Carbon Nanotube/Polyurethane Coating for Improving Interface Properties in Carbon Fiber Composite

ABSTRACT Although carbon nanotube (CNT) can enhance the interfacial properties of carbon fiber‐reinforced polymer composites (CFRP) through the mechanical anchoring effect, they suffer from issues such as uneven dispersion and poor matrix wettability. Meanwhile, polyurethane (PU) offers high adhesion and flexibility, enabling the formation of a continuous interfacial layer and alleviating stress concentration while lacking sufficient reinforcement efficiency. To leverage the synergistic advantages of both, this research employed a one‐pot method to prepare PU/CNT solutions with varying CNT contents. PU/CNT coatings were applied to carbon fiber surface to simultaneously improve the mechanical properties and resistance to wet‐heat aging of CFRP. The tensile strength of the modified CF‐PU/CNT monofilament reached a maximum of 3.47 GPa, representing a 12.66% increase compared to desized CF. Thanks to the synergistic strengthening effect of the flexible matrix dispersion and nano‐unit reinforcement provided by the PU/CNT coating, the interfacial failure mode of the CFRP shifted from being dominated by interfacial delamination to resin matrix cohesive failure. The interfacial shear strength (ILSS), transverse fiber bundle tensile strength (TFBT) and interfacial shear strength (IFSS) of the CF‐PU/CNT‐based composite increased to 73.33, 40.06 and 70.19 MPa, respectively, representing increases of 32.27%, 39.79% and 45.98% compared to the desized CF‐based composite. Moreover, the CF‐PU/CNT‐based composite exhibits excellent resistance to wet heat, with an ILSS retention rate of up to 96.10%, which is higher than the 86.32% observed in the desized CF‐based composite. This research provides insights for the design of synergistic interfacial reinforcement in CFRP.