What is a Thermoplastic Elastomer (TPE)?
A Thermoplastic elastomer, or TPE is a flexible and rubber-like material that processes like plastic. A TPE is a true thermoplastic, which does not require vulcanization or curing.
Thermoplastic elastomers are processed using a variety of plastic manufacturing equipment such as, injection molding, extrusion, and blow molding.
A TPE can be utilized in advanced processing such as, overmolding and two-shot molding, and can also undergo secondary operations such as, welding and bonding to various materials.
Thermoplastic elastomers offer part design flexibility and easy bonding to other thermoplastic substrates.
Types Of Thermoplastic Elastomer (TPE)
Thermoplastic elastomers are used in almost every industry and there are many types of thermoplastic elastomers on the market.
#1. Styrenic Block Copolymers (TPE-S).
Styrenic block copolymer thermoplastic elastomers, commonly known as TPE-S materials, are either made from SBS or SEBS.
Styrene Butadiene Styrene (SBS) is a type of TPE whose molecular structure consists of repeated styrene and butadiene units with styrene end caps.
This structure creates hard blocks of styrene and soft blocks of butadiene. SBS is the most common TPE. Styrene Ethylene Butylene Styrene (SEBS) is made by hydrogenating SBS, a process that breaks down the butane mid-block into ethylene butadiene.
This process improves the TPE’s heat and chemical resistance, gives it good weathering resistance, and better protection against UV and ozone. SEBS can bond to other thermoplastics. It is ideal for outdoor applications.
#2. Thermoplastic Polyolefins (TPE-O or TPO).
TPO materials, often referred to as thermoplastic olefins, are thermoplastic elastomers that blend polypropylene or polyethylene with an elastomer such as: EPDM, EPR, EO, or EB.
These elastomers are typically not cross-linked. The various constituents are mechanically blended together. TPO has good thermal and chemical resistance.
It does not exhibit many elastomeric properties and has a relatively high hardness of 80 on the Shore A scale.
TPO is used in applications where standard polypropylene is not tough enough. TPO can be processed using injection molding, extrusion, or blow molding.
#3. Thermoplastic Vulcanisates (TPE-V or TPV).
TPVs (Thermoplastic Vulcanisates), like TPOs, are made from a mixture of polypropylene and EPDM. However, in this case, the EPDM is vulcanized during compounding.
TPVs have a wider hardness range. They also exhibit better elastomeric properties than TPOs. TPVs can resist temperatures up to 120°C and are widely used in vehicle engine compartments.
TPV materials can be formed using standard melt-processing techniques like injection molding.
#4. Thermoplastic Polyurethanes (TPE-U or TPU).
TPU (Thermoplastic Urethane) is formed by reacting diisocyanates with either a type of polyester or polyether polyol.
The diisocyanates form the hard segments whereas the polyethers or polyesters form the soft segments.
TPUs can be easily modified by changing the polyol and diisocyanate blend. TPU is typically processed with injection molding, extrusion, and blow molding.
#5. Thermoplastic Copolyesters (TPE-E or COPE or TEEE).
TPE-Es (Thermoplastic Copolyesters) are high-performance thermoplastic elastomers that share many properties with thermosetting elastomer polymers while having the advantage of being melt-processible.
TPE-Es are block copolymers that typically consist of hard segments made from polybutylene terephthalate alongside soft segments made from various polyesters. TPE-E is widely used in the medical industry.
#6. Melt Processable Rubber (MPR).
MPR is an alternative to vulcanized rubber and consists of a cross-linked halogenated polyolefin mixed with plasticizers and stabilizers.
The primary purpose of MPR is to create rubber-like parts using thermoplastic processing equipment. MPR outperforms many other rubbers below an operating temperature of 120C.
#7. Thermoplastic Polyether Block Amides (TPE-A).
TPE-As consist of soft segments made from either polyethers or polyesters as well as hard segments made from polyamide.
Different polyamides can be used such as polyesteramide (PEA), polyether ester amide (PEEA), or polycarbonate-esteramide (PCEA).
The properties of an individual TPE-A depend heavily on the type of polyamide involved. TPE-A can be bonded to thermoplastic polyamides.
Properties of TPEs
Thermoplastic elastomers (TPE) have a range of physical and chemical properties, here are the details:
Physical properties:
- Flexibility: TPEs exhibit excellent flexibility, allowing them to be easily stretched and compressed, and to recover their original shape.
- Softness: TPEs have a soft and rubber-like texture, providing a comfortable feel and touch.
- Elasticity: TPEs display high elasticity, enabling them to withstand repeated stretching without permanent deformation.
- Processability: TPEs can be processed using common thermoplastic manufacturing techniques like injection molding, extrusion, and blow molding.
- Melting point: TPEs have a specific melting point range, typically between 180°C and 250°C, which allows them to be melted and reshaped multiple times.
Chemical properties:
- Compatibility: TPEs can be easily blended or co-extruded with other thermoplastics, enhancing their versatility and allowing for customized material properties.
- Resistance to chemicals: TPEs exhibit good resistance to various chemicals, oils, and solvents, making them suitable for applications where contact with such substances is expected.
- Weather resistance: TPEs often show excellent resistance to weathering, including UV radiation, maintaining their properties and appearance over extended periods of outdoor exposure.
- Recycling: TPEs are recyclable, making them environmentally friendly and contributing to sustainable manufacturing practices.
How is TPE Made?
Thermoplastic elastomers are made by copolymerising two or more monomers through either block or graft polymerisation methods.
Block techniques create long-chain molecules with various sequences, or blocks, of hard and soft segments. Graft polymerisation methods involve grafting one polymer chain to another as branches.
These techniques cause one of the monomers to develop a hard or crystalline segment which acts as a thermally stable component.
This component softens and flows under shear unlike the chemical cross-links between the polymeric chains in conventional, thermoset rubber. Meanwhile, the other monomer develops a soft or amorphous segment that contributes to the rubbery characteristics of TPE.
Varying the ratio of the monomers used, as well as the lengths of hard and soft segments, allows the properties of the finished TPE to be controlled.
However, graft methods offer more possibilities to vary the copolymer because both the backbone monomer and the grafted branches can be hard and glassy, rubbery, or somewhere in between.
In both block and graft production methods the environmental and fluid resistance are entirely predictable.
TPEs are usually produced in pellet form and added to the same type of injection moulding machine as rigid thermoplastics.
Colourants can be added to the compound during production or blended in automatically or manually at the injection moulding machine.
How to Process TPEs?
The two most important manufacturing methods with TPEs are extrusion and injection molding. TPEs can now be 3D printed and have been shown to be economically advantageous to make products using distributed manufacturing.
#1. Injection molding.
Injection molding is by far the most important technique for processing TPE material. The main reason for this is the high productivity of injection molding and the clean, residue-free processing.
In injection molding, the molten plastic is injected into a mold, making the final product an exact copy of the mold. The behavior of TPEs in this process corresponds to that of other thermoplastics in the hot runner.
The co- and insert-injection processes are equally suitable for this application. Injection molding is mainly used to produce solid parts, such as tools or components, which can be produced in high volumes and with great precision.
#2. Extrusion.
Extrusion is one of the most popular processes for manufacturing tubes, profiles, etc. from thermoplastic elastomers. In this continuous process, the material is shaped by forcing it through a die whose cross-sectional profile the material takes.
In extrusion, TPE pellets are fed into the extruder’s hopper are then heated and melted by a spiral screw rotating in a heated barrel.
The screw conveys the molten plastic through a die to create continuous lengths of molds with the same profile, which are then cooled.
Unlike injection molding, extrusion usually yields a semi-finished or intermediate product that must be further processed.
This process can be used to produce very complex cross-sections with a very good surface finish and a high degree of design freedom.
#3. Extrusion blow molding.
Another important process for shaping profiles is TPE extrusion. In extrusion, molten plastic is extruded into a mold or die. Air is then blown into the mold or tool to create the desired shape.
The dominant technology here is the single-screw extruder. However, other extruders, such as triple-screw extruders, are also used.
Extrusion is used to produce even complex hollow parts such as bottles and containers. In addition to the production of profiles, extrusion is also used for sheets, pipes and other shapes.
#4. Other thermoplastic elastomer processing methods.
In addition to the injection molding, extrusion and extrusion blow molding methods described above, other methods are also used for processing TPEs – although in some cases to a lesser extent. These include two component (2k) processing, melt calendering, thermoforming, hot welding and compression molding.
#5. 3D printing.
Another area of application for TPE material is now 3D printing, for which materials with rubber-like properties were out of the question for a long time.
Flexible TPE filaments are used here to produce flexible or customizable parts, such as smartphone covers. Thermoplastic polyurethane (TPU) is the most commonly used material for 3D printing.
On the other hand, for specialized applications such as the processing of PLA, acrylonitrile butadiene styrene (ABS) and polycarbonate (PC), the TPS from Kuraray are particularly well-suited.
Advantages Of Thermoplastic Elastomer (TPE)
#1. Versatile compounds and sizing.
Thermoplastic elastomers are extremely versatile, making it easy to customize the material for the product’s final use and service environment.
TPE tubing can range from soft and jelly-like to rigid and hard. TPE tubing can also be made in a range of custom sizes, ranging from an inner diameter of 0.063 inches to an outer diameter of one inch.
The wall thickness of TPE tubing can be customized as well. Learn more about different thermoplastic elastomer types >
#2. Resistant.
Thermoplastic elastomer (TPE) is naturally chemical resistant and can be made flame retardant as well. TPE products have outstanding chemical properties and stability, even when exposed to a broad range of temperatures and environmental factors.
This resistance to extreme variables contributes meaningfully to the quality and durability of the final product.
#3. Consistency.
Thermoplastic elastomer materials require little to no compounding and no reinforcing agents, stabilizers, or cure systems.
As a result, there is virtually no variation between batches. This contributes to improved consistency in both raw materials and fabricated products.
The consistency of TPE makes it a desirable alternative to rubber or plastic in certain applications.
#4. Eco-friendly.
Thermoplastic elastomers are an excellent choice from an environmental standpoint. TPE materials made from non-toxic recyclable plastics are highly eco-friendly.
TPE consumes less energy during production than other materials and can often be recycled by molding or extruding.
#5. Safe for the medical and food & beverage industries.
TPE is naturally latex-free and is safe for patients who are sensitive or allergic to latex. Depending on how it’s processed, TPE can be soft to the touch.
This makes TPE a good choice for healthcare products that make direct contact with the patient, since that pleasant feel can make a difference in the patient’s comfort.
Also, TPE is easy to sterilize, which is critical in both healthcare environments and the food and beverage industry.
#6. Cost effective.
TPE can be an efficient and cost-effective alternative to other materials, such as natural rubber latex, silicone, and polyvinyl chloride (PVC) compounds.
TPE requires less processing and shorter fabrication times than other materials, which can significantly lower final costs.
#7. Melt properties.
One of the defining characteristics of TPE is its processability as a melt at elevated temperatures. This makes TPE a great choice for high-volume injection molding and extrusion.
#8. Color matching.
TPE responds well to color and dye and can be customized to match a full spectrum of colors and finishes, including fluorescents. TPE also has good clarity properties, which can be beneficial for medical tubing and other applications.
#9. Growing market.
Worldwide usage of thermoplastic elastomers has been growing steadily for several decades. Because the material and performance properties of TPE are valuable in so many contexts, many industries are continuing to discover new and innovative ways to use TPE.
TPE is also being explored as an alternative material for plastic and rubber products. This will likely contribute to continued demand and use into the future.
Disadvantages of Thermoplastic Elastomer (TPE)
Although TPR materials offer many advantages, they also come with some disadvantages:
- Brittleness or loss of flexibility outside of their service temperature range
- Less resilience, or the ability to snap back, than natural or synthetic rubber
- The potential for creep, or deformation over time under a constant load, that can result in dimensional changes
- Limited resistance to ultraviolet (UV) light, a potential problem in outdoor applications
- Limited bonding capability to other materials, which can complicate overmolding or the use of adhesives for product assembly
Applications of Thermoplastic Elastomer (TPE)
- Automotive: Weather seals, shock dust boots, bumpers, exterior & interior parts, exterior & interior trims, instrument panels, air ducts, pipe grommets, glass encapsulation, drive belts, high/low pressure pipes, mats for motor scooters, and o-rings
- Construction: Extruded seals for doors and windows, simple or co-molded hydraulic seals, glazing seals, and pipe seals
- Consumer goods: Magnetic seals for refrigerators, power tool handles, remote control covers, mobile phone covers, push-button panels, and shock absorbing protections for vacuum cleaners
- Medical: Breathing tubes, syringe seals 7 tips, ventilation masks, bags, seals, valves, and catheters
- Electronics: Sheaths for condensers, plugs and loose sockets, specialty cables, and mobile phone components
- Footwear & sporting goods: Items for diving (flippers, snorkels, masks) and skiing (ski pole handles, ski boots), sports goods, and shoe soles
- Industrial: Anti-vibration mounts, inlet pipes, exhaust manifolds, seals, drum suspension bushes, shock absorbers, and roof membranes