NBR (nitrile rubber) is a so-called elastomer, i.e. a plastic that is dimensionally stable but elastically deformable. NBR consists of polymer chains formed from the monomers 1,3-butadiene and acrylonitrile. The special chemical linkage of these monomers provides the elastic properties of the plastic.

The physical and chemical properties of NBR (acrylonitrile butadiene rubber) are influenced by:

• the cross-linking of the individual polymer chains with each other
• the mixing ratio of the two monomers
• mixing with other plastics, such as PVC or SBR
• the addition of fillers

The properties of acrylonitrile-butadiene rubber can be specifically modified. The proportion of acrylonitrile in the finished product plays a key role here. A low acrylonitrile content provides greater flexibility at low temperatures, but at the expense of lower resistance to mineral oils and fuels. Conversely, an increased acrylonitrile content in the NBR results in better fuel resistance but poorer low-temperature resistance.

The physical properties of NBR

Acrylonitrile butadiene rubber is gas and liquid tight, so it is a commonly used material for hoses in many industries.

With the differences in the chemical structure of nitrile rubber, the density also varies between 1.35 g/cm3 and 1.50 g/cm3. The density depends on the number of links between the polymer chains.

The same applies to the hardness.

Strong mechanical resistance characterizes nitrile rubber

Nitrile rubber is characterized by mechanical properties that make the plastic highly attractive for use in sealing applications. These include:

• high tensile and tear strength
• high abrasion resistance
• low compression set
  
  

High thermal resistance is one of the key properties of NBR

Acrylonitrile butadiene rubber is resistant over a temperature range of -30 °C to +120 °C. Like most other physical properties, temperature resistance is determined by the ratio of the different monomers: A low acrylonitrile content provides stability down to -30 °C. With increasing acrylonitrile content, the nitrile rubber is suitable for high-temperature applications up to 120 °C.

The chemical nature is extremely resistant

Nitrile rubbers are characterized by very high resistance to a large number of chemical compounds. These include both organic and inorganic substances:

• nonpolar hydrocarbons such as mineral oils, greases and fuels, as well as propane, butane and natural gas
• polar hydrocarbons such as alcohols
• silicone oil
• water and water vapor as well as acids and alkalis

Low resistance to chlorinated hydrocarbons, brake fluids and flame-retardant pressure fluids. Similarly, resistance to ozone and UV radiation is very low..

Other advantages of NBR

Nitrile rubber has been classified as physiologically harmless and thus food safe. This means that plant components made of acrylonitrile butadiene rubber can also be used for beverage and food production.

In addition, nitrile rubber does not become electrostatically charged. Due to the fact that there is no risk of sparking, nitrile rubber is therefore also used as an oil or fuel line.

NBR was developed in 1930 and manufactured on an industrial scale just four years later. The following raw materials are used to produce rubber compounds such as acrylonitrile-butadiene rubber:

• Rubbers
• plasticizers
• fillers
• Other chemicals

A distinction is made between active and inactive fillers:

The properties of NBR can be adapted to specific purposes by active fillers

The most commonly used active fillers are carbon blacks and silicas. As their name suggests, they significantly influence the mechanical properties of the rubber. As mixed-in substances, they attach themselves to the rubber molecules, thus increasing strength, tear resistance and abrasion resistance.

Inactive fillers are a cost-effective alternative for the further processing of NBR

Inactive fillers mainly serve as inexpensive extender and do not influence the mechanical properties. These include, for example, kaolins and chalks.

Plasticizers have a simplifying effect on the subsequent processing of the nitrile rubber and thus reduce manufacturing costs. Inexpensive materials such as mineral oils are generally used here.

Added chemicals influence the properties of the finished product. For example, agents to protect against aging, dyes or blowing agents that increase the volume of the elastomer are added to acrylonitrile butadiene rubber.

Synthesis of nitrile rubber

NBR is synthesized by the emulsion polymerization process from acrylonitrile and 1,3-butadiene. This process is characterized by several advantages:

• very high reaction speed
• simple reaction control with high yields
• rapid dissipation of the reaction energy generated

The degree of crosslinking and thus the physical properties of the finished acrylonitrile-butadiene rubber can be specifically influenced by the reaction temperature selected. A cold polymerization produces a less strongly crosslinked plastic than a warm polymerization.

In principle, two different processes can be used to produce nitrile rubber:

• the discontinuous process in rolling mills and internal mixers
• the continuous synthesis with the aid of a mixing extruder
  
  

Which process is mainly used today?

In the meantime, the process with continuous feeding of the substances to be mixed has become established. This enables consistent quality and a cost-effective manufacturing process, as the warm reaction mixture is brought directly from an extrusion die into the desired shape.

Due to its good physical properties and resistance to many chemicals, acrylonitrile butadiene rubber is widely used in many industries, for example as NBR seals or hose assemblies. These include:

• Research and medical technology
• automotive industry
• Food industry
  
  

In research, NBR ensures a safe and sterile laboratory environment

NBR is mainly used as so-called nitrile rubber gloves in the medical and laboratory sector. In contrast to the classic latex gloves, this protective equipment is also well tolerated by allergy sufferers.

Due to its good chemical resistance, NBR is also used to manufacture seals and test tube stoppers.

A proven material in the automotive industry

Due to its excellent resistance to fuels and lubricants, NBR finds a wide range of applications in vehicle construction and engine technology. Acrylonitrile butadiene rubber as a natural rubber substitute is mainly used in the automotive supply industry. It is used as a sealing material for O-rings, diaphragms, valves, couplings and hoses..

Due to its thermal and chemical resistance, NBR is also used in the food industry

Due to its physiological harmlessness, NBR is used as a hose material in water and beverage production. NBR is also used in the food production sector, for example for conveyor belts.

Nitrile rubber is also used in the following areas

Its good abrasion resistance and low compression set make NBR an ideal material for rugged shoe soles.

Due to its chemical resistance to mineral oils, NBR is used as a seal in hydraulic and pneumatic systems. Likewise, piping and hose systems of biogas plants can be manufactured from nitrile rubber.

Acrylonitrile butadiene rubber offers some advantages over other plastics due to its chemical and physical properties:

• NBR and EPDM/EPM are characterized by high temperature resistance. This is why NBR is used in the form of seals and hoses in engine technology.
• Resistance to mineral greases is lower in CSM than in nitrile rubber. Acrylonitrile butadiene rubber is far superior to comparable materials in terms of resistance to fuels, mineral oils, lubricating greases and other animal and vegetable oils and fats.
• In contrast to CR, NBR impresses with its higher chemical resistance. Compared with acrylonitrile butadiene rubber, CR has only average resistance to mineral oils and greases.
• NBR is characterized by higher mechanical elasticity than FPM/FKM.

Acrylonitrile butadiene rubber is used at Sattler primarily for the production of rubber seals for the sanitary and automotive industries. Please feel free to contact us for an individual offer - we will find the right solution for you!