*4.2.1 Interfacial polymerization*

*Nano- and Microencapsulation - Techniques and Applications*

recovery rate was recorded for the assemble comparatively for the same collection time with no significant changes in size and morphology [55]. Also, Lee and coworkers [61] designed functionable poly-styrene-random-glycidyl methacrylate that was used to fabricate microparticles via electrospraying. They further studied the influence of both polymer factors and process parameters on the size and morphology of the fabricated microparticles. Their results showed that polymer structure and properties can be used to tune the structural parameters of the capsules [61]. Jet cutting method for droplet generation: This technique commercialized by geniaLab is a rarely used but cost effective technique that depends on a set of cutting wires that serve as a cutting tool for a jet of liquid as it rotates about its axis to generate uniformly sized droplets that is shaped as a result of surface tension. It is suited for cutting high viscosity liquids that harden on cooling or by ionotropic gelation. The drops generated are generally in the size range of 120 μm to 3 mm. Paulo and colleagues [62] recently x-rayed the process parameters requisite for the generation of optimally suited calcium alginate beads using the jet cutter. A maximum flow rate of 49 mL/ minute yielded beads of about 2 mm size. Increasing the rotational speed of the cutter decreased the bead size by 50% though increased the tangential velocity of the droplets leading to a larger space requirement for product collection [62]. Other parameters such as gravitational force, surface tension, viscosity and flow rate were also noted. A major limitation is the cutting loss occurring with each cut of the liquid jet.

*(a) Coaxial assembly for electrospraying. (b) Inner and outer coaxial needles [59].*

Phase inversion and separation occurs in a system due to mass transfer. Usually, for phase inversion to be induced, a polymer solution is exposed to a miscible nonsolvent. When a polymer solution is exposed to its non-solvent, the solvent molecules would move out of the polymer while the non-solvent will move in. The first step in the process is to dissolve a polymer in its solvent. The second step is to cast the polymer solution. The third step is to initiate phase separation by immersion of the cast polymer in a coagulation bath containing the non-solvent. Other methods that have been used to induce phase separation is non-solvent vapor [63]. Ammendola and colleagues [63] used the phase inversion technique to prepare fragrance loaded cellulose acetate microcapsules. They then compared the vapor induced phase separation with immersion induced phase separation. Their study showed that the

**18**

*4.1.7 Phase inversion*

**Figure 7.**

In this technique, the wall material is made to form at the oil-in-water interface of dispersed oil drops. Monomers of the wall forming polymer (usually multifunctional) is first dissolved in the core material and then emulsified in the aqueous continuous phase containing other polymerization reactant. Polymerization ensues right after on both sides of the interface of the dispersed oil drops with water leading to the formation of rigid capsule walls [64]. Particle sizes as low as 3 μm can be achieved though most commercialized capsules from this technique are in the range of 20–60 μm. This technique can also be employed for reverse emulsions. The polymerization occurs across the interface of the droplets. Four major groups of polymers have been employed and include polyamides, polyurea, polyurethane and polyesters in applications that spans the fields of agriculture, pharmaceutics, cosmetics, and energy storage materials. Interfacial polymerization is a well-controlled technique capable of delivering targeted sizes and morphology. An interfacial polymerization approach has been developed that makes use of safer polymers for cosmetic and internal use is the transacylation interfacial polymerization. In this approach, biodegradable oligosaccharides, polysaccharides such as acacia; and polyethylene glycol, and alginate are used in the internal and external phases respectively or vice versa. On mixing the two phases, acacia reacts with the carboxylic acid group of the propylene glycol leading to the overall attachment of alginate and release of polyethylene glycol. The operational shell material is made up of acacia-alginate polymer that does not require further crosslinking [65].
