Study on interface matching between carbon fiber surface states and polyimide resin matrix

With the rapid development of the aviation industry, advanced aero-engines have imposed increasingly stringent requirements on material properties. To meet the demand for enhancing the thermal resistance and load-bearing capacity of polyimide composites, this study investigates the interfacial compatibility between the surface characteristics of carbon fibers and the polyimide resin matrix. The surface characteristics of carbon fibers under three different treatment conditions are characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and surface energy measurements, and the corresponding polyimide composites are fabricated. The interfacial compatibility between carbon fibers and the resin matrix is evaluated by testing the thermal resistance and interfacial strength of the composites. Results reveal that the surface activity of untreated carbon fibers is relatively low, leading to interfacial cracks in the as-prepared composites, with an interlaminar shear strength (ILSS) of merely 64.5 MPa. In contrast, electrochemically treated carbon fibers exhibit a high content of surface active functional groups, and the ILSS of the resultant composite reaches 111 MPa, with a weight loss rate of only 6.5% after thermal aging at 400 ℃ for 100 h. Composites prepared from electrochemically treated carbon fibers coated with epoxy sizing demonstrate superior interfacial properties; however, their glass transition temperature T_g decreases by approximately 40 ℃ compared to those reinforced with unsized carbon fibers. This indicates that epoxy sizing compromises the thermal resistance of polyimide composites. Therefore, optimizing the sizing agent for carbon fibers represents a viable strategy to improve the interfacial compatibility of polyimide composites.