Five major surface modification methods and characteristics of white carbon black
At present, the industrial production of white carbon black is mainly by precipitation method. The white carbon black produced contains a large number of polar groups such as hydroxyl groups on its surface, which leads to problems such as easy adsorption of water molecules, poor dispersion, and easy secondary aggregation, thus affecting the industrial application effect of white carbon black. Therefore, the surface of white carbon black needs to be modified before industrial application to improve its industrial application performance.
At present, the chemical surface modification of white carbon black mainly includes surface grafting modification, coupling agent modification, ionic liquid modification, macromolecular interface modification and blending modification. Although each modification process has its own advantages and characteristics, the current industrial application is mainly based on coupling agent modification.
1. Surface grafting modification of silica
The principle of surface grafting modification method is to graft macromolecular polymers with the same properties as the matrix polymers (such as rubber) on the surface of white carbon black by chemical grafting method. On the one hand, it can enhance the force between particles and matrix and change the polarity of particle surface, on the other hand, it can also improve the dispersion of white carbon black itself.
It is suitable for grafting polymers with small molecular weight, and the conditions for grafting polymers with high molecular weight are harsh.
2. Modification of silica coupling agent
The principle of coupling agent modification is to use some functional groups on the coupling agent to react with hydroxyl groups on the surface of white carbon black, so as to change the structure and distribution of groups on the surface of white carbon black to improve the compatibility with the matrix and its dispersion. Coupling agent modification is one of the most widely used modification methods because of its good modification effect and high controllability of reaction.
At present, silane coupling agent, siloxane coupling agent and silazane coupling agent are widely used. In practical application, the main process of coupling agent modification is divided into four steps: mixed reaction, cooling separation, repeated washing and precipitation.
3. Modification of white carbon black by ionic liquid
Ionic liquids, also known as room temperature ionic liquids, are molten salts composed of organic cations and organic or inorganic anions that are liquid below 100 ℃. Ionic liquid is used to modify white carbon black by replacing traditional organic phase modifiers with ionic liquid modifiers. Compared with traditional organic phase modifiers, ionic liquid has the advantages of being liquid at room temperature, strong conductivity, high stability and good solubility, and it is not volatile and easy to produce pollution, which is more in line with the requirements of green production, but the modification effect is poor.
The ionic liquid modification process is relatively simple. A certain amount of absolute ethanol is added into the mixed system of white carbon black and ionic liquid, and then it is put into a thermostatic water bath for reaction. After the reaction is sufficient, the modified white carbon black can be obtained by drying.
4. Interface modification of silica macromolecules
The modifier used for macromolecular interface modification is a macromolecular polymer containing polar groups. During the modification reaction with white carbon black particles, the main chain of macromolecular interface modifier can maintain the basic main chain structure while introducing more polar epoxy groups, so as to improve the compatibility between white carbon black particles and the matrix and achieve a better interface modification effect. The method can be used with the coupling agent to reinforce the matrix, but the reinforcement effect is low when used alone.
5. Blending modification of white carbon black
The blending modification is to improve the overall performance of rubber products by combining the advantages of white carbon black and other materials. This method can combine the advantages of the two modifiers to enhance the comprehensive performance of the matrix, but the modification effect is closely related to the ratio of modifiers.
For example, carbon black and white carbon black are both good reinforcing agents in the rubber industry, among which carbon black is one of the most commonly used reinforcing agents in the rubber industry. The special structure of carbon black can enhance the tensile and tear strength of rubber materials and improve their wear resistance, cold resistance and other properties; As a reinforcing agent, white carbon black can significantly improve the rolling resistance and wet skid resistance of rubber products, but its use alone is not as effective as carbon black. A lot of research shows that the combination of carbon black and white carbon black as reinforcing agent can combine their advantages to improve the overall performance of rubber products.