Influence of Molecular Weight and Temperature on the Pyrolysis Behavior of Polyethylene

The pyrolysis technique is a useful recycling method for waste polyethylene (PE). Various PEs with different molecular weights have been produced and are widely used. The major pyrolysis products of PE include alkadienes (C_nH_2n-2), alkenes (C_nH_2n), and alkanes (C_nH_2n+2). In this study, the differences in pyrolysis behavior of PE based on its molecular weight and the pyrolysis temperature (423-764 °C) were investigated using four types of PEs, with M_w = 2.0 × 10³, 16.0 × 10³, 28.3 × 10³, and 56.8 × 10³ g/mol. More specifically, the pyrolysis products were compared in terms of their type (alkanes, alkenes, and alkadienes) and size (the number of carbon atoms). The order of production was alkenes > alkanes > alkadienes. The alkadiene/alkene ratios tended to increase with the PE molecular weight and size of the pyrolysis products. The alkadiene/alkene ratio increased until the pyrolysis temperature reached 670 °C. The alkane/alkene ratios tended to decrease as the PE molecular weight increased; however, they increased with the increasing size of the pyrolysis products. The alkane/alkene ratio decreased as the pyrolysis temperature increased, until it reached 670 °C. The formation of alkenes was more favorable than that of alkadienes and alkanes.