Nitrile Butadiene Rubber (NBR), commonly known as nitrile rubber, is a synthetic elastomer widely used in industrial applications. This synthetic rubber is engineered to perform reliably in environments that would typically degrade natural rubber and other polymers. NBR is recognized for its unique combination of flexibility and resistance capabilities, making it a prevalent choice for sealing solutions and applications requiring fluid resistance.
Chemical Structure and Synthesis
Nitrile Butadiene Rubber is a copolymer built from two different monomer units: acrylonitrile (ACN) and butadiene (BD). The polymerization process links these two monomers to form the final rubber structure. Butadiene forms the hydrocarbon backbone, providing flexibility and elastic properties, while acrylonitrile units introduce polar groups that influence the material’s characteristics.
The percentage of acrylonitrile content, typically ranging from 18% to 50%, is the primary factor dictating NBR’s final performance. A higher ACN content increases the rubber’s polarity, enhancing its resistance to non-polar solvents like petroleum-based oils and fuels. However, increasing ACN decreases flexibility and raises the glass transition temperature, limiting performance in cold environments. Manufacturers adjust this ratio to balance oil resistance and low-temperature flexibility for specific application requirements.
Defining Characteristics
The most notable characteristic of NBR is its exceptional resistance to various oils, fuels, and chemicals. This resistance is particularly strong against petroleum-based fluids, including hydraulic fluids, gasoline, and mineral oils. The polar nature introduced by the acrylonitrile groups prevents non-polar oil molecules from penetrating and swelling the rubber structure.
NBR also exhibits favorable mechanical properties, including high tensile strength and superior resistance to abrasion and tear. This durability makes it a robust material for dynamic applications subject to friction and mechanical wear. It maintains functional characteristics across a broad temperature range, generally from -40°C to +120°C, depending on the specific formulation.
NBR does have specific limitations that make it unsuitable for certain environments. The material has poor resistance to weathering, specifically ozone and ultraviolet (UV) light exposure, meaning it is not recommended for outdoor applications. Furthermore, NBR shows poor compatibility with highly polar solvents, such as ketones, halogenated hydrocarbons, and certain brake fluids.
Primary Commercial Applications
NBR is heavily utilized in the automotive and aerospace industries due to its resilience against oils and fuels. It is manufactured into essential sealing components, such as O-rings, gaskets, and shaft seals, necessary for maintaining fluid integrity in engines and transmission systems. NBR’s resistance to non-polar liquids makes it indispensable for preventing leaks of motor oil and gasoline.
The material is also a common choice for fluid handling systems, specifically hoses and tubing designed for the transfer of fuel, oil, and hydraulic fluid. Its low gas permeability, particularly in higher ACN grades, is valuable for applications involving pressurized gases. NBR is also the primary material for disposable gloves in the medical and safety sectors, offering a latex-free alternative with good barrier protection.
NBR is also used in manufacturing molded goods, such as footwear, floor mats, and various types of rollers. Its strong mechanical properties and resistance to abrasion make it suitable for use in specialized adhesives and binders.