The reason why the reinforcing agent can improve the hardness and mechanical strength of the rubber product is because the surface of the reinforcing agent particles is in physical contact with the rubber macromolecule, and the active surface of the reinforcing agent particle and the rubber molecular chain combine to form a strong chemical bond. The formation of "bonded rubber" has both physical and chemical effects.

The precipitated silica particles contain a plurality of silanol groups. The infrared spectrum shows that there are three types of hydroxyl groups on the surface of silica: siloxy groups, isolating light groups, and hydrogen bonding. The Si-O-bond of the molecular structure center of silica has polarity and great binding ability, which makes the white carbon black particles have high surface activity and can interact with rubber molecules. The rubber hydrocarbon base of the polymer during the rubber compounding process. The break generates free radicals and interacts with the surface layer of SiO-OH.

In addition, the amorphous state of the silica particles and the crystallization are disordered, causing the surface layer to form an electrostatic field, which induces an effect on the unsaturated double bonds of the rubber polymer, thereby promoting the combination of the two.
1. Effect of particle size
The precipitated white carbon black particle size is divided into a primary particle size and a secondary structure particle size. Generally speaking, the secondary structure is broken during the rubber compounding process, so the most important factor affecting the performance of the rubber compound is the original particle size. The original particle size of the precipitated silica is 8-110 nm, the particle size is fine, the dispersion performance is good, and the effective area in contact with the rubber is also large, which is obviously advantageous for rubber reinforcement. From the rubber reinforcing mechanism, the amount of OH in the surface layer of silica is directly related to the reinforcing effect.

      American chemist R•K•ILer summed up the following rules in the study of the relationship between the size of primary particles of hydrogels and the number of hydroxyl groups. This regularity reveals the effect of the particle size of silica on the strength of rubber compounds (see Table 1). It can be seen that the smaller the d, the more active groups, the stronger the interaction between the particles and the rubber, and the greater the strength.

Table 1 Primary particle size and hydroxyl number relationship  

The structure of silica is similar to that of carbon black, which is spherical, and the individual particles are in surface contact with each other and are branched in a chain. This structure is called "secondary structure". The chain structure acts as a hydrogen bond force to form a cluster of aggregate structure. This structure is reversible by external force damage. Its structural size is reflected by the oil absorption value (the oil absorption value refers to the adsorption of 1 gram of white carbon black). The number of milliliters of dibutyl phthalate (DBP). The larger the oil absorption value, the higher the structure. The larger the structure, the more the chain structure of the white carbon black is aggregated, and the reinforcing effect on the rubber is also good. However, the precipitation method of white carbon black with high oil absorption value in the rubber compound must be broken. This branch chain structure consumes more work and energy, so that it is evenly dispersed in the rubber. Refining time. The white carbon black oil absorption value of 2.0-3.5cm3 / g can meet the tire requirements.

The specific surface area of the precipitated silica is also an important indicator of the structural properties of the product. Although the current national standards take into account the specific test conditions for the test surface conditions of the various manufacturers, they are divided into six categories: A, B, C, D, E, and F according to the numerical level. From the quality survey of hydrated silica (silica) in the national rubber precipitation method over the years, the comprehensive physical properties of the rubber compound are based on B (161-190m 2 /g) white carbon black, but only consider "reinforcement". ", Class A (≥ 190 m2 /g) with a higher specific surface area is better. However, in the practice of production and use, the high specific surface area of carbon black is often encountered, but the physical properties of the rubber compound are very poor, which is caused by the production of many silica gels in the production process of silica.