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https://www.hydermanrubber.com/technical-overview-of-nr-sbr-rubber-sheet.html

NR/SBR rubber sheet, a blend of natural rubber (NR) and styrene-butadiene rubber (SBR), combines the favorable traits of both elastomers to offer a balanced performance profile. Below is a detailed review of its key physical and chemical properties, useful as a reference for design, selection, and application.

1. Tensile Strength & Elongation

One of the primary performance metrics of NR/SBR rubber sheets is tensile strength (the maximum stress before failure) and elongation at break (the strain it can undergo before breaking).

• The NR component contributes high elasticity and resilience, enabling relatively high elongation values.

• Typical values for a good-quality NR/SBR sheet might reach around 2.5 MPa (≈ 25 kg/cm²) or more in tensile strength and 200–300 % elongation (or even higher, depending on formulation).

• However, the exact values depend heavily on the blending ratio, filler loading (e.g. carbon black), crosslink density, and the quality of compounding.

2. Hardness (Shore A)

The hardness of NR/SBR sheets is typically measured in Shore A scale, indicating the material’s resistance to indentation.

• NR/SBR sheets are often available in hardness ranges from 35 ShA to 80 ShA or more.

• For example, Trelleborg offers NR/SBR sheets in hardnesses of 35 to 80 ShA.

• A hardness of 60 ± 5 ShA is common for general-purpose NR/SBR rubber sheets.

• The choice of hardness is a trade-off: harder sheets resist deformation better under load, but softer sheets provide better sealing compression and flexibility.

3. Compression Set (Permanent Deformation)

Compression set refers to the permanent deformation remaining after the material has been compressed and then released — i.e. how much it fails to recover.

• NR/SBR blends generally present low compression set (i.e. good recovery), which is favorable in sealing or gasket applications.

• The exact value depends on crosslink density, temperature, and time of compression. Well-designed blends aim to keep compression set minimal under expected service conditions.

4. Abrasion Resistance

Abrasion or wear resistance is critical for rubber sheets used in sliding, impact, or abrasive environments.

• NR/SBR exhibits excellent mechanical properties and is well suited to high-wear environments such as mining or heavy-duty industrial use.

• The blend combines the toughness of NR with the durability of SBR to better resist surface wear.

• Recent research on rubber wear mechanisms shows that under wet sliding the wear rates of SBR may increase notably compared to dry sliding, while NR tends to perform more stably across conditions.

• In practice, optimizing filler type (e.g. high abrasion carbon black) and crosslinking helps reduce the wear rate further.

5. Low-Temperature & High-Temperature Performance

The operating temperature window is a key limitation of many rubber materials.

• The NR portion typically allows flexibility down to –50 °C (or lower) in some formulations.

• For high temperatures, pure NR has a more limited upper bound (around +90 °C).

• On the other hand, SBR is relatively more stable at elevated temperature and improves aging resistance, so NR/SBR blends may be serviceable up to ~ 100–110 °C in favorable formulations.

• However, exposure above this may accelerate degradation (e.g. chain scission, oxidation).

6. Aging & Ozone Resistance

Rubber exposure to oxygen, ozone, UV, and heat can lead to embrittlement, cracking, and property decline.

• SBR contributes somewhat better aging and temperature resistance compared to pure NR, but NR/SBR still has limited ozone and UV resistance.

• Without adequate stabilizers (antioxidants, anti-ozonants), surface cracking (ozone cracking) may occur under high ozone or UV environments.

• Proper compounding with protective additives is essential to enhance longevity in outdoor or harsh conditions.

7. Chemical Resistance (Acids, Bases, Salts, Oils, etc.)

The chemical compatibility is a major constraint—users must ensure the medium in contact is non-aggressive to NR/SBR.

• NR/SBR shows good resistance to inorganic acids, alkalis, and salts in moderate concentrations.

• It also resists water and many non-aggressive aqueous solutions reasonably well.

• However, its resistance to oils, hydrocarbons, solvents, and organic chemicals is poor — SBR especially tends to swell or degrade in contact with mineral oils, fuels, petrol, aromatic solvents.

• Therefore, NR/SBR sheets are not recommended for direct contact with oil-rich environments; for those cases, nitrile (NBR) or other oil-resistant elastomers are preferred.

8. Density / Specific Gravity

The density (or specific gravity) of NR/SBR sheets gives insight into material compactness and filler content.

• Common specific gravity values for NR/SBR blends range from ~ 1.30 to ~ 1.60 g/cm³, depending on hardness, filler load, and compound formulation.

• For instance, Teknikum specifies a density of 1.30 g/cm³ for its NR/SBR 60 ShA sheet.

• Higher densities usually correlate with higher filler content (e.g. carbon black, mineral fillers), which can enhance strength and wear resistance but reduce flexibility.

9. Surface Treatment & Reinforcement

Beyond the bulk compound properties, the surface finish and internal structure further influence performance.

• NR/SBR sheets may be supplied with smooth (polished) surfaces or textured/embossed surfaces for grip, anti-slip, or aesthetic purposes.

• Textile or fabric reinforcement (e.g. nylon, polyester, cotton plies) can be embedded in the rubber (i.e. “ply insertion”) to improve tear resistance, dimensional stability, and mechanical strength under tension.

• Some sheets might have one side smooth, one side fabric, or dual-sided treatments as per application needs.

• Proper surface finishing ensures better mating with mating parts (for sealing surfaces) or reduces friction in sliding contact.

The NR/SBR rubber sheet is a widely used general-purpose elastomeric material thanks to its balanced profile: good tensile and elongation, moderate hardness options, adequate wear resistance, and acceptable performance in moderate thermal and chemical environments. Its limitations (especially in oil resistance and ozone/UV durability) must be taken into account in design and selection.

https://www.hydermanrubber.com/technical-overview-of-nr-sbr-rubber-sheet.html
Hyderman Rubber & Plastic Co., Ltd.

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