2 Natural Fibres

K. Sangeetha

Objectives:

• Introduction to Natural fibres
• Classification of Natural
• fibres Manufacturing  /  preparatory process,  properties  and  end uses  of  Natural fibres.

INTRODUCTION

Fibres are the raw materials for all fabrics. Natural fibres have their origin from plants, animals and minerals. In most of the history, people used only natural materials or fibres for making cloth. The archaeological evidence indicates that flax and wool were woven into fabrics from the 6th century BC.

CLASSIFICATION

The natural fibre is the term covers a broad range of fibres obtained from natural sources such as plant, animal and mineral.

Figure: Classification of Natural Fibre

1. Plant Fibres

Plant fibres comprises of cellulose: Eg. Cotton, jute, flax, linen, ramie, sisaland hemp. Natural fibres can be further classified into,

1.  Seed fibres, collected from seeds or seed cases. Eg. Cotton and kapok.

2.  Fruit fibres, collected from the fruit of the plant. Eg. Coir

3. Bast fibres, collected from the bast or skin surrounding the stem of the plant.

Eg. Jute, flax, ramie and banana fibres.

4. Leaf fibres, collected from leaves. Eg. Pineapple, sisal and agaves.

The commonly used natural fibres are cotton, jute, flax, hemp, sisal and coir.

II. Animal Fibres

• Animal fibres are commonly obtained from hair or fur of animals and generally comprise proteins.
• Silk fibres are extracted from the cocoon of the silkworm. The fibres are spun into a smooth, shiny fabric with sleek texture.
• Wool refers to the hair of the goat or sheep.  The individual wool strands arecoated with scales and tightly crimped, as a whole it is coated with an oil known as lanolin,which is waterproof and dirt proof. Wool is commonly used for making warm clothing.The bulk yarn produced from carded fibre is referred to as Woollen, while a fine yarn spunfrom long fibres which are combed to be parallel are referred to as Worsted.
• Cashmere, the hair of the Indian Cashmere goat.
• Mohair, the hair of the North African Angora goat, is a type of soft wool.
• Alpaca  wool,  Ilama  wool  and  camel  hair  are  the  other  animal  fibresgenerally used in the production of jackets, coats, blankets and other warm coverings.
• Angora refers to hair of the Angora rabbit and is long, thick and soft.III.Mineral Fibres

Mineral fibres are naturally occurring fibre or slightly modified fibre procured from minerals.

Ex. Asbestos.

Plant Fibres

1.Seed fibres: Cotton

Cotton is of tropical origin but can also be cultivated successfully in temperate climates with well-distributed rainfall. Cotton is a fibre that grows from the surface of seeds in the pods or bolls, of a bushy mallow plant. The fibres are twisted, flat and ribbon like structure with a wide inner hollow (lumen) with an elongated single cell composed of 90% cellulose, 6% moisture and the remainder consists of natural impurities. The protective wax like coating is present at the outer surface of the fibre. The basic parameters that judge the quality of cotton are the grade, the colour and the length of the fibres and the character.

Production Process

The cultivated cotton bolls are cleaned to separate seeds, dirt, pods and short lint and then compressed into bales, which permits economical storage and transportation. The Cotton fibres are then converted into yarns and then to fabric.

Properties of Cotton Fibre

•  Good strength.
• Comfortable and Soft hand.
• Good absorbency.
• Good Color retention.
• It absorbs dye and Print well.
• Drapes well.
• Easy to sew and handle
• Machine-washable.
• Dry-cleanable

End Uses

Cotton is used in apparel, home furnishing and industrial fabrics. Cotton T-shirts and underwear are preferred for their absorbency and ease care. Men’s shirts and summer suits contain cotton and the fibre is predominant in women’s and children’s wear. Most of the bed sheets and pillow cases are blends of cotton and polyester and 100% cotton sheets are also available.

2.  Fruit fibres: Coir

Coconut fibres are extracted from the outer shell of a coconut fruit. It is called as coir fibre, which is coarser, thicker and durable fibre used for preparing many items from rope to floor mats. The fibre contains 46% lignin and 44% cellulose, the higher lignin composition in fibre makes it stiffer.

The fibres are extracted from both matured and immature coconuts. The quality of fibre depends upon their maturity. Brown color fibres are from matured coconuts which are thick, strong and have high abrasion resistance. White fibres are from immature coconuts which are smoother and finer, but also weaker.

Properties

Both brown and white coir consist of fibres length ranging from 4-12 inches. The fibers that are 8 inches long are called bristle fibre. Shorter fibres, which are also finer in texture, are called mattress fibre.

• Length in inches…6-8
• Tenacity (g/Tex) …10.0
• Breaking elongation%….30%
• Diameter in mm….0.1 to 1.5

After removal of coconut with shell from coconut fruit, the outer part of coconut is used for fibre extraction. They are soaked for about six to ten months depending upon the water quality, either immersed completely or partially this process is called as retting. After retting the decomposed particles are removed either by beating the fibre with wooden boards or with mechanical decorticators. They are then washed and dried. The dried fibres are used for spinning.

Uses

Coir is used in doormats, sacking, rope, brushes, rugs, mattresses, insulation panels and packaging, in geo textiles, automobiles and agro textiles.

3.    Bast fibres:

a. Linen

Linen fibres are found just behind the bark in the multi-layer stem of the flax plant. The fibres are removed from the woody stem and the inner pith called pectin. The fibres that are clamped together are rotted away, spun and used. Linen is suitable for the production of cordage, twine and linen thread for fine towelling and dress fabrics. Linen fabric is suitable for warm weather clothing. It feels cool in summer but appears crisp and fresh. Household linens are more supple and soft to touch.

Production Process

Flax plants with blue flowers yield the finest linen fibres. After about 90 days from seed planting, the matured stem of the plants are used for fibre extraction. The plants are either cut or often pulled out from the ground by hand, are tied in bundles are used for extraction. However, the plants are pull from the ground using the fairly efficient machines.

The plant is passed through coarse combs, which removes the seeds and leaves from the plant. This process called rippling is mechanized in many of the flax-producing countries. The woody bark which surrounds the fibre are decomposed by water or chemical retting, which loosens the pectin or gum that attaches the fibre to the stem.

Then the flax plants are squeezed and dried. The decomposed stalks are sent through the fluted rollers in order to break the stem and to separate the fibers from the bast. The process of breaking the stems into small pieces is termed as shives. The shives are then scutched using the machine to remove the broken shives with rotating paddles and thus the fibers are released from the stalks.

The fibres are straightened by combing to prepare them for spinning. Combing separates the short fibres from the longer and more luxurious linen fibres.

Physical and Chemical Properties of Flax

1. Strength

Flax is one of the strongest natural fibre, two to three times stronger than cotton and is second in strength after silk. Flax also increases about 20% in strength when wet.

2. Elasticity

Linen has no significant elasticity. It is the least elastic of natural fibres.

3. Resilience

Linen is relatively stiff and has little resilience.

4. Absorbency

Absorbency of linen is better than cotton. It absorbs moisture and dries more quickly. It has very good wicking properties. This makes the fibre comfortable to wear but difficult to dye and finish. It is therefore excellent for handkerchiefs and towels.

5. Density

Flax is one of the heavier cellulosic fibres.

6. Lustre

Flax has a silky lustre due to the natural waxes found in the fibre. If this wax is removed by chemicals or solvents, the fibre becomes brittle and harsh.

7. Effect of Light

Flax has good resistance to sunlight, but it will gradually deteriorate from

exposure.

8. Effect of Heat

Linen scorches and flames similar to cotton.

9. Drapability

Linen has more body than cotton and drapes better.

10. Resistance to Mildew

Dry linen has good resistance to attack by insects and microorganisms mildew, but stored in a warm, humid atmosphere supports the rapid growth of the fungus.

11. Heat conductivity

Linen allows the heat of the body to escape thus it is most suitable  for summer clothing.

12. Wash ability

Linen gives up stains readily.

13. Shrinkage

Linen shrink less than cotton and it is a great deal.

14. Reaction to Alkalis

Like cotton it has high resistant to alkalis. It can also be mercerized.

15. Reaction to Acids

Damaged by diluted hot acids and concentrated cold acids.

16. Affinity for Dyes

Has poor affinity for dyes. But it is possible to obtain good fastness dyed linen.

17. Resistance to Perspiration

Deterioration   is   obtained   with   acid   perspiration    and   not   with   alkali perspiration.

Uses

Linen is used for apparels, home and commercial furnishing items and industrial products.

3.Bast fibres: b. Jute

Jute is the cheapest natural fibre produced in large amount and has variety of usage. Since it is the plant material it comprises of cellulose and lignin. It is a lingo cellulosic fibre and falls into the bast fibre category.

Cultivation

To grow jute, farmers scatter the seeds on cultivated soil. The plants are thinned out at 15-20 cm tall. About four months after planting, harvesting begins. The plants are harvested after flowering, but before the flowers go to seed.

The warm and wet climate is suitable for growing jute. Thus jute is cultivated immediately after summer and during the fall season were the temperature ranging between 70-100°F and relative humidity of 70 – 80 %.

Retting

Retting is the process of extracting fibre from the stem or bast of the bast fibre plants. There are various types of retting namely chemical retting (using chemicals), mechanical retting (Hammering), vapour / stem / dew retting, microbial or water retting. Among them, the water or microbial retting is a century old but the most popular process in extracting fine bast fibres. The selection of retting depends upon the availability of water and cost of retting process.

The jute fibres are extracted from the jute plant were the small stalks are harvested for pre retting and is brought before 2 weeks of harvesting. If the fibre can easily be removed from the hard core of jute represents the crop is ready for harvesting.

The harvested jute stalks are tied into bundles and kept in the soft running water for 20 days. If the quality of the jute is better, the retting process may require less time. When the jute stalk is well retted, the stalk is grabbed in bundles and hit with a long wooden hammer to make the fibre loose from the jute core. After loosening the fibre, the fibre is washed with water and squeezed for dehydration. The extracted fibres are further washed with fresh water and allowed to dry on bamboo poles.

Properties of Jute

Good quality jute is coloured yellowish-white and silver-grey and has a lustrous appearance. The individual cells in jute are shorter than those of any of the other bast fibres. Jute is the weakest of the cellulose fibres when dry and must therefore be spun into coarse yarns. The average strength of jute is about 3.5 gm/denier. Resiliency is poor, and fabrics do not return to shape after deformation without treatment such as washing and ironing.

Jute has low sunlight resistance and poor colour fastness. It is also brittle and subject to splitting and snagging. It is readily damaged by the action of weather, moisture and abrasion.

Jute cannot be bleached white since it breaks in strong bleaches; hence it is used in its natural colour. To overcome the natural odour of jute and to make it softer, the chemical finishes can be used. Reaction of Jute to chemicals and heat is similar to other cellulosic fibres.

Uses

Jute is used for making sacks and cloth for wrapping bales of raw cotton. The jute fibres are woven into fabrics and utilised for curtains, chair coverings, carpets, area rugs, hessian cloth, and backing for linoleum.

3. Bast fibres: c. Hemp

The hemp fibre is obtained from the stem of the hemp plant and it is commonly called as “bast”, meaning it grows as a stalk from the ground. Hemp fibres can be 3 to 15 feet long, running the length of the plant. The hemp fibre naturally may be creamy white, brown, grey, black or green and it depends on the process used to remove the fibre.

Harvesting

The plants are cut at 2 to 3 cm above the soil and left on the ground to dry. The common method used for harvesting is Mechanical harvesting by using specially adapted cutter-binders or simpler cutters. The cut hemp is laid to dry for up to four days. This was traditionally followed by retting, either water retting or dew retting. Modern processes use steam and machinery to separate the fibre, a process known as thermo-mechanical pulping.

Properties

Hemp fibres has the characteristics of superior strength and durability. Hemp fibres are resistance to ultraviolet light rays, has good comfort and absorbency (8%).

Uses

Hemp is used for a wide variety of purposes, including the manufacture of cordage of varying tensile strength and clothing.

4. Leaf fibres: Pineapple

The fibre from the leaf of the pineapple frequently is labelled as “pina”. Matured pineapple leaves are used for fibre extraction. The fibres are extracted by either machine decortications or retting. After fibre extraction they are washed and dried for further process.

Properties and Uses of Pina

The commercial Pina fibers comes from the Philippines and its length is about 5 – 10 cm and are strong and lustrous. The matured fibre is white and especially soft and lustrous. In the Philippine Islands, it is woven into fine cloth, which is soft, durable and resistant to moisture.

Fabrics range in hand from crisp to very soft. Delicately embroidered clothing and accessories are often made of pina, it is also a cordage fibre. It is used for ship cables, power transmission cables and driving cables. Light coloured fibres are spun into coarser yarn, which are used for clothes and bags. Fine fibres are used for making interior fabrics. It is also used as a material for summer hats, brushes and paper making material.

I. 1. ANIMAL FIBRES SILK

Silk is also termed as “the queen of fibres”. Silk fibre constitutes of protein and can be woven into textiles. It is fine, strong and lustrous fibre composed of fibroin produced by the fibrous secretion of silkworms (cocoons). Silk appears as a triangular (prism) like structure which makes the cloth lustrous by reflecting the light at different angles.

Life cycle of silkworms

The life cycle of silkworm has the stages such as egg, larvae, cocoon, chrysalis and flies. The cycle begins with eggs of adult moth, the larvae emerges which feeds on mulberry leaves. This larvae is termed as silkworm which spins to form a cocoon around itself and transform into chrysalis. Then it breaks and emerges as a moth. Before the cocoon breaks it can be reeled into skeins.

Production Process: Sericulture

The cultivation of silkworm for the production of silk is termed as sericulture.

a. Breeding Silkworms

The breeding is carried out with the healthiest moths where the eggs are categorized, graded and tested for infection. The healthiest eggs are incubated and hatched usually in seven days They emerge as 3.2 mm long. They are maintained in a controlled environment. Breeding can occur normally three times per year.

b. Feeding the Larva

The larva (silkworm) feed on finely chopped mulberry leaves regularly for 20 – 35 days. The worms are about 3.5 inches in this period. They also shed their skins four times and changes its color to pink from grey.

c. Spinning the Cocoon

The silkworm constructs a symmetrical wall (cocoon) around itself by tossing its head front and back. The insoluble protein like filament called fibroin and sericin, a soluble gum is secreted from each of two glands called the spinneret located under the jaws of the silkworm. The sericin hardens as soon as it is exposed to air. Thus results in bave, the raw silk fibre. The caterpillar spins a cocoon and transforms from pupa to the chrysalis.

d. Stoving the Chrysalis

The moth emerges from breaking of cocoon by the chrysalis. Hence the chrysalis must be destroyed by stoving (application of heat) so that it does not break the silk filament.

e.The Filature – Sorting and Softening the Cocoons

The filature, the process of preparing silk thread from the cocoons sorting under different characteristics such as colour and size, so that the finished product can be of uniform quality. The sorted cocoons are then softened by soaking in hot water to loosen the sericin.

f.Reeling the Filament

Reeling can be done manually or automatically. The cocoon is brushed to locate the end of the fibre, threaded through a porcelain eyelet and the fibre is reeled onto a wheel. At the end of each filament a new fibre is twisted onto it to make a continuous thread.

g. Packaging the Skeins

The raw silk filaments are reeled into skeins. These skeins are packaged into bundles weighing 5 – 10 pounds (2 – 4 kg), called books. The books are further packaged into bales of 133 pounds (60 kg) and transported to manufacturing centres.

h. Forming Silk Yarn

Silk thread or yarn is formed by twisting the reeled silk. The skeins of raw silk are categorized and are soaked in warm water mixed with oil or soap to soften the sericin and then dried. As the silk filaments are reeled onto bobbins, they are twisted in a particular manner to achieve a certain texture of yarn. The silk yarn is put through rollers to make the width more uniform. The yarn is inspected, weighed, packaged and finally shipped to fabric manufacturers.

Fibre Properties

a. Physical Properties

Shape: Rounded corners with Triangular shaped cross section.

Lustre: Silk is a bright fibre with a natural shine.

Covering power: Due to thin filament form silk fibres have poor covering power.

Hand: Silk has soft texture, smooth and not slippery.

Denier: 4.5 g/d (dry); 2.8-4.0 g/d (wet)

b.Mechanical properties

Strength: Strongest of all the natural fibres; lose up to 20% of its strength when wet.

Elongation/elasticity: Moderate to poor elasticity.

 Resiliency: Moderate wrinkle resistance

c.  Chemical Properties

Absorbency: Good moisture regain of 11%.

Electrical Conductivity: A poor conductor of electricity suitable for cool weather.

Resistance to Ultraviolet Light: Weakened if exposed to too much sunlight.

Resistance to Biological Organisms: Attacked by insects, especially if left dirty.

Resistance to Acids: Yellowed by perspiration and dissolve in sulphuric acid.

End Uses

The Silk fibre may be use either with blend of other fibres for luxury apparels and household textiles. Silk fabrics has wide range of constructions and weights. Silk fabric is used for making men’s neckties. It has good hand and drape. Silk fibers are also made into handmade rugs, fine draperies and upholstery fabrics.

Very fine silk filaments are used in eye surgery. Silk sutures still are used by surgeons. The protein fibre is believed to be more compatible with human tissues than sutures of other materials.

2. WOOL

Wool fibre is derived from sheep. It was probably the first animal fibre to be made into cloth. The art of spinning wool into yarn was developed in 4000 B.C. The wool is soft, curl and dense hair obtained from sheep and other mammals like goat and alpaca. The fibres consist of protein called keratin covered by minute overlapping scales. The length of the fibre ranges from 1.5 to 15 inches depending on the breed of the sheep. The fibre consists of three essential components such as cuticle (outer layer), cortex (inner layer) and medulla.

Production Process

The following are the major steps necessary to process wool from the sheep are: shearing, grading and sorting, cleaning and scouring, carding, spinning, weaving and finishing.

a. Shearing

Sheep are sheared usually in spring once a year. A shearer can shear up to 200 sheep per day. The fleece recovered from a sheep can weigh between 6 and 18 pounds. Most of the sheep are still sheared by hand. New technologies are also developed to use computers and sensitive robot-controlled arms to do the clipping.

b. Grading and Sorting

Grading is the breaking up of the fleece based on overall quality as high quality does not always mean high durability. From different parts of the body the wool is broken up into sections of different quality fibres in sorting. The wool comes from the shoulders and sides of the sheep is the best quality used for clothing. To make rugs the lesser quality comes from the lower legs of the sheep used. Based on the measurement of the wool’s diameter in microns the wool is also separated into grades.

c. Cleaning and Scouring

Raw or grease wool refers to the wool taken directly from the sheep which contains dirt, sand, grease and dried sweat (suint). The weight of contaminants is about 30-70% of the fleece’s total weight. To remove these contaminants, the wool is scoured in a series of alkaline baths containing water, soap and soda ash or a similar alkali. The byproducts (lanolin) from this process are saved and used in a variety of household products. The excess water from the fleece is squeezed using rollers but not allowed to dry completely. Then the wool is treated with oil to increase manageability.

Differences between Woollen and Worsted

In the spinning operation, the wool roving is drawn out and twisted into yarn. Woollen yarns are chiefly spun on the mule spinning machine. Worsted yarns are spun on any kind of spinning machine mule, ring cap or flyer.

The differences between woollen and worsted yarns are as follows:

• Strength: Wool fabrics are said to be very durable at the same time wool fibres are weak. Wool has excellent Flexibility. 20,000 times without breaking wool can be bent back. Resilience: Its resiliency is greatest when it is dry and lowest when it is wet.

• Heat Conductivity: It is said to be poor conductor of heat, to retain its normal temperature they permit the body and are excellent for winter clothing.
• Absorbency: Without feeling damp wool can absorb about 20% of its weight in water. Cleanliness and
• Wash ability: To wool fabric dirt tends to adhere. If the fabric is washable consequently wool requires frequent dry cleaning or laundering.
• Effect of Heat: At 100° C wool becomes harsh and slightly at higher temperature it begins to decompose.

• Effect of Light: Weakened by prolonged exposure to sunlight.

b. Chemical Properties

• Resistance to Mildew: Mildew develops if left in a damp condition.

• Reaction to Alkalis: Quickly damaged by strong alkalis. Hence mild alkali in warm or cool water can be used in scouring the raw wool fibers to remove grease. Acids Reaction: Damaged by hot sulphuric acid and not affected by other acids even when heated.

• Affinity for Dyes: High affinity for dyes. The use of chrome dyes assures fastness of colour and effectively a variety of other dyes used.

• Perspiration Resistance: Weakened by alkali perspiration as it generally cause discolouration.

• Flammability: Burns very slowly and it is self-extinguishing and is normally regarded as flame-resistant.

Press Retention: Has good press retention. It takes and holds creases well and is set by use of pressure, heat and moisture.

End Uses

Suits, overcoats, dresses and underwear are commonly made from wool. In addition to clothing, wool has been used for felt, carpeting, insulation and upholstery.

II. Mineral Fibres: Asbestos

Asbestos is non-metallic and non-inflammable in nature. Asbestos fibre could be woven as fabrics for various uses like curtains for theatres, industrial uses, etc. Since it is a flame-resistant fibre, it can be used in the manufacture of safety clothing for fire fighters and insulation products like hot-water piping.

Manufacturing

The first step begins with fiberizing asbestos and freeing it from rock impurities. The fibres are then carded into a sheet, and then separated into roving which are wound on jack spools, and spun into yarn. Yarn can be made into thread, cord or rope. Metallic yarns are made by adding strands of fine brass, copper or lead wire to the strands of asbestos. The yarns can be woven into fabrics.

Crude fibre is  generally prepared for spinning at the factory where it is to be spun.

Preliminary treatment of fibre is usually accomplished in a pan crusher. Crude fibre is fed into the pan and scrapers push the fibre under the rotating wheel. This operation is very critical since it can mechanically break the fibres. Special techniques and such engineered rolls as rotary-toothed cylinders have been devised to reduce damage of fibres.

After crushing, the fibres are transferred to opening devices which actually fiberize the product further. The opened fibres pass over shaking screens or through trammel screens where they are again cleaned. Final operation generally involves lifting of suitable asbestos fibres by air suction.

Blending of such fibres as asbestos with cotton can be performed in the preliminary mixing operation prior to the carding operation. However, the blending is generally performed during the carding operation. Carding rolls are fitted with a series of sharp steel bristle rotating brushes which comb the fibres into specific positions. During this combining operation short fibres and minute contaminating products such as rocks are removed. The result of carding is that opened asbestos fibre is formed into a loose continuous sheet or blanket.

Properties

• Resistant to micro-organisms or insects.
• Resistant to heat, burning and chemical attack.
• Possess high tensile strength.
• Possess low electrical conductivity.
• Flexible enough to aid spinning.

• UsesAsbestos is used in insulation, building-construction materials, textiles, missile and jet parts, and in friction products such as brake linings.

REFERENCES:

•  Corbman, Bernard P. Textiles: Fiber to Fabric. 6th ed. McGraw-Hill, 1983.
•  Deshpande, Chris. Garrett Educational Corporation, 1995.
• Jerde, Judith. Encyclopedia of Textiles. NY: Facts on File Inc., 1992.
• Koob, Katharine. Linen Making in New England. North Andover, MA: Merrimack Valley Textile Museum, 1978.
• Parker, Julie. All About Silk: A Fabric Dictionary & Swatchbook. Rain City Publishing, 1992.
•  Scott, Philippa. The Book of Silk. Thames & Hudson, 1993.
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