During the National Meeting & Exposition of the American Chemical Society (ACS), researchers from Washington State University presented findings that reveal that a new approach to turning lignin into carbon fiber to produce a lower-cost material strong enough to build car or aircraft parts.
Originally, Oak Ridge National Lab (ORNL) tested lignin but found that it could not produce fibers without “chainstoppers” that reduce the molecular weight of the polymer and ultimately make the fibers brittle and weak. Therefore, ORNL decided to use a lower grade of polyacrylonitrile (PAN) precursor to carbon fiber. However, while expensive, PAN-based carbon fiber is coarser and therefore suitable for applications that are more demanding that what glass can provide, but not quite as demanding as aerospace-grade CFRP.
WSU’s new research, however, outlines a different approach. To develop a strong, yet cheaper carbon fiber, Birgitte Ahring, Ph.D., and her team mixed lignin with PAN in varying amounts so that the weaker carbon fibers made with lignin are reinforced by PAN carbon fibers. The team melded the polymers together into a single fiber using a process called melt spinning.
“You elevate the temperature of the polymer blend until it melts, so it can flow,” says Jinxue Jiang, Ph.D., another member of the team. “Then, you spin these polymer melts until the fiber forms.”
Using a variety of methods, including nuclear magnetic resonance spectroscopy, calorimetry and electron microscopy, the researchers evaluated the fibers’ structural and mechanical characteristics. They found that they could get away with as much as 20-30 percent lignin without sacrificing strength. The lignin carbon fibers could, the researchers say, have automobile applications such as internal parts, castings and tire frames.
The researchers say their next step will be taking their fibers to an automobile manufacturing plant to test their strength in a real-world scenario.
“If we can manage to get a fiber that can be used in the automobile industry, we will be in a good position to make biorefineries more economically viable, so they can sell what they usually would discard or burn,” Ahring says. “And the products would be more sustainable and less expensive.”