Aarhus University researchers have developed an advanced method for recycling polyurethane foam from products like mattresses. This breakthrough holds great promise for the industry, as it allows for the cost-effective recovery of the original material components. Polyurethane (PUR) is an incredibly versatile plastic used in a wide range of applications, from mattresses to wind turbine blades.
Despite its numerous uses, the environmental impact of discarded PUR products is a significant concern, with most of them ending up in landfills or being incinerated.
The reliance on fossil oil as the primary source for the main components of PUR poses a significant challenge. With the global market for PUR expected to reach nearly 31.3 million tons by 2030, there is a pressing need for sustainable alternatives.
While efforts to depolymerize PUR and reuse its components show promise, cost-effective methods must be developed to ensure that these recycled materials can effectively compete with virgin resources.
The researchers from Aarhus University have devised a breakthrough method for breaking down PUR foam using acid (acidolysis). Their innovative approach allows for the separation of broken-down PUR into polyol and isocyanate in one single step by heating flexible PUR foam to 220°C in a reactor with succinic acid. This advancement has the potential to significantly enhance the recyclability of PUR foam.
The solid part of the product mixture that is filtered out is transformed into a so-called diamine in a simple hydrolysis process, which is used in the production of isocyanates and, thus, PUR. In this way, the researchers are able to recover up to 82 weight percent of the original material from flexible PUR foam – used in mattresses – as two separate fractions of diamines and polyols.
“The method is easy to scale up,” points out one of the study’s authors, Steffan Kvist Kristensen, assistant professor at the Interdisciplinary Nanoscience Center (iNANO) at Aarhus University.
The potential for recycling PUR foam waste from production factories is enormous. However, there is a need for further development to handle PUR waste from consumers. While there is progress towards a circular economy, each manufacturer in the PUR industry uses unique formulae, posing challenges in achieving a real recycling economy. These challenges include waste sorting, logistics, sorting PUR into types, and depolymerization, which is only a small part of the solution.
The combination of acidolysis and hydrolysis has been successfully tested on regenerated PUR foam and rigid PUR foam by AU researchers, indicating promising results for recycling. However, the journey towards achieving a circular economy remains a complex one.
Rigid PUR foam, commonly used as insulation materials, is still in its early stages of being transformed into valuable raw materials. Ongoing research includes testing the new technology on various polyurethane materials to further explore their recyclability. Additionally, efforts are being made to investigate the reuse of dicarboxylic acid, a key component in the process. Furthermore, the recycled materials will be put to the test to develop new products, demonstrating the potential of this technology to truly establish a circular economy.
Journal reference:
- Thomas B. Bech, Bjarke S. Donslund, Steffan K. Kristensen, and Troels Skrydstrup. Chemical separation of polyurethane via acidolysis – combining acidolysis with hydrolysis for valorisation of aromatic amines. Green Chemistry, 2024; DOI: 10.1039/D4GC00819G