Nitrile rubber (NBR or Buna N) is perhaps the most commonly used sealing elastomer. NBR’s ubiquity stems from its resistance to petroleum based fuels and lubricants together its low cost. Nitrile elastomers are copolymers of acrylonitrile and butadiene. There are a number of various common variations of nitrile compounds.
The acrylonitrile (ACN) can be varied from 18-50%. Low ACN content gives better low temperature properties but poorer fuel and polar lubricant resistance. Standard NBRs usually have around 34% ACN content.
Cure system – Sulfur Cured vs. Peroxide Cured
Standard Nitriles are usually sulfur cured. Sulfur cured compounds bring better low temperature properties but are more inclined to harden under higher temperatures. Peroxide cured nitriles have superior heat resistance and lower compression sets but are more difficult to process which makes them more expensive.
Other Common Variations
- Nitriles are often internally lubricated. This to facilitate installation and reduce friction for dynamic applications.
- Nitriles can be formulated with only “white list” ingredients as specified in 21.CFR 177.2600 for applications where the seal will be in contact with food or beverages.
- Can be submitted for approval by the national sanitation foundation (NFS) for use in drinking water applications.
- Can be submitted for approval to underwriters laboratories (UL) for use in applications as prescribed in UL157.
- Can be combined with polyvinyl chloride (PVC) to create resistance against fuel, ozone and weather.
- ASTM D 1418 Designation: NBR
- ISO/DIN 1629 Designation: NBR
- ASTM D2000 / SAE J 200 Codes: BF, BG, BK, CH
- Standard Color(s): Black
- Hardness Range: 40 to 90 Shore A
- Relative Cost: Low
Standard Low Temperature: -40°C / -40°F
Standard High Temperature: 100°C / 212°F
Special Compound Low Temperature: -55°C / -67°F
Special Compound High Temperature: 125°C / 275°F
|Performs well in||Does not perform well in|
|Petroleum based oils and fuel||Aromatic hydrocarbons|
|aliphatic hydrocarbons||Automotive break fluid|
|vegetable oils||Chlorinated hydrocarbons|
|silicone oils and grease||Ethers|
|Dilute acids||Phosphate ester and hydraulic fluids|
|Water below 100°C (212°F)||Strong acids|
|Ozone / weathering /sunlight|