What Is Nitrile? A Guide to Nitrile O-Rings and Seals

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.

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Key Benefits

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.

Common Applications

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.

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Limitations

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. 

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What Is Nitrile? A Guide to Nitrile O-Rings and Seals

When is nitrile rubber the right choice for sealing and insulation? This common elastomer is known by many names, including Buna-N, NBR, and acrylonitrile butadiene. There are plenty of trade names for nitrile, too. No matter what you call it, nitrile rubber offers good resistance to oils, fuels, and chemicals. Temperature and environmental conditions are limiting factors, however, and may require the selection of a more expensive material such as Viton&#;.

In this article from Elasto Proxy, you&#;ll learn about nitrile&#;s advantages and disadvantages. You&#;ll also examine NBR compounds, compare commercial and specialty Buna-N, and consider some typical nitrile applications. Elasto Proxy supplies specialty nitrile products to a variety of industries and can create a custom sealing solution that meets your specific requirements. Nitrile isn&#;t the only oil-resistant elastomer, but it&#;s a cost-effective choice compared to some other compounds.

Nitrile Advantages and Disadvantages

Nitrile rubber provides good-to-excellent resistance to many oils and solvents. Examples include:

• animal and vegetable oils
• crude petroleum oil
• kerosene and gasoline
• liquified petroleum (LP) gases
• motor oils
• mineral oil based hydraulic fluids
• silicone greases and oils

For engineers and buyers, it&#;s important to understand that nitrile&#;s resistance to petroleum oils is limited by temperature. According to most chemical resistance charts, nitrile resists petroleum oil at temperatures up to 250° F (121° C). If your application requires both oil resistance and higher temperature resistance, a fluorocarbon such as Viton&#; may be required instead. Nitrile is also unsuitable for highly polar solvents such as acetone, which is used in some food processing and medical applications.

Nitrile&#;s advantages include good physical properties such as resistance to compression set, tearing, and abrasion. Typically, NBR or Buna-N comes in durometers (Shore A) ranging from 20 to 95 for applications that require a softer or harder rubber. Nitrile resists water, but provides poor resistance to weather, ozone, and aging. Acrylonitrile butadiene is also unsuitable for some applications because Buna-N won&#;t withstand temperatures that are colder than -40° F (-40° C).

Nitrile Compounds and Specialty Grades

Through compounding, material suppliers have developed different types of nitrile with enhanced material properties. For example, hydrogenated nitrile butadiene rubber (HNBR) can withstand slightly higher temperatures than NBR and provides improved resistance to polar fluids. Carboxylated nitrile butadiene rubber (XNBR) has a higher compression set than Buna-N and offers improved tear and abrasion resistance. Nitrile can also be blended with polymers such as polyvinyl chloride (PVC).

For engineers and buyers, choosing the right type of nitrile may involve comparing commercial rubber to specialty grades. Commercial grades generally cost less and are available in higher minimum order quantities (MOQs). Specialty grades generally cost more and have larger MOQs, but they&#;re custom compounds with improved properties. ASTM D provides a standard way to describe elastomers and uses the designations BF, BG, BK, and CH with both standard and specialty nitrile.

Nitrile Products and Custom Fabrication

Nitrile rubber products are used in the aerospace, defense, infrastructure, medical and health, and mobile equipment industries. Specific uses include:

• floor mats
• grommets
• hydraulic hoses
• lip seals
• O-rings
• oil seals
• vehicle transmission belts

Nitrile rubber is also used in appliance seals, medical gloves, and the bumpers for bowling alleys.

Buna-N or NBR is supplied as sheets, rolls, and profiles. Most nitrile rubber is black, but other colors are available. Nitrile seals and gaskets are usually made of solid sheets or extrusions, but closed cell Buna-N sponge rubber is used in applications that require a conformable gasket material. Water jet cutting supports fast, precise NBR gasket fabrication and eliminates the need to pay for or wait for tooling.

Find Nitrile Rubber for Sealing and Insulation

Do you need nitrile seals or gaskets? Do you have questions about Buna-N, or are you wondering whether HNBR or XNBR might be a better choice your application? Maybe you&#;re considering Viton&#; or a specialty grade nitrile when a commercial NBR would meet your requirements. For design assistance, help with material selection, and expert gasket fabrication, contact Elasto Proxy.

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