Nitrile Butadiene Rubber (NBR)

What is Nitrile Rubber?

NBR stands for Nitrile Butadiene Rubber, which is is a highly versatile and resilient elastomer (rubber-like material). It is composed of nitrile butadiene (polymer) containing acrylonitrile along with other molecules. These molecules include carbon, hydrogen, and nitrogen. Its structure consistently comprises of:

  • Butadiene backbone (carbon-carbon chain)
  • Acrylonitrile moiety bound to the carbon

Therefore, the special characteristics of NBR rubber originate from its distinctive molecular structure. This structure carries both polar and nonpolar groups.

The first commercial NBR rubber was introduced by Bayer in the 1930s. These rubbers are now produced by numerous companies.

What are the Advantages of Nitrile Rubber?

The strong carbon-carbon chemical structure and high bond energy give NBR rubber its unique performance properties. Several benefits of NBR rubber include:

  • Wide service temperature range – excellent thermal and oil resistance (-C-C- binding energy is higher than many other rubber compounds)
  • Excellent resistance to attack by oils, fuels, and chemicals
  • Readily resistant to wear and abrasion
  • Excellent flexibility and low compression set
  • Low cost
  • Good tensile strength and elongation at break
  • Moderate resistance to heat aging
  • Good impermeability to gases
  • High mechanical stability
  • Excellent compatibility with metals

NBR rubber can withstand temperatures (-40°C to 120°C) depending on the duration of exposure. Parts made of NBR rubber when exposed to oils, fuels, and chemicals for long periods. This results in minimal change in physical properties. Unlike many other rubbers, NBR rubber is not significantly affected by oils.

As compared to other rubber types, NBR rubber has a high acrylonitrile content in its structure, and hence, it has better:

  • Oil resistance
  • Fuel resistance
  • Chemical resistance
  • Abrasion resistance
  • Mechanical stability
  • Gas impermeability

What are the limitations of Nitrile Rubber?

Despite the superior oil resistance, heat tolerance, and mechanical properties that make NBR rubber favored in many applications, there are some significant limitations and drawbacks to consider.

  • Limited resistance to weather and ozone
  • Low resistance to aromatic and chlorinated solvents
  • Poor resistance to polar solvents and oils
  • Limited temperature range for continuous use
  • Decreased flexibility at low temperatures
  • Vulnerable to degradation from UV light

What are the Applications of Nitrile Rubber?

NBR rubber’s applications are diverse, extending from the automotive industry to specialized medical equipment.

  • O-rings
  • Oil seals
  • Hoses
  • Automotive gaskets
  • Fuel systems
  • Industrial belts
  • Hydraulic hoses
  • Roll covers
  • Disposable gloves
  • Footwear soles

Comparison with Other Rubber Types

Comparing NBR rubber with other rubber materials highlights its unique attributes and helps identify applications where it may or may not be the best fit.

NBR vs. Natural Rubber (NR)

  • Oil Resistance : NBR significantly outperforms NR in oil resistance, making it the preferred choice for applications exposed to oils and fats.
  • Wear Resistance : NR tends to have superior wear resistance, making it suitable for high-abrasion applications.
  • Temperature Range : NBR offers a wider temperature range than NR, especially in terms of heat resistance.
  • Cost : NR generally costs less than NBR, making it more attractive for cost-sensitive applications.

NBR vs. Fluoroelastomers (FKM)

  • Chemical Resistance : FKM surpasses NBR in chemical resistance, especially against oils, solvents, and at high temperatures.
  • Temperature Range : FKM has a broader temperature range, able to withstand higher temperatures than NBR.
  • Cost : FKM is significantly more expensive than NBR, which can be a deciding factor in its selection.
  • Processing : FKM processing is more complex and costly than NBR, making NBR a more accessible option for various applications.

NBR vs. Silicone Rubber (SiR)

  • Temperature Resistance : SiR excels over NBR in both high and low-temperature resistance.
  • Weathering Resistance : SiR offers superior resistance to ozone, UV, and other weathering factors compared to NBR.
  • Oil Resistance : NBR is superior in oil resistance, particularly against petroleum-based oils.
  • Cost and Processing : SiR is more expensive and requires more complex processing than NBR, but it is preferred for specific environmental conditions.

NBR vs. Ethylene Propylene Diene Monomer (EPDM)

  • Oil Resistance : NBR is much more oil-resistant than EPDM, making it suitable for oil-exposed applications.
  • Weathering Resistance : EPDM provides better resistance to weathering, ozone, and UV light compared to NBR.
  • Application Areas : EPDM is widely used in outdoor and automotive applications for its excellent environmental resistance, while NBR is favored in oil-related and industrial chemical applications.