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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 applications at present.
1. Surface grafting modification of silica
The principle of surface grafting modification is to graft macromolecular polymers with the same properties as the matrix polymer (such as rubber) onto the surface of silica through chemical grafting. On the one hand, this can enhance the interaction force between 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. When the molecular weight of the grafted polymer is higher, the conditions are harsh.
2. Modification by silica ionic solution
Ionic liquids, also known as room-temperature ionic liquids, are molten salts composed of organic cations and organic or inorganic anions, and are in liquid state below 100℃. Ionic liquid modification is to use ionic liquid modifiers instead of traditional organic phase modifiers to modify silica. Compared with traditional organic phase modifiers, ionic liquid has advantages such as being liquid at room temperature, having strong electrical conductivity, high stability and good solubility. Moreover, it is non-volatile and less likely to cause pollution, which is more in line with the requirements of green production. However, the modification effect is relatively 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 placed in a constant temperature water bath for reaction. After the reaction is complete and dried, modified silica can be obtained.
3. Interfacial modification of silicon dioxide macromolecules
The modifier used in macromolecular interface modification is a macromolecular polymer containing polar groups. During the modification reaction with silica particles, the molecular main chain of the macromolecular interface modifier can introduce more polar epoxy groups while maintaining the basic main chain structure, thereby improving the compatibility between silica particles and the matrix and achieving a better interface modification effect. This method can synergistically reinforce the matrix with the coupling agent, but the reinforcing effect is relatively low when used alone.
4. Modification by using silica in combination
Concurrent modification is achieved by combining silica with other materials, leveraging their respective advantages to enhance 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.
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