Full definition
Nitrile Rubber (NBR), an acrylonitrile-butadiene copolymer, is the standard elastomer used primarily for its exceptional resistance to various mineral oils, fuels, greases, and hydraulic fluids. This unique combination of properties makes NBR the most widely utilized sealing material across numerous industries. The performance of NBR can be significantly influenced by the acrylonitrile (ACN) content in its formulation. A lower ACN content (18-24%) offers excellent low-temperature flexibility, allowing it to maintain functionality down to -40°C. However, this flexibility comes at the cost of reduced oil resistance. The most commonly used formulation contains a medium ACN level (28-36%), which provides a balanced performance for general-purpose applications. For scenarios demanding maximum oil resistance, high ACN content (38-50%) is employed, although this variant exhibits diminished performance at lower temperatures.
NBR exhibits remarkable mechanical properties, with a hardness range of 40-90 Shore A. Its tensile strength lies between 10-25 MPa when carbon black is added, alongside an impressive elongation capacity of 200-600%. It is classified under ASTM D2000 standards as BF for low ACN content, BG for medium, and BK for high ACN content. The operational temperature range for standard NBR is from -40 to +100°C, with intermittent exposure up to +120°C. Despite its strengths, NBR has limitations, especially concerning its resistance to ozone and ultraviolet exposure; thus, it often requires the incorporation of antiozonants or blending with materials like PVC for enhanced durability. Furthermore, NBR does not perform well in the presence of polar solvents, strong acids, or UV light.
The applications of NBR are extensive and varied. It is predominantly used for O-rings, which are one of the most specified sealing solutions in industrial applications. Other common usages include oil seals, fuel hoses, hydraulic seals, gaskets, nitrile examination gloves, printing press rollers, and flexible couplings. Additionally, NBR can also be found in modified forms, such as NBR/PVC blends to improve ozone resistance and carboxylated XNBR for enhanced abrasion and tensile strength. With a global production level of approximately 800,000 tonnes per year, NBR continues to be a critical component in manufacturing and engineering processes worldwide.