With the ever-increasing problem of plastic waste around the world, the majority of which ends up in landfills, a new study could help in the fight against rubbish pollution. Researchers at the University of Colorado Boulder have devised an innovative approach to recycling a common type of plastic using electricity and some chemical reactions to the extent that you can actually see the plastic break apart.


Most recyclable plastic doesn’t end up being recycled, and some types of recycling involve energy-intensive processessuch as melting or dissolving in corrosive acid, but this can change the material properties of plastic. The team therefore explored ways of using the basic molecular ingredients of old plastic bottles – the chemical groups that hold the polymer together – to make new ones.


As reported in the journal Chem Catalysis [Pham et al. Chem Catal. (2023) DOI: 10.1016/j.checat.2023.100675], they focused on polyethylene terephthalate (PET), a polymer used in plastic bottles, films and packaging, but less than one-third of which is recycled, using electrolysis to break the molecules apart.


Pieces of the plastic were ground up and mixed with a molecule known as [N-DMBI]+ salt before a small electric voltage was applied. In the presence of electricity, this molecule forms a reactive mediator that provides its extra electron to the PET so that the grains of plastic come undone. In the lab, the PET began to disintegrate within minutes, with the reaction progress being observed in real time as the solution turned a deep pink color before becoming clear as the polymer breaks apart.


Molecular ‘mock-ups’ of these polymers were synthesized to examine how they break down. This understanding allowed the team to realize the chemistry for the breakdown of solid polymers needed a molecule that can shuttle electrons from an electrode to the solid, which can be regenerate many times, acting as the catalyst. As co-author Oana Luca told Materials Today, “This opens the door to an approach for study of breakdown of several other types of polymers, several of which are not currently recycled.”


With many of the largest-scale industrial processes being carried out electrochemically, which electricity-driven methods could offer a scalable alternative to thermal or traditional chemical method, while the electricity-driven aspect of this study could lead to coupling with renewable energy sources down the line.


Although this is a useful start, much remains to be done to optimize the process and to scale it up so it can be applied on an industrial scale. The team also want to develop the chemistry involved to occur fully in air, as well as to show it can work on a range of esters-based materials.

“This opens the door to an approach for study of breakdown of several other types of polymers, several of which are not currently recycled.”Oana Luca