Of natural and synthetic rubbers

Table 11.14 Production of natural and synthetic rubbers 1983-1992 ( 000 tonnes) (International Institute of Synthetic Rubber Producers)...

H. L. Fischer, Chemistry of Natural and Synthetic Rubbers, Reinhold, New York (1957). 

In this part, we will discuss AFM images and nanomechanical data obtained in smdies of natural and synthetic rubbers, thermoplastic elastomers (TPE), and their vulcanized counterparts— thermoplastic vulcanizates (TPV). 

Trade Names of Natural and Synthetic Rubber Symbol... 

The reactions of intramolecular isomerization occur and are important in the oxidation of natural and synthetic rubbers. The peroxyl radical addition to the double bond occurs very rapidly. For example, the peroxyl radical adds to the double bond of 2-methylpropene by 25 times more rapidly than abstraction of hydrogen atom from this hydrocarbon (see Chapter 4). Therefore, the oxidation of polymers having double bonds proceeds as a chain process with parallel reactions of P02 with double and C—H bonds including the intramolecular isomerization of the type [12] ... 

Fluorination of polyethylene surfaces leads to an increase in the surface energy, some degree of cross-linking and a reduction of the free volume of the polymer. All of these effects impart on the surface of the polymer a barrier that is very impermeable to hydrocarbon solvents. A blow-moulding process, in which a low concentration of fluorine in nitrogen is used as the blow-moulding gas, is used for the production of plastic fuel tanks for the automotive industry (Airopak , Air Products) [51]. Post-treatment of hydrocarbon surfaces with fluorine is an alternative technology and techniques for the surface fluorination of natural and synthetic rubber have been described [52]. 

Table 3.2 Coefficient of vulcanization of natural and synthetic rubbers...

The serious development of synthetic rubbers commenced in the late 1930s and early 194(ls. accelerated by a cutoff of supplies of natural rubber because of political turmoil and war. Synlhetic rubbers fall into two major classifications (1) general-purpose rubbers, the major volume of which is nevertheless used for tire production and (2) specialty rubbers that essentially find little use in (ires, hut that are important for a number of other categories. Synthetic rubbers have not replaced natural rubber for numerous uses. For large, heavy-duty truck and bus tires, natural rubber tends to mn considerably cooler and wears better than a blend of natural and synthetic rubbers. On the other hand, a tire (read made of a blend of styrene-butadiene (SBR) and butadiene rubber (polybutadiene) wears longer than natural rubber in conventional automobile, usage, where lower temperatures can be maintained. 

Sulfur and selenium react with many organic molecules. For example, saturated hydrocarbons are dehydrogenated. The reaction of sulfur with alkenes and other unsaturated hydrocarbons is of enormous technical importance hot sulfurization results in the vulcanization (formation of S bridges between carbon chains) of natural and synthetic rubbers. 

The engineering property that is of interest for most of these applications, the modulus of elasticity, is the ratio of unit stress to corresponding unit strain in tension, compression, or shear. For rigid engineering materials, unique values are characteristic over the useful stress and temperature ranges of the material. This is not true of natural and synthetic rubbers. In particular, for sinusoidal deformations at small strains under essentially isothermal conditions, elastomers approximate a linear viscoelastic... 

In the above experiment, we note that a relatively smaller fraction (40-60%) of the total moisture associated with bromobutyl stoppers was extractable while about 75% of the total moisture was extracted from the stopper containing a blend of natural and synthetic rubbers. We postulate that stoppers made from synthetic elastomers have a higher amount of bound water than those made from a blend of natural and synthetic rubbers. The natural rubber component in the blend presumably imbibes more moisture that is relatively free and consequently more easily extractable upon drying. Moreover, bound water is less likely to effuse into the lyophilized product than free water. 

Copper Inhibitor 50 [Du Pont]. TMfor 50% disalicylalpropylenediamine and 50% aromatic solvent. Used to prevent catalytic action of copper on oxidation of natural and synthetic rubbers. 

Use To accelerate vulcanization of natural and synthetic rubber and latex compounds. 

International Rubber Study Group, Brettenham House, 5-6, Lancaster Place, Strand, London, Rubber Statistical Bulletin, monthly, 1946-. U. S. and world historical data on production, consumption, and supply of natural and synthetic rubber. 

Rubber Manufacturers Association, 444 Madison Ave., New York, U.S,A. Rubber Statistics, monthly with annual summaries. Production, consumption, and supply of natural and synthetic rubber and shipments of rubber tires and casings. 

Polymeric sulfur is produced commercially as insoluble sulfur (IS) and is used in the rubber industry [56] for the vulcanization of natural and synthetic rubbers since it avoids the blooming out of sulfur from the rubber mixture as is observed if Ss is used. The polymeric sulfur (trade-name Crys-tex [57]) is produced by quenching hot sulfur vapor in liquid carbon disulfide under pressure, followed by stabilization of the polymer (against spontaneous depolymerization), filtration, and drying in nitrogen gas. Common stabilizers [58] are certain olefins R2C=CH2 like a-methylstyrene which obviously react with the chain-ends (probably -SH) of the sulfur polymer and in this way hinder the formation of rings by a tail-bites-head reaction. In this industrial process the polymer forms from reactive small sulfur molecules present in sulfur vapor [59] which are unstable at ambient temperatures and react to a mixture of Ss and on quenching. 

Based on wide experience, The Plant Lining Group of the former Federation of British Rubber and Allied Manufacturers (FBRAM) had prepared a code of practice to be followed by industry to ensure satisfactory standards of lining materials, polymers and workmanship [9]. The leading members of this Federation were BTR Industries Ltd., Dunlop Rubber Ltd., Dexine Rubber Ltd., Nordac Ltd., and Redfern s Bredbury Ltd. This code sets out the advice of the Plant Lining Group for vessels to be lined with compounds of natural and synthetic rubbers ... 

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