Natural fibres, impurities cotton

Alkali treatment Mercerization or alkali treatment with strong alkali bases was developed as a method for cotton fibre modification by John Mercerin 1850 [55], It is a common method to produce high quality natural fibres, by removing the natural and artificial impurities from the fibre surface. The chemical treatment reduces the fibre diameter and thereby increases the aspect ratio [26]. Mercerization is usually performed applying aqueous solutions of sodium hydroxide (NaOH), at reaction times of 30 min up to 3 hr. 

The loom state cotton fabric contains about 8-12% natural impurities of total weight of the fibre. These impurities mainly consists of waxes, proteins, pectic substances and mineral matters. In addition to this, the mechanically held impurities called motes are present containing seed-coat fragments, aborted seeds and leaves etc. that clinge to the fibre. Apart from these, the loom-state fabric is also contaminated with adventiteous oils such as machine oils, tars, greases etc. 

Approximately 45 million tons of fibres, of which over 50% are cotton, are consumed each year for textile purposes [33]. Although synthetic fibres do not contain any natural impurities, they produce considerable amount of pollutants during wet processing. Table 13.10 gives the characteristics of different processes wastes... 

M ht scouring operations in which these surface-active compounds are commonly used varv according to the nature of the fibre and the amount and composition of the impurities to be removed. In the case of cotton the cellulose of w hich it is composed is stable to dilute solutions of alkali at the boil. I he imphrities which must be removed are natural oils and waxes, proteins, pectic substances, natural colouring matter, and adventitious dirt. The basic principle of cotton scouring is to boil the goods for several hours at atmospheric, or under elevated, pressure with a 2 per cent solution of sodium h) droxide. 

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