Cotton - Vegetable Fibres

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Chapter: Pharmacognosy and Phytochemistry : Fibres, Sutures and Surgical Dressings

Epidermal trichomes of the seeds of cultivated species of the Gossypium herbaceum and other species of Gossypium (G. hirsutum, G. barbadense) freed from impurities, fats and sterilized, belonging to family Malvaceae.


COTTON

 

 

Synonyms

 

Raw cotton, purified cotton, absorbent cotton.

 

Biological Source

 

Epidermal trichomes of the seeds of cultivated species of the Gossypium herbaceum and other species of Gossypium (G. hirsutum, G. barbadense) freed from impurities, fats and sterilized, belonging to family Malvaceae.

 

Geographical Source

 

United States, Egypt, some parts of Africa, and India.

 

History

 

There are about 39 species of Gossypium worldwide which are native to the tropics and warm temperate regions. Three species are native to South Africa, of these, Gossypium hirsutum from Mexico has become the predominant species in commercial cotton production worldwide. About 90% of the world commercially produces cotton from G. hirsutum. G. barbadense contributes to 8% of the market while the remaining 2% belongs to the old world cotton grown in South and South-East Asia.

 

Gossypium herbaceum or the African-West Asian cotton: Gossypium herbaceum is the indigenous species in India. It is native to semidesert conditions like in sub-Saharan Africa and in Arabia. It is a perennial shrub. It is widely cultivated in Ethiopia and also in Persia, Afghanistan. Turkey, North Africa, Spain, Ukraine, Turkestan, and China (first cultivation in China reported was in about A.D. 600). It reaches a height of 2–6 feet, with palmate hairy leaves, lobes lanceolate, acute yellow petals and a purple spot in centre, capsule when ripe splits itself and exposes the loose white clump surrounding the seeds and strongly adhering to the outer coating. G. herbaceum requires warm weather to ripen its seeds.

 

Gossypium arboreum or the Pakistani-Indian cotton: It is native to Northwest India and Pakistan. The use and production of cotton dates back to 2000 BC, by the Harappan civilization of the Indus Valley. Some of them are tall perennial while others are short annuals. People of Nubia are considered to be the first cotton weavers of Africa. This cotton variety extended into other parts of Africa (Nigeria) that became a cotton-manufacturing centre from the 9th century onwards.

 

Gossypium barbadense or South American cotton: G. bar-badense gives the Sea Island, or long-stapled cotton. The oldest cotton textiles recorded from South America date to 3600 B.C. The first sign of domestication of cotton species comes from Peruvian coast where cotton bolls dating to 2500 B.C. were found. Cotton became a commercial slave plantation crop in the West Indies and as a result of it Barbados in 1650s became the first British West Indian colony to export cotton. Later on around 1670, planting of G. barbadense also began in the British North American colonies.

 

Gossypium hirsutum or Mexican cotton: G. hirsutum are found in coastal vegetation of Central and Southern North America and also in the West Indies. There are evidences of cotton remains dating back to 3500 B.C. in the Tehuacan Caves in Mexico and even the Spanish explorers have found cotton cultivation in the 1500s.

 

Cultivation, Collection, and Preparation

 

Cotton is cultivated by means of seed sowing method. The seeds are sown in rows of about 4–5 ft in distance. Proper fertilizers are provided timely. The cotton plants are shrubs or small trees that bare fruits (capsules) after flowering. The capsule consists of three to five seeds and is covered with hairs. The bolls are collected when ripe, separated from the capsule, dried, and subjected to the ginning press for processing. In ginning process, hairs and seeds are put before the roller with a small space, which separates the trichomes from the seeds. The short and long hair separated by delinter. Short hairs are known as ‘linters’, which are used in the manufacturing inferior grade cotton wool, whereas long hairs are used for preparation of cloth. The seeds remain after the removal of hair is used for the preparation of cotton seed oil and oil cake for domestic animal feed. The raw cotton so obtained is full of impurities like the colouring matter and fatty material. It is then subjected to further purification by treating it with dilute soda ash solution under pressure for about 15 hours. It is then bleached and washed properly, dried, and packed. The packed cotton is then sterilized using radiations.

 

Description



 

Chemical Constituents

 

It consists of 90% of cellulose, 7–8% of moisture, wax, fat and oil 0.5% and cell content about 0.5%. Purified cotton has almost cellulose and 6–7% of moisture.

 

Chemical Tests


1.     On ignition, cotton burns with a flame, gives very little odour or fumes, does not produce a bead, and leaves a small white ash; distinction from acetate rayon, alginate yarn, wool, silk, and nylon.

 

2.     Dried cotton is moistened with N/50 iodine and 80% w/w sulphuric acid is added. A blue colour is produced; distinction from acetate rayon, alginate yarn, jute, hemp, wool, silk, and nylon.

 

3.     With ammoniacal copper oxide solution, raw cotton dissolves with ballooning, leaving a few fragments of cuticle. Absorbent cotton dissolves completely with uniform swelling, distinction from acetate rayon, jute, wool, and nylon.

 

4.     In cold sulphuric acid (80% w/w) cotton dissolves; distinction from oxidized cellulose, jute, hemp, and wool.

 

5.     In cold sulphuric acid (60% w/w) cotton, is insoluble; distinction from cellulose wadding and rayons.

 

6.     In warm (40°C) hydrochloric acid it is insoluble; distinction from acetate rayon (also silk, nylon).

 

7.     It is insoluble in 5% potassium hydroxide solution; distinction from oxidized cellulose, wool, and silk.

 

8.     Treat it with cold Shirla stain A for 1 min and wash out. It shows shades of blue, Tilac or purple; distinction from viscose, acetate rayons, alginate yarn, wool, silk, and nylon.

 

9.     Treat it with cold Shirla stain C for 5 min and wash out; raw cotton gives a mauve to reddish-brown colour and absorbent cotton a pink one; distinction from flax, jute, hemp. The Shirla stains may be usefully applied to a small piece of the whole fabric under investigation to indicate the distribution of more than one type of yarn.

 

10. It does not give red stain with phloroglucinol and hydrochloric acid; distinction from jute, hemp, and kapok.


Uses

 

Cotton is used as a filtering medium and in surgical dressings. Absorbent cotton absorbs blood, pus, mucus, and prevents infections in wounds.

 

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