A new recycling process could reduce millions of tons of plastic waste

Around 100 million tons of multilayer thermoplastics are produced each year worldwide. 40% of the total is made up of waste from the production process itself and, since it was not possible to separate the polymers, virtually all of that plastic ends up in landfills or incinerators.

Now, engineers at the University of Wisconsin-Madison have designed a method to recover the polymers in these materials using solvents. Scientists have dubbed this technique as STRAP (Solvent-Targeted Recovery and Precipitation) processing.

The method separates the polymers in a commercial plastic composed of common layering materials polyethylene, ethylene vinyl alcohol and polyethylene terephthalate. And the resulting separate polymers appear chemically similar to those used to make the original film.

Scientists hope to use the recovered polymers to create new plastic materials. This shows that the process can help close the recycling cycle. It could also allow multilayer plastic producers to recover 40% of the plastic waste produced during manufacturing and packaging processes.

George Huber, professor of chemical and biological engineering at UW-Madison, said: “We proved it with a multilayer plastic. We have to try other multilayer plastics and we have to scale this technology. “

The technique is based 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 can calculate the solubility of target polymers in solvent mixtures at varying temperatures. This reduces the number of potential solvents that could dissolve a polymer. The team can then experimentally explore candidate solvents.

Van Lehn said, “This allows us to tackle these much more complex systems, which is necessary if you intend to make a dent in the world of recycling.”

Finally, the aim is to develop a computational system that will allow scientists to discover combinations of solvents to recycle a wide range of multilayer plastics. Likewise, the group intends to examine the environmental effect of the solvents it uses and create a database of green solvents that will enable them to more readily balance the effectiveness, cost and environmental impact of various solvent systems.

The project stems from UW – Madison’s experience in catalysis. For decades, the university’s chemical and biological engineering researchers have pioneered solvent-based reactions to convert biomass, such as wood or agricultural waste, into useful chemicals or fuel precursors. Much of this experience also translates into the recycling of solvent-based polymers.

Journal reference:

1. Theodore W. Walker et al. Recycling of multilayer plastic packaging materials by solvent targeted recovery and precipitation. DOI: DOI: 10.1126 / sciadv.aba7599