An atomic insight into reaction pathways and temperature effects in the degradation of polyethylene, polypropylene and polystyrene

Abstract

Increasingly severe environmental pollution has spurred widespread concern regarding thermoplastics degradation. However, a lack of better understanding at the atomic level hinders the regulation of the related degradation processes. Through theoretical studies of three different typical plastics, first-principles calculations showed two basic reaction pathways for degradation: depolymerization and hydrogen-transfer-induced chain scission. The analyses of the reaction rates were consistent with those of the degradation energy barriers. Even at high temperatures, the differences in depolymerization and hydrogen transfer reactions in reaction rates and thermal perturbation probabilities are still greater than three orders of magnitude. Moreover, dynamic simulations confirm the existence of two reaction pathways and demonstrate that the two pathways occur sequentially. Our findings enrich the understanding of the basic processes of plastic degradation and may provide a reference for pyrolytic processing in waste management.