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The differences between TPE and TPR: a handy guide

clock 6 minutes | 14 Jan 2019

Granules of plastic polymers in glass jars

You’re not alone if you’re unsure of the differences between TPE and TPR.

Both TPE and TPR belong to the family of Thermoplastic Elastomers – and while, at the moment at least, there isn’t a defined industry standard to distinguish them, it’s clear where the confusion lies.

On the surface, their characteristics appear to be the same:

TPE

TPR

High-flexural fatigue resistance

High-flexural fatigue resistance

Resistant to tears and abrasions

Resistant to tears and abrasions

High-impact strength

High-impact strength

Good dielectric properties

Good dielectric properties

Excellent weather and chemical resistance

Excellent weather and chemical resistance

Recyclable

Recyclable

Temperature range:
-22°F to 284°F (30°C to 140°C)

Temperature range:
-22°F to 284°F (-30°C to 140°C)


So what’s the difference between TPE and TPR?

TPE and TPR definitely offer some differences, which really comes down to their base materials. TPE is modified from SEBS base material and TPR is often modified from SBS.

To better understand the difference in the manufacturing processes behind TPE and TPR, we must first break down the meaning of SEBS base material and SBS.

What are SEBS and SBS?

Styrene Ethylene Butylene Styrene Block Copolymer (SEBS) is the product of hydrogenated SBS. But what exactly is SBS? It’s styrene-butadiene-styrene block copolymer, which offers soft-touch characteristics utilised extensively by designers – especially in hand tools.

What does this mean in relation to SEBS? It’s the act of introducing molecular hydrogen to unsaturated molecules in special reaction conditions. What this does is ensure the molecular structure becomes saturated, which offers anti-aging properties, as well as resistance to yellowing. On top of this, it also ensures higher heat and corrosion resistance than SBS, therefore resulting in a higher performance output of TPE over TPR.

TPE choices

There’s a lot to choose from, with TPE groups available, including:

With the flexibility of plastics and rubber, both TPE and TPR are used widely in engineering, but for different applications. In TPR, specifically, its unsaturated molecular structure is similar to that of rubber, which gives it its elastic feel.

The Shore durometer scale

TPEs are certainly thermoplastic, but they still offer similar elasticity to their cross-linked rubber counterpart. This is determined by its softness or hardness, which is monitored on a scale known as the Shore durometer.

Available as soft gel materials – from 20 Shore OO up to 90 Shore AA – TPEs possess similar qualities to crosslinked rubber. After reaching 90 Shore AA, they are introduced to the Shore D scale, which means they can be formulated to achieve a hardness of up to 85 Shore D.

TPRs are available in a wide range of durometers, from 20 Shore OO to 85 Shore D – again, this aligns with TPE.

What is TPE?

Made up of soft and hard domains, TPEs are multiphase materials in their solid state. Some engineers may wonder why they’re rubbery – and there’s a very good reason for this.

The temperature range and unique design of a TPE is determined by its glass transition temperature during the rubbery phase, as well as the melt temperature or glass transition during the hard phase of its manufacture.

Containing more than one type of polymer – an elastomer which is responsible for giving a material its elastic properties – TPE compounds, or TPE-S, as it’s sometimes known, can be used for a variety of purposes in the world of engineering. Some of TPEs applications include:

Food

Since anything that comes into contact with food needs food-contact approval via the country it’ll be used and sold in, food-contact approved TPEs are ideal for making components for baby food. Think miniature spoons or toddler cup spouts.

O-rings

Conventionally made from thermoset rubbers, TPE sealing rings can be coloured or white. They can be co-moulded to make two component seals and they’re much more efficient in terms of their manufacture. They’re also environmentally friendly, because they use less energy than thermoset rubbers and can be made in less time.

Medical and health care

We all know that healthcare applications must meet strict, regulatory standards. This is where TPEs come in, as they can be sterilised using ethylene oxide, autoclaves or gamma irradiation. Elsewhere, they can be manufactured to offer high purity and be biocompatible, as well as offering an alternative to silicone, PVC, rubber or latex.

Cap and closure liners

Conveniently acting as a seal between the bottle’s contents and the external environment for metal crows and plastic caps, bottle cap liners tend to be manufactured from PVC. That said, TPE liners offer a host of benefits over PVC. One of them is the fact that they protect against oxygen transmission. It’s worth knowing that TPEs can be designed for everything from cap and closure liners in milk to the very same for carbonated soft drinks.

What is TPR?

TPR has qualities that combine the properties of rubber with the moulding capabilities of thermoplastics. Think of custom-fitted floor mats in cars, for example. TPR is also standard material for truck-bed liners.

Characteristics of TPR:

  • Holds its shape
  • It comes in varying levels of flexibility
  • Flexibility can be increased by adding more rubber to the chemical makeup
  • Can be formulated so the rubber smell is not noticeable
  • Lightweight
  • Can be coloured to your requirements

TPR is used in applications which require gluing, such as footwear and toys, while TPE doesn’t react well to adhesives. You’ll also find TPR at work in:

  • Tubing
  • Wire and cable
  • Sealants
  • Bitumen additives
  • Automotive trim
  • Gaskets
  • Packaging
  • Film and sheet

Similar to TPE, TPR incorporates the flexibility of rubber and plastics – and in terms of combustion, TPR emits thicker and darker smoke when burning, as opposed to TPE. When using thermoplastic elastomers, engineers are able to stretch them to moderate elongations. They can then be returned to the original shape; what this does is offer a much longer life. On top of this, the fact that the TPR provides a better physical range than other materials is also a big draw.

Feel the difference

TPE is matte and has a smooth appearance. It has a light astigmatism, too. It feels smoothly and comfortable. In contrast, TPR is somewhat more viscous, especially when the temperature is around 30˚ to 40˚C/ 86˚ - 104˚.

Comparing their chemical resistance

TPE

TPR

Dilute Acid

Excellent

Excellent

Dilute Alkalis

Excellent

Excellent

Oils and Greases

Excellent

Excellent

Aliphatic Hydrocarbons

Excellent

Excellent

Aromatic Hydrocarbons

Moderate

Good

Halogenated Hydrocarbons

Moderate

Moderate

Alcohols

Excellent

Good


In Manufacturing

TPEs can offer significant cost savings – and the reason for this is they can be processed on plastics machinery, therefore reducing the overall price per project. Combining the aesthetics of conventional thermal rubber with the ease of processing which comes with manufacturing them, TPEs are suitable for high-volume injection moulding.

With shorter processing times, TPE – like TPR – is also 100% recyclable. They can be used up to five times each, although different grades may vary. This consistency ensures engineers can rely on TPE for their project. Energy saving and requiring less man power overall, TPEs are lightweight and can be blow-moulded or thermoformed.

Often, the cost can come down to the number of cavities that can be fabricated for each stage of the manufacturing process, with the TPE process needing around four cavity moulds on a 30-second moulding cycle. With four cavities needed on a 30-second cycle, eight parts per minute can mean 480 are required per hour.

The rubber process can mean twice as many cavities are needed. But engineers are advised not to be put off. The reason is that the TPE process will probably still offer benefits in terms of cost.

TPRs combine the look, feel, and elasticity of thermoset rubber with the processability of plastic. Which brings us right back to where we started – the qualities TPR and TPE have in common. TPR can also be used in injection moulding. It, too, can be blow moulded and thermoformed. Because it’s so malleable, it’s ideal as a custom moulding material.

It is thought that rubber materials offer improved tensile strength and that TPE materials are still deemed ‘inferior’ in terms of their physical properties. You should judge the project and its components on their merits, using the right tools and kit for the job and ensuring plenty of forward-planning is in place.

TPE vs TPR: how do they differ?

You’ve been given the long version. If you’re still confused, then think of it this way: TPE is essentially a softer version of TPR. TPE is used when a bit more flexibility and softness is what you’re after.

At a glance:

Thermo-plastic Elastomer Type

Manufacturing Process and differences

Pros

Cons

Applications

TPE

Modified from SEBS base material
Its surface is matte with light astigmatism

Flexibility of plastics and rubber
It’s smooth and comfortable

Emits thinner smoke when burning

Food products,
Medical and
healthcare,
sealing rings,
cap and
closure liners

TPR

Modified from SBS
Its particles have a reflective, glossy surface

Flexibility of plastics and rubber
Reflection is more apparent

Emits thicker, darker smoke when burning

Products
which need
gluing with
adhesives, or
which require
a glossy
surface or
colouring

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