Uses of Elastomers

Elastomers are used in a wide range of industrial, transportation, domestic, construction and aerospace end-applications. The major consumer of both natural and synthetic rubber is the tyre industry. Five types natural rubber (NR), styrene butadiene rubber (SBR), polybutadiene, polyisoprene and the butyl (and halobutyl) rubbers are used in massive quantities around the world. Smaller applications for rubbers include conveyor belting, footwear, pharmaceutical closures, plant lining, hoses, extruded goods, flooring, power cables, gaskets and seals, and many, many other applications. 

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Similar to these hard plastic applications, the use of elastomers has a number of advantages over silicon as biosensor housing material. Besides fabrication cost and brittleness as described above (PDMS is about 50 times less expensive than siUcon on a per volume basis), moving parts are extremely difficult to make in the stiff silicon material without increasing the overall size significantly. Also, valves, which will be discussed in more detail below, need a soft material as valve seat to close completely (thus, elastomers have to be... 

Chief among the synthetic elastomers is SBR, a copolymer of butadiene (75%) and styrene (25%) produced under free-radical conditions it competes with natural rubber in the main use of elastomers, the making of automobile tires. All-cis polybutadiene and polyisoprene can be made by Ziegler-Natta polymerization. 

There are several underwater uses of elastomers In which they are subjected to mechanical stresses. This can be static wherein the rubber Is stretched and held at a certain elongation while In service. Or It can be dynamic wherein a seal, for example. Is subjected to mechanical agitation, vibration, etc. 

A principal use of elastomer blends is in sidewalls of automotive tires. The reduction of hysteresis losses ( rolling resistance ) is a principal design target. 

The formulation and use of elastomer blends is technologically demanding. Miscible blends are widely used but usually not recognized since analytical separation of the vulcanized elastomer is experimentally difficult. Immiscible blends require excellent phase dispersion and interfacial adhesion typical of all polymer blends. In addition, they require control of filler distribution and crosslink density in each component. This is due to the need for mechanical integrity in vulcanized elastomers. 

Finally, the use of elastomer bitumen increases Marshall stability, but it may also increase the Marshall flow above the limiting value. This increase cannot be taken as a drawback, since the nature of the test is such that it does not take into account the recovered (elastic) deformation during unloading and in effect does not simulate dynamic loading. Regarding the optimum binder content of the asphalt with or without modified bitumen, it was found that, when asphalt concrete mixtures were tested, the optimum binder content as determined by the Marshall procedure was not significantly different (Nikolaides and Tsochos 1992). 

The term antiozonant denotes any additive that protects rubber against ozone deterioration. Most frequently, the protective effect results from a reaction with ozone, in which case the term used is chemical antiozonant. Ozone is generated naturally by electrical discharge and also by solar radiation in the stratosphere. These sources produce ground-level ozone concentrations of 1-5 parts per hundred million (pphm). In urban environments, however, ozone reaches much higher levels, up to 25 (pphm) due to the ultraviolet photolysis of pollutants. Only a few parts per hundred million of ozone in air can cause rubber cracking, which may destroy the usefulness of elastomer products. Some desirable properties of an antiozonant additive are as follows ... 

Successfiil industrial fications have been reported [Groh Van der Werfi 1982], particular in the pressnig of solvmts, which would preclude the use of elastomer belts. Noxious, corrode vapours are handled by closing the entire filter in vapour-ti enclosures. A further important advantage over other SLS systems is the control of cake cracking by minimisation of the area between flooded filtration and wash zones on the belt. 

Blends of elastomers are of technological and commercial importance since they allow the user to access properties of the final blended and vulcanized elastomer that are not accessible from a single, commercially available elastomer alone. These potentially improved properties include chemical, physical, and processing benefits. In reality, all blends show compositionally correlated changes in all of these properties compared to the blend components. The technology of elastomer blends is largely focused on the choice of individual elastomers and the creation of the blends to achieve a set of final properties. This chapter shows some of the instances of the uses of elastomer blends. Empirical guidelines for the creation of novel blends of elastomers is a comparatively more difficult proposition. 

Use of Elastomer Gaskets or Materials of Low Coefficient of Friction. Rubber absorbs motion, thereby avoiding slip at the interface. Polytetra-fluoroethylene (Teflon) has a low coefficient of friction and reduces damage. Because of their relatively poor strength, materials of this kind are expected to be effective only at moderate loads. 

For all practical engineering uses of elastomers we require good flexibility and, therefore, it is essential that we use them only at temperatures which are comfortably above the glass transition. This is generally no problem for natural rubber with a Tg of —70°C, or cis-butadiene rubber with a Tg of — 108°C (—160°F). But many elastomers, especially those which have been designed to be highly heat or oil resistant, have much higher Tgs and this... 

Elastomer epoxies generally contain nitrile rubber as the elastomeric component. This system is also referred to as a modified or toughened epoxy. One of the applications of widest use is in films and tapes. Elastomer epoxies cure at low pressures and low temperatures over a short time interval. This is achieved by adding a catalyst to the adhesive formulation. Bond strengths of elastomer epoxies are lower than those of nylon epoxies. However, the major advantage of elastomer epoxies is their sub-zero peel strengths, which do not decrease as fast as those of nylon epoxies. In addition, the moisture resistance of elastomer epoxies is better than that of nylon epoxies but not as good as that of vinyl-phenolics or nitrile-phenolics. Limitations to the use of elastomer epoxies include poor water immersion resistance and poor properties when exposed to marine conditions. 

A review is presented of the literature describing the surface discolouration problem of tyre black sidewalls and approaches to the formulation of a black sidewall compound to eliminate this surface discolouration upon exposure to ozone. Methods include use of non-staining antiozonants and use of elastomers with saturated backbones such as EPDM, halobutyl rubbers and brominated isobutylene-co-para-methylstyrene. 67 refs. USA... 

This comprehensive article highlights to problems that occur due to failure of pump seals and valve seats and the consequent costs to the plant operators. The article highlights particularly Kalrez perfluoroelastomer from Du Pont, which combines chemical resistance and resilience and so extends the use of elastomers into areas where mbbers had previously failed. The article supplies full details of the material and its properties. 

The most important commercial use of elastomer blends is in the huge tire market. These blends are generally phase separated and represent one of the largest single applications for immiscible or miscible blends. Ckjmpatibilization is achieved via crosslinking reactions across the interface. The use of SBR/PB (polybutadiene) and NR(natural rubber)/PB for tread, NR/SBR/PB and NR/PB for carcass, NR/PB and NR/SBR for sidewall and NR/SBR/PIB... 

Due to the increased use of elastomer adhesives, there has been a strong need to develop experimental techniques leading to reliable engineering data in less time, and which generate materials data that can be implemented into modem design tools such as finite element simulation and used to predict the durability of adhesive joints under specific service conditions. 

Elastomer life prediction methods will continue to evolve and be an area of strong interest in the future. End-use applications, like seals used in ultra deep-water subsea production equipment, continue to increase in severity. Additionally, even more mimdane uses of elastomers can benefit from life prediction through more cost-effective material selection and reduced warranty costs. 

During the last decade, the tremendous strides taken in the exploration and exploitation of space have placed new environmental demands on the engineering use of elastomers. In particular, the use of rubber polymers in cryogenic and space applications (in the binder of some solid rocket propellants and in low temperature seals, for example) requires that rubber withstand extremely low temperatures. Under these conditions, rubber can become brittle and cracks can propagate easily through the material. In the case of solid rocket propellants, these cracks can lead to uneven and uncontrolled burning. As one practical technique for increasing... 

The most novel elastomer of known structure has a multimodal distribution of network chain lengths. In the bimodal case, it consists of a combination of unusually short network chains (molecular weights of a few hundred) and the much longer chains typically associated with elastomeric behavior (molecular weights of ten or twenty thousand). One use of elastomers having such a bimodal distribution is possibly to improve the ultimate properties of an elastomer. 

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