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the enclosure of small solid particles and their aggregates (granules) or drops of liquid within a thin, durable shell with various definite properties, such as permeability, fusibility, and solubility (or insolubility) in given media. The size of microcapsules is usually 10-1 to 10-4 cm. The material of the shell makes up a few percent of the total mass of the capsule.
Microencapsulation consists in dispersion of the material in a suitable gaseous or liquid medium, with subsequent coating of the particles or droplets of the dispersed phase by a layer of the capsule material, which is introduced into the system as a separate phase or separates from the surrounding (dispersion) medium as a result of physical or chemical processes. The microcapsule shells may at first be liquid, solidifying upon heating or cooling or the action of chemical reagents. Various macromolecular compounds, including those of biological origin, such as gelatin, are often used as the capsule material.
The technological methods of microencapsulation are extremely varied. They are based on physical and chemical processes of condensation, phase transitions, and various types of surface interphase effects. In each specific case, the methods used are dictated by the properties and composition of the components, as well as by the intended use of the microcapsules.
Microencapsulation is used to protect various powdered products from caking and the action of moisture and atmospheric oxygen, to avoid premature interaction of chemically reactive compounds, and to provide safe storage and handling of aggressive and poisonous substances. Microencapsulation is finding increased application in the production of timed-release drugs, biologically active substances for agriculture (pesticides, growth regulators, and fertilizers), and various composition materials, such as glues.
REFERENCESEncyclopedia of Polymer Science and Technology, vol. 8. New York,
1968. Page 719.
L. A. SHITS