Photo-Oxidation Mechanisms in Wool. A Study of the Photoprotective Effect of a Thiourea/Formaldehyde Treatment

Abstract

Mixtures of thiourea and formaldehyde, when applied to natural protein fibers such as wool or silk, are known to inhibit the photo-oxidation and discoloration of these materials in sunlight. This paper examines the mechanisms underlying the photostabilization of wool by thiourea/formaldehyde (TUF). The photostabilization depends markedly on the spectral composition of the light source and involves a combination of processes which include quenching of uv-induced singlet- and triplet-excited species in wool and sensitization of the fiber to photobleaching in visible light. The photoyellowing behavior is closely related to the intrinsic luminescence properties of the fiber, and the role of the excited species in the photo-oxidation of wool are discussed.