Effect of Additives on Agglomeration in Aqueous Coating with Hydroxypropyl Cellulose.

Abstract

Water-soluble hydroxypropyl cellulose (HPC) was applied to fine lactose powder (53-63 μm) by the Wurster process. The effects of various additives on agglomeration were studied by the binding strength of membrane materials, the droplet size and the surface morphology of coated particles. The agglomeration was also computer-simulated by a previously reported model.Methyl cellulose (MC) and sodium alginate (ALG) increased the mass median diameter of droplets at 10% addition to HPC, while the other additives exhibited no significant effect on the droplet size distribution. The production of coarse droplets induced by MC and ALG led to the agglomeration of 76 and 87% cores, respectively, though they reduced the binding strength of HPC. Polyethyleneglycol (PEG) reduced the agglomeration by weakening the binding strength of HPC in particular. NaCl, which was incompatible with HPC, reduced agglomeration by hindering HPC from forming homogeneous film. The computer simulation indicated that the smalleste sizes of droplets causing the agglomeration were 44-71 μm. With MC and ALG the weight fraction of coarse droplets causing the agglomeration reached 5.7 and 4.4%, respectively; however, it was less than 1% with the other additives. Such a minor quantity of droplets caused the agglomeration of cores of 18% (PEG and NaCl) to 69% (polyvinyl alcohol). It was suggested that the agglomeration enhancing factor, K, migth well reflect the state of fluidization.