This is an interesting question. Though there is a significant difference in the way both are produced, and in the ideal application of each, one is not necessarily better than the other. Both are polymers, which are substances made up of large molecules composed of many repeated sub-units. Each display highly valued properties and are used in many industrial and household applications.
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Natural rubber is made from the sap of trees, called Heveabrasiliensis, which grow on plantations in South America and South Asia. The sap, a sticky, milky liquid, is harvested through a process called tapping where incisions are made in the trees causing natural latex to trickle into containers. Because It is a natural product and ecologically friendly, it is the perfect material for environmentally-conscious consumers. Though it is an important raw material and used in many industries, natural rubber can be difficult to process.
There is no variation in natural rubber. It is generally all harvested and processed the same way, which produces the same product universally. Natural rubber is generally more-supple than other rubber types and can be used in a variety of forms. It is ideal for use in wiper blades, machine skirting, and even as drum practice pads. It is also used to make tires, gloves, and rubber mats.
Despite having highly valued properties, natural rubber demonstrates poor resistance to atmospheric oxygen, ozone, oils, and various hydrocarbon solvents. In addition, natural rubber products do not have the same high levels of chemical and temperature resistance as nitrile rubber. This is because synthetic rubbers, in general, are engineered to include certain properties, such as resistance to specific substances, whereas natural rubber is a product which has been derived from nature. In terms of industrial uses, natural rubber is more suited for light to medium grade applications that do not involve overly abrasive temperatures and chemical conditions. When you think of natural rubber, think rubber bands – no other product has elongation like natural rubber. Natural rubber is also used in wiper blades and machine skirting.
By way of contrast, nitrile rubber, also known as NBR or Buna-N, is a man-made polymer produced under controlled conditions. It was developed during World War II in response to a growing need for oil-resistant rubber that could serve as a more durable alternative to natural rubber. It is produced using petroleum-based materials, and is a synthetic rubber copolymer of acrylonitrile (ACN) and butadiene. This means that it is not a natural product and its production can have some detrimental effects to the environment. Despite this, the demand for nitrile rubber continues to grow.
NBR has properties that make it an excellent solution for sealing applications. Unlike natural rubber, it has a superior level of resistance against synthetic and natural grease products and is highly recommended for use in areas where petroleum products are present. It can be used to provide long-lasting machinery components which might be exposed to fuel or lubricants. In commercial kitchens, it is common for cooking oil or food grease to spill or splatter. Nitrile rubber sheeting ensures that kitchen products will remain effective longer. Nitrile sheets can also be used in laboratories, where spills of caustic agents are likely. It can be found in 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.
Nitrile rubber also offers resistance to heat aging – often a key advantage over natural rubber, which can harden and lose its damping capability. Nitrile rubber is also a great material choice for applications that require abrasion resistance and metal adhesion. Because it is produced artificially, it is easier to make. It doesn’t need to be produced in a certain region or at a certain time of year, and does not rely on weather. The main advantage of NBR over natural rubber is NBR’s ability to trap and retain gas. Synthetic nitrile rubber holds nitrogen bubbles within its structure making it the perfect choice for closed cell sponge applications. Natural rubber allows these bubbles to pass right through the cell wall, making it the weakest material for this use.
Nitrile rubber has come a long way since its war-forced beginning, and is now used in a huge variety of machinery and everyday settings.
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.
See also
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References
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