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Plastics & Elastomers
Thermoplastic Elastomers (TPEs)

Thermoplastic Elastomers 101: An Ultimate Guide

Thermoplastic elastomers (TPEs) are one of the most versatile plastics in today’s market bridging between the service properties of elastomers and the processing properties of thermoplastics. The cost effectiveness and design flexibility enable TPEs to be used in many major end-user markets, including consumer products, electronics, medical devices, automotive, and much more. Explore this comprehensive guide and learn everything you need to know about TPEs.

Overview

What are Thermoplastic Elastomers (TPEs)?

What are Thermoplastic Elastomers (TPEs)?

Introduced commercially in the 1960s, ThermoPlastic Elastomer (TPE) is a polymer material with the characteristics of thermoset vulcanized rubber and thermoplastic. TPE exhibits high elasticity of thermoset vulcanized rubber at room temperature and good processability of thermoplastic at high temperature.

The principal difference between thermoset elastomers/rubbers and thermoplastic elastomers is in the type of the crosslinking bond in their structures. In fact, crosslinking is a critical structural factor which contributes to imparting high elastic properties. TPEs provide the simplest way of achieving outstanding properties by simply varying the blend compositions and the viscosity of the components and compounding ingredients at a low cost.

A thermoplastic elastomer must fulfill the following three essential characteristics:

  • The ability to be stretched to moderate elongations and, upon the removal of stress, return to something close to its original shape
  • Processable as a melt at elevated temperature
  • Absence of significant creep

TPE is considered as an efficient and cost-effective alternative for latex, silicone rubber, and polyvinyl chloride (PVC) compounds. Its rubber like properties have enabled TPE to replace rubber significantly in several applications. Today, they are used in many applications, like adhesives, footwear, medical devices, automobile parts, household goods, etc., where they offer elasticity benefits over a wide temperature range.

TPE materials have the potential to be recyclable since they can be molded, extruded, and reused like plastics, but they have the typical elastic properties of rubbers which are not recyclable owing to their thermosetting characteristics.

Advantages & Disadvantages of TPEs

Advantages & Disadvantages of TPEs

Advantages Disadvantages
  • Simpler processing, lower energy consumption & lower finished part costs due to shorter fabrication times
  • Easily be insert molded with olefin materials, such as PP, without use of adhesives
  • Very good electrical insulation properties
  • Heat and oil resistance (within a specific temperature range)
  • Low permeability and colorable
  • Can be produced in a variety of hardness grades
  • Melting at elevated temperature limits the use of parts from TPEs for certain applications
  • Comparatively higher cost than thermoset rubbers
  • Shear sensitive
  • Low resistance to aromatics

Rubber vs TPE: When to Select What?


Take this course to gain greater control over your elastomeric part performance by choosing the right material (rubber vs TPE) in your end application (tires, seals, gaskets, medical equipments…)

Rubber vs TPE: When to Select What?



Classification and Chemistries of TPE Materials

Classification and Chemistries of TPE Materials

After years of development, TPE can be categorized based on various methods, i.e. based on constituent chemical building blocks, methods of polymerization and processability. Generally, thermoplastic elastomers can be categorized into the following classes:


Each category has a slight difference in its chemistry and therefore offers different properties.

Chemistries of Thermoplastic Elastomers (TPE)
Chemistries of Thermoplastic Elastomers (TPE)


The simplest TPE materials are like ABA block copolymers, where:

  • A is a hard thermoplastic at room temperature but soften at elevated temperatures (e.g. polystyrene, polyethylene, or polypropylene)
  • B is a soft elastomer (e.g. polydimethylsiloxane, polybutadiene, polyisoprene or poly (ethylene-propylene))


Thermoplastic Styrenic Block Copolymers (SBC or TPE-S)


Styrenic thermoplastic elastomers are the largest group among TPE materials and probably the most versatile as they can be produced over a variety of hardness values. They include distinctly different main types:

  • SBS: Styrene-butadiene-styrene block copolymer
  • SIS: Styrene-isoprene-styrene block copolymer
  • SEBS: Styrene-ethylene-butylene-styrene block copolymer
  • SEEPS: Styrene-ethylene-ethylene-butylene-styrene block copolymer
  • SEPS: Styrene-ethylene-propylene-styrene block copolymer
  • SEPS-V: Styrene-ethylene-propylene-styrene block copolymer, cross-linkable

Styrenic block copolymers are amorphous and opaque polymers. They have elastomer segments with relatively short lengths so each elastomer may pass through a few hard domains before it ends. The various advantages of styrenic TPEs include:

  • High tensile strength and modulus
  • Good miscibility
  • Good abrasion resistance
  • Good electrical properties
  • Large variety in hardness
  • High friction coefficient (corresponds to that for NR)
  • Colorless & good transparency

Styrenic TPEs Structure
Styrenic TPEs Structure
(Source: Thermoplastic Elastomers, Edited by Prof. Adel El-Sonbati)


Thermoplastic Elastomer Polyolefins (TPO or TPE-O)


This is relatively a new class among thermoplastic elastomeric materials as compared to styrenic block copolymers. They are blends of polypropylene or polyethylene and ethylene-propylene-diene rubber and nitrile rubber (NBR) to provide an elastomeric element.

TPO mainly has two kinds of production processes: one is blending compound type, and the other is reactor type. Blending compound type includes dynamic vulcanization (TPV) and mechanical blending (CTPO).

Polyolefin block copolymers are amorphous and transparent polymers. Polyolefins are chemically inert, extremely flexible, nontoxic, very light weight and sterile.


Thermoplastic Vulcanizates (TPV or TPE-V)


TPV is a milestone in the development of elastomeric alloys. TPV is replacing traditional thermosetting vulcanized rubber in more and more applications, becoming one of the most promising polymer material varieties. This class of TPE differs fundamentally from those discussed previously in that they derive their physical and elastomeric qualities from mechanically combining various thermoplastics with, typically, thermoset rubbers and not via chain segment structure as in the case of block copolymer TPE.

TPVs mainly include silicone rubber TPV (TPSiV), acrylate rubber TPV (ACM), TPV based on NR or ENR, polyolefin elastomer (EOC) / PP TPV)

The properties of thermoplastic vulcanizates majorly include:

  • Excellent barrier properties
  • Small permanent deformation
  • Good mechanical properties
  • Good properties at low temperatures
  • Fatigue durability
  • Good liquid and oil resistance

Elastomeric alloys are blends of elastomers and thermoplastics that can be processed using thermoplastic processing methods.


Thermoplastic Polyurethanes Elastomer (TPU or TPE-U)


TPUs are block copolymers with urethane backbone linkages. One type of block, the hard segment, is formed by the addition of a chain extender to a diisocyanate. The other type is the soft segment and consists of long flexible polyether or polyester chains that interconnect two hard segments. Polyether or polyester based TPU offers specific property benefits, particularly in regard to chemical resistance.

Hard Segments: Diisocyanates, short chain diols (The most commonly used are 1,4-butanediol and to a lesser extent, 1,6-hexanediol and 1,4-dihydroxyethoxybenze)

Soft Segment: Long chain diols (the hydroxyl-terminated polyesters and polyethers. Examples of typical polyester types are the polycarbonate and polycaprolactone glycols and in the case of the polyethers, poly (oxypropylene) and poly (oxytetramethylene) glycol)

Thermoplastic Urethane Elastomers - Hard and Soft Segments
TPUs composed of alternating hard segment and soft segment structures
(Source: Thermoplastic Elastomers, Edited by Prof. Adel El-Sonbati)

Advantages of thermoplastic urethane elastomers include:

  • Good abrasion resistance & tear strength
  • Good stiffness properties
  • Low friction coefficient (depends on hardness)
  • Good oxygen, ozone, and weather resistance

Learn more about how Thermoplastic Polyurethane (TPU) is produced, its main properties and benefits which enable various industries to produce advance products.

Thermoplastic Elastomers: Key Features & Applications


Thermoplastic Copolyester Elastomer (COPE or TEEE or TPE-E)


Thermoplastic polyester elastomers (TPEEs) are a type of block linear copolymers containing a hard-crystalline segment (polybutylene terephthalate, PBT - crystalline phase, providing strength) and a soft amorphous segment (polytetramethylene oxide glycol, PTMO - continuous segment).

The rigidity, polarity and crystallinity of the TPEEs hard segment make them have outstanding strength and excellent high temperature resistance, creep resistance, solvent resistance and impact resistance. The low glass transition temperature and saturation of the soft segment polyether make it have excellent low temperature resistance and aging resistance. It combines the excellent elasticity of rubber and the processability of thermoplastics.

In more general terms, the key characteristics of these materials are:

  • Excellent dynamic properties, for example creep and fatigue
  • Exceptional resistance to oils and greases, good general resistance to chemicals
  • Excellent strength over a wide range of temperatures
  • Excellent heat resistance (long term 165°C)
  • Good electrical insulation properties
  • Low moisture absorption
  • Excellent dimensional stability


Thermoplastic Polyamide Elastomer (COPA or PEBA or TPE-A)


Thermoplastic polyamide elastomer (TPE-A) is a newly developed class of alternating block copolymer elastomers. It consists of soft segments of polyesters or polyethers and a rigid block of polyamide. The polyamide can be for example polyesteramide (PEA), polyetheresteramide (PEEA), polycarbonate-esteramide (PCEA) or polyether-block-amide (PE-b-A).

The properties of thermoplastic polyamide elastomers depend strongly on the type of polyamide block, the type of polyether block and the length and number of blocks. The key properties of TPE-A include:

  • Good processability
  • High temperature resistance (up to 170°c)
  • Good solvent resistance
  • Creep dimensional stability
  • Wear resistance
  • Good low temperature flexibility
  • Impact resistance and elastic recovery
  • Excellent bonding to polyamide engineering materials

Thermoplastic Polyamide Elastomers
The structure of thermoplastic polyamide elastomers.
(Source: Thermoplastic Elastomers, Edited by Prof. Adel El-Sonbati)


Emergence of Biobased TPEs

Emergence of Biobased TPEs

To reduce dependence on non-renewable resources such as petroleum and achieve sustainable development of the polymer materials industry, bio-based polymer materials are favored by more and more people. Bio-based thermoplastic elastomers are a type of thermoplastic elastomer materials prepared from biomass monomers, whose resources are very sustainable because their monomers are derived from organisms in nature.

The bio-based thermoplastic elastomers are made using several bio-based raw materials, such as starch ranging from 30%–50%, castor & canola oil, polyols from vegetable oils & fatty acids, corn & soybean oil. Some of the popular commercial bio-based TPE grades include:



Properties and Processing of TPEs

Properties and Processing of TPEs

The ultimate properties achieved in any TPE material are governed by the chemistry, nature of the constituents, and its morphology. A specific property will vary with the relative proportions of hard and soft phases, so a range of TPE materials are available within each TPE group.

Mechanical Properties - The mechanical strength and modulus (stiffness), abrasion, hardness (can be a limited range), compression and tension set, and tear resistance of the TPE above room temperature and below the softening point are significantly influenced by the hard phase.

Hardness Range
Hardness Range of Thermoplastic Elastomers


Flexibility - The elastic soft phase generates the rubber-like properties of elongation, flexure, low-temperature performance, dynamic properties, and to some extent tensile strength by virtue of strain-induced crystallization of chain segments.

Electrical Properties - Electrical insulation properties are dependent on the level of polarity present in the TPE. Most TPE materials will give a level of electrical insulation. Here, the essentially nonpolar olefinic TPO and TPV materials and SEBS TPE (dependent on other compounded polymer and additives) display good to excellent electrical insulation properties.

Thermal Properties - Key to the performance of TPE is its thermal properties both in terms of its overall performance and ease of melt processing. The glass transition temperature (Tg) of the hard phase governs in part the mechanical performance at room temperature and above, while the soft phase controls the subroom temperature performance and brittle point.

Chemical Performance - Chemical resistance is determined by the chemistry of the TPE and its morphology. Nonpolar amorphous TPE materials, styrenics, have somewhat limited chemical resistance to a broad range of solvents.

UV Stability - The environmental resistance of TPE types is a key consideration especially for outdoor applications, particularly in the automotive sector. All the TPE family are susceptible to a greater or lesser extent to the effects of high-energy UV radiation.

 Properties SBCs TPOs TPVs TPUs COPEs PEBAs
Specific Gravity 0.9-1.1 0.89-1.0 0.9-1.0 1.1-1.3 1.1-1.3 1.0-1.2
Shore Hardness 3A-60D 60A-75D 35A-50D 60A-85D 90A-72D 60A-75D
Low Temp. Limit, °C -70 -60 -60 -70 -65 -40
High Temp. Limit (Cont.), °C 120 120 135 120 125 170
Compression Set Resistance at 100°C F P G F/G F F/G
Resistance to Hydrocarbon Fluids F/G P G/E F/E G/E G/E
Resistance to Aq. Fluids G/E G/E G/E F/G P/G F/G
P=Poor, F=Fair, G=Good, E=Excellent


Processing Methods of TPE


TPEs are technologically very attractive because they can be processed as thermoplastics using existing conventional thermoplastic machinery. TPE is utilized in all the major fabrication processes, for example, injection molding, extrusion, blow molding, calendaring, film extrusion, and thermoforming.

When heated, thermoplastic elastomer shows good flow properties. They solidify rapidly on cooling. This allows for the use of a highly productive thermoplastic processing equipment while processing thermoplastic elastomer. Several elastomeric products are hence produced. TPEs also require little or no compounding and do not require the addition of reinforcing agents, stabilizers, or cure systems.

A typical PVC equipment can be used. Drying at 80°C for 2 hours is recommended and maximum permissible moisture is 0.1%.


Injection Molding


Injection molding is by far the most used technique in TPE processing due to its high productivity and because it is a clean process with no waste formation. It is used in a great variety of applications ranging from tubes or foams to finished articles; it can be applied to the co- or insert-injection. During injection molding, TPEs behave as the other thermoplastics in hot runner without major problems.

  • Recommended compression ratio: 2:1 to 3:1
  • Recommended screw L/D: 20-24
  • A mold temperature of 25-50°C is recommended
  • A mold temperature of 160-200°C is recommended, depending on hardness range


Extrusion


The extrusion of TPEs is essential in the shaping of many different profiles. The use of single-screw extruders is predominant, but some other extruders are used, such as those equipped with three-section or barrier screws. Extrusion is also applied to other shapes: foams, tubes, sheets, etc.

  • Melt temperature: 180-190°C
  • Best results are obtained with screw L/D of 24 and compression ratio of 2.5:1 to 3.5:1


3D Printing


Materials with rubber-like properties or rubber are widely used for a great range of applications where the elastic properties of rubber are required. Since 3D printing with rubber was long not thought possible (rubber is a thermoset material), manufacturers started looking for a 3D printing alternative to rubber.

TPE filament is a flexible 3D printing material that feels and acts much like flexible rubber. There are several types of TPE, with Thermoplastic polyurethane (TPU) being the most commonly used among 3D printing filaments for FDM and powder for use in SLS machines. Flexible filaments can be used to make parts that can bend or must flex to fit their environment: stoppers, belts, springs, phone cases, and more.


3D Printing TPE with the Airwolf 3D HD


Find Suitable Thermoplastics Elastomer Grade


View a wide range of thermoplastics elastomer grades (TPE-S, PEBA, TSiV, TPC, etc.) available today, analyze technical data of each product, get technical assistance or request samples.

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1 Comments on "Thermoplastic Elastomers 101: An Ultimate Guide"
Mário C Jul 22, 2021
Very interesting description of these materials.

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