Index

    NBR (Nitrile Rubber)

    NBR or nitrile, also known as Buna-N, is the most commonly used elastomer in the seal industry. It is a copolymer of two monomers; acrylonitrile (ACN) and butadiene. This specific copolymer is also referred to as acrylonitrile butadiene rubber, emphasizing its two main components. NBR, which stands for Nitrile Butadiene Rubber, is the standard material for hydraulics and pneumatics.

    The properties of NBR rubber are ruled by the ACN content. This content is broken down into three categories:

    • High nitrile: >45% ACN content
    • Medium nitrile: 30 – 45% ACN content
    • Low nitrile: <30% ACN content

    The higher the ACN content, the better the resistance of the elastomer to hydrocarbon oils, but it has less flexibility at low temperatures. Conversely, with a lower ACN content, the material offers better flexibility at low temperatures. Therefore, medium nitrile, a balance between acrylonitrile and butadiene in the rubber, is the most widely specified due to its good overall balance in most applications. It often surpasses many other elastomers in terms of compression set, tear, and abrasion resistance.

    Through the process of hydrogenation (HNBR), carboxylic acid addition (XNBR), and PVC blending (NBR/PVC), the nitrile polymer, in its various forms (known as acrylonitrile butadiene rubber or acrylonitrile-butadiene rubber), can be engineered to meet a more specified range of physical or chemical requirements.

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    NBR molecule

    Strengths & Limitations

    Temperature Resistance

    • Low temperatures around -30°C (up to -55°C for special types)
    • High temperatures up to +120°C (PVC blends can be limited to around +70°C)

     

    Chemical & Ageing resistance

    Strengths

    • Oil-based fluids like gasoline, petroleum, kerosine, etc.
    • Mineral oils, fats, and greases
    • Vegetable oils, fats, and greases

     

    Limitations

    • Resistant to many acids and bases
    • Hot water
    • Steam
    • Ozone, UV, and sunlight
    • SIP and CIP cleaning processes

     

    Material Comparison

    • NBR offers better mineral oil and grease resistance
    • EPDM has better high and low temperature resistance
    • NBR is not steam resistant
    • EPDM provides overall wider chemical resistance (except for oils, greases, fats)
    • NBR is less resistant to ozone, UV, and sunlight

    • NBR is much cheaper than FKM
    • NBR features, by average a much better compression set than FKM
    • FKM offers much higher temperature resistance
    • FKM has much wider chemical resistance

    • NBR is lower cost than VMQ
    • NBR offers better mineral oil and grease resistance
    • NBR is less resistant to ozone, UV, and sunlight
    • NBR is less temperature resistant in high and low temperatures

    NBR Compound overview

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