Fluid-bed microencapsulation of ascorbic acid

Ascorbic acid has been fluidized and microencapsulated with three different hydrophobic coating materials by the top-spray method. The experiments were conducted with polymethacrylate coating material formulated as a water dispersion, and ethyl-cellulose and waxy coating material both formulated as organic solutions. Characteristics of the fluidized bed procedure in conical geometry have been determined by estimation of two parameters: bed porosity and total pressure drop. A satisfactory agreement between experimental and calculated values has been reached. The following properties of the microencapsulated ascorbic acid have been determined: core content, bulk and tapped density, crystal size distribution prior and after microencapsulation, surface morpholgy and release profile. The comparison and evaluation of different hydrophobic coating materials have been performed on the basis of these findings.