Full definition
Nitrile (NBR), also known as acrylonitrile-butadiene rubber, is a synthetic copolymer that is widely recognized for its exceptional resistance to oils, fuels, greases, and hydraulic fluids. This makes it the predominant elastomer used in sealing applications across various industries. The defining characteristic of NBR is its acrylonitrile (ACN) content, which typically ranges from 18% to 50%. As a rule of thumb, a higher ACN content correlates with improved oil resistance; however, this comes at the expense of its low-temperature flexibility and resilience. For instance, low ACN grades (18-24%) are commonly used for applications such as flex-fuel hoses, where low temperatures are a concern, as they maintain their flexibility down to -40°C. In contrast, high ACN grades (38-50%) are ideal for applications requiring superior oil resistance, such as seals in refineries, but lose some flexibility at lower temperatures (Tg = -10°C).
The ASTM D2000 classification further categorizes NBR into grades based on their ACN content: BF for low ACN, BG for medium ACN, and BK for high ACN. NBR exhibits a hardness range of 40-90 Shore A, tensile strength of 10-25 MPa, and impressive elongation capabilities of 200-600%. This combination of properties makes it suitable for a variety of applications, including O-rings, oil seals, fuel hoses, hydraulic seals, gaskets, gloves, and even printing rollers. The operational temperature range for NBR is generally from -40°C to +100°C, with short-term exposure tolerating up to +120°C.
However, NBR does have its limitations. It is prone to degradation when exposed to ozone and UV radiation, necessitating the use of antiozonants or blending with materials such as PVC to enhance its stability. Additionally, NBR is not recommended for use with polar solvents, including ketones and esters, which can compromise its integrity. Despite these drawbacks, NBR remains the most widely produced specialty rubber globally, thanks to its versatile performance characteristics and cost-effectiveness in various industrial applications.