The effect of essential oil chemical structures on Pickering emulsion stabilized with cellulose nanofibrils

Abstract

Nanocelluloses are non-toxic and biodegradable biopolymers with high potential for application as solid emulsion stabilizers. In this work, cellulose nanofibrils were used a Pickering emulsion stabilizer for different essential oils (cinnamon cassia, cardamom, and ho wood). Emulsions were evaluated by droplet sizes, microstructure, emulsion storage stability, stability towards shear, rheological behavior, and FT-Raman. The droplets showed spherical shapes and an average diameter ranging from 10 to 20 μm, depending on the essential oil physicochemical properties and CNF-surface coverage (SC). CNF-Cardamom showed the highest SC values, indicating that CNF formed an interconnected three-dimensional network around the oil droplets, and CNF-Ho wood showed the lowest values, directly reflecting in the emulsion stability. The rheological data evidenced the network formation in the CNF-emulsions and their pseudoplastic behavior, and CNF-cardamom showed the strongest network structure, resulting in a higher thixotropic hysteresis loop area (398 s−1). The FT-Raman analysis was decisive to correlate the emulsion stability with the EO chemical structure. Cardamom and Cinnamon chemical structures are stable, and the electron pairs in resonance favor the electronic attraction between the components, resulting in a steric stabilization, forming a cellulose nanofibers three-dimensional network. Ho wood has the most reactive chemical structure, and CNF addition induced the hydrogen bonding between both materials, forming a monolayer around the oil drops and inducing droplets coalescence. This work correlated the EO stabilization with the CNF morphology and highlighted the importance of the compounds' chemical structure in the emulsions' stability, which are essential for further studies in Pickering emulsion essential oils CNF-stabilized.