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New TPU Grade an Alternative to EVA in Footwear

Image: Huntsman/Shincell running shoes
The recyclable Irogran TPU is easily expanded into foam sheets for insole, midsole, and forepart footwear applications. Other uses, notably in automotive, are being explored.

A new thermoplastic polyurethane (TPU) developed by Huntsman is reportedly fully recyclable, UV protected, and can be extruded into a film and then easily expanded into foam sheets. Irogran TPU was developed by Huntsman in conjunction with the Shincell New Material Co. Ltd., which is using the material to create foam sheets for insole, midsole, and forepart insert applications by global footwear brands. 

Designed as an alternative to EVA, the new material has high energy-return properties and provides long-lasting cushioning performance, according to Huntsman. The TPU film can be easily expanded in a high-pressure vessel using gas-assisted technology, without requiring additional chemicals typically needed for foaming or cross-linking. This makes the resulting expanded foam sheet, and any post-production scraps and final footwear components, lightweight and easy to recycle, said Huntsman in its announcement.

Popularity of expanded TPU sparks Huntsman, Shincell collaboration

The growing popularity of expanded TPU sheets in the footwear sector prompted initial in-depth discussions with Shincell about how best to improve the production process, said Huntsman. During a technical briefing, Shincell cited several objectives:

  • Productivity increase, less waste, and reduction in overall energy consumption;
  • a material that was free of toxic or volatile chemicals, and that could be expanded without the use of butane, fluoride, or azodicarbonamide foaming agents;
  • a comfortable, durable, long-lasting TPU system that would be suitable for use in high-performance sports shoes;
  • a material that outperforms EVA in terms of cushioning set properties;
  • recyclablaility.  

“As a business, we are focused on providing our customers with clean, environmentally friendly, high-performance, lightweight materials. When we decided to find a partner to help us improve the sustainability of our foam sheets, I knew Huntsman was the company to talk to,” said Dr Xiulei Jiang, founder of Shincell, who had a relationship with Huntsman prior to founding his company. “Huntsman has always provided me with a consistently high level of support, and I knew our strong working relationship and shared core values would bring this project to fruition quickly and efficiently. The team has come up with a very special product that satisfies all of our requirements. We see numerous novel applications for this versatile, recyclable material within footwear, and beyond.”

Huntsman/Shincellinsole made from Irogran TPU

Irogran TPU has high energy-return properties and provides long-lasting cushioning performance, according to Huntsman.

Recyclability, chemical-free expansion make material a "game changer"

Shincell produces expanded foam sheets that its customers in the footwear sector cut into the required shapes and sizes. Because this particular grade of Irogran TPU is recyclable, Shincell can collect any excess or scrap material from its customers for reuse. Upon collection the scraps are ground down and reformulated. They can also be sold on to other customers. 

Yi Li, Business Development Manager at Huntsman, said: “Shincell came to us with a really clear vision and set of technical requirements. It was great to work together on this project and create such a novel material. The fact that it can be expanded without the use of chemicals and easily recycled is a game changer. We are sure news of its development will generate lots of interest from material specifiers in different parts of the footwear sector.” 

Shincell is currently testing the new grade of Irogran TPU for other consumer applications and is exploring its potential use in the automotive industry. Other softer grades of the material are also in the development pipeline. 

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