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8/13/2019 Effect of carbon molecular sieve sizing with poly(vinyl pyrrolidone) K-15 on carbon molecular sievepolysulfone mi
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Available online at www.sciencedirect.com
Journal of Membrane Science 307 (2008) 5361
Effect of carbon molecular sieve sizing with poly(vinyl pyrrolidone) K-15 oncarbon molecular sievepolysulfone mixed matrix membrane
W.A.W. Rafizah, A.F. Ismail
Membrane Research Unit, Faculty of Chemical and Natural Resources Engineering,
Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia
Received 20 April 2007; received in revised form 29 August 2007; accepted 8 September 2007
Available online 14 September 2007
Abstract
Mixed matrix membranes (MMMs) comprising polysulfone (PSF) Udel P-1700 and 30 wt% carbon molecular sieve (CMS) particles (
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54 W.A.W. Rafizah, A.F. Ismail / Journal of Membrane Science 307 (2008) 5361
achieving almost four times higher selectivity in CO2/N2 and
O2/N2compared to pure Matrimid, the O2and CO2permeabil-
ity was decreased at least fortyfold. Mahajan et al., [7] on the
other hand, proposed to maintain the polymer flexibility during
membrane formation by casting at temperature close to the Tgof the polymer matrix. Several workable MMMs using inter-
mediate Tg polymers have been successfully fabricated using
this approach[1113].Conversely, this approach is not practi-
cal for high Tg polymers because it is very difficult to find a
non-volatile solvent with enough high boiling point to meet the
required temperature during membrane formation [6]. The addi-
tion of plasticizer is also not practical because it could worsen
the intrinsic gasseparation performance of the polymer [1220].
Poly(vinyl pyrrolidone), PVP is a common chemical used as
additive in casting solution for preparation of phase inversion
PSF[2223].It is known as an agent for suppressing macrop-
ore formation in phase inversion membranes. Otherwise, PVP
is an established thermoplastic sizing in composite technology.
The effectiveness of using PVP as a sizing agent to promote
the adhesion between inorganic substrate with polymer matrixhas been extensively reported in fiber reinforced polymer matrix
composites development[24,25].The sizing technique, which
is a surface coating approach deserves a noteworthy considera-
tion and can be adapted in MMMs development. Sizing known
as coating or finishes are widely used to protect fiber surface
from damage, improve the fiber wetting by matrix and pro-
tect fiber surface reactivity [26,27]. Sizing could increase the
strength of the interphase by introducing more chemical reac-
tive site and/or more surface area for adhesion [2831] involving
neither complicated chemical reaction nor grafting process. The
functional groups along sized fibers can react and/or interact
with the matrix, giving rise to strong interactions between thefiber and the matrix[32,33].Furthermore, the entanglement of
polymer sizing and polymer matrix molecules via inter-diffusion
mechanismstrengthens the interphaseadhesion[28]. Inspired by
these successful findings, the application of PVP can be poten-
tially adapted for mixed matrix membrane development with the
intention of improving the compatibility of the inorganic sieving
material with the matrix polymer.
In this study, the modification of CMS particles using siz-
ing technique was explored. Physical deposition of PVP K-15,
sizing agent onto the surface of CMS particles was employed
by treating the CMS particles in sizing bath solution containing
110 wt% PVP K-15 in isopropanol solution prior to embed-
ment into the polymer matrix. In order to analyze the impacts of
CMS sizing with PVP K-15 on the morphology and separation
performance of membrane, MMM films comprising 30wt% of
PVP K-15-sized CMS in polysulfone Udel P-1700 were fab-
ricated and were characterized using TGA, DSC, FESEM and
pure gas permeation test.
2. Experimental
2.1. Raw material
A commercial Udel P-1700 polysulfone, purchased from
Amoco Performance Inc., USA was chosen as the polymer
matrix phase. It has an average molecular weight of 45,000.
The solvent,n-methyl-2-pyrrolidone (NMP) supplied by Merck
was used as received. The molecular sieve entities were car-
bon molecular sieve particles synthesized from polyacrilonitrile
(PAN) precursor described elsewhere [34]. The pore sizes ofPAN-based CMS could range from 4 to 6 A, which make them
suitable for use as molecular sieve[35].The CMS particle size
was reduced to less than 25m as verified by FESEM. Poly
(vinylpyrrolidone) kollidone 15 or PVP K-15 with the average
molecular weight of 10,000 was purchased from Merck, Ger-
many. Reagent grade isopropanol (Merck, Germany) was used
as the solvent to dissolved PVP K-15. Prior to any use, PSF
and CMS particles were preconditioned in a vacuum oven at
100 and 250 C, respectively for 12 h to remove trapped mois-
ture.Table 1summarizes the chemical structures and molecular
weights of PSF and PVP used in this study.
2.2. Preparation of PVP K-15-sized CMS
The flaky and white powder of PVP K-15 was dissolved in
isopropanol to produce dilute solution with the concentration of
110 wt% PVP K-15. An intended amount of CMS particleswas
added to the PVP K-15 sizing bath solution and stirred at 30 rpm
for 1 h. Then, the sized CMS were filtered from the excess solu-
tion using Whatman 40 filter paper. The sized CMS cake was
rinsed with isopropanol to remove unadsorbed polymer before
further dryingin a vacuum oven at 50 Cfor24h.Asimilarrange
Table 1
Chemical structures and molecular weights of PSF and PVP
Polymer Chemical structure Molecular weight
PSF (Udel, P-1700) 45,000
PVP K-15 10,000
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W.A.W. Rafizah, A.F. Ismail / Journal of Membrane Science 307 (2008) 5361 55
Fig. 1. Preparation of PSFPVP-sized CMS suspension.
of PVP bath solution has been studied to size carbon and glass
fiber in Refs.[30,36].This working range was chosen because
of several considerations. First, conformation of the bound poly-
mer chains on solid surface may vary with increasing polymer
solution concentration[36].A dilute PVP solution is needed to
wet the particle surface and provide easy access to the polymer
chains to conform. However, a very dilute solution reduces the
possibility of chain attachment. As a result, some part of the
CMS surface will be left unoccupied. The possibility of chainattachment is likely to increase by increasing the concentra-
tion of PVP in bath solution. Therefore, a suitable concentration
of PVP bath solution that can easily wet the particle surface
and provided sufficient chain attachment at the same time was
selected within this bath concentration range. In addition, damp-
ing effect of PVP on carbon surface was encountered when PVP
K-15 bath concentration used exceeding 10 wt%. A thick layer of
PVP formed on the CMS surface and prolonged drying duration
was required. This problem was also reported in Refs.[30,36].
2.3. Fabrication of membrane
There are several approaches to prepare polymersieve sus-
pension. For this study, 25 wt% PSF in NMP solution was first
prepared by dissolving pre-dried PSF pellets in NMP and stirred
for 12 h at temperatures of 6070C. In separate flask, the
intended amount of PVP-sized CMS was wet with small amount
of NMP. Then, the PSF dope solution was gradually added
into the flask containing wet CMS and stirred at 30 rpm. PSF
dope solution addition and stirring process were repeated until
a homogenous suspension solution was obtained. The sequence
for preparation of PSFPVP-sized CMS suspension is summa-
rized inFig. 1. The following casting process was performed
using the protocol outlined in Fig. 2. Forming a fine non-
supported mixed matrix membrane film is a very challengingtask because the membrane film becomes more opaque, brittle
and easy to break during testing upon inclusion of CMS parti-
cles. This phenomenon has been discussed in Refs. [4,17,21]. In
this study, it wasfound that the thickness of workable membrane
films could range from 60 to 70 m and were kept in vacuum
oven at 60 C prior to characterization to avoid contamination
by moisture or impurities.
2.4. Polymer and membrane characterization
Thermogravimetry analysis (TGA) using Mettler Toledo
thermogravimetry analyzer (TGA TSO800GC1) was performed
Fig. 2. Casting procedure of mixed matrix membrane at elevated temperature.
in order to determine the weight of sizing (Wsizing) on the sur-
face of the CMS particles. One gram of sized CMS was heated
in N2 atmosphere from 30 to 800
C with the heating rate of10 Cmin1 and the weight of sizing and estimated sizing thick-
ness was calculated using the following expressions:
Wsizing =Wi Wf
Wf 100 (1)
estimated sizing thickness on CMS =Wi Wf
PVP1000ACMS(2)
whereWirepresents the initial weight of the sized CMS (g), Wfis denoted for the final weight of CMS sample after heating (g),
PVPis the density of PVP (1.1 kg m3) andACMSis the surface
area of CMS (151.53 m2 g1).
Considering that the strength of interfacial adhesion is alsoinfluenced by the compatibility of sizing polymer with polymer
matrix, it is vital to verify the miscibility of these two polymers
during fabrication [37]. In order to determine the miscibility
of PSF/PVP blend, the glass transition temperature (Tg) of the
polymers was analyzed with differential scanning calorimetry
(Mettler Toledo DSC 822e). Sample was cut into small pieces,
weighed and placed into pre-weighed aluminum crucible. Then,
the sample was heated from 30 to 300 C with a heating rate of
10 Cmin1 in the first cycle to remove the thermal history. The
sample was cooled from 250 to 30 C at the rateof 10Cmin1.
The same heating procedure was repeated in the second heat-
ing cycle. Tg of the sample was determined as the midpoint
temperature of the transition region in the second heatingcycle.
Attenuated total reflection fourier transformed infrared
(ATR-FTIR) was used to correlate the changes in chemical
environment on the CMS surface before and after sizing pro-
cess. The pre-dried sample of either unsized CMS or sized CMS
was pressed against a 45 incidence germanium element. The
IR-spectra were recorded on Thermo Nicolet 5700 ATR-FTIR
spectroscopy, which is supplied by Thermo Nicolet Corporation
and Spectra Tech, USA. Based on the IR-spectra, a qualitative
difference in the distribution of functional groups on the surface
of sized CMS and unsized CMS could be made. In addition, the
miscibility of PVP K-15 in PSF matrix was confirmed by ana-
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56 W.A.W. Rafizah, A.F. Ismail / Journal of Membrane Science 307 (2008) 5361
lyzing the spectra shifts or the intensity changes of characteristic
groups of PSF and PVP K-15 in PSF/PVP blend.
Gas permeationproperties for mixed matrix membranes were
determined using variable-volume constant-pressure method
with a permeation cell described elsewhere[38].Each pure gas
(99.97% purity) was tested in the sequence of N2 and O2 and
measured three times for each membrane. The measurement
was performed at 30 C at 1.5 bar. The pure gas permeability
was determined using the following expression:
Pi =Vil
Atp(3)
where i represents the gas penetrant i, Vi is the volume of gas
permeated through the membrane (cm3, STP),l the membrane
thickness (cm),A the effective membrane area (cm2),tthe per-
meation time (s) and p is the transmembrane pressure drop
(cmHg). The selectivity was obtained using Eq.(4):
i/j=Pi
Pj
(4)
wherei/jis the selectivity of gaspenetrant i to gaspenetrantj, PiandPjare the permeability of gas penetrantiandj, respectively.
Field emission scanning electron microscope (FESEM) was
used to qualitatively analyze the morphology of the fabricated
membrane films and observed the compatibility between the
sieves and the polymer matrix. Prior to testing, the film samples
were fractured in liquid nitrogen in order to achieve a clean
break. The samples were then mounted on a stainless steel stand
with carbon tape and coated with 15 nm of gold using a sputter
coater.
3. Results
3.1. Effects of carbon molecular sieve sizing with
poly(vinyl pyrrolidone) K-15 on polysulfonecarbon
molecular sieve interphase
From the thermal gravimetry analysis, the estimated sizing
level on the CMS particles after sizing in 10 wt% PVP K-15
in isopropanol solution bath was about 10.2 wt% and the siz-
ing thickness was approximately 7 A. ATR-FTIR analysis was
also performed in order to correlate the changes in the chemi-
cal environment on the CMS surface before and after the sizing
process. This technique, which probes approximately the first
2m of the sample surface was used to verify the deposition ofPVP K-15 on the CMS surface. The analytical evaluations of the
ATR-FTIR spectra of the unsized CMS and PVP-sized CMS are
presented inFig. 3.They are consistent with the earlier reports
[36,39,40].A qualitative difference in the distribution of func-
tional group on the sized CMS and the unsized CMS can be
noted.
Based on the FTIR analysis presented in Fig. 3, the
highlighted regions represent the presence of two important
characteristic bands for PVP K-15. The infrared absorption at
1654 and 1289 cm1, respectively corresponds to the amide I
carbonyl (-C O) band and amide III (CN stretching) band of
PVP[41,42].The surface of unsized CMS on the other hand is
Fig. 3. Infrared spectra forPVP K-15, unsized CMS andPVP K-15-sized CMS.
almost inert with no apparent appearance of characteristic peak.
However, the presence of characteristic peaks of PVP could beobserved in the sized CMS spectra. The emergence of these
peaks becomes more prominent in the spectrum of CMS surface,
which was sized in 10 wt% PVP K-15 bath solution. This find-
ing supports that PVP was successfully deposited on the carbon
surface. The most sufficient and stable sizing level was achieved
by sizing the CMS particles in 10 wt% PVP K-15 bath solution
comparedto sizing using 1 and 5 wt% PVP K-15 bath concentra-
tion. This is because as the concentration of PVP in bath solution
increases, the possibility of PVP chains to successfully adsorb
and conform onto the CMS surface was also increased. Adsorp-
tion of PVP chains per area of CMS increased, thus forming a
stronger adherence to the surface[43].The peak at 2360 cm1
in FTIR spectra presented inFig. 3could be attributed to CO2peak. CO2peaks arecommon in IR spectra (2349 cm
1) because
of presence in air. There is a possibility that the background
correction run was not often enough to compensate for environ-
mental conditions and can be easily detected within such a low
absorbance range (
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W.A.W. Rafizah, A.F. Ismail / Journal of Membrane Science 307 (2008) 5361 57
Table 2
Glass transition temperature of PSF, PVP and PSF/PVP blend
Polymer Composition Tg (C)
PSF 1 183.01
PVP 1 188.04
PSF/PVP 32:1 183.93
analysis to study the miscibility of their polymer blend. Tg of
pure PSF, pure PVPand PSF/PVP blend arepresented in Table 2.
DSC curves for these polymers are also depicted in Fig. 4.The
DSC scan for PSF/PVP blend exhibited a single Tg located at
183.93 C, which is consistent with the miscibility character of
PSF/PVP K-15 mixture. As suggested by Walsh and Roston
[46],the Tg of a miscible blend can be predicted using simple
Fig. 4. DSC curves of (a) pure PSF, (b) pure PVP and (c) PSF/PVP blend.
Table 3
Peak assignments of polysulfone
Wavenumber (cm1) Probable assignment
1585 Benzene ring stretch
1504, 1488 Aromatic carbon groups (skeletal vibration)
1323, 1294 Sulfonate groups vibration
1241,1014 Antisymmetric COC stretch
1151 RSO2R
series, parallel and logarithms models.
Series model : 1
Tgb=
x1
Tg1+
x2
Tg2(5)
Parallel model : Tgb = x1Tg1 + x2Tg2 (6)
Logarithms model : lnTgb = x1ln Tg1 + x2ln Tg2 (7)
wherex1 andx2 is the composition of polymer 1 and polymer
2, respectively,Tgb
the glass transition temperature of polymer
blend, Tg1 the glass transition temperature for polymer 1 and
Tg2 is the glass transition temperature for polymer 2. The Tgof
PSF/PVP blend obtained from DSC results is in a good agree-
ment with predicted value proposed by these three models. This
finding further confirmed the miscibility of PVP in PSF.
In order to further understand the nature of the PSF/PVP K-
15 mixture at molecular level, the blend was studied by means of
ATR-FTIR spectroscopy. Although ATR-FTIR probes approx-
imately the first 2m of the sample surface, in this study it
was assumed that the resultant spectrum could represent the
whole part of the blend film. Studies of molecular interaction in
polymer blending system using FTIR has been performed and
discussed in Refs.[4245].The spectra of immiscible polymersare basically the sum of the spectra components in pure poly-
mers. In contrast, anyspecific interactions occurring between the
characteristic groups of pure polymers in miscible blend were
indicated by frequency shifts or absorption intensity changes
[4245].FTIR spectra for pure PSF, PVP K-15 and PSF/PVP
K-15 blend are presented in Fig. 5 for comparison. The probable
peak assignment for pure PSF and PVP K-15 are summarized
inTables 3 and 4, respectively. These results are consistent with
[38,4245].
Comparison of PSF/PVP K-15 blend spectrum with the
spectra of PSF and PVP K-15 reveals the occurrence of
interactions between the characteristic groups of PSF and
PVP K-15 in the miscible blend. These interactions are
indicated by frequency shifts involving several characteristic
groups and absorption intensity changes. The strongest shift
which is about 24 cm1 has been detected for amide car-
Table 4
Peak assignments of poly(vinyl pyrrolidone)
Wavenumber (cm1) Probable assignment
1654 Amide C O and CN stretch vibration
1493/1461/1423/1374 CH deformation of cyclic CH2groups
1289 Amide III band (CN stretch)
1071 CO
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58 W.A.W. Rafizah, A.F. Ismail / Journal of Membrane Science 307 (2008) 5361
bonyl group (C O) (16541679 cm1), the secondary shift
which is about 12 cm1 can be observed for sulfonate groups
(13231322 cm1 and 12941293 cm1) and COC stretch-
ing mode (12411240 cm1). Obvious changes in absorption
intensity are detected for sulfonate group (stretching vibration
at 1150 cm1) and aromatic carbon group (skeletal vibration
assigned at 1322 and 1293 cm
1
). In addition, a peak locatedat 1289 cm1 which assigned for amide III band (CN stretch-
ing mode) is no longer observable in the PSF/PVP K-15 blend
spectrum. Probably the frequency of this peak has shifted or
its absorption intensity has been reduced and overlapped with
the sulfonate group vibration of PSF at 1294 cm1. As a result
a single peak at 1293 cm1 appears in PSF/PVP K-15 blend
spectrum. Kapantaidakis et al.[44]reported that a similar trend
of the absorption intensity changes were also observed for sul-
fonate groups and aromatic carbon groups in their PI/PSF blend
polymer.
Thisanalysis suggests the occurrenceof interactions and mix-
ing of PSF and PVP K-15 at the molecular level. The spectra
shifts and intensity changes of characteristic groups of PSF andPVP K-15 could be attributed to the inter-molecular interaction
within PSF/PVP K-15 blend. In agreement with Sionkowska
[42]and Zeng et al.[45],the spectra shift of bands such as the
significant shifting of amide carbonyl group band in PVP and the
sulfonate group band in PSF suggests the interactions between
PSF and PVP have occurred. The good compatibility between
these two polymers can be rationalized by interaction mainly
contributed by C O group in PVP chain and sulfonate group
in PSF chain. This result was supported by Kapantaidakis et
al.[44]who studied the miscibility between PI/PSF blend. The
occurrence of interaction at molecular level due to C O group
in PI and sulfonate group in PSF has been observed.
3.2. Effects of carbon molecular sieve sizing with
poly(vinyl pyrrolidone) K-15 on polysulfonecarbon
molecular sieve mixed matrix membrane morphology
A qualitative assessment was conducted by using FESEM
images in order to compare the morphology of the fabri-
cated MMM containing PVP-sized CMS and MMM containing
untreated CMS. Fig. 6 reveals the comparison of the cross-
sectionalimages of theunmodified MMMand MMM containing
PVP-sized CMS. Both of these membranes were loaded with
30 wt% of CMS. In all FESEM images, CMS particles (
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W.A.W. Rafizah, A.F. Ismail / Journal of Membrane Science 307 (2008) 5361 59
Fig. 6. Comparison of FESEM micrographs for the cross-section of PSFCMS mixed matrix membrane with 30 wt% CMS loading: (a) containing unmodified CMS
under 1000magnification, the white bar indicates 10m; (b) containing unmodified CMS under 2500magnification, the white bar indicates 1m; (c) containing
PVP-sized CMS under 1000 magnification, the white bar indicates 10 m; (d) containing PVP-sized CMS under 2500 magnification, the white bar indicates1m.
interaction with the surrounded PSF matrix by introducing more
reactive side groups such asC O that can form specific inter-
action with sulfonate group of PSF. The interaction between
PVP K-15 and PSF matrix has been confirmed via ATR-FTIR
results. This finding indicates the occurrence of intimate mixing
at molecular level between the PVP K-15 sizing layer and PSF
matrix. In addition, it is envisioned that as PSFPVP interphases
are in contact, some of the PVP chains possibly migrate into the
PSF region via inter-diffusion mechanism. The inter-diffusion
mechanism between polymer interphases was also discussed
by Sperling[43]and Laot[37].These chains finally entangledwithin the PSF network and strengthen the interphase region.
3.3. Effects of carbon molecular sieve sizing on gas
permeation of mixed matrix membranes
The gas permeation results for unmodified MMMs and
MMMs containing PVP-sized CMS are listed in Table 5.The
O2and N2permeability for PSFPVP-sized CMS MMMs were
higher than those of pure PSF membranes and lower than those
of the unmodified PSF-CMS30 MMMs. These MMMs exhib-
ited the highest O2/N2 selectivity, which was almost 1.7 times
of the selectivity in unmodified MMMs.
The gas transport through mixed matrix membrane can occur
through three main pathways, which are through dense PSF
matrix, highly selective CMS and/or through non-selective gaps
or voids between the matrix wall and sieve particles. Dense PSF
matrix provides a very selective but highly resistive pathway to
the gas flow. Gas transport through CMS particles is less resis-
tive than that of dense PSF matrix and offers the most selective
pathway because CMS is capable of discriminating between size
and shape differences of the gas penetrants. The gaps or voids
conversely allow the bypassing of gas through its unselective
and non-resistive pathways. The gas transport through the gaps
Table 5
Comparison of gas permeation between PSFCMS30 and PSFPVP K-15-sized
CMS mixed matrix membranes for O2and N2
Membrane CMS (wt%) PO2 (barrers) PN2 (barrers) O2/N2
PSF 0 1.58 (0.28)a 0.29 (0.04) 5.50
PSF-CMS30 30 6.77 (0.01) 1.82 (0.06) 3.69
PSFPVP-sized
CMS
30 6.52 (0.23) 1.08 (0.04) 6.05
a Values in parenthesis is standard deviation; 1 barrer = 1 1010 (cm3
STP cm (cm2 s cmHg)).
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60 W.A.W. Rafizah, A.F. Ismail / Journal of Membrane Science 307 (2008) 5361
is assumed to be the Knudsen diffusion. As supported by the
FESEM images inFig. 6(a) and (b), a gross bypassing of gas
could occur through the submicron gaps between the polymer
matrix wall and the CMS particles in PSF-CMS30. Since the
gas transport through those unselective gaps has been assumed
to be the Knudsen diffusion, the degree of increment in N 2per-
meability became larger and exceeded the degree of increment
of O2permeability due to gas flow through CMS pathway. As a
result, these membranes exhibited higher O2and N2permeabil-
ity with poor selectivity compared to pure PSF membrane. On
the other hand, the FESEM images in Fig. 6(c) and (d) reveal
that the interfacial gaps were almost invisible in PSFPVP-sized
CMS MMMs structure indicating that the gap size between the
polymer matrix wall and CMS particles has been extensively
reduced. The transport resistance of this pathway increased and
suppressed the permeation of gas via Knudsen diffusion mech-
anism. More penetrant gases were directed to flow through
CMS pathway. This was supported by a substantial reduction in
N2 permeability for PSFPVP-sized CMS MMMs, which was
about 41% from the N2 permeability in PSF-CMS30. A con-siderable improvement in O2/N2 selectivity was also achieved
by using PSFPVP-sized CMS whereby the selectivity was
enhanced from 3.69 to 6.05. The findings of this study prove
that the PVP K-15 sizing layer not only capable of inducing the
interfacial adhesion of PSF matrix and CMS particles but also
allowing the gas transport through these two phases to proceed
without creating additional non-selective and resistive layer in
the interphase region.
4. Conclusions
In this study, MMMs were successfully fabricated by com-bining polysulfone, Udel P-1700 and PVP K-15-sized CMS.
CMS sizing with PVP K-15 has brought a dramatic impact on
the adhesion of the CMS and PSF matrix. ATR-FTIR analysis
demonstratedthat the sizingagent (PVP K-15) hasbeen success-
fully deposited onto the external surface of CMS and intimate
interactions at molecular level between miscible blend of PSF
matrix and PVP K-15 sizing polymer has also been established.
The FESEM images revealed a considerable improvement in
the interfacial adhesion between PSF matrix and CMS particles
was achieved in PSFPVP K-15-sized CMS MMMs compared
to that of unmodified PSFCMS MMMs. The voids or gaps
surrounding the CMS was reduced to a great extend suggest-ing that the PVP K-15 sizing layer has successfully bridged the
matrix and sieve phases by physically inducing the molecular
interactions with both PSF matrix and CMS particles. With the
absence of interfacial voids, a substantial recovery of separation
performance can be achieved without adversely worsen the gas
permeability or sacrificing selectivity.
Acknowledgements
Theauthor would like to express sincere gratitudeto National
Science Fellowship (NSF) from Ministry of Science, Technol-
ogy and Innovation Malaysia (MOSTI) for the financial support.
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