No abstract

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 CO 2 and CO and the generation of more incombustible gases including H 2 O and NH 3 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.

A unique hybridized intumescent flame retardant named reduced-graphene-oxide-modified ammonium polyphosphate (RGO-APP) was successfully synthesized via the simple hydrothermal method and reduced process. Then, the obtained RGO-APP was applied in epoxy resin (EP) for flame retardancy reinforcement. The addition of RGO-APP results in a significant reduction in heat release and smoke production from the EP, which is attributed to EP/RGO-APP producing a more compact and intumescent char against the heat transfer and combustible decomposition, thus enhancing the fire safety of EP, as confirmed by char residue analysis. Especially, the EP containing 15 wt% RGO-APP acquires a limiting oxygen index (LOI) value of 35.8% and shows a 83.6% reduction in peak heat release rate and a 74.3% reduction in peak smoke production rate compared with those of pure EP. The tensile test exhibits that the presence of RGO-APP favors the enhancement in tensile strength and elastic modulus of EP due to the good compatibility between flame retardant and epoxy matrix, as supported by differential scanning calorimetry (DSC) and scanning electron microscope (SEM) analyses. This work provides a new strategy for the modification of APP, thus facilitating a promising application in polymeric materials.