Nitrile rubber (NBR) o-rings, also known as Buna N, are one of the most commonly used sealing elastomers due to resistance to petroleum-based fuels and lubricants and its relatively low price. Nitrile elastomers are copolymers of acrylonitrile and butadiene. There are a number of common variations of nitrile compounds.
The acrylonitrile (ACN) content of the polymer chains can vary from 18% to 50%. Lower ACN content gives better low-temperature properties but inferior resistance to fuels and polar lubricants. Higher ACN content gives lesser quality low-temperature properties but improved fuels and polar lubricants resistance. Standard NBRs typically have 34% ACN content.
Standard Nitrile o-rings are usually sulfur-cured. Sulfur-cured compounds offer better low-temperature properties but are more prone to hardening with high temperatures. Peroxide-cured nitrile o-rings have better heat resistance and lower compression sets but are more expensive and more difficult to process.
Buna O-rings, Nitrile O-rings, NBR O-rings offer excellent sealing and mechanical properties at low cost. Buna Nitrile O-rings have resistance to common lubricants and are recommended for crude oil, gasoline, propane, petroleum oils and water. Nitrile Buna O-rings are used in engines, gearboxes, aircraft pumps, and water applications.