Nitrile Rubber (NBR)
Nitrile rubber, also known as NBR or Buna N, is one of the most commonly used sealing elastomers due to its 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 be varied from 18% to 50%. Lower ACN content gives better low temperature properties but poorer fuels and polar lubricants. Higher ACN content gives poorer low temperature properties but improved fuels and polar lubricants resistance. Standard NBRs typically have 34% ACN content.
Cure system - Sulfur-Cured vs. Peroxide-Cured
Standard Nitriles are usually sulfur-cured. Sulfur-cured compounds offer better low temperature properties but are more prone to hardening with high temperatures. Peroxide-cured nitriles have better heat resistance and lower compression sets but are more expensive and are more difficult to process.
Other Common Variations
Nitriles can be formulated with only "white list" ingredients as specified in 21.CFR 177.2600 for use in applications where the elastomer will be in contact with food or beverages.
Nitriles can be submitted for approval by the National Sanitation Foundation (NSF) for use in drinking water applications.
Nitriles can also be submitted for approval to Underwriters Laboratories (UL) for use in applications as prescribed in UL157.
Nitriles are often internally lubricated to improve ease of installation or reduce friction for dynamic applications.
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