Issue Date: September 26, 2011
Getting The Steel Out
The Lamborghini Sesto Elemento sports car, set to go into limited production late next year, will harness a powerful V10 engine to accelerate from zero to 60 mph in 2.5 seconds. Its cousin, the Gallardo LP 560-4 Spyder, takes 1.5 seconds longer to get up to that speed. The biggest difference between the two is that the Sesto is a carbon fiber car weighing in at just 2,200 lb. The aluminum-framed Spyder weighs a hefty 3,417 lb.
Buyers of the Sesto will benefit from corrosion-free composites similar to those that also fill out the frames of big planes such as the new Boeing 787 Dreamliner and the Airbus A350. Although most drivers can’t afford a Lamborghini—much less the $3 million Sesto Elemento—they may yet have their chance at buying an affordable carbon-fiber-based vehicle.
Automakers are increasingly looking to combine emission-limiting propulsion technologies with stiff, lightweight carbon composite frames. Their hope is that the new components will replace steel and aluminum in the assembly of energy-efficient hybrid and all-electric vehicles.
Not everyone thinks automakers will succeed with carbon fiber cars. Anthony J. Roberts, an expert in carbon fiber technology who heads AJR Consultant, argues that “a lot of the talk about automotive use of carbon fiber is hype” meant to make companies look environmentally responsible.
As Roberts points out, carbon fiber is expensive. It’s generally made by polymerizing the petrochemical acrylonitrile into polyacrylonitrile, or PAN. PAN is then extruded into fibers and carbonized in a high-tech oven. The fiber is next woven into a “preformed” part and then infused with epoxy or other resins.
Industrial-grade carbon fibers suitable for use in cars cost close to $30 per kg, Roberts says. High-end vehicle builders can afford expensive carbon fiber parts. “But how many people will really spend an extra $5,000 to $6,000 beyond the usual cost for a small car to own an electric car with a carbon composite body?” he asks.
Although Roberts is skeptical, several automakers are pushing ahead with plans to make carbon fiber composites an integral part of a new generation of electric cars intended mostly for inner-city use. They will be going beyond fiberglass composite body panels, already found in some cars, to create structural composite components that are now the province of metal.
In 2013, BMW plans to launch two mass-produced vehicles with carbon fiber composite passenger cages: the battery-powered i3, formerly known as the Megacity, and the hybrid i8, which can run on batteries or an internal combustion engine. Two years ago, the carmaker formed a joint venture with carbon fiber maker SGL Carbon to make carbon fiber parts for the i3 series.
Similarly, automaker Daimler started a joint venture earlier this year with Japanese carbon fiber producer Toray Industries to develop mass production techniques for carbon fiber-reinforced components. The partners plan to start producing parts for Mercedes-Benz passenger vehicles next year. Daimler has also hooked up with resins maker BASF to design an all-electric concept vehicle, the Smart Forvision, with a passenger cage and doors made of carbon fiber composites.
Audi, the high-end Volkswagen brand, plans to incorporate more carbon fiber into mass-produced cars. Earlier this year, Audi formed a partnership with Voith, a German machinery parts maker, to develop an automated process chain to make high-volume carbon fiber car parts.
Resin makers are also eager to get in on the action surrounding carbon fiber composites. Earlier this month, Huntsman Advanced Materials said it was launching a multi-million-dollar engineering study to expand its McIntosh, Ala., epoxy manufacturing facility so it can meet growing demand from composite makers. A few months ago, BASF invested more than $10 million in a research team to advance development of lightweight composites for the auto industry.
In June, epoxies producer Dow Chemical said it intends to form a joint venture with Turkish carbon fiber maker Aksa Akrilik Kimya Sanayii. Although the two firms have been light on details, automotive use of “carbon fibers and derivatives” is one of the opportunities behind their cooperative effort.
The U.S. government is also flexing its muscle to push carbon fiber technology. Oak Ridge National Laboratory has spent a decade on developing alternative carbon fiber feedstocks and lower energy fiber production processes. The lab is building a $35 million pilot carbon fiber facility and recently held the first meeting of a consortium intended to transfer technology developed at the lab to industry.
Consultant Roberts says automotive applications are now just a tiny portion of the industrial carbon fiber market, which he sets at roughly 16,000 metric tons per year. Total global fiber demand, including aerospace and sporting goods, is about 40,000 tons. He projects that overall fiber demand will nearly quadruple by 2020. Industrial fiber demand is likely to increase almost sevenfold to 105,000 tons.
However, much of the industrial growth, Roberts predicts, won’t come from the auto industry. More promising markets, he says, include turbine blades for offshore wind energy projects, compressed natural gas storage tanks, and components for deep-sea oil-drilling platforms. Big automakers have been looking at carbon fibers since the mid-1970s, he says, and have never really gotten serious about them.
But many automakers believe the time for automotive carbon fiber composites has come. Stefan Kienzle, who heads materials manufacturing at Daimler Research & Advanced Engineering, says that Daimler started to use carbon fiber composites a decade ago. “Today, we’re prepared for broader use,” he says. As Kienzle sees it, the three most important reasons to use carbon fiber composites are their light weight, their “safety potential,” and the reduction in the number of parts needed to assemble a car.
Less weight means lower vehicle energy consumption. Properly designed carbon fiber parts are so strong they will easily carry the weight of batteries and electric propulsion systems while also protecting passengers in the event of a crash. In addition, one composite component often can replace four metal components, reducing assembly time and cost.
Using Toray’s resin transfer molding process and Daimler’s auto production expertise, the partners expect to speed up composite part making and cut the $125-per-kg cost by more than half. That’s still much higher than the $7.00 per kg it costs to make a steel part. But add in cost savings from assembly and tooling and Daimler figures it can produce a competitively priced composite part.
The firm had another important reason to tie up with Toray: It needed a guaranteed source of carbon fiber, Kienzle says, and Toray is the top global producer. In the past, industrial-grade carbon fiber users have been left in the lurch as companies rushed to fill large orders for high-priced aerospace-grade fiber.
Although Daimler has produced carbon-fiber-based cars—the high-end Mercedes-Benz SLR McLaren is a notable example—carbon fiber’s use in mass production vehicles so far has been limited to nonstructural components.
Like Daimler, BMW expects to change that. When the German firm introduces the i series cars in 2013, they will contain carbon fiber drawn from a production line that stretches from PAN synthesis in Otake, Japan, to fiber production in Moses Lake, Wash., and woven preform manufacturing in Wackersdorf, Germany. SGL Automotive Carbon Fibers, BMW’s joint venture with SGL, has invested about $135 million so far in the facilities, according to Andreas Wuellner, one of two managing directors of the venture.
Both sides will benefit, Wuellner explains. SGL gets to deepen its involvement in the industrial carbon fiber sector, and BMW gets an ensured supply of fiber and textile preforms for car parts. The carbon fiber composite parts that BMW will manufacture in Landshut, Germany, will be 50% lighter than steel and 30% lighter than aluminum, Wuellner says.
The supply chain is long and a bit complex, Wuellner admits, but it has certain advantages. SGL joined with Mitsubishi Rayon, an established maker of PAN and carbon fiber, to build the Otake PAN plant. It will supply feedstock for the Moses Lake fiber plant, which will run on low-cost, renewable hydroelectric power. Transportation costs and environmental impact will be kept under control, he says, by shipping materials by boat and rail each step of the way from Japan to Germany.
Overall, the partners say, the emissions of the all-electric BMW i3, from manufacturing to the end of its life, will be one-third less than those of a comparable vehicle with a high-efficiency internal combustion engine. If the car were to consume electricity solely from hydropower or photovoltaic sources, emissions would be 50% less, they assert.
Resin makers such as BASF say they are working on technologies to speed up the curing of epoxy fiber parts. Christian Fischer, president of polymer research at BASF, says the company has developed specialty epoxies for the resin transfer molding process. The resins quickly and completely saturate a woven preformed part, preventing “dry areas that might negatively affect mechanical properties,” he says. Only then is the curing process initiated with heat.
Although thermoset epoxies are the most advanced of the resins used to create carbon fiber composites, BASF is also working on polyurethane and nylon systems. Fischer says thermoplastic resins are especially promising because they would facilitate end-of-life recycling of composite parts.
Huntsman, a significant supplier of epoxies for aerospace composites, has developed new epoxies suited for automotive parts, says Marketing Manager Klaus Ritter. “Our main focus is to speed the resin curing process,” he says, from 10 minutes to 60 seconds.
As chemical makers such as BASF and Huntsman look to improve the resins used in composites, others have been working on ways to reduce carbon fiber precursor and processing costs. For example, carbon fiber producer Zoltek has a project with papermaker Weyerhaeuser to turn low-cost lignin left over from paper production into a carbon fiber precursor. That project is slated to receive $3.7 million in financial assistance from the Department of Energy.
One of the longer-running efforts to lower the cost of carbon fiber has been going on at DOE’s Oak Ridge National Laborataory since the late 1990s. The lab has explored both the development of alternative fiber precursors and ways to lower fiber processing and carbonization costs. Achieving those goals would contribute to U.S. energy independence through such things as lighter-weight vehicles and high-performance windmill blades, says Tom Rogers, the lab’s director of commercialization strategy partnerships.
Cliff Eberle, composite materials technology development manager at Oak Ridge, tells C&EN that almost all carbon fibers today are made from PAN in a high-energy process. After fiber formation, about 50% of the fiber mass is lost during the carbonization treatment.
Among the projects the lab has worked on is the development of polyethylene-based precursors that contain more carbon by weight than PAN and are easier to process. The resulting fibers, which have about half the performance of PAN-based fiber, would be good for auto body panels but not structural components, Eberle suggests. However, the lab’s target is to develop higher-performing fibers for use in structural components.
Lignin precursors are plentiful, inexpensive, and not derived from oil, but are particularly challenging, he says, because the quality varies greatly “depending on the plant source, where the plant is grown, and the season of harvest.” PAN lends itself to making a good fiber, but “lignin is a complex molecule, and it is hard to get it to build the ladder structures we want,” he says.
Oak Ridge has also worked on technologies to reduce the time and energy needed to make carbon fiber by a factor of two or three, Eberle says. The use of plasma and microwave heat treatments could both speed up the process and lower overall processing costs, he says.
The Carbon Fiber Composite Consortium, which Oak Ridge lab managers created as a technology exchange and transfer organization, met with 26 members for the first time this month. Among the major fiber makers, SGL and the Toho Tenax division of Japan’s Teijin are members. Also members are U.S.-based carbon electrode maker GrafTech International and petrochemical maker Saudi Basic Industries Corp., which plans to build a carbon fiber plant in Saudi Arabia based on technology licensed from Italy’s Montefibre.
Dow and 3M are among the resin makers that have joined the consortium. The others are mostly parts manufacturers such as Advanced Composites Group and finished good suppliers such as office furniture maker Steelcase and French car seat maker Faurecia.
The consortium has its critics, however. Zsolt Rumy, president of Zoltek, says he is unconvinced of the benefit in joining. “We’ve made more progress on lignin precursor research in six months than the Oak Ridge Lab did over the last few years,” he contends.
Dee James (D. J.) DeLong, former general manager of BP Amoco Carbon Fibers, which was bought by Cytec Industries in 2004, says he is skeptical of efforts to develop alternative fiber feedstocks that require a lot of processing. He is even more leery of exotic microwave and plasma carbonization techniques, when electric furnaces suffice. DeLong’s company, DeLong & Associates, is now the U.S. carbon fiber distributor for Turkey’s Aksa.
Others are on the fence about taking part in the consortium. “We don’t see much there yet,” says Billy Harmon, R&D director for Cytec Carbon Fibers, which focuses mostly on aerospace-grade fiber. “But we are negotiating with them now and may join them in the future.”
If carbon fiber makers hope to gain more than a toehold in the auto market, they’ll have to make efforts on their own or with industry consortia to make composites more affordable. A lignin-based carbon fiber costing 30% less than PAN-based fiber would be an enormous breakthrough enabling even the most cost-conscious carmakers to use composites, Daimler’s Kienzle argues. “I think the chemical industry has to do more homework on the basic material for carbon fibers to bring costs down,” he says. ◾
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