Phosphorus based organic-inorganic hybrid materials prepared by reactive processing for EVA fire retardancy

A new ethylene vinyl acetate (EVA)-based hybrid material containing silicon and phosphorus has been developed in order to improve fire retardancy of EVA. The preparation of the hybrid material was based on exchange reaction between acetoxy groups from EVA and ethoxysilane groups from diethylphosphatoethyltriethoxysilane (SiP). The exchange reaction was characterized by NMR spectroscopy, showing the presence of silicon in the crosslinking bridges bonded to unreacted phosphonate groups. The formation of the crosslinked network was characterized by rheology and TGA-GC-MS. The influence of silicon and phosphorus on the thermal behaviour and the flame retardancy of EVA was investigated by thermogravimetric analysis (TGA) and cone calorimeter. The results showed a synergistic effect between silicon and phosphorus on the fire properties for low charge contents (1.3 wt% of silicon and 1.4 wt% of phosphorus). The peak heat release rate (PHRR) measured in a cone calorimeter decreased by 35% for EVA hybrid materials compared to pure EVA due to the formation of a compact charred layer. The charred residue was analysed by NMR spectroscopy and showed the presence of silicophosphorated complexes.