Hollow fibers, fabrics poly

Feng et al. [32] studied the morphology of the inner and outer surfaces of hollow fibers fabricated from poly(etherimide) by TM-AFM. The hollow fibers were fabricated by the dry-wet phase inversion method at two different bore fluid flow rates, 0.1 and 0.4 mLmin and their effect on the surface morphology was investigated. The average pore sizes on the inner surface were 39.8 and 81.9 nm, respectively, for 0.1 and 0.4 mLmin while those on the outer surface were 218.4 and 93.4, respectively, for 0.1 and 0.4 mLmin h It is interesting to note that the pore size increased with an increase in the bore fluid flow rate at the inner surface, while the opposite was the case at the outer surface. 

Khulbe et al. [4] conducted an AFM study of the cross section of UF poly(ether-imide) hollow fibers, fabricated by the dry-wet spinning method at various air gaps. 

Hollow-fiber fabrication methods can be divided into two classes (62,63). The most common is solution spinning, in which a 20-30% polymer solution is extruded and precipitated into a bath of a nonsolvent, generally water. Solution spinning allows fibers with the asymmetric Loeb-Sourirajan structure to be made. An alternative technique is melt spinning, in which a hot polymer melt is extruded from an appropriate die and is then cooled and solidified in air or a quench tank. Melt-spun fibers are usually relatively dense and have lower fluxes than solution-spim 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. 

Hollow fibers and spheres of zeolite (labeled as HFZ and HSZ, respectively) were successfully fabricated using carbon fibers and polystyrene (PS) spheres as templates respectively, through layer-by-layer technique, coupled with removal of the templates by calcination. The optimum performance conditions to obtain these kinds of materials were systematically studied. The wall thickness and composition of these novel materials can be readily tailored by varying the number of nanozeolite/PDDA (poly(diallyldimethyl ammonium chloride)) deposition cycles and zeolite type used, respectively. The properties of these novel materials were characterized by means of XRD, IR and SEM. 

Ghasem, N., Al-Marzouqi, M., Duaidar, A. 2011. Effect of quenching temperature on the performance of poly(vinylidene fluoride) microporous hollow fiber membranes fabricated via thermally induced phase separation technique on the removal of CO2 from C02-gas mixture. Int. J. Greenh. Gas Control 5 1550-1558. 

Barzin et al. characterized poly(ether sulfone) (PES) hollow fibers for hemodialysis by both ultrafiltration experiments and AFM [66]. Hollow fibers were fabricated from poly(ether sulfone) (Ultrason E6020 58 000 flakes from BASE Co.) by the... 

Fig. 6.10. AFM image of the cross section of a UF poly(etherimide) hollow fiber membrane fabricated at a 50-cm air gap. The sample was prepared by cutting the hollow fiber with a sharp edge. The white arrow shows the direction from the inner surface toward the outer surface. Reprinted from [4]. Copyright 2006, with kind permission from Elsevier...

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. 

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. 

Setiawan L, Wang R, Li K, Fane AG. Fabrication of novel poly(amide-imide) forward osmosis hollow fiber membranes with a... 

Amphiphilic Pluronic triblock copolymers of two blocks of poly-(ethylene oxide) (PEO) and poly(propylene oxide) in between have worth as both the surface modifier and pore former in the fabrication of membranes (77). The effect of Pluronics with different molecular architectures and contents as a pore forming additive for the fabrication of poly(ethersulfone) ultrafiltration hollow fibers has been investigated. 

By introducing hydroxyapatite nanowhiskers of poly(iV-vinyl-2-pyrrolidone) and poly(vinylidene fluoride), hollow fiber membranes were fabricated using the wet-spinning method (78). An aqueous solution containing 90% iV-methyl-2-pyrrolidone was used as bore liquid. The effects of the two additives and the S5mergism on the morphologies, surface properties, permeation performances, antifouling ability and the mechanical properties of the membranes were characterized by various analytical techniques. 

L. Shi, R. Wang, Y. Cao, C. Feng, D.T. Liang, and J.H. Tay. (2007). Fabrication of poly(vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP) asymmetric micropo-rous hollow fiber membranes, J. Memb. Sci. 305 215-225. 

D.F. Li, T.S. Chung, R. Wang, and Y. Liu. (2002). Fabrication of fluoropolyimide/poly-ethersulfone (PES) dual-layer asymmetric hollow fiber membranes for gas separation, J. Memb. Sci. 198 211-223. 

X. Shen, Y. Zhao, L. Chen, X. Feng, D. Yang, Q. Zhang, D. Su, Structure and performance of temperature-sensitive poly(vinylidene fluoride) hollow fiber membrane fabricated at different take-up speeds. Polymer Engineering and Science, 53 (2013) 571-579. 

L. Setiawan, R. Wang, S. Tan, L. Shi, A.G. Fane, Fabrication of poly(amide-imide)-polyethersulfone dual layer hollow fiber membranes applied in forward osmosis by combined polyelectrolyte cross-linking and depositions. Desalination, 312 (2013) 99-106. 

Dong and Jones Jr. reported on the preparation of submicron electrically conductive polypyrrole/poly(methyl methacrylate) coaxial fibers and conversion to polypyrrole tubes and carbon tubes [47]. In this study, PMMA fibers with an average diameter of 230 nm were initially fabricated by electrospinning as core materials. The PMMA fibers were subsequently coated as templates with a thin layer of PPy by in situ deposition of the conducting polymer from aqueous solution. Hollow PPy nanotubes were produced by dissolution of the PMMA core from PPy/PMMA coaxial fibers. Furthermore, high temperature (1000 °C) treatment under an inert atmosphere can be used to convert PPy/PMMA coaxial fibers into carbon tubes by complete decomposition of the PMMA fiber core and carbonization of the PPy wall (Figure 4.13). 

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