NBR - Butadiene Nitrile Rubber
Acrylonitrile butadiene rubber (NBR), usually shortened to nitrile, is a unique elastomer. It can be produced by free-radical emulsion polymerization of butadiene with 15 to 45 percent acylonitrile either hot (hot rubber) or cold (cold rubber):
NBR grades with high acrylonitrile content have better oil and abrasion resistance, whereas grades with low acrylonitrile content have better low temperature flexibility and resilience. In general, nitrile rubbers have only moderate physical properties but good abrasion and excellent oil and hydrocarbon solvent resistance. However, they are not suitable for use with polar solvents. Nitrile rubbers also have low gas permeability particularly those with high nitrile content but poor ozone and modest heat resistance. To improve the physical properties, nitrile rubbers are sometimes carboxylated (XNBR) which improves their temperature resistance.
Many properties can be adjusted by varying the acrylonitrile content in the nitrile rubber. The higher the nitrile content, the higher the resistance to aromatic hydrocarbons and the lower the nitrile content, the better the low temperature flexibility.
- High Nitrile: > 45 % Nitrile
- Medium Nitrile: 30 - 45%
- Low Nitrile: < 30%
The best overall balance for most applications is a medium nitrile content.
COMMERCIAL NBR Elastomers
Major manufacturers of NBR rubber are Lanxess, Zeon, and LG Chem. Fucntionalized liquid NBR rubbers are available from CVC (Emerald Performance Materials).
NBR’s are used where excellent oil resistance is required. They are widely used in sealing applications, particularly for oils and gasoline (aliphatic and aromatic hydrocarbons). Major applications include gaskets, seals, diaphragms, gasoline hoses, liners, tubing, O-rings and cable jacketing. Carboxylated grades find also uses as rubber tougheners in many epoxy formulations.
Typical grades have a working temperature range of -25°C to +100°C. Some low acrylonitrile materials are suitable for application down to -50°C and some peroxide cured grades go up to +150°C.