pH control in the dyeing of polyamide with acid dyes

In this study, we report a number of pH control systems for the dyeing of polyamide fibres in a closed dyeing procedure. These include a phosphate buffer system and four pH sliding systems (ammonium sulphate and three hydrolysable organic esters). The dyeing properties of these systems are compared with their ability to control the pH. In comparison with sodium dihydrogen phosphate and ammonium sulphate, hydrolysable organic esters showed a much more effective pH sliding and, consequently, showed higher dyebath exhaustion and colour yields. They also showed very low conductivity, typically less than 0.5 mS. However, no difference in the levelness of the dyed samples among the five acid donors studied was observed and no difference in colour fastness of the dyed fabrics under various pH control systems was detected.