Elastomer i c

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ELASTOMER

An elastomer is a polymer with the property of elasticity. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, and is preferred when referring to vulcanisates. Each of the monomers which link to form the polymer is usually made of carbon, hydrogen, oxygen and/or silicon. Elastomers are existing above their glass transition temperature, so that considerable segmental motion is possible. At ambient temperatures rubbers are thus relatively soft (E~3MPa) and deformable. Their primary uses are for seals, adhesives and molded flexible parts.

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BACKGROUND Elastomers are usually thermosets (requiring vulcanization) but may

also be thermoplastic (see thermoplastic elastomer). The long polymer chains cross-link during curing, i.e., vulcanizing. The molecular structure of elastomers can be imagined as a 'spaghetti and meatball' structure, with the meatballs signifying cross-links. The elasticity is derived from the ability of the long chains to reconfigure themselves to distribute an applied stress. The covalent cross-linkages ensure that the elastomer will return to its original configuration when the stress is removed. As a result of this extreme flexibility, elastomers can reversibly extend from 5-700%, depending on the specific material. Without the cross-linkages or with short, uneasily reconfigured chains, the applied stress would result in a permanent deformation.

Temperature effects are also present in the demonstrated elasticity of a polymer. Elastomers that have cooled to a glassy or crystalline phase will have less mobile chains, and consequentially less elasticity, than those manipulated at temperatures higher than the glass transition temperature of the polymer.

It is also possible for a polymer to exhibit elasticity that is not due to covalent cross-links, but instead for thermodynamic reasons.

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EXAMPLES OF ELASTOMER Unsaturated rubbers that can be cured by sulfur vulcanization: Natural Rubber (NR) Synthetic Polyisoprene (IR) Butyl rubber (copolymer of isobutylene and isoprene, IIR)

Halogenated butyl rubbers (Chloro Butyl Rubber: CIIR; Bromo Butyl Rubber: BIIR)

Polybutadiene (BR) Styrene-butadiene Rubber (copolymer of polystyrene and

polybutadiene, SBR) Nitrile Rubber (copolymer of polybutadiene and acrylonitrile, NBR),

also called Buna N rubbers Hydrogenated Nitrile Rubbers (HNBR) Therban and Zetpol

Chloroprene Rubber (CR), polychloroprene, Neoprene, Baypren etc. (Note that unsaturated rubbers can also be cured by non-sulfur

vulcanization if desired).

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Examples of Elastomer (Continued)

Saturated Rubbers that cannot be cured by sulfur vulcanization: EPM (ethylene propylene rubber, a copolymer of ethylene and

propylene) and EPDM rubber (ethylene propylene diene rubber, a terpolymer of ethylene, propylene and a diene-component)

Epichlorohydrin rubber (ECO) Polyacrylic rubber (ACM, ABR) Silicone rubber (SI, Q, VMQ) Fluorosilicone Rubber (FVMQ) Fluoroelastomers (FKM, and FEPM) Viton, Tecnoflon, Fluorel, and

Dai-El Perfluoroelastomers (FFKM) Tecnoflon PFR, Kalrez, Chemraz,

Perlast Polyether Block Amides (PEBA) Chlorosulfonated Polyethylene (CSM), (Hypalon) Ethylene-vinyl acetate (EVA)

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Examples of Elastomer (continued)

Various types of elastomers: Thermoplastic elastomers (TPE), for example Elastron, etc.

Thermoplastic Vulcanizates (TPV), for example Santoprene TPV

Thermoplastic Polyurethane (TPU)

Thermoplastic Olefins (TPO)

The proteins resilin and elastin

Polysulfide Rubber

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Brief Description of Elastomeric Components commonly use in Curtain Wall:

1. EPDM RUBBER

EPDM rubber is commonly used in weatherseals on curtain walls and all vehicles. This includes door seals, window seals, trunk seals, and sometimes hood seals. Frequently these seals are the source of noise due to movement of the door versus the car body. This is due to friction between the EPDM rubber and the mating surface (car painted sheet metal or glass). This can be alleviated using specialty coatings that are applied at the time of manufacture of the weatherseal, not as an aftermarket application. Such coatings can also greatly increase the chemical resistance of EPDM rubber.EPDM is used as a covering to waterproof roofs and gaskets.

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2. SILICONE RUBBER

Silicone rubber offers good resistance to extreme temperatures, being able to operate normally from -55°C to +300°C. At the extreme temperatures, the tensile strength, elongation, tear strength and compression set can be far superior to conventional rubbers although still low relative to other materials. Organic rubber has a carbon to carbon backbone which can leave them susceptible to ozone, UV, heat and other ageing factors that silicone rubber can withstand well. This makes it one of the elastomers of choice in many extreme environments.

Compared to other organic rubbers, however, silicone rubber has a very low tensile strength. For this reason, care is needed in designing products to withstand even low imposed loads. Silicone rubber is a highly inert material, it is used in many medical applications and in medical implants. However, typical medical products like breast implants and catheters have failed because of poor design.

Recently, silicone rubber formed the matrix of the first autonomic self-healing elastomer. The microcapsule-based material was capable of recovering almost all of the original tear strength.

Material cost is extremely high.

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3. ISOPRENE

Isoprene was first isolated by thermal decomposition of natural rubber. It is most readily available industrially as a byproduct of the thermal cracking of naphtha or oil, as a side product in the production of ethylene. About 20M kg are produced annually. About 95% of isoprene production is used to produce cis-1,4-polyisoprene—a synthetic version of natural rubber

Isoprene is a colorless, volatile liquid hydrocarbon obtained in processing petroleum or coal tar and used as a chemical raw material. When a catalyst is use it yields synthetic rubber that closely resemble the natural product.

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4. NEOPRENE

Its chemical inertness makes it well suited for industrial applications such as gaskets, hoses, and corrosion-resistant coatings. It can be used as a base for adhesives, noise isolation in power transformer installations, and as padding in external metal cases to protect the contents while allowing a snug fit. Neoprene weather stripping is commonly used in fire doors as its fire resistance is higher than exclusively hydrocarbon based rubbers, also resulting in its appearance in combat related attire such as gloves and face masks. Neoprene is also used as a contrast in some jewelry designs.

Neoprene or polychloroprene is a family of synthetic rubbers that are produced by polymerization of chloroprene.[1] It is used in a wide variety of applications, such as in wetsuits, laptop sleeves, orthopedic braces (wrist, knee, etc.), electrical insulation, liquid and sheet applied elastomeric membranes or flashings, and car fan belts. Neoprene is the trade name used by DuPont Performance Elastomers.

It is used in numerous products, such as shoe soles, hoses, and adhesives, that require better resistance than natural rubber to oil, solvents, heat and weathering.

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5. SANTOPRENE

SantopreneTM is a thermoplastic elastomer (TPE). It is the mixture of in-situ cross linking of EPDM rubber and polypropylene. It is supplied as pre-compound material which is able to process by conventional thermoplastic tools. SantopreneTM is a thermoplastic compound that is processed in much the same way as any type of plastic. The difference is that SantopreneTM possesses the same levels of flexibility and durability that are commonly found with natural rubber compounds. Because of the longer life of santoprene in both extreme hot and cold environments, the material is often preferred over the use of rubber.

Its compound is available in hardness grade from 35 Shore A to 60 Shore D. It has good compression set at room temperature and moderate performance at high temperature up to 135 °C. Service temperature is 135 °C (permanent) and 150°C (temporary). Environmental aging resistance, electrical properties, and liquid resistance are about the same as EPDM and it can replace EPDM in certain applications.

Commonly use as gaskets and setting blocks.

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6. POLYPROPYLENE OR POLYPROPENE

Polypropylene or polypropene (PP) is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles (e.g. ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.

Polypropylene is reasonably economical, and can be made translucent when uncolored but is not as readily made transparent as polystyrene, acrylic or certain other plastics. It is often opaque and/or coloured using pigments. Polypropylene has good resistance to fatigue.

Polypropylene has a melting point of ~160°C (320°F), as determined by Differential scanning calorimetry (DSC).Commonly use as appliance housing, dishwasher-proof containers, and outdoor furniture.

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7. POLYURENTHANE RUBBER

POLYURENTHANE limited shelf stability ―Moisture conscious" Easy to handle with simple mixing ratios and

good fluidity. Can be used for pouring practically any type

of cementitious material, casting resin or foam formulation.

Cost of material is far below that of the silicones and appreciably lower than polysulfides.

From the standpoint of general utility and economy, the polyurethanes surpass all other types.

The best known polyurethane are flexible foam – used as upholstery material, mattresses, and the like.

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DUROMETER GUIDELINES GLASS EDGE BLOCK = EPDM 80 – 90 DUROMETER SHORE ―A‖.

GLASS SETTING BLOCK = SILICONE COMPATIBLE RUBBER 80 – 90 DUROMETER SHORE ―A‖.

ANTI-WALK BLOCK = EPDM 80 – 90 ±5 DUROMETER SHORE ―A‖.

WEATHER-STRIPPING GASKET = PEROXIDE CURE EPDM 70 DUROMETER SHORE ―A‖. (e.g. Bulb, Flipper & Cover Cap)

WEDGE GASKET = PEROXIDE CURE EPDM 65 ±5 DUROMETER SHORE ―A‖.

THERMAL INSULATOR = NEOPRENE 85 ±5 DUROMETER SHORE ―A‖.

PRESET GASKET = PEROXIDE CURE EPDM 65 ±5 DUROMETER SHORE ―A‖.

FILLER BLOCK = 30ppi POLYURENTHANE OPEN CELL FOAM

WEEP BAFFLES BLOCK = 30ppi POLYURENTHANE OPEN CELL FOAM.

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SHORE DUROMETER Durometer is one of several measures

of the hardness of a material. Hardness may be defined as a material's resistance to permanent indentation. The durometer scale was defined by Albert F. Shore, who developed a measurement device called a durometer in the 1920s. The term durometer is often used to refer to the measurement, as well as the instrument itself. Durometer is typically used as a measure of hardness in polymers, elastomers and rubbers.

An automotive tire tread typically ranges from 50A to 70A, depending on the application.

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DUROMETERS OF VARIOUS COMMON MATERIALS:

There are several scales of durometer, used for materials with different properties. The two most common scales, using slightly different measurement systems, are the ASTM D2240 type A and type D scales. The A scale is for softer plastics, while the D scale is for harder ones. However, the ASTM D2240-00 testing standard calls for a total of 12 scales, depending on the intended use; types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R.

Each scale results in a value between 0 and 100, with higher values indicating a harder material.