RELEASE BEHAVIOR OF INORGANIC-SHELL MICROCAPSULES PREPARED BY SPRAY-DRYING

Microcapsules with a shell of colloidal silica of nm order and a core of magnesium hydroxide carbonate and SiC having a size of a few microns were prepared by spray-drying suspensions of these materials. The influences of the methods of dispersing the suspensions and the volume fraction of magnesium hydroxide in the core materials on the release profiles of microcapsules were investigated. It was found that the release rate increased as the volume fraction of magnesium hydroxide carbonate increased, and that dispersion by an ultrasonic homogenizer resulted in a smaller release rate compared to the use of a turbine mixer. The release profiles of the microcapsules proved to be expressed by a diffusion model. The effective diffusion coefficients became large with increasing volume fraction of magnesium hydroxide carbonate, resulting from the increase of pore volume in the shell of microcapsules. The difference in effective diffusion coefficient, resulting from the various dispersing methods used, was not attributed to the shell structure of the microcapsules.