Microcapsules with reactive shells

The use of binders has some drawbacks, however. The amount used should be high enough for a good fixation, but should not disturb the controlled release. A microcapsule covered with a binder may be harder to break, or the binder layer may prevent the release from the fabric after the microcapsule has been broken. Binders may also mask the surface properties of the fibers in the fabric. In order to increase and to ameliorate the use of microcapsules as controlled deHvery vehicles for textiles, microcapsules with reactive shells that bond covalently to the fibers have been developed (e.g., reactive groups used in reactive dyestuffs). Such choice is not unlimited because the microcapsules should be able to withstand the conditions necessary for the binding reaction to occur ... 

A key feature of encapsulation processes (Figs. 4a and 5) is that the reagents for the interfacial polymerisation reaction responsible for shell formation are present in two mutually immiscible Hquids. They must diffuse to the interface in order to react. Once reaction is initiated, the capsule shell that forms becomes a barrier to diffusion and ultimately begins to limit the rate of the interfacial polymerisation reaction. This, in turn, influences morphology and uniformity of thickness of the capsule shell. Kinetic analyses of the process have been pubHshed (12). A drawback to the technology for some apphcations is that aggressive or highly reactive molecules must be dissolved in the core material in order to produce microcapsules. Such molecules can react with sensitive core materials. 

Stable core-shell microcapsules, which have a similar profile of properties as MF capsules but do uot use formaldehyde, are hitherto uukuowu iu the free market. FoUmauu Co. has succeeded iu mauufacturiug stable microcapsules without the most reactive aldehyde-kuowu formaldehyde, which are comparable with MF techuology iu terms of chemical aud physical resistauce. 

Interfacial polymerization techniques can be used to prepare robust microcapsules (about 4 pm) that have selectively incorporated functionality such as catalytic groups in their liquid-core domains. The synthesis of these particles is achieved via an oil-in-oil emulsion in combination with interfacial polymerization methods and allows for the encapsulation of substrates not compatible with water-in-oil or oil-in-water emulsion systems (Kobalija and McQuade, 2006). Often these capsules have polyurea shells that can be formed from w/o emulsions containing reactive polyols and isocyanates. This has been very elegantly demonstrated by McQuade and coworkers for the DMAP-catalyzed acylation transformation of an alcohol within the protected environment of polyurea microcapsules formed from reaction of a polyisocyanate and a poly(vinyl alcohol) in the presence of an amine catalyst (Price et ah, 2006 Poe et al, 2007). 

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