Facile synthesis of phosphorus-containing benzotriazole flame retardant for enhancement of mechanical and fire properties of epoxy resins

The preparation of flame retardant, strong yet tough, and transparent epoxy resin (EP) composites faces significant challenge. In this study, a phosphorus-containing benzotriazole flame retardant PDI was successfully synthesized. It was important to highlight that the EP/PDI-11 % achieved a limiting oxygen index (LOI) of 32 % and was classified as UL-94V-0 rating. Furthermore, it exhibited a significant reduction in both total smoke production (TSP) and peak heat release rate (pHRR), which decreased by 64.1 % and 46.9 % respectively when compared to EP. Meanwhile, PDI simultaneously enhanced the mechanical strength and toughness of EP, and adding 5 wt% PDI resulted in a 27.2 % improvement in tensile strength, a 53.3 % increase in elongation at break and a 91.4 % increase in impact strength for EP-5 %. Notably, PDI had the ability to promote curing, and the curing peak temperature of EP was advanced by about 20 ℃. In addition, PDI enhanced the insulation and UV resistance properties of EP/PDI, and the high transparency of EP/PDI composites also maintained.