Pyrolysis characterization and mechanism studies of different structural plastics: A comparative study at optimal temperatures

Thermal conversion technology is an effective means to transform waste plastics into high-value-added products. This study explored the thermal decomposition characteristics and cracking mechanism of four different types of plastics (polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET)) for thermal conversion technology. The findings revealed that PP exhibited the highest hydrogen yield, reaching 3.56 mmol/g at 510°C. PET's gas production was predominantly comprised of carbon monoxide and carbon dioxide. PVC gas products contained a significant amount of HCl, followed by hydrogen and methane. For solid products, the carbon yield followed the order PET > PVC > PS > PP, with the carbon content of PET accounting for 35.63% of the total products. PP and PS demonstrated higher oil yields for liquid products than PET and PVC. The oil yield of PP was 94.38%. Further analysis of the cracking mechanism found that during the thermal decomposition process, plastics underwent random fragmentation, leading to reactions such as β-scission, intramolecular and intermolecular hydrogen transfer, rearrangement, cyclization, etc., due to structural variations. This work provided foundational data for the thermal decomposition studies of different types of plastics.