Fluorescent Whitening Agents

Abstract

Immersion of fluorescently whitened wool in aqueous solutions of reducing agents during exposure to simulated sunlight has been shown to retard or prevent photoyellowing. The most effective reducing agents of the wide range examined were thioglycolic acid, sodium sulfite, and trishydroxymethylphosphine. Less photodecomposition of trytophan and histidine residues occurs during irradiation of either whitened or unwhitened wool in solutions of these reagents than in water, which may explain, in part, the role of reducing agents in inhibiting photoyellowing. In contrast, a study of bleached wool containing the bis(triazinylamino)stilbene whitener (I) showed that reducing agents do not affect signifi icantly the course or extent of photodecomposition of the whitener. Reducing agents were less effective inhihitors of yellowing when padded onto wool and dried than when used in aqueous solution. However, treatment of fluorescently whitened wool with tetrakishydroxymethylphosphonium chloride (THPC) by padding was found to provide good protection against yellowing in sunlight, especially for exposure in the wet state. Unfortunately the protective effect was not very durable to washing. The sulfonated triphenyl phosphine (II) was substantive to wool but provided good protection against yellowing only at high concentrations. Two water-soluble antioxidants of the hindered phenol type were also tested but were found to be ineffective.