The document summarizes research on the effect of the speed of the support material on the structure of electrospun polyamide 6.6 (PA6.6) nanofiber webs. Nanofiber webs were produced at three different speeds and analyzed. It was found that decreasing the speed, and thus increasing the covering time, resulted in thicker nanofibers being formed. While the average fiber diameter did not significantly change, the distribution of fiber diameters shifted to include more larger fibers. The document proposes using parameters like the percentage of fibers in the first distribution peak and the average diameter of the two main peaks as better ways to characterize nanofiber web structure compared to just the average diameter.

1. The International Istanbul Textile Congress 2013
May 30th to June 1th 2013, Istanbul, Turkey
1
ESTIMATION OF STRUCTURE OF WEB FROM ELECTROSPUN
NANOFIBRES
J. MALAŠAUSKIENĖ and R. MILAŠIUS
Kaunas University of Technology, Department of Textile Technology, Lithuania
jolanta.malasauskiene@stud.ktu.lt
Abstract: To produce nanofibres with uniform diameter is very sophisticated, because there are a lot of
parameters which has influence on the diameter of nanofibres. The analysis of various works shows that the
diameter of nanofibres always is distributed in different distributions. Its mean that to compare the averages
values is not correct from mathematical statistic point. The average diameter of nanofibres is the main
parameter for nanofibre characterization, but changes in average value do not suppose the changes in other
characteristics, for example modal value or wide of the value distribution and etc. For this reason the new
criterions are proposed. The percentage quantity and the modal value of the first distribution also the
average diameter of two peaks of distribution (modal value and the value of the second highest peak) can be
used for estimation of nonwoven structure, because these parameters can be used for comparing various
webs of nanofibres. Therefore, these parameters allow to estimate how various parameters influence the
structure of the web.
Keywords: electrospinning, nanofibre, diameter, distribution.
1. Introduction
Electrospinning is a simple process that spins ultrafine fibres of diameters ranging from 10 nm to several
hundred nanometers. Electrospun webs from polymer solution have attracted significant attention because of
their unique properties such as high porosity along with small pore sizes large surface area per mass ratio,
flexibility and small diameter. Due to these characteristics nonwoven materials from nanofibres are used for
medical applications, composite, filtration, and etc [1-2].
The diameter of nanofibres is one of the most important parameter related with elecrospinning process.
Electrospinning process and the morphology of electrospun nanofibres, such as fiber diameter and
uniformity, depend on the solution properties (solution concentration, solution viscosity, polymer type,
polymer molecular weight, and surface tension), technological parameters (applied voltage, volume flow rate,
distance between electrodes, and covering time of support material) and ambient conditions (temperature,
humidity, and atmosphere pressure). Sometimes the influence of these parameters is visible very well, but
not always. Many researches work in this area, but until this day there is no common agreement about the
influence of the same parameter on the structure of nanofibres [1-6]. It is possible that the differences
between the results occur because there is no common methodology for nanofibre diameter
characterization.
The analysis of various works shows that the web of nanofibres usually consists from nanofibres with
different diameters. Sometimes the distributions of nanofibres diameter are closes to log normal distribution,
but this distribution does not have the theoretical basic, because all nanofibres are manufactured at the
same time. Describing the diameter of nanofibres by means of normal distribution, when the distribution of
nanofibres differs from this one is not appropriate too. Therefore, it is difficult to compare the averages
values when the character of dispersions of nanofibres differs [7-9]. Only the average value can not
characterise nanofibres and the new criterions are needed. The goal of this article is to study the influence of
the speed of support material on the structure of electrospun webs from PA 6.6 and to propose the new
criterions for the quality of nonwoven structure estimation.
The mathematical analysis and comparison with well known statistical distributions shows that distribution of
nanofibres diameter is very close to compound distribution from several normal distributions. It means that
the web in electrospinning process usually consists from several nanofibres with different diameter. The
reasons of this phenomenon by different authors are explained in some ways [10-12].

2. The International Istanbul Textile Congress 2013
May 30th to June 1th 2013, Istanbul, Turkey
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Various polymers can be successfully electrospun into nanofibres. The most often polymers used in this
process are nylon, polystyrene, polyacrylonitrile, PEO, water-soluble polymers and others. PA6.6 is a
commonly polymer used due to its mechanical strength, thermal dimensional stability and higher moisture
absorption.
2. Materials and methods
2.1 Materials
The spinning solution was prepared by dissolving a weighed amount of PA6.6 granules in formic acid (85 %)
under constant stirring for 12 hours to attain solution with concentration of 8 %. The solution was stirred at
the temperature of the room.
2.2 Electrospinning technique
The web of PA6.6 nanofibres was prepared by electrospinning equipment of “NanospiderTM
” (Elmarco,
Chech Republic). This equipment consists of rotating electrode to spin fibers directly from the polymer
solution. The roller spinning electrode is partially submerged in polymer solution. A grounded collector
electrode is fitted at the top of the spinner. By increasing electrostatic forces between electrodes, many
Taylor cones from the polymer solution are formed on the rotating electrode. Only when the electrostatic
charge overcomes the surface tension a charged jet of polymer solution ejected from the Taylor cone. A jet
is moving toward upper electrode and lay on substratum material. During the experiments, webs from
nanofibres were formed only using electrodes with tines.
During all the experiments, the distance between electrodes was 13 cm; the applied voltage was 70 kV. The
temperature of environment was T = 24 ± 2° C and the relative air humidity was φ = 50 ± 2 %. The speed of
support material was changed. The first part of experiment was carried out when the speed of support
material was v = 0.010 m/s, the time of covering was t = 25 s. The second: v = 0.006 m/s, t = 42 s, and the
third: v = 0.002 m/s, t = 125 s.
2.3 Characterisation of nanofibre morphology
The structure of electrospun PA6.6 web was observed by Scanning Electron Microscopy (SEM) SEM - FEI
Quanta 200 (Netherlands). The diameter of nanofibres was measured using the analysis system LUCIA
Image 5.0, with an accuracy ± 0.01 nm. All nanofibres were measured from 5 different SEM images.
3. Results
The SEM images of the web at the different speed of support material are presented in Figure 1. It is evident
that the speed of support, herewith the covering time has a significant influence on the structure of PA6.6
nanofibres. At the lowest speed, hense at the highest covering time, mostly nanofibres were formed on the
support material. During the experiment 5 SEM images for each variant has been made. The 165 diameters
of PA6.6 nanofibres for the first variant, 200 diameters of nanofibres for the second variant and 288
nanofibres for the thirst variant were found and measured.
a. b. c.
Figure 1. SEM images of PA6.6 webs, when the speed of support material: a) v = 0.010 m/s (t = 25 s); b) v = 0.006 m/s
(t = 42 s); c) v = 0.002 m/s (t = 125 s)

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After the analysis of experimental data it was observed that the speed of support material has not a
siignifficant influence on the average diameter of PA6.6 nanofibres. The average diameter of the first,
second and third parts of experiment is d̅ = 357 nm, d̅ = 373 nm and d̅ = 382 nm, respectively. The difference
between average values is less than ± 3.5 %.
For the deeper analysis of the structure of nowoven web, the frequency distributions of all parts of
experiment are presented in Figure 2.
0
2
4
6
8
10
12
14
16
18
20
22
25-75
75-125
125-175
175-225
225-275
275-325
325-375
375-425
425-475
475-525
525-575
575-625
625-675
675-725
725-775
775-825
Diameter of nanofibres, nm
Frequencydistribution,%
I part of experiment
II part of experiment
III part of experiment
Figure 2. Frequency distributions of PA6.6 nanofibres
From Figure 2 it is evident that at higher covering time, hense at lower speed of support material thicker
nanofibres were formed. In the range from 0 to 275 nm, 32.2 % of nanofibres was measured at the highest
speed and only 21 % of nanofibres was measured at the lowest speed. Up to 325 nm, 50 % was measured
at the highest speed of support material, while at the lowest speed 66 % of nanofibres was measured. It is
possible that thicker nanofibres are formed when several nanofibres stick together and do not separate
before reaching the upper electrode.
Analyzing the histograms in Figure 2 we can observe that the distribution of the third part of experiment has
only one obvious peak. For this reason this distribution is very close to normal distribution. However, the
histograms of the first and of the second series of experiment have several peaks, so in both cases we can
state that diameter of nanofibres is distributed by compoud distribution from several normal distributions.
When the diameter of nanofibres is distributed in compound distribution, the average value of diameter can
not estimate the structure of the web exactly. With the average value of nanofibres the modal value and the
percentage quantity of the first distribution are proposed. The percentage quantity of nanofibres distributed in
the first distribution is 32.2 % (first part of experiment). The percentage quantity of the second variant is only
24.04 %. Higher percentage quantity means more unique structure of the web. The modal value in both
cases is 200 nm. Finally, the of distribution is proposed for estimation of nonwoven structure. From the
histograms presented in Figure 2 the average diameter of two peaks has been calculated: dˈ = 375 nm (third
part of experiment); dˈ = 350 nm (second part of experiment) dˈ = 250 nm (first part of experiment).
According to all results it was decided that at the higher speed of support material more unique structure and
thinner nanofibres are formed.

4. The International Istanbul Textile Congress 2013
May 30th to June 1th 2013, Istanbul, Turkey
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4. Conclusions
 The distributions of electrospun PA6.6 nanofibres diameter are closes to compound distribution,
consisted of several normal distributions.
 At the lower covering speed more unique structure and thinner nanofibres are formed.
 The speed of support material does not have a significant influence on the average value of PA6.6
nanofibres diameter but have a significant influences on the structure of nanofibre web.
 The percentage quantity, the modal value of measurements of the first distribution and the average
diameter of two peaks of distribution can be used for comparison of nanofibres diameter.
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