Introduction

What is Microencapsulation ?

Application of Microencapsulation

Hot melt coating

Cyclodextrins

Extrusion

Emulsion Stabilisation

Jet break-up Processes

Super Critical Fluid technology

Complex Coacervation

Introduction

Complex coacervation, (or phase separation), is the first large application of a microencapsulation technology. In fact this chemical process of microencapsulation was developed in the 1950s by National Cash Register (NCR, USA) to produce a two-component ink system for carbon less copy paper. It is based on the ability of cationic and anionic water-soluble polymers to interact in water to form a liquid, polymer-rich phase called a complex coacervate.

Technology

Complex coacervation is the separation of an aqueous polymeric solution into two miscible liquid phases : a dense coacervate phase and a dilute equilibrium phase. The dense coacervate phase wraps as a uniform layer around suspended core materials. Complex coacervation can result spontaneously upon mixing of oppositely charged polyelectrolytes in aqueous media. The charges must be large enough to induce interaction, but not too large to cause precipitation.

Complex coacervation parameters are the pH, the ionic strength, the temperature, the molecular weight and the concentration.

Complex coacervation occurs with the neutralization of two oppositely charged polymers. The core material such as an oily phase is dispersed in an aqueous solution of the two polymers. A change is made in the aqueous phase (pH) to induce the formation of a polymer rich phase that becomes the wall material. The coacervates are usually stabilized by thermal treatment, crosslinking or desolvation techniques.

So basically complex coacervation process consists of three steps :

[1] Formation of an oil-in-water emulsion

[2] Formation of the coating

[3] Stabilization of the coating

The microcapsules are usually collected by filtration or centrifugation, washed with an appropriate solvent and subsequently dried (air-dried or by standard techniques such as by fluid bed or spray drying).

Application

The applicability of complex coacervation is enormous but has been limited due to its relatively high costs. It includes the encapsulation of :

  Flavors
  Vitamins
  Fragrances (scratch and sniff)
  Liquid Crystals for display devices
  Ink systems for carbonless copy paper
  Active ingredients for drug delivery
  Bacteria and cells