Thermoplastic elastomers (polyurethane rubber, AU, EU and other TPEs)
Thermoplastic elastomers (TPEs) are a range of copolymers or a physical mix of polymers (usually a plastic and a rubber).
Those based on mixed polymer systems consist of polymers with both plastic and elastic properties. Traditional elastomers are thermosetting materials with covalent crosslinks between the polymer chains (formed during the ‘vulcanization process’), but require processing using different methods to higher-volume thermoplastics, e.g. higher temperatures, longer processing times etc.
The major difference between thermosetting elastomers and TPEs is the type of crosslink utilized. In TPE’s, the crosslink is a covalent bond; the crosslinking in TPEs is a weaker dipole, hydrogen bond, or a covalent bond within only one of the phases of the material.
TPEs have elastomeric properties and can be processed
TPEs are useful in that they have elastomeric properties, yet can be processed using methods more common in plastics processing (blow molding, thermoforming, and heat welding). TPEs also have advantages with respect to environmental impact when compared to traditional thermosetting rubbers: TPEs have the potential to be recycled since they can be moulded, extruded and re-used like plastics, but also require less energy during processing.
The most common types of commercial TPEs include:
- elastomeric alloys (TPE-v or TPV)
- thermoplastic polyurethanes (AU/EU)
- styrenic block copolymers
- polyolefin blends
- thermoplastic copolyester
- thermoplastic polyamides
Due to the variety of materials available, each family will offer different chemical and thermal resistance. Related to the differences in crosslinking, TPEs have relatively poor heat resistance and can show high compression set at elevated temperatures when compared to thermosetting elastomers. Therefore, TPEs are often used in less demanding applications such as door seals, bumpers, extruded profiles, etc.
Polyester-urethane (AU), polyether-urethane (EU)
Polyurethane is a thermoplastic resin with elastomeric type properties. It exhibits outstanding mechanical and physical properties when compared to other elastomers.
It has high resistance (abrasion and tear) and poses the highest tensile strength available to any elastomer. Typically, polyurethanes have working temperatures of approximately –40°C to +82°C. AU has outstanding resistance to petroleum-based oils and hydrocarbon fuels and EU monomer has resistance to water, grades being classed as either hydrolysis-resistant or not.
Ether-based urethanes (EU) are suitable for low temperature flexibility applications
The ester-based urethanes (AU) provide improved abrasion, heat, and oil swell resistance. Over a temperature range of -40°C to +82°C (-40°F to +180°F), resistance to petroleum-based oils, hydrocarbon fuels, oxygen, ozone and weathering is good. However, polyurethanes quickly deteriorate when exposed to acids, ketones and chlorinated hydrocarbons. Certain types of polyester urethanes (AU) are also sensitive to water and humidity. Polyether-urethanes (EU) offer better resistance to water and humidity.
The inherent toughness and abrasion resistance of polyurethane (EU) seals is particularly suitable to hydraulic systems where high pressures, shock loads, wide metal tolerances, or abrasive contamination are anticipated.
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