Current Status Of Carbon Fiber Surface Modification

 

The purpose of carbon fiber surface modification is mainly to improve the interfacial bonding performance between carbon fiber and matrix resin by increasing the surface roughness and surface activity of carbon fiber, so as to improve the interfacial shear strength of composite materials. The general effects of carbon fiber surface treatment can be summarized as eliminating surface impurities of carbon fiber, increasing the specific surface area of ​​fiber; improving the wettability of carbon fiber to resin matrix; introducing reactive functional groups on the surface of the material to produce cross-linked chemical bonds with resin matrix; forming an interfacial transition zone between carbon fiber and resin, etc.

 

 

Common carbon fiber surface treatment methods include physical methods and chemical methods. Physical methods mainly improve the physical interlocking and embedding effect of the interface between carbon fiber and matrix by increasing the specific surface area and roughness. For example, coating method heat treatment, etc. Chemical methods use the increase of chemical functional groups on the surface of carbon fiber to improve the bonding effect of chemical bonds to improve the interlayer bonding strength of the composite material interface. The main methods are:

 

1. Anodic Oxidation Method;

 

2. Liquid Phase Oxidation Method;

 

3. Gas Phase Oxidation Method;

 

4. Plasma Oxidation Method;

 

5. Grafting Method, etc.

 

 

At present, there are also two or more methods combined to treat the carbon fiber surface successively or simultaneously. This method is called composite surface treatment method.

 

At present, major carbon fiber producing countries such as Japan and the United States have considered the process sequence of carbon fiber surface modification and the many factors affecting the quality of carbon fiber such as pre-oxidation, carbonization, and graphitization of polyacrylonitrile precursor, which has become an indispensable and important process component in the preparation of carbon fiber.

 

Due to the advantages of simple process operation, continuous production, and easy control of treatment conditions, the electrochemical oxidation method has been widely used in the industrial field. Major foreign carbon fiber production companies (Toray Corporation of Japan, Zoltek Corporation of the United States, the former R.K. Company and SGL Corporation of Germany) still mostly use this anodic oxidation method.

 

Due to the limitations of some treatment conditions and environment, modification methods such as plasma treatment and ozone treatment are still in the experimental stage. For the surface modification of small amounts of carbon fiber, oxidizing agents and air heating oxidation methods can be used. This type of method has the advantages of intermittent treatment and simple operation, but its oxidation process is relatively intense and the operating conditions are difficult to control.

 

my country’s carbon fiber research started not too late, but it has developed slowly, and its total production capacity is not yet up to par with a company in an important foreign carbon fiber producing country.

 

This is mainly because there are many problems in the preparation process of domestic carbon fiber. Most of the raw materials are civilian acrylic fiber stock solution, which has a high impurity content, which can easily cause the final performance of carbon fiber to be unstable and the discrete coefficient is often too large. Many domestic carbon fibers have not undergone the surface treatment step, and the interlaminar shear strength of the composite materials produced is low.