Measurement of oxidation stability of polyolefins by thermal analysis

Isothermal differential thermal analysis has been used to study the thermal stability of polybutene and crosslinked polyethylene in the temperature range from 120°C to 240°C. Oxidation induction times were measured from 2 min up to 7250 h. The Arrhenius-plots of DTA results showed curvature at 150°C, so straight line extrapolations from short-term experiments at elevated temperatures to low temperatures and long times are not possible. Oxidation induction time and mechanical failure in oven ageing experiments coincided over the measured temperature range. Decrease in the molecular weight of polybutene accelerated after the end of the induction period. Thermoanalytically measurable residual thermal stability decreased linearly with ageing time and is a more sensitive indicator of the beginning of thermal degradation than measurement of tensile properties. Finally, the extraction of stabilizer by hot water was measured by isothermal DTA.