The work, reported in Polymer Degradation and Stability, provides an efficient way to re-use the expensive carbon fiber and other materials that make up the composites.
Carbon fiber reinforced plastics are particularly popular with the aviation industry because they are light and strong. The difficulty comes when it’s time to recycle them. These types of plastics are cured and can't easily be undone and returned to their original materials.
Historically, researchers mostly have tried grinding them down mechanically or breaking them down with very high temperatures or harsh chemicals to recover the expensive carbon fiber. However, the carbon fiber is often damaged in the process. Also, the caustic chemicals used are hazardous and difficult to dispose of.
In their project, Jinwen Zhang, a professor in the School of Mechanical and Materials Engineering, and his team developed a new chemical recycling method that used mild acids as catalysts in liquid ethanol at a relatively low temperature to break down the thermosets. To break down cured materials effectively, the researchers raised the temperature of the material so that the catalyst-containing liquid can penetrate into the composite and break down the complex structure. Zhang used ethanol to make the resins expand and zinc chloride to break down critical carbon-nitrogen bonds.
"It is critical to develop efficient catalytic systems that are capable of permeating into the cured resins and breaking down the chemical bonds of cured resins," he said.
The researchers were able to preserve the carbon fibers as well as the resin material in a useful form that could be easily re-used.
Photo caption: Jinwen Zhang with his carbon fiber recycling research team.
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