Thermoplastic Elastomers (TPE) Explained
Thermoplastic elastomers combine the flexibility of rubber with the easy processing of plastic. This article explains their structure, processing, the difference from cross-linked elastomers and typical applications.
- TPE combine the elasticity of rubber with the thermoplastic processability of plastic.
- They consist of hard segments for strength and soft segments for elasticity.
- Unlike cross-linked elastomers, TPE can be re-melted, moulded and recycled.
- Processed by injection moulding and extrusion, ideal for high volumes.
- Limitation: TPE soften under heat; for continuously high temperatures, cross-linked elastomers are often the better choice.
What are thermoplastic elastomers?
Thermoplastic elastomers (TPE) are a class of polymers that combine the properties of elastomers and thermoplastics in a single material. Elastomers exhibit high elasticity and return to their original shape after being stretched. Thermoplastics are plastics that become mouldable when heated and retain their shape when cooled.
TPE combine both: at room temperature they behave elastically like rubber, and at higher temperatures they can be moulded like a plastic. It is precisely this combination that makes the material so versatile, because rubber-like flexibility can be combined with the simple, economical processing of thermoplastics.
A blend of thermoplastic and elastomer
At the molecular level, TPE consist of hard and soft segments. The hard segments, often made of crystalline polymers, give the material strength and dimensional stability. The soft segments, frequently made of amorphous polymer, provide the elasticity. By adjusting the ratio of these segments, TPE can be tailored to specific applications.
| Segment | Function | Typical building blocks |
|---|---|---|
| Hard segments | Strength, dimensional stability | Polypropylene (PP), polyethylene (PE) |
| Soft segments | Elasticity, flexibility | EPDM, styrene block copolymers (SBC) |
The result is a material that offers both the processability of plastics and the flexibility of rubber. If you would like to brush up on the basic terms around sealing materials, you will find some orientation in the O-ring basics.
Processing, injection moulding and recycling
The manufacturing of TPE is a precise process. In simplified terms, the following steps take place:
- Selecting the raw materials: the right polymers for the hard and soft segments are determined.
- Mixing the polymers: the polymers are mixed in a high-temperature process so that hard and soft segments are distributed at the molecular level.
- Forming: the molten TPE is pressed through a die (extrusion) or injected into a mould (injection moulding). This produces films, tubes, profiles, seals and other components.
- Cooling: after forming, the material cools, hardens and takes on its final shape.
- Post-processing: if required, the TPE is cut, embossed or coated.
A decisive advantage: TPE can be re-melted and reshaped. Production scrap and end-of-life parts can be reheated and processed again. This reduces waste and makes TPE a recyclable alternative to conventional rubber in many applications. In addition, the manufacturing process requires less energy than some other materials, and precise moulds result in less material waste.
Difference from cross-linked elastomers
Conventional elastomers such as NBR, EPDM or FKM are vulcanized. During this process the polymer chains cross-link chemically and form a permanent, three-dimensional network. This network cannot be re-melted. Cross-linked elastomers are therefore not re-mouldable and, in the classic sense, not meltable.
With TPE, by contrast, the cohesion of the hard segments is physical rather than the result of permanent chemical cross-linking. When heated, these physical bonds dissolve and the material becomes mouldable; when cooled, it solidifies again. This difference explains the key properties:
| Feature | Cross-linked elastomers | Thermoplastic elastomers (TPE) |
|---|---|---|
| Cross-linking | chemical (vulcanization) | physical, via hard segments |
| Re-melting | not possible | possible |
| Recycling | severely limited | readily recyclable |
| Processing | vulcanization in the mould | injection moulding, extrusion |
| Upper temperature limit | usually higher | limited by softening |
Properties, advantages and limitations
TPE offer a special combination of properties:
- Flexibility and elasticity: TPE can be stretched and deformed and return to their original shape.
- Thermoplastic processability: unlike conventional rubber, they can be moulded when heated and solidify when cooled, which simplifies production.
- Resistance: TPE withstand many chemicals and weathering influences, which increases their service life. For a specific assessment per medium, see the media resistance overview.
- Good colourability: TPE can be coloured easily, an advantage for the appearance of many products.
These advantages come with limitations. Because the cohesion is physical, TPE soften as the temperature rises. The maximum service temperature is therefore, in many cases, below that of cross-linked high-performance elastomers. For continuously high temperatures or aggressive media, conventional elastomers or high-performance materials are often the better choice.
TPE types at a glance
TPE is an umbrella term for several material families with different properties:
| TPE type | Properties | Trade names |
|---|---|---|
| Styrene block copolymers (SBC) | high elasticity, good UV and weathering resistance | Kraton®, Styroflex® |
| Thermoplastic polyolefins (TPO) | good impact strength, chemical-resistant, recyclable | Engage®, Catalloy® |
| Thermoplastic polyurethanes (TPU) | high abrasion resistance, oil- and solvent-resistant, flexible in the cold | Elastollan®, Desmopan® |
| Thermoplastic vulcanizates (TPV) | good heat resistance, flexible, very easy to process | Santoprene®, Sarlink® |
| Thermoplastic polyester elastomers (TPE-E, COPE) | high heat resistance, good chemical resistance, high strength | Hytrel®, Arnitel® |
| Amide-based TPE (PEBA) | very high elasticity and strength, low density, good UV resistance | Pebax®, Vestamid® |
Applications of TPE
TPE are used in many industries:
In medical technology, TPE are particularly valuable because they are biocompatible and sterilizable and can be formulated without harmful plasticizers or latex. This increases patient safety.
Frequently asked questions
What are the main advantages of TPE over conventional materials?
Can thermoplastic elastomers be recycled?
In which industries are TPE mainly used?
What makes TPE suitable for medical technology?
How do TPE differ from vulcanized rubber?
