The combination of aluminum trihydroxide (ATH) and melamine borate (MB) as fire retardant additives for elastomeric ethylene vinyl acetate (EVA)

Abstract

Fire retardancy and smoke release of ethylene vinyl acetate (vinyl acetate content of 60%, EVA) with aluminum trihydroxide (ATH) and melamine borate (MB) was evaluated by mass loss cone calorimetry, limiting oxygen index (LOI), UL-94 and a home-made smoke test and compared to materials already reported in literature. It was found that the combination of ATH and MB results in improved fire retardant properties as well as in decrease smoke release in comparison to the virgin polymer. To evaluate the contribution of MB in the material, the decomposition mechanism of EVA-ATH-MB was examined. First, using scanning electron microscopy (SEM), it was shown that ATH and MB are evenly dispersed in the polymeric matrix. The thermal decomposition of EVA-ATH-MB was investigated by thermogravimetric analysis (TGA). Gases released in a fire scenario were analyzed using mass loss calorimeter coupled with a Fourier transform infrared spectrometer (MLC-FTIR). The condensed phase of EVA-ATH-MB was examined using solid state nuclear magnetic resonance (NMR) of 13C, 27Al and 11B. Moreover, thermal conductivity of EVA-ATH-MB in function of the temperature was measured and compared to that of EVA-ATH materials containing melamine (MEL) or melamine phosphate (MP) instead of MB. It was found that EVA-ATH-MB is protected through a gas and a condensed phase mechanism, whereas MB contributes to the formation of a protective layer due to formation of boron oxide, boron nitride and BNO structures at the sample surface. The formed boron species further lead to decrease of the thermal conductivity in the range of the ignition temperature of the polymer leading to ignition at longer times of EVA-ATH-MB in comparison to the other tested materials.