Synergistic effect of modified anhydrous magnesium carbonate and hexaphenoxycyclotriphosphazene on flame retardancy of ethylene-vinyl acetate copolymer

Ethylene-vinyl acetate copolymer (EVA) is widely used in various applications; however, its flammability limits its application in wire and cable industries. In this study, 3-methacryloxypropyltrimethoxysilane (KH570) was successfully grafted onto the surface of anhydrous magnesium carbonate (AMC) by alkali activation treatment. The KH570 modified AMC (AMC@KH570) was then introduced into the EVA matrix along with hexaphenoxycyclotriphosphazene (HPCTP) to assess their effects on the flame retardancy and mechanical properties of EVA composites. The results illustrate a significant synergistic effect in enhancing the flame retardancy of EVA composites by using AMC@KH570 and HPCTP, and the limiting oxygen index (LOI) and vertical burning test (UL-94) of EVA filled with 5 wt% HPCTP and 45 wt% AMC@KH570 (mAMC/H-45-5) reached 27.6% and V-0, respectively. The flame retardant mechanism was investigated by thermogravimetric/infrared (TG-IR) spectroscopy and residual carbon composition analysis. The results show that the thermal decomposition of AMC@KH570 and HPCTP consists of gas dilution, free radical quenching, and catalytic carbonization. Furthermore, KH570 works as a bridge to improve the compatibility of AMC and EVA matrix, which offsets the mechanical loss of EVA to some extent. The present research provides a new path to modify AMC and fabricate EVA composites with excellent flame retardant properties.