Bio-based phosphorus-containing benzoxazine towards high fire safety, heat resistance and mechanical properties of anhydride-cured epoxy resin

Endowing anhydride-cured epoxy resin (EP) with excellent flame retardancy while maintaining good comprehensive properties has become a great challenge. In this context, a bio-based phosphorus-containing benzoxazine monomer (SFD-BOZ) composed of DOPO, furfurylamine, salicylaldehyde and paraformaldehyde was successfully synthesized via a two-step reaction, and then blended into EP/methyltetrahydrophthalic anhydride (MeTHPA) system. Though SFD-BOZ exhibited no significant effect on the curing activity of EP/MeTHPA system, the introduction of SFD-BOZ made FREP show better heat resistance. Besides, the flame retardancy of EP was markedly improved due to the incorporation of SFD-BOZ. The modified EP with 20.7 wt% SFD-BOZ achieved V-0 rating of UL-94 and obtained limited oxygen index (LOI) value of 35.2%, which was 76% higher EP. Also, its peak heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) dramatically declined by 53%, 36% and 45% as compared to that of EP, respectively. Furthermore, the flexural and tensile strengths of modified EP showed the maximum increments of 9% and 49%, respectively. The incorporation of SFD-BOZ manifested the potential for developing high-performance epoxy resin.