New Breakthrough Recycling Method Could Cut Down On Millions Of Tons Of Plastic

A team of engineers from the University of Wisconsin-Madison has discovered a method for recycling multilayered plastics using solvents. They have named this technique as Solvent-Targeted Recovery and Precipitation (STRAP) processing.

A paper outlining the proof-of-concept appeared on Nov. 20, 2020, in the journal Science Advances.

What is Multi-Layered Plastics?
Multilayer plastics are basically plastics made with various layers of different polymers. These hi-tech sounding plastics are found everywhere from food to medical supply packaging.

These plastics are widely used because specific properties of layered polymers can keep moisture from fouling sterile syringes or light and oxygen from making potato chips stale.

Every year the world produces around 100 million tons of multilayer thermoplastics which can have up to 12 layers of different polymers.

What is the problem with Multi-Layered Plastics?
1. The story sounds good till here but the main problem is that these plastics are impossible to recycle with the conventional methods.
2. With the increasing complexity of the multilayer plastics, the difficulty of identifying solvents that can dissolve each polymer also increases.

The new method shows a big hope to recycle multi-layered plastics. Let us dig deeper into this technique.

This technique uses a series of solvents washes which are guided by thermodynamic calculations of polymer solubility. As a part of proof-of-concept, the team used this process to separate the polymers in a commercial plastic composed of polyethylene, ethylene vinyl alcohol, and polyethylene terephthalate.

The team claims that the separated chemicals were similar to the initial chemicals used to make those plastics.

The team now hopes to use the recovered polymers to create new plastic materials, demonstrating that the process can help close the recycling loop.

“We’ve demonstrated this with one multilayer plastic,” says Huber, professors of chemical engineering at UW-Madison. “We need to try other multilayer plastics and we need to scale this technology.”

With this method, the researchers have solved the first problem that is recycling multilayered plastics. But then comes the second problem, how to make the method work for complex multilayer plastics.

To solve the second problem, STRAP uses on a computational approach used by Van Lehn called the Conductor-like Screening Model for Realistic Solvents (COSMO-RS) to guide the process.

COSMO-RS is able to calculate the solubility of target polymers in solvent mixtures at varying temperatures, narrowing down the number of potential solvents that could dissolve a polymer. The team can then experimentally explore the candidate solvents.

“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,” says Van Lehn, professors of biological engineering at UW-Madison.

The ultimate goal of the research is to develop a computational system which can find solvent combinations to recycle all sorts of multilayer plastics.

Journal References:
Theodore W. Walker, Nathan Frelka, Zhizhang Shen, Alex K. Chew, Jesse Banick, Steven Grey, Min Soo Kim, James A. Dumesic, Reid C. Van Lehn, George W. Huber. Recycling of multilayer plastic packaging materials by solvent-targeted recovery and precipitation. Science Advances, 2020; 6 (47): eaba7599 DOI: 10.1126/sciadv.aba7599

Press Release: University of Wisconsin-Madison