Preparation of microcapsules

Model Membranes and Their Characteristics Liposome preparation and size characterization, 171, 193 preparation of microcapsules from human erythrocytes use in transport experiments of glutathione and its S-conjugate, 171, 217 planar lipid-protein membranes strategies of formation and of detecting dependencies of ion transport functions on membrane conditions, 171,... 

Various techniques have been developed for the preparation of microcapsules with diameters of 1-5000 pm one of these involves the method of interfacial polycondensa-tion.The following example describes the microencapsulation of a dyestuff, which has practical application in the manufacture of carbon-free copy paper. 

Kondo, K., Otono, T. and Matsumoto, M. (2004) Preparation of microcapsules containing extractants and the application of the microcapsules to the extractive fermentation of lactic acid. Journal of Chemical Engineering of Japan, 37, 1. 

Gelatin-acacia complex coacervation has been used in the preparation of microcapsules of vitamin Pindolol-loaded alginate-gelatin beads have been developed for the sustained release of pindolol. ... 

Benoit JP, Richad J, Thies C. Preparation of microcapsules containing active substances coated with a polymer. France, WO 9813136, 1998. 

Fig. 1.5 Preparation of microcapsules with a double emulsion technique. A primary water-in-oil (W/O) emulsion (step 1) serves as the oil phase for secondary emulsification step with a water phase...

The development of early encapsulation technology and preparation of microcapsules dates back to 1950s when Green and coworkers produced microencapsulated dyes by complex coacervation of gelatin and gum Arabic, for the manufacture of carbonless copying paper. The technologies developed for carbonless copy paper have led to the development of various microcapsule products in later years. 

Pense, A. M. Vauthier, C. Benoit, J. P. Preparation of microcapsules containing water-soluble amphi-philes by interfacial polycondensation. EP 407257, 1991. 

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 ... 

PECs have gained much attention in the past few years because of their potential applications in scientific and industrial interest. These can be used as membranes, " " for coating on films and fibers, for isolation and fractionation of proteins, for isolation of nucleic acid, - for binding pharmaceutical products, as supports for catalysU, and for preparation of microcapsules for drug delivery. Many of the applications are based on the functional properties of the polyelectrolytes " ... 

Microcapsules with a narrow size distribution containing oily core material can be prepared by a Shirazu porous glass (SPG) emulsification technique, followed by a suspension polymerization process. The SPG membrane is a special porous glass membrane with very uniform pore size. Guang Hui Ma et al. have reported the preparation of microcapsules containing hexadecane (oil core) using poly(styrene-... 

Microcapsules containing liquid pesticide have certain drawbacks. One example is when the pesticide is itself both volatile and toxic and has a high vapor pressure. A second example is when the capsule shell is strong and thick. In the first case, the pesticide diffuses very rapidly from the capsules and its odor initially repels the pest. Diffusion from the capsules is rapid, however, and when they are empty the pests return to the site (e.g., crops). In the second case, the capsules do not release the pesticide to produce a minimum effective level at the application site, and so pestiddal action is not achieved. In order to overcome these problems, a WO patent disclosed the preparation of microcapsules of pesticides containing pest attractant using a capsule-in-capsule approach [50]. As shown in Figure 5.18, the outer capsule contains pest attractant or food, in which the iruier capsule containing the pesticide, is encapsulated. 

Currently, many techniques are available for the preparation of microcapsules, though no single technique can be considered ideal . In view of the diversity and size of the microencapsulation field, the relevance of some techniques is outlined in Table 7.1 [2]. 

Selection of the wall material, core material and other additives has a substantial effect on the preparation of microcapsules with high strength, and with sufficient toughness and desirable size. 

As formerly mentioned, complex coacervation is one of the most employed methods in the preparation of microcapsules aimed at application on textiles. However, use of toxic reagents for a cross-linked coacervate shell (such as glutaraldehyde) is a big limitation in even greater exploitation of a complex coacervation approach. Research on more environmentally friendly coacervate shell should be continued and expanded. 

In light of environmental awareness, relevant research should be directed toward more sustainable reagents for the preparation of microcapsules but also in binding them to textiles. This aspect would widen the range of current applications. Furthermore, biodegradability of textile structures should especially be addressed, in particular regarding novel vehicles for intra-body delivery of drugs. 

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