(142d) Advanced Polymeric Membranes With Tailored Surface Properties

Advanced polymeric membranes with tailored surface properties

Mathias Ulbricht, Marc Birkner, Sven Frost, Mahendra Kumar, Miao Li, Mathias Quilitzsch, Thorsten Pieper, Nico Stahra, Robert Sulc

Lehrstuhl für Technische Chemie II, Universität Duisburg-Essen, 45117 Essen, Germany; mathias.ulbricht@uni-essen.de

Membrane technologies have been established in a wide range of industrial processes. However, in advanced separation and reaction engineering, membranes applied as separator or contactor can offer yet many more distinct advantages [1].

The majority of synthetic membranes are made from polymers because barrier and surface properties can be varied in wide ranges with help of established scalable manufacturing processes. Significant efforts have been made to further improve membrane performance by focusing on barrier properties (high selectivity, high flux) or surface properties (affinity, antifouling). Membrane fouling is still a major obstacle because it reduces productivity and product quality and increases energy consumption and need of additional chemicals for cleaning; hence, efficiency and sustainability of membrane processes are reduced.  

In this presentation, we will discuss how tailored surface functionalizations can significantly improve the performance of established membranes and can also contribute to the development of membranes using novel separation principles. With respect to the preparation/manufacturing, two general routes will be outlined, i) membrane formation from functional copolymers or blends of established membrane polymers with functional copolymer additives, and ii) post-functionalization of membranes by (reactive) coating or grafting methods (cf. [2,3]). Important recent trends in the field will be illustrated with examples from own research.

One focus will be on ultra- and microfiltration membranes with hydrophilic, low-fouling surfaces. Such membranes can be obtained by phase separation of polymer solutions (route i)), either using tailored block copolymer additives (e.g. [4,5]) to established membrane polymers or de novo synthesized copolymers [6]. If the hydrophilic functional blocks comprise also groups which can reversibly bind certain molecules or particles, the resulting membranes can be used for combined separations using both size-selective barrier and adsorber surface properties. Another combined separation mechanism is the charge-enhanced selectivity in ultrafiltration, for instance of proteins [6].

With respect to route ii), we will discuss recent progress toward ultra- and nanofiltration membranes with reduced fouling and improved cleaning. Thin-film hydrogel composite membranes obtained by graft copolymerization of hydrogels initiated at the membrane surface had been tailored with respect to the important parameters selectivity, flux and antifouling, either for selective separation of proteins and other nanoparticles [7] or for fractionation of smaller molecules and ions [8]. With zwitterionic grafted polymers and their stimuli-responsive properties it is also possible to develop more active antifouling and cleaning strategies, for instance based on a reversible conformation of the grafted “protective” layer change between operation and cleaning conditions. Finally, we will demonstrate that well-controlled grafting of a thermo-responsive polymer from the surface of ultrafiltration membrane pores can yield membranes where the size-selectivity can be tuned by the reaction conditions and the fractionation of nanoparticles can be reversibly switched by temperature.

All these strategies have relevance to widen the scope of the membrane applications and thus to contribute to the implementation or improvement of sustainable technologies.

[1]     E. Drioli, L. Giorno (Ed.), Membrane operations: Innovative separations and trans­formations, Wiley–VCH, Weinheim, 2009.

[2]     M. Ulbricht, Polymer 2006, 47, 2217.

[3]     Q. Yang, N. Adrus, F. Tomicki, M. Ulbricht, J. Mater. Chem. 2011, 21, 2783.

[4]     H. Susanto, N. Stahra, M. Ulbricht, J. Membr. Sci. 2009, 342, 153.

[5]     E. Berndt, M. Ulbricht, Polymer 2009, 50, 5181.

[6]     M. Kumar, M. Ulbricht, RCS Advances 2013, accepted.

[7]     P. D. Peeva, T. Knoche, T. Pieper, M. Ulbricht, Ind. Eng. Chem. Res. 2012, 51, 7231.

[8]     R. Bernstein, E. Antón, M. Ulbricht, ACS Appl. Mater. Interf. 20