SBR (Styrene-Butadiene Rubber) Technical Guide

1. What Is SBR (Styrene-Butadiene Rubber)?

SBR (Styrene-Butadiene Rubber) is the most consumed synthetic rubber in the world, accounting for over 40% of total global synthetic rubber production. It is a random copolymer of styrene (typically 23.5% by mass) and butadiene, produced by either emulsion polymerization (ESBR) or solution polymerization (SSBR). First developed by IG Farben in Germany in the 1930s (as Buna-S) and industrialized by the U.S. Rubber Reserve during World War II (as GR-S — Government Rubber-Styrene), SBR was the original replacement for natural rubber when supply chains were disrupted.

Under ASTM D2000 / SAE J200, SBR is classified as AA, BA (Class A = service temperature 70°C; oil resistance Class A = no oil resistance). Under ISO 1629, the designation is "SBR."

The defining feature of SBR is its abrasion resistance. For applications where mineral-oil contact is absent and heat exposure is moderate, SBR provides the best cost-per-kilometer-worn performance of any general-purpose rubber.

2. ESBR vs SSBR: Two Production Routes

ESBR dominates the market by volume (>85% of SBR production) due to its lower cost and massive installed capacity. SSBR is preferred for high-performance tire treads where low rolling resistance and high wet grip are needed simultaneously — a combination that ESBR cannot deliver as effectively.

3. Key SBR Grades

4. Mechanical and Physical Properties

Critical note: SBR is a non-crystallizing rubber. Unlike NR, which self-reinforces under strain (strain-induced crystallization contributes 5–8 MPa additional strength), SBR relies entirely on reinforcing fillers for useful mechanical strength. Unfilled (gum) SBR has a tensile strength of only 2–5 MPa — roughly one-fifth that of unfilled NR. This is why carbon black type and dispersion quality are more critical for SBR compounding than for NR.

5. Abrasion Resistance — The Defining Feature

SBR's abrasion resistance was the property that made it the dominant tire polymer. Under the DIN 53516 / ISO 4649 abrasion test, SBR compounds with N330 carbon black (50 phr) show typical volume loss of 80–120 mm³. This is comparable to NR (90–130 mm³ under the same conditions) and substantially better than EPDM (150–250 mm³).

For conveyor belt covers based on SBR:

SBR achieves its best abrasion performance when the styrene content is in the 23–35% range. High-styrene SBR (40–50% styrene) shows improved abrasion but at the cost of increased stiffening at low temperatures (Tg rises from -55°C to approximately -30°C).

6. Blending for Performance Enhancement

SBR is almost never used alone in demanding applications. The following blends are industry standard:

7. Limitations and Design Considerations

1. No inherent oil resistance: SBR swells severely in mineral oils and hydrocarbon solvents. Do not use in any application involving oil contact.

1. Poor ozone resistance: SBR's unsaturated backbone is highly susceptible to ozone cracking. Requires antiozonants (6PPD, waxes) for outdoor use. Ozone cracks appear perpendicular to the strain direction when threshold strain (~5–10%) is exceeded.

1. Low heat resistance: Continuous service limited to 80°C; NR and EPDM outperform SBR at elevated temperatures. Above 100°C, SBR embrittles rapidly.

1. Poor tear resistance: Non-crystallizing nature limits tear strength; NR has 2–3× the tear resistance of SBR.

1. Requires carbon black reinforcement: Unfilled SBR is mechanically useless (<5 MPa tensile). Filler selection, loading, and dispersion quality are critical — poorly dispersed carbon black creates failure-initiating flaws.

1. Higher hysteresis than NR: SBR has a higher tan δ at 60°C (typically 0.15–0.20 vs. NR 0.08–0.12), meaning higher heat buildup under dynamic loading — an issue in large truck tires and thick-section conveyor belts where internal temperatures can exceed safe limits.

8. SBR vs. NR: Selection Criteria

For conveyor belt covers: use SBR where total cost of ownership is the driving metric and oil/heat exposure is absent. Use NR where cuts, gouges, and dynamic flexing are the primary failure modes.

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Nanjing Yuhang Rubber Co., Ltd. is a leading manufacturer of industrial rubber products in China, supplying SBR-based conveyor belts, rubber sheets, footwear soles, and industrial components to customers in over 75 countries. Our in-house compounding facilities produce optimized SBR/NR and SBR/BR blends tailored to your specific abrasion and mechanical requirements, verified to ASTM D412, ISO 37, and DIN 22102 standards.

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