SBR: Core material of tires
As a pillar variety of synthetic rubber, styrene butadiene rubber (SBR) has reshaped the rubber industry since its introduction. This elastomer, which is copolymerized by styrene and butadiene, is widely used in many fields such as automobile tires, mechanical seals, and daily necessities due to its balanced performance, stable supply, and controllable cost. It is a basic material for modern industry.
The research and development and industrialization of SBR originated from the breakthrough of natural rubber supply restrictions. In the early 20th century, natural rubber was the only elastomer material, and its production was greatly affected by the tropical climate and geopolitics of Southeast Asia.
During World War II, the disruption of the natural rubber supply chain directly promoted the climax of synthetic rubber research and development. SBR quickly became a mainstream synthetic rubber variety because of its easy availability of raw materials (styrene and butadiene can be obtained from petrochemicals) and its performance close to that of natural rubber.
Today, the global annual output of SBR has exceeded 4 million tons, accounting for more than one-third of the total output of synthetic rubber, and has become a key material supporting the development of modern industry.
In terms of performance characteristics, SBR shows significant technical advantages and unique shortcomings. Compared with polybutadiene rubber (BR), the performance optimization of SBR is particularly obvious: through the introduction of styrene monomer, the polarity of the molecular chain is enhanced, which increases the tensile strength of SBR by more than 30%, and the wear resistance under dynamic load is increased by 20%-25%, making it more suitable for making tire treads that withstand repeated friction.
At the same time, SBR has better mixing compatibility with reinforcing fillers such as carbon black and white carbon black. The filler is more evenly dispersed during the mixing process, which can reduce the internal defects of the rubber compound. This feature makes it more competitive in mechanical rubber products that require high strength.
Compared with natural rubber (NR), the performance of SBR shows the characteristics of "overall equivalence and partial deficiency". In terms of basic indicators such as hardness, elastic modulus, and aging resistance, the differences between the two are small, which makes SBR a direct replacement for natural rubber in most general scenarios.
However, SBR has three obvious shortcomings: First, the heat accumulation effect is significant. When rolling at high speed or deforming repeatedly, the internal temperature of the rubber increases 15%-20% faster than that of natural rubber, which can easily lead to early aging of tires and other products; second, the raw rubber has poor viscosity, and tackifiers such as rosin resin need to be added during processing to ensure the adhesion of the film; third, the tensile strength of the unvulcanized film is low, and it is more likely to break during the molding process such as calendering and extrusion, and the processing parameters need to be optimized.
These performance characteristics directly determine the application of SBR. In the tire industry, SBR occupies a core position, and about 70% of SBR production is used in tire manufacturing. Among them, tread rubber is the main application scenario of SBR.
Through the synergistic effect with carbon black, it can give tires excellent wear resistance and wet skid resistance; sidewall rubber uses the flex resistance of SBR to reduce the risk of cracking during driving. In the automotive industry, SBR is widely used in sealing strips, shock absorbers, dust covers and other parts. Its stable weather resistance can ensure the long-term reliable operation of automobiles in an environment of -30℃ to 80℃.
In the field of mechanical manufacturing, conveyor belts, sealing rings, rubber rollers and other products made of SBR have become an economical choice to replace natural rubber with good dimensional stability and cost advantages.
The production process technology of SBR is also constantly upgrading. The current mainstream emulsion polymerization SBR (E-SBR) and solution polymerization SBR (S-SBR) have their own focuses: E-SBR has a mature process and low cost, which is suitable for large-scale production of general grades.
S-SBR can accurately control the microstructure through molecular design, and can produce high-performance varieties with low rolling resistance and high grip, which is particularly suitable for the needs of new energy vehicle tires. In recent years, breakthroughs have been made in the research and development of bio-based SBR.
The carbon footprint of SBR synthesized from plant-based styrene and butadiene monomers is reduced by more than 30% compared with traditional products, providing a new path for the green transformation of the rubber industry.
