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Effect of Particle Size of Precipitation Silica on Properties of Rubber Products
Jan 18, 2019

                 Effect of Particle Size of Precipitation Silica on Properties of Rubber Products

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The reason why reinforcing agent can improve the hardness and mechanical strength of rubber products is that the surface of reinforcing agent particles contacts with rubber macromolecules to produce physical adsorption, while the active surface of reinforcing agent particles and rubber molecular chains combine to form solid chemical bonds to form "bonded rubber", which has both physical and chemical effects.

Silica particles prepared by precipitation method contain many kinds of silanol groups. Infrared spectra show that there are three kinds of hydroxyl groups on the surface of silica: silica, isolated light group and hydrogen bond. The Si-O bond in the molecular structure center of silica has polarity and strong binding ability, which makes silica particles have high surface activity and can interact with rubber molecules. In the process of rubber refining, the rubber alkyl groups of macromolecule break to form free radicals and interact with the surface layer of silica to form OH. In addition, the amorphous shape of silica particles and the disordered crystallization result in the formation of electrostatic field on the surface layer, which induces the unsaturated double bonds of rubber polymers and promotes the combination of the two.

Now we would like to discuss the effect of particle size on properties of rubber products.

The particle size of precipitated silica can be divided into original particle size and secondary structure particle size. Generally speaking, the secondary structure of silica is broken in the process of rubber mixing, so the primary particle size is the most important factor affecting the properties of rubber compound. The original particle size of precipitated silica is 8-110 nm. Fine particle size makes it dispersible and has large effective contact area with rubber, which is obviously beneficial to rubber reinforcement.

From the mechanism of rubber reinforcing, the amount of OH on the surface of silica is directly related to the reinforcing effect. American chemist R. K. ILer summarized the following rules in his research on the relationship between the size of primary particles and hydroxyl number of hydrogels, which revealed the influence of silica particle size on the strength of rubber compound.It can be seen that the smaller d, the more active groups, the stronger the interaction between particles and rubber, and the greater the strength.