Ultrafiltration membrane characterization

Sinee this technique is based on the Kelvin equation, it is applicable only to mesopores, limited by the gas and working pressure. However, these limits can be considered as ranging from 2 to 50 mn. The method has been used and eompared wifli other ultrafiltration membrane characterization methods, with very good results [54,117—119]. 

Membrane Characterization The two important characteristics of a UF membrane are its permeability and its retention characteristics. Ultrafiltration membranes contain pores too small to be tested by bubble point. Direc t microscopic observation of the surface is difficult and unreliable. The pores, especially the smaller ones, usually close when samples are dried for the electron microscope. Critical-point drying of a membrane (replacing the water with a flmd which can be removed at its critical point) is utihzed even though this procedure has complications of its own it has been used to produce a Few good pictures. 

Subsequently, a clear Juice is obtained by ultrafiltration. A serious problem in this process is the fouling of the ultrafiltration membrane, causing a reduced flux rate. For apple processing, the material responsible for this effect has been isolated and extensively characterized [2-4]. It appeared to consist mainly of ramified pectic hairy regions (MHR), which were not degraded by the pectolytic enzymes present in the technical pectinase preparation. 

Larbot, A., J. A. Alary, C. Guizard, L. Cot and J. Gillot. 1987. New inorganic ultrafiltration membranes Preparation and characterization. Int. J. High Technology Ceramics 3 145-51. 

Nystrom, M., M. Lindstrom and E. Matthiasson. 1989. Streaming potential as a tool in the characterization of ultrafiltration membranes. Colloids di Surfaces 36 297-312. 

Table 2.5 Marker molecules used to characterize ultrafiltration membranes...

The separation and characterization of submicron-sized particles in water is difficult, in particular because of artifacts from sampling and concentration techniques. Lead et al. (1997) have presented a critical review of the different techniques for separation and analysis of colloids (filtration, dialysis, centrifugation, but also volta-metry, gels (DET/DGT), field-flow fractionation, SPLITT). Ultrafiltration membranes have been developed with nominal cutoff sizes ranging from the thousands of daltons (Da) to hundreds of thousands of daltons, which have been used to separate the colloidal pool into several fractions. 

Dalven PI, Hildebrandt JR, Shamir A, Faccetti AJ, Hodgins FT, and Gregorh HP. Acrylonitrile-hased copolymers S3mthesis, characterization, and formation of ultrafiltration membranes utilized for the immobiUzation of proteins. J. Appl. Polym. Sci. 1985 30 1113-1132. 

G. Capannelli, I. Becchi, A. Bottino, P. Moretti and S. Munari, Computer driven poro-simeter for ultrafiltration membranes, in K.K. linger,]. Rouquerol, K.S.W. Sing and H. Krai (Eds.), Characterization of Porous Solids I, Studies in Surface Science and Catalysis Vol. 39, Proc. of the lUPAC Symposium (COPS I), Bad Soden, Germany, April 1988, Elsevier, Amsterdam, pp. 283-294. 

Information about the porous support layer rather than the skin layer. The techniques used by these authors, as well as those reviewed by Pusch and Welch (21), provide valuable Insight Into the mechanism of membrane formation and thus may assist membrane scientists In developing better membranes. However, many of these techniques do not characterize the membrane under the conditions of application for example, the ultrafiltration membranes (23,24) are dried prior to gas sorption studies and microscopy. Therefore, caution must be exercised In Interpreting the results of these characterization methods and relating them to membrane performance and transport mechanisms. 

Several attempts to characterize quantitatively pore structures in ultrafiltration membranes have been described in the literature. Preusser(lJ analyzed surface porosities of Amicon membranes, using a carbon replica technique and a high-resolution transmission electron microscopy (TEM). A similar approach was... 

The method of thermoporometry, developed by Brun, Lallemand, Quinson and Eyraud( ), represents another method applicable, at least in principle, to characterization of pore volume in ultrafiltration membranes (, ). However, for asymmetric membranes, pore volumes explored by thermoporometry may not be the volumes associated with membrane skins and "functional" pores. 

Nystrom, M., Pihlajamaki, A., and Ehsani, N., Characterization of ultrafiltration membranes by simultaneous streaming potential and flux measurements, J. Membr. Sci., 87, 245, 1994. 

We have been studying this problem as an extension of our research on the fouling of membrane by the deposition of suspended matters (jL). We first studied on the resistance of gel layer to permeation (2), next on the characterization of ultrafiltration membranes O) regarding the solute rejection, and lastly on the effect of gel layer on the solutes rejection and fractionation. Though this paper is mainly concerned with this last aspect, we want to quickly review the previous results. 

Recently, Ulbricht and coworkers [131] have reported the preparation of low-fouling ultrafiltration membranes by simultaneous photograft copolymerization of hydrophilic poly(ethylene glycol) methacrylate onto a polyethersulfone (PES) membrane. A broad characterization using flux measurement and sieving curve... 

Amicon Diaflo ultrafiltration membrane offer a selection of macrosolute retentions ranging from 500 to 300,000 molecular weight as cahbrated with globular macrosolutes. These values correspond to pore sizes between about 1 and 15 nm. Each membrane is characterized by its nominal out-off, that is, its abihty to retain molecules larger than those of a given size. 

Zhu, L.-R, Xu, L., Zhu, B.-K., Feng, Y.-X., and Xn, Y.-Y. 2007. Rreparation and characterization of improved fouling-resistant RRESK ultrafiltration membranes with amphiphilic RRESK-graft-PEG copolymers as additives. Journal of Membrane Science 294 196-206. 

Arthanareeswaran, G., Mohan, D., and Raajenthiren, M. 2010. Preparation, characterization and performance studies of ultrafiltration membranes with polymeric additive. Journal of Membrane Science 350 130-138. 

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