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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