An elastomer is a polymer with the property of elasticity. In other words, it is a polymer that deforms under stress and returns to its original shape when the bao tay is removed. The term is a contraction of the words "elastic polymer." There are many types of elastomers, most of which are rubbers. The term elastomer is therefore often used interchangeably with the term rubber. Other elastomers, which melt when heated, are classified as thermoplastic.

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Rubbers (both natural & synthetic) are widely used for the manufacture of tires, tubes, hoses, belts, matting, gloves, toy balloons, rubber bands, pencil erasers, và adhesives. Thermoplastic elastomers are used in manufacturing processes, such as by injection molding. Thermoplastic polyurethanes are used for various applications, including the production of foam seating, seals, gaskets, and carpet underlay.


Contents


Properties


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A is a schematic drawing of an unstressed polymer, và B is the same polymer under stress. When the căng thẳng is removed, B returns lớn the A configuration. (The dots represent cross-links.)

Elastomers are amorphous polymers with considerable segmental motion. Their general molecular khung has been likened lớn a "spaghetti & meatball" structure, where the meatballs signify cross-links between the flexible polymer chains, which are lượt thích spaghetti strands. Each polymer chain is made up of many monomer subunits, & each monomer is usually made of carbon, hydrogen, & oxygen atoms, & occasionally silicon atoms.

Most elastomers are thermosets—that is, they require curing (by heat, chemical reaction, or irradiation). In the curing process, the long polymer chains become cross-linked by covalent bonds, the material becomes stronger, and it cannot be remelted and remolded. Some elastomers are thermoplastic, melting khổng lồ a liquid state when heated & turning brittle when cooled sufficiently. In thermoplastic elastomers, the polymer chains are cross-linked by weaker bonds, such as hydrogen bonds or dipole-dipole interactions.

The elasticity is derived from the ability of the long chains lớn reconfigure themselves to lớn distribute an applied stress. Covalent cross-linkages, in particular, ensure that the elastomer will return to lớn its original configuration when the bức xúc is removed. As a result of this extreme flexibility, elastomers can reversibly extend from 5 lớn 700 percent, depending on the specific material. Without the cross-linkages or with short, uneasily reconfigured chains, the applied găng would result in permanent deformation.

The temperature of the polymer also affects its elasticity. Elastomers that have been cooled khổng lồ a glassy or crystalline phase will have less di động chains, & consequently less elasticity, than those manipulated at temperatures higher than the glass transition temperature of the polymer. At ambient temperatures, rubbers are thus relatively soft (Young"s modulus of about 3 MPa) and deformable.

Examples of elastomers

Unsaturated rubbers that can be cured by sulfur vulcanization:

Synthetic Polyisoprene (IR)Butyl rubber (copolymer of isobutylene & 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 & acrylonitrile, NBR), also called Buna N rubbersHydrogenated Nitrile Rubbers (HNBR) Therban và ZetpolChloroprene Rubber (CR), polychloroprene, Neoprene, Baypren etc.

(Note that unsaturated rubbers can also be cured by non-sulfur vulcanization if desired).

Saturated Rubbers that cannot be cured by sulfur vulcanization:

Epichlorohydrin rubber (ECO)Polyacrylic rubber (ACM, ABR)Silicone rubber (SI, Q, VMQ)Fluorosilicone Rubber (FVMQ)Fluoroelastomers (FKM, và FEPM) Viton, Tecnoflon, Fluorel, Aflas và Dai-ElPerfluoroelastomers (FFKM) Tecnoflon PFR, Kalrez, Chemraz, PerlastPolyether Block Amides (PEBA)Chlorosulfonated Polyethylene (CSM), (Hypalon)Ethylene-vinyl acetate (EVA)

Various other types of elastomers:

Thermoplastic elastomers (TPE), for example Elastron, etc.Thermoplastic Vulcanizates (TPV), for example Santoprene TPVThermoplastic Polyurethane (TPU)Thermoplastic Olefins (TPO)Polysulfide Rubber

Uses

Most elastomers are rubbers, including both natural and synthetic varieties. They are used mainly for the manufacture of tires và tubes. They are also used khổng lồ produce goods such as hoses, belts, matting, gloves, toy balloons, rubber bands, pencil erasers, và adhesives. As a fiber, rubber (called "elastic") is valuable for the textile industry. Ethylene propylene rubber (EPR) is useful as insulation for high voltage cables. Thermoplastic elastomers are relatively easy to use in manufacturing processes, such as by injection molding.

Polyurethanes are widely used in high-resiliency, flexible foam seating, seals, gaskets, carpet underlay, Spandex fibers, and electrical potting compounds.

Mathematical background

Using the laws of thermodynamics, găng definitions, và polymer characteristics,<1> ideal bao tay behavior may be calculated using the following equation:

σ =nkT<λ 12+λ 1−1>displaystyle sigma =nkT

*
}" />

where ndisplaystyle n

*
is the number of chain segments per unit volume, kdisplaystyle k
*
is Boltzmann"s Constant, Tdisplaystyle T
*
is temperature, và λ 1displaystyle lambda _1
*
is distortion in the 1 direction.

These findings are accurate for values up lớn approximately 400 percent strain. At that point, alignment between stretched chains begins lớn result in crystallization from noncovalent bonding.

Although Young"s Modulus does not exist for elastomers because of the nonlinear nature of the stress-strain relationship, a "secant modulus" can be found at a particular strain.

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See also

Notes


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