'Green' plastics could help reduce carbon footprint

February 11, 2009

More than 20 million tons of plastic are placed in U.S. landfills each year. Results from a new University of Missouri study suggest that some of the largely petroleum-based plastic may soon be replaced by a nonpolluting, renewable plastic made from plants. Reducing the carbon footprint and the dependence on foreign oil, this new 'green' alternative may also provide an additional cash crop for farmers.

"Making plastics from plants is not a new idea," said Brian Mooney, research assistant professor of biochemistry with the MU Interdisciplinary Plant Group. "Plastics made from plant starch and soy protein have been used as an alternative to petroleum-based plastics for a while. What is relatively new - and exciting - is the idea of using plants to actually grow plastics."

By employing a number of modern molecular techniques, scientists are able to introduce three bacterial enzymes into the model plant Arabidopsis thaliana. When combined with two enzymes from the plant, an organic polymer is produced. The polymer, known as polyhdroxybutyrate-co-polyhydroxyvalerate, or PHBV, is a flexible and moldable plastic that can be used to produce a wide range of products, such as grocery bags, soda bottles, disposable razors and flatware. When discarded, the plastic is naturally degraded into water and carbon dioxide by bacteria in the soil.

"Of the two plant enzymes that supply the chemical precursors for PHBV, one is produced in the mitochondria. Recently, we've successfully modified plants so that this enzyme is diverted to the chloroplast, which has been defined as the best place in the plant to produce PHBV," said Mooney, who is also associate director of the Charles Gehrke Proteomics Center in the MU Christopher S. Bond Life Sciences Center. "We also confirmed that a stable, functional complex is formed."

These recent advances potentially remove two of the remaining technological hurdles limiting the ability of companies from turning acres of weeds into plastic factories. The next step, said Mooney, is to see if the technique works in 'real' plants, such as switchgrass. Mooney along with Douglas Randall, professor of biochemistry at MU, have already initiated conversations with scientists at the Donald Danforth Plant Science Center in St. Louis, Mo., and the Cambridge, Mass.-based, environmental tech company Metabolix Inc.

Metabolix and the Danforth Center were recently awarded a $1.14 million grant from the Missouri Technology Corporation to produce a "double-crop" that would produce both a bioplastic and an oil for biodiesel refineries. Metabolix has already successfully produced one form of biodegradable plastic in switchgrass, but yield is too low. MU researchers hope their advances will lead to higher yield of a more useable plastic.

More information: Mooney reviews the production of biodegradable plastics in "The second green revolution? Production of plant-based biodegradable plastics," which appears in the latest issue of BJ Plant.

Source: University of Missouri-Columbia

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