A strategy to construct multifunctional ammonium polyphosphate for epoxy resin with simultaneously high fire safety and mechanical properties

Abstract Obtaining a well balance between the high fire safety and mechanical performance of epoxy resins (EP) is still a challenge for the traditionally intumescent flame retardant. Herein, a new strategy was constructed to realize the highly uniform dispersion of zeolitic imidazolate framework-67 (ZIF-67) on the ammonium polyphosphate (APP) through the coordination reaction of the pre-bonded Co2+ cations with phosphate and 2-methyimidazole. The as-obtained ZIF-67@APP in the loading of 5 wt% endowed EP with a LOI value of 28.5% and UL-94 V0. Furthermore, peak of heat release rate (PHRR) and smoke production rate (SPR) of ZIF-67@APP/EP were greatly decreased by 67.4% and 46.2% compared to EP with 5 wt% APP. The improved fire safety of ZIF-67@APP/EP was ascribed to the faster formation of the expanded char owing to the catalysis of cobalt cation. Meanwhile, the good compatibility between ZIF-67@APP and EP also presented better mechanical properties.