A Novel Linear-Chain Polyamide Charring Agent for the Fire Safety of Noncharring Polyolefin

A novel linear-chain polyamide charring agent named poly(piperazinyl oxalamide) (PPOA) was prepared successfully. Thermogravimetric analysis (TGA) proved that PPOA had a charring capability that was better than those of traditional polyamide charring agents. After incorporation of PPOA into ethylene-vinyl acetate copolymer/ammonium polyphosphate (EVA/APP), the flame retardancy of EVA/APP was dramatically improved. At 25.0 wt % APP/PPOA(3:1), the OI value of the EVA/APP/PPOA system was 31.5%; its UL-94 rating was V-0. Both the peak of heat release rate (PHRR) and the peak of smoke production rate (peak SPR) for the EVA/APP/PPOA system decreased remarkably compared with that of EVA containing 25.0 wt % APP. The analysis of the charring mechanism of PPOA demonstrated that abundant heterocyclic aromatic structures were formed during the decomposition of PPOA, which endowed the PPOA with excellent charring capability and resulted in the low risk of combustion of the EVA/APP/PPOA system.