Preparation of expandable graphite with silicate assistant intercalation and its effect on flame retardancy of ethylene vinyl acetate composite

A halogen-free intumescent flame retardant expandable graphite composite (EG), with an initial expansion temperature of 202 degrees C and expansion volume of 517 mL g(-1), was successfully prepared via a facile two-step intercalation method, i.e. using KMnO4 as oxidant and H2SO4, Na(2)SiO(3)9H(2)O as intercalators. The prepared EG flame retardant was characterized by field emission scanning electron microscope, X-ray diffraction spectroscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy. Furthermore, flame retardancy and thermal property of various ethylene vinyl acetate copolymer (EVA) composites, including EVA/EG and EVA/EG/APP (ammonium polyphosphate) specimens, were studied through limiting oxygen index instrument (LOI), vertical combustion UL-94 rating, thermal gravimetric and differential thermal analysis. The results indicate that the EVA/EG and EVA/EG/APP composites exhibit a better flame retardancy. Addition of EG at a mass fraction of 30% leads LOI of 70EVA/30EG composite improved to 28.7%. Even more, the synergistic effect between EG and APP improves the LOI of 70EVA/10APP /20EG composite to 30.7%. This synergistic efficiency is attributed to the formation of compact and stable layer-structure, and the prepared EG can make EVA composite reach the UL-94 level of V-0. POLYM. COMPOS., 36:1407-1416, 2015. (c) 2014 Society of Plastics Engineers