effect of solution concentration and co-solvent ratio on electrospun ...

EFFECT OF SOLUTION CONCENTRATION AND CO-SOLVENT
RATIO ON ELECTROSPUN PEG FIBERS
Hazim J. Haroosh, Deeptangshu S. Chaudhary <strong>and</strong> Gordon D. Ingram
Department <strong>of</strong> Chemical Engineering, Curtin University, Perth, WA 6845, Australia
Corresponding author’s E-mail address: d.chaudhary@curtin.edu.au
ABSTRACT
Electrospinning is a unique method for the synthesis <strong>of</strong> nan<strong>of</strong>ibers from polymer <strong>solution</strong>s,
<strong>and</strong> is suitable for a broad range <strong>of</strong> polymeric materials. Because <strong>of</strong> its flexibility,
electrospun nan<strong>of</strong>ibers have been obtained from various polymeric systems <strong>and</strong> for a wide
range <strong>of</strong> applications. Poly (ethylene gly<strong>co</strong>l), PEG, is widely used in the biomedical field,
especially in tissue growth, because <strong>of</strong> its unique properties, including lack <strong>of</strong> toxicity <strong>and</strong>
good bio<strong>co</strong>mpatibility. However, due to its low molecular weight, the electrospinning <strong>of</strong>
PEG has not been studied widely – the very low vis<strong>co</strong>sity <strong>of</strong> the spinning <strong>solution</strong> hinders
electrospinning <strong>and</strong> can instead lead to electrospraying (a process <strong>of</strong> bead formation). This
research work focuses on electrospun high molecular weight PEG nan<strong>of</strong>ibers <strong>and</strong> nanomesh
made from six different <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s <strong>of</strong> PEG dissolved in a 2:1
chlor<strong>of</strong>orm:methanol mixture, along with an investigation into the <strong>effect</strong> <strong>of</strong> <strong>co</strong>-<strong>solvent</strong> <strong>ratio</strong>
on the fiber diameters <strong>and</strong> morphology at different <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s. The results showed that
for PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s <strong>of</strong> 25–35% wt/v, a bimodal distribution in the fibrous structure
<strong>co</strong>uld be obtained. For the same formulation, uniform fiber morphology was obtained with
two distinct diameters, a large 400-500 nm structure <strong>and</strong> a significantly smaller 40-60 nm
structure. The increase in the polymer <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> did not affect the <strong>solution</strong>
<strong>co</strong>nductivity; however, an increase in the amount <strong>of</strong> chlor<strong>of</strong>orm increased the average fiber
diameter due to reduced electrical <strong>co</strong>nductivity <strong>of</strong> <strong>solution</strong> <strong>and</strong> increased <strong>solution</strong> vis<strong>co</strong>sity.
From a <strong>co</strong>mparison <strong>of</strong> the electrical <strong>co</strong>nductivity to the vis<strong>co</strong>sity <strong>of</strong> the <strong>solution</strong>, it is
suggested that the vis<strong>co</strong>sity played a dominant role in <strong>co</strong>ntrolling fiber morphology.
Scanning Electron Micros<strong>co</strong>py, X-ray Diffraction <strong>and</strong> Differential Scanning Calorimetry
studies were used to characterize <strong>and</strong> to underst<strong>and</strong> the structure-property relationship <strong>of</strong>
the polymer.
INTRODUCTION
The highly versatile technique called electrospinning <strong>co</strong>mbines two techniques, namely
electrospraying <strong>and</strong> spinning (Agarwal et al., 2008). Electrospinning has received much
<strong>co</strong>nside<strong>ratio</strong>n in the last decade, not only because <strong>of</strong> its versatility in spinning a broad
variety <strong>of</strong> polymeric fibers, but also due to its ability to produce fibers in the nanometer to
micron range <strong>co</strong>nsistently (Bhardwaj <strong>and</strong> Kundu, 2010; Cui et al., 2010). These fibers have
extremely high specific surface area due to their small diameters, <strong>and</strong> nan<strong>of</strong>iber mats can be
extremely porous with good pore inter<strong>co</strong>nnection. These unique characteristics, in addition
to the functionalities <strong>of</strong> the polymers themselves, support the potential use <strong>of</strong> nan<strong>of</strong>ibers
with many desirable properties in advanced applications (Jian et al., 2008; Zhang et al.,
2007).

H. Haroosh, D. Chaudhary , G. Ingram
In electrospinning, a high electrical field is applied to the droplet <strong>of</strong> a fluid <strong>solution</strong>
flowing from the tip <strong>of</strong> a needle, which acts as one <strong>of</strong> the electrodes. This leads to droplet
deformation <strong>and</strong> to the production <strong>of</strong> a charged <strong>co</strong>ne <strong>of</strong> droplets that accelerate towards a
<strong>co</strong>unter-electrode <strong>co</strong>llector. The process leads to the formation <strong>of</strong> unbroken fibers on the
<strong>co</strong>llector (Agarwal et al., 2008; Frenot <strong>and</strong> Chronakis, 2003).
Biodegradable, hydrophobic polymers normally have good mechanical strength but
lack affinity for biological cells, while hydrophilic polymers generally have high cell
affinity (Jiang et al., 2004). In addition, natural biopolymers generally <strong>of</strong>fer better
bio<strong>co</strong>mpatibility <strong>and</strong> biodegradability than synthetic polymers, <strong>and</strong> are more suitable for
biomedical applications. Furthermore, materials from natural sources are advantageous
because <strong>of</strong> their inherent properties <strong>of</strong> biological re<strong>co</strong>gnition, including presentation <strong>of</strong>
receptor-binding lig<strong>and</strong>s <strong>and</strong> susceptibility to cell-triggered proteolytic degradation <strong>and</strong>
remolding (Li et al., 2006; Yao et al., 2007). However, electrospinning <strong>of</strong> these natural
biopolymers is <strong>of</strong>ten difficult <strong>co</strong>mpared to synthetic polymers because their processability
is practically poor <strong>and</strong> the fibers demonstrate low mechanical strength, especially in their
swollen state (Jiang et al., 2004). PEG is a hydrophilic <strong>and</strong> water-soluble polymer (Wang et
al., 2006). PEG otherwise known as poly(oxyethylene) or poly(ethylene oxide) (PEO), is a
synthetic polyether that is readily available in a range <strong>of</strong> molecular weights. Materials with
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H. Haroosh, D. Chaudhary , G. Ingram
range <strong>of</strong> 25–28 kV. The electrospinning process was carried out at 24ºC. The resulting
fibers were deposited on a flat aluminum foil <strong>co</strong>llector. The distance between the needle tip
<strong>and</strong> the target was 13 cm. The thickness <strong>of</strong> the fiber mat ranged from 350 to 490 µm.
Characterization techniques
The vis<strong>co</strong>sity <strong>of</strong> <strong>solution</strong> was measured by using a Vis<strong>co</strong> 88 vis<strong>co</strong>meter from Malvern
Instruments (UK). It has a built-in temperature sensor <strong>and</strong> uses double gap geometry to
provide extra sensitivity for measuring low-vis<strong>co</strong>sity fluids. The electrical <strong>co</strong>nductivity <strong>of</strong>
the <strong>solution</strong> was measured by using a WP-81 Waterpro<strong>of</strong> Conductivity meter (TPS,
Australia). The morphology <strong>of</strong> electrospun nan<strong>of</strong>ibers was observed with an Evo 40XVP
scanning electron micros<strong>co</strong>pe (Zeiss, Germany) <strong>and</strong> the accelerating voltage was set at
5 kV. Before SEM observation, the samples were sputter-<strong>co</strong>ated with platinum. Fiber
diameter was calculated from the SEM images by using an in-house developed scanning
program, which analyses a minimum <strong>of</strong> 150 fibers from multiple scanned SEM images.
The X-ray diffraction measurements <strong>of</strong> the prepared samples were performed in a
Bruker Dis<strong>co</strong>ver 8 diffractometer (Germany) operating at 40 kV <strong>and</strong> 40 mA using Cu-Kα
radiation that was monochromatised with a graphite sample monochromator with a 2θ
range from 5° to 35° at a scanning rate <strong>of</strong> 0.05°/s. Thermal analysis was performed using a
DSC6000 Perkin Elmer (USA) differential scanning calorimeter with Cry<strong>of</strong>ill liquid
nitrogen <strong>co</strong>oling system. Approximately 10 mg <strong>of</strong> fiber was sealed in aluminum pans <strong>and</strong>
the thermal behavior was analyzed during heating <strong>and</strong> <strong>co</strong>oling between 10°C <strong>and</strong> 190°C
with a ramp rate <strong>of</strong> 10°C/min.
RESULTS AND DISCUSSION
Effect <strong>of</strong> PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>
During the process <strong>of</strong> electrospinning, a number <strong>of</strong> parameters can greatly influence the
properties <strong>of</strong> the generated fibers. Among various parameters, the polymer <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> is
the most significant factor in the process (Xie <strong>and</strong> Buschle Diller, 2010; Yao et al., 2007).
Figure 1a <strong>and</strong> b show that using PEG at <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s <strong>of</strong> 15 <strong>and</strong> 20%, respectively, with a
2:1 chlor<strong>of</strong>orm:methanol <strong>solvent</strong> led to the formation bead structures. This <strong>co</strong>uld be
because <strong>of</strong> the low vis<strong>co</strong>sity at those PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s as shown in Fig. 2a. There is a
lower limit to the polymer <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> or vis<strong>co</strong>sity that must be exceeded for successful
electrospinning, as extensive molecular entanglements are prerequisites for the formation <strong>of</strong>
a stable <strong>and</strong> <strong>co</strong>ntinuous charged jet (Chen et al., 2010; Chuangchote et al., 2009). At low
polymer <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s, the degree <strong>of</strong> chain entanglement is not high enough to withst<strong>and</strong>
the Coulombic stretching force acting on the charged jet, causing the jet to break up into
smaller jets that, as a result <strong>of</strong> surface tension, then break up further <strong>and</strong> form beads
(Arayanarakul et al., 2006).
Figures 1c, d <strong>and</strong> e demonstrate that increasing the PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> to 25, 30 <strong>and</strong>
35%, respectively, leads to the formation <strong>of</strong> fibrous structures. Interestingly, the structures
<strong>co</strong>ntain mixtures <strong>of</strong> fibers <strong>of</strong> two more-or-less uniform diameters, a large average diameter
<strong>and</strong> a small average diameter, with the same morphology. Figures 1c, d <strong>and</strong> e show
homogenous fibers with large average diameters <strong>of</strong> 540, 490 <strong>and</strong> 405 nm, respectively. This
trend is in <strong>co</strong>ntrast to results reported elsewhere that show that high polymer <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s
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H. Haroosh, D. Chaudhary , G. Ingram
lead to larger fiber diameters (Chen et al., 2009; Hsu et al., 2010; Li et al., 2006; Qian et al.,
2010; Spasova et al., 2007; Um et al., 2004), while for the smaller diameter fibers group,
higher PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s produced thicker fibers: PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s <strong>of</strong> 25, 30 <strong>and</strong> 35%
produced small fibers <strong>of</strong> average diameter 39, 48 <strong>and</strong> 57 nm <strong>and</strong> minimum diameters <strong>of</strong> 25,
29 <strong>and</strong> 34 nm, respectively. In addition, Fig. 3a <strong>and</strong> b show the network structure <strong>of</strong> the
small fibers, while Fig. 3c <strong>and</strong> d illustrate the interaction between the small <strong>and</strong> large fibers,
where it is noted that the small fibers lie on the surface <strong>of</strong> the large fibers <strong>and</strong> help to link
them together.
Fig. 1: SEM micrographs <strong>of</strong> electrospun PEG fibers using a 2:1 chlor<strong>of</strong>orm:methanol
<strong>solvent</strong> <strong>and</strong> various PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s: (a) 15%, (b) 20%, (c) 25%, (d) 30%, (e) 35% <strong>and</strong>
(f) 40%. The scale in the micrographs is 10 µm.
Fig. 2: Effect <strong>of</strong> PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> on (a) vis<strong>co</strong>sity <strong>and</strong> (b) electrical <strong>co</strong>nductivity <strong>of</strong> the
<strong>solution</strong> for a 2:1 chlor<strong>of</strong>orm:methanol <strong>solvent</strong>.
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H. Haroosh, D. Chaudhary , G. Ingram
Fig. 3: SEM micrographs <strong>of</strong> the small diameter structure for electrospun PEG. The scale in
(a) <strong>and</strong> (b) is 100 nm, while in (c) <strong>and</strong> (d) it is 1000 nm <strong>and</strong> 2000 nm, respectively. The key
information given by (c) <strong>and</strong> (d) is the morphology <strong>and</strong> the way fibers are linked.
Interestingly, when the PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> reaches 40%, the smaller fibers in the
structure disappear <strong>co</strong>mpletely <strong>and</strong> the formulation produces a mono-disperse nan<strong>of</strong>iber
matrix with beads, as seen in Fig. 1f. It can be seen that within the matrix, the large fibers
have inhomogeneous diameters <strong>and</strong> the average fiber diameter was found to be 730 nm,
which is significantly higher than the diameters produced at lower PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s.
Further, as shown in Figure 2b, above 25% polymer <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> there is no significant
increase in the electrical <strong>co</strong>nductivity <strong>of</strong> the <strong>solution</strong>, indicating that the dominant factor
influencing the fiber structure was the <strong>solution</strong> vis<strong>co</strong>sity. This is typical behavior since it is
known that higher vis<strong>co</strong>sities generally leads to failure in forming a polymer jet, as the
electric force is not able to ‘carry’ the thick <strong>solution</strong> (Um et al., 2004).
Effect <strong>of</strong> <strong>co</strong>-<strong>solvent</strong> <strong>ratio</strong>
Selecting an appropriate <strong>solvent</strong> system is crucial for successful electrospinning (Han et al.,
2010; Hsu et al., 2010). From Fig. 4, it can be seen that the <strong>ratio</strong> <strong>of</strong> the <strong>co</strong>-<strong>solvent</strong>s had a
large <strong>effect</strong> on the diameters <strong>and</strong> homogeneity <strong>of</strong> the fibers formed. Similar to our previous
results with different PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s, fibrous structures were produced with two moreor-less
uniform fiber diameters in the same morphology. Increasing the amount <strong>of</strong> methanol
in the <strong>solution</strong> reduced the average fiber diameter for the larger fibers. Since increasing the
fraction <strong>of</strong> methanol in the <strong>solvent</strong> reduces the vis<strong>co</strong>sity (see Fig. 5a), such behavior is
typical <strong>of</strong> electrospun nan<strong>of</strong>ibers <strong>and</strong> this behavior is in <strong>co</strong>ntrast to the behavior seen with
change in <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> <strong>of</strong> PEG (see Fig. 3c, d <strong>and</strong> e). However, the average fiber diameter
for the smaller fibers reduced with reducing vis<strong>co</strong>sity <strong>and</strong> increasing <strong>co</strong>nductivity, which is
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H. Haroosh, D. Chaudhary , G. Ingram
similar to our finding with <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> change. For example, in Fig. 4a, the chlor<strong>of</strong>orm to
methanol <strong>ratio</strong> was 1:0 (that is, pure chlor<strong>of</strong>orm) <strong>and</strong> a uniform fiber structure with a large
average diameter <strong>of</strong> 870 nm was produced. By increasing the amount <strong>of</strong> methanol to give a
chlor<strong>of</strong>orm:methanol <strong>ratio</strong> <strong>of</strong> 3:1, the average large fiber diameter decreased to 703 nm. As
reported in the previous section, a 2:1 <strong>solvent</strong> <strong>ratio</strong> produced an average large fiber
diameter <strong>of</strong> 405 nm (Fig. 1e). Further increasing the amount <strong>of</strong> methanol to a 1:1 <strong>ratio</strong>
resulted in broken fibers, <strong>and</strong> the average diameter also decreased to 395 nm. When the
<strong>ratio</strong> <strong>of</strong> chlor<strong>of</strong>orm to methanol was reduced even further to 1:2, fibers were produced that
<strong>co</strong>ntained some beads, <strong>and</strong> the average diameter was reduced to 301 nm.
Fig. 4: SEM micrographs <strong>of</strong> electrospun PEG fibers for 35% PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> <strong>and</strong>
various <strong>ratio</strong>s <strong>of</strong> chlor<strong>of</strong>orm:methanol: (a) 1:0, (b) 3:1, (c) 1:1 <strong>and</strong> (d) 1:2. The scale in the
micrographs is 10 µm. Results for a 2:1 <strong>ratio</strong> appear in Fig. 1e.
The observed behavior <strong>of</strong> fiber diameter with PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> <strong>and</strong> <strong>co</strong>-<strong>solvent</strong>
<strong>ratio</strong> may be partly explained by two properties <strong>of</strong> the spinning <strong>solution</strong>, namely the
vis<strong>co</strong>sity <strong>and</strong> the electrical <strong>co</strong>nductivity. Figure 5 shows that both vis<strong>co</strong>sity <strong>and</strong> electrical
<strong>co</strong>nductivity were influenced by the chlor<strong>of</strong>orm:methanol <strong>ratio</strong>, while there was only a
significant change in vis<strong>co</strong>sity when the PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> was changed at <strong>co</strong>nstant <strong>co</strong><strong>solvent</strong>
<strong>ratio</strong>, as shown in Fig 2. Furthermore, the volatilities <strong>of</strong> <strong>solvent</strong>s significantly affect
the solidification process, <strong>and</strong> influence the morphologies <strong>of</strong> the electrospun nan<strong>of</strong>ibres
(Abdul Rahman et al., 2010; Qian et al., 2010). The volatility <strong>of</strong> chlor<strong>of</strong>orm less than that
<strong>of</strong> methanol <strong>and</strong> this is probably the cause <strong>of</strong> uniformity <strong>of</strong> structure formed when the
amount <strong>of</strong> chlor<strong>of</strong>orm is higher than methanol. It is thought that the decreasing the
vis<strong>co</strong>sity <strong>of</strong> the spinning <strong>solution</strong> results in a decrease in the diameters <strong>of</strong> the fibers <strong>and</strong> a
higher vis<strong>co</strong>sity tends to fabricate fibers with larger diameter (Arayanarakul et al., 2006;
Yao et al., 2007; Zamani et al., 2010). In terms <strong>of</strong> the <strong>effect</strong> <strong>of</strong> electrical <strong>co</strong>nductivity, as
shown in Fig. 5b, an increase in the amount <strong>of</strong> methanol led to increase in the <strong>co</strong>nductivity,
because methanol has a higher dielectric <strong>co</strong>nstant than chlor<strong>of</strong>orm: 33 for methanol
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H. Haroosh, D. Chaudhary , G. Ingram
<strong>co</strong>mpared to 4.8 for chlor<strong>of</strong>orm (Bhardwaj <strong>and</strong> Kundu, 2010). When the electrical
<strong>co</strong>nductivity <strong>of</strong> a <strong>solution</strong> increases, more electric charges are carried by the
electrospinning jet. Thus, higher elongation forces are imposed to the jet under the
electrical field (Zamani et al., 2010). On the other h<strong>and</strong>, by increasing the <strong>solution</strong>
<strong>co</strong>nductivity, bending instability can be increased during electrospinning. So, the jet path
be<strong>co</strong>mes longer <strong>and</strong> more stretching <strong>of</strong> the <strong>solution</strong> is induced. Both higher elongation
forces <strong>and</strong> greater bending instability resulted in fibers with lower diameter (Lee et al.,
2010; Saraf et al., 2009).
Fig. 5: Effect <strong>of</strong> chlor<strong>of</strong>orm to methanol <strong>solvent</strong> <strong>ratio</strong> on (a) vis<strong>co</strong>sity <strong>and</strong> (b) electrical
<strong>co</strong>nductivity <strong>of</strong> the <strong>solution</strong> for a 35% PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>.
Crystallinity <strong>and</strong> thermal properties
XRD was carried out to investigate the <strong>effect</strong> <strong>of</strong> the PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> <strong>and</strong> <strong>co</strong>-<strong>solvent</strong> <strong>ratio</strong>
on the structure <strong>of</strong> the electrospun nan<strong>of</strong>ibers. Figure 6 shows the XRD patterns for the
fibers produced from <strong>solution</strong>s with PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s <strong>of</strong> 25% <strong>and</strong> 35% dissolved with
different <strong>co</strong>-<strong>solvent</strong> <strong>ratio</strong>s. There is no significant change in the XRD pattern for either
formulations, but it can be seen that the diffraction peaks <strong>of</strong> PEG, at angles <strong>of</strong> 2θ = 13.2°
<strong>and</strong> 18.65°, there appeared small shoulders when the nan<strong>of</strong>ibers <strong>co</strong>ntained the higher
<strong>solution</strong> <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>, while the shoulders disappeared at the low <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> <strong>of</strong> PEG.
Moreover, for 35% PEG <strong>solution</strong>, two small peaks at 2θ = 13.6° <strong>and</strong> 2θ = 27.95° were not
seen in samples with 25% PEG. We found that the crystallinity (%C) for a PEG
<strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> <strong>of</strong> 35% was higher than for 25% PEG, <strong>and</strong> there is no significant change in
either the melting enthalpy (∆Hm) or the melting temperature (Tm) <strong>of</strong> the nan<strong>of</strong>ibers (Table
1). This indicates that the changes in polymer <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> or the <strong>co</strong>-<strong>solvent</strong> <strong>ratio</strong> do not
change the molecular behavior, but the primary change occurs in the bulk re-arrangements,
as seen in the morphology <strong>and</strong> structural changes.
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H. Haroosh, D. Chaudhary , G. Ingram
Tab.1: DSC results for nan<strong>of</strong>ibers with different PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s <strong>and</strong> different <strong>co</strong><strong>solvent</strong>
<strong>ratio</strong>s. Experiments were repeated for three sets <strong>of</strong> samples; st<strong>and</strong>ard deviation for
Tg <strong>and</strong> Tm values are < 1%.
Sample %C
PEG 35%, chlor<strong>of</strong>orm: methanol <strong>ratio</strong> 1:0 89.15 67.92 204.83
PEG 25%, chlor<strong>of</strong>orm: methanol <strong>ratio</strong> 2:1 81.05 65.02 214.76
PEG 35%, chlor<strong>of</strong>orm: methanol <strong>ratio</strong> 3:1 87.71 65.55 207.46
PEG 35%, chlor<strong>of</strong>orm: methanol <strong>ratio</strong> 2:1 88.24 65.50 210.85
Fig. 6: X-ray diffraction patterns for selected samples showing the relative position <strong>of</strong> the
intercalation peak due to different <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s <strong>of</strong> PEG <strong>and</strong> <strong>co</strong>-<strong>solvent</strong> <strong>ratio</strong>s.
CONCLUSIONS
Tm ( o C) ∆Hm (J/g)
This investigation focused on the morphological evolution <strong>of</strong> electrospun nan<strong>of</strong>ibers
produced at six different <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s <strong>of</strong> PEG that were dissolved in a 2:1
chlor<strong>of</strong>orm:methanol <strong>solvent</strong>, <strong>and</strong> it also studied the <strong>effect</strong> <strong>of</strong> five different <strong>co</strong>-<strong>solvent</strong>
<strong>ratio</strong>s on the fiber diameters <strong>and</strong> morphology at <strong>co</strong>nstant PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>. Some
interesting behavior for the fibrous structures was observed: a structure having a bimodal
distribution <strong>of</strong> fiber diameters with the same morphology was produced for PEG
<strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s <strong>of</strong> 25, 30 <strong>and</strong> 35%. In terms <strong>of</strong> spinning <strong>solution</strong> properties, there was no
significant <strong>effect</strong> <strong>of</strong> increasing the PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> on the <strong>solution</strong>’s electrical
<strong>co</strong>nductivity, especially for PEG <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s above 25%; however, the <strong>solution</strong>’s
vis<strong>co</strong>sity did change <strong>co</strong>nsiderably, <strong>and</strong> this was the main factor influencing the fibrous
structure. When changing the <strong>co</strong>-<strong>solvent</strong> <strong>ratio</strong>, both vis<strong>co</strong>sity <strong>and</strong> <strong>co</strong>nductivity varied
<strong>co</strong>nsiderably, <strong>and</strong> both <strong>co</strong>uld have affected fiber diameter. Also, more uniform structures
8

H. Haroosh, D. Chaudhary , G. Ingram
formed when the <strong>ratio</strong> <strong>of</strong> chlor<strong>of</strong>orm was higher than methanol. The crystallinity <strong>of</strong> fibers
produced from a high <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong> PEG <strong>solution</strong> was greater than for low <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>.
Using different <strong>co</strong>-<strong>solvent</strong> <strong>ratio</strong>s or different polymer <strong><strong>co</strong>ncent<strong>ratio</strong>n</strong>s did not significantly
change either the melting enthalpy or the melting temperature <strong>of</strong> the nan<strong>of</strong>ibers; the
dominant change was visible in the bulk rearrangement, as seen in the fiber morphology.
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BRIEF BIOGRAPHY OF PRESENTER
Hazim Haroosh is currently a PhD student in the Chemical Engineering Department at
Curtin University. He received his B.Sc. <strong>and</strong> M.Sc. degrees in Chemical Engineering from
Tikrit University, Iraq. He worked in The State Company for Drug Industries <strong>and</strong> Medical
Appliances, Samara (SDI), Iraq, as the Assistant Chief Engineer. He has h<strong>and</strong>s-on
experience in quality <strong>co</strong>ntrol <strong>and</strong> management, project planning <strong>and</strong> environmental impact
assessment, <strong>and</strong> he was the director <strong>of</strong> the Wastewater Treatment Department. He is a
member <strong>of</strong> the Iraqi Engineers Association.
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