NAMS 2002 Workshop - ICOM 2008

Membrane and Surface Modification III – 1 – Keynote
Friday July 18, 9:30 AM-10:15 AM, Honolulu/Kahuku
Modification of Polyethersulfone Nanofiltration Membranes
K. Boussu, Katholieke Universiteit Leuven, Heverlee, Belgium
K. Schols, Katholieke Universiteit Leuven, Heverlee, Belgium
B. Van der Bruggen (Speaker), Katholieke Universiteit Leuven, Heverlee, Belgium -
bart.vanderbruggen@cit.kuleuven.be
The top layer of commercial polymeric nanofiltration membranes for use in
aqueous applications is in most cases composed of polyamide or
polyethersulfone (PES). The main advantage of using PES membranes is the
very high chemical and thermal stability. However, these membranes also have a
high hydrophobicity (pernicious for membrane fouling) and a wide pore
distribution (pernicious for a distinct separation between two components). To
minimize these inadequacies, membrane modification is a valuable option, which
can be performed in two different ways: by working on the polymer used (e.g., by
sulfonating, chlorinating, addition of a copolymer) or by working on the existing
membrane top layer (e.g., by grafting, plasma treatment,..).
This study focuses on different modification (or more specifically hydrophilization)
techniques, applied on both commercial and laboratory-made PES nanofiltration
membranes. The surfaces of these membranes were hydrophilized by means of
the grafting technique, which implies that hydrophilic monomers (like acrylamide
or methacrylic acid) were grafted on active places on the membrane surface after
a redox reaction with K2S2O8 and K2S2O3. Moreover, in case of the laboratorymade
membranes, the polymer can also be hydrophilized, e.g. by sulfonating.
Starting from this hydrophilic polymer, a membrane was prepared by using the
DIPS technique (Diffusion Induced Phase Separation).
After modification, the membranes were characterized thoroughly for the
hydrophobicity (by contact angle measurements), the roughness (by AFM), the
chemical composition of the top layer (by ATR-FTIR) and the size of the pores. A
cross-flow nanofiltration set-up was used to study the performance (i.e., water
permeability and membrane fouling) of the modified membranes. By comparing
the characterization results of the unmodified with the modified membranes, the
degree of modification was checked. Moreover, for each characteristic, the
behaviour was followed as a function of time, to have an idea about the
modification mechanism (reversible or irreversible).