PVC is the kind of plastic that no one wants to deal with because it has its own unique problems. It contains a lot of plasticizers, which contaminate everything in the recycling stream and are usually very toxic. In addition, it quickly releases hydrochloric acid with some heat, affecting recycling equipment and causing chemical burns to the skin and eyes.
Researchers at the University of Michigan, led by first author Danielle Fagnani and principal investigator Anne McNeil, have discovered a way to chemically recycle PVC into usable material. They found a way to use the phthalates in the plasticizers – one of the most harmful components of PVC – to mediate the chemical reaction.
To recycle PVC that doesn’t require heat, scientists began exploring electrochemistry. Along the way, the team discovered that the plasticizer that poses one of the biggest recycling problems can be used to break down PVC. The plasticizer increases the effectiveness of the approach and the electrochemical method uses hydrochloric acid to address the problem.
Fagnani said, “We found that it still releases hydrochloric acid, but at a much slower, more controlled rate.”
“PVC is a polymer with a hydrocarbon backbone composed of single carbon-carbon bonds. Attached to every other carbon group is a chlorine group. Under heat activation, hydrochloric acid quickly pops out, resulting in a carbon-carbon double bond along the backbone of the polymer.
However, the research team introduces an electron into the system using electrochemistry, giving the system a negative charge. As a result, the carbon-chloride bond is broken, releasing a chloride ion that is negatively charged. The rate at which electrons are introduced into the system, which determines how quickly hydrochloric acid is created, can be measured by scientists because they use electrochemistry.
Industries can then use the acid as a reagent in other chemical processes. Arenes are a class of small compounds that can be chlorinated using chloride ions. These arenas have applications in both agricultural and medicinal components. According to McNeil, the crew is currently investigating a target for the leftover polymer material. According to Fagnani, the finding shows how researchers can approach the chemical recycling of other challenging materials.
Fagnani said, “Let’s be strategic with the additives in plastic formulations. Let’s look at the use during and after use from the additives perspective. The current group members are trying to further improve the efficiency of this process.”
McNeil said, “It is a failure of humanity to create these amazing materials that have improved our lives in many ways, but at the same time to be so short-sighted that we didn’t think about what to do with the waste. In the United States, we’re still stuck with a 9% recycling rate, and that’s just a few types of plastic. And even for the plastics we recycle, this leads to increasingly lower quality polymers. Our liquor bottles will never become liquor bottles again. They become textiles or a bench in the park and end up in the rubbish dump.”
- Fagnani, DE, Kim, D., Camarero, SI, et al. Use of waste poly(vinyl chloride) to synthesize chloroarenes by plasticizer-mediated electro(de)chlorination. Wet. Chem. (2022). DOI: 10.1038/s41557-022-01078-w