Dyeing Behavior of Indigo Reduced by Indirect Electrolysis

Abstract

Dispersed indigo dyestuff can be reduced by indirect electrolysis using an iron (II)-triethanolamine complex. The iron (III) form of the complex can be transformed to the iron (II) form by cathodic reduction, thus leading to a regenerable reducing agent. Electrochemically reduced indigo is tested in laboratory scale dyeing experiments, and the results of different reduction conditions in the dyebath are discussed. The influence of the concentration of the complex-system on the build-up of color depth and shade with increasing number of dips is discussed and compared with samples of the standard dyeing procedure using sodium dithionite as reducing agent. The results of the latter conventional process show that the dyestuff in the dyebath behaves in a manner similar to that when a regenerable Fe(II)-complex is used as the reducing agent.