Development and evaluation of 3D printable conductive inks using F-MWCNTs/MWCNTs for direct ink writing of electronic circuits

Direct ink writing (DIW) is a flexible 3D printing technique used to create electrical components using specialized inks. The present work focuses on the formulation of functionalized multi-walled carbon nanotube (F-MWCNT)/ multi-walled carbon nanotube (MWCNT) conductive inks for the fabrication of electronic circuits using the DIW technique. The process of acid-functionalization of MWCNTs with nitric acid has been discussed. The acid-functionalization of MWCNTs introduces carbonyl (C=O) and hydroxyl (–OH) groups, attributed to carboxyl (–COOH) groups on their surfaces, as confirmed by Fourier transform infrared analysis. The functionalized MWCNTs show less entanglement between them, and the enhanced structural order is obtained as confirmed by scanning electron microscopy and X-ray diffraction, respectively. The stepwise formulation of inks with F-MWCNT/MWCNT concentrations ranging from 1 to 3% by weight has been presented. Rheological characterization showed that the inks formulated exhibited shear-thinning behavior, making them satisfactory for application in DIW. The electronic circuits were successfully printed, and F-MWCNT ink (3 wt.%) exhibited the highest electrical conductivity of 2.11 × 10^–2 S/cm, while the MWCNT ink (1 wt.%) had the lowest electrical conductivity of 2.73 × 10^–3 S/cm. The results indicated that the F-MWCNT has uniform dispersion in the polyvinyl alcohol (PVA) matrix, leading to superior electrical conductivity compared to the pristine MWCNT case.