Rubber using alternative compounds

Solution adhesives consist of solid rubber dissolved in a solvent such as toluene, naphtha, or trichloroethane. The solvent used will depend on the drying and flammability considerations in the application. Milled raw rubber can be shredded and agitated in the solvent until a clear solution is obtained. Other components are added at this stage and mixed uniformly. Alternatively, the solid rubber can be compounded with other components and the mix dissolved in the solvent. 

Alpha brass coating is used on steel to improve the adhesion of rubber to the steel. It reacts both with sulfur, producing zinc sulfide, and with the rubber. Organic cobalt compounds catalyze the reaction and necessitate high sulfur dosing. Resor-cin-formaldehyde-silica systems are an alternative. The brass layer is not needed if isocyanates are used as the adhesion promoter, although solvents are then required. Aqueous dispersions of chlorinated or sulfochlorinated polyethylenes cross-linked with polynitroso compounds offer an alternative [32]. 

Rubbers. Plasticizers have been used in mbber processing and formulations for many years (8), although phthaHc and adipic esters have found Htde use since cheaper alternatives, eg, heavy petroleum oils, coal tars, and other predominandy hydrocarbon products, are available for many types of mbber. Esters, eg, DOA, DOP, and DOS, can be used with latex mbber to produce large reductions in T. It has been noted (9) that the more polar elastomers such as nitrile mbber and chloroprene are insufficiendy compatible with hydrocarbons and requite a more specialized type of plasticizer, eg, a phthalate or adipate ester. Approximately 50% of nitrile mbber used in Western Europe is plasticized at 10—15 phr (a total of 5000—6000 t/yr), and 25% of chloroprene at ca 10 phr (ca 2000 t/yr) is plasticized. Usage in other elastomers is very low although may increase due to toxicological concerns over polynuclear aromatic compounds (9). 

Where resorcinol adhesives are not suitable, resins can be prepared from modified resorcinol [128], Characteristic of these types of resins arc those used for tyre cord adhesives, in which a pure resorcinol-formaldehyde resin is used, or alternatively, alkyl resorcinol or oil-soluble resins suitable for rubber compounding are obtained by prereaction of resorcinol with fatty acids in the presence of sulfuric acid at high temperature followed by reaction with formaldehyde. Worldwide more than 90% of resorcinol adhesives are used as cold-setting wood adhesives. The other most notable application is as tyre cord adhesives, which constitutes less than 5% of the total use. 

Alternative approaches consist in heat extraction by means of thermal analysis, thermal volatilisation and (laser) desorption techniques, or pyrolysis. In most cases mass spectrometric detection modes are used. Early MS work has focused on thermal desorption of the additives from the bulk polymer, followed by electron impact ionisation (El) [98,100], Cl [100,107] and field ionisation (FI) [100]. These methods are limited in that the polymer additives must be both stable and volatile at the higher temperatures, which is not always the case since many additives are thermally labile. More recently, soft ionisation methods have been applied to the analysis of additives from bulk polymeric material. These ionisation methods include FAB [100] and LD [97,108], which may provide qualitative information with minimal sample pretreatment. A comparison with FAB [97] has shown that LD Fourier transform ion cyclotron resonance (LD-FTTCR) is superior for polymer additive identification by giving less molecular ion fragmentation. While PyGC-MS is a much-used tool for the analysis of rubber compounds (both for the characterisation of the polymer and additives), as shown in Section 2.2, its usefulness for the in situ in-polymer additive analysis is equally acknowledged. 

Recently, Lattimer et al. [22,95] advocated the use of mass spectrometry for direct analysis of nonvolatile compounding agents in polymer matrices as an alternative to extraction procedures. FAB-MS was thus applied as a means for surface desorption/ionisation of vulcanisates. FAB is often not as effective as other ionisation methods (El, Cl, FI, FD), and FAB-MS is not considered particularly useful for extracted rubber additives analysis compared to other methods that are available [36], The effectiveness of the FAB technique has been demonstrated for the analysis of a live-component additive mixture [96]. 

Many rubber compounds have a tendency to stick in the mould cavity after vulcanisation and require some type of mould release agent. The substances used are surface-active materials such as detergents, soaps, wetting agents, silicone emulsions, aqueous dispersions of talc, mica and fatty acids, applied by spray or brush. Alternatively, dry types based on polytetrafluoroethylene or polyethylene, usually carried in a solvent, can be aerosol applied. An alternative is the addition of an incompatible material to the rubber compound which will bleed to the rubber surface during vulcanisation. 

Many types, such as pine tar, are distillates from pine tree farming in Scandinavia. Pine tar is a dark viscous liquid used at about 3-7 phr dosage level. It does not affect hardness levels to the same extent as the equal amount of petroleum oil. From the nature of its sources it can vary in acidity and thus has tended to be replaced by cheaper more predictable alternatives which are available from the residues of petroleum distillation. Tack improvement of rubber compounds is derived from the presence of colophony resin derivatives. 

An alternative method to that of using a spreading machine or a calender for the initial preparation of fabrics for application of rubber (for composite product assembly) can be by the use of dip coaters. Application of rubber compound by this method ensures a better penetration of the fabric interstices than can be achieved by conventional frictioning techniques using calenders. More delicate fabrics which would not be strong enough for calender application can also be treated with rubber by this technique. 

Vulcanization by the traditional curing methods utilized in the rubber industry is based on sulfur or sulphur-containing compounds and is also the most widely applied technique for curing liquid rubbers containing macromolecules with double bonds. Chinons, peroxides, phenol formaldehyde resins, and other compounds are often used for curing liquid rubbers as an alternative sulfur vulcanization. 

Latexes find wide use in industrial and consumer applications, particularly in the areas of synthetic rubber and coatings. Latex paints, for example, provide excellent alternatives to older, oil-based (alkyd) paints, which release substantial quantities of organic solvents to the atmosphere as they dry. Because volatile organic compounds (VOCs) are a factor in depleting the ozone layer, many industrial nations are striving to develop products... 

A major use of selenium has been in photoelectric devices. Its conductivity increases with illumination, and this provides a way of measuring light intensity or operating electrical switches. However, newer types of photocells are available that are made of other materials (such as cadmium sulfide). A second and more important use of selenium is in rectifiers to convert alternating current to direct current. Also, some pigments contain selenium and tellurium compounds, and both elements have been used in vulcanization of rubber. Selenium compounds have been used in dandruff treatment shampoos, and low levels of selenium may be necessary for dietary balance. Some studies have shown that persons whose diets are deficient in selenium may have a higher incidence of heart attacks. 

Another solvent widely studied and known to be the cause of serious effects is benzene, which is found in petrol and is also used in the shoemaking industry. Extensive studies have been carried out in Turkey, for example, where it has been used in shoemaking. The use of benzene has now been phased out in many countries but it continues to be used in others. It has been extensively used as a starting point for the production of other chemicals and as a solvent in the manufacture of rubber, paint, and plastics, and in printing. It has been added to petrol as an alternative anti-knock additive to lead compounds. 

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