Formulation of Bio-based Aqueous Digital Inks using Palm Kernel Oil and Jatropha Oil-derived Ethoxylates: Rheology, Dispersion Stability, and Print Performance

Abstract

This study evaluated aqueous digital inks formulated with nonionic ethoxylated surfactants derived from palm kernel oil (PKO) and Jatropha oil. The surfactants, previously optimised by fatty-alcohol ethoxylation, had hydrophilic-lipophilic balance values of 11.0 and 10.8, respectively, and were incorporated into pigment-based aqueous ink systems containing humectants, co-solvent, binder, biocide, and deionised water. Molecular-weight distribution, material-efficiency metrics, rheological behaviour, surface tension, zeta potential, pH, density, nozzle open-time, and print quality were assessed and compared descriptively with a commercial reference ink containing a synthetic surfactant. Gel permeation chromatography gave polydispersity indices of 1.05 for the PKO-derived ethoxylate and 1.08 for the Jatropha-derived ethoxylate. Based on the reported process mass balances, reaction mass efficiencies were 92.4% and 89.6%, while recalculated E-factors were 0.08 and 0.12 kg waste/kg isolated surfactant, respectively. Both ink formulations showed Newtonian flow within the tested shear-rate range, with viscosities of 8.42 ± 0.15 and 9.12 ± 0.22 mPa·s. Surface tensions were 29.1 and 30.8 mN/m, and zeta potentials were −38.4 and −35.2 mV for the PKO- and Jatropha-based inks, respectively. The PKO- and Jatropha-based inks produced optical densities of 2.15 ± 0.04 and 2.08 ± 0.05, adhesion ratings of 5B and 4B, and water-resistance values of 94.5% and 91.2%. No nozzle failure was observed during the 30-min decap test for either bio-based formulation. Under the conditions examined, both formulations exhibited physicochemical and print-performance characteristics close to the commercial reference, supporting further evaluation of vegetable-oil-derived ethoxylates as functional surfactants for aqueous digital inks.