Cellulose-coated oil-in-water emulsions: from molecular solutions to encapsulated droplets

Sofia Napso, Chemical Engineering, Technion - Israel Institute of Technology, Haifa, Israel
Dmitry Rein, Chemical Engineering, Technion - Israel Institute Of Technology, Haifa, Israel
Rafail Khalfin, Chemical Engineering, Technion - Israel Institute Of Technology, Haifa, Israel
Yachin Cohen, Chemical Engineering, Technion - Israel Institute Of Technology, Haifa, Israel

Cellulose is the most abundant renewable material in nature, yet only a minute fraction of its annual natural production is utilized as a raw material for fabrication of synthetic products, or biofuel. Its processing requires harsh solvents or procedures considered to be detrimental to the environment. Cellulose solutions in an ionic-liquid and its binary mixture with a polar organic co-solvent are of significant interest and have been studied extensively in the last decade, mostly by rheological measurements. However, the solution structure of cellulose in these solvents is not fully resolved. In this work, the structure and thermodynamic properties of cellulose solutions in mixtures of an ionic liquid and a polar organic solvent were studied by small-angle x-ray scattering. These measurements indicate that cellulose molecules are dissolved essentially as individual chains without any significant aggregation, and that these solvents can be considered as “good” solvents for cellulose. Furthermore, the dissolved cellulose chains readily form a unique encapsulation coating in oil-in-water or water-in-oil emulsions by mixing water, oil and cellulose solution in an ionic liquid. A more practical alternative is to form a hydrogel from the cellulose/ionic liquid solution by coagulation with water and applying it to homogenized oil/water mixtures. Structural information on the emulsion particles and the nature of the cellulose coating itself, was obtained using cryogenic electron microscopy and fluorescence microscopy imaging, and their size was analyzed by light scattering. The structure of the coating shell is relevant for specific applications such as controlled release of functional hydrophobic compounds, encapsulated phase-change materials for thermal control in textiles or insulation, and cellulose enzymatic hydrolysis for alternative fuel production from biomass.