High-performance carbon fibers fabricated from coal and waste plastics

Abstract

Carbon fibers (CFs) are valuable in applications such as aircraft, automobiles, wind turbines, and energy storage devices. However, the production cost of CFs is high due to the use of conventional precursor polyacrylonitrile, and an affordable substitute is imperative. For the first time, this work combined cheap coal and waste plastic material to fabricate CFs. Currently, conventional disposal methods for waste plastics lack sustainability and profitability. Despite its unpopularity as an energy source, coal can serve as a feedstock for chemicals and materials. High-density polyethylene (HDPE), a commonly used plastic, was hydrogenolyzed into a plastic-derived liquid (PDL). PDL served as an effective solvent during mild solvolysis liquefaction of coal, and the acquired coal–plastic liquid was modified into mesophase coal–plastic liquids (MCPLs). MCPLs were melt-spun and heat-treated into CFs through different heat treatment conditions. The diameters of the CFs were 8.2–45.8 μm, and the Young's modulus and tensile strength were 75–759 GPa and 0.54–4.03 GPa, respectively. The CFs belong to the categories of general-purpose and high-performance CFs. The high-performance CFs (diameter: 8.2 μm, Young's modulus: 759 GPa, and tensile strength: 4.03 GPa) are comparable to commercial and laboratory CFs whose precursors are coal–tar pitch featuring low coal-to-pitch yield, or coal liquefied by conventional, costly solvents. Analysis shows the PDL enhances hydrogen transfer, stabilizes radicals, and promotes mesophase development during thermal treatment. The mechanisms valorizing coal and plastics simultaneously to high-performance CFs are proposed. This work demonstrates a novel and sustainable valorization pathway for waste plastics and coals. Future work will explore industrial-scale plant design, techno-economic analysis, and life-cycle assessment to quantify the economic and environmental impacts.

Keywords: Environmentally unfriendly polyacrylonitrile; Valorization of waste plastic and coal; Low CO₂-emission; High-performance carbon fiber.