CAS: Repurposing Polyethylene Waste Using Ring-Chain Equilibria

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Plastics have transformed our lives, largely for the better by providing light-weight, durable materials that can be shaped and stretched. This said, plastics have generated a significant waste problem, with most plastics sent to the landfill after only one use. These end-of-life outcomes negatively impact our planet and are unsustainable. As such, there is an urgent need to develop new methods to reuse plastic waste. With funding from the Macromolecular, Supramolecular, and Nanochemistry Program of the Chemistry Division, Professor Anne J. McNeil of University of Michigan Ann Arbor is utilizing ring-chain equilibria to recycle polyethylene, which is one of the most widely produced plastics in the world. Ring-chain equilibria is a method for polymer recycling in which, under dilute conditions, linear polymers are quantitatively transformed into macrocyclic compounds. When the concentration is increased, linear polymers are regenerated via the reverse process. In this research, a series of chemical reactions are developed to depolymerize different polyethylene scaffolds into cyclic compounds. The developed methodology is utilized to convert post-consumer polyethylene waste into virgin-quality polyethylene. Polyethylene is also repurposed into value-added block copolymers containing important functional chemical groups. The primary goal of the team's outreach efforts is to increase the local community's understanding of the lifecycle of plastics, ranging from petroleum-derived and bio-sourced monomers through their different post-disposal fates. To accomplish this goal, the research team is developing and implementing hands-on activities for children on the plastics lifecycle. In addition, an interactive display for a local children’s museum is being created. Venues such as NerdNite and online publishing are implemented to reach adults. This project enables the participating graduate and undergraduate researchers to gain highly interdisciplinary training in organic and inorganic chemistry, as well as polymer synthesis and characterization. The training also prepares them for careers in teaching and in the chemical industries. The research team is developing alkane metathesis for reversible cyclodepolymerization of polyethylene (PE). Research activities include the evaluating of alkane metathesis conditions in the cyclodepolymerization of PE, and the elucidation of the impact of unsaturation levels on cyclodepolymerization rates. The research group identifies optimized dehydrogenation catalysts for each PE scaffold and generates new PE macrocycles that may exhibit unique properties. Finally, the group convert post-consumer PE waste into virgin-quality PE, and repurposes PE into value-added block copolymers containing halogen, polar, or alkyl functional groups. This work tackles the grand challenge of polyolefin recyclability and has the potential to have a significant impact on society, both within the scientific community and in the general public. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.