Microstructural optimization of lignin‐based carbon fiber: Effects of purification and high‐temperature heat treatment

Abstract Lignin is a renewable biomass polymer with a carbon content of more than 60% and has been extensively studied for making lignin‐based carbon fibers (CFs). However, impurities and high carbohydrate content in lignin materials severely limit their molding in melt spinning, and pre‐oxidation and carbonization processes also affect the subsequent preparation of CFs. This paper presents a detailed study of lignin‐based carbon fiber preparation. Pretreatment increased lignin's decomposition temperature to 302.1°C and enabled melt‐spun fiber preparation. Then, pre‐oxidation and carbonization of lignin fibers were further discussed. The pre‐oxidized fibers prepared at 280°C and 0.4°C min −1 have high thermal stability and excellent carbonization performance. The lignin‐based carbon fibers (LCFs) prepared at 1100°C and 3°C min −1 have the highest degree of graphitization, and the surface is smooth without obvious holes. Under these conditions, LCFs have a graphitization degree of 1.50 and conductivity of 62.50 S cm −1 , making them suitable for sensors and capacitors. Highlights Effects of pretreatment on lignin structure and properties have been studied. Effects of pre‐oxidation and carbonization on the lignin fibers were studied. Lignin‐based carbon fibers with high conductivity were obtained.