RELEASE BEHAVIOR OF INORGANIC-SHELL MICRO CAPSULES 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 micron s were prepared by spray-drying suspensions of these materials. The in fluences of the methods of dispersing the suspensions and the volume f raction of magnesium hydroxide in the core materials on the release pr ofiles of microcapsules were investigated. It was found that the relea se rate increased as the volume fraction of magnesium hydroxide carbon ate increased, and that dispersion by an ultrasonic homogenizer result ed in a smaller release rate compared to the use of a turbine mixer. T he release profiles of the microcapsules proved to be expressed by a d iffusion model. The effective diffusion coefficients became large with increasing volume fraction of magnesium hydroxide carbonate, resultin g from the increase of pore volume in the shell of microcapsules. The difference in effective diffusion coefficient, resulting from the vari ous dispersing methods used, was not attributed to the shell structure of the microcapsules.