Synthesis of a bio-based reactive toughening agent and its application in toughening epoxy resin

Toughening epoxy resins with modifiers without compromising their modulus and mechanical strength poses a significant challenge. In this work, a bio-based N-heterocyclic-containing reactive toughening agent, HPESZ, was synthesized based on cinnamon derivatives and succinic anhydride. And then the HPESZ was incorporated into the bisphenol A epoxy resin/4, 4 '-diaminodiphenylmethane (E44/DDM) curing system to evaluate its effect on the toughening of epoxy resins. The results suggested that the impact strength of the E44/5 %HPESZ/DDM blended system achieved a peak value of 72.4 kJ m- 2, representing a 90.0 % increase over the E44/DDM system (38.1 kJ m- 2). Subsequently, the toughened system was characterized using scanning electron microscopy and atomic force microscopy to explain its phase structure and toughening mechanism. The cured system produced the chemically induced microphase separation, and the presence of epoxide groups and terminated hydroxyl groups enhanced the interfacial compatibility of E44/DDM, thereby increasing the impact strength. Moreover, the flexural strength, flexural modulus, hardness, and Young's modulus of the blended system were also improved simultaneously. In conclusion, HPESZ is a reactive bio-based toughening agent with promising practical applications.