Facile construction of polypyrrole microencapsulated γ‐Fe2O3 for simultaneously enhancing the flame retardancy and smoke toxicity suppression of intumescent flame‐retardant epoxy resins

Abstract For effectively strengthening the comprehensive properties of intumescent flame‐retardant epoxy resins (EPs), a microencapsulating γ‐Fe 2 O 3 by polypyrrole (PPy) named PPy‐Fe 2 O 3 was synthesized and used as a synergist to simultaneously enhance the flame retardancy, smoke toxicity suppression and mechanical strength of EP composites containing diaminodiphenylmethane modified ammonium polyphosphate (DDP). The results demonstrate that the mixture of PPy‐Fe 2 O 3 and DDP exhibits a surprising synergistic effect on strengthening the comprehensive properties of EP composites. Specifically, EP composite containing 0.2 wt% PPy‐Fe 2 O 3 and 9.8 wt% DDP achieves the UL94 V‐0 rating with a limiting oxygen index (LOI) value of 35.5%, while 10 wt% DDP only imparts a UL94 V‐1 rating and a LOI value of 34.0% to EP. Furthermore, 0.2 wt% PPy‐Fe 2 O 3 shows a 11.0% reduction in peak smoke production rate and a 12.3% reduction in peak heat release rate of the EP/DDP system. The enhanced fire security of EP/DDP/PPy‐Fe 2 O 3 is attributed to the formation of more phosphorus‐rich structures retained in the char, thus reducing the release of harmful gases including NH 3 , CO, and CO 2 , and generating more incombustible gases including H 2 O to weaken burning intensity. Meanwhile, the satisfactory compatibility of PPy‐Fe 2 O 3 with epoxy matrix imparts a superior mechanical strength to EP composites.