Simultaneously improving the fire safety and mechanical properties of epoxy resin with iron phosphonated grafted polyethylenimine

Endowing epoxy resins with enhanced flame retardancy, toughness and strength as well as glass transition temperature (Tg) simultaneously is a big challenge in academia and industry fields. Herein, a hyperbranched multifunctional additive (PEIP-Fe) was designed, which was prepared through a Mannich condensation reaction of polyethyleneimine and phosphorous acid and followed by combining with ferric. When 3 wt% of PEIP-Fe was incorporated into epoxy resin, the impact strength, tensile strength, flexural strength and Tg were all enhanced due to the multiple toughening mechanisms, good compatibility and the increased cross-linking density. Simultaneously, fire safety such as flame retardancy, smoke suppression and toxicity were all improved. The flame-retardant mechanism was verified in both condensed-phase and gas-phase by catalytic charring and free radical scavenging, forming compact and continuous char layer and releasing phosphorus-containing species respectively. This work provides new thinking for the design of multifunctional and high efficiency additives for epoxy resin.