Indigo Dyeing of Polyamide Using Enzymes for Dye Reduction

Classical processes of indigo dyeing use sodium dithionite as reducing agent, causing enormous environmental problems. In this paper, a new process of indigo reduction using NADH-dependent reductases from Bacillus subtilis in the presence of redox mediators is presented. The efficiency of mediated enzymatic indigo reduction on the dyeing of decitex polyamides 6 and 6,6 was studied at 60 degrees C, pH 7 and 11, and different indigo concentrations. The color values and color fastness properties (to wash, light and perspiration) were evaluated and compared to chemically indigo-dyed polyamides. The results indicated that the dyeing properties were pH, time and polyamide type dependent, resulting in the greater color depth of morphologically more amorphous polyamide 6,6 dyed at pH 11 for 90 minutes. Both the alkaline and acid perspiration fastness properties of the dyeings were very good, whereas the dyeings displayed poorer fastness of 3-4 to light and wash. Successful reuse of the enzyme was confirmed.