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Nitrile, chemically, is
a copolymer of butadiene and acrylonitrile.
Acrylonitrile content varies in commercial products from
18% to 50%. As the nitrile content increases, resistance
to petroleum base oils and hydrocarbon fuels increases,
but low temperature flexibility decreases. Due to its
excellent resistance to petroleum products, and its
ability to be compounded for service over a temperature
range of -35°C to +120°C (-30°F to +250°F), nitrile is
the most widely |
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used elastomer
in the seal industry today. Also many military rubber
specifications for fuel and oil resistant O-rings require
nitrile based compounds. It should be mentioned that to
obtain good resistance to low temperature, it is often
necessary to sacrifice some high temperature resistance.
Nitrile compounds are superior to most elastomers with
regard to compression set, tear, and abrasion resistance.
Nitrile compounds do not possess good resistance to ozone,
sunlight, or weather. They should not be stored near
electric motors or other ozone generating equipment. They
should be kept from direct sunlight. However, this can be
improved through compounding. 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. Special low-temperature compounds are available for
mineral oil-based fluids. By hydrogenation, carboxylic acid
addition, or PVC blending, the nitrile polymer can
meet a more specified range of physical or chemical
requirements. |
