A facile strategy to construct multifunctional microencapsulated urea ammonium polyphosphate for epoxy resins towards satisfied fire safety, thermal stability and compatibility

Enhancing the fire safety of epoxy resin (EP) concomitant with less mechanical performance degradation is still a challenge for traditional flame retardants. Hence, polypyrrole (PPy) was used as a film material to fabricate microencapsulated urea ammonium polyphosphate (UAPP) for simultaneously improving the fire safety, thermal stability and compatibility of epoxy composites. The obtained polypyrrole-coated urea ammonium polyphosphate (PPy-UAPP) at a load of 10 wt% endows the EP with a UL94 V-0 rating and a limiting oxygen index (LOI) value of 32.3%, while 10 wt% ammonium polyphosphate (APP) only endows EP with a LOI of 28.5%. Furthermore, the peak heat release rate (PHRR) and peak smoke production rate (PSPR) of EP containing 10 wt% PPy-UAPP are decreased by 12.3% and 21.4% compared to EP containing 10 wt% APP. The decreased fire hazard of EP/PPy-UAPP is attributed to the reduction of hazardous gases including CO2 and CO and the generation of more incombustible gases including H2O and NH3 to reduce the combustion intensity. Meanwhile, the good compatibility between EP matrix and PPy-UAPP endows the resulting EP composites with a superior balance between fire safety and mechanical properties.