Preparation of ethanol-gels as hand sanitizers formed from chitosan and silica nanoparticles

Abstract

The application of chitosan as a gelling agent in hydro-alcoholic hand sanitizers has rarely been studied due to its insolubility in ethanol. In this study, high-ethanol-content gels were prepared with chitosan in combination with silica nanoparticles. The properties of the gels were investigated by FTIR, XRD, SEM, rheological measurement and the zone of inhibition test against bacteria. The results showed that the adsorption of silica nanoparticles on the chitosan inhibited the precipitation of chitosan in ethanol. The chitosan/silica fibres entangled with each other, and gelation occurred in the solvent with high ethanol concentration due to the solvent-driven effect. The gelation process was related to the concentrations of ethanol, chitosan, and silica nanoparticles. A stable gel could be formed at a chitosan concentration as low as 0.5%, with an ethanol concentration up to 80%. All the gels exhibited pseudoplastic behaviour and had frequency-dependent profiles in the viscoelastic spectrum of non-Newtonian liquids, behaving in a solid-like manner. The limited linear viscoelastic region of all samples was<1%. The optimal silica concentrations (OSCs) for various chitosan concentrations in 75% ethanol were proposed by rheological analysis as a reference to optimize the sensory and textural properties of gels. These gels showed antibacterial activity, which introduced a potential application as hand sanitizers. This research provides a method of preparing novel high-ethanol-content gels, highlights the application of solvent-driven effects in gelation, and identified some suggestions for future research.