Natural and Man-Made Fibres

Transcription

1 Natural and Man-Made Fibres Sangita Srivastava, M.Sc., D.Phil. Associate Professor and Head Department of Home Science University of Allahabad Allahabad, India Pushpa Publishing House Vijaya Niwas, 198, Mumfordganj, Allahabad , India

2 Natural and Man-Made Fibres First Edition 2012 Pushpa Publishing House All rights reserved. No part of this book may be reproduced in any way or by any means without prior permission of the Publisher. ISBN-13: Price: INR Published and printed by Pushpa Publishing House, Vijaya Niwas, 198, Mumfordganj, Allahabad , India.

3 Dedicated to My Parents Professor R. N. Srivastava and Dr. Pratibha Srivastava

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5 Preface This book is being brought out for students who are pursuing courses in apparel and textile designing. Before taking a step towards apparel designing, it is of great importance to know about different textile fibres. The book covers in its varied chapters all details about fibres - natural and man-made. This book covers the story of all natural fibres beginning from where they are obtained, and how many processes the fibres undergo before the yarn making and fabric making process. It is interesting to study how each fibre has properties different from the other. A lot of fibre properties make an appearance in the fabric due to the environment in which the fibre was grown and also because of its molecular structure. Some changes on the surface of the fibre can be brought about by the use of finishes which enhance their appearance and make the fabrics perform better. I have tried my best to cover almost all man-made fibres and natural fibres to give a comprehensive detail about the properties each one of them possess, and how and where they are used. The author owes immense gratitude to Pushpa Publishing House, for publishing this book, and all those who have been involved in the shaping-up of this book. I am thankful to my research scholar Ms. A. Fatima for her constant help from time to time.

6 Preface I am greatly indebted to my husband Justice Vikram Nath for his constant encouragement and valuable advice. I should say he has been the wind beneath my wings. I am also thankful to my office staff Ms. Neeta for her understanding approach in the Department of Home Science, University of Allahabad at various testing times. I am sure that the students will find it as a useful and valuable book in the field of clothing and textile. Sangita Srivastava

7 Contents Chapter 1: Textile Fibres 1 Chapter 2: Cellulosic Fibre - Cotton 21 Chapter 3: Linen (Flax) - Cellulosic Fibre 31 Chapter 4: Minor Cellulosic Fibres 39 Chapter 5: Wool - The Protein Fibre 51 Chapter 6: Silk - The Queen of Textile Fibres 63 Chapter 7: The Non-Thermoplastic Man-Made Fibres - Rayon 79 Chapter 8: Man-Made Fibres 89 Chapter 9: Polyesters 105 Chapter 10: Yarn 119 Chapter 11: Finishing 131 Chapter 12: Laundry 143

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9 Chapter 1: Textile Fibres F ibres are the basic fundamental units which are the components of yarn. The yarn is then woven, knitted or bonded to make a fabric. All fibres have merits and demerits or we may say they are a mixture of good and bad qualities. There is no perfect fibre. One type of fibre cannot posses all good qualities. For example, if it is absorbent it will have no crease retention. Nylon is a strong fabric but it does not absorb moisture, hence it cannot be used in the summer months. Until the turn of twentieth century, all fibres were obtained from natural resources. The most common fibres into usage were cotton, silk, linen and wool. However, wool and linen were more in use because of easier manufacturing. Cotton was difficult to spin by hand because of its short length. Silk was always expensive. When spinning and weaving became power operations, cotton became the most widely used fabric. A position it holds even today. In the last hundred years, as new textile fibres are hitting the market every other day, the consumer is the king having umpteen choices to choose from. What should be the qualities of a good fibre? A fibre to be spinnable must have sufficient length, pliability, strength, and cohesiveness to form a yarn. Milkweed and kapok are examples of fibres that are too brittle to spin into yarns. Extremely long fibre or filaments need not be cohesive since the fibres are not spun into yarns in the conventional way. Fibres must also be abundantly available and constant in supply for use. All fibres are long and have diameter in microns. Natural fibres

10 Natural and Man-Made Fibres lack uniformity because of weather conditions, nutrition and soil fertility. That is why they vary in quality also. In today s world, researches are being done to produce textiles which can perform more technical functions. Nanotechnology has made headway in preparing a special jacket for soldiers. The textile will immediately sense blood on itself and convey message to the mobile phone which starts making emergency calls. Also, cotton fibres with stain resistance, which may require no laundry, have been prepared using nanotechnology. Man-made fibres are more uniform in size and quality because it is possible to control the entire production process. The production process can be varied or improvised as per requirement. Fibre weaknesses can be minimized during yarn production. Finishes are used to enhance texture, appearance and feel of the fabric. Nanotechnology has created a range of new textiles for medical and surgical purposes. Cotton is being made such that it catches no dirt and stain and also the softness and pliability of cotton is not altered because of this surface finish. Fibre structure Fibres differ from one another In physical structure includes length, diameter, surface contour, crimp, cross-section shape and molecular arrangement. Fibre length Fibres are obtained from the manufacturers in the following form. Filament Monofilament and multifilament Staple Natural 2

11 Textile Fibres Man-made staple Filament tow Filament Silk is the only natural filament fibre. All man-made fibres are extruded from the spinneret as filament, but some are reduced to staple and used in the form only. While others are used as both filament and staple. Yarns made from filament are of two types. Multifilament and monofilament. Multifilament yarns are made up of a number of tiny filaments twisted together. The size and number of the filament may vary. Yarns of this type are smooth and give a smooth surface texture, softness, lustre, luxurious drape. They are used in lingerie, blouses, and other dresses. Monofilaments yarns are composed of a single solid strand of great strength and smoothness. Very sheer hosiery is made from these monofilament yarns. Large monofilaments are used for car seat covers and screenings, also other such things. Staple fibre All staple fibres either natural or man-made are short in length, and are measured in inches. They range from three quarter of an inch to fifteen inches. The word staple derives meaning from the fourteenth century as a descriptive term for merchandize. Later it came to mean basic commodities in a particular business. Still later it was used to express the length of wool and cotton fibres. During World War I Germany began the practice of cutting artificial silk into short lengths for use in cotton and wool type fabrics as there was shortage of these fibres. The word staple as applied to these cut fibres and is now the standard name for any fibre of a length 3

12 Natural and Man-Made Fibres expressed in inches. All natural fibres with an exception of silk are staple. Filament tow Filament tow is a collection of many parallel filaments without twist which are grouped together in rope form. Light tow of 500 to 500,000 denier is made into staple fibre by the tow-to-top direct spinning system. The tow is fed into a machine through leveling rolls, passes between two rolls which travel at a faster rate of speed and create tension that causes the fibres to break at their weakest point. The strand is then drawn out to yarn size, twisted and wound on bobbin. Direct spun yarns have high degree of strength and uniformity than conventionally spun yarns. Dense compact rainwear fabrics can be made by using the direct spun yarns in the filling direction. When these shrink they bring the warp yarn closer. Man-made filament and staple are spun by different equipment, often in different factories, because of the different number of holes needed in the spinnerets. Fibre diameter The finer the diameter of a fibre the finer the fibre. The thicker the fibre the more body it has the stiffer it is. Fineness is a major factor in determining the quality. It is measured in microns. Diameter Range for Natural Fibres Cotton Flax Wool Silk 16 to 20 microns 12 to 16 microns 10 to 70 microns 11 to 12 microns 4

13 Textile Fibres The diameter of man-made fibres is determined according to end use. It is controlled by the size of the spinneret and by stretching during or after spinning. The fineness of the man-made fibre is measured in denier. For any fibre the higher the denier the more coarse the fibre. Surface contour refers to the surface of the fibre along its shaft. Natural fibres grow in certain shapes and are not uniform throughout their length. Man-made fibres within certain limitations can be made in any desired shape. They are exactly the same diameter throughout, they can be altered into thick or thin as per the requirement. Fibre shape is determined by end use. For blending natural fibre with, man-made the man-made fibre is prepared to be of the same thickness as that with which it has to blend. Wool is the only fibre which has a broken surface caused by overlapping sections like fish scales or shingles, no man-made fibre has so far been produced with the effect of broken surface. Cross-sectional shape The cross-sectional shape is important because it contributes to the surface appearance of the fibre. It contributes towards imparting properties like lustre, bulk, and body to the fibre. It also affects the hand or the feel of the fabric. Circular shape is achieved by extruding the spinning solution through circular holes, by melt spinning process. Or by stretching when it is wet. These fibres make compact rather than spongy yarns. Circular cross-sections with serrated edges result from shrinking of the fibre in a coagulating bath during wet spinning. Many serrations give high lustre. 5

14 Natural and Man-Made Fibres Figure 1.1. Cross-section of fibres. Polygonal shape is found only in flax. It gives lustre to the fibre. Oval Shape also gives good cover and a pleasing hand that is neither silky nor harsh. Triangular shape occurs in silk and has been achieved in some of the new man-made fibres by using a highly viscous solution, melt spinning through triangular holes, but it cannot be stretched after spinning. Lobular or multiform shape probably results from evaporation of the solvent during dry spinning. It gives a good hand. Dog bone or dumbbell makes wool like yarns and fabric. Flat ribbon like shape is used for crisp lustrous fabric and imitation straw. Wild silk is somewhat of this shape. Y shaped cross-section give excellent cover and bulk. It is used for stuffing where warmth is required. 6

15 Textile Fibres Hollow centre fibres give buoyancy. They are seldom used on clothing but are excellent for life jackets. Other fibre shapes are possible and if a new shape adds a new property to a fibre, it may well be prepared. The scope for further shapes is ever there. Crimp Crimp is that property of fibre which imparts waviness along the length of the fibre. Fibre crimp increases cohesiveness, resiliency, and resistance to abrasion and gives increased bulk to the fibre. A fibre may have mechanical crimp, natural or inherent crimp and latent or chemical crimp. Mechanical crimp Mechanical crimp is imparted by passing the fibres through fluted rollers to produce a two-dimensional wave. The bends in this crimp are angular as compared to rounded in the natural crimp fibres. To make the crimp permanent heated rollers are used. Natural crimp occurs in wool and cotton. Cotton has twodimensional twist called convolutions. Latent or chemical crimp Latent or chemical crimp exists in the fibre in an under developed state. Until the garment is immersed in water and it coils and curls. Some of the man-made fibres like rayon, acetates and orlon posses this latent crimp. Man-made Figure 1.2 Natural 7

16 Natural and Man-Made Fibres Molecular arrangement It is about how the molecules in a fibre are joined together and the length of the molecule help to determine the property of a particular fibre. Fibres are made of long straight chain molecules called linear polymers. The arrangement of molecules resembles the arrangement of fibres in a yarn. The molecules may be parallel to the fibre axis or at right angles to the axis or spiral as they are in cotton and flax. This is called molecular orientation. Most of the fibres are parallel making the fibre crystalline. If the arrangement is not orderly than it is amorphous. When the man-made fibres are drawn from the spinneret the molecular structure is usually amorphous. Drawing and stretching aligns the molecules parallel to each other and also make the fibre more compact. It also henceforth reduces the diameter. When the linear molecules are packed together there is greater attraction between the hydrogen atoms of the chain. This is called hydrogen bonding. These bonds are weak cross-links but because they are so many of them they make the fibre stronger. Fibres which are highly oriented are stronger fibres e.g. Nylon. Figure 1.3 Chemical composition Cellulose fibres are poly hydroxyl alcohols. Protein fibres are composed of various amino acids. Acetates are polyesters of cellulose. 8

17 Textile Fibres Nylon fibres are polyamides. Polyester fibres are esters of dihydric alcohols. Acrylic fibres are addition polymers of acrylonitrile. Modacrylics are co-polymers of acrylonitrile and other substances. Nytril fibres are addition polymers of vinylidine dinitrile. Saran fibres are addition polymers of vinyl chloride. Vinal fibres are addition polymers of vinyl alcohol. Spandex fibres are elastomers composed of poly ureththane. Olefin fibres are addition polymers of ethylene, propylene or other olefin units. We can see that there are chemical differences in the molecular arrangement of fibres. These differences explain the reactivity of fibres, each different from the other. Fibre Properties Abrasion Resistance Abrasion resistance is the property of the fibre to withstand the rubbing or abrasion it gets in everyday usage. Inherent toughness, natural pliability and smooth filament surface are fibre characteristics that contribute to abrasion resistance. The following fibres are arranged in order of their resistance to abrasion: nylon, polyester, acrylic, wool, cotton, rayon, acetate. Strength The strength of a fibre is defined as the ability to resist strain and stresses and is expressed as tensile strength. Or as tenacity (grams per denier). Strong fibres have long molecular chains. Degree of polymerization is the term used to describe the length of the 9

18 Natural and Man-Made Fibres molecule chain. The D.P. of cotton is about 10,000 while that of regenerated cellulose is 300 to 500. Strong fibres are highly oriented while weak fibres contain large sections of amorphous area. Strong fibres make strong yarns. Thus, the fine strong fibred yarns may be used in the production of sheer fabrics extremely sheer nylon hose are possible because of the high strength of the fibre. Ramie, flax, nylon, dacron and vinyon are high tenacity fibres. While silk, cotton, zefran, dynel, creslan, orlon, saran are fibres which have medium tenacity. Rayon and wool are low in strength. Cohesiveness Cohesiveness is the ability of the fibres to cling together during spinning. This is an important property in staple but not in filament. Cohesiveness occurs because of natural crimp and unevenness in the fibre structure. Resiliency Resiliency is the property of the fibre or fabric to spring back to its original shape after it is stretched or deformed. This may happen over a period of time. A resilient fabric has good crease recovery, and hence requires no ironing. Resilient fabrics also retain high bulk and do not pack well when in use. This property enhances the beauty of the fabric and it is also easy to care fabric. All these properties of resiliency, elasticity, pliability and elongation are due partially because of the natural crimp in the fibre. All protein fibres have molecular crimp. Nylon has a folded molecular structure as it comes from the spinneret and it is cold drawn to retain some of the crimp. Cross-linkages and side chains help to explain these properties. Cross-linkages help to prevent the molecules from sliding over one another. Man-made, cotton and flax can be chemically cross-linked. 10

19 Textile Fibres This is on the basis of wash and wear finish. However, too many cross-linkages may affect the fibre adversely and it may become very harsh. Stability Stability is an important property a fibre must have for its easy care and upkeep. Stability is the retention of sizes. A stable fibre does not stretch, sag or shrink. Stable fibres make a stable fabric and a stable fabric can be converted into any useable apparel. Plasticity Plasticity is the property of a fibre to enable the user to shape it permanently or semi permanently by moisture, heat and pressure, or by heat and pressure alone. This property relates to the ease of beauty and care as well as the durability of the fibre. This is important from the consumer stand point. Wool has this property because of its scale structure and its lack of stability. Thermoplastic fibres are those which soften on heating. These fibres can be permanently shaped by heat. Thermoplastic fibres are all heat sensitive but vary in degree of sensitivity. They should not be washed in hot water. When the fibres are heated they either decompose or melt. Melting consists of separating the molecules. It is believed that cellulose fibres do not melt because of the large molecule size and because of the strong attraction forces of the hydroxyl groups. Protein fibres do not melt because of the presence of crosslinkages. Heating causes the molecule to vibrate with such force that they tear themselves apart or melt. Thus, we know how heat sensitivity affects production and care of fabrics. Comfort The properties of fabric which are associated with comfort are 11

20 Natural and Man-Made Fibres density, absorbency, hygroscopicity, and conductivity of electricity and heat. Absorbency Absorbency is the property of the fibre to take up moisture and is expressed in terms of moisture regain. This is the amount of moisture that a bone dry fibre will absorb from the air under standard conditions of temperature and moisture. Absorbent fibres make fabrics which are comfortable because they take up the perspiration readily. That is why they feel comfortable on hot and humid days. Absorbent fibres do not build up static electricity which also makes them more comfortable in dry, cold weather. Dry cold fibres are hydrophilic or water loving while non-absorbent ones are hydrophobic or water hating. Absorbency is an important property from the beauty point of view since they are easier to dye; absorbency is also related to resiliency. They tend to wrinkle more. Absorbency is due to the chemical structure of the fibre. This has many hydroxyl groups available, are very absorbent. Protein fibres which have many hydroxyl groups are very absorbent. Proteins fibres which have reactive amino (NH2) and (COOH) groups are very absorbent, highly oriented groups are not absorbent. Highly oriented groups are less absorbent than fibres with many amorphous areas. Since the water molecules get no space to penetrate. Wicking and wetting Wicking is that property which refers to conduction of moisture along the fibre or through the fibre. The fibre itself does not absorb the moisture. This property is related to surface wetting and nonabsorption of moisture by the fibre. 12

21 Textile Fibres Electrical conductivity This is related to the buildup of static electricity charges on the fibre. A good conductor does not build up static electricity charge. Heat conduction Heat conduction is largely a yarn or fabric property. Since fabrics are neither warm nor cool. However, because of the physical structure of the fibre they tend to make cool or warm clothing. Heat comes from the body if fabrics permit the body heat to escape like in cotton and flax they are cool fibres, if they do not permit body heat to escape they are warm fabrics for example wool. Beauty and hand Fibre properties related to beauty and hand are terms used to describe the fabric like soft, lofty, warm, silk like, and wool like are descriptive words which in other words is also known as hand. Loft Loft or compressenal resiliency refers to the ability of the fibre, yarn, or fabric to spring back to its original thickness after being compressed. In fibres loft is because of crimp. This property is good in sweater, blankets and shawls. Cover Fibres with irregular cross-section and with crimp curl or twist to give better cover for protection purposes. Cover means concealment or protection on the surface. Body The overall look or rigidly firm appearance of the fibre may be termed to be the body of the fibre. 13

22 Natural and Man-Made Fibres Drape The manner in which the cloth hangs is called the drape of the fabric. It may be soft and limp, or stiff, and buoyant. Fabrics which have a nice fall on the body are said to have a good drape, and for example silk has a good drape. It falls on the body with very elegant lines. Lustre Lustre is light reflected from the surface. It differs from shine in that it is more subdued since the light rays reflecting on the surface are broken up. Smooth flat fibre reflects more light than round or rough fibres. Fibres with many striations have high lustre, for example Rayon. Yarns of long fibres which are laid together with little or no twist reflect more light than yarns with shorter length. Manufactured fibres are delustred to make them close to look natural. Oil or pigment is added to the solution before it is extruded out of the spinneret. Lustre Shine Figure 1.4 Colour Affinity to take and hold colour is largely contributed to the chemical composition of the fibre. Absorbent fibres take dye more readily than non-absorbent ones. 14

23 Textile Fibres Chemical resistance The chemical reactivity of each fibre depends on the arrangement of the molecules it contains. Dry-cleaning solvents, perspiration, soap, synthetic detergents, bleaches, atmospheric gases, soot, and sunshine may all cause chemical degradation on some or all of the fibres. Alkali strengthens the cotton fibre. Alkali and chlorine may be used to make wool shrink resistant. Scientifically controlled use of chemicals brings about beneficial mordants and finishes. Resistance to moth and mildew Fibres without natural resistance should have protective finishes to prevent moth and mildew. Also, often it is due to the chemical composition of the fibre. These properties enhance the usage of protected fabric for clothing. Flammability Flammability depends upon the air incorporated in the fibre. Combustible finishes and dyes make the fibre flammable. Anti flammable dyes must be used to protect the fibre and make it nonflammable. Elasticity Elasticity is the property of any stretched fibre to return to its normal shape soon as it is out of use. e.g. socks. Pliability of flexibility Pliability refers to the fibre to softly fold in any possible direction. It is because each fibre has the ability to fold that it can be converted into a three-dimensional outfit. They are easy to twist in to yarns. 15

24 Natural and Man-Made Fibres Stiffness and rigidity This property is just the opposite of pliability. Rigidity is important to any fibre because it determines the insertion of any twist to the fibre. Elongation Elongation is the deformation caused due to stretching. It is expressed as percentage of original length. For example if a fabric is 100 cm and it can be stretched to 110 cm before it breaks then its elongation is 10 percent. 10 percent elongation is desirable. Elongation varies at different temperatures it is different when wet and when it is dry. The table below shows the elongation of certain fibres under standard condition. Dry fibre Percent elongation Wool 25 to 35 Acrilan 35 Dynel 39 Vycron 31 to 35 Creslan 32 Fortel 3o to 35 Nylon 26 to 32 Nylon staple 16 to 42 Rayon 15 to 30 Silk 20 Acetate 25 Cotton 5 to 9 Flax 6 to 7 Glass 2 Avril 5 to 9 Dacron 16 to 42 16

25 Textile Fibres Classification of Textile Fibres Fibres may be broadly classified into 3 groups: a. Natural fibres. b. Man-made fibres (non-thermoplastic). c. Man-made fibres (thermoplastic). Figure

26 Natural and Man-Made Fibres Figure

27 Textile Fibres Nature is abounded with different kinds of fibrous materials. Man has learnt to extract and synthesize fibres from available natural resources and also chemicals. The fibre which is the basic single unit out of which all fabrics are prepared, has properties which are inherent to the material from which it has been extracted. Some such properties are length, strength, pliability, diameter, abrasion resistance and nature of the surface area. Along with all these properties the fibre must be pleasant to the touch both as to texture and temperature, absorbent to some extent so that they can be dyed and be comfortable to wear; can be cleaned, they should be light weight if used for apparel, resilient, durable and available at an affordable price. No fibre is perfect. All of them are lacking in a few or many of these characteristics. Modern production methods have overcome some of the difficulties in making fibres into fabrics. Blending is done to impart properties of two different fibres to produce a good yarn for a fabric. All fibres, whether natural or man-made are chemically known as polymers. Polymers are the result of a process called polymerisation. It is defined in Hackh s dictionary as a reaction in which two or more molecules of the same substance combine to form a compound the new molecular weight being a multiple of that of the original compound [monomer] or the structural arrangement in which two or more different monomers or types of groups are present in alternate sequence in a chain [copolymer]. In simple polymerisation, units (molecules) of the same compound combine to form the long chain. In hetropolymerisation, polymerisation occurs between two different kinds of units, only one of which is capable of polymerisation by itself. A simple compound A and another simple compound B can form a long chain of polymer A A A A A A A 19

28 Natural and Man-Made Fibres or make a series of B B B B B B B Both of these are simple polymers. But if we can, in some way, make units of A combine with B into a molecular chain, we have a copolymer A B A B A B A B If we introduce a compound, C, which we cannot make polymerisation happen by itself, it can cause it to combine in a chain with either A or B or with both, we have a hetropolymer, e.g. A A A C A A A C A A A The natural fibres are simple polymers (cotton, linen) or copolymers (wool, silk) and among the man-made fibres may be found all three types of polymers. This explanation helps to understand the complex nature of textile fibres in a simple way. 20

29 Chapter 2: Cellulosic Fibre - Cotton I ndia was the first country to manufacture cotton. Among the latest finds at Mohenjo-Daro were a few scraps of cotton were found sticking to the silver vase. This shows that cotton had been produced in India as far back as even the fourth millennium B.C. Historians speak of the beautiful painted and printed cloth which was sold in Egypt and some parts of Europe long before the time of Alexander. Figure 2.1 It is generally accepted that wool first came into use and cotton came later. It is not known when India first started to trade with Europe, but the word Carbasina (Sanskrit word Karpasa) for cotton suggests that it must have been in use before 200 B.C. To the Greeks who came to India with Alexander India was a land of mystery. They were so surprised to see cotton that they called it

30 Natural and Man-Made Fibres wool produced in nuts. They wrote wild trees in India bear fleeces in their fruits, surpassing those of sheep in beauty and excellence. Properties of cotton Cotton is the seed hair of the shrub which bears the botanical name of Gossypium, a member of the mallow family. The shrub grows to 6 feet tall height. From 80 to 110 days after planting the plant bears beautiful creamy white blossoms, which turn pink and fall off and are replaced by a green triangular pod called boll. The fibre develops within the boll. The boll is the size of a walnut. The mature boll bursts open from the fibre pressure, exposing the fluffy mass of white cotton fibres. Cotton is classified according to fibre length, fineness, lustre and geographical location. Figure 2.2 After cotton is picked several steps are necessary before it can be spun into yarn, like ginning, baling, grading marketing, opening, picking, carding, combing, drawing, roving, spinning winding and spinning and twisting. 22

31 Cellulosic Fibre - Cotton Figure 2.3 Ginning: Ginning is the process by which seeds are removed. Several ginning machines have been designed. Shown in figure is a ginning machine. Roller gins are used for long-fibre cottons and saw gins are used for intermediate and short fibre cottons. Eli Whitney, is famed for the invention of cotton gin, an invention of great importance in the development of cotton industry. A ginning process, carried out at the seed crushing mills removes the linters. Baling: After ginning the cotton is compressed into bales, usually square in shape, the bales are covered with burlap to protect the fibre and are banded with steel bands to keep the bale in shape and to make it manageable for handling. Bales vary in weight from 250 lb to 500 lb for square bales. Grading: Quality of cotton according to staple, microns colour and foreign whiteness and spottiness. Grading determines the quality rating of cotton and the price. It will bring to the market in relation to the price of standard grades in that particular season. 23

32 Natural and Man-Made Fibres Grading is done bale by bale. Grade is based on colour, foreign matter and preparation. Degree of whiteness, spottiness and other discolourations of various types affect the colour rating. There are six colour variations for upland cotton grey, extra white, white, spotted, tinged, and yellow stained. Foreign matter consists of broken leaves, bits of twigs, sand and dust. Preparation refers to the quality of ginning, whether fibres have been cut, tangled, bunched etc. and is designated as A, B, C. The classes for grading of cotton from best to poorest are middling fair, strict good middling, middling, low middling. Staple: An average staple length is determined from three properties. The average length, character which includes strength, maturity and fineness. The effect of these qualities on texture and properties of fabric and in converting fibres to yarn. The average length is very important to the manufacturer in making the necessary adjustment to his machinery. Character: Character of cotton includes strength, fibre maturity, fineness, spirality, convolutions, ability of the fibre to cling together and body (softness, harshness, hardness). Marketing: Marketing includes all transactions from the time the cotton leaves the producer until it is accepted at the mill. Some cotton is sold directly from producer to mill, but most of it goes through a series of selling operations. Most cotton is actually handled often in bales of 100 of the same grade around the cotton markets of world. The largest being New York, Liverpool, New Orleans, Memphis and Houston. In India, cotton is produced in Orissa, Maharashtra, some places in Punjab. Many of the series of marketing steps are the small markets or in the cotton exchanges. The spot markets are the small markets dotted through the cotton producing areas and cotton mill areas of the country where the cotton farmer sell their cotton to small merchants or to 24

33 Cellulosic Fibre - Cotton cooperatives. The cotton sale is an organization something like the stock exchange, deals only in futures market with no actual cotton bales and sometimes no samples of cotton are present. But future sales made on the basis and grading. Properties Microscopic Cotton fibres have twisted flattened appearance much like a twisted ribbon. As it grows the fibre develops a primary and a secondary wall. The centre part is the lumen. The Lumen carries liquid to the living cell. When the boll opens the liquid dries up rapidly causing the lumen to collapse. The fibre then assumes the characteristic twisted or spiral form. Long fibre cottons have more twists per unit length than other cottons and mercerised cottons of all types often show fewer twists than the unmercerised cotton. Chemical properties The chemical composition of typical cotton is 94% cellulose, 1.3% protein and 0.9% other things including sugars. The cellulosic content of raw cotton varies Figure 2.4 from 88% to 96% depending on the variety of cotton soil and growing condition. Cotton fibres are very absorbent. This accounts for their comfortableness, especially in hot climate. In the process of absorbing the fibres tend to swell considerably in cross-section area. Their length is little affected. This fact is utilized in some of 25

34 Natural and Man-Made Fibres the finishing processes. Cotton is decomposed by strong acids hot or cold and is deteriorated by weak, hot acids. Strong sulphuric acid is used for parchmentizing by the Haberlein process. Permanent organdy finish is given by this process. Fabric is dipped in sulphuric acid for a momentary treatment. Figure 2.5 Internal structure of cotton The cotton fibre which are visible to the naked eye, when viewed under high magnification as with electron microscope are shown to be comprised of many layers of tiny fibrils arranged in definite spiral pattern with the different layers at right angles to each other. This structure as the fibre ripens may account to the twisting of the fibre as it dries. The picture shows the layered structure of cotton fibre as revealed by the microscope after staining and swelling treatment. 26 Figure 2.6

35 Cellulosic Fibre - Cotton Mercerisation Mercerisation is a process which was discovered by John Mercer in 1853, a calico printer. Mercerisation is accomplished by dipping the fabric in 18 to 23% solution of caustic soda for one half to two minutes at room temperature with the cloth held under tension. Mercerised cotton has increased lustre and increased strength. The fibre becomes more cylindrical. Mercerised cotton is stronger, has increased affinity to dyes so that less dye is needed, dyes more evenly has greater affinity for resins and other finishing compounds and is more sheer in appearance. It soils less easily than unmercerised cotton. Physical properties of cotton Cotton fibres are most often creamy white in colour, although the colour varies with variety, type of soil in which it is grown and the climate. Rain and dust on the open boll stain the fibre. Egyptian cotton has a reddish brown cast and is darker in colour than the Sea Island upland cotton. Usable cotton fibres of different variety vary in length from 0.5 to 2.5 inches, and in diameter from 6 to 26 microns, with specific gravity of 1.50 to Cotton is thus one of the shorter fibres intermediate in width and its density is higher than most of the other fibres. Cotton has medium tensile strength compared to other fibres, but when wet its strength increases as much as 30%. The increase in strength is very important when working in tropical or very humid climates where moisture and perspiration are likely factors that must be taken into consideration. Cotton has medium abrasion resistance and high flex resistance. Cottons low resiliency means that cotton fabric will wrinkle and that wrinkles will not straighten out but will require ironing for removal. Cotton may be stored for long periods with no 27

36 Natural and Man-Made Fibres apparent loss of strength and this also may cause yellowing. Prolonged exposure to sunlight causes great loss of strength. Cotton scorches if ironed with very hot iron. This causes damage and loss of strength. Cotton is readily refreshed by washing and ironing. It is considered to be the least expensive fibre in terms of upkeep, because cotton without damaging the fibre can be sterilized in boiling water or in a steam autoclave it is usually considered to be the most antiseptic of all fibres. It is widely used in hospitals for operating room materials and uniforms also for the fact that cotton presents no problem of dangerous accumulation of static electricity. Biological properties Under conditions of high humidity mildew, bacteria, yeast will grow on cotton. Starched cotton is more likely to be attacked than unstarched cotton. This attack weakens the fibre and also leaves behind a disagreeable odour. Silverfish and termites also attack cotton. Cotton fabrics may be treated to protect them from attacks by microorganisms, but the treatment may change the appearance and texture of the fabric so much that its uses are limited. These treatments are important for outdoor fabrics such as lawn tents, lawn furniture, and camp furnishing where appearance is not as important as end usage. Major cash crop Cotton is the major cash crop of India with the death of antidumping regulations. India expects a substantial increase in its textile trade. Caught in the spinning wheel are the 3 countries US, China and India. The biggest problem is that U.S. The United States gives big subsidies to its cotton farmers. So India is importing cheap raw cotton. The strange thing is that while India is now importing raw cotton it is also exporting, mainly to Bangladesh and China - through a private procurement and export 28

37 Cellulosic Fibre - Cotton regime, due to which the local farmer is affected. More than 70 countries globally produce and export cotton. Of these eight countries are responsible for almost 80% of global output. The world s cotton market is dominated by the U.S. which is the second largest producer after China. Despite these reasons India started exporting cotton in In 2005, India exported 800,000 bales. Export from India is increasing. The cotton exported from India is middling staple. It is of a very ordinary quality. Cotton farming in India (SWOT analysis) Cotton plants grow almost all over India. Black cotton soil of south India is the best soil for growing cotton. Part of Orissa, some places in Gujarat, Punjab and Haryana seem to be favourable. Cotton requires a humid climate and a rainfall of 12 to 15 cm. Approximately 700 kg/hectare cotton is produced all over the world. America, Australia and Brazil produce about 1200 kg/hectare. The per hectare yield of India is 300 kg/hectare. Although cotton is an important cash crop of our country but the reason for this low productivity are many. Poor agricultural processing. Dependence of farming on rain water. Poor irrigation facility. Poor ginning. Although large land mass of India about 9.5 million acres is used for the cultivation of this cash crop, it also guzzles a lot of water. One cotton plant needs 700 to 1300 mm water depending on the growing period in the early stages. Only 35% of the area is irrigated rest is rain fed. Due to poor farming facility the produce is of a very inferior quality. Cotton exported from India is medium staple cotton, which is a below average variety of cotton. 29

38 Natural and Man-Made Fibres Uses Cotton plant in Indian tradition is much more than the source of raw material for textile above. Cotton flowers give us nectar and if bee keeping is planned, it gives highly flavoured healthy and tasty honey. Cotton seed oil is a well-known edible oil. It is also used in Vanaspati formulations. In Ayurveda, equal quantity of ginger is used for external application to relieve pains due to rheumatism and arthritis. Roots of cotton plants are used for female diseases. Leaves are good for green manuring. Oil cake is a cattle feed and a good raw material for industrial adhesive besides being a good manure. Figure 2.7. General steps in manufacturing cotton textile goods. 30

39 Chapter 3: Linen (Flax) - Cellulosic Fibre I t is known that linen was produced in Egypt long ago to be a developed art by 3400 B.C. A robe of this fabric is said, could be drawn through a small finger ring. From ancient Egypt, with the rise of sea travel and trade the use of linen spread around the Mediterranean Sea. In due time France, Belgium and Holland became famous for the quality of the linen produced. Ireland became predominant. The Irish climate is ideal for the spinning and weaving of linen as dampness keeps the fibre tough rather than brittle. Figure 3.1 Botanical name of linen is linum usitatissimum, a name indicative of its many early uses. The term flax is derived from Anglo Saxon and old high German words. Linen designates both plant and fibre. Flax is a slender straight stemmed plant with narrow, medium green lance like leaves which grow to a height of

40 Natural and Man-Made Fibres 2 to 4 feet. The longest stemmed varieties are planted for fibre. The plant branches near the top into few branches, which in turn bear the half inch wide blossom and the seed boll. The different varieties may be coloured pink, purple, white or azure blue. The white and the blue are of commercial importance. Blue flowered flax is considered to have better spinning qualities than white. Flax grows in a temperate climate under a wide variety of climatic conditions but does best with cool, even temperature and considerable rain fall, it requires a growing season of 85 days to 100 days. The height of the plant, the fibre length and the quality of the fibre varies greatly with soil and climatic conditions. Flax does not require a rich soil the seedbed must be carefully prepared. Once planted no special care is required except to keep the weeds down. While the plants are young, flax is subject to some rather severe plant diseases. So it is usually rotated from field to field rather than grown in the same field year after year. Flax fibres occur in bundles just inside the relatively stiff cuticle outer wall and surrounding the woody central part of the stem. The fibres are bound together within the bundles by a cellular tissue sometimes called the phloem and by gums and waxes. These substances are largely removed during processing allowing the individual flax fibres to be separated. Formerly flax cultivation was almost entirely a series of hand operation but now, as in other agricultural endeavours it is becoming more mechanized. The stage at which flax is harvested depends on the end product desired. Flax for seed is harvested when stems and seed bolls are quite dry and are yellowish brown in colour but still moist and supple. 32

41 Linen (Flax) - Cellulosic Fibre Processing Flax stem is then put to pulling, retting and scutching. Pulling: Pulling is the removal of the whole plant including the root system from the soil. Unbroken stems are required for maximum fibre length and also to prevent staining of the fibres within the stem during the drying and retting processes. This is also now a mechanized procedure. Retting: Retting is a process by which the brittle outer cuticle layer of the stem is broken down and at least partially destroyed by fermentation through bacterial action and by moisture allowing the fibre groups to be removed. There are several methods of retting all of them slimy odorous and unpleasant, making this a most disagreeable process of flax production. Removing the cuticle by chemical treatment is called chemical retting but the fibre extracted is of a poor quality. Dew retting: This is a slower process than other processes. Since it is slower than other processes it takes 2 to 3 weeks. Water for retting must be clean and free from minerals. Especially iron that Figure 3.2 might discolour or damage the fibre and it should preferably be soft water. During retting the water penetrates to the inner parts of the stalk via small flaws in the cuticle or bark causing the inner cells to swell and burst the cuticle. This in turn increases moisture absorption and permits greater penetration of bacteria which act 33

42 Natural and Man-Made Fibres upon pectin s, the substances surrounding the fibre bundles, changing them into soluble sugars. Running and stagnant water retting are carried out in similar fashion. The flax bundles are placed in crates that are weighed down with stone to keep the entire length of the stem submerged in water after bacterial action commences and gases form. Tank retting: This is another form of retting, which is carried on in specially built tanks. Constant lukewarm water temperature is maintained. In tanks, fermentation can be closely controlled by maintaining the ph of water. The water penetrates to the inner part of the stalk via small flaws in the cuticle or bark causing the inner cells to burst and swell. This in turn increases moisture absorption and permits greater penetration of bacteria which act on pectins surrounding the fibre bundles. After retting the fibre bundles are dried with drier. Decortication: Although decortication is a process of scraping the cuticle and woody centre it is also used for substitute retting. Scutching: Scutching is the process of removing the dried retted fibre from the woody remainder of the plant stem. The first step is the breaking operation in which the butted parallel stems are passed through a series of fluted rollers, which break up woody portion of the straw into fine pieces called shives which can Figure

43 Linen (Flax) - Cellulosic Fibre be beaten out and which leave the long linen fibres largely undamaged. The resulting long fibres are called line or flax. Flax fibre has been designated by five grades according to fibre length and colour, general conditions and lustre. A good quality spinning fibre is fine soft strong and has a somewhat cold and oily feel and a glossy sheen. The fibre is strong, absorbs moisture and has good wicking ability. When blended with cotton it makes an excellent fabric for summer wear. Properties Physical properties It is the strongest of all vegetable fibres. It is stronger wet than dry. Colour of linen varies from a creamy white to brown, the depth of colour largely depending on time and condition of retting. It may be bleached to white. Linen fibre varies from 12 to 30 inches in length and 5 to 28 microns in diameter. Linen has low elongation and resilience. Ironing when quite damp is necessary to restore its freshness. It crushes and wrinkles readily unless treated for crease resistance. It becomes softer and more lustrous with frequent laundering. Because of its strength linen is a very durable fibre. Untreated linen feels cool to the touch and is one of the most absorbent fibres owing to its wicking ability. It absorbs rapidly and is quick Figure 3.4 to dry. It is one of the most comfortable fabrics for warm climates. Linen is sometimes considered to be an expensive fabric, but today it is competitive in price with many other fabrics. Its durability should be taken into account when considering its cost. 35

44 Natural and Man-Made Fibres Linen fabrics can be flattened and made more lustrous and soft during manufacture by a beating process called beetling, in which the fabric is pounded with hundreds of tiny hammers. This process does not harm the fibre, but destroys part of the cementing substance between the fibres and gives it more sheen and smoothness by reducing the space between the weave. Linen is being blended with cotton to make the blue denim jean more comfortable the good qualities of linen e.g. absorbency and also its property of wicking have rendered significant boost to blending cotton and linen to make jeans comfortable in summer. Linen can be distinguished from other commonly used textile fibres by its distinctive appearance. As seen in cross- sections the fibres are round to polygonal usually five sided with rather rounded corners. Linen has a natural lustre it does not need mercerisation. It can be satisfactorily bleached or treated with a resin for crease resistance and other properties. It is the strongest of all vegetable fibres. Linen is a very durable fibre because of its strength and good quality. It is readily refreshed on ironing. Microscopic structure When viewed through microscope linen can be distinguished from other commonly used textile of bamboo or various types of cane, because of transverse lines or nodes, a characteristic of most of the bast fibres. Immature fibres are oval in shape with much larger lumen. Raw flax Figure

45 Linen (Flax) - Cellulosic Fibre fibres are composed of about 71.5% cellulose, 10.7% water, 9.4% gums, pectin etc. 6.0% extract, 2.4% fat and waxes, and 1.3% ash. When boiled off and bleached linen becomes pure cellulose. Linen may be attacked by mildew, resin finishes tend to cut down on the likelihood of microorganism attack on both linen and cotton. Uses and by-products It is largely used as apparel, ladies blouses, shoes, handbags, hats, textile furnishing which include drapery and upholstery fabrics, towels and damask and other napery and rug. Industrial uses include sewing threads for leather goods. Linen has long been in use for fire hose because of its great strength, low elasticity and quick absorption of water, so that it becomes wet quickly and can be handled comfortably (temperature wise) and is not likely to catch fire as long as water is going through it. By products of linen are from the seeds. The most important by product is linseed oil. This is a valuable oxidizing (thus drying) ingredient in many outdoor paints. Flax seed is an important ingredient in some medicines and drugs. 37