Challenge in recycling composite material

The transition to a circular economy, in which raw materials are efficiently reused, is one of the most pressing challenges of our time. In this context, the recycling of composite materials is a particularly interesting but complex topic. Composites, characterized by their composite structure of different materials, offer unparalleled strength and lightness. These properties make them indispensable in industries such as aerospace, automotive and wind energy. However, the same properties that make composites so valuable also present significant obstacles to their recycling

Why is recycling composite material so difficult?

Unlike single plastics such as polyethylene and polypropylene, composite materials are composed of two or more components to take advantage of a combination of material properties. They consist of a matrix (usually a polymer) and a reinforcing material such as glass or carbon fibers. Recycling these materials is complex because of the heterogeneity of their composition. While metals such as aluminum and steel are relatively easy to recycle by melting and remolding, composites require a completely different approach. The three main recycling methods for composites are mechanical, thermal and chemical recycling, each with its own advantages and disadvantages.

What are possible solutions?

There are a number of possible solution approaches:

  1. Mechanical recycling: Mechanical recycling involves reducing composite material by grinding and milling. This results in fiber-rich and resin-rich fractions that can be reused as filler in new composites. Although this method is relatively simple and inexpensive, it results in a significant loss of material quality. The fibers that remain are short and have largely lost their original strength, limiting their applications to less critical parts
  2. Thermal chemical recycling: Thermal recycling, which includes pyrolysis and incineration, offers a different approach. Pyrolysis, in which composites are broken down at high temperatures in a low-oxygen environment, allows fiber recovery while converting the resins to gases and oils. While this method is more efficient in preserving fiber quality, it is energy intensive and can lead to some degree of fiber degradation. In addition, the cost of thermal recycling is significant, which limits its commercial viability.
  3. Chemical recycling with solvents: This uses solvent-based chemical processes to separate the matrix from the fibers, often leaving the fibers of higher quality. However, this process is not yet commercially viable and may cause environmental problems due to the use of solvents. Solvents for this process can include water, glycols or acids. Another possibility is the use of supercritical fluids, such as supercritical water and supercritical alcohols, where under high temperatures and pressures and lye as a catalyst, the composites can be decomposed and separated. Much research is still needed to refine these methods and make them commercially viable
  4. Innovation in materials development: development of new, more easily recyclable composite materials and more efficient separation technologies continues to be needed. This will be able to improve the economic and environmental feasibility of recycling.

Applications and future prospects

Despite the technical challenges, recycling composites offers significant environmental benefits. Recycling fibers and resins can reduce the demand for new raw materials and reduce the carbon footprint of sectors such as aerospace and automotive. The Airbus PAMELA project, which focuses on recycling end-of-life aircraft, has shown that it is possible to recycle up to 90% of an aircraft. Boeing has launched similar initiatives to recover carbon fiber from their aircraft .

In the automotive industry, where weight reduction is crucial for fuel efficiency, composites are increasingly being considered. However, limited market demand for recycled composites and the high cost of recycling remain significant obstacles. Innovations such as self-reinforced composites and the use of natural fibers can help overcome these challenges .

Conclusion: the road to circular composites

Recycling composite materials is still in its infancy, but the potential benefits are enormous. Meeting these challenges will require a concerted effort by designers, engineers, researchers and policy makers. Only by developing innovative recycling technologies and creating markets for recycled materials can we realize the full potential of composites in a circular economy. As with any technological advance, this process will take time, resources and a determined focus on sustainability. But the reward – a world where we consume less, recycle more and preserve our planet for future generations – is well worth it.