Encapsulation of solid particles

Encapsulation of Solid Particles by the Concentrated Emulsion Polymerization Method [35]... 

Fluidized-bed coating is more suitable for encapsulation of solid particles. It can also be used for liquids, if they are first absorbed on a porous sohd. The soUd particles to be coated are placed in a coating chamber and suspended by an air stream in a cycKc flow (Figure 5.87) past a nozzle (at the bottom of the chamber) which sprays the Uquid coating phase onto the particles. Carried up into the chamber by the air stream, the coated particles dry by evaporation of the solvent, fall back to the chamber bottom to be carried again by the air stream past the spray nozzle and up into the coating chamber. The cycle is repeated until the coating attains the desired thickness. 

Inorganic Materials. Sol-gel chemistry involves first the formation of a sol, which is a suspension of solid particles in a liquid, then of a gel, which is a diphasic material with a solid encapsulating a solvent A detailed description of the fundamental chemistry is available in the literature. The chemistry involving die must commonly used precursors, the alkoxides (M(OR) ,). can be described in terms of two classes of reactions ... 

Figure 44 presents a scanning electron micrograph of a capsule in which alumina particles are encapsulated in crosslinked polyacrylamide. Table 20 lists under PLA1 the amounts of the components involved in the preparation of these capsules. The capsules have a polyhedral shape and their sizes are larger (around 5 pm) and more uniform than the polymer latexes free of solid particles. Some of the cells of the gel coalesce during polymerization, forming bulk phases. As a result, some unencapsulated solid particles were also observed. 

While the hterature has demonstrated the viabihty of nanoencapsulation via miniemulsion technology, a great many issues remain. These include the use of surfactant systems to stabihze the solid colloidal particles and bring them into the monomer droplets, uniformity of encapsulation (a uniform [small] number of solid particles per polymer particle for a minimum number of polymer particles, not including the encapsulated sohd), and complete coverage of the solids by the resultant polymer coating. 

Microencapsulation is a technique which, as its name suggests, involves the encapsulation of small particles of dmg, or solution of dmg, in a polymer film or coat. Microspheres, on the other hand, are solid but not necessarily homogenous particles which can entrap drug. Although the terms tend to be used interchangeably, we retain the distinction here. Microspheres can be prepared also by a variety of techniques which are briefly discussed in the section on nanoencapsulation below. 

PerrutM., 2003. Method for encapsulating fine solid particles in the form of microcapsules. Brevet FR2811913, US2003157183. 

Figure 4c also describes the spontaneous polymerization of para-xylylene diradicals on the surface of solid particles dispersed in a gas phase that contains this reactive monomer (12) (see Xylylene Polymers). The poly(p-xylylene) polymer produced forms a continuous capsule shell that is highly impermeable to the transport of many penetrants, including water. This is an expensive encapsulation process, but it has produced capsules with impressive barrier properties. It is a type B encapsulation process, but is included here for the sake of completeness. 

One of the main goals of academic research is the encapsulation of organically modified clay in miniemulsion droplets and, upon polymerization, in latex particles. In order to achieve this, it is necessary to have only droplet nucleation and to avoid secondary nucleation. There are examples in the literature of encapsulation of inorganic particles via miniemulsion polymerization, but there is no clear evidence of successful encapsulation of clay or only under limited conditions (low solids content, high surfactant loading) in papers devoted to miniemulsion polymerization of waterborne polymer-clay nanocomposites. 

API (acetaminophen in this case) is heated above the wax melting point, but below that of the drug component. This process results in a suspension of the drug particles in the molten wax. When a nozzle is used to spray the atomized suspension onto cooled air, the molten droplets of suspension congeal, thus allowing the liquid components to encapsulate the solid API and resulting in packets of API particles encased in solidified wax. 

Microencapsulation means the envelopment of liquid droplets or solid particles with natural or synthetic polymers.The encapsulation of a substance with a polymer membrane is undertaken for various reasons, for example, as protection against moisture, or to obtain delayed dissolution of fertilizers, herbicides, or drugs by microencapsulation with semipermeable membranes. 

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