Melamine-based biomass-containing P/N synergistic flame retardants confer superb flame retardancy and toughness to epoxy resins

Epoxy resin (EPs) coatings for aircraft need to have good flame retardant properties and toughness. On the other hand, to meet the needs of sustainable development, EPs also have high environmental friendliness and low cost requirements. In light of this, a one-pot approach was used to create a bio-based phosphorus‑nitrogen synergistic flame retardant (MDV) employing DOPO, vanillin, and MA as raw materials. The results showed that MDV can give EP superb flame retardancy and toughness. With the addition of 3 wt% MDV, the tensile and flexural strengths of EP composites increased by 13.6 % and 14.5 %, respectively, and the impact strength increased from 13.9 KJ/m² to 43.1 KJ/m². The excellent toughness enhancement comes from the fact that the structure of MDV itself can preferentially consume and dissipate energy when counteracting external impacts. In addition, MDV/EP also has excellent flame retardant properties, showing good self-extinguishing capability off fire in tests. Compared with pure EP, the total heat release (THR) and peak heat release rate (PHRR) of 7-MDV/EP composites were reduced by 45.3 % and 64.5 %, respectively. Mechanistic analyzes showed that the segregation of the condensed phase and the gas-phase flame-retardant effect both originated from the P/N synergistic effect, which was the source of the excellent flame-retardant effect of MDV/EP.