Bioplastics lifts garbage out of the trash heap
Published: June 19, 2007
Carbon dioxide. Orange peels. Chicken feathers. Olive oil. Potato peels. E. coli bacteria. It is as if chemists have gone Dumpster diving in their hunt to make biodegradable, sustainable and renewable plastics. Most bioplastics are made from plants like corn, soy, sugar cane and switch grass, but scientists have recently turned to trash in an effort to make so-called green polymers, essentially plastics from garbage.
Geoff Coates, a chemist at Cornell, one of the leaders in the creation of green polymers, pointed to a golden brown square of plastic in a drying chamber.
“It kind of looks like focaccia baking, doesn’t it?” Coates said. “That’s almost 50 percent carbon dioxide by weight.”
Coates’s laboratories occupy almost the entire fifth floor of the Spencer T. Olin Laboratory at Cornell, and have a view not only of Cayuga Lake and the hills surrounding the school in New York State, but of a coal power plant that has served as a kind of inspiration. It was here that Coates discovered the catalyst needed to turn CO2 into a polymer.
With Scott Allen, a former graduate student, Coates has started a company called Novomer, which has partnered with several companies on joint projects. Coates imagines CO2 being diverted from factory emissions into an adjacent facility and turned into plastic.
The search for biocomposite materials dates from 1913, when both a French and a British scientist filed for patents on soy-based plastic.
“There was intense competition between agricultural and petrochemical industries to win the market on polymers,” said Bernard Tao, a professor of agricultural and biological engineering at Purdue.
Scientist Scott Allen drains the polymer reactor
after a processing at Cornell University
in Ithaca, N.Y., May, 2007.
Much of the early research on bioplastics was supported by Henry Ford, who believed strongly in the potential of the soybean. One famous 1941 photo shows Ford swinging an ax head into the rear of a car to demonstrate the strength of the soy-based biocomposite used to make the auto body. But soy quickly lost out to petrochemical plastics.
“In those days you had a lot more oil around,” Tao said. “You didn’t have to wait until the growing season.”
And there was another problem: permeability. The soy plastic was not waterproof. “Petroleum is biologically and relatively chemically inert, ” Tao explained. “Most living systems require water.”
Fossil fuels quickly dominated the plastics market. Now, agriculture-based plastics are back in the running, and with the type of catalysts developed by Coates and others, a whole new array of polymers has become commercially viable.
Choosing carbon dioxide as a feedstock for a polymer was not an obvious choice. It was what Coates called “a dead molecule.”
Mix carbon dioxide with an epoxide, he said, “and the two would just stare at each other for a hundred years.” The key is in finding the right catalyst to open a pathway for the carbon dioxide and the epoxide to bond.
“Catalysts are like a matchmaker who make a marriage and then can go off and make other marriages,” Coates said. “They accelerate a reaction without being consumed by that reaction.” His catalyst – beta-diiminate zinc acetate, or “zinc-based pixie dust,” in Coates’s words – was designed to speed “a reaction from a geological time scale to the laboratory time scale.”
Green polymer businesses seem to be springing up everywhere.
Rodenburg BioPolymers, a Dutch company, makes plastic from potato waste. Metabolix, based in Boston, grows a natural form of polyester inside genetically modified E. coli bacteria.
Tao, of Purdue, said history was repeating itself, in a way. “Its almost like we’re seeing the same competition over who will dominate the plastic market as we did a hundred years ago,” he said. “But this time it is a very different race.”