The fire retardant mechanism of ethylene vinyl acetate elastomer (EVM) containing aluminium trihydroxide and melamine phosphate

The fire retardancy and smoke release of ethylene vinyl acetate (vinyl acetate content of 60%, EVM) with aluminium trihydroxide (ATH) and melamine phosphate (MP) are evaluated by cone calorimetry, the limiting oxygen index (LOI), UL-94 and a home-made smoke test. It was found that EVM-ATH has better fire retardant properties and a lower smoke emission than the pure polymer. The partial substitution of ATH by MP led to a further increase in the LOI but the earlier ignition of the material measured by cone calorimetry. Moreover, less smoke is released for EVM-ATH-MP than for EVM-ATH. The fire retardant mechanism was investigated for EVM-ATH and EVM-ATH-MP to evaluate the role of MP in the material. The dispersion of the additives was examined by scanning electron microscopy (SEM) showing that all additives are homogenously dispersed in the matrix. The thermal decomposition, the condensed and the gas phase mechanism of both materials was investigated using thermogravimetric analysis (TGA), a mass loss calorimeter coupled with a Fourier transform infrared spectrometer (MLC-FTIR), pyrolysis-gas chromatography-mass spectrometry (py-GCMS), and the solid state nuclear magnetic resonance (NMR) of C-13, Al-27 and P-31. It was shown that both materials are protected by a gas and condensed phase mechanism. The endothermic decomposition of ATH has a cooling effect and dilutes the fuel through the release of water. In the condensed phase, it was found that both materials are protected through the formation of a physical barrier. It is evidenced that the barrier formed for EVM-ATH-MP exhibits higher insulative properties than that of EVM-ATH.