Thermoplastic Elastomers TPE, TPR
Designers increasingly use TPEs due to the significant cost savings possible because their ability to be processed on plastics machinery. Conventional rubber, whether natural or synthetic, is a thermosetting material that must undergo a chemical cross-linking reaction during moulding or extrusion, typically called curing or vulcanization. Due to this reaction it is not generally processable in standard thermoplastic equipment. The time that it takes for the vulcanization reaction to complete is influenced by many factors, however it is typical that this is somewhere between 1 minutes and several hours. The thermoplastic moulding and extrusion processes used for TPEs, on the other hand, avoid the cross-linking step and can achieve very fast cycles times, which can be as little as 20 seconds. Environmental an cost pressures require more and more materials to be recycleable, TPE processing scrap, reject parts or end of life products can be easily reprocessed, whereas most thermosetting elastomers end up as land fill.
Additional advantages over thermoset rubber provided by TPEs include excellent colourability and a lower density.
Here is why Teknor Apex TPEs are among the fastest-growing plastics materials:
- TPEs are a unique class of engineering materials combining the look, feel and elasticity of conventional thermoset rubber with the processing efficiency of plastics.
- The melt-processability of TPEs makes them very suitable for high-volume injection moulding and extrusion. They can also be reclaimed and recycled.
- As elastomers, TPEs exhibit high elasticity. Our range of grades encompasses rubberlike properties and offer a wide range of durometers, low compression set, and high elongation.
|Excellent flexural fatigue resistance||Good electrical properties|
|Good tear & abrasion resistance||Resistance to Low & High Temperatures from -30degC to +140degC|
|High impact strength||Colourability|
|Low specific gravity||Recyclable|
|Excellent resistance to chemicals & weathering||Possess low Compression Set|
|Co-injection & co-extrusion with Polyolefins & certain Engineering Plastics|
Grades available in the TPE industry
There are seven main TPE groups available commercially and these are listed in approximate ascending price order:
1) Styrenic Block Copolymers (TPE-S) SBS is based on two-phase block copolymers with hard and soft segments. The styrene end blocks provide the thermoplastic properties and the Butadiene mid-blocks provide the elastomeric properties. SBS is probably the highest volume TPE-S material produced and is commonly used in footwear, adhesives, bitumen modification and lower- specification seals and grips, where resistance to chemicals and aging a lower priority. SBS when hydrogenated becomes SEBS, as the elimination of the C=C bonds in the butadiene component generated ethylene and butylenes mid-block, hence the SEBS acronym. SEBS is characterised by much improved heat resistance, mechanical properties and chemical resistance. Monprene ® Tekron ® and Elexar ® products from Teknor Apex are good examples of hydrogenated styrenic block copolymers.
2) Thermoplastic Polyolefins (TPE-O or TPO) These materials are blends of polypropylene (PP) and un-crosslinked EPDM rubber, in some cases a low degree of cross-linking is present to boost heat resistanc and compression set proprties. They are used in applications where there is a requirement for increased toughness over the conventional PP copolymers, such as in automotive bumpers and dashboards. The properties are restricted to the high end of the hardness scale, typically >80 Shore A and with limited elastomeric properties.
Historically these products were mechanical blends of the 2 polymers, Telcar® from Teknor Apex is one example of this type of TPE-O. However with new catalyst technology it is now possible to blend the EPDM and PP in the reactor, therefore these types of TPEs are now available from major polymer manufacturers. These products are suited to high volume low cost applications, however there is still a market for custom mechanical blended TPE-O
3) Thermoplastic vulcanisates (TPE-V or TPV) These materials are the next step up in performance from TPE-O. These too are compounds of PP and EPDM rubber, however they have been dynamically vulcanised during the compounding step. They have seen strong growth in EPDM-replacement for automotive seals, pipe seals, and other applications where a heat resistance of up to 120degC is required. Shore hardness values range typically from 45A to 45D. The Uniprene ® series from Teknor Apex is a very good example of TPE-V materials and are available from 15 Shore A to 50 Shore D. Uniprene XL increases the upper temperature limit towards 140 C with big improvements in long terms compression set resistance versus standard TPE-V materials.
There are a number of new TPE-Vs being introduced, termed “Super TPVs” which are based on engineering plastics blended with high performance elastomers, which can offer greatly improved heat and chemical resistance.
4) Thermoplastic polyurethanes (TPE-U or TPU) These materials can be based on polyester or polyether urethane types and are used in applications where a product requires excellent tear strength, abrasion resistance, and flex fatigue resistance. Examples include shoe soles, industrial belting, ski boots, and wire and cable. Hardness is restricted to the high end of the Shore A scale, typically >80 Shore A.
5) Thermoplastic copolyesters (TPE-E or COPE or TEEE) are used where increased chemical resistance and heat resistance up to 140degC are needed. They also exhibit good fatigue resistance and tear strength and so are used in automotive applications such as blow moulded boots and bellows, wire and cable, and industrial hose applications. Again hardness is restricted to the high end and is typically between 85A to 75D.
6) Melt processable rubber (MPR) is designed for more demanding applications requiring chemical resistance, particularly resistance to oil and grease, where MPR replaces crosslinked nitrile rubber. It also possesses properties similar to those of vulcanised rubber in noise-dampening applications and has similar stress relaxation properties. Applications of MPR include automotive components, such as weather strips, and hand grips, where a good bonding to PVC, polycarbonate, or ABS is required. Compression set values are still much higher than for thermosetting elastomers so the penetration into the higher performance sealing market has been limited.
7) Thermoplastic polyether block amides (TPE-A) These products offer the good heat resistance , have good chemical resistance and bonding to polyamide engineering plastics. Their applications include cable jacketing and aerospace components.
Styrenic block copolymer
Melt Processable Rubber
Thermoplastic Olefinic elastomer
Thermoplastic Polyester Elastomer
Thermoplastic Amide Elastomer
Thermoplastic Polyurethane elastomer
Due to the wide range of TPEs on the market and the ever expanding range of applications it is critical that the designers and specifiers of products using TPEs remain abreast of the most recent innovations from industry suppliers. The following is only a snapshot of what can be achieved with TPE materials and we strongly urge readers to contact Chem Polymer/Teknor Apex to discuss their application in detail and obtain the most up-to date advice.
Tensile Strength 0.5 - 2.4 N/mm²
Notched Impact Strength no break Kj/m²
Thermal Coefficient of expansion 130 x 10-6
Max Cont Use Temp up to 140 oC
Density 0.91 - 1.3 g/cm3
RESISTANCE TO CHEMICALS
Dilute Acid ****
Dilute Alkalis ****
Oils and Greases ****
Aliphatic Hydrocarbons ****
Aromatic Hydrocarbons **
Halogenated Hydrocarbons **
KEY * poor ** moderate *** good **** very good
Current case studies
Typical applications from the range of materials are shown below:
|Wire and Cables
Elexar® TPE-S compounds are a quality family of elastomer compounds specifically targeting wire & cable, fibre optic, and electrical applications. Their unique blend of processability, functionality, customization and properties makes them the first choice of both design engineers and processors.
Power and Hand Tools
Monprene® and Tekbond® elastomers are an elite brand of TPEs offering some distinct advantages. Their unique blend of bondability to a wide range of substrates,, processability, functionality, and properties make them the first choice of many design engineers and processors.
Monprene ® and Tekbond® TPEs are a series of proprietary elastomer compounds that enable over-molding to engineering thermoplastics, add tactile and visual enhancement and provide a functional performance such as resistance to skin oils. Therefore these materials offer the ability to enhance the quality of any writing product.
Tekron® features the feel and flexibility of rubber while offering the benefits of easy handling for the end user. This series of compounds from Teknor Apex has a wide range of approvals for Air Bag Covers and is able to satisfy -35 C in-chamber deployment, whilst eliminating the painting process required by materials such as COPE.
|Grips and Handles
Telcar® Thermoplastic Rubbers offer a wide range of performance benefits such as a rubbery appearance and hot air aging up to 125 degrees C, excellent tear strength, ozone and weathering resistance, fluid resistance to acids, bases, and other aqueous based fluids.
|Plugs, Seals and Grips
Uniprene® is a specially designed thermoplastic vulcanizate (TPV). It performs like cured EPDM with the feel of thermoset rubber…but processes with the ease and speed of a thermoplastic olefin (TPO). Uniprene® TPVs have mechanical and recovery properties comparable to most vulcanized elastomers and are superior in performance to most thermoplastic elastomers (TPEs). Uniprene XL pushes the boundaries of performance even further. Please see below for more detail.
History of Thermoplastic Elastomers/Rubbers (TPR/TPE)
The first thermoplastic elastomer became available in 1959 and since this time a plethora of new variations of such materials has become available. There are six main TPE groups found commercially; styrenic block copolymers (TPE-S), polyolefin blends (TPE-O), elastomeric alloys, thermoplastic polyurethanes (TPE-U), thermoplastic copolyesters (TPE-E) and thermoplastic polyamides (TPE-A).