Reactive organophosphorus flame retardant for transparency, low-flammability, and mechanical reinforcement epoxy resin

To maintain transparency and improve flame retardancy and mechanical properties of epoxy resin, a reactive organophosphorus flame retardant (DPDDM) was designed and synthesized, which was derived from 3,4-dihydroxybenzaldehyde, 4, 4′- diamino diphenylmethane and 9,10-dihydro-9-oxa –10- phosphaphenanthrene-10-oxidein two steps. Compared with neat epoxy resin (EP), the tensile strength and flexural strength of the EP with 5% DPDDM increased by 28.6% and 42.8%, respectively, indicating that DPDDM can significantly improve the mechanical properties of EP materials. Meanwhile, the DPDDM modified EP materials have good transparency and the EP with 5% DPDDM passed the V-0 rating and had the limiting oxygen index as high as 34%. Cone calorimeter test results showed that the heat release and smoke generation of the modified materials were significantly lower than the unmodified materials, which were reduced by 32.6% and 64.6%, respectively, indicating that the modified materials can greatly improve the safety of fire prevention. This work provides a new approach to prepare transparent epoxy resin with good mechanical properties and excellent flame retardancy.