Spinning hollow fibers

Hollow-fiber permeators, 26 22 Hollow fibers, 13 389-390 cellulose ester, 26 19 cellulosic, 26 18-20 ion-exchange, 26 15 mechanical considerations and dimensions for, 26 5-7 natural polymer, 26 23 polyacrylonitrile, 26 23 polyamide, 26 21-22 post-treatment of, 26 13-14 preparation of, 26 3 production of, 19 757 with sorbent walls, 26 26 technology of, 26 27 wet spinning of, 25 816, 817-818 Hollow-fiber spinning processes, 26 7-12 Hollow fiber spinning technology,... 

These solvents include tetrahydrofuran (THF), 1,4-dioxane, chloroform, dichloromethane, and chlorobenzene. The relatively broad solubility characteristics of PSF have been key in the development of solution-based hollow-fiber spinning processes in the manufacture of polysulfone asymmetric membranes (see Hollow-fibermembranes). The solvent list for PES and PPSF is short because of the propensity of these polymers to undergo solvent-induced crystallization in many solvents. When the PES structure contains a small proportion of a second bisphenol comonomer, as in the case of RADEL A (Amoco Corp.) polyethersulfone, solution stability is much improved over that of PES homopolymer. 

Hollow fiber spinning dopes and preparation procedures vary over a wider range than their flat-sheet equivalents, but some representative dopes and spinning conditions taken from the patent literature [98,103,104] are given in Table 3.4. 

FIGURE 5.66 Schematic diagram of a hollow-fiber spinning process. (After Chung, T. S. and Hu, X. 1997. /. Appl. Polym. Sci.y 66, 1067. With permission. )... 

G.G. Lipscomb, The melt hollow fiber spinning process steady-state behavior, sensitivity and stability, Polym. Adv. Tech., 5 (1994) 745-758. 

Y. Su, G.G. Lipscomb, H. Balasubramanian, and D.R. Lloyd, Theoretical Observations of Recirculation Regions in the Bore Fluid during Hollow Fiber Spinning, AIChEJ, 52 (2006) 2072-2078. 

H. Balasubramanian, Heat-Mass-Momentum Transfer in Hollow Fiber Spinning, Dissertation, University of Texas, 2004. 

Manufacture of gas-separation membrane modules is largely a machine-assisted, labor-intensive operation. Polymer dopes are typically prepared batchwise with sufficient hold time to insure uniformity. The membrane performance is largely controlled by the polymer precipitation step and very dependent upon phase behavior and precipitation kinetics. Thus, it is essential that processing conditions be maintained as uniformly and as constant as possible if product quality and uniformity is to be preserved. For this reason, membrane-fihn formation and hollow-fiber spinning processes are usually operated continuously or for extended run times. Since the intermediate film or fiber must eventually be converted into discrete items, the continuous process is typically interrupted by collection of the membrane formed on spools or fiber skeins where it may be inventoried briefly before batch processing into the final assembly resumes. 

A complete hollow-fiber spinning system is shown in Figure 19. Fibers are formed almost instantaneously as the polymer solution leaves the spinneret. The amount of evaporation time between the solution exiting the spinneret and entering the coagulation bath is a critical variable. If water is forced through the... 

Solubility of the three commercial polysulfones follows the order PSF > PES > PPSF. At room temperature, all three of these polysulfones as well as the vast majority of other aromatic sulfone-based polymers can be readily dissolved in a handful of highly polar solvents to form stable solutions. These powerful solvents include NMP, DMAc, pyridine, and aniline. 1,1,2-Trichloroethane and 1,1,2,2-tetrachloroethane are also suitable solvents but are less desirable because of their potentially harmful health effects. In addition to being soluble in the aforementioned list, PSF is also readily soluble in a host of less polar solvents by virtue of its lower solubility parameter. These solvents include tetrahydrofuran (THF), 1,4 dioxane, chloroform, dichloromethane, and chlorobenzene. The relatively broad solubility characteristics of PSF have been key in the development of solution-based hollow-fiber spinning processes in the manufacture of polysulfone asymmetric membranes (see Membrane Technology). The solvent list for PES and PPSF is short because of the propensity of these polymers to undergo solvent-induced crystallization in many solvents. When the PES structure contains a small proportion of a second bisphenol comonomer, as in the case of RADEL A (British Petroleum) polyethersulfone, solution stability is much improved over that of PES homopolymer. 

Figure 3.7. Schematic diagram of hollow fiber spinning system. (Reproduced from [35] with permission.)...

Hollow fiber spinning is usually based on the dry-wet phase inversion process that involves the following four steps ... 

Figure 16.1 Hollow-fiber spinning unit (dry-jet wet spinning).

Hollow fiber spinning of a Newtonian liquid, in which there are two free surfaces, is discussed in... 

For unsupported polymeric membranes (i.e. hollow fibers), spinning parameters are cracial factors that must be controlled during hollow fiber preparation. These parameters include the amount and types of polymer, solvents, and additives mixed irrto the spimung dope, the dope and bore fluid flow rates, the fibre take-up velocity, the air gap distance (unless wet spinning is used), and the coagulant bath temperature [31,71]. The main challenges in hollow fiber spinning, as proposed by Puri [72], are ... 

After the polymer is fully dissolved, the solution is degassed for 48 h by the ultrasonic method (Branson Ultrasonics) to remove tiny air bubbles. Finally, the homogeneous solution is stored in a bottle and is ready for hollow fiber spinning. 

Fig. 5.2 Schematic diagram of hollow fiber spinning system (i) nitrogen cylinder, (2) dope reservoir (2) gear pump (4) on-line filter, (5) syringe pump (6) spinneret (7) forced convective tube (S) roller (9) take-up drum (10) refrigeration/heating unit (11) coagulation bath (12) washing/ treatment bath (13) take-up bath (14) schematic spinneret. [1]...

A next-future application of MOFs is predicted for MOF-oiganic polymer-based mixed matrix membranes in hollow fiber or spiral wound geometry. Established membrane production technologies such as hollow fiber spinning or foil casting can be used for the preparation of mixed matrix membranes. Further, MOFs match much better with organic polymers than zeolites, for example, even if the latter have been hydrophobized, such as by silylation. 

The choice of the membrane module is mainly determined by economic considerations. The production costs in a membrane production plant are sensitive to the produced volume. In a hollow fiber spinning plant operating continuously, the membrane costs are in a range of 2 5 per m of membrane area. An equivalent of spiral-wound modules" would cost 10-100 per m. ... 

BAEC) coated hollow fibers spinning at 750 RPM. Thrombus deposition on (b) uncoated and (c) BAEC-coated hollow fibers exposed to bovine blood. (Adapted from Polk, A.A., Maul, T.M., and McKeel, D.T. 2010. Biotechnol Bioeng 106 490-500.)... 

Figure 6 Illustration of asymmetric hollow fiber spinning process.

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