Common elastomers

The primary considerations for the use of plastic materials in fuel and oil systems include resistance to swelling, softening, or embrittlement. Also important are flexibility and stability under a wide range of temperatures. Information on some common elastomers and plastics used in fuel systems is provided in TABLE 9-8. 

The polymeric materials usually used to manufacture rigid closures are practically the same as those seen under plastic containers (Section 6.1.3.2). The same impurities are therefore to be expected in these packaging components. On the other hand, though made of polymeric materials, elastomeric closures present a different structure. In the manufacture of rubber, elastomer, the chief component, is combined with other chemicals to produce a material with specific properties that meet target needs, such as its above-mentioned ability to reseal on repeated use. Table 28 lists the common elastomers used in the pharmaceutical industry and their monomeric structures. 

TABLE 28 Common Elastomers Used in the Pharmaceutical Industry... 

Ethanol is much less aggressive to elastomers than methanol. Most common elastomers will work satisfactorily with ethanol including Buna-N, Vi ton, fluorosilicones, neoprene, and natural rubber [3.10]. Teflon and nylon are compatible and work well with ethanol. Cork will deteriorate badly in contact with... 

Surface treatments consist of washing with solvent, abrading, or, in the most demanding applications, cyclizing with acid. The most common elastomers to be bonded in this way include nitrile, neoprene, urethane, natural rubber, SBR, and butyl rubber. It is more difficult to achieve good bonds with silicones, fluorocarbons, chlorosulfonated polyethylene, and polyacrylate. 

Some common elastomers with salient features are as follows 113... 

Physical properties such as adhesion to metals tear resistance, abrasion resistance, resistance to diffusion of gas as well as resistance to dilute and concentrated acids, aliphatic and aromatic hydrocarbons, ketones, oil and gasoline, water absorption, oxidation, ozone, sunlight, heat aging, low temperature and flame of the common elastomers are documented in the literature.114 Rating of elastomers with respect to resistance to the factors cited above are in terms of outstanding, excellent, very good, good, fair and poor. 

Oxidative and UV degradation. Polymers that contain sites of unsaturation, such as polyisoprene and the polybutadienes, are most susceptible to oxygen and ozone oxidation. Figure 14.27 illustrates a typical oxidative degradation of a common elastomer. The figure shows the combined effect of light and oxygen (photolysis) and the action of ozone (ozonolysis). 

Table 2 Common elastomers used in parenteral packaging components...

Elastomeric Components for the Pharmaceutical Industry Table 3 Chemical structures of common elastomers... 

Polyisoprene (R = CH3) with a c/s-1,4 configuration is common in nature in different species of piants and is known as natural rubber. Trans-polyisoprene is found in two naturai resins known as gutta-percha and balata. Natural or synthetic polyisoprenes, as well as polybutadiene, are among the most common elastomers with many practical uses. Other elastomers with extensive practical applications are copolymers, many of them using butadiene or isoprene in the starting monomer mixture. 

Figure 8.2 shows a diagram of tear versus temperature for some common elastomer compounds used in the automobile industry. The slope of the diagram should be considered if one is operating on a wider range of service temperatures. For instance, if an... 

The choice of elastomer has the greatest effect on a formulation. The most common elastomers that can be used for closures for injectable products are given in Table 12.5. Of these elastomers, natural rubber, synthetic polyisoprene, butyl, chlorobutyl and bromobutyl rubber are typically used for the manufacture of rubber closures and stoppers used in the packaging and administration of parenterals. 

Thus Vestenamer 8012, used as a blending material, seems to offer considerable possibilities for the improvement of properties of the more common elastomers and can be expected to be used in various specialist applications wherever such improvements are critical. 

Elastomers or rubbers are flexible materials that are mainly used in tires, hoses, and seals as adhesives or as impact modifiers of thermoplastics. They exhibit high resistance to impact, even at low temperatures at which materials increase their rigidity. Eor some of the applications (e.g., tires or hoses), these materials have to be slightly crosslinked once they are formed into the desired shape in order to impart them dimensional stability, since otherwise they tend to slowly flow. Elastomers are polymers that are used above their glass-transition temperature (Tg). Some examples of common elastomers are polybutadiene, which is used as an impact modifier of rigid plastics SBR (copolymer of styrene and butadiene), mainly used in tires EPDM (copolymer of ethylene, propylene, and a diene monomer, usually norbornene) NBR (copolymer of acrylonitrile and butadiene) and so on. 

For the production of chemical safety gloves, the supply industry uses only polymers as raw materials. The most common elastomer is natural rubber, obtained from natural resources (Indian rabber tree ficus elastica"). All others are manmade. 

It should be noted that many refer to flexible thin films (commonly elastomers) as membranes, regardless of their dimensions, presumably because they are easily deformed by relatively low pressures (relative to atmospheric pressure). Here, we adopt the classical mechanics definition of membrane, that is, a stretch-dominated structure (as opposed to bending-dominated). 

FIGURE 1.1 Repeat units for some common elastomer molecules. 

In Fig. 3 i/e will demonstrate the thermoelastic behavior of the LC-elastomer with m = 3 (x=0) at constant load (mean relative deformation X=0.78). Above T in the isotropic state cr and the modulus arespectively increase linearly with increasing temperature corresponding to the behavior of common elastomers. 

Table 1 provides a general list of common elastomers that are resistant to oxidative degradation. (Source Handbook of Polymer Science and Technology Volume 2 - Performance Properties of Plastics and Elastomers, N. P. Cheremisinoff - editor, Marcel Dekker Inc., New York, 1989). 

Hoses There are a variety of rubber hoses found under the hood, made from various types of elastomers. The most common elastomer used is ethylene-propylene-diene (EPDM) with a reinforcement material, mostly rayon yam and aramid yam. The rnbber hoses are lighler in weight than metal and can better endure the harsh vibrations from engine-vehicle and vehicle-road interactions. They can also be formed into a variety of shapes. With the ever-shrinking size of the engine compartment this is very important. 

Wet chlorine gas, that is to say gas at low pressure, does not require tongue-and-groove flanges and can be confined by soft PVC and most of the common elastomers. Some polymeric gaskets require steel reinforcement, and some develop protective layers of chlorinated polymer. 

Several elastomers can be used in rubber-based adhesives. The elastomer provides the backbone of the adhesive, so the main performance of the adhesive is provided by the rubber properties. However, several specific properties for application are imparted by adding other ingredients in the formulations. The most common elastomers used in rubber-based adhesives are natural rubber (NR), butyl rubber (BR) and polyisobutylenes, styrene-butadiene rubber (SBR), nitrile rubber (NBR) and polychloroprene rubber Neoprene) (CR). 

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