Surface modification methods and characteristics of silica 5

At present, the industrial production of silica is mainly based on precipitation method, and the surface of the produced silica contains a large number of polar groups such as hydroxyl groups, which leads to the problems of easy adsorption of water molecules, poor dispersion and easy secondary aggregation, thus affecting the industrial application effect of silica. Therefore, most of silica needs surface modification before industrial application 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, macromolecular interface modification and combined modification, etc. Although each modification process has its own advantages and characteristics, coupling agent modification is mainly used in industrial application at present.

1. Surface grafting modification of silica

The principle of surface grafting modification method is to graft macromolecules with the same properties as matrix polymers (such as rubber) on the surface of silica by chemical grafting method. On the one hand, it can enhance the interaction between particles and matrix and change the polarity of particle surface, on the other hand, it can also improve the dispersibility of silica 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 that some functional groups on the coupling agent react chemically with hydroxyl groups on the surface of silica, so as to change the group structure and distribution on the surface of silica and improve the compatibility with the matrix and its own dispersibility. Coupling agent modification has the advantages of good modification effect and high reaction controllability, and is one of the widely used modification methods at present.

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: mixing reaction, cooling separation, repeated washing and precipitation.

3. Modification of silica ionic liquid

Ionic liquid, also known as room temperature ionic liquid, is a molten salt composed of organic cations and organic or inorganic anions, which is liquid below 100℃. 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 has the advantages of being liquid at room temperature, strong conductivity, high stability and good solubility, and it is non-volatile and not easy to produce pollution, which is more in line with the requirements of healthy production, but the modification effect is poor.

The process flow of ionic liquid modification is relatively simple. A certain amount of anhydrous ethanol is added to the mixed system of silica and ionic liquid, and then it is put into a constant temperature water bath for reaction. After the reaction is sufficient, it is dried to obtain modified silica.

4. Macromolecular Interface Modification of Silica

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 introduce more polar epoxy groups while maintaining the basic backbone structure, so as to improve the compatibility between silica particles and the matrix and achieve better interface modification effect. This method can cooperate with coupling agent to reinforce the matrix, but the reinforcement effect is low when used alone.

5, silica combined with modification.

Combined modification is to improve the overall performance of rubber products by combining silica with other materials and combining their respective advantages. This method can combine the advantages of two modifiers to enhance the comprehensive properties of the matrix, but the modification effect is closely related to the ratio of modifiers.

For example, carbon black and silica are both good reinforcing agents in rubber industry, among which carbon black is one of the commonly used reinforcing agents in rubber industry. The special structure of carbon black can enhance the tensile and tear strength of rubber materials and improve their wear resistance and cold resistance. As a reinforcing agent, silica can significantly improve the rolling resistance and wet skid resistance of rubber products, but its effect is not as good as that of carbon black alone. A large number of studies show that the combination of carbon black and silica as reinforcing agent can combine their advantages to improve the overall performance of rubber products.