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 ¼ 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.

In the present work, colemanite, a hydrated calcium borate, was used as co-filler in aluminium hydroxide/ethylene-vinyl acetate copolymers (ATH/EVA). The presence of colemanite showed an improvement of the fire properties of composites. However, this additive does not act as a synergistic agent with ATH, but seems to increase significantly fire properties by his own. The formation of an expanded layer during cone calorimetry tests insulates the sample and reduces the heat release rate (HRR) values. The performance is ascribed to the hardening of the barrier layer due to the modification of colemanite structure at high temperature. Moreover, to study its mechanisms of fire retardancy and to investigate its potential synergistic effects, colemanite was also introduced as co-filler in magnesium hydroxide (MH)/EVA, ATH/ethylene-methyl acrylate (EMA) and MH/EMA composites.

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In the present work, diatomite was used as co-filler in aluminium hydroxide/ethylene-vinyl acetate composites (ATH/EVA). This silica-based marine sediment acts as a synergistic agent with ATH, to increase the flame retardant properties of EVA composites. When diatomite was used with ATH the formation of an expanded layer during cone calorimetry tests was observed. This layer presents a complex structure which better insulates the sample and reduces the heat release rate (HRR). Rheological measurements, such as complex viscosity obtained with an ARES apparatus, suggest an influence of the viscosity of the sample melt. We assume that the viscosity of the EVA composites is influenced by the porosity of the diatomite. Better residue cohesion was also obtained in presence of diatomite.

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