Safety and tread comfort from scrap tires

Shoes are subjected to enormous stress. When we walk in them every day and press them against hard surfaces, the inevitable consequence is that every shoe wears out at some point – and must be disposed of. It is hardly surprising that sustainability has become an increasingly important topic in the shoe industry. „It‘s been discussed for more than a decade, but now we‘ve reached the point where customers actually want to buy sustainably produced shoes,“ says Klaus Hülsmann, Director Sports in the High Performance Polymers business line. One type of shoe that has received comparatively little attention so far is the safety shoe. For these shoes, in particular, the issue of wear is very relevant: Safety shoes have to be replaced regularly, even at Evonik locations. To address this need, Evonik has developed a new, sustainable high-performance plastic from their eCO product range: In the production of the polyamide 12 elastomer (PEBA) VESTAMID® eCO, half of the fossil resources are replaced by feedstock from used tires. This plastic is ideally suited for shoe soles. „We are turning a waste material into a valuable material that is used afterwards at the same level,“ says Hülsmann.

PEBA molding compounds have been used in shoes for more than 40 years, especially in sports shoes. For understandable reasons since the polyether block amides are elastic, chemical-resistant and impact-resistant. They are suitable for compact shoe components such as outsoles or heel parts – but especially in the form of foam sheets for sports shoe soles, which need to be lightweight, durable and resilient. “The rebound far surpasses that of other soft foams; so we’re really talking about a premium class here,” says Hülsmann. In other words, anyone who performs with a VESTAMID® PEBA foam sole in their shoe gets most of the energy used back. At the same time, the shoe’s low weight makes it very comfortable to wear. This makes it ideal for sports shoes, where all these properties come together to ensure better running times and less foot stress. For a long time, no one thought of safety shoes in this context. 

Everything changed in 2020, when product developer Lothar Merk from BIG Arbeitsschutz GmbH took a close look at the question of what characteristics a safety shoe should actually possess. “Look at the factories, there you will find athletes every day who have to deliver non-stop top performance,” he says. “Covering kilometers, standing all day, climbing scaffolding – not in comfortable athletic shoes, but in heavy work shoes.”

It’s worth taking a look back: the history of the safety shoe begins about one hundred years ago. In the early days of industrialization, workers put on what they had always worn every day: Clogs. This did indeed lead to injuries time and again, and in contrast, “newfangled” safety boots with steel toecaps were beginning a minor revolution. They significantly reduced the number of accidents. In the decades that followed, the focus of further development was on the obvious aspect: safety. 

For a long time, less attention was paid to shoe design, ignoring the fact that sturdy, heavy shoes bring their own problems: They do not cushion steps, and a lot of energy is lost when running. In addition, the many kilometers of walking on hard industrial floors put disproportionate strain on joints, knees and even the back. Many people wear safety shoes every day for much longer periods and cover more distance with them than with any other footwear. In short, it makes a lot of sense to think about how a foam can be used in safety shoes to cushion, provide support and return the energy of the footfall to the wearer.

These were precisely the questions Merk and his team at BIG had for their RUNNEX® safety shoes – and why they turned to VESTAMID® PEBA. Together with Evonik they developed flexible foams specifically for safety footwear, which both sides describe as an exciting and rewarding project. After all, implementing a new technology requires expertise from both sides. “I would say that the market for safety footwear has changed significantly,” says Hülsmann. “For a long time, the whole industry moved rather conservatively in exploring new developments for both comfort and safety, but it’s really all about the end consumer.” The wearer would like to wear work shoes that are not only safe, but also comfortable and complement their personal style. Which brings us back to the question of sustainability.

“We produce VESTAMID® by using circular raw materials obtained from used tires,” outlines Hülsmann. Since sustainability is not limited to the selection of raw materials, the production process uses renewable energy exclusively in production, which reduces the carbon dioxide footprint by a total of 42 percent. Evonik wants to demonstrate that sustainably produced plastics are not only possible, but are a real solution for the future. However, this requires joint projects with customers to develop products – like the safety shoe.

The new eCO product range is emblematic of this: renewable or circular raw materials, with reduced carbon dioxide emissions during production – all delivered with the same quality and at the same performance level. “VESTAMID® eCO is an alternative without limitations in this case,” says Hülsmann. “And the scrap tires are a way to obtain the raw material sustainably – there could certainly be others, but we are proving that this way definitely works now.”