Making 'Green' Plastics From Oranges

By Roland Piquepaille

Once again, I'm amazed by the creativity of scientists. Researchers at Cornell University have made a brilliant and environmentally friendly discovery: plastics made from orange peel and a greenhouse gas. By adding a zinc catalyst to a mix of citrus fruits, such as oranges, and carbon dioxide, they found a way to make a new polymer called polylimonene carbonate, very similar to polystyrene, a petroleum-based plastic. This is a double whammy: it will reduce existing carbon dioxide, almost certainly responsible for the global warming effect, while reducing future emissions. Of course, time will pass between this discovery and its practical applications. But ultimately, this will greatly beneficial to all of us. Read more...

A Cornell University research group has made a sweet and environmentally beneficial discovery -- how to make plastics from citrus fruits, such as oranges, [which contain limonene oxide ]and carbon dioxide.

Limonene is a carbon-based compound produced in more than 300 plant species. In oranges it makes up about 95 percent of the oil in the peel.

In industry, explains Geoffrey Coates, a Cornell professor of chemistry and chemical biology, the orange peel oil is extracted for various uses, such as giving household cleaners their citrus scent. The oil can be oxidized to create limonene oxide. This is the reactive compound that Coates and his collaborators used as a building block.

The other building block they used was carbon dioxide (CO₂), an atmospheric gas that has been rising steadily over the past century and a half -- due largely to the combustion of fossil fuels -- becoming an environmentally harmful greenhouse gas.

By using their catalyst to combine the limonene oxide and CO₂, the Coates group produced a novel polymer -- called polylimonene carbonate -- that has many of the characteristics of polystyrene, a petroleum-based plastic currently used to make many disposable plastic products.

The above diagram shows the very simple process of making polymers by adding a catalyst to a mix of limonene oxide and carbon dioxide (Credit: Cornell University)

And here is Coates's conclusion.

"Almost every plastic out there, from the polyester in clothing to the plastics used for food packaging and electronics, goes back to the use of petroleum as a building block," Coates observes. "If you can get away from using oil and instead use readily abundant, renewable and cheap resources, then that's something we need to investigate. What's exciting about this work is that from completely renewable resources, we were able to make a plastic with very nice qualities."

The research work has been published by the Journal of the American Chemical Society (Vol. 126, No. 37, September 22, 2004, Pages 11404-11405, Link).

Here is a direct link to the abstract of this paper called "Alternating Copolymerization of Limonene Oxide and Carbon Dioxide."

For more information, you can check these pages about Geoffrey Coates and his research group.

Here is what Coates says about his research on polymers created from renewable resources, and more specifically about the copolymerization of CO₂ and epoxides.

Carbon dioxide is an ideal synthetic feedstock since it is abundant, inexpensive, nontoxic, and nonflammable. Although it is estimated that Nature uses CO₂ to make over 200 billion tons of glucose by photosynthesis each year, synthetic chemists have had embarrassing little success in developing efficient catalytic processes that exploit this attractive raw material. There has been considerable recent interest in the development of catalysts for the alternating copolymerization of carbon dioxide with epoxides to produce aliphatic polycarbonates. Due to the low cost and accessibility of the monomers and the attractive properties of polycarbonates, the development of new, efficient initiators for this polymerization process is a significant scientific goal. We have recently discovered a new class of well-defined, highly active zinc-based catalysts that copolymerize carbon dioxide and epoxides under exceptionally mild conditions. These catalysts are remarkable since they are several orders of magnitude more active than the current commercial catalysts.

Let's hope that this discovery quickly leaves the lab...

Sources: Sarah Davidson, Cornell University news release, January 17, 2005; and various websites

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• Biotechnology
  
• Chemistry
  
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• Environment
  
• Materials