Hollow fiber spinning, parameters

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 ... 

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. 

Hollow fibers have been used since the 1960s in many applications such as reverse osmosis, ultrafiltration, membrane gas separation, artificial organs, and other medical purposes. There are several advantages to hollow fibers over the flat sheet membranes the most important is their high surface-to-volume ratio. The use of hollow fibers has become popular in many industrial sectors since Mahon first patented the hollow fiber membranes [56]. The morphology and performance of hollow fibers are complex functions of many parameters involved in their manufacturing. McKelvey summarized the effect of spinning parameters on the macroscopic dimensions of hollow fibers [57]. 

The general process for preparation of the precursors consists of four steps, i.e. dope formation, casting/spinning, dehydration and post-treatment. There are many parameters that will affect the precursor properties during the preparation process. An example for the optimization of spinning condition was reported by He et al., who reported that the optimal conditions for spinning cellulose acetate hollow fiber membranes was found to be as follows bore fluid, water+ NMP (85%) air gap 25 mm bore flow rate, 40% of dope flow rate (2.2 mL min ) and temperature of quench bath, 50... 

Hollow fiber membranes with a positively charged nanofiltration selective layer have been fabricated by using asymmetric microporous hollow fibers made from a Torlon PAI type as the porous substrate followed by a post-treatment with poly(ethyleneimine) [79]. The membrane structure and the surface properties can be tailored by adjusting the polymer dope composition, spinning conditions, and the posttreatment parameters. 

In the fabrication of FIFMMRs, the porous hollow fiber membranes with asymmetric structures are first prepared through a phase-inversion/ sintering technique, which has been described in Chapter 2 of this book and in many recent publications [31]. The microstructure of the hollow fibers can be tailored as expected for different applications by modulation of the suspension composition and the spinning parameters [32, 33]. Aran et al. [5,21] developed porous AI2O3 FIFMMRs with various geometrical parameters for gas-liquid-solid (G-L-S) reactions. The Pd-AhOa catalyst... 

Key Spinning Parameters on PVDF Hollow-Fiber Formation and the... 

Ceramic hollow-fiber support can be fabricated by a phase inversion-based extrusion/sintering technique [3], which allows a more flexible control over the membrane macro/microstructures by adjusting fabricating parameters such as air-gap, extrusion rate, internal coagulant composition, and the amount of nonsolvent additive in the spinning suspensions [4]. Such unique structural diversity delivers... 

The book, Hollow Fibers (Scott, 1981) is an excellent practical source for details about the large-scale manufacture of hollow fibers. The effect of spinning parameters on both the macroscopic dimensions and permeation performance of polysulfone ultrafiltration hollow fibre membranes has been studied by several people (Kim et al., 1995, Liu et al., 1992, McKelvey et al., 1997, and Lee et al., 1995). The latter paper uses a factorial design to study the effects of various spinning parameters, and gives optimal spinning conditions for ultrafiltration performance. 

For gas separation hollow fibers, there have been a few systematic studies on the effect of spinning parameters on both the macroscopic dimensions and permeation performance. One paper studies silicone rubber coated polyimide hollow fibres (Chung et al., 1992), another silicone rubber... 

Effect of Spinning Parameters on the Separation Performance of PPO Hollow Fibers... 

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