We all try to recycle plastic, but it doesn't always work as easily as we would like it to. The main reason is that when plastic is broken down, either by heat or chemicals, it doesn't happen very smoothly. Instead, the tiny pieces (molecules) inside the plastic behave differently—some break down easily, but others get stuck.
Up until now, we haven't had a way to easily see these individual molecules moving around and getting stuck during the recycling process. But now, scientists at the College of Chemistry have created a brand-new way of tracking what the molecules are doing using a scientific technique called NMR spectroscopy.
NMR (Nuclear Magnetic Resonance) spectroscopy is a powerful analytical technique that uses strong magnetic fields and radio waves to determine the structure, dynamics, and composition of molecules (similar to the MRI used in hospitals).
"You can think of it like recording a traffic map inside the material—we can see where molecules move freely, where they become trapped, and how they transition between those regions," said Sophia Fricke, a postdoc at the College of Chemistry who is also a fellow at the Pines Magnetic Resonance Center. She recently published a paper at Science Advances that introduces this approach.
The impact? This "traffic map" (i.e., correlation of frequency-dependent diffusion) reveals why some plastics can be efficiently chemically recycled, while others resist breakdown, and it points the way toward designing new materials that can be fully deconstructed and reused.
More importantly, it gives scientists the instructions they need to design the next generation of plastics that are engineered from the start to be fully and efficiently broken down and reused, making true, closed-loop recycling possible.
This is a breakthrough because chemical recycling is all about letting a molecule move freely enough to react. By showing us how structural features like crosslinking can lead to "traffic jams" real-time, this technique can help engineers fine-tune molecular design to inform the next generation of easily recyclable plastics.
End to end sustainability
In mechanical sorting, plastics are ground down repeatedly and lose value over time, eventually ending up in a landfill, while chemical recycling breaks down plastics into their original chemical building blocks (similar to Lego pieces) and aims to fit them back together into new materials.
This new approach provides a tool to further advance chemical recycling abilities by enabling measurement of plastics that are more easily integrated into everyday life and easier to break down. "Part of the goal of chemical recyclability is that it doesn't rely so much on humans," said Fricke. "Asking people to sort the trash from the plastics and the glass can cause the downstream cycle to fail, meaning we already aren't really setting things up well to begin with."
Furthermore, the portable (or benchtop) NMR systems, which are used for this type of plastic analysis, are designed around permanent magnets rather than the superconducting magnets used for traditional, high-field NMR. "It's the size of a printer that sits on a desktop," said Fricke. "It does not require cryogenic cooling with liquid helium, which is increasingly difficult to source and incurs high environmental cost." In short, the entire approach dramatically improves sustainability.
A fully circular plastic economy?
"Our goal is to provide tools that can improve materials design that translate directly to industry," said Fricke.
Established companies and startups could both benefit – with manufacturers using the approach to design the next generation of plastics. Chemical recyclers could increase the efficiency and speed of their recycling facilities, leading to cleaner inputs and higher output quality. And startups could commercialize the portable NMR technology for this specific application.
In short, this approach is moving the industry beyond simply separating plastics and toward the fundamental goal of engineering a fully circular plastic economy.
"We also believe that this technique will be widely applicable to other processes," said Fricke. "We have been exploring its use in batteries and energy materials, carbon capture frameworks, and other systems with complex molecular dynamics."