Evaluating the Emulsifying Capacity of Cellulose Nanofibers Using Inverse Gas Chromatography

Cellulose nanofibers (CNFs) are attracting increasing attention as emulsifiers owing to their high emulsifying capacity, biocompatibility, and biodegradability. The emulsifying capacity has been experimentally shown to depend not only on the type of oil but also on the chemical structure of the CNF surface. However, the theoretical relationship between these two factors and emulsification remains unclear, and therefore, industrial applications are limited. Here, we assess the desorption energy (DE) of CNFs from the oil surface in o/w emulsion for various CNF/oil combinations to understand the mechanism of emulsification. Two types of surface-carboxylated CNFs having different cationic counterions, namely, sodium and tetrabutylammonium ions, were used as emulsifiers. The surface free energies of the CNFs were evaluated using inverse gas chromatography, and the nonpolar Lifshitz-van der Waals γ^LW, electron-acceptor γ⁺, and electron-donor γ^- components were obtained from the chromatography profiles based on the van Oss-Chaudhury-Good theory. CNF with tetrabutylammonium ions was found to have a higher γ⁺ component than CNF with sodium ions. Therefore, the emulsion stability improved with oils having high γ^- components owing to the increase in the DE value; this was verified through both theoretical calculations using a fibrous model and experimental dynamic interfacial tension measurements. Our approach is useful for predicting the emulsifying capacity of CNFs, and it should contribute toward the design of novel CNF-based emulsions.