The process used for producing lignin-based carbon fibers is illustrated in Figure . The first step is the pretreatment of lignin, which includes purification, refining, additional modification, and blending. Pretreatment is an essential step for making lignin spinnable. Pretreated lignin is converted into fibers by spinning, such as melt-spinning, solutionspinning, or electrospinning. Before melt-spinning (the most common method of lignin extrusion), pelletization of lignin is recommended to improve its spinnability. Then, the fiber is subjected to thermostabilization, which reduces the thermoplastic behavior of lignin. After that, the fibers are carbonized to induce mechanical, electrical, and thermal properties .