Today's KNOWLEDGE Share : Innovative recycling method for carbon fibre

Today's KNOWLEDGE Share

Fraunhofer EMI: Innovative recycling method for carbon fibre

Researchers from the Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI have developed a technology that makes it possible to reclaim continuous carbon fibres from composite materials without diminishing material quality. High-power lasers are used for local degradation of the matrix of multi-layered fibre-reinforced plastics at high temperatures. This method offers not only ecological benefits but also considerable economic potential.

Carbon fibre composites are exceptionally strong and lightweight, making them preferred materials in many industries. But the disposal and recycling of these high-performance materials pose significant challenges. The research team at Fraunhofer EMI has now developed a process in which fibres from used composites are efficiently prepared for reuse  without adversely affecting their mechanical properties. Current recycling methods for fibre-reinforced plastic involve a shredding step, which shortens the fibres and leads to a downcycling.

The researchers at Fraunhofer EMI use a high-power laser for controlled reclamation of the fibre reinforcement from thermosetting composites. This method is especially relevant for pressurized hydrogen tanks, where a continuous carbon fibre roving is wound around a plastic liner to make the tank able to withstand high internal service pressures of up to 700 bar.

The advantage of this innovative recycling method lies in the ability to remove the thermosetting matrix surrounding the carbon fibres via a local pyrolysis, while leaving the fibres themselves nearly undamaged. What makes this process special is that we perform the pyrolysis of the matrix and the unwinding of the fibre roving simultaneously, at a reasonable speed without damaging the carbon fibres.

The challenge lies in defining the optimum process window, as the matrix thermal degradation occurs at temperatures of 300 to 600 degrees Cel, while the fibres might start getting damaged when the temperature reaches about 600 degrees Celsius. We found a very good compromise between the process efficiency and the quality of the recycled material. Our results show that the continuous fibres reclaimed in this way have the same excellent performance properties as new fibres.

The innovative method offers not only ecological benefits but also considerable economic potential for recycling companies. Because heat is applied locally and the fibre roving is continuously reclaimed at the same time, there is no need for the long pyrolysis times and high process costs typically required when working with the thick-walled hydrogen tanks. Furthermore, the laser-assisted reclamation process requires only about one-fifth of the amount of energy required to produce new fibres. Those are key advantages in the current context of rising energy costs and increasing environmental requirements.

source: Fraunhofer EMI /JEC Composites