Resveratrol-Based Waterborne Non-Isocyanate Polyurethane Sizing Agent for Enhancing Interfacial Bonding of Carbon Fiber Composites

Synthesizing waterborne polyurethane sizing agents via an isocyanate-free route to enhance the interfacial adhesion of carbon fiber composites remains challenging. Herein, a novel aqueous non-isocyanate polyurethane (CNIPU) was prepared via amineolysis of a CO 2 -derived resveratrol-based five-membered cyclic carbonate. The CNIPU with repeating hydroxyl and carbamate segments was used as a sizing agent due to its strong chemical compatibility with epoxy resin, significantly improving the interfacial bonding strength of CF/EP composites. Results demonstrated that the sizing agent with 1.5% wt. CNIPU concentration achieved the most substantial interfacial enhancement in the composites. The interfacial shear strength was 134.14 MPa and the interlayer shear strength was 78.33 MPa, which were 147.35% and 46.25% higher than those of the unprimed CF/EP composites, respectively. The synthesis of CNIPU enables potential replacement of traditional polyurethanes with eco-friendly non-isocyanate polyurethane sizing agents.