Elastomer
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An elastomer is a
Rubber-like solids with elastic properties are called elastomers. Polymer chains are held together in these materials by relatively weak intermolecular bonds, which permit the polymers to stretch in response to macroscopic stresses.
Elastomers are usually
Crosslinking most likely occurs in an equilibrated polymer without any solvent. The free energy expression derived from the Neohookean model of rubber elasticity is in terms of free energy change due to deformation per unit volume of the sample. The strand concentration, v, is the number of strands over the volume which does not depend on the overall size and shape of the elastomer.[4] Beta relates the end-to-end distance of polymer strands across crosslinks over polymers that obey random walk statistics.
In the specific case of shear deformation, the elastomer besides abiding to the simplest model of rubber elasticity is also incompressible. For pure shear we relate the shear strain, to the extension ratios lambdas. Pure shear is a two-dimensional stress state making lambda equal to 1, reducing the energy strain function above to:
To get shear stress, then the energy strain function is differentiated with respect to shear strain to get the shear modulus, G, times the shear strain:
Shear stress is then proportional to the shear strain even at large strains.[5] Notice how a low shear modulus correlates to a low deformation strain energy density and vice versa. Shearing deformation in elastomers, require less energy to change shape than volume.
Examples
Unsaturated rubbers that can be cured by sulfur vulcanization:
- Natural polyisoprene: cis-1,4-polyisoprene natural rubber (NR) and trans-1,4-polyisoprene gutta-percha
- Synthetic polyisoprene (IR for isoprene rubber)
- Polybutadiene (BR for butadiene rubber)
- polychloroprene, neoprene
- isobuteneand isoprene, IIR)
- Halogenated butyl rubbers (chloro butyl rubber: CIIR; bromo butyl rubber: BIIR)
- Styrene-butadiene rubber (copolymer of styrene and butadiene, SBR)
- Nitrile rubber (copolymer of butadiene and acrylonitrile, NBR), also called Buna N rubbers
- Hydrogenated nitrile rubbers (HNBR) Therban and Zetpol
Saturated rubbers that cannot be cured by sulfur vulcanization:
- EPM (propene) and EPDM rubber (ethylene propylene diene rubber, a terpolymer of ethylene, propylene and a diene-component)
- Epichlorohydrin rubber (ECO)
- Acrylic rubber (ACM, ABR)
- Silicone rubber (SI, Q, VMQ)
- Fluorosilicone rubber (FVMQ)
- Tecnoflon, Fluorel, Aflasand Dai-El
- Perfluoroelastomers (Kalrez, Chemraz, Perlast
- Polyether block amides (PEBA)
- Chlorosulfonated polyethylene (CSM)
- Ethylene-vinyl acetate (EVA)
Various other types of elastomers:
- Thermoplastic elastomers (TPE)
- The proteins resilin and elastin
- Polysulfide rubber
- Elastolefin, elastic fiber used in fabric production
- Poly(dichlorophosphazene), an "inorganic rubber" from hexachlorophosphazene polymerization
See also
- Liquid elastomer molding
- Rubber elasticity
References
- ISBN 978-1859572627. Archivedfrom the original on 2017-02-07. Retrieved 7 February 2017.
- ^ Gent, Alan N. "Elastomer Chemical Compound". Encyclopædia Britannica. Archived from the original on 2017-02-07. Retrieved 7 February 2017.
- ISBN 1851662200. Archivedfrom the original on 2017-02-07. Retrieved 7 February 2017.
- ISSN 1359-8368.
- ISSN 0167-577X.