Researchers have found an inexpensive way to make plastic from plants that could compete with Coca-Cola's PlantBottle (above).

Coca-Cola

Here’s a sweet recipe for cheap, green plastic—sugar and corncobs

Plastic has a huge carbon footprint: Producing the petroleum-based material accounts for at least 100 milion tons of carbon emissions each year. Now, a team of researchers at the University of Wisconsin in Madison has invented an inexpensive way to make plastic with a much lighter touch, from sugar and corncobs. If it can be made cheaply enough, the material could one day replace one of the world’s most common plastics—polyethylene terephthalate (PET)—found in food packaging, soda bottles, and even polyester fabric.

“There’s a genuine interest in this as a new plastic,” says Matthew Kanan, a chemist at Stanford University in Palo Alto, California, who was not involved in the work. Not only does it come from renewable resources, but it’s better than PET at sealing out gases like oxygen and carbon dioxide, which is critical for preserving foodstuffs.

Petroleum has served for decades as the starting material for almost all plastic—from polyethylene to propylene. But the oil crisis of the 1970s pushed researchers to search for alternatives made not of petroleum, but from plants. DuPont and other chemical companies have made headway. But scientists have continued to search for a biobased alternative to PET, and the most promising is polyethylene furandicarboxylate (PEF). Researchers have managed to make one of PEF’s major building blocks, furandicarboxylic acid (FDCA), from renewable sources. But it has been impossible to do cheaply.

So University of Wisconsin chemical engineer Jim Dumesic and his team set out to find a way to lower that cost. After 10 years, they found the key to doing so is a potent a solvent called γ-valerolactone (GVL). GVL is a colorless liquid that can be derived from renewable sources such as corncobs. When Dumesic and his colleagues added GVL to water along with an organic acid catalyst, they transformed fructose—a sugar found in fruits, veggies, and corn syrup—into an organic compound that is a precursor to FDCA. And because GVL works so well, Dumesic’s team needed to use only small amounts of fructose to produce abundant quantities of pure FDCA.

The new method solves three problems for plastics production, says University of Wisconsin chemical engineer Ali Hussain Motagamwala, a co-author of the paper. First, it uses a renewable carbon source instead of fossil fuels. Second, previous attempts to make FDCA from renewables required using corrosive acids, and therefore expensive reactors, which aren’t needed in the new approach. Finally, scientists can use the end product, FDCA, as a catalyst in the reaction and recycle the GVL solvent, which lowers the cost and uses less energy than current methods. “It makes the process much more green,” he says.

But one kind of green doesn’t necessarily lead to another. To find out whether the technique is economically viable, Motagamwala analyzed the likely cost of scaling it up. He found the method could produce FDCA at a selling price of $1490 per metric ton, just $45 more than the current method for making PET. But Motagamwala estimates that streamlining the GVL approach could slash the cost of producing FDCA by nearly $200, the team reported last week in Science Advances, making it considerably cheaper than the competition.

But it will only work if they can bring other costs down. Other methods to make FDCA from fructose use cobalt, a relatively cheap and abundant metal, Kanan notes. However, the new renewable FDCA approach also uses platinum, a rare and expensive metal that may make the process more costly in the long run. Another concern is whether using fructose makes environmental or economic sense; for commodity-scale plastics, the sugar is commonly derived from crops. Producing enough FDCA to make a dent in the polyester market would stress the sugar supply and may mean a considerable carbon footprint, Kanan says.

Still, he sees the new work as a step in the right direction. “Ultimately, if I'm making my plastic out of fossil fuels, [that means] I'm changing carbon from the ground into the atmosphere,” he says. “Whereas if it's coming from plants you at least have a possibility of making a product that's carbon neutral or even carbon negative.”