Nano‐Magnesium Hydroxystannate Promotes Phosphorylation of Ammonium Polyphosphate and Piperazine Pyrophosphate to Improve the Flame‐Retardant and Smoke‐Suppressant Properties of Epoxy Resins

ABSTRACT This study first synthesized nanocubic, well‐dispersed magnesium hydroxystannate (MHS) and developed a novel composite flame retardant (MHS‐APP‐PAPP) by combining MHS with ammonium polyphosphate (APP) and piperazine pyrophosphate (PAPP) to mitigate smoke/toxic gas emissions from burning epoxy resin (EP). At 10 wt% loading, MHS‐APP‐PAPP/EP achieved a 37.3% limiting oxygen index (LOI) and UL‐94 V‐0 rating. Cone calorimetry tests showed 71.3%, 42.0%, and 71.0% reductions in peak heat release rate, total heat release, and total smoke production compared to pure EP, respectively. The decomposition products (MgO, Sn, and SnO 2 ) from MHS promoted crosslinking of APP/PAPP phosphate groups to form SnP 2 O 7 and phosphate networks. Concurrently, phosphoric/hypophosphoric acids from APP/PAPP enhanced char formation through dehydration, creating a dense barrier against heat, oxygen, and toxic gases while trapping free radicals. Piperazine groups in PAPP compensated for EP's carbon deficiency. The composite also maintained EP's mechanical properties by improving interfacial compatibility between the flame‐retardant additives and the polymer matrix. This multipathway, multielement synergy effectively addresses both flame spread and smoke suppression challenges in EP combustion.