Upcycling: Turning plastic bags into adhesives
While plastic bags clog the waste stream, recycling them isn’t financially attractive, since they’re usually turned into very low-value products. If polyethylene packaging could be processed into high-value products, more of them would be recycled instead of ending up in landfills. (iStock photo)
While many cities and eight states have banned single-use plastics, bags and other polyethylene packaging still clog landfills and pollute rivers and oceans.
One major problem with recycling polyethylene, which makes up one-third of all plastic production worldwide, is economic: Recycled bags end up in low-value products, such as decks and construction material, providing little incentive to reuse the waste.
A new chemical process developed at the University of California, Berkeley, converts polyethylene plastic into a strong and more valuable adhesive and could change that calculus.
“The vision is that you would take a plastic bag that is of no value, and instead of throwing it away, where it ends up in a landfill, you would turn it into something of high value,” said John Hartwig, the Henry Rapoport Chair in Organic Chemistry at UC Berkeley and leader of the research team. “You couldn’t take all of this recycled plastic — hundreds of billions of pounds of polyethylene are produced each year — and turn it into a material with adhesive properties, but if you take some fraction of that and turn it into something that is of high value, that can change the economics of turning the rest of it into something that is of lower value.”
For most plastics, recycling means chopping it up and forming it into generic products, in the process tossing out many of the properties painstakingly engineered into the original plastic, such as pliability and ease of processing. And while new methods of recycling can break down plastics into their chemical constituents for use as fuels or lubricants, these products, too, are low-value and can be environmentally questionable — another fossil fuel to burn — or have a short lifetime.
To make recycling more attractive, researchers and the plastics industry have been looking for ways to “upcycle” — that is, convert recycled plastic into something more valuable and longer-lived.
The chemical process that Hartwig and his colleagues developed keeps many of the original properties of polyethylene, but adds a chemical group to the polymer that makes it stick to metal: something polyethylene normally does poorly. His team showed that the modified polyethylene can even be painted with water-based latex. Latex easily peels off standard low-density polyethylene, referred to as LDPE.
The paper describing this process will be published online Dec. 17 in the journal Chem and will appear in January’s printed edition.
Hartwig’s team also included UC Berkeley graduate student Adam Uliana. The work was supported by the U.S. Department of Energy (DE-AC02- 05CH11231) and the National Institutes of Health (R37 DE014193).