UNSW researchers develop simple method for breaking down plastics

UNSW researchers have developed a new recycling method that can work on a variety of plastics and uses sunlight, air and a cheap, common chemical.

According to a statement from the university, the process could break down seven different types of polymers by 90 per cent in under 30 minutes (and 97 per cent after three hours.) 

The team’s work was published in the journal Macromolecular Rapid Communications and can be accessed here.

“Our proposal here is to make the simplest system to degrade polymers,” said Dr Maxime Michelas, adding that the approach was inspired by previous research using electricity to try to create the same reaction.

“The problem with the previous approach is you need a lot of different things, like electrodes, or co-solvents, or co-initiators, or co-catalysts, so the system is more and more complex.

“More importantly, the previous system only was able to degrade a limited range of polymers. In our study, we successfully expanded the range of polymers, including polyvinyl chloride, poly(meth)acrylates (typically used in various products, such as paint), and polyvinyl acetate.”

The team’s method is described as requiring a polymer to be dissolved with a solvent before starting the degradation process, then exposing the solution to ferric chloride and a light source. 

A purple light in a controlled environment containing pure oxygen was first used, before switching to a combination of sunlight and ambient air. The latter worked, just “a little slower”.

Professor Cyrille Boyer, whose research group Michelas works in, said that waste management services could use the process at their sites.

“We are creating very simple organic compounds (such as acetone) after the degradation of these polymers,” said Boyer. 

“These molecules can then be further degraded by bacteria, for example, and completely removed from the environment or reused as feedstock to create new polymers.”  

Of the limitations to the new method, Boyer said “We need to use an organic solvent, and unfortunately our system is not compatible with water.

“If it was, we would directly use it in water, degrade the plastic or the microplastic present in wastewater to form small organic compounds that could be digested by bacteria using a bioreactor.”

Further than that, additional work is needed on the byproduct from the process. 

“We can degrade the plastic, but we don’t control what exact product we are making when it degrades,” explained Boyer.

He added that the work continues by looking for new catalysts that can work in water. If one could be found, “I think this will open a lot of opportunities”.

Picture: Related work from the research team showing polystyrene breaking down in solvent. (credit Maxime Michelas and Cyrille Boyer, UNSW)