Scientists at the Department of Energy’s Oak Ridge National Laboratory (ORNL) have demonstrated a method for converting plastic waste into higher-value materials. By chemically “editing” polymer chains, they upcycle discarded plastics — such as tire-grade polybutadiene and consumer-grade acrylonitrile butadiene styrene (ABS) — into new structures with improved performance. This approach could tackle the nearly 450 million tons of plastic discarded globally each year, of which only about 9% is recycled.
Credit: Adam Malin/ORNL, U.S. Dept. of Energy
To upcycle the polymers of discarded plastics, chemists at Oak Ridge National Laboratory invented a way to generate new macromolecules with more valuable properties than those of the starting material.
“This is CRISPR for editing polymers,” said ORNL’s Jeffrey Foster, whose team published its findings in the Journal of the American Chemical Society. “However, instead of editing strands of genes, we are editing polymer chains. This isn’t the typical plastic recycling ‘melt and hope for the best’ scenario.”
How it works
In the lab, researchers shred waste plastic and dissolve it in a solvent at around 40° C. A ruthenium catalyst breaks and reforms the polymer backbone’s double bonds between carbon atoms. This metathesis reaction generates new polymer chains that include original material and newly introduced building blocks. Because the process rearranges existing components rather than discarding them, it boasts a high “atom economy.” “That means that we can pretty much recover all the material that we put in,” Foster noted.
Potential advantages
Traditional mechanical recycling tends to degrade a polymer’s properties with each re-melt, making it progressively less valuable. ORNL’s technique, in contrast, adjusts the polymer’s molecular structure to create stronger, more heat-resistant, or more flexible materials than their initial components. The method could be adapted for various plastics, potentially including some thermoset materials, which are notoriously difficult to recycle once they’ve hardened.
Drawbacks and challenges
- Preprocessing requirements: Waste plastics often need to be separated, cleaned, and shredded before dissolving, which adds complexity and cost.
- Selective chemistry: The approach relies on having functional groups or double bonds in the polymer backbone, so not all plastics are immediately suitable.
- Use of solvents and catalysts: Although the ruthenium catalyst is effective, it requires a controlled environment, along with specific solvents such as dichloromethane, raising concerns about large-scale implementation and environmental impact.
- Scaling to industry: While lab results are promising, developing the infrastructure for widespread industrial use — complete with specialized reactors and consistent feedstock streams — presents logistical and financial challenges.
Future directions
Researchers intend to explore new polymer subunits to create robust thermoset materials, such as epoxies or vulcanized rubber, that can maintain or enhance their properties after upcycling. They also hope to optimize solvents for greater environmental sustainability and refine preprocessing to streamline the waste feedstock. “Some preprocessing is going to be required on these waste plastics that we still have to figure out,” said Foster.
