Transparent, flame retardant, mechanically strengthened and low dielectric EP composites enabled by a reactive bio-based P/N flame retardant

• A reactive bio-based P/N flame retardant (named VTP) as a multifunctional additive was prepared successfully. • VTP simultaneously improved the flame retardancy, glass-transition temperature and dielectric properties of EP. • EP/VTP composites exhibited the excellent smoke suppression and improved mechanical properties. With the application of epoxy resin (EP) in high-end fields such as electronics and appliances, 5 G communication, rail transit interior decoration and so on, the requirements of flame retardant, lightweight and high performance are also put forward for EP products. Thus, it is of great significance to prepare EP composites with excellent comprehensive properties. For the sake of achieving this target, we synthesized a reactive bio-based P/N flame retardant (named VTP) as a multifunctional additive to develop high-performance EP composites with excellent flame retardance, mechanical properties, transparency and thermal oxidation stability. As expected, VTP possessed excellent flame-retardant efficiency thanks to the synergism of tetrazoles, phosphaphenanthrene and vanillin, only 5 wt% of which made EP/VTP-5% sample achieve UL-94 V-0 rating, increased limiting oxygen index (LOI) value to 30.5%, and reduced the peak of heat release (PHRR) and total smoke production (TSP) by 36.1% and 37.9% respectively. Besides, the tensile strength and glass transmission temperature (T g ) of EP/VTP composites were increased as compared to unmodified EP, as well as high transparency was retained. This work provided a very good idea and experimental basis for the preparation of high-performance EP resin.