Polymer science team develops additive capable of “recycling” a wide range of plastics

There is no need to remember that plastic production and pollution have continued to increase over the years: the evidence is all around us. What if we could recycle plastic in a truly sustainable way?

It is precisely this question that is raised by Reika Katsumata, assistant professor and doctoral student. student Autumn Mineo in the Department of Polymer Science and Engineering (PSE) in the College of Natural Sciences, who is experimenting with polymer recycling to identify new environmentally friendly chemicals and technologies for polymer reprocessing.

Their research is published in the journal Angewandte Chemie International Edition.

The realities of recycling

We would all like to think that, despite our best efforts to avoid non-recyclable items, the Styrofoam cups we occasionally throw in the trash could eventually be reconstituted into a brand new cup with little or no environmental impact, but the process of Recycling is more complicated than that.

Mechanical recycling leverages harsh temperatures and processing conditions to reinvent certain post-consumer waste streams into new products. Repeated exposure to these conditions results in degradation of the material over time and a corresponding deterioration in its properties, a result often referred to as “downcycling.”

Alternatively, some polymers can be chemically broken down and reformed, improving cycle longevity and material robustness. However, chemical recycling is not possible for most commodity polymers used today.

Upcycling through chemistry

Katsumata and his team sought to create a more sustainable process for recycling and reprocessing polymers through what is called addition-fragmentation-transfer (AFT) chemistry, a field focused on bond exchange reactions based on radicals. “Common plastics are large molecules called polymers, made up of repeating units, or ‘monomers,'” Katsumata explained. “Many polymers cannot be chemically broken down or reformed because the carbon-carbon single bonds that hold the monomers together are relatively stable.”

To address this stability issue, PSE researchers developed an additive that copolymerizes with conventional monomers and generates main chain units possessing the exchange capacity via AFT chemistry.

“This dynamic bonding can promote both scission (or cutting) and extension of the polymer to complete closed-loop recycling,” Katsumata said. “Additionally, the dynamic nature of our additive facilitates further chemical modifications with the potential to ‘upcycle’ or increase product value, by taking commodity plastic waste and forming new types of specialized polymers, such than adhesives based on block copolymers. »

This work identified a new monomer compatible with existing polymer synthesis methods, which creates a dynamic bond between monomer units that can be harnessed to break down plastic after use. These smaller fragments of polymers, called oligomers, remain reactive and can serve as starting points from which new polymers can grow.

The team discovered that the cycle of polymer degradation (chain scission) and regeneration (chain extension) can be repeated and modified to change the extent of scission and extension.

To raise awareness

A key driver of this research was the desire to drive innovation. “Our research has advanced fundamental knowledge of AFT chemistry by revealing latent reactivity after polymerization,” Katsumata said. “Additionally, we hope that our work has inspired polymer industries to invest in copolymerization strategies and other recycling technologies, particularly as they relate to polyolefin products.”

Katsumata and the PSE team believe this research can provide the basis for new recycling methods and the identification of environmentally friendly chemicals and techniques, providing a glimpse into a future in which plastic and other difficult materials will be managed more sustainably.