Cooling polymer solution

Extrusion Processes. Polymer solutions are converted into fibers by extmsion. The dry-extmsion process, also called dry spinning, is primarily used for acetate and triacetate. In this operation, a solution of polymer in a volatile solvent is forced through a number of parallel orifices (spinneret) into a cabinet of warm air the fibers are formed by evaporation of the solvent. In wet extmsion, a polymer solution is forced through a spinneret into a Hquid that coagulates the filaments and removes the solvent. In melt extmsion, molten polymer is forced through a multihole die (pack) into air, which cools the strands into filaments. 

Phase Inversion (Solution Precipitation). Phase inversion, also known as solution precipitation or polymer precipitation, is the most important asymmetric membrane preparation method. In this process, a clear polymer solution is precipitated into two phases a soHd polymer-rich phase that forms the matrix of the membrane, and a Hquid polymer-poor phase that forms the membrane pores. If precipitation is rapid, the pore-forming Hquid droplets tend to be small and the membranes formed are markedly asymmetric. If precipitation is slow, the pore-forming Hquid droplets tend to agglomerate while the casting solution is stiU fluid, so that the final pores are relatively large and the membrane stmcture is more symmetrical. Polymer precipitation from a solution can be achieved in several ways, such as cooling, solvent evaporation, precipitation by immersion in water, or imbibition of... 

A schematic diagram of the polymer precipitation process is shown in Figure 8. The hot polymer solution is cast onto a water-cooled chill roU, which cools the solution, causing the polymer to precipitate. The precipitated film is passed through an extraction tank containing methanol, ethanol or 2-propanol to remove the solvent. Finally, the membrane is dried, sent to a laser inspection station, trimmed, and roUed up. The process shown in Figure 8... 

HoUow-fiber fabrication methods can be divided into two classes (61). The most common is solution spinning, in which a 20—30% polymer solution is extmded and precipitated into a bath of a nonsolvent, generally water. Solution spinning allows fibers with the asymmetric Loeb-Soufirajan stmcture to be made. An alternative technique is melt spinning, in which a hot polymer melt is extmded from an appropriate die and is then cooled and sohdified in air or a quench tank. Melt-spun fibers are usually relatively dense and have lower fluxes than solution-spun fibers, but because the fiber can be stretched after it leaves the die, very fine fibers can be made. Melt spinning can also be used with polymers such as poly(trimethylpentene), which are not soluble in convenient solvents and are difficult to form by wet spinning. 

Phthahc resins are usually processed to an acid number of 25—35, yielding a polymer with an average of 1800—2000. The solution viscosity of the polymer is usually followed to ascertain the polymer end point. The resin is cooled to 150°C and hydroquinone stabilizer (150 ppm) is added to prevent premature gelation during the subsequent blending process with styrene at 80°C. The final polymer solution is cooled to 25°C before a final quaUty check and dmmming out for shipment. 

Dry polymers can be stored for up to 2 years, but are hygroscopic and absorb moisture from the air. Keep them in sealed bags in a cool, dry storeroom. Batches of polymer solutions made from dry polymers should be used within 24 hours. 

All attempts to isolate efficient process giving a white solid polymer which appears to have repeating keteneimine units. This assignment is consistent with the very strong absorption at 2140 cm.-1 in the infrared spectrum. ... 

Figure 9 Qualitative phase diagram of a polymer solution showing phase separation both on heating (at the lower critical solution temperature) and on cooling (at the upper critical solution temperature). (From Ref. 31.)...

A typical commercial reactor consists of a vertical tube, up to 10 m in height, into the top of which the monomer is fed continuously. As polymerization proceeds, the increasingly viscous polymer solution travels down the column. Molten polymer is drawn from the bottom of the reaction tube and is subsequently cooled and chopped into pellets. The final manufacturing stage consists of exposing the pellets to a strong vacuum at a slightly elevated temperature to remove residual monomer and water. 

A portion of each solution was retained for analysis of carb-oxylate content at zero time. Samples of the polymer solutions were weighed into glass jars, the pH adjusted to 8.5 and the jars were sealed with tightly fitting screw caps. The jars were placed in thermostatted ovens at 90°, 108°, and 120°C. After the appropriate time, the jars were removed, cooled and weighed to ensure no loss of contents, prior to analysis for hydrolysis. 

Fig. 17 B/E-p dependence of the critical temperatures of liquid-liquid demixing (dashed line) and the equilibrium melting temperatures of polymer crystals (solid line) for 512-mers at the critical concentrations, predicted by the mean-field lattice theory of polymer solutions. The triangles denote Tcol and the circles denote T cry both are obtained from the onset of phase transitions in the simulations of the dynamic cooling processes of a single 512-mer. The segments are drawn as a guide for the eye (Hu and Frenkel, unpublished results)...

Tg (-22 °C) of a homogeneous 70/30 PNIPAM-water mixture. Observation of samples by scanning electron microscopy and optical microscopy revealed that the morphology of the polymer-rich phase is preserved only if the polymer solutions are brought to zone C. Polymer solutions heated to zone B undergo demixing upon quench-cooling [160]. Aqueous solutions of PVCL, PNIPMAM, and PNIPMA exhibit similar behaviour [157,158,369,370]. 

The measurements were carried out while increasing the temperature in 0.5 °C increments at intervals of 30 min., using an aqueous solution of the polymers in Pyrex tubes(5 ml volume). Each tube contained a short glass rod which was used to stir the solution after being filled with the polymer solution of 0.05 -2.5 wt %, each tube was evacuated and sealed. The warm up to 70 °C was carried out in a water bath. The cloud point was taken as the temperature at which phase separation was first noted it was compared with the temperature at which the solution first became clear again while cooling. 

In the first zone, the solution is heating for starting polymerisation, but because of the exothermic reaction, cooling becomes necessary in the second and third zones. The polymer solution is then extruded as fine strands into a devolatilising vessel. This vessel is heated to a temperature of 225°C and then the solvent and unreacted monomer is removed. The molten material is fed into an extruder, then cooled and finally chopped. 

Propane was selected as solvent for the isobutene for experiments down to -145° the aluminium chloride was dissolved in ethyl chloride, for the work at lower temperatures a mixture of ethyl chloride and vinyl chloride was used. Although these catalyst solutions were made up at -78° they were yellow, and as stated above, they probably contained some hydrogen chloride and other catalytically active decomposition products. The polymerisations were carried out by running the cooled catalyst solution into the monomer solution. Polymer was formed, and came out of solution, almost immediately, and the reaction was very fast even at the lowest temperature (-185°) and lowest monomer concentration (0.6 mole/1). After the reaction was over, propanol at the reaction temperature was added to the reaction mixture to deactivate the catalyst. 

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