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

We use “hot melt“ terminology because it consists of a re-crystallization of molten lipids around the nucleus leading to the protection of either liquid or solid phase material from its environment. Such shell is able to release under precise conditions* its content (*pH for enteric release for example). This is a very important concept which can be applied by different technologies with many application such as :

  Food (enteric control release),
  Feed (taste masking),
  Pharmaceuticals (complex pellet containing several drugs by multi-layer coating),
  Cell protection for storage,
  Chemical (washing powder),
  Agro-chemical (pesticides).

Technology

The technology to be applied will depend on the way the particles are considering before the encapsulation process. We’ve got 2 possibilities :

1- Individualization of the particles before encapsulation

In this case the separation of the particles prior to encapsulation is operated in a gas stream (air in general). Then once the fluidization is optimum (individual repartition of the particles), the molten coating material is applied in very tiny droplets by a regulated nozzle. The particle are embedded by the droplets which create over time a veritable protecting shell.

The nozzle atomizing the matrix can be applied either at the bottom (Bottom spray process) or at the top (Top spray process) of the fluidized particles.

For the Bottom spray the use of the Wurster column (a conical partition chamber inside the fluidized chamber) forces the particles to come close to the nozzle so that they will receive equal amounts of coating material. But since it does slow down the process, many industrial work in a bottom spray process without Wurster column. As an intermediary solution, the spouted bed system, by devices at the bottom to guide the fluidizing gas stream and a special geometry of the process chamber, the particles are forced to come close the atomizing nozzle.

In the top spray process, as you can see on the picture above, the particles also are suspended in a gas stream, but the shape of the vessel is designed for an optimal circulation of all particles to come as close as possible to the nozzle, air volume is adjusted to have the center of the particle stream very close to the nozzle.

2- Blending of the matrix and the substrate to be protected before separation

Compare to the previous chapter, a wide range of technologies to form microcapsules using mechanical separation exist, we have :

  The spray cooling, chilling or congealing, whereby a slurry of molten matrix material and substrate is sprayed through into a cooling chamber, where the droplets solidify rapidly. Spraying can be effected through a conventional nozzle or by a specially-designed nozzle, where separation of the particles is assisted by ultrasonic frequencies.

Sometimes the slurry is molten and saturated under pressure with CO2 into a supercritical fluid and sprayed directly from the pressure vessel (see the details in the supercritical fluid section).

  The spinning disk, where a slurry of molten matrix and substrate is ejected into small droplets by centrifugal velocity into a cooling chamber. Also the spinning disk technology has been improved by the ultrasonic assistance in launch of the particles from the disk.

  The extrusion process, a slurry of molten matrix and substrate is extruded through a small diameter orifice into small particles and allowed to cool down below crystallization temperatures. We will developp this important technology in a separated chapter (see extrusion section).

  The high shear pelletising, is a process by which micro-capsules are formed though the addition of the coating material, which melts during the process and excess material is freed from the substrate though the application of mechanical pressure to the capsule.