Coacervation

Coacervation, also called phase separation, was the technique developed in the 1950s by National Cash Register Co.

Coacervation involves the separation of a liquid phase of coating material from a polymeric solution and wrapping of that phase as a uniform layer around suspended core particles. Coacervation may be brought about when the surface energies of the core material and coating material are adjusted varying some parameter of the system such as temperature, pH, or composition, for example. The coating material is then solidified by means of heat, cross- linking, or solvent removal techniques (Bakan, 1973).

The microcapsules are usually collected by filtration or centrifugation, washed with an appropriate solvent, and subsequently dried by standard techniques such as spray drying or fluidised bed drying to yield free-flowing, discrete particles.

Simple coacervation deals with systems containing only one colloidal solute (e.g., only gelatine), while complex coacervation deals with systems containing more than one solute (e.g., gelatine and gum acacia) (Luzzi and Gerraughty, 1964.).

Coacervation may also be subdivided into aqueous phase separation and nonaqueous phase separation techniques.

Aqueous phase separation - which has been used to encapsulate citrus oil, vegetable oils, and vitamin A - requires a hydrophilic coating, such as gelatine or gelatine-gum acacia, and water- insoluble core particles. The resulting microcapsules may contain payloads of 85-90% and can release their contends by pressure, hot water or chemical reaction.

In nonaqueous phase separation, the coating is usually hydrophobic and the core may be water-soluble or water immiscible. This process has been investigated for the encapsulation of solid food additives such as ferrous sulphate (Balassa and Fanger, 1971).
Coacervation is a very efficient but expensive process.