Evolution of products during the degradation of polyethylene in a batch reactor

The thermal degradation of two polyethylene samples (LDPE and HDPE) has been carried out in a batch reactor under dynamic conditions. The evolution of products generated after regular intervals of 5 min (temperature increments of approximately 25 °C) has been analyzed. The behaviour of LDPE and HDPE has been compared, and no differences in the quantity and weight fraction of the gaseous products obtained have been found. For both polymers, n-paraffins are the major products at the very beginning of the process, while as the decomposition proceeds 1-olefins are more abundant. The condensed fraction is much larger than the gaseous fraction and its analysis reveals some differences between the behaviour of LDPE and HDPE at the beginning of the degradation process. These differences disappear at higher temperatures where more similar trends are observed. 1-Olefins, n-paraffins, dienes and olefins with wide carbon number distributions are the most important condensed compounds obtained in the thermal degradation of both polyethylenes. The formation of 1-olefins and n-paraffins begins at slightly lower temperatures than for dienes and olefins. On the other hand, as the temperature increases, the amount of low and high molecular weight compounds increases at the expense of intermediate molecular weight products and the former become the most important by the end of the degradation process. This behaviour could be related to the thermal cracking of waxes through secondary reactions.