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Kraton (polymer)
Encyclopedia
Kraton is the trade name given to a number of high performance elastomer
s manufactured by Kraton Polymers , and used as synthetic
replacements for rubber
. Kraton polymers 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 the Shell Oil Company
in the 1960s.
blocks and rubber blocks. The rubber blocks consist of polybutadiene
, polyisoprene or their hydrogenated equivalents. The tri-block with polystyrene
blocks at both extremities linked together by a rubber block is the most important polymer structure observed in SBC. If the rubber block consist of polybutadiene, the corresponding triblock structure is: poly(styrene-block-butadiene-block-styrene) usually abbreviated as SBS. Kraton D (SBS and SIS ) and their selectively hydrogenated versions Kraton G (SEBS and SEPS) are the major Kraton polymer structures. The microstructure of SBS consists of domains of polystyrene arranged regularly in a matrix of polybutadiene, as shown in the TEM
micrograph. The picture was obtained on a thin film of polymer cast onto mercury
from solution, and then stained with osmium tetroxide.
The glass transition temperature (Tg) of the polybutadiene blocks is typically -90 °C and Tg of the polystyrene blocks is +100 °C. So, at any temperature between about -90 °C and +100 °C Kraton SBS will act as a physically crosslinked elastomer
. If Kraton polymers are heated substantially above the Tg of the styrene-derived blocks, that is, above about 100 °C, like 170 °C the physical cross-links change from rigid glass
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 a thermoplastic elastomer
(TPE). The polystyrene blocks form domains of nanometre
size in the microstructure, and they stabilise the form of the moulded material. Depending on the rubber to polystyrene ratio in the material, the polystyrene domains can be spherical or form cylinders or lamellae. The hydrogenated Kraton polymers named Kraton G exhibit improved resistance to temperature (processing at 200–230 °C is common), to oxidation and to UV. SEBS and SEPS due to their polyolefinic rubber nature present excellent compatibility with polyolefins and paraffinic oils.
flexible, which is necessary if the asphalt is to be used to coat a surface that is below grade or for highly demanding paving applications like F1 racing tracks. Kraton based compounds are also popular for use in non-slip knife handles. 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 Kraton G1650 into a white-oil (liquid paraffin) and adding colours if required.
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
s manufactured by Kraton Polymers , and used as synthetic
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...
replacements for rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
. Kraton polymers 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 the Shell Oil Company
Shell Oil Company
Shell Oil Company is the United States-based subsidiary of Royal Dutch Shell, a multinational oil company of Anglo Dutch origins, which is amongst the largest oil companies in the world. Approximately 22,000 Shell employees are based in the U.S. The head office in the U.S. is in Houston, Texas...
in the 1960s.
Properties
Kraton polymers are styrenic block copolymer consisting of polystyrenePolystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
blocks and rubber blocks. The rubber blocks consist of polybutadiene
Polybutadiene
Polybutadiene is a synthetic rubber that is a polymer formed from the polymerization process of the monomer 1,3-butadiene.It has a high resistance to wear and is used especially in the manufacture of tires, which consumes about 70% of the production...
, polyisoprene or their hydrogenated equivalents. The tri-block with polystyrene
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
blocks at both extremities linked together by a rubber block is the most important polymer structure observed in SBC. If the rubber block consist of polybutadiene, the corresponding triblock structure is: poly(styrene-block-butadiene-block-styrene) usually abbreviated as SBS. Kraton D (SBS and SIS ) and their selectively hydrogenated versions Kraton G (SEBS and SEPS) are the major Kraton polymer structures. The microstructure of SBS consists of domains of polystyrene arranged regularly in a matrix of polybutadiene, as shown in the TEM
Transmission electron microscopy
Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...
micrograph. The picture was obtained on a thin film of polymer cast onto mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
from solution, and then stained with osmium tetroxide.
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
. If Kraton polymers are heated substantially above the Tg of the styrene-derived blocks, that is, above about 100 °C, like 170 °C the physical cross-links change from rigid glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
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 a thermoplastic elastomer
Thermoplastic elastomer
Thermoplastic elastomers , sometimes referred to as thermoplastic rubbers, are a class of copolymers or a physical mix of polymers which consist of materials with both thermoplastic and elastomeric properties...
(TPE). The polystyrene blocks form domains of nanometre
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
size in the microstructure, and they stabilise the form of the moulded material. Depending on the rubber to polystyrene ratio in the material, the polystyrene domains can be spherical or form cylinders or lamellae. The hydrogenated Kraton polymers named Kraton G exhibit improved resistance to temperature (processing at 200–230 °C is common), to oxidation and to UV. SEBS and SEPS due to their polyolefinic rubber nature present excellent compatibility with polyolefins and paraffinic oils.
Applications
Kraton polymers are always used in blends with various other ingredients like paraffinic oils, polyolefins, polystyrene, bitumen, tackifying resins, fillers to provide a very large range of end-use products ranging from hot melt adhesives to impact modified transparent polypropylene bins, from medical TPE compounds to modified bitumen roofing felts or from oil gel toys to elastic attachments in diapers. It can make asphaltAsphalt
Asphalt or , also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits, it is a substance classed as a pitch...
flexible, which is necessary if the asphalt is to be used to coat a surface that is below grade or for highly demanding paving applications like F1 racing tracks. Kraton based compounds are also popular for use in non-slip knife handles. American Motors (AMC) used this polymer plastic on the AMC Eagle
AMC Eagle
The AMC Eagle is a compact-sized four-wheel drive passenger vehicle that was produced by American Motors Corporation . The AMC Eagle line of vehicles inaugurated a new product category of "sport-utility" or crossover SUV....
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 Kraton G1650 into a white-oil (liquid paraffin) and adding colours if required.