Photosensitisation and Tendering by Vat Dyes

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Abstract
The relative activities of a number of vat dyes have been compared for the following photosensitised reactions– (a) tendering of viscose, (b) autoxidation of tetialin, (c) polymerisation of styrene, and (d) deactivation of the excited dyes by oxygen.The tendering activities show no correlation with (c) or (d) but sliow a moderato correlation with (b). It is concluded that the tendering of colluloso in tho presence of water involves a preliminary oxidation of hydi'oxyl ion by tho oxcited dye, and not a transfer of energy to oxygon as Egerton has postulated. The main tendering action involves hydrogen poroxide as an intermediate, in agreement with Egerton. The detailed mechanism is discussed.The tendering of dry cellulose, or of nylon, silk, or cellulose acetate, probably involves non–chain oxidations of the fabrics by the excited dyes. A mechanism is postulated which accounts for the non–formation of hydrogon poroxido in the absence of moisture.The quantum yield and the intensity oxponont in the tendering of moist cellulose have boon ostimatod. The effect of the distribution of dye in the fibre has also been studied.

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