Thermoplastic elastomers (TPEs) combine the good processing properties of plastics with the elastomer properties that are so important for product developers and designers. Thermoplastic elastomers consist of thermoplastic end blocks and an elastic midblock. As regards their structure and behaviour, they belong to a material class that is positioned between plastics (thermoplastics) and rubber (elastomer) and have gradually been developed into a material class of their own.
They enhance products and enable processors to position their products ahead of those of their competitors. In addition, TPEs also fulfil technical functions that have up to now only been available with elastomers. The use of TPEs does not only offer a range of product advantages but also has significant commercial benefits for processors. Similar to thermoplastics, TPEs become plastic when heated and elastic when cooled down again. In elastomers, this behaviour is due to chemical cross-linking. In TPEs, it is the result of physical cross-linking, and any changes in behaviour caused by heating are reversible. When the material is cooled down, new cross-links are established, which bond the elastic blocks into rigid three-dimensional networks. This means that TPEs show elastic properties that are similar to those of elastomers, while allowing for repeat deformation and recovery as known from thermoplastics. Thermoplastic elastomers are thus free-flowing and formable
The use of TPEs offers a number of key advantages:
- Easy thermoplastic processing
- Short cycle times
- Low energy consumption
- Thermal stability, providing large processing window
- Multi-component processing and thus reduced assembly costs
- Combination of two materials (hard-soft composite)
- 100% recyclable
- Versatile dying options, including colour effects for more advanced design
A TPE based on styrene block copolymers are commonly referred to as a TPS. TPS can be further classified in SEBS, SBS, SEPS and SEPS-V. KRAIBURG TPE produces mainly SEBS (styrene-ethylene-butylene-styrene) compounds.
In this material, styrene end blocks are attached to an elastic segment (e.g. ethylene-butylene). SEBSs are used in adhesives such as hot-melts, or as the soft component in 2C injection moulding materials.
Polymers are classified in four groups, based on their network structure: thermoplastics, elastomers, duromers and thermoplastic elastomers (TPEs) Thermoplastics consist of long linear one-dimensional polymer chains that are held together by weak physical forces such as intermolecular interactions. When exposed to heat or shear forces, they become free-flowing and formable. When cooled down, the material becomes again rigid. As this process is purely physical, it can be repeated at any time and as often as necessary (example: polypropylene).Duromers are tightly cross-linked polymers that do not melt under high temperature and retain their network structure. At room temperature, they are hard and brittle (example: epoxy resin).Elastomers, often referred to as rubbers, are chemically cross-linked and extremely elastic. They are not formable after vulcanisation. The macro-molecules are cross-linked and coiled. The material can be temporarily deformed by compression and stress forces and returns to its original structure as soon as the forces are no more applied (example: NR).Thermoplastic elastomers consist of thermoplastic end blocks (e.g. polystyrene ) and an elastic midblock (e.g. ethylene-butylene). This makes the material free-flowing and formable. When the material is cooled down, physical cross-links are established, which bond the elastic blocks into rigid three-dimensional networks. Thermoplastic elastomers thus have the properties of elastomers but can be processed in the same way as thermoplastics.
TPEs are used in a versatile range of applications in various sectors, meeting the industry-specific requirements. They are for example used for control elements in car interiors , for exterior window trims and "under-the hood" seals. TPEs are also found in industrial products such as tool handles and cable sheathing. In consumer goods, TPEs are used in toys, sports equipment, packaging and hygiene products such as toothbrushes and razors. For medical applications, compounds that meet particularly stringent requirements have been developed. Medical TPE products include drip chambers, seals and medical hoses.