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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 1931 at BASF and Bayer, then part of chemical conglomerate IG Farben. The first commercial production began in Germany in 1935.[2][3]
IG Farben plant under construction approximately 10 kilometres (6.2 mi) from Auschwitz, 1942The 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 1988 Buna was a remaining trade name of nitrile rubber held by BASF.
Production
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Krynac 33110 F nitrile rubber balesEmulsifier (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 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 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
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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 30–90 Tensile failure stress, ultimate 500-2500 PSI Elongation after fracture in % 600% maximum Density Can be compounded around 1.00 g/cm3Applications
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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 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).[6]
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 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)
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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.
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References
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Gaskets are mechanical seals that are designed to fill the gap between two mating surfaces. In fluid processing and handling equipment, they prevent process fluids from escaping the system and contaminants from entering the system. This ensures the system does not waste valuable materials or experience damage from the unwanted materials.
Given the critical function gaskets perform in fluid systems, it is important to select the right one for the intended application. One of the key elements to keep in mind when designing and selecting a gasket is the material, which significantly impacts the component’s performance. However, since there are numerous gasket material options available, it can be difficult or daunting to choose the one that best suits your needs. That’s why you should partner with an experienced gasket manufacturer; they have the knowledge and skills to ensure you receive the right gasket.
At Custom Gasket Manufacturing, we’ve specialized in the manufacture of custom gasket solutions for over 50 years. Our team has what it takes to deliver a gasket solution that fully meets your specifications and standards. Below, we provide an overview of the rubber gasket materials available to help you determine which material is most appropriate for your application.
While gaskets can be made from a variety of materials, one of the top choices is rubber. Rubber comes in a wide range of formulations and grades, each of which offers distinct characteristics that make it suitable for different applications:
Neoprene is a synthetic rubber made by polymerizing chloroprene. It is also known as polychloroprene. It is highly versatile, finding application in various harsh environments across a wide range of industries due to its resistance to acids, alkalis, grease and oil, ozone, sun, and weathering. It also exhibits excellent resistance to flexing and twisting and broad temperature suitability (-40° F to +230° F, intermittent to +250° F).
Custom Gasket Manufacturing works with the following neoprene grades:
Nitrile rubber—also known as Buna-N or NBR—is the most commonly used elastomeric material for gaskets and seals. It exhibits excellent resistance to acids, alkalis, gasoline, hydraulic fluids, and petroleum-based compounds. It also can tolerate temperature ranges of -40° F to +212° F. Nitrile is also ideal when gas permeability, water permeability, and wear-and-tear from abrasion are a concern.
Custom Gasket Manufacturing works with the following nitrile grades:
EPDM rubber is an ethylene and propylene copolymer. It can resist damage from acids, alkalis, aging, heat, oxidants, ozone, sunlight, steam, and water. It is also color stable and highly durable, which makes it suitable for use in outdoor environments. It can withstand temperatures from -40° F to 250° F, intermittent to +275° F.
Custom Gasket Manufacturing works with the following EPDM grades:
Silicone rubber is a high-performance elastomer. It exhibits excellent high- and low-temperature properties, withstanding temperatures ranging from -75° F to +500° F. It also resists damage from aging, oxygen, ozone, UV light, water, and weathering.
Custom Gasket Manufacturing works with the following EPDM grades:
Viton is high-performance rubber material characterized by its excellent resistance to chemicals and high temperatures. It also has high tensile strength and low compression set. It is suitable for use in temperatures ranging from -15° F to +400° F, intermittent to +500° F.
Custom Gasket Manufacturing works with the following Viton grades:
SBR—also known as red rubber—is a synthetic copolymer of styrene and butadiene. It is a resilient and cost-efficient option for flanged gaskets. Key properties include excellent tensile strength, impact strength, abrasion resistance, heat resistance, and low-temperature flexibility. It is suitable for use in temperatures ranging from -67° F to +180° F.
Custom Gasket Manufacturing works with the following SBR grades:
Butyl rubber is an isobutylene and isoprene copolymer. It has excellent low gas, air, and moisture permeability. Additionally, it offers outstanding resistance to abrasion, acids, alkalis, heat aging, oxygen, ozone, sunlight, tearing, and weathering. It is suitable for use in temperatures ranging from -60° F to +250° F.
Custom Gasket Manufacturing works with butyl rubber in a variety of grades, thicknesses, and hardness. Gaskets can come with or without pressure-sensitive adhesive backing.
Natural rubber is an elastomeric material derived from the milky sap or latex of the rubber tree. It is also known as gum rubber. It has excellent tensile strength, resilience, resistance to abrasion and tearing, compression set, and moldability. It also remains soft and flexible at low temperatures. It is suitable for use in temperatures ranging from -60° F to +175° F.
Custom Gasket Manufacturing works with the following natural rubber grades:
*made entirely from FDA-approved ingredients per 21 CFR 177.2600
Cloth-inserted rubber refers to rubber sheet material impregnated with cotton, fiberglass, polyester, or nylon fabric. The cloth provides reinforcement to the material, improving its dimensional stability in high compression load applications and its tear resistance when fastened.
Custom Gasket Manufacturing works with the following cloth-inserted rubber:
Polyurethane combines the elasticity of rubber with the strength and durability of metal. It has the greatest toughness and abrasion resistance of all elastomeric materials. It outperforms plastic, steel, and other rubbers with regard to resistance to chemicals, heat, and solvents and offers excellent tensile strength, compression strength, tear strength, hardness, and more. It is suitable for use in temperatures ranging from -60° F to +180° F.
Custom Gasket Manufacturing works with polyurethane in a variety of grades, thicknesses, colors, and hardness. FDA-approved materials are available for food and beverage industry applications.
Gaskets for the food and beverage industry must be made from FDA-approved materials. These materials are deemed safe for use with consumable products as they demonstrate an inherent resistance to bacterial buildup, a broad working temperature range, excellent chemical resistance. Additionally, they are odorless and tasteless.
Custom Gasket Manufacturing works with the following food-grade rubber materials:
Need assistance choosing the right rubber material for your gasket application? Turn to the experts at Custom Gasket Manufacturing! Equipped with extensive manufacturing experience and capabilities, our team can deliver a high-quality gasket, seal, or other rubber product solution on time and in budget. To learn more about our custom gaskets, contact us today. For pricing details, request a quote.
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