(466f) 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.