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Textile fibre-1

Technically the term “fibre” or textile fibre means a unit of matter which is capable of being spun into a

yarn or made into a fabric of any nature or character.

According to textile institute, fibres are defined as the units of matter characterized by fineness, flexibility

and high ratio of length to thickness.

The most useful fibres should have length to breadth ratio more than 1000:1

Typical ratios for several natural fibres are as follows:

Cotton=1400, wool=3000, silk=33×106

Classification of textile fibre:-

Classification of textile fibres can be done in many ways. Some of them are as follow

a) Classification according to their nature and origin

b) Classification according to their ability to attract water, i.e. moisture absorption.

c) Classification according to their thermo plasticity.

a) Classification according to their origin:-

i) Natural fibres ii) Man-made fibres

i) Natural fibres:-

The term natural fibres means any fibre that exists as such in the natural state. They are obtained from

plants, animals, or minerals and can be further classified into three following groups

Vegetable fibres:

Fibres growing on the seeds cotton, kapok etc

Fibres are grown as the skin of plants stem Flax, Ramie, Hemp, jute etc

Fibres collected from leaves sisal, abaca or marila etc.

Animal fibres:-

After the coagulation of the mucus thrown up by the body of silk wonk silk fibre

Fibres are found from Hairy fibre sheep wool, cashmere wool, camel wool, mohair etc.

Minerals fibres: - The only natural fibre occurring from minerals in asbestos. There are several

kinds of asbestos fibres, all of which are fire resistant and not easily destroyed or degraded by

natural process. They are usually used as the non combustible insulation materials.

ii) Man made or artificial fibre: Manmade fibres mean any fibre which is derived by an artificial

process from any substance. The man made fibre can be classified in four groups:

Regenerated fibre: the fibres regenerated from natural cellulose sources like wood pulp or cotton linters

are referred to as regenerated fibres. However a certain variation in degree of polymerization occurs

resulting in some modified physical properties of the regenerated fibres that essentially differ from the

original one. i.e. viscose rayon, polynosic, cupro, lyocell etc belong to this category.

Cellulose fibre:

Cellulose fibre belong all those fibres which consists completely or to a large part of cellulose.

Cellulose is a long chain of linked sugar molecules. With regard to the chemical constitution, I is a

hydrophilic long stretehed macromolecule with primary and secondary hydroxyl (-OH) groups.

Textiles fibres are composed of pure cellulose are:

Natural cellulosic fibre: Abaca, cotton, coin, jute, flax, hemp, sisal etc.

Man made cellulosic fibres: Viscose rayon, cupro, lyocell

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Cotton:

Cotton is a natural cellulose, seed, mono-cellular, staple fibre.

Chemical composition for raw cotton:-

The cotton polymer:-

The cotton polymer is a linear, cellulose polymer. The repeating unit in the cotton polymer is cellobiose

which consists of two glucose units.

The cotton polymer consists of about 5000 cellobiose unit that is its DP (degree of polymerization) is about

5000. It is very long, linear polymer, about 5000 nm in length and about 0.8 nm thick.

The most important chemical groupings on the cotton polymer are the hydroxyl (-OH) groups. These are

also present as methanol groups or -CH2OH. Their polarity gives rise to hydrogen bonds between the –OH

groups of adjacent cotton polymers.

Cotton is a crystalline fibre. Its polymer system is about 65 to 70 percent crystalline and correspondingly

about 35-30 5 amorphous.

Physical properties of cotton

i. Tenacity: the strength of cotton fibres is attributed to the good alignment of its long polymers (that is

its polymer system is about 70% crystalline), the countless, regular, hydrogen bond formations between

adjacent polymers and the spiraling fibrils in the primary and secondary cell walls. It is one of the few

fibres which gains strength when wet. It is thought this occurs because of a temporary improvement in

polymer alignment in the amorphous region of the polymer system. The improvement alignments when

wet result in an increase in the number of hydrogen bonds, with an approximate 5 % increase in fibre

tenacity.

ii. Elastic plastic nature: The cotton fibres are relatively inelastic because of its crystalline polymer

system and for this reason cotton textile wrinkle and crease readily. Only under considerable strain will

cotton polymers give and side past with one another. They are usually prevented from doing so by their

extreme length and countless hydrogen bonds which tend to hold them within their polymer system,

components Percentages

(%)

Cellulose 94

Protein 1.3

Pectic substance 1.2

Ash 1.2

Fat and wax 0.6

Organic acid, sugar &

others

1.7

Figure: Morphological diagram of cotton fibre.

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iii. Hydroscopic nature: the cotton fibre is very absorbent owing to the countless polar –OH groups; these

attract water molecules, which are also polar. However the water can only enter the polymer system in

its amorphous regions, as the inter polymer spaces in the crystalline regions are too small for the water

molecules. Aqueous swelling of cotton fibre is due to a separation or forcing apart of polymers by the

water molecules in the amorphous region only.

Moisture absorption of fibre at 65% RH and 20ºc

iv. Thermal properties: Cotton fibre shows an excellent resistance to thermal decomposition. They have

ability to conduct heat energy and do not allow any destructive heat accumulation. Thus they can

withstand high temperature. Excessive application of heat energy causes the cotton fibre to char and

burn. Without any prior melting. This is an indication be attributable to the extremely long fibre

polymers and the countless hydrogen bonds they form.

v. Effect of light: The visible area of the spectrum of the sunlight lies naughty between 400 and 800 nm

(violet to red). The light having a wave length less than 400 nm, is the ultraviolet portion of the sun

light. In order to carry out a breakage or degradation of cellulose structure of cotton, it is required to

have a wave length of the light less than about 340 nm. This is why under the action of day light cotton

is not subjected to any change at all. But there is a gradual loss of strength in case of prolonged

exposure and the color turns yellow. The degradation reaction is further promoted by high temperature

and high humidity. It has been observed that a considerable loss of the strength (about 50% of the

initial value) of various textile fibres occurs by exposing them to the sun light for a longer period of

time.

Types of fibre Degradation period (hours)

Natural silk 200

Viscose 900

Cotton 940

Flux 999

Wool 1120

The effect of light may be varying depending on the type and structure of goods. For example, the heavy

fabric are more resistance to day light than the light fabric. It has been reported that the strength of grey

cotton fabrics is reduced not as much as the bleached one when both are exposed to the sun light together

for the same period of time. They higher sensitivity of bleached cotton to the day light is attributable to

same metal contents (e.g. copper, manganese, iron etc) added to fibre during processing that may promote

the oxidation process.

Fibre Moisture content

(%) Cotton (Raw) 7-8

Cotton

(Mercerized)

11.0 Flux 9-10

Jute 10.5

Viscose (normal) 13.5

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Chemical properties of cotton:

i. Effect of acid: Cotton fibres are weakened and destroyed by acids. Acidic conditions hydrolyse the

cotton polymer at the glycoside O2 atom, which links the two glucose units to form the cellobiose unit.

As the degradation proceeds, cellulose loses its strength gradually and ultimately a complete rupture of

total infrastructure takes place giving a friable powder. The degree of modification of the properties

depends however to a large extent on the time of contact, temperature and concentration of acid.

ii. Effects of alkalis: The glucosidal linkage of cotton cellulose is highly resistant to alkali particularly at

lower temperature. The resistance is attributed to the lack of attraction between cotton polymers and

alkalis. But the boiling in 1 % solution of caustic soda causes weight of cotton due to the removal of

non cellulose substance4 from the fibres.

The treatment with a strong solution of caustic soda, known as mercerization, is usually performed 28-

30 „Be‟ caustic soda. Mercerization is usually done in textile processing of cellulosic fibres with a view

to improve their affinity to dye stuffs, dimensional stability, chemical reactivity, luster, tensile strength

and smoothness. The treatment under tension assists the cotton polymers align themselves in a regular

way leading to an increase in hydrogen bond formation which is responsible for the additional strength

of the fibre. Luster is due to primarily to reflection from large group of the smoothed fibre surfaces.

When treatment is carried out under tension, the swollen fibre takes on a smooth cylindrical form

becoming more regular in structure, enabling it to reflect the incident light more evenly. This results in

increasing the luster of the fibre.

iii. Effect of bleaches: The most common bleaches used on cotton textile materials are sodium

hypochlorite and sodium perborate. Sodium hypochlorite (NaOCl) is a yellowish liquid, smelling of

chlorine. Sodium perborate (NaBO2H2O2, 3 H2O) is a white powder, contained in most commonly

available domestic laundry detergents. Sodium hypochlorite bleaches cotton textile materials at

prevailing room temperature. However bleaching with sodium perborate is more effective when the

laundry solution exceeds 50ºc in temperature.

iv. Effect of micro organisms: Cotton fibre can be resist moths and most insects, but its natural

constituents that serve as food for the fungi; do make it a candidate for mildew. Mildew causes

weakening and noting the fibre material often characterized by a mostly smell. Cotton fibres also

contain mineral substance, which promote their growth. The presence of starchy material as a sizing on

a finishing agent also promotes the growth of the mildew. Nevertheless the micro organism can obtain

their necessary carbon from the cotton cellulose. If the textile industries it is frequently necessary to

store the fabric for a considerable time. If they are not properly stored on no protection are taken, the

mildew can develop. Besides of the attack of bacteria can be so harmful that the loss in weight of

fabrics may be up to 17.5%. A widely used method of protecting cotton fibres from attack of micro

organism is the application of some substance such as cupper napthenate ((CH2)nCOO)2 Cu and

polychlorophenols, which either inhibit further development or kill the micro organisms. It is also

possible to winds the organism by chemical modification of the fibre. The partial substitution of

hydroxyl groups of glucose units, as for instance, partial acetylation imparts an appreciable degree of

rot resistance. This is why the acetate fibre is less susceptible to bacteria than natural and regenerated

cellulose fibres.

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Cotton ginning:

Cotton as it is picked in the field still contains the seed and is known as “seed cotton”. The fibre constitutes

about one third of the total weight of seed cotton, the remainder being seed.

Ginning is accomplished commercially with either a “saw” gin used mainly for intermediate and short

staple cottons. Roller ginning is slower and more expensive than saw ginning, production per unit being in

the ratio of about 1:10, but it eliminates damage to the long fibres.

After the cotton has been gathered, the cotton fibres are to be separated from the seeds by a process known

as “Ginning” in which it is passed between rotating knife roller where by cotton fibres are pulled off the

seed. The ginned cotton fibre is technically known as “Lint”. The seeds are then collected to be utilized for

the manufacture of cotton seed oil, and the residue used as fodden. At the present time these seeds are

furthers declined by passing through specially constructed gins. The fibre obtained is known as “Linters”.

It is widely used both as a filter in mattresses and upholstery and after purification as chemical or rayon

pulp.

The lint fibres collected after the ginning process will have their upper end tapering to a point while basal

end is open.

Ginning process:-

When it has been cut off from the seed, fragments of seed coat, leaves or stem and accidental dirt may also

be present in the ginned cotton.

The ginned cotton is graded, depending on the quality of the fibre before pressing them into bales. The

fibres which are packed into bales are then dispatched to the spinning molls.

Specification of cotton:

Points Description

Shape and length Fairly uniform in width, 12-20 micrometers. Length varies from 1 cm to 6

cm (0.5 to 2.5 inches). Typical length is 2.2 cm to 3.2 cm

Luster Low

Tenacity (strength) At dry>3.0-5.0 g/d; at wet > 3.3-6.0 g/d

Resiliency Low

Density 1.54-1.56 g/cm3

Moisture absorption Raw (7-8.5%); Mercerized 11%

Fineness Diameter from 11μm – 22 μm

Figure: Cotton ginning

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Silk:

Silk are usually referred to as queen of the fibre as it is only natural, protein filament fibre. Traditionally

established with wealth rank and it has always been expensive.

Structure of silk:

Silk consists of chiefly of amino acids with low

molecular weights. The polypeptide chains of the

silk may contain relatively few side chains. The

raw silk strand consists of two silk filaments

encased by a protein called sericin.

The thickness of raw silk strand and its uneven

and irregular surface are due to the coating of

sericin which gives raw silk a coarse handle.

The amount of sericin is usually 22-23% of the weight of raw silk. The ability of a silk cocoon to withstand

prolonged exposure to weather shows that sericin is very weather resistant.

Silk is very fine, regular, translucent filament. It may be up to 600 m long but averages about 300 m in

length. Depending upon the health, diet and state under which silk larvae extruded the silk filaments; their

diameter may vary 12 μm to 30μm.

Under magnification, cultivated silk fibres are triangular to oval in cross section, while wild silk has to flat

ribbon like shape. The degummed filaments are smooth-surfaced and semi transparent, while the raw silk

is darkens. It has also been recalculated by electron microscopic examination that silk fibre is composed of

minute filaments that are often referred to as fibrils. The fibrils are about 10 μm in diameter and often

liable for the formation of small tufts on the surface of the fabric.

The silk filament is usually slightly twisted about itself, the angle of light reflection changes continuously.

As a result the intensity of the reflected light is broken, resulting in a soft subdued lustre.

Chemical composition:

The content of the substances in silk is not constant and varies in a wide range that depends on the species

of silk worm and on the condition and place of rearing. On an average the chemical composition of raw

silk is as follows:

Components % of each component

Fibroin 72-75

Sericin 22-23

Ash ( inorganic salt) 0.1-1.5

Wax and fat 1.4-2.7

Salts 0.3-1.6

Longitudinal view of silk fibre

Figure: silk cocoon

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The silk fibroin is composed of long chain amino acid unit joined by peptide link with hydrogen bonding

between parallel of chains.

Physical properties of silk

i. Tenacity: The silk filament is strong. The strength is due to its linear and very crystalline polymer

system. These two factors permit many more hydrogen bonds to be formed in a much more regular

manner. When wet, silk losses strength. This is due water molecules hydrolyzing a significant number

of hydrogen bonds and in the process weakening the silk polymer.

ii. Elastic plastic nature: Silk is considered to be more plastic than elastic because it‟s very crystalline.

Polymer system does not permit the amount of polymer movement which could occur in a more

amorphous system. Hence if the silk textile material is stretched excessively, the silk polymers which

are already in a stretched state will slide past each other. The process of stretching ruptures a

significant number of hydrogen bonds. When stretching causes, the polymer do not return to their

original position but remain in new position. This disorganizes the polymer system of silk which is

seen as a distortion and wrinkling or creasing of the silk textile material.

iii. Thermal properties: silk is more sensitive to heat than wool. This is considered to be partly due to

lack of any covalent cross links in the polymer system of silk, compared with the disulphide bonds

which occur in the polymer system of wool. The existing peptide bonds, salt linkages and hydrogen

bonds of the silk polymer system tend to break down once when the temperature exceeds 100ºc.

However prolonged exposure to heat can result in scorching. The brown to black discoloration of

scorched silk is due to the formation of minute particles of carbon which are black in color.

iv. Action of light: silk is more sensitive to light than any other natural fibre. Prolonged exposure to

sunlight can cause partially spotted color changes. The effect of sunlight is more pronounced in

presence of atmospheric oxygen. Curtains made of silk should be therefore protected from the

degradation of sun light giving an extra lining to the light shade. Silk is more susceptible to the

tendering action of light in presence of metallic weighting, which is supposed to be the catalytic action

of metallic salts used in the weighting process.

v. Hygroscopic nature: silk belong to widely absorbent fibres. Like wool, it absorb water well (standard

moisture regain 11%) but dries fairly quick. The absorption of water molecules takes place in the

amorphous regions of the fibre, where the water molecules compete with the free active side groups in

the polymer system to form cross links with the fibroin chains, as a result loosening of the total in front

structure takes place accompanied by a decrease in the force required to rupture the fibre and an

increase in extensibility. The absorption of moisture can vary quickly depending the moisture content

of the atmosphere. On an average it can absorb water up to 30% of its weight without feeling wet. Silk

does not dissolve in water. Treatments of silk even in boiling water for a short period of time does not

cause any deter mental effect on the properties of the silk fibre. But on prolonged boiling silk fibre

tends to loss its strength to some degree which is thought to occur because of hydrolysis action of

water. However silk fibroin withstands the effect of boiling water better than wool.

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Chemical properties of silk

i. Effect of acids: silk is degraded more rapidly by acids than is wool. This is because unlike the wool

polymer system with its disulphide bonds there are no covalent cross links between silk polymers. Hot

concentrated acids rapidly decompose silk. More specifically, concentrated sulfuric and hydrochloric

acid especially when hot, cause hydrolysis of the peptide linkages and readily dissolve silk. Weak (5%

solution) and cold hydro fluorine (HF) acids does not have any harmful action on silk, but it removes

all inorganic weighting materials from the fibre. The use of this acid is therefore suggested to be used

in order to restore the excessively weighted silk to its original condition.

ii. Action of alkali: Alkaline solutions cause the silk filament to swell. This is due to partial separation of

the silk polymers by the molecules of alkali. Salt linkage, hydrogen bonds and vander waal‟s force hold

the polymer system of silk together. Since these inter polymer forces of attraction are all hydrolysed by

the alkali, dissolution of the silk filament occurs readily in an alkaline solution. It is interesting to note

that initially this dissolution means only a separation of silk polymers from each other. However

prolonged exposure would result in peptide bond hydrolysis, resulting in polymer degradation and

complete destruction of the silk polymer. The yellowing of white or dulling of colored silk materials on

laundering is due to filament surface rearrangement of polymer as well some polymer degradation.

These two factors affect light reflection and result in yellowing or dulling. Short treatment with soap

and ammonia does not have any effect on silk but only silk gum is removed. Through on prolonged

boiling in soap the fibroin may also attacked.

iii. Action of bleaches: silk fibroin is highly sensitive to oxidizing agents. The attack of oxidizing agent

may takes place in the peptide bonds of adjacent amino groups and resulting in the weight and strength

loss of the fibre. It has been observed that a peracetic acid causes more rapid destruction of the fibroin

than hydrogen per oxide does. The action of reducing agents on silk fibre is still a little bit obscure.

Since extensive investigation have not been carried out on it. It is however reported that the reducing

agents that are commonly found is used in te4xtile processing such as hyposulfite, sulfurous acids and

their salts do not exercise any destructive action on silk fibre.

Silk weighting

The silk is very expensive and the prices of its buying and selling either in thread or in fabric form are

fixed according to weight of the goods.

During scouring and degumming, silk may lose 25% of its weight. This loss in weight can be restored or

ever increased by subjecting a treatment with some chemicals, such as tannin iron, stannic chloride, starch

and sugar etc. the process of increasing the weight without any negative influence of appearance, luster,

hand feel and other related textile physical properties of silk fibre is known as silk weighting.

In general weighted silk fabrics are not strong as those made from pure silk. Tin, phosphate and silicate

used for weighting may lead to produce brittle fibre in course of time. The degradation of tin weighted silk

can be prevented to a considerable extent by treating with the solution, containing ammonium sulfo

cyanide, glycerol and tannin. Treatment of weighted silk (tin phosphate silicate process) with thiourea and

with hydrosulfite formaldehyde compounds also decreases the tendering action of weighted materials.

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End uses

Silk is widely used as follow-

Apparel Dresses, blouses, skirts, jackets, pants etc.

Home fashions Curtains, draperies and upholstery.

Others Parachute

Types of silk:

A variety of silk fibre is found considering certain factors related its quality and method of production.

Some well known varieties are outlined below.

Types of silk Description

Raw silk

Tussah silk

Bombyx mori

Reelea silk or thrown silk It is the term for silk fibre

Spun silk Silk made from broken cocoons (from which the moths have already emerged)

and short fibres; feels more cotton.

Weighted silk

Pure silk If the natural gum or sericin is removed from the silk and no further material is

added to increase the weight of the fibre, i.e. silk containing no metallic

weighting is called pure silk. Pure silk is exclusively soft and possesses fine

luster.

Composed by:

Md. Mahbub Ur Rahman

Id: 2008100400042

Batch: 8th

(2)