Carbon fiber has excellent properties such as high specific strength, high specific modulus, fatigue resistance, and corrosion resistance, and is widely used in aerospace, military industry, sports equipment and other fields. The mechanical properties of carbon fiber reinforced polymer matrix composites depend to a large extent on the interface properties between the carbon fiber and the matrix. The smooth surface of the carbon fiber, high inertness, and few chemically active functional groups result in the interface between the carbon fiber and the matrix resin. The adhesion is weak, and the interface phase often becomes the weak link of composite materials. The interface microstructure of carbon fiber composites is closely related to interface properties. In the final analysis, the surface polarity of carbon fiber lies in the surface morphology of the carbon fiber and the type of chemical functional groups. The increase of active groups and the increase of roughness on the surface of carbon fiber are beneficial to the increase of carbon fiber surface energy. The physical properties of carbon fiber surface mainly include surface morphology, surface groove size and distribution, surface roughness, surface free energy and so on. From the perspective of surface morphology, the surface of carbon fiber has many pores, grooves, impurities and crystals, which have a great influence on the bonding performance of composite materials. The chemical reaction activity on the surface of carbon fiber is closely related to the concentration of active groups, and these active groups are mainly oxygen-containing functional groups such as hydroxyl, carboxyl and epoxy groups. The number of functional groups on the surface of carbon fiber depends on the surface electrochemical treatment method and the degree or temperature of fiber carbonization. For example, acid treatment will give the fiber different functional groups from alkali treatment. For the same treatment conditions, the higher the carbonization temperature, the more functional groups. less. Low modulus carbon fiber generally has more functional groups due to its lower degree of carbonization, and it will react with epoxy groups in the preparation of epoxy-based composites, while the reaction of high modulus carbon fiber systems can be ignored. There is mainly a weak interaction between fiber and resin. Numerous studies have shown that controlling the interface microstructure of composite materials through carbon fiber surface modification can effectively improve the interface properties of composite materials, which is also one of the research hotspots in the field of carbon fiber composite materials.
There are many surface treatment methods for carbon fiber, which can be divided into surface chemical reaction and coating treatment. Surface chemical reactions are divided into oxidation treatment and non-oxidation treatment. Oxidation treatment is divided into low-temperature or high-temperature gas phase oxidation, chemical or electrochemical method of liquid phase oxidation and anodic oxidation. Non-oxidation treatment is to deposit more active carbon and other substances on the surface of carbon fiber, such as whisker method, polymer grafting method, etc.