Thursday, February 2, 2023

Recycling previously unrecyclable plastic

A way to recycle PVC that does not require heat.

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PVC is the kind of plastic that no one wants to deal with because it has its own unique set of problems. It contains a lot of plasticizers, which contaminate everything in the recycling stream and are usually very toxic. Moreover, it releases hydrochloric acid rapidly with some heat, corroding the recycling equipment and causing chemical burns to the skin and eyes.

University of Michigan researchers, led by study first author Danielle Fagnani and principal investigator Anne McNeil, have discovered a way to recycle PVC into usable material chemically. They found a way to use the phthalates in the plasticizers—one of PVC’s most noxious components—as the mediator for the chemical reaction.

To recycle PVC that does not require heat, scientists began exploring electrochemistry. Along the way, the team discovered that the plasticizer that presents one of the significant recycling difficulties could be used to break down PVC. The plasticizer increases the approach’s effectiveness, and the electrochemical method uses hydrochloric acid to tackle 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 rapidly pops off, resulting in a carbon-carbon double bond along the polymer’s backbone.”

However, the study team introduces an electron into the system using electrochemistry, which gives the system a negative charge. As a result, the carbon-chloride link is broken, releasing a chloride ion that is negatively charged. The speed at which electrons are brought into the system, which determines how soon hydrochloric acid is created, can be measured by scientists because they are utilizing electrochemistry.

Industries can then employ the acid as a reagent in other chemical processes. Arenes are a class of tiny compounds that can be chlorinated using chloride ions. These arenas have applications in both agricultural and medicinal components. The crew is currently exploring a purpose for the leftover polymer material, according to McNeil. According to Fagnani, the finding demonstrates how researchers may approach the chemical recycling of other challenging materials.

Fagnani said, “Let’s be strategic with the additives in plastic formulations. Let’s consider the during-use and end-of-use from the perspective of the additives. Current group members are trying to improve the efficiency of this process even more.”

McNeil said“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. 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, ending up in a landfill.”

Journal Reference:

  1. Fagnani, D.E., Kim, D., Camarero, S.I., et al. Using waste poly(vinyl chloride) to synthesize chloroarenes by plasticizer-mediated electro(de)chlorination. Nat. Chem. (2022). DOI: 10.1038/s41557-022-01078-w
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