Precipitation white carbon black 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 has the possibility of chemical combination with rubber macromolecules. This is the 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.


1、 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


2、 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.


3、 Common white carbon black activator (PEG)


Polyethylene glycol (PEG) is very common and useful in all walks of life. In rubber, it is mainly used to neutralize the acidity of filler, accelerate the vulcanization rate and cross-linking density. It has good water solubility, good compatibility with many organic components, excellent lubrication, moisture retention, dispersion, and can also be used as an antistatic agent and softener.


Generally, PEG-4000 is used in rubber. If the molecular weight of PEG-4000 is too low, the compatibility is poor, it is easy to precipitate, and it is a liquid, it is not easy to add, the molecular weight is too high, the alcohol group per unit weight is small (low hydroxyl value), and the acid neutralization effect is poor. Because the molecular weight of 4000 is a solid sheet, it is easy to process, add, and not easy to precipitate, and the polymer with medium molecular weight has good compatibility with rubber, PEG-4000 is generally selected.


The functions of PEG can be summarized as follows:


1. Processing aids can improve the extrusion speed of rubber compound, improve the demoulding property, make the surface of products bright, and also help to discharge moisture during vulcanization. PEG-4000 has a good lubrication effect when applied to tires and rubber molded products, making the surface of products smoother. In the production process of natural rubber and synthetic rubber, it can also be used as internal release agent. The utility model has the advantages of no volatilization, no ash change in production, and the mold is kept clean after demoulding. Moreover, the surface of molded products is more smooth and clean due to its addition.


2. Vulcanizing active agent, which plays a role in regulating the bonding performance of raw rubber and filler (especially white), and also plays a role in reducing Mooney and improving the curing rate, especially for thiazole accelerants, which can improve the curing rate and crosslinking degree. Especially in the formula of extrusion microwave continuous vulcanization reinforced by EPDM white CB. Products bonded with metal should preferably not use PEG


3. The active agent of acid filler, especially for white carbon black, can be used as the treatment agent of white carbon black to activate the curing system. Wet the surface of acidic filler such as white carbon black. One reaction is neutralization, and the other is similar to covering. Because acid filler will adsorb, please note that it is an adsorption accelerator. The amount used is in direct proportion to the amount of acid surface area of acid filler. We can basically understand that the acidic surface has been neutralized. Of course, other vulcanization reactions will also be acidic, such as HS. I'll leave it to zinc oxide


4. The activated dispersant, when used as the activated dispersant in the rubber compound with various fillers and colors, can reduce or eliminate the influence of fillers on vulcanization, make various additives disperse evenly, extend the scorching time, and improve the physical and mechanical properties of rubber products. In all kinds of colored rubber products, it can make the products bright in color. Due to its polarity, it can also enhance the absorption of microwave by non-polar rubber (such as EPDM).