Raw Cotton Wool, Absorbent Cotton
Cotton consists of the epidermal trichomes of the seeds of Gossypium herbaceum Linn and other species of Gossypium of the family Malvaceae.
Gossypium species are cultivated for commercial production of cotton in the United States of America West Indies, Peru, Brazil, India, China and Egypt. Cotton plants are also now cultivated in Nigeria and Bangladesh.
Preparation of Raw Cotton:
Bolls of cotton are collected from the ripe and dehisced fruits of Gossypium The trichomes are separated from the seeds by a ‘ginning’ process using a machine called ‘gin’, in which the trichomes are drawn through a narrow space. The masses of these separated trichomes constitute Raw Cotton. Raw cotton thus prepared contains impurities, chiefly colouring matter, and about 0.6 percent of wax and oil, which form a thin film around the fibres and render them non-absorbent. Raw cotton is then variously treated, combed and spinned to convert it to yarn or thread, which are woven to make fabrics and cloths.
Preparation of Absorbent Cotton Wool:
Absorbent Cotton Wool is prepared from the various cotton wastes obtained during the processing of raw cotton for making yarns. The wastes are loosened and then boiled for 10 to 15 hours under a pressure of about 30 lbs. in a dilute solution of caustic soda and soda ash. This treatment removes the fatty cuticle and renders the trichomes absorbent. The boiled material is then washed thoroughly with water, bleached with dilute sodium hypochlorite solution and treated with very dilute hydrochloric acid. The bleached mass of fibres is then dried, loosened, scutched, and carded by using appropriate machines. The resultant product is a thin continuous film of absorbent cotton wool. Several such films are superimposed on one another and rolled.
Macroscopical and microscopical characters:
Cotton wool is a loose mass of thin filaments, soft to touch and white in colour. Absorbent cotton wool is more white than the raw cotton, which has a brownish tint. When pulled apart, a wad of cotton wool separates with resistance and in a dragging fashion forming a thin film of fibres being finally separated. When placed on the surface of water raw cotton floats while absorbent cotton rapidly sinks. The cotton trichomes are tubular, flattened and twisted with large lumen. The apex is rounded. The cellulose wall of the raw cotton fibre is covered with a waxy cuticle. When treated with ammoniacal copper oxide solution (CUOXAM) raw cotton fibres dissolve with ballooning, while those of absorbent cotton dissolves with uniform swelling, Cotton dissolves in 80 percent cold sulphuric acid.
Different commercial varieties of cotton can be distinguished by the length of staple of the trichomes. The staples of the important Yarietles of cotton are as follows: Sea Island, up to 54.5 mm: Egyptian. 31 to 38 mm; Peruvian and Brazilian, 29 to 30 mm and Indian 21.4 to 29.2 mm.
Raw cotton contains about 90 percent of cellulose and small amounts of wax. fat. remains of protoplasm and ash. Absorbent cotton is almost pure cellulose.
Cotton is used as the chief material for many surgical dressings. It is also used as a filtering medium and an insulating material.