Why should silica be modified? What methods are there?
The surface layer of silica has a large number of hydroxyl groups, which interact with each other, thereby affecting the overall performance of the material. For example, silica agglomerates due to the hydrophilic nature of the surface hydroxyl groups. Because of this phenomenon, when the rubber composite material is subjected to a certain load, the relative friction force inside the material will increase, affecting the mechanical properties of the composite material.

Because of a large number of hydroxyl groups, which are alkaline, silica will also be weakly alkaline. When encountering some alkaline accelerators, it will react with them, which will cause some problems in the vulcanization process of rubber composites. Influence, will lead to a longer time for rubber vulcanization, which will produce a series of chain reactions, such as increasing internal friction, reducing crosslinking density and so on. It can be seen that in order to meet the modification requirements, it is very necessary to reduce the number of hydroxyl groups on the surface of silica, improve the compatibility and hydrophobicity, and reduce the agglomeration ratio in the rubber matrix, and then prepare materials that meet the requirements.
Usually, in the modification process of silica, related chemical materials are mainly used, and appropriate technological means are set at the same time to promote the reaction between the hydroxyl groups on the surface and the modified materials, thereby reducing the amount of hydroxyl groups on the surface. In traditional industrial and practical applications, it is divided into two types according to the properties of modifiers, namely organic and inorganic modification. Among them, the modification method of organic matter is widely accepted, which can be divided into three types according to the process method, dry method, wet method and autoclave method. For the modifier that has been determined, it can be matched with different modification methods to achieve different modification effects. There are many modification techniques, and they each have their own advantages and disadvantages.

1 By grafting the surface of silica particles to polymers with similar properties, it is commonly known as the surface grafting modification method: it is suitable for grafting polymers with smaller molecular weights, but the conditions for grafting are also very strict;
2 Silane coupling agent modification method: In the preparation process, the functional group on the coupling agent reacts with the hydrophilic group of the particle, and on this basis, the material is modified;
3 The method of ionic liquid modification: the silica is placed in the particle liquid to react with it to improve the dispersibility of the silica. Although this method has low pollution and is easy to operate, the modification effect is poor;
4 Macromolecular interface modification: This modification method has poor effect when used alone, but can cooperate with the coupling agent in a specific environment;
5 The combined modification method is to combine a variety of modification methods, take advantage of their strengths and avoid their weaknesses, and integrate their respective advantages to improve the quality of modification. For example, the in-situ modification method first developed by Michelin, roughly realizes the process of adding silane coupling agent and silica and other substances to the rubber during mixing, and the two react under certain system conditions. There is some force between the coupling agent and the rubber mixture, which can not only destroy the aggregates of silica, but also hydrophobically modify the silica. However, this method requires a lot of energy and is difficult to control efficiently, so appropriate improvements should be made to avoid these defects. In addition, the remaining coupling agent is likely to remain in it and affect the properties of the composite material.
6 There is also a dry modification technology similar to in-situ modification: its purpose is to obtain highly hydrophobic silica through the reaction of silane coupling agent and silica under high temperature conditions. However, in this process , also consumes a lot of energy.