New opportunities through chemical recycling

Carbon fiber-reinforced plastics (CFRP) are becoming increasingly relevant because of their strength and stiffness, in addition to having a significantly lower specific weight compared to other rigid materials.  

The increasing importance of carbon-based composites, however, poses problems because the amount of waste is also rising at the same time. In particular, composites with a duromer resin matrix made of epoxy resins cannot be recycled to date because duromers are neither fusible nor soluble. In addition, epoxy resins are particularly chemically inert.

Innovative solution approach of the Technical Universities of Nuremberg and Aschaffenburg

The chemical recycling of epoxy resin-based materials could be realized for the first time through an innovative solution approach and offers new perspectives. With the help of the efficient process developed by the Technical Universities of Nuremberg (Department of Macromolecular Chemistry) and Aschaffenburg (Department of Resource Efficiency) for epoxy resin-based carbon fiber composites, it is possible to recover both undamaged fibers and recyclable oligomers. Recovery of carbon fibers from carbon fiber-reinforced epoxy resins while maintaining the original properties of the fibers is possible.

By using a special organic chemical reaction to cleave carbon-nitrogen bonds, amine-cured epoxy resins can be dissolved. The oxidative degradation of the resin with hydrogen peroxide follows the so-called Cope elimination. Initial results indicate selective cleavage of the epoxy resin, which facilitates reuse of the oligomeric cleavage products.

Process enables recovery of nearly epoxy-free carbon fibers

Current developments in the project show that massive epoxy resin bodies can be dissolved by five hours of swelling followed by 15 hours of thermolysis. Analysis demonstrated the formation of the expected oligomers. It is particularly noteworthy that the reaction was carried out at mild temperatures (< 200°C) and ambient pressure, and the length of the carbon fibers was limited only by the component used.

Last but not least, this innovative process for carbon fiber-reinforced epoxy resins allowed the carbon fibers to be recovered with almost no epoxy resin. In the process, the tensile strength of the recycled fiber remained almost unchanged. The aim is to use the oligomers produced during the cleavage process to synthesize new epoxy resins, thus creating a closed material cycle.