Thermoplastic Elastomers TPE, TPR

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Thermoplastic Elastomers TPE, TPR

Introduction

The formal definition of a thermoplastic rubber or elastomer (TPE) is a polymer blend or compound which, above its melt

temperature, exhibits a thermoplastic character that enables it to be shaped into a fabricated article and which, within itsdesign temperature range, possesses elastomeric behaviour without cross-linking during fabrication. This process is

reversible and the products can be reprocessed and remoulded.

Properties

Even though TPEs are thermoplastic, they exhibit elasticity similar to that of a cross-linked rubber. A key indicator is their

softness or hardness value as measured on the Shore durometer scale. Like crosslinked rubber, TPEs are available as very

soft gel materials from 20 Shore OO up to 90 Shore A, at which point they enter the Shore D scale and can be formulated to

give hardness values up to 85 Shore D, which designates a material that is very hard.

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.

Additio nal advantages o ver thermoset ru bber provid ed by TPEs include excellent colourabil ity an d a lowe r density.

Teknor Apex manufactures one of the worlds most diversified ranges of TPE compounds. These are supplied under six trade

names that represent different technologies, including di- and tri-block hydrogenated styrene block copolymers (Tekron,

Elexar, and Monprene), thermoplastic polyolefin blends (Telcar), thermoplastic vulcanizates (Uniprene), and over-molding

compositions designed to bond to diverse polar substrates (Tekbond).

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 rubberwith 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 exhib it h igh elastici ty. Our range of grades encompasses ru bberlike properties and offer a wide range

of durometers, low compression set, and high elongation.

Main Characteristics

Excellent flexural fatigue resistance Good electrical properties

Good tear & abrasion resistanceResistance to Low & High Temperatures from -30degC to

+140degC

High impact strength Colourability
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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


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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.

Polymer Types:

TPE-S

Styrenic block copolymer

MPR

Melt Processable Rubber

TPE-O

Thermoplastic Olefinic elastomer

TPE-E

Thermoplastic Polyester Elastomer

TPE-VThermoplastic Vulcanisate

TPE-AThermoplastic Amide Elastomer

TPE-U

Thermoplastic Polyurethane ela stomer

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.

PHYSICAL PROPERTIES

Tensile Strength 0.5 - 2.4 N/mm

Notched Impact Strength no break Kj/m

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 **

Alcohols ****

KEY * poor ** moderate *** good **** very good

Current case studies

Typical applications from the range of materials are shown below:


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Wire and Cables

Elexar TPE-S compounds are a quality family of elastomer compounds specifically targeting wire & cable, fibre

optic, and electrical ap plications. 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.

Pen Grips

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 enh ance the qual ity of any writing product.

Airbag Covers

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 rubberbut processes with the ea se 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 p ushes 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).

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Thermoplastic Elastomers TPE, TPR