Microcapsules, formation

Several other investigators have reported microencapsulation methods based upon polyelectrolyte complexes [289, 343]. For example, oppositely-charged polyelectrolytes (Amberlite IR120-P (cationic) and Amberlite IR-400 (anionic)) were recently used along with acacia and albumin to form complex coacervates for controlled release microcapsule formations [343]. Tsai and Levy [344,345] produced submicron microcapsules by interfacial crosslinking of aqueous polyethylene imine) and an organic solution of poly(2,6 dimethyl... 

Dobetti and Pantaleo (38) investigated the influence of hydrodynamic parameters per se on the efficiency of a coacervation process for microcapsule formation. They based their work on that of Armenante and Kirwan (39) who described the size of the smallest eddies or vortices generated in a turbulent regime on a microscopic scale in the vicinity of the agitation source, i.e., microeddies, as... 

Burgess, D.J. (1994). Complex coacervation microcapsule formation. In Dubin, P., Bock,... 

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. 

Microcapsule Format for delivery (i.e., liquid or powder) Storage stability Stability to different process conditions Release properties Particle size Payload (bioactive core loading) Cost of production... 

Table 3 lists some of the typical polymer-polymer coacer-vation systems investigated for microcapsule formation. 

Fig. 5 Stroboscopic images of microcapsule formation via midair collision between two component liquids (scale bar = 100 pm) (A) and bright-field microscope images of microcapsules (B). The left and streams are 0.25% alginate solution and 4% PLGA solution, respectively. The nozzle orifice diameter d = 60 pm volumetric flow rate Q = 0.6 ml/min and forcing frequency / = 10.6 kHz. (From Ref...

The structural capsules start to be formed in films subjected to deformation in liquids until some tension threshold. Microcracks and microvoids appear and are filled with the inhibiting liquid under tensile stresses exceeding the polymer flow limit. Capillary channels connecting these voids with the process liquid and with each other start to merge or open in the course of structural transformations but do not disappear fully. The liquid may move over the network of the formed channels beyond the polymer matrix limits or concentrate in some voids able under certain conditions to enlarge the manifold. Thermal treatment of the deformed film intensifies the relaxation processes in the polymer matrix, the film shrinks in the tension direction and the capillaries between voids link up densely, thus insulating liquid particles from each other. If the film is treated in the extended state, a more complex mechanism of microcapsule formation is realized [4]. Cl liberation from microcapsules is related to their ability to break spontaneously under residual... 

FIGURE 5.82 Microcapsule formation by interfacial and in situ polymerization. A and B are reactants, while— (A-B) —and—(A) —are polymeric products. See text for explanation. (After Thies, C. 1989. Biomaterials and Medical Applications, Encyclopedia Reprint Series, J. I. Kroschwitz, ed., pp. 346-367. John Wiley, New York.)... 

Burgess, D.J., Dubin, PL., Bock, J., Davis. Schulz. Complex Coacervation Microcapsule Formation in Macromolecular Complexes in Chemistry and Biology, Springer-Verlag Berlin, Germany, 1994, pp. 285-300. 

Currently, two methods for coacervation are available, namely simple and complex processes. The mechanism of microcapsule formation for both processes is identical, except for the way in which the phase separation is carried out. In simple coacervation a desolvation agent is added for phase separation, whereas complex coacervation involves complexation between two oppositely charged polymers. 

Figure 1.17 Schematic representation of microcapsule formation by spinning disk.

The large surface area of microcapsules allows for the formation of a uniform and continuous coating on the surface of the fabric as well as in between the fibers (Liu et al., 2013). The reasons for microcapsules playing an important role in the controlled release of active agents could be found in the uniformity and reproducibility in release (Singh et al., 2010). The following sections will focus on microcapsule formation and their embedding into textile stmctures. 

Richardson JJ, Teng D, Bjommalm M, Gunawan ST, Guo J, Cui J, et al. Fluidized bed layer-by-layer microcapsule formation. Langmuir 2014. 

Many pairs of oppositely charged Polyelectrolytes (qv) are able to form a liquid complex coacervate suitable for microcapsule formation. Normally, gelatin is the positively charged polyion, because it is readily available and forms suitable complex coacervates with a wide range of polyanions. Polyanions typically used include gum arabic, polyphosphate, poly(acrylic acid), and alginate. 

The methods used for microcapsule formation have been recently reviewed. The most widely used procedure involves the gelation of charged polyelectrolytes around the cell core. The popular alginate-L-polylysine microcapsules, for example, are obtained in the following sequence ... 

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