A study has been made of the action of near‐ultraviolet and visible radiation on anaerobic solutions of 1‐ and 2‐piperidinoanthraquin‐ones in different organic solvents, and on polymer films dyed with these dyes. In the absence of oxygen, 1‐piperidinoanthraquinone is reduced to the anthrahydroquinone on irradiation in solution and on nylon films. Under similar conditions, 2‐piperidinoanthra‐quinone is reduced to the anthrone in organic solvents, but the photochemical changes are more complex on polymer films. 1‐Piperidinoanthraquinone doss not sensitise the photochemical degradation of nylon or cellulose acetate yarn. The results suggest that there is no definite relation between the ease of photoreduction of a dye and its ability to sensitise the photochemical degradation of textile fibres.
The effect of (a) short‐wave ultraviolet radiation (mainly 253‐7 mμ) and (b) near‐ultraviolet and visible radiation on polymer films dyed with the two disperse dyes, 1‐methylaminoanthraquinone and 1,4‐bismethylaminoanthraquinone, has been studied. Dyes on nylon films undergo reduction when exposed in dry nitrogen to 253‐7‐mμ radiation. The effect of near‐ultraviolet and visible radiation is different; in dry nitrogen, 1‐methylaminoanthraquinone on N‐methoxymethylnylon film is reduced to the same extent as with 253‐7‐mμ radiation, but on other nylon films (nylon 6, nylon 6.6, and nylon 11) the reduction observed with this dye is much smaller. There is no evidence of reduction of 1,4‐bismethylaminoanthraquinone on any of the nylon films. On cellulose acetate film, neither dye is reduced on exposure in dry nitrogen, by either source of radiation. The significance of these results in relation to the photo‐sensitised degradation of textile fibres is discussed.
A study has been made of the action of near‐ultraviolet and visible radiation on anaerobic solutions of 1‐methylaminoanthraquinone and 1,4‐bismethylaminoanthraquinone in different organic solvents. Fading in hydrogen‐containing solvents occurs by reduction, but substantial fading is also observed in carbon tetrachloride solution.
The action of (a) near‐ultraviolet and visible radiation and (b) short‐wave ultraviolet radiation (mainly 253.7 nm) on cellulose Alms dyed with three acylaminoanthraquinone vat dyes has been studied. Photoreduction to the acid leuco derivative of the dye is observed only on exposure to 253.7‐nm radiation. One dye (l‐benzamidoanthraquinone) has also been studied in anaerobic ethanolic solution. On exposure of this solution to near‐ultraviolet and visible radiation, the dye is readily reduced to the anthrahydroquinone. Photo‐reduction occurs readily in ethanol but with considerable difficulty on cellulose. There seems to be no correlation between the ability of the vat dye to sensitise the photochemical degradation of cellulose textiles and its ability to be photoreduced on cellulose.
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.
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