Elastomer

Elastomer

Overview
An elastomer is a polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 with the property of viscoelasticity
Viscoelasticity
Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just...

 (colloquially "elasticity"), generally having notably low Young's modulus
Young's modulus
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...

 and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber
Rubber (disambiguation)
Natural rubber is a latex material, originally from the Para rubber tree.Rubber may also refer to:- Science and industry :*Synthetic rubber, general term for many types of man-made rubbers...

, although the latter is preferred when referring to vulcanisates
Vulcanization
Vulcanization or vulcanisation is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur or other equivalent "curatives." These additives modify the polymer by forming crosslinks between individual polymer chains. Vulcanized material is...

. Each of the monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

s which link to form the polymer is usually made of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and/or silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

.
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Encyclopedia
An elastomer is a polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 with the property of viscoelasticity
Viscoelasticity
Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just...

 (colloquially "elasticity"), generally having notably low Young's modulus
Young's modulus
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...

 and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber
Rubber (disambiguation)
Natural rubber is a latex material, originally from the Para rubber tree.Rubber may also refer to:- Science and industry :*Synthetic rubber, general term for many types of man-made rubbers...

, although the latter is preferred when referring to vulcanisates
Vulcanization
Vulcanization or vulcanisation is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur or other equivalent "curatives." These additives modify the polymer by forming crosslinks between individual polymer chains. Vulcanized material is...

. Each of the monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

s which link to form the polymer is usually made of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 and/or silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

. Elastomers are amorphous polymers existing above their glass transition temperature, so that considerable segmental motion is possible. At ambient temperatures, rubbers are thus relatively soft (E
Young's modulus
Young's modulus is a measure of the stiffness of an elastic material and is a quantity used to characterize materials. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. In solid mechanics, the slope of the stress-strain...

~3MPa) and deformable. Their primary uses are for seal
Seal (mechanical)
A mechanical seal is a device which helps join systems or mechanisms together by preventing leakage , containing pressure, or excluding contamination...

s, adhesive
Adhesive
An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...

s and molded flexible parts.

Background


Elastomers are usually thermosets (requiring vulcanization
Vulcanization
Vulcanization or vulcanisation is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur or other equivalent "curatives." These additives modify the polymer by forming crosslinks between individual polymer chains. Vulcanized material is...

) but may also be thermoplastic
Thermoplastic
Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...

 (see thermoplastic elastomer
Thermoplastic elastomer
Thermoplastic elastomers , sometimes referred to as thermoplastic rubbers, are a class of copolymers or a physical mix of polymers which consist of materials with both thermoplastic and elastomeric properties...

). The long polymer chains cross-link
Cross-link
Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...

 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.

Examples of elastomers


Unsaturated rubbers that can be cured by sulfur vulcanization
Vulcanization
Vulcanization or vulcanisation is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur or other equivalent "curatives." These additives modify the polymer by forming crosslinks between individual polymer chains. Vulcanized material is...

:
  • Natural polyisoprene
    Terpene
    Terpenes are a large and diverse class of organic compounds, produced by a variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium. They are often strong smelling and thus may have had a protective...

    : cis-1,4-polyisoprene natural rubber (NR) and trans-1,4-polyisoprene gutta-percha
    Gutta-percha
    Gutta-percha is a genus of tropical trees native to Southeast Asia and northern Australasia, from Taiwan south to the Malay Peninsula and east to the Solomon Islands. The same term is used to refer to an inelastic natural latex produced from the sap of these trees, particularly from the species...

  • Synthetic polyisoprene (IR for Isoprene
    Isoprene
    Isoprene , or 2-methyl-1,3-butadiene, is a common organic compound with the formula CH2=CCH=CH2. Under standard conditions it is a colorless liquid...

     Rubber)
  • Polybutadiene
    Polybutadiene
    Polybutadiene is a synthetic rubber that is a polymer formed from the polymerization process of the monomer 1,3-butadiene.It has a high resistance to wear and is used especially in the manufacture of tires, which consumes about 70% of the production...

     (BR for Butadiene Rubber)
  • Chloroprene
    Chloroprene
    Chloroprene is the common name for the organic compound 2-chlorobuta-1,3-diene, which has the formula CH2=CCl-CH=CH2. This colorless liquid is the monomer for the production of the polymer polychloroprene, a type of synthetic rubber...

     rubber (CR), polychloroprene, Neoprene
    Neoprene
    Neoprene or polychloroprene is a family of synthetic rubbers that are produced by polymerization of chloroprene. Neoprene in general has good chemical stability, and maintains flexibility over a wide temperature range...

    , Baypren etc.
  • Butyl rubber
    Butyl rubber
    Butyl rubber is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for Isobutylene Isoprene Rubber. Polyisobutylene, also known as "PIB" or polyisobutene, n, is the homopolymer of isobutylene, or 2-methyl-1-propene, on which butyl rubber is based...

     (copolymer of isobutylene
    Isobutylene
    Isobutylene is a hydrocarbon of significant industrial importance. It is a four-carbon branched alkene , one of the four isomers of butylene. At standard temperature and pressure it is a colorless flammable gas.-Uses:...

     and isoprene, IIR)
    • Halogenated
      Halogenation
      Halogenation is a chemical reaction that incorporates a halogen atom into a molecule in substitution of hydrogen atom. Halogenation takes place in the gas phase. There are four types of halogenation: fluorination, chlorination, bromination, and iodination...

       butyl rubbers (chloro butyl rubber: CIIR; bromo butyl rubber: BIIR)

  • Styrene-butadiene
    Styrene-butadiene
    Styrene-Butadiene or Styrene-Butadiene-Rubber is a synthetic rubber copolymer consisting of styrene and butadiene. It has good abrasion resistance and good aging stability when protected by additives, and is widely used in car tires, where it may be blended with natural rubber...

     Rubber (copolymer of styrene and butadiene, SBR)
  • Nitrile rubber
    Nitrile rubber
    Nitrile rubber, also known as Buna-N, Perbunan, or NBR, is a synthetic rubber copolymer of acrylonitrile and butadiene. Trade names include Nipol, Krynac and Europrene....

     (copolymer of butadiene and acrylonitrile
    Acrylonitrile
    Acrylonitrile is the chemical compound with the formula C3H3N. This pungent-smelling colorless liquid often appears yellow due to impurities. It is an important monomer for the manufacture of useful plastics. In terms of its molecular structure, it consists of a vinyl group linked to a nitrile...

    , NBR), also called Buna N rubbers
    • Hydrogenated
      Hydrogenation
      Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...

       Nitrile Rubbers (HNBR) Therban and Zetpol

(Unsaturated rubbers can also be cured by non-sulfur vulcanization if desired).

Saturated rubbers that cannot be cured by sulfur vulcanization:
  • EPM (ethylene propylene rubber
    Ethylene propylene rubber
    Ethylene propylene rubber is an insulation used for high voltage cables. It has improved thermal characteristics over more traditional cables, such as cross-linked polyethylene, enabling a smaller cross sectional area for the same load carrying capacity...

    , a copolymer of ethylene
    Ethylene
    Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

     and propylene
    Propylene
    Propene, also known as propylene or methylethylene, is an unsaturated organic compound having the chemical formula C3H6. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons, and it is also second in natural abundance.-Properties:At room temperature and...

    ) and EPDM rubber
    EPDM rubber
    EPDM rubber , a type of synthetic rubber, is an elastomer which is characterized by a wide range of applications. The E refers to ethylene, P to propylene, D to diene and M refers to its classification in ASTM standard D-1418. The M class includes rubbers having a saturated chain of the...

     (ethylene propylene diene rubber, a terpolymer of ethylene, propylene and a diene
    Diene
    In organic chemistry a diene or diolefin is a hydrocarbon that contains two carbon double bonds.Conjugated dienes are functional groups, with a general formula of CnH2n-2. Dienes and alkynes are functional isomers...

    -component)
  • Epichlorohydrin
    Epichlorohydrin
    Epichlorohydrin is an organochlorine compound and an epoxide. This is a colorless liquid with a pungent, garlic-like odor, moderately soluble in water, but miscible with most polar organic solvents. Epichlorohydrin is a highly reactive compound and is used in the production of glycerol, plastics,...

     rubber (ECO)
  • Polyacrylic rubber (ACM, ABR)
  • Silicone rubber
    Silicone rubber
    Silicone rubber is an elastomer composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations...

     (SI, Q, VMQ)
  • Fluorosilicone Rubber (FVMQ)
  • Fluoroelastomer
    Fluoroelastomer
    A fluoroelastomer is a special purpose fluorocarbon-based synthetic rubber. It has wide chemical resistance and superior performance, especially in high temperature application in different media....

    s (FKM
    FKM
    FKM is the designation for about 80% of fluoroelastomers as defined in ASTM D1418. Other fluorinated elastomers are perfluoro-elastomers and tetrafluoro ethylene/propylene rubbers . All FKMs contain vinylidene fluoride as a monomer...

    , and FEPM) Viton
    Viton
    Viton is a brand of synthetic rubber and fluoropolymer elastomer commonly used in O-rings and other molded or extruded goods. The name is a registered trademark of DuPont Performance Elastomers L.L.C.....

    , Tecnoflon, Fluorel, Aflas and Dai-El
  • Perfluoroelastomers (FFKM) Tecnoflon PFR, Kalrez, Chemraz, Perlast
  • Polyether block amides (PEBA)
  • Chlorosulfonated polyethylene (CSM), (Hypalon)
  • Ethylene-vinyl acetate
    Ethylene-vinyl acetate
    Ethylene vinyl acetate is the copolymer of ethylene and vinyl acetate. The weight percent vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene....

     (EVA)

"The definitions are not authentic as the Rubber which is classified in World Customs Organisation Books in Chapter 40, where as the above definitions stating all rubber and different polymers in same chapter which is classified in Chapter 39 of the World Custom Organisation's Harmonised Commodity for Description and coding system. One should go through all differentiation while editing between Plastics and articles thereof and Rubber and articles thereof."

Various other types of elastomers:
  • Thermoplastic elastomer
    Thermoplastic elastomer
    Thermoplastic elastomers , sometimes referred to as thermoplastic rubbers, are a class of copolymers or a physical mix of polymers which consist of materials with both thermoplastic and elastomeric properties...

    s (TPE)
  • The protein
    Protein
    Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

    s resilin
    Resilin
    Resilin is an elastomeric protein found in many insects. The protein was first discovered by Torkel Weis-Fogh in the locust wing-hinge. As of 2005 it is the most efficient elastic protein known . The elastic efficiency of the resilin isolated from locust tendon has been reported to be 97 %...

     and elastin
    Elastin
    Elastin is a protein in connective tissue that is elastic and allows many tissues in the body to resume their shape after stretching or contracting. Elastin helps skin to return to its original position when it is poked or pinched. Elastin is also an important load-bearing tissue in the bodies of...

  • Polysulfide
    Polysulfide
    Polysulfides are a class of chemical compounds containing chains of sulfur atoms. There are two main classes of polysulfides: anions and organic polysulfides. Anions have the general formula Sn2−. These anions are the conjugate bases of the hydrogen polysulfides H2nSn...

    rubber