Carbon fiber reinforced polymer (CFRP) is very popular because it is incredibly strong for its weight, or incredibly light for its strength, depending on how you look at it.
CFRP has become a status symbol, too, because you get that highly desirable weight/strength performance at a very high cost. CFRP is expensive. One of the reasons you don’t see much of it in architectural applications is affordability. In aerospace, where weight has a significant impact on the performance of the finished product and the cost of operating it, CFRP is a premium material that pays for itself in performance. In architecture, where weight is worth something but not that much, CFRP is mostly still too expensive to use other than in structural repair applications.
If CFRP was a lot less expensive, it might lose some of its status, but gain a lot of new applications. The thing that makes CFRP expensive is the carbon fiber (CF) reinforcement. CF is expensive to make, and the composites world is eagerly seeking a way to bring down the price of the fiber.
That may come to pass, if 4M Carbon Fiber Technologies has its way. 4M has developed a new method of performing one of the three major steps of production. They already have it working on a demonstration scale, and they are currently building a scaled up version, moving towards industrial-scale production. Their system currently lowers the cost of by 20%, using the same feedstock that is currently used in conventional production. They may soon be able to slash the cost of in half!
A bit of background on CF production: CF is the result of processing a precursor – usually polyacrylonitrile (PAN) to remove almost everything but the carbon. There are three major steps in this conversion process.
Oxidation – also called stabilization – is the first, longest, and the most energy-intensive of the three. Oxidation by conventional technology is of running a continuous band of PAN through an oven. The fiber band is pulled through a series of oven units, where it snakes around a several sets of rollers, keeping it in the oven environment for a total of about 100-120 minutes. The second step, carbonization, takes about 5 minutes, and the final step, surface treatment, about 90 seconds.) The length of time that the precursor must be in the oxidization oven is directly tied to the amount of energy that is consumed to stabilize it.
The technological revolution 4M offers is plasma oxidation, which takes only about 30 minutes. Plasma, the fourth phase of matter, creates a highly reactive environment, which enables oxidation to take place more quickly in two ways. First, the plasma environment transfers heat to the precursor more efficiently than hot air. Second, the plasma environment is chemically different than normal air, and it accelerates oxidation.
“We’re able to create this plasma that stands there hour after hour,” explains Rodney Grubb, president of 4M. “It breaks down the air into really reactive ions and other reactive species, which oxidize fiber more quickly and more completely, more deeply.”
Because the process is so reactive and fast, the length of the oven is reduced by 2/3 vs. the conventional process for the same throughput. Energy consumption (and cost) is reduced by 75%. It also saves a lot of factory floor space, or allows 3 times as much production in the same space.
In the conventional process, the cost of conversion from precursor to finished CF is about $6/lb, and about 1/3 of that is energy consumption. Cutting the energy cost from $2.00 down to $0.50 makes a big difference.
The process has other forms of savings. The shorter oven is less prone to mechanical problems with the fiber feed-through. “Fiber handling is potentially troublesome when you’re running hundreds of thousands of fibers through those ovens. That’s where rats occur, where you break fibers. If you reduce the problems, you increase uptime. You have less rollers, less fiber handling.”
How significant is the impact of less handling? It depends on how proficient the producer is. According to Grubb, “a really good operator will get 285 days out of the year uptime, a really good operator. It’s not unusual for production to be down in the 50% – 60% range.” A system that reduces downtime lowers cost. Grubb says this is only one of several “operational benefits.”
Grubb’s company, 4M, is a partnership between RMX Technologies (the owner of the plasma oxidation technology), oven-maker Litzler, and acrylic fiber producer Dralon. RMX developed the plasma oxidation technology as part of a collaboration with the US Dept. of Energy’s Oak Ridge National Laboratory that began in 2004.
4M has been running a small plasma oxidation oven for about 2 years. It is capable of producing 1 ton of CF per year. 4M has been oxidizing batches of precursor for a variety of CF producers, to demonstrate the efficacy of their system. The producers have been bringing in their own precursor, running it through 4M’s oven, and then performing the carbonization and surface treatment steps on their own equipment.
The tested results of these demonstration runs are not publicly available. 4M does this work under confidentiality agreements, the producers using it perform their own testing but don’t share it. However, Grubb is able to report in general about the that comes out of it. “They’re telling us that the fiber seems to be “better” and seems to be a stronger fiber.” Stronger, specifically, in terms of tensile strength. The system is making better fiber using the same precursor as conventionally-produced CF.
This gives rise to the other major cost-reduction expectations. The improved tensile strength appears to be caused by plasma oxidation acting more deeply into the thickness of the fiber. If it can make better fiber from the same precursor, could it make the same CF from a lesser-grade, less expensive precursor?
Most of the PAN that is made is textile grade, and costs about $1.50/lb. Higher-grade PAN, necessary for making acceptably strong CF in the conventional process, costs about $6.00/lb.
4M is working on the possibility of using something more like textile-grade PAN, and making up the performance difference through its more effective oxidation. “We are working with several of worlds’ leading PAN producers,” explains Grubb, “to validate that we can use textile grade PAN to make industrial grade CF. It’s never going to be aerospace grade. But we believe we can take a lower-grade precursor and make an acceptable CF. If we can use the textile precursor, we can cut the price half.”
They have even experimented with bio-based precursor sources. “We’ve processed a lignin fiber and converted it to CF. It was more of a mat. That’s been done before, but using conventional technology, they were taking 10 hours to process the kind of mat we processed in 2 hours.”
The commercial roll-out of plasma oxidation technology is probably not very far off. “We’ve been running the 1-ton machine for a couple years,” Grubb says. “Now the question is, is it scalable? We’re building a 175-ton machine now. It will be operational in about a year.”
True industrial-level production will require a 1500-ton machine. It would cost about $6 million, consistent with cost of current tech for oxidation step.
“The projection for the auto industry is 3x-4x demand growth per year,” Grubb continues. “We’re being primarily driven by that. If the market really grows the way Composites World magazine is saying it will, there will be need for a minimum of 100 new production lines in the next decade, if there’s no reduction in cost. If there’s a significant cost reduction, we could need as many as a thousand new lines.”
And of course, if the cost comes down, architectural applications may well increase, driving demand even higher. CF may lose its chic, but its performance will still be every bit as cool.