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. • A bio-based reactive toughening agent HPESZ was synthesized. • The impact strength of the E44/5 %HPESZ/DDM blended system was increased by 90.0 %. • The toughening mechanism resulted from chemically induced phase separation. • It can significantly toughen epoxy resin without compromising its mechanical properties.