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Nitrile rubber, also known as nitrile butadiene rubber, NBR, Buna-N, and acrylonitrile butadiene rubber, is a synthetic rubber derived from acrylonitrile (ACN) and butadiene.[1] Trade names include Perbunan, Nipol, Krynac and Europrene. This rubber is unusual in being resistant to oil, fuel, and other chemicals.

NBR is used in the automotive and aeronautical industry to make fuel and oil handling hoses, seals, grommets, and self-sealing fuel tanks. It is also used in the food service, medical, and nuclear industries to make protective gloves. NBR's stability at temperatures from 40 to 108 °C (40 to 226 °F) makes it an ideal material for aeronautical applications. Nitrile butadiene is also used to produce moulded goods, footwear, adhesives, sealants, sponges, expanded foams, and floor mats.

Its resilience makes NBR a useful material for disposable lab, cleaning, and examination gloves. Nitrile rubber is more resistant than natural rubber to oils and acids, and has superior strength, but has inferior flexibility.

History

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Nitrile rubber was developed in at BASF and Bayer, then part of chemical conglomerate IG Farben. The first commercial production began in Germany in .[2][3]

IG Farben plant under construction approximately 10 kilometres (6.2 mi) from Auschwitz,

The Buna-Werke was a slave labor factory located near Auschwitz and financed by IG Farben. The raw materials came from the Polish coalfields.[4] Buna rubber was named by BASF A.G., and through Buna was a remaining trade name of nitrile rubber held by BASF.

Production

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Krynac F nitrile rubber bales

Emulsifier (soap), acrylonitrile, butadiene, radical generating activators, and a catalyst are added to polymerization vessels in the production of hot NBR. Water serves as the reaction medium within the vessel. The tanks are heated to 3040 °C to facilitate the polymerization reaction and to promote branch formation in the polymer. Because several monomers capable of propagating the reaction are involved in the production of nitrile rubber the composition of each polymer can vary (depending on the concentrations of each monomer added to the polymerization tank and the conditions within the tank). There may not be a single repeating unit throughout the entire polymer. For this reason there is also no IUPAC name for the general polymer.

Monomers are usually permitted to react for 5 to 12 hours. Polymerization is allowed to proceed to ~70% conversion before a shortstop agent (such as dimethyldithiocarbamate and diethylhydroxylamine) is added to react with (destroy) the remaining free radicals and initiators. Once the resultant latex has shortstopped, the unreacted monomers are removed through a steam in a slurry stripper. Recovery of unreacted monomers is close to 100%. After monomer recovery, latex is sent through a series of filters to remove unwanted solids and then sent to the blending tanks where it is stabilized with an antioxidant. The yielded polymer latex is coagulated using calcium nitrate, aluminium sulfate, and other coagulating agents in an aluminium tank. The coagulated substance is then washed and dried into crumb rubber.[3]

The process for the production of cold NBR is very similar to that of hot NBR. Polymerization tanks are cooled to 515 °C instead of heating up to 3040 °C close to ambient temperature (ATC). Under lower temperature conditions, less branching will form on polymers (the amount of branching distinguishes cold NBR from hot NBR).

Properties

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The raw material is typically yellow, although it can also be orange or red tinted, depending on the manufacturer. Its elongation at break is 300% and possesses a tensile strength of 10 N/mm2 (10 MPa). NBR has good resistance to mineral oils, vegetable oils, benzene/petrol, ordinary diluted acids and alkalines.

An important factor in the properties of NBR is the ratio of acrylonitrile groups to butadiene groups, referred to as the ACN content. The lower the ACN content, the lower the glass transition temperature; however, the higher the ACN content, the better resistance the polymer will have to nonpolar solvents as mentioned above.[5] Most applications requiring both solvent resistance and low temperature flexibility require an ACN content of 33%.

Property Value Appearance Hardness, Shore A 3090 Tensile failure stress, ultimate 500- PSI Elongation after fracture in % 600% maximum Density Can be compounded around 1.00 g/cm3

Applications

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A disposable nitrile rubber glove

The uses of nitrile rubber include disposable non-latex gloves, automotive transmission belts, hoses, O-rings, gaskets, oil seals, V belts, synthetic leather, printer's form rollers, and as cable jacketing; NBR latex can also be used in the preparation of adhesives and as a pigment binder.[citation needed]

Unlike polymers meant for ingestion, where small inconsistencies in chemical composition/structure can have a pronounced effect on the body, the general properties of NBR are insensitive to composition. The production process itself is not overly complex; the polymerization, monomer recovery, and coagulation processes require some additives and equipment, but they are typical of the production of most rubbers. The necessary apparatus is simple and easy to obtain.

In January , the European Commission imposed fines totaling 34,230,000 on the Bayer and Zeon groups for fixing prices for nitrile butadiene rubber, in violation of the EU ban on cartels and restrictive business practices (Article 81 of the EC Treaty and Article 53 of the EEA Agreement).[6]

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Hydrogenated nitrile butadiene rubber (HNBR)

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Hydrogenated nitrile butadiene rubber (HNBR) is produced by hydrogenation of NBR. Doing so removes the olefinic groups, which are vulnerable to degradation by various chemicals as well as ozone. Typically, Wilkinson's catalyst is used to promote the hydrogenation. The nitrile groups are unaffected. The degree of hydrogenation determines the kind of vulcanization that can be applied to the polymer.[7]

Also known as highly saturated nitrile (HSN), HNBR is widely known for its physical strength and retention of properties after long-term exposure to heat, oil, and chemicals. Trade names include Zhanber (Lianda Corporation), Therban (Arlanxeo [8]), and Zetpol (Zeon Chemical). It is commonly used to manufacture O-rings for automotive air-conditioning systems.[9] Other applications include timing belts, dampers, servo hoses, membranes, and seals.[10]

Depending on filler selection and loading, HNBR compounds typically have tensile strengths of 2031 MPa at 23 °C. Compounding techniques allow for HNBR to be used over a broad temperature range, 40 °C to 165 °C, with minimal degradation over long periods of time. For low-temperature performance, low ACN grades should be used; high-temperature performance can be obtained by using highly saturated HNBR grades with white fillers. As a group, HNBR elastomers have excellent resistance to common automotive fluids (e.g., engine oil, coolant, fuel, etc.).

The unique properties and higher temperature rating attributed to HNBR when compared to NBR has resulted in wide adoption of HNBR in automotive, industrial, and assorted, performance-demanding applications. On a volume basis, the automotive market is the largest consumer, using HNBR for a host of dynamic and static seals, hoses, and belts. HNBR has also been widely employed in industrial sealing for oil field exploration and processing, as well as rolls for steel and paper mills.

Carboxylated nitrile butadiene rubber (XNBR)

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An alternative version of NBR is carboxylated nitrile butadiene rubber (XNBR). XNBR is a terpolymer of butadiene, acrylonitrile, and acrylic acid.[11] The presence of the acrylic acid introduces carboxylic acid groups (RCO2H). These groups allow crosslinking through the addition of zinc (Zn2+) additives. The carboxyl groups are present at levels of 10% or less. In addition to these ionic crosslinks, traditional sulfur vulcanization is applied.

See also

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References

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Which is the Best Material for Your Oil Seal?

An oil seal is basically a simple device, which is used to stop dirt, dust, water, and other contaminants from entering the shaft equipment. It is also known by other names like elastomeric lip seal, lip seal, shaft seal, or rotary shaft seal. The seal, while doing its job, helps retain the lubrication of a rotary shaft equipment. These seals are mainly used to protect the bearings used in a rotating shaft.

Materials Used to Make Oil Seals:

Oil seals can be made from a vast range of materials depending upon the application. Some common materials used to manufacture oil seals include:

1. Silicone: The widest range of operating temperature range is provided by silicone compounds. They offer an amazing temperature range from -90°F to 340°F. Nonetheless, in dry running conditions, these compounds do not perform well. It is always advisable to avoid the usage of silicone compounds with oxidized oils and EP (Extreme Pressure) compounds.
2. Viton®: Viton® compounds are said to offer the widest operating temperature range varying from 40°F to 400°F. These are considered as the premium materials for the lip seals. In addition to this, these compounds are highly resistant to chemicals and abrasion. These qualities help Viton® deliver better good performance. Unlike silicone compounds, Viton® performs well in dry running applications.
3. Nitrile Buna-N: Most companies consider Nitrile Buna-N 70 durometer compound to be the perfect material for oil seals. The compound has several benefits, which makes it the first choice of material in a wide range of applications. Oils seals that are made from this material have a wide operating temperature range from -65°F to 250°F. In addition to this, this material is compatible to work with water, as well as common mineral oil and greases.

Above mentioned are some materials used for manufacturing oil seals. Each material has its own set of pros and cons. Therefore, selection of materials should be made on the basis of the application. There are quite a variety of materials to choose from. If you find it tricky to select the right material for oil seals, you can always ask an expert. SSP Manufacturing, Inc. is one such expert in manufacturing oil seals in the USA. Please contact us by : +1-888-238- or with any questions.

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