Change afoot: UCSD develops recyclable, biodegradable flip-flop

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To do its part to reduce plastic and waste found in the oceans and landfills, UC San Diego has partnered with La Jolla-based Algenesis Materials to create commercial-quality, biodegradable flip-flops made from algae.

The team of researchers formulated polyurethane foams made from algae oil to meet commercial specifications for midsole shoes and the foot bed of flip-flops. The results of their study were published in Bioresource Technology Reports.

“The paper shows that we have commercial-quality foams that biodegrade in the natural environment,” said UCSD biological sciences professor Stephen Mayfield. “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.”

The project was led by graduate student Natasha Gunawan from the labs of Mayfield and physical sciences professor Michael Burkart, and by Marissa Tessman from Algenesis, a materials science and technology company.

A flip-flop foot bed is pulled from a mold.

A flip-flop foot bed is pulled from a mold.

(Courtesy)

“Our goal was to make a version of the flip-flop — which we consider to be the official shoe of San Diego — renewable and biodegradable,” said UCSD scientist Skip Pomeroy, whose team measured the biodegradation of the shoe. “We wanted to make something that can be fully recycled.

“Recycling plastic now involves taking some of the ground-up plastic and put it into new plastic. But the plastic is never as good as when it is 100 percent new. … This can be chemically broken down and completely reconstructed into a pool noodle or an adhesive or something else.”

That is, if it is recycled in a proper facility.

In addition to devising the right formulation for the commercial-quality foams, the researchers worked with Algenesis to not only make the shoes but to degrade them as well, according to UCSD. Mayfield said scientists have shown that commercial products such as polyesters, bioplastics and fossil-fuel plastics can biodegrade, but only in the context of lab tests or industrial composting.

“We redeveloped polyurethanes with bio-based monomers [molecules that can be bonded to identical molecules to form a polymer] from scratch to meet the high material specifications for shoes while keeping the chemistry suitable, in theory, so the shoes would be able to biodegrade,” Mayfield said.

What if they are just thrown away, like the millions tossed in the trash worldwide?

“They go away,” Pomeroy said. “We proved which fungi and bacteria go after these foams and what is used to consume them. We kept track of the chemistry. They won’t be floating in the ocean 150 years from now.”

The standard life of a flip-flop is about two years, yet most are made out of plastics that can last thousands of years in landfills or the ocean, he said.

According to UCSD, Pomeroy’s team put the customized foams to the test by immersing them in traditional compost and soil. The team discovered that the materials degraded after just 16 weeks.

“At worst, this is a zero-carbon footprint operation,” he said. “When you make something out of petroleum, even if it is biodegradable, you are still adding carbon dioxide into the air. With this, we are taking carbon dioxide out of the air, and if the flip-flop is recycled, it becomes a whole new product.”

The potential impact goes far beyond footwear.

“By picking things with economic value, it proves the concept from start to finish, from the lab to working industry,” Pomeroy said. “Companies would want to make purposely biodegradable materials if they see how it goes from the lab to the consumer. Wouldn’t it be great if these materials would go away when they are dumped in a landfill? People buy ocean recreation material like boogie boards when they go on vacation and then throw it away when they go home. It frustrates me as a chemist that the end-of-life costs are not included in the creation of a product.”

UCSD is working with a commercial partner — which doesn’t want to be identified yet — to manufacture the shoe for public purchase.

“We’re trying to manufacture them in this hemisphere, mainly in Mexico,” Pomeroy said. “We want them out by Christmas, and I think we’re on track. But that is not taking COVID-19 into consideration.” ◆



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