WSU team recycles carbon fibre composites

Washington State University researchers have developed a method of recycling carbon fibre plastics that are used in modern aircraft and wind turbines.

Prof Jinwen Zhang with his carbon fiber recycling research team (credit: WSU)
Prof Jinwen Zhang with his carbon fibre recycling research team (Credit: WSU)

The work, reported in Polymer Degradation and Stability, is claimed to provide an efficient way to re-use the carbon fibre and other materials that make up the composite parts.

Carbon fibre reinforced plastics are utilised in a number of industries because they are light and strong but they are also difficult to break down or recycle.

Thermoplastics can be melted and re-used but most composites used in planes are thermosets that are cured and can’t easily be undone and returned to their original materials.

To recycle the materials, researchers have so far tried grinding them down mechanically or breaking them down with very high temperatures or harsh chemicals to recover the carbon fibre. A problem with the latter process lies in the caustic chemicals that are hazardous and difficult to dispose of. They also destroy the matrix resin materials in the composites, creating a mixture of chemicals and an additional waste problem.

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.

In particular, it was the combination of chemicals that proved effective, said Zhang. 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 in a statement.

The researchers were able to preserve the carbon fibres as well as the resin material in a useful form that could be easily re-used. They have filed for a patent and are working to commercialise their methods.