CONTINUOUS SULFUR DYEING WITHOUT REDUCING AGENTS - FULLY REDUCED SULFUR-BLACK-1 BY CATHODIC REDUCTION

The electrochemical reduction of sulfur dyes was examined with regard to the substitution of nonregenerable reducing agents in dyeing proces ses. The redox behavior of Leuco Sulfur Black 1 was characterized by p hotometric and potentiometric methods. In the presence of a surplus of reducing agent, the disulfide groups and the quinoneimine groups were reduced. A comparable degree of dye reduction could be achieved by ca thodic reduction. The cathodically reduced sulfur dye had a reduction capacity of sufficient magnitude to serve as a reducing agent and anti oxidant by itself. The cathodically reduced dye was used for one-bath pad-steam dyeing experiments. The color depth and shade of the dyed sa mples corresponded to standards dyed with the use of reducing agents, thus indicating that full substitution of reducing chemicals by cathod ic dye reduction can be achieved. The described electrochemical techni que offers ecological and economic advantages in combination with sulf ide free sulfur dyeing.