Insights into the pyrolysis mechanisms of epoxy resin polymers based on the combination of experiments and ReaxFF-MD simulation

Epoxy resin offers promising properties in composites, while its cross-linked structure prevents the disposal of waste composites. Pyrolysis is an essential technique for the breakdown of epoxy resin polymers, but the fundamental reaction mechanisms need to be clarified. In this study, the combination of experimental studies and the reactive force field molecular dynamic (ReaxFF-MD) simulation were performed to determine the formation mechanisms of pyrolysis products considering the secondary reactions of intermediates. The pyrolysis process was divided into the cleavage and polycondensation stages based on the carbon atom numbers of the largest cluster. The cleavage stage began with the removal of side-chain substituents, followed by the breakdown of the primary epoxy resin chain, resulting in the generation of pyrolysis gas products, of which the OH, C-C-O, and CH3 groups were identified as the critical intermediates in the creation of H2O, CO, and CH4, respectively. Meanwhile, the simultaneous evolution of liquid pyrolysis products (bisphenol A, phenol, and benzene) was established. After the epoxy resin chains were completely cracked, the unsaturated hydrocarbon intermediates underwent the dehydrogenation and polymerization reactions, causing the formation of pyrolysis char and the continuous generation of H2, H2O, and CO. The findings could provide some guidance to selectively regulate the pyrolysis of epoxy resin matrix composites.