Additive Manufacture of Electrically Conductive Carbon Structures from Direct Ink Writing (DIW) and Laser-Induced Carbonization of Lignin-based Inks

Abstract

Sustainable additive manufacturing of electrically conductive carbon structures requires a renewable materials-based process that enables precise control over shape and conductivity. We report the additive manufacturing of conductive carbon films based on direct ink writing (DIW) followed by laser-induced carbonization of three lignin-based inks (α, β, and γ). The inks were characterized to assess viscosity, yield stress, and shear-thinning behaviour. Subsequently, printing parameters—substrate temperature, speed, and nozzle diameter—were selected to establish a stable processing window for DIW-ink processing. A systematic three-factor analysis of variance (ANOVA) was performed to assess the impact of these parameters on the geometry and electrical resistivity. Among the formulations, ink α demonstrated the most consistent extrusion and the lowest average resistivity ((2.6 $\pm 0.8)$×${10}^{-4}$ Ωm), indicating good electrical conductivity and print fidelity. The nozzle size significantly affected the printed width, whereas the temperature and speed ranges considered in the experiments had a negligible impact on the printed material properties. Raman spectroscopy reveals that the printed structures exhibit low defect levels and two-dimensional carbon peaks, indicating that the conductive carbon lines are composed of few-layer graphene. The hybrid manufacturing process of DIW and laser-induced carbonization with the optimized printing parameters (50–70 °C and 85–135 mm/s) yielded uniform, defect-free lines with the lowest electrical resistivity and is suitable for printing conductive carbon structures for sensing and energy storage applications.