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Researchers Develop Biodegradable Plastic That Won’t Leave Microplastics Behind

A plastic container lying on a beach.
Credit: Beth Jnr / Unsplash.
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Microplastics – tiny fragments of plastic measuring less than 5 millimeters in diameter – are constantly being shed by plastic products, either during regular daily use or as they break down in landfill.

Depending on the type of plastic, these microplastics can take anywhere between 100–1,000 years to break down fully, leaving a huge window of time for these plastics to accumulate in the environment. But the environment isn’t the only place where these microplastics can build up – recent studies have discovered microplastics in the bodies of many different animal species, including humans.

Now, researchers from the University of California San Diego (UC San Diego) and materials science company Algenesis have developed a new type of algae-based plastic that fully biodegrades in less than seven months, even at the microplastic level. Their research is published in Nature’s Scientific Reports.

New plastic is eaten up by microbes

The plastic developed by the research team is a bio-based thermoplastic polyurethane (TPU-FC1) that can be used to make coated fabrics or injection-molded objects.

“When we first created these algae-based polymers about six years ago, our intention was always that it be completely biodegradable,” said Robert Pomeroy, a professor of chemistry and biochemistry at UC San Diego and an Algenesis co-founder. “We had plenty of data to suggest that our material was disappearing in the compost, but this is the first time we’ve measured it at the microparticle level.”

For their new study, the team ground down samples of their plastic to form fine microparticles, then used three different measurement tools to track how these microplastics would behave when placed in compost.

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The first test makes use of the fact that when soil microbes break down a material, they will release amounts of carbon dioxide (CO2). Using a respirometer, the researchers could monitor the emission of CO2 over time. They found that their TPU-FC1 had a near-identical CO2 evolution to cellulose – a material considered to be 100% biodegradable. In contrast, samples of non-biodegradable petroleum-based plastic particles left in the compost showed no CO2 evolution over the 200-day study period.

Particle counts were also performed at 0, 90 and 200 days by using water to separate the buoyant plastics from the compost and staining the plastics with a fluorescent Nile Red solution. This showed that at 90 and 200 days, almost 100% of the petroleum-based microplastics remained in the compost. However, after 90 days only 32% of the algae-based particles could be recovered, falling to 3% by the end of 200 days. This means that 97% of the algae-based microplastics had fully biodegraded.

Finally, these results were confirmed using traditional gas chromatography-mass spectrometry (GC-MS) analysis, which was able to detect the presence of the monomer units that made up the algae-based polymer plastic. This shows that the polymer was being effectively broken down back to its starting materials, the researchers explain. Scanning electron microscope (SEM) images also found evidence to show that microorganisms were colonizing the biodegradable microplastic particles during the composting process.

Creating eco-friendly plastic

While research into the health effects of microplastics and different routes for microplastic remediation is underway, relatively little is known about the effects that microplastics are having on the environment and the food chain.

“We're just starting to understand the implications of microplastics. We've only scratched the surface of knowing the environmental and health impacts,” said Michael Burkart, a professor of chemistry and biochemistry at UC San Diego and a co-founder of Algenesis. “We're trying to find replacements for materials that already exist, and make sure these replacements will biodegrade at the end of their useful life instead of collecting in the environment. That's not easy.”

“This material is the first plastic demonstrated to not create microplastics as we use it,” added study co-author Stephen Mayfield, a professor at the UC San Diego School of Biological Sciences and a co-founder of Algenesis. “This is more than just a sustainable solution for the end-of-product life cycle and our crowded landfills. This is actually plastic that is not going to make us sick.”

While the development of a truly biodegradable plastic is a notable step forward, the research team is realistic about this being only one step on a much longer road to viability. Next, they want to be sure that their biodegradable polymer can be used with pre-existing manufacturing equipment that was built for petroleum-based polymers. The team has already begun to work with several other companies with the hope of making functional products from this UC San Diego-pioneered plastic. This includes a partnership with Trelleborg for use in coated fabrics and RhinoShield for cellphone cases.

“When we started this work, we were told it was impossible,” Burkart said. “Now we see a different reality. There's a lot of work to be done, but we want to give people hope. It is possible.”

Reference: Allemann MN, Tessman M, Reindel J, et al. Rapid biodegradation of microplastics generated from bio-based thermoplastic polyurethane. Sci Rep. 2024;14(1):6036. doi: 10.1038/s41598-024-56492-6

This article is a rework of a press release issued by the University of California San Diego. Material has been edited for length and content.