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Researchers from the (Fraunhofer EMI, Breisgau, Germany) report that they have developed a technology that makes it possible to reclaim continuous carbon fibers from composite materials, without diminishing material quality. High-power lasers are used for local degradation of the matrix of multilayered fiber-reinforced polymers (FRP) at high temperatures, offering a solution with ecological benefits and economic potential.

Some current FRP recycling methods involve a shredding step, which shortens the fibers and leads to downcycling. Unlike these methods, Fraunhofer EMI uses a high-power laser for controlled reclamation of the fiber reinforcement and thermoset matrix. Researchers say this method is especially relevant for recycling wound structures, such as pressurized hydrogen tanks, where a continuous carbon fiber roving is wound around a plastic liner to make the tank able to withstand high internal service pressures of up to 700 bar.

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The advantage of this recycling method lies in the ability to remove the the thermoset matrix surrounding carbon fibers via a local pyrolysis, while leaving the fibers themselves nearly undamaged. “We perform the pyrolysis of the matrix and the unwinding of the fiber roving simultaneously, at a reasonable speed without damaging the carbon fibers,” explains project manager Mathieu Imbert.

A challenge to this process lies in defining the optimum process window — the thermoset matrix’s thermal degradation occurs at temperatures of 300-600°C, while fibers might start getting damaged at around 600°C.

“We found a good compromise between the process efficiency and the quality of the recycled material,” Imbert says. “Our results show that the continuous fibers reclaimed in this way have the same performance properties as new fibers, which makes this method highly attractive.”

Because heat is applied locally, and the fiber 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 thick-walled hydrogen tanks. Furthermore, the laser-assisted reclamation process requires only about one-fifth of the amount of energy required to produce new fibers. These are key advantages in the current context of rising energy costs and increasing environmental requirements.

The research, part of the DigiTain project, funded by the German Federal Ministry for Economic Affairs and Climate Action, is slated to run until the end of 2025. Fraunhofer EMI researchers are currently working to make the process even more energy-efficient and to further improve the quality of the reclaimed fibers.