Potentiostatic studies on indirect electrochemical reduction of vat dyes

Dispersed vat dyestuffs can be electrochemically reduced by indirect electrolysis using iron–triethanolamine complex as a reducing agent. The application and mechanism of indirect electrolysis as a reduction technique are described in detail in this paper. Electrochemically reduced vat dye is tested on a laboratory scale in dyeing experiments, and the results of different reduction conditions are discussed. The influence of the concentration of the complex-system on the build-up of colour depth, shade and fastness is discussed and compared with samples of the standard dyeing procedure using sodium dithionite as the reducing agent. The new process offers environmental benefits as well as prospects for improved process stability, because the state of reduction in the dye-bath can be readily monitored by measuring the reduction potential.