Cationization of cotton for low-salt or salt-free dyeing

Abstract

Cotton acquires negative charge in aqueous medium and thus repels negatively charged dye anion during dyeing. Such repulsion between fibre and dye is offset by using large quantity of salt in dye bath, particularly for reactive dyes. A low dye bath exhaustion also leads to low dye fixation of reactive dyes on cotton. Thus, the use of high salt concentration and low reactive dye fixation lead to environmental problems related to highly coloured effluent with high salt content. These problems can be overcome by improving the dye substantivity of cotton in the absence of salt or with low salt additions. One such approach is cationization of cotton which is critically reviewed in the present paper. Majority of the chemicals used for introducing cat ionic sites in cotton are themselves not safe environmentally. Therefore, there is a need to explore the potentiality of the cationization route using ecofriendly chemicals. The use of chitosan, a polymer derived from chitin, is a step forward in this direction.