Synthesis of a Multielement Flame Retardant and Its Application in Epoxy Resin

For the purpose of obtaining flame-retardant epoxy resin (FREP) with exceptional comprehensive properties, a multielement flame retardant SVPM was synthesized by sulfathiazole, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), methylvinyldichlorosilane and vanillin. The effects of SVPM on the thermal stability, heat resistance, mechanical behavior and flame retardancy of epoxy resin (EP) were systematically revealed, and the flame-retardant mechanism of SVPM was deeply explored. In the presence of only 0.12 wt% phosphorus content in the system, FREP achieved V-0 rating of vertical combustion (UL-94) and the limiting oxygen index (LOI) value reached 31.1%. Additionally, SVPM reduced the smoke and heat release of EP. The mechanical properties of EP were enhanced by SVPM; specifically, the maximum increment of tensile strength and flexural strength of FREP were 26.23% and 16.67% respectively. The investigation of flame-retardant mechanism showed that the phosphorus-containing free radicals and SO2 decomposed by SVPM can quench the active free radicals in the combustion process, thus interrupting the chain reaction of combustion, and the noncombustible gas generated by SVPM during combustion can reduce the concentration of combustible volatiles. In the condensation phase, phosphoric acid and silicon dioxide produced by SVPM degradation can promote the stability and densification of the char layer, eventually effectively reducing the combustion intensity.