Linings elastomers

Flgire 5 Comparison of the storage modulus of a tackified (dark line) and an untaddfied (lighter line) elastomer as a fundion of temperature. Also shown is the Dahlquist criterion which indicates the point at which the tackified material displays tack. 

Figure 3.4 is a display of data which confirms the predictions of Eq. (3.46). For T and a constant-the case in these experiments—Eq. (3.46) predicts that a plot of Uj versus 1 /M should yield a straight line with an intercept proportional to 1/M(,. The elastomers on which the experiments were conducted were copolymers of isobutylene containing a small amount of isoprene. The polymers... 

Plastics and Elastomers. Common plastics and elastomers (qv) show exceUent resistance to hydrochloric acid within the temperature limits of the materials. Soft natural mbber compounds have been used for many years as liners for concentrated hydrochloric acid storage tanks up to a temperature of 60°C (see Rubber, natural). SemUiard mbber is used as linings in pipe and equipment at temperatures up to 70°C and hard mbber is used for pipes up to 50°C and pressures up to 345 kPa (50 psig). When contaminants are present, synthetic elastomers such as neoprene, nitrile, butyl. 

Fig. 2. Sphemlitic moiphology of thermoplastic elastomer where the heavy lines represent polyester segments (184).

Epichlorohydrin. Commercial polyester elastomers include both the homopolymer and the copolymer of epichl orohydrin with ethylene oxide. The very polar chloromethyl groups create basic resistance to oil for these polymers, and they have been extensively used in fuel lines however, the desire for lower fuel permeation is causing a search to be made for other polymers (10) (see Elastomers, synthetic-polyethers). 

Materials of Construction. GeneraHy, carbon steel is satisfactory as a material of construction when handling propylene, chlorine, HCl, and chlorinated hydrocarbons at low temperatures (below 100°C) in the absence of water. Nickel-based aHoys are chiefly used in the reaction area where resistance to chlorine and HCl at elevated temperatures is required (39). Elastomer-lined equipment, usuaHy PTFE or Kynar, is typicaHy used when water and HCl or chlorine are present together, such as adsorption of HCl in water, since corrosion of most metals is excessive. Stainless steels are to be avoided in locations exposed to inorganic chlorides, as stainless steels can be subject to chloride stress-corrosion cracking. Contact with aluminum should be avoided under aH circumstances because of potential undesirable reactivity problems. 

Gaskets uti1i2ed in ethyleneamine service generally are made of Grafod flexible graphite or polytetrafluoroethylene (TEE). There is no single elastomer that is acceptable for the entire product line, although TEE may be considered as an alternative to elastomers across the product line. However, because TEE is not a tme elastomer, it may not always prove suitable as a replacement. 

Swing Check Valves These valves (Fig. 10-156) are used to prevent reversal of flow Normal design is for use only in horizontal lines, where the force of gravity on the disk is at a maximum at the start of closing and at a minimum at the end of closing. Unhke most other valves, check valves are more likely to leak at low pressure than at high pressure, since fluid pressure alone forces the disk to conform to the seat. For this reason elastomers are often mounted on the disk. Swing checkvalves are available with low-cost insert bodies. 

Rubber and Elastomers Rubber and elastomers are widely used as lining materials. To meet the demands of the chemical indus-tiy, rubber processors are continually improving their products. A number of synthetic rubbers have been developed, and while none has all the properties of natural rubber, they are superior in one or more ways. The isoprene and polybutadiene synthetic rubbers are duphcates of natural. 

The ability to bond natural rubber to itself and to steel makes it ideal for lining tanks. Many of the synthetic elastomers, while more chemically resistant than natural rubber, have veiy poor bonding characteristics and hence are not well suited for hning tanks. 

No need to cool hot water - If the seal s elastomer can take the temperature, and the fluid is pressurized above its vapor pre.ssure, the cooling line can be eliminated. 

Figure 12.30 Potential uses of polyphosphazenes (a) A thin film of a poly(aminophosphazene) sueh materials are of interest for biomedical applications, (b) Fibres of poly[bis(trifluoroethoxy)phosphazene] these fibres are water-repellant, resistant to hydrolysis or strong sunlight, and do not burn, (c) Cotton cloth treated with a poly(fluoroalkoxyphosphazene) showing the water repellaney eonferred by the phosphazene. (d) Polyphosphazene elastomers are now being manufaetured for use in fuel lines, gaskets, O-rings, shock absorbers, and carburettor eomponents they are impervious to oils and fuels, do not bum, and remain flexible at very low temperatures. Photographs by eourtesy of H. R. Allcock (Pennsylvania State University) and the Firestone Tire and Rubber Company.

Feed inlet and overflow connections are elastomer lined spool-piece adapters. 

Prior to 1940, the use of synthetic elastomers in linings was negligible, but the advent of the Second World War, and the consequent loss of natural rubber sources to the Allies, led to the use of synthetic rubber, namely a styrene-butadiene copolymer which, whilst not having all the properties of natural rubber, proved to have adequate anti-corrosive performance. 

For satisfactory operation, the rubber lining must be adequately bonded to the substrate it is protecting. BS 6374 part 5 gives definitive load to peel levels for various elastomers, but it is usually required that, on separation, the rubber should tear rather than part either at the primer/rubber interface or the primer/substrate interface. 

In addition to the two-phase TPEs, two new technologies have emerged. They are the metallocene-catalyzed polyolefin plastomers (POPs, the name given to Exxon s EXACT product line) and polyolefin elastomers (POEs, DuPont Dow Elastomer s ENGAGE), and reactor-made thermoplastic polyolefin elastomers (R-TPOs). These new types of TPEs are often called metallocene elastomers-TPEs (MEs-TPEs) [87]. The new POPs and POEs are essentially very low-molecular-weight-Unear low-density PEs (VLMW-LLDPE). These new-generation TPEs exhibit mbber-like properties and can be processed on... 

Before dealing with reinforcement of elastomers we have to introduce the basic molecular features of mbber elasticity. Then, we introduce—step-by-step—additional components into the model which consider the influence of reinforcing disordered solid fillers like carbon black or silica within a rabbery matrix. At this point, we will pay special attention to the incorporation of several additional kinds of complex interactions which then come into play polymer-filler and filler-filler interactions. We demonstrate how a model of reinforced elastomers in its present state allows a thorough description of the large-strain materials behavior of reinforced mbbers in several fields of technical applications. In this way we present a thoroughgoing line from molecular mechanisms to industrial applications of reinforced elastomers. 

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