Photoyellowing of wool. Part 2: Photoyellowing mechanisms and methods of prevention†

Part 1 of this review discussed the effects of light on wool keratin and the factors that affect the rate of photoyellowing. Part 2 describes the various photochemical mechanisms that have been proposed to account for photoyellowing of wool by sunlight, and focuses in particular on their strengths and weaknesses. The mechanisms involved in the rapid photoyellowing of wool treated with a fluorescent whitening agent are described in some detail since this remains a serious commercial problem. Existing methods for reducing the rate of wool photoyellowing are reviewed, together with a discussion of the remaining scientific and technical challenges to achieve bright, white wool fabrics and garments of high photostability.