The effect of silica on cellulose acetate...

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.



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-


Fig. 3 SEM micrograph of the surface of silica-

cellulose acetate membrane with heating

process at 1000C

E. Ernawati et al.



443

Fig. 4 SEM micrograph of the cross-section of


Fig. 5 SEM micrograph of the cross-section of silica-


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.

References

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Membrane transport properties of

pervaporation and vapor permeation in ethanol-

water system using polyacrylonitrile and

cellulose acetate membranes. Journal of

Chemical Engineering of Japan. 24 (3) : 334-

339.

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444

Kittur, A.A., S.M Tambe, S.S. Kulkarni, M.Y.

Kariduraganavar. 2004. Pervaporation separation

of water-Acetic acid mixtures through NaY

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