Thickener technology

L. Svarovsky and A. J. Walker, "The Effect of Eeed Thickening on the Performance of a Horizontal Vacuum Belt Eilter," 1st World Congress Particle Technolog)/, Part IV, 331 Event of EFCE, Apr. 16—18, 1986, NMAmbH, Ni>mburg, Germany, 1986. 

Solvent Evaporation. This encapsulation technology involves removing a volatile solvent from either an oil-in-water, oil-in-oil, or water-in-oH-in-water emulsion (19,20). In most cases, the shell material is dissolved in a volatile solvent such as methylene chloride or ethyl acetate. The active agent to be encapsulated is either dissolved, dispersed, or emulsified into this solution. Water-soluble core materials like hormonal polypeptides are dissolved in water that contains a thickening agent before dispersion in the volatile solvent phase that contains the shell material. This dispersed aqueous phase is gelled thermally to entrap the polypeptide in the dispersed aqueous phase before solvent evaporation occurs (21). 

Aqueous dispersions are alternatives to solutions of Hquid and soHd resins. They are usuaUy offered in 50% soHds and may contain thickeners and cosolvents as stabilizers and to promote coalescence. Both heat-reactive (resole) and nonheat-reactive (novolak) systems exist that contain unsubstituted or substituted phenols or mixtures. A related technology produces large, stable particles that can be isolated as discrete particles (44). In aqueous dispersion, the resin stmcture is designed to produce a hydrophobic polymer, which is stabilized in water by an interfacial agent. 

From a physical point of view, suspensions are usually unstable systems, as the solid phase almost always tends to form a sediment. One of the most important aims with this type of dosage form must therefore be to prevent sedimentation. As this ideal condition can usually not be achieved, it is at least attempted to reduce the sedimentation rate and, above all, to make any sediment easy to redisperse. A number of auxiliaries are used in pharmaceutical technology to achieve this. They include thickeners, hydrophilic polymers, sugars and sugar alcohols, surfactants and electrolytes [296]. In spite of its insolubility, crospovidone can be classed as a hydrophilic polymer. 

---