Blog

Aug 30, 2023

Researchers Develop Method To Upcycle Foam Popularly Used For Insulation, Mattresses, And Shoes

Polyurethane foam, often used for construction, is difficult to recycle. Researchers from ... [+] Northwestern University and the University of Minnesota developed a method to upcycle polyurethane

Polyurethane foam, often used for construction, is difficult to recycle. Researchers from ... [+] Northwestern University and the University of Minnesota developed a method to upcycle polyurethane into high-quality plastics and rubbers.

While it is popular for use in furniture, shoes, and construction as insulation, polyurethane foam poses an urgent recycling problem. The material is not easy to repurpose, and as concerns about sustainability continue to rise, the demand for recyclable products is on the incline from both businesses and consumers. Most of the sponge-like material ends up landfills or downcycled, a term coined to characterize when a repurposed product is lower-quality than the original. So, a method which will upcycle polyurethane into better materials is sought-after among scientists.

New research published in ACS Central Science, a journal of the American Chemical Society, offers a solution. Researchers demonstrated a technique which transforms polyurethane into hard plastics and rubbers.

The reason repurposing polyurethane is tricky is because the foam is thermoset, meaning it’s irreversibly hardened during a chemical curing process when it’s made. The resulting foam’s chemical bonds cannot be melted down, so once it’s no longer good for use, there aren’t a ton of options beyond tossing it into the garbage. It may be rebonded, often into carpeting, ground up into a new foam, or chemically recycled into products such as oil or gas. Because polyurethanes make up nearly a third of the thermoset materials market, they can contribute a staggering amount of waste.

Scientists from Northwestern University and the University of Minnesota developed a method which uses “twin-screw extrusion” to make polyurethane materials reprocessible. First, they introduced the polyurethane to a catalyst which made the material more malleable, meaning it could be shaped without breaking. Though the foam which had been catalyzed responded better to being heated and shaped in a mold cavity — a process known as compression molding — the researchers determined there was still trapped air within the foam causing inhomogeneity in the material which led to cracking.

They decided to look toward methods other than compression molding. To homogenize the polyurethane more effectively, the scientists used micro-compounding. Micro-compounding involves mixing polymer formulations at high temperatures with a twin screw extruder, a machine in which two rotating screws mix materials in a heated barrel.

By processing it with the extruder, the scientists removed the excess air from the foam without cracking or breaking the material. Instead, the resulting soft, film product can be made into durable plastics for a variety of uses, such as shoe cushioning, wheels for skateboards or shopping carts, and car bumpers.

In the future, the researchers hope their process will be used to upcycle other commercially used thermoset materials.