Once discarded, spongy polyurethane foam typically just ends up in landfills, where it takes up a lot of space. Thanks to a newly-developed process, however, it could soon be recycled into higher-quality rubbers and hard plastics.
Commonly used in products such as mattresses, insulation and cushions, polyurethane foam has very strong chemical bonds that prevent it from being melted down and recycled. Some groups have attempted to convert it into a recyclable solid form, by compressing it to remove its air pockets. Unfortunately, though, the resulting materials have tended to crack or be unevenly blended.
As it is, when the foam does get repurposed at all, it's usually just shredded into lower-value fibers that are used in carpeting.
In an effort to expand the recycling possibilities, scientists from the University of Minnesota and Illinois' Northwestern University devised a process that begins with polyurethane foam waste being mixed with a catalyst solution. This makes the foam malleable – although it's soft and squishy when in its original form, it isn't malleable at that point, as it springs back to its previous shape after being compressed.
Next, the treated foam is run through a machine known as a twin screw extruder, which utilizes two intermeshed co-rotating screw drives to grind up the material, removing the air from it in the process. What ultimately results is either a hard plastic or a flexible rubber, that are actually higher-value products than the original foam. Among other things, they could be used in products such as automobile bumpers, wristwatch bands, and shopping cart or skateboard wheels.
"Our latest work effectively removes air from polyurethane foams and remolds them into any shape," says Northwestern's Prof. William Dichtel, who led the study along with Minnesota's Assoc. Prof. Christopher Ellison. "This could pave the way for industry to begin recycling polyurethane foam waste for many relevant applications."
A paper on the research was published this Wednesday in the journal ACS Central Science.