White carbon black (precipitation method) is a common name for white reinforcing filler used in rubber industry to precipitate hydrated silica. There are a large number of silanol groups on the surface of white carbon black particles, which may be chemically combined with rubber macromolecules. It is a basic condition for white carbon black to become an inorganic reinforcing agent for rubber. The surface of white carbon black has strong chemical adsorption activity, which is related to the surface hydroxyl of white carbon black. It can combine with water in the form of hydrogen bond to form a multi-molecular adsorption layer. In addition, it can also adsorb many small organic molecules. In order to obtain the best physical properties of rubber, we usually add alcohol and amine activators to the formula.

Negative effects of silanol groups on silica：

1. Silica absorbs moisture in the air during storage to stabilize its structure, i.e. moisture absorption
2. The silica rubber is easy to form hydrogen bond and self agglomerate during mixing, resulting in high Mooney viscosity and difficult mixing and processing
3. Hydrophilicity of silica and hydrophobic rubber macromolecules repel each other, affecting the dispersion of silica in rubber
4. Active hydrogen ions easily adsorb amine materials such as zinc oxide and accelerator, resulting in delayed vulcanization and decreased rubber properties

Activated agent of white carbon black and its action mechanism：

1. Active agent of alcohol and alcohol amine
Auxiliaries such as alcohol and ethanolamine, such as polyethylene glycol (PEG) and triethanolamine, are first adsorbed by white carbon black during rubber mixing, reducing the adsorption of white carbon black, protecting amine accelerants, antioxidants and zinc oxide from being adsorbed by white carbon black, so that the vulcanization performance of rubber compound is not disturbed.

2. Dispersant of zinc salts
Silica alcohol group (｜ Si-OH) on the surface of white carbon black is very easy to react with zinc fatty acid in cation exchange to form ｜ Si-OZnR, etc. The hydrogen ions on the silanol base are replaced, which weakens the polarity of the white carbon black surface, reduces the self polymerization of surface groups, reduces the Mooney viscosity of the rubber compound, and benefits the dispersion of white carbon black, but does not improve the physical properties.

3. Silane coupling agent
The silane coupling agent is actually a kind of surfactant with hydrophilic and lipophilic groups. The hydrophilic group is replaced by the active hydrogen ion of the silanol group, while the lipophilic group is accepted by the rubber matrix, forming the chemical bond of white carbon black silane rubber matrix. The coupling agent improves the physical properties of the rubber material. Compared with carbon black, it is difficult to mix, has low modulus, and has poor wear resistance.