Currently, there are several theories regarding the mechanism of reinforcing effect of carbon black, including the molecular chain sliding theory, the bound rubber theory, the filler network theory, the carbon black surface structure theory, and the van der Waals network theory.
1.1 Molecular Chain Sliding Theory
The molecular chain sliding theory suggests that the rubber chains adsorbed on the surface of carbon black have certain mobility. Under stress, the rubber chains slide on the surface of the carbon black particles. After the external force is removed, the rubber material shrinks and gradually returns to its original state through a long period of recovery. Adsorption and desorption reach a new dynamic equilibrium, and the rubber material restores or approaches its original state.
1.2 Bound Rubber Theory with Double Layer Model
This theory model proposes that the bound rubber adsorbed on the periphery of carbon black consists of an inner glassy hard layer and an outer viscous hard layer. As stress gradually increases, the contribution to the modulus increase from the oriented viscous hard layer is significant. On the other hand, the restricted movement of polymer molecules in the glassy hard layer does not contribute to modulus increase.
1.3 Filler Network Theory
With the increase of the carbon black content, a filler network structure can be formed between the carbon black particles. The interaction between fillers, between fillers and polymers, and the distance between aggregate particles are important factors affecting the formation of filler networks.
1.4 Carbon Black Surface Structure Theory
This theory suggests that the surface of active fillers is uneven, and the reinforcement of elastomers is influenced by the roughness and size range of the surface structure of active fillers. This structure has a significant impact on the volume effect or the interaction between fillers and aggregates.
1.5 Van der Waals Network Theory
This theory proposes that when rubber is deformed, the deformation of the bound rubber between filler particles is much greater than the macroscopic deformation, so that the filler particle aggregates can produce internal slip. The reinforcement effect of rubber is related to the thickness distribution of the bound rubber, and the critical stress that causes particle separation is the van der Waals stress between particles.
Progress in the Application Research of Carbon Black in Rubber
2.1 Application in Tires
Xu Shichuan et al. studied the application of CF series carbon black in the transition layer, airtight layer of all-steel radial tires, and the ply layer of the load-bearing bias tires. The results showed that the physical properties of rubber were improved when using CF604 carbon black in all-steel radial tires and load-bearing bias tires; the bonding strength and durability of the ply layers of finished tires were improved, and the cost was reduced. Li Aifa et al. found that when using dual-phase carbon black CRX2125 in the tread rubber to replace an equal amount of N134 carbon black, the physical properties of the rubber were basically unchanged, while heat generation, wear resistance, and rolling resistance were reduced. The durability and heat generation of finished tires were improved, while the production cost slightly increased.
2.2 Styrene-Butadiene Rubber (SBR)
Xu Shuaifeng et al. found that high-structure carbon black filled SSBR raw rubber had poor processing performance, while the high-structure BL series carbon black filled SSBR vulcanized rubber had higher tensile stress, tensile strength, tear strength, and reinforcement factor than the low-structure N220 and N330 carbon black filled vulcanized rubber. Zhang Hao et al. studied the effect and mechanism of carbon black content on the rheological properties of T2003 and 2305 grade SSBR. The results showed that after filling with carbon black, the extruded appearance of T2003 and 2305 mixed rubber was significantly improved compared to raw rubber.
2.3 Acrylonitrile-Butadiene Rubber (NBR)
Liang Lei et al. studied the properties of HNBR filled with different carbon black (N330, N550, N770, N990), zinc methacrylate, and N770 carbon black mixed with zinc methacrylate. The results showed that as the carbon black particle size increased, the mechanical properties of the rubber decreased, the Payne effect decreased, and the compression permanent deformation decreased. Compared to other carbon blacks, N770 filled rubber had the best overall performance. Wang Bingxin et al. investigated the influence of carbon black particle size, structure, and content on the crosslink density and mechanical properties of NBR composites. The results showed that the addition of carbon black increased the crosslink density of the vulcanized rubber, which increased with the amount of carbon black used and decreased with increasing particle size. The influence of carbon black structure on chemical crosslink density was greater than that on physical crosslink density. As the carbon black structure increased, the tensile strength and tensile stress of the vulcanized rubber increased, while the tear strength decreased.
2.4 Natural Rubber (NR)
Wang Xuefei et al. studied the physical and dynamic mechanical properties of in-situ grafted modified carbon black reinforced natural rubber (NR). The results showed that the comprehensive performance of the vulcanized rubber was the best when the modifier dosage was 4.5 parts. Guan Bingfeng et al. studied the effect of modified carbon black on the properties of NR. The results showed that compared to ordinary carbon black, the interaction between the modified carbon black and rubber was weakened, resulting in a decrease in the mass fraction of carbon black bound to rubber.
2.5 Silicone Rubber
Liu Xueyi and other researchers studied the effect of carbon black loading, curing agent dosage, and curing time on the physical and electrical properties of rubber. The results showed that carbon black loading, curing agent dosage, and curing time all have an impact on the physical and electrical properties of rubber. Among them, the carbon black loading has the most significant effect on the electrical conductivity of rubber. When the carbon black loading is 20 parts, the curing agent dosage is 7 parts, and the curing time is 11 minutes, the resulting rubber has the best physical and electrical properties.
2.6 Others
The researchers found that the larger the particle size of carbon black, the less binding gel is formed in the rubber matrix, and the lower the crosslink density. When rubber is subjected to alternating stress, the energy loss caused by friction between rubber molecular chains and carbon black surface increases, and the loss factor peak of the vulcanized rubber shows an increasing trend.
Nowadays, the EU regulations have implemented new labeling requirements for tires, putting forward stricter requirements for the development of environmentally friendly and green tires. The products of carbon black manufacturers are continuously developing towards high energy and specialization, with a very wide range of applications. As a professional manufacturer, we will continue to conduct research and meet the needs of actual production in the future.