Correlation of physical parameters of an oil in water emulsion with manufacturing procedures and stability

Abstract

The effect of nine process variables for the manufacture of a semi solid paraffin-in-water emulsion prepared with two nonionic surfactants, steareth 21 and sorbitan oleate were examined initially and following ageing for 2 and 4 years. The techniques employed included differential scanning calorimetry (DSC), small angle X-ray diffraction (SAXD) and microscope (differential interference contrast (DIC) and crossed polars). A previous paper (Lashmar, Int. J. Pharm., (1993) 59–67) used particle size analysis and theological techniques to evaluate the emulsions. It was concluded that the total DSC enthalpy change was an important indicator of the stability of an oil-in-water emulsion and that the appearance of a sample under crossed polars could be used as a guide. SAXD was not found to be suitable for evaluation of process parameters. The thermal properties of the emulsions and their appearance under crossed polars suggested that the homogenisation speed of the manufacturing vessel probably was the single most important factor for the production of a stable emulsion and that extending the homogenisation time would improve the stability of the emulsion. Cooling the emulsion slowly appeared to benefit its stability, whereas the speed at which the water phase was added to the oily phase during the emulsification process, the emulsification temperature and the speed of the agitator during cooling seemed to have little effect on the stability of the emulsion. Adding the surfactants to the aqueous phase before emulsification and adding the oil phase to the water phase during the emulsification produced inferior emulsions. On cooling, the optimum stability was achieved when the agitator was stopped around the temperature corresponding to the lower cooling exotherm for the sample. Results from this and the previous paper (Lashmar, 1993) indicated that the droplet size and the rheological properties could be manipulated by process parameters without affecting the stability of the product. A later paper will investigate other techniques to evaluate emulsions and manufacturing parameters.