Styrene-butadiene rubber, commonly known as SBR, is a widely used synthetic elastomer. It serves as a versatile alternative to natural rubber. SBR is recognized for its balance of performance characteristics and cost-effectiveness, making it one of the most produced synthetic rubbers globally.
Composition and Synthesis
SBR rubber is a copolymer, formed from two monomers: styrene and butadiene. The typical composition involves approximately 75% butadiene and 25% styrene, although this ratio can be adjusted to influence the final properties of the rubber. Both styrene and butadiene are derived from petrochemical sources, specifically crude oil refining.
The production of SBR primarily occurs through a process called polymerization, where the individual monomer molecules link together to form long polymer chains. The most common method for this is emulsion polymerization, where the monomers are dispersed in water with emulsifying agents and then reacted under controlled temperatures using a chemical initiator. Another method, solution polymerization, also produces SBR, with different resulting polymer structures and properties.
After the polymerization, the resulting rubber compound undergoes further processing. Fillers like carbon black are often added, which significantly enhance the material’s strength and abrasion resistance. The rubber is then subjected to vulcanization, a curing process that involves adding sulfur or other agents to create cross-links between the polymer chains, thereby improving its elasticity, strength, and overall durability.
Distinctive Properties
SBR rubber exhibits several useful characteristics. It possesses good abrasion resistance, making it suitable for applications that experience wear and friction. The material also has good tensile strength and can withstand significant stretching forces without permanent deformation, alongside good elasticity and impact strength. These properties contribute to its overall resilience and durability.
SBR maintains its properties across a temperature range, from -20 to 70 degrees Celsius, and offers reasonable heat resistance compared to natural rubber. It also demonstrates good electrical resistance and is resistant to water, alcohols, and glycol-based brake fluids. SBR is relatively inexpensive to produce.
Despite its advantages, SBR has limitations. It shows poor resistance to oils, mineral greases, gasoline, and chlorinated and aromatic hydrocarbons, leading to swelling and degradation upon exposure. SBR also has low resistance to ozone and can be affected by sunlight, which can lead to cracking and premature aging if not protected by additives. Its tear strength can be lower without reinforcement.
Everyday Uses
SBR rubber is extensively used in various products encountered daily, largely due to its desirable properties and cost-effectiveness. Its most prominent application is in the manufacturing of tires, where it is a primary component in car and truck tires, often making up about 50% of the material. SBR’s excellent abrasion resistance and durability contribute to the long lifespan and grip of tire treads.
The material is also a common choice for conveyor belts, where its robust nature helps it endure the friction and wear of transporting various materials. SBR’s ability to withstand repeated stress makes it a suitable option for these demanding industrial applications. In footwear, SBR is widely utilized for shoe soles and heels due to its durability, flexibility, and anti-slip characteristics.
SBR rubber is also found in gaskets and hoses, particularly in applications that do not involve exposure to oils or extreme temperatures. Its water resistance and ability to form effective seals make it suitable for plumbing and HVAC systems. Additionally, SBR is used in some electrical insulation, and historically, it was even used in chewing gum.