Preparation, Characterization And Emulsion Stabilization Mechanism Of Cellulose Regenerated From Phosphoric ACID

Native cellulose has a highly crystalline structure stabilized by a strong intra-and intermolecular hydrogen-bond network. It is usually not considered as a good gelling material and emulsion stabilizer due to its insolubility in water. Chemical modification is generally necessary to obtain cellulose derivatives for these applications. In this study, we have shown that by simply disruption the hydrogen-bond network of cellulose with phosphoric acid treatment, the regenerated cellulose can be a good gelling material and emulsion stabilizer. Microscopy, X-ray diffration and Fourier transform infrared spectroscopy analysis have confirmed that the regenerated cellulose has significant less crystallinity in the structure of cellulose II. Stable aqueous suspensions and opaque gels that resist flowing can be obtained with the regenerated cellulose at concentrations higher than 0.6% and 1.6%, respectively. Moreover, it can effectively stabilize oil-in-water emulsions at concentrations less than 1% by a mechanism that combines network and Pickering stabilization.The regenerated cellulose was prepared by dissolution of microcrystalline cellulose with phosphoric acid and subsequent regeneration in water. Its suspension rheological properties as affected by the concentration of cellulose, ionic strength, pH and temperature were studied. It forms a three dimensional (3D) network at concentration above 0.71% that displays a typical shear-thinning behavior with weak thixotropic tendency. Its flow properties are similar to that of microfibrillated cellulose by a three-region (shear thinning-plateau or shear thickening-shear thinning) viscosity profile, where ionic strength and pH have little influence. However, increasing temperature causes a reduction of viscosity in both low and high shear rate regions. Viscoelastic analysis confirms ionic strength and pH have no influence, but increasing temperature decreases the storage modulus, which is explained by the weakening or disruption of intermolecular interactions, such as hydrogen bonds and Van der Waals forces at elevated temperatures.Fresh-prepared emulsions stabilized with cellulose contents of around 0.07-0.56% w/v are not stable against creaming. Increasing cellulose content to 0.83%, the emulsion remains completely stable for months. During storage, all previous gravitationally unstable liquid-like emulsions have been transformed into stable gel-like emulsions. Fluorescence microscopy and emulsion polymerization demonstrate the absorption of cellulose on the surface of oil droplets. The emulsion stabilization mechanism of regenerated cellulose is a combination of Pickering and network mechanism. Rheology study has shown that the cellulose stabilized emulsions are shear-thinning attractive emulsions with typical gel characteristic.Our study explored a more practical way of using non-derivative cellulose in the food industry as thickening agent and emulsion stabilier.