Investigation into the reaction of reactive dyes with carboxylate salts and the application of carboxylate-modified reactive dyes to cotton

Ink-jet printing of cellulosic fabrics with reactive dyes typically requires that the fabric is pretreated with alkali, prior to printing, to facilitate efficient fixation of the dye. In this paper we evaluate the use of sodium formate and other carboxylate salts as a neutral (pH 6.5) pretreatment process. The thickened, prepared-for-print pad liquor contained at least 50 gdm⁻³ of the selected carboxylate salt and was applied to the cotton fabrics by a pad-dry procedure. The fabric was then ink-jet printed with reactive dye inks, followed by standard steaming and washing-off processes. The pH of the carboxylate salt pretreatment was 6.5 and the aqueous extracts from the print fabrics at the end of the steaming process remained at pH 6.5. It was observed that even at pH 6.5, in the presence of selected carboxylates, significant reactive dye fixation could be achieved on a cotton substrate, whereas in the absence of the carboxylate, very little or even zero fixation was achieved. Infrared and capillary electrophoresis analyses of model reactions of reactive dyes with the carboxylate salts indicated that reactive ester residues were formed, and which subsequently promoted reaction with the cellulosic substrates. In addition to improving reactive dye fixation in ink-jet printing, the carboxylate-modified dyes were also demonstrated to improve long-liquor dyeing properties on cotton substrates. As an extension of this carboxylate-based printing process, the incorporation of lithium acetate (100 gdm⁻³) into the ink formulation was further studied and it was demonstrated that the necessity for a preparative pretreatment process could be eliminated.