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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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. 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 used in the nuclear industry to make protective gloves. NBR's stability at high 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. Nitrile gloves are therefore more puncture-resistant than natural rubber gloves, especially if the latter are degraded by exposure to chemicals or ozone. Nitrile rubber is less likely to cause an allergic reaction than natural rubber.
Emulsifier (soap), acrylonitrile, various butadiene monomers (including 1,3-butadiene, 1,2-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 30–40 °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). One repeating unit found throughout the entire polymer may not exist. 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 diethyl hydroxylamine) is added to react with the remaining free radicals. 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.
The process for the production of cold NBR is very similar to that of hot NBR. Polymerization tanks are heated to 5–15 °C instead of 30–40 °C. Under lower temperature conditions, less branching will form on polymers (the amount of branching distinguishes cold NBR from hot NBR).
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 in the polymer backbone, 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. Most applications requiring both solvent resistance and low temperature flexibility require an ACN content of 33%.
|Hardness, Shore A||30–90|
|Tensile failure stress, ultimate||500-2500 PSI|
|Elongation after fracture in %||600% maximum|
|Density||Can be compounded around 1.00 g/cm3|
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.
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. Among the highest producers of NBR are China and Taiwan.
In January 2008, 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).
Hydrogenated nitrile butadiene rubber (HNBR)
Hydrogenated nitrile butadiene rubber (HNBR) is produced by hydrogenation of NBR. Doing so removes the olefinic groups, which are vulnerable to chemical degradation. 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.
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 ), and Zetpol (Zeon Chemical). It is commonly used to manufacture O-rings for automotive air-conditioning systems. Other applications include timing belts, dampers, servo hoses, membranes, and seals.
Depending on filler selection and loading, HNBR compounds typically have tensile strengths of 20–31 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)
An alternative version of NBR is carboxylated nitrile butadiene rubber (XNBR). XNBR is a terpolymer of butadiene, acrylonitrile, and acrylic acid. 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.
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|Wikimedia Commons has media related to Nitrile rubber.|
- Manufacturing capabilities in Nitrile Rubber
- Nitrile Rubber Selection Guide Robinson Rubber Products
- Nitrile Rubber, AAA Acme Rubber Co
- Risk Assessment of Butadiene, CAS No. 106-99-0, EINECS No.203-450-8, June 2001
- Existing Substances Evaluation: Butadiene, The Green Lane, Environment Canada
- Antitrust: Commission fines synthetic rubber producers € 34.2 million for price fixing cartel, EUROPA Portal
- Information & Resource Site on Nitrile Gloves, Archived from the original on August 5, 2013