Chemical Reactions between Dyes and Wool

Abstract

Work on the application of chlorotriazinyl reactive dyes to wool is reviewed. It is shown that, under the hot acidic dyeing conditions that must be used to obtain satisfactory dyeings on untreated wool without the aid of solvents, the fixation, and hence the wet–fastness properties, is limited by the absorption of hydrolysed dye. The possibility of applying dichlorotriazinyl dyes to shrink–resist–treated wool under alkaline conditions and at low temperatures is discussed.The application to wool of dyes containing acrylamido groups is considered in detail. This group does not hydrolyse in the dyebath. Consequently, very high levels of fixation to the fibre can be attained under appropriate conditions, and the relation between fixation and fastness to severe wet treatments is demonstrated. The mechanism of the reaction of acrylamido dyes with wool has been studied. Reactivity towards model compounds in solution suggests that reaction with primary and secondary amino groups and with thiol groups is the principal mechanism of their reaction with wool, and the importance of amino groups is also indicated by the relative reactivity of an acrylamido dye towards wool, silk, and nylon. Amino–acid analyses of wool dyed to heavy depths with unmetallised and 1: 2 metal–complex acrylamido dyes show that reaction takes place predominantly with the –amino group of lysine residues, there being no evidence of reaction with the thiol group of cysteine nor with histidine residues.Preliminary work with a chloroacetyl reactive dye suggests that this group reacts with both cysteine and histidine residues.