1. The International Istanbul Textile Congress 2013
May 30th to June 1th 2013, Istanbul, Turkey
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EFFECTS OF DIFFERENT STERILIZATION METHODS ON
ELECTROSPUN POLYESTER NANOFIBERS
S. DUZYER1
, A. HOCKENBERGER1*
, E. EVKE2
, Z. KAHVECI2
, A. UGUZ3
1
Faculty of Engineering & Architecture, Textile Engineering Department, Uludag University, Bursa
16059, Turkey
2
Faculty of Medicine, Histology & Embryology Department, Uludag University, Bursa 16059,
Turkey
3
Faculty of Engineering & Architecture, Mechanical Engineering Department, Uludag University,
Bursa 16059, Turkey
sengonul@uludag.edu.tr
Abstract: The aim of this study to investigate the effects of different sterilization methods on electrospun
polyester nanofibers and polyester fabrics. The study consists of two parts. In the first part, polyethylene
terephthalate (PET) nanofibers with different concentrations of 10, 15 and 20 wt.% were produced by
electrospinning. PET nanofiber mats were sterilized by Ethylene oxide, autoclave and UV sterilization
methods. The surface characteristics of the nanofibers were examined by scanning electron microscope
(SEM) and contact angle measurements. Mechanical characteristics of the nanofiber mats were evaluated
by Instron studies. In the second part, effects of different sterilization methods on polyester fabrics were
investigated. Therefore, most used sterilization methods (ethylene oxide, autoclave and UV sterilization)
were applied to the polyester fabric. The results showed that different sterilization methods made significant
changes on the surfaces of the nanofibers depending on the PET concentration. It was seen that the fiber
structure was damaged especially with the ethylene oxide sterilization. As for the fabrics, different
sterilization methods didn’t make any significant changes on the surfaces of the PET fabrics. Mechanical
performance tests on nanofiber mats showed that Young’s modulus and elongation at break decreased
significantly with autoclave sterilization. Mechanical tests on PET fabrics showed that Young’s modulus
decreased and the elongation at break increased with different sterilization methods. It was concluded that
UV sterilization affected the nanofiber mats less and gave less damage to the nanofiber mats.
Keywords: sterilization, electrospinning, nanofiber, polyethylene terephthalate
1. Introduction
In order to use textile materials in medical applications, all materials implanted within the body or placed in
contact with corporeal fluids must be sterilized otherwise microorganisms may cause deleterious effects [1].
There are many sterilization methods reported in the literature including ethylene oxide sterilization,
autoclave (steam) sterilization, dry heat, ultraviolet (UV) and gamma radiation, immersion in alcohol aqueous
solutions at different concentrations. The sterilization method must be selected carefully since it can affect
the chemical and physical properties of the samples [1,2].
Polyethylene terephthalate (PET) is a linear polymer and is widely used in textiles. It has a unique
combination of physical and chemical properties. PET polymer is used in medical applications such as
sutures, surgical mesh, vascular grafts and surgical gowns. This polymer is used for critical procedures
where high strength and predictable long-term performance is emphasized. It is preferable because of its
characteristics including biostability, non-allergenic and non-toxic properties [3].
The characteristics of electrospinning technique such as high porosity, small pore sizes with an
interconnected structure and a large surface area per unit volume, make them attractive in a variety of
applications, including medical applications [4].
The aim of this study to investigate the effects of different sterilization methods on electrospun polyester
nanofibers and polyester fabrics. Since, PET surfaces can be used in the medical field as nanofiber mats or
woven fabrics depending on the application area, the effect of different sterilization methods were
investigated in both forms. From this point of view, this study consists of two parts. In the first part, effects of
different sterilization methods on PET nanofibers were investigated. In the second part, effects of different
sterilization methods on polyester fabrics were investigated. Therefore, most used sterilization methods
(ethylene oxide, autoclave and UV sterilization) were applied to the textile surfaces.

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2. Materials and Methods
2.1 Materials
In this study commercially available plain weave 100% polyester (PET) fabric and PET pellets were used in
order to produce electrospun nanofibers. PET solutions with different concentrations were prepared by the
dissolution of PET pellets in trifluoroacetic acid (TFA) (50 wt. %) and dichloromethane (DCM) (50 wt. %)
solvents. All chemicals were commercially available from Sigma-Aldrich and used as received without any
further purification.
2.2 Methods
PET nanofibers were produced by an electrospinning device (Inovenso NanoSpinner24) in the Laboratories
of Uludag University, Textile Engineering Department (Bursa, Turkey)
The jet flows upward from the surface of a pendant drop of fluid toward a rotating drum. Table 1 shows the
spinning parameters of the produced nanofibers. All experiments were carried out in air at room conditions.
Table 1. Electrospinning parameters of nanofibers
Concentration (wt.%) Voltage(kV) Distance (mm) Flow Rate (ml/h) Collector Speed (rpm)
10 10 10 1 250
15 10 10 1 250
20 10 10 1 250
The surface morphologies of the fabrics and the nanofibers sterilized by different methods were evaluated by
scanning electron microscopy (SEM) using Carl Zeiss Evo 40 (Uludag University, Bursa,TURKEY) and JEOL
840JXA model scanning electron microscopes (TUBITAK MAM, Gebze-TURKEY).
The contact angle of the fabrics and electrospun nanofiber mats were measured using KSV-The Modular
CAM 200 contact angle measurement system (Uludag University, Bursa-TURKEY). A distilled water drop
was dispersed on each sample using a micropipette; the image of each drop was captured by the camera
connected with a computer based image capture system. The images were captured as quickly as possible
after water droplet was placed onto the sample surface, and photographed in less than 1 s.
Mechanical characteristics of the PET fabrics and nanofiber mats were evaluated by Instron Universal
Testing Machine (Model No. 4301) in the Laboratories of Uludag University, Textile Engineering Department
(Bursa, Turkey). For nanofiber mats, the tests were carried out in the winding direction and for the PET
fabric, in the warp direction.
For PET fabrics color change measurements and drape measurements were performed. Color changes after
sterilization procedures were instrumentally determined using a Macbeth Spectrophotometer (MS 2020+)
coupled to a PC under D65/100 illuminant and the measurements were taken according to AATCC Test
Method 173. The control sample was taken as the standards and the sterilized fabrics were taken as the
trials when calculating the color differences (∆E) values.
Drape measuments of the PET fabrics were performed by SDLATLAS M213 Fabric Drape Tester (Uludag
University, Bursa-TURKEY). The test was performed on fabric samples of 30 centimeters in diameter
supported on a disk 18 centimeters in diameter.
Sterilization Methods
Before cell culture studies, fabrics and nanofibers should be sterilized. Although there are many researches
about sterilization of fabrics, there isn’t enough information about sterilization of nanofiber mats. Therefore,
most used sterilization methods (ethylene oxide sterilization, autoclave sterilization and UV sterilization) were
applied to the nanofiber mats produced from different concentrations of PET. All sterilization applications
were carried out according to the standard method procedures used in the sterilization unit of the Medical
Faculty of Uludag University.
1. Ethylene oxide sterilization: PET fabrics and nanofiber mats with different concentrations were sterilized in
the sterilization unit of Medical Faculty in Uludag University. In this procedure, PET fabric and nanofiber
mats were treated by ethylene oxide for 4 hours at 55°C. After treatment, samples were left at room
conditions for 4 hours.

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2. Autoclave sterilization: PET fabrics and nanofiber mats with different concentrations were sterilized in
Class B type autoclave (Dentsan) in Prof. Dr. Sermin Paker Cell and Embryo Culture Laboratory in Histology
and Embryology Department of Medical Faculty in Uludag University. The samples were placed in an
autoclave, then the air at 121 °C was evacuated to a vacuum about 1.1 bar for 4 minutes. The vacuum cycle
was repeated for 4 minutes for 3 times. The procedure was continued with sterilization for 15 minutes and
drying for 10 minutes then. The cycle was completed with the last vacuum for 4 minutes.
3. UV sterilization; PET fabrics and nanofiber mats with different concentrations were sterilized in laminar
flow sterile cabinet (Thermo, Hera guard, model HPH) in Prof. Dr. Sermin Paker Cell and Embryo Culture
Laboratory in Histology and Embryology Department of Medical Faculty in Uludag University. Samples were
washed first with ethylene alcohol and 3 times with Phosphate buffered salin (PBS) solution. Afterwars,
samples were sterilized in the cabinet under UV light for 1 hour. The procedure was repeated for both sides
of the samples.
3. Results
3.1 Experimental results of pet nanofiber mats
The morphology of the nanofiber mats were investigated by SEM studies. Figures 1-3 show the SEM
micrographs of the nanofiber mats sterilized by ethylene oxide, autoclave and UV sterilization method,
respectively. It can be seen that, different sterilization methods didn’t make any significant changes on the
surfaces of the PET fabrics.
Nanofibers produced from PET, formed nonwoven surfaces with different diameters and were placed
randomly in the nanofiber mat depending on the polymer concentration. It was also observed that, with the
increasing polymer concentration, nanofibers with larger diameters and fewer beads were produced because
of the increasing viscosity of the polymer solutions. Table 2 shows the diameter distribution of the
nanofibers. The SEM images also showed that PET nanofibers were not exactly aligned in the mat and PET
nanofibers electrospun from 10% wt. solution had a non-uniform cross-section along the fiber length. With
the increasing polymer concentration, it was observed that the fiber cross-section became more uniform.
Although thicker fibers were produced from 20% wt. solution, fiber diameters were mostly uniform along the
fiber length.
Different sterilization methods made significant changes on the surfaces of the nanofibers. Among all
sterilization methods, it was seen that UV sterilization method gave less damage to the surfaces for all
concentrations. It was seen that among all sterilization methods, ethylene oxide sterilization affected the
surfaces most. For the nanofibers produced from 10% wt. solution, agglomeration of the fiber bundles was
observed with ethylene oxide sterilization. For the nanofibers produced from 15% wt. solution, the effect of
ethylene oxide sterilization was quite decreased, fiber uniformity was disturbed along the length. For the
nanofibers produced from 20% wt. solution, effect of ethylene oxide sterilization was less intense compared
to the nanofibers produced from %10 wt. solution. For autoclave sterilization, it was observed that diameter
along the fiber length was not uniform in lower concentrations (10% wt. and 15%wt.). With all sterilization
procedures an increase in diameter (Table 2) was observed for all concentrations. As a result, stiffer handle
was observed.
It has also been observed that with decreasing fiber diameter, the effect of sterilization method on the fiber
surface was more pronounced.
Figure 1. SEM micrographs nanofibers produced from 10% wt. PET solution, a) non-sterilized, b) ethylene
oxide sterilized, c) autoclave sterilized, d) UV sterilized, respectively.

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Figure 2. SEM micrographs of nanofibers from 15% wt. PET solution a) non-sterilized, b) ethylene oxide
sterilized, c) autoclave sterilized, d) UV sterilized, respectively.
Figure 3. SEM micrographs of nanofibers produced from 20% wt. PET solution, a) non-sterilized, b) ethylene
oxide sterilized, c) autoclave sterilized, d) UV sterilized, respectively.
Table 2. Diameters of the nanofiber mats produced from different PET concentrations and sterilized by
different methods
Material (PET) Diameter (µm) %CV
10% wt.(non-sterilized) 0,66 46,97
10% wt.(sterilized by ethylene oxide) 0,91 20,88
10% wt. (sterilized by autoclave) 0,94 34,47
10% wt. (sterilized by UV) 0,66 45,76
15% wt. (non-sterilized) 0,87 27,59
15% wt. (sterilized by ethylene oxide) 1,88 42,55
15% wt. (sterilized by autoclave) 1,46 21,37
15% wt. (sterilized by UV) 1,34 25,37
20% wt. (non-sterilized) 2,36 27,80
20% wt. (sterilized by ethylene oxide) 2,92 77,81
20% wt. (sterilized by autoclave) 2,33 37,39
20% wt. (sterilized by UV) 2,48 16,61
Contact angle of the surfaces one of the most important properties in order to understand the surface
characteristics of the fibers like adhesion, wettability, absorption.
Table 3 shows the contact angles of the nanofiber mats produced from different concentrations and sterilized
by different methods.
Table 3. Contact angles of the nanofiber mats produced from different concentrations and sterilized by
different methods.
Material (PET) Contact Angle (°)
10% wt.(non-sterilized) 132,71
10% wt.(sterilized by ethylene oxide) 122,90
10% wt. (sterilized by autoclave) 127,41
10% wt. (sterilized by UV) 97,05
15% wt. (non-sterilized) 140,02
15% wt. (sterilized by ethylene oxide) 122,67
15% wt. (sterilized by autoclave) 124,12
15% wt. (sterilized by UV) 115,21
20% wt. (non-sterilized) 141,71
20% wt. (sterilized by ethylene oxide) 109,02
20% wt. (sterilized by autoclave) 136,12
20% wt. (sterilized by UV) 112,53

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For nanofiber mats, the measurement results show that contact angle values change depending on the
polymer concentration. The results show that with the decreasing fiber diameter, the nanofiber mats get
super hydrophobic structure. Different sterilization methods also affect the surface properties of the
nanofibers. The contact angle values decreased with the different sterilization methods. It was seen that
there was a decrease in contact angles with UV sterilization. This decrease did not follow a regular regime
with the increasing polymer concentration and it was not a significant change.
In order to understand the mechanical performances of the PET nanofiber mats, mechanical tests were
performed. Table 4 shows the Young modulus and elongation values of the nanofiber mats sterilized by
different sterilization methods. Figure 4 shows the stress- strain curves of the nanofiber mats. It was seen
that nanofibers produced from 20% wt. PET solutions show the higher modulus and lower elongation. It was
recorded that Young modulus and the elongation values of the nanofiber mats were changed with different
sterilization methods. This change was more significant especially with autoclave sterilization. It was also
seen that the modulus and the strain at break decreased most with the autoclave sterilization. Since the
surfaces became stiffer with the sterilization, the modulus values were decreased.
Table 4. Young modulus and elongation values of the nanofiber mats sterilized by different sterilization
methods
Material Young Modulus (MPa) Elongation (%)
10% wt.(non-sterilized) 137,4 104,68
10% wt. (sterilized by ethylene oxide) 218,1 99,12
10% wt. (sterilized by autoclave) 125,7 36,83
10% wt. (sterilized by UV) 132,8 121,72
15% wt. (non-sterilized) 154,7 99,35
15% wt. (sterilized by ethylene oxide) 148,7 62,86
15% wt. (sterilized by autoclave) 79,68 32,08
15% wt. (sterilized by UV) 124,8 84,87
20% wt. (non-sterilized) 224,1 55,95
20% wt. (sterilized by ethylene oxide) 222,5 53,37
20% wt. (sterilized by autoclave) 85,3 23,12
20% wt. (sterilized by UV) 219,6 78,52
3.2. Experimental results of pet fabrics
The morphology of the PET fabrics sterilized by different methods were investigated by SEM studies. Figure
4 shows the image of the non-sterilized fabric. Figures 5-7 show the SEM micrographs of the fabrics
sterilized by ethylene oxide, autoclave and UV sterilization method, respectively. It can be seen that, different
sterilization methods didn’t make any significant changes on the surfaces of the PET fabrics.
Figure 4. SEM micrographs of single fiber of PET fabric sterilized by different methods, a) non-sterilized,
b) ethylene oxide sterilized, c) autoclave sterilized, d) UV sterilized, respectively.

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Figure 5. SEM micrographs PET fabric sterilized by different methods, a) non-sterilized, b) ethylene oxide
sterilized, c) autoclave sterilized, d) UV sterilized, respectively.
Table 5 shows the contact angle values of Pet fabrisc sterlized by different methods. For the sterilized
fabrics, it was seen that UV sterilization increased the contact angle most.
Table 5. Contact angles of the PET fabric sterilized by different methods.
Material Contact Angle (°)
PET fabric (non-sterilized) 54,71
PET fabric (sterilized by ethylene oxide) 69,23
PET fabric (sterilized by autoclave 77,28
PET fabric (sterilized by UV) 115,19
Instron tests were also performed on PET fabrics sterilized with different sterilization methods. Table 6
shows the Young ‘s modulus and elongation at break values of the fabrics. Although it was seen that the
Young’s modulus decreased and the elongation at break increased with different sterilization methods,
effects of sterilization methods on mechanical properties were not significant.
Table 6. Young’s modulus and elongation values of PET fabrics sterilized by different methods.
Material (PET) Young’s modulus (MPa) Elongation (%)
non-sterilized 358,34 31,97
sterilized by ethylene oxide 429,14 23,59
sterilized by autoclave 428,64 26,45
sterilized by UV 422,38 27,13
The color measurement tests were performed on fabric samples sterilized by different methods. Table 8
shows the color properties of the fabrics sterilized by different methods.
Table 7. Color Properties
Material (PET) ∆E ∆L* ∆a* ∆b* Hunter 60
non-sterilized - - - - 85.756
sterilized by ethylene oxide 0.984 0.247 -0.358 0.883 83.548
sterilized by autoclave 5.930 -1.245 -0.653 5.781 68.400
sterilized by UV 1.029 0.943 0.135 -0.389 88.033
Non-sterilized fabrics were used as reference. The results showed that, fabrics sterilized by ethylene oxide
were lighter, more green and more yellow compared to non-sterilized fabrics. Fabrics sterilized by autoclave
were darker, more green, more yellow and fabrics sterilized by UV were lighter, less green and less yellow
compared to non-sterilized fabric. It was seen from the ∆E values that autoclave sterilization changed the
color of the sample most. It was also seen that ethylene oxide sterilization method did not make any
significant change in color.
Drape is defined as ‘the extent to which a fabric will deform when it is allowed to hang under its own weight’.
Drape is a critical textile characteristics in determining how clothing conforms to the shape of the human
silhouette. It prescribes the fabric deformation produced by gravity when a part of the fabric is directly
supported. [5]. Drape measurements were also performed to understand how different sterilization methods
affected the physical properties of the PET fabric. Table 8 shows the drape coefficient values of the Pet
fabrics sterilized by different methods. It was seen that autoclave sterilization made the fabric more rigid.
Table 8. Drape coefficient values of the Pet fabrics sterilized by different sterilization methods

7. The International Istanbul Textile Congress 2013
May 30th to June 1th 2013, Istanbul, Turkey
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Material (PET) Drape Coefficient(DC)
non-sterilized 51,74
sterilized by ethylene oxide 46,88
sterilized by autoclave 39,63
sterilized by UV 51,29
4. Conclusion
The results showed that different sterilization methods have significant effects on nanofiber mats and
conventional woven fabrics. SEM results showed that UV sterilization method did not change the surface
properties. Also, from SEM results it was concluded that all the sterilization methods did not affect PET
fabric.
The contact angle measurements showed that different sterilization methods also affect the surface
properties of the nanofibers and PET fabrics. The contact angle values decreased with the different
sterilization methods. For nanofiber mats, it was seen that there was a decrease in contact angles with UV
sterilization. This decrease did not follow a regular regime with the increasing polymer concentration and
was not a significant change. For the sterilized fabrics, it was seen that UV sterilization increased the contact
angle most.
Mechanical performance tests on nanofiber mats showed that nanofibers produced from 20% wt. PET
solutions show the higher modulus and lower elongation. It was also seen that the modulus and the strain at
break decreased with the autoclave sterilization. For PET fabric, it was seen that the Young’s modulus
decreased and the elongation at break increased with different sterilization methods, but effects of
sterilization methods on mechanical properties were not significant.
Color measurement studies on PET fabrics showed the effects of different sterilization methods. It was seen
from the ∆E values that autoclave sterilization changed the color of the sample most. It was also seen that
ethylene oxide sterilization method did not make any significant change in color. Drape measurements on
PET fabrics also showed that autoclave sterilization made the fabric more rigid.
Acknowledgements
This study is a part of the PhD thesis of the first author. The study is supported by The Scientific and
Technological Research Council of Turkey (Project number: 110M793) within the COST ACTION MP 1206
"Electrospun Nano-fibres for Bio Inspired Composite Materials and Innovative Industrial Applications".
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