A bio-based hyperbranched flame retardant for epoxy resins

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%.