Technical FAQ: Micro-carbon pollution

A look at some of the concerns surrounding new and repurposed carbon fiber materials in the production of bikes and bike parts.

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Dear Lennard,
I enjoy your tech articles on VeloNews, and as I’ve written before, your repair manuals are the perfect gift to include with a customer’s new bike. I consider your notoriety worthy and as such you have a bully pulpit from which to draw attention to new ideas that we as cyclists can discuss and hopefully help the bike industry go in directions that are good for us as well as the industry.

As you know, a carbon bike frame (nor wind turbine propellers, as well) and components can’t be recycled. They end up in a landfill, and now we have a new product that will be a “solution” for this lack of recyclable trash. The plan is to grind them up and put it in our tire sealant.

I believe this is worse than having a bunch of old, broken carbon fiber frames in a pile — rather than atomizing them and putting the material into the environment, in molecular form, which makes the carbon particles all the more irretrievable than when the material is still a large piece.

I hope you can take a few minutes to think about this and present it to your constituents so we can come to a consensus about this problem. I do not think this form of carbon recycling is supportable, and we should push back on this idea and not support this product as a danger to our environment.
— Michael

Dear Michael,
I am indeed taking a few minutes to think about this and am presenting it here with the intent of getting feedback that can continue to educate all of us. With the recent studies in the news finding microplastics in the blood of humans, I appreciate you bringing up this issue of forever contamination of our environment with stuff we humans have made. It has me thinking about my own past contributions to micro-pollution in my favorite pastimes: skiing and cycling. For many decades, I focused much of my training, time, travel, and attention on cross-country ski racing, and the advent of fluorinated ski waxes that made the skis so very fast in warm or high-humidity conditions was an absolute revelation. Now, after decades of being dispersed on snowy trails all over the world, those waxes and ski preparations are banned in the World Cup, as what makes them so hydrophobic, fast and durable is that they are PFAS (perfluorinated alkanes) — the “forever chemicals” we now know to avoid. Those PFAS on the bottoms of thousands of pairs of skis in each of the mass-participation ski marathons I used to do every winter got into the snow, which melted and sent it into the rivers, the oceans, and the marine life, and probably back into our bodies. And I still have lots of these super-expensive fluorinated powders and fluorinated block waxes sitting on my ski-preparation workbench and am wondering what the heck to do with them. And that also has me thinking about “dry” chain lubes, many of which have PFAS in them. A high percentage of their volume also tends to be toxic solvents keeping the “dry” slippery ingredients in a solution; those solvents evaporate quickly and are more powerful greenhouse gases than CO2 is. Thanks for encouraging me to think about how we contribute to these global problems and what steps we can take to reduce those contributions.

As for your question, I have no way of judging whether it’s preferable to put whole carbon frames in the landfill or to grind them up and put them in tire sealant. So, I consulted the man behind that sealant, Josh Poertner. Having been engineering director at Zipp for many years before purchasing Silca, Josh has as much experience with carbon fiber as anybody I know. Here is what he has to say about it:

“Firstly, we have to realize that virtually every sealant product on the market currently contains some sort of plastic and/or micro-plastic granules manufactured from virgin petroleum stock for the purpose of being a sealant additive. While companies like to talk about their safe additives, our testing has found micro-plastic beads in nearly all of them, with many using plastic glitter, plastic platelets, plastic micro-spheres, etc., all of which can end up in the environment in the event of a puncture, and all of which have an entire supply chain of raw material and energy consumption required to support it.

Similarly, many sealants already contain glass fibers, again, from virgin stock, produced purely as an additive to the sealant. A handful contain ground or milled carbon fibers at <1mm lengths as an additive, and of the two brands doing this, both are using virgin fiber, which could have been used as an additive in composite materials, plastic injection molding, etc., and yet it ended up in sealant.

So, with our vision of using longer fiber, we started our testing with virgin fiber and found that in the longer lengths, the “sizing” (which is a thin liquid epoxy coating on the fibers to promote adhesion in structural uses) was problematic in that it caused the fibers to want to stick together, which prohibited proper dispersion in the sealant. Chemically stripping the sizing was an option but was one that seemed environmentally irresponsible, as it is the sizing and epoxy components of the composite that represent the largest environmental risk.

Then we discovered CFR, a company that has been working to solve the carbon recycling solution for nearly 10 years and whose process has an exceptionally low footprint—orders of magnitude smaller than that required to produce new fiber. This process involves pyrolyzing the composite (heating in a vacuum) and results in three outputs: raw carbon fibers, methane gas from the epoxy which is recycled into the process as the energy source, and liquid petroleum that can be used as jet fuel. Once this process is started, it is completely energy-independent and can run off-grid, with each 100kg of composite producing enough energy to heat the next 100kg and so on… This is notable, as the recycling of many materials actually requires more energy input than producing virgin material in the first place. This process, however, is entirely self-sustaining.

Lastly, many have worried about any carbon fibers which may escape into the environment in the event of a puncture, or at the end of sealant life when the old sealant is discarded. It is important to remember that any health and safety risk traditionally linked to carbon fiber is either related to the contact with uncured sizing or epoxy coatings on the raw material, which in our case has been turned into jet fuel. Or, it is related to raw fibers being inhaled if they are allowed into the air, which is impossible in our case, as the fibers are dispersed in a solution of liquid latex.

Finally, in a detailed environmental review of this product, it was confirmed that raw pyrolyzed carbon fiber, which is only one heating away from becoming activated charcoal (the filter in most water filtration systems and a common fish tank additive) and is also a pulverization process away from becoming carbon black (the thing that makes your tires and shoe soles black), when dispersed in latex (rubber), presents no more environmental risk than particulates of carbon black dispersed in rubber left behind by your tires or your shoe soles. Essentially, that skid mark you left behind on that rock is nearly identical to any sealant which may escape on the trailside. Furthermore, the carbon is so efficient at stacking up behind the cut in the tire that it is exceptionally rare for any of the carbon to escape, even in the case of large punctures.

Lastly, having been involved in the production of composite parts for nearly 20 years, I think that we all have to be honest with ourselves here. Carbon fiber composites are perhaps the most environmentally unsound raw material and production processes possible. These parts require unbelievable amounts of raw materials and energy to produce at every single step. They also result in rather large amounts of scrap and waste throughout, and, up until now, they have had absolutely no possibility for recycling or reclamation. Now that technologies for recycling these materials are becoming mature, the new problem is that there is no real market for recycled or reclaimed products, and for this to work, there must be a market to buy the outputs of these processes for some use. Our use of recycled carbon clearly isn’t going to save the earth, but I hope that as one of the first companies using recycled carbon commercially, we can help create a mindset that allows other companies to see potential in these materials. However, at the very least, I can say that our use of this material reduces the footprint of this sealant by more than 10x when compared to what it would be, had we chosen to work with virgin carbon or glass fibers. That is something we are very proud of.
— Josh Poertner, Silca president and CEO

I appreciate your bringing up this question, Michael, because it gave me and us an opportunity to delve more deeply and question how we do things as individuals and as an industry devoted to a non-polluting mode of transportation.
― Lennard

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder ( and purveyor of non-custom huge bikes (, a former U.S. national team rider, co-author of The Haywire Heart,” and author of many bicycle books including Zinn and the Art of Road Bike Maintenance,”DVD, as well as Zinn and the Art of Triathlon Bikesand Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn on Twitter.

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