Definition of TPE

Thermoplastic elastomers (TPEs) are plastics that behave like elastomers at room temperature but can be plastically deformed by the application of heat, allowing them to be processed like thermoplastics.

The combination of elastic restoring force and thermoplastic processability is characteristic. After solidification, TPE retains its shape. Upon reheating, it can be melted again and further processed. Thus, thermoplastic elastomers combine the advantages of rubber (especially elasticity and flexibility) with those of thermoplastics (especially recyclability and ease of processing).

Terminology – What are thermoplastic elastomers?

TPE refers to a family of materials, not a single chemical structure. Within this material family, distinctions are made according to the primary backbone material (styrene, polyolefin, polyurethane, copolyester) corresponding to chemical subgroups.

Figure 1: TPE Material Family

History of TPE

In the 1960s, American plastics manufacturers were looking for materials that combined elastomeric properties with the easy processability of thermoplastics. The first commercially developed and marketed TPE types were primarily used in the packaging, footwear, and household goods industries.

In the 1980s and 1990s, TPE-O, TPE-V, and TPE-U/TPE-A systems were systematically developed, meaning that TPE and its variants are now used in many industries such as automotive, electronics, medical technology, and the food industry.

Chemical composition of TPE

Thermoplastic elastomers are made up of a combination of thermoplastic and elastomeric components. These exist either as block copolymers or as blend systems. The thermoplastic building blocks provide processability, while the elastomeric building blocks give the material rubber-like elasticity.

These structures lead to a physical, non-covalent crosslinking that can be temporarily dissolved upon heating and restored upon cooling. (Illustrative example: spaghetti in a colander – after cooling, the spaghetti sticks together, forming a clump that loosens again when reheated. The spaghetti can then move and realign relative to each other.)

Industrially, TPE-S based on styrene block copolymers are the most important. These include materials such as styrene-ethylene-butylene-styrene (SEBS), styrene-butadiene-styrene (SBS), styrene-ethylene/propylene-styrene (SEPS), and styrene-isoprene-styrene (SIS). These materials consist of hard styrene blocks and soft elastomeric segments, which give the respective TPE material its designed mix of strength and flexibility.

Different morphology of TPE

The morphology of TPEs and polymer blends is significantly shaped by the type of phase separation and the different structures of the hard and soft segments. The segments can be arranged in three typical structural principles: polymer blends, block copolymers with crystalline hard segments, and block copolymers with amorphous hard segments. These different morphologies are crucial for properties such as resilience, thermal resistance, etc., of the materials.

Figure 2: TPE morphologies as a separate representation based on Kaiser, W.: „Kunststoffchemie für Ingenieure“, 2021

In polymer blends, the individual polymer segments exist as separate phases, resulting in a phase-separated morphology where the polymer components are not fully miscible. This leads to the formation of inhomogeneous phases with distinct domains, similar to oil and water. Such systems are frequently employed in TPE-O and TPE-V, where the elastomeric properties arise from the combination of different polymer phases.

In contrast, block copolymers with crystalline hard segments show significantly stronger coupling of the individual microstructures. The hard segments arrange themselves into crystalline regions with high order, which act as physical cross-linking points. These crystallites give the material stability, while the soft segments in between provide elasticity and deformability.

In contrast, block copolymers with amorphous hard segments do not form crystallites, but rather glass-like hard domains. These also act as crosslinking points, but without the high order of crystalline regions. As a result, the morphology is usually finer and more strongly influenced by interactions between the block segments. Such systems are typical of TPE-S and combine a flexible matrix with dispersed amorphous hard domains, thereby creating a balanced ratio between elasticity and strength.

Eigenschaften von TPE

The properties of TPE can be divided into chemical, mechanical, and physical properties. Furthermore, some TPE formulations are suitable for special applications that comply with specific drinking water, medical technology, and fire protection standards.

Chemical properties of TPE

TPE typically exhibits good resistance to many media as well as to weathering and UV radiation, especially when stabilised with suitable additives. However, unstabilised TPE-S are susceptible to UV radiation and oxidative stress; TPE-O and TPE-V types are often significantly more resistant to water than other TPE systems.

Many TPE variants are free of plasticisers and can be used for food-grade or electrical applications. In terms of oil and grease resistance, TPE systems generally lag behind classic elastomers such as NBR or FKM. However, TPE-U formulations exhibit good oil and grease resistance in this area.

Mechanical properties of TPE

Mechanically, TPE offers high flexibility, good elongation, and generally sufficient tear and tensile strength, with performance and specific properties depending heavily on the material's respective chemical base. TPE-S and TPE-O exhibit good elastic properties under moderate loads, whereas TPE-U has significantly higher abrasion and wear resistance. TPE materials are generally available in a wide hardness range from 20–90 Shore A (frequently around TPE 80 Shore A).

Compared to classically cross-linked rubber, TPEs show greater stress relaxation and higher compression set, particularly at higher temperatures and under prolonged stress. This makes TPEs primarily a material for components with limited continuous or intermittent load.

Physical Properties of TPE

Thermoplastic elastomers (TPEs) are characterised physically by their thermoplastic nature: they melt at elevated temperatures. This makes them easy to process and means they can be remelted after solidifying and, for example, recycled. The density is usually in the range of classic plastics (approx. 0.9–1.2 g/cm³), with TPE-U types tending to be slightly denser than TPE-S or TPE-O systems.

TPE variants exhibit good electrical insulation properties and good weather resistance, particularly when UV and oxidation stabilizers are used. Compared to classic silicone, TPE types are generally less resistant to high temperatures but are significantly more cost-effective and easier to process.

Certifications of TPE

Certifications, for example for drinking water contact, biocompatibility, or fire protection, must always be evaluated based on the specific material used. However, the basic chemistry of the TPE material often allows conclusions to be drawn about typical fields of application and thus also about common certifications.

TPE-A are copolyamides and TPE-Cs are copolyesters, which typically do not directly meet common standards for medical use, drinking water contact or enhanced fire protection. However, certain materials of these classes are suitable for medical applications, provided that relevant standards such as ISO 10993 or other medical quality standards are complied with for the respective material. Furthermore, these materials may also be qualified for drinking water contact or fire protection after appropriate testing, provided this is specified in the material's data sheet.

TPE-S are styrene block copolymers, TPE-O are polyolefin elastomers, TPE-U are urethane elastomers and TPE-V are vulcanised olefin elastomers, each with typical areas of application. A wide range of product variants is available, particularly for TPE-S and TPE-U, including types with medical and flame-retardant properties. These materials are therefore often used for cable sheathing with fire protection requirements, as well as for medical applications and those involving contact with drinking water. TPE-O and TPE-V materials are also frequently found in drinking water applications and technical seals; many specific materials in these classes are certified accordingly.

Processing of TPE

The production of thermoplastic elastomers does not require a crosslinking step like vulcanisation. This allows for shorter cycle times in production and less post-processing. Furthermore, recycling the material is significantly easier than with conventional elastomers due to its meltability.

Technically, TPEs are mainly processed using injection moulding and extrusion. In these processes, TPE granules are melted in the screw (typically at 180–220 °C) and introduced under pressure into moulds or profiles. Tool temperatures are usually between 25 and 60 °C, depending on the wall thickness and the desired surface quality.

Figure 3: TPE granules

Due to their thermoplastic base, TPEs are very well suited for multi-component injection moulding, overmoulding and coextrusion without the need for additional cross-linking or adhesion agents. However, due to their low temperature resistance, processing and storage conditions must be carefully controlled to avoid sticking or thermal degradation.

Various TPE variants compared to conventional elastomers

TPE vs. classic rubber

TPE materials and classic rubbers (e.g. EPDM, NBR, SBR, silicone VMQ) fulfil similar functions in many areas, but differ fundamentally in structure, processing and long-term behaviour.

Structurally, conventional rubber is chemically cross-linked by vulcanisation, whereas TPEs are physically and thermoreversibly cross-linked. Due to their thermoplastic-elastomeric structure, TPE materials are recyclable, whereas rubber can only be recycled to a limited extent. TPE is mainly processed by injection moulding or extrusion. While both rubber and elastomers are compounded, rubber production requires vulcanisation, which leads to longer cycle times.

Conventional rubber generally offers higher temperature and media resistance, as well as better long-term elasticity than thermoplastic elastomers. TPEs, on the other hand, are easier to process, require less post-processing, and are more recyclable.

In technical applications, TPE components are ideal for applications with moderate temperature and media exposure, where flexible, fast-processing, and recyclable solutions are required (e.g., handles, seals). Rubber, on the other hand, remains the preferred choice for high-load, high-temperature, and long-term sealing applications (e.g., engine seals, high-pressure O-rings, silicone seals).

TPE and its sub-variants

TPEs form an extensive family of materials, with individual subtypes TPE-A, TPE-C, TPE-U (TPU), TPE-O, TPE-V and TPE-S differing significantly in their properties and cost profiles. The following compares the various TPE subtypes in terms of their properties and typical applications.

Thermal plastic elastomer type	Material basis	Typical characteristics	Typical applications
TPE-A	Polyether-Block-Amide (PEBA)	High mechanical strength; very good abrasion resistance; good cold flexibility; good elastic recovery; relatively good resistance to chemicals and greases; often more resilient than other TPEs.	Heavy-duty technical hoses; compressed air and fuel lines; cable sheathing; gears and sliding components; sports and medical technology when flexibility and strength need to be combined.
USB-C	Copolyester Elastomers	High heat distortion resistance; good fatigue and rebound properties; good resistance to oils, fats and many solvents; good dynamic strength; often stiffer and more temperature-stable than TPE-S.	Technical Profiles; Bellows; Protective Caps; Hoses; Vehicle and Mechanical Engineering; Dynamically Loaded Moulded Parts; Applications with High Temperature and Media Exposure.
TPE-U	Thermoplastic polyurethane	Very high resistance to abrasion, cutting and tearing; high tensile strength; good damping; very good resistance to oil and fuel depending on the type; wide hardness range from soft to hard.	Automotive interior and exterior applications; sealing lips; covers; simple profiles; housing elements; consumer goods; components with a focus on cost, weight, and processability.
TPE-V	Dynamically vulcanised, cross-linked PP/EPDM compounds	Rubber-elastic with partially cross-linked elastomer phase; very good permanent elasticity; good compression set properties; good heat and media resistance; better elasticity stability than many TPE-Os.	Automotive seals; window and door seal profiles; hose systems; sealing mats; technical sealing elements; applications with long-term compression and temperature changes.
TPE-S	Styrene block copolymers	Soft; good grip; very good processability; low density; good appearance and feel; good cold flexibility; limited resistance to oils, greases and hydrocarbons, depending on the type.	Soft-touch surfaces; grips; hand tools; seals for less aggressive media; consumer goods; cable sheathing; medical and hygienic applications; packaging and simple moulded parts.

Table 1: Material comparison of the different TPE variants

TPE-A, TPE-C and TPE-U are usually of interest when higher mechanical or thermal requirements are present. TPE-O and TPE-S are chosen when cost, processability and good everyday elasticity are more important than maximum performance. TPE-V often lies between elastomer-like behaviour and good temperature stability, and is therefore particularly used in sealing applications.

Cost comparison of TPE systems versus other elastomers

The economic efficiency of TPE is particularly evident when compared to classic elastomers and high-performance rubbers. TPE or TPE-U (TPU) is positioned in the lower to mid-price range, making it significantly more cost-effective than specialised high-performance variants such as HNBR or FKM. Particularly in applications where moderate thermal and chemical resistance is sufficient, TPE materials (cost factor approx. x1.3) are preferred over special high-performance elastomers like FKM (cost factor approx. x3.7) or FVMQ (cost factor approx. x3.6).

Within the TPE family, TPE-S and TPE-O offer the most cost-effective entry point. Due to their simple composition and excellent processability, these TPE materials are suitable for non-critical consumer goods or simple structural components. In the mid-price segment are TPE-V and TPE-C, which offer particularly improved weather and temperature resistance and are therefore often used as TPE seals or similar components in the automotive industry. At the upper end of the TPE spectrum are TPE-U and TPE-A, whose higher prices are primarily justified by sophisticated chemical base structures and high chemical resistance. TPE-U and TPE-A are the technical choice when high wear resistance and chemical robustness are required, but are closer in price to more cost-effective rubber variants.