Tailored Polyurethane Coating for Improving Interfacial Performance and Hydrothermal Aging Resistance of Carbon Fiber/Epoxy Composites

ABSTRACT Carbon fiber‐reinforced polymer composite (CFRP) faces increasingly stringent demands on interfacial adhesion and hydrothermal aging resistance due to its complex service environments. Among these, the hydrothermal aging resistance of the CFRP interfacial zone is pivotal to determining overall performance. Herein, a simple, efficient carbon fiber surface modification method that preserves fiber strength was proposed. This method employed hydroxyl‐terminated polybutadiene (HTPB), α‐cyclodextrin (α‐CD), and isophorone diisocyanate (IPDI) as polymerization units to prepare a water‐resistant polyurethane (PU) via a one‐pot process. This PU was then applied as a coating onto the fiber surface. Research findings indicated that the PU coating synergistically boosted interfacial adhesion via both mechanical interlocking and chemical bonding interactions within the composite. Compared to desized CF composite, CF‐PU composite reached maximum ILSS and TFBT values of 62.33 and 35.87 MPa, representing increases of 16.62% and 24.93%, respectively. Furthermore, the hydrophobic components and highly crosslinked molecular structure within the PU coating delayed water molecule erosion and diffusion at the interface, thereby strengthening the hydrothermal aging resistance of the composite. The ILSS retention rate of CF‐PU composite reached a maximum of 93.83%, surpassing the 87.21% achieved by desized CF composite. This research will provide valuable references and insights for the design and development of high‐performance, hydrothermal‐aging‐resistant composites.