Multi-layer constructs, the plastic packaging used for some food and beverage items like juice boxes and bags of chips, are composed of multiple layers of different materials. Because the different materials can't be separated, this packaging is not recyclable, and ends up in landfills or the environment.
Three chemical engineering researchers at the University of Pittsburgh — Eric Beckman, Susan Fullerton and Sachin Velankar — are working on a solution that would use variations of a common recyclable plastic, polyethylene, to form all of the layers of an alternative packaging, which in turn, would also be recyclable.
Beckman, who also serves as co-director of Pitt's Mascaro Center for Sustainable Innovation, said multi-layer constructs are widely used because they're easy to produce and highly effective.
"They keep food fresh, you don't have to refrigerate these things necessarily, they're easy to transport because they don't weigh very much. So they do the job they're designed to do, it's just that the designers never thought about the end of life [for the product before]," said Beckman.
The key to these designs, Beckman said, is that different layers in the construct are able to perform different functions, like creating barriers to oxygen and moisture or defining the strength and even color of the packaging.
The challenge for his team, said Beckman, is to figure out how to tweak polyethylene at the molecular level so that it adopts different properties related to the intended function of each layer.
"Polyethylene is really just a simple chain of carbons," said Beckman. "So, we're trying to do an awful lot by really just playing with how chains of polyethylene line up, but ... we don't want to change how the atoms themselves are connected. That's really the last thing we want to do, because then we don't have polyethylene anymore and we've pretty much ruined what we set out to do."
Beckman said that when it's time for the packaging to be recycled, these different structures will go away once the polyethylene is melted down, leaving it free to be re-purposed.
According to a study by Research & Markets, the United States produces more than 4 million tons of un-recyclable multi-layer constructs each year.
Beckman, Fullerton and Velankar won a $200,000 grant to advance their work as part of the Ellen MacArthur Foundation's Circular Materials Challenge. Beckman accepted the prize on behalf of the team earlier this year at the World Economic Forum in Davos, Switzerland.