Synergistic effect between a novel triazine-based flame retardant and DOPO/HPCP on epoxy resin

In this paper, a triazine-based flame retardant (TAT) was synthesized from cyanuric chloride and aniline. Its chemical structure was characterized by Fourier transform infrared (FTIR) spectroscopy, H-1 nuclear magnetic resonance, and elemental analysis. Two kinds of novel intumescent flame-retardant epoxy systems were obtained with the incorporation of TAT and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) or hexa-phenoxy-cyclotriphosphazene (HPCP). The flame retardancy of the obtained epoxy samples was evaluated using limited oxygen index, vertical burning (UL94), and cone calorimeter tests. The results indicated that there was a synergistic effect between TAT and DOPO or HPCP. The flame-retardant mechanism was investigated by thermogravimetric analysis (TGA), thermogravimetric analysis/infrared spectrometry (TGA-FTIR) coupled with the morphology and chemical analysis of the char residues. During combustion, DOPO or HPCP decomposed to release phosphorus-containing free radicals with quenching effect. The morphology study showed that the introduction of DOPO or HPCP promoted the carbonization of epoxy matrix and the formation of a phosphorus-containing viscous char layer, while the pyrolysis gases derived from the decomposition of TAT caused the char layer to expand. The main reason of the promotion of flame retardancy of epoxy samples was that the simultaneous addition of TAT and DOPO or HPCP led to the formation of a compact and intumescent char layer that restricted the transfer of heat and combustible volatiles and simultaneously protected the underlying matrix.