Flame retardancy effect of phosphorus graphite nanoplatelets on ethylene-vinyl acetate copolymer: Physical blending versus chemical modification

A novel modified exfoliated graphite nanoplatelets (GNP-g-APP), resulting from grafting ammonium polyphosphate (APP) on exfoliated graphite nanoplatelets (GNP) was prepared and evaluated as flame retardant for ethylene-vinyl acetate copolymer (EVA). The effect of modification on the thermal stability and flame retardancy of EVA was discussed. Thermogravimetric analysis (TGA), UL-94, pyrolysis combustion flow calorimeter (PCFC), and mass loss calorimeter (MLC) analyses were employed for the evaluation of the thermal stability and flame retardancy of composites. The introduction of 20 wt.% GNP-g-APP into EVA resulted in significant enhancement in flame retardant properties with respect to the system containing physical mixture of GNP and APP. The former blend exhibited 57% decrease in the peak of heat release rate (pHRR), and 35% reduction in the total heat release (THR) than the latter one in MLC test. Thus, pHRR was decreased from 940 kW.m(-2) for neat EVA to 403 kW.m(-2) for EVA containing GNP-g-APP. V0 rating (auto-extinguishable behavior) was also observed in UL 94 chemically modified sample. According to the present study, chemical modification of GNP with APP is more effective than a physical mixing of GNP and APP in improving the flame retardant properties of EVA.