Abstract
An analysis of the mechanism of photochemical ageing of aliphatic polyamides (PAs) and of model compounds is made, on the basis of work carried out by the present authors and of work published in the literature on photolysis and photochemical oxidation of PAs. It is shown that this process is a complex combination of alternating reactions, the ratio of the rates of which is dependent on the conditions of diffusion of oxygen in the sample during the time of irradiation, on the degree of photochemical oxidation and on the intensity and spectral composition of the light capable of causing photoinitiation. Possible ways in which the products are formed, are discussed. Criteria of diffusion control are obtained. It is shown that in the primary photochemical process scission of peptide bonds occurs. Differences observed in the relative rates of scission, formation of radicals and absorption of oxygen in direct and sensitized photochemical oxidation of a PA are explained by difference in the ratio of the rates of primary and secondary photochemical processes.
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