Elastomer Designations

Many of the elastomers have common names or trade names as well as the chemical name. For example, polychloraprene also goes imder the name of neoprene (DuPont s tradename) or Bayprene (Mobay Corp s tradename). In addition, they also have an ASTM designation that for polychloroprene is CR. 

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CSPE. Chlorosulfonated polyethylene (CSPE), a synthetic mbber manufactured by DuPont, is marketed under the name Hypalon. It can be produced as a self-curing elastomer designed to cure on the roof. The membrane is typically reinforced with polyester and is available in finished thicknesses of 0.75 to 1.5 mm. Because CSPE exhibits thermoplastic characteristics before it cures, it offers heat-weldable seams. After exposure on the roof, the membrane cures offering the toughness and mechanical set of a thermoset. The normal shelf life of the membrane for maintaining this thermoplastic characteristic is approximately six months. After the membrane is fully cured in the field, conventional adhesives are needed to make repairs. 

Manufacturer Trade Type Grade name elastomer designation Oil content (phr) Mooney viscosity (T + 8 ) at 127 C Ethylene content Diene type Diene content Molecular weight distribution classification... 

Hoffman D, Gong G, PinchukL, and Sisto D. Safety and intracardiac function of a silicone-pol)oirethane elastomer designed for vascular use. Clin Mater, 1993, 13, 95-110. 

Elastomers Prepared. The three elastomers discussed herein were prepared from PPG, toluene-2,4-diisocyanate (TDI), and either LHT-240 or TIPA. Elastomers prepared by a one-step procedure are designated LHT-240 and TIPA, indicative of the triol used. A third elastomer, designated Tri-NCO, was prepared by first reacting LHT-240 with all of the required TDI for two hours at 50°C to obtain a triisocyanate (or essentially... 

Elastic recovery, 19 744 in olefin fibers, 11 227—228 Elastic scattering, 24 88-89 Elastic springs, in virtual two-way SMA devices, 22 346-347 Elastic waves, 17 422 Elastohydrodynamic (EHD) lubrication regime, 15 211-212 Elastomer-coated dies, in bar soap manufacture, 22 752 Elastomer designations, ASTM, 9 552t Elastomeric fibers, dyeing, 9 204 Elastomeric polycarboranylsiloxanes,... 

Gallagher Corporation. "Cast and Molded Components of Polyurethane Elastomers— Design and Application Guide." Trade Paper (1994) 35. 

The manufacture of polyurethane prepolymers is discussed, and details are included of their storage, shelf life, melt time, heat stability, curing agents, and levels of curative. The machinability of polyurethane elastomers, design suggestions, use in food handling applications, and common causes of failure are also examined. 

Hydrogenation of the diolefinic midblock of a S-B-S copolymer gives an elastomer, designated Kraton G, which is favored for HMPSA applications, in spite of lower tack than the S-I-S copolymer, because of greater resistance to oxidative breakdown. Since poly(isoprene) degrades primarily by chain scission while poly(butadiene) tends to crosslink, mixtures of S-I-S and S-B-S polymers are sometimes used to minimize the effects of degradation. 

Extmsion techniques are used to make tubes, rods, gaskets, preforms, etc. Standard mbber equipment may be used to extmde fluorosihcone elastomers. The green strength of fluorosihcones is less than that of typical fluorocarbon elastomers, and this should be considered when designing the feed system. 

At strains over 300% the stress occurs mostiy in the amorphous regions up to the point where the sample breaks. AH of the grades exhibit permanent set, and the curves of grades with a Shore Hardness of 55 and higher exhibit a yield point. This means that parts have to be designed for low strains to stay within the area of elastic recovery. Special grades of elastomer are available to provide hydrolysis resistance (194), improved heat aging (195), and improved uv-stabihty (196). 

Moreover, commercially available triblock copolymers designed to be thermoplastic elastomers, not compatihilizers, are often used in Heu of the more appealing diblock materials. Since the mid-1980s, the generation of block or graft copolymers in situ during blend preparation (158,168—176), called reactive compatibilization, has emerged as an alternative approach and has received considerable commercial attention. 

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

Nitrile Rubber. Nitrile mbbers are made by the emulsion copolymerization of acrylonitrile (9—50%) and butadiene (6) and designated NBR. The ratio of acrylonitrile (ACN) to butadiene has a direct effect on the properties on the nature of the polymers. As the ACN content increases, the oil resistance of the polymer increases (7). As the butadiene content increases, the low temperature properties of the polymer are improved (see Elastomers, SYNTHETIC-NITRILE RUBBER). 

Fluoroelastomers. The fluoroelastomers were introduced to the mbber industry in the late 1950s by the DuPont Company. They were made by modification of Teflon polymers and designed to have exceUent heat and chemical resistance, but remain elastomeric in nature. They were very expensive and have found use in limited appHcations. However, with the increasing demand in the automotive and industrial market for improved reHabUity and longer Hfe, the elastomeric fluoroelastomers have made significant inroads into these appHcations (see Elastomers, synthetic-fluorocarbon ELASTOTffiRS). 

Silicone. SiHcone elastomers have a sdoxy backbone with methyl, vinyl, and phenyl groups attached. The elastomers are designated by their chemical composition, as foUows methyl siHcone (MQ), methyl vinyl siHcone (VMQ), methyl phenyl siHcone (PMQ), methyl phenyl vinyl siHcone (PVMQ), and fluorovinyl methyl siHcone (FVMQ). 

Amine Cross-Linking. Two commercially important, high performance elastomers which are not normally sulfur-cured are the fluoroelastomers (FKM) and the polyacrylates (ACM). Polyacrylates typically contain a small percent of a reactive monomer designed to react with amine curatives such as hexamethylene-diamine carbamate (Diak 1). Because the type and level of reactive monomer varies with ACM type, it is important to match the curative type to the particular ACM ia questioa. Sulfur and sulfur-beating materials can be used as cure retarders they also serve as age resistors (22). Fluoroelastomer cure systems typically utilize amines as the primary cross-linking agent and metal oxides as acid acceptors. 

There are seven principal classes of accelerators and several miscellaneous products that do not fit into these classes. In addition, many proprietary blends of several accelerators are sold which are designed as cure packages for a specific appHcations. Choosing the best cure system is a responsibiUty of the mbber chemist and requites extensive knowledge of each accelerator type and its appHcabiUty in each elastomer. Table 5 shows a rule of thumb comparison of the scorch/cure rate attributes for the five most widely used classes of accelerators used in the high volume diene-based elastomers. 

Designing With Elastomers, Rubber Energy Group. 

The purpose of this article is to provide a brief overview of the materials designated synthetic elastomers and the elastomeric or mbbery state. Subsequent entries describe the individual classes of elastomers in detail. Table 1 provides a fundamental description of the principal classes of synthetic elastomers. Table 2 gives the widely accepted ASTM abbreviations for synthetic mbbers. 

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