Sustainable Enhancement of Carbon Fiber/Epoxy Interface via Eco‐Friendly MPN / PEI co‐Deposition: A Synergistic Approach Integrating Metal Polyphenol Networks and Bio‐Based Coatings

ABSTRACT At present, there have been numerous studies on the surface modification of carbon fibers (CF); however, there are still problems such as toxic reagents and complex modification processes. This study proposes an environmentally benign modification strategy featuring mild reaction conditions and high efficiency, aiming to enhance both the interfacial bonding capacity between CF and epoxy resin matrices and the resultant mechanical performance. The metal polyphenol networks (MPN) were synthesized through coordination between tannic acid (TA) and Fe ³⁺ ions, which were subsequently co‐deposited with polyethyleneimine (PEI) via phenol‐amine conjugation to construct a hybrid MPN/PEI coating on fiber surfaces. The effect of the mass ratio of MPN to PEI on the deposition process was investigated. Maximum interfacial enhancement was achieved at an optimal MPN:PEI mass ratio of 1:2, as evidenced by comprehensive characterization. The interlaminar shear strength (ILSS), interfacial shear strength (IFSS), flexural strength, and transverse fiber bundles tensile strength (TFBT) of the composites were 84.17 MPa, 81.27 MPa, 1215.68 MPa, and 38.62 MPa, respectively, which were increased by 52.15%, 66.71%, 126.89%, and 89.97%, respectively, compared to the untreated CF composites. The use of biological materials for simple and efficient deposition provides a new idea for CF surface modification.