Download Report

23
CHAPTER 3
MATERIALS AND METHODS
3.1
INTRODUCTION
The present study is focused on the effect of material variables,
machine variables and processing treatments on dynamic elastic behavior of
cotton / spandex knitted fabrics. In order to study these objectives, different
kinds of knitted fabrics were produced. The fabric samples were subjected to
heat setting, dyeing and compacting, and tested for their dynamic elastic
properties. The details of the materials used and the experimental procedures
adopted in the study are described in this chapter.
3.2
MATERIALS
3.2.1
Yarns and Fabrics
In general, 14.76 tex cotton hosiery yarn and 20 denier spandex was
used to produce spandex back plated cotton knitted fabric. The spandex brand
name called Texlon produced by Hyosung Chemical Inc Ltd, was used
throughout the study.
3.3
METHODS
3.3.1
Fabric Production
In order to produce spandex back plated cotton knitted fabric, the
circular single jersey machine was used. In a circular knitting machine, there
24
are multiple numbers of feed positions arranged in a circular form, so as to
feed individual knitting positions as the knitting needles, carried by the
moving cylinder, are rotated past the positions.
1. Variable diameter pulley drive shafts
2. Variable diameter pulleys
3. Belt drive
4. Positive storage and spandex feeder drive pulley
5. Spandex yarn feeder
6. Spandex drum surface driven rods
7. Spandex package
8. Guide roll and stop motion for spandex yarn
9. Spandex yarn
10. Carrier plate
11. Cotton yarn
12. Needle
13. Positive storage feeder
Figure 3.1
Drive to cotton and spandex yarn packages
Figures 3.1 and 3.2 show one feed position of a circular knitting
machine having a series of knitting needles that move reciprocally in response
to a cam below a rotating cylinder that holds the needles.
25
For plating knit operations, spandex yarns are fed from separate
attachment called memminger lycra attachment. The spandex packages were
kept on the surface driven rods and directly fed to needle through guide roller
and stop motion. The cotton yarns are fed from the positive storage feeders.
This attachment gets drive from separate variable diameter pulleys from the
machine. Spandex packages get drive from the surface driven rollers in its
attachment. The cotton yarn loop length and spandex feed tension adjustments
can be varied for the two yarns separately.
(a) Spandex supply package (b) Positive storage feeder for cotton yarn
Figure 3.2 Feeding of cotton and spandex yarns
A spandex and cotton yarns are delivered to the knitting needles by
a carrier plate. The carrier plate simultaneously directs both the yarns to the
knitting position. The spandex and cotton yarns are introduced to the knitting
needles at a same rate to form a single jersey knit fabric as shown in
Figure 3.3.
26
1. Spandex yarn
2. Change of direction roll
3. Cotton yarn
4. Carrier plate
5. Needle
6. Spandex yarn plated on back side of fabric
7. Cotton yarn at front side of fabric
8. Loops formed by needles
9. Spandex yarn feed slot
10. Guide hole for cotton
Figure 3.3
Knitting of spandex and cotton yarns
The cotton yarn is delivered from the package to a positive storage
feeder that passes the yarn to the carrier plate and knitting needles. The yarn
passes through a guide hole in the carrier plate. Optionally, more than one
cotton yarn may be fed to the knitting needles through different guide holes in
the carrier plate. The spandex is delivered from a surface driven package and
passes through a broken thread detector and a guide slot within the carrier
plate. The guide slots are separated from one another in the carrier plate so as
to present the cotton yarn and spandex to the knitting needles (laycock 2006).
27
For single jersey knitted fabric in circular knitting machines, the process of
co-knitting spandex is called “plating”. In this process, cotton and spandex
yarns are knitted parallel to each other. The cotton yarn forms loops in the
face side of the fabric and the spandex forms loops at the back side of the
fabric. The formation of loops with cotton and spandex yarns is shown in
Figures 3.4 (a) and (b).
(a) Needle loop formation
(b) Spandex plated cotton fabric structure
Figure 3.4
3.3.2
Processing Treatments
3.3.2.1
Heat setting
Plating technique
The cotton / spandex single jersey knitted fabric was heat set at
2000C using heating chamber (ASKME Make, chamber length of 228.6 cm
and fabric stretch at width wise direction is 25% of machine diameter). Cotton
fabric was n’t heat set.
3.3.2.2
Dyeing
Spandex fibres are less fastness to dyes than most companion
fibers, and this must be taken into account during dyeing and subsequent wet
28
processing. Dyeing temperature above 104°C will lower the spandex fineness.
Spandex will start melting losing its fibre shape, and will result in lower
power. When dyeing temperature goes above 120°C, it will result in spandex
degradation (26).
The spandex plated cotton knitted fabric was first bleached using
hydrogen peroxide bleaching for two hours. Then peroxide nutrition treatment
was given for one hour. Wetting oil was added to dye bath. The fabric
samples were dyed with 2% shade hot brand reactive dyes. The fabric was
soaked in the dye bath for four hours. Again the samples were treated with
salt and soda and steamed at 650C temperature. Then, the sample was treated
with soap solution and acetic nutrition treatment for one hour.
3.3.2.3
Compacting
These fabrics were compacted using tubular compacting machine
(Albert make, Speed of 4 meters per minute, Chamber length of 1 meter,
26 % over feed, Fabric stretch in width wise direction was kept at 11% of
machine diameter and at the temperature of 940C). Then, the fabrics were
relaxed for 48 hours.
3.3.3
Testing
3.3.3.1
Determination of dynamic work recovery
Assessment of dynamic work recovery of the fabrics is a newly
developed method based on the Kawabata (1982) evaluation system for fabric
total handle measurement. The evaluation method is based upon tensile
resilience (RT %) measurement of Kawabata Evaluation System. The RT
measurement will produce stress strain hysteresis for applied force of 500 gf / cm
(constant rate of loading). For this applied force, the fabric extension is in the
range of 5 – 15 %. But, elastic fabrics or garments expand (due to body skin
29
movement) up to 50 % as mentioned in the chapter 1.1. The dynamic work
recovery of the fabric (equation (3.1)) is evaluated by constant rate of
elongation principle using Instron.
r
e20-50%
Tensile energy (loading) =
∫ F de
0
s
e20 - 50%
∫ F de
Tensile energy (unloading ) =
0
s
e20-50%
∫ F de
Dynamic work recovery % = e20-050% X 100
r
F
∫ de
0
r
s
F = Stress value during loading ( F ) and unloading ( F ),
where,
e = strain (%), de = extension with respect to time.
That is,
Tensile energy (unloading)
Dynamic work recovery % =
Χ 100
Tensile energy (loading)
The simplified form as mentioned in Figure 1.4,
Area under unloading curve
Dynamic work recovery % =
Χ 100
(3.1)
Area under loading curve
3.3.3.2
Fabric stress strain analysis
The fabrics were tested for their dynamic elastic behaviour such as
dynamic work recovery and stress at specific extension based on ASTM D
4964 – 96 method (CRE principle) at different extension levels such as 20%,
30
30%, 40% and 50% extension using Instron tester. Since, human body
movement expands the skin by 10 to 50% at different parts (Voyce et al.
2005), The applied load was 5 KN at a speed of 500 millimeters per minute
for 10 cycles, 10 sample size and gauge length of 100 mm.
3.3.3.3
Geometrical characteristics
The average wales per centimeter and courses per centimeter were
measured with the help of counting glass. The average loop length was
measured with the aid of the HATRA course length tester (method described
in B.S. Handbook no. 11, 1974, pp 4/102-4/106). The fabric areal density was
measured using an electronic scale according to method ISO 3801:1977. The
fabric thickness was measured with the aid of thickness gauge (under the
applied load of 50 grams per square centimeter) according to method ISO
5084:1996. Fabric geometrical characteristics were measured at ten different
places in the fabric in each case.
The given materials and methods are common for all the chapters
from 4 to 9. The detailed specifications of the materials, machines and process
treatments are discussed under each objective mentioned in the respective
chapters.