Water-Based Production of Carbon Fibers from Lignin and Alginate

Lignin, a promising precursor of low-cost carbon fibers, faces a significant challenge for environmentally friendly processing: Kraft lignin’s insolubility in water. To address this issue, the enzyme Bilirubin oxidase from Bacillus pumilus has been employed to modify lignin’s solubility. This treatment results in aqueous solubilization and condensation, evidenced by a nearly 5-fold increase in molecular weight. Crucially, the carbon content after pyrolysis remains intact, which is essential for carbon fiber production. Consequently, this modified lignin is well-suited for carbon fiber manufacturing. In this study, a solution of the treated lignin and alginate, acting as a plasticizer, was wet-spun into calcium chloride and ammonium persulfate baths, producing fibers composed entirely of biopolymers. Following carbonization, without the need for a stabilization step, the resulting fibers exhibited mechanical properties that compared with the properties of fibers produced in organic solvents or with oil-based plasticizers. The optimal mechanical properties were achieved with 67% lignin content, yielding a Young’s modulus of 39 ± 6 GPa and a tensile strength of 457 ± 54 MPa. These findings demonstrate the successful development of 100% bio-sourced fibers under environmentally friendly conditions.