Carbon-reinforced plastic composites are one the remaining 15% of wind turbine materials that currently cannot be commercially recycled. These composites contain thermoset matrix resins which can’t easily be recovered once they have been cured.
Finding a scalable, cost-effective, method to recycle these materials is increasingly more pressing, as the first wind turbines near their 20 to 30 life spans. By 2049, over 6.5 million tonnes of wind blade material waste in estimated to be produced worldwide, with the US expected to produce roughly 16% of this volume, and the European Union another 30%.
A Washington State University research team has developed a new chemical recycling method that uses a mild Lewis acid as the catalyst and an industrial solvent to break down the thermosets. The team says the high boiling point organic solvent is ‘eco-friendly and benign’ and that ‘people are used to it in industry’.
The method preserves the carbon fibers as well as the resin material in a useful form that can be easily re-used. It works at moderate temperatures below 200 C and ambient pressure without the need for a pressure chamber, which saves operational and capital costs.
In a first stage of the chemical recycling process, the researchers shred the composite material into chips. They then break down the carbon fiber in the solvent for three hours, reportedly preserving its strength properties. Once the matrix resin has been dissolved, it is collected through water precipitation. The method does not generate any secondary waste, according to the team, and can be operated in a continuous or semi continuous process.
Unlike traditional mechanical recycling processes, this process does not damage the valuable carbon fiber. And unlike other chemical recycling processes using high temperatures or harsh materials, it does not use hazardous and difficult to dispose of chemicals as catalysts. Those methods also often create additional waste problems because they destroy the matrix resin material that must then be disposed of. The new process, on the other hand, can collect the matrix resin and reuse the solvent.
“Then we can bring that solvent back, and since it has that really good temperature, and long-term stability, we can recover it and reuse it for the next batch of recycling,” said graduate student Brian Bliss. “That means that as we scale up, we can reduce costs in the process.”
“Our process is novel, creative, and unique because this is the first time we can do the recycling in a continuous process and under a moderate temperature,” added Jinwen Zhang, a professor in the School of Mechanical and Materials Engineering who is leading the project. “That’s a huge benefit for recycling. The continuous chemical recycling process hasn’t been seen anywhere else.”
As part of the award, the researchers will be working to optimize their process, scale it up, and demonstrate it in semi-batches.
The competition is expected to help the environment by lowering the United States’ need to extract and process raw materials. The reuse of more critical materials would also decrease dependence on imports, which would make domestic supply chains less susceptible to price volatility and disruptions, the Department of Energy said in a statement.