Comparison of O/W emulsions produced using cross-flow SPG membranes and a microfluidizer

The oil-in-water emulsions consisting of vegetable (rape seed) oil as the dispersed phase and 2 wt % Tween 80 dissolved in demineralized water as the continuous phase were produced using Shirasu-porous-glass (SPG) membranes and Microfluidizer (Microfluidics Corp., Newton, MA, USA). The mean pore size of the membranes used was in the range of 0.4-6.6 μm and the wall porosity 53-60 %. The hydraulic membrane resistance was inversely proportional to the square of the mean pore size according to the equation: Rm = 0.056dp -2, where Rm and dp are in m-1 and m, respectively. The shear stress at the membrane surface was 8 Pa and the transmembrane pressure was 10 % higher than the cappilary pressure. Using SPG membranes under these conditions, the emulsions with a mean droplet size 3.5 times larger than the mean pore size and the span of the droplet size distribution of 0.26-0.45 were produced. Therefore, the SPG technology is very suitable for producing emulsions with a narrow droplet size distribution over a wide range of mean droplet sizes (0.2-30 μm) using small mechanical stresses. On the other hand, a Microfluidizer is more appropriate device for producing emulsions with a very low mean droplet size (0.08-0.2 μm). However, the span of the droplet size distribution curves for the emulsions produced using Microfluidizer typically range between 0.91 and 2.7.