Production of water-containing polymer microcapsules by the complex emulsion/solvent evaporation technique. Effect of process variables on the microcapsule size distribution.

The complex emulsion/solvent evaporation technique was employed for the production of water-containing polymer microcapsules. The inner phase of the microcapsules consisted of an aqueous solution of gelatin. Several polymers (e.g. poly(styrene), poly(methyl methacrylate), ethyl cellulose, poly(vinyl chloride)) were utilized as wall-forming materials and the effect of the polymer type on the size and the surface characteristics of the microcapsules was experimentally investigated. The size of the microcapsules was strongly affected by the conditions applied during the formation of both simple (w/o) and complex (w/o)/w emulsions. Poly(styrene) microcapsules with a mean Sauter diameter in the range of 4-12 microns were prepared by varying the rate of agitation (1500-4000 rpm) and the concentration of stabilizer (potassium oleate, 0.1-1.5% w/v) used in the formation of the (w/o)/w emulsion. High stabilizer concentrations and agitation rates resulted in a significant reduction of the mean size of the complex droplets and in a simultaneous increase of the breadth of the capsule size distribution.