Expansion behaviour and thermal degradation of tri(acryloyloxyethyl) phosphate/methacrylated phenolic melamine intumescent flame retardant system

Tri(acryloyloxyethyl) phosphate (TAEP) was blended with methacrylated phenolic melamine (MAPM) in different ratios to obtain a series of UV curable intumescent flame retardant resins. The cured TAEP/MAPM samples greatly expanded when burning. Their expansion behaviour and flame retardance of the cured resins were characterized by the volume ratio after and before combustion, and by limiting oxygen index. A distinct synergistic effect was found between TAEP and MAPM. TAEP-0.30MAPM sample showed the highest expansion degree (104) and the highest LOI value (41) among all resins. The degradation was monitored by thermogravimetric analysis and in-situ Fourier-transform infrared spectroscopy. A degradation mechanism is suggested in which the phosphate group in TAEP first degraded to form poly(phosphoric acid)s, which further catalysed the degradation of the material to form char with emission of nitrogen volatiles from MAPM, leading to the formation of expanding char. The morphologic structures of crusts of the formed chars were observed by scanning electron microscopy, demonstrating the synergistic effect between TAEP and MAPM.