A green solvent system for conductive carbon inks – effects of cyrene/water ratio on print pattern definition and electrical performance

Mixtures of cyrene (a biobased, non-hazardous solvent) and water exhibit an enhanced ability to disperse carbon nanofibres, compared to either of the pure solvents. Furthermore, physical properties such as the viscosity and surface tension also strongly vary with the mixing ratio of the two components. These beneficial effects are utilised for the development of conductive inks with properties suitable for screen printing. The printing quality displays a distinct optimum for the 80:20 (w/w) cyrene/water mixture, which also exhibits the highest viscosity and dispersion stability. By contrast, the electrical performance of the printed structures is highest for the ink based on water alone. These findings highlight that there is no direct, straightforward correlation between macroscopic printing quality and functional performance of conductive inks based on these carrier media. Instead, the electrical properties are determined by the complex interactions between the ink components during the printing and drying processes, and by the resulting spatial distribution of the materials in the printed structures. The results indicate that cyrene/water mixtures have potential for functional ink formulations with reduced environmental footprints in application areas such as green printed electronics. • Cyrene/water mixtures are good dispersants for carbon nanofibres. • The mixtures produce more stable dispersions than either of the pure solvents. • They allow the formulation of functional carbon paste suitable for screen printing. • Ink viscosity and printing behaviour can be tuned by varying the cyrene/water ratio. • The electrical performance of the paste is strongly influenced by the solvent ratio.