There’s a reason I’m writing this week’s post about carbon fiber sustainability. That’s because I a have the honor of presenting a talk about this very subject on Wednesday this week in Salt Lake City. Composites World is holding their Carbon Fiber Conference this week in Salt Lake, and I have been invited to give a talk on this subject there, and also participate on a panel of “experts” talking about the use of carbon fiber for deep diving submersibles. I’m sure anyone can guess what that panel is going to talk about and most probably get it right.
This is the title slide from my presentation just so that my audience gets to see at least what I’m going to talk about. And as it turns out this is a very timely topic for discussion.
Carbon fiber is not exactly a “green” or sustainable material, and the world is beginning to take notice now that a tremendous amount of it is being used in nearly every industry where people want to save weight. I have written before that carbon fiber not only has made it into commercial aerospace – the Boeing 787 and Airbus A350 are the prime examples. It has also made into the automotive industry in a large way, into the wind turbine business in a large way (especially in Europe) and also is enabling a new generation of urban air mobility vehicles – air taxis if you will.
The problem with it is that carbon fiber has a very large “carbon footprint” currently. The precursor for most carbon fiber – acrylonitrile – is made entirely from the petrochemical industry today – big oil. And the processing plants and vacuum ovens that are used to make the fibers are all fired by oil. So, there is more carbon sent up into the atmosphere from the development of the carbon fiber than ends up in the fiber itself.
That being said, there is a lot of movement in the sustainability business for carbon fiber, especially in Europe, but also here in the U.S. In fact, Composites World which is probably the best the composites manufacturing business publication has a new microsite dedicated to carbon fiber sustainability. Companies all over the developed world are collecting all of the used carbon fiber parts that they think they can recycle and doing things with quite a bit of it. And while most of the more promising sustainability efforts are still in University research labs and have not made it into the “real world” of a profitable business yet, there are several avenues that are going to bear fruit very soon. I have written about a few of those fairly recently, and my intent in this newsletter is to collect a few of the more promising ones and provide a brief summary of where we are in the process of rendering carbon fiber into a sustainable material for the future.
To continue this discussion, I need to first explain what I mean by sustainability – especially when it comes to carbon fiber. I have said this before but it bears repeating. What we have now is what is called a “linear economy” for carbon fiber – and composites in general, meaning that we use extractive industries (big oil) to make our carbon fiber, we use the products we make with it, and when we’re done with them they become part of a landfill. What we need to get to is a “circular economy”, which means that we use sunlight and the natural world around us for our raw materials and energy sources for making the carbon fiber and when we’re done using the products, we turn them back into usable raw materials to make more products. A graphic that I like is inserted below.
I like this graphic because it tells the complete story. Anyway, where are we in this journey to make carbon fiber and composites in general sustainable. There are actually three avenues that are being worked on right now. The first is of course finding a way to get the carbon fiber back into its original form from the waste stream that is developing. And as most of you that have read my posts for some time know, this is not easy. It isn’t easy for a reason. The glue that we stick these fibers together with is intentionally long lasting and hard to get back apart. That is the good part about composites – they last a long time under extremely harsh conditions. This is something every boat owner knows quite well. But it is also the bad part about composites because at the end of their useful life they are still hard to take apart. Currently most of this material is chopped up or ground up, and the resin is burned or baked out of it in a process called pyrolysis, or dissolved out of it with strong acids in a process called solvolysis. Neither of these keep the resin precursors intact, so that is lost. And the resulting carbon fiber is not as high quality as the fiber that the mills originally produced.
There are of course projects underway to attempt to solve most of these problems. For instance, there is work going on to make modifications to the composite resins that are inherently easier to take apart at the end of their useful life. These typically come from petroleum precursors, like the resin I talked about a few months ago from CIDETEC in Spain (https://surfaceengineering.cidetec.es/en/home) where they have added a couple of disulfide groups to an epoxy backbone that render this thermoset resin into a thermoplastic at high enough temperatures, so you can melt it right out of the fibers and reuse both. CIDETEC is maturing this technology from a TRL (Technical Readiness Level) 3 to a 5 (see https://en.wikipedia.org/wiki/Technology_readiness_level for an explanation of TRL levels).
There are also epoxy resins being developed using plant-based precursors. An organization in France has developed a plant-based epoxy they call Greenpoxy® that they have used in a completely bio-based sailboat hull using flax fiber.
Finally, there is also work going on to develop plant-based carbon fiber. I have talked about this also in this space, and am going to talk about it at the Carbon Fiber Conference in a couple of days as well. Southern Research in Birmingham, Alabama has used biomass sugars – actually long chain polysaccharides – to derive Acrylonitrile (ACN) which is then polymerized into Polyacrylonitrile (PAN) to be used as a precursor for carbon fiber – most of which is now made from petroleum based PAN. They got a research grant from DOE to develop this stuff, and are now in the throes of commercializing it with a US based fiber manufacturer – Solvay. It turns out that by using waste biomass they can make PAN for less than what it costs to make it from petroleum. This is primarily because the process for making it from plant based sugars is much easier than making PAN from petroleum, primarily because the plant already has some Nitrogen as part of it, and it doesn’t have to be added like what has to be done with petroleum based PAN. And, on top of that, the prices for these two feed stocks are going in different directions – oil always goes up in price, and the biomass based sugars are coming down because the forest products industry can make money on it rather than having to pay money to bury it in a landfill somewhere. They are not allowed to burn this stuff off any more either.
As, as you can tell by now, I am actually quite hopeful that we are headed in the right direction, and that is what I plan to talk about in Salt Lake this week. I’m sure that I can post the presentation to my website once I have given it, but I don’t want to ruin the suspense in case anyone that reads this plans to be at the conference. And, like I said earlier, I am going to talk about carbon fiber use in deep diving submersibles. And, yes I do have a background in that area, so I’m fairly certain that I know how to avoid what happened down near the Titanic earlier this year in the North Atlantic. I’ll post that to my website as well sometime next week.
And, finally, for those of you that have not heard or those that have not done so yet, my book has been published and is for sale. 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 one that is not signed, except that I charge $8 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’s a picture of the book, for those of you just tuning in.
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