Effect of electric current on Beads formation in Electrospinningof Poly(vinyl alcohol)
Y. Kadomae, T. Taniguchi, M. Sugimoto and K. Koyama
Department of Polymer Science and Engineering, Yamagata University, Japan
Abstract

We investigate formation of beads on electrospinning by changing processing parameters, suchas strength of electric field, applied voltage, distance between the tip of needle and the collector,and humidity. From the results of experiments done by changing processing parameters, it
seems that beads formation is related to electric charges at the tip of the sample. In order toclarify relation between the electric charge stored at the tip of the samples and beads formation,
electric current measurements are performed in electrospinning process. As the results ofelectric current measurements, it is found that the time dependence of the observed electric
current can be classified into two typical patterns (I) and (II). In the first pattern (I), the electric
current is stable during the measurement. In this case (I), beads are not observed. On the otherhands, in the pattern (II), the electric current is unstable during a measurement. In this case (II),many beads are formed. From averages of electric currents, a strength of tensile force that actson the sample tip is calculated. It is found that the strength of tensile force in the case (II) is
stronger than that of the case (I) with stable electric currents. This result indicates that beads
formation is enhanced by a higher electric current.

1 Introduction
Electrospinning is one of spinning techniques to produce nonwoven consist of ultra thin fibers
from a polymer solution or melt by applying a high voltage between a tip of needle and agrounded collector. This technique enables us to easily fabricate ultra thin fibers than theconventional fiber spinning processes based on melt and solution spinnings. The electrospun
fibers have quite thinner diameters and larger surfaces than those obtained by the conventional
fiber spinning processes. These unique characteristics bring us possibilities of a number ofapplications, for example, filtration for nano-sized materials, tissue scaffolding and otherbiomedical applications. One of the most serious problems in applications of electrospinning isa formation of beads on fibers. The formation of beads makes functions of products deteriorate.
It is reported that the formation of beads depend on electric field strength [1]. However, theorigin of formation of beads is still not clear. In this work, we focused on relation between
electric charges at the tip of the sample and beads formation.

2 Experiments-SamplePVA (Poly vinyl alcohol) solution was used in this study. PVA with molecular weight of
40,000 g/mol was dissolved in distilled water and which was prepared to be 15wt%.
-Electrospinning
The apparatus of electrospinning is shown in Fig.1.
Electrospinning was performed at room temperature in thehorizontal mode. Experimental conditions were as follows;
the distance between the tip of needle and the collector
was changed from 5 to 20cm, the applied voltage waschanged from 4.5 to 18kV, and humidity was controlled in
the range of 50 ~ 60 %. The electric charge stored at thetip of the sample was measured by ammeter which wasFig.1 Scheme of electrospinning apparatus.
attached to the grounded collector. The current
measurement was performed every 0.5s. The electrospun
samples were observed by Scanning Electron Microscopy (SEM).

3 Results and discussion
Figure 2 shows SEM images at different distances,
but under the same strength of electric field ((a) 9kV
and 10cm, (b) 13.5kV and 15cm, and (c) 18kV and20cm). In case of 4.5kV and 5cm, the electrospinning
could not be realized since the strength of applied
voltage is too low to elongate the sample. In case (a),beads on electrospun fibers were not observed. On
the other hands, in cases of (b) and (c), many beads
were formed. The results of electric current
measurements are shown in Fig.3. From these results,observed electric currents could be classified into
two typical patterns (I) and (II). In the first pattern (I),the electric current is stable during the measurement.
On the other hands, in the pattern (II), the electric
current is unstable during a measurement. Figure 4
shows averages of electric currents. Strength oftensile force that acts on the sample tip is calculated
as shown in Table 1. These results show that theelectric currents are different even at the same
electric field strength. Additionally, amount of beadsformation on electrospun fibers is different among
these three cases, namely the beads are easily formed
with increasing the tensile force. We concluded thatthe higher tensile force incites unstable deformationof sample at the tip of needle.

Fig.2 SEM image of electrospun PVA fibers at
different distances between the tip of needle and thecollector, (a)10cm, (b)15cm and (c)20cm, and atconstant strength of electric field, 0.9kV/cm.

(b),(c)(a)Table 1 Calculated tensile forces.

Spinning condition

Tensile force[cN](a) 9kV, 10cm

1.8(b) 13.5kV, 15cm

2.4(c) 18kV, 20cm

3.0Fig.3 Results of current measurements inelectrospinning under condition (a), (b) and (c).

4 Summary
We found that the pattern of electric current isdrastically changed by varying the distance between
tip of the needle and the collector while keeping theelectric field strength constant. At the stable current,
the beads were not formed. On the other hand, when
the current was unstable, many beads were easily
formed. Additionally, the higher tensile force

incites beads formation.

Fig.4 Relation between currents and voltages
in cases (a), (b) and (c).

5 References
1. Geng XY, Kwon OH, Jang JH, Electrospinning of chitosan dissolved in concentrated acetic
acid solution, Biomaterials, 26(27), 5427-5432 (2005)