Hydrogenated Nitrile Butadiene Rubber, known as HNBR, is a high-performance synthetic elastomer specifically engineered for demanding operational environments. This material is a derivative of standard Nitrile Butadiene Rubber (NBR). HNBR is valued for its superior mechanical strength and extended durability, and is typically selected for components that must maintain integrity while exposed to aggressive chemicals, high heat, and significant physical stress.
Defining HNBR and the Role of Hydrogenation
HNBR begins as Nitrile Butadiene Rubber, which is a copolymer composed of acrylonitrile and butadiene segments in its polymer chain. Conventional NBR contains carbon-carbon double bonds within its butadiene units, a feature that chemists refer to as unsaturation. These double bonds are the molecular weak points that make NBR susceptible to degradation from heat, oxygen, and ozone exposure.
The transformation into HNBR involves a precise chemical process called hydrogenation. During this reaction, hydrogen atoms are introduced to the NBR polymer chain, which selectively saturates the unstable carbon-carbon double bonds. This structural modification converts the reactive double bonds into more stable single bonds, creating a highly saturated nitrile elastomer, sometimes called HSN. The degree of acrylonitrile (ACN) content, which can range from approximately 17% to 50%, is maintained and continues to dictate the material’s oil and fuel resistance.
This saturation of the polymer backbone fundamentally alters the material’s performance profile at a molecular level. By removing the sites that are vulnerable to chemical attack and thermal breakdown, the resulting HNBR exhibits significantly improved thermal stability and mechanical strength, allowing it to function reliably in conditions that would cause rapid failure in many other elastomers.
Superior Physical and Chemical Performance Traits
One of the most notable improvements is its high-temperature resistance, allowing for continuous service over a broad range, typically from -40°C to 165°C, with some compounds tolerating short-term excursions up to 170°C. This thermal stability prevents the material from hardening or softening prematurely, ensuring sealing force is maintained over time.
HNBR also demonstrates exceptional mechanical properties, particularly high tensile strength and resilience. HNBR compounds commonly achieve tensile strengths between 20 and 31 megapascals (MPa), which is a measure of the force required to pull the material apart. This strength, combined with excellent resistance to abrasion, makes it highly suited for dynamic applications involving continuous movement and friction. Wear resistance is notably superior to NBR, with some tests showing HNBR to be two to three times more resilient in petroleum media.
The material is also prized for its resistance to volume swell and degradation when exposed to various aggressive fluids. It has an excellent resistance profile against common automotive fluids such as engine oil, coolant, and fuel, as well as industrial substances like aliphatic hydrocarbons and some refrigerants. Furthermore, the saturated structure provides outstanding resistance to ozone and oxidation, which is a significant weakness of conventional NBR.
Common Industrial Uses
HNBR is a preferred material for seals, gaskets, and belts in the automotive industry. It is used in components such as engine seals, fuel system hoses, and synchronous (timing) belts that operate near hot engine parts and are constantly exposed to oil and fuel vapors. The material’s ability to withstand high operating temperatures and dynamic stress makes it ideal for these under-the-hood applications.
In the oil and gas sector, HNBR is essential for exploration and processing equipment where conditions are particularly harsh. It is frequently formulated into downhole sealing components, packers, and blow-out preventers that must maintain integrity against high pressure and corrosive fluids like hydrogen sulfide and crude oil. The material’s durability and chemical resistance ensure reliable operation deep underground where replacement is difficult and costly.
HNBR’s robust nature also makes it a standard choice for heavy industrial machinery and equipment. It is utilized in hydraulic system seals, gaskets, and rollers in steel and paper mills where components are subjected to high mechanical loads and continuous abrasive action. Its low compression set at high temperatures allows seals to maintain their shape and function over extended periods, preventing system leaks and maximizing equipment uptime.