You might not think plastic and beer have much in common, but in the case of PHAs, there’s some surprising overlap. The bio-based plastic is derived from what amounts to bacteria guts, a polymer the microorganisms use to turn food into energy stored away for a rainy day. To make that polymer into something usable for humans, PHA scientists and entrepreneurs grow the bacteria in big vats under specific conditions, feeding them with vegetable oil, sugar, or methane gas and waiting to harvest the results. So far, kinda like beer.

Here’s where it gets a little different. When the bacteria have gotten so full and roly-poly that they’re barely bacteria anymore—when their cells have gone from around 3% polymer to upwards of 95%—they’re subject to a purification process that bursts their membranes and brings the polymer out of solution. The resulting white powder is combined in pellets that then can be made into straws and takeout containers. Voila: plastic that’s not just made without fossil fuels but is also fully compostable, biodegrading in both your backyard and the ocean.

We’ve known about bacteria’s capacity to manufacture plastic since the 1920s. But it took until 1983 to figure out how to get the polymers from inside the bacteria into human hands and until quite recently for that to happen on a scale that could be commercialized. “If you think of what we knew in the early 20th century about bacteria, microscopy, evolution, all those things have rapidly evolved,” says Mango Materials CEO Molly Morse. Only in the last decade have we had the tool set to make PHAs a reality.

small white plastic pellets

Pellets made from PHA biopolymers. Photo courtesy of Mango Materials

Now, there are over 150 types of PHAs, which differ based on the length of their molecules, how they’re structured, which microorganisms are producing them, and what those microorganisms are fed. The longer the molecule chains, the more flexible and stretchable the plastic is; the shorter they are, the more brittle the material becomes. PHAs melt and flow like petroplastics and they can be turned into sheets or molded into many forms. That makes them great for all kinds of applications with one thing in common: whether in backyard compost, in industrial composting facilities, or in the ocean, they’ll completely biodegrade within six months. 

The big difference is that petroplastics are synthetic, and while bacteria may attempt to break them down, those organisms lack enzymes to break the plastics’ carbon-carbon bonds, making full degradation impossible. But since bacteria already use PHAs to store energy, they have built-in ways to both recognize and break them down. That’s what makes PHAs uniquely biodegradable—but only in specific settings. To understand why this is possible, “think about wood,” says Danimer Chief Technology Officer Phil Van Trump. If you build your desk out of wood, it won’t just disappear out of your house one day; it needs the right environment for that. “But in your yard, it’s a different story. Put it back in that environment, and bacteria and fungi will recognize it as food and start in on it.”

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Of course, there are some drawbacks. In plastic-nerd parlance, PHAs have a “narrow processing window,” which means that their melting point and the point at which heat transforms them chemically into something else are only 10 degrees apart. That limits the ways they can be processed to stand in for petroplastics—for example, in materials that are subjected to very high heat or need very high mechanical strength, like airplane windshields, car bumpers, or bulletproof vests. But PHAs' biggest drawback is cost. Production is relatively expensive, especially the part of the process that draws the polymer out of the bacteria, says Amar Mohanty, a polymer and plastics engineer at the University of Guelph in Canada. Though there are different techniques for doing so, they often require large amounts of expensive chemicals like acetone or chloroform. “And to get a really purified polymer, you need to repeat the steps two or three times,” adds his colleague, fellow engineer Manjusri Misra.

PHAs, like other bioplastics, also release methane when they degrade under anaerobic conditions (like in landfills). Since methane is a major contributor to greenhouse gas emissions, some critics worry that if PHA products grow popular and then are improperly disposed of, they may end up contributing to the climate crisis. In response, Van Trump and Mohanty stress the importance of developing proper waste-disposal infrastructure along with PHA technology, including industrial composting and digesters. “There’s growing we need to do as a society with how much we stick in landfills,” Van Trump says. 

In her work at Mango Materials, Morse has taken the methane release issue in a different direction, since Mango’s PHA bacteria actually feed on methane to grow their polymer. Mango has even partnered with Silicon Valley Clean Water in Redwood City, California, to build a digester on site and harness the methane coming off the city’s waste. At just that single location, Mango could produce up to 10 million pounds of PHA plastic per year.

And then there’s the question of toxicity. In a recent study, Lisa Zimmerman, a biologist at Goethe University in Germany, tested 40 different bioplastics, including one PHA product, and found they were not on average any less toxic than regular plastics. And when chemicals from the bioplastics leached into an environment where Zimmerman was raising microorganisms, many of them (including those from the PHA product) exhibited the potential to simulate hormones and interrupt the organisms’ metabolisms. Since some of the products she tested were not toxic, Zimmerman sees her result as an impetus to increase industry transparency. “The problem is that the product composition is not made openly available, so it’s really hard for other producers to integrate those less harmful chemicals,” she says. “To scale up, it would really help if it was openly communicated what is in the product.” 

2 plastic caps and roll of plastic film

Plastic caps (left) and film (right) produced from PHA biopolymers. Photos courtesy of Mango Materials

Still, all the people interviewed for this article see the current moment as a time with enormous potential for bioplastics. As recently as 2014, when Mango applied for funding through the National Science Foundation to work on marine plastic pollution, their application was denied because the foundation “didn’t believe plastics in the ocean were a problem,” Morse says. She’s seen huge societal change since then, even noticing a difference just within the period of the COVID-19 pandemic. “People are at home staring at their trash cans wondering where all this stuff is going,” she says. “We’ve seen interest in the past 12 months like never before.”

Van Trump also sees a major change in the attitudes of the corporations Danimer is partnering with, like Pepsi, Nestle, and Bacardi, which now seem more willing to invest in solutions to the plastics problem. “We’re growing like a weed,” he says of Danimer, which just opened new facilities in Georgia and Kentucky. And Van Trump and Morse both point out that price and scale are intimately connected. Bioplastics like PHAs are competing against a petroplastics industry producing in simply enormous volumes, with some single plants producing a billion pounds a year—and economies of scale make it possible for petroplastics companies to keep their prices low. “The industry has had 70 to 80 years to optimize and build capacity,” Van Trump says. He holds out hope, though, that “when we get to the scales of the ‘traditional’ polymers, then costs will come down dramatically.”

In fact, Mohanty says the current problem for PHAs is the opposite of what it was in the days of Metabolix: too much demand and not enough production capacity. He expects the industry will grow into that demand in the coming decade, especially as widespread single-use petroplastic bans go into effect. The key, in the meantime, is to educate consumers about their options and to build enough infrastructure that all those new PHA containers and films and straws don’t end up in landfills. Of our voracious plastic appetite, he says, “If we cannot stay away from it, we have to find ways to handle it.”

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