A multi‐element flame retardant for rail transit to improve the flame retardant performance of epoxy resin while reducing smoke density

Abstract A P/N/Si structure flame retardant DTBD was successfully synthesized by 3,5‐diaminobenzoic acid, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), triphenylsilanol, and benzaldehyde. The chemical structure of DTBD was analyzed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectra, which showed that DTBD was successfully synthesized. By analyzing the curing behavior, the addition of DTBD promoted the curing of epoxy resin (EP). According to the limited oxygen index (LOI) and UL‐94 vertical combustion tests, it can be shown that the introduction of DTBD makes the epoxy resin have good self‐extinguishing properties. Py‐GC/MS analysis showed that the phosphorus free radicals and ammonia generated in the gas phase of DTBD could quench and dilute by capturing reactive free radicals and refractory gases. DTBD could improve the tensile and flexural properties of epoxy resin. According to the European flame retardant standard EN45545‐2, the Ds of EP‐15 and EP‐20 obtained HL1 grade. With the increase in DTBD content, the VOF 4 of modified EP also gradually decreased, and both EP‐15 and EP‐20 obtained HL2 grade.