DoE advances lower-cost carbon fiber R&D

The U.S. Department of Energy is encouraging development of non-PAN-based carbon fiber to reduce material costs and help it move more substantially into the automotive market.

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Improving vehicle fuel efficiency is a major research priority in the U.S., where transportation systems are 95 percent dependent on petroleum-based fuels. Of the nation’s petroleum resources, roughly 55 percent are currently imported from abroad.

To reduce dependence upon foreign sources, the U.S. Department of Energy’s (DoE) National Energy Policy calls for an aggressive agenda to reduce petroleum demand through energy efficiency while increasing energy supply and diversifying sources. As part of DoE’s Vehicle Technologies Program, Oak Ridge National Laboratory (ORNL, Oak Ridge, Tenn.), its partners and the Automotive Composites Consortium (ACC, Southfield, Mich., one of eight consortia that form the United States Council for Automotive Research or USCAR) are working to replace steel in vehicles with carbon fiber composite material, a lighter polymer matrix composite that reduces vehicle weight and fuel demand. ORNL is also exploring the use of carbon composites in wind energy generation, oil exploration, power transmission, pressurized gas storage and solar energy collection, as well as multiple industrial applications. Key to developing high-performance composites for these industries is the prior development of less-expensive carbon fiber and composite production technologies.

The cost of carbon fiber is currently the largest impediment to using carbon fiber composites. In 2007, baseline studies of DoE’s carbon fiber research portfolio showed that industrial scale-up of conventional processes to very-high-volume production (ultralarge production lines) would still result in fiber cost of about $8/lb, using traditional carbon fiber-grade polyacrylonitrile (PAN) precursors. Petroleum-based PAN costs fluctuate with crude oil prices, which results in varying carbon fiber production costs. Because the precursor accounts for more than half the cost of fiber manufacturing, ORNL and partners are working with domestic pulp and paper producers and with current and future ethanol producers to use lignin and textile-based PAN alternatives that could reduce carbon fiber production costs to between $5/lb and $7/lb.

Lignin, a complex compound commonly derived from wood, costs significantly less than PAN and is largely independent of oil prices. When extracted in liquid form via kraft wood pulping, lignin requires purification before it is suitable for melt spinning into fiber, but the purification step might be reduced or eliminated when using lignin from ethanol production processes. The first sustained melt spinning of multifilament fibers from lignin took place at ORNL in 2007 over a period of many hours, without interruption. The demonstration represented a significant breakthrough in the development effort, most notably with respect to the excellent structural characteristics of the spun fibers.

Currently, lignin used for high-volume, lower-cost carbon fiber production is limited to kraft pulping of wood. Resources are expected to grow as biomass refineries come to fruition, producing lignin as the by-product of cellulosic ethanol. Ideally, lignin could help offset the high cost of producing cellulosic ethanol from biomass.
ORNL’s textile-based precursors, developed with Portugal’s FISIPE SA, a producer and distributor of textile acrylic fibers, are lower-cost, higher-volume fibers that demonstrate the potential to reduce carbon fiber cost by more than $2/lb, compared to typical carbon fiber-grade PAN, textile-based precursors. Due to similarities in processing textile-based and conventional precursors, the former could be incorporated into current production processes, offering potential cost savings to existing carbon fiber conversion facilities.

During its investigation of alternative precursors, ORNL has developed new processing technologies that improve efficiency and reduce carbon fiber costs. The work includes the design of an advanced oxidation reactor that enables higher-volume production and more rapid oxidation in a continuous and seamless process. During the process, PAN precursor fibers undergo advanced stabilization, using a thermochemical process, and then oxidize rapidly through a proprietary oxidation module. To date, oxidative stabilization time has been decreased to one-third that required by conventional thermal methods. ORNL researchers also have developed Microwave Assisted Plasma (MAP) technology that could replace the low- and high-temperature carbonization ovens in conventional use, processing pre-oxidized fiber at more than 160 inches/min.

Initial development of these advanced processing technologies is being conducted using conventional carbon fiber precursors. Plans include the integration of all advanced precursors and conversion processes so that there is an “advanced technology” line for conversion of either conventional PAN or alternative precursors, resulting in significant cost savings.

ORNL hosted the Workshop on Low Cost Carbon Fiber Composites for Energy Applications in March 2009, focusing on the commercialization of low-cost carbon fibers and carbon fiber-reinforced composites. This invitation-only event brought together manufacturers and end-users from several industries and throughout the carbon fiber composites value chain to adopt a national perspective and develop information on research, development and demonstration (RD&D) needs and strategies for government and industry to accelerate the introduction of low-cost carbon fiber composite technologies into the commercial marketplace.

The workshop generated recommendations for RD&D plans for the stakeholders, for appropriate roles of government and industry in the development and for application of lower-cost carbon fiber composites and programs to address the identified RD&D needs and strategies. Follow-up strategies and partnerships are being developed.