Synthetic natural rubbers chlorination

Synthetic rubbers are also used for particular applications. Hypalon (trademark, E. I. du Pont de Nemours) has a good resistance to strongly oxidising chemicals and can be used with nitric acid. It is unsuitable for use with chlorinated solvents. Viton (trademark, E. I. du Pont de Nemours) has a better resistance to solvents, including chlorinated solvents, than other rubbers. Both Hypalon and Viton are expensive, compared with other synthetic, and natural, rubbers. 

Uses Solvent for elastomers, natural rubber, synthetic rubber heat-transfer liquid transformer and hydraulic fluid wash liquor for removing C4 and higher hydrocarbons sniff gas recovery agent in chlorine plants chemical intermediate for fluorinated lubricants and rubber compounds fluid for gyroscopes fumigant for grapes. Not produced commercially in the U.S. 

Synthetic polyisoprenes are superior to natural rubber in terms of consistency of properties. The are also freer of contaminants, and are preferred for applications that require lighter color, for personal care items and for derivatization to chlorinated and cyclized rubber products that are used in the adhesives and coatings industries. 

A general rule is that natural rubbers have better mechanical properties than the synthetic rubbers but the latter have better corrosion resistance. Natural rubbers are superior in certain applications such as with wet chlorine and hydrochloric acid. Natural rubber-based ebonite provides good resistance for such application at higher temperatures up to 90 °C. Corrosion resistance increases with increasing hardness, from a range of 60 on the Shore A scale to 80 on the Shore D scale. Higher proportions of sulfur increase the hardness range in the Shore D scale. 

Synthetic polyisoprene rubbers were found by Harries during 1910 [19], to be successfully hydrochlorinated. These synthetic polyisoprenes resemble natural rubber, which is also a polymer of isoprene which occurs naturally and therefore hydrogen chloride is rapidly added when the rubber is exposed to it thus forming a protective film of chlorinated rubber or hydrogen chloride. Polybutadiene, and butadiene acrylonitrile rubbers do not add hydrogen chloride from hydrochloric acid. 

Some synthetic rubbers are superior to natural rubber in some ways. Neoprene is a synthetic elastomer (an elastic polymer) with properties quite similar to those of natural rubber. The basic structural unit is 2-chloro-l,3-butadiene, commonly called chloroprene, which differs from isoprene in having a chlorine atom rather than a methyl group at carbon 2 of the 1,3-butadiene chain. 

As natural rubber is a product of nature, its properties are determined by the biochemical pathway by which the polymer is synthesized in the plant. In the case of natural rubber the polymerization process cannot be tailored like that of synthetic rubbers. The only option to modify natural rubber is after it has been harvested from the tree. The important modified forms of natural rubber include hydrogenated natural rubber, chlorinated natural rubber, hydro-halogenated natural rubber, cyclized natural rubber, depolymerised liquid natural rubber, resin modified natural rubber, poly(methyl methacrylate) grafted natural rubber, poly(styrene) grafted natural rubber, and epoxidized natural rubber [33,34]. Thermoplastic natural rubber prepared by blending natural rubber and PP is considered as a physically modified form of natural rubber. 

Isohutanol [78-83-1] (2-methyl-l-propanol) is a colorless, neutral liquid with a characteristic odor. It exhibits limited miscibility with water. Most organic solvents are miscible in practically all proportions with isobutanol. Isobutanol readily dissolves most natural and synthetic resins. Waxes dissolve satisfactorily only on heating. Cellulose esters and ethers, natural rubber, neoprene, chlorinated rubber, and polymers such as polystyrene and poly(vinyl chloride) are insoluble in isobutanol. 

Chlorinated rubber resins are produced by the chlorination of synthetic and natural rubbers. The chemical structure shown in Fig. 13.3 is synthesized by the addition of chlorine to unsaturated double bonds until the resin contains 65% chlorine. These resins have similar properties to those of vinyl resins. Plasticizers are added to increase elasticity and resin adhesion. These coatings are resistant to water but have poor resistance to sunhght. 

Orientations in elongated mbbers are sometimes regular to the extent that there is local crystallization of individual chain segments (e.g., in natural rubber). X-ray diffraction patterns of such samples are very similar to those obtained from stretched fibers. The following synthetic polymers are of technical relevance as mbbers poly(acrylic ester)s, polybutadienes, polyisoprenes, polychloroprenes, butadiene/styrene copolymers, styrene/butadiene/styrene tri-block-copolymers (also hydrogenated), butadiene/acrylonitrile copolymers (also hydrogenated), ethylene/propylene co- and terpolymers (with non-conjugated dienes (e.g., ethylidene norbomene)), ethylene/vinyl acetate copolymers, ethyl-ene/methacrylic acid copolymers (ionomers), polyisobutylene (and copolymers with isoprene), chlorinated polyethylenes, chlorosulfonated polyethylenes, polyurethanes, silicones, poly(fluoro alkylene)s, poly(alkylene sulfide)s. 

Semi-synthetic polymers Chemically modifled natural polymers are classifled as semi-synthetic polymers. Some examples are epoxidised natural rubber (ENR), chlorinated natural rubber (Chlororub), nitrocellulose, carboxy methyl cellulose (CMC) and cellulose acetate. 

For metal adhesion, polyisocyanates are best mixed into a solution of a synthetic or chlorinated rubber. Table 8.3 compares the adhesion of natural rubber tyre tread to mild steel using a polyisocyanate priming cement with that obtained using a chlorinated rubber cement. PVC also adheres well to most substrates treated with diisocyanate adhesion primers. 

Natural rubber does not have as satisfactory a resistance to fuels and vegetable and animal oils as elastomeric thermoplastics and synthetic rubbers. Natural rubber has good resistance to acids and alkalis. It is soluble in aliphatic, aromatic, and chlorinated solvents, but natural rubber does not dissolve easily because of its high molecular weight. Synthetic rubbers have better aging properties. Synthetic rubbers will harden over time, whereas natural rubbers will soften over time. 

Elastomers can be divided into two general categories, natural rubber and synthetic rubbers. Synthetic elastomers in turn are either termed general purpose rubbers (GPR) or special purpose rubbers. Natural rubber is generally obtained from southeast Asia or Africa. Synthetic rubbers are produced from monomers obtained from the cracking and refining of petroleum. The most common monomers are styrene, butadiene, isoprene, isobutylene, ethylene, propylene, and acrylonitrile. There are monomers for specialty elastomers which include acrylics, chlorosulfonated polyethylene, chlorinated polyethylene, epichlorohy-drin, ethylene-acrylic, ethylene-octene rubber, ethylene-propylene rubber, flu-oroelastomers, polynorbornene, polysulfides, sihcone rubber, thermoplastic elastomers, urethanes, and ethylene-vinyl acetate. 

Natural rubber/chlorosulfonated polyethylene rubber blends also exhibited immiscibility. Chlorosulfonated polyethylene rubber is the synthetic rubber used for applications in electric cables, hoses for liquid chemicals, waterproof cloths, floor tiles, and oil-resistant seals. It is chosen to blend with natural rubber to improve the resistance of natural rubber to ozone, oil, heat, flame and non-polar chemicals. This is due to the effect of the polarity of the chlorine groups in the chlorosulfonated polyethylene rubber. The tensile strength, elongation at break, and tear strength of these blends decreased with the increasing chlorosulfonated polyethylene rubber contents. In addition, the compatible natural rubber/chlorosulfonated polyethylene rubber blends were improved by adding the epoxidized natural rubber (Epoxyprene 25) as a... 

Now the world elastomerie market eonsists of the natural rubber (NR)-40% and synthetic rubbers-60%. According to forecasts of experts the tendency of increase in a share of NR is observed. It is supposed that by 2015-2020 its share will make 50%. For the purpose of expansion of a scope of natural rubber manufacturing of NR with the content of chlorine from 0.5 to 15% is of interest since it is known that such content of halogen doesn t worsen flexural properties of rubber. 

Binders of paints are normally vegetable oils, e.g., - linseed, dehydrated - castor, - soybean, ->tung and - oiticica oils as such (-xlrying oils) or in modified form (->alkyd resins). They are often combined with numerous synthetic resins. Natural resins (- resins, natural) are also applied in special applications where their high price is acceptable. Decorative - casein paints for plaster walls have lost importance. Chlorinated and cyclized - rubber are also in use (swimming pool coatings). 

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