A Complete Guide to Nitrile Rubber

Nitrile rubber, also known as Buna-N or NBR, is an oil and fuel resistant synthetic rubber commonly used for sealing and edging applications. With an annual production that exceeds 36 million metric tons, Nitrile is expected to continue to gain popularity due to an increase in the demand for synthetic rubbers within the automotive, engineering and industrial industry sectors. NBR rubber has a diverse range of properties that makes it a suitable material for manufacturing rubber extrusions that will come into contact with oils, fuels, alcohols, hydraulic fluids and chemicals. It is also a durable material that exhibits excellent tensile strength and abrasion resistance.

Nitrile can be cut into strips from large sheets or extruded to create bespoke sealing solutions. These products can be manufactured using solid nitrile or a closed-cell sponge in a range of hardnesses and densities.

This guide provides a detailed explanation of the history of nitrile rubber and discusses the advantages and disadvantages of using this material for manufacturing rubber extrusions.

There are many advantages for using nitrile rubber for bespoke extrusions and gaskets. As a compound with exceptional resistance to most fluids, nitrile is a reliable material commonly used across various industry sectors. Some of the key benefits of using nitrile include;

• Oil and Fuel Resistance: The most sought after benefit of nitrile rubber is its resistance to oils, fuels and petroleum-based fluids. As a material that does not easily swell or degrade, nitrile provides a long-lasting and reliable choice for applications involving contact with these substances. Nitrile is hydrophobic, which means that it repels water allowing it to resist the penetration of oil and water-based liquids. The level of oil resistance depends on the amount of acrylonitrile in the rubber compound. A higher ratio makes the rubber less resistant to swelling from oil contact, but results in the seal becoming slightly stiffer at lower temperatures.
  
  
• Chemical Resistance: Although harsh chemicals will cause most rubber compounds to breakdown and degrade, nitrile performs well against a broad spectrum of chemicals, including acids and solvents. 
  
  

As well as demonstrating an excellent resistance to most fluids, products made from nitrile also display exceptional functional properties that further expand their application within the automotive and engineering industry sectors. These properties include;

• Durability: NBR rubber is known for its durability, long service life and abrasion resistance. Together with its ability to withstand oil and fuel, nitrile is suitable for tough and dirty industrial applications such as conveyor belts, o rings and engine hoses. Seals manufactured from nitrile also demonstrate good flexibility and are unlikely to be stretched during installation.
  
  
• Temperature Resistance: Nitrile can effectively operate within a moderate temperature range between -40°C and 120°C. Although there are other materials such as Silicone more suitable for high temperature applications, these materials have a poor resistance to oil and fuel. These characteristics make nitrile one of the best and affordable oil resistant rubber compounds suitable for use within a modest temperature range.
  
  
• Water Resistance: As either a solid or closed-cell sponge, nitrile rubber can withstand short-term exposure to water and is suitable for applications where exposure to moisture is a concern. However, pro-longed or continuous exposure to water may lead to swelling, softening and reduce the rubbers mechanical properties.
  
  
• Compression Set: NBR exhibits a good resistance to compression set. Seals manufactured from nitrile maintain their shape and sealing properties after prolonged compression.
  
  
• Hybrid Compounds: It is possible to blend nitrile with other expanded materials, such as PVC, to make hybrid compounds with increased oil resistance at a lower cost. By itself PVC should not come into contact with large amounts of oil. However, combining this material with expanded nitrile creates a hybrid material at a significantly lower cost with a fair resistance to substances that would normally cause PVC to degrade.

Although nitrile rubber has many advantages within the automotive and engineering industry, there are occasions where it is unsuitable for some applications. In this instance it is sometimes worth considering alternative materials such as EPDM, Silicone or Viton. Some of the disadvantages of NBR rubber include;

• Ozone and UV Stability: Nitrile is susceptible to damage from ozone and ultraviolet radiation which can cause cracking and degradation. Seals manufactured from nitrile are not well suited for outdoor applications that will experience prolonged exposure to sunlight. In such cases, other rubber materials such as EPDM, Silicone or Viton, with better UV resistance may be more suitable.
  
  
• Cost: Applications that do not require a rubber material resistant to oils and fuels, would be better suited with a lower cost compound such as EPDM or Silicone. However, in comparison to other oil and fuel resistant materials such as Viton, nitrile offers an affordable alternative. The minimum order quantity for a bespoke nitrile extrusion is around 100 metres, depending on the size and complexity of the profile.

Nitrile rubber is available in a selection of grades and hardnesses to suit different applications. As a material that can be extruded or cut from sheet and manufactured in both sponge and solid variants, nitrile offers a solution to most sealing applications. The formulation and hardness of nitrile can vary, so selecting the correct grade is essential for optimal performance within a particular environment.