Plastic (32 page)

PLA was one of the first biopolymers to reach the market. But others are on their way, all using different technologies to get there. One of the most intriguing developments is the use of microorganisms to produce entirely new types of biopolymers. DuPont is employing
E. coli
bacteria to produce a biobased synthetic textile marketed under the brand name Sorona, and a Cambridge, Massachusetts, biotech company, Metabolix, has harnessed a different type of bacterium to create what it claims is a completely sustainable new biopolymer, which it calls Mirel.

Metabolix isn't using just any old bacteria. It's employing an unusual group of microbes that store energy not as fat but as a natural polymer called polyhydroxyalkanoate, or PHA. The microbes are ubiquitous, present in soil, air, the sea, even our bodies—and as a result, so is PHA. Metabolix founder Oliver Peoples learned about these microbes back in the late 1980s when he was a freshly minted chemist doing postdoc work at MIT. He saw in them a vehicle for producing a biobased polymer, a plastic that one day could even be grown in plants. It took more than a decade, but he eventually succeeded in genetically engineering those microbes to be "super producers" of PHA and devising methods of fermenting them in vats of dextrose corn sugar to produce huge quantities of the polymer. The microbes stuff themselves silly on the sugar and are now so efficient at converting it into PHA that it makes up 80 percent of their weight. The fluffy white polymer is then extracted, dried, and turned into pellets of Mirel. On a recent summer day when I visited Metabolix's offices in Cambridge, spokesman Brian Igoe walked me through labs where the Mirel was being grown. The room had a slightly yeasty smell from the yellowish microbial broth fermenting in stainless steel vats. Igoe likened the process to making beer. "But it's the most high-tech beer you've ever tasted."

The locked greenhouse down the hall, however, contained Peoples's ultimate dream. In that small rooftop space, a miniature prairie sprouted under banks of fluorescent lights. There were dozens of pots filled with switchgrass plants that had been genetically modified to grow PHA in their cells. "If you look at the stems and leaves of this switchgrass here, it has this kind of white finish to it," Igoe said, holding out a leaf for me to examine. That slightly white cast was the PHA; it made up about 6 percent of the plant's tissue. Nearby were several pots of tobacco plants, which were also growing PHA. (Tobacco DNA is so easily manipulated, the plant is the botanical equivalent of the lab rat in gene technology.) One day, the company hopes, plants such as these could be a source of useful plastic. The plant would be harvested and dried, the PHA extracted and turned into Mirel, while the leftover biomass could be burned for energy.

Peoples wasn't the first to see the possibilities of those micro plastics producers. Scientists at Imperial Chemical Industries in Britain tried to commercialize the technology in the 1980s with no success and passed the torch to Monsanto. In the late 1990s Monsanto reported that it had succeeded in creating a PHA plastic, and one credit card maker announced it would issue a "green earth" credit card from the new polymer. But before that could happen, Monsanto decided to pull the plug on its entire bioplastics division. Plant-based plastics were considerably more expensive than those made from fossil fuels, and Monsanto wasn't convinced there was a market willing to pay the added costs of going green.

But Peoples is certain the math can be made to work and that there is a market eagerly awaiting the arrival of green plastics. Grain giant Archer Daniels Midland has bought into Peoples's vision. In 2004, ADM formed a joint venture with Metabolix to start producing Mirel on a commercial scale. After repeated delays, the joint venture's plant in Clinton, Iowa, finally fired up in early 2010.

Bioplastics do cost more than petro-plastics—PLA is two to three times the price, though Davies said that price difference begins to evaporate when the price of oil passes eighty dollars a barrel. Mirel is even more expensive, but Peoples insists he isn't trying to compete with conventional plastics or, for that matter, PLA. He's positioning Mirel as "a premium product," a polymer that can be made into a film or foam or a rigid material and that has one big advantage over petro-based plastics: it readily biodegrades. That's the virtue Peoples is depending on to conquer just a handful of carefully picked end markets, including packaging, agricultural applications, and consumer products, such as gift cards. Indeed, in 2008 Metabolix struck a deal with Target to provide enough Mirel for millions of gift cards for the Christmas season that year. The cards gave Target an opportunity to shore up its green credentials while providing Metabolix a visible platform to announce its new plastic to the world.

Mirel and Ingeo are still a long way from being household names. When production at its Nebraska plant reaches full capacity, NatureWorks will still be making only 350 million pounds of its bioplastic a year; Metabolix is able to produce about a third that much. Even if you count the various other biopolymers in existence and under development, the total barely registers in a world awash in fossil-fuel-based plastics.

Still, bioplastics are generating so much buzz because they're seen as holding the answer to many of our plastic woes—the rehabilitated partner who can transform this troubled relationship we're in. But before we commit to yet another family of polymers, it's worth asking the question Tim Greiner posed: Just what problems do bioplastics solve?

When I asked Michigan State polymer chemist Ramani Narayan, he had a single answer: the looming threat of climate change. Because biopolymers are made from "renewable sources of carbon"—what the rest of us call plants—they can reduce the amount of global-warming carbon dioxide we're sending up into the atmosphere. The CO2 that's released at the bioplastic's end of life can be recaptured by the new plants that sprout in the next season. Bioplastics move us back inside the protective loop of the natural carbon cycle: the neatly balanced output and uptake of CO2 that has sustained life on earth for eons. Even a single-use gift card that's immediately tossed in a landfill stays within that natural cycle if the card is made of a biopolymer, said Narayan.
Petro-plastics, on the other hand, exist outside that loop, which is why their CO
₂
emissions constitute a climate threat.

The benefit Narayan describes is quantified in the complex accounting of carbon calculations. Fossil-fuel-based plastics generate anywhere from two to nine kilograms of carbon dioxide for every kilogram of polymer produced. Plant-based plastics generate far less CO2, even when you factor in all the oil used to fertilize, grow, and harvest the crops. PLA produces just 1.3 kilograms of carbon dioxide for every kilo of polymer produced.
Mirel's carbon profile is a little higher because it takes more energy to make, but Narayan says it still beats conventional plastics.

Narayan has spent decades developing corn plastics. But he's not wedded to corn as a feedstock—any type of plant-based raw ingredient would have the same beneficial effect, he said. Indeed, agricultural crops—especially genetically modified crops—are probably not the best source of feedstocks.
Critics point out the perversity of growing a food crop to make plastic in a world full of people who are hungry, and there's the additional drawback of the large amounts of land and water and oil-based fertilizers needed to raise it. A more sustainable and economical source of raw materials is waste—the vast quantities produced by us and the rest of the natural world. After all, conventional plastics are derived from the waste produced in processing fossil fuels; the ingenious use of that waste was what gave plastics an economic leg up in the first place.

Bioplastics producers are already exploring the possibilities posed by downed forest trees and the leftovers from paper and pulp production—surprisingly large sources of cellulose—as well as yard clippings and the remnants of harvested crops, such as corn stover and sugar-cane bagasse. By one estimate, such sources add up to 350 million metric tons a year, enough to substantially supplement fossil-fuel feedstocks.
But there's also the waste we produce every day—our garbage, and even our sewage. Scientists around the world are dumpster-diving for waste materials that can be used as plastic feedstocks, exploring the possibilities of chicken feathers, orange peels, potato peels, carbon dioxide; even the methane emitted from landfills that is now sometimes recovered for energy. Stanford University chemist Craig Criddle is working with methane-eating microbes, relatives of the ones employed by Metabolix. He's found that after gorging on methane, they can produce prodigious quantities of a polymer similar to PHA and that the polymer can biodegrade back to methane. Though the technology is still in early stages, it promises a neatly closed production loop.
So too does the work of Cornell University chemist Geoff Coates, who has developed a way to capture carbon dioxide emitted from the scrubbers on power plants and transform it into a biodegradable type of polypropylene carbonate plastic; it's now being commercially produced in small batches.
None of these alone could replace the fossil fuels used in plastics, but there is no reason to believe we need just a single replacement. Part of petroleum's magic is that it has been able to do so many things so well. A more sustainable approach to plastics production (not to mention energy production) will almost certainly require developing multiple resources in the context of what is locally available and feasible. One measure of success will be how well bioplastic products, such as biopolymer credit cards, reduce an individual's carbon footprint.

But that's not the only plastic problem that biopolymers address. They also promise a safer chemical profile—certainly safer than the PVC typically used in credit cards. No hazardous compounds are required to knit a PLA or Mirel daisy chain. As Rossi noted, "I'd much rather live next to NatureWorks' plant in Nebraska than a petroleum-refining facility." And as producers of green plastics, NatureWorks and Metabolix have a vested interest in protecting how their resins are used and processed by manufacturers farther down the supply chain. "This sounds self-serving, but we are being held to a higher standard," said Davies. "From the get-go, we have to follow this extended producer responsibility model where we can't put products into the market without knowing where they go and what's happening to them."

Both NatureWorks and Metabolix claim to be committed to avoiding the addition of harmful chemicals by downstream processors and to being practitioners of the evolving science known as green chemistry. (Green chemistry goals include making synthetic chemicals with as few toxic substances and processes as possible, generating the minimum amount of waste, and producing compounds that won't persist in the environment.
) NatureWorks, for instance, requires any manufacturer using its plastic to abide by a "prohibited substances list," which bars the use of various known persistent organic pollutants, endocrine disrupters, heavy metals, carcinogens, and other dangerous chemicals.

If you browse the shelves of bioplastic products, you'll notice that the most common problem they claim to address is plastic's stubborn durability. "Go ahead, throw it away! No composting required," boasts a maker of picnic forks, suggesting that once discarded, they will simply melt away. Fork gone; problem solved. But advertising, even the greenest, seldom tells the whole story.

I thought I knew what
biodegradable
meant, but in talking with experts, I came to realize it's a far more complicated process than my hazy notion of something just "breaking down." The term has a precise scientific meaning:
biodegradable
in this context means that the polymer molecules can be completely consumed by microorganisms that turn them back to carbon dioxide, methane, water, and other natural compounds. "The key word is
complete,
" cautioned Narayan. It doesn't count as biodegradation if only a portion of the polymer can be digested.

That distinction is why Narayan has criticized my purportedly biodegradable Discover card. His studies show that despite the PVC-microbe bait, the micro-critters consume only about 13 percent of the card; after that, the process plateaus.
It's also at the heart of a controversy over a rash of plastic bags that are marketed as "oxo-biodegradable." They're made of conventional plastics blended with an additive that causes them to break up when exposed to the sun. The bags do quickly crumble, but there's little evidence that the resulting plastic bits are ever fully consumed by microbes. Instead, critics contend, they may simply litter the earth with yet more tiny flakes of plastic.

Another complication affecting a product's biodegradability is that the process unfolds in different ways, depending on the material, the setting, and the microbes in residence. A felled tree is eminently biodegradable. In a steamy rainforest teeming with fungi and microbes, it could be gobbled up in a matter of months. Yet if it topples in the hot, dry desert where there are few microorganisms around, it will petrify long before it can be consumed. And if it sinks to the anaerobic bottom of a river, it will be preserved for centuries because the microbes that digest wood need oxygen to do their work. Plastics are intrinsically more difficult to break down than wood, but their capacity to biodegrade is a function of a polymer's chemical structure, not its starting ingredients. There are fossil-fuel-based plastics that will biodegrade (often used to make compostable bags and film),
and there are plant-based plastics that won't.

In principle, both PLA and Mirel are biodegradable. In practice, it occurs more easily with Mirel. I could take a used Mirel gift card and toss it into my backyard compost bin, where microbes would digest it, creating lovely rich dark humus, over the course of a few months. The same would happen, though at a slower rate, if I lost it in the park, or even if I dropped it in the ocean. Mirel is just about the only plastic available today—petro- or plant-based—that will break down in a marine environment. So while you wouldn't want to build a dock with it, it could be a great material for plastic packaging, especially of foods and goods designed for shipboard use. Indeed, the U.S. Navy is exploring the use of Mirel utensils, plates, and cups.