Nitrile (often referred to as buna-N rubber or perbunan) is the most commonly used elastomer in the seal industry. Nitrile is a copolymer of two monomers: acrylonitrile (ACN) and butadiene. The properties of these rubber compounds are determined by its ACN content, which is broken down into three classifications:
- High nitrile >45% ACN content,
- Medium nitrile 30-45% ACN content,
- Low nitrile <30% ACN content.
The higher the ACN content, the better its resistance to hydrocarbon oils. The lower the ACN content the better its flexibility in low temperature applications. Medium nitrile is, therefore, most widely specified due to its good overall balance in most applications. Typically, nitriles can be compounded to work over a temperature range of –35°C to +120°C and are superior to most elastomers in regard to compression set, tear and abrasion resistance.
Nitrile / NBR usage
NBR is the standard material for hydraulics and pneumatics. NBR resists oil-based hydraulic fluids, fats, animal and vegetable oils, flame retardant liquids (HFA, HFB, HFC), grease, water, and air. Nitriles should be protected from direct sunlight. However, this can be improved through compounding by hydrogenation, carboxylic acid addition, or PVC blending, the nitrile polymer can meet a more specified range of physical or chemical requirements. Special low-temperature compounds are available for mineral oil-based fluids.
Special NBR variants like XNBR and NBR-PVC blends can be developed in-house on request.
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