2.1.9 Absorbent Cotton
Synonyms Purified cotton; Cotton wool; Surgical cotton.
Biological Source Cotton comprises of the epidermal trichomes (or hairs) from the seeds of different species of Gossypium, such as : G. herbaccum; G. hirsutum; G. barbedense; belonging to the family Malvaceae. In fact, absorbent cotton or purified cotton consists exclusively of the trichomes that are completely freed from adhering impurities, fat, properly bleached and finally sterilized.
Geographical Source Cotton is produced on large scale in USA, Egypt, China, India, South America and certain parts of Africa. Egyptian cotton–yarn enjoys a world-wide reputation. Both India and China are not only self-sufficient in the production of absorbent cotton but also exports a substantial quantity to various countries.
Preparation The cotton plant after flowering bears fruits which are also called ‘capsules’ or ‘balls’. These are usually 3-5 celled. Once the fruit ripens they open-up widely that contains a number of seeds per loculus. The brown coloured seeds are normally surrounded with a thick mass of white hairs. The long-lint hairs are known as ‘staple’ or ‘floss’; whereas the short-fuzz hairs are called ‘linters’. The cotton fibres (i.e., mass of white hairs) along with their seeds are collected manually by hand picking. The raw cotton is subjected to a mechanical process called ‘ginning’ whereby only the hairy substance is collected separately and the undesired substances, such as: dirt, leaf-fragments and other foreign materials are removed separately. ‘Delintering’ is the mechanical process which discards the short hairs that eventually passed along with the cotton fibres obtained from the ‘ginning’ process. The raw segregated long-sized cotton hairs are subsequently freed from colouring matters and traces of wax and oil coating the hairs which render them non-absorbent. The treated absorbent cotton obtained above is processed through the ‘carding machine’ so as to arrange the fibres in parallel direction and also to get rid of immature fibres completely. Short fibres are once again removed by ‘combing’ mechanically. Finally, the processed cotton fibres are defatted (with alkali) washed, bleached (with chlorinated soda) and then washed (with diluted mineral acid). It is again washed, dried, recarded and sterilized.
Description White, soft, fine, filament like hairs appearing under the microscope as hollow, flattened and twisted bands, striate and slightly thickened at the edges, practically odorless and tasteless. Cotton fibres are usually 2.5 to 4.5 cm in length and 25 to 35 µ in diameter.
Chemical Constituents Absorbent cotton is mostly cellulose 93-94% and moisture 6-7%
Uses
1. It is employed as surgical dressings.
2. It is mostly used in the textile industry to prepare a wide range of fibres.
3. It is invariably employed as its derivatives to be recognized as the most versatile adjunct in pharmaceutical formulations, for instance:
Microcrystalline cellulose – as Tablet Disitegrant
Carboxymethyl Cellulose (CMC) – as Binder and thickening agent;
Cellulose acetate phthalate – as an Enteric coating material;
Ethyl Cellulose – as Binder and Film
Methyl Cellulose coating substance;
Hydroxypropyl methyl Cellulose
Oxidised Cellulose – as local Haemostatic;
Purified ‘Rayon’ – as Surgical aid;
Pyroxylin – as an ingredient in the preparation of Collodian and nail polishes.
4. It is used as a filtering medium and also as an insulating material.
5. Pharmaceutical grade cotton seed oil is used as an emolient and in the preparation of Steroidal Hormone Injections.
6. It is used for making explosives.
