- Kraton (polymer)
Kraton is the trade name given to a number of high performance
elastomer s manufactured by Kraton Polymers, and used as synthetic replacements forrubber . Kraton offers many of the properties of natural rubber, such as flexibility, high traction, and sealing abilities, but with increased resistance to heat, weathering, and chemicals. It was first made by the chemical division of theShell Oil Company in the 1960s.Properties
Kraton is a
block copolymer consisting ofpolystyrene andpolybutadiene regions. The microstructure consists of domains of polystyrene arranged regularly in a matrix of polybutadiene, as shown in theTEM micrograph. The picture was obtained on a thin film of polymer cast onto mercury from solution, and then stained withosmium tetroxide .The
glass transition temperature (Tg) of the polybutadiene blocks is -70°C andTg of the polystyrene blocks is +100°C. So, at any temperature between about -70°C and +100°C Kraton will act as anelastomer . If Kraton is heated substantially above the Tg of the styrene-derived blocks, that is, above about 100°C, the physicalcross-links change from rigidglass y regions to flowable melt regions and the entire material flows and therefore can be cast, molded, or extruded into any desired from. On cooling, this new form resumes its elastomeric character. This is the reason such a material is called athermoplastic elastomer . The polystyrene blocks form domains ofnanometre size in the microstructure, and they stabilise the form of the moulded material. Depending on the precise composition of polystyrene in the material, the domains can be spherical or formlamellae . Similar structures have been found in block polymers made frompolyisoprene andpolystyrene .Applications
Kraton has a broad range of applications that spans from bumpers to bellows, vibrational dampers, couplers, and grommets. Also used throughout the automotive, major and small appliances, and aerospace industries. American Motors (AMC) used this polymer plastic on the
AMC Eagle for the wheel arch flares that flowed into rocker panel extensions. Some grades of Kraton can also be dissolved into hydrocarbon oils to create "shear thinning" grease type products that are used in the manufacture of telecommunications cables containing optical fibres. Another use is the creation of "gel candles", which can be formed by dissolving a tri-block Kraton into a white-oil (liquid paraffin) and adding colours if required.Kraton costs in the range of US$1 per kilogram and is also used in rubber footwear and shoe soles, as well as for hot melt adhesives. It can make
asphalt flexible, which is necessary if the asphalt is to be used to coat a surface that is below grade. Kraton is also popular for use in non-slip knife handles.References
*Lewis, PR and Price, C, "Electron Microscopy of sym-SBS block polymers", Polymer (1972), 13, 20-26.
* [https://secure.microplastics.com/MaterialData.aspx?mat=THERMOPLASTIC%20RUBBER%20KRATON%207705.htm Micro Plastics Material Data sheet for Kraton G polymers based on SEBS (styrene ethylene butylene styrene)] , retrieved on2008-06-01 .
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