Paper-making waste could slash carbon fiber costs 25% while cutting petroleum use

Carbon fiber made with waste lignin could reduce reliance on petroleum-derived materials while cutting production costs by 25%, according to engineers at Washington University in St. Louis.

The researchers developed a carbon fiber precursor that replaces half of the petroleum-based polyacrylonitrile, or PAN, traditionally used to make the material. They also added single-walled carbon nanotubes to improve the fiber’s internal structure and mechanical performance.

Carbon fiber is widely used because it combines high strength with low weight. It is used in cars, aircraft, wind turbines, sports equipment, and other applications where reducing weight without sacrificing strength is important.

But conventional carbon fiber production depends heavily on PAN, a synthetic polymer derived from petroleum. PAN can account for as much as half of the total manufacturing cost, while producing and processing petroleum-based materials adds to the carbon footprint.

Waste material replaces petroleum

The new approach uses lignin, a renewable biopolymer generated as a byproduct of paper production and biorefineries. It is one of the most abundant natural polymers on Earth, but large quantities are typically treated as waste or burned for energy.

By incorporating lignin into the carbon fiber precursor, the researchers reduced PAN use by 50%. The resulting process also reduced production costs by 25% and substantially lowered carbon emissions, according to the team.

However, replacing PAN alone was not enough. Carbon fiber used in demanding applications needs a highly organized internal structure to deliver the required mechanical properties.

The researchers addressed that problem with single-walled carbon nanotubes. The nanotubes act like nanoscale rebar inside the polymer mixture, helping guide the arrangement of crystals as the precursor is converted into carbon fiber.

“Crystallization alignment is critical for carbon fiber quality,” Joshua Yuan, the Lucy & Stanley Lopata Professor and chair of energy, environmental and chemical engineering at WashU McKelvey Engineering, said.

Nanotubes guide stronger fibers

The researchers first developed a nanotube template that could mix with lignin and PAN while promoting crystallization and molecular alignment.

The resulting precursor solution was then processed through wet spinning, in which the material is extruded through small openings to form fibers. The fibers underwent tension-assisted heat treatment before a final optimized carbonization step converted them into carbon fiber.

The three-stage process increased the amount of crystalline material while the nanotubes helped orient those crystals. The researchers say this produced a highly aligned structure capable of meeting quality requirements for automotive applications.

“All these together allow us to create lignin-based renewable carbon fiber that has highly aligned crystalline structure,” Yuan said.

The approach could make carbon fiber more accessible to applications where its cost has been a barrier. Automobiles are one potential market, but the material could also be used in wind turbines, sports equipment, aerospace components and energy infrastructure.

The researchers describe automotive manufacturing as an initial target because vehicles can benefit from lightweight structural materials. Lower-cost carbon fiber could also expand its use beyond high-end applications.

The work demonstrates a way to combine a renewable waste material with nanoscale reinforcement rather than simply substituting one material for another. It also shows how controlling the internal structure of a fiber can compensate for changes in its chemical composition.

“For the first time, this allows us to create renewable carbon fiber that reaches the high standard of quality used in automobile manufacturing,” Yuan said.

The research was published in the journal*Matter*.