SKZ-project aims to enable gentle recycling of polyurethane composites without the use of harsh chemicals

Fiber-reinforced composites have become an indispensable material of the modern age. Whether in wind turbines, aircraft manufacturing, or lightweight construction in the automotive sector – their combination of high durability and excellent mechanical properties, coupled with low weight, makes this class of materials indispensable for many industries. At the same time, the high durability of the thermoset matrix and the strong bond between the matrix and the fibers make recycling extremely challenging, which is why most composites are currently either incinerated or landfilled.

To improve the sustainability of composites, the German Plastics Center SKZ is therefore collaborating with RWTH Aachen University to research a novel approach to recycling using enzymes. Enzymes are widespread in nature where they catalyze specific reactions with high efficiency. This mechanism can also be harnessed technologically to selectively break down polymers at defined sites without destroying the entire molecular structure. In this way, polymers can be gently broken down into valuable building blocks that can be used to produce new polymers. Polyurethanes are promising for this approach, as their urethane groups, from which they derive their name, have great potential for enzymatic cleavage.

Recover raw materials of the same quality
The goal of the new research project “EnzyReput” is to develop a process for breaking down glass-fiber-reinforced polyurethane thermosets using enzymes in such a way that the raw materials – namely, glass fibers and polyurethane resin – can be recovered with constant quality, enabling the production of a new composite with comparable mechanical properties. To this end, customized enzymes for the cleavage of urethane groups will be developed and tested. With the long-standing experience of the Chair of Biotechnology at RWTH Aachen University in developing enzymes for polymer cleavage and SKZ’s extensive expertise in resin development and materials testing, the two partners are ideally positioned for this endeavor.

“The recycling of composites is still in its infancy. We are confident that this approach could represent an entirely new type of recycling”, explains Dominik Uhl, Scientist in the Crosslinked Materials division at SKZ. “Unlike chemical recycling methods, enzymes allow us to use low temperatures, making this a very energy-efficient process. At the same time, we do not need aggressive chemicals to break down the polymers, which means we also protect the matrix, fibers and the environment.”

Extracting glass fibers from the matrix
A particular focus is on extracting the glass fibers, which are firmly anchored in the composite, from the matrix without causing mechanical or chemical damage to the fibers, so that the fibers can be reused while maintaining consistent quality. Therefore, the project initially focuses on short and long glass fibers, since they – unlike continuous fibers – allow to grind composite components into granulates without heavily damaging the fibers, which offers a number of advantages for recycling.

The “EnzyReput” project aims to further explore the potential of enzymes in the field of polymer recycling and lay the groundwork for composite recycling. The goal is to reduce the waste problem associated with composites and lower the demand for resource-intensive virgin materials, thereby improving the sustainability of this outstanding class of materials.

Funding
The “EnzyReput” research project (grant reference number RU 2607/4-1) is funded by the German Research Foundation (DFG).

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