Stepwise fractionation extracted lignin for high strength lignin-based carbon fibers

Lignin is a low-cost and sustainable alternative precursor for manufacturing carbon fibers (CFs). However, the properties of lignin-based CFs are inferior due to the heterogeneity and complex three-dimensional structure of lignin. In this work, a facile stepwise fractionation extraction method is devised to extract lignin. This stepwise fractionation extraction method effectively removes the small molecular branching structure of lignin, thus obtaining fractionated lignin with a high molecular weight, narrow polydispersity index, and linear structure. Based on the results of XRD and Raman spectroscopy, the high molecular weight, narrow polydispersity index, and linear structure are conducive to improving the graphitization degree of CFs. Compared with the lignin-based CFs from original lignin, the tensile strength and Young's modulus of the lignin-based CFs from the fractionated lignin increase significantly, extraordinarily approaching those of PAN-based CFs. This facile stepwise fractionation extraction method for lignin is promising for the industrial production of high performance lignin-based CFs.