The blades of a wind turbine are typically designed to be replaced about every 20 years. As wind energy becomes increasingly popular, experts estimate that by 2050 more than two million tons of blade material could be decommissioned each year. However, one research team has developed a new binding resin, the ingredient that holds their fibrous material together, that can be transformed into more valuable substances.
“We’ve specifically designed a system with the end of life in mind,” says John Dorgan, a professor of chemical engineering and materials science at Michigan State University, who worked on developing the new resin. “After being used for years to strengthen wind turbine blades or other structures, the resin can be recycled back into another turbine blade or downcycled into a composite material that can be used to make plastic products. It can also be upcycled to produce shatter-resistant acrylic plexiglass, a superabsorbent polymer used in diapers and the food preservative potassium lactate”.
Size and value are two main obstacles to recycling these structures. “To start with is just the fact that they’re very large, and they’re meant to be very durable—to last in the weather for 20 or more years. So they’re just a hard thing to disassemble and move around,” explains Aubryn Cooperman, a wind energy analyst at the National Renewable Energy Laboratory, who was not involved in the new resin’s development. Another problem “is that they’re made from materials that are as low-cost as possible [that will] still get the performance you need.” For maximum efficiency, wind turbine blades must be both light and strong, so engineers typically craft them from fiberglass bonded together with a polymer resin. In theory, this material can be recycled, but researchers say the resulting product is not particularly valuable. “The main problem is: it’s simply uneconomic to do it,” Dorgan says. “It’s cheaper to just bury it in the ground than it is to reprocess it into something useful.”
To solve this problem, Dorgan and his colleagues decided to develop a new polymer resin that could bind a large fiberglass structure firmly together while it is in use and that could be turned into a variety of products when the time comes to retire the blade. The team produced resin by dissolving polylactide, a polymer derived from plants, in a synthetic monomer called methyl methacrylate (MMA). Next, the researchers used vacuum pressure to pull the resin through glass fibers. After the fibers had been impregnated with the liquid, the resin hardened, producing solid fiberglass panels.
To recycle their experimental fiberglass panels, the researchers soaked the panels in the MMA monomer, which dissolved the hardened resin—then the researchers physically removed the glass fibers. The recovered “syrup” was used to make fresh fiberglass panels, which had the same physical properties as the originals.
But the leftover resin also has other potential uses. “What would really drive recycling of wind turbines is if you could turn them into something that’s worth more money or by using it to [make high-value] products out of it,” Dorgan says.
Putting the recovered resin through different chemical reactions allowed the team to extract new compounds. One substance produced this way was polymethyl methacrylate, an acrylic polymer better known as plexiglass, which is used to make a vast variety of goods, ranging from windows to car headlights. Cooking the resin at a high temperature produced poly(methacrylic acid), a superabsorbent material used in diapers and other products. A little more processing resulted in potassium lactate, which is added to a variety of foods as a preservative.
“I’m trying to push the boundaries of how people think about recycling,” he explains. “It’s about creating additional options and getting people to think about ‘What really are the limits on recycling?’ And as far as I know, nobody’s ever reprocessed a durable composite material into something that can be eaten.”
