COTTON FIBRE
people learned to cultivate cotton plants in their fields.
In Europe, wool was the only fibre used to make clothing. Then from the Far East came tales of plants that grew "wool". Traders claimed that cotton was the wool of tiny animals called Scythian lambs, that grew on the stalks of a plant. The stalks, each with a lamb
as its flower, were said to bend over so the small sheep could graze on the grass around the plant. These fantastic stories were shown to be untrue when Arabs brought the cotton plant to Spain in Middle Ages.
History
Nobody seems to know exactly when people first began to use cotton, but there is evidence that it was cultivated in India and Pakistan and in Mexico and Peru 5000 years ago. In these two widely separated parts of the world, cotton must have grown wild. Thenpeople learned to cultivate cotton plants in their fields.
In Europe, wool was the only fibre used to make clothing. Then from the Far East came tales of plants that grew "wool". Traders claimed that cotton was the wool of tiny animals called Scythian lambs, that grew on the stalks of a plant. The stalks, each with a lamb
as its flower, were said to bend over so the small sheep could graze on the grass around the plant. These fantastic stories were shown to be untrue when Arabs brought the cotton plant to Spain in Middle Ages.
#General considerations
Cotton is cuitivated in 80 countries with an approximate area of 32 million hectares. Cultivation period varies from 175 days to 225 days depending on variety. Cotton is harvested in two seasons- summer and winter.Saw ginned cotton is more uniform and cleaner than Roller Ginned Cotton. But fibres quality is retained better quality in Roller Ginning than Saw Ginning which has high productivity. Cotton Fibre is having a tubular structure in twisted form. Now. researchers have developed coloured cotton also. As on date, percentage of Cotton fibre use is more than synthetic fibres. But, its share is gradually reducing. Cotton is preferred for under garments due its comfort to body skin. Synthetics have more versatile uses and advantage for Industrial purposes.
#Cultivation and harvesting
●Cotton is grown in about 80 countries. For a good crop of cotton a long, sunny growing season with at least 160 frost-free days and ample water are required.●Well drained, crumbly soils that can keep moisture well are the best.
●In most regions extra water must be supplied by irrigation.
●Young plants appear about 5 days after planting the seeds.
●The first flower buds appear after 5-6 weeks, and in another 3-5 weeks these buds become flowers.
●Each flower falls after only 3 days leaving behind a small seed pot, known as the boll.
●Each boll contains about 30 seeds, and up to 500000 fibres of cotton.
●Each fibre grows its full length in 3 weeks and for the following 4-7 weeks each fibre gets thicker as layers of cellulose build up the secondary cell walls.
●While this is happening the boll matures and in about 10 weeks after flowering it splits open.
●The raw cotton fibres burst out to dry in the sun.
●Now is time for harvesting.
●Most cotton is hand-picked.This is the best method of obtaining fully grown cotton because unwanted material, called "trash", like leaves and the remains of the boll are left behind.
●Also the cotton that is too young to harvest is left for a second and third picking.
●A crop can be picked over a period of two months as the bills ripen.
#Micro-structure of the cotton fibre
The cotton fibre is a single plant cell. Its cross-section is oval. However, like all plant cells, cotton has a distinct cuticle, well developed primary and secondary walls, and a lumen.
(a) Cuticle:-
◆The cuticle is the very outside' or 'skin'of the cotton fibre. It is composed of a waxy layer (cotton wax) onlya few molecules thick.
◆wax protects the fibre against chemical and other degrading agents.
◆Kier boiling and bleaching during cotton finishing removes much of the cuticle or wax.
◆This enables cotton to absorb moisture more quickly.
(b) Primary cell wall:-
◆It is immediately under the cuticle, is about 200 nm thick.◆It is composed of very fine threads of
cellulose, called fibrils.
◆The fibrils spiral at about 70°
to the fibre axis. This spiralling imparts strength to the primary cell wall and, hence, to the fibre.
(c) Secondary cell wall:-
◆Beneath the primary cell wall lies the secondary cell wall, which forms the bulk of the fibre.◆Its fibrils are about 10 nm thick, but of undefined length.
◆The secondary wall spiral at about 20° to 30° to the fibre axis.
◆Much of the strength and stability
of the cotton fibre and, hence, of the yarns and fabrics may be attributed to these spiralling fibrils.
(d) Lumen:-
◆The hollow canal, running the length of the fibre, is called the lumen. Its walls are the innermost, concentric layers of spirals of the secondary cell wall.◆The lumen was once the central vacuole of the growing
cotton fibre.
◆It was full of cell sap, which was composed of a dilute, aqueous solution of proteins, sugars, minerals and cell-waste products.
◆When the sap evaporated, its constituents remained behind to
contribute to the colour of the cotton fibre.
◆Further, as the sap evaporated, the pressure inside the fibre became less than the atmospheric pressure
on the outside.
◆This caused the fibre to collapse inward resulting in the characteristic kidney-shaped cross-section of the cotton fibre.
#The polymer system
◆The repeating unit in the cotton polymer is cellobiose which consists of two glucose units.
◆The cotton polymer consists of about 5000 cellobiose units, i.e. its degree of polymerisation is about 5000.
◆It is a very long, linear polymer, about 5000 nm in length and about 0.8 nm thick.
◆Its polymer system is about 65 to 70% crystallineand,correspondingly, about 35-30% amorphous.
#cotton grading
The East Indian Cotton Association (EICA) Ltd. maintains standards of Indian cottons for 23 descriptions of cottons based on varieties and geographical divisions. Each description has the following six grades-1. Extra superfine
2. Superfine
3. Fine
4. Fully good
5. Good
6. Fully good fair
# Composition
cellulose:- 94 %Protein:- 1.3%
Ash:- 1.2 %
Wax:- 0.6%
Sugar:- 0.3%
Traces of pigments and others:- 2.6%
# Properties of cotton
(A) Physical properties
(i) Tenacity: 3-5 g/denier (dry)fii) Breaking elongation: 5-7 %
(ii) Moisture regain: 7-8%
(iv) Specific gravity: 1.52 g/cc.
(B) Chemical properties
(i)Effect of acids:-
Weakens and destroyed by acids. Acids hydrolyse the cotton polymer.
(ii)Effect of alkalies:-
Cotton fibres are resistant to alkalies and are uneffected by normal laundering.
Cotton fibres are resistant to alkalies and are uneffected by normal laundering.
(iii) Effect of bleaches:-
The most common bleaches on cotton textile materials are sodium hypochlorite (NaOCH)and sodium perborate (NaBO2. H2O2. 3 H2O). They are oxidising bleaching agents and are most effective in alkaline conditions.
The most common bleaches on cotton textile materials are sodium hypochlorite (NaOCH)and sodium perborate (NaBO2. H2O2. 3 H2O). They are oxidising bleaching agents and are most effective in alkaline conditions.
(iv) Effect of oxidising agents:-
No injury to fibres if treated under controlled conditions.
No injury to fibres if treated under controlled conditions.
(v) Effect of mildew:-
Cotton is readily attack by moth and mildew, So it has to be saved from their attack by suitable methods.
Cotton is readily attack by moth and mildew, So it has to be saved from their attack by suitable methods.
(vi)Effect of light:-
Prolonged exposure to sunlight Weakens the cotton due to the formation of degradation
products of cellulose, so the fabric made from cotton should not be
exposed to direct sun-light for a longer period and be kept in cool environment for drying after washing.
Prolonged exposure to sunlight Weakens the cotton due to the formation of degradation
products of cellulose, so the fabric made from cotton should not be
exposed to direct sun-light for a longer period and be kept in cool environment for drying after washing.
(vii) Effect of Heat:-
Cotton fibre have the ability to conduct heat energy and they can withstand hot ironing temperature. Cotton can be heated upto 150°c without any damage. It scorches at 245°C and burns.
Cotton fibre have the ability to conduct heat energy and they can withstand hot ironing temperature. Cotton can be heated upto 150°c without any damage. It scorches at 245°C and burns.
# Uses
◆Cotton is exclusively used in apparel fabrics for men and women wears and household fabrics like bed sheets, towels, rugs and carpets.◆Cotton is blended with other man-made fibres like polyester, viscose, acrylic etc. to be used for variety of purposes.
◆It can also be used in industrial applications as tyre cords, bags, shoes and medical supplies and equipments.
This is dummy text. It is not meant to be read. Accordingly, it is difficult to figure out when to end it. But then, this is dummy text. It is not meant to be read. Period.
ConversionConversion EmoticonEmoticon