Mechanistic Insights into the Thermal Degradation of Polytetrafluoroethylene

Synthetic fluoropolymers, notably poly- and perfluorinated alkyl substances (PFAS), are widely utilized in various industrial applications, such as kitchenware, textiles, and flame-resistant materials. The presence of C-F bonds endows many fluoropolymers with significant wettability, along with thermal and chemical stabilities, and distinctive friction characteristics. However, there are growing concerns regarding the toxicity of fluoropolymers in living organisms, attributed to their strong affinity for proteins and their persistence in the environment. A combustion-based methodology has been proposed to mitigate the concentrated presence of fluoropolymers in open-air conditions. As expected, identifying the key decomposed compounds produced from combustion process is not a trivial task. Therefore, theoretical approaches have often been employed to forecast the potential products formed during experimental thermal decomposition conditions.

In this study, the degradation mechanism of polytetrafluoroethylene (PTFE) has been investigated via the combination of density theory (DFT) calculations and molecular dynamics (MD) simulations. Additional analysis of the enthalpic and entropic contributions to the production of key reaction intermediates, including perfluorocyclobutane (C₄F₈), was considered. Coupling with DFT-based kinetic parameters, the microkinetic modelling was also designed to understand the concentration profiles of major products from combustion reactions. Overall, such combined theoretical approaches may serve as a reference to identify key products of the thermal degradation processes of various fluoropolymers.