Concurrently improving fire safety and processability of ethylene vinyl acetate copolymer by expandable graphite and polyphosphoric acid

Ethylene vinyl acetate copolymer (EVA) was modified by expandable graphite (EG) and polyphosphoric acid (PPA) in melt state and the obtained EVA/EG/PPA composite was studied regarding its fire behavior, thermal endurance, water resistivity, processability, and mechanical property. The outcomes evince that the combination of EG and PPA in proper mass ratio can improve fire retardancy, thermal stability, processability, and reduce smoke and toxic gas releases of EVA upon combustion significantly. The EG/PPA combination exhibits very high flame retardant efficiency to EVA in that only 10 wt% loading is enough to make EVA obtain V-0 rating in UL-94 test. Moreover, the flame-retarded EVA/EG/PPA composite displays excellent water resistance and acceptable mechanical property. The EVA/EG/PPA (90/7.5/2.5) composite can produce coherent intumescent char on composite surface, which has good heat endurance and hinders heat transmission from fire to interior of composite. The flame retardation occurs in condensed phase and the intumescent char plays a pivotal role. The presence of PPA endows EVA composite with good melt flowability, which has presented a striking contrast to other flame retardants.