Thermal oxidation products and kinetics of polyethylene composites

The thermal oxidation behavior of high-density polyethylene (HDPE) composites was investigated at 60 °C, 90 °C and 110 °C, using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The inorganic fillers do not modify the thermal oxidation mechanisms of HDPE. However, they have great effects on the thermal oxidation kinetics-both the activation energy and the pre-exponential factor increase. That means that although the addition of inorganic fillers retards the onset of thermal oxidation of HDPE, once the oxidation begins, it proceeds much faster than that of HDPE. Stability evaluation of HDPE composites by TGA was not consistent with the result by FTIR. The inorganic fillers influence the oxidation products and their distribution greatly. HDPE/STC and HDPE/mica oxidations were delineated by large amount of carbonyl formation, especially esters and ketones, while HDPE/wollastonite and HDPE/diatomite showed minimum carbonyl formation. In HDPE composites, there is a good relation between the carboxylic formation and the carbonyl index.