Modification of silica and the effect on application of rubber

Abstract

Silica is an amorphous material that consist of silicon and oxygen atoms in a tetrahedral arrangement interconnected to form a non-regular three-dimensional network of Si−O−Si bonds with silanol groups (Si−OH) present inside the structure and on the surface. As to rubber fillers, silica is of fundamental importance in many rubber applications. However, on the surface of silica, there are massive silanol groups, leading to the strong polarity of silica. The highly polar silica has a poor compatibility with the non-polar rubber matrix, which results in the weak interaction between the silica and rubber matrix. Meanwhile, conventional silica cannot be easily dispersed in the non-polar rubber due to the poor compatibility. Good dispersion of silica in rubber matrix to achieve proper reinforcement effect remains a major issue for the external silica loading in rubber matrix. Therefore, in order to eliminate the drawbacks of silica and improve the compatibility between silica and rubber molecules, it is necessary to reduce the concentration of silanol groups on the surface of silica through surface medication before use, otherwise the incorporation of silica will make no contribution to the improvement of rubber performance. This paper mainly summarizes the effects of the types of modifying agents, the modified process and the interactions mechanism between silica and polymer matrix on the dispersibility and reinforcing efficiency of silica particles. At the same time, the effect of silica prepared with different modified ways on the properties of silicone rubber and tire rubber was also discussed. In addition, the review forecasted that the silica with low cost, high dispersion, functionalization and refinement will be the main development trend in the future. It must be pointed out that with the appearance and development of green tire, the structure design and surface modification of silica have been extensively attracted more attention. Particularly, liquid phase in-situ surface-modification technique can be applied to fabricate high-performance silica with a cost-effective manner in the three kinds of modified methods including wet modification process, the dry process and liquid phase in-situ surface modification. The mechanism of liquid phase in-situ surface modification mainly has two aspects. On the one hand, high dispersible nano-silica or high reactive nano-silica is feasibly prepared by introducing different organic modified agent in the surface of inorganic nanoparticles with combined chemical bonds at the beginning stage of preparation of nanoparticles. On the other hand, in order to ensure the dispersion of nanoparticles with original particle morphology in polymer matrix, the surface microstructure of the nanoparticles can be effectively changed by using various modified functional groups and controlling the modifier dosage. Rubber materials with high performance prepared through in-situ synthetic technology is easily fabricated by directly introducing nano-silica in the polymerization process of rubber, which will be an effective way to design new structure of the rubber materials.