No or Low Salt Dyeing: Is It Possible??? Many one might have got surprised, but its possible. Almost all cotton dyes are anionic during dyeing, but due to the negative is Zeta-potential of cotton in water among other things, anionic dyes have medium to poor affinity for cotton. Auxiliaries such as electrolytes are required for efficient use of dyes and for dyeing textile with high color strength. Despite electrolyte concentrations of 10 gpl or more, excess dye remains in the effluent after dyeing. The dye left in the effluent, together with the high salt concentration, increases the cost of dyeing, the burden of effluent treatment, and environmental pollution as well.
One solution to this problem is to improve the affinity of anionic dyes for cotton. This is mainly accomplished by introducing cationic groups onto cotton to add an ionic attraction between dye and fiber. Fibers treated with these cationic agents, or agents that can form cationic sites under dyeing conditions, show such a remarkable increase in affinity for anionic dyes that no salt is necessary to assist dye sorption. In most of these cationic agents, nitrogen supplies the cationic sites. The agents are fixed onto cotton by covalent bonds either between cotton or their own reactive groups or by a cross linking agent.
The author is associated with the Department of Textile Chemistry, D.K.T.E. Societys Textile & Engineering Institute, Ichalkaranji, Dist-Kolhapur (M.S.)