In the conventional process of dyeing cotton, vat dyes and especially indigo are traditionally reduced by sodium dithionite in the presence of sodium hydroxide as alkali. This technique presents various disadvantages (ecological problems, problems of storage, difficulty of control of the process, colour variation of the dyed fabrics etc). The present paper reports a novel promising eco-friendly technique of cotton dyeing. This new technique consists essentially of using sodium borohydride as reducing agent instead of sodium dithionite. The experimental conditions were determined. The evaluation of the performance of this reaction was carried out by establishment of potentiometric titration procedure of the leuco-indigo concentration in the dyeing bath.
In this study, the effect of the sodium borohydride amount on indigo reduction yield was investigated. It appears that the reduction yield increased with increasing of the amount of reducing agent until 100% of sodium borohydride. After this value, the reduction yield remained quite constant. The dyeing quality of cotton fabrics was also studied in these conditions. This quality was evaluated by using the CIELAB colorimetric coordinates L*a*b* as well as the colour yield (K/S) of the dyed samples. It seems that generally these colorimetric parameters depended closely of the reduction yield.
Indigo reduction reaction, sodium borohydride, cotton dyeing process
