Pyrolysis Kinetics of Polytetrafluoroethylene (PTFE)

Abstract

Polytetrafluoroethylene (PTFE) is widely used in fields such as propellants and flame retardants. However, this is still a vacancy of detailed kinetic mechanisms to describe the complete decomposition of PTFE in the gas phase. The current work addresses this issue by conducting ab initio calculations for key reactions involved in the PTFE pyrolysis system. The potential energy surfaces (PESs) of PTFE unimolecular and bimolecular reactions are determined at the DLPNO-CCSD(T)/cc-pVTZ//B3LYP-D3/6–31++G(d,p) level. Rate constants and branching ratios of the main reaction pathways are calculated by solving the RRKM master equation, and the thermochemical properties of related species at the DLPNO-CCSD(T)/CBS level are calculated via the atomization method. The current study found that the initial decomposition of PTFE is dominated by the CC scission reactions and free radical (H, OH, CF, CF₂, and CF₃) abstraction reactions, forming the corresponding free radical species. Further β-CC scission reactions dominate the overall kinetics and continuously generate CF₂CF₂. Self-decomposition and free radical–driven decomposition of PTFE produce small molecules such as HF, FOH, CF₂, CF₃, and CF₄. This work provides quantitative predictions of the detailed decomposition reaction pathways of gas-phase PTFE and will lay a solid foundation for the development of detailed kinetic mechanisms for PTFE combustion and degradation.