Correlating different techniques in the thermooxidative degradation monitoring of high-density polyethylene containing pro-degradant and antioxidants

Different techniques were used to assess the effect of a primary and a secondary antioxidant, separately, and in combination with a pro-degradant (manganese stearate) on the thermooxidative abiotic degradation of high-density polyethylene (HDPE). The parameters measured over time at three temperatures (60, 70 and 80 °C) were variation in carbonyl index (CI), by means of infrared spectroscopy; reduction in tensile strain at break, by means of mechanical testing; reduction in molar mass distribution by means of size exclusion chromatography (SEC). Regardless of the presence of primary or secondary antioxidants, the same levels of degradation were attained. However, contrary to the secondary antioxidant, the primary antioxidant significantly increased induction time of HDPE oxidative degradation processes, evidenced by the shift in the “CI versus time” curve and by the considerably longer time for the strain at break to reach minimal values. Increase in thermooxidation temperature reduced induction time significantly.