Highly efficient halogen-free flame-retardant ethylene vinyl acetate rubber via covalent grafting strategy

A single-molecule intumescent flame-retardant (ABDP) was designed and synthesized for the intrinsic flame-retardant modification of ethylene vinyl acetate rubber (EVM). Through peroxide-initiated radical reactions, ABDP was covalently grafted onto the EVM molecular chain, constructing a P–N flame-retardant network. The mechanical, thermal and fire performances of the resulting composites were systematically investigated. The composite containing 16wt % ABDP (ABDP16) facilitated the formation of a continuous and highly graphitized intumescent char layer in the condensed phase, reducing the peak heat release rate (PHRR) and peak smoke production rate (PSPR) by 52.1 % and 46.1 %, respectively, while markedly enhancing thermal stability and tensile strength. After magnesium hydroxide (MH) was introduced, the EVM16 composite achieved a limiting oxygen index (LOI) of 30.7 % and a V-0 rating in the UL-94 test, with the PHRR and PSPR reduced by 77.2 % and 70.6 %, respectively. Moreover, its fire-growth index (FGI) decreased from 13.1 to 1.53 kW/(m 2 ·s). The metal oxides generated from the decomposition of MH were anchored within the char layer, yielding a compact, continuous barrier that effectively suppressed gaseous-fuel transport and heat diffusion. This work provides a feasible flame-retardant molecular-design strategy for developing highly efficient, durable and eco-friendly intrinsically flame-retardant EVM composites.