Carbon Fiber Surface Functionalization Strategies for Enhancing the Performance of Carbon Fiber‐Reinforced Composites: A Review

ABSTRACT Carbon fibers (CFs) are widely used as reinforcing components in composites due to their exceptional properties, such as high tensile strength and thermal stability. Owing to their inert and smooth surfaces, CFs lack polar groups, resulting in weak bonding performance in fiber‐polymer composites. To improve the poor bonding between CFs and polymer resin, various surface treatment methods are employed to increase the reactive sites, surface roughness, and introduce functional groups. Among various techniques, oxidation methods effectively introduce oxygen‐rich functional groups onto the CF surface, which enables covalent bond formation, enhances the interface, and facilitates effective stress transfer between fiber and matrix. Such treatment enhances the interlaminar shear strength (ILSS) by 43.3%. However, prolonged treatment can weaken the strength of fibers. Similarly, silane treatment significantly enhances adhesion through chemical interactions at the fiber‐resin interface. This treatment increases the ILSS by 49.27% and flexural strength by 106.57%. Plasma‐based surface treatment increases surface roughness and introduces active sites, offering a faster alternative for surface modification. The incorporation of nanoparticles as fillers into resins or CFs enhances the thermal, electrical, and mechanical performance of the composites. Additionally, multi‐step methods that combine different techniques offer better fiber‐matrix bonding and promote the multi‐functionality of CF‐reinforced composites.