nitrile rubber

Nitrile rubber, also called NBR or acrylonitrile-butadiene rubber, is a synthetic elastomer formed by polymerizing acrylonitrile monomer with butadiene. The resulting polymer chain contains repeating units of both materials, typically in ratios between 18 and 50 percent acrylonitrile. This copolymer produces a material tougher and more chemically resistant than natural rubber, making it the standard choice for gaskets, seals, and membranes in environments where mineral oils, fuels, and solvents are present.

The acrylonitrile content directly controls the rubber's properties. Higher acrylonitrile percentages increase resistance to oils and swelling, but reduce flexibility and low-temperature performance. A 40 percent acrylonitrile formulation, for instance, handles most petroleum-based hydraulic fluids reliably, while lower ratios around 25 percent offer better performance at temperatures below negative 30 degrees Celsius. Manufacturers select the grade based on the specific chemical exposure and temperature range the sealing surface will encounter.

Use in construction and industrial sealing

In construction, nitrile rubber appears primarily as seals and gaskets in pumps, compressors, and hydraulic systems. Concrete saws, pile drivers, and pneumatic tools all rely on nitrile seals because building sites frequently expose equipment to diesel fuel, chain-saw oil, and brake fluid. The material maintains elasticity across the temperature swings common to outdoor work, from morning cold to afternoon heat, without permanently deforming or hardening.

Nitrile rubber degrades under prolonged exposure to ozone, sunlight, and certain strong solvents like ketones and aromatic hydrocarbons. Field failures typically involve O-rings or shaft seals that harden and lose compression after extended exposure to high temperatures above 100 degrees Celsius, or seals that swell excessively if exposed to incompatible synthetic oils. Users must verify fluid compatibility before installation; many hydraulic failures trace back to using a nitrile seal in a system with ester-based hydraulic fluid, which the rubber cannot tolerate.

The name reflects its chemical composition: the nitrile group (C triple bond N) from the acrylonitrile monomer is the defining structural feature that grants the rubber its oil resistance. This distinguishes it clearly from natural rubber, butyl rubber, and EPDM, each of which offers different resistance profiles and cost-performance tradeoffs. For general industrial sealing across temperatures from negative 20 to 80 degrees Celsius in the presence of mineral oils, nitrile remains the workhorse material.