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Emulsion Stabilization with Functionalized Cellulose Nanoparticles Fabricated Using Deep Eutectic Solvents

1
Fibre and Particle Engineering Research Unit, University of Oulu, P.O. Box 4300, FI-90014 Oulu, Finland
2
Department of Bioproducts and Biosystems, Aalto University, P.O. Box 16300, FI-00076 Aalto, Finland
*
Author to whom correspondence should be addressed.
Molecules 2018, 23(11), 2765; https://doi.org/10.3390/molecules23112765
Received: 28 September 2018 / Revised: 18 October 2018 / Accepted: 24 October 2018 / Published: 25 October 2018
(This article belongs to the Special Issue Emerging Trends in Nanocelluloses)
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Abstract

In this experiment, the influence of the morphology and surface characteristics of cellulosic nanoparticles (i.e., cellulose nanocrystals [CNCs] and cellulose nanofibers [CNFs]) on oil-in-water (o/w) emulsion stabilization was studied using non-modified or functionalized nanoparticles obtained following deep eutectic solvent (DES) pre-treatments. The effect of the oil-to-water ratio (5, 10, and 20 wt.-% (weight percent) of oil), the type of nanoparticle, and the concentration of the particles (0.05–0.2 wt.-%) on the oil-droplet size (using laser diffractometry), o/w emulsion stability (via analytical centrifugation), and stabilization mechanisms (using field emission scanning electron microscopy with the model compound—i.e., polymerized styrene in water emulsions) were examined. All the cellulosic nanoparticles studied decreased the oil droplet size in emulsion (sizes varied from 22.5 µm to 8.9 µm, depending on the nanoparticle used). Efficient o/w emulsion stabilization against coalescence and an oil droplet-stabilizing web-like structure were obtained only, however, with surface-functionalized CNFs, which had a moderate hydrophilicity level. CNFs without surface functionalization did not prevent either the coalescence or the creaming of emulsions, probably due to the natural hydrophobicity of the nanoparticles and their instability in water. Moderately hydrophilic CNCs, on the other hand, distributed evenly and displayed good interaction with both dispersion phases. The rigid structure of CNCs meant, however, that voluminous web structures were not formed on the surface of oil droplets; they formed in flat, uniform layers instead. Consequently, emulsion stability was lower with CNCs, when compared with surface-functionalized CNFs. Tunable cellulose nanoparticles can be used in several applications such as in enhanced marine oil response. View Full-Text
Keywords: cellulose nanocrystals (CNCs); cellulose nanofibrils (CNFs); nanoparticle; stabilization; o/w emulsion; surface-functionalization; deep eutectic solvent (DES) cellulose nanocrystals (CNCs); cellulose nanofibrils (CNFs); nanoparticle; stabilization; o/w emulsion; surface-functionalization; deep eutectic solvent (DES)
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Ojala, J.; Visanko, M.; Laitinen, O.; Österberg, M.; Sirviö, J.A.; Liimatainen, H. Emulsion Stabilization with Functionalized Cellulose Nanoparticles Fabricated Using Deep Eutectic Solvents. Molecules 2018, 23, 2765.

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