Abstract
The processing and photo-stabilising action of an n-alkyl substituted p-hydroxybenzoate light stabiliser (Cyasorb UV2908) is examined in high density polyethylene using normal and derivative ultraviolet-visible and infra-red spectrophotometry and hydroperoxide analysis. In comparison with two related systems—2,6-di-tert-butyl- p-cresol (Topanol OC) and 4-hydroxy-3,5-di-tert-butylbenzoic acid (Shell Acid)—it proved to be an effective light stabiliser, particularly when compared with its performance in polypropylene. The photo-stabilising action of the p-hydroxybenzoate light stabiliser is found to be dependent on the initial concentration of hydroperoxide groups in the polymer, indicating it to be an effective alkoxy and hydroxy radical scavenger. Unlike its behaviour in polypropylene, it did not suppress hydroperoxide formation during processing, indicating it to be ineffective as a macroalkyl radical scavenger in high density polyethylene. Its inability to photolyse to give active quinone products and its good compatibility and alkoxy and hydroxy radical terminating properties are key factors which are responsible for its light stabilising function in high density polyethylene.
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