E. Ernawati et al.
Proceeding of The International Seminar on Chemistry 2008 (pp. 441-443)
Jatinangor, 30-31 October 2008
441
The effect of silica on cellulose acetate membranes
Evy Ernawati*, Rina L.N. Safitri, Yati B. Yuliati
Department of Chemistry, Faculty of Mathematics and Natural Sciences,
Universitas Padjadjaran, Bandung
*e-mail: [email protected]
Abstract
The silica filled cellulose acetate membrane was prepared by phase inversion processes
with immersion precipitation. The morphological changes of the pores of the membranes,
surface structure, and thermal performance were studied by methods of scanning electron
microscopy (SEM) and thermogravimetric analysis (TGA). SEM imaging of membranes
showed that pores of the silica filled cellulose acetate membrane was denser than cellulose
acetate membrane without silica and the silica particles are finely dispersed in polymers.
While heating process can make the pore of membrane become denser. TGA analysis it
was found that the silica-filled cellulose acetate membrane have higher thermal stability
compared with cellulose acetate membrane.
Keywords : cellulose acetate, silica
Introduction Cellulose acetate membranes is one of the
hydrophilic membranes that can be used as the raw
material of membrane and also it can be synthesized
from natural cellulose (Meenakshi et al., 2002). The
cellulose acetate properties are almost the same as the
sodium alginate properties that have ability in
dehydrating organic aqueous solutions (Kittur et al.,
2004). The cellulose acetate membrane is hygroscopic
that can cause the membrane become easily swelling
so that the separation process become bad (Kataoka et
al., 1991). Mineral addition into the membrane system
can change the mechanical and physical strengness,
improve the membrane structure, and also have a big
chance for developing its complex material of
mineral-polimer that is used as separating membranes
(Okumus, 2003; Wara et al., 1995). While these
studies have demonstrated the changes in membrane
properties with mineral filler addition.
In this work, we report the effects of silica
particels on the microstructure development and
thermal stability of membranes cast from silica/
cellulose acetate/acetone by SEM and TGA methods.
Materials and Methods
General
The preparations of membrane were carried out by
immersion precipitation. There were three kind of
membranes that were prepared which were cellulose
acetate membrane, silica-filled cellulose acetate
membrane without heating, and silica-filled cellulose
acetate membrane by heating at 100ºC for 24 hours.
The influence silica on cellulose acetate membranes
based on the microstructure development and the
effect of heating membrane were exhibited by SEM
(scanning electron microscope) and TGA
(thermogravimetric analysis)
Materials
Cellulose acetate (CA) polymer was provided by
Aldrich with 39.8% of acetyl, natural silica from
Jambi (98% SiO2), and acetone.
Preparation of membranes
The cellulose acetate membranes were prepared
from 20% w/w of cellulose acetate that was diluted by
80% w/w acetone homogenously. In the next step, the
solution was kept on the refrigerator for debubbling
process and then was molded on the glass plates.
Finally, the membranes were immersed in the water
for solvent removing. The silica-filled cellulose
acetate membranes were prepared from cellulose
acetate 20% w/w that was diluted by acetone and
then added by silica 10 % w/w. The next process was
similar with the preparation of cellulose acetate
membranes. The preparation silica-filled cellulose
acetate membranes with heating process was treated
similarly with the preparation of silica-filled cellulose
acetate membranes without heating. But the process is
followed by heating process at 100ºC for 24 hours.
Results and Discussion
SEM imaging of membranes showed that the
cellulose acetate membranes(Fig.4) and the silica-
cellulose acetate membranes (Fig.5) were asymmetric
with a thin top layer and relatively thick, porous,
bottom layer.
ISBN 978-979-18962-0-7
E. Ernawati et al.
Proceeding of The International Seminar on Chemistry 2008 (pp. 441-443)
Jatinangor, 30-31 October 2008
442
The mineral addition on the membran can change
the porous structure (Okumus, 2003). It can be seen
that in the silica-filled membrane (Fig. 2 and 5), the
surface and the top layer of cellulose acetate
membrane become denser and thicker than silica-
unfilled membrane (Fig.1 and 4), while the silica
particles are finely dispersed in polymers.
Moreover, heating process can also ease the pore
formation. This mean that the pore of membrane
become denser. It can be shown in Fig.3 and 6 from
SEM analyzed.
According to Wara et al., 1995, the system
separates, by interdiffusion of the three components,
into a continuous cellulose acetate/acetone phase and
a discontinuous water droplet phase. If interdiffusion
is rapid, the system instantaneously separates or
demixes, and the water phase nucleates near the top
surface beneath a dense polymer skin. These droplets
grow in size and progress downward through the
coating. If interdiffusion is slower, the system
demixes after a time delay, and water droplet form
throughout the coating thickness. The pore structure is
determined by the water droplet configuration.
Consequently, the pore structure consists of
macrovoids for instantaneous demixing and a small
pore network delayed demixing.
Silica addition into the cellulosa acetate membrane
can change pores structure of membrane from
macrovoid into microvoid. This change to explain that
silica particles can make interdiffusion process on
water droplet form is slow
Fig.7 and Fig. 8 show the result of TGA of
cellulosa acetate membrane and silica-cellulosa
acetate membrane. The membranes have degradation
stages. The first degradation stage of cellulosa acetate
membrane at 49oC and the weight loss 3,9%. The
second degradation stage between 334,9 oC and 372,5
oC and the residu was 15.6%. In the third degradation
stage was 500 o
C and the residu was 12%. While the
first degradation stage of silica-cellulosa acetate
membrane at 340,8 o
C and the weight loss 4,7%. The
second degradation stage at 372,5 oC oC and the residu
was 43%. In the third degradation stage was 500 o
C
and the residu was 40,3%. The residu of silica-
cellulosa acetate membrane was higher than cellulosa
acetate membrane. This increase in the residu to
explain that the high thermal stability of silica-
cellulosa acetate membrane.
Fig. 1 The SEM micrograph of the surface of
cellulose acetate membrane
Fig. 2 SEM micrograph of the surface of silica-
cellulose acetate membrane
Fig. 3 SEM micrograph of the surface of silica-
cellulose acetate membrane with heating
process at 1000C
E. Ernawati et al.
Proceeding of The International Seminar on Chemistry 2008 (pp. 441-443)
Jatinangor, 30-31 October 2008
443
Fig. 4 SEM micrograph of the cross-section of
cellulose acetate membrane
Fig. 5 SEM micrograph of the cross-section of silica-
cellulose acetate membrane
Fig. 6 SEM micrograph of the cross-section of silica-
cellulose acetate membrane with heating
process at 1000C
Fig. 7 TGA curve of the cellulose acetate membrane
Fig. 8 TGA curve of the silica- cellulose acetate
membrane
Conclusions SEM imaging of membranes showed that the
cellulose acetate membranes and the silica-cellulose
acetate membranes were asymmetric with a thin top
layer and relatively thick, porous, bottom layer. The
pores structure of the silica-filled cellulose acetate
membrane become denser than those without silica
modification. Silica particles were distributed
homogenly throughout the cellulose acetate networks.
While heating process can also ease the pore
formation. TGA analysis it was found that the silica-
filled cellulose acetate membrane have higher thermal
stability compared with cellulose acetate membrane.
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E. Ernawati et al.
Proceeding of The International Seminar on Chemistry 2008 (pp. 441-443)
Jatinangor, 30-31 October 2008
444
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