Thermally induced phase separation method

Nam, Y.S., Park, T.G., 1999. Biodegradable polymeric microceUular foams hy modified thermally induced phase separation method. Biomaterials 20, 1783. 

Thermally induced phase separation method In this method, phase inversion is introduced by lowering the temperature of the polymer solution. A polymer is mixed with a substance that acts as a solvent at a high temperature and the polymer solution is cast into a film. When the solution is cooled, it enters into an immiscible region due to the loss of solvent power. Because the solvent is usually nonvolatile, it must be removed with a liquid that is miscible with the solvent but not miscible with the polymer. 

Similarly, Guan et al. (2007) developed an elastomeric poly (ester urethane)-urea scaffold by a thermally induced phase separation method for the release of bFGF. The scaffold maintained bFGF bioactivity over a period of 21 days and showed a two-phase protein release pattern, characterized by a fast initial release of about 30% in the first 2 days, followed by a slow release over a period of 4 weeks. 

FIGURE 6.3 Electrospinning set up for thermally induced phase separation method. 

Rajabzadeh S, Maruyama T, Ohmukai Y, Sotani T, Matsuyama H. Effect of additives on the morphology and properties of poly(vinyledene flouride) blend hollow fiber membrane prepared by the thermally induced phase separation method. Sep Purif Technol 2009 66 76-83. 

There have been many studies on the morphology of hollow fibres but few relate systematically the spinning conditions to the morphology of the hollow fibres. The effect of spinning conditions on the anisotropy of pore size (the change in pore size across the fibre wall) has been systematically studied for the formation of microporous fibres using the thermally induced phase separation method (Batarseh, 1999). 

Several main synthesis methods widely applied to produce carbon nanotube-polyurethane nanocomposites were summarized above. In addition, latex technology (27), thermally induced phase separation (28), electrospinning (29,30) and many other methods also show their own advantages and promises, however, these methods will not be discussed here. 

Hydrophilic MF membranes can be made by the dry-wet phase inversion technique, which can also be used to make PVDF membranes. On the other hand, other hydrophobic microflltration membranes are made by the thermally induced phase separation technique. In particular, semicrystalline PE, PP, and PTFE are stretched parallel to the direction of film extrusion so that the crystalline regions are aligned in the direction of stretch, while the noncrystalline region is ruptured, forming long and narrow pores. Hydrophobic membranes do not allow penetration of water into the pore until the transmembrane pressure drop reaches a threshold called the liquid entry pressure of water (LEPw). These membranes can therefore be used for membrane distillation. The track-etching method is applied to make microfiltration membranes from PC. 

Thermally-induced phase separation has been applied to the production of polysilane foams. Variation of polymer concentration, solvent type, and cooling rate have been used to refine the macrostructure. Both these membrane production methods rely on the formation of aggregates of controlled size and shape as discussed in the previous section. 

Yang M.C., Perng J.S., Comparison of solvent removal methods of microporous polypropylene tubular membranes via thermally induced phase separation using a novel solvent Camphene, J. Polym. Res. Taiwan, 6(4), 1999, 251-258. 

Another scaffold fabrication technique is thermally induced phase separation (TIPS) [34,46,84,147-149]. TIPS involves decreasing the temperature of a polymer solution to obtain a polymer-rich and polymer-poor phase. Following phase separation, the solvent is removed using one of a number of methods (freeze drying, evaporation) resulting in the formation of pores in the polymer stracture. TIPS can also be combined with the use of porogens to increase void fraction, have better control over pore size, or improve pore interconnectivity. 

Methods used for preparing of poly(ester urethane)-urea scaffolds are electro-spinning, solvent casting/salt leaching, phase inversion, laser excimer, and thermally induced phase separation. Electrospun poly (ester urethane)-ureas are elastomeric and the synthesis method allows control of fiber diameter, porosity, and degradation rate. All these properties aid in the development of soft tissue scaffolds. However, electro-spinning produces fibers with unacceptably small pore sizes. Thermally induced phase... 

Kim Jeong R, Kim Ji Hoon, Lee Young Moo, and Drioli Enrico. Thermally induced phase separation and electrospinning methods for emerging membrane applications A review. AIChE. J. 62 no. 2 (2016) 461-490. DOI 10.1002/aic.l5076. 

The phase-separation method was developed at Kent State University in the late 1980s. It consists of in sitn segregation of liqnid crystalline microdroplets from a homogeneous mixture of liquid crystal and polymer/prepolymer, indnced by a factor that gave the techniqne its name, as follows (a) polymerization-induced phase separation (PIPS) (b) solvent-induced phase separation (SIPS) and (c) thermally induced phase separation (TIPS). 

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