Tuesday, August 4, 2020
TEXTILE FIBRES
TEXTILE FIBRES
Objectives:
1. Introduction about textiles.
2. To know about the textile fibres and their classification.
3. Primary and secondary characteristics of textile fibres.
INTRODUCTION
Textiles are called as second skin for humans. Textile material helps us to protect our body from environment. It helps for aesthetic appeal and special purposes also decoration. A textile fabric is a flexible material consisting of either natural or artificial fibres arranged to form like a thread often referred to as Yarn. Yarn is produced by spinning the fibres with short fibres or long strands. Textile fabrics are produced by weaving , knitting, knotting,crocheting etc with yarn or pressing fibres together (non-woven).Textile fabrics are used in various areas of application that includes agricultural, medical, automobile, geo textiles, home textiles and protective textiles. So textile plays an important role in our daily life.
Textile fibre
The basic element of textile is fibres, which are usually converted in to yarn and then fabric. A textile fibre can be natural or artificial. Textile fibres are either collected or extracted or manufactured from a variety of sources and their quality vary considerably in term of strength, colour, texture, size, shape and surface quality. A textile fibre's physical and chemical properties always have a high impact on characteristics and end use performance.
Textile fabrics can be prepared by using natural fibres or artificial fibres. Some yarns are made from single variety of fibre, whereas mixing or blending various types of fibres in different combinations produce variety of quality in the product. So mixing of different fibres and proportions can be planned according to the product’s quality requirement. Fibres either can be mixed in spinning process is called as blending, or different varieties of yarns can be combined in weaving process is called as mixing. The fabrics are termed as ‘blended’ and ‘union’ fabrics respectively. For example - Polyester-cotton and silk-cotton.
Classification of Fibres:
Fibres are the basic elements for textiles and they can be either procured from plants and animals or manually prepared in industry. Natural fibres are collected or extracted from fibre yielding plants, but artificial fibres are manufactured by regenerating natural cellulose, protein and synthesising chemicals. Artificial fibres can be produced in large quantity with less cost compared to natural fibres.
The fibres can be classified according to their source (I) or their fibre length (II). According to the source it is classified as natural or artificial and according to the fibre length- staple or filament.
CLASSIFICATION: I
As per the source broadly classified into two categories such as
1. Natural fibres
2. Artificial fibres
Which are again classified into many sub-groups based on their source of origin.
Figure: Classification of Fibres
1. Natural fibres:
Natural fibres are the fibres which have their origin from the natural sources like plants, animals and minerals. These fibres are again classified into following types.
A. Plant fibres:
The plant fibres are also called as Cellulosic fibres. These fibres are extracted from various parts of the plants such as seed, fruit, bast, stem and leaf. These fibres include cotton, linen, jute, flax, ramie, sisal, hemp, coir and so on. These fibres are categorised into following sub-groups based on their origin from plants.
a. Seed fibres: These are the fibres obtained from seeds of the plant. E.g. Cotton and Kapok.
b. Fruit husk fibres: Fibres which are extracted from fruits of the plant are termed as fruit husk fibres. E.g. Coir (coconut fibre) and palm fibre.
c. Bast fibres: These fibres are also termed as Stalk fibres. The fibres are obtained from the stalk or stem of the plant. E.g. Flax, jute, hemp, ramie and banana fibres.
d. Leaf fibres: Fibres are collected from plant leaves. E.g. Sisal and pine-apple.
B. Animal fibres:
Animal fibres generally comprises of proteins. These fibres are commonly obtained from hair or fur of the animals or from cocoons. These types include fibres like silk, wool and hair of rabbit, mohair, catgut, camel, alpaca and so on. These fibres are divided into three groups such as
a. Silk: The fibre or filament obtained by unwinding the cocoons of the silkworm. These fibres are generally fine, smooth and lustrous.
b. Wool: It refers to the hair of the domestic sheep or goat. These fibres are coarse, crimpy, warm and dull.
c. Hair: These are the minor fibres obtained from the hair of animal species like angora, camel, rabbit, cashmere and alpaca.
C. Mineral fibres:
These are the naturally occurring fibres modified from the minerals. Asbestos is the only commercially available natural mineral fibre.
2. Artificial fibres:
Artificial fibres are also termed as man-made fibres. In general, artificial fibres are extruded from the spinneret as a filament by modifying the cellulose, protein or synthesising chemicals. These fibres are flexible, fine, durable and resistant. The artificial fibres are categorised into different groups based on their extraction.
A. Regenerated Biopolymers:
Regenerated biopolymers are the fibres obtained by modifying the cellulose obtained from the plants. The manufacturing process consists of bringing a natural high polymer substance into solution in a suitable way and extruding this solution through a nozzle, regenerating the same high polymer in the form of a solid filament. These fibres are again categorised into two groups namely,
a. Polynucleic acid / Polyamino acid: The group includes fibres obtained from materials such as DNAs, collagen, elastin, soy proteins and silk proteins.
b. Cellulosic: The fibres obtained from modifying the natural celluloses. This group includes fibres such as acetate, polynosic, rayon, triacetate and microbial cellulose.
B. Synthetic polymers:
The chemicals are synthesised into polymers by various process and are extruded as filaments. Some examples of synthetic polymers are elastane, kevlar, acrylics, polyamides, polyesters, polyolefin, polyurethane and vinylone.
C. Minerals:
The minerals are made in the form of fibres by following several steps. The following are some of the examples of mineral fibres. Basalt, carbon, ceramic, glass, metallic fibres such as gold and silver zari threads, silicon carbide and stainless steel. These fibres are strong and durable.
CLASSIFICATION: II
According to the fibre length fibres are classified into two categories such as
1. Staple fibres
2. Filament fibres
1. Staple fibres
Short length fibres are called as staple fibres and they vary from ½ inch to 18 inches. All the natural textile fibres (Cotton, wool and flax) except silk fibre are staple fibres. The length and quality of natural textile fibre vary according to seed variety, quality of soil, fertilizers, climatic conditions, cultivation methods and fibre extraction or collection methods. The artificial staple fibres are produced as long filament and cut into small lengths determined by the end-use desired.
2. Filament fibres
Long textile fibres are called as filament fibres. Silk and artificial fibres are filament fibres. The artificial fibres are long measured in metres and have less variation because they are manufactured based on the end use.
FIBRE PROPERTIES
To be spinnable, a textile fibre must have sufficient length, strength, texture, pliability and cohesiveness to form as a yarn or thread. A good textile fibre is always be available and constant in supply to be economically suitable for mass production. To produce such a fabric the manufacturer chooses fibres, yarns, weaves and finishes with a combination of properties which will give the type of serviceability a consumer wants.
1.Primary or basic Characteristics of Textile Fibre
The basic or primary properties of textile fibre are
1.1 Fibre length
1.2 Strength
1.3 Fineness
1.4 Crimp
1.5 Cohesion
1.6 Spinnability
1.7 Density
1.8 Colour
1.9 Lustre
1.1. Fibre length – length is one of the most important property for textile fibres. Textile Fibre length is measured in inches or centimetres and it should possess range from three- quarters of an inch to 18 inches.
1.2. Strength – the second most important property of textile fibre is its strength. Strength is paramount in determining its serviceability or durability. Strength of a fibre is the ability to resist strains and stresses or maximum tension it sustains before it breaks. Fibre strength is determined either by single or by bundle of fibres. Tensile strength is expressed as pounds per square inch (PSI) or in tenacity (breaking load per unit fineness) as grams per denier.
Strength varies from fibre to fibre and textile industry requires atleast I gram per denier. Some textile fibres gain strength when wet, some lose strength and some are unaffected by water. The fibre elongates or extends when the load or force is applied. The amount of extended length (elongation) in percentage is called as fibre extension.
Extension=elongation*100/initial length
1.3. Fineness – In a fibre, the ratio or relationship of length to width or cross-sectional area is expressed as its fineness. The fineness is sometime defined in terms of its diameter which is suitable for circular cross-section fibres. Textile fibres either natural or artificial come in various forms and cross-sectional shapes like wool -circular, cotton and silk- irregular cross-sectional shapes. The fibres with irregular cross-section are measured for fineness by taking the mass of a known length of fibre which is termed as linear density and is expressed as weight per unit length. In case of coarse fibres the length is 700 times more than the width. For very fine fibres the ratio is upto 1:5000. Usually fine textile fibres can produce fine yarn and fine fabrics. Fibre properties, characteristics and end uses are determined by the fibre fineness.
1.4. Crimp - Crimp refers to the waves or bends that occur along the length of a fibre. Fibre crimp increases cohesiveness, resiliency, and resistance to abrasion of fibre. Fibre with more crimp mingles with other fibres which aids in spinning and produces a thin yarn. It helps a fabric to maintain the thickness of the yarn and fabric with better compressional resistancy and loft. Wool has natural crimp which is favourable to the production of bulky yarns that aids in thermal insulation. Manmade fibres may be given a permanent crimp as per the requirements.
1.5. Cohesion - Cohesiveness is the ability of fibres to cling together or adhering to one another when spun into yarn. This property is due to nature of the surface, physical shape and contour of the individual fibre. This is important in staple fibres. Whereas cohesiveness is unimportant in filament fibres because long fibres can be twisted together without true cohesion between fibres.
1.6. Spinnability – when a fibre is spinnable it is considered as suitable for textiles. So textile fibres either staple or filament must be able to hold a twist. Spinnability includes several physical properties each having an effect on the ability of the fibres to be spun into yarn. The fibres must also have a certain degree of friction against one another to stay in place when pull is applied to the yarn.
1.7. Density - Density and specific gravity are measured of the weight of a fibre. 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. For any given weight, the fabrics made from low density fibre will have a bulkier appearance than those made from high- density fibres.
1.8. Colour – Most natural fibres have some natural colour. The colour of artificial fibres can be changed as per the need.
1.9. Lustre - Lustre is the shine, sheen or brightness of a fibre caused by reflection of light. The physical structure and shape of fibre influences the lustre. 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 form yarns. Manmade fibres can be delustered by adding oil or pigments to the solution from which the fibre is spun. Various finishing methods are used for changing the unwanted lustre by depositing on or within the fibre.
2. Secondary Characteristics of Textile Fibre
The secondary properties of textile fibre is
2.1. Elasticity
2.2. Plasticity
2.3. Flexibility
2.4. Rigidity
2.5. Resilience
2.6. Uniformity
2.7. Absorbency
2.8. Wicking or Wetting
2.9. Abrasion Resistance
2.1. Elasticity - Elasticity means the ability of a stretched material to return immediately to its original size. It is an essential property that a fibre must have certain amount of extensibility so as to withstand sudden strains placed on it.
2.2. Plasticity - Plasticity is the property of a fibre which enables the user to shape it semi- permanently or permanently by moisture, heat and pressure or by heat and pressure alone. Both fine and coarse wool fibres are usefully become annealing like plastic under the influence of heat and moisture.
2.3. Flexibility - Pliability or flexibility is the ease of bending or shaping. Pliable fibres are easily twisted to make yarns. Any textile fibre must be sufficiently flexible because it will be subjected to considerable twisting, bending and flexing during spinning, weaving, processing and during its use. Flexibility in fabrics resist splitting when folded or creased many times in the same place.
2.4. Rigidity - Stiffness or rigidity is the opposite of flexibility. Fabric rigidity is the resistance to bend or crease. Both rigidity and weight together makes up the body of the fabric.
2.5. 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. Polyester always shows good recovery after deformation due to its higher resiliency than cotton, silk and wool fabrics which show delayed wrinkle recovery.
2.6. Uniformity –This means the evenness of the individual fibres in length and diameter or size. Uniform dimension supports the fibre to make better and smoother yarn. Artificial fibres are more uniform than natural fibres. Uniformity in fibre and yarn is an important property which influences the strength of the resulting yarn and smooth surface in fabric. The more uniform the yarn the stronger is the yarn.
2.7. Absorbency - Absorbency is the ability of a fibre to take up moisture and is expressed in percentage. It depends upon the chemical and physical structure and properties of the fibre as well as humidity or temperature of the surroundings. Moisture regain percentage is the percentage of moisture that a bone-dry fibre will absorb from the air under standard conditions of temperature and humidity. The ability of a fibre to absorb moisture is directly related to wet processing processes like dyeing, finishing, washing, shrinkage, soiling and drying. Staple fibres hold more water than filament fibres since they are packed less compactly and create a sponge-like condition in the yarn and fabric. For this reason staple fibre fabrics require a longer drying time. The fabrics made from low regain fibres dry quickly. The fabrics made from high regain fibres are considered as comfortable fabrics because of their absorption-desorption properties. Absorbency is very much required for apparel fabrics as the sweat needs to be absorbed into the fabric to keep the wearer dry. The moisture absorption in fibres affects its strength and dimensional, mechanical, electrical and frictional properties.
2.8. Wicking or Wetting - Wicking or wetting refers to the conduction of moisture or water along the fibre or through the fabric, although the fibre itself does not absorb much moisture. This property is related to surface wetting and is not the same as absorbency.
2.9. Abrasion Resistance - Abrasion resistance is the ability of a fibre to withstand the rubbing or abrasion it gets in everyday use. If a textile fibre is able to withstand the abrasion forces or absorb and scatter these forces without any damage, it is called as fibre with good abrasion resistance. Inherent toughness, natural pliability and smooth filament surface are fibre characteristics that contribute to abrasion resistance. A rigid and brittle fibre always shows poor resistance than a tough and more plastic fibre. Dyes and finishes used in textiles affect the abrasion resistance.
3. Other Characteristics of Textile Fibres
3.1 Capillarity or Porosity
3.2 Static Electric Resistance
3.3 Chemical Resistance
3.4 Flammability or Inflammability
3.5 Resistance to Moths and Mildew
3.1. 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, to finish with a lubricant or 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 of capillarity.
3.2. 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 case of synthetic fibres which have extremely low electrical conductivity and generally absorb too little moisture to provide a path where the static electricity can be carried away. Static electrical properties create problems in packaging and sewing.
3.3. Chemical Resistance - The chemical reactivity of each fibre depends on the arrangement of the elements in the molecule and the reactive groups it contains. Dry-cleaning solvents, perspiration, soap, synthetic detergents, bleaches, atmospheric gas, soot and sunlight may all cause chemical degradation on some or all of the fibres.
3.4. Flammability or Inflammability - Flammability or inflammability refers to the ease of ignition and the speed and length of burning. Non-flammable fibres will not burn. Flammability depends not only on the chemical composition but also on the air incorporated in the yarn or fabric. Finishes can also be added to make fibres non-flammable.
3.5. Resistance to Moths and Mildew - Resistance to moths and mildew is due to the chemical composition of the fibre. These properties are important to the consumer because they indicate the type of care needed during use as well as during storage. Fibres with less or without natural resistance must have protective finishes added or have their chemical composition changed to make them resistant.
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