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introduction
1. INTRODUCTION
Clothes make the man/woman. William Shakespeare, in the play 'J-Jam!ei'.
put this in his own inimitable style:
"Costly thy habits as thy purse can buy, But not express 'd infancy; rich, not gently,
For the apparel oft proclaims the man.
In every aspect of life man strives for quality and perfection as nothing endures
like quality. So too it is with the textile industry. The all-pervading influence of
textiles on our daily lives is so profound that we definitely need to know more
about the industry that clothes us.People have used textiles of various types for
protection from the elements, for adornment, and even to display one's status and
wealth.
The term 'TEXTILE" was originally applied only to woven fabric. It is
nowadays applied to fibres, yarns or products made from fibres and fabrics.
Fabric is the material that is used to make clothing or household articles. Fashion
is a way of life and has a profound impact on modern lifestyles, which are
becoming more and more informal in keeping with a pursuit for relaxation and
easing of levels of stress. The numerous types of yarns and fabrics of varying
structures have enabled innovation and production of multifarious products in the
textile industry. A textile was originally a woven fabric, but the terms 'textile"
and the plural "textiles" are now also applied to fibres, filaments and yarns, both
natural and manufactured, and most products for which these are a principal raw
material. The term textile is now based on the products in the following
categories: threads, cords, ropes, knotted or tufted cloth, and braids (as in
macrame), woven, knitted and nonwoven fabrics (www.apparelsearch . corn).
Textiles pervade our lives from birth to death as they are used in
production and processing of many items of day-to-day living. The textile
industry is the largest economic activity after agriculture, providing direct and
indirect employment to lakhs of weavers and boosting our export earnings.
Textiles are classified according to their component fibres into silk, wool,
linen, cotton, synthetic fibres as rayon, nylon and polyesters, and some inorganic
fibres such as cloth of gold, glass fibre, and asbestos cloth. Value or quality in
textiles depends on several factors, such as the quality of the raw material used
and the character of the yarn spun from the fibres, whether clean, smooth, fine, or
coarse and whether hard, soft, or medium twisted (popular.ebay.com)
Qutun, Kutan and Qutan are all varied pronunciations of the word Cotton
which is derived from the Arabic for the same. Its widespread utility and its status
as an indispensable, all-pervading necessity in human life has earned cotton the
title of 'white gold". Cotton is amongst the oldest fibres known to man and has
become an universal commodity of commerce and human clothing. Cotton has
become the backbone of the textile industry and market accounting for almost half
the world's total consumption of textiles. Cotton grows in sub-tropical climate
and is a fibre removed from the ball or seedpod that grows on a plant of the
botanical genus Gossypium, a member of the Mallow family. Cotton consists of
cellulosic and non-cellulosic components (www. cotton inc.com).
One of the key factors that decide any end product is the quality of raw
material. Cotton, particularly, is known for it's wide variation in characteristics.
The variations can be attributed to factors such as genetic, environmental and
ginning conditions. The increasing quality awareness of customers and
technological developments in textile machinery has put in stringent quality
demands on textile fibres (Ramaswamy, 2005).
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Cotton is known for its qualities like good strength. elasticity, heat
conductivity and high resistance to degradation by heat. Cotton is characterized
by excellent properties like absorbency, comfort, drape, high wet strength.
softness, water retaining strength, insulating and non-allergic properties. Cotton
has little lustre but softness and durability are its most important qualities
(Nimkar, 2006). Cotton fabrics are comfortable to wear especially in hot and
humid climate, and it can be laundered easily as it withstands high temperature
well and does not scorch easily. Cotton is also known for its quick absorbency of
dyes and amenability to printing. Cotton's inherent properties make it the most
favoured textile fibre despite the advent of regenerated synthetic man made fibre.
especially for woven and knitted fabrics. This despite it's drawbacks like wrinkle
resistance, inability to maintain shape and lack of fastness in colour (Sharma et
at., 2003).
The increased versatility of techniques, adaptability towards new fibres and
growth in consumer demand for wrinkle resistant stretchability and snug, fitting
design have contributed to knitting's popularity in recent years. The Indian
apparel industry has grown enormously since the mid-80 when the cotton knitting
industries were producing only inner wear out of grey and blended fabric made
out of coarse yarns. In recent years it has added a new star performer to its
production, namely, knitted garments, particularly cotton knitwear.
The knitwear industry in India began with the first cotton knitwear unit in
Calcutta in 1882 and a woolen in Ludhiana in 1902. Although knitwear units are
widely dispersed across the country, yet about 90% of the units are concentrated
in Tirupur, Calcutta, Ludhiana, Delhi and Bombay. Cotton is the mainstay of the
Indian knitwear industry.
Knits and Knitwear occupy a place of prominence and priority in the
industry of textiles. The global demand for knits and knitwear has been expanding
at a faster pace compared to the demand for wovens due to it is being less
expensive and more comfortable. As a consequence, an estimated 45% of the
clothing needs in developed countries are met by the knitwear industry, the major
international producers being: China, Hongkong, Taiwan, Italy. Germany, Korea,
Thailand, Brazil and Israel (Desai, 2005).
Of all the methods of fabric production, knitting is the latest and simplest
method, which is flexible and adaptable to changing styles and designs. Use of
knitted fabrics for apparels has caught on internationally. The knitting industry
plays a key role in the Indian economy and this can be gauged from the fact that
one sixth of yarn production is consumed by the knitting industry alone (Desai.
2005).
The aesthetically pleasing appearance, loose elastic structure, and comfort
and softness of knits as compared to wovens, make them ideal to be used in
sportswear, innerwear, sweaters, casual wear and fashion apparel. The wrinkle
freeness and better drape makes knitted fabrics the favorite of the fashion world.
Knitted fabrics also enjoy greater acceptance among a variety of other end users,
- thus placing higher demand on the quality as well as appearance of the fabric so
as to cope with changing fashion trends. The one drawback of knits is the lack of
stability, durability and fastness properties. Modern technology has enabled high
quality knitted construction; in shaped and unshaped fabric form, and they expand
into a wide range of apparel and domestic clothing, making them popular due to
their economy and inherent favorable qualities for the human body of all age
groups.
Knitting is one of several ways to turn thread or yarn into cloth. Unlike
woven fabric, knitted fabrics consist entirely of horizontal parallel courses of
yarn. The courses are joined to each other by interlocking loops in which a short
loop of one course of yarn is wrapped over the bight of another course. Knitting is
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the process of making cloth with single yarn or set of yarns moving in only one
direction. It is the technique of constructing textile structures by forming
continuous length of yarn into vertically intermeshed loops. It is the production of
fabrics by formatting loops with yarns, which are interlaced in a variety of ways
to form the fabric (Spencer, 2005).
Warp and Weft knitting are actually similar fabric manufacturing processes
in that they both utilize needles to form and intermesh loops. The main difference
between these two systems lies in the manner in which the yarn is fed to the
needles. In weft knitting, a single yarn end may be fed to all the needles and
knitting progresses around, or across, the machine (NIIR Board. 2004). Weft
knitting is done using a single set of yarns, which consists of a single yarn, and
warp knits involving a number of yarns. As a fabric forming - technique, knitting,
especially weft knitting, is the fastest and most flexible, and adaptable to changes
in design. In warp knitting, all the loops making up a single course are formed
simultaneously. Thus, the length of each vertical column of loops, the wales,
increases at the same time.
Circular weft knitted fabrics are highly elastic and extensible, providing
comfort in varied postures to the wearer. In circular weft knitting the loops of
yarns are formed by a single weft thread. The loops are formed more or less
across the width of the fabric usually with horizontal rows of loops, or courses,
being built up one loop at a time. The knit loop is characterized by its geometry or
by the way in which an observer views it. Geometrically, an open loop is one in
which the forming yarns do not cross at the bottom of the loop. In a closed loop,
yarn crossing takes place. In weft knits, the machine- knitting steps are Loop
pulling, running, clearing, yarn feeding, and knock-over (Liao and Adanur, 1998).
Reasons for shrinkage or methods for predicting it have been given little
attention, not because of their lack of importance but because of the complexity of
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knitted structures. Shrinkage of a knitted fabric is determined by a number of
factors such as fibre characteristics, stitch length. machine gauge, yarn twist,
knitting tension and washing and drying methods. Factors mostly responsible for
shrinkage are known to be the swelling of yarn and the relaxation of internal
stress, since these are imposed on yarn during the knitting process. The important
aspect of shrinkage in a cotton fabric is that dimensional change resulting from
immersion in water is retained even after the fabric is dried (Vishwanathan,
2004).
The geometry of ioop migration and curvature change upon wetting and
drying of the fabric explain the lengthwise shrinkage. Also, widthwise shrinkage
is explained by the relationship between wale spacing and yarn diameter. Cotton
is a visco-elastic material in a dry state. However when it is immersed in water, its
behaviour tends to become more like plastic material. Cotton fibre decreases by
one-third upon wetting. As the fabric dries out, the configuration of the yarn in
loops tends to remain unchanged from that assumed in the wet stage.
This phenomenon is best observed by comparing two yarns from fabric
taken before and after washing. If this is done, it will be found that the dried
unwashed sample tends to return to its original state configuration; but the sample
of the yarn from a washed fabric, which has been allowed to dry in the knitted
state, will, upon unraveling, tend to remain in the configuration of the loop. Thus,
it is not surprising that the washed shrunk fabric will not return to its original
shape after drying, but retains the new dimensions resulting from wetting.The
foregoing analysis vividly describes the shrinkage of cotton jersey and it's
derivative fabrics by means of a geometrical analysis.
Thus, the broad subject of the stabilization of knitted fabrics have to be
considered under two main headings such as stability to relaxation and stability to
stress. Stability to stress is concerned with the degree of distortion of knitted
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fabrics related to the loadings that manufacturing processes almost invariably
produce, the permanence or semi-permanence of such distortions, and their
significance in the final product. Instability, which is a property of the
construction of the knitted fabric, is common to all fabrics, particularly those
knitted from hydrophilic yarn, and are called relaxation shrinkage. It is difficult to
understand how knitted goods behave on finishing and during domestic washing,
because of the inter-action of so many factors (Anand et al., 2004).
All knitted fabrics comprise a number of knitted loops. The knitted loops
can be regarded as the structural unit and a rectangle can be drawn to contain this
unit. Whatever affects the shape and size of this rectangle, and however it is
affected, will affect the size of the knitted fabrics correspondingly. If the effect on
this rectangle is known or has been determined, and since the number of loops in
the width of the fabric and in the length can be determined, the dimension of the
fabric can be known. This unit rectangle containing the knitted loop has two
relevant parameters: its shape and its size.
The shape is mainly determined by the treatment history of the fabric.
Knitted goods are produced in the knitting machine under tension. In service they
are also subjected to tensions both widthways and lengthways. The great virtue of
knitted goods is their extensibility, - their ability to accommodate both shape and
movement. On removal of these tensions, the structure in theory should spring
back to its "natural" shape and dimensions. In practice, friction at the various
points of contact between loops and between fibres in the yarn precludes the
complete return to the original state. During movement, finishing, and various
relaxation procedures, the fibres and loops are jostled and friction is progressively
overcome, enabling the "natural" relaxed shape to be gradually achieved. Even on
just standing, some degree of relaxation occurs resulting in the unit rectangle
changing shape (Choi and Ashdown, 2000).
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The finishing or finishes of fabrics has an important bearing on the
dimensional stability of the fabric. A finish is permanent if it remains unaffected
through all the conditions of wear and treatments to which the fabrics may be
subjected to in normal life. Finishing processes are carried out to improve the
natural properties or attractiveness of the fabric and to increase its serviceability.
The term finishing, in a broad sense, covers all the fabric undergoes after leaving
the knitting machine to the stage at which it enters the market. Thus, the term
includes scouring, bleaching, dyeing, mercerization; brushing and enzyme finish
of the gray cloth.
Finishing fabrics means a wet processing. The effect of wet processing is
to change the shape of each loop, mainly by changing the stiffness, the specific
volume and the twist liveliness of the yarn. In addition, wet processing will
change the weight of the yarn by removing impurities and adding chemicals, and
will change the average length of yarn in each loop by yarn shrinkage. Different
types of wet processing procedures will change the shape, weight and length of
the loop differently and therefore they affect the shape, weight and length
differently.
Scouring is an important operation by which natural impurities are
removed. Bleaching is an essential finishing process used to remove natural
colouring materials and to render the clothes white. Mercerization gives lustre,
strength, dye-affinity and abrasion resistance to fabrics. Mercerization is generally
carried out for cotton fabrics only and facilitates dyeing. Mercerization involves
treatment of clothes with cold caustic soda. Dyeing gives attractiveness to the
fabric and brushing gives soft feel and enzyme finish gives permanent
improvement of fabric softness and smoothness (Gupta, 2004).
Textile fibres can be considered to be three-dimensional rod -shaped
materials having enormous surface-to-volume ratios compared to most materials.
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The internal geometry of the knits is highly irregular, the mesh is also expected to
be highly distorted and irregular and so the mechanical properties of knits differ
for different knit structures, says Walsh (2000). The perception of clothing
comfort can be described as a progressive process, involving three fundamental
elements: physical properties of fabrics, psychological sensory perceptions and
subjective comfort evaluation, viewed Wong asw (2004).
In considering textile products, the property described as handIe' is the
one most widely used by both industry and the consumer in determining the
acceptability of goods for their end use. Handle is a term used to describe the
combination of stimuli subjectively derived from textile assessment of, the
mechanical properties of the fabric. Matsuo et al. (2003) conclude that five basic
models exist to view handle of fabrics. Namely tensile, shearing, bending,
compression and surface friction.
Jersey is a circular-knit or flat-knit fabric made with a plain stitch in which
the loops intermesh in only one direction. As a result, the appearance of the face
and the back of a Jersey fabric is wholly different. Jersey is the most widely used
single - faced knitted fabric formed to open loops passing one through the other in
the same order explain Padma and Subramanium (2003). When tuck stitches are
introduced along with the plain stitch (knit stitch) they produce different
structures known as derivative fabrics of single Jersey. Single jersey structures
find widespread use in manufacturing underwear and knitted fabric for sportwear,
hosiery goods, and other knit wear.
Therefore, the controlling of the most important,parameters are required to
produce quality fabrics, namely, course length, GSM,and dimensional stability.
Calculations of the dimensions of the fabric after shrinkage are very important. In
case of knitted fabric the average ioop size and shape integrated over a unit area
would give the requirement. The dimensions of a fabric knitted from a particular
yarn depend mainly upon three factors: the hulking contraction of the yarn, the
loop length and the nature of the finishing treatment.
Since the problems of knitted fabrics are associated more on the
dimensional stability, there is an urgent need to assess the dimensional stability of
the knitted fabrics, even before they are made so that the manufacturer is able to
gauge the dimensional stability during manufacturing and finishing stages as well
as at the time of wear and tear.
The present research aims at predicting precisely the dimensional stability
and mechanical properties of the single jersey and its derivative fabrics made
from the yarn of known properties, machine settings and finishing treatments.
Objectives of the study are to
elicit information from the industries about fabrication, wet processing
and kinds of knit structures existing.
fabricate four structures of knit fabrics with different three loop lengths.
wet process the produced knit fabrics
study the effects of relaxation and finishing treatments at three loop
lengths and to determine the dimensional stability of the four structures.
investigate the mechanical and low stress mechanical properties of the
four structures in their gray and finished state at three loop lengths.
assess the comfort property of these fabrics by observing the
wickability.
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