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Elastomers in service

As occurs with other plastic materials, elastomers, undergo certain processes before being used, such as cross-linking reactions, that lead to the formation of three-dimensional networks. Also it is necessary to incorporate certain chemical substances such as antioxidant agents, fillers, or plasticizers during their manufacture. These operations are aimed at improving the properties [Pg.111]

Vulcanization of a rubber or an elastomer consists in creating chemical cross-links among the polymer chains in order to form a three-dimensional network. There are various types of cross-linking agents, and the most commonly used are described below. The process of vulcanization with sulfur is the most widely used. It is easy to obtain a broad variety of [Pg.112]

Organic peroxides are another type of cross-linking agents. Vulcanization by means of peroxides is a free radical process that leads to the formation of carbon-carbon covalent bonds between chains. Below we show a diagram of the process  [Pg.113]

The networks obtained through vulcanization by peroxides display high thermal stability. Nevertheless, the peroxide vulcanization process allows less control of the vulcanization than the sulfur process. Consequently it [Pg.113]

Currently, vulcanization processes for natural rubber and other diene rubbers are being carried out by reacting nitrophenols with dusocyanates. In this way, cross-links of the urea type are produced, as shown in the following diagram  [Pg.114]


Ways to Lessen Risk of Explosive Decompression (ED) Damage for Sealing Elastomers in Service... [Pg.649]

Thus, the first questions posed in studying the strength of elastomers (and other materials as well) are where and under what conditions does fracture begin Also, what laws govern the growth of a crack once it has been initiated This chapter seeks to answer such questions, first in a general way and then with particular reference to important modes of failure of elastomers in service. It does not deal with the rather complex problem of the strength of composite structures, such as a pneumatic tire, which involves failure of adhesive bonds at interfaces between the components as well as fracture of the components themselves. [Pg.473]

These thermoplastic natural mbber elastomers have a place in the modem world, where recycling has become so important, and when excessive heat is not found in service. Thus, footwear, gla2ing seals, sports goods, hose, domestic products, and a whole range of automotive products have already been identified for such use. It must be noted, however, that tines are not a potential market for these materials, because of the high temperatures which result from emergency braking. [Pg.272]

Mihtary interest in the development of fuel and thermal resistant elastomers for low temperature service created a need for fluorinated elastomers. In the early 1950s, the M. W. Kellogg Co. in a joint project with the U.S. Army Quartermaster Corps, and 3M in a joint project with the U.S. Air Force, developed two commercial fluorocarbon elastomers. The copolymers of vinyUdene fluoride, CF2=CH2, and chlorotrifluoroethylene, CF2=CFC1, became available from Kellogg in 1955 under the trademark of Kel-F (1-3) (see Fluorine compounds, ORGANic-POLYcm.OROTRiFLUOROETHYLENE Poly(vinylidene) fluoride). In 1956, 3M introduced a polymer based on poly(l,l-dihydroperfluorobutyl acrylate) trademarked 3M Brand Fluorombber 1F4 (4). The poor balance of acid, steam, and heat resistance of the latter elastomer limited its commercial use. [Pg.508]

Free radicals are initially generated whenever polymer chains are broken and carbon radicals are formed. These effects occur during manufacture and in service life. Many elastomers are observed to oxidize at relatively low temperature (about 60°C), where carbon-hydrogen and carbon-carbon bond cleavages are highly unlikely. It has been demonstrated [52] that traces of peroxides impurities in the rubber cause low-temperature oxidation of rubber. These initiating peroxides are present in even the most carefully prepared raw rubber polymer [53]. [Pg.641]

TPEs from thermoplastics-mbber blends are materials having the characteristics of thermoplastics at processing temperature and that of elastomers at service temperature. This unique combination of properties of vulcanized mbber and the easy processability of thermoplastics bridges the gap between conventional elastomers and thermoplastics. Cross-linking of the mbber phase by dynamic vulcanization improves the properties of the TPE. The key factor that controls the properties of TPE is the blend morphology. It is essential that in a continuous plastic phase, the mbber phase should be dispersed uniformly, and the finer the dispersed phase the better are the properties. A number of TPEs from dynamically vulcanized mbber-plastic blends have been developed by Bhowmick and coworkers [98-102]. [Pg.1055]

The styrenic thermoplastic elastomers are the only type which are fully compounded in the manner of conventional elastomers. In this case, however, the addition of carbon black, or other fillers, does not give reinforcement. Additions of polystyrene, or high impact polystyrene, and oil are used to vary hardness and tear strength, and fillers can be used to cheapen the material. Other added polymers, e g., EVA, can be used to increase ozone resistance. These materials also require antioxidants for protection during processing and service life, and the poor UV stability restricts their use in outdoor applications. [Pg.119]

The description of the physical properties of fluoroelastomers is necessarily less precise than that of fluoroplastics because of the major effect of adding curatives and fillers to achieve useful cross-linked materials of a given hardness and specific mechanical properties Generally, two parameters are varied increasing cross-link density increases modulus and decreases elongation, and raising filler levels increases hardness and decreases solvent swell because of the decreased volume fraction of the elastomer In addition to these two major vanables, the major determinants of vulcanizate behavior are the chemical and thermal stabilities of its cross-links The selection of elastomer, of course, places limits on the overall resistance to fluids and chemicals and on its service temperature range... [Pg.1112]

When an elastomer is placed in service, some factors have to be taken into account. These factors reduce the service life of the elastomer and are related to the service temperature, service time, thickness of the elastomer, and the presence of oxygen. [Pg.114]

This seetion describes the various substances that are added to an elastomer in the manufacturing process, to improve its properties and extend its service life. [Pg.116]

Although the last two characteristics also occur in nonreinforced rubber, they become important only when high deformations (5 < ) < 7) are achieved, situations not very usual when the elastomer is in service. [Pg.118]

The transfer of hydrophobicity onto solid pollution layers is possible by the diffusion of LMW that is contained in the silicone elastomers. This means that LMW diffuses into this layer and is lost when the layer is removed. In service this can be caused by wind or rain. To enable comparison of different materials, it was found useful to evaluate the dynamics of this process by measuring the dynamic contact angles on the surface of such pollution layers. For the tests, the procedure with a pollution layer of fumed silica described in [9] was used. With respect to a lifetime of high-voltage outdoor insulators of at least 25 years, we have to ask at the same time for the long-time effects and the repeatability of the transfer effect. [Pg.774]

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. [Pg.161]

Temperature effects are important, not only in high temperature applications, but also during accelerated aging of a material for laboratory study and subsequent evaluation of in-service life-time. Solubility of water In Neoprene Increases greatly with temperature as does permeation rate. The relative permeation rates of 3.5% saltwater and deionized water were shown to depend on elastomer composition. [Pg.170]

Riteflex BP. p oechstCdanese] Ther-moidastic polyester elastomer alloy for demanding qiplicSn e.g., automobile fasda, subject to abuse in service. [Pg.318]

Aging changes in mechanical behavior of PNF elastomers were reported with time, temperature, degree of cross-linking (radiation and chemical), and fluid and other environmental conditions for in-service evaluations ASTM and other practical tests were employed. Property changes and conditions are detailed in several references. ... [Pg.751]

Latex lENs. Latex interpenetrating elastomer networks, latex lENs, are latex blends that have been cross-linked after film formation. They are named after the early works of Frisch and co-workers, who called these materials interpenetrating elastomer networks (Frisch et al. 1969b). Many latex blends, as used in coatings especially, are cross-linked as finally used in service. [Pg.695]

Rubber matrices have commonly been used as a second phase to improve the toughness of brittle thermoplastic materials, such as polypropylene and polyethylene. These systems, commonly referred to as polyolefin thermoplastic elastomers (TPOs), are a special class of thermoplastic elastomers that combine the processing characteristic of plastics at elevated temperatures with the physical properties of conventional elastomers at service temperature, playing an increasingly important role in the polymer material industry. Polyolefin blends attract additional interest due to the possibility of recycling plastic wastes, avoiding the complex and expensive processes of separation of the different components. [Pg.198]

Oxidative aging, elastomers n. Breaking down of an elastomer through the action of oxygen on the polymer itself or on other ingredients of the compound. The process may be signaled by change of color, visible deterioration of the part surface, or lowered performance in service. [Pg.687]


See other pages where Elastomers in service is mentioned: [Pg.85]    [Pg.111]    [Pg.85]    [Pg.111]    [Pg.399]    [Pg.1112]    [Pg.221]    [Pg.634]    [Pg.648]    [Pg.653]    [Pg.654]    [Pg.56]    [Pg.208]    [Pg.124]    [Pg.10]    [Pg.102]    [Pg.1112]    [Pg.119]    [Pg.130]    [Pg.331]    [Pg.362]    [Pg.428]    [Pg.591]    [Pg.510]    [Pg.108]    [Pg.140]    [Pg.589]   
See also in sourсe #XX -- [ Pg.111 ]




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