Silanol groups and siloxane groups on the surface of silica, these groups are easy to adsorb moisture. Appropriate moisture can prevent coagulation between the white carbon black particles. When the rubber is kneaded, the temperature rises and the water is separated from the silanol group. The white carbon black is in better contact with the rubber. If the white carbon black is removed in advance, The hydroxyl groups between the filler particles will be hydrogen-bonded. This hydrogen bond network structure will thicken the viscosity of the rubber compound. This combination is firm, resulting in hardening of the rubber compound and poor performance. In severe cases, so-called structures will appear. Chemical. Since the gas phase method white carbon black is extremely low in moisture, it is easy to be structurally formed. Therefore, it is said that the moisture is too low and it is difficult to disperse, which is disadvantageous for performance. In terms of surface properties, adsorbed water can be regarded as a surface modifier which can passivate the hydroxyl groups on the surface of silica. The moisture, pH and surface active groups of silica are inseparably closely related. The siloxane group on the surface of silica is non-polar, thus forming its hydrophobic part; the hydroxyl group is polar. This constitutes its hydrophilic portion. Therefore, the hydrophobic and hydrophilic partial groups of silica are an amphoteric substance. The hydroxyl group has the dual characteristics of alcohol and acid, so it is also called silanol group. The silanol group has solid acid properties, so the PH value after neutralization. It will rise to alkaline, so the rise of moisture will neutralize the silanol group to some extent, and the pH of white carbon will naturally rise. When the moisture of the silica is too low, the active groups on the surface are more active, and the adsorption of the accelerator is strengthened, so that the vulcanization rate of the rubber is slowed down, and it is difficult to disperse and mix in the rubber. If the moisture content of the silica is too high, the scorch time and the positive vulcanization time will be shortened. The acidic surface of the filler has an adsorption effect on the promoter. In fact, the acidic pH of the filler increases the surface group of the silica and is more active. It has been proved that the powdered white carbon black increases with the storage time, pH and water. There will be a rising trend, and the vulcanization rate of the rubber will increase accordingly.
The molecular formula of silica is SiO2·nH2O, one of which can volatilize or evaporate water during heating or production operations. This part of the water is reversible, that is, after heating to 105 °C in the technical requirements of silica. The weight of water lost over a period of time is called the heat reduction, which is what we often call the moisture content of silica, which is a reversible adsorption water. Heating to 1000 degrees removes all moisture and some organic impurities in the silica, and the weight subtracted from the group is called the ignition loss.
ISO/DIS5794/3 stipulates that the heating loss should be controlled at 4-8%, and the ignition loss should be controlled at ≦7%. It has been proved that the white carbon black moisture control at 6-8% can give the rubber compound a stable vulcanization rate. And good dispersion.