Researchers recycle wind turbine blade materials to make improved plastics

(Press-News.org) PULLMAN, Wash. – A new method to recycle wind turbine blades without using harsh chemicals resulted in the recovery of high-strength glass fibers and resins that allowed Washington State University researchers to re-purpose the materials to create stronger plastics.

The innovation provides a simple and environmentally friendly way to recycle wind turbine blades to create useful products.

Reporting in the journal, Resource, Conservation, and Recycling, the team of researchers cut the lightweight material that is commonly used in wind turbine blades, called glass fiber-reinforced polymer (GFRP), into approximately two inch-sized blocks. They then soaked the flakes in a bath of low-toxicity organic salt in pressurized, superheated water for about two hours to break down the material. They then re-purposed its components to make stronger plastics.

“It works very well, especially considering the mild conditions that we applied,” said Cheng Hao, a former graduate student in the School of Mechanical and Materials Engineering and co-first author on the paper. “The solvent is a green solvent, and also the temperature is acceptable for this purpose.”

The GFRP material has traditionally been very difficult to recycle. While thermoplastics, the type of plastic used in milk bottles, can be melted and easily re-used, the glass-fiber composites are typically made with thermosets. These types of composites are cured and can’t easily be undone and returned to their original materials. The first generation of modern wind turbines made of composites from the 1990s are now reaching the end of their lifetimes, creating a significant challenge for disposal. The glass fiber-reinforced material makes up about two-thirds of a wind turbine blade’s total weight. Furthermore, when the blades are made, about 15% of the material is also wasted in manufacturing.

 “As wind energy grows, recycling and reusing wind turbine waste is becoming increasingly urgent,” said Jinwen Zhang, corresponding author and a professor in the School of Mechanical and Materials Engineering. “This recycling method is scalable, cost-effective, and environmentally friendly, providing a sustainable solution for reusing large quantities of glass fiber reinforced waste.”

In their work, the researchers soaked the blade material in a mild solution of zinc acetate, which is used in medicines, such as in throat lozenges and food additives. The mild solution allowed the researchers to recover glass fibers and resins in good condition which they then added directly to thermoplastics to produce strong composite materials with up to 70% of the recycled glass fiber materials. Moreover, the researchers were able to recover and reuse most of the catalyzing zinc acetate solution through simple filtration.

 “The ease of the catalyst recovery enhances the overall sustainability and cost-effectiveness of the method,” said Zhang, who conducts research in the Composite Materials and Engineering Center.  

When the researchers added the recycled material to nylon plastic and tested it, they found that the additional fibers made the nylon more than three times stronger and more than eight times stiffer. They also found that the recycled GFRP material can reinforce other plastics, such as polypropylene and the type of plastics used in milk jugs and shampoo bottles.

“For this work, we didn’t need to fully break down all the bonds and push the reaction to completion,” said Baoming Zhao, co-first author and research assistant professor in the Composite Materials and Engineering Center, “As long as we can break the cross-linked network into smaller pieces, and they are melt processable, we can compound that with nylon and get a new composite. We are not separating the resin from the fiber – we just blend everything with nylon and get a new composite.”

 The researchers are continuing studies to make the chemical conditions even easier for recycling by reducing the requirements for pressurization. Working with WSU’s Office of Commercialization they also hope to develop blade materials that are fully recyclable in the first place.

The work was funded by the Department of Energy’s Office of Energy Efficiency and Renewable Energy.

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