Chapter 7 Coating and encapsulation processes in powder technology

Abstract

Publisher Summary Coating of particulate materials is a fundamental operation widely practiced in a variety of chemical industries including pharmaceuticals, food, fertilizer, cosmetics, biomedical, and nuclear. The coating process involves the covering of particulate materials including seeds, agglomerates, pellets, and powders with a surrounding layer of a coating agent (or coating material). The coating process can be applied to a variety of substrates ranging from submicron particles to very large objects. The coating thickness might vary from a few nanometers (chemical deposition) to several micrometers (film coating) or even several millimeters (e.g. sugar coating). There are several methods to introduce the coating agent into the system: dispersed or dissolved in an easily evaporable solvent, molten, or applied in the form of a very fine dry powder. In majority of cases, the final deposited layer (or coating layer) is a solid-phase material called a “shell.” In a few singular applications the coating layer can also be a liquid film. Furthermore, the introduction of a liquid into a particulate system leads most often to formation of liquid bridges among wetted particles. This behavior results in agglomeration phenomenon, which consists of adhesion of several elementary particles to form bigger entities called “agglomerates.” Another term subject to controversy in the technical and scientific literature is “encapsulation,” which is generally admitted to be a special kind of coating. In this chapter, the term encapsulation is used to distinguish one of the two following special cases: (1) the coating process is performed by immersion in a liquid phase, and (2) the product core constitutes of a liquid-phase formulation.