Corn Plastic to the Rescue

Wal-Mart and others are going green with “biodegradable” packaging made from corn. But is this really the answer to America’s throwaway culture?

Nature Works has figured out how to make plastic out of corn. (Ex0artefact)
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Wal-Mart, which has begun using PLA containers in some stores, has also switched packaging on high-end electronics from PET to a sandwich of cardboard and PLA. “It has a smaller packaging footprint, it’s completely biodegradable and it costs less,” says Kistler. What Wal-Mart says about PLA’s biodegradable nature is true, but there’s an important catch.

Corn plastic has been around for 20 years, but the polymer was too expensive for broad commercial applications until 1989, when Patrick Gruber, then a Cargill chemist looking for new ways to use corn, invented a way to make the polymer more efficiently. Working with his wife, also a chemist, he created his first prototype PLA products on his kitchen stove. In the beginning, it cost $200 to make a pound of PLA; now it’s less than $1.

The polymer has had to get over some cultural hurdles. In the mid-1980s, another bio-based plastic appeared on grocery store shelves: bags made from polyethylene and cornstarch that were said to be biodegradable. “People thought they would disappear quickly,” recalls Steven Mojo, executive director of the Biodegradable Products Institute. They didn’t. Will Brinton, president of Woods End, a compost research laboratory in Mt. Vernon, Maine, says the bags broke into small fragments of polyethylene, fragments that weren’t good for compost—or public relations. “It was a big step backward for the biodegradability movement,” he adds. “Whole communities abandoned the concept of biodegradable bags as a fraud.”

According to a biodegradability standard that Mojo helped develop, PLA is said to decompose into carbon dioxide and water in a “controlled composting environment” in fewer than 90 days. What’s a controlled composting environment? Not your backyard bin, pit or tumbling barrel. It’s a large facility where compost—essentially, plant scraps being digested by microbes into fertilizer—reaches 140 degrees for ten consecutive days. So, yes, as PLA advocates say, corn plastic is “biodegradable.” But in reality very few consumers have access to the sort of composting facilities that can make that happen. NatureWorks has identified 113 such facilities nationwide—some handle industrial food-processing waste or yard trimmings, others are college or prison operations—but only about a quarter of them accept residential foodscraps collected by municipalities.

Moreover, PLA by the truckload may potentially pose a problem for some large-scale composters. Chris Choate, a composting expert at Norcal Waste Systems, headquartered in San Francisco, says large amounts of PLA can interfere with conventional composting because the polymer reverts into lactic acid, making the compost wetter and more acidic. “Microbes will consume the lactic acid, but they demand a lot of oxygen, and we’re having trouble providing enough,” he says. “Right now, PLA isn’t a problem,” because there’s so little of it, Choate says. (NatureWorks disputes that idea, saying that PLA has no such effect on composting processes.) In any event, Norcal says a future PLA boom won’t be a problem because the company hopes to convert its composters to so-called anaerobic digesters, which break down organic material in the absence of oxygen and capture the resulting methane for fuel.

Wild Oats accepts used PLA containers in half of its 80 stores. “We mix the PLA with produce and scraps from our juice bars and deliver it to an industrial composting facility,” says the company’s Tuitele. But at the Wild Oats stores that don’t take back PLA, customers are on their own, and they can’t be blamed if they feel deceived by PLA containers stamped “compostable.” Brinton, who has done extensive testing of PLA, says such containers are “unchanged” after six months in a home composting operation. For that reason, he considers the Wild Oats stamp, and their in-store signage touting PLA’s compostability, to be false advertising.

Wal-Mart’s Kistler says the company isn’t about to take back used PLA for composting. “We’re not in the business of collecting garbage,” he says. “How do we get states and municipalities to set up composting systems? That is the million-dollar question. It’s not our role to tell government what to do. There is money to be made in the recycling business. As we develop packaging that can be recycled and composted, the industry will be developed.”

For their part, recycling facilities have problems with PLA too. They worry that consumers will simply dump PLA in with their PET. To plastic processors, PLA in tiny amounts is merely a nuisance. But in large amounts it can be an expensive hassle. In the recycling business, soda bottles, milk jugs and the like are collected and baled by materials recovery facilities, or MRFs (pronounced “murfs”). The MRFs sell the material to processors, which break down the plastic into pellets or flakes, which are, in turn, made into new products, such as carpeting, fiberfill, or containers for detergent or motor oil. Because PLA and PET mix about as well as oil and water, recyclers consider PLA a contaminant. They have to pay to sort it out and pay again to dispose of it.


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