New recycling methods can make polyurethane materials sustainable
Researchers at the University of Minnesota, who are part of a national team at the Center for Sustainable Polymers, have found a better way to recycle a multifunctional plastic material called polyurethane, which could prevent the material from becoming waste.
Past attempts to recycle polyurethane waste have resulted in a decline in material quality. Now, researchers have found a way to use an innovative method to recycle waste polyurethane into a material of equal or higher quality.
Their findings are reported in ACS Central Science, a journal published by the American Chemical Society.
“We are quite excited about this new research from the Center for Sustainable Polymers, because of the huge potential for recycling polyurethane materials that are normally considered waste,” says Marc Hillmyer, a professor of chemistry at the University of Minnesota and director of the Center for Sustainable Polymers at the University of Minnesota. It also shows how the powerful combination of polymer chemistry and polymer processing can be applied to help solve environmental problems.”
Polyurethane is all around us. Polyurethane is found in mattresses, insulation, footwear, building materials, car suspension systems, carpet liners, and many other products. The wear and replacement of these products creates a large amount of waste and creates a need for new polyurethanes, which are often made of toxic chemicals.
Conventional polyurethane cannot be recycled simply by heating because the material is made up of polymer networks held together by strong chemical bonds that do not flow when heated. In contrast, polyurethane can only be degraded to a less useful material by mechanical or chemical recycling methods. Other methods in the past have enabled innovative types of polyurethanes to have broken and reconstituted crosslinks that enable them to be recycled. But this approach requires industry to commercialize new starting materials, and it won’t solve the problem of traditional waste lingering in landfills. These methods have also not been tested on foam (a very common form of polyurethane products).
In the new study, researchers from the University of Minnesota and Northwestern University ground up the polyurethane foam, or film, and then mixed the particles in a catalyst solution. After drying, the particles are compressed to form a new film. The compressed film forms a good quality product, but the compressed foam produces a cracking and uneven material.
The researchers solved this problem by developing a twin-screw extrusion process that improved the mixing of recycled foam and the removal of air compared to compression molding methods. The new method could be used to continuously recycle large amounts of polyurethane waste currently in landfills and newly generated, they said.
“During the extrusion process, the polyurethane flows like a liquid under the action of the catalyst and the air is removed.” “This reaction process is similar to one already used for other purposes in the plastics industry, which means the technology can have a rapid impact,” said Christopher Ellison, a professor of chemical engineering and materials science at the University of Minnesota and one of the senior authors of the study.
The research was primarily funded by the National Science Foundation through the Center for Sustainable Polymers.
The study’s authors, from the Department of Chemical Engineering and Materials Science at the University of Minnesota, include associate professor Christopher J. Ellison, postdoctoral assistant Kailong Jin, and undergraduate student William Dean. The authors, from Northwestern’s Department of Chemistry, include William R. Dichtel, Professor; Daylan T. Sheppard, PhD student; Leslie S. Hamachi, postdoctoral researcher; and David J. Fortman, visiting PhD former scholar. Fortman is also a former graduate researcher in the Department of Chemistry and Chemical Biology at Cornell University.