Pyrolysis behavior of automotive polypropylene plastics: ReaxFF molecular dynamics study on the co-pyrolysis of polypropylene and EPDM/POE

The pyrolysis mechanism of automotive polypropylene (PP) plastics is essential for their recycling. Ethylenepropylene-diene monomer (EPDM) rubber and polyolefin elastomers (POE) are two common additives used in automotive polypropylene plastics, but little is known about the influence of the above two on PP pyrolysis. In this work, the molecular models of EPDM and POE were constructed. Then the pyrolysis behaviors of PP, EPDM, and POE were investigated by reactive force field molecular dynamics (ReaxFF MD), and also the co-pyrolysis of PP and EPDM/POE. The results showed that the content of C40+ products decreased rapidly and the other components were formed in 300-400 ps (2000-2500 K) in all the systems. The co-pyrolysis of PP and EPDM promoted the formation of the tar and delayed the formation of C40+ products. While the co-pyrolysis of PP and POE increased the gas formation, especially C2H2 and C3H4, but inhibited the formation of heavier components. It was also found that C2H2 was mainly from C2H3, C3H5, and C5H6, and C3H4 was mainly from C3H3, C3H5, C4H7, C6H8, and C6H9. The contents of C2H3, C3H3 and C3H5 were significantly high in the PP-POE system. Finally, the associated radical reactions were observed in the overall reaction pathways.