Sequential Oxidative and Reductive Bleaching of Wool in a Single Bath

Abstract

A new bleaching process applicable to wool was developed in which an oxidative step (hydrogen peroxide) is combined with a subsequent reductive step (thiourea, thiourea dioxide, or sodium hydroxymethanesulfinate) in a single-bath process. Ox idative followed by reductive bleaching is normally a two- or three-step treatment done in separate baths. Effective bleaching with reduced time and equipment use is achieved by the new single-bath process with a specific order of reagent addition. Although the reductive stage of such a single-bath process may be achieved by the complete decomposition of unspent hydrogen peroxide and then addition of reductive substances such as thiourea dioxide or sodium hydroxymethanesulfinate with necessary pH adjustment, one may take advantage of the unspent hydrogen peroxide to form a reductive substance in situ by reaction with thiourea followed by an appropriate pH adjustment to 7-8. In all the cases above, greatly superior bleaching with less physical damage is achieved with the new process compared with conventional single- or multi- bath processes.