title: Liquid-core nanocellulose-shell capsules with tunable oxygen permeability.
abstract: Encapsulation of oxygen sensitive components is important in several areas, including those in the food and pharmaceutical sectors, in order to improve shelf-life (oxidation resistance). Neat nanocellulose films demonstrate outstanding oxygen barrier properties, and thus nanocellulose-based capsules are interesting from the perspective of enhanced protection from oxygen. Herein, two types of nanocellulose-based capsules with liquid hexadecane cores were successfully prepared; a primary nanocellulose polyurea-urethane capsule (diameter: 1.66 μm) and a bigger aggregate capsule (diameter: 8.3 μm) containing several primary capsules in a nanocellulose matrix. To quantify oxygen permeation through the capsule walls, an oxygen-sensitive spin probe was dissolved within the liquid hexadecane core, allowing non-invasive measurements (spin-probe oximetry, electron spin resonance, ESR) of the oxygen concentration within the core. It was observed that the oxygen uptake rate was significantly reduced for both capsule types compared to a neat hexadecane solution containing the spin-probe, i.e. the slope of the non-steady state part of the ESR-curve was approximately one-third and one-ninth for the primary nanocellulose capsule and aggregated capsule, respectively, compared to that for the hexadecane sample. The transport of oxygen was modeled mathematically and by fitting to the experimental data, the oxygen diffusion coefficients of the capsule wall was determined. These values were, however, lower than expected and one plausible reason for this was that the ESR-technique underestimate the true oxygen uptake rate in the present systems at non-steady conditions, when the overall diffusion of oxygen was very slow.
authors.affiliation: University of Copenhagen, Dept. of Pharmacy, Universitetsparken 2, 2100 Copenhagen, Denmark. Electronic address: svagan@kth.se.
authors.forename: A J
authors.initials: AJ
authors.lastname: Svagan
authors.affiliation: University of Copenhagen, Dept. of Chemistry, Universitetsparken 5, 2100 Copenhagen, Denmark.
authors.forename: C
authors.initials: C
authors.lastname: Bender Koch
authors.affiliation: KTH Royal Institute of Technology, Dept. of Fibre and Polymer Technology, 100 44 Stockholm, Sweden. Electronic address: mikaelhe@kth.se.
authors.forename: M S
authors.initials: MS
authors.lastname: Hedenqvist
authors.affiliation: KTH Royal Institute of Technology, Dept. of Fibre and Polymer Technology, 100 44 Stockholm, Sweden.
authors.forename: F
authors.initials: F
authors.lastname: Nilsson
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Glasser
authors.affiliation: Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany; Freiburg Institute for Advanced Studies (FRIAS), Albert-Ludwigs-Universität Freiburg, Albertstraße 19, 79104 Freiburg, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Baluschev
authors.affiliation: University of Copenhagen, Dept. of Food Science, Rolighedsvej 30, 1958 Frederiksberg C, Denmark.
authors.forename: M L
authors.initials: ML
authors.lastname: Andersen
keywords: Cellulose nanocrystals; Electron spin resonance; Liquid-core capsules; Low oxygen permeability; Nanofibrillated cellulose; Oximetry