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Environ. Sci. Technol. Carbon balls A new method converts waste plastics such as grocery bags to pure carbon microspheres.

Plastic grocery bags are handy and durable, but after the bread and milk are put away, most of the bags wind up in landfills. Now Vilas Pol, a materials scientist at Argonne National Laboratory, has found a way to "upcycle" discarded plastics into carbon microspheres, which could play important roles in consumer products, such as toner and paint (Environ Sci. Technol. DOI 10.1021/es100243u).

Pol's idea was inspired by a 2007 ban on plastic grocery bags in San Francisco. To eliminate the need for such bans, he wanted to figure out a way to give bags a second life after they were used, abused, and thrown out.

Recycling is not the solution, Pol says. For recycling to yield chemically pure products, Pol points out that plastics made of different polymers must be separated —an extra step that is not often taken.

Instead, Pol wants to upcycle waste plastics into more-valuable products. So, he developed a method in which hydrocarbon polymers, even mixtures, produce carbon microspheres. For the new method, he places waste plastics, such as polyethylene bags and disposable polystyrene cups, into a closed, heatable reactor. Using mass spectrometry, Pol found that at 700°C, the chemical bonds between the carbons and hydrogens break down.

The products are solid carbon, as well as hydrogen and hydrocarbon gases. Pol says that the upcycling process could provide an environmentally friendly alternative to typical methods that produce solid carbon. He generates the same product but starts with discarded plastics instead of fossil fuels.

Using electron microscopy, Pol found that the carbon product takes the form of microspheres with diameters in the range of 3 to 10 μm. The microspheres are paramagnetic and conductive, making them suitable, Pol says, for incorporation in tires, toner, paints, and lubricants, as well as in anode materials for rechargeable batteries. Microspheres made of other materials, such as glass and polymers, already find commercial use in many products.

But Raymond Teller, an environmental scientist at the Pacific Northwest National Laboratory, warns that commercial applications may be far off. "There is no well-established market use for carbon microspheres," he says. "That is not to say that there aren't excellent potential uses for this material; however, a viable product line has yet to be identified." Pol, however, says that he is working with several companies that are interested in licensing the technology and developing applications.