Thermoplastic Rubber (TPR)
KMA SA Marketing doesn’t only supply TPR we also custom formulate compounds for many of our clients. See our products page for more information on what we can supply.
Ever wondered what rubber is? More importantly, what ‘TPR’ on the bottom of your shoe sole means? Well that’s why I am here today; to help clarify these questions.
TPR- Our Rubbery Friend
Thermoplastic Rubber, TPR, is a material which has both the characteristics of rubber and plastic. Like all plastics when people talk about “rubber”, they don’t usually specify what kind. There are many different kinds of rubber, but they all fall into two broad types: natural rubber (from trees) and synthetic rubber (man-made/ artificial).
As in its name TPR is thermoplastic, a form of synthetic rubber. This means that it melts into a liquid when heated and becomes solid when cooled.
Unlike natural rubber (latex) extracted from the rubber tree, TPR is man-made from the polymer SBS (Styrene-butadiene-styrene). SBS is a tertiary “block copolymer” which means that there are blocks of each monomer (styrene – butadiene – styrene ) within the polymer instead of a random distribution.
Natural rubber and synthetic rubbers are similar in some ways however, they’re made by entirely different processes and chemically quite different.
Once natural rubber has been vulcanized1 or cured it cannot be recycled. TPR however can be recycled/ remoulded as is does not have cross-linked bonds like natural rubber which allows it to re-crystallised several times.
Why is TPR found in shoe soles?
TPR’s have been common in shoe production since the 1960s. Some of the popular reasons why they use TPR for shoe soles include: it is an inexpensive material, it is easy to mould, it is lightweight, it has great slip resistance, its flexing resistance, it can be created in a wide range of colours and supplied in a wide range of different harnesses in order to suit it’s final application.
It can also be formulated to provide weather resistance, UV resistance and low temperature flexibility.
What else is TPR used for?
Aside from footwear products TPR can also be used for the manufacturing of: gaskets, toys, automotive applications and general purpose moulded goods.
What is the difference between TPE and TPR?
TPR’s and TPE’s (thermoplastic elastomer) are both thermoplastics.
However, TPR is made from the polymer SBS (styrene and butadiene) and TPE’s are normally made from the quaternary block co-polymer (e.g. SEBS -Styrene Ethylene Butylene Styrene) however TPE’s can also cover materials made from polyurethane and ethylene based materials. TPE consist of materials with both thermoplastic and elastomeric properties.
TPE has a better chemical and abrasion resistance than TPR and is commonly used in in the shoe and automotive industries.
1 Vulcanization or vulcanisation is a chemical process for converting natural rubber into durable materials by treating it with sulfur at a high temperature