Hollow-fiber membranes solvent spinning

Khayet et al. prepared a number of poly(vinyhdene fluoride) hollow fiber membranes for ultrafiltration using the solution spinning method. N,N-dimethylaceta-mide (DMAc) was the solvent, and ethylene glycol was the nonsolvent additive [37]. The effect of the concentration of ethylene glycol in the PVDF spinning solution, as well as the effect of the concentration of ethanol either in the bore liquid or in the coagulation bath, on the morphology of the hollow fiber membrane was stud-... 

Asymmetric hollow fiber membranes of polysulfone, polyethersulfone, and polyphenylsulfone can be prepared by phase inversion spinning solvent/nonsolvent dopes, i.e., N-methylpyrrolidone/formamide. These asymmetric hollow fiber membranes possess a microscopically observable skin supported by a porous open cellular network. The walls of the open cells of the matrix are composed of arrays of interconnected spherical micelles. With increasing proximity to the outer surface, the packing density of the spherical micelles increase with a concomitant decline in interstitial porosity. At the outer surface layers, the packing of the micelles becomes... 

For polymeric hollow fiber membranes, spinning parameters are crucial factors that must be controlled during the preparation of membranes. These parameters include the amount and type of polymers, solvents, additives mixed into the spinning dope solution, the dope and bore fluid rate, the kind of bore fluid, the fiber take-up velocity, the air-gap distance (unless wet spinning is used), and the coagulant bath temperature and the kind of coagulant bath. 

Hollow fiber membranes are generally solvent spun and as such can be considered a sub-group of solvent spinning. Major polymers used in these processes are polysulfone, Polyvinylidene diflouride(PVDF) and polyether-sulfone. The major applications are hemodialysis, water purification, and air separation. This is a huge business that has been growing at over 10% per annum for many years. Although the product usage in annual tons is very small, the end-use revenue is in billions (Anon., 2011). 

The PEI substrate hollow fibers were prepared using the dry - wet spinning technique to form integrally skinned asymmetric hollow fiber membranes. Two different polymer solution compositions were utilized. In the first case a 22.5 wt% solution of PEI in dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP), containing 1.0 - 1.5 wt% of lithium nitrate was used following the method similar to that described by Deng and others. In the second case a spinning procedure described by Kneifel and Peinemann was adopted. Here NMP was used as the solvent and y-butyrolactone (GBL) was used as the nonsolvent. 

This is a systematic study of the effect of several variables in the spinning process on the dimensions, morphology and CO2/CH4 gas separation performance of poly (2,6-dimethyl-1, 4-phenylene oxide) (PPO) hollow fiber membranes. Hollow fibers were prepared by the dry-wet spinning method from solutions of PPO in trichloroethylene using the non-solvent methanol as the bore liquid and for the gelation bath. 

These solvents include tetrahydrofuran (THF), 1,4-dioxane, chloroform, dichioromethane, and chloroben2ene. The relatively broad solubiHty characteristics of PSF have been key in the development of solution-based hoUow-fiber spinning processes in the manufacture of polysulfone asymmetric membranes (see Hollow-fibermembranes). The solvent Hst for PES and PPSF is short because of the propensity of these polymers to undergo solvent-induced crysta11i2ation in many solvents. When the PES stmcture contains a small proportion of a second bisphenol comonomer, as in the case of RADEL A (Amoco Corp.) polyethersulfone, solution stabiHtyis much improved over that of PES homopolymer. 

A suitable polymer material for preparation of carbon membranes should not cause pore holes or any defects after the carbonization. Up to now, various precursor materials such as polyimide, polyacrylonitrile (PAN), poly(phthalazinone ether sulfone ketone) and poly(phenylene oxide) have been used for the fabrication of carbon molecular sieve membranes. Likewise, aromatic polyimide and its derivatives have been extensively used as precursor for carbon membranes due to their rigid structure and high carbon yields. The membrane morphology of polyimide could be well maintained during the high temperature carbonization process. A commercially available and cheap polymeric material is cellulose acetate (CA, MW 100 000, DS = 2.45) this was also used as the precursor material for preparation of carbon membranes by He et al They reported that cellulose acetate can be easily dissolved in many solvents to form the dope solution for spinning the hollow fibers, and the hollow fiber carbon membranes prepared showed good separation performances. 

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. 

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