What is the difference between NBR and FPM?

Chemical compound

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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 industries 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 molded 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

Nitrile rubber was developed in 1931 at BASF and Bayer, then part of the chemical conglomerate IG Farben. The first commercial production began in Germany in 1935.

The Buna-Werke was a slave labor factory located near Auschwitz and financed by IG Farben. The raw materials came from the Polish coalfields. Buna Rubber was named by BASF A.G., and through 1988 Buna was a remaining trade name of nitrile rubber held by BASF.

Production

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 30–40°C to facilitate the polymerization reaction and 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 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, aluminum sulfate, and other coagulating agents in an aluminum 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 cooled to 5–15°C instead of heating up to 30–40°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

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 it possesses a tensile strength of ≥ 10 N/mm2 (10 MPa). NBR has good resistance to mineral oils, vegetable oils, benzene/petrol, and 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. Most applications requiring both solvent resistance and low-temperature flexibility require an ACN content of 33%.

Applications

The uses of nitrile rubber include powder-free 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 or 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 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 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.

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.

See Also

References

Comparison of two of the most commonly used elastomers – Viton™ O Rings vs Nitrile O Rings

As two of the most widely used elastomers, Viton™ (FKM/FPM) and Nitrile (NBR) have some great properties. Both provide a supreme compression set and have an extensive range of purposes in both domestic and industrial installations. Nevertheless, they are not totally equal in their properties, and it's essential to consider which is better for your specific application. Below, you can find information about Viton™ O Rings vs Nitrile O Rings:

Viton™ is a trademark of The Chemours Company FC and refers to Fluorocarbon (FKM/FPM) O Rings. Numerous types of FKM/FPM/Viton™ O Rings are available with different fluorine levels which enhance performance in specific applications.

General Temperature Range

Between -40°C and +250°C

Shore A Hardness

Between 50 and 95 Shore A

Industries

Virtually all industries, including Aerospace & Defence, Agriculture, Automotive, Energy, Food & Drink, Industrial, Offshore Drilling, Petrochemical, Rail, Semiconductor.

Key Uses

• In a huge variety of applications – from aircraft engines to vehicle components (especially where resistance to corrosive fuels and liquids is a must)
• Automotive fuel handling
• In various mechanical devices that require maximum resistance to high temperatures
• General industrial seals and gaskets
• In applications where high resistance is needed to chemical attacks and high temperature
• Food applications

Resistance

• Resistant to the majority of chemicals
• Resistant to mineral acids and halogenated hydrocarbons
• Excellent tolerance for high temperatures
• Resistant to oils, fuels, hydraulic fluids, and hydrocarbons as well as aromatics and solvents
• Resistant to degradation by UV, weather, ozone, and mold
• Resistance to gasoline, alcohol, acids, water, oils, oxidation, aging, radiation, heat, and water

Key Features

• Very low gas permeability
• Excellent for vacuum applications
• Self-extinguishing
• Dynamic
• Low compression set
• Tensile strength
• The superior swell in high octane and oxygenated fuels

Available Specifications

• Food & Pharma: FDA, EC1935/2004 & EC2023/2006 European Regulations, 3A 18-03 Sanitary standards, BGW, USP Class VI
• Water: WRc, WRAS, DVGW, KTW, ACS, NSF 61, W270
• Oil & Gas: NORSOK M-710, NACE, TOTAL GS PVV 142/03, DIN EN 549
• Aerospace & Defence: Defence Standard 02/337, MIL-Spec, ASTM D-2000 (SAE J200)
• Other: UL, DIN EN 14241-1, MIL-R-83248

Limitations

• Less tolerant of low temperatures
• Poor low-temperature flexibility
• Not recommended for ketones, amines, hot water, steam, polar solvents

Nitrile (NBR) is also called Buna-N. O Rings made out of Nitrile are probably the most affordable and most commonly used elastomer seals.

General Temperature Range

Between -40°C and +135°C

Shore A Hardness

Between 40 and 90 Shore A

Industries

Virtually all industries, including Aerospace & Defence, Agriculture, Automotive, Biotechnology, Bus Truck & Trailer, Food & Drink, Marine, Pharmaceutical, Pump & Gas, Water

Key Uses

• General-purpose, especially in applications where the seal will be exposed to hydrocarbons, oils, petrol, water, and hydraulic fluids
• Marine, Automotive, and Aircraft fuel structures
• Off-road equipment
• Oil resistant applications of all sorts
• Low-temperature military uses
• Hygienic applications
• Food applications

Resistance

• Superb resistance to petroleum-based oils and fuels
• Excellent resistance to hydraulic fluids, water, alcohol, and silicone greases
• Excellent resistance to oil, air, alcohols, diluted acids, gasoline, hydraulic fluids, vegetable oil, motor oil, mineral oil, water, hydraulic fluids, engine coolants, alkalines, and diluted acids

Key Features

• Excellent abrasion and tear resistance
• Great tensile strength
• Compression set resistance
• Good impermeability
• Heat resistance
• Cold resistance
• Cost-effective (very economical)

Viton™ O Rings vs Nitrile O Rings – Which is the Right Choice?

Looking at these two materials, it’s quite easy to notice some advantages of Viton™, which would make it a favorite when choosing between Viton™ and Nitrile (NBR). For instance, if your installation requires the material to perform at constant high temperatures of 100°C and more, Nitrile (NBR) will not be suitable. A similar situation will occur when your application is exposed to UV, ozone, and/or weather; Nitrile (NBR) will degrade and most likely fail.

It is clear that Viton™ (FKM/FPM) is a better material in most situations, excluding at sub-zero temperatures, where Nitrile (NBR) turns out to be a much better performer.

Our experienced team will guide all aspects of production, including prototyping, testing, and final part manufacture. Depending on the application, M Barnwell Services and its manufacturing partners offer full batch traceability throughout the manufacturing process and the issuing of BS EN ISO 10204 certification when available. If you require further information regarding Viton™ and Nitrile O Rings, please contact a member of the team.

E & O.E. M Barnwell Services endeavors to ensure that all content is correct. We have gathered this information from manufacturing partners. (Viton™ is a trademark of The Chemours Company FC, LLC. M Barnwell Services does not manufacture Viton™ products)

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