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Researchers Use Algae to Make Biodegradable Flip-Flops

The shoes break down in about 18 weeks under the right conditions

Prototype biodegradable flip-flops made using algae. (Stephen Mayfield, UC San Diego)
smithsonianmag.com

Through human negligence and ocean currents, the sparsely inhabited Cocos (Keeling) Islands some 1,300 miles northwest of Australia have become a kind of sieve for plastic pollution at sea. A 2019 study estimated the 26 islands in the horseshoe-shaped chain had accumulated 414 million pieces of human debris weighing roughly 238 tons. Among those many tons of plastic were some 977,000 shoes, predominantly flip-flops.

Now, researchers looking to cut down on this popular shoe’s environmental footprint have developed biodegradable flip-flops using algae, reports Mike Blake for Reuters.

"We need to change our habits and take on the personal responsibility to use less plastic in our lives," Mike Burkart, a biochemist at UCSD who worked on the project, tells Alaa Elassar of CNN. “But plastic is very useful material all around us, so we need to get to the point where when someone's buying a product, they insist it's biodegradable."

To make the sandals, the team from the University of California, San Diego (UCSD) used oil extracted from algae as the basis for a polyurethane foam, which is typically made using petroleum.

“We begin by growing algae and we grow them in raceway ponds where we can grow them up to very high density,” Burkart tells Reuters. “At that point when they are fully grown, we take the water out of them...and basically we’re able to get the algae down to a very viscous paste.”

Oils, also called fats or lipids, are then extracted out of this paste and used as the basis for a polymer.

Formulating a biodegradable foam that still met commercial specifications for footwear required hundreds of attempts, and ultimately the result still relies on a substantial amount of petroleum. Writing in the journal Bioresource Technology Reports, the team says their flip-flop foam is made using 52 percent biocontent, or material derived from the algae oil.

Despite nearly half the shoe being made from traditional, non-renewable sources the study’s experiments indicate the resulting foam lost 71 percent of its mass after spending two weeks buried in soil. Burkart tells CNN that the shoes should completely break down in about 18 weeks under the right conditions in soil or compost.

“The paper shows that we have commercial-quality foams that biodegrade in the natural environment,” Stephen Mayfield, a microbiologist at UCSD and co-author of the research, tells Chris Jennewein of the Times of San Diego. “After hundreds of formulations, we finally achieved one that met commercial specifications. These foams are 52 percent biocontent—eventually we’ll get to 100 percent.”

A variety of footwear companies have approached the lab about utilizing their product, and the first of those are expected to become available in January 2021, per CNN.

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