A vanillin derivative P/N/S-containing high-efficiency flame retardant for epoxy resin

In order to improve the flame-retardant properties of epoxy resin (EP) without sacrificing the mechanical properties, a high-efficient P/N/S-containing reactive flame retardant (VTZD) was synthesized by a facile one-pot method from vanillin, 2-aminobenzothiazole and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and used in epoxy-amine thermosets. When 5 wt% of VTZD was added with merely 0.31 wt% of phosphorus, the LOI value of cured resins increased to 32.7%, and the thermosets achieved a UL-94 V-0 rating. Furthermore, the peak heat release rate and the total heat release of the VTZD-modified EP decreased by up to 34.66% and 32.49%, respectively, in comparison to those of the original EP. Subsequently, the residual char morphology and structure of epoxy thermosets were investigated, as well as the pyrolysis behavior of VTZD. The flame-retardant mechanism was discussed in detail, and it confirmed that VTZD exhibited a bi-phase flame retardant effect. In addition, the mechanical properties of the cured products were well maintained and even improved. All the results demonstrated that the VTZD was a bio-based high-efficiency flame retardant for EP with a broad prospect in practical applications.