What are Thermoplastic Elastomers (TPEs)?
What are Thermoplastic Elastomers (TPEs)?
ThermoPlastic Elastomer (TPE) was introduced commercially in the 1960s. TPE is a polymer with the characteristics of:
- Thermoset vulcanized rubber — It exhibits high elasticity at room temperature.
- Thermoplastic — It exhibits good processability at high temperatures.
There is a principal difference between thermoset elastomers/rubbers and thermoplastic elastomers. This lies in the type of crosslinking bond in their structures. Crosslinking is a critical structural factor that contributes to imparting high elastic properties.
Need clarification on rubber vs. TPE selection? Ace your selection process by choosing the right material (rubber vs TPE) in your end application.
A thermoplastic elastomer must fulfill the following three essential characteristics:
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The ability to be stretched to moderate elongations. Upon the removal of stress, return to something close to its original shape.
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Processable as a melt at elevated temperature
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Absence of significant creep
TPEs help in achieving outstanding properties. This is by varying the blend compositions, viscosity of the components, and compounding ingredients at a low cost. It is considered as an efficient and cost-effective alternative for:
The rubber-like properties have enabled TPE to replace rubber in several applications. Today, they find use in applications that offer elasticity benefits over a wide temperature range. These include adhesives, footwear, medical devices, automobile parts, household goods, etc.
TPE materials have the potential to be recyclable. This is because they can be molded, extruded, and reused like plastics. But, the typical elastic properties of rubbers are not recyclable. This feature owes to their thermosetting characteristics.
Key advantages and disadvantages
Knowing the pros and cons of Thermoplastic Elastomers (TPEs) is important. It is crucial for making informed decisions about the:
- product design,
- manufacturing, and
- material selection
It ensures that products are safe to use, cost-effective, and capable of meeting their intended purpose.
| Advantages |
Disadvantages |
- Simpler processing, lower energy consumption, and lower finished part costs due to shorter fabrication times
-
Easily insert molded with olefin materials, such as polypropylene (PP), without the use of adhesives
-
Very good electrical insulation properties
-
Heat and oil resistance (within a specific temperature range)
-
Low permeability and colorable
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Can be produced in a variety of hardness grades
|
- Melting at elevated temperatures limits the use of parts from TPEs for certain applications
-
Comparatively higher cost than thermoset rubbers
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Shear sensitive
-
Low resistance to aromatics
|
How to classify TPEs based on chemistry?
How to classify TPEs based on chemistry?
The simplest TPE materials are like ABA block copolymers, where:
- A is a hard thermoplastic at room temperature. But it softens at elevated temperatures. For example, polystyrene, polyethylene, or polypropylene
- B is a soft elastomer, for example, polydimethylsiloxane, polybutadiene, polyisoprene, or poly (ethylene-propylene)
After years of development, TPE can be categorized based on various aspects. These include 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 thus they offer different properties. Click on each category to get more infomation.
Thermoplastic styrenic block copolymers (SBC/TPE-S)
Styrenic thermoplastic elastomers are the largest group among TPE materials. They are the most versatile as they can be produced over a variety of hardness values. They include different main types:
- SBS: Styrene-butadiene-styrene block copolymer
- SIS: Styrene-isoprene-styrene block copolymer
- SEBS: Styrene-ethylene-propylene-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. This allows each elastomer to pass through a few hard domains before it ends.
Styrenic TPEs Structure
(Source: Thermoplastic Elastomers, Edited by Prof. Adel El-Sonbati)
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
Thermoplastic elastomer polyolefins (TPO/TPE-O)
This is a new class among thermoplastic elastomeric materials as compared to SBC. They are blends of polypropylene or polyethylene, ethylene-propylene-diene rubber, and nitrile rubber (NBR). NBR provides an elastomeric element.
Themoplastic polyolefins (TPO) has two kinds of production processes:
- Blending compound type — It includes dynamic vulcanization (TPV) and mechanical blending (CTPO).
- Reactor type
Polyolefin block copolymers are amorphous and transparent polymers. Polyolefins are chemically inert, extremely flexible, nontoxic, very lightweight, and sterile.
Thermoplastic vulcanizates (TPV/TPE-V)
Thermoplastic vulcanizate (TPV) is a milestone in the development of elastomeric alloys. TPV is replacing traditional thermosetting vulcanized rubber in several applications. Thus, it is becoming one of the most promising polymer material varieties. TPVs include silicone rubber TPV (TPSiV), acrylate rubber TPV (ACM), TPV based on NR or ENR, and polyolefin elastomer (EOC)/PP TPV.
This class of TPE differs fundamentally from those discussed before. In that, they derive their physical and elastomeric qualities from mechanically combining various thermoplastics with thermoset rubbers. This does not happen by chain segment structure as in the case of block copolymer TPE.
The properties of thermoplastic vulcanizates include:
- Excellent barrier properties
- Small permanent deformation
- Good mechanical properties
- Good properties at low temperatures
- Fatigue durability
- Good liquid and oil resistance
Note: Elastomeric alloys are blends of elastomers and thermoplastics. They can be processed using thermoplastic processing methods.
Thermoplastic polyurethane elastomers (TPU/TPE-U)
TPUs are block copolymers with urethane backbone linkages. They have two types of blocks. They are:
- Hard segment — It is formed by the addition of a chain extender to a diisocyanate. For example, diisocyanates, short-chain diols (commonly used are 1,4-butanediol and lesser used are 1,6-hexanediol and 1,4-dihydroxyethoxybenze).
- Soft segment — It consists of long flexible polyether or polyester chains. This interconnects two hard segments. For example, long-chain diols (hydroxyl-terminated polyesters and polyethers).
Polyether or polyester-based TPU offers specific property benefits, particularly chemical resistance. The typical polyester types are polycarbonate and polycaprolactone glycols. The polyether types include poly (oxypropylene) and poly (oxytetramethylene) glycol.
TPUs composed of alternating hard segment and soft segment structures
(Source: Thermoplastic Elastomers, Edited by Prof. Adel El-Sonbati)
Check out the production process of TPU, its main properties, and benefits. Learn how TPUs enable various industries to produce advanced products.
Advantages of thermoplastic urethane elastomers include:
- Good abrasion resistance
- Good tear strength
- Good stiffness properties
- Low friction coefficient (depends on hardness)
- Good oxygen, ozone, and weather resistance
Thermoplastic copolyester elastomers (COPE/TEEE/TPE-E)
Thermoplastic polyester elastomers (TPEEs) are a type of block linear copolymers. They contain the following:
- Hard crystalline segment — It is a crystalline phase. It provides strength. For example, polybutylene terephthalate (PBT). The rigidity, polarity, and crystallinity of the hard segment of TPEEs provide them:
- outstanding strength,
- excellent high-temperature resistance,
- creep resistance,
- solvent resistance and
- impact resistance.
- Soft amorphous segment — It is a continuous segment. For example, polytetramethylene oxide glycol (PTMO). The low glass transition temperature and saturation of the soft segment polyether make it:
- excellent low-temperature resistant
- aging resistant.
It combines the excellent elasticity of rubber and the processability of thermoplastics. In more general terms, the key properties of these materials are:
- Excellent dynamic properties (like 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 elastomers (PEBA/COPA/TPE-A)
Thermoplastic polyamide elastomer (TPE-A) is a newly developed class. It belongs to alternating block copolymer elastomers. It consists of soft segments of polyesters or polyethers and a rigid block of polyamide. Examples of polyamide can be:
- polyesteramide (PEA),
- polyetheresteramide (PEEA),
- polycarbonate-esteramide (PCEA), or
- polyether-block-amide (PE-b-A).
The structure of thermoplastic polyamide elastomers.
(Source: Thermoplastic Elastomers, Edited by Prof. Adel El-Sonbati)
The properties of thermoplastic polyamide elastomers depend strongly on several aspects. These include 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
TPEs Moving Towards Sustainable Options
TPEs Moving Towards Sustainable Options
Biobased Thermoplastic Elastomers (TPEs) provide environmental and sustainability benefits to the manufacturers. The presence of biobased content helps them create more environmentally friendly TPE versions. Here are some key reasons why biobased TPEs are significant:
- Reduced carbon footprint: Biobased TPEs are derived from renewable resources. These include plant-based feedstocks (e.g., corn, soyabean, sugarcane, etc.). They absorb carbon dioxide (CO2) during their growth. This lowers greenhouse gas emissions compared to TPEs made from fossil fuels.
- Reduced dependency on fossil fuels: Petroleum-derived TPEs are finite. Biobased TPEs can be grown annually making them a sustainable and readily available resource. Hence, Biobased TPEs help reduce the industry's reliance on fossil fuels.
- Biodegradability and compostability: Some biobased TPEs can break down naturally over time. This reduces the persistence of plastic waste in the environment. This is important for applications where disposal is a concern (like single-use items).
- Consumer preference: Many consumers are becoming increasingly environmentally conscious while choosing a product. They are seeking products made from sustainable materials. Biobased TPEs help manufacturers meet these consumer demands for eco-friendly and sustainable options.
- Regulatory support: Encouraging the use of biobased TPEs has become the focus of suppliers globally. They make sure that their product(s) meet the regulations that can vary significantly from one region or country to another.
Emergence of biobased TPEs
Biobased thermoplastic elastomers are a type of thermoplastic elastomer material. They are prepared from biomass monomers. Their resources are very sustainable as their monomers are derived from organisms in nature.
The biobased thermoplastic elastomers are made using several bio-based raw materials. For example, starch ranging from 30% to 50%, castor & canola oil, polyols from vegetable oils & fatty acids, and corn & soybean oil. Some of the popular commercial bio-based TPE grades include:
What are the main properties of TPE?
What are the main properties of TPE?
The properties achieved in any TPE material are governed by several factors. These include the chemistry, nature of the constituents, and their morphology. A specific property will vary with the relative proportions of hard and soft phases. This allows a range of TPE materials to be available within each TPE group.
i) Mechanical properties — The hard phase influences:
- mechanical strength and modulus (stiffness),
- abrasion and hardness (can be a limited range),
- compression and tension set, and
- tear resistance of the TPE above room temperature and below the softening point.
Hardness Range of Thermoplastic Elastomers
ii) Flexibility — The elastic soft phase generates the rubber-like properties of:
- elongation
- flexibility
- low-temperature performance
- dynamic properties
It also influences tensile strength to some extent. This happens by strain-induced crystallization of chain segments.
iii) Electrical properties — Electrical insulation properties depend on the polarity of TPE. Most TPE materials will give a level of electrical insulation. Here, the nonpolar olefinic TPO, TPV materials, and SEBS TPE display good to excellent electrical insulation properties. SEBS TPE is dependent on other compounded polymers and additives.
iv) Thermal properties — Key to the performance of TPE is its thermal properties. This is in terms of its performance and ease of melt processing. The Tg of the hard phase, in part, governs the mechanical performance at room temperature and above. Whereas, the soft phase controls the subroom temperature performance and brittle point.
v) Chemical performance — Chemical resistance is determined by the chemistry of the TPE and its morphology. Limited chemical resistance to a broad range of solvents can be found in:
- non-polar amorphous TPE materials
- styrenics
vi) UV stability - The environmental resistance of TPE types is a key consideration. It is important for outdoor applications, particularly in the automotive sector. All the TPE families 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-temperature limit, °C |
-70 |
-60 |
-60 |
-70 |
-65 |
-40 |
| High-temperature 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 aqueous fluids |
G/E |
G/E |
G/E |
F/G |
P/G |
F/G |
| P=Poor, F=Fair, G=Good, E=Excellent |
How are TPEs processed?
How are TPEs processed?
TPEs are technologically very attractive. This is because they can be processed as thermoplastics. This is done by using existing conventional thermoplastic machinery. TPE is utilized in all the major fabrication processes. For example:
- Injection molding,
- Extrusion,
- 3D printing.
When heated, thermoplastic elastomer shows good flow properties. They solidify rapidly on cooling. This allows the use of highly productive thermoplastic processing equipment while processing thermoplastic elastomers. Several elastomeric products are hence produced. TPEs also need little or no compounding. They do not need 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. The maximum permissible moisture is 0.1%.
Efficient TPE processing with injection molding
Injection molding is by far the most used technique in TPE processing. This is due to its high productivity and 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 other thermoplastics in hot runners without major problems.
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Recommended compression ratio: 2:1 to 3:1
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Recommended screw L/D: 20-24
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A mold temperature of 25-50 °C is recommended
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A mold temperature of 160-200 °C is recommended, depending on the hardness range
Related Read: Understand in detail the injection molding process, its types, and the design and manufacturing of mold.
Optimizing TPE extrusion: Process parameters and equipment
The extrusion of TPEs is essential in the shaping of many different profiles. The use of single-screw extruders is predominant. Other extruders that are used include those equipped with three-section or barrier screws. Extrusion is also applied to other shapes like foams, tubes, sheets, etc.
-
Melt temperature: 180-190 °C
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Best results are obtained with screw L/D of 24 and compression ratio of 2.5:1 to 3.5:1
Related Read: Get details about the extrusion equipment, its design and functions, processing techniques, troubleshooting, and more.
Exploring TPE filament: A flexible 3D printing alternative to rubber
Materials with rubber-like properties or rubber are used in a great range of applications. They are used where the elastic properties of rubber are required. 3D printing with rubber was long not thought possible (rubber is a thermoset material). Manufacturers have 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. Thermoplastic polyurethane (TPU) is the most used among 3D printing filaments. It is used for FDM and powder for use in SLS machines. Flexible filaments can be used to make parts that can bend or flex to fit their environment. These include stoppers, belts, springs, phone cases, and more.
3D Printing TPE with the Airwolf 3D HD (Credits: Airwolf 3D)
Other methods for processing TPEs are blow molding, calendaring, film extrusion, and thermoforming.
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