Chemical engineers at UNSW have developed a way of breaking down a range of plastics, including polystyrene, using just sunlight, air and a common chemical compound used in high school experiments.
The process works at room temperature and uses iron trichloride (also known as ferric chloride), which is cheap and widely available.
Research that was recently published in Macromolecular Rapid Communications showed the method can break down seven distinctive types of polymers by 90 per cent in less than 30 minutes. The reduction increases to 97 per cent after three hours.
The process works on polymers that include polyvinyl chloride and poly(ethylene glycol), a widely-used polymer that’s found in cosmetics and pharmaceutical products.
The polymer must be dissolved with a solvent before starting the degradation process.
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From there, simply exposing the solution to ferric chloride and a light source breaks down the solution which eventually becomes clear.
Maxime Michelas, a researcher from the School of Chemical Engineering working in Professor Cyrille Boyer’s group, said it could provide significant benefit for the world.
“I think it’s very important to degrade the polymer and turn it into another feedstock we can use for other things, or just to reduce the amount of microplastics in the world,” Michelas said.
Boyer’s team first used dim, purple light in a controlled environment with pure oxygen. Starting and stopping the degradation process was as simple as turning the light switch on and off.
When the team used sunlight instead of purple light and exposed their test environment to ambient air the process still worked, it was just a little slower.
“Our proposal here is to make the simplest system to degrade polymers,” Michelas said.
He said the project is inspired by previous research in the area where electricity was used 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.”
Boyer said waste management services could use the process at their sites. From there, the remaining product could become raw material for another product.
“We are creating very simple organic compounds (such as acetone) after the degradation of these polymers,” Boyer said. “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.”
While the process of breaking down the polymer with sunlight, air and ferric chloride after it’s been dissolved by solvent is environmentally friendly, the use of solvent presents some limitations.
“We need to use an organic solvent, and unfortunately our system is not compatible with water,” Boyer said.
“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.”
Boyer said there’s also some tinkering needed with the byproduct that comes out at the end of the process.
“We can degrade the plastic, but we don’t control what exact product we are making when it degrades.”
Boyer’s team is working on finding new catalysts that can operate in water, which would be beneficial for the environment.
“If we can find a catalyst that works in water, I think this will open a lot of opportunities,” Boyer said.