Single Bath Full Bleaching of Wool Using Sodium Trithiocyanurate in Place of Thiourea

A single bath full bleaching procedure for textile materials has been developed. In this procedure, following oxidative bleaching using hydrogen peroxide, the peroxide bath is converted to a reductive bath by addition of thiourea and bleaching continues without the need for a fresh bath for the reductive step. Such full bleaching is easy, economical and very effective in inducing improved whiteness. One drawback is the toxic nature of thiourea. Thiourea, though easily handled and thoroughly consumed in this procedure, is classified as a carcinogen unlike its oxidized counterpart, thiourea dioxide (formamidinesulfinic acid). This work presents how thiourea may be replaced by sodium trithiocyanurate (Na,TTCA), which is not classified as a carcinogen. Full bleaching with the modified protocol is just as effective as the procedure using thiourea, but Na,TTCA was found to be most effective at 90% of the stoichiometric weight to peroxide, as opposed to 70% for thiourea; the Na,TTCA process was more sensitive to the pH of the rinse bath than the thiourea process; and the Na,TTCA reagent is more expensive than thiourea. Nevertheless, the attractiveness of using Na,TTCA is the avoidance of a achievement of exceptional whiteness over conventional peroxide bleaching.