A Mild In Situ Nano‐ CuS ‐Based Modification of Carbon Fiber for CF /Nylon 6 Composites

The interfacial characteristics of carbon fiber (CF)‐reinforced polymer (CFRP) composites critically determine their mechanical performance. While CFs modified with nanoparticles demonstrate efficacy in interface regulation of composites, conventional methodologies are typically accompanied by limitations, including high cost of raw materials, nanoparticle agglomeration tendencies, and demanding synthesis conditions, rendering them impractical for large‐scale applications. This study presents a simplified, cost‐effective technique for in situ synthesis of inorganic copper sulfide (CuS) nanoparticles on CF surfaces. Utilizing copper chloride dihydrate (CuCl 2 ·2H 2 O) and sodium sulfide nonahydrate (Na 2 S·9H 2 O) as precursors, nano‐CuS particles with diverse chemical structures and physical morphologies were controllably synthesized in situ on CF surfaces by regulating the ratio of copper‐to‐sulfur ions. Results indicate significantly improved surface activity, wettability, and smooth surface morphology for the modified CFs. Consequently, the resulting CFO–CuS 1:1 /Polyamide 6 (PA6) composites manifest superior interfacial and mechanical properties, with an interlaminar shear strength (ILSS) of 65.8 MPa and flexural strength of 959.0 MPa. These values represent 19.6% and 24.8% improvements over unsized CF/PA6 composites, respectively. In addition, the thermal conduction performance of CFO–CuS 1:1 /PA6 composites has been significantly improved. This investigation provides a practical strategy for using nanomaterials to modify CF surfaces to enhance interface adhesion and functional properties.