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FIBRE SCIENCE AND TECHNOLOGY UNIT I TEXTILE FIBRES Textile fibres can be defined as the textile substance that is very small in diameter in relation to their length or in other words fibre is the material which is several hundred times longer than its thickness. Fibre is the basic component of any t...

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FIBRE SCIENCE AND TECHNOLOGY

UNIT I

TEXTILE FIBRES Textile fibres can be defined as the textile substance that is very small in diameter in relation to their length or in other words fibre is the material which is several hundred times longer than its thickness. Fibre is the basic component of any textile material. There are different types of fibres around us in daily use. Fibres with a short length are called as staple fibres, whereas fibres with long length are called as filaments.

Types of Textile Fibres 1. Natural Fibres 2. Man-Made Fibres

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Natural Fibres Fibres which are obtained from the natural origin directly or indirectly referred as natural fibres. Fibres obtained from the natural origin can be further sub-classified into three different categories based on their different natural origins. Classification of natural fibre is as follows – 1. Vegetable Fibres 2. Animal Fibres 3.

Mineral Fibres

Vegetable Fibres These fibres are basically cellulosic fibres. Besides their use as textiles, these fibres are also used in the manufacturing of papers. Vegetable fibres are basically obtained from various parts(Organs) of the plants such as seeds, bast, leaf, fruit, stalk, etc. Seed fibres are obtained from seeds such as cotton, kapok, etc. the cotton fibres are widely used for the apparel purpose, medical uses, and other textile applications. Leaf fibres are obtained from leaves of plants such as Palf, sisal, agave, etc. Leaf fibres are used for marine ropes and cement reinforcement. Fruit fibres are obtained from the fruit of the plant such as coir fibre (coconut fruit). These fibres are mainly used for manufacturing doormats, carpets, etc. Bast fibres are obtained from the bast surrounding to the stem of the plant. Such as jute, hemp, flax, ramie, etc. These fibres have more strength, durability and do not get affected by moisture so that they are used for manufacturing durable yarns, fabrics, packaging material and paper. Stalk fibres are extracted from stalks of the plant – such as straws of rice, wheat, and other crops. Bamboo and grass fibre is also included. Animal Fibres The fibres are obtained from animals are called as animal fibres. The fires are mainly made up of protein molecules. The basic element of a protein molecule is carbon, nitrogen, hydrogen, oxygen. Wool (Hair fibres obtained from the animals) & silk fibres are common examples of animal fibres. The fibres obtained from the sheep are referred as wool fibres, in the way the hair of the horse, camel, goat are also obtained as fibre. 90% of hair fibres are wool fibres used various applications. 2

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Silk is very delicate filament. It is obtained from silkworms. Silk formation takes place by the secretion of proteinous molecules in liquid form through the glands of the silkworm, It is located on the head of the worm. This liquid proteinous material gets converted into the solid filament. During this secretion process, the worm forms cocoons from which silk is extracted. The sericulture of the silkworm is called as the rearing of the silkworm. The Fibres obtained from the feathers of the birds is called as avian fibres. Mineral Fibres These are the inorganic materials shaped into fibres. Asbestos is the example of mineral fibre. These fibres are fireproof, resistance to acid so that these fibres mainly found in the industrial application. Man-Made Fibres As the name itself indicates these textile fibres are made by man to meet the particular requirements. The chemical composition, structure, and properties are significantly modified during the manufacturing process. Depending on the raw material chosen for making these textile fibres – fibres can be further subclassified into 3 categories – 1. Regenerated Man-Made 2. Synthetic Fibres 3. In-Organic Fibres Regenerated Synthetic Regenerated synthetic textile fibres are also called as semi-synthetic fibres. These fibres are made up of naturally long chain polymer structure, which is modified and partially degraded by a chemical process to enable the polymerization reaction to form the fibres. Most of the semi-synthetic fibres are called cellulose regenerated fibres. Examples: Viscose rayon, modal, cupra (Rayon), bamboo viscose, tencell. The cellulose required comes from various sources such as rayon from the tree wood, modal from the beech trees, seacell from seaweed. In the manufacturing process of these fibres, cellulose is fairly reduced to the pure viscose form and then foam and then foamed into the fibre form by extrusion through the spinnerets.

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Synthetic Fibre Synthetic fibres are manufactured from the petrochemicals. Examples – Polyester, nylon, acrylic, etc. These fibres are formed by the polymerization of monomers. Once the polymer is formed, it can be formed into a filament by converting that polymer into fluid form and then extruding the molten or dissolved polymer through narrow holes to give filaments. To form the fibre from molten polymer it gets passed through the spinneret. An alteration in structure, design and in other words – aspects of yarn can be done by altering the polymers used for it. These fibres are generally very strong, fine and durable with very low moisture absorbency property so that these fibres are also called as hydrophobic fibres. In-Organic Fibre These textile fibres are also called as metallic fibres. Metallic fibres are drawn from the ductile metals such as copper, gold, silver and can be extruded or deposited from more brittles such as nickel, aluminum and iron. From stainless steel also fibres can be formed. These fibres are not that much widely used but these fibres have their special applications in technical textile. Classification of textile fibers can be done in many ways. Some of them are as follows: Classification according to their nature and origin: Flow charts 2–9 show the classification of main natural and manmade fibers used normally in textile applications. The fibers are normally classified as natural and manmade. Among natural sub grouping is made as animal origin, vegetable origin and mineral origin. The manmade fibers are further sub grouped as regenerated fibers and synthetic fibers. Natural fibers are those fibers which are available from the natural sources, viz. plants, animals, minerals, etc. The mineral fibers are also referred as miscellaneous inorganic fibers. Manmade fibers are those fibres which are developed by man. Man possesses a natural instinct of imitating nature and its products. Textiles are no exception to it. He does it either using some natural resources and/or chemicals to produce fibres, artificially. Therefore, sometimes back in their earlier development stages, manmade fibres were also called Artificial Fibres.

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FIBRE SCIENCE AND TECHNOLOGY

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If the manmade fibers are obtained from cellulosic base material then they are termed as regenerated cellulosic manmade fibers; if they are manufactured from synthesizing using various chemicals like the petroleum products then they are called synthetic manmade fibers. Manmade fibers can be broadly classified into regenerated fibers, synthetic fibers and miscellaneous inorganic fibers. Regenerated natural-polymer fibers (polymer is a fiber forming substance) are those fibers which are regenerated by using natural source as a base and are chemically shaped to filament form, e.g. viscose rayon, cuprammonium rayon, acetate rayon, casein ardil, etc.

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Synthetic fibers are those fibers where only chemicals are used in the manufacture of such fibers. They do not require natural raw material as a base for the manufacture, as in the case of 8

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regenerated fibres. For example, hexamethylenediamine and adipic acid are used in the manufacture of nylon and dimethyl terephthalate and ethylene glycol in the production of polyester fibre etc. The chemicals are converted into materials capable of forming fibers and these substances are manipulated into fibrous form. In another way, synthetic fibers can also be classified in two groups, viz. (a) Heterochain fibers, e.g., polyester, polyamide, polyurethane, polyurea fiber, etc., (b) Carbochain fibers, e.g. polyacrylonitrile, polyvinyl alcohol, polyvinyl chloride, polyolefi n and special purpose fluorine, etc., containing fibres. The macromolecules of heterochain fibres contain in their main chain carbon atoms and atoms of other elements, such as, oxygen and nitrogen. These polymers are usually obtained by polycondensation or polymerization of cyclic compounds. The macromolecules of heterochain fibers have a carbon skeletal chain, i.e., they contain only carbon atoms in the main chain. Such polymers are obtained by polymerization. Miscellaneous inorganic fibers are those fibers which are made from substances such as metal and glass. Both these materials have been used by man for a long time in forms other than textile fibres. Thus malleable and ductile nature suggested the use as textile fibres long ago, but the cost and technical difficulties hindered its wide use. Modern developments in converting both these materials into textiles have overcome the difficulties to ensure their modest regular use. Classification according to their ability to absorb moisture: From the point of view of wet processing the ability to bleach, mercerize, dye and give different finishes using chemicals to textile materials successfully depends on the ability to absorb moisture. The fibres which absorb moisture are called Hygroscopic or Hydrophilic fibres. Hydrophilic fibres are characterized by the presence of hydrophilic groups which attract water. For example, all the natural fibres have groups in their molecules which attract water. Moisture absorption of hydrophilic fibres is higher than hydrophobic fibres. Hydrophobic fibres are those which do not readily absorb moisture. All synthetic fibres, so far produced, contain very few water attracting groups. Absence of water attracting groups accounts for their low moisture absorption. The fibres which have lower moisture absorption are difficult to dye and bleach. Another disadvantage is that they develop static electricity charges quicker than hydrophilic fibers. This is an important factor which is responsible for some troubles during mechanical processing of fibers.

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Classification according to their thermoplasticity: The textile fibres can also be classified into two types, viz. 

Thermoplastic type



Non-thermoplastic type

Thermoplastic types are those which are deformable by heat and pressure, without accompanying chemical changes. This suggests that the thermoplastic types of fibres can be softened by heat, which means they can be moulded and heat set. The fibres which do not possess the above characteristic are designated as non-thermoplastic. Most of the synthetic fibres have thermoplastic properties. Regenerated acetate rayon may melt when ironed hot, and polyvinyl chloride (PVC) fibres are most heat sensitive type. Some synthetic fibres have thermoplastic properties which are more pronounced than those of acetate, notably polyamide and polyester. This property of thermoplasticity is used to heat set fabrics made from them and confer on them the dimensional stability. Also this quality is used to convert these fibres into new type of yarn such as Textured Yarn. Classification according to their utility: The textile fibres can be broadly classified into two types under this category, viz. 

Major textile fibres



Minor textile fibres

Major textile fibres are those which are widely used as textiles by the textile industry, e.g., cotton, wool, silk, jute, viscose rayon, acetate rayon, nylon, polyester, etc. Minor textile fibres are those which are used to a very much less extent as textiles (by the textile industry), e.g. banana fibres, abaca fibres, asbestos fibres, bamboo fibres, soybean fibres, pineapple fibres, metallic fibres, milk fibres, casein fibres, alginate fibres, rubber, etc.

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ESSENTIAL PROPERTIES OF FIBRES

PRIMARY CHARACTERISTICS OF TEXTILE FIBRE The primary properties of textile fibre is 1. Staple length 2. Tensile strength, 3. Fineness, 4. Spinnability 5. Uniformity Staple length - Staple fibres are short in length, measured in inches and range from three-quartos of an inch to 18 inches in length. All the natural fibres, except silk, are staple fibres. Any filament fibre can be cut into staple of a length determined by the end-use desired. Tensile strength - Strength of a fibre is the ability to resist strains and stresses. It is expressed as tensile strength which is measured in pounds per square inch (PSI) or as tenacity which is measured in grams per denier. Some fibres gain strength when wet, some lose strength, and some are unaffected by water. Fineness – In a fibre, the ratio or relationship if length to width or cross sectional area is expressed as its fineness. In coarse fibres the length is about 700 times more than the width. The ratio may be even 5000 in case of very fine fibres. Only fine fibres can produce fine yarn. Fineness does much to determine properties and characteristics of particular fibre and it also determines the end use of fibres. Spinnability – Spinnability includes several physical properties each having an effect on the ability of the fibres to be spun into yarn. For Example: Staple fibres must have to be capable of taking a twist. They must have a certain degree of friction against one another to stay in place when pull is applied to the yarn. And they must be able to take on hole special finishes for lubrication during spinning or to provide additional surface resistance to abrasion. Uniformity –This means the evenness of the individual fibres in length and diameter. A fibre possessing this property can produce reasonably even threads. This is also important in connection with the strength of the resulting yarn. The more uniform the yarn the stronger the yarn.

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SECONDARY CHARACTERISTICS OF TEXTILE FIBRE The secondary properties of textile fibre is 1. Crimp 2. Elasticity 3. Cohesion 4. Density 5. Plasticity 6. Absorbency 7. Resilience 8. Capillarity or Porosity 9. Color 10. Luster 11. Flexibility 12. Rigidity 13. Abrasion resistance 14. Static electric resistance Crimp - Crimp refers to the waves or bends that occur along the length of a fibre. Wool has natural crimp. Manmade fibres may be given a permanent crimp. Fibre crimp increases cohesiveness, resiliency, and resistance to abrasion. It helps fabrics maintain their thickness. Elasticity - Elasticity means the ability of a stretched material to return immediately to its original size. Cohesion - Cohesiveness is the ability of fibres to cling together. This is important in staple fibres, but unimportant in filament fibres. Density - Density and specific gravity are measured of the weight of a fiber. Density is the weight in grams per cubic centimetre. Specific gravity is the ratio of the mass of the fibre to the mass of an equal volume of water at 40°C. The weight of a fabric is determined by the density or specific gravity of the fibres. Plasticity - Plasticity is that property of a fibre which enables the user to 'shape it semipermanently or permanently by moisture, heat, and pressure or by heat and pressure alone. Absorbency - Absorbency is the ability of a fibre to take up moisture and is expressed as percentage of moisture regain, which is the percentage of moisture that a bone-dry fibre will 12

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absorb from the air under standard conditions of temperature and humidity. The ability of a fibre to absorb moisture is directly related to washability, dyeing, shrinkage, absorption of aqueous finishes, comfort on humid days, and soiling. Staple fibres hold more water than filament fibres since they pack less compactly and create a sponge-like condition in the yarn and fabric. For this reason staple fibre fabrics require a longer drying time. Resilience - Resiliency is the ability of a fibre or fabric to recover, over a period of time, from deformation such as stretching, compressing, bending or twisting. A resilient fabric has good crease recovery, hence requires a minimum of ironing. Resilient fabrics also retain high bulk. Capillarity or Porosity - These two terms express properties with the similar influence on the ability of a textile fibre or yarn to accept and hold a dye, a finish a lubricant or even resin in order to increase the wrinkle resistance of a fabric or to give it a wash and wear finish. Liquids passed rapidly through porosity. In the case of the passage of these liquids through the hollow centre or lumen in cotton or through small voids on the surface of wool fibre. It is usually regarded as the effect of the mechanism capillarity. Color – Most natural fibre have some colour. The synthetic fibres too have a slight creamy or yellow colour. For Example: Silk is yellow to tan, Wool is brownish tint, Cotton is a creamy white or brown Luster - Lustre is the shine, sheen or brightness of a fibre caused by reflection of light. Smooth fibres reflect more light than rough or serrated fibres; round fibres reflect more light than flat fibres. Filaments which are laid together with little or no twist reflect more light than short fibres which must be twisted together to forth yarns. Manmade fibres can be delustered by adding oil or pigments to the solution from which the fibre is spun. Flexibility - Pliability or flexibility is the ease of bending or shaping. Pliable fibres are easily twisted to make yarns. They make fabrics that resist splitting when folded or creases many times in the same place. Rigidity - Stiffness or rigidity is the opposite of flexibility. It is the resistance to bending or creasing. Rigidity and weight together make up the body of the fabric. Abrasion resistance - Abrasion resistance is the ability of a fibre to withstand the rubbing or abrasion it gets in everyday use. Inherent toughness, natural pliability, and smooth filament surface are fibre characteristics that contribute to abrasion resistance.

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Static electric resistance - Phenomenon of static electricity creates a problem in the spinning and other processing of textile fibres especially in rooms with very low relative humidity. The problem is much more severe in the case of synthetic fibres which have extremely low electrical conductivity and generally absorb too little moisture to provide a path where y the static electricity can be carried away. Static electrical properties create problems in the packaging and in the sewing. OTHER CHARACTERISTICS OF TEXTILE FIBRE 1. Wicking or wetting 2. Chemical resistance 3. Resistance to moths, and mildew 4. Flammability or inflammability Wicking or wetting - Wicking or wetting refers to the conduction of moisture along the fi...