Polymer evaporation

Several parenteral microencapsulated products have been commercialized the cote materials ate polypeptides with hormonal activity. Poly(lactide— glycohde) copolymers ate the sheU materials used. The capsules ate produced by solvent evaporation, polymer-polymer phase separation, or spray-dry encapsulation processes. They release their cote material over a 30 day period in vivo, although not at a constant rate. 

Dynamics and Pattern Formation in Evaporating Polymer Solutions 191... 

These two examples show that regular patterns can evolve but, by definition, dissipative structures disappear once the thermodynamic equilibrium has been reached. When one wants to use dissipative structures for patterning of materials, the dissipative structure has to be fixed. Then, even though the thermodynamic instability that led to and supported the pattern has ceased, the structure would remain. Here, polymers play an important role. Since many polymers are amorphous, there is the possibility to freeze temporal patterns. Furthermore, polymer solutions are nonlinear with respect to viscosity and thus strong effects are expected to be seen in evaporating polymer solutions. Since a macromolecule is a nanoscale object, conformational entropy will also play a role in nanoscale ordered structures of polymers. 

The tendency toward Pu(IV) polymerization is of considerable practical importance in process operations involving plutonium solutions. Dilution of an acidic plutonium solution with water can result in polymerization in localized regions of low acidity, so plutonium solutions should be diluted instead vdth acid solutions. Polymerization can result from leaks of steam or water into plutonium solutions or by overheating during evaporation. Polymer formation can clog transfer lines, interfere with ion-exchange separations, cause emulsification in solvent extraction and excessive foaming in evaporation, and can result in localized accumulation of plutonium that may create a criticality hazard [CS]. 

Microencapsulation is common in pharmaceutical industry, particularly when sustained release of a medication is required. Ethyl cellulose is a common coating material. Most capsules are formed by solvent evaporation, polymer-polymer phase separation, or fluidized-bed coating process. Common examples of encapsulated drugs include aspirin, acetaminophen, ampidlhn, and potassium chloride. Orally administered capsules serve to conceal an unpleasant taste and reduce gastrointestinal irritation that can be caused by oral unencapsulated drug. 

Arshady R. Microspheres and microcapsules, a survey of manufacturing techniques. 3. Solvent evaporation. Polymer Engineering Science. 1990 30 915-924. 

Bormashenko, E., Pogreb, R., Stanevsky, O., Bormashenko, Y., Stein, T., Gengehnan, O. Mesoscopic patterning in evaporated polymer solutions new experimental data and physical mechanisms. Langmuir 21, 9604—9609 (2005)... 

Some of the processing parameters are the nature of the solvent (polarity, conductivity, solubility, rate of evaporation), polymer concentration (viscosity, surface... 

Bormashenko E, Pogreb R, StanevskyO, Bormashenko Y, Gendelman O. (2005) Formation of honeycomb patterns in evaporated polymer solutions Influence of the molecular weight. Mater Lett 59 3553-3557. 

In the case of polymer nanocomposite preparation, the frequently utilized methods are usually solution based (Rahman and Chung, 2013 He et al., 2011 Bu et al., 2013). First, the polymer is dissolved in a suitable solvent, and the solution is then cast after evaporation, polymer films can be obtained. The chosen filler is directly added into the solution, often with ultrasonication for a homogenous dispersion. The methods used in this case are film casting (Figure 16.13) or drop casting (Figure 16.14) (Rahman et al.. 

Electrospinning stage Solution rheology Solvent evaporation Polymer conformation... 

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