Research on the co-pyrolysis kinetic and synergistic effect of waste PP and LDPE mixed plastics

Pyrolysis behaviors of polypropylene (PP), low-density polyethylene (LDPE), and their mixtures are investigated by Thermal Gravimetric Analysis (TGA) under varying heating rates to research the co-pyrolysis kinetic and synergistic effect. Model-free methods (Flynn-Wall-Ozawa method, Kissinger-Akahira-Sunose method, and Starink method) and model-fitting techniques (Malek method, Coats-Redfern method) were utilized to determine key kinetic parameters. The average activation energy are 224.69–225.19 kJ/mol for PP, 186–188.5 kJ/mol for LDPE, 195.64–197.48 kJ/mol for PP/LDPE composites. Model-fitting analysis was employed to elucidate the thermal pyrolysis mechanisms. For PP and LDPE, the A_3/2 mechanism was found to be the governing pathway, whereas the PP/LDPE blends exhibited the A₁ mechanism. Subsequently, compensation effect equations were derived to elucidate the synergistic interactions between PP and LDPE during co-pyrolysis process. The co-pyrolysis of PP and LDPE mixtures exhibit a lower pyrolysis temperature compared to the individual materials. Furthermore, the activation energy and pre-exponential factor results indicate a promotion effect in the early stage and an inhibiting effect in the later stage of the pyrolysis process.