Preparation of carbon fibers from a lignin copolymer with polyacrylonitrile

In this study, we have developed an economically viable and technologically sound process for the production of low-cost carbon fibers (CFs) made of lignin copolymer with acrylonitrile (AN). Initially, lignin, a by-product of the pulp and paper industry, is copolymerized with AN in dimethysulfoxide (DMSO) by the radical copolymerization. The resulting copolymer was confirmed by a Fourier transform infrared (FT-IR), 13C, and 1H nuclear magnetic resonance (NMR) spectroscopy, showing the presence of the CN group of polyacrylonitrile (PAN) co-eluting with ether, hydroxyl, and aromatic groups that are attributed to lignin. This provided evidence that a PAN–lignin copolymer was synthesized. Using a wet-spinning process, the PAN–lignin copolymers are then spun into fibers with an average tensile strength of 2.41 gf/den, a tensile strain of 11.04%, and a modulus of 22.92 gf/den. The CFs are prepared by the subsequent thermal treatment of the spun fibers. Differential scanning calorimeter (DSC) analysis of the PAN–lignin copolymer-based spun fibers displays a downshifted exothermic peak at 285.83 compared with the homopolymer PAN-based as-spun fibers, which provides evidence that lignin is cooperated with the oxidative stabilization reactions. The stabilized fibers are carbonized by heating from room temperature to 800 °C in a nitrogen atmosphere. This study shows the potential for a number of recycled and renewable polymers to be incorporated into wet-spun fibers for production of CF feedstocks, thereby reducing the supply cost using the current commercial technology.