Suppression of agglomeration in fluidized bed coating I. Suppression of agglomeration by adding NaCl

Abstract

Fluidized bed coating was carried out with aqueous spray solution at various additional amounts of NaCl, using water-soluble hydroxypropyl cellulose (HPC) or hydroxypropylmethyl cellulose (HPMC) as membrane material, and spherical granules made of crystalline cellulose (Celphere™) as core particle. The mean particle diameter, density and surface morphology of the coated particles were studied. The viscosity of the spray solution was studied with a corn-plate viscometer at various additional amounts of NaCl, temperatures and concentrations of the spray solution. Agglomeration of particles was clearly suppressed by adding NaCl to the aqueous spray solution in both cases of HPC and HPMC. The mean particle diameter of the coated particles decreased with the increasing additional amount of NaCl in the spray solution. The viscosity of HPC water solution began to decrease at over 6% (w/v) NaCl concentration at 30°C. The NaCl concentration required to reduce the viscosity of the HPC solution became lower as temperature became higher. When the viscosity of the solution decreased, turbidity and/or precipitate were observed. These results suggest that the suppression of agglomeration was caused by the reduction in the viscosity of the spray solution through salting-out of the polymeric membrane materials.