Physical properties of elastomers

The styrene-diene triblock copolymer consists of individual chains of three blocks, an elastomeric diene block in the center and a thermoplastic styrene block on each end. This polymer is called a thermoplastic elastomer. It exhibits some of the physical properties of elastomers at use temperature and is as pro-cessable as conventional plastics (5). The styrene/diene triblock copolymer has the unique morphology of glassy polystyrene domains in the rubbery diene matrix. Therefore, such an elastomer does not require conventional vulcanization since the glassy polystyrene domains act as physical crosslinks. 

The elastomeric polypropylene materials studied in this chapter are from a class of thermoplastic elastomers since they possess the physical properties of elastomers along with the processing characteristics of thermoplastics. These materials are characterized by a low degree of crystallinity (23-26), where the crystalline regions dispersed in the amorphous matrix essentially provide physical cross-links to the amorphous elastomeric segments of the chain (19, 20). The size and distribution of these crystalline regions in the amorphous matrix thus have important influences on the mechanical properties. 

Drapkin A E, Marey A1, Dmitriev V S, Physical Properties of Elastomers, Leningrad, Khimiya, 33, 1975. 

Privalko V P, Handbook of Physical Properties of Elastomers, Kiev, Naukova dumka, 1984,330. 

Figure C.9 Effect of cure time on the physical properties of elastomers. AT is the heat buildup in a compression-flex test. (Ref Billmeyer, F.W., Textbook of Polymer Science, Interscience, New York, 1965, p. 539)...

The introduction of thermoplastic elastomers (TPEs) during the late 1950s is one of the most important developments in the field of polymer science and technology. TPEs are a relatively new class of material, a blend of rubber and thermoplastic that combine a wide range of the physical properties of elastomers, such as elasticity, at room and service temperatures, and the excellent... 

FLUOROTRIAZINES Riag-fluoriaated triaziaes are used ia fiber-reactive dyes. Perfluoroalkyl triaziaes are offered commercially as mass spectral markers and have been iatensively evaluated for elastomer and hydraulic fluid appHcations. Physical properties of representative fluorotriaziaes are listed ia Table 13. Toxicity data are available. For cyanuric fluoride, LD g =3.1 ppm for 4 h (iahalatioa, rat) and 160 mg/kg (skin, rabbit) (127). 

Quahty control testing of siUcones utilizes a combination of physical and chemical measurements to ensure satisfactory product performance and processibihty. Eor example, in addition to the usual physical properties of cured elastomers, the plasticity of heat-cured mbber and the extmsion rate of TVR elastomers under standard conditions are important to the customer. Where the siUcone appHcation involves surface activity, a use test is frequently the only rehable indicator of performance. Eor example, the performance of an antifoaming agent can be tested by measuring the foam reduction when the sihcone emulsion is added to an agitated standard detergent solution. The product data sheets and technical bulletins from commercial siUcone producers can be consulted for more information. 

The physical properties of block copolymer TPE also depend on the type and arrangement of the blocks. Table 5 compares the property advantages of various block copolymer thermoplastic elastomers. 

Oil resistance demands polar (non-hydrocarbon) polymers, particularly in the hard phase. If the soft phase is non-polar but the haid phase polar, then swelling but not dissolution will occur (rather akin to that occurring with vulcanised natural rubber or SBR). If, however, the hard phase is not resistant to a particular solvent or oil, then the useful physical properties of a thermoplastic elastomer will be lost. As with all plastics and rubbers, the chemical resistant will depend on the chemical groups present, as discussed in Section 5.4. 

Thermoplastic elastomers (TPES), as the name indicates, are plastic polymers with the physical properties of rubbers. They are soft, flexible, and possess the resilience needed of rubbers. However, they are processed like thermoplastics by extrusion and injection molding. 

The chemistry of synthetic polymers is similar to the chemistry of small molecules with the same functional groups, but the physical properties of polymers are greatly affected by size. Polymers can be classified by physical property into four groups thermoplastics, fibers, elastomers, and thermosetting resins. The properties of each group can be accounted for by the structure, the degree of crystallinity, and the amount of cross-Jinking they contain. 

After almost half a century of use in the health field, PU remains one of the most popular biomaterials for medical applications. Their segmented block copolymeric character endows them with a wide range of versatility in tailoring their physical properties, biodegradation character, and blood compatibility. The physical properties of urethanes can be varied from soft thermoplastic elastomers to hard, brittle, and highly cross-linked thermoset material. 

Akhtar, S. Morphology and Physical Properties of Thin Films of Thermoplastic Elastomers from Blends of Natural Ruhher and Polyethylene, Rubber Chem. Technol. 61, 599-583, 1988. 

Physical properties of carbon black-filled EPR and EPDM elastomers have been found to be comparable with the suUur-cured analogues [372]. Aromatic oils increase the optimum dose requirement for these compounds due to the reaction of the transient intermediates formed during radiolysis of the polymer with the oil as well as energy transfer which is particularly effective when the oil contains aromatic groups. The performance and oxidative stability of unfilled EPDM as well as its blend with PE [373], and the thermal stabdity and radiation-initiated oxidation of EPR compounds are reported by a number of workers [374,375]. 

Polymer stereochemistry is important because of its effect on the physical properties of an elastomer. For example, cis-... 

Elastomers containing fluorine, also called fluorelastomers. These combine the good physical properties of organic elastomers with the thermal stability of inorganic materials. Trade names are Viton, Fluorel, Kel-F and Technoflon. 

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