How to make cheap, biodegradable plastic from grass
We’ve been hearing a lot about using grasses in biofuel production. Now, researchers are genetically engineering these same grasses to produce a biodegradable polymer. Technology Review reports.
Most plastics sold today come from petroleum -- whereas switchgrass is a large, hardy plant found everywhere in the U.S. except the west coast.
Metabolix in Cambridge, Massachusetts, is already selling a biodegradable polymer. Two decades ago, MIT scientists discovered metabolic genes that allow bacteria to naturally produce a polymer called PHA -- but that requires bacteria feeding on plant sugars in expensive fermenters. A plant-based process would require less equipment and only marginal land.
To realize their plants-to-plastics vision, Metabolix scientists are now working on inserting those genes, along with others that regulate growth, into plants:
- First, they coax the plant to produce and store a type of PHA called PHB, used to make injection-molded products that house electronics.
- Months later, industrial processes extract PHB from cut and dried grass.
- There are also chemical production methods: extract PHB using solvents or use heat to convert PHB into crotonic acid which could be used as feedstock for polymers.
- They think leftover grass could be burned as a biomass energy source.
The switchgrass must produce 10 percent of its weight in PHB to be economically competitive:
The company has already nearly doubled the PHB content in switchgrass, from 1.2 percent in 2008 to 2.3 percent last year, including 7 percent in the leaves.
The process, however, still emits carbon with fossil-fuel-based fertilizers and fossil-fuel-powered harvesting machines. But Metabolix’s chief scientific officer, Oliver Peoples, predicts it would be cleaner overall than producing plastic from fossil fuels.
Products like biodegradable plastic shopping bags are still considered niche items. But if estimations are correct, the company could sell the plant-based polymer at less than half of today’s prices, making it economical for wide use.
[Via Technology Review]
Image: Bob Nichols, USDA via Flickr
This post was originally published on Smartplanet.com