Influence of metallic additives on thermal degradation and liquefaction of high density polyethylene (HDPE)

Abstract

This study evaluates the effect of typical polymer fillers on the thermal degradation of a commodity plastic to produce liquid fuels. HDPE was degraded in the presence and absence of some metallic additives such as Al(OH) 3·xH 2O, AlCl 3, Al 2O 3, CaCO 3, CuO, ZrO 2, and Fe 2O 3. Liquefaction of HDPE in the presence of selected additives was also carried out to verify the thermal gravimetric data. The HDPE liquefaction conditions such as temperature, effect of H 2 or N 2 pressure, and time were established before studying the effect of additives. At 50% weightloss, Al 2O 3 increased the degradation temperature by ~30 °C, whereas ZrO 2 and CaCO 3 decreased it by ~30 and 70 °C, respectively. All the additives were thermally stable below 600 °C except AlCl 3 and Al(OH) 3·xH 2O. Under the experimental conditions used, the thermal degradation trend of HDPE in the presence of Al 2O 3 was clearly reflected in the liquefaction product analysis. With Al 2O 3, the liquefaction of HDPE was delayed, which in turn resulted in wax formation. It was further proved by simulated distillation and gel permeation chromatographic analysis. More gas in the presence of ZrO 2 and more oil (85%) in the case of CaCO 3 were produced when compared to the liquefaction of HDPE alone (75%). However, the simulated distillation and GPC analysis of these products obtained at the end of 30 min liquefaction time did not show significant variation when compared to that of HDPE alone. The nature of gas did not affect the oil yield. However, the temperature and time were critical in obtaining the maximum oil yield.