To address the issues of weak interfacial bonding and insufficient interlaminar properties in carbon fiber/polyetheretherketone (CF/PEEK) thermoplastic composites, this study employed a three-step method consisting of “thermal pretreatment—sulfuric acid oxidation—silane coupling” to chemically graft graphene oxide (GO) and nanosilica (NS) onto the carbon fiber surface, respectively. The study systematically compared the effects of these two nanoreinforcements on interfacial structure and mechanical properties. FTIR, XPS, and SEM results indicate that GO bonds firmly to carbon fibers via amide bonds, while NS bonds via Si-O-C bonds, significantly enhancing the fiber surface roughness and chemical reactivity; When the KH550 content was 6 wt%, the GO-modified system achieved a maximum interfacial shear strength (ILSS) of 15.2 MPa for CF/PEEK, representing a significant 44.7% increase compared to the unmodified CF/PEEK; the tensile strength (TPB) also reached a maximum of 170.2 MPa, with a growth rate of 63%, outperforming both the NS-modified and unmodified systems. Fracture surface morphology confirms that GO effectively suppresses resin delamination, facilitating a transition from “fiber pull-out” to “resin cohesive failure.” This study provides an efficient and controllable GO chemical grafting strategy for interfacial reinforcement of CF/PEEK composites, offering significant reference value for promoting their application in high-end fields such as aerospace, automotive, and biomedical industries. (1) Proposing a novel method for grafting graphene oxide onto carbon fiber. (2) This experiment is more environmentally friendly as it does not use organic reagents. (3) Proposing the grafting of novel nanomaterials onto carbon fiber. (4) Revealing the “critical coverage” phenomenon of silane coupling agent KH550.
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