Carbon black is an important product, which is made from incomplete combustion or cracking of hydrocarbons. It is widely used in rubber, plastics, coatings, batteries and other fields. At present, carbon black is mainly used as rubber reinforcing filler, which is the second largest rubber material after raw rubber. Carbon black can improve the physical properties of rubber, such as strength, hardness, wear resistance and tear resistance. Different carbon blacks have different effects on the improvement of properties, which is closely related to the structure of carbon black. In addition, carbon black can fill the gap between rubber molecules, reduce the cost of rubber, and improve the processing fluidity and demoulding of rubber. However, carbon black has a large specific surface area and strong intermolecular force, which makes it easy to agglomerate into large particles in the dispersion medium during processing, and it is difficult to disperse stably in the matrix, which directly affects the quality of carbon black filled rubber products and is not conducive to the improvement of rubber mechanical properties. Therefore, the use of ordinary carbon black in rubber has limitations, such as poor dispersibility and weak binding force with rubber. In order to solve these problems, modified carbon black has become an important research direction.

Mechanism of carbon black reinforcing rubber

The mechanism of carbon black reinforcing rubber can be summarized as surface adsorption layer theory and molecular chain sliding theory. The surface adsorption layer theory believes that the addition of vulcanizing agent and carbon black makes the rubber form a heterogeneous structure with different properties. The molecular chain sliding theory believes that different rubber chains adsorbed on the surface of carbon black are stretched under stress, thereby achieving stress distribution.

Modification method of carbon black

After the modification of carbon black, its original structure changes, which in turn affects the reinforcing properties of rubber composites. At present, the methods commonly used to modify carbon black include oxidation modification, plasma modification, surface grafting modification and surface adsorption modification.

Plasma modification

Plasma treatment of carbon black is a very popular way, which can provide two advantages : one is that it only occurs on the surface of carbon black and does not change the volume of carbon black ; the second is the use of different atmospheres of oxidation and reduction. The interaction process between plasma and material surface is very complex, and different types of plasma reaction processes are different. The factors affecting the interaction between plasma and material surface include : particles involved in the reaction, such as electrons, free radicals, positive and negative ions, positive and negative ion groups, neutral atoms, molecules and photons ; the plasma state parameters, such as electron energy, electron density, ion energy and ion density, etc. ; surface materials, such as metal, polymer, organic or inorganic particles ; the surface state of the material, such as chemical composition, cleanliness and roughness. At present, the commonly used modified carbon black plasma is divided into argon plasma and oxygen plasma. However, with the development of plasma, other forms of plasma modified carbon black have appeared.

Argon plasma modification

The primary structure is the smallest unit of carbon black. Aggregate is a spatial network structure formed by van der Waals force between carbon black aggregates. It is the secondary structure of carbon black, which is easy to be destroyed during rubber mixing. The specific surface area, structure degree and surface activity are the three basic characteristics of carbon black, and the specific surface area affects the blackness and dispersion of carbon black when mixed with rubber. The structure degree can be calculated by oil absorption. The higher the oil absorption value, the higher the structure of carbon black. The surface activity corresponds to the groups on the surface and plays an important role in the filler-matrix and filler-filler interactions. The surface activity of carbon black can be changed by argon ion treatment, and the dispersibility can be improved.

Oxygen plasma modification

Compared with argon plasma modification, oxygen plasma treatment of carbon black also has a similar effect. Oxygen generates strong oxidizing active substances such as oxygen radicals or ozone under the action of electric field. These active substances further oxidize nano-carbon black, so that a large number of oxygen-containing functional groups are attached to the surface of nano-carbon black. After oxygen plasma treatment, the carbonyl and hydroxyl groups of carbon black increase significantly, and the dispersion stability in water is also greatly improved.

Plasma modification of carbon black mainly has the following advantages : ( 1 ) Plasma modification generally only reacts on the surface of the material and does not affect the internal structure of the material, which can keep the main structure of the material intact. ( 2 ) Most of the gas in the plasma modification method exists in the form of highly active free radicals, so the reaction in the plasma is not controlled by the thermodynamic equilibrium. ( 3 ) The temperature of cold plasma can be kept in the greenhouse, so the oxygen-containing functional groups of carbon black after oxidation are not easy to decompose. ( 4 ) The plasma modification method avoids the exclusion of waste gas and waste liquid in the gas phase and liquid phase oxidation methods, and the plasma modified carbon black does not require subsequent treatment of the product. Therefore, plasma modification has received great attention as a method with good application prospects.