Subject rubber molecule

The prevulcanization of natural rubber in latex form has also been a subject of much investigation. The cross-linking mechanism is not yet fully understood, but the water apparently plays a major role in it. Irradiation results in the cross-linking of the rubber molecules and in coarsening of the latex particles. A process of cross-linking of natural rubber latex has been developed to the point that it can be used for an industrial-scale application. The irradiation is performed in aqueous media by electron beam without a prorad (sensitizer) at a dose of 200 kGy (20 Mrad) or in the presence of n-butyl acrylate at considerably lower doses, typically 15 kGy. The cross-linked film exhibits physical properties comparable to those obtained from sulfur cured (vulcanized) film. As an alternative, the addition of a variety of chloroal-kanes makes it possible to achieve a maximum tensile strength with radiation doses of less than 5 Mrad (50 kGy). ... 

Reviews on the subject of brass-plated steel cord-natural rubber adhesion have been written by van Ooij who has done much of the work in the field. Van Ooij [46] has given a model for rubber-brass adhesion, in which a copper sulfide layer forms on the brass before the onset of crosslink formation. The thin film of copper sulfide has good adhesion and cohesion. In addition, the film is so porous that rubber molecules can become entangled with it. It is not required that the film forms simultaneously with the formation of crosslinks during vulcanization but, rather, it is required that the copper sulfide film be completely formed before crosshnking starts. Indeed, adhesion between brass-plated steel and natural rubber can frequently be improved by the use of the retarder, CTP [4] or by using a more delayed action accelerator such as N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) [47]. 

The non-rubber components not only have a biological function but also influence both the methods of coagulation to form dry rubber and also the techniques of latex technology. These matters have been discussed at length elsewhere (e.g. Blackley, 1966) and do not form part of the subject matter of this book. Where, however, the nonrubber constituents can affect the reactivity of the rubber molecule, this will be considered at the appropriate point. 

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.)... 

I, too, was caught up in the wave of enthusiasm for this new science which had the lofty goal of relating the properties of materials to their molecular structure, and, in the end, to "tailor-making molecules for specific properties. Since one of the big developments at that time was the newly-started synthetic rubber programs of the American and Canadian governments, I chose the topic of the emulsion copolymerization of butadiene-styrene as the subject of my doctoral dissertation. 

Since the pioneering work of Kuhn, the solvent freezing point depression observed in swollen crosslinked rubbers has been the subject of many works. The observed AT can be attributed to two origins. A sizable AT is accounted for by the lowering of the thermodynamic potential of solvent molecules in a polymer solution derived from the Flory theory, and the additional AT observed for crosslinked rubbers has been attributed to confinement effects, fn 1991, Jackson and McKenna [32] studied... 

Rubber and rubber-like materials are systems of molecules—monomers or mers—that are subject to two types of interactions. The first type are covalent interactions that tie monomers into long chains, which are typically 100 or more mers long. The second type are nonbonded interactions, which occur between pairs of mers that are not covalently bonded to each other. We are concerned here with an examination of how nonbonded interactions are generally treated in theoretical studies of rubber elasticity and with the limitations of this approach. 

The synthesis of rubber on a commercial scale has been the subject of much investigation. The chief difficulty has been to prepare isoprene from a substance that can be obtained in large quantities at a low cost. Turpentine yields but a small percentage of isoprene when heated and cannot serve, therefore, as the source of the hydrocarbon. The amyl alcohol which is obtained from fusel oil (76) can be converted into a dichloro-pentane of the structure (CH3)2CC1CH2CH2C1, which, when passed over lime at a high temperature, yields isoprene as the result of the loss of two molecules of hydrochloric acid —... 

Microbial degradation of synthetic rubbers will be a subject of fiirther study. A rubber product is made from a number of complex ingredients, and smaller molecules in a synthetic polymer (e.g., stearate, process oils, and waxes in vulcanized synthetic rubber) may be decomposed by microorganisms. A clear distinction must be made between the superficial growth of microorganisms on non-rubber constituents in a synthetic polymmrs and the biodegradation of the rubber hydrocarbon [23]. 

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