Nitrile Butadiene Rubber (NBR): Structure, Properties, and Industrial Performance

Nitrile Butadiene Rubber (NBR): Structure, Properties, and Industrial Performance

1. Introduction

Nitrile Butadiene Rubber (NBR) is a synthetic elastomer widely recognized for its outstanding resistance to oils, fuels, and many chemicals. Since its commercial development in the 1930s, NBR has become a critical material across automotive, industrial, oil & gas, and sealing applications. Its balanced combination of mechanical strength, abrasion resistance, and chemical stability makes it one of the most important specialty rubbers in modern industry.

NBR is particularly valued in environments where conventional natural rubber (NR) or styrene-butadiene rubber (SBR) would degrade rapidly due to exposure to hydrocarbons. As industrial systems continue to operate under harsher chemical and thermal conditions, NBR remains a material of choice.

2. Chemical Structure and Composition

NBR is a copolymer synthesized from butadiene and acrylonitrile (ACN) via emulsion or solution polymerization. The ratio of acrylonitrile content, typically ranging from 18% to 50%, plays a decisive role in determining the rubber’s final properties.

• Low ACN content (18–25%)

  • Higher elasticity

  • Better low-temperature flexibility

  • Lower oil resistance

• Medium ACN content (26–35%)

  • Balanced oil resistance and flexibility

  • Common for general industrial use

• High ACN content (36–50%)

  • Superior resistance to fuels and oils

  • Higher tensile strength

  • Reduced low-temperature performance

The polar nitrile group (–C≡N) is the key functional component that enhances resistance to non-polar solvents such as oils and fuels.

3. Mechanical and Physical Properties

NBR exhibits a robust set of mechanical properties, which can be further tailored through compounding and vulcanization.

Key properties include:

• Tensile strength: 10–25 MPa (compound dependent)

• Elongation at break: 300–600%

• Hardness: 40–90 Shore A

• Good abrasion and tear resistance

• Moderate compression set resistance

The rubber’s performance can be significantly enhanced by fillers (carbon black), plasticizers, antioxidants, and curing systems (sulfur or peroxide).

4. Chemical and Environmental Resistance

One of NBR’s most significant advantages is its excellent resistance to petroleum-based oils, fuels, greases, and hydraulic fluids. It also demonstrates good resistance to:

• Aliphatic hydrocarbons

• Alcohols

• Weak acids and bases

However, NBR has limitations:

• Poor resistance to ozone, UV radiation, and weathering

• Limited resistance to aromatic hydrocarbons and ketones

• Inferior heat resistance compared to HNBR or FKM

To overcome these limitations, additives or surface protection measures are often employed.

5. Processing and Vulcanization

NBR is compatible with conventional rubber processing techniques such as:

• Compression molding

• Injection molding

• Extrusion

• Calendering

Vulcanization systems typically include:

• Sulfur curing for flexibility and cost efficiency

• Peroxide curing for improved heat and aging resistance

The choice of curing system directly influences compression set, thermal stability, and service life.

6. Industrial Applications

NBR’s property profile makes it indispensable across numerous industries:

Automotive

• Fuel hoses

• Oil seals

• Gaskets

• O-rings

Industrial & Manufacturing

• Conveyor belts

• Printing rollers

• Rubberized fabrics

Oil & Gas

• Blowout preventer seals

• Packings

• Drilling components

Medical & Safety

• Disposable nitrile gloves

• Protective membranes

In glove manufacturing, NBR has largely replaced natural latex due to its latex-protein-free composition, reducing allergy risks.

7. Comparison with Other Elastomers

Compared to SBR and NR, NBR offers superior oil resistance but inferior weathering resistance. Against fluoroelastomers (FKM), NBR is more economical but less heat and chemical resistant. This balance of performance and cost explains its continued dominance in mid-range applications.

8. Future Outlook

Ongoing innovation in polymer modification and sustainable processing is shaping the future of NBR. Developments include:

• Bio-based butadiene feedstocks

• Low-temperature NBR grades

• Enhanced recyclability

As industries demand materials that combine durability, cost efficiency, and regulatory compliance, NBR will remain a cornerstone elastomer for decades to come.