W. Richard Bowen and Nidal Hilal 4

5.4 MODIFICATION OF MEMBRANEs wITH sULPHONATED 163
The lower adhesion for modified PVDF membranes compared to the
initial PVDF especially at DM 348 �g cm �2 suggests that the hydrophobic
interactions are playing the dominant role where the higher hydrophobicity
of initial membranes results in increasing its adhesion compared to
modified membranes.
5.4 ModIfICAtIon of MEMbrAnES wIth
SulPhonAtEd Poly(EthEr-EthEr KEtonE) PolyMErS
One of the most widely used materials in the manufacture of filtration
membranes is polysulphone, due to its excellent mechanical, thermal and
chemical stability. Unfortunately a high degree of hydrophobicity possessed
by unmodified polysulphone membranes renders them prone to
fouling by a wide range of solutes. To improve membrane effectiveness by
reducing fouling, and particularly biofouling, hydrophilic polymers may
be incorporated into membranes or the membranes modified by the addition
of extra functional groups by, for instance, sulphonation. The addition
of charge bearing groups to the membrane surface will not only decrease
the degree of hydrophobicity of the membrane but can also cause increased
rejection of particles and solutes of identical charge [25].
Poly(ether-ether ketone) (PEEK or poly(oxy-1,4-phenyleneoxy-1,4-
phenylcarbonyl-1,4-phenylene) is a very chemically stable polymer,
soluble only in strong acids. This includes concentrated sulphuric or
chlorsulphonic acid, which yields a sulphonated PEEK (SPEEK) [26, 27].
Studies of solubility of SPEEK suggest that it is more hydrophilic than
merely sulphonated polysulphone [28].
Studies have been carried out to investigate the effectiveness of using
SPEEK as a charged polymer additive to polysulphone membranes to
not only reduce fouling by the introduction of charged groups, but also
as a pore-forming agent due to its hydrophilicity [29, 30]. In particular
here we will report the use of AFM in the characterisation of the effects
of the SPEEK additives on surface morphology and fouling resistance.
All membranes were characterised using AFM-obtained topographies.
In Figure 5.21 example images of a plain polysulphone membrane and
a membrane of polysulphone blended with 5% SPEEK are shown. Data
obtained from AFM images, including average pore size (r p), root mean
square (rms) roughness and surface porosity, are summarised in Table 5.6.
Little variation is seen in rms roughness, although there is a trend for
decreasing roughness with higher SPEEK content. Porosity variation
follows a similar trend to that calculated from permeability of the membrane
to water [29], but of a much smaller magnitude, suggesting that the
increase in water permeability as SPEEK content increases is only partly