Window frames, casing cladding, siding and flooring are made of PVC or contain PVC. It coats electrical wires and includes materials such as shower curtains, tents, blankets and clothing.
It also has a zero percent recycling rate in the United States.
Now researchers at the University of Michigan, led by the study’s first author Danielle Fagnani and Principal Investigator Anne McNeil, have found a way to recycle PVC into a chemically usable material. Researchers found a way to use phthalates in plasticizers, one of the most harmful components of PVC, to mediate a chemical reaction. Their results have been published in the journal Nature Chemistry.
“PVC is the kind of plastic that nobody wants to deal with because it has its own unique problems,” said Fagnani, who completed his postdoctoral research in UM’s Department of Chemistry. “PVC usually contains a lot of plasticizers, which contaminate everything in the recycling stream and are usually very toxic. It also releases hydrochloric acid very quickly with low heat.”
Plastic is typically recycled by melting it down and turning it into inferior materials in a process called mechanical recycling. But when heat is applied to PVC, one of its main components, called plasticizers, leaches out of the material very easily, McNeil says.
They can then slide into other plastics entering the recycling stream. In addition, hydrochloric acid is easily released from PVC with heat. It can corrode recycling equipment and cause chemical burns to the skin and eyes – not ideal for recycling plant workers.
In addition, phthalates – a common plasticizer – are highly toxic endocrine disruptors, meaning they can interfere with thyroid hormone, growth hormones, and hormones involved in reproduction in mammals, including humans.
So to find a way to recycle PVC that didn’t require heat, Fagnani began researching electrochemistry. Along the way, he and the team discovered that plasticizer, one of the biggest challenges in recycling, could be used in a method to break down PVC. In fact, the plasticizer improves the efficiency of the method, and the electrochemical method solves the problem of hydrochloric acid.
“We found that it still releases hydrochloric acid, but in a much slower, more controlled way,” Fagnani said.
PVC is a polymer with a hydrocarbon backbone, Fagnani says, and is made up of single carbon-carbon bonds. A chlorine group is attached to every other carbon group. Under thermal activation, the hydrochloric acid quickly pops off, leading to the formation of a carbon-carbon double bond along the polymer backbone.
But the research team instead uses electrochemistry to introduce an electron into the system, causing the system to become negatively charged. This breaks the carbon-chloride bond and results in a negatively charged chloride ion. Because researchers use electrochemistry, they can measure the rate at which electrons are brought into the system — which controls how quickly hydrochloric acid is produced.
Industry can then use the acid as a reagent for other chemical reactions. Chloride ions can also be used to chlorinate small molecules called arenes. These arenes can be used in pharmaceutical and agricultural components. There is material left over from the polymer, which McNeil says the team is still looking for uses for. Fagnani says the research shows how researchers could think about chemical recycling of other difficult materials.
“Let’s be strategic with the additives in plastic products. Let’s think about in-use and end-of-use from an additive perspective,” said Fagnani, who is now a researcher at Ashland, which is focused on making biodegradable specialty additives for consumer products such as laundry detergents, sunscreens and shampoos. “The current group members are trying to make this process even more efficient.”
The focus of McNeil’s lab has been developing ways to chemically recycle various plastics. Breaking plastics into its parts can produce non-degradable materials that industry can incorporate back into production.
“Mankind’s failure has been to create these incredible materials that have improved our lives in so many ways, but at the same time to be so short-sighted that we didn’t think about what to do with the waste,” McNeil said. “In the US, we’re still stuck at a 9 percent recycling rate, and that’s just a few types of plastic. And even the plastics we recycle lead to lower and lower quality polymers. Our drink bottles never become Drink Bottles again. They become a textile or a park bench, which then ends up in a landfill.”
HT
Source: ANI
Source: The Nordic Page