| Styrene-butadiene | |
|---|---|
| Identifiers | |
| CAS number | 9003-55-8 |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Styrene-butadiene or styrene-butadiene rubber (SBR) 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. It was originally developed prior to World War II in Germany,[1] but during the War was used extensively by the USA to replace natural rubber supplies from the far-east, that had been captured by the Japanese.
SBR can be produced by two basically different processes: from solution (S-SBR) or as emulsion (E-SBR)[2]. In the first instance the reaction is ionic polymerisation, in the emulsion polymerization case the reaction is via free radical polymerization. In that process; Low pressure reaction vessels are required and usually charged with styrene and butadiene, the two monomers, a free radical generator and a chain transfer agent such as an alkyl mercaptan and water. Mercaptans controls molecular weight and high viscosity product from forming. The anionic polymerization process is initiated by alkyl lithium and water not involved. High styrene content rubbers are harder but less rubbery.
It is not to be confused with a thermoplastic elastomer made from the same monomers, styrene-butadiene block copolymer.
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The material was initially marketed with the brand name Buna S. It derives this name from: Bu for butadiene, Na for sodium (natrium in several languages including Latin, German and Dutch), and S for styrene.[3][4]
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.