Plastic from Plants: Is It an Environmental Boon or Bane?

Plant-based plastics are beginning to replace petroleum. But as the price drops and usage rises, will the advantages outweigh the disadvantages?
David Biello Scientific American 26 Oct 10;

More than 2.5 billion plastic bottles—partially made from plants—are already in use around the world in a bid to replace petroleum as the fundamental building block of everyday plastics. The so-called PlantBottle from the Coca-Cola Co. is made by converting sugars from sugarcane farmed in Brazil into the polyethylene terephthalate (PET) plastic commonly used in the ubiquitous clear bottles for various beverages. Fully recyclable, the bottles debuted at the 2009 U.N. Copenhagen Climate Conference and Vancouver Olympics, and are now on sale from Japan to Chile and across the U.S.

Most importantly from Coke's point of view, none of the six other major varieties of plant-based plastic can keep the carbonation from leaking out. "It's not only to hold carbonation, it's just to hold water," explains chemist Shell Huang, Coca-Cola's director of packaging research. "You can lose moisture through the bottle wall" with some of the other available plant-based polymers.

But can plants become more widely used as building blocks of ubiquitous plastics? In a sense it is back to the future with biopolymers—the very first plastics were produced by German chemists in the 19th century via a fermentation processes. Yet, earlier in October, Frito-Lay withdrew a high-profile example of plant-based plastic for the majority of its SunChips bags. Why? Not because it was unsafe or failed to compost as advertised but because the sound of the crinkling plastic was louder than customers liked.

"Only a Frito-Lay brand is big enough…so that the final product is cost-competitive," said Marc Verbruggen, president and CEO of NatureWorks, the provider of the bioplastic in the SunChips bags—as well as in products ranging from tea bags to diapers—in a 2009 interview. "Biopolymers will be the next generation of plastics."

The PlantBottle might prove that point, helped by the fact that it is a different form of plastic from that which made up the failed SunChips bag. The first step in making it is fermenting ethanol from the sugarcane in Brazil. That ethanol is then exported to India where it is processed as monoethylene glycol, or MEG—which comprises roughly 30 percent of a typical PET bottle. The rest is composed of traditional, petroleum-derived plastic. "This is the most sustainable raw material for now," Huang says. "Longer term, our goal is to make [the plastic] from plant waste," such as the lignin or cellulose in the sugarcane's leaves and stems.

Making the PlantBottle has thus far saved roughly 70,000 barrels of oil by the company's calculations—and the plastic resin, indistinguishable from its petroleum-based analog, can be exported throughout the world. "We are making PET from a renewable resource so there's a lower carbon footprint, and we can take advantage of existing infrastructure to recycle it," Huang explains. Plus, "the carbon is captured in the [plastic of the] bottle and never goes back to the air."

Of course, plant-based plastics run into the same problem as plant-based fuels—directly or indirectly they have an impact on food production. Whereas making ethanol from sugarcane in Brazil is energy efficient—more energy is embedded in the ethanol than goes into growing and harvesting the plants—replacing a significant fraction of the global demand for plastics, let alone fuels, would require converting large swaths of yet more Brazilian land into sugarcane fields. And one of the leading bioplastics—Ingeo, made by NatureWorks, owned by Cargill—relies on heavily fertilized and thus energy-intensive corn (unlike sugarcane) to make polylactic acid, or PLA, which now appears in products such as the SunChips bags or Stonyfield Farm yogurt cups.

"In the long run this could become an issue," admits Frederic Scheer, CEO of Cereplast, which plans to introduce an algae-based bioplastic product, in addition to a starch-based biopolymer it already markets, by the end of 2010. "You cannot have access to farmland without creating pressures on the food system."

Thus far, bio-based plastics have only replaced roughly 1 percent of the hundreds of billions–kilogram global plastics market, according to Lux Research, although that percentage may grow in coming years. The majority of those plastics, like PLA, are not recyclable, but rather compostable using high heat (temperatures of roughly 60 degrees Celsius).

"It takes 77 million years to make fossil fuels and 45 minutes to use as a coffee cup," says Cereplast's Scheer, noting that his industry can use the residue of government-mandated production of biofuels, such as ethanol from corn. "It makes no sense."

Regardless of the environmental logic, the plant-based plastics remain more expensive. "There is, right now, a bit of a price-up charge that we are absorbing, not passing it along to consumers," Lisa Manley, Coca-Cola's group director of sustainability communications, says of the PlantBottle. But "if you look at the volatility of pricing for petroleum—in short order and over the long term—the price comparisons will be at parity, and perhaps better."

That is why Coca-Cola, at least, is now working toward a 100 percent plant-based plastic bottle. "We don't have a definite timeline but we already did a feasibility study," Huang says. "It is technically feasible to make a 100 percent plant bottle from the material."