2024-03-04 10:30:26
As global demand for carbon fiber reinforced polymers (CFRP) continues to grow due to their exceptional properties, their poor recyclability will soon become a major issue for the industry. Fortunately, research into new recyclable CFRPs is increasing, as are technical innovations regarding fiber recovery.
CFRPs are composite materials used in many industries, particularly in aeronautics and wind power. According to POLYVIA, the demand for CFRP tripled between 2010 and 2020 and is expected to exceed 190 kilotons by 2050. On the other hand, it is clear that the question of their end of life will very soon become worrying, since by 2025, the generation annual CFRP waste will reach 20 kilotons.
However, for the future, the scenarios are clear: we already know that this figure will be around 38 kt per year following 2030, in particular because of the numerous wind farms which are reaching the dismantling phase. Finally, the problem will only get worse in the decades to come, when it will also be a question of dismantling of aircraft such as the A350, composed of more than 50% CFRP!
Towards recyclable and repairable CFRP composites
In a article published in open accessAmerican researchers from Oak Ridge National Laboratory explain that they have developed a carbon fiber reinforced vitrimer composite (CFRV), recyclable in a closed loop and whose properties are similar to thermosetting materials.
The secret comes from exceptional interfacial adhesion, which results from the synergy between:
- a base polymer modified by a boronic ester;
- a multidiol crosslinker;
- carbon fibers functionalized with a diol.
Furthermore, the recyclable nature of this material is directly linked to the dynamic crosslinking of the base polymer, which makes it possible to break the chemical bonds. But this is not the only advantage of this material: like other vitrimer-based composites, it is compatible with the thermoforming process, which is not the case for thermosets.
Recycling current CFRPs is difficult, but not impossible!
As this example shows, new recyclable composites that are easier to use are therefore in development, but what should we do with current CFRPs when they reach the end of their life?
You should know that they are too often wrongly considered as non-recyclable. Indeed, although their recycling is difficult, it is not technically impossible and new recycling methods are developing, boosted by an emerging carbon fiber market which aims to be very dynamic.
Many industrialists are thus launching into the battle to exploit the immense deposit of carbon fibers that waste constitutes. Several fiber recovery techniques therefore exist, a subject that we have already covered in recent articles.
The French SME Extracthive, for example, uses solvolysis, that is to say the use of a heated solvent to separate the matrix from the carbon fiber. Her PHYre® process thus makes it possible to recover carbon fibers whose cost does not exceed that of new fiber and whose mechanical performance is almost identical.
For its part, the startup Xcrusher has developed a process for separating carbon fibers based on the circulation of strong electrical currents with the aim of sublimating the resin. In the interview he gave us in 2021, Abdelaziz Bentaj, founder and director of Xcrusher, explained to us that this process made it possible to produce long fibers whose tensile capacity is equivalent to 90% of that of new fibers.
Finally, if the pyrolysis separation technique also makes it possible to separate the matrix from the fiber, it has the disadvantage of producing residues around the fibers, which makes it unusable directly. But here once more, innovative methods are appearing to improve the process: this is notably the case of a technique developed by researchers at the University of Sydney which consists of adding an oxidation step at high temperature in order to eliminate the residues.
If you want to explore the subject in more depth, we advise you to read the guide to recycling and eco-design of composites established by POLYVIA. You will find there in particular an exhaustive directory of the players in the treatment of composite waste.
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