Flame retardant mechanism of phosphorous-containing green flame retarded epoxy: a molecular dynamics study

Flame-retardant (FR) chemistry of epoxy resins (EP) is microscopic and sophisticated, where retardant additives are engineered at the local polymer chains to facilitate carbonisation and radical exchanges during pyrolysis. Although analyrical experiments have been extensively performed to elucidate the thermal degradation characteristics of FR-contained polymers, dynamic and atomistic observations for comprehending the FR mechanism and reaction pathways during pyrolysis remains, specifically when crosslinked EP and bio-based architectures are involved in the FR systems. In this study, we utilised Reactive Molecular Dynamics simulations (MD-ReaxFF) to analyse the pyrolysis behaviour of resveratrol- and phosphorous-contained green FR epoxy systems. The MD models were comprised of a recent synthesised bio-based FR, DPOR, and EP matrices to investigate the pyrolysis mechanisms of polymer and species spectrums. The results showed that the inclusion of DPOR generally reduced the number of alkene products and shifted the pyrolysis behaviour towards long-chain products via dehydration. A series of parametric studies were also conducted to predict the char yield of EP and EP/DPOR systems using periodic removal functions. This study provides valuable insights into the mechanism of bio-based FRs and their effectiveness on epoxy pyrolysis. Moreover, MD simulations provide valuable atomistic details that can be utilised to extract kinetic parameters, examine pyrolysing volatiles, and enhance the accuracy of predictions related to EP charring. The MD-ReaxFF simulations offer an effective analytical tool for evaluating and optimising EP systems with respect to their flammability characteristics and charring properties.