Treatment of cellulose with cationic, nucleophilic polymers to enable reactive dyeing at neutral pH without electrolyte addition

Reactive dyeing of cotton requires very high concentrations of salt, which pollutes freshwater courses. The dyeing effluent is highly colored as a result of high levels of hydrolysis of the dye, and high volumes of water are used in the wash‐off process to remove the hydrolyzed dye in order to achieve the excellent wash‐fastness levels expected. A substantive cationic, nucleophilic polymer was applied to cotton as a pretreatment agent prior to dyeing. This enabled salt and alkali to be completely eliminated from the dyeing process, significantly reducing the duration of the dyeing process and requiring less than 50% of the volume of water compared with those of the standard reactive dyeing processes. Dyeings secured using the pretreatment method required one simple washing stage to give wash‐fastness values equal to those observed for the standard reactive dyeings that required several wash‐off stages. The color strength of the pretreated dyeing was also slightly higher than that of the standard dyeings, and this was attributable to a reduction in dye hydrolysis and hence a higher fixation.