Mesoscale Simulation of Polymer Pyrolysis by Coarse-Grained Molecular Dynamics: A Parametric Study

Fullcomprehension of the pyrolysis of polymer materials is crucialfor the design and application of thermal protection systems; however,it involves complex phenomena at different spatial and temporal scales.To bridge the gap between the abundant atomistic simulations and continuummodeling in the literature, we perform a novel mesoscale study ofthe pyrolysis process using coarse-grained molecular dynamics (CGMD) simulations. Polyethylene (PE) consisting of united atoms includingimplicit hydrogen is considered a model polymer, and the configurationalchange of PE in thermal degradation is modeled by applying the bond-breakingphenomenon based on bond energy or bond length criteria. A cook-offsimulation is implemented to optimize the heuristic protocol of bonddissociation by comparing the reaction products with a ReaxFF simulation.The aerobic hyperthermal pyrolysis under oxygen bombardment is simulatedat a large scale of hundreds of nanometers to observe the intricatephenomena occurring from the surface to the depth inside the material.The intrinsic thermal durability of the model polymer at extreme conditionswith and without oxygen environment can be effectively simulated fromthe proposed mesoscale simulation to predict important thermal degradationproperties required for continuum-scale pyrolysis and ablation simulations.This work serves as an initial investigation of polymer pyrolysisat the mesoscale and helps understand the concept at a larger scale.