Fire retardant benefits of combining aluminum hydroxide and silica in ethylene-vinyl acetate copolymer (EVA)

The flame retardancy of ethylene-vinyl acetate copolymer filled with metal hydroxides (aluminum hydroxide - ATH and magnesium hydroxide - MDH) and silica was investigated. Several composites containing only metal hydroxides or a combination of metal hydroxides and silica (ratio silica/hydrated filler = 0.18) were prepared and tested using pyrolysis-combustion flow calorimeter, thermogravimetric analysis and cone calorimeter at various heat fluxes. It was observed that silica provides benefits when the amount and other properties of the fillers allow the formation of an insulating mineral layer. In such cases, silica does not modify the first peak of heat release rate in cone calorimeter tests, but reduces or completely suppresses the breakdown of the insulating layer near the end of the combustion (assessed by the intensity of the second peak in the heat release rate as function of time). This effect is particularly obvious at lower heat flux, the insulating layer protects the underlying polymer, which is therefore not completely degraded.