Dextran fouling of polyethersulfone ultrafiltration membranesâCauses, extent and consequences

In a recent paper [Susanto, Ulbricht, J. Membr. Sci. 266 (2005) 132], we showed that dextran does foul polyethersulfone (PES) ultrafiltration (UF) membranes by contact of the solution with the membrane surface without flux through the membrane. In this work, dextran fouling was visualized using atomic force microscopy (AFM) and quantified by ATR-IR spectroscopy and by the mass balance in simultaneous diffusionâadsorption measurements (SDAM). Good correlations have been found between the water flux reduction due to dextran adsorption and the quantitative data for bound dextran on the PES membranes. Further, a pronounced effect of dextran size on adsorptive membrane fouling was identified. Contact angle and zeta potential measurements with non-porous films, where solute entrapment in pores can be ruled out, gave additional clear evidence for dextran binding on the PES surface. Complementary data for adsorption and fouling of porous membranes and non-porous films by the protein myoglobin indicated that the larger fouling tendency for protein than for dextran is due to a higher surface coverage of PES by the adsorbed biomacromolecule layer. Data for batch UF confirm the conclusions from the static contact experiments because significant fouling is observed for PES membranes (more severe for myoglobin than for dextrans), while no fouling is seen for a cellulose-based UF membrane with the same nominal cut-off. Finally, two mechanisms for the attractive PESâdextran interaction â multiple hydrogen bonding involving the SO2 groups of PES and âsurface dehydrationâ of the relatively hydrophobic PES â are discusse

Advanced functional polymer membranes

AbstractThis feature article provides a comprehensive overview on the development of polymeric membranes having advanced or novel functions in the various membrane separation processes for liquid and gaseous mixtures (gas separation, reverse osmosis, pervaporation, nanofiltration, ultrafiltration, microfiltration) and in other important applications of membranes such as biomaterials, catalysis (including fuel cell systems) or lab-on-chip technologies. Important approaches toward this aim include novel processing technologies of polymers for membranes, the synthesis of novel polymers with well-defined structure as ‘designed’ membrane materials, advanced surface functionalizations of membranes, the use of templates for creating ‘tailored’ barrier or surface structures for membranes and the preparation of composite membranes for the synergistic combination of different functions by different (mainly polymeric) materials. Self-assembly of macromolecular structures is one important concept in all of the routes outlined above. These rather diverse approaches are systematically organized and explained by using many examples from the literature and with a particular emphasis on the research of the author's group(s). The structures and functions of these advanced polymer membranes are evaluated with respect to improved or novel performance, and the potential implications of those developments for the future of membrane technology are discussed

Effects of photo-initiation and monomer composition onto performance of graft-copolymer based membrane adsorbers

Photo-initiated surface-selective graft copoly- merisation onto polypropylene (PP) microfiltration membranes is an improved method to prepare porous membrane adsorbers [1]. The potential versatility and economic value of this method motivated us to further investigate main parame- ters for control of membrane adsorber function- ality. In this work we studied the influence of photo initiator concentration and entrapping time in the initiator immobilization step and of monomer solution composition in the photo- grafting step. Benzophone (BP) dissolved in heptane was used in the photo initiator coating step. The functional monomer acrylic acid (AA), the diluent monomer acrylamide (AAm) and the cross-linker methylene bisacrylamide (MBAA) were used to prepare grafted copoly- mer layers with weak cation-exchange groups in the second step. For the characterization we focussed on the degree of grafting (DG) via gravimetry, ATR-IR spectroscopy, membrane permeability as a function of solution pH and ionic strength and dynamic protein binding capacities and recovery from membrane chro- matography experiments. Using the membranes with best performance, the separation of protein mixture was also investigated

Development of polymer blend ultrafiltration membranes with combined size and charge selectivity

Protein separation is a relevant technology for pharmaceutical industry, food-processing and biotechnology sector. Research activities are currently actively devoted to the development of high-performance ultrafiltration membranes with high permeability at maximum selectivity. Nevertheless, the efficiency of the fractionation of bio-macromolecules is often hindered by fouling processes which reduce the global performance. Based on size exclusion ultrafiltration separation process, fractionation of proteins can be achieved only for proteins with significantly different molecular weights. However, the introduction of electrostatic repulsion between a charged membrane and a protein could allow to overcome this limitation. From these considerations, we intend to develop polymer blend ultrafiltration membranes with combined size and charged selectivity in order to achieve the challenging separation of two proteins with very similar molecular weight. Amongst different modification approaches, polymer blending has emerged as an interesting method because it allows to develop new or advanced material properties and it is easily scaled up. More precisely, the use of sulfonated poly(arylsulfone)s became more and more attractive since it could be used to enhance the membrane permeability and to tune the charge of the membrane surface. In this work, flat sheet ultrafiltration membranes made of polysulfone and various types of sulfonated poly(arylsulfone)s were prepared via non-solvent induced phase separation method (NIPS). The type of sulfonated polymer as well as the overall degree of sulfonation was systematically varied. The performance of the new membranes was assessed in terms of water permeability, molecular weight cut-off and fouling resistance. Two types of model molecules - bovine serum albumin (BSA) and hemoglobin (Hb) - were then employed to evaluate single protein rejection and protein fractionation selectivity. An optimization of the membrane selectivity was conducted by adjusting the filtration conditions (eg. concentration, pH, ionic strength). Preliminary experiments toward quantitative separation of the two proteins were further conducted in diafiltration mode. In the present study, we demonstrate the possibility to tune the membrane properties using variations of the degree of sulfonation: a broad range of ultrafiltration membranes with different barrier pore sizes and surface charge were developed. Overall, the work provides interesting and relevant findings for the development of robust charged ultrafiltration membranes for protein separation

Catalytic membranes and applications thereof

In one aspect, catalytic membranes are described herein. In some embodiments, a catalytic membrane comprises a surface functionalized with a polymer, the polymer comprising cellulose solubilization functionalities and acid functionalities for the catalytic hydrolysis of cellulose and/or hemicellulose

Catalytic membranes and applications thereof

Describe catalytic membranes. In some embodiments, a catalytic membrane comprises a surface functionalized with a polymer, the polymer comprising cellulose solubilization functionalities and acid functionalities for the catalytic hydrolysis of cellulose and/or hemicellulose

Thermo-Responsive Hydrophilic Support for Polyamide Thin-Film Composite Membranes with Competitive Nanofiltration Performance

Poly(N-isopropylacrylamide) (PNIPAAm) was introduced into a polyethylene terephthalate (PET) nonwoven fabric to develop novel support for polyamide (PA) thin-film composite (TFC) membranes without using a microporous support layer. First, temperature-responsive PNIPAAm hydrogel was prepared by reactive pore-filling to adjust the pore size of non-woven fabric, creating hydrophilic support. The developed PET-based support was then used to fabricate PA TFC membranes via interfacial polymerization. SEM–EDX and AFM results confirmed the successful fabrication of hydrogel-integrated non-woven fabric and PA TFC membranes. The newly developed PA TFC membrane demonstrated an average water permeability of 1 L/m2 h bar, and an NaCl rejection of 47.0% at a low operating pressure of 1 bar. The thermo-responsive property of the prepared membrane was studied by measuring the water contact angle (WCA) below and above the lower critical solution temperature (LCST) of the PNIPAAm hydrogel. Results proved the thermo-responsive behavior of the prepared hydrogel-filled PET-supported PA TFC membrane and the ability to tune the membrane flux by changing the operating temperature was confirmed. Overall, this study provides a novel method to fabricate TFC membranes and helps to better understand the influence of the support layer on the separation performance of TFC membranes

Thermo-responsive hydrophilic support for polyamide thin-film composite membranes with competitive nanofiltration performance

Poly(N-isopropylacrylamide) (PNIPAAm) was introduced into a polyethylene terephthalate (PET) nonwoven fabric to develop novel support for polyamide (PA) thin-film composite (TFC) membranes without using a microporous support layer. First, temperature-responsive PNIPAAm hydrogel was prepared by reactive pore-filling to adjust the pore size of non-woven fabric, creating hydrophilic support. The developed PET-based support was then used to fabricate PA TFC membranes via interfacial polymerization. SEM–EDX and AFM results confirmed the successful fabrication of hydrogel-integrated non-woven fabric and PA TFC membranes. The newly developed PA TFC membrane demonstrated an average water permeability of 1 L/m2 h bar, and an NaCl rejection of 47.0 % at a low operating pressure of 1 bar. The thermo-responsive property of the prepared membrane was studied by measuring the water contact angle (WCA) below and above the lower critical solution temperature (LCST) of the PNIPAAm hydrogel. Results proved the thermo-responsive behavior of the prepared hydrogel-filled PET-supported PA TFC membrane and the ability to tune the membrane flux by changing the operating temperature was confirmed. Overall, this study provides a novel method to fabricate TFC membranes and helps to better understand the influence of the support layer on the separation performance of TFC membranes

Magnetically responsive membranes

The invention provides permeable magnetically responsive filtration membranes that include a filtration membrane polymer base suitable for fluid filtration; hydrophilic polymers conjugated to the surface of the filtration membrane polymer; and magnetic nanoparticles affixed to the ends of a plurality of the hydrophilic polymers, wherein the hydrophilic polymers are movable with respect to the surface of the filtration membrane polymer surface in the presence of an oscillating magnetic field