How chemists are tackling the plastics problem

Rorrer said researchers are also looking at what materials they should use. Cobalt is more common and cheaper than some of the other catalysts they’ve tried, like ruthenium and platinum, but they’re still looking for other options. A better understanding of how catalysts work could allow them to replace cobalt with cheaper, more abundant catalysts, Rorrer said.

The ultimate goal will be a fully hybrid plastic recycling system, Rorrer said, “and that framework isn’t entirely far-fetched.”

However, achieving that vision will require some tweaking. Polyethylene and polypropylene are simple chains of carbon and hydrogen, while some other plastics contain other elements, such as oxygen and chlorine, which can pose challenges to chemical recycling methods.

For example, if polyvinyl chloride (PVC), which is widely used in bottles and tubes, is rolled up in this system, it can neutralize or poison the catalyst while also creating toxic gaseous byproducts, so researchers still need to find other ways to treat that plastic .

Scientists are also pursuing other ways to do mixed plastic recycling. In a study published in Science In October, researchers used a chemical process along with genetically engineered bacteria to break down a mixture of three common plastics.

The first step, which involves chemical oxidation, cuts the long chains, creating smaller molecules that contain oxygen. This method works because the oxidation process is “quite indiscriminate”, affecting a wide range of materials, explains Shannon StahlThe study’s lead author and chemist at the University of Wisconsin.

Oxidation of plastic produces products that can then be gobbled up by soil bacteria. By altering the bacteria’s metabolism, the researchers could eventually create new plastics, like new forms of nylon.

Research is still underway, say Alli Werner, a biologist at the National Renewable Energy Laboratory and one of the authors of the Science study. In particular, the team is working to better understand the metabolic pathways that bacteria are using to make products so they can speed up the process and make larger amounts of useful materials.


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