Pyrolysis Mechanism of a Cyclotriphosphazene-Based Flame-Retardant Epoxy Resin by ReaxFF Molecular Dynamics

Cyclotriphosphazene derivatives can effectively improve the flame retardancy and fire safety of epoxy resins (EPs) via their influence on the pyrolysis process. In this work, the effects of hexa(5-methyl-2-pyridinoxyl)cyclotriphosphazene (HMPOP) incorporation on the initial pyrolysis of an EP at 500-3500 K were studied using the ReaxFF method. The pyrolysis fragments, initial reaction pathways, and main products were identified for the EP and EP/HMPOP composites. The activation energies were derived by fitting the weight percentage curves for solid species during the pyrolysis reactions and the obtained values were in good agreement with experimental data. The initial EP pyrolysis reactions included four major decomposition modes, which primarily involved the cleavage of C-O and C-N bonds. The main pyrolysis products were H2O, CO, C2H4, and CH2O. HMPOP bonded with the oxygen-containing fragments to form larger molecular fragments and reduced the amounts of C0-C4 products, especially that of the harmful gas CH2O. Thus, HMPOP promoted the formation of carbon clusters and reduced the generation of combustible gases, ultimately decreasing the capacity for fire propagation.