|Ph.D Student||Napso Sofia|
|Subject||Cellulose - Coated Oil-in-Water Emulsions|
|Department||Department of Chemical Engineering||Supervisors||Professor Yachin Cohen|
|Dr. Dmitry Rein|
|Full Thesis text|
Environmental concerns and increasing global demand for fossil resources despite their scarcity encourage the development of renewable alternative raw materials. Cellulose, being the most abundant renewable biopolymer on earth, has a great potential to serve as alternative resource. However, only a minute fraction of its annual natural production is utilized as a raw material for fabrication of synthetic products, or as a source for biofuel. Its processing requires harsh solvents or procedures considered to be detrimental to the environment and are increasingly regulated. Ionic liquids (IL) are powerful “green” solvents capable of dissolving cellulose for further processing. In this research, solutions of cellulose in an IL and its mixture with a polar organic co-solvent were studied by small-angle x-ray scattering (SAXS), to evaluate the structure and thermodynamic solution properties, providing direct evidence of molecular dissolution of the cellulose chains without any significant aggregation. Furthermore, the dissolved cellulose chains or the amorphous cellulose hydrogel regenerated from such solution were used for the fabrication of a unique encapsulation coating in oil-in-water (o/w) emulsions. This unique emulsion system is stabilized by exploiting the amphiphilic character of the molecularly dissolved cellulose chains or of the amorphous cellulose hydrogel. The cellulose chains interact with both water and oil molecules at the oil/water interface on the oil droplet stabilizing the emulsion without using any additional surfactants. The structure of these cellulose-coated o/w emulsion particles, in particular the cellulose coating shell characteristics (thickness, porosity and composition), was studied by using a combination of direct imaging methods, cryogenic electron microscopy (cryo-EM) and fluorescence microscopy with quantitative analysis using small-angle neutron scattering (SANS) measurements. The results suggest a new type of multi-layered emulsion particle: an oil core, surrounded by an inner shell composed of a porous cellulose gel, encapsulated by a dense outer cellulose shell, a few nanometers in thickness. The suggested multi-compartment structure of the emulsion particles is highly relevant for numerous applications ranging from fabrication of polymer-coated capsules for health-care and nutrition products to micro-reactors for cost-effective biofuel processing.