A bio-based hyperbranched flame retardant for epoxy resins

[Display omitted] •A novel bio-based hyperbranched flame retardant was prepared from itaconic anhydride.•It significantly improved both toughness and flame retardancy of epoxy resins at low phosphorus content.•It exhibited both gas and condensed phase flame retardant mechanisms.•Epoxy thermosets with hyperbranched flame retardant scored V-0 rating in the UL-94 test.•Limiting oxygen index of epoxy resin increased to 36.3%. A novel hyperbranched flame-retardant polymer (referred to as ITA-HBP) was synthesized from itaconic anhydride as a renewable starting material. Upon the incorporation of ITA-HBP, both the toughness and flame-retarding ability of epoxy resins with low phosphorus contents increased simultaneously increased the toughness and flame retardant properties of epoxy resin with low phosphorus contents. The impact strength, fracture toughness and fracture energy of the epoxy resins are significantly enhanced by 133.2%, 78.7% and 124.7% respectively due to the in situ reinforcing and toughening effects induced by ITA-HBP. At the same time, the incorporated ITA-HBP exhibited a remarkable flame-retarding activity in the gas phase due to the production of phosphorus radicals and in the condensed phase due to the formation of a phosphorus-rich char layer of the epoxy resin. The addition of ITA-HBP considerably reduced the peak heat release rate, total heat release and smoke release of the epoxy resin. At a phosphorus content of 0.26 wt%, the ITA-HBP/epoxy thermosets scored V-0 rating in the UL-94 test and showed a limiting oxygen index of 36.3%.