Wide-Temperature-Range Curing and Interfacial Strengthening of Carbon Fiber-Reinforced Polyimide Composites via a Low-Temperature-Curable, High-Temperature-Resistant Aqueous Poly(amic acid) Salt Sizing Agent

Carbon fiber-reinforced polyimide (CF/PI) composites have emerged as critical materials driving technological advancements in the aerospace, high-end equipment manufacturing, and electronic/electrical industries. However, the inherent surface inertness of carbon fibers results in weak interfacial bonding within the composites, which limits their broader application. Additionally, the high curing temperature of phenylethynyl-terminated polyimide resins imposes significant constraints on the available surface modification strategies. To address these challenges, a water-based sizing agent comprising a phenylethynyl-functionalized polyester ammonium salt (PAAS) was developed. This agent features a low curing temperature and enables the construction of a wide-temperature-range interphase. As a result, the interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) of the CF/PI composites were significantly enhanced, reaching 21.7% and 25.09%, respectively. Furthermore, the composites demonstrated a high strength retention rate of 97.79% after a high-temperature treatment. Additionally, this PAAS sizing agent significantly enhances the wettability, storage stability, and tensile strength of carbon fiber monofilaments. These findings hold significant implications and promising applications for the molecular design and interfacial construction of high-temperature-resistant, high-strength CF/PI composites.