No abstract

Lignin is considered as a promising bio-sourced precursor for more sustainable and low-cost carbon fibers (CFs). However, lignin-based CFs generally have a poor graphitic structure, compared to polyacrylonitrile CFs. In this paper, we present an original approach that uses graphene oxide liquid crystal (GOLC) as a templating agent to promote the formation of graphitic structure in the fibers at low carbonization temperature. Both lignin and hybrid lignin/GOLC CFs were carbonized/graphitized up to 2700 °C. Structural analyses by X-ray diffraction, Raman spectroscopy and electrical measurements manifest a significant improvement in graphitic structure and a preferred orientation of graphene planes for lignin/GOLC fibers. These effects are the result of axial propagation of the templated graphitic order nucleated by the large GO flakes. The current approach reveals the possibility of preparing low-cost lignin-based CFs with improved graphitic structure and high electrical conductivity at low temperature for electrochemical or smart textile applications.

Graphitic structures, unlike polymers and metals, cannot be directly printed in 3D. We demonstrate here that graphitic structures can be shaped in 3D by using direct-ink writing (DIW) of lignin-graphene oxide solutions that are then dried and carbonized. Lignin is a promising precursor for the elaboration of bio-based carbon materials because of its low cost, natural availability and high carbon content. The rheology of the inks is controlled by the presence of graphene oxide (GO) in order to make the solutions viscoelastic and printable. The GO flakes are found to align during ink extrusion. This behavior is understood by considering the applied extrusion shear stress and the yield stress of the inks. By adjusting the relative fraction of GO and lignin, it is possible to change the density, the graphitic order, and thus the electrical and mechanical properties of the printed materials. In particular, GO promotes not only graphitic order but also porosity. By contrast, high amounts of lignin allow preparing denser but less ordered carbon structures. The possibility to vary density and properties offers an opportunity for the development of graphitic 3D materials with tunable properties.