Covestro and the Brazilian footwear manufacturer Calçados Beira Rio are jointly developing concept shoes with more sustainable material solutions. An elegant women's shoe and a comfortable casual shoe are used as examples to illustrate the variety of possibilities – from upper to lining, from sole to heel.
Both shoes feature Covestro products derived from alternative raw materials such as CO2, biomass and plastic waste. These are a valuable resource as they provide carbon that can be put to use beneficially in a circular economy, instead of being released into the atmosphere as waste gas, said the company. Covestro said it is pioneering the use of such raw materials to reduce its dependence on fossil materials and increase the sustainability of the value chain.
One example is the upper and inner lining of the two shoes. The base is a soft polyurethane foam that ensures a good fit and comfortable footfall. Here, a polyol was used that contains up to 20 % carbon dioxide and is marketed by Covestro under the name cardyon. The CO2 replaces some of the fossil raw materials previously used, but does not compromise the favourable properties of conventionally produced foam, said the company.
Two different types of thermoplastic polyurethane (TPU) are found in the outer soles of both women's shoes. One of them is also based on cardyon; while in the other, 60 % of the carbon content is derived from biomass. As a result, both products have a lower CO2 footprint than fossil-based TPU and help close the carbon cycle.
According to Covestro, footwear manufacturers such as Beira Rio want to offer more sustainable products for the benefit of their customers, but also want to improve hygienic conditions in production. That's why they are increasingly relying on water-based raw materials, which emit significantly fewer volatile organic components (VOCs) than the solvent-based substances used in the past.
Insqin technology is used in the lining, upper and heel of the women's pump, as well as in the synthetic upper material of the casual shoe. This technology is based on water-based polyurethane raw materials and was developed specifically for a more sustainable textile coating. Aqueous adhesives with the polyurethane dispersion Dispercoll U provide the necessary strength in the upper and outer sole of both shoes.
Covestro said it is also focusing on the recovery of plastic waste as part of its strategic programme to support the circular economy, and is working with partners to develop new value-adding cycles to achieve this. For example, used polycarbonate products are shredded, cleaned, possibly mixed with new plastic and reused as recycled Makrolon. In women's shoes, this lends lasting strength to the insole and heel.