Carbon fiber (CF), as a low-density, high-strength, high-modulus ratio fiber material, has good abrasion resistance, heat resistance, dimensional stability, and acid and alkali resistance. Reinforcement materials with broad application prospects.
Because the surface of the carbon fiber is inert, the stress load between the carbon fiber and the matrix material in the composite cannot be effectively transmitted, which directly affects its performance and limits its large-scale application. Therefore, the surface treatment of the carbon fiber is required. Surface modification technology is used to improve the surface activity of carbon fibers, strengthen the interface properties between carbon fibers and matrix materials, improve the bonding effect between them and the matrix, and thereby increase the value of fiber materials in industrial applications.
Coating method
The coating method refers to coating a layer of polymer, metal particles, or inorganic nonmetals and their composites on the surface of carbon fibers. The purpose is to change the surface wettability of the carbon fibers and increase the compatibility between the polymer matrix and the carbon fibers. Surface coating treatment not only participates in the formation of the interface phase between the fiber / matrix, reduces the thermal residual stress between the fiber / matrix during the manufacturing process of the composite material, but also reduces the stress concentration and averages the fiber surface properties.
Plasma treatment
The plasma spraying process is a high-speed collision deposition process in which a molten or semi-molten material is sprayed onto a pretreated substrate to form a coating. Plasma treatment has the advantages of simple operation, environmental protection technology, and low damage to the properties and mechanical strength of the raw silk. It has become a widely used research method.
Gas phase oxidation
The gas-phase oxidation method uses hot air, oxygen (O2), carbon dioxide (CO2), ozone (O3) and other gases as a medium to oxidize CF. After treatment, the specific surface area and surface roughness of CF increase, and the types of oxygen functional groups on the surface and The number has also increased, thereby improving the comprehensive mechanical properties of CF reinforced composites.
Liquid phase oxidation
The liquid phase oxidation method uses concentrated nitric acid, concentrated sulfuric acid, hydrogen peroxide and other oxidants to contact CF for a long time, and forms groups such as carboxyl and hydroxyl groups on the surface of the fiber to enhance the binding force with the resin.
Electrochemical oxidation
Electrochemical oxidation uses the conductive properties of CF, uses CF as the anode, graphite, copper plate or nickel plate as the cathode, and uses a solution of different acid and alkali salts as the electrolyte under the action of a DC electric field to surface treat CF. method. The role of surface electrochemical oxidation treatment is a composite process of layer-by-layer oxidation etching and functional group changes.
Surface grafting
The surface grafting method is to place carbon fibers in a reactive monomer atmosphere, and under the action of an initiator, the monomers react with the reactive groups or edge carbon atoms on the fibers.
Energy beam processing
Utilize the structural change of the material itself or introduce other materials to improve the surface properties during the energy beam scanning process. The fiber will roughen the surface under the irradiation of the energy beam and improve the adhesion to the substrate.
Rare Earth Treatment
Due to the chemical activity of the rare earth element and according to the chemical bond theory, the rare earth element can coordinate with the C, O, and N atoms on the surface of the carbon fiber and chemically bond. The rare earth element has a large amount of charge. Attracting electrons in the carbon-carbon bonds of carbon fibers causes the electrons of the carbon-carbon bonds to shift, which makes it easier to introduce functional groups onto the surface of the carbon fibers.
The key of carbon fiber modification technology is to improve the degree of combination of carbon fiber and matrix and improve the performance of composite materials. As environmental issues become increasingly prominent, the cost reduction, greening and continuous production of carbon fiber surface treatment technology will be the focus of research in the future.