Polymer membrane modification

Most recently, significant research efforts have been focused on materials compatibility and adhesion at the zeoHte/polymer interface of the mixed-matrix membranes in order to achieve enhanced separation property relative to their corresponding polymer membranes. Modification of the surface of the zeolite particles or modification of the polymer chains to improve the interfacial adhesion provide new opportunity for making successful zeolite/polymer mixed-matrix membranes with significantly improved separation performance. 

A second surface modification has been reported by Yamamoto et al. These workers added stearic acid to their carbon paste mixture. This produced an electrode which was relatively insensitive to ascorbic acid and DOPAC relative to dopamine. It is theorized that this electrode works because of electrostatic repulsion of the anionic ascorbate and DOPAC by surface stearate groups. Ionic repulsion has also been employed by covering the surface of the working electrode with an anionic polymer membrane. Gerhardt et al. used Nafion, a hydrophobic sulfonated perfluoro-polymer, to make a dopamine selective electrode. This electrode exhibited selectivity coefficients as large as 250 1 for dopamine and norepinephrine over ascorbic acid, uric acid, and DOPAC. 

Chemical modifications of PPO by electrophilic substitution of the aromatic backbone provided a variety of new structures with improved gas permeation characteristics. It was found that the substitution degree, main chain rigidity, the bulkiness and flexibility of the side chains and the polarity of the side chains are major parameters controlling the gas permeation properties of the polymer membrane. The broad range of solvents available for the modified structures enhances the possibility of facile preparation of PPO based membrane systems for use in gas separations. 

Because most of the established membrane polymers can not meet all the performance requirements for a membrane dedicated to a particular application, membrane modifications are gaining rapidly increasing importance. Membrane modification is aimed either to minimize undesired interactions, which reduce membrane performance (e.g., membrane fouling), or to introduce additional interactions (e.g., affinity, responsive or catalytic properties) for improving the selectivity or creating an entirely novel separation function [3]. Three general approaches can be distinguished ... 

A wide variety of polymeric membranes with different barrier properties is already available, many of them in various formats and with various dedicated specifications. The ongoing development in the field is very dynamic and focused on further increasing barrier selectivities (if possible at maximum transmembrane fluxes) and/ or improving membrane stability in order to broaden the applicability. This tailoring of membrane performance is done via various routes controlled macro-molecular synthesis (with a focus on functional polymeric architectures), development of advanced polymer blends or mixed-matrix materials, preparation of novel composite membranes and selective surface modification are the most important trends. Advanced functional polymer membranes such as stimuli-responsive [54] or molecularly imprinted polymer (MIP) membranes [55] are examples of the development of another dimension in that field. On that basis, it is expected that polymeric membranes will play a major role in process intensification in many different fields. 

S.P. Nunes, B. Ruffmann, E. Rikowski, S. Vetter, and K. Richau. Inorganic modification of proton conductive polymer membranes for direct methanol fuel cells. Journal of Membrane Science 203, 215-225 2002. 

Our research with the SLMs has centered on the synthesis of highly stable membranes for long term metal ion transport. Since it is advantageous to maintain polypropylene as the basic support structure due to its commercial availability, a versatile membrane modification technique has been found to be that involving interpenetrating polymer networks [IPNs]... 

Keywords Fuel cells, Grafting, Membranes, Polyelectrolyte complexes, Sulfo-nated polymers. Surface modification... 

In 1968, Ontario Research Foundation developed a series of segmented polyether polyurethanes as polymer membrane materials for reverse cosmosis, ultrafiltration and hemodialysis. The elastomers of recent implant studies are polyurea-urethanes( .) with modification of the synthesis limited to only one variable— the chain length of the polyether component. 

Membranes Photografting is a fashionable method in the modification of polymer membranes. [ 100] Polymeric membranes play an important role in various membrane... 

TABLE 13.4 Modification of Polymer Membranes via Photografting Method... 

Plasma Modification of Polymer Fibers and Polymer Membranes... 

Application of Polymer Membranes for Gas Separation Enhancement of Polymer Membrane Selectivity by Plasma Polymerization and by Plasma Modification of Polymer Surfaces... 

Microwave plasma modification of the surfaces of siloxane membranes (particularly lestosil and polycaibosil membranes) and acetate cellulose membranes is an example of plasma fabrication of asymmetric highly selective gas-separating polymer membranes (Arbatsky etal., 1988,1990). A schematic ofthe microwave plasma installation is showninFig. 9-34. 

Chemical and Stmctural Modification of Surface Layers of Gas-Separating Polymer Membranes by Microwave Plasma Treatment... 

Theoretical Model of Modification of Polymer Membrane Surfaces in After-Glow of Oxygen-Containing Plasma of Non-Polymerizing Gases Lame Equation... 

Theory. The relationship of the chemical aspects of complexatlon reactions to the performance of facilitated transport membranes Is discussed by Koval and Reyes (108). They describe a procedure which can be used to predict and optimize the facilitated transport of gases, Including measurement of the appropriate equilibrium, transport, and kinetic parameters and structural modification of the carrier to Improve the performance of the membrane. Examples of this procedure and carrier modification are given for derivatives of Fe(II) tetralmlne complexes which reversibly bind CO In nitrile solvents (118). Experimental challenges In the measurement of the appropriate properties for other membrane configurations such as reactive Ion exchange membranes and reactive polymer membranes are also discussed. 

The main aim for FCC gasoline desulfurization is to remove thiophenic sulfur compounds. Membranes made from polar polymers with solubility parameter close to thiophenic sulfur are used for desulfurization of gasolines by PV It is evident that solubility parameter of primary sulfur components of gasolines, that is, thiophenic sulfur components, is 19-21 (J/cm )", while for other hydrocarbons, these values are 14-15 (J/cm )". This difference can be exploited for separation by PV. Solubility parameter values of most of the polymers used as membrane material lie in the range of 21-26 (J/cm )". Thus, membranes made from these polymers afford good selectivity for thiophenic sulfur. Apart from various homopolymers, chemically and physically modified polymers have also been used for per-vaporative desulfurization. Some of these modifications include using different types and amounts of cross-linkers, blending two polymers, and copolymerization. Composite and treated ionic membranes have also been tried for this separation. Polymer membranes tried for this separation include PDMS/PAN, PDMS/PEI, PDMS/PES, PDMS/ ceramic, polyetherimine (PI)/polyester, PEG/PES, and PU/PTEE. ... 

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