Styrene-butadiene
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| ECHA InfoCard | 100.127.439 |
CompTox Dashboard (EPA)
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Styrene-butadiene or styrene-butadiene rubber (SBR) describe families of synthetic rubbers derived from styrene and butadiene. These materials have good abrasion resistance and good aging stability when protected by additives. About 50% of car tires are made from various types of SBR. The styrene/butadiene ratio influences the properties of the polymer: with high styrene content, the rubbers are harder and less rubbery.[1] SBR is not to be confused with a thermoplastic elastomer made from the same monomers, styrene-butadiene block copolymer.
Types of SBR
SBR is derived from two monomers, styrene and butadiene. The mixture of these two monomers are polymerised by two basically different processes: from solution (S-SBR) or as an emulsion (E-SBR).[2]
Emulsion polymerisation
E-SBR produced by emulsion polymerisation is initiated by free radicals. Reaction vessels are typically charged with the two monomers, a free radical generator, and a chain transfer agent such as an alkyl mercaptan. Radical initiators include potassium persulfate and hydroperoxides in combination with ferrous salts. Emulsifying agents include various soaps. By "capping" the growing organic radicals, mercaptans (e.g. dodecylthiol), control the molecular weight, and hence the viscosity, of the product. E-SBR is more widely used. Typically, polymerizations are allowed to proceed only to ca. 70%, a method called "short stopping". In this way, various additives can be removed from the polymer.[1]
Solution polymerisation
Solution-SBR is produced by an anionic polymerization process. Polymerisation is initiated by alkyl lithium compounds. Water is strictly excluded. The process is homogeneous (all components are dissolved), which provides greater control over the process, allowing tailoring of the polymer. The organolithium compound adds to one of the monomers , generating a carbanion that then adds to another monomer, and so on. Relative to E-SBR, S-SBR is increasingly favored because it offers improved wet grip and rolling resistance, which translate to greater safety and better fuel economy, respectively.[3]
Buna S
The material was initially marketed with the brand name Buna S. Its name derives Bu for butadiene and Na for sodium (natrium in several languages including Latin, German and Dutch), and S for styrene.[4][5]
Properties
| Property | S-SBR | E-SBR |
|---|---|---|
| Tensile strength (MPa) | 18 | 19 |
| Elongation at tear (%) | 565 | 635 |
| Mooney viscosity (100 °C) | 48.0 | 51.5 |
| Glass transition temperature (°C) | -65 | -50 |
| Polydispersity | 2.1 | 4.5 |
Applications
The elastomer is used widely in pneumatic tires, shoe heels and soles, gaskets and even chewing gum. It is a commodity material which competes with natural rubber. Latex (emulsion) SBR is extensively used in coated papers, being one of the most cost-effective resins to bind pigmented coatings. It is also used in building applications, as a sealing and binding agent behind renders as an alternative to PVA, but is more expensive. In the latter application, it offers better durability, reduced shrinkage and increased flexibility, as well as being resistant to emulsification in damp conditions. SBR can be used to 'tank' damp rooms or surfaces, a process in which the rubber is painted onto the entire surface (sometimes both the walls, floor and ceiling) forming a continuous, seamless damp proof liner; a typical example would be a basement.
Additionally, it is used in some rubber cutting boards.
History
SBR is a replacement for natural rubber. It was originally developed prior to World War II in Germany.[6] Industrial manufacture began during World War 2, and was used extensively by the U.S. Synthetic Rubber Program to produce Government Rubber-Styrene (GR-S); to replace the Southeast Asian supply of natural rubber which, under Japanese occupation, was unavailable to Allied nations.[7][8]
See also
References
- ^ a b Werner Obrecht, Jean-Pierre Lambert, Michael Happ, Christiane Oppenheimer-Stix, John Dunn and Ralf Krüger "Rubber, 4. Emulsion Rubbers" in Ullmann's Encyclopedia of Industrial Chemistry, 2012, Wiley-VCH, Weinheim. doi:10.1002/14356007.o23_o01
- ^ International Institute of Synthetic rubber Producers, Inc. (IISRP) article on S-SBR (retrieved 2011-12-02)
- ^ H.-D.Brandt et al. "Rubber, 5. Solution Rubbers" in Ullmann's Encyclopedia of Industrial Chemistry, 2012, Wiley-VCH, Weinheim. doi:10.1002/14356007.o23_o02
- ^ Mark Michalovic (2000) "The Story of Rubber. Germany: The Birth of Buna" from The Polymer Learning Center and Chemical Heritage Foundation
- ^ Evonik Industries Invention and Production of Buna
- ^ Malcolm Tatum What is syrene-butadiene rubber from Wisegeek
- ^ Wendt, Paul (1947). "The Control of Rubber in World War II". The Southern Economic Journal. 13 (3). Southern Economic Association: 203–227. doi:10.2307/1053336.
{{cite journal}}:|access-date=requires|url=(help) - ^ Rubber Matters: Solving the World War II Rubber Problem & Collaboration. chemheritage.org. Retrieved July 11, 2013.