The effects of bleaching on the photostability of white fleece wools

The photostability of Merino fleece wools shows moderate heritability and therefore could be improved by selection. However, wool used for bright whites and pastel shades is always bleached with hydrogen peroxide during processing to improve its colour, and bleaching is known to reduce photostability. This paper describes the effects of peroxide bleaching on two groups of Merino fleece wools having the same range of initial yellowness but differing photostabilities. After peroxide bleaching, there was no significant difference in photostability between the two groups, suggesting that genetic selection of sheep for higher photostability would only offer a commercial benefit for production of bright white and pastel shades if yellowness is reduced to such an extent that peroxide bleaching is unnecessary. A more viable short-term approach would be to use a water-soluble UV absorber to reduce the rate of photoyellowing, if a means of applying the UV absorber to bleached wool without reducing its whiteness could be achieved.