Fast and Reproducible Fabrication of Polymer Ultrafiltration Membranes Using Nanoparticles As Pore - Forming Template

Fast and reproducible fabrication of polymer ultrafiltration membranes using nanoparticles as pore - forming template

 

Christoph R. Kellenberger, Norman A. Luechinger and Wendelin J. Stark

 

Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology (ETH Zurich), Wolfgang-Pauli-Str. 10, HCI E 107, ETH Hönggerberg, Zurich 8093, Switzerland

 

Presenting author email: christoph.kellenberger@chem.ethz.ch

 

Polymeric ultrafiltation membranes play an important role in mass separation processes in the biopharmaceutical industry. They are not only used to purify and concentrate proteins but also for the filtration of viruses during antibody production. Commercial ultrafiltration membranes are nowadays produced by a technique called phase inversion. Therefore, a phase separation has to be induced in a previously homogeneous polymer solution by precise control of temperature, time and solvent to non-solvent ratio. This process unfortunately is limited by the number of parameters that have to be controlled simultaneously during production and by the broad pore size distribution that decreases the selectivity of the resulting membranes (Peinemann, Nunes, 2008).   

            

We present a novel approach towards the production of ultrafiltration polymer membranes which are fabricated by a facile and fast procedure. This process is based on the use of soluble (degradable) carbonate nanoparticles (Huber 2005; Loher 2005; Grass 2005). The nanoparticles act as the pore template and the process can be applied on numerous polymers. Membranes can be fabricated by a simple two-step procedure. A polymer solution (polymer dissolved in a solvent) containing dispersed soluble nanoparticles is used as the starting material. At first, this solution is roll-coated on a substrate (e.g. glass) and after evaporation of the solvent a solid polymer film (with incorporated soluble nanoparticles) is obtained. Choosing the right weight ratio of nanoparticles to polymer in the applied dispersion is crucial. During the evaporation of the solvent the particles in the polymer film will agglomerate in the polymer matrix to form a completely interconnected template. Therefore, in a second step the polymer film can be turned porous by simple dissolution of the soluble nanoparticle template in a mild acid. The pore formation of the resulting membrane is different to state-of-the art techniques. Here, the pore size and number of pores is exactly defined by the size and number of nanoparticles, as they serve as a direct template of the finally obtained pores. Therefore, the pore formation is very reliable yielding a narrow pore size distribution that guarantees the high selectivity of the membrane. Additionally, the soluble nanoparticle template dissolution in a mild acid is very fast (< 10s) which can be run at ambient conditions without the need for precise and simultaneous control of various process parameters.

            

The use of CaCO₃ nanoparticles (50nm in size) in a polyethersulfone (PES) or polysulfone (PSU) matrix led to the formation of a polymer membrane with a molecular weight cut-off (MWCO) of 1400kDa, whereas the use of SrCO₃ nanoparticles (17nm in size) in a PES matrix led to a MWCO of 150kDa. This demonstrates that the pore size of the filtration membranes can directly be tuned by the nanoparticle size. The MWCO of the according membranes was examined using a dextran rejection profile test that is widely accepted among membrane manufacturers (Tkacik, Michaels, 1991).

 

Figure 1: Top view on PES membrane with a MWCO of 150kDa (a). Cross section of the same membrane (b). Typical dextran rejection profile of a 1400kDa MWCO membrane (c).

 

Peinemann, K. V., Nunes, S. P. (2008) Membranes for life sciences. WILEY-VCH Verlag GmbH&Co.

Huber, M., Stark, W. J., Loher, S., Maciejewski, M., Krumeich, F., Baiker, A. (2005) Chem. Commun. 5, 648-50.

Loher, S., Stark, W. J., Maciejewski, M., Baiker, A., Pratsinis, S. E., Reichardt, D., Maspero, F., Günther, D. (2005) Chem. Mater. 17, 36-42.

Grass, R. N., Stark, W. J. (2005) Chem. Commun., 14, 1767-1769.

Tkacik, G., Michaels, S. (1991) Nature Biotechnology, 9, 941 – 946.