RELATION BETWEEN SPINNING CONDITION AND
BEADS FORMATION IN ELECTROSPINNING OF
POLY (VINYL ALCOHOL)
Y. Kadomae, M. Sugimoto, T. Taniguchi, K. Koyama
Department of Polymer Science and Engineering, Yamagata University, Japan, kadomae@ckpss.yz.yamagata-u.ac.jp
We investigate formation of beads on electrospinning by changing conductivity of poly(vinyl alcohol) (PVA) aqueoussolutions and spinning conditions, such as applied voltage, distance between the tip of needle and the collector, andhumidity. From the results of experiments done by changing conductivity of PVA aqueous solutions and spinning
conditions, we found that the beads formation is suppressed at lower electric charges. When the applied voltage changes
to be same electric charge in respective distances between the tip of needle and the collector, beads less fibers arefabricated in all cases.

Introduction
Electrospinning is one of spinning techniques to produce nonwoven fabrics consist of ultra thin fibers from polymer
solutions or melts by applying a high voltage between a tip of needle and a grounded collector. This technique enables
us to easily fabricate ultra thin fibers than the conventional fiber spinning processes based on melt and solutionspinnings. The electrospun fibers have quite thinner diameters and larger surfaces than those obtained by theconventional fiber spinning processes. These unique characteristics bring us possibilities of a number of applications,for example, filtration for bacteria or nano-sized materials, tissue scaffolding and other biomedical applications. One of
the most serious problems in applications of electrospinning is a formation of beads on fibers. The formation of beads
makes functions of products deteriorate. It has been reported that the beads formation is related to the jet instability suchas a bending instability due to change the surface tension or electric field strength [1, 2]. The jet instability depends onthe electric charges [3]. Therefore, we focused on the electric charges in electrospinning processes. In the present study,
we changed the spinning conditions which relate to the electric charges in the electrospinning, for example, appliedvoltages, distance between the tip of needle and the collector, electric conductivity of PVA aqueous solutions by adding
salt (NaCl) and relative humidity. We investigated relation between the electric charges and beads formation inelectrospinning of PVA.

Experimental-Samples
The sample used in this study was poly(vinyl alcohol) (PVA) solution.
PVA with molecular weight of 40,000g/mol was purchased from
Aldrich Chemical Corporation and dissolved in distilled water. The
concentration of PVA aqueous solution was adjusted to be 15wt%,
because beads were formed easier at this concentration than otherconcentrations in possible electrospinning processes. In order to change
the conductivity of PVA solutions, the salt (NaCl) was added to PVA
solutions at different concentration from 0.01 to 0.25wt%.

Distance Collector[L]
Liquid jetPolymer
Solution
Syringe

Ammeter
NeedleFabrics
High Voltage
Power Supply [V]AGND

Fig.1 Electrospinning set-up.
-Electrospinning
Using the PVA solution, electrospinning was performed at room temperature in the horizontal mode as shown in
Fig.1. Experimental conditions were as follows; the distance between the tip of needle and the collector was changed
from 5 to 20cm, the applied voltage was changed from 4.5 to 24kV, relative humidity was controlled in the range from20 to 75%, and feed rate of PVA solution was set to be 0.5ml/h. The electric charge on the electrospun fibers wasevaluated by electric current measurements with an ammeter which was attached to the grounded collector. The current
measurement was performed every 0.5s.
The electrospun samples for Scanning Electron Microscopy (SEM) observation were dried under vacuum at 30oC for
one day. Diameters of obtained fibers were measured by an image analysis software. To investigate averages diameterof electrospun fibers, we randomly selected fibers more than one hundred and measured their diameters at threepositions that were randomly selected on each fiber in SEM images of magnification of 15,000. Beads were exceptedfrom the diameter evaluation of electrospun fibers.

The Polymer Processing Society 23rd Annual Meeting

Conclusion
From the results of all experiments, we found thatthe beads formation is induced the higher electric
current in the electrospinning of PVA. The electric
current is closely related to charge density of fibers.
This result indicates that the formation of beads can besuppressed completely without changing average
diameters of fibers by controlling the charge density offibers. We succeeded in making beads less nanofibersof 80nm.
References
1. H. Fong; I. Chun; D. H. Reneker Polym. 1999, 40,4585.
2. W. W. Zuo; M. F. Zhu; W. Yang; H. Yu; Y. M.
Chen; Y Zhang Polym. Eng. Sci. 2005, 45, 704.
3. A. L. Huebner J. Fluid Mech. 1969, 38, 679.

Fig.2 SEM images of electrospun fibers at different
distances between the tip of needle and the collector,
L=5cm, 10cm and 15cm at same applied voltage of 9kV.

Fig.3 SEM images of resultant fibers at same electric
current condition (0.2µA), (a) 7.5kV and 5cm, (b) 9kV and10cm, (c) 12kV and 15cm, (d) 14kV and 20cm.
Frequency distribution [%]Results and Discussion
Fig.2 shows the effect of distance (L) between thetip of needle and the collector on electrospinning of
PVA at the constant applied voltage (9kV). In case of
L=20cm, the electrospinning could not be realized
since the strength of applied voltage is too low toelongate the sample. At the distance is 5cm, the manybeads were formed. On the other hands, beads-lessfibers were fabricated at L=10cm and 15cm,
respectively. Then, the beads formation tends to makeeasier with increasing the electric current. Furthermore,higher electric conductivity enhances the beads
formation in experiment about the effect of electric
conductivity on electrospinning of PVA.
Fig.3 shows the results of SEM observation atdifferent combinations of distance and voltage thatgive the same electric current (0.2µA). Fig.4 shows thefiber diameter distribution of electrospun fibers. At theconstant electric current (0.2µA), even though theapplied voltage and distance between the tip of needle
and the collector are different, beads-less fiber wasfabricated in all cases. Additionally, average diameterand distribution of fiber diameter are almost same asshown in Fig.3. These results indicate that the electric
current is highly related to formation of beads.

60504030(a)7.5kV, 5cm(b)9kV, 10cm(c)12kV, 15cm(d)14kV, 20cm

2010050

75100

125

150 175

200 250

Fiber diameter [nm]Fig.4 Diameter distribution of electrospun PVA fibers atsame electric current condition (0.2µA), (a) 7.5kV and 5cm,(b) 9kV and 10cm, (c) 12kV and 15cm, (d) 14kV and 20cm.

The Polymer Processing Society 23rd Annual Meeting