Exploring pyrolysis mechanism of waste PET in different degrees of polymerization to regulate the pyrolysis products

M Li and YF Jia and DZ Chen and G Yuan and KZ Qian and LJ Yin and KG Wang and L Hong and YY Hu, POLYMER DEGRADATION AND STABILITY, 233, 111175 (2025).

DOI: 10.1016/j.polymdegradstab.2025.111175

Polyethylene terephthalate (PET) is widely used in plastic products, and after their life time, the PET products can be converted into chemicals, oils or gases through the pyrolysis process. Understanding the pyrolysis mechanism of PET can offer valuable insights for controlling the resulting products. This study combines reactive force field molecular dynamics (ReaxFF MD) simulation with Py-GC/MS and TG-FTIR experiments to investigate the pyrolysis mechanism of PET, and the influence of degree of polymerization (DP) on the products. The results show that the DP primarily affects the secondary reaction products at high temperatures, but with minimal influence on reaction rate or products from the initial chain scission. Through isothermal pyrolysis it can be revealed that stochastic chain scission is a key step at the initial stages, yielding primary products such as CO2 and ethylene. The study also finds that PET's ester bonds are firstly cleaved during pyrolysis, leading to the formation of carboxyl groups through interactions with hydrogen radicals, and H2O and H2 are the main products of the secondary reactions, which is proved by TG-FTIR experiments. Both the Py-GC/MS experiments and simulation results show that the production of benzene derivatives follows a "V-shaped" pattern, showing rapid decreases and increases as temperature rises, while CO2 and C2 yields decrease at higher pyrolysis temperatures. This research offers valuable insights into degradation mechanism of PET's at high-temperature in atomic level, providing a foundation for controlling and optimizing its pyrolysis products.

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