During a recent visit to Oak Ridge National Laboratory (ORNL), we spoke with Cliff Eberle, Technology Development Manager of the lab’s Polymer Matrix Composites Division. Among the many topics we discussed was the launch* this year of ORNL’s Carbon Fiber Composites Consortium, which lists among its goals the development of carbon fiber for use in automotive applications. Key to this goal is the task of making carbon fiber cheaper. The Automotive Composites Consortium estimates that in order for the material to be a feasible solution for widespread automotive use its price needs to fall between $5/lb and $7/lb ($11/kg and $15.40/kg), about half of today’s selling price.

Production of the material involves a complex process. It begins with putting a carbon-fiber precursor – typically polyacrylonitrile (PAN), a derivative of petroleum, although rayon and pitch are occasionally used – through a series of mechanical, thermal, and chemical processes. According to Cliff, the PAN precursor contributes 43% of the final carbon fiber price, thus offering ample opportunity to reduce costs by utilizing alternative cheaper precursors. ORNL is currently exploring precursors composed of textile-grade PAN, polyolefins, and lignin.

Portuguese acrylic-fiber manufacturer FISIPE supplies ORNL’s textile-grade PAN, which is 30% cheaper than standard PAN. While the textile PAN’s quality would be insufficient for high-performance applications like aerospace, Cliff said that it has already surpassed its automotive mechanical performance targets of 250 ksi (1.72 GPa) tensile strength and 25 Msi (172 GPa) modulus. Its biggest drawback thus far, however, has been significant batch-to-batch variability in mechanical properties.

The second alternative precursor ORNL is researching is fibers based on polyolfefins, which are less expensive than PAN. What’s more, due to their higher carbon content – 86% for polyethylene vs. 68% for PAN – polyolefins offer a higher yield from precursor to fiber. Traditionally, the biggest hurdle encountered when using this precursor has been the required sulfonation step that requires several hours of processing time. But Cliff said ORNL has demonstrated its process can work in less than one hour at pilot scale. However, the Laboratory has yet to reach the required mechanical properties using this precursor.

While both PAN and polyolefins are petroleum derivatives, ORNL is also developing a carbon fiber synthesis process from a lignin-based precursor. This method has the potential to be the cheapest, as it is based on an inexpensive, plentiful, and renewable resource. But it is also the least far along in development. Lignin is a much more complex molecule than PAN or polyolefin, and there is no commercially available source – though ORNL believes that sufficiently pure lignin could be readily extracted from pulp mills and biorefineries.

Comparatively lower strength and modulus requirements for automotive applications have enabled ORNL to pursue cheaper precursors. But reducing raw material costs is just one piece of the puzzle for broader adoption of carbon-fiber reinforced plastic (CFRP). Manufacturing composite parts consists of several additional steps, including preforming, molding, curing, cooling, and then trimming before final assembly (see the report “Chasing Cars: Can Composites Catch Up to Steel?“)*. Cycle times vary widely, but even the quickest of processes require several minutes – orders of magnitude longer than those used for steel, as metal stamping takes just seconds. Additionally, most molding processes suffer from much higher variability than the stamping and forming processes used for steel. In order for CFRPs to be a viable option beyond niche high-performance and electric vehicles, these production throughput and consistency issues will also need to be addressed.

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During a recent visit to Oak Ridge National Laboratory (ORNL), we spoke with Cliff Eberle, Technology Development Manager of the lab’s Polymer Matrix Composites Division. Among the many topics we discussed was the launch* this year of ORNL’s Carbon Fiber Composites Consortium, which lists among its goals the development of carbon fiber for use in automotive applications. Key to this goal is the task of making carbon fiber cheaper. The Automotive Composites Consortium estimates that in order for the material to be a feasible solution for widespread automotive use its price needs to fall between $5/lb and $7/lb ($11/kg and $15.40/kg), about half of today’s selling price.

Production of the material involves a complex process. It begins with putting a carbon-fiber precursor – typically polyacrylonitrile (PAN), a derivative of petroleum, although rayon and pitch are occasionally used – through a series of mechanical, thermal, and chemical processes. According to Cliff, the PAN precursor contributes 43% of the final carbon fiber price, thus offering ample opportunity to reduce costs by utilizing alternative cheaper precursors. ORNL is currently exploring precursors composed of textile-grade PAN, polyolefins, and lignin.

Portuguese acrylic-fiber manufacturer FISIPE supplies ORNL’s textile-grade PAN, which is 30% cheaper than standard PAN. While the textile PAN’s quality would be insufficient for high-performance applications like aerospace, Cliff said that it has already surpassed its automotive mechanical performance targets of 250 ksi (1.72 GPa) tensile strength and 25 Msi (172 GPa) modulus. Its biggest drawback thus far, however, has been significant batch-to-batch variability in mechanical properties.

The second alternative precursor ORNL is researching is fibers based on polyolfefins, which are less expensive than PAN. What’s more, due to their higher carbon content – 86% for polyethylene vs. 68% for PAN – polyolefins offer a higher yield from precursor to fiber. Traditionally, the biggest hurdle encountered when using this precursor has been the required sulfonation step that requires several hours of processing time. But Cliff said ORNL has demonstrated its process can work in less than one hour at pilot scale. However, the Laboratory has yet to reach the required mechanical properties using this precursor.

While both PAN and polyolefins are petroleum derivatives, ORNL is also developing a carbon fiber synthesis process from a lignin-based precursor. This method has the potential to be the cheapest, as it is based on an inexpensive, plentiful, and renewable resource. But it is also the least far along in development. Lignin is a much more complex molecule than PAN or polyolefin, and there is no commercially available source – though ORNL believes that sufficiently pure lignin could be readily extracted from pulp mills and biorefineries.

Comparatively lower strength and modulus requirements for automotive applications have enabled ORNL to pursue cheaper precursors. But reducing raw material costs is just one piece of the puzzle for broader adoption of carbon-fiber reinforced plastic (CFRP). Manufacturing composite parts consists of several additional steps, including preforming, molding, curing, cooling, and then trimming before final assembly (see the report “Chasing Cars: Can Composites Catch Up to Steel?“)*. Cycle times vary widely, but even the quickest of processes require several minutes – orders of magnitude longer than those used for steel, as metal stamping takes just seconds. Additionally, most molding processes suffer from much higher variability than the stamping and forming processes used for steel. In order for CFRPs to be a viable option beyond niche high-performance and electric vehicles, these production throughput and consistency issues will also need to be addressed.

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