Mechanistic action of a new p‐hydroxybenzoate light stabiliser in polypropylene film: A spectroscopic study

Abstract

AbstractThe photostabilising action of a new aliphatic p‐hydroxybenzoate light stabiliser has been examined in polypropylene film together with the aid of 3,5‐di‐tert‐butyl‐4‐hydroxybenzoic acid by both normal and derivative UV absorption and IR spectroscopy, and hydroperoxide analysis. The stabiliser has also been examined in solution together with a number of related compounds using micro‐second flash photolysis. During processing the stabiliser operates as an effective chain breaking donor by terminating macroalkyl radicals and inhibiting the formation of hydroperoxides. Under both monochromatic (365 nm) and polychromatic (λ > 320 nm) irradiation conditions the decomposition of the stabiliser shows a direct dependence on initial hydroperoxide concentration in the film, indicating that it operates as an effective light stable alkoxy and hydroxy radical scavenger. The protective effect of a peroxide decomposer confirms this mechanism. Evidence is also presented to show that under photosensitised radical attack the presence of the long aliphatic hydrocarbon chain has a powerful protective effect on the molecule. On flash photolysis of all the compounds studied end‐of‐pulse transient absorption spectra were assigned to phenoxy radicals. The radicals decayed by a second order process to give dimeric coupling products. The nature of these products are discussed and identified for the compounds studied. The technique of flash photolysis is concluded to be a useful method for assessing anti‐oxidant activity.