Low cost carbon fibre breakthrough

While its properties might be considered premium, so too is the price tag associated with carbon fibre production and processing, making the lightweight material out of reach of the mass market. James Bakewell finds out if this is about to change?

Oak Ridge near Knoxville in Tennessee was founded with innovation in mind. In 1941 the city didn't exist, but by 1945 it had a population of 75,000 and was the largest of three sites in the USA working on the Manhattan Project, which yielded the world’s first nuclear weapons.

Oak Ridge National Laboratory (ORNL) was established in 1943 and has a proud tradition of developing world changing technologies for more peaceful purposes. Now, with the help of its researchers, the US Department of Energy (DoE) and a three time Tour de France winner – it could become famous for affordable carbon fibre.

ORNL is a founding partner in the Institute for Advanced Composites Manufacturing Innovation (IACMI), a $259 million public-private partnership established in 2015 with the goal of accelerating the development and adoption of technologies for the low cost, energy efficient manufacture of advanced polymer composites for vehicles, wind turbines and compressed gas storage.

In 2013, ORNL, The Ford Motor Company and Dow Chemical opened the Carbon Fiber Technology Facility (CFTF) in Oak Ridge. Supported by a $35 million DoE grant, the 3900m2 complex features a 120m meltspun fibre line to produce raw fibre materials. The facility also features a thermal conversion line that can produce 25 tonnes a year of polyacrylonitrile (PAN) based fibre and can convert both melt-spun and solution-spun precursors.

Over the summer, a process developed at the CFTF made the leap from laboratory to industry, and it could have a profound effect on how carbon fibre is used.

LeMond Composites – established by former professional cyclist and entrepreneur Greg LeMond – has licensed the technology that it claims could reduce the cost of carbon fibre by as much as 50%, and the energy used in its production by more than 60%.

LeMond says: “As a result of the affordability of this carbon fibre we believe that worldwide mass adoption will be inevitable.”

The company plans to launch its first product in 2018. Amit Naskar, one of the inventors of the technology and the group leader for carbon and composites at ORNL's Materials Science and Technology Division, says: “Carbon fibre manufacturing using PAN-based precursors is well-known and it has been practiced by industry for several decades. Most of the industrial carbon fibre manufacturers have their own established chemistry for precursor fibres and those are well-optimised.

“In this particular case ORNL successfully produced carbon fibres from an industrial textile fibre that was not intended to be used as carbon precursor.”

The resulting fibres demonstrate tensile strength, tensile modulus and strain-to-failure values exceeding 2.8 GPa, 275 GPa, and 1%, respectively—meeting the performance criteria set out by many automotive manufacturers for the high-volume production of carbon fibre-reinforced plastic (CFRP) parts.

Less than 5% of the PAN fibre produced globally is used for the production of carbon fibre, with the balance being used by textile industry. Textile-grade PAN is a commodity product and is therefore significantly cheaper than high-quality PAN, and it is readily available from a variety of global suppliers. However, producing carbon fibres with usable properties from this precursor is challenging, and their ultra-large tow format (300–610 k compared with 12–24 k) makes them fragile and difficult to handle.

Over the last ten years or so, ORNL – together with partners such as Portuguese acrylic fibre manufacturer Fisipe (which has been acquired by BMW’s carbon fibre partner SGL Group) – has been working to overcome these same problems.

With a Provisional Patent Application (62/273,559) in the works, Naskar is understandably cagey with regards to the specifics of how the technology works, and how it delivers the reported cost and energy savings.

Generally speaking, however, he says these savings result from a combination of factors: the precursor types; the processing of the precursors; the volume throughput (presumably owing to the large tow count); and the oxidation and carbonization operations used.

During the oxidation stage of carbon fibre production polymer materials are oxidized (or stabilized) before carbonisation. The thermoplastic precursor is converted to a thermoset material that can no longer be melted. Oxidation is the most time-consuming phase of the multistep carbon fibre conversion process.

An example of the kind of oxidation process that LeMond might use can be seen in another technology licensed by ORNL this year, in this instance to RMX Technologies.

A co-inventor of this plasma-based oxidation process, ORNL researcher Felix Paulauskas, says: “In conventional systems, it generally takes between 80 and 120 minutes for oxidation. We found a way to cut the time by a factor of 2.5–3 times, so we can process fibre in 25–35 minutes.”

Compared with conventional oxidation techniques, the team’s plasma technology reduces unit energy consumption by 75% and lowers production costs by 20%, while maintaining or improving the quality of the resulting carbon fibre.

Naskar says that ORNL has not demonstrated the weaving of the low-cost carbon fibre as of yet. What he does say, however, is: “The material was used in chopped fibre composites and stitch bonded composite manufacturing. Those composites exhibit equivalent properties. Also, the processors will have the potential to develop new fibre handling methodologies.”

One such processer is Chomarat, which is working on the development of non-crimp fabrics using heavy-tow (457k) carbon fibres from ORNL. Through the development of one of its core products, C-Ply, the company has experience of using large-tow (50k) carbon fibre to make lightweight fabrics (100 g.m-2) with virtually no defects.

LeMond now plans to build its first carbon fibre line at its premises adjacent to the CFTF in Oak Ridge, and is in discussions with a number of carmakers.

Will the venture be a success? ORNL certainly has the pedigree, and Greg LeMond's background as an elite athlete suggests that he is unaccustomed to failure.

He concludes: “Our close proximity to ORNL adds a value beyond measure and we are looking forward to future collaborations with them. Additionally, with the input of the University of Tennessee, IACMI and the emerging composites corridor, I believe the Knoxville area will become the world hub for carbon fibre in the future.”

James Bakewell

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