The Complete Guide to TPE (updated)

I previously published an article about the different categories of TPE. This is that article with some updates including 1 additional material that I think should be classified as a TPE.

The acronym TPE refers to thermoplastic elastomer. These materials are sometimes referred to as TPR or thermoplastic rubber. TPE and TPR are different names for the same thing. Basically, a soft, flexible, impact resistant material that can be melt processed in traditional injection molding equipment. Traditional rubber materials are thermoset materials that are processed using a wide variety of techniques.

TPE is a broad category of materials. There are a number of different materials that can be called TPE’s. My attempt here is to provide a description of 8 different categories of material types that fall under the umbrella term of TPE. Within each of these 8 categories, there are sub categories of materials but the difference between those sub-categories is of less significance than the differences between the 8 categories themselves.

Here are the 8 categories of TPE that are currently on the market:

1. Styrenic Block Copolymers (SBC)
2. Thermoplastic Polyolefins (TPO)
3. Thermoplastic Vulcanizate (TPV)
4. Thermoplastic Polyurethanes (TPU)
5. Thermoplastic Copolyesters (TPC-ET or COPE)
6. Thermoplastic Polyamides (TPA-ET or PEPA or PEBA)
7. Polyvinyl Chloride (PVC)
8. Ionomer

Advantages of TPE:

1. Easier to process. TPEs can be processed on traditional injection molding machines.
2. Faster cycle times in manufacturing.
3. Recyclable. Scrap made during manufacturing can be easily put back in the process and TPE parts can be recycled at the end of life.
4. Better appearance. TPE materials offer a wide variety of appearance options which is great for things like automotive interior applications.

Advantages of Rubber:

1. Higher heat resistance. Rubber, being a thermosetting material can take a lot of heat.
2. Better chemical resistance
3. Better compression set. Compression set refers to how the material rebounds or bounces back after being compressed.

Description of each type of TPE:

1. Styrene Block Copolymers (SBC)

What is it: SBC (styrenic block copolymer) materials are block copolymers and terpolymers (more than two polymers) of styrene and butadiene. This is a broad category of materials that covers a number of different formulations. Material designated as SBS, SEBS, SEPS, SIS and SEP are all styrenic block copolymers. You can look up what all those acronyms stand for if you want but I won’t bore you. Some manufacturers just refer to their material as SBC which means they’re being a bit cagey about the exact make-up of the material. A book could be written about the differences between all of the different SBC formulations but there are more similarities than differences so I will just cover the basics here. SBC materials are not typically injection moldable so most commercial grades are SBC that is compounded with polypropylene or polyethylene.

Here are the highlights:

• Hardness range from 15 Shore A to 50 Shore D
• The softest TPE available
• Good glossy appearance with a smooth surface feel similar to polypropylene
• Highest tensile elongation of any TPE (stretchiest)
• Available in clear
• Less heat resistant than TPV
• More flexible than TPV
• Poor chemical resistance to oil.
• Maximum continuous service temperature 230F
• Common trade names include Kraton, Sunprene, Multiflex
• Applications include gel inserts for shoes, grips for pens and toothbrushes and appliance knobs

2. Thermoplastic Polyolefin (TPO)

What is it: TPO is a compounded blend of polypropylene and un-crosslinked EPDM rubber. Most grades of TPO contain some type of mineral filler. These tend to be harder materials ranging from 30 Shore D and up. They tend to be classified by flexural modulus rather than hardness.

Here are the highlights:

• Available in flexural modulus from 90,000 to 350,000 psi.
• Combination of high stiffness and high impact strength
• Excellent appearance
• Some grades are paintable
• Weatherable grades are available
• Maximum continuous service temperature 230F
• Common trade names include Hifax, Mytex, Polyfort
• Applications include automotive bumper fascias, automotive interior panels

3. Thermoplastic Vulcanizate (TPV)

What is it: TPV is a compounded blend of polypropylene and cross linked EPDM rubber. TPV tends to be very soft and flexible. It is similar in properties to SBC.

Here are the highlights:

• Hardness range from 35 Shore A to 50 Shore D
• Has a matt finish appearance and a very rubber like feel
• Not available in clear. Natural TPV is a light cream color similar to ABS.
• Not as flexible as SBC
• More heat resistant than SBC
• Good chemical resistance
• Runs better if dried but many molders do not dry it
• Maximum continuous service temperature 240 F
• Common trade names include Santoprene, Geolast, Sarlink, Trexprene
• Applications include power tool housings, automotive boots and grommets, automotive cup holder inserts, door bumpers

4. Thermoplastic Polyurethane (TPU)

What is it: TPU materials are block copolymers formed by the reaction of diisocyanates with short chain diols or long chain diols. They are the best wearing TPE materials and have the highest tensile strength.

Here are the highlights:

• Hardness range from 70 Shore A to 80 Shore D
• The best rebound of any TPE
• The best wear properties of any TPE
• High tensile strength, even for softer grades
• High tear strength
• Must be dried
• Difficult to mold, degrades easily
• Annealing parts improves performance
• Expensive
• Ester based grades are most common and offer the best properties
• Ether based grades offer better hydrolysis resistance
• Heavier than other TPEs with a density around 1.24 g/cm³
• Maximum continuous service temperature 200 F
• Common trade names include Elastollan, Desmopan, Estane, Irogran, Texin
• Applications include in-line skate and skateboard wheels, automotive suspension bushings, running shoe arch supports and medical tubing

5. Thermoplastic Copolyesters (TPC-ET or COPE)

What is it: TPC-ET materials are copolymers of bifunctional aromatic polyesters. They are the highest heat TPEs available and can take repeated bending forces without breaking.

Here are the highlights:

• Hardness range from 80 Shore A to 80 Shore D
• Higher stiffness than other TPEs
• Can be repeatedly flexed without fracture
• Maximum continuous service temperature 290 F
• Common trade names include Hytrel, Arnitel
• Applications include automotive CV joint boots, coiled air hose tubing

6. Thermoplastic Polyamides (TPA-ET or PEPA or PEBA)

What is it: TPA-ET materials are copolymers obtained by polycondensation of a carboxylic acid poyamide with alcohol terminated polyether. Think of it as nylon based TPE. It offers properties similar to TPC-ET. This is not a commonly used material that seems to find a home mostly in medical applications.

Here are the highlights:

• Hardness range from 80 Shore A to 70 Shore D
• Can be repeatedly flexed without fracture
• Good oil resistance, even at high temperatures
• Expensive
• Maximum continuous service temperature 290 F
• Common trade names include Vestamid
• Applications include breathable films and medical tubing.

7. Polyvinyl Chloride (PVC)

What is it: PVC is produced by polymerization of vinyl chloride monomer. Plasticizers, primarily phthalates, are blended into the material to make it soft and flexible. Unlike the other materials here, PVC is available in both a rigid and a flexible form. We will focus on the flexible version here.

Here are the highlights:

• Hardness range from 35 Shore A to 55 Shore D
• Excellent chemical resistance
• Excellent appearance
• Very poor heat resistance
• Poor compression set or rebound
• Heavier than other TPEs, with density around 1.25 g/cm³
• Available in clear
• Poor wear and tear strength properties
• There are concerns about plasticizers causing adverse health effects
• Maximum continuous service temperature 176 F
• Common trade names include Geon, Hy-Vin, Polyvin, Vinika
• Applications include tubing, flooring, automotive interior panel covering

8. Ionomer

What is it: Ionomer is polyethylene copolymer with ionic molecules interspersed into the polymer chain. Here is the thing that makes ionomers unique. The strange thing about the ionic bond is that it dramatically reduces in attraction at elevated temperatures. The ions make the material act like a thermoset at room temperature and like a thermoplastic at elevated temperatures. Essentially a melt process-able thermoset. The ions basically cross-link the polymer chains at lower temperatures. Chemists refer to ionomers as reversible crosslinkers.

The bottom line is that this reversible crosslinking gives ionomers unique properties. They are extremely tough, have extremely high impact strength at low temperatures and excellent abrasion resistance. They also have excellent melt strength which means that even above the melting point, they are pretty strong. This makes them excellent for making sheet and film.

Here are the highlights:

• Hardness range from 35 to 70 Shore D
• Excellent low temperature impact strength
• Excellent oil and grease resistance
• Scratch resistance
• High gloss
• Available in clear
• Maximum continuous service temperature 140 F
• Common trade names include Surlyn, Formion
• Applications include food packaging film, golf ball out skins and cosmetics packaging

TPE materials, with the exception of PVC, are a relatively new addition to the thermoplastics market having been invented less than 30 years ago. The market for TPE continues to see a large amount of growth outpacing the broader thermoplastics market. The technological advancements that continue in the TPE industry can be a little difficult to keep up with. For instance, in the last 25 years or so, TPO has almost entirely replaced RIM materials for automotive bumper facias.

I hope this breakdown helps to clarify the differences between these materials and help you in choosing the right TPE for your application.