Controllable construction of gradient modulus intermediate layer on high strength and high modulus carbon fibers to enhance interfacial properties of epoxy composites by efficient electrochemical grafting

The interface is a fundamental and crucial research topic throughout the development of carbon fiber reinforced polymer composites. However, it is a huge challenge to solve the problem of fiber surface inertness thoroughly to enhance the interfacial bonding with the resin, especially for high modulus carbon fibers with higher degree of graphitization and fewer microcrystalline active points for commercial production. This manuscript reports that different monomers were selected to in situ electrografting on the fiber surface to design and control the physical/chemical structure and rigidity/flexibility of the interface. The interfacial bonding performance of the composites was greatly improved, interlaminar shear strength (ILSS), interfacial shear strength (IFSS) and transverse fiber bundle tensile strength (TFBT) were increased by 15.9%, 46.8% and 39.6%, respectively, and the tensile strength of the single fiber was also increased by 12.7%. This simple, efficient (1–3min), environmental (water as solvent) and economical method shows great application prospects of fiber surface treatment technology in the next generation.