2.14 Microencapsulation
43
material is imbedded in a polymeric matrix. In this method, the particles are formed
by evaporation of the solvent from the matrix.
2.14.1.2 Emulsification
This is a physical process which involves the preparation and dispersion of a core
material in a polymer solution, emulsification of the dispersion in water or other
organic solvent and removal of liquid from the dispersed second phase by heating
the system to solidify and to encapsulate the core material. This process has been
employed for preparing polymer encapsulated particles for electrophoretic displays
[227], pressure-fixable toner particles [228] and cosmetic applications [229]. When
this process is employed with small particulates such as dye or pigment, diffusion of
the core material from the dispersed second phase to the continuous phase can cause
inefficient encapsulation.
2.14.1.3 Phase Separation
The phase separation process is used for encapsulating water-immiscible core materials in aqueous media. By this process, any pair of oppositely charged polyelectrolytes capable of forming a liquid complex coacervate can be used for encapsulation. One typical example of the phase separation process is complex coacervation. The complex coacervate adsorbs on the core material, forming microcapsules.
The coating of complex coacervate is gelled by cooling and then cross-linked with
glutaraldehyde or formaldehyde to form capsules. In this process, a core material
insoluble in the solvent is dispersed in a solvent, and a polymer soluble in the solvent
is preferentially adsorbed by the dispersed core material. The polymer encapsulates
the dispersed core material and forms the microcapsules. The wall of the microcapsule is solidified by the addition of a non-solvent or a cross-linking agent. Hawlader
et al. [230] have investigated the encapsulation of a PCM by the coacervation method.
2.14.1.4 Spray Drying
In spray drying, a coating material is dissolved in a carrier solvent such as water
or any organic solvent. Then, the core material is dispersed in the carrier solution
and emulsified using a surfactant that forms an oil-in-water emulsion. This emulsion
in the form of small droplets with a high surface area is sprayed into a hot drying
chamber. Dry powder is formed in the drying chamber by rapid evaporation of water
from the droplets. This process was commercially employed to encapsulate flavours
with gum arabic in 1927. Since then, it has become a low-cost process capable of
producing a range of microcapsules with good yields.
43
material is imbedded in a polymeric matrix. In this method, the particles are formed
by evaporation of the solvent from the matrix.
2.14.1.2 Emulsification
This is a physical process which involves the preparation and dispersion of a core
material in a polymer solution, emulsification of the dispersion in water or other
organic solvent and removal of liquid from the dispersed second phase by heating
the system to solidify and to encapsulate the core material. This process has been
employed for preparing polymer encapsulated particles for electrophoretic displays
[227], pressure-fixable toner particles [228] and cosmetic applications [229]. When
this process is employed with small particulates such as dye or pigment, diffusion of
the core material from the dispersed second phase to the continuous phase can cause
inefficient encapsulation.
2.14.1.3 Phase Separation
The phase separation process is used for encapsulating water-immiscible core materials in aqueous media. By this process, any pair of oppositely charged polyelectrolytes capable of forming a liquid complex coacervate can be used for encapsulation. One typical example of the phase separation process is complex coacervation. The complex coacervate adsorbs on the core material, forming microcapsules.
The coating of complex coacervate is gelled by cooling and then cross-linked with
glutaraldehyde or formaldehyde to form capsules. In this process, a core material
insoluble in the solvent is dispersed in a solvent, and a polymer soluble in the solvent
is preferentially adsorbed by the dispersed core material. The polymer encapsulates
the dispersed core material and forms the microcapsules. The wall of the microcapsule is solidified by the addition of a non-solvent or a cross-linking agent. Hawlader
et al. [230] have investigated the encapsulation of a PCM by the coacervation method.
2.14.1.4 Spray Drying
In spray drying, a coating material is dissolved in a carrier solvent such as water
or any organic solvent. Then, the core material is dispersed in the carrier solution
and emulsified using a surfactant that forms an oil-in-water emulsion. This emulsion
in the form of small droplets with a high surface area is sprayed into a hot drying
chamber. Dry powder is formed in the drying chamber by rapid evaporation of water
from the droplets. This process was commercially employed to encapsulate flavours
with gum arabic in 1927. Since then, it has become a low-cost process capable of
producing a range of microcapsules with good yields.