Rubber Chlorinated natural

Many other polymers compete with cellophane such as polyethylene which is extruded as a tough film or in greater thickness as a nonbreakable bottles. Vinyl products used in films are polystyrene, polyesters, and nylon. A chemical derivative from nature rubber, chlorinated rubber, gives films of extraordinary stretch ability. 

Copolymer of styrene and acrylonitrile Copolymer of styrene and butadiene Natural rubber Chlorinated polyethylene Chlorosulfonated polyethylene Polyamides Polyesters Polyurethanes Polysulfones Polyacrylates Polyacrylamides Polydimethylsiloxane Copolymer of vinylidene fluoride and hexafluoropropylene... 

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. 

In the case of the system natural rubber-chlorine the reaction is complex. Fully chlorinated natural rubber contains about 65% chlorine compared with the 51% that would be obtained if the only reaction were one of addition. Hence at some stage some substitution is necessary. This is not altogether surprising since although linear alkenes give predominantly addition products (A), alkenes branched at the double bond give predominantly allylic substitution, for example as with 2-methyl-2-butene (B). 

Recommended for polymers natural rubber chlorinated, SB rubbers, EPDM ... 

The close structural similarities between polychloroprene and the natural rubber molecule will be noted. However, whilst the methyl group activates the double bond in the polyisoprene molecule the chlorine atom has the opposite effect in polychloroprene. Thus the polymer is less liable to oxygen and ozone attack. At the same time the a-methylene groups are also deactivated so that accelerated sulphur vulcanisation is not a feasible proposition and alternative curing systems, often involving the pendant vinyl groups arising from 1,2-polymerisation modes, are necessary. 

It was found that the amount of chlorine that could be removed (84-87%) was in close agreement to that predicted by Flory on statistical grounds for structure Figure 12.10(a). It is of interest to note that similar statistical calculations are of relevance in the cyclisation of natural rubber and in the formation of the poly(vinyl acetals) and ketals from poly(vinyl alcohol). Since the classical work of Marvel it has been shown by diverse techniques that head-to-tail structures are almost invariably formed in addition polymerisations. 

Treatment of natural rubber with chlorine gives a product, chlorinated rubber, with a maximum chlorine content of 65% corresponding to the empirical formula C10H11CI7. Such a compound corresponds neither to a hypothetical simple addition to the double bond (Figure 30.6 (I)) nor to a product with a-methylenic substitution in addition (II). 

As with c -polyisoprene, the gutta molecule may be hydrogenated, hydro-chlorinated and vulcanised with sulphur. Ozone will cause rapid degradation. It is also seriously affected by both air (oxygen) and light and is therefore stored under water. Antioxidants such as those used in natural rubber retard oxidative deterioration. If the material is subjected to heat and mechanical working when dry, there is additional deterioration so that it is important to maintain a minimum moisture content of 1%. (It is not usual to vulcanise the polymer.)... 

Fig. 6. Transmission IR spectra of chlorinated natural rubber, solvent cast from xylene, (a) Before heating, and (b) after heating at 170°C for 30 min [62].

In all the compositions, the DCP-cured blends showed better properties than the corresponding unvulcanized samples. Choudhary et al. [30] further demonstrated the use of EPDM, chlorinated PE, chlorosulfo-nated PE, maleic anhydride modified polyethylene, and blends of epoxidized natural rubber-sulfonated EPDM as compatibilizers in NR-LDPE (low-density PE) blends. 

When two polymers interact or react with each other, they are likely to provide a compatible, even a miscible, blend. Epoxidized natural rubber (ENR) interacts with chloro-sulfonated polyethylene (Hypalon) and polyvinyl chloride (PVC) forming partially miscible and miscible blends, respectively, due to the reaction between chlorosulfonic acid group and chlorine with epoxy group of ENR. Chiu et al. have studied the blends of chlorinated polyethylene (CR) with ENR at blend ratios of 75 25, 50 50, and 25 75, as well as pure rubbers using sulfur (Sg), 2-mercapto-benzothiazole, and 2-benzothiazole disulfide as vulcanizing agents [32]. They have studied Mooney viscosity, scorch... 

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. 

Chlorination of natural rubber, involving both addition and substitution (with some cyclization), yields a product with improved chemical and corrosion resistance. Chlorination of polyethylene in the presence of sulfur dioxide results in substituting both chloride and sulfonyl chloride groups into the polymer. A commercially useful material is one which contains about 12 chlorides and one sulfonyl chloride per 40-45 repeating units. This extensive substitution converts the polyethylene, a plastic, into an elastomer by destroying crystallinity. 

The chlorine atom also confers an increased level of resistance to oils, so that the oil resistance of polychloroprene is roughly intermediate between natural rubber and nitrile rubber, and is often sufficient for many applications. Polychloroprene is also self-extinguishing in flame tests. 

Organic solvents are used to make the rubber dough. Natural rubbers are soluble in rubber solvent (a specific petroleum fraction) or naphtha. Nitrile and polychloroprene compounds require aromatic or chlorinated hydrocarbons as solvents. Often mixtures of solvents are used. 

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. 

The chlorination of low molecular weight natural rubber from Guayule (Parthenium Argentatum Grey) has been accomplished. The structure of the chlorinated product is consistent with that of chlorinated Hevea rubber. The use of Azo-bis-isobutyronitrile was as a catalyst resulted in increased chlorine content with a concomitant reduction in molecular weight, thereby allowing the preparation of lower viscosity grades of chlorinated rubber. 

Chlorination and hydrochlorination of natural rubber are industrial processes carried out on solutions of uncrosslinked rubber in chlorinated solvents [Allen, 1972 Ceresa, 1978 ... 

Chlorination of natural rubber (NR) is carried out with chlorine in carbon tetrachloride solution at 60-90°C to yield a chlorinated rubber containing about 65% chlorine, which corresponds to 3.5 chlorine atoms per repeat unit. The process is complex and includes chlorine addition to the double bond, substitution at allylic positions, and cyclization. Chlorinated rubber has high moisture resistance and is resistant to most aqueous reagents (including mineral acids and bases). It is used in chemical- and corrosion-resistant paints, printing inks, and textile coatings. Bromination of butyl rubber is also practiced [Parent et al., 2002]. 

Graft polymers were obtained by mastication of a 60/40 blend of natural rubber and chlorosulphonated polyethylene (/). From 10-55% natural rubber was obtained as side chains. Grafting presumably proceeds by transfer of chlorine atoms to the rubber radicals to give grafting sites for combination with rubber radicals. Soluble linear polymers were also obtained by mastication for 50-180 min under nitrogen for a blend 50/50 of natural rubber and a polyurethane rubber (Vulcaprene A) (/). 

Polyethylene Chlorinated polyethylene Chlorosulfonated polyethylene Natural rubber... 

Now the lone chlorine atom has found itself isolated since the zinc only extracts two adjacent chlorines. Such a result is called reactant isolation, and one wishes to predict the chlorine concentration left in the polymer as a function of time. It was shown by Flory76 that the fraction of chlorines unreacted should approach e 2, and this was used in fact by Marvel77 to determine the structure of polyvinyl chloride. Other examples are the condensation of the polymer of methyl vinyl ketone76 and the vulcanization of natural rubber.78 The vulcanization studies supply another example where a molecular structure was determined by a kinetic scheme. The complete time dependence of the process was recently derived by Cohen and Reiss24 using a novel method of multiplets, which will now be outlined. 

The resilience of gum neoprene vulcanizates is little lower than natural rubber but it decreases with increased filler incorporation. Therefore, the resilience of most practical neoprene compounds is higher than that of natural rubber with comparable volume loading. Because of the presence of chlorine in the neoprene molecule, products made from neoprene resist combustion to a greater degree than products made from non-halogen bearing rubbers. This means neoprene can be compounded to meet the flammability requirements of the Mine Safety and Health Administration (MSHA) USA or similar requirements as might be stipulated by any other countries,... 

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