WOOD WASTE-DERIVED ORGANOSOLV LIGNIN-BASED CARBON FIBERS FOR ENERGY STORAGE APPLICATIONS

Abstract

This study examined the feasibility of recycling wood waste to produce organosolv lignin suitable as a precursor for carbon fibers. Mixed wood waste, pine, and elm sawdust were used as feedstock. Lignin was isolated using an organosolv method with a mixture of formic and acetic acids, which reduced the use of aggressive reagents and facilitated environmentally friendly biomass processing. The structural, morphological, and thermal properties of the resulting lignin samples were analyzed using scanning electron microscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analysis, and Raman spectroscopy. The isolated lignin contained aromatic, phenolic, hydroxyl, methoxyl, and methyl functional groups. Nuclear magnetic resonance spectroscopy revealed a predominance of syringyl structural fragments over guaiacyl ones, indicating favorable thermal stability for subsequent carbonization. Composite fibers were fabricated from the resulting lignin using polyacrylonitrile as the electrospinning polymer. The influence of the spinning solution composition and heat treatment conditions on the fiber morphology and structure was studied. A lignin to polyacrylonitrile ratio of 30:70 proved optimal, ensuring the production of continuous, defect-free fibers with an average diameter of approximately 97 nm. After carbonization at 800 °C under a nitrogen atmosphere, carbon nanofibers with an average diameter of approximately 47 nm and a developed porous structure were obtained. These results demonstrate the potential of organosolv lignin obtained from wood waste as a renewable precursor for carbon nanofibers and electrode materials for energy storage systems. The carbonized fibers exhibited a developed specific surface area of 549.7 m2/g, while the sample carbonized at 800 °C showed the highest electrochemical performance, with a specific capacitance of 136.4 F/g for supercapacitors and a discharge capacity of 797 mAh/g for lithium-ion batteries.