Anastasiia Mikhalchan, IMDEA MATERIALS
They can replace CO²-intensive materials like copper, steel, and aluminum in the construction, aerospace, automotive, and other industries, and are also the global bet for an ongoing energy transition.
Carbon nanotubes, filaments 2,000 times thinner than a hair, are already used in batteries suitable for portable electronic devices, and increasingly in structural composites, electrical cables, and sensors in smart textiles and wearable technology. But can they be recycled? What if we fill the world with carbon nanotubes and they end up being the big problem of the new century?
Currently, the global production capacity of carbon nanotubes (CNT) is around 10 kt/year, a rate that is increasing by approximately 30% annually. And this could accelerate to megaton scale if initiatives like Carbon Hub succeed and nanocarbons become available as co-products of turquoise hydrogen. They are even expected to replace metals.
However, as far as we know, there has been no attempt to exploit the recycling of carbon nanotube (CNT) materials on a macroscale from their composites. Are they useful after use? Is it worth starting to research the process of reusing carbon nanotubes now?
Recyclable?
At the IMDEA Materials Institute, we have just published an innovative paper in the journal Carbon that demonstrates, for the first time, the ability to recycle high-performance carbon nanotube (CNT) sheets while preserving their shape, structural alignment, mechanical and electrical properties, and intrinsic flexibility.
The macromaterials of the future are a novel substitute for commonly known individual CNT powders. At IMDEA Materials, we develop unique fibers, threads, and fabrics made from billions of interconnected CNTs forming nanoscale networks. They are flexible, lightweight, strong, and conduct electricity and heat, and can be used in many engineering applications.
These CNT fibers and sheets possess high structural strength and flexibility, as well as high mechanical, electrical, and thermal properties. This allows their use in structural reinforcement in composite laminates, printable strain/stress sensors, electrical conductors, and flexible battery anodes, among other applications. These properties are what make them so versatile.
Our goal was to check to what extent their properties remain intact after being subjected to a recycling process.
Thermal Treatment
We subjected sheets of varying density (including commercial ones) to a two-step thermal treatment process.
The recycled CNT sheets demonstrated almost total retention of mechanical and electrical properties. This demonstrates that high-performance materials made from carbon nanotubes are recyclable and can be reused in the same application as structural reinforcement, electrical conductors, and flexible battery anodes, among other applications.
Like Lego®
The recycled sheets could return to their initial state, like building blocks. CNTs can dissolve and turn into liquid crystalline solutions, which could then be respun into a new high-quality fiber.
It would be like breaking down a Lego model into its individual bricks, and then rebuilding the original model with the same shape, robustness, and quality.
This is not possible with conventional carbon fibers because their structure is made of crystallites that fuse, so they cannot be broken down into individual crystallites and regraphitized into a continuous fiber filament.
In contrast, carbon nanotubes can dissolve and be respun into a fiber, something that is already done on a commercial scale.
Reusing new materials will allow us not to repeat the mistakes of the past. Shall we start?
Anastasiia Mikhalchan, Senior Associate Researcher of Nanostructured Composites, IMDEA MATERIALS
This article was originally published in The Conversation. Read the original (in Spanish).
