| Abstract: | The action of (a) near-ultraviolet and (b) short-wave ultraviolet radiation (mainly 253.7 nm) on nylon 6 and cellulose films dyed with one non-sensitising and two sensitising vat dyes has been studied. Photoreduction (in nitrogen) to the acid leuco derivative of the dye is observed only on exposure to 253.7-nm radiation. Vat dyes desensitise the degradation of cotton by 253.7-nm radiation, but there is no simple relation between this desensitising effect and their sensitising effect with near-ultraviolet and visible radiation. Degradation of vat-dyed cotton by 253.7-nm radiation is not increased by the reduction of the dye to the acid leuco form. Radical formation is unrelated to fibre degradation. The experimental evidence favours the concept of Kautsky's activated oxygen as an intermediary in the photosensitised degradation of cotton by near-ultraviolet and visible radiation, rather than that of hydrogen abstraction. |
