SBR Rubber

Styrene-Butadiene Rubber (SBR) is a synthetic copolymer of styrene (approx. 23%) and butadiene (approx. 77%), produced by either emulsion (E-SBR) or solution (S-SBR) polymerization. It is the most widely used synthetic rubber worldwide and is also known historically as Buna S or GR-S (Government Rubber-Styrene). Standards: SBR per ASTM D1418, classified as AA under ASTM D2000 for standard sulfur-cured grades.

SBR offers a balanced combination of abrasion resistance, mechanical strength when reinforced, and low cost. It blends well with Natural Rubber (NR) and Polybutadiene Rubber (BR) to optimize properties for specific applications, which is why it dominates global tire production.

Primary applications include:

• Passenger car and light-truck tire treads (largest single market)
• Industrial rolls (printing, paper, textile)
• Conveyor belts requiring abrasion resistance
• Vibration dampers and anti-vibration mounts (engine mounts, machinery isolators)
• Footwear soles and heels
• Mechanical goods: bushings, gaskets, hoses, mats
• Adhesives and sealants

Unreinforced SBR has relatively poor tensile strength (approx. 2-3 MPa). With carbon black reinforcement (typically N220, N330 or N550 grades at 40-70 phr), tensile strength increases to 15-25 MPa and abrasion resistance improves substantially, which makes SBR suitable for demanding applications such as tire treads.

The figures below are polymer-family guidance, not a specification. The usable range of any given part depends on the grade, the compound, the cure system, exposure time and the actual service conditions.

• Standard sulfur-cured SBR: typically -40°C to +100°C (-40°F to +212°F)
• Special low-temperature compounds: down to approximately -55°C (-67°F)
• Continuous service above 100°C accelerates aging due to backbone double bonds

Always confirm the temperature range against the specific compound datasheet and validate it under the real service conditions.

Standard SBR compounds range from 40 to 90 Shore A, with most industrial applications between 50 and 70 Shore A.

SBR performs well in:

• Water and aqueous solutions
• Alcohols (methanol, ethanol, glycols)
• Silicone oils and greases
• Glycol-based brake fluids (DOT 3, DOT 4, DOT 5.1) in suitably formulated compounds, though EPDM is normally the preferred choice for this service. Silicone-based DOT 5 is not compatible with SBR
• Weak (dilute) acids and bases
• Animal and vegetable oils (limited)

SBR has poor resistance to:

• Petroleum oils, fuels, and aliphatic or aromatic hydrocarbons
• Mineral oils and greases
• Halogenated solvents
• Strong acids and oxidizers
• UV radiation, ozone, and weathering (due to the unsaturated backbone)

Not in standard formulations. The unsaturated polymer backbone is susceptible to ozone cracking, UV degradation, and oxidation. For outdoor applications, EPDM is the preferred choice. SBR can be used outdoors only when protected with antiozonants, waxes, and UV stabilizers, and even then service life is limited.

SBR is produced as either E-SBR (emulsion) or S-SBR (solution, a premium grade with better rolling resistance). It is almost exclusively sulfur-cured (CV, conventional vulcanization, or EV, efficient vulcanization). Sulfur cure provides good dynamic properties but limits heat resistance compared with peroxide cure.

SBR and NR are frequently blended. There is no single universal ratio: passenger tire compounds vary widely between tread, sidewall and tire type, and the blend is set per application. Key differences:

• NR: higher tensile strength, better tear resistance, better low-temperature flexibility
• SBR: better aging in heat, lower cost, more consistent quality. Abrasion resistance is often better than NR in tread-type compounds, but this depends heavily on the reinforcement and the full compound system
• Blends combine properties of both materials

The table compares polymer families at a general level. Actual performance is set by the specific grade, the compound formulation, the cure system and the service conditions, and must be confirmed for each application.