Carbon fiber is widely used as a reinforcing phase in polymer composites due to its high specific modulus and specific strength, good electrical conductivity, corrosion resistance and low linear thermal expansion coefficient. In particular, the aerospace and transportation sectors are increasingly using carbon fiber instead of metal to reduce the quality of aircraft and transportation tools and improve their fuel efficiency and dynamic performance. However, due to the small number of active carbon atoms on the surface edge and the low surface energy, carbon fiber exhibits inert characteristics and poor wettability with the resin matrix. The internal pores generated during the production of carbon fiber composites will also lead to the discontinuity of the interface between the fiber and the matrix, which will adversely affect the mechanical properties of the composites, especially the interfacial shear, interlaminar shear and impact resistance. Therefore, it is of great significance to improve the bonding degree between carbon fiber and matrix and give full play to the excellent performance of carbon fiber to improve the performance of composite materials.

Plasma treatment on the surface of carbon fiber can effectively improve the interfacial properties between fiber and matrix.

Carbon fiber plasma treatment

The plasma treatment method is to bombard the fiber surface with high-energy ions produced by gas discharge to treat the surface of carbon fiber.

Low-temperature plasma includes a large number of active particles, such as high-energy electrons, ions, free radicals, excited gas atoms and molecules, and photons. These particles interact with the surface of carbon fiber, such as etching and cleaning, oxidation, grafting, activation, polymerization, etc., which is the basis of low-temperature plasma treatment of carbon fiber surface.

On the one hand, high-energy particles bombard the fiber surface to excite, ionize and break chemical bonds of fiber molecules, produce various polar groups and free radicals on the fiber surface, improve the wettability of the fiber surface, and thus increase the adhesion of the resin on the fiber surface.

On the other hand, high-energy electrons cause a sputtering effect by accelerating active ions at lower temperatures, which can remove impurities on the fiber surface, roughen the fiber surface, and form a mechanical interlocking between the fiber and the resin matrix.

Oxygen plasma treatment can also increase the concentration of oxygen-containing groups on the surface of carbon fibers and improve the roughness of the fiber surface. The plasma treatment method only improves the bonding ability between the fiber surface and the matrix by changing the chemical and physical structure of the fiber surface layer, without changing most of the mechanical properties of the fiber body.

The use of low-temperature plasma to treat the surface of carbon fibers has a series of advantages, such as clean and environmentally friendly, time-saving and efficient, less damage to fibers, and suitable for continuous production. Of course, the biggest advantage of using low temperature plasma to treat the surface of carbon fiber is that the hydrophobicity and chemical inertness of the surface of carbon fiber are well improved, and the interfacial properties of the formed composite are improved.