Nitrile, commonly known as NBR or Buna-N, is a synthetic rubber composed of acrylonitrile (ACN) and butadiene. Based on the formulated ratio of ACN and butadiene, the working properties of nitrile seals may vary. For example, lower ACN content equates to lower glass transition temperature, while higher ACN content leads to better resistance to nonpolar solvents. Nitrile elastomers are widely used for their desirable working properties and economical cost.
Nitrile o-rings, gaskets and other sealing devices offer a number of beneficial properties. Some of the top features include:
- Resistance to petroleum-based oils and fuels, silicone greases, hydraulic fluids, water and alcohols
- Maintains flexibility in low temperatures
- Low compression set
- High tensile strength
- High abrasion resistance
- Can be compounded for FDA standards
Nitrile seals are able to withstand temperatures ranging from -40°F to +257°F, with special compounds ranging from -67°F to +275°F in dry heat only. Additionally, carboxylated nitrile offers superior abrasion resistance, while still having improved oil resistance.
Nitrile rubber is used in many applications in a wide range of industries, including automotive, aerospace, marine and military. Among these industries, nitrile is commonly used in applications such as:
- Off-road equipment
- Aircraft, automotive and marine fuel systems
- Automotive transmission belts
- Oil seals
- Static and dynamic hydraulic seals
- Disposable non-latex gloves
When it comes to disposable gloves, nitrile rubber is more resistant than natural rubber to oils and acids. However, natural rubber offers greater flexibility. Nitrile rubber gloves are more resistant to punctures or degradation when exposed to certain chemicals, making them an optimal choice in many applications.
While nitrile is an excellent elastomer for many reasons, there are some limitations to be aware of. For starters, nitrile compounds are easily attacked by small amounts of ozone, which reduces compatibility with outdoor exposure over long periods. Additionally, nitrile rubber is commonly compounded with phthalate type plasticizers, which can migrate out of the rubber compound and cause greater issues with certain plastics.
It’s also important to note the dangers of some commercial quality nitriles on the market. These compounds are typically a mixture of SBR and nitrile, which is done to cheapen the product. The danger arises when customers expect certain characteristics of nitrile that come from ACN content, but commercial quality nitrile contains no more than 10% of ACN. Be sure to check with an engineer to ensure the right levels of each compound are present in your product before applying.
Have questions about nitrile rubber?
Ask an engineer today.