Chemistry breakthrough creates usable products out of unrecyclable PVC

2022-11-30

Advances in chemistry continue to bring new materials into the realm of recyclability, and new work from a team at the University of Michigan has taken aim at one of the most problematic to reuse. The scientists have developed a method of converting waste PVC (polyvinyl chloride) into usable products, opening up some interesting new possibilities when it comes to this traditionally unrecyclable material.

PVC sits in the top handful of plastics in terms of production and volume, and is put to use in everything from piping and flooring, to shower curtains and clothes. Its recycling rate in the US, however, sits at zero, with efforts to recycle the material hindered by its toxic contents.

“PVC is the kind of plastic that no one wants to deal with because it has its own unique set of problems,” said study first author Danielle Fagnani. “PVC usually contains a lot of plasticizers, which contaminate everything in the recycling stream and are usually very toxic. It also releases hydrochloric acid really rapidly with some heat.”

Plasticizers are added to common plastics to improve their durability and flexibility, but some of them carry serious risks to human health, with BPA a particularly well-known example. Another is phthalates, known as “everywhere chemicals” due to their widespread use in everyday products, and which have been linked to endocrine disruption, childhood cancers and premature death.

The phthalates in PVC are one of the material’s most harmful ingredients, and these, along with other plasticizers, leach out during conventional recycling that relies on heat treatment. This process also releases hydrochloric acid from the PVC, which can cause chemical burns and corrode recycling equipment.

Fagnani and her colleagues were therefore experimenting with ways of recycling PVC that don’t rely on heat, which led to a novel electrochemistry technique with some exciting potential. The team used electrons to break down the carbon-chlorine bonds in the material, and by using one of the PVC plasticizers to mediate the process, were able to carefully control the release of hydrochloric acid.

“What we found is that it still releases hydrochloric acid, but at a much slower, more controlled rate,” Fagnani said.

This allows the acid to be collected and used as a reagent for other chemical reactions, while the process also produces chlorine ions that can be used to chlorinate molecules for use in pharmaceutical and agricultural products. The method also leaves other materials behind that the scientists are trying to find uses for, so there is room for improvement, but they say the work shows how chemical recycling can be leveraged to give problematic materials a second life.

“It’s a failure of humanity to have created these amazing materials which have improved our lives in many ways, but at the same time to be so shortsighted that we didn’t think about what to do with the waste,” said principal investigator Anne McNeil. “In the United States, we’re still stuck at a 9% recycling rate, and it’s only a few types of plastics. And even for the plastics we do recycle, it leads to lower and lower quality polymers. Our beverage bottles never become beverage bottles again. They become a textile or a park bench, which then ends up in a landfill.”

The research was published in the journal Nature Chemistry.

New Atlas, 30 November 2022
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