Plastic Doesn’t Grow on Trees, But it Grows in Grass Now
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CREDIT: Paper Mate |
With the help of genetically engineered microbes, scientists have created plants that can churn out “green” plastic that might some day replace the petroleum-based kinds used in everything from ballpoint pens to disposable food containers.
Metabolix, a Massachusetts-based biotech company, is using this process to make polyhydroxyalkanoate (PHA) – a biodegradable polymer similar to polypropylene (found in yogurt containers) – inside the stems and leaves of switchgrass, oilseed and sugarcane crops.
These plastic-producing crops are currently growing in the company’s Cambridge-based greenhouse and should be in commercial field trials within two to three years, according to the company.
Fattening up microbes
The bioplastics that do exist today are made “from” plant matter instead of “in” plant matter. Here, special bacteria feed on the sugars lodged inside certain crops and spit out plastic.
“We’ve engineered microbes that consume corn sugar during fermentation and convert it to a bioplastic we call Mirel,” said Rick Eno, CEO at Metabolix.
“Just as humans would produce fat if they eat too much corn syrup, these microbes get ‘fat’ with bioplastic.," Eno said.
The bioplastic is then separated from the plastic-producing bugs and made into little pellets that can be molded into products such as water bottles.
Products sporting the Mirel plastic include compostable trash bags, and most recently, a “green ” line of ballpoint pens from pen-maker Paper Mate.
CREDIT: Metabolix
Turning crops into mini-factories
Instead of feeding plant-derived sugars to the plastic-producing microbes, in the new method the researchers insert three genes from the bugs into the plants. The result: Crops that make bacterial proteins, in this case plastic.
These genes give the plant new instructions, telling it to re-direct some of its internal chemicals toward making plastic.
“The [plastic] precursor chemicals are naturally made in the plant,” Mooney said. “However, in the presence of the bacterial genes, the precursors are re-directed from their normal uses to make the plastic.”
While a somewhat simple concept, there are several hurdles that must be overcome before these plastics find their way into consumer products.
For one thing, it's expensive. Making plastics this way costs about four times more than petroleum-based plastic, said Brian Mooney, professor at the University of Missouri, who is doing research in a similar area.
Another problem is that in this process, each plant produces relatively little plastic, Mooney said.
So far Metabolix has produced 6 percent in switchgrass and hopes to up this amount over the next few years.
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