NAMS 2002 Workshop - ICOM 2008

Membrane and Surface Modification III – 5
Friday July 18, 11:45 AM-12:15 PM, Honolulu/Kahuku
Effect of Surface Modifying Macromolecules Stoichiometric Ratio on
Composite Hydrophobic/Hydrophilic Membranes Characteristics and
Performance in Membrane Distillation
M. Qtaishat (Speaker), University of Ottawa, Ottawa, Canada - mrasool@eng.uottawa.ca
T. Matsuura, University of Ottawa, Ottawa, Canada
M. Khayet, University Complutense Madrid, Madrid, Spain
This study aims to develop novel hydrophobic/hydrophilic composite membranes
that are made specifically for membrane distillation (MD). The concept of
hydrophobic/hydrophilic composite membrane for MD was firstly proposed by
Khayet et al. [1,2]; where surface modifying macromolecules (SMMs) were
synthesized and blended with the host polyetherimide (PEI) to prepare composite
membranes. Those membranes were further tested for desalination by direct
contact membrane distillation (DCMD). The SMMs were prepared from
methylene bis-p-phenyl diisocyanate (MDI), diethylene glycol (DEG) and
oligomeric fluoroalcohol, Zonyl BA-LTM of average molecular weight 443 (BAL).
The stoichiometric ratio for SMMs synthesis was 3(MDI): 2(DEG): 2(BAL).
Suk et al. [3] later developed new surface modifying macromolecules (nSMM), in
which DEG in the earlier work was replaced by aminopropyl poly(dimethyl
siloxane) (PDMS). They used these nSMMs together with the host
polyethersulfone (PES) to prepare membranes for MD. It is worth mentioning that
blending DEG based SMM yielded better DCMD fluxes than blending nSMM [1-
3].
In this study further improvement of MD performance was attempted by changing
the nSMM structures. To this end, the stoichiometric ratio of nSMM components
was altered systematically in nSMM synthesis; i.e. nSMM1
2(MDI):1(PDMS):2(BAL); nSMM2, 3(MDI):2(PDMS):2(BAL); nSMM3:
4(MDI):3(PDMS):3(BAL).
The newly synthesized SMMs were characterized by the gel permeation
chromatography and the elemental analysis to know the molecular weight and
fluorine content, respectively. The results showed that fluorine content decreased
with increasing the PDMS stoichiometric ratio. Furthermore, the newly developed
SMMs were blended with PEI host polymer to prepare composite
hydrophobic/hydrophilic membranes. This was done in a single casting step by
the phase inversion method. The details of membrane casting are as follows. A
predetermined amount of PEI was dissolved in dimethylacetimide (DMAc)/gbutyrolactone
(GBL) mixture, into which nSMM was added. The composition of