Blends membrane applications

The effect of annealing temperatures (65 - 250 °C) and blend composition of Nafion 117, solution-cast Nafion , poly(vinyl alcohol) (PVA) and Nafion /PVAblend membranes for application to the direct methanol fuel cell is reported in [148], These authors have found that a Nafion /PVAblend membrane at 5 wt% PVA (annealed at 230 °C) show a similar proton conductivity of that found to Nafion 117, but with a three times lower methanol permeability compared to Nafion 117. They also found that for Nafion /PVA (50 wt% PVA) blend membranes, the methanol permeability decreases by approximately one order of magnitude, whilst the proton conductivity remained relatively constant, with increasing annealing temperature. The Nafion /PVA blend membrane at 5 wt% PVA and 230 °C annealing temperature had a similar proton conductivity, but three times lower methanol permeability compared to unannealed Nafion 117 (benchmark in PEM fuel cells). 

Kerres, J., Ullrich, A., Meier, R and Haring, T. 1999. Synthesis and characterization of novel acid-base polymer blends for application in membrane fuel cells. Solid State Ionics 125 243-249. 

Kerres, J., Ullrich, A., Haring, T., Baldauf, M., Gebhardt, U. and Preidel, W. 2000. Preparation, characterization and fuel cell application of new acid-base blend membranes. Journal of New Materials for Electrochemical Systems 3 229-239. 

Sulfonated EPDMs are formulated to form a number of rubbery products including adhesives for footwear, garden hoses, and in the formation of calendered sheets. Perfluori-nated ionomers marketed as Nation (DuPont) are used for membrane applications including chemical-processing separations, spent-acid regeneration, electrochemical fuel cells, ion-selective separations, electrodialysis, and in the production of chlorine. It is also employed as a solid -state catalyst in chemical synthesis and processing. lonomers are also used in blends with other polymers. 

From a functional point of view, Nguyen et al. examined the pervapora-tion characteristics of CA/P(VP-co-VAc) blends for application as alcohol-selective membrane materials [107]. The blend membranes were shown to be very efficient in the removal of ethanol from its mixture with ethyl tert-butyl ether (ETBE). ferf-butyl ethers are octane-value enhancers for gasoline, and the synthesis requires an excess of alcohol in the reaction to reach high... 

Nam, K. et al., Acid-Base Proton Conducting Polymer Blend Membrane, U.S. Patent Application 2003/0219640, November 27, 2003. 

Chen X, Liu JH, Feng ZC, and Shao ZZ. Macroporous chitosan/carboxymethylclellulose blend membranes and their application for lysozyme adsorption. J. Appl. Polym. Sci. 2005 96 1267-1274. 

Van Zyl AJ and Kerres JA. Development of new ionomer blend membranes, their characterization and their application in the perstractive separation of alkene-alkane mixtures. II. Electrical and facilitated transport properties. J Appl Pol Sci 1999 74 422-427. 

Dynamic membranes originated in the research at the Oak Ridge National Laboratory in the 196O s. Development has produced commercial ultrafiltration and hyperfiltration membranes for industrial separation applications. Research continues in several laboratories to improve the selectivity and productivity of the membranes and to tailor them for specific applications. The development of dynamic membranes and current research is reviewed briefly. Research on polyelectrolyte blend membranes is described in detail as a representative method for tailoring dynamic membranes. 

Blends of a PAI and poly(aryl ether ketone) exhibit improved solvent resistance and hydrolytic stability. Blends of sulfonated poly(ether ether ketone) and PAI have been tested as membrane materials for direct methanol fuel cells. Miscible blends can be obtained. Blends of poly(urethane)s (PU)s and PAI, as the minor component have been reported for membrane applications. The resulting membranes are immiscible. Phase separation occurs when the amount of PU decreases. 

Zavastin, D., Cretescu, I., Bezdadea, M., Bourceanu, M., DrSgan, M., Lisa, G., Mangalagiu, I., Vasic, V., Savic, J. (2010). Preparation, characterization and applicability of cellulose acetate-polyurethane blend membrane in separation techniques, U icochenrfihgjAsgec 370,120-128. 

Sivakumar, M., Malaisamy, R., Sajitha, C. J., Mohan, D., Mohan, V., Rangarajan, R. (1999). Ultrafiltration application of cellulose acetate-polyurethane blend membranes, EurPoJjimJf, 35,1647-1651. 

Apart from these, CS membranes find applications in the field of hemodialysis. The excellent fitm-forming nature and high mechanical strength of CS membranes made it a suitable candidate for hemodialysis application. For example, chitosan-poly(ethylene oxide) blend membranes showed improved permeability and blood compatibility due to their hydrophilic and porous nature [28]. However, the cellulosic membranes and synthetic membranes (made up of polyaryle-thersulfone, polyamide, PVP, polycarbonate, and PAN) have a well-established hemodialysis field as compared to CS-based membranes. 

Kerres J, Zhang W, Jorissen L, Gogel V (2002) Application of different types of polyaryl-blend-membranes in DMFC. J New Mater Electrochem Syst 5 97-107... 

Kim DH, Kim SC (2008) Transport properties of polymer blend membranes of sulfimated and nonsulfonated polysulfones for direct methanol fuel cell application. Macromol Res... 

Oh SY, Park JY, Yu DM, Hong SK, Hong YT (2012) Preparation and characterization of acid-acid blend membranes for direct methanol fuel cell applications. Macromol Res 20 121-127... 

Bi H, Wang J, Chen S, Hu Z, Gao Z, Wang L, et al. Preparation and properties of cross-linked sulfonated poly(arylene ether sulfone)/sulfonated polyimide blend membranes for fuel cell application. J Membr Sci 2010 350(l-2) 109-16. 

However, no single material possesses all of these qualities. Those that are chemically resistant are difficult to process, and vice versa. These limitations have been overcome by the formation of polymer blends for membrane application. Polymer blends of many types have become the dominant material class of polymers in commercial practice over the last 30 years with much research in this area. 

Another important characteristic of the membrane for DMFC application is the proton conductivity of the membrane. Table 13.3 also shows the proton conductivity at room temperature and 100% RH for Nafion 112, SPEEK, and SPEEK/cSMM membranes. The proton conductivity of Nafion 112 is 1.20 x 10 S/cm, highest of all the three membranes. The proton conductivity for SPEEK is 3.3 x 10 S/cm. Interestingly, the proton conductivity of the SPEEK/cSMM blend membrane is 6.4 X 10 S/cm, about twice as high as that of SPEEK. This result is expected from the simultaneous increase in the water uptake, since the proton conductivity relies... 

The novel developed membrane materials should have potential applications on a large scale. The composite membrane preparation and its evaluation therefore must present promising results before testing the membranes in a real gas mixture. Single gas (CO2, H2, N2 and CH4) measurements of Pebax /PEG blend membrane at high pressure (up to 20 bar) and at 293 K presented higher CO2 fluxes than pristine copolymer (Figure 12.14). 

The phase behavior and morphology of phase-separated polymer blends play a vital role in the design of membrane transport properties (Robeson 2010). Numerous applications of polymeric membranes involving gas and liquids are known. Although different transport models have been utilized successfully to relate morphology with transport properties, there is enough room for improvements as membrane applications continue to grow in such areas as gas separation. 

In EP07708077A3 (Dabou et al. 1996), gas separation polymer membranes were prepared from mixtures of a polysulfone, Udel P-1700 and an aromatic polyimide, Matrimid 5218. The two polymers were proven to be completely miscible as confirmed by optical microscopy, glass transition temperature values and spectroscopy analysis of the prepared mixtures. This complete miscibility allowed for the preparation of both symmetric and asymmetric blend membranes in any proportion from 1 to 99 wt% of polysulfone and polyimide. The blend membranes showed significant permeability improvements, compared to the pure polyimides, with a minor change in the selectivity. Blend membranes were also considerably more resistant to plasticization compared with pure polyimides. This work showed the use of polysulfone-polyimide polymer blends for the preparation of gas separation membranes for applications in the separation of industrial gases. 

Polyaniline (PANi) has been studied extensively for its electroactive characteristics and potential applications in electrical devices, such as polymer electrodes and sensors [46]. Semi-conductive membranes from PVDF/PANi blends in V-methyl-2-pyrrolidone (NMP) solutions were prepared by phase inversion in an aqueous solution of poly(styrenesulfonic acid) (PSSA) [47]. Entrapment of a stoichiometric amount of PSSA dopant molecules into the blend membrane occurred during phase inversion process and gave rise to a semi-conductivity membrane. At a PANi content of above 15 wt%, the entrapped PSSA chains were present in stoichiometric amount and dispersed evenly throughout the blend membrane. The membranes prepared by this method had an asymmetry structure with a dense skin layer and a porous inner layer. The surface resistance of the blend membrane decreased with the increase in PANi weight fraction. A surface resistance of about 10 i2/cm was obtained for the PSSA-doped PVDF/PANi (65/35, w/w) membrane. 

---