5 model drape meter.

46 105 A circular specimen of about 30 cm is supported, on a circular disk of about 12.5cm diameter and unsupported area drapes over the edge. Drape Coefficient = Area of annular ring under projection of draped sample Total area of annular ring (3.40) Schematic diagram of measuring fabric drape coefficient is illustrated in Figure Figure 3.30 Schematic Diagram of Measuring fabric Drape coefficient Area of annular ring under projection of draped sample DC% = 100 Total area of annular ring (3.41) If the specimen were say a 30 cm gramophone record or draping would occur and the area of projection from the periphery would equal the area of record. With fabrics the material will assume some folded configuration and the shape of the projected area will not be circular but something like the shape shown in Figure 3.31.

47 106 Figure 3.31 Projected out line of the Draped specimen Drape coefficient, F is determined by considering areas, Let, A D = the area of the specimen A d = the area of the supporting disk and A S = the actual projected area of the specimen F is the ratio of the projected area of the draped specimen to its in draped area, after deduction of the area of the supporting disc. F A A s d (3.42) D A A d The number of tests to get minimum CV in the estimate for drape coefficient of fabrics was determined by conducing 5,10,15 30 tests each time. Table 3.8 shows the levels of CV for different number of tests.

48 107 Table 3.8 CV values for varying numbers of tests S.No No of tests Coefficient of variation CV% It is clear from the above that the coefficient of variation stabilized at N = 10 and therefore the improvement in CV values is relatively less with higher number of reading. Hence 10 tests per samples were carried out for assessing the drape coefficient of fabrics. A Brother (D B2 B ) sewing machine was used for sewing radial and circular seams in all the samples. The stitch density was 4 stitches for centimeter, the needle size was 12 and the thread was polyester and the ticket number 80.Machine loading and the thread tension were all ways kept constant. All specimens were ironed at standard temperature. The seam allowance for seam was 5mm.Commercially available white poplin was used as lining material. Figure 3.32 shows the different types of radial and circular seams. With lining Warp seam Weft seam 45 o angle seam Wrap and weft seam 45 o and 135 o angle seam Circular seam Circular seam hem Circular hem Figure 3.32 Radial and circular seams

49 CANTILEVER STIFFNESS TEST Cantilever is an instrument that was introduced by Peirce in It is the earliest method used to measure fabric stiffness by determining bending length. Figure 3.33 illustrates this testing method. The following equation was developed to calculate the fabric stiffness: Figure 3.33 Cantilever Stiffness Test (3.43) where, G - flexural rigidity M: fabric mass per unit area Θ - angle fabric bends to C - bending length L: hanging fabric length. If the fabric is too limp, the cantilever method does not provide a satisfactory result. In this case, the hanging loop method was used to measure stiffness of fabric.

50 BURSTING STRENGTH Instrument used : Hydraulic Bursting Tester Principle The pressure in a liquid is exerted in all directions and this phenomenon of a liquid is used for testing bursting strength in hydraulic bursting tester. The maximum fluid applied to a circular specimen in distending applied to a circular specimen in distending it to rupture. It is expressed in kilogram force per square centimeter. The test specimen is placed on the area of the sample to be tested over the diaphragm so that it lies in a flat tensionless condition. It is clamped securely by means of the clamping ring. The pressure is increased smoothly so that the bursting strength pf the fabric is reached in 20 +/- 3 seconds. The bursting strength and the bursting distension of the specimen is noted. The tests with other specimens or at other places on the sample are repeated as the case my be to have least 10 acceptable measurements ABRASION RESISTANCE Martindale abrasion tester based on ISO (AATCC 93) accelerator method was used. A circular specimen is subjected to a define and rubbed against an abrasive medium (standard fabric) in a translational movement tracing a lissajous figure. The specimen holder containing the abrasive medium is additionally freely rotatable around its own axis perpendicular to plane of the

51 110 specimen. The evaluation of abrasion resistance is determined from the mass loss of the test specimen. A B Percentage of weight loss = 100 A (3.44) Initial weight of the fabric Final weight of the Fabric after abrasion = A = B Total effective mass of abrasion load is 595 ± 7 grams DIMENSIONAL STABILITY The general procedures for preparing and making out of samples are based on BS 4931.Preparation, making and measuring of textile fabrics in tests for assessing Dimensional change. The dimensional stability of a fabric is a measure of the extent to which it keeps its original dimensions subsequent to its manufacture. It is possible for the dimensions of a fabric to increase but any change is more likely to be a decrease or shrinkage. Fabric shrinkage can cause problems in two main areas either during garment manufacture or during subsequent laundering. For measuring dimensional stability, a fabric size is taken as 10cm x10cm.the original length of ends and picks and weft should be measured initially before it wets. After it is washed and dried in flat drying method. After drying, the fabric length of ends and picks were measured. By measuring the length and width, area shrinkage percentage can be calculated.

52 WETTING Principle The working of the tester includes various electrical and electronics principles. The water drop falls on to the fabric, which actuates the time until the drop is absorbed fully by the fabric.at this moment, the timer stops automatically. The wettability of the fabric is determined by the time taken for full absorption, in seconds. The tester is fabricated with a digital clock whose circuit is modified to actuate the stop watch timer of the clock during experimentation process in order to determine the wettability of the fabric Working The fabric to be tested is cut to a sample size of 2x2cm. Dismantle all the plates of the tester in order to place the sample. Before mounting the sample on to the tester the two leads are fixed with a gap of 2 to 3mm between them on the fabric holder. The fabric sample is then placed on the lead. The lead should be placed right below the burette tip so that the drop of waterfalls on the fabric right above the lead for the convenience of the user; there is a marking on the holder platform where the lead is to be placed. After mounting the fabric the plate with the infra-red sensor along the spacers and the third plate are also placed. The burette is then inserted into the hole of the third plate. Meanwhile power supply is given to the main circuit box and the clock is set to stop watch timer mode and the timer is reset to read zero seconds. Now the experimental set up is ready for experimentation. A drop of

53 112 water is allowed to pass through the infra-red sensor. Care should be taken so that the drop falls rightly between the sensor space and it is of the right size. When the drop passes through the sensor, it triggers the relay which actuates the timer. When the drop is fully absorbed, the liquid bridges the separated lead and the liquid sensing circuit closes and hence triggers the next relay which stops the timer. Note the value indicated in the timer which indicates the wettability on the particular fabric COLOUR STRENGTH MEASUREMENT The Dyeability of the yarn through colour strength is a measurement of the degree of fixation was measured by data computer colour matching system interfaced with spectrophotometer using Kubelka-Munk function. K S 2 1 R (3.45) 2R where, R - Reflectance value at wavelength of maximum absorption K - Absorption coefficient S - scattering coefficient