Product analysis for polyethylene degradation by radiation and thermal ageing

The oxidation products in crosslinked polyethylene for cable insulation formed during thermal and radiation ageing were analyzed by FTIR-ATR. The products were composed of carboxylic acid, carboxylic ester, and carboxylic anhydride for all ageing conditions. The relative yields of carboxylic ester and carboxylic anhydride increased with an increase of temperature for radiation and thermal ageing. The carboxylic acid was the primary oxidation product and the ester and anhydride were secondary products formed by the thermally induced reactions of the carboxylic acids. The carboxylic acid could be produced by chain scission at any temperature followed by the oxidation of the free radicals formed in the polyethylene. The results of the analysis led to formulation of a new oxidation mechanism which was different from the chain reactions via peroxy radicals and peroxides.

► Products analysis of polyethylene degradation by radiation and thermal ageing.
► Components of carbonyl compounds produced in polyethylene by thermal and radiation oxidation were determined by FTIR.
► Carbonyl compounds comprised carboxylic acid, carboxylic ester, and carboxylic anhydride.
► Carboxylic acid was the primary oxidation product of chain scission at any oxidation temperature.
► Carboxylic ester and carboxylic anhydride are secondary products formed from carboxylic acid at higher temperature.