Natural polysaccharide mediated hybrid intumescent flame retardant enables epoxy resin with high fire safety and mechanical performance.

Effectively integrating synergistic flame retardancy and mechanical preservation for high-performance epoxy resins (EP) remains a great challenge. Herein, we demonstrate a natural polysaccharide-assisted assembly strategy to fabricate custard apple-like hybrid intumescent flame retardant (ZTA) that combines the synergistic advantages of ammonium polyphosphate (APP), tannic acid (TA), and zinc borate (ZB) endows EP with high flame retardancy, smoke/toxicity suppression, and mechanical preservation. Leveraging biomass TA as interface binder to provide multiple noncovalent and coordination anchor sites, ZB microparticles are rapidly assembled on the APP surface to form ZTA with protuberant microparticles. Synergistic hybrid carbonization, dilution effects, and physical barrier effects impart EP with highly improved fire safety. The resulting EP/ZTA composite with only 5 wt% ZTA can rapidly self-extinguish and achieve a UL-94 V0 rating, while simultaneously exhibits an impressive suppression in fire growth rate (-61.7 %), peak of heat release rate (-53.8 %), and peak of smoke release rate (-44.2 %). Notably, the protuberant surface and compatible interface contribute to the in-situ formation of mechanically locked structures, making ZTA tightly clasp matrix and ensuring highly preserved mechanical performance of EP. This work presents a feasible effective strategy to produce high-performance epoxy resin with simultaneously improved flame retardancy, smoke/toxicity suppression, and mechanical preservation.