Effect of high shearing on the rheological/structural properties of highly concentrated w/o emulsions

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2009.Emulsion explosives are classified as highly concentrated water-in-oil emulsions with high droplet volume fraction that exceeding the close packing limit of spherical droplets. These emulsions are commonly used as re-pumpable materials. Thus, the shearing action resulting from the transportation process of these materials has a tremendous impact on their structures and functionality and might reduce the shelf-life and performance of the products. Therefore the main goal of this research was to investigate the stability of highly concentrated water-in-oil emulsion under shearing using a newly designed piston-pumping instrument. The results of measurement included the droplet size distribution, microscopic observation, flow and viscoelastic properties of the materials. Neither crystallisation nor other destabilisation phenomena such as coalescence, partial coalescence, or phase inversion occurred during the shearing process of these emulsions, regardless of their formulation content. It was found that the high shearing action within this research experimental window induced droplet refinement. The changes in droplet size distribution were achieved by multipass flow through a small orifice set as outlet of the piston-chamber pumping instrument, and intensive shearing provided the shift of the droplet sizes to the smaller-size side of the distribution. Their distributions were wider and of Gaussian type. Two models were proposed and used to fit the refinement evolution and the width of distributions respectively