“By recycling carbon fiber waste, you are preserving that entrained energy that is already invested in the primary fiber. That makes economic sense,” says Gledhill. When carbon fiber composite waste goes into a landfill, you lose that entrained energy and have downstream environmental costs.
Reclaimed carbon fibers retain most of their mechanical properties. After pyrolysis, carbon fibers show only a four percent reduction in tensile strength and a two percent reduction in tensile modulus, according to Gledhill.
But recycled carbon fibers differ in one significant way from virgin carbon fibers; the reclaimed fibers are short and discontinuous, rather than continuous. That limits their use in some applications.
“But it also opens up a whole new world of different products that can use short fiber,” says Gledhill. “For example, ELG takes our short fiber and runs it through a carding line [which aligns the fibers] to make a non-woven mat. That is a completely new product that is being brought to market, and that non-woven mat can be substituted in some cases for primary prepreg material or sheet molding compound, which are made from primary fiber.”
Allred says one way to improve the usefulness of reclaimed carbon fiber would be finding a way to align the short carbon fibers. “That would produce a volume fraction up around 50 percent, essentially doubling your mechanical properties,” he adds.
Developing new manufacturing methods could lead to the creation of new, high-value-added products that incorporate these reclaimed fibers, says Ozcan. One IACMI project team is currently working to develop a process and the necessary equipment to align these recycled short carbon fibers. For another project, IACMI is working with BASF, ORNL and the University of Tennessee, Knoxville, to develop high-volume, high-speed processing and material technologies that use short carbon fibers to produce automotive body panels with a Class A surface appearance and the necessary mechanical properties.
Glass Fiber Challenges
Carbon fiber recycling is paving the way to explore fiber recovery technologies that may benefit glass fibers in the future. There have been several attempts made at glass fiber recycling, but it’s met with less success than carbon fiber recycling because of the business model needed to support a fiber recovery program. There is a much greater need, however, as more than 90 percent of the world’s composites are made with glass fibers.