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

ABSTRACT 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.