At present, the industrial production of white carbon black is mainly by precipitation method. The surface of white carbon black produced contains a large number of polar groups such as hydroxyl, which leads to the problems of water molecules adsorption, poor dispersion and secondary aggregation, which affects the industrial application effect of white carbon black. Therefore, most of silica needs surface modification before industrial application to improve its application performance.

1. Surface grafting modification of silica
The principle of surface grafting modification method is to graft macromolecular polymer with the same properties as the matrix polymer (such as rubber) on the surface of silica through 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 silica itself. It is suitable for grafting polymers with small molecular weight, and the conditions are harsh when the molecular weight of the grafted polymer is high.

2. Modification of silica with coupling agent
The principle of coupling agent modification is to use some functional groups on the coupling agent to react with the hydroxyl groups on the surface of silica to change the group structure and distribution on the surface of silica to improve the compatibility with the matrix and its dispersion. The coupling agent modification has the advantages of good modification effect and high controllability of reaction, and is one of the most widely used modification methods at present.

3. Modification of silica with ionic liquid
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 ℃. Ionic liquid modification is to use ionic liquid modifier instead of traditional organic phase modifier to modify white carbon black. Compared with traditional organic phase modifier, 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.

4. Interfacial modification of silica macromolecules
The modifier used for macromolecular interface modification is a macromolecular polymer containing polar groups. During the modification reaction with silica particles, the molecular 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 silica particles and matrix, and achieve better interface modification effect.
This method can reinforce the matrix with the coupling agent, but the reinforcement effect is low when used alone.

5. Modification of white carbon black
Blending modification is to improve the overall performance of rubber products by combining the advantages of silica 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 modifier ratio.

For example, carbon black and white carbon black are good reinforcing agents for the rubber industry. 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; White carbon black as a reinforcing agent can significantly improve the rolling resistance and wet skid resistance of rubber products, but its effect is not as good as carbon black alone. A large number of studies have shown that the combination of carbon black and white carbon black as reinforcing agent can improve the overall performance of rubber products by combining their advantages.