Greener Shopping Bags?

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Metabolix expects that the first dedicated production plant for its polyhydroxyalkanoate (PHA) polymer will begin generating up to 110 million pounds of the natural polyester per year next year. The plant, which ADM is building adjacent to its Clinton, IA, corn wet mill, uses corn sugar to feed fermentation vessels filled with bacteria that have been genetically engineered by Metabolix to produce the polymer. Corn stocks will be burned to power the process. "We'll reduce greenhouse-gas emissions by about two-thirds and petroleum usage by about 80 percent compared to traditional petroleum-based plastics," says Metabolix vice president Brian Igoe.

Igoe says PHA will break down without the high temperatures found in industrial composting facilities. That means that bags or other products made from Metabolix's polymers will degrade if they drift into wetlands or the ocean. "We're not saying that our products are environmentally disposable--nobody would encourage that solution--but the reality is that we have very leaky collection systems," Igoe says. He adds that those environmental benefits are central to Metabolix's marketing plan because Metabolix's polymer will cost three times as much as petroleum-based polymers.

But in many applications, including PHA-based bags that Igoe says could hit the market by the end of this year, the user will be willing to pay a premium. He thinks that many consumers are ready to do so--especially if they get to keep the convenience of plastic they've grown accustomed to. "Plastic bags are very functional," says Igoe. "If you have a bag that has the environmental benefits we have, you're going to see a lot more usage. There's definitely a group of people out there willing to pay for cleaner and greener solutions."

Ironically, just as biodegradable plastics are matching the performance of conventional plastics and finding willing markets, the success of biofuels is creating a new challenge: a rapidly rising demand for corn sugar. The use of corn sugar to produce ethanol has boosted food prices, doubling, for example, the price of tortillas in Mexico and sparking street protests. (See "Ethanol Demand Threatens Food Prices.") Manufacturers of food-based plastics such as Metabolix could see their costs rise too. They might have to price the petroleum-free bag beyond what even San Francisco's green buyers will pay.