Chemistry

Polymer editing allows waste to be upcycled into higher-performance plastics

To upcycle discarded plastic polymers, chemists at Oak Ridge National Laboratory have invented a method to produce new polymers with more valuable properties than the starting materials. Credit: Adam Malin/ORNL, U.S. Department of Energy

Chemists at the Department of Energy’s Oak Ridge National Laboratory have discovered a way to create new polymers with more valuable properties than the starting materials by editing polymers from discarded plastics. Upcycling could help improve the approximately 450 million tonnes of plastic thrown away each year worldwide, of which only 9% is recycled. The rest is incinerated or disposed of in landfills, oceans, or other locations.

ORNL’s invention has the potential to change the environmental fate of plastics by rearranging polymeric components to customize their properties. The subunits of the molecule join together to create polymer chains, which are then joined to the main chain through cross-linking molecules to form multipurpose plastics. The composition of the polymer chains determines the strength, stiffness, and heat resistance of the plastic.

Molecular editing is so promising that it is the basis of two Nobel Prizes in Chemistry. In 2005, an award was presented to the developer of the metathesis reaction. Metathesis reactions create double bonds between carbon atoms in rings and chains that can be exchanged to create new molecules limited only by your imagination. Similarly, in 2020, an award was presented to the developers of CRISPR, the “genetic scissors” for editing strands of DNA, a biopolymer made of nucleotide subunits that carry the code for life.

“This is CRISPR for editing polymers,” said ORNL’s Jeffrey Foster, who led the study published in the Journal of the American Chemical Society. “But instead of editing gene chains, we’re editing polymer chains. This is not the typical ‘melt and hope for the best’ scenario of plastics recycling.”

ORNL researchers have precisely compiled a commodity polymer that contributes significantly to plastic waste. In some experiments, the researchers used soft polybutadiene, which is common in rubber tires. Other experiments used sturdy acrylonitrile butadiene styrene, plastic toys, computer keyboards, ventilation pipes, protective headgear, vehicle trim and moldings, and kitchen utensils.

In this animation, discarded plastic polymers are edited to produce polymers that can be reused in other products. The composition of the polymer chains determines the properties of the resulting plastic. Credit: Jacquelyn DeMink/ORNL, U.S. Department of Energy

“This is waste that is not recycled at all,” Foster said. “We are using this technology to address an important part of the waste stream, which has a significant impact just by saving mass and energy from material that currently goes to landfill. It will bring.”

Dissolution of waste polymer is the first step in creating drop-in additives for polymer synthesis. The researchers shredded synthetic or commercially available polybutadiene and acrylonitrile-butadiene-styrene, soaked the materials in the solvent dichloromethane, and performed a chemical reaction at low temperatures (40 degrees Celsius) for less than two hours.

Ruthenium catalysts promoted polymerization, or addition of polymers. Industrial companies are using the catalyst to make durable plastics and effortlessly convert biomass such as vegetable oils into fuels and other high-value organic compounds, highlighting its potential for use in chemical upcycling. Masu.

The molecular components of the polymer backbone contain functional groups, or clusters of atoms, that serve as reactive sites for modification. In particular, double bonds between carbons increase the potential for chemical reactions that allow polymerization. The carbon rings open at double bonds to form polymer chains, and each functional polymer unit grows by sliding directly in, preserving the material. Plastic additives also help control the molecular weight of synthetic materials, and thus their properties and performance.

If this material synthesis strategy can be extended to a wider range of industrially important polymers, it could provide an economically viable path to reusing manufacturing materials that are currently only used in a single product. For example, upcycled materials may be softer and more stretchy than the original polymer, or perhaps easier to mold and cure into durable thermoset products.

Scientists upcycled plastic waste by employing two processes in parallel. Both are types of metathesis, meaning a change of location. Double bonds are broken and formed between carbon atoms, allowing the subunits of the polymer to be exchanged.

One process, called ring-opening metathesis polymerization, opens carbon rings and stretches them into chains. Another process, called cross-metathesis, inserts chains of polymer subunits from one polymer chain into another.

Traditional recycling fails to capture the value of discarded plastic because it reuses polymers that deteriorate and become less valuable each time they are melted and reused. In contrast, ORNL’s innovative upcycling leverages existing components and incorporates the mass and properties of waste materials to provide additional functionality and value.

“The new process has high nuclear economy,” Foster said. “That means you can recover almost all the material you put in.”

ORNL scientists have demonstrated that this process uses less energy and produces fewer emissions than traditional recycling, and can efficiently integrate waste without compromising polymer quality. Foster, Ilya Popovs, and Tomonori Saito conceptualized the ideas in this paper. Nicholas Galan, Isaiah Dishner, and Foster synthesized monomer subunits and optimized their polymerization. Joshua Damron conducted nuclear magnetic resonance spectroscopy experiments to analyze reaction kinetics. Jackie Zheng, Chao Guan, and Anisur Rahman characterized the mechanical and thermal properties of the final material.

“The vision is that this concept can be extended to any polymer that has some kind of backbone functionality that reacts,” Foster said.

Scaling up and extending the use of other additives could mine a wider range of waste types for their molecular building blocks, dramatically reducing the environmental impact of other difficult-to-process plastics. Masu. A circular economy, where waste is reused rather than thrown away, becomes a more realistic goal.

Next, the researchers are interested in seeing if they can change the types of subunits within the polymer chain and rearrange them to create high-performance thermoset materials. Examples include epoxy resins, vulcanized rubber, polyurethanes, and silicones. Thermoset materials cannot be remelted or remolded once cured due to their crosslinked molecular structure. Therefore, recycling has become an issue.

Researchers are also interested in optimizing solvents for environmental sustainability during industrial processing.

“These waste plastics will require some sort of pre-treatment, which we still need to understand,” Foster said.

Further information: Jeffrey C. Foster et al, “Polyalkenamers as drop-in additives for ring-opening metathesis polymerizations: a promising upcycling paradigm,” Journal of the American Chemical Society (2024). DOI: 10.1021/jacs.4c10588

Provided by Oak Ridge National Laboratory

Citation: Polymer editing allows waste to be upcycled into high-performance plastics (January 17, 2025) from https://phys.org/news/2025-01-polymer-upcycle-higher-plastics.html 2025 1 Retrieved on March 17th

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