Reviewed by Lexie CornerJan 20 2025
Chemists at the Department of Energy’s Oak Ridge National Laboratory have developed a method for producing new macromolecules with improved properties by modifying the polymers in discarded plastics. This research is published in the Journal of the American Chemical Society,
Upcycling may help address the approximately 450 million tons of plastic discarded globally each year, of which only 9 % is recycled. The majority is either incinerated or ends up in landfills, oceans, or other environments.
ORNL’s approach involves rearranging polymeric building blocks to alter the properties of plastics. By combining molecular subunits to form polymer chains and cross-linked structures, this method creates plastics with tailored properties, such as improved strength, rigidity, and heat resistance. These characteristics depend on the composition of the polymer chains.
Molecular editing has been recognized for its transformative potential, as evidenced by two Nobel Prizes in Chemistry. In 2005, the prize was awarded for the development of the metathesis reaction, which enables the rearrangement of carbon-carbon double bonds to create new molecular structures. In 2020, the prize recognized the development of CRISPR, a technique for editing DNA, a biopolymer composed of nucleotide subunits that encode genetic information.
This is CRISPR for editing polymers. 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.
Jeffrey Foster, Study Lead, Oak Ridge National Laboratory
ORNL researchers developed a method to modify commercial polymers, which are a major contributor to plastic waste. Their experiments focused on soft polybutadiene, commonly found in rubber tires, and tough acrylonitrile butadiene styrene, used in products such as plastic toys, computer keyboards, ventilation pipes, protective headgear, automobile components, and kitchen appliances.
Foster added, “This is a waste stream that's really not recycled at all. We are addressing a significant component of the waste stream with this technology. That would make a pretty big impact just from conservation of mass and energy from materials that are now going into landfills.”
The initial step in synthesizing drop-in polymer additives involves dissolving waste polymers. The researchers shredded synthetic or commercial polybutadiene and acrylonitrile butadiene styrene and immersed them in dichloromethane, a solvent, for under two hours to facilitate a chemical reaction at a low temperature (40 °C).
A ruthenium catalyst was used to aid polymerization, a process that adds polymer chains. This catalyst has previously been applied in industrial processes to create durable plastics and convert biomass, such as plant oils, into fuels and other organic compounds, demonstrating its suitability for chemical upcycling.
The polymer backbone contains molecular building blocks with functional groups, which serve as reactive sites for modification. Double bonds between carbon atoms are particularly significant, as they increase the likelihood of chemical processes that enable polymerization.
During the reaction, a carbon ring opens at a double bond, forming a polymer chain that grows as additional polymer units are added. This process conserves material while allowing control over the molecular weight of the synthesized material, influencing its characteristics and performance.
Expanding this technique to include a wider range of industrially relevant polymers could provide a cost-effective way to reuse manufacturing materials currently used for single products. The upcycled materials could have properties such as increased flexibility or improved moldability, enabling the production of durable thermosets.
The researchers utilized two metathesis-based methods to upcycle plastic waste. In ring-opening metathesis polymerization, carbon rings open and elongate into chains. In cross-metathesis, polymer subunits are exchanged between chains.
Traditional recycling methods degrade polymers with each cycle of melting and reuse, limiting their value. ORNL’s upcycling approach uses existing molecular building blocks to retain the mass and features of waste materials while adding utility and value.
“The new process has high atom economy. That means that we can pretty much recover all the material that we put in,” Foster added.
ORNL scientists demonstrated that this technique, which uses less energy and produces fewer emissions than conventional recycling methods, effectively incorporates waste materials while preserving polymer quality. Foster, Ilja Popovs, and Tomonori Saito developed the core concepts presented in the paper.
Nicholas Galan, Isaiah Dishner, and Foster worked on producing monomer subunits and refining their polymerization process. Joshua Damron conducted nuclear magnetic resonance spectroscopy to analyze reaction kinetics. Jackie Zheng, Chao Guan, and Anisur Rahman studied the mechanical and thermal properties of the resulting materials.
Foster stated, “The vision is that this concept could be extended to any polymer that has some sort of backbone functional group to react with.”
If scaled up and expanded to include additional additives, the approach could utilize a wider range of waste materials as sources for molecular building blocks, reducing the environmental impact of difficult-to-process plastics. This development could support a circular economy, where waste materials are reused rather than discarded.
The researchers aim to explore different subunits within polymer chains and rearrange them to develop high-performance thermoset materials. These include epoxy resins, vulcanized rubber, polyurethane, and silicone. Thermosets, once cured, cannot be remelted or reshaped due to their crosslinked molecular structure, making their recycling more challenging.
The team is also focused on improving the environmental sustainability of solvents used during industrial processing.
Foster concluded, “Some preprocessing is going to be required on these waste plastics that we still have to figure out.”
The study was supported by the DOE Office of Science Materials Science and Engineering program and the ORNL Laboratory Directed Research and Development program.
Polymer editing can upcycle plastic waste
In this animation, polymers of discarded plastics are edited to generate macromolecules that may be reused in other products. The makeup of the polymer chains determines the properties of resulting plastics. Video Credit: Adam Malin/ORNL, U.S. Dept. of Energy
Journal Reference:
Foster, J. C., et. al. (2024) Polyalkenamers as Drop-In Additives for Ring-Opening Metathesis Polymerization: A Promising Upcycling Paradigm. Journal of the American Chemical Society. doi.org/10.1021/jacs.4c10588