 Abstract | Reverse osmosis membrane desalination technology has come a long way since
the Loeb and Souririjan type membranes of the 1960s. Advances in production
and engineering processes have overcome many inherent system limitations,
however some remain. Truly biofouling-resistant membranes are yet to be
realised, and membrane compaction remains an issue.
In this thesis methods for mitigating these two membrane limiting factors have
been investigated; polymeric modification and nanoparticle inclusion.
In the first part of the project, a detailed study of the polymerisation of poly(2hydroxyethyl
methacrylate) via activators regenerated by electron transfer atom
transfer radical polymerisation was undertaken. Conditions were chosen to be
commercially attractive. The modified membranes were studied with fourier
transform infrared spectroscopy (FTIR), x-ray photospectroscopy, nuclear
magnetic resonance, and thermogravimetric analysis. Results showed that by
varying the initial monomer volume and/or the polymerisation reaction time it
was possible to create a series of modified membranes with a range of polymer
graft densities, thus indicating the livingness of the polymerisation reaction.
In order to evaluate the ideal graft density, the properties of the modified
membranes were further investigated. The polymer coating was clearly visible
using scanning electron microscopy and an increase in surface roughness was
observed with atomic force microscopy, in both cases confirming the increase in
polymer graft density. Water contact angle studies explored the relationship
between surface morphology and wettability, indicating conformational changes
in the polymer. Hydrolysis had little effect on modified membrane filtration
properties when soaked at pHs outside the recommended range for pristine
cellulose acetate membrane (CAM).
Unique aquarium biofouling tests were performed, and showed a decrease in
biofouling for the modified membranes. Stirred-cell experiments were used to
evaluate the filtration properties of the modified membranes. From the results it
was possible to determine optimum conditions for membrane modification to
obtain a polymer graft density with maximum biofouling resistance and minimum
loss of filtration properties.
In the second part of the project, aminopropylisobutyl polyhedral oligomeric
silsesquioxane (POSS) was investigated as a nanocomposite additive. Since
nanoparticle agglomeration and leaching were identified as issues in
nanocomposite materials, an anchored nanoparticle was synthesised using
isocyanate chemistry to attach POSS to cellulose acetate (CA). This anchored
nanoparticle was compared to un-anchored POSS as an additive in CA membrane
casting solutions at loadings of 0.5, 1.0 or 5.0 wt%. FTIR and energy dispersive
X-ray microanalysis showed the anchored nanoparticle to have better dispersion
in the resulting membranes. The nanocomposite membranes showed greater flux
of water and salt than an unmodified CA control. Membrane compaction was
mitigated at low nanoparticle loadings. Dynamic Mechanical Analysis (DMA)
results suggest POSS has a plasticisation effect on the CA matrix. |
