Microcapsules preparation processes

Recently, many synthetic polymers such as urea/formalin resin, melamine/formalin resin, polyester, and polyurethane have been widely used as the wall material for the microcapsule, though the gelatin microcapsule is still used. Microcapsules using a synthetic polymer wall have several advantages over those using a gelatin wall (1) the preparation process is simple, (2) the size of the microcapsules is well balanced, (3) the microcapsule concentration can be increased twofold or more and (4) the microcapsules have a high resistance to water and many chemicals. Synthetic microcapsules are prepared by interfacial polymerization or in situ polymerization. 

Raez, I., Dredan, J., Antal, I., and Gondar, E. (1997). Comparative evaluation of microcapsules prepared by fluidization atomization and melt coating process. Drug Develop. Industrial Pharma. 23, 583-587. 

Figure 15.2 is a microscope image of the polyurea microcapsule prepared through a similar process. 

The different steps to consider must be well defined the preparation of microcapsules (composition, process), their storage, and their final use. 

The coacervation method has widely been employed for the preparation of microcapsules. This process comprises five basic steps ... 

The development of the preparation processes of liquid microcapsules (see Chapter 5) provides a new opportunity for the application of composite coatings in the protective treatment of metal surfaces. Some liquid substances which possess specific properties can be encapsulated (Fig. 9.1) and used to form composites ei-... 

Interfacial polymerization is a widely used chemical method characterized by the fact that the microcapsules prepared in this way possess high strength and stability thus, they are not easy to break. In this process, two reactive monomers are dissolved in water and an organic solvent respectively, while the core materials are dissolved in a solvent of the dispersed phase. An oil-in water or water-in-oil emulsion is formed by mixing the two immiscible solutions, with the addition of an emulsifier. The two reactive monomers in the two phases migrate to the interface of the emulsion droplets and react to form a polymer at the interface by polycondensation this acts as a wall material to encapsulate the core materials in the emulsion droplets to form microcapsules. The major disadvantages of this method are its complexity and the slowness of the reaction. In addition, many unwanted side products are produced. 

Liu R, Ma GH, Wan YH, Su ZG. 2005a. Influence of process parameters on the size distribution of PLA microcapsules prepared by combining membrane emulsification technique and double emulsion-solvent evaporation method. Colloids Surf B 45 144-153. 

Gardner, D. L., Battelle Development Corp., Process of preparing microcapsules of lactides or lactide copolymers with glycolides and/or c-caprolactones, U.S. Patent 4,637,905, A,... 

Guang Hui Ma et al. [83] prepared microcapsules with narrow size distribution, in which hexadecane (HD) was used as the oily core and poly(styrene-co-dimethyla-mino-ethyl metahcrylate) [P(st-DMAEMA] as the wall. The emulsion was first prepared using SPG membranes and a subsequent suspension polymerization process was performed to complete the microcapsule formation. Experimental and simulated results confirmed that high monomer conversion, high HD fraction, and addition of DMAEMA hydrophilic monomer were three main factors for the complete encapsulation of HD. The droplets were polymerized at 70 °C and the obtained microcapsules have a diameter ranging from 6 to 10 pm, six times larger than the membrane pore size of 1.4 p.m. 

Fig. 11.4. Laser confocal and SEM of the materials prepared according to the process depicted in Fig. 11.3. Photographs show individual stages in the cell-mediated lithography of polymer surfaces using Listeria monocytogenes (left column a, c, e, g) and Staphylococcus aureus (right column b, d, f, h) as templates. Imprinted microcapsules (a, b) and solid polymer beads before (c, d) and after (e, f) the removal of template cells, (g, h) Show the imprint sites after reacting the beads with fluorescent-labelled Concanavalin A.

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