(1) Moisture
The moisture of the precipitated silica includes: free water and bound water. The free water on the surface of the silica is easily removed under heat. The free water is too small, indicating that the surface of the white carbon black is not much light, which reduces the activity of the white carbon black, and causes the white carbon black to aggregate during the mixing, which is difficult to be distributed in the rubber. The surface water is less, which not only affects the vulcanization rate, but also reduces the reinforcing effect. The free water is slightly higher, the mixing rubber has good operation performance, the powder feeding speed is fast, the dust is flying less, the wrapping roll is good, and the vulcanization speed is slightly faster. However, the water content is too high, the heat is large, the scorch is easy to burn, the agglomeration, the dispersion is uneven, the surface of the vulcanized rubber is easy to bubble, and the physical and mechanical properties are also correspondingly decreased. Generally, the surface water at 6 to 8% can best isolate the white carbon black molecules, thereby preventing the particles from re-aggregating, and evenly distributing in the rubber compound during the mixing, which is advantageous for performance improvement and speeding up the vulcanization. The combined water is “internal” of silica, which is relatively stable and can be removed above 400 °C. The general content is 4.0-7.0%. If the combined water is too much, it indicates that the gel content generated during the reaction is high, the activity of the finished product after drying is small, and the reinforcing effect on the rubber is also small. The combination of too little water indicates that the dehydration is too heavy during the reaction process, and the tendency of sanding is large, which is also unfavorable for reinforcement.

(2) PH value
The acidity and alkalinity of white carbon black have a great influence on the vulcanization of the rubber compound. The acid white carbon black retards the rubber compound to vulcanize, and the alkalinity promotes the vulcanization, but the excessive alkalinity is unfavorable for reinforcing. PH is slightly acidic white carbon black, which is beneficial to the tensile and wear resistance of rubber compounds and products. Therefore, the pH value of white precipitated silica for rubber is generally 6-8, which is close to neutral.

(3) Surface modification treatment
The surface modification treatment of silica refers to the purpose of adding a coupling agent to the silica to achieve its hydrophobicity. After the coupling agent is added, CH 3 O-(methoxy) at one end of the coupling agent reacts with the silanol group on the surface layer of the white carbon black, and the other end reacts with the gelatin molecule, that is, the coupling agent is in the white carbon. The “bridge” effect between black and rubber. There are many ways to modify the surface of silica, and the most common one is to treat it with a silane coupling agent (such as Si-69).

(4) Influence of impurities
Precipitated silica is easy to bring in impurities such as Cu, Fe, Mn in the preparation process. Although these trace impurities have little effect on the physical properties of the rubber, in order to make the rubber products have excellent oxidation resistance and aging resistance, Cu is still required. The Fe and Mn contents are reduced to a certain limit. In this regard, GB 10517 specifies the precipitated silica: Cu ≤ 30 mg / kg, Mn ≤ 50 mg / kg, Fe ≤ 1000 mg / kg.
     
The sodium salt in the production of white carbon black by precipitation is difficult to avoid in the production, but the sodium content is too high to be used as a reinforcing filler for natural or synthetic rubber, and the transparency of the rubber is obviously not good. However, in the production process, the reaction synthesis process is controlled to prevent the formation of excessive Na+ gel and the rinsing of the semi-finished slurry, and the sodium salt content can be reduced to less than 0.5%. Such precipitation method has no properties on the rubber. Very influential,
in conclusion
1. The physical and chemical indicators of the precipitation method directly affect the various properties of the rubber compound, and the reinforcing properties depend on it.
Particle size, structure, surface properties and types and content of impurities.
2. G B 10517 Precipitated hydrated silica for rubber (white carbon black) The specific surface area and particle size index that are not specified in the technical conditions have a significant effect on the physical properties of the rubber compound. The production enterprises should strictly stabilize the production operation and gradually improve the measurement and control means.
3. Precipitation method In the production process of silica, special attention should be paid to “anti-gelation”. Only silica with very low “gel” composition can have good activity and satisfactory physical and chemical indicators.

(Source: This information is from the internet. If you have any infringement issues, please contact us.)