A sea change for plastic pollution: New material biodegrades in ocean water

Plastics, now ubiquitous in the modern world, have become a rising threat to human and environmental health. Around the planet, evidence of plastic pollution stretches from grocery bags in the deep sea to microplastics in our food supplies and even in our blood.

Seeking solutions to counteract the rise in plastic trash, scientists at the University of California San Diego have developed new biodegradable materials that are designed to replace conventionally used plastic. After proving their polyurethane foams biodegrade in land-based composts, an interdisciplinary team of scientists including UC San Diego biologist Stephen Mayfield and chemists Michael Burkart and Robert "Skip" Pomeroy have now shown that the material biodegrades in seawater. The results are published in the journalScience of the Total Environment.

The researchers are working to address a plastic pollution problem now described as a global environmental crisis. In 2010, researchers estimated that 8 billion kilograms of plastic enter the ocean in a single year, with a steep escalation predicted by 2025. Upon entering the ocean, plastic waste disrupts marine ecosystems, migrates to central locations and forms trash gyres such as the Great Pacific Garbage Patch, which covers an area more than 1.6 million square kilometers. These plastics never degrade, but rather break up into ever-smaller particles, eventually becoming microplastics that persist in the environment for centuries.

Working with study coauthor Samantha Clements, a marine biologist and scientific diver at Scripps Institution of Oceanography, the UC San Diego researchers conducted a series of tests of their biodegradable polyurethane materials -- currently used as foams in the first commercially available biodegradable shoes (sold by a spinoff company called Blueview) -- at Scripps' Ellen Browning Scripps Memorial Pier and Experimental Aquarium. The pier's location provided scientists the access and a unique opportunity to test materials in the natural nearshore ecosystem, which is the exact environment where rogue plastics are most likely to end up.

The team found that an assortment of marine organisms colonizes on the polyurethane foam and biodegrades the material back to their starting chemicals, which are consumed as nutrients by these microorganisms, in the ocean environment. Data from the study suggest that the microorganisms, a mix of bacteria and fungi, live throughout the natural marine environment.

"Improper disposal of plastic in the ocean breaks down into microplastics and has become an enormous environmental problem," said Mayfield, a professor in the School of Biological Sciences and director of the California Center for Algae Biotechnology. "We've shown that it's absolutely possible to make high performance plastic products that also can degrade in the ocean. Plastics should not be going into the ocean in the first place, but if they do, this material becomes food for microorganisms and not plastic trash and microplastics that harm aquatic life."

Shoes, including flip-flops, the world's most popular shoe, make up a large percentage of plastic waste that ends up in the world's oceans and landfills. To fully test and analyze their polyurethane materials, developed at UC San Diego over the last eight years, the study joined experts in biology, polymer and synthetic chemistry and marine science. Foam samples were exposed to tidal and wave dynamics and tracked for molecular and physical changes using Fourier-transform infrared spectroscopy and scanning electron microscopy. The results showed that the material started to degraded in as little as four weeks. The researchers then identified microorganisms from six marine sites around San Diego that are capable of breaking down and consuming the polyurethane material.

"No single discipline can address these universal environmental problems but we've developed an integrated solution that works on land -- and now we know also biodegrades in the ocean," said Mayfield. "I was surprised to see just how many organisms colonize on these foams in the ocean. It becomes something like a microbial reef."

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Lab turns trash into valuable graphene in a flash

Graphene sheet model

That banana peel, turned into graphene, can help facilitate a massive reduction of the environmental impact of concrete and other building materials. While you're at it, toss in those plastic empties.

A new process introduced by the Rice University lab of chemist James Tour can turn bulk quantities of just about any carbon source into valuable graphene flakes. The process is quick and cheap; Tour said the "flash graphene" technique can convert a ton of coal, food waste or plastic into graphene for a fraction of the cost used by other bulk graphene-producing methods.

"This is a big deal," Tour said. "The world throws out 30% to 40% of all food, because it goes bad, and plastic waste is of worldwide concern. We've already proven that any solid carbon-based matter, including mixed plastic waste and rubber tires, can be turned into graphene."

As reported in Nature, flash graphene is made in 10 milliseconds by heating carbon-containing materials to 3,000 Kelvin (about 5,000 degrees Fahrenheit). The source material can be nearly anything with carbon content. Food waste, plastic waste, petroleum coke, coal, wood clippings and biochar are prime candidates, Tour said. "With the present commercial price of graphene being $67,000 to $200,000 per ton, the prospects for this process look superb," he said.

Tour said a concentration of as little as 0.1% of flash graphene in the cement used to bind concrete could lessen its massive environmental impact by a third. Production of cement reportedly emits as much as 8% of human-made carbon dioxide every year.

"By strengthening concrete with graphene, we could use less concrete for building, and it would cost less to manufacture and less to transport," he said. "Essentially, we're trapping greenhouse gases like carbon dioxide and methane that waste food would have emitted in landfills. We are converting those carbons into graphene and adding that graphene to concrete, thereby lowering the amount of carbon dioxide generated in concrete manufacture. It's a win-win environmental scenario using graphene."

"Turning trash to treasure is key to the circular economy," said co-corresponding author Rouzbeh Shahsavari, an adjunct assistant professor of civil and environmental engineering and of materials science and nanoengineering at Rice and president of C-Crete Technologies. "Here, graphene acts both as a 2D template and a reinforcing agent that controls cement hydration and subsequent strength development."

In the past, Tour said, "graphene has been too expensive to use in these applications. The flash process will greatly lessen the price while it helps us better manage waste."

"With our method, that carbon becomes fixed," he said. "It will not enter the air again."

The process aligns nicely with Rice's recently announced Carbon Hub initiative to create a zero-emissions future that repurposes hydrocarbons from oil and gas to generate hydrogen gas and solid carbon with zero emission of carbon dioxide. The flash graphene process can convert that solid carbon into graphene for concrete, asphalt, buildings, cars, clothing and more, Tour said.

Flash Joule heating for bulk graphene, developed in the Tour lab by Rice graduate student and lead author Duy Luong, improves upon techniques like exfoliation from graphite and chemical vapor deposition on a metal foil that require much more effort and cost to produce just a little graphene.

Even better, the process produces "turbostratic" graphene, with misaligned layers that are easy to separate. "A-B stacked graphene from other processes, like exfoliation of graphite, is very hard to pull apart," Tour said. "The layers adhere strongly together.

But turbostratic graphene is much easier to work with because the adhesion between layers is much lower. They just come apart in solution or upon blending in composites.

"That's important, because now we can get each of these single-atomic layers to interact with a host composite," he said.

The lab noted that used coffee grounds transformed into pristine single-layer sheets of graphene.

Bulk composites of graphene with plastic, metals, plywood, concrete and other building materials would be a major market for flash graphene, according to the researchers, who are already testing graphene-enhanced concrete and plastic.

The flash process happens in a custom-designed reactor that heats material quickly and emits all noncarbon elements as gas. "When this process is industrialized, elements like oxygen and nitrogen that exit the flash reactor can all be trapped as small molecules because they have value," Tour said.

He said the flash process produces very little excess heat, channeling almost all of its energy into the target. "You can put your finger right on the container a few seconds afterwards," Tour said. "And keep in mind this is almost three times hotter than the chemical vapor deposition furnaces we formerly used to make graphene, but in the flash process the heat is concentrated in the carbon material and none in a surrounding reactor.

"All the excess energy comes out as light, in a very bright flash, and because there aren't any solvents, it's a super clean process," he said.

Luong did not expect to find graphene when he fired up the first small-scale device to find new phases of material, beginning with a sample of carbon black. "This started when I took a look at a Science paper talking about flash Joule heating to make phase-changing nanoparticles of metals," he said. But Luong quickly realized the process produced nothing but high-quality graphene.

Atom-level simulations by Rice researcher and co-author Ksenia Bets confirmed that temperature is key to the material's rapid formation. "We essentially speed up the slow geological process by which carbon evolves into its ground state, graphite," she said. "Greatly accelerated by a heat spike, it is also stopped at the right instant, at the graphene stage.

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