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Materials Planet Care

352: STRAP, or Solvent-Targeted Recovery and Precipitation processing

Problem:

While a bag of chips might not look very complex on the outside, it is in fact a multi-layered plastic bag. Polyethylene is made up of several extremely thin films stacked on top of each other to provide strength, flexibility, and integrity. The layers are chemically incompatible when it comes to breaking them down. They simply cannot be recycled en masse like soda bottles can.

Solution:

STRAP, or Solvent-Targeted Recovery and Precipitation processing.


University of Madison-Wisconsin professors of chemical and biological engineering George Huber and Reid Van Lehn and their students have created a technique called that could be the solution.
The key to the new process is to selectively dissolve a single polymer layer in a solvent system in which the targeted polymer layer is soluble, but the other polymer layers are not. In other words, you need to break down each polymer layer individually, and use a solvent to dissolve them one at a time.

STRAP relies 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.

The researchers have. In a study published November 20th 2020 in the journal Science Advances, the researchers lay out their case for why the technique could start a recycling revolution.

The Madison-Wisconsin team tested their process using a real-world multilayer film built by Amcor Flexibles, which designs pouches and bags for food, drinks, healthcare, and other essentials.

The process achieved separation of these three components with nearly 100 % material efficiency

The goal is to eventually develop a computational system that will allow researchers to find solvent combinations to recycle all sorts of multilayer plastics.

The team is continuing its research on STRAP processing through the newly established Multi-University Center on Chemical Upcycling of Waste Plastics, directed by Huber. Researchers in the $12.5 million U.S. Department of Energy-funded centre are investigating several chemical pathways for recovering and recycling polymers.

The STRAP process could eventually level up to take on current levels of plastic waste.

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