Rubber, nitrile

Nitrile rubber is a copolymer of butadiene and acrylonitrile. It has the special property of being resistant to hydrocarbon liquids. 

The copolymerization occurs in an aqueous emulsion. When free radicals are used, a random copolymer is obtained. Alternating copolymers are produced when a Zieglar-Natta catalyst is employed. Molecular weight can be controlled by adding modifiers and inhibitors. When the polymerization reaches approximately 65%, the reaction mixture is vacuum distilled in presence of steam to recover the monomer. 

The ratio of acrylonitrile/butadiene could be adjusted to obtain a polymer with specific properties. Increasing the acrylonitrile ratio increases oil resistance of the rubber, but decreases its plasticizer compatibility. 

Nitrile rubber is one of the most widely used elastomers and is known for its superior high- and low-temperature performance and its exceptional oil, petrol and solvent resistance. Typical applications include hoses, shoes and flooring. 

Nitrile rubber is generally easy to bond with cyanoacrylates (Table 4.8) and the use of a primer is not normally necessary. Of the other adhesives tested, the two-part acrylics and the UV acrylics showed promising adhesion. 

All shear strengths are given as guidelines only and may vary considerably depending on grade of rubber, fillers, surface finish, etc. 

Aromatic mineral oil plasticizers are highly compatible with nitrile rabber, NBR, naphthenic oils are only partially compatible, and paraffinic mineral oil plasticizers are incompatible with nitrile rabber.Dibenzyl ether, phthalates, and poly glycol ether are the most freqnently nsed plasticizers in NBR. Also, synthetic or fatty acid esters, vulcanized vegetable oils (factice), chloroparaffins, and phosphate plasticizers are infrequent use. 

The following plasticizers have been used in formulations of various nitrile rabber 

Although numerous plasticizers can be used in nitrile rabber applications, DOP is the most frequent choice. 

30 phr fatty acid ester in an article molded from NBR/PVC=80/20  

These data show that low to moderate concentrations are used in articles composed of NBR or having high NBR content whereas blends with PVC utilize higher concentrations of plasticizers. 

NBR is made as an emnlsion with a free radical initiator. Therefore, the mechanisms of polymerisation and branch (gel) formation are very similar to those of E-SBR. Polymers are made with an acrylonitrile (AN) content of, for example, 28, 33 or 40 weight percent, depending upon the required oil resistance. The copolymerisation is described as random but the reactivity ratio is such that it is biased towards an alternating sequence. Becanse of this and because AN is the minor component, it is used up early and polymer formation at a later stage of polymerisation becomes butadiene rich [7]. In order to have a uniform composition among polymer chains, the monomer mixture of the prescribed ratio is metered in with the progress of polymerisation. 

Distribution of the monomer units in the polymer is dictated by the reactivity ratios of the two monomers. In emulsion polymerization, which is the only commercially significant process, reactivity ratios have been reported (4). IfMj = butadiene andM2 = acrylonitrile, then = 0.28, and r2 =0.02 at 5°C. At 50°C, Tj = 0.42 and = 0.04. As would be expected for a combination where = near zero, this monomer pair has a strong tendency toward alternation. The degree of alternation of the two monomers increases as the composition of the polymer approaches the 50/50 molar ratio that alternation dictates (5,6). Another complicating factor in defining chemical stmcture is the fact that butadiene can enter the polymer chains in the cis (1), trans (2), or vinyl(l,2) (3) configuration  

In a copolymer of 33% acrylonitrile, the most common composition for commercial products, the butadiene occurs in the approximate ratio of 90% trans, 8% vinyl, and 2% cis. At higher acrylonitrile content the cis configuration disappears, and at lower levels it increases to about 5% the vinyl configuration remains approximately constant (6,7). Since actual compositions of commercial nitrile mbbers are between 15 and 50% acrylonitrile, they also vary somewhat in sequence distribution and in the content of the three isomeric butadiene configurations. 

This combination of monomers is unique in that the two are very different chemically, and in thek character in a polymer. Polybutadiene homopolymer has a low glass-transition temperature, remaining mbbery as low as —85° C, and is a very nonpolar substance with Htde resistance to hydrocarbon fluids such as oil or gasoline. Polyacrylonitrile, on the other hand, has a glass temperature of about 110°C, and is very polar and resistant to hydrocarbon fluids (see Acrylonitrile polymers). As a result, copolymerization of the two monomers at different ratios provides a wide choice of combinations of properties. In addition to providing the mbbery nature to the copolymer, butadiene also provides residual unsaturation, both in the main chain in the case of 1,4, or in a side chain in the case of 1,2 polymerization. This residual unsaturation is useful as a cure site for vulcanization by sulfur or by peroxides, but is also a weak point for chemical attack, such as oxidation, especially at elevated temperatures. As a result, all commercial NBR products contain small amounts ( 0.5-2.5%) of antioxidant to protect the polymer during its manufacture, storage, and use. 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Nitrile rubbers are produced over a wide range of monomer ratios and molecular weights, so thek physical constants and basic polymer properties also cover a range of values. Some of the more widely used properties are Hsted ki Table 1. 

Major polymer applications gaskets, packing, automotive hoses, seals, industrial hoses, printing rolls, belt covers, footwear, hose jackets, polymer modification, tires 

Important processing methods vulcanization, coating, molding 

Typical fillers calcium carbonate, kaolin, carbon black, talc, zinc oxide, cellulose fibers 

Typical concentration range carbon black - 25-50 wt%, calcium carbonate - 20-50 wt%, kaolin -2-40 wt%, talc 30-40 wt%, cellulose fiber 5-15 wt%, zinc oxide - 2-6 wt% 

Methods of filler pretreatment silane treatment of carbon black during mixing with rubber co-precipitation of cellulose xanthate and NBR latex  

There is no formally accepted method of classifying the different grades of BIMSM. However, an informal classification could be based on the amounts of para-methyl-styrene and the level of bromination that determines the different grades of BIMSM. 

BIMSM may be used instead of halobutyl rubber because it possesses a saturated backbone that imparts a heat aging resistance superior to XIIR. Also, tires can be constructed with a BIMSM-based innerliner that will hold air longer than conventional innerliners based on XIIR. 

Of course, before BIMSM was invented, XIIR (halobutyl rubber) was (and still is) extensively used for tire innerliners. If there were a shortage of BIMSM, the tire industry should be able to return to XIIR-based innerliners. 

Nitrile rubber is a copolymer of acrylonitrile and butadiene (BD) with the standard abbreviation of NBR. NBR is produced by emulsion polymerization, and it dates back to the 1940s. The emulsion polymerization process developed for NBR is somewhat similar to the emulsion process developed for SBR in the same time period. 

As a specialty elastomer, a rather large quantity of nitrile rubber is consumed. About one billion pounds of NBR are manufactured in the world each year, almost 4% of the total production of synthetic elastomers. The reason for its relatively large worldwide use is simply that this polymer is a relatively inexpensive rubber for use 

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Nitrile rubber is also known as nihile-butadiene rubber (NBR), government rubber nitrile (GRN), and Buna N. 

Nitrile rubber (butadiene-acrylonitrile rubber) (also ... 

NBRin pLASTOMERS, SYNTHETIC - NITRILE RUBBER] (Vol 8) -cis-l,4-polyisoprene in pLASTOMERS SYNTHETIC - POLYISOPRENE] (Vol 9)... 

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