Abstract
Plastic pyrolysis is widely promoted as a techno-economic industrial scale recycling strategy. Nevertheless, the fate and reactivity of plastic chemical additives during pyrolysis are mostly overlooked in product quality and environmental release assessments. Here, we present an integrated modeling framework to elucidate the role of additives in plastic pyrolysis and evaluate the implications of their transformation products and environmental releases. Using high-density polyethylene (HDPE) as a case study, chemical additives of concern are selected based on occurrence, concentration data, and potential risk to human health and the environment. Bond dissociation energies are predicted using a machine learning model to identify dominant radical species formed under pyrolytic conditions. These additive-derived radicals are incorporated into an automatic chemical reaction mechanism generator that constructs kinetic models composed of elementary chemical reaction steps. These kinetic models are simulated using kinetic Monte Carlo (kMC) methods to predict product distributions and yields. The results show that common additives readily form stabilized alkyl and aryl radicals at energies accessible during pyrolysis, enabling their active participation in polymer degradation pathways. These interactions influence product formation and may contribute to the generation of environmentally relevant by-products. Overall, this study provides a mechanistic and risk-informed perspective on plastic pyrolysis, emphasizing the importance of explicitly accounting for additive chemistry in the development of safer and more sustainable chemical recycling technologies.Disclaimer: The views expressed in this work are those of the authors and do not necessarily represent the views or policies of the EPA.