The Influence of pH on the Reflectance and Photostability of Wool to Sunlight

Abstract

Clean wool fabrics show reversible changes in reflectance according to the pH to which they are conditioned and are markedly brighter when acidified. Photobleaching in sunlight occurs independently, regardless of season or pretreatment, and is followed by yellowing. The period of photobleaching is shorter when the fabric is at a low pH, and the subsequent yellowing on continued exposure is also faster. Conversely, photobleachlng is slower and yellowing is retarded if the fabric is neutral or slighly alkaline. Photobleaching can be accounted for by the destruction of a fugitive yellow chromophore, possibly accompanied by generation of blue-fluorescent products. Yellowing is a result of much more prolonged photochemical action, producing coloured degradation compounds. The reversible reflectance associated with pH may be related to the ionization of the carboxyl groups of the wool proteins.