Fiber material

Thermodynamics of recycling aluminum and carbon fiber structures

This article originally appeared on Velo News

Have a question for Lennard? Please email him at [email protected] to be included in the Technical FAQ.

Dear Lenard,
The Technical FAQ regarding the reuse of carbon fiber includes the following statement from Josh Poertner:

“Recycling many materials such as aluminum actually requires more energy than producing virgin materials in the first place.”

I think he remembers badly. Aluminum is among the materials for which the difference in energy required to extract ore compared to recycling is the largest – up to 20 to 1.
— Francois

Dear Francisco,
This is correct when it comes to recycling aluminum cans. Here is Josh Poertner’s answer to your question:

“I was able to get a response from the guy I first got this treat from 20 years ago. He’s now quite senior at Alcoa and had some interesting things to say but didn’t want to be recorded Long story short for cans and basic aluminum you are right aluminum is super efficient to recycle so we will be changing the language on our site about that and happy to change that in my comments to VN concerning the greater recycling of aluminium.

The 10:1 number comes from airplane recycling and was apparently a statistic started about 20 years ago about why we would park airplanes in graveyards and not recycle them because it took more energy to tear them down, separating the different qualities of aluminium, stripping the finishes and coatings, etc. then melt it. It seems to have improved a lot these days, although there are apparently still issues with contamination, alloying, etc. which make recycling structural aluminum much more energy intensive than something like cans. Alcoa even opened a specific recycling facility to recycle aircraft, as the process is much more involved on the cleaning/stripping side of things and also more dangerous due to the use of modern lithium-aluminum which are both more lighter and stiffer than traditional aluminum but pose serious fire and explosion hazards compared to normal things!

We will be removing this from our site now that we know it is both obsolete and even then it was too limited in scope.

–Josh Poertner, President of Silca

Thank you for raising this point, Francisco.

Dear Lenard,
The column on the environmental impact of micro-carbon particles is particularly thought-provoking. While I find Josh Poertner’s answer to your question interesting, and at the risk of sounding like a hopeless pedant, I have to take issue with his statement: “Once this process is started, it is completely independent of the energy and can operate off-grid, with each 100kg of composite producing enough energy to heat the next 100kg and so on. To the best of my knowledge, this goes against physics as we currently understand it. (Warning, if Silca has come up with a formula for perpetual energy, its potential application is far beyond sealing tubeless tires!) I’m not trying to give Josh a hard time; I just think that if we want to have a serious discussion around this huge problem in cycling, we also have to be rigorous in our science.

Dear Lorene,
Thanks for shining the spotlight on this; it is a useful thing to ponder. While physics tells us there is no free lunch, I’m not sure that applies here, as there is a lot of energy stored in the carbon matrix that is released when its decomposition into fibers. Here’s what Josh Poertner has to say about it.

“It’s not my process, so I’m just using language similar to what I hear from our supplier who invented the process, which is definitely a mix of patents and trade secrets that we’re not aware of. However, my understanding is that the process is to heat the composite matrix to a temperature to separate the constituent sub-components from each other, and some of these sub-components are then able to release much more energy when they burn at higher temperatures when used as a power source when fed back into the process itself.

In my mind, this process is more like something like extracting oil from shale, it takes energy to extract oil from shale, but the energy potential of the oil itself is far greater than what is needed for the release first.

–Josh Poertner, President of Silca

While Newton’s second law of thermodynamics says that not all heat energy can be converted to work in a cyclical process, we’re not talking about making a perpetual motion machine here. If we break down the structure of carbon and reconstruct that same structure again, then your statement is correct; there is no way to do this without adding more energy. However, when breaking down a structure into a less complex state, taking some of the energy stored in the structure and then using it to break down the next structure and still have energy for other things is exactly what we do every day while eating. . That’s what food is: something an organism consumes to obtain more energy than is used to obtain, chew and digest food.

Taking this analogy further, we humans were able to develop the big brains we have by developing methods to obtain more energy-dense foods, such as meat from large animals, than simply foraging could provide. Our primate ancestors had disproportionately larger digestive tracts needed to break down less energy-dense foods; a higher percentage of the energy obtained from food was consumed in breaking down the food, leaving less available for his brain. The amount of energy stored in food partly determines how much energy we will have left for external work after eating the food.

There is a lot of energy stored in a carbon structure. We can consider it as the food of this process; Breaking down an energy-dense structure provides the ability to have energy left over after breaking it down. It makes sense to me that this process could release some of the energy stored in a given mass of the carbon matrix, use it to break down the next unit of similar mass, and still have energy left over.

Dear readers,
Regarding Josh Poertner, some of you might be interested in this podcast interview he did with me last fall for his excellent Marginal Gains podcast series. This segment covers my story and how my love affair and understanding of bikes has grown over the years. I think you might find it instructive.

Lennard Zinn, our longtime tech writer, joined VeloNews in 1987. He’s also a custom frame builder ( and supplier of non-custom huge bikes (, former team rider American national, co-author of The broken heart“, and author of numerous books on cycling, including Zinn and the art of road bike maintenance“, “DVDs, as well as Zinn and the art of triathlon bikesand “Zinn’s Intro to Cycling: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s degree in physics from Colorado College.

To follow @lennardzinn on Twitter.

For exclusive access to all of our fitness, gear, adventure and travel stories, plus discounts on travel, events and gear, sign up for Outside+ today.