Encapsulation of Solid Particles by the Concentrated Emulsion Polymerization Method

11 Encapsulation of Solid Particles by the Concentrated Emulsion Polymerization Method [35] 

Encapsulation is a process in which tiny particles or droplets are covered by a coating [36-43]. Its role is either to isolate the active ingredient or to control the rate by which it leaves the capsule. As examples for the first case, one can mention the isolation of vitamins from oxygen or of a reactive core from chemical attack, and for the second case, the control of the rate of release of drugs or pesticides. Numerous encapsulation techniques have been suggested. Most of the encapsulations of the active solid materials have been carried out for solids larger than 1 pm. 

In this section the concentrated emulsion polymerization method is employed to encapsulate submicron inorganic powders. In a first step, a stable colloidal dispersion of the powder in an aqueous solution of a monomer containing an appropriate dispersant and a suitable initiator was prepared. This colloidal dispersion was subsequently employed as the dispersed phase of a concentrated emulsion whose continuous phase, decane, contained a surfactant. 

The role of the surfactant is to stabilize the gel-like concentrated emulsion. Upon heating at 40 °C, polymerization took place and the solid particles were encapsulated in the polymer. 

Scanning electron micrographs of alumina powders dispersed in water in the absence and presence of dispersant show that the agglomeration of the solid particles decreases tremendously in the presence of the dispersant. The agglomerates are larger than 10 pm in the absence of dispersant and smaller by more than one order of magnitude in its presence. 

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