At present, the industrial production of white carbon black is mainly based on the precipitation method, and the produced white carbon black contains a large number of polar groups such as hydroxyl groups on the surface, which makes it very easy to adsorb water molecules, has poor dispersion, and is prone to secondary aggregation, etc. problems, thus affecting the industrial application effect of white carbon black. Therefore, before industrial application, most of the white carbon black needs to be surface modified to improve its industrial application performance.
At present, the chemical surface modification of silica mainly includes surface grafting modification, coupling agent modification, ionic liquid modification, macromolecule interface modification and combined modification, etc. Although each modification process has its own advantages And characteristics, but the current industrial application is mainly based on the modification of the coupling agent.
1. Surface graft modification of silica
The principle of the surface graft modification method is to graft a macromolecular polymer with the same properties as the matrix polymer (such as rubber) on the surface of silica by chemical grafting. On the one hand, it can enhance the force between the particles and the matrix. And change the polarity of the particle surface, on the other hand, it can also improve the dispersion of silica itself.
It is suitable for grafting polymers with smaller molecular weights, and the conditions for grafted polymers with higher molecular weights are harsh.
2. Silica coupling agent modification
The principle of coupling agent modification is to use part of the functional groups on the coupling agent to chemically react with the hydroxyl groups on the surface of silica, thereby changing the group structure and distribution on the surface of silica to improve compatibility with the matrix and its own dispersion. Coupling agent modification has the advantages of good modification effect and high reaction controllability, and is one of the most widely used modification methods at present.
Currently widely used coupling agents include silane coupling agents, siloxane coupling agents and silazane coupling agents. In practical application, the main process of coupling agent modification is divided into four steps: mixing reaction, cooling separation, repeated washing and precipitation.
3. Silica ionic liquid modification
Ionic liquids, also known as room temperature ionic liquids, are molten salts composed of organic cations and organic or inorganic anions, which are liquid below 100°C. Ionic liquid modification is to use ionic liquid modifier instead of traditional organic phase modifier to modify silica. Compared with traditional organic phase modifier, ionic liquid phase has liquid state at room temperature, strong conductivity and high stability. It has the advantages of good solubility and non-volatility, and is not 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. Add a certain amount of absolute ethanol to the mixed system of silica and ionic liquid and then put it in a constant temperature water bath for reaction. After the reaction is sufficient, dry it to obtain modified silica. .
4. Modification of silica macromolecule interface
The modifier used for macromolecular interface modification is a macromolecular polymer containing polar groups. During the modification reaction with silica particles, the molecular backbone of the macromolecular interface modifier can be introduced There are more polar epoxy groups while maintaining the basic main chain structure, so as to improve the compatibility between the silica particles and the matrix, and achieve a better interface modification effect. This method can cooperate with the coupling agent to strengthen the matrix, but the reinforcing effect is low when used alone.
5. White carbon black and modification
Co-modification is the co-modification of silica and other materials, combining their respective advantages to improve the overall performance of rubber products. 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 the modifiers.
For example, both carbon black and white carbon black are 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 its wear resistance, cold resistance and other properties; and white carbon black as a reinforcing agent can significantly improve the rolling resistance and wet skid resistance of rubber products, but its effect alone is not as good as carbon black. A large number of studies have shown that the combination of carbon black and silica as a reinforcing agent can combine the advantages of both to improve the overall performance of rubber products.