Improved thermal properties of epoxy resin modified with polymethyl methacrylate-microencapsulated phosphorus-nitrogen-containing flame retardant

Epoxy resin (EP) composites with improved thermal resistance were fabricated. To solve the problem of low thermal resistance derived from phosphazene flame-retardant additives, we designed a system based on flame-retardant microcapsules P(H), with hexaphenoxycyclotriphosphazene as the core and polymethyl methacrylate as the shell. The core-shell structure was characterized and confirmed. The thermal resistance of the cured EP composites containing 1 wt% P(H) microcapsules was improved because of the increased glass transition temperatures. The P(2.75H)/EP composites can reach a limited oxygen index of 30.5% and V-1 rating in UL-94 tests. Heat and gas release rates were reduced during combustion tests. Residual images implied that the P(H) microcapsules may promote the formation of a flame-retardant char layer. Pyrolysis analysis demonstrated that the P(H) microcapsules can decompose in two procedures to produce flame-retardant gas components. Therefore, the flame-retardant mechanism involved the flame inhibition effect in the gas phase, and the charring effect in the condensed phase. Epoxy resin composites with improved thermal resistance and flame retardancy were fabricated based on P(H) microcapsules.