Recently, I met a representative of World Auto Steel, actually the Director, Cees ten Broek, at a Lightweight Transportation conference in Stuttgart. He told me about a paper study that had been funded by World Auto Steel, (a consortium of Steel companies), and written by a professor at UC Santa Barbara. Their findings were that if the entire Life Cycle Analysis is taken into consideration, that carbon fiber is worse for the environment than steel because the manufacturing of carbon fiber generates more greenhouse gasses than steel (per Kg) and carbon fiber is not recyclable. I had heard about this study about a year ago, when it was first released, but could not find out more at the time.
A link to study is provided in the following link: http://www.worldautosteel.org/life-cycle-thinking/greenhouse-gas-materials-comparison-model/
The Downloads are called “Version 3 Model”, and “User’s Guide”, check them out.
Here are the problems I found with this study:
For one thing, it looks like the amount of heat energy it takes to make a Kg of material was compared 1 to 1 between carbon fiber and steel, but since carbon fiber would produce a vehicle structure that weighs only half that of the steel it replaces, that should have been accounted for, but I don’t see that calculation. Then, a composite structure is usually made of about half its weight in fibers, (45%-65%), and the rest is a thermoset resin, like epoxy or polyester. However, I don’t see any calculations for the carbon footprint of making these polymer matrix materials.
The second issue I saw was that the life cycle of the vehicle was assumed to be exactly the same as a steel vehicle, even though a composite vehicle structure would never rust, corrode, or fatigue. Why was the life cycle assumed to be the same? The marine industry tried to do a life cycle analysis of fiberglass boats, several years ago, but they found that they just never reached the end of their useful life – they just rebuilt their engines, repainted them, and kept going. (The study included boats up to 30 years in age). After working on that study for years, they just gave up. I would have thought that the environmental impact of a vehicle that never rusts, or fatigues would be very positive, yet the University of California study makes it look like the useful life of composites is the same as steel. Even if you assumed the composite structured vehicles would only last twice as long as a steel one, (a conservative assumption) that would have had a significant effect on its Life Cycle Analysis.
Third, I noticed that recycling information was completely absent, (all zeros in their list of data) even though carbon fiber is quite recyclable and a great deal of work has gone into the development of recycling of carbon fiber. Boeing, and BMW are already recycling their off-fall from the production of the 787 and the i3, (as are Plasan, Trek Bicycles) but none of that information made its way into the study. Currently MIT-RCF is working on developing markets for the recycled CF. See their website: http://mitrcf.com/
Finally, the author of the study took great pains to point out that different grades of steel and aluminum have a different carbon footprint and different mechanical properties, but they simply lumped all glass fiber and all carbon fiber into one simplistic category. This is striking because of how truly diverse the composite materials are. There are many different grades of carbon fiber, and glass fiber, as well as other fibers like nylon, Aramids, polypropylene, and cellulosic fibers. When it comes to resins, (the other ~50% of a composite), there are polyesters, vinyl esters, DCPD, epoxies and polyurethanes, not to mention a variety of thermoplastics. In addition to these little facts that were conveniently left out of the equation, the optimized composite structure is most likely not going to be pure carbon fiber or pure glass fiber. (And don’t forget the cores).
It may have been a simple mistake that the author of the study, Roland Geyer (firstname.lastname@example.org), didn’t know that all composites are not the same, or didn’t know that CF is being widely recycled in large volume, and didn’t know that thermoset resins make up about half the content of almost any composite, and just did not realize the longer life cycle of composites would change its average useful life. Or it could have been that he knew his study was funded by the consortium of steel manufacturers, World Auto Steel, and he didn’t want them to be upset about the findings.
Hopefully, he responds to either of the two emails I have sent him in the last week, or responds to the composites community as a whole by commenting on this blog. Because without his own response, we just don’t know if it was a simple case of making a series of mistakes, or deliberately slanting the data to please his sponsors.
Andy Rich, Chairman Composites Division SPE