Improvement of light fastness of natural dye: effect of ultraviolet absorbers containing benzotriazolyl moiety on the photofading of red carthamin

While the contribution of ultraviolet absorbers to synthetic dyes has been investigated by several workers, there have been few studies pertaining to the use of functional ultraviolet absorbers as a means of improving the light fastness of natural dyes. In this paper, numerous potential ultraviolet absorbers were prepared to prolong the life of natural dye carthamin. The effects of these compounds in reducing photofading were examined on a polymer substrate. The use of commercial ultraviolet absorbers was not necessarily useful in improving the light fastness of the colour. However, benzophenone-type ultraviolet absorbers containing a built-in ultraviolet absorber moiety markedly retarded the photofading rate. It is proposed that 2,2',4,4'-tetrahydroxy-5-methylbenzotriazolylbenzophenone and its derivatives may be used as effective stabilisers in the fading of natural dyes.