1. The International Istanbul Textile Congress 2013
May 30th to June 1th 2013, Istanbul, Turkey
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ELECTROSPINNING OF CELLULOSE ACETATE AND USE OF SUCH
FIBRES IN LAYERED MEMBRANES
P. Heikkilä, Y. Shen, A. Grönroos, J. Houni and J. Sarlin
VTT Technical research centre of Finland
pirjo.heikkila@vtt.fi
Abstract: Eletcrospinning method can be used in preparation of sub-micron and nanosized fibres. The main
commercial application of electrospun materials is aerosol filtration, but they can also be used in various
other application including medical and water filtration membranes. Cellulose acetate (CA) is widely used in
membrane applications. CA is soluble to acetone, which evaporates very fast in electrospinning process and
thus is difficult to be used in materials preparation due to nozzle blocking. In this presentation we will study
improving electrospinnability of CA by reduce nozzle blocking tendency. This was carried out, firstly, using
solvent mixtures containing also solvent with higher boiling point, and secondly, by using excess solvent feed
onto tip of the nozzle. In addition to evalution of these methods we also present premilinary results
concerning use of these fibres in membrane applications.
Keywords: electrospinning, cellulose acetate, solvent mixture, coaxial nozzle, membranes
1. Introduction
Membranes are semipermeable barrier materials allowing certain compounds to pass through whilst
rejecting others. Natural membranes have important role in many biological processes and man made
membranes have become important in recent 50 years for various separation processes – especially liquid
processes. Membranes can be divided into two types: microporous membranes and nonporous dense
membranes. [1] Electrospinning produces microporous sheet materials, which can be utilized in membrane
applications [2,3].
In electrospinning polymer solution is drawn into fibres in electrostatic field arranged between a nozzle and
a collector. Electrostatic field stretches the polymer solution into fibres at the same time when the solvent is
evaporating. Diameters of formed fibres are typically sub-micron range and they can be collected as
interconnected nanofibre web onto surface of substrate. Fibre quality and morphology depends on several
factors. The morphology of nanostructures forming onto collector varies from droplets (electrospray) to fibres
(electrospinning) depending on mainly on solution properties such as polymer concentration and viscosity,
but also on solvent properties and solubility of polymer into solvent. Diameters of formed droplets or fibres
are typically sub-micron range. [4,5]
Blocking of nozzles is one problem in electrospinning, especially when using volatile solvents with low boiling
point. This problem can be overcome, for example, using mixtures of solvents [6, 7] as well as solvent feed
onto tip of the nozzles [8, 9].
2. Experimental
Cellulose acetate with molecular weights of 100,000 (CA100k) from Acros organics) and 50,000 (CA50k) from
Aldrich) were used in trials. Solvents were acetone, N,N-dimethyl acetamide (DMAc) and their mixture.
Polymer solutions with various concentrations were prepared by adding polymer into heated solvent/solvent
mixture, and stirring in magnetic heater until polymer was fully dissolved.
Electrospinning was carried out with horizontal electrospinning setups: Setup 1) single nozzle setup with
Eltex KNH64 voltage source; Setup 2), multinozzle setup with 20 needles and Simco BP50 voltage source
and Setup 3) single nozzle setup Simco CM5-30P voltage source and coaxial nozzle. Electrospinning setups
are presented in Figure 1.

2. The International Istanbul Textile Congress 2013
May 30th to June 1th 2013, Istanbul, Turkey
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a) b) c)
Figure 1. Electrospinning: a) Setup 1, b) Setup 2 (at Tampere University of Technology) and c) Setup 3
Preliminary trials were carried out using Setup 1, and samples for membrane characterization with Setup 2.
In both of these setups frequent cleaning of the nozzles was a necessity. Samples for fibre characterization
were prepared on paper and samples for preliminary membrane studies were prepared using wet-laid
nonwoven material (Trinitex K 662 50) as base material. Samples are listed in Table 1.
Table 1. Samples prepared in this study
Studied property Polymer C Solvent Setup Parameters
Fibre morphology
and effect of solvent
CA50k 15 wt% Acetone 1 20 kV, 10 cm, 16G
Acetone-DMAc (4:1) 1 20 kV, 10 cm, 16G
CA100k 10 wt% Acetone 1 20 kV, 10 cm, 18G
Acetone-DMAc (4:1) 1 20 kV, 10 cm, 18G
Membrane CA100k 20 wt% Acetone-DMAc (1.7:1) 2 35 kV, 15 cm, 22G
Use of solvent feed CA100k 20 wt% Acetone 3 20 kV, 10 cm, 18G
The coaxial needle assembly (Figure 2a) was built for Setup 3 from polypropylene holder and feeding
needles. Different needles can be plugged into the holder with tight fitting. The inner diameter of the spinning
solution needle is 0.84 mm (18G) and the outer needle is about 4mm. The acetone vapour is prepared in a
flask on a heated plate. The flask is filled with a 100ml of acetone and heated on a hot plate at 25°C to 30°C.
A hydrocarbon gas is fed into the flask to carry the acetone vapour and feed it into the coaxial needle. The
setup is shown in Figure 2b.
a)
gas feeding
needle plug
spinning
solution
needle plug
outer
needle plug
b)
Electric heater
coaxial needle
acetone
rotating drum
collector
syringe
acetone saturated gas mixture carrying gas
power
supply
Figure 2. Schematic of a) coaxial nozzle and b) electrospinning setup with acetone gas feed.
Appearance of electrospun fibres was studied using SEM imaging. Water flow through the sample was
measured with Millipore lab filter suitable for micro and ultrafiltration with filtration area of 0.004 m
2
and
maximum pressure of 6.2 bar. Filtration tests were carried out at room temperature, and in this case without
pressure (=only hydrostatic pressure) until 150-210 ml of permeate was gone through.
3. Results and Discussion
3.1 Solvent mixtures
Electrospinning of CA fibres using pure acetone as solvent was possible, but process was operational only
short period of time prior to blocking. With acetone-DMAc mixture (4:1) process was operational longer even
though some dry polymer was accumulating onto tip of the needle. The fibre size and fibre diameter

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May 30th to June 1th 2013, Istanbul, Turkey
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distribution of fibres spun from acetone solution were much larger than those of fibres spun from mixture with
less volatile solvent. Due to quick evaporation of acetone in the tip of the needle the concentration changes
during the process, which can explain large fibre distribution. Poorer solubility of CA into DMAc can explain
why more beads were observed in fibres spun from solvent mixture. Appearance of CA fibres electrospun
using acetone and mixture of acetone and DMAc (4:1) as solvent is presented in Figure 3.
a) b)
c) d)
Figure 3. Appearance of 15% CA50k a) in acetone and b) in acetone-DMAc mixture, and 10% CA100k c) in acetone and d)
in acetone-DMAc mixture.
3.2 Membrane samples
Fibres obtained with 20 wt% CA solution had mean fibre diameter in µm range. Fibres were fused together in
many of the crossing points, which could be an advantage in membrane applications [2]. Otherwise the
coating was not optimal: fibre diameter had relatively large diameter distribution, and there were some larger
polymer structures also occurring within the coating. Electrospun fibres were obtained onto sample materials
using several coating cycles with multinozzle Setup 2. Coating layer thicknesses of samples were 1.2 g/m
2
(6
cycles, Espin1), 2.4 g/m
2
(12 cycles, Espin2) and 3.6 g/m
2
(18 cycles, Espin3). These layers smoothed the
surface without affecting the flux of the material. Appearance of fibres, base material and fibre layer obtained
with single cycle are presented in Figure 4, and effect of electrospun layer onto flux in Figure 5.

4. The International Istanbul Textile Congress 2013
May 30th to June 1th 2013, Istanbul, Turkey
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a) b)
c) d)
Figure 4. Appearance of fibres a) and b), base material c) without and d) with electrospun fibres obtained with one cycle.
Figure 5. Effect of electrospun fibres coating on membrane flux.
3.3 Solvent feed
It was also tested to feed liquid acetone to the outer needle directly using a syringe pump. However, the flow
at the exit of the needle does not seem stable. Also the liquid acetone does not always cover the whole outer
layer of the spinning solution. Clogging due to dry polymer skin still happens. Excess amount of liquid
acetone also dilutes the spinning solution; it was difficult to get fibre without beads formation.
When the saturated gas mixture is fed to the outer needle, a faint flame like flow can be seen with the aid of
bright light. This may be related to the refractive index difference between the gas mixture and the
surrounding air. The gas mixture surrounds the inner needle quite well based on visual observations. The
flask has to be heated slightly in order to produce more saturated vapour. If the heating is not enough,
clogging still happens. Overheating creates too much vapour which condenses in the plastic tubing and drips
out of the needle. The pressure also easily builds up. At 21°C room temperature, 25 - 30°C heating works in
general quite well. The electrospinning can continue for at least 10 minutes without clogging. Appearance of
electrospun fibres prepared with vapour feed is presented in Figure 6.

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a) b)
Figure 6. Appearance of CA fibres electrospun with acetone vapour feed onto nozzle
4. Conclusion
We have shown that the morphology of electrospun cellulose acetate fibres can be adjusted by changing Mw
of polymer, and using different solvents mixtures. These electrospun fibre layers can be used in order to
even up the surface of membrane base material in layered membrane structures without affecting too much
on flow properties. We have also used solvent fume feed onto tip of the nozzle in order to reduce blocking
tendency of acetone based cellulose acetate solutions and, thus, improve long term electrospinning
processability of cellulose acetate.
Acknowledgements
Authors thank Tampere University of Technology, Department of Materials Science for possibility to use
continuous electrospinning setup.
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