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Synthesis and Characterization of Polysulfone (PSU)/Philippine Halloysite
(PH-HAL) Nanostructured Membrane via Electrospinning
Ruth R. Aquino , Marvin S. Tolentino , Niel Karl G. Arcamo1, John Patrick N. Gara1, and Blessie A. Basilia1,2
1Mapúa University, School of Chemical, Biological, and Materials Engineering and Sciences, 658 Muralla St., Intramuros Manila, 1002
Philippines
2Industrial Technology Development Institute, Department of Science and Technology, Bicutan, Taguig City, Metro Manila,1631Philippines
Abstract.Membrane technology is widely used in many separation processes because of its multi-disciplinary
characteristics. One of the techniques that is used in the fabrication of membranes is the electrospinning process
which can create nanofibers from a very wide range of polymeric materials. In this study, electrospun nanostructured
fibrous composite membranes of polysulfone (PSU), commercial halloysite (COM-HAL), and Philippine halloysite
(PH-HAL) were synthesized. The concentrations of COM-HAL and PH-HAL were both varied from 0.5%, 1%, and
2%. The FTIR results showed that there were changes in the intensity of the PSU-IR spectra which confirmed the
presence of COM-HAL and PH-HAL in the synthesized membranes. The SEM revealed that nanofibers can be
successfully produced by the addition of LiCl salt in PSU with varying HAL concentrations. Also, it was observed
that the addition of HAL with varying concentrations have no significant effect on wettability due to the strong
hydrophobic character of the PSU membrane. Moreover, it was found from the analysis of mechanical properties that
the tensile strength of the membranes weakened by the addition of HAL due to its weak interaction with PSU.
1 Introduction
Membrane technology is an emerging technology which
can be used in many separation processes. Numerous
membrane processes emerged in which applications are
based on different separation principles and mechanisms.
Various techniques and fabrication methods have been
explored to synthesize membranes, and one of those
techniques is the electrospinning process.
Electrospinning is a versatile process that can create
nanofibers from a very wide range of polymeric materials.
The practicality of electrospinning has been greatly
improved with recent advances in mass production
scalability, leading to higher production rate and lower
cost materials. Moreover, the addition of salt
concentration to polymer solution improves the nanofiber
formation of the membrane [1]. One of the widely-used
polymer materials for electrospinning is polysulfone
(PSU). Since it exhibits excellent thermal, mechanical,
chemical stability, and low cost, PSU is widely used in
separation processes such as water and wastewater
treatment, chemical, metallurgical, and bioseparation area.
Previous research studied the influence of addition of
nanoclay such as halloysite (HAL) on PSU
nanocomposite to serve as excellent support for
nanoparticles due to their unique geometry and properties.
However, most of the work done on the addition of clay
to PSU nanocomposite membranes had been prepared
using dispersion methods.
This study focused on the synthesis and
characterization of a nanostructured PSU/HAL
membranes via electrospinning process. Specifically, this
study aims to: (1) determine the effect of LiCl on the
surface morphology of the nanostructured membrane; and
(2) compare the following mixtures of electrospun
membranes: pure PSU, PSU/LiCl, PSU/LiCl with
commercial halloysite (PSU/LiCL/COM-HAL), and
PSU/LiCl with Philippine halloysite (PSU/LiCl/PH-HAL)
using different characterization techniques; namely, (a)
effect of HAL addition on the chemical composition of
the membrane by Fourier Transform Infrared (FTIR)
analysis, (b) surface morphology through Scanning
Electron Microscopy (SEM), (c) wettability of the surface
with the use of contact angle goniometer, and (c)
mechanical properties using the Universal Testing
Machine.
Considering the low cost and availability of PSU and
HAL, this study would serve as guide on the proper and
efficient way of fabricating PSU incorporated with HAL.
Also, this undertaking may serve as a gateway for further
improvements and use of PSU/LiCl/HAL nanofiber
membrane via electrospinning into various areas of
applications.
2 Methodology
PSF, with an average molecular weight of 35,000, and
COM-HAL were both obtained from Sigma-Aldrich.
Lithium chloride (LiCl) salt and anhydrous
dimethylacetamide 99.8% (DMAc) were obtained from
the Mapúa University Chemical Supplies. PH-HAL was
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© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0
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MATEC Web of Conferences 213, 03001 (2018) https://doi.org/10.1051/matecconf/201821303001
ACMME 2018
obtained from the Department of Science and
Technology of the Philippines. The electrospinning
procedure was partly based on methodology of Chang
and Lin (2009) [1]. PSU mixtures were prepared at
different compositions; specifically, pure PSU, PSU/LiCl,
PSU/LiCl with varying concentrations of COM-HAL
(0.5%, 1% and 2%), and PSU/LiCl with varying
concentrations of PH-HAL (0.5%, 1% and 2%). 40 g of
each polymer solution was prepared and stirred at 60 °C
for 6 h. Initially, the solvent was prepared in a media
bottle and preheated by submerging it in a water bath at
60 °C for 15 mins prior to dissolving the solutes. The
flow rate of the solution and the voltage was set to 1.0
mL h-1 and 25 kV, respectively. The tip-to-collector
distance was set to 15 cm. The equipment used to detect
the chemical components and functional groups of the
membranes was PerkinElmer Spectrum 100 FT-IR
Spectrometer. The electrospun membranes were
subjected to SEC Mini-SEM SNE-3200M micrograph
analysis with 10 kV accelerating voltage for the
comparison of surface morphologies. Moreover, 25 fiber
diameters were measured using ImageJ ver. 1.50i
software to calculate the average fiber diameter. Also,
contact angle goniometer was used to determine the
wettability of the membranes. The mechanical properties
of the membranes were determined using Instron 3225
Single Column UTM.
Figure 1.a.) IR spectrum of thesynthesized PSU/COM-HAL membranesandb.) expected PSU/HAL membrane IRspectrum.
3 Results and discussion
3.1 Effect of HAL on chemical composition of
the membranes
Based on the results of FTIR analysis (Figure 1.a.), the IR
spectra of PSU and PSU/COM-HAL at different
concentrations of COM-HAL were observed. For pure
PSU, band peaks of the different functional groups
present were determined having the following
wavenumbers: 1013 cm-1 and 1103 cm-1 (aromatic C–H
in-plane bend); 1148 cm-1 and 1171 cm-1 (O=S=O
symmetrical stretch); 1239 cm-1 (C–O–C symmetrical
stretch); 1292 cm-1 and 1322 cm-1 (O=S=O symmetrical
stretch); 1488 cm-1 and 1586 cm-1 (C=C–C aromatic ring
stretch); 2966 cm-1 (methyl C-H
asymmetrical/symmetrical stretch).The band peaks in the
IR spectra of PSU were all evident which confirmed the
presence of PSU in the membrane. Moreover, the HAL
IR spectra were also observed in accordance to the FTIR
analysis by Bordeepong et al. (2011) [2]. The similarity
between the obtained IR spectra for PSU/COM-HAL
(Figure 1.a) and the expected IR spectrum for PSU/HAL
(Figure 1.b) confirmed the interaction between PSU and
HAL.
3.2 Effect of LiCl and HAL to the membrane
surface morphology
Figure 2.b illustrates the SEM image of the electrospun
PSU with the addition of LiCl, and as observed smooth
fibers without beads and uniform fibers were produced as
compared with pure PSU (Figure 2.a).
The obtained results confirmed that the addition of
salt improved the conductivity of polymer solution which
helps fiber formation significantly [1], but as observed, it
also resulted to the decrease in the average fiber diameter
from 697.37 ± 193.20 nm for pure PSU to 372.72 ±
130.50 nm for PSU/LiCl (Figure 3).
With regards to the addition of HAL to PSU/LiCl,
curvy fibers with slight spindle-like bead can be observed
with 0.5% COM-HAL (Figure 2.c) with an average fiber
diameter of 521.78 ± 166.14 nm. Further increase in
COM-HAL concentration (1% and 2%) showed no
significant changes in the surface morphologies (Figures
2.d and 2.e), but it can be seen that the average fiber
diameter somehow increases (Figure 3). For the addition
of PH-HAL to PSU/LiCl, 0.5% and 1% concentrations
resulted to the formation of spindle-like bead and bead-
on-string morphologies (Figures 2.f and 2.g) with an
average fiber diameter of 403.38 ± 99.000 nm. It can be
seen in Figure 3, an increasing trend can also be observed
for the average fiber diameter as the concentration of PH-
HAL increases.
The SEM micrographs revealed that the average fiber
diameter decreased significantly with the addition of LiCl
to PSU membrane. Conversely, the incorporation of
COM-HAL and PH-HAL on the membrane increased the
average fiber diameter.
3.3 Effect of HAL to the wettability of the
membrane
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The contact angle of water on pure PSU was
approximately 142 ± 2.94° which is in good agreement
with the strong hydrophobic nature of PSU. Based on the
contact angle measurements of water on the electrospun
membranes, the addition of LiCl and HAL had no
significant effect on the wettability of the membranes
(Figure 4). The statistical analysis that was conducted,
wherein p-value was greater than the significance level,
also showed that hydrophobicity of the composite
membranes was not affected by the incorporation of HAL.
Although HAL is hydrophilic in nature, the increasing
HAL content caused the surface of the nanofiber
membranes to become rougher, which led to the decrease
of the interfacial tension and surface energy [3]. Thus, the
contact angle measurements lie within the range of each
other.
3.4Effect of HAL to the mechanical properties of
the membranes
As shown in Figure 5.a, increasing the concentration of
PH-HAL decreases the tensile strength of the composite
membrane. This is due to the weak interaction between
PSU and HAL. The phenomenon was observed in the
study of Peng et al. (2009) [4] in which they stated that
the addition of nanoclay to the nanocomposites loss of
tensile strength is due to the decreasing uniaxial
orientation. Similar effect can be also observed with the
addition of COM-HAL. Although there is a sudden
increase in the tensile strength at 1% COM-HAL, the
statistical analysis resulted to a p-value greater than the
significance level suggesting that the addition of COM-
HAL and PH-HAL had no significant effect to the tensile
strength of the membranes. Moreover, it can be seen on
the graph (Figure 5.b) that the addition of PH-HAL
increased the maximum strain of the membrane as
compared to the effect of adding COM-HAL. For the
modulus (Figure 5.c), the incorporation of LiCl had no
effect, but the values decreases with the addition of both
COM-HAL and PH-HAL (0.5% and 2%). A sudden
Figure 2. SEM micrographs of the electrospun membranes: a.) pure PSU; b.) PSU/LiCl;
PSU/LiCl/COM-HAL at c.) 0.5%, d.) 1%, and e.) 2% COM-HAL concentrations; and
PSU/LiCl/PH-HAL at f.) 0.5%, g.) 1%, and h.) 2% PH-HAL concentrations.
Figure 3. Effect of LiCl and HAL to the average fiber diameter of the membranes.
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increase that can be observed at 1% concentration was
due to the poor dispersion of the clay to the composite
films resulting to high modulus. Considering the
maximum tensile extension (Figure 5.d), the values
increases with the concentration of COM-HAL, but no
specific trend can be seen with the addition of PH-HAL.
In general, decrease in the mechanical properties can be
observed due to the effect of increasing HAL content
which weakened the membrane; thus, decreasing the
tensile strength [5]. However, upon statistical treatment
of the data gathered, the p-values were found to be large
and greater than the significance level which suggest that
the addition of COM-HAL and PH-HAL at the
concentrations used had no significant effect on the PSU
membrane.
Figure 4. Contact angle measurements for the fabricated membranes
Figure 5. Mechanical properties of the electrospun membranes: a.) Tensile Strength, b.) Tensile Strain, c.) Modulus, and d.) Maximum
Tensile Extension.
4 Conclusion
The researchers were able to synthesize nanofibrous
membranes of PSU which contains COM-HAL and PH-
HAL by electrospinning technique. It was observed form
the SEM micrograph that the addition of LiCl salt
produced bead free nanofibers with reduced average fiber
diameters. The FTIR analysis verified the hydrogen
bonding interaction of PSU and HAL with changing band
peaks intensities from 3600 cm-1 to 3900 cm-1. The
addition of HAL on the membrane had no significant
effect on the wettability of PSU. The composite
membranes produced were evidently remained
hydrophobic even with the incorporation of hydrophilic
HAL. Also, the addition of COM-HAL and PH-HAL to
the membrane decreased its mechanical strength. That is
due to the exfoliation of the clay which optimized the
number of available reinforcing elements; thus,
increasing the matrix rigidity while often decreasing its
fracture toughness [5]. However, the statistical analysis
suggested that there was no significant difference in the
values.
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