Using cellulose nanofibers isolated from waste hop stems to stabilize dodecane or olive oil-in-water Pickering emulsions

Abstract

TEMPO-oxidized cellulose nanofibers (TOCNF) were isolated from agricultural waste hop stems and used as stabilizers of oil-in-water Pickering emulsions. The TOCNF-stabilized emulsions were prepared using two types of oils (dodecane and olive oil), different TOCNF concentrations (0.5%, 0.8%, and 1.0% in the continuous phase), and multiple oil/water ratios (10–30% oil by weight). The stability of dodecane/TOCNF (d-CNF) and olive oil/TOCNF (o-CNF) emulsions were investigated over one month at ambient temperature. While the instability behavior in d-CNF and o-CNF emulsions was different, their stabilities were enhanced with TOCNF concentrations and/or the lower oil ratios. The addition of TOCNF above 0.8% prevented separation for one month by sufficiently covering the oil/water interface and forming the entangled structure in the continuous phase. The mean diameter of oil droplets (dv) in d-CNF emulsions was 5–14 µm, depending on the initial TOCNF loading. As for o-CNF emulsions, dv was relatively smaller than that of d-CNF (3–8 µm), and flocculation and Ostwald ripening were considered to dominate the destabilization at o/w 10/90 showing a monomodal droplet size distribution, while coalescence also contributed at o/w 20/80, showing a bimodal distribution.