Saturated hydrocarbon rubber

Manganese, copper, iron, cobalt and nickel ions can all initiate oxidation. Untinned copper wire can have a catastrophic effect on natural rubber compounds with which it comes into contact. Inert fillers for use in rubbers are usually tested for traces of such metal ions, particularly copper and manganese. The problem is perhaps less serious in saturated hydrocarbon polymers but still exists. 

The effect of ozone is complicated in so far as its effect is largely at or near the surface and is of greatest consequence in lightly stressed rubbers. Cracks are formed with an axis perpendicular to the applied stress and the number of cracks increases with the extent of stress. The greatest effect occurs when there are only a few cracks which grow in size without the interference of neighbouring cracks and this may lead to catastrophic failure. Under static conditions of service the use of hydrocarbon waxes which bloom to the surface because of their crystalline nature give some protection but where dynamic conditions are encountered the saturated hydrocarbon waxes are usually used in conjunction with an antiozonant. To date the most effective of these are secondary alkyl-aryl-p-phenylenediamines such as /V-isopropyl-jV-phenyl-p-phenylenediamine (IPPD). 

Krishnamoorti, R. in Miscibility of Blends of Saturated Hydrocarbon Elastomers. Rubber Division, Proceedings of the American Chemical Society, Nashville, TN, Sept. 29-Oct. 2, 1998, Paper No. 33, 1-14. 

Saturable dye absorber, 14 677 Saturated aqueous salt solution, 9 34 Saturated calomel electrode (SCE), 9 571 Saturated fatty acids, 10 829, 830 Saturated hydrocarbons adsorbent affinity, 1 674 adsorption by zeolites, 1 624 fluorine reactivity with, 11 831 isomerization of, 12 172—173 Saturated polyester resins, based on trimethylpentanediol, 12 673 Saturated polyesters, 10 7 Saturated synthetic rubber, 10 705 Saturation and coating processes, 10 12-13 Saturation bonding, 17 509-510 Saturation color, 19 262 Saturation concentration, 15 677 Saturation index... 

This same possibility exists with rubber closures, though not to the same degree. If the compounds sought in the sample are clearly not oil soluble, then lubricated stopcocks can be used. Olefins and aromatic compounds are generally more readily soluble and more easily lost under these circumstances than are saturated hydrocarbons or oxygenated compounds. 

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. 

Thus, ethylene, obtained from petroleum or natural gas hydrocarbons, is also a mon< Qer for the direct formation of a plastic such as polyethylene, or of an elastomer such as Ethylene-Prop ene-Termonomer (EPT) rubber. Acetic add, produced in several stq> from acetylene or ethylene, is also produced directly by the oxidation of a mixture of saturated hydrocarbons (naphtha). 

Rubbers are plasticized with petroleum oils, before vulcanization, to improve processability and adhesion of rubber layers to each other and to reduce the cost and increase the softness of the final product. Large quantities of these oil-extended rubbers are used in tire compounds and related products. The oil content is frequently about 50 wt% of the styrene-butadiene rubber. The chemical composition of the extender oil is important. Saturated hydrocarbons have limited compatibility with most rubbers and may sweat-out. Aromatic oils are more compatible and unsaturated straight chain and cyclic compounds are intermediate in solvent power. 

Halogenation of saturated hydrocarbon polymers can hardly be controlled and is frequently assodated with chain degradation phenomena In contrast, the presence of randomly distributed olefinic unsaturations, allows selective halogenation reactions by adopting appropriate conditions. For instance, butyl rubber can be chiorinated or brominated in allylic positions and chloro-butyl or bromo-butyl rubber results The latter polymers are very interesting since they exhibit fast curing rates when sulfur and ZnO are introduced in the formulations. 

Secondary aromatic amines are effective antioxidants in the protection of saturated hydrocarbon polymers (polyolefins) against autooxidation. Their role in the stabilization of unsaturated hydrocarbon polymers (rubbers) is more complex depending on their structure, they impart protection against autooxidation, metal catalyzed oxidation, flex-cracking, and ozonation. The understanding of antioxidant, antiflex-cracking and antiozonant processes together with involved mechanistic relations are of both scientific and economic interest. 

Saturated hydrocarbon polymers are also crosslinked by the action of organic peroxides, though branching reduces the efficiency. Polyethylene is crosslinked by dicumyl peroxide at an efficiency of about 1.0, saturated EPR gives an efficiency of about 0.4, while butyl rubber cannot be cured at all. For polyethylene, the reaction scheme is similar to that of the unsaturated elastomers. 

Saturated hydrocarbons are dehydrogenated when heated with sulfur, and further reaction with alkenes occurs. An application of this reaction is in the vulcanization of rubber, in which soft rubber is toughened by cross-linking of the poly-isoprene chains, making it suitable for use in, for example, t)Tes. The reactions of sulfur with CO or [CN] )deld OCS (16.13) or the thiocyanate ion (16.14), while treatment with sulfites gives thiosulfates (equation 16.21). 

Ellul [27] subjected EPDM/polypropylene and natural rubber/polypropylene blends to various halogenation treatments, namely fluorine/carbon dioxide, sodium hypochlorite/ acetic acid and bromine water. With the natural rubber blend, there was a substantial uptake of fluorine, chlorine and bromine in the surface regions as indicated by energy dispersive X-ray analysis and with all three pre-treatments the adhesion to an acrylic tape was greatly enhanced. In contrast, with the EPDM blend, fluorine was the only reagent which reacted with the rubbers and only this treatment resulted in a significant increase in adhesion to the acrylic tape. The above results can be explained in terms of the different concentrations of carbon-carbon double bonds in the two blends. Substantial incorporation of chlorine and bromine could occur with the natural rubber-polypropylene blend but not with the EPDM blend. However, fluorine gas will react readily with saturated hydrocarbons [28,29] and therefore the incorporation of fluorine into the EPDM blend is not surprising. 

There are many formal resemblances between the oxidation of saturated hydrocarbons including polymers such as polyethylene, diene rubbers such as natural rubber and low molecular weight analogues such as squalene. The principal features common to these systems are as follows ... 

The chemical reactivity of a polymer is, in large measure, the reactivity of its molecular components. Natural rubber, for example, undergoes deterioration when ozone attacks the double bonds of the polymer chain a saturated hydrocarbon chain, like polyethylene, is resistant to such attack. Celluloses offer their hydroxyl groups to a variety of reagents and thus make it possible to modify properties. Reaction with nitric acid produces NITROCELLULOSE, from which propellant (guncotton) and plastic (Celluloid) products are formed. Reaction with acetic acid produces cellulose acetate, which can be fabricated into films, sheets, and other useful forms ... 

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