The Building of Microseparation Interface Structures and Reinforcement Mechanisms in Carbon Fiber/Epoxy Composites

ABSTRACT Polyurethane (PU) offers significant potential for modulating the interfacial performance in carbon fiber‐reinforced polymer (CFRP) composites due to its molecular design flexibility, high abrasion resistance, and high elongation. However, the key contribution of its unique microphase separation structure to interfacial toughening is often neglected. Here, we synthesized PU with different microphase separation structures via a one‐pot method by adjusting the ratio of hydroxyl‐terminated polybutadiene (HTPB) to α‐cyclodextrin (α‐CD). The resulting PU was subsequently used as a sizing agent on the fiber surface to boost the interfacial and mechanical performance of the composite. The findings indicated that, due to the protective effect and enhanced microphase separation of the PU coating, the tensile strength (TS) of CF‐PU augmented to 3.39 GPa, marking a 10% improvement over desized CF. Moreover, the PU microphase separation structure could further optimize the mechanical performance of the CFRP by synergistically integrating rigid support and flexible cushioning. The CF‐PU composite indicated superior performance over the desized CF composite, with interlaminar shear strength (ILSS) reaching 66.29 MPa and transverse fiber bundle tensile strength (TFBT) reaching 37.71 MPa. This strategy provides a research approach for fully leveraging the interfacial toughening effect of the PU coating and for designing high‐performance carbon fiber composites.