Reactive molecular dynamics simulations of plastics pyrolysis with additives: Comparison of ReaxFF branches and experimental results

In this work, the efficiency of the combustion and aqueous branches of the reactive potential ReaxFF are compared through pyrolysis investigations from reactive molecular simulations of three polymers: polyethylene (PE), polystyrene (PS) and polypropylene (PP) with additive compounds. Thermogravimetric analyses were implemented, computing the weight loss percentage along with analyzes of the pyrolysis products. Three force fields were considered: the CHON-2019 and the CHOSFClN potentials coming from the combustion branch and the CHONCl-2022_weak potential coming from the aqueous branch. The results show that both CHON-2019 and CHONCl-2022_weak force fields give similar results in adequacy with the experimental results and are better than the CHOSFClN force field from the combustion branch. They can correctly predict the kinetic order of polymer degradation and identify the species formed and their quantities. As a result, the latest versions of the ReaxFF potential, belonging to the aqueous branch, are well suited to study the pyrolysis processes and may give equal or better results than force fields from the combustion branch. Furthermore, force fields from the aqueous branch seem to be more reliable for the investigation of the effect of the additives’ role on plastic pyrolysis. Finally, an important aspect presented in this article is the use of statistical simulations for the different investigations. An uncertainty estimation of 30 K was computed from ten thermogravimetric analyses simulated with ReaxFF on the PP pyrolysis.