Assembly of phytic acid-Ni2+ via bionic poly-dopamine-mediated to construct a core-shell MgCO3 for fire-safe EVA composites

A mussel-inspired polydopamine-assisted layer-by-layer assembly combined with a metal-chelating strategy using phytic acid was employed to synthesize a novel multi-level core-shell magnesium carbonate-based flame retardant (AMC@PDA@PA-Ni) for enhancing the fire safety of ethylene vinyl acetate (EVA) copolymers. The incorporation of 50 wt% AMC@PDA@PA-Ni increased the LOI of the EVA composite to 30.3 %, achieving a UL94 V-1 rating. Compared to pristine EVA, the composite exhibited a 63.3 % reduction in peak heat release rate (pHRR) and a 66.7 % decrease in peak smoke release rate (pSPR). At elevated temperatures, the combined effects of AMC's gas-solid phase flame retardancy, the phosphorus-containing flame retardant's quenching action, and the transition metal nickel's catalytic charring capability significantly contributed to the composite's superior fire resistance. Additionally, the tensile strength of the EVA/AMC@PDA@PA-Ni composite increased by 97.6 % relative to EVA/AMC, attributed to the PDA modification, which enhanced filler dispersion and interfacial adhesion. This study introduces a facile and effective strategy for developing bio-based multi-level core-shell hybrid flame retardants with outstanding fire resistance and mechanical strength retention.