Flame-Retardant Flexible Polyurethane Foams with Highly Efficient Melamine Salt

A highly efficient flame-retardant melamine salt (DPPMA) was synthesized from diphenylphosphinic acid (DPPA) and melamine (MA). The chemical structure of DPPMA was characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis, and the thermal degradation behavior was investigated by thermogravimetric analysis (TGA). Subsequently, flexible polyurethane foams (FPUFs) were prepared with DPPMA. Limiting oxygen index (LOI) tests, vertical burning tests, and cone calorimetric tests were carried out to investigate the combustion of the materials. The results showed that the FPUF with only 5 php DPPMA passed the vertical burning test and had an increased LOI value of 22%. The corresponding flame-retardant mechanism was systematically investigated by FTIR spectroscopy, TGA, and energy-dispersive X-ray (EDX) spectrometry. The results revealed that DPPMA released NH3 and H2O to dilute the combustible gas and phosphorus-containing radicals during combustion, which consumed the active free radicals produced by the FPUF.