Reinforcement of lignin-based carbon fibers with functionalized carbon nanotubes

In an effort to increase the mechanical properties of lignin-based carbon fibers, carbon nanotubes grafted with lignin (CNTs-g-L) were synthesized by grafting lignin molecular chains onto the surface of CNTs to improve the interfacial adhesion between CNTs and lignin chains. The addition of CNTs-g-L improved the melt spinnability of lignin, and continuously spooled Lignin/CNTs-g-L melt spun fibers and their carbonized fibers were obtained. The interaction between CNTs-g-L and lignin phases improved the thermal stability of lignin but disordered the graphitic structure of lignin-based carbon fibers. The well-orientated CNTs-g-L increased the tensile strength of lignin-based carbon fibers from 171.2 MPa to 289.3 MPa when 0.5% CNTs-g-L was incorporated. However, due to voids generated by the breakage of chemical links in the functionalized CNTs, the tensile strength of carbon fibers obtained thus decreased with further increases in the CNTs-g-L content.