The chemical composition the copolymer of nitrile rubber is that of
acrylonitrile and butadiene. The content of acrylonitrile found in
commercial applications range from 18% to 50%. An increase in the percentage
of nitrile content corresponds to an enhancement in petroleum base oil
resistance and hydrocarbon fuel resistance. However, flexibility at low
temperature is reduced in the process.
NBR o-rings are among the most extensively used elastomeric sealing components in the seal industry. It has a service temperature range from -35 degrees celsius to 120 degree celsius. NBR o-rings have properties that make it suitable for use when seals are in constant direct contact with petroleum products. O-Rings based on nitrile compounds have excellent resistance to oil and fuel, and are often specified for use in many military applications.
Good resistance to high temperature is often a trade off to low temperature resistance, and vice versa. Superior characteristics of nitrile compounds as compared to other elastomers include abrasion and tear resistance and compression set. However, weathering and exposure to ozone and ultraviolet degradation are not some of the advantages in the use of nitrile rubber.
NBR compounds are sensitive to ultraviolet degradation and should not be directly exposed to sunlight. However, improvement in this area can be attained through compounding. In both hydraulic and pneumatic applications, NBR is specified as the standard material.
NBR compounds used in the manufacturing of nbr o-rings offer excellent resistance to hydraulic fluids, vegetable and animal oils and fats. Included in the list are flame retardant fluids, air and water and grease. Nitrile can also be compounded for low temperature applications invloving mineral oil-based liquids. Specific requirements in terms of chemical and mechanical properties can also be attained through hydrogenation, PVC blending and carboxylic acid addition.
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