{"id":101957,"date":"2024-10-24T17:34:56","date_gmt":"2024-10-24T22:34:56","guid":{"rendered":"https:\/\/engineering.wisc.edu\/?post_type=news&p=101957"},"modified":"2024-10-25T08:51:23","modified_gmt":"2024-10-25T13:51:23","slug":"ask-an-expert-whitney-loo-explains-plastics-recycling-and-the-challenges-of-sustainability","status":"publish","type":"news","link":"https:\/\/engineering.wisc.edu\/news\/ask-an-expert-whitney-loo-explains-plastics-recycling-and-the-challenges-of-sustainability\/","title":{"rendered":"Ask an expert: Whitney Loo explains plastics recycling and the challenges of sustainability"},"content":{"rendered":"\n

Whitney Loo<\/a> is the Conway Assistant Professor of chemical and biological engineering<\/a>. Loo studies polymers, which are \u201cmacromolecules\u201d composed of many repeating units. They are the building blocks for many plastics. Polymers can be difficult to break down for reuse because they\u2019re so large and sometimes complex. Loo\u2019s research group is looking at new ways to design and reuse polymers for a sustainable future. In this interview, she discusses some of the challenges with recycling polymers, and how future developments in the field may bolster sustainability efforts.<\/p>\n\n\n\n

Q: The term \u201cpolymers\u201d often brings plastics to mind\u2014and plastics are infamously difficult to recycle and poor for sustainability. What is it about polymers like plastics that makes them so challenging to use sustainably?<\/h6>\n\n\n\n

A: Polymers are large molecules made up of many subunits, or monomers. Typically, a lot of these monomers are derived from petrochemical precursors, like ethylene, butadiene, styrene; these are chemicals that we essentially make from oil. So even from the beginning, they\u2019re not necessarily a very sustainable option because they\u2019re starting as petroleum byproducts.<\/p>\n\n\n\n

The other reason is what happens at the end of their product life. The most conventional recycling method is mechanical recycling. Let\u2019s say you have a plastic water bottle, typically made of polyethylene terephthalate, or PET, which you\u2019ll see on the bottom of your water bottle as a number 1. You\u2019d take that water bottle, chop it up into smaller pieces, and form it into a new bottle through a heat-intensive process. Mechanical recycling is very energy-intensive, but before you can even get to that, you must separate all of your plastics.<\/p>\n\n\n\n

Because polymers are very long molecules, they don\u2019t like to mix. So what happens in some recycling centers, by hand or by machine, is that all of those different plastics you throw in the recycling bin have to be sorted before they can be recycled. That also makes plastic recycling really expensive\u2014but making these same materials from virgin products is, by contrast, extremely inexpensive. So it can be easier to just throw plastics away and make new ones rather than recycle old plastics into new products.<\/p>\n\n\n\n

Another type of recycling is chemical recycling, which refers to \u201cundoing\u201d the reaction that created the polymer in the first place. That can be done thermally, with traditional catalysts, or via microbes that generate enzymes to trigger those same reactions. The other type of recycling that is more application-focused is solvent-based recycling. If you have a multi-component material, different types of solvents can selectively dissolve different components in that material to generate virgin polymers or materials that can be used to fabricate new multi-component products. That\u2019s typically used a lot for films and packaging.<\/p>\n\n\n\n

Q: You talked about how plastics come from petrochemicals, which includes some inherent environmental challenges. Can we make plastics from more sustainable source materials?<\/h6>\n\n\n\n

A: There\u2019s a lot of ongoing research in developing new precursors to build plastics that come from non-petrochemical sources. Some of that is looking at using lignin, which is a byproduct from trees and is a waste product from the paper industry.<\/p>\n\n\n\n

There has also been research on using microbes to more sustainably generate new monomers from different sugars, bacteria and yeasts. There\u2019s a lot of work happening in the sustainable catalysis world of taking abundant materials and using catalysis to transform those materials into monomers without using petrochemical-derived feedstocks.<\/p>\n\n\n\n

These developments are at different phases, and we\u2019re at the point where we\u2019re starting to see some scale-up pilot-plant industrial-scale testing for some of these options. It will be interesting to see what works in the coming years. Because so many of these materials come from fossil fuels and because we still rely on fossil fuels for gasoline for cars and energy, it\u2019s going to be hard to beat those economics\u2014however, we still need to be ready for when the day comes that we have better, more sustainable solutions for those other parts of our lives.<\/p>\n\n\n\n

Q: What are some other avenues you see to reduce the environmental impact of plastics?<\/h6>\n\n\n\n

A: Broadly, most of my research group\u2019s projects focus on sustainability in one aspect or another. We have some projects on mechanical recycling, where we are developing \u201ccompatibilizers\u201d that will hopefully enable recycling of mixed-waste plastic streams without that presorting process.<\/p>\n\n\n\n

That process is one of the biggest barriers to recycling. In wealthy countries, you may have machines and other instrumentation that can help automate some of that process. But there are many countries where recycling is done by someone walking down the street, picking up whatever they find, and dropping it off at a recycling center. If you have to add sorting to that, it directly increases the time, energy and costs that go into recycling.<\/p>\n\n\n\n

My group is targeting plastic materials with very high mechanical integrity and a very long shelf life. We\u2019re trying to translate single-use plastics\u2014like Styrofoam coffee cups or water bottles, which are brittle, bendy materials\u2014into really resilient materials that could, for example, be used in a park bench. Maybe that park bench isn\u2019t going to sit there forever, but we can take something that would have had a lifespan of a few days and give it a lifespan of 60 to 100 years. We\u2019re focused on taking our current waste and finding ways to reuse it in longer-lifetime materials because that helps reduce energy costs if we don\u2019t have to recycle it continuously.<\/p>\n\n\n\n

Q: Your research also touches on energy storage. How do polymers play into that?<\/h6>\n\n\n\n

A: Our energy-storage work focuses particularly on polymer electrolytes for lithium-metal batteries. Lithium-ion batteries are what we use pretty widely today, and those use a graphite anode or an electrode, where there\u2019s about one lithium atom for every six carbon atoms. So if you need a certain amount of lithium, you\u2019re going to have to increase the size of everything else. With lithium-metal batteries, we can take out all of the supporting graphite matrix and move to using pure lithium. That greatly increases the energy storage.<\/p>\n\n\n\n

We use polymers as the supporting material that pushes the ion during the charge-and-discharge cycle from one electrode to the other. We like polymers because they\u2019re solid and provide more mechanical support for the batteries. They provide stable interfaces and are non-flammable. Right now, lithium-ion batteries typically use flammable liquid electrolytes. Lithium itself is flammable. So if we want to put more lithium in our batteries, we need to make sure that the rest of it isn\u2019t also going to be flammable as well.<\/p>\n\n\n\n

Featured image caption: Whitney Loo, Conway Assistant Professor of chemical and biological engineering, discusses sustainability challenges stemming from plastics during an interview. Credit: Joel Hallberg. <\/em><\/p>\n\n\n\n

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