NBR Nitrile rubber properties
Nitrile butadiene rubber (NBR) has a Shore A hardness between 40 and 95, and a continuous service temperature range of -55 °C to 108 °C (-67 °F to 226 °F) depending on the formulation and acrylonitrile (ACN) content. This synthetic elastomer stands out for its excellent resistance to oils, fuels, hydraulic fluids, and many chemicals. Typical density ranges from 0.96 to 1.00 g/cm³ (960–1000 kg/m³). Its combination of mechanical strength, flexibility, and chemical stability makes it a reference material for gaskets, seals, hoses, and sealing components in the automotive, oil & gas, and process industries.
Chemical Composition
Section titled “Chemical Composition”NBR is a random copolymer of acrylonitrile and butadiene. The ratio between the two monomers determines the final properties of the elastomer; the higher the acrylonitrile (ACN) content, the better the oil and solvent resistance, but the lower the low-temperature flexibility. The typical monomer composition of commercial grades is presented below:
| Monomer | Typical Mass Content |
|---|---|
| Acrylonitrile (ACN) | 18 % – 50 % |
| Butadiene | 50 % – 82 % |
In addition to the monomers, formulations include curing agents (sulfur or peroxides), reinforcing fillers such as carbon black or silica, plasticizers, antioxidants, and other processing additives.
Mechanical Properties by Treatment Condition
Section titled “Mechanical Properties by Treatment Condition”The mechanical properties of NBR vary according to the curing system, ACN content, type and loading of reinforcement. The values presented correspond to standard vulcanized compounds reinforced with carbon black, tested at 23 °C (73 °F) according to ISO 37 and ISO 7619 methods.
| Property | Typical Range (metric / imperial) |
|---|---|
| Tensile strength | 5 – 25 MPa / 725 – 3625 psi |
| Elongation at break | 100 – 800 % |
| Shore A hardness | 40 – 95 |
| Modulus at 100% elongation | 2 – 10 MPa / 290 – 1450 psi |
| Tear strength (trouser) | 10 – 40 kN/m / 57 – 228 lbf/in |
| Compression set (70 h / 100 °C) | 10 – 50 % |
For grades with high ACN content (≥ 40 %), the highest values of hardness and tensile strength are obtained, while elongation decreases. Peroxide-cured compounds exhibit better heat aging resistance and lower permanent set than sulfur-cured ones.
Physical and Thermal Properties
Section titled “Physical and Thermal Properties”The density of NBR is typically between 0.96 and 1.00 g/cm³ (960–1000 kg/m³), and its usual color is black due to the incorporation of carbon black, although colored grades can be produced.
| Property | Typical Value (metric / imperial) |
|---|---|
| Density | 0.96 – 1.00 g/cm³ / 60 – 62.4 lb/ft³ |
| Glass transition temperature (Tg) (depending on ACN) | -55 to -20 °C / -67 to -4 °F |
| Continuous service range | -55 to 108 °C / -67 to 226 °F |
| Thermal conductivity | 0.25 W/(m·K) / 1.73 BTU·in/(h·ft²·°F) |
| Specific heat | 1.5 – 2.0 kJ/(kg·K) / 0.36 – 0.48 BTU/(lb·°F) |
| Coefficient of linear thermal expansion | 160 – 230 × 10⁻⁶ K⁻¹ / 89 – 128 × 10⁻⁶ in/in/°F |
| Volume resistivity (electrical insulation) | 10¹⁰ – 10¹² Ω·cm |
| Air permeability (24 h, 23 °C) | 0.5 – 2.0 × 10⁻¹⁷ m²/(Pa·s) (approx.) |
Flame resistance is low, and most grades are flammable unless flame retardant additives are incorporated. Water absorption is less than 1 % under ambient conditions, making it suitable for applications with occasional moisture contact.
Applications
Section titled “Applications”NBR is widely used in sectors where resistance to oils, fuels, and greases is required, together with good elasticity and sealing capability. The main applications by industry are:
Automotive
- Fuel and oil hoses.
- Seals, O-rings, and engine shaft seals.
- Diaphragms and membranes in fuel systems.
- Gaskets in transmissions.
Oil & Gas
- Seals and gaskets for valves and pumps.
- Hoses for mud and drilling fluids.
- Roller coverings in crude handling systems.
- Expansion joints and flexible connectors.
General Industrial
- Chemical protection gloves (laboratories, cleaning, food).
- Roller coverings in graphics and paper industries.
- Extruded profiles for door and window sealing.
- Anti-slip sheets and mats.
Food and Pharmaceutical
- Hoses for food liquid transfer (approved grades).
- Gaskets in food processing equipment.
- Metering pump components.
Aerospace
- Self-sealing fuel tank seals.
- Static and dynamic seals in hydraulic systems.
Comparison with Similar Materials
Section titled “Comparison with Similar Materials”The following table compares representative properties of standard NBR (33 % ACN, 70 Shore A) with other elastomers used in sealing applications.
| Property | NBR | HNBR | EPDM | FKM (standard) |
|---|---|---|---|---|
| Shore A hardness (typical range) | 40 – 95 | 50 – 90 | 40 – 90 | 55 – 90 |
| Temperature range (°C / °F) | -55 to 108 / -67 to 226 | -40 to 165 / -40 to 329 | -50 to 150 / -58 to 302 | -20 to 250 / -4 to 482 |
| Oil and fuel resistance | Excellent | Excellent | Poor | Excellent |
| Weather and ozone resistance | Good | Very Good | Excellent | Excellent |
| Abrasion resistance | Good | Very Good | Good | Moderate |
| Relative cost | Low | Medium | Low | High |
HNBR (hydrogenated nitrile rubber) offers superior thermal and mechanical performance compared to NBR, while maintaining similar chemical resistance, so it is used when service temperatures exceed 120 °C (250 °F). EPDM is preferable for outdoor applications but is not suitable for contact with hydrocarbons. FKM provides the highest thermal and chemical resistance, although its cost is high.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is NBR and what is it used for?
Section titled “What is NBR and what is it used for?”NBR (nitrile butadiene rubber) is a synthetic elastomer with excellent resistance to oils, fuels, and greases. It is mainly used in the manufacture of gaskets, seals, hoses, gloves, and molded parts for the automotive, oil & gas, and chemical industries.
What is the working temperature range of NBR?
Section titled “What is the working temperature range of NBR?”NBR can operate continuously between -55 °C and 108 °C (-67 °F to 226 °F), although grades with low acrylonitrile content maintain better low-temperature elasticity, and those with high content exhibit better performance in hot conditions for short periods.
How resistant is NBR to oils and fuels?
Section titled “How resistant is NBR to oils and fuels?”NBR is considered one of the elastomers with the best resistance-to-cost ratio against mineral oils, diesel, gasoline, and petroleum-based hydraulic fluids. Resistance improves as the acrylonitrile content of the polymer increases.
What is the difference between NBR and HNBR?
Section titled “What is the difference between NBR and HNBR?”HNBR is the hydrogenated version of NBR. This saturation of the polymer chain gives it significantly superior heat, ozone, and aging resistance, with a temperature range up to 165 °C (329 °F), while maintaining similar chemical resistance.
What is the typical hardness of NBR?
Section titled “What is the typical hardness of NBR?”The Shore A hardness of NBR can be formulated over a very wide range, from 40 (very soft) to 95 (hard). The most common values in sealing applications are between 60 and 80 Shore A.
How does NBR compare to EPDM in automotive applications?
Section titled “How does NBR compare to EPDM in automotive applications?”NBR is chosen when the component is in contact with oils or fuels (fuel hoses, engine gaskets), while EPDM is the preferred choice for applications exposed to the weather, such as weatherstripping and coolant hoses, due to its better ozone and atmospheric resistance.
Sources Consulted
Section titled “Sources Consulted”- azom.com: https://www.azom.com/article.aspx?ArticleID=1724
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/elastomers-rubbers-d_1788.html
- steelnumber.com: https://www.steelnumber.com/en/steel_composition_eu.php?name_id=319