Cheap coal and waste plastics valorized to carbon fibers

Carbon fibers (CFs) are advanced materials that benefit various applications, including light-weight components for aircraft, automobiles and wind turbine blades. At present, the predominant feedstock is expensive polyacrylonitrile. A team of scientists used cheap coal and waste plastics to produce liquefied coals, which were subsequently fabricated into general-purpose and high-performance carbon fibers. This process has the potential to decrease the price of CFs and contribute to environmental and economic sustainability. Their work is published in Industrial Chemistry & Materials on October 3, 2025.

To produce carbon fibers, liquefied coal is a less-expensive alternative to polyacrylonitrile, as its heavier fractions can be melt-spun into CFs. This material features high carbon content, and its polyaromatic structure lends itself to being heat-treated into the graphitic structures of CFs. Coal liquefaction requires a solvent, and the most commonly-used solvents are hydrogenated oil from coal liquefaction or petroleum refineries.

Dr. Eddings, a corresponding author and a professor at University of Utah, said, “to avoid the costly use of these solvents and to address a significant environmental concern, our team proposed using hydrogenolyzed waste plastics as the solvent. The solvent becomes part of the liquefied coal mixture that is subsequently fabricated into CFs. In this manner, the expense and complexity of solvent recycling is also avoided.”

The team used high-density polyethylene (HDPE) to demonstrate the approach of using a plastic-derived solvent for the liquefaction of coal for CF production. The HDPE was hydrogenolized into a solvent that was then mixed with Utah Sufco coal at a solvent-coal mass ratio of 1:1. The liquefied coal was separated into different fractions, and the heaviest of these were thermally treated to yield the desired mesophase content. Different thermal upgrading conditions were tested, and three mesophase coal-plastic liquid (MCPLs) were produced. Each of them was melt-spun into one category of fresh CFs and were subsequently carbonized into one bundle of CFs at 1500 ℃. The spinning conditions were controlled to minimize the diameters of the fresh CFs. It was found that one bundle of CFs had the smallest diameter (10.8 μm), the highest Young’s modulus, and tensile strength (194 and 0.85 GPa, respectively). That corresponding category of fresh CFs was then heat-treated using an optimized stabilization temperature and prolonged carbonization time at 1500 ℃. The diameter, Young’s modulus and tensile strength of the resulting CFs were 11.7 μm, 238 GPa, and 1.15 GPa, respectively, consistent with general-purpose CFs (GPCFs). These CFs were subsequently graphitized at 2800 ℃, and the diameter, Young’s modulus and tensile strength were 8.2 μm, 759 GPa, and 4.03 GPa, respectively, identifying them as high-performance CFs (HPCFs).

Dr. Fan, a corresponding author and a professor at University of Wyoming, said, “This research demonstrated that a liquid derived from hydrogenolyzed plastics can successfully function as a solvent for coal liquefaction, and that the heavier fractions of the liquefied coal/plastic mixture can be fabricated into CFs.”

The next step of this research is to use real-life waste plastics to produce solvents, and during liquefaction, we should investigate lower temperatures and hydrogen pressures, and also research different coal types. The potential applications will be in manufacturing industries, including automobile, aerospace, sporting equipment and wind turbine blades.

The research team includes Zhe Chen (first author), Tongtong Wang, Sean Tang, Sabin Gautam, Nilay Saha, Piumi Samarawickrama, So Tie and Maohong Fan (corresponding author) from University of Wyoming; Wenjia Wang and Eric Eddings (corresponding author) from University of Utah.

This research is funded by the United States Department of Energy.

Industrial Chemistry & Materials is a peer-reviewed interdisciplinary academic journal published by Royal Society of Chemistry (RSC) with APCs currently waived. ICM publishes significant innovative research and major technological breakthroughs in all aspects of industrial chemistry and materials, especially the important innovation of the low-carbon chemical industry, energy, and functional materials. Check out the latest ICM news on the  blog.