Wind energy is a fast-growing industry, with new installations growing 53 percent in 2020 alone, according to the Global Wind Energy Council. The massive fiberglass wings can be as long as half a football field and are getting bigger – the bigger the wing, the more electricity is produced. This poses a problem when the blades outlive the mechanical parts of the turbines. They are usually disposed of in landfills, which undermines the whole concept of sustainable energy production.
Fortunately, John Dorgan, a chemical engineer at Michigan State University, has developed a new polymer resin that can be recycled not only into a new generation of turbine blades, but also into materials for a variety of commercial uses. This includes making car taillights, diapers, kitchen sinks and even edible gummy bears. He described his research at a meeting of the American Chemical Society in Chicago this week.
Dorgan refers to his approach as “molecular flexibility,” inspired in part by an article he once read by Isaac Asimov that described a future in which humans would be able to resynthesize raw protons, neutrons, and electrons into anything what they wanted. “It’s almost like the replicator of star trekwhere they can just make atoms into anything they want — ice cream trucks or new clothes or whatever,” Dorgan said during a press conference at the ACS meeting. “Of course we’re a long way from the replicator idea, but we took inspiration from things like that.”
Dorgan has long worked with one of his favorite polymers: Polyactide, or PLA, which was originally developed to create biodegradable, sustainable packaging. PLA can also be used as a fiber to make textiles and clothing. Dorgan’s current Department of Energy-funded project is investigating how wind turbine blades can be manufactured in a more energy-efficient manner. So he naturally wondered if PLA could be used as a recyclable binder resin.
The Dorgan lab made their new composite resin by dissolving PLA in a synthetic monomer called methyl methacrylate (MMA), resulting in a syrupy resin. They used vacuum pressure to pull the resin through fiberglass, causing the resin to cure into solid sheets of fiberglass. These panels can be recycled by dissolving them in fresh monomer, allowing researchers to re-cast new panels for the next generation of wind turbines. “The holy grail of polymer recycling is always going back from one application to the same application,” he said. “We can do that with these materials. We went through several cycles and showed that the mechanical properties can be maintained.”
The next step is to make some medium sized turbine blades and test them in the field. But Dorgan admits its resin isn’t ready to scale to the levels needed to meet the wind power industry’s current needs. There simply isn’t enough bioplastic made with its lab-based process, and it will take time to develop a large-scale production process.
Fortunately, it is also possible to reuse the resin for other applications, both downcycle and upcycle. For the former, take the material and grind it up, maybe add some more polymer to the mix, and it’s perfect for injection molding, a common plastic manufacturing technique. Dorgan also produced an artificial stone, which he then used to create a large kitchen sink and the MSU Spartan logo.
Beyond this simple mechanical processing, Dorgan found he could chemically modify these materials for upcycling applications. “We can actually digest one of the components of the PLA polymer with just a simple base like an alkaline solution,” he said. “Think of baking soda or baking soda in the kitchen — something pretty bland in terms of its chemical activity.”
This breaks down the PLA into an eco-friendly metabolite called monolactic acid, and Dorgan was able to recover the polymethyl methacrylate (PMMA) in the material — better known as plexiglass, which is used to make windows and car taillights. Increasing the temperature can convert the PMMA into polymethacrylic acid, a superabsorbent polymer used in diapers. Another by-product of alkaline digestion is potassium lactate, which Dorgan has been able to purify for food-grade applications. He even used it to make gummy bears in the lab.
And yes, he ate those gummy bears with no ill effects. “A carbon atom that comes from a plant like corn or grass is no different than a carbon atom that comes from a fossil fuel.” said Dorgan. “It’s all part of the global carbon cycle, and we’ve shown that we can move from biomass in the field to durable plastic materials and back to food.”
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