Photoyellowing of wool. Part 1: Factors affecting photoyellowing and experimental techniques

The yellowing of wool exposed to sunlight is a serious commercial shortcoming compared to cotton and synthetic fibres, particularly when photostable brilliant whites and bright pastel shades are required. Part 1 of this review discusses the effects of light on wool keratin and the factors that affect the rate of photoyellowing, including oxidative bleaching, fluorescent whitening and the presence of moisture. The effect of variation of the wavelength of light, particularly attenuation of the ultraviolet wavelengths in sunlight by window glass that can result in photobleaching of wool is described. The experimental techniques that have been used to study the complex photochemistry involved in yellowing, and to identify the nature of the yellow chromophores formed, are also discussed. Part 2 of the review will focus on the photochemical mechanisms involved, and discusses potential ways for improving wool's photostability.