Eco‐Friendly Waterborne‐Hydrolyzed‐Silk‐Fibroin Sizing for Enhanced Interfacial Properties in High‐Modulus Continuous Carbon Fiber/Epoxy Composite

High‐modulus continuous carbon fiber (HMCCF) composites face interfacial challenges that limit their mechanical performance, while conventional sizing agents raise environmental concerns. This study introduces a sustainable, water‐soluble sizing agent derived from hydrolyzed silk fibroin (HSF) to modify HMCCF surfaces. Characterization reveals that HSF sizing significantly enhances surface energy and introduces active groups (e.g., COOH, NH 2 ), improving fiber wettability and interfacial adhesion with epoxy resin (EP). Optimal performance is achieved at 2 mg/mL HSF concentration (HMCCF‐HSF2/EP), where interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) increase to 63.33 and 76.62 MPa, respectively. Mechanistic studies confirm that HSF forms a stress‐buffering and energy‐dissipating interphase through covalent/hydrogen bonding, enabling efficient stress transfer. This work pioneers a fully bio‐based, eco‐friendly sizing strategy for high‐performance HMCCF/EP composites.