Crystal Morphology of Hydrogenated Castor Oil in the Crystallization of Oil-in-Water Emulsions: Part I. Effect of Temperature

Abstract

Crystallization of hydrogenated castor oil-in-water emulsions has been studied by polarized light microscopy, scanning electron microscopy, X-ray powder diffraction, and differential scanning calorimetry. Three types of crystal morphologies have been observed: rosettes, fibers, and irregular crystals. The energy barrier to nucleation for fibers is suggested to be higher than that of rosettes. Irregular crystals are thermodynamically less stable and tend to transform into stable polymorphs. Under isothermal crystallization at a temperature of 70 °C, mainly rosettes are observed. With an increase of supercooling, by decreasing the temperature to 55 °C, more fibers form due to a lower energy barrier to nucleation. If the crystallization temperature is set to 45 °C, irregular crystals form first and then transform into rosettes. A nonisothermal crystallization study shows that at a cooling rate of 1 °C/min, more rosettes and fibers are produced compared to a higher cooling rate of 5 °C/min, which produces more irregular crystals.