8/3/2019 Seminar Buna s

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Styrene-Butadiene or Styrene-Butadiene-Rubber (SBR) is asynthetic rubbercopolymer

consisting ofstyreneandbutadiene. It has goodabrasionresistance and good aging stability

when protected by additives, and is widely used in cartires, where it may be blended with

natural rubber. It was originally developed prior toWorld War IIin 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 athermoplastic elastomermade from the same monomers,styrene-butadieneblock copolymer.

Buna S-The material was initially marketed with the brand name Buna S. It derives thisname from: Bu forbutadiene,Na forsodium(natriumin several languages including Latin,

German and Dutch), and S forstyrene.

Properties

Glass transition temperatureapproximately 55 C (67 F), but varies with styrenecontent[5]

Possible temperature range of use: approximately -40 to 100 C (-40 to 212 F) Chemical Type: styrene-butadiene (copolymer) Trade names (common): GRS, Buna S, SBR Elongation (%): 450-500 Shore A hardness: 50-90[6] Major application characteristics: good physical properties; excellent abrasion

resistance; but sensitive to oil, wastewater andozone; electrical properties good, but

not outstanding

Applications Theelastomeris used widely in pneumatictires, shoe heels and soles,gasketsand evenchewing gum. It is a commodity material which competes withnatural

rubber. Latex (emulsion) SBR is extensively used incoated 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 rubbercutting boards.

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