The role of carbon black in tires

Carbon black is a major raw material in tire products, accounting for approximately 30% of its usage, ranking second only to polymers. Because carbon black can greatly improve the physical properties of rubber, it is the most important reinforcing agent for tire products, especially for systems mainly composed of synthetic rubber. Without reinforcement, its own strength has no practical value. The reinforcement effect of rubber can be defined as the improvement of the service life of rubber products, generally through the reinforcement of the modulus, hardness, wear resistance, and other aspects of the elastomer. For automotive tires, the most meaningful aspect is the correlation between reinforcement and rubber wear.
Carbon black has strong adsorption capacity, and its interaction with hydrocarbon rubber is physical and does not involve chemical reactions. The fundamental reason for carbon black reinforced rubber is the adhesion of elastomer molecules on the surface of carbon black, because carbon black particles have micropores. When the micropore size is very small, making it impossible for the elastomer molecules to enter, the area contained in the pores does not have any effect on the reinforcement; Reinforcement cannot be achieved when the elastic molecules are too large to enter the voids of the permanent structure. The formation of carbon black gel is a prerequisite for reinforcement. This carbon black gel is an infinite carbon black elastomer network. In the glassy state below the glass transition temperature, carbon black gel does not exist, and the reinforcement effect disappears. Therefore, the reinforcement of rubber by fillers is limited to the rubber state of the elastomer. When the elastomer is in the glass state, the fillers have little or no reinforcement effect. In carbon black gel, the cross-linking of bonding network is caused by filler, and the interaction between reinforcing particles and elastomer and the bonding strength are the key to reinforcement.
Carbon black is a colloidal substance composed of carbon elements, and the size, morphology, and surface activity of aggregates determine its reinforcing properties. Carbon black aggregates are firmly sintered together, and cannot be separated by ordinary processes during rubber processing. When measuring the reinforcing effect of carbon black on rubber, the specific surface area, structure, and surface activity are important indicators. In addition, important parameters such as carbon components (such as coke), non carbon components (such as ash and moisture), and dispersion level in carbon black should also be considered.