Synergistic Effect between Modified Graphene Oxide and Ammonium Polyphosphate on Combustion Performance, Thermal Stability and Mechanical Properties of Polylactic Acid

To improve the thermal stability, ZF-GO (graphene oxide (GO) modified by zinc ferrite (ZF)) is prepared. In view of the anti-dripping function of ZF-GO and flame retardant effect of ammonium polyphosphate (APP), the influence of ZF-GO, APP, mixture of ZF-GO and APP on combustion performance, thermal stability and mechanical properties of polylactic acid (PLA) is investigated. Results show that the modification of GO by ZF significantly improves the residue of ZFGO by 34.7%. The char-forming capability and unique network structure of ZF-GO prevent the melt dripping of PLA. Although APP can increase the limiting oxygen index of PLA, there is still melt dripping. The combination of ZF-GO and APP improves the residual yield of 94PLA/3ZF-GO/3APP by 4.3 times relative to pure PLA, and the UL-94 level reaches V-0. The two additives show synergistic char-forming effect, and there is both physical carbonization and chemical carbonization. The incorporated fillers can decrease the total heat release (THR) of PLA composites. Specifically, the THR and peak value of heat release rate of 94PLA/3ZF-GO/3APP decrease by 21.2% and 53.9%, respectively. For the PLA/ZF-GO/APP system, plenty of residues and the anti-dripping network structure are key factors to get good flame retardancy. Addition of ZFGO and APP reduces the tensile strength, but the tensile elongation of the modified PLA composites is improved. 94PLA/ 3ZF-GO/3APP shows good integrated performance.