Surface treatment Technology of carbon Fiber Composites

Carbon fiber is a fibrous carbon material made from a fiber polymer whose decomposition temperature is lower than the melting temperature and is made by solid phase pyrolysis of thousands of degrees. The carbon element in its chemical composition accounts for more than 90% of the total mass. Carbon fiber is rarely used as a material alone, and most of it is used in the form of composite materials.

Surface oxidation method

The surface properties of carbon fibers mainly depend on the surface morphology, specific surface area, active specific surface area, surface energy and surface functional groups. The oxygen-containing functional groups on the surface of carbon fiber are mainly carboxyl group, hydroxyl group and carbonyl group. After surface treatment, the oxygen-containing functional groups on the surface of carbon fiber will increase. The main surface treatment methods of carbon fiber are: surface oxidation, surface coating, surface deposition and so on.

Surface oxidation is one of the important methods to improve and adjust the surface properties of carbon fiber. Surface oxidation treatment can produce oxygen-containing groups on the surface of carbon fiber, which leads to a chemical reaction between resin and matrix and strengthen the bond between matrix and interface. But at the same time, it will also destroy the structure of carbon fiber, so that the physical and chemical properties of carbon fiber are affected. Surface oxidation is mainly divided into gas phase oxidation, liquid phase oxidation and electrochemical oxidation.

Gas phase oxidation is to oxidize the fiber surface by oxidizing gas, and then introduce polar groups into the fiber surface to make the fiber surface have a certain roughness to improve the interface performance between the fiber and the resin matrix.

Liquid phase oxidation is a method that uses liquid medium to oxidize the surface of carbon fiber. The commonly used liquid media are concentrated nitric acid, mixed acid, strong oxidant and so on. The liquid phase oxidation method is milder than the gas phase oxidation method, which is not easy to cause the transition etching and cracking of the fiber, and there are more oxygen-containing groups under certain conditions.

Surface coating method

The principle of surface coating modification is that a certain polymer is coated on the surface of carbon fiber to change the structure and properties of the interfacial layer of the composites. adapt the interface polarity to improve the interface bond strength and provide a plastic interface layer that can eliminate the stress in the interface.

Carbon fiber surface coating can not only effectively improve the oxidation resistance of carbon fiber surface, but also maintain the strength of carbon fiber composites.

Surface deposition method

Surface deposition methods can be divided into chemical vapor deposition (CVD), pyrolysis coating method and whisker method. Chemical vapor deposition is a chemical method to introduce the plastic interface of activated carbon at the interface of carbon fiber and resin to relax stress, so as to improve the interfacial properties of composites, while the pyrolysis coating method uses CVD method to deposit alkanes or carbides on the surface of carbon fiber to form a film or whisker, which can increase the specific surface area of carbon fiber and improve the morphology and structure of carbon fiber.

On the other hand, whisker is deposited on the surface of carbon fiber to produce silicon carbide, perovskite metal, hydrogen masonry and other whiskers by CVD method. This method can obviously improve the interlaminar shear strength of carbon fiber, but it is expensive and difficult to deal with accurately, so it can not be used in industry.

With the in-depth study of carbon fiber and metal composites, more and more surface treatment technologies of carbon fiber composites will be developed, which will continue to promote the popularization, application and rapid development of carbon fiber composites in various industries.

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