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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

1

Mulberry spun silk 60 Nm

Tasar spun silk 60 Nm

Eri spun silk 60 Nm

2

Nylon 6 multifilament

20 Denier

34 Denier

40 Denier

70 Denier

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3.3 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

Figure 3.1 Hollow Yarn Preparation in Ring Spinning System

Gate Tensioner

Disc Pre-tensioner

Staple feed

Core Filament

Core Yarn delivery

Drafting Rollers

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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

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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

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 3.3. 16.6 tex spun

silk yarns were produced from mulberry, tasar and eri types.

Figure 3.3 Plan of Work

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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)

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Dimensional stability

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

Compression Thermal conductivity

(Lee’s apparatus)

Recovery

Drape with Seams

Twist Factor Abrasion Resistance

Bending Regidity Wicking and Wetting

Wicking Dyeability

Dimensional stability

Bursting strength

Flexural rigidity

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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

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Table 3.2 Details of yarn samples produced to study the effect of hollowness

S.No Type of silk

Nylon multifilament

denier

Hollowness (%)

Yarn linear density

Nm ----Tex

Twist αM

No of Samples

1 Mulberry

Nil 0 60-----16.6 66 1 2 20 11 59-----16.9 64.4 1 3 34 17 59-----16.9 62.8 1 4 40 22 58-----17.2 61.5 1 5 70 32 60-----16.6 59.7 1 6

Tasar

Nil 0 60-----16.6 69.9 1 7 20 11 60-----16.6 65.36 1 8 34 17 59-----16.9 63.57 1 9 40 22 59-----16.9 60.6 1

10 70 32 60-----16.6 59.3 1 11

Eri

Nil 0 59-----16.9 70.26 1 12 20 11 60-----16.6 68.37 1 13 34 17 59-----16.9 64.8 1 14 40 22 58-----17.2 61.2 1 15 70 32 60-----16.6 60.2 1

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.

3.4.1 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.

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3.4.2 Initial Modulus

The initial modulus, which is expressed in g/tex, is obtained by

taking the slope of the stress strain curve.

3.4.3 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.cm2) = kWL2 cos θ / tan θ (3.1)

where, k is a constant the value of which is around 0.0047

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.cm2 and has the dimensions ML3T-2.

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Figure 3.4 Flexural rigidity by loop ring method

3.4.4 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/cm2 and parameters LC, WC and RC were obtained for representing

compression.

3.4.5 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 L1 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

L2. When stress was removed, the yarn recovered back to a length of L3.

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Figure 3.5 Elastic Recovery

Figure 3.6 Recovery curve (Wilding)

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The recovery was measured using the formula,

L2 – L3 Recovery = 100 (3.2) L2 - L1

L1 = Length of the yarn without tension.

L2 = Extension the yarn after subjected it to a stress.

L3 = Recovered length.

3.4.6 Dimensional Stability

This refers to the shrinkage of yarns in water .This test was carried

out as per ISI.

3.4.7 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

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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.

3.4.8 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.

3.4.8.1 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 ist zone = 2π ri h (3.3)

where, h = width of zone ; ri = mean radius of zone.

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Since ‘h’ is constant ri = [i-1/2]h (3.4)

Area of zone = 2π h2 [i-1/2] (3.5)

Area occupied by the

fibers in this zone = 2π h2 [i-1/2] µi (3.6)

where, µi = packing density of ist zone.

The total area of fibers in yarn cross section,

µ21ir2s

n

1I

2e

(3.7)

n = Number of zones.

Total packing density Packing density of each zone = 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.

A1

An (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

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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.

75

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

1 0 24 24 24 24 24 24 153 154 155 0.16 0.18 0.19

2 11 24 24 24 24 24 24 152 153 154 0.17 0.19 0.20

3 17 24 24 24 24 24 24 151 152 152 0.18 0.20 0.21

4 22 24 24 24 24 24 24 150 150 151 0.18 0.21 0.21

5 32 24 24 24 24 24 24 148 149 150 0.20 0.22 0.23

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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, 15 ..…50 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% 1 10 3.52 2 15 2.71 3 20 2.47 4 25 2.5 5 30 2.38 6 35 2.35 7 40 2.34 8 45 2.30 9 50 2.32

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.

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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.

3.7.1 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.

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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

3.7.1.1 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

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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

Em

odFWT (3.11)

where, WT: Tensile Energy or the work done while stretching the fabric until

maximum force.

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WT

(1/2) F m ε m LT =

ε - tensile strain

εm - the strain at the upper limit load

Fm - 500 gf/cm

F - tensile load as function of strain

(3.12)

where,

LT - Linearity

RT% - WT 100WT

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

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LT : Linearity of load-extension curve

Area (a) + (b) (WT) LT = (3.14) Area Δ ABC*

500gf/ cm EMT ΔABC = (3.15)

2 100

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

3.7.1.2 Shear Test Using KES-FB-1

The shear test using the KES-FB-1 is shown in Figures 3.9 and 3.10.

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.

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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

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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

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Referring to Figure 3.13, hand calculation can be done as below.

cm/gf222baG

(3.17)

where, G = Shear stiffness.

2 cmgfdcHG /22

(3.18)

where, 2HG = Hysteresis of shear force at 0.5° of shear angle.

cm/gf22

feG

(3.19)

where, 2HG 5 = Hysteresis of shear force at 5° of shear angle.

Figure 3.13 Shear Hand Calculation

3.7.1.3 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

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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

1. K

Kcos1X (3.20)

2. K

KsinY (3.21)

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K

Candcm1C (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 .cm2 / cm)

Figure 3.15 Schematic Illustration of the Bending Mechanism

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

2BB

B bf (3.25)

Similarly to finding bending rigidity, to find bending hysteresis,

2HB, and the average of the two hysteresis width at curvature ±1 is taken.

Thus,

2

HBHB2HB2 bf (3.26)

88

Figure 3.17 Bending Test Diagram

3.7.1.4 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

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 3.19. 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

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 WCLC

Area ABC*

(3.27)

91

102( gf/cm2 50 ABC * m

(3.28)

WC : Compressional Energy

WC = Area (a) + (b)

WC = INT × 0.1

RC: Compressional resilience

INT

100INTB RC (3.29)

To : Thickness value of X-axis at Pm=0.5gf/cm²

Tm: Thickness value of X-axis at Pm=50gf/cm²

EMC O m

o

T T 100T

(3.30)

3.7.1.5 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.

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.

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.

Contactor holder Contactor for

friction detecting

Sample Winding drum

Chuck A Weight for tension

Tension device Chuck B

Frictional force transducer

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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.)

PF µ (3.31)

The µ value differs while roughness detector moving on the sample

surface

maxLo

max

dLµL

1 µ (3.32)

where,

L - distance on fabric surface

Lmax - the sweep length

MMD - deviation of the frictional coefficient

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Thus,

maxLo

max

dLµµL

1 MMD (3.33)

Figure 3.23 Surface Roughness Curves

where,

L - distance on fabric surface

Lmax - 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.

maxLo

max

dLZZL

1 SMD (3.34)

95

The parameters used by Kawabata are listed in Table 3. 7

Table 3.7 Parameters describing fabric mechanical and surface

properties

Parameter symbol Description Unit Tensile

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/m2

RT Tensile resilience (%) Shear

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

Bending

B Bending rigidity µN.m 2HB Hysteresis of bending movement mN

Compression

LC Linearity of compression-thickness curve None WC Energy in compressing fabric under 5 kPa J/m2 RC Compression resilience (%) To Fabric thickness at 50 Pa pressure mm Tm Fabric thickness at 5 KPa pressure mm

Weight W Mass per unit area g/m2 Surface

MIU Coefficient of friction None MMD Mean deviation of MIU None SMD Geometrical roughness µm

3.7.1.6 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.

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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

97

Figures 3.25 to 3.28 show four testing units of the KES-FB

instrument

Figure 3.25 KES-FB Bending testers

Figure 3.26 KES-FB Compression tester

98

Figure 3.27 KES-FB Tensile tester

Figure 3.28 KES-FB Surface tester

3.8 FABRIC COMFORT PROPERTIES

3.8.1 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

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b [Ws1/2/m2K] introduced by Hes (1987) was used. The principle of the

Alambeta instrument is given in Figure 3.29.

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

H

1 3 2 8

6 4 5 9 7 10

11

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 1000. The resulting

thermal contact discomfort is generally known and this is measured. Hes

introduced a parameter called thermal absorptiveness to evaluate the warm-

cool 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

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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 31092. The

measurements were repeated 5 times on randomly chosen parts of the fabrics,

and average values and standard deviations were calculated.

3.8.2 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 T2, 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

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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 T1. The two thermometers T1 and T2 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.

3.8.2.1 Procedure The steam is passed through the chamber A and the temperature

indicated by the thermometers T1 and T2 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 T1 and T2, r the radius and X the thickness of experimental

(ebonite) disc D and K its thermal conductivity,

Heat conducted by the specimen = d

TTKA 21 (3.36)

Heat lost by the disc = r2h2

rh2MSR

(3.37)

103

At steady state

r2h2

rh2MSRd

TTKA 21

(3.38)

r2h2*TTA

rh2MSRdK21

(3.39)

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 T2. 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.

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3.8.3 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., 4x10-2m/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.

3.8.4 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.

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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.

Area of annular ring under projection of draped sample

Drape Coefficient = Total area of annular ring (3.40)

Schematic diagram of measuring fabric drape coefficient is

illustrated in Figure 3.30.

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.

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Figure 3.31 Projected out line of the ‘Draped’ specimen

Drape coefficient, F is determined by considering areas,

Let, AD = the area of the specimen

Ad = the area of the supporting disk and

AS = 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.

dD

ds

AAAAF

(3.42)

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.

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Table 3.8 CV values for varying numbers of tests

S.No No of tests Coefficient of variation CV% 1 5 6.2 2 10 4.53 3 15 4.44 4 20 4.34 5 25 4.28 6 30 4.27

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 –B737-402) 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.

Figure 3.32 Radial and circular seams

With lining Weft seam Warp seam 45o angle seam

Circular hem

45o and 135o angle seam

Circular seam hem

Circular seam

Wrap and weft seam

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3.9 CANTILEVER STIFFNESS TEST

Cantilever is an instrument that was introduced by Peirce in 1930. 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.

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3.10 BURSTING STRENGTH

Instrument used : Hydraulic Bursting Tester

3.10.1 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.

3.11 ABRASION RESISTANCE

Martindale abrasion tester based on ISO 12947-3 (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

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specimen. The evaluation of abrasion resistance is determined from the mass

loss of the test specimen.

Percentage of weight loss = 100A

BA

(3.44)

Initial weight of the fabric = A

Final weight of the Fabric after abrasion = B

Total effective mass of abrasion load is 595 ± 7 grams.

3.12 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.

111

3.13 WETTING

3.13.1 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.

3.15.2 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

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.

3.13 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.

R2R1

SK 2 (3.45)

where,

R - Reflectance value at wavelength of maximum absorption

K - Absorption coefficient

S - scattering coefficient