Synergistic flame retardant mechanism of fumed silica in ethylene-vinyl acetate/magnesium hydroxide blends

The flammability characterization and synergistic flame retardant mechanism of fumed silica in the ethylene-vinyl acetate/magnesium hydroxide (EVA/MH) blends were studied by cone calorimeter test (CCT), thermogravimetric analysis (TGA), limiting oxygen index (LOI), and UL-94 test. The results showed that the addition of a given amount of fumed silica apparently increased the LOI value and decreased the loading of MH in EVA blends while keeping the V-0 rating in the UL-94 test. The data obtained from the CCT indicated that the addition of fumed silica not only greatly reduced the heat release and mass loss rates, but also depressed the smoke release during the combustion of EVA/MH blends. The morphological and TGA data showed further evidence that this synergistic flame retardant mechanism of fumed silica in the EVA/MH materials is mainly due to the physical process of fumed silica acting as enhanced char/silica layers in the condensed phase which prevents the heat and mass transfer in the fire. By adding fumed silica into EVA/MH blends and reducing the total amount of fillers, the elongation at break of samples is doubled, while the fire resistance of the blends is maintained.