Now For the State of the Art in Carbon Fiber Recycling
- Ned Patton
- Oct 29
- 8 min read
Last week I went through the state of the art in wind turbine blade recycling, which could alternatively have been titled “state of the art in glass fiber recycling” because most of the wind turbine blades that have come to the end of their useful life or are nearing their demise are primarily made of glass fiber composites. In some of the larger blades, there is a carbon fiber spar cap that I have talked about previously, but even those blades are predominantly glass fiber.
So I thought I would cover carbon fiber recycling and reuse this week because the need to reclaim carbon fiber from used aerospace parts and from some of the larger wind turbine blades with carbon fiber spar caps is upon us or very shortly will be.
Again, there are the three methods of recycling carbon fiber parts like the spar caps of these used wind turbine blades. First is the mechanical method of just grinding them up and adding them to something to strengthen it. I won’t be talking about that because that at least in the sense of maintaining the properties of the fiber that made it useful in the first place, mechanical recycling does not do that, which really can’t be part of a circular economy for carbon fiber composites.
There is, however, one semi-mechanical process for recycling carbon fiber composites that has been commercialized and is being used by Hexcel and soon to be used by Siemens Gamesa to recycle their carbon fiber production waste. I have written about the new composite scrap recycling facility near the Hexcel site in Salt Lake City in previous posts, so this should not come as much of a surprise. And by semi-mechanical what is meant is that the Fairmat process first uses a cold atmospheric plasma to separate the fibers and resin and from what is left they make chips that they infuse with a thermoplastic and use that material to mold new carbon fiber composites. They do not grind up the carbon fiber composite. Instead they cut the carbon fiber parts or scrap into a standard size piece and then use their cold plasma to break up the resin.
The other two methods are the same as what you do with glass fiber composites, a thermal method and a chemical method, although the thermal method can operate at a much higher temperature if little care is taken to retain the properties of the resin. This is the pyrolysis vs thermolysis method difference where typical high temperature pyrolysis destroys the resin and lower temperature thermolysis (sometimes also called low temperature pyrolysis) does not.
The chemical means of removing the resin from the fiber in end of life carbon composites is similar to what is done for glass composites, with a couple of notable differences. Some of the chemistry that can be used to remove resin from carbon fiber composites can chemically alter glass fibers and make them lose some of their strength. These chemical processes have been shown to work, but since they can’t be used for glass composites, there are not good examples of where companies are scaling them up since the biggest problem that we have right now is used wind turbine blades which are mostly fiberglass.
I’m going to repeat myself a bit here from last week, but it does appear that Composite Recycling has done more than most in this particular recycling method. They have already scaled up their thermolysis process for removing resin from fiber, whether that fiber is glass or carbon fiber, and they have actually built machines and are recycling end of life fiberglass wind turbine blades now and will be using their machines to recycle end of life boat hulls very soon. They have demonstrated that their process also works well for end of life carbon fiber composites since all they have to do is to calibrate the temperature and processing time for each batch of different epoxy or polyester based fiber composites. In the case of wind turbine blades, if the spar cap is carbon fiber, the fiberglass part of the blade can be first separated from the carbon fiber part of the blade and each of the two can then be put into one of these machines that has been calibrated to handle that particular blend of fiber and resin.
In another example of thermal methods, Mitsubishi Chemical acquired a couple of fully industrial scale carbon fiber recycling companies back in 2020 and has fully integrated them into their global carbon fiber recycling and reclamation program. The acquisition was CFK Valley Stade Recycling GmbH & Co KG and carboNXT GmbH, both German companies and both of which use a pyrolysis process to recycle carbon fiber from both end of life carbon fiber composite parts as well as aerospace manufacturing scrap materials. They demonstrated recently that they have integrated these processes well enough that they can end up with a more continuous mat sort of material that can then be infused with either thermoset or thermoplastic material to make new carbon fiber composite parts. The fiber that results from these processes largely retains its virgin properties, but the resin itself, at least in the case of carboNXT is not retained since the temperature of their pyrolysis process is so high.
Here in the US, Carbon Conversions uses a pyrolysis process to remove the resin from the fiber and leaves behind a useful carbon fiber product albeit in shorter lengths than the original carbon fiber composite part or piece of processing scrap. They do have a 50,000 square foot facility in Lake City, South Carolina that does all of this processing, and they actively market their products to automotive manufacturers and the sporting goods industry where this form of carbon fiber is good enough and comes at a low enough cost that it makes good business sense. And, while the resin is completely lost in their process, they do have an industrial scale process for reclaiming carbon fiber that would otherwise be sent to a landfill. And they have also gotten sufficient certifications for their recycled materials that the auto industry can use them and get their use approved by the Department of Transportation for non-primary structure.
On the chemical front, there is a company in Europe (Luxembourg and the UK) called Uplift360 that has developed a low temperature solvent-based chemical recycling process they call CHEMR that can remove the resin from a carbon fiber composite and retain the properties of the fiber. The solvent apparently can be recycled in their process and reused to dissolve more resin. While they do not talk much about what they do with the dissolved resin, one can only imagine that it is potentially reusable as well, at least in some form, once it is separated from the solvent. This company, whose process was developed using UK defense funding, has recently done a demonstration in partnership with Italian defense company Leonardo by recycling an end of life helicopter blade from a Leonardo aircraft and used the resulting carbon fiber to create a prototype drone arm for another defense application for Leonardo. And they were able to demonstrate this starting with an R&D contract that got initiated in May of this year resulting in the demonstration in early October of this year. Uplift360 is working on scaling up their technology within the defense sector in Europe and looks to be poised to scale rather quickly.
Here in the US, NREL has partnered with Arizona State University to demonstrate a method developed by this partnership that uses concentrated acetic acid at a fairly high temperature to dissolve epoxies from carbon fiber composites. This process is very rapid, results in high quality carbon fiber and a liquid from which the acetic acid can be easily removed and reused. The remarkable thing about this particular process is that not only is it very fast, non-toxic, and leaves clean fiber behind, it also leaves the chemistry of the monomers of the resin intact, so once the acetic acid is removed from the liquid that results from this process the resulting liquids are very nearly ready to use again as new resin. In addition, the method is very inexpensive, since concentrated acetic acid is cheap and easily sourced industrially in large quantities since it is one of the more prevalent organic acids used in hydrocarbon chemistry of all types, including in the food processing industry. It is after all just concentrated white vinegar.
In another interesting development, researchers at the University of Kansas and USC have developed a two step process for recycling carbon fiber scrap and end of life parts that involves a fungus to consume one of the breakdown products of the epoxy resin. What these researchers have demonstrated is a two step process whereby they first chemically break down the epoxy resin to remove it from the carbon fiber, resulting in benzoic acid as one of the main byproducts of the breakdown. The University of Kansas contribution comes from Professor Berl Oakley, Distinguished Provessor of Molecular Biology at UK, who bred a strain of a very common fungus, Aspergillus nidulans (think penicillin) to enable it to feast on the benzoic acid component of the breakdown of the epoxy resin. The fungus uses the benzoic acid to produce a toxin called OTA which currently has little use but is under investigation as a potential antibiotic or anti-inflammatory drug.
So, that’s the latest on the business of recycling of carbon fiber composites into useful fiber and in several instances useful resin precursors that can be made back into new composite parts. While the overall recycling process for carbon fiber composites still is dominated by the mechanical means that I mentioned briefly at the outset of this post, at least there are some promising alternatives to grinding them up, some of which are actually being scaled up to where they may become the processes of choice in the not too distant future.
That’s about it for this week’s post. As always, I hope everyone that reads these posts enjoys them as much as I enjoy writing them. I will post this first on my website – www.nedpatton.com – and then on LinkedIn. And if anyone wants to provide comments to this, I welcome them with open arms. Comments, criticisms, etc. are all quite welcome. I really do want to engage in a conversation with all of you about composites because we can learn so much from each other as long as we share our own perspectives. And that is especially true of the companies and research institutions that I mention in these posts. The more we communicate the message the better we will be able to effect the changes in the industry that are needed.
My second book, which may be out in the late fall, is a roadmap to a circular and sustainable business model for the industry which I hope that at least at some level the industry will follow. Only time will tell. At least McFarland announced it in their Fall Catalog. And this time it is under a bit different category – Science and Technology. Maybe it will get noticed – as always that is just a crap shoot.
As I have said before, my publisher and my daughter have come to an agreement about the cover. So, I’ve included the approved cover at the end of this post. Let me know whether or not you like the cover. Hopefully people will like it enough and will be interested enough in composites sustainability that they will buy it. And of course I hope that they read it and get engaged. We need all the help we can get.
Last but not least, I still need to plug my first book. “The String and Glue of our World” pretty much covers the watershed in composites, starting with a brief history of composites, then introducing the Periodic Table and why Carbon is such an important and interesting element. The book was published and made available August of 2023 and is available both on Amazon and from McFarland Books – my publisher. However, the best place to get one is to go to my website and buy one. I will send you a signed copy for the same price you would get charged on Amazon for an unsigned one, except that I have to charge for shipping. Anyway, here’s the link to get your signed copy: https://www.nedpatton.com/product-page/the-string-and-glue-of-our-world-signed-copy. And as usual, here are pictures of the covers of both books.
