Some Experimental Observations on the Photochemical Degradation of Dyed Cotton

Abstract

The photochemical oxidation of cotton by the air is sensitised by sulphur and basic dyes, as well as by vat dyes. As with vat dyes, so too with sulphur dyes, there is a correlation between the colour of the dye and its sensitising action. With the basic dyes there is no such relation between colour and sensitising action. The only direct dye so far observed to accelerate the photochemical oxidation iH the thiazole dye Primuline. The introduction of the azo group into the Primuline molecule by oxidation, or by diazotising and coupling, diminishes or destroys its photochemical action.Very small amounts of copper may exert a large effect on the photochomieal action of all classes of dyes. The effect is a complicated one, but its net result is to diminish greatly the sensitising action of the most active dyes.Many dyes liberate hydrogen peroxide on irradiation in moist air, but this action is preventod by tho presence of small amounts of copper and of some other metals.There is a strong positive correlation between the liberation of peroxide by a dye on irradiation and its accelerating effect on the photochemical oxidation. Tho accelerating sulphur dyes do not, however, liberate detectable amounts of peroxide on irradiation.