J. Ind. Eng. Chem., Vol. 13, No. 6, (2007) 1002-1008

Preparation of Electrospun Porous Ethyl Cellulose Fiber by

THF/DMAc Binary Solvent System

Ju Young Park, Sung Woo Han, and In Hwa Lee†

Department of Environmental Engineering, BK21 Team for Biohydrogen Production, Chosun University, Gwangju

501-759, Korea

Received June 21, 2007; Accepted September 6, 2007

Abstract: Morphological change of electrospun fiber with various solvent was conducted to figure out solvent

effect on the surface of ethyl cellulose nanofiber. THF (bp 66 o

C) and DMAc (bp 165 o

C) binary solvent sys-

tem was introduced and electrospinning was performed with different ratio of THF/DMAc including each pure

solvent at 100 µL/min flow rate of 15 % (w/v) ethyl cellulose dissolved in the solvent. The applied voltage was

10, 13, 15, and 20 kV under 10 cm tip-to-collector distances. Morphology of fibers was evaluated by SEM im-

age through the various magnification. Regular holes were formed on the surface of fiber from pure THF and

80 % THF in DMAc, while smooth surface was observed for the pure DMAc and 80 to 20 % DMAc ratio in

THF. As the electric conductivity increased, the diameter of electrospun fiber decreased. In case of binary sol-

vent, the average diameter decreased from 1100 to 500 nm as increased the ratio of DMAc from 20 to 80 %.

Keywords: electrospinning, ethyl cellulose, nanofiber, binary solvent, morphology

Introduction1)

Cellulose is a naturally occurring polymer of particular

interest due to its abundant availability and biodegrada-

bility. These properties make cellulose fiber useful in a

wide range of area such as filtration, biomedical applica-

tions and protective clothing [1]. Unfortunately however,

there is a few research article has been reported on the fi-

ber of cellulose and its derivatives produced by the elec-

trospinning method. Ethyl cellulose is a kind of cellulose

ether, and it shows good thermostability and electric

properties. The film made from ethyl cellulose has quite

good permeability, it has been widely used industrial air

filter [2].

Electrospinning has been extensively investigated for

the preparation of nanofibers exhibiting high surface

area-to-volume and length-to-diameter ratios. These

characteristics are essential for practical applications

such as separation membranes. The characteristic of fiber

during electrospinning depends on the solution properties

such as viscosity, surface tension, conductivity, boiling

†To whom all correspondence should be addressed.

(e-mail: ihlee@chosun.ac.kr)

point and dielectric constant [3]. The morphology of

electrospun nanofibers also depends on the electrospinn-

ing parameters such as polymer concentration, spinning

distance and solvent properties [4].

Ultrafine porous fibers were prepared by the rapid

phase separation during the electrospinning process when

a highly volatile solvent was used [5]. Wendorff and

coworkers prepared porous fibers from poly-L-lactide,

polycarbonate, and polyvinylcarazole with methylene

chloride [6] and these porous nanofibers have potential in

applications such as nanofiltration and functional nano-

tubes by fiber templates [7-9]. Han reported for the pre-

paring the porous fiber and non-porous from cellulose

triacetate using methylene chloride and ethanol mixed

solvent [5]. At this paper, mixed solvents had low vapor

pressure by adding larger amount of ethanol and sub-

stantially the solidification of polymer became dominant,

resulting in the non porous fiber structure. The dielectric

constant of solvent has a significant influence on elec-

trospinning. If a solvent of a higher dielectric constant is

added to a s solution to improve the electro spinnability

of the solution, the interaction between the mixtures such

as the solubility of the polymer will also have an impact

on the morphology of the electrospun fibers [4]. When

Preparation of Electrospun Porous Ethyl Cellulose Fiber by THF/DMAc Binary Solvent System 1003

Table 1. Properties of Solvents used in This Study

Solvent b.p (oC) ε

aµb

THF 66 7.47 1.7

DMAc 165 37.8 3.72a Dielectric constant at 20

oC,

b Dipolemoment in Debyes.

DMF added to polystyrene (PS) solution, beads are

formed even though electro spinnability should improve

due to higher dielectric constant of DMF [10].

In this study, we try to prepare the porous nanofiber

from ethyl cellulose dissolved in a THF/DMAc binary

solvent system having a different boiling temperature

and dielectric constant. Also, we want find out the role of

solvent on the morphology of electrospun ethyl cellulose

fiber through observing the magnified images of the fiber

prepared with various solvent ratio using THF and

DMAc those are having different solvent properties. We

expect the more volatile solvent make a hole due to the

high evaporating rate during electropinning.

Experimental

Materials

Ethyl cellulose, tetrahydrofuran (THF), and dimethyla-

cetamide (DMAc) purchased from Sigma. These chem-

icals were used without further purification. The basic

properties of these solvents are summarized in Table 1.

Preparation and Characterization of Ethyl Cellulose

Solutions

Ethyl cellulose solutions having a different ratio of bi-

nary solvent were prepared with 15 % (w/v) ethyl cellu-

lose dissolved in the THF/DMAc according to volume

ratios of 100/0, 80/20, 60/40, 50/50, 40/60, 20/80, and

0/100. The viscosity and the conductivity of the prepared

solution were measured by viscometer (LVDV II+,

Brookfield Co., USA) and conductivity meter (CM-11P,

TOA Electronic Ltd). Surface tension for each solution

was measured tensionmeter (K9, Kruss Co., Germany).

Characterization

The morphology of electrospun ethyl cellulose fibers

Figure 1. Schematic and photo of electrospinning apparatus.

such as status of surface, diameter of fiber were observed

by Image microscope (Sometech Inc, Korea) and Scann-

ing electron microscope (FE-SEM, Hitch 8400s, Japan),

respectively. The diameter of the electrospun fibers is de-

termined with image analyzer (imageJ).

Electrospinning Process

The schematic experimental system used for the electro-

spinning process is shown in Figure 1. The eletrospin-

ning system composed as follows, syringe pump (200

series, KD Scientific Inc., USA) used as injector having

plat capillary tip 0.8 mm diameter and connected high

voltage DC power supplier generating positive DC vol-

tages up to 50 kV (DC power supply PS/ER 50R06

DM22, Glassman high voltage Inc., USA).

Grounded counter electrode was connected to collector

which covered with aluminum foil. Positive voltage ap-

plied to polymer solution controlled between 10 and 20

kV with stepwise increase. The concentration of ethyl

cellulose solution for fiber formation was fixed with 15

% (w/v). The flow rate were fixed to 100 µL/min and tip

to collector distance (TCD) is fixed at 10 cm. All electro-

spinning were carried out at the room temperature.

Results and Discussion

Effect of Solution

For the preliminary experiment electrospun of ethyl cel-

lulose performed with each THF and DMAc as a single

solvent. We prepare electrospun solution with 15 %

(w/v) ethyl cellulose dissolve in the THF or DMAc.

Electrospinning carried out at 100 µL/min flow rate, ap-

plied voltage was 15 kV under 10 cm tip-to collector dis-

tance (TCD). Figure 2 shows SEM images of electrospun

ethyl cellulose fiber for the various solvent. The result of

electrospinning, both THF and DMAc formed electro-

spun ethyl cellulose fiber (Figures 2(a) and (c)). In case

of THF, hole was formed on the surface of fiber, on the

contrary DMAc gave a smooth surface of nanofiber

(Figures 2(b) and (d)). For the further study, we evaluate

the effect of THF/DMAc binary system according to ratio

of solvent.

Ju Young Park, Sung Woo Han, and In Hwa Lee1004

(a) (b)

(c) (d)

Figure 2. SEM image on the surface of electrospun ethyl cellu-

lose with various solvents (ethyl cellulose; 15 % (w/v), applied

voltage; 15 kV, flow rate; 100 µL/min, TCD; 10 cm) (a) THF

(× 150), (b) THF (× 1000), (c) DMAc (× 1200), (d) DMAc (×

10000).

Effect of Binary Solvent Ratio

From the preliminary experiment, it was found that the

morphology of the fibers depends on the solvent si-

gnificantly. We prepare various solutions with fixed 15

% (w/v) ethyl cellulose according to volume ratios of

80/20, 60/40, 50/50, 40/60, and 20/80. Figures 3 and 4

show SEM image of electrospun ethyl cellulose fibers

prepared from different ratios of THF/DMAc (v/v). El-

(a) (b) (c)

(d) (e)

Figure 3. Low magnified SEM image of the electrospun ethyl cellulose fiber with various solvent ratio; (a) THF/DMAc = 80/20, (b)

THF/DMAc = 60/40, (c) THF/DMAc = 50/50, (d) THF/DMAc = 40/60, (e) THF/DMAc = 20/60 (ethyl cellulose; 15 % (w/v), ap-

plied voltage; 20 kV, flow rate; 100 µL/min, TCD; 10 cm) (× 1000).

ectrospinning was performed for the various ratio of

THF/DMAc including each pure solvent at 100 µL/min

flow rate of 15 % (w/v) ethyl cellulose dissolved under

applied voltage 20 kV applied to 10 cm tip-to-collector

distances (TCD). It was found that the addition of DMAc

gave the changes not only surface structure of fiber but

also the fiber diameter (Figures 3 and 4). Regular holes

were formed on the surface of fiber from pure THF

(Figure 4(a)) and 80 % THF in DMAc (Figure 4(b)),

while smooth surface was observed in pure DMAc

(Figure 4(g)) and 80 to 20 % DMAc in THF (Figures

4(c)∼(e)). We studied about chemical properties of

solvent including boiling point and dielectric constant

with various THF/DMAc ratios.

Chemical Properties of Ethyl Cellulose Solutions

The chemical properties of the polymer solution have

the most significant influence in the electrospining proc-

ess and the resultant fiber morphology. The surface ten-

sion has a part to play in the formation of beads along the

fiber length. The viscosity of the solution and its elec-

trical properties will determine the extent of elongation

of the solution. This will in turn have an effect on the di-

ameter of the resultant electrospun fibers [4].

Figures 5 and 6 are plots of viscosity and surface

tension of ethyl cellulose solution with different solvent

ratio of THF and DMAc. The properties of viscosity and

surface tension of binary solvent are less than each single

component. Comparing the morphology of electrospun

fiber and above results, the properties of viscosity and

surface tension did not affect significantly on the poro-

Preparation of Electrospun Porous Ethyl Cellulose Fiber by THF/DMAc Binary Solvent System 1005

(a) (b) (c)

(d) (e) (f)

(g)

Figure 4. High magnified SEM image of the electrospun ethyl cellulose fiber with various solvent ratio; (a) only THF (× 1000), (b)

THF/DMAc = 80/20 (× 6000), (c) THF/DMAc = 60/40 (× 3000), (d) THF/DMAc = 50/50 (× 20000), (e) THF/ DMAc = 40/60 (×

30000), (f) THF/DMAc = 20/60 (× 40000), (g) only DMAc (× 100000) (ethyl cellulose; 15 % (w/v), applied voltage; 20 kV, flow

rate; 100 µL/min, TCD; 10 cm).

Figure 5. Viscosity change of ethyl cellulose solution for the

various solvent ratio.

sity of fiber.

On the contrary the electric conductivity plays the

important role on the average diameter and shapes of the

Figure 6. Surface tension change of ethyl cellulose solution for

the various solvent ratio.

fiber. Figure 7 show the electric conductivities of

solvent, THF is almost insulator and DMAc is conductor

and the conductivities of mixed solvents are increase as

Ju Young Park, Sung Woo Han, and In Hwa Lee1006

Figure 7. Electric conductivity change of ethyl cellulose sol-

ution for the various solvent ratios.

the DMAc ratio increased.

As the electric conductivity increase, the electrospun fi-

ber diameter decreased. For the binary solvent the aver-

age diameter decreased from 1100 to 500 nm as in-

creased the ratio of DMAc from 20 to 80 %.

The distributions of diameter for the fiber were plotted

at Figure 9 as a function of solvent ratio. As DMAc ratio

increase, that is increase the electric conductivity, the

distribution of the diameter is shift to regular shape.

Such results can be explained by Taylor cone theory

(a) (b) (c)

(d) (e)

Figure 9. The distribution about fiber diameter of electrospun ethyl cellulose as a function solvent ratio; (a) THF/DMAc = 80/20, (b)

THF/DMAc = 60/40, (c) THF/DMAc = 50/50, (d) THF/DMAc = 40/60, (e) THF/DMAc = 20/80 (ethyl cellulose; 15 % (w/v), ap-

plied voltage; 20 kV, flow rate; 100 µL/min, TCD; 10 cm).

Figure 8. The average diameter of electrospun fiber as a func-

tion of THF/DMAc solvent ratios (applied voltage 20 kV, flow

rate 100 µL/min, TCD; 10 cm).

[11], as the electric conductivity increased the mobility

of solution increased in the high voltage of electric field

owe to abundant electric charges in the solution. We

could concluded that as DMAc ratio increase caused

electric conductivity increase in the mixed solvent,

consequently the diameter of fiber are decreased and

distribution of the fiber became more regular.

The dielectric constant of a solvent known as a

significant property for the electrospinning. Generally, a

Preparation of Electrospun Porous Ethyl Cellulose Fiber by THF/DMAc Binary Solvent System 1007

(a) (b)

(c) (d)

Figure 10. 1000× magnified SEM image of electrospun ethyl

cellulose fiber under different applied voltage; (a) 10 kV, (b)

13 kV, (c) 15 kV, and (d) 20 kV (ethyl cellulose; 15 % (w/v),

THF/DMAc = 20/80 (v/v), flow rate; 100 µL/min, TCD; 10

cm).

solution with a greater dielectric property reduces the

beads formation and the diameter of electrospun fiber

[12]. Solvent such as N,N-Dimethylformanide (DMF)

contributes to the solution increasing its dielectric

property to improve of the fiber morphology [13].

In case of ethyl cellulose solution under THF solvent,

bead formed due to low dielectric constant (7.47). While

the dielectric constant of DMAc (37.8) was higher than

THF (7.47), the diameter of ethyl cellulose fiber became

more uniform fiber as DMAc ratio increased. Practically,

as DMAc ratio increased, the diameter of ethyl cellulose

fiber decreased to approximately from 1000 nm in THF

single solvent system to 400 nm in DMAc single solvent

system (Figure 3).

The formation of micro hole on the fiber surface owe to

the volatility difference of two solvent, THF and DMAc.

(a) (b) (c)

Figure 11. 2000× magnified SEM image of electrospun ethyl cellulose fiber under different applied voltage; (a) 10 kV, (b) 13 kV, (c)

20 kV (ethyl cellulose; 15 % (w/v), THF/DMAc = 60/40 (v/v), flow rate; 100 µL/min, TCD; 10 cm).

The boiling points of THF and DMAc are 65 and 165 o

C,

respectively. Because of THF is higher vapor pressure

than DMAc, THF evaporate rapidly during electro-

spinning, while a considerable amount of less volatile

solvent remains within ethyl cellulose fiber. Conse-

quently, microhole on the surface of fiber could be

formed by elctrospinning of the ethyl cellulose with the

high boiling point solvent. Practically only THF was

used as a solvent, blockage of tip observed, while DMAc

was a single solvent jets appeared to be continuous with-

out a blockage. These phenomena also attributed to

mainly from boiling point difference of two solvent [14].

Effect of Applied Voltage

A series of experiments was performed with 15 % (w/v)

ethyl cellulose solution in 20/80 THF/DMAc volume ra-

tio solvent under applied voltage was varied from 10 to

20 kV and the tip-to target distance was fixed at 10 cm.

The results are shown in Figure 10. There was a slight in-

crease in fiber diameter upon increasing the applied

voltage. Also, as the voltage increased, the shape of fiber

became more regular electrospun web. Increasing the ap-

plied voltage will increase electrostatic repulsion force

for fluid jet, which favors thinner-fiber formation. But

there was not observed a remarkable difference in the

morphology. Corona discharge was occurred over 20 kV

applied voltage, and it prevent electrospinning.

Figure 11 show the effect of the applied voltage on 15

% (w/v) ethyl cellulose solution (with a 60/40 THF/

DMAc volume ratio) 10 cm tip to collector distance

(TCD). With an increasing applied voltage, the diameter

of electrospun fibers gradually decreased, and the shape

of fiber was become regular. The structure of electrospun

ethyl cellulose fiber became the full developed fiber from

bead likeover 20 kV while mixed shapes observed in the

range of 10 to 15 kV of applied voltage. As the applied

voltage increased to 10, 13, and 20 kV, the average di-

ameter of fibers decreased 998, 821, and 763 nm

respectively.

Ju Young Park, Sung Woo Han, and In Hwa Lee1008

Conclusion

The morphology of electrospun fiber is very diverse

with the kinds and ratio of solvent in the THF/DMAc bi-

nary system. The diameter of the ethyl cellulose fibers

were influenced by ratio of solvent in the THF/DMAc bi-

nary system. Regular holes were formed on the surface

of fiber from pure THF and 80 % THF in DMAc, while

smooth surface was observed in pure DMAc and 80 to 20

% DMAc in THF. As DMAc ratio increased, the electric

conductivity increased almost linearly. For the mixed

solvent the average diameter decreased from 1100 to 650

nm as increased the ratio of DMAc from 20 to 80 %. In

terms of the applied voltage, the structure of ethyl cellu-

lose electrospun fiber changes at 10 kV from bead like to

full developed fiber as voltage increased to 20 kV.

Acknowledgments

This study was supported by research funds from

Chosun University, 2002.

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