Cambridge firm developing growable plastic

Creating a biodegradable polymer from plants

Team leader Maria Somleva checked the growth of genetically modified switchgrass at Metabolix in Cambridge.
Team leader Maria Somleva checked the growth of genetically modified switchgrass at Metabolix in Cambridge.(Matthew J. Lee/Globe Staff)

The plants growing in a greenhouse on Erie Street in Cambridge bear neither flower nor fruit and, in truth, are downright homely. Tall plumes of switchgrass, once the dominant species of the North American prairie, are domesticated here, sprouting from black pots under skylights and heat lamps.

Underappreciated switchgrass is experiencing second life as a major science project; it is widely used to make alternative fuels and, on Erie Street, to make plastic. In July, the Cambridge company Metabolix Bioplastics received a US patent for its method of supercharging production of the molecule in switchgrass that is used to make biodegradable plastic, and is now working to produce the polymer in high enough concentrations to make the technique commercially viable.


“It’s a matter of changing the genetic makeup of the plant so that it takes carbon and turns those plants into a plastics factory,” said Metabolix chief executive Rick Eno.

The company’s modifications to switchgrass allow the plant to produce a naturally occurring molecule in unnaturally large quantities. The molecule, polyhydroxybutyrate, or PHB, is responsible for storing energy in plants, much like fat cells store energy in humans. Extracted from switchgrass blades, it also can serve as the raw material for plastic production, replacing the petroleum currently used in manufacturing virtually all of the world’s plastics.

For Metabolix, the patent represents a significant step toward developing a biodegradable plastic material that can compete with the cost of conventional plastics. It comes as the use of bioplastics is soaring around the world. In 2009, global production of compostable bioplastics totaled just 6,000 tons, according to European Bioplastics, a German firm that tracks the industry. In 2011, the most recent year for which data is available, production totaled 675,000 tons, and is expected to top 5 million by 2016.

Dawit Abreham, a greenhouse research assistant at Metabolix in Cambridge, checked the height of genetically modified switchgrass.
Dawit Abreham, a greenhouse research assistant at Metabolix in Cambridge, checked the height of genetically modified switchgrass.(Matthew J. Lee/Globe Staff)

Metabolix, meanwhile, received $6 million from the US Department of Energy in 2011 as part of a broad government initiative to promote research and development of biobased products.


Genetically modified switchgrass could supply plastic producers today, but its commercial appeal is limited by its inefficiency. Right now, only 7 percent of each blade of grass, by weight, is PHB. Metabolix is experimenting with increasing that yield in plants at its Cambridge facility, and at a second greenhouse at the University of Massachusetts Amherst.

Eno estimates the company will have to hit the 10 percent threshold to compete with the cost of petroleum-based plastics.

“It’s definitely achievable; it’s just a matter of time,” said Stephen P. McCarthy, director of the Center for Biodegradable Polymer Research at UMass Lowell. “I think it’s achievable in three to five years.”

If Metabolix nails its target, the next step will be field tests to determine whether its genetically modified switchgrass could be planted in mass quantities, thrive in real weather conditions, and most importantly, offer a cost-effective alternative to fossil fuels.

“We’ve never counted on a green premium — people paying more because it’s green,” Eno said. “What we do see is green differentiation, meaning if a customer has two choices that provide the same performance and one is renewable, quite often the renewable choice gets the nod. People are concerned about the environment, but we have to compete on the economic merits.”

Already, Metabolix has more than 100 clients making biodegradable plastics from molecules the company produces through a different process: fermentation. Down the hall from the greenhouse is a laboratory that resembles a mad scientist’s brewery. Inside 20-liter fermentation vessels, genetically modified microbes feed on sugar, converting carbon into plastic-making polymers similar to the ones produced by switchgrass.


Popular uses for the Metabolix polymers include compostable plastic bags for yard waste and everyday shopping, and agricultural film used to suppress weed growth and retain water. Most client companies are based in Europe, Eno said, though Target has experimented with making biodegradable gift cards, and Papermate with biodegradable pens.

For now, making the molecules through the fermentation initiative is more cost-effective than growing them in switchgrass, which is why fermentation-based plastics already are on the market. But Metabolix is wagering that in the long run, when its modified switchgrass can produce PHB in higher concentrations, plant-based production will be the cheapest option available.

“The benefit of the switchgrass approach is the plant does all the work,” Eno said. “It’s basically just taking CO2, sunlight, and water and producing plastics and chemicals.”

Callum Borchers can be reached at callum.borchers@globe.com. Follow him on Twitter @callumborchers.