SAN DIEGO—Coming soon: flip-flops that are designed to fall apart.
Scientists at the University of California San Diego have succeeded in using algae oils to formulate commercial-quality polyurethane foams that can be used in the midsole of shoes and the footbed of flip-flops.
The UCSD team collaborated with start-up company Algenesis Materials on the project. It's the latest sustainable PU application to come out of the labs of Michael Burkart and Stephen Mayfield at UCSD.
"We have commercial-quality foams that biodegrade in the natural environment," Mayfield said. "After hundreds of formulations, we finally achieved one that met commercial specifications."
The current foams are 52 percent biocontent, but the aim is ultimately to reach 100 percent.
The team went back to the drawing-board for the PUs made with bio-based monomers to ensure that the resulting foams would meet the high specifications required for shoes. Importantly, the chemistry was designed so that the polymers would, in theory, biodegrade.
Often, they said, commercial plastics can biodegrade, but only in lab tests or industrial composting, not in more normal circumstances. The new PU's biodegradation credentials were checked out by immersing them in compost and soil, and they degraded within 16 weeks. All the molecules produced were accounted for, and the biodegrading microorganisms identified.
"We took the enzymes from the organisms degrading the foams and showed that we could use them to depolymerize these polyurethane products, and then identified the intermediate steps that take place in the process," Mayfield said. "We then showed that we could isolate the depolymerized products and use those to synthesize new polyurethane monomers, completing a 'bioloop.' "
The next step will be to determine the economics of producing the PU and the flip-flops at scale.
"The life of material should be proportional to the life of the product," Mayfield said. "We don't need material that sits around for 500 years on a product that you will only use for a year or two."