Jochen Meier-Haack

An in‐situ ATR‐FTIR study on polyelectrolyte multilayer assemblies on solid surfaces and their susceptibility to fouling

In-situ attenuated total reflection (ATR)-FTIR spectroscopy was used to monitor the consecutively alternating adsorption of polyethylenimine (PEI) and poly(acrylic acid) (PAC) onto both Si crystals (SiO) and CO2 plasma-treated polypropylene (PP) films. The vibration band vas(COO−) and v(CO) of PAC are diagnostic for the polyelectrolyte layer build-up and sensitive to protonation changes. Human serum albumine (HSA) adsorption experiments revealed a strong decrease of fouling for the PP films, which were modified with polyelectrolyte multilayers, in comparison to the unmodified ones.

Polyelectrolyte multilayer membranes for pervaporation separation of aqueous-organic mixtures

Abstract Composite membranes for pervaporation of water/alcohol mixtures were prepared by consecutive alternating adsorption of poly(acrylic acid) (polyanion) and poly(ethylenimine) (polycation) on a polyamide-6 substrate. The influence of preparation conditions on the pervaporation separation properties of polyelectrolyte multilayer composite membranes was studied. Variation of polyelectrolyte concentration of the dipping solution and adsorption time had only a minor effect on the membrane performance. On the other hand, high molecular weight polyelectrolytes had a high impact on membrane performance. A separation factor α of 2500 was observed for a membrane having four double layers. Best results were obtained when the adsorption temperature was raised from 25°C to 80°C A membrane with two double layers showed a separation factor α of 900.

Influence of thermal treatment on the pervaporation separation properties of polyamide-6 membranes

Abstract Integrally-skinned asymmetric polyamide-6 membranes were prepared by casting 15 wt.% solution of polymer in 85 wt.% formic acid onto a glass plate and precipitation in water at 4°C. The obtained membranes were dried for 1 h at different temperatures ranging from 25 to 140°C in air and from 25 to 200°C in vacuum, respectively. The pervaporation separation properties of such treated membranes were studied with binary water-2-propanol mixtures consisting of 5 to 95 wt.% water. The membranes showed water permselectivity over a wide range of the feed composition. Thereby the water permselectivity reached a maximum at low water contents in the feed mixture. The selectivity was improved by thermal treatment of the membranes at temperatures above the glass transition temperature T g of polyamide-6 (≈60°C). However, the permeate flux decreased with increasing drying temperature due to the removal of entrapped water from amorphous domains, the formation of new crystalline domains and the decrease of the pore size and of the specific surface area during the thermal treatment. These effects were confirmed by dsc measurements, X-ray scattering experiments and BET measurements.

Microporous membranes from polyolefin-polyamide blend materials☆

An alternative method using established polymer processing and membrane formation processes to prepare hydrophilic membranes based on acid modified polyolefins is introduced. This process includes blend formation by reactive extrusion of functionalized polyolefins (polypropylene; PP) and a hydrophilic polyamide (PA). In a first step the pore formation is realized by extracting non-covalently bound polyamide. The resulting membranes are tested by pure water as well as protein filtration. The properties are discussed in terms of permeate flux, retention capability and fouling behavior.

Effect of Polyelectrolyte Complex Layers on the Separation Properties and the Fouling Behavior of Surface and Bulk Modified Membranes

The effect of polyelectrolyte complex layers on the separation and filtration properties and on the fouling behavior of surface and bulk modified membranes were studied using two different separation processes, namely pervaporation and microfiltration. Therefore two different membrane types were employed. The microfiltration tests were conducted using a commercially available polypropylene membrane (Celgard 2400). The pervaporation experiments were performed on a home-made polyamide-6 pervaporation membrane.

Fouling Reduction by Graft‐Modification with Hydrophilic Polymers

Abstract Flat sheet polypropylene microfiltration membranes were successfully graft‐modified with acrylic acid using the macroinitiator method. The surface modification induced a change in the course of fouling. Unmodified membranes showed the strong form of critical flux during filtration of protein solution, while for the surface modified membranes the weak form of critical flux was determined. Although the critical flux could be shifted towards higher values (from ca. 20 l/m2h to>40 l/h2m) by the surface modification, the permeability decreased by a factor of 6.

Modifizierung von Polyaramid-Ultrafiltrationsmembranen durch Elektronenbestrahlung

Die Bestrahlung von Polyaramid-Ultrafiltrationsmembranen (PA-UF-Membranen; NADIR® UF-PA-5) mit energiereichen Elektronen ergab im Energiedosisbereich von D≈150 bis 200 kGy eine Erhohung des Ruckhaltevermogens R von 93 auf 98%. Entgegen der ublichen Erfahrung trat dabei keine Reduzierung des Permeatfluswertes JPVP auf. Durch ζ-Potentialmessungen und IR-spektroskopische Untersuchungen konnte der Einbau von zusatzlichen Carboxygruppen durch die Bestrahlung nachgewiesen werden, die diesen Effekt im wesentlichen verursachen. Electron beam irradition of polyaramide ultrafiltration membranes (PA-UF membranes; NADIR® UF-PA-5) led to an increase of retention R from 93% to 98% in the applied dose range between 150 and 200 kGy. Contrary to common findings, no reduction of permeate flux JPVP was observed. The formation of carboxy groups caused by electron beam irradiation was confirmed by ζ-potential measurements and ATR-FTIR spectroscopic investigations.

Polymer chain mobility in polyelectrolyte multilayers

Free-standing polyelectrolyte multilayer membranes have been formed by the layer-by-layer technique using a dip-coating apparatus. The polymer-chain mobility has been studied by 1H relaxation in the rotating frame T 1rho NMR with 13C chemical shift resolution. For each of the individual polymers a single relaxation component has been observed for all resolved signals. In the multilayer a significantly different relaxation time T 1rho has been observed with a minor second component. The interaction between the oppositely charged polyelectrolytes influences the molecular mobility.

Polymer Membranes for Sustainable Technologies

Membrane-based processes have found wide acceptance and are used as powerful alternatives for conventional techniques such as distillation, extraction, or energy production. Frequently, membranes prepared from commodity polymers do not have the desired properties for the various applications. For example, fouling is still an unsolved problem in membrane applications, which is closely related to surface properties of both the membrane and the foulant. To meet the requirements for the various tasks, membranes with tailor-made properties are needed. In this contribution on the one hand surface modification techniques are described, which are used to (a) obtain microfiltration membranes with low-fouling tendency and (b) to prepare membranes with required properties in pervaporation separation applications. On the other hand modification/functionalization of polymers for use as ion-exchange membranes in energy-producing systems (fuel cells) are discussed. The focus is set on surface modification with polyelectrolytes and polyelectrolyte multilayer systems. This versatile technique enables the preparation of porous membranes with adjustable surface charge and low-fouling tendency without interference of permeate quality. Dense pervaporation membranes based on polyelectrolyte multilayer systems, with high selectivities and moderately high flux were obtained. The performance of such membranes can be controlled by the polyelectrolytes used (charge density) and the preparation conditions (e.g. temperature). Finally, a short introduction of new membrane materials based on fully aromatic polymers as alternatives to perfluoroalkylsulfonic acids, such as Nafion, is given.