Researchers at the Massachusetts Institute of Technology, in conjunction with other institutions including the Oak Ridge National Laboratory in Tennessee, recently detailed a process for producing lower-cost carbon fibers. Rather than using high-value precursors such as polyacrylonitrile, which can account for around 60% of the value of finished fibers, they instead turned to petroleum pitch.
Described by MIT research scientist Nicola Ferralis as the ‘dregs’ left over at the end of the oil refining process, pitch is a hodgepodge of mixed heavy hydrocarbons. “That’s actually what makes it beautiful in a way,” she said, “because there’s so much chemistry that can be exploited. That makes it a fascinating material to start with.” A similar material, coal pitch, which can be sourced from coking of coal for use in industries such as steel production, was also used in the research.
Working in collaboration with researchers at Oak Ridge National Laboratory, who have extensive expertise in manufacturing carbon fibers under a variety of conditions, from lab scale all the way up to pilot-plant scale, the team set about finding ways to predict the performance of pitch as a precursor for fiber production.
As it turned out, “The process that you need to actually make a carbon fiber [from pitch]is actually extremely minimal, both in terms of energy requirements and in terms of actual processing that you need to do,” said Ferralis.
Graduate student Asmita Jana explained that pitch is made of a heterogeneous set of molecules with properties that should vary dramatically – the exact opposite of what is needed in a consistent material for industrial use.
However, by using molecular dynamic simulation to model the ways bonds form and cross-link between the constituent molecules, Jana was able to develop a way of predicting how a given set of processing conditions would affect the resulting fiber properties. “We were able to reproduce the results with such startling accuracy,” she said, “to the point where companies could take those graphs and be able to predict characteristics such as density and elastic modulus of the fibers.”
The research found that density, followed by alignment and functionality of the molecular constituents dictated the mechanical properties of finished fibers more strongly than the size and shape of the molecular constituents.
Impressively, the research showed that not only could fibers be produced at a much lower cost than currently, but by adjusting the starting conditions when processing the pitch, fibers with isotropic properties could be created. This was achieved by carefully controlling the density of the carbon fibers during production, which maximized the interconnected bonding between the molecules.
The full paper detailing the research has been published in Science Advances.