Engineers from the University of Wisconsin-Madison have created a new solvent-based method in recycling plastics, particularly the multi-layered plastics used in food and medicine packaging.
Multi-layered plastics are used on these products because of its heat resistance and oxygen and moisture control properties ensuring storage stability to food items and medicine. However, their utility comes with a price as they are hard to recycle using existing methods.
Each year, there are about 100 million toms of multilayer plastics produced, wherein each of them has as many as 12 layers of various polymers. It creates 40% of its waste during manufacturing and since there is no way to separate polymers, most of them end up in the landfill, according to Science Daily.
But now, engineers have created a novel way of recycling polymers using a solvent which they call the Solvent-Targeted Recovery and Precipitation (STRAP) processing.
STRAP: The Solvent-Based Method to Recycle Plastics
The study, published in Science Advances, explains that using a series of solvent washes guided by thermodynamic calculations of polymer solubility the STRAP method can separate polymer in multilayer plastics, like ethylene vinyl alcohol, polyethylene, and polyethylene terephthalate.
The team hopes that the recovered polymers can be used to create plastic materials to show that the method can close the recycling loop of polymers. More specifically, STRAP could allow manufacturers of multi-layered plastics to recover 40% of the plastic waste produced during the first phase of the production.
"We've demonstrated this with one multilayer plastic," says chemical engineering professor George Huber. "We need to try other multilayer plastics and we need to scale this technology."
It has become more difficult to identify solvents that can dissolve each polymer as the complexity of polymers increases. Biological engineering Reid Van Lehn uses a computational approach with regards to this in which he applied to STRAP. This is called the Conductor-like Screening Model for Realistic Solvents (COSMO-RS).
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Using Solvents to Dissolve Polymers
The COSMO-RS can calculate the solubility of each polymer in solvent mixtures at different temperatures that narrow down the number of solvents that could dissolve it. In that way, the researchers can experiment with possible solvents to be used.
"This allows us to tackle these much more complex systems, which is necessary if you're actually going to make a dent in the recycling world," Van Lehn said.
Eventually, the researchers wanted to create a computational system that can find solvent combinations to recycle any types of multilayer plastics. Also, they want to see how these solvents will affect the environment when used and establish a database of green solvents that balances the efficacy, cost, and environmental impact of different solvent systems.
For now, the engineers continue their STRAP research through the newly established Multi-University Center on Chemical Upcycling of Waste Plastics.
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