The industrial production of silica mainly adopts the precipitation method. The surface of the produced white carbon black contains a large number of polar groups such as hydroxyl groups, which leads to problems such as easy adsorption of water molecules, poor dispersion, and secondary aggregation. Thereby affecting the industrial application effect of silica. Therefore, most silica needs surface modification treatment before industrial application to improve its industrial application performance.
Chemical surface modification of silica at this stage mainly includes surface graft modification, coupling agent modification, ionic liquid modification, and polymer interface modification and combination modification, etc. Although each modification process has its own advantages and characteristics, current industrial applications are mainly based on coupling agent modification.
1. Surface graft modification of silica
The principle of surface grafting modification method is to graft polymers with the same properties as the matrix polymer (such as rubber) on the surface of silica through chemical grafting polymer. On the one hand, it can enhance the force between particles and matrix. And changing the polarity of the particle surface can also improve the dispersion of silica itself.
It is suitable for grafting polymers with smaller molecular weights. The conditions for grafting polymers with higher molecular weights 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 chemically react with the hydroxyl groups on the surface of the silica, thereby changing the silica Structure and distribution of surface groups 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 currently one of the most widely used modification methods.
Coupling agents currently widely used include silane coupling agents, siloxane coupling agents and silazane coupling agents. In practical applications, 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 liquids, also known as room temperature ionic liquids, are molten salts composed of organic cations and organic or inorganic anions. They are liquid below 100°C. Ionic liquid modification uses ionic liquid modifiers instead of traditional organic phase modifiers to modify silica. Compared with traditional organic phase modifiers, ionic liquid phase is liquid at room temperature, has strong conductivity and high stability. It has the advantages of good solubility, non-volatility, and less pollution, and 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 to the mixed system of silica black and ionic liquid, and then placed in a constant temperature water bath for reaction. After the reaction is completed, it is dried to obtain modified white carbon black.
4. Interface modification of silica macromolecules
The modifier used in polymer interface modification is a polymer containing polar groups. During the modification reaction with silica particles, the molecular skeleton of the macromolecular interface modifier can be introduced to maintain the basic main chain structure while having more polar epoxy groups, thereby improving the silica The compatibility between particles and matrix achieves better interface modification effect. This method and coupling agent can synergistically strengthen the matrix, but the reinforcement effect is poor when used alone.
5. Modification of silica and carbon black
Combination modification is to combine silica black with other materials to improve the overall performance of rubber products by combining their respective advantages. This method can combine the advantages of the two modifiers to improve the overall performance of the matrix, but the modification effect is closely related to the ratio of the modifiers.
For example, carbon black and silica are both good reinforcing agents in the rubber industry. Among them, 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. Improve its wear resistance, cold resistance and other properties; as a reinforcing agent, white carbon black can significantly improve the rolling resistance and wet slip resistance of rubber products, but the effect alone is not as good as carbon black. Numerous research papers�, The combined use of carbon black and silica as reinforcing agents can combine the advantages of both to improve the overall performance of rubber products.
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