The effectiveness of centrifugation as the compacting method in preparing high filler composites has been investigated. Different size and shape of fillers were used to ensure efficient filler space filling. In situ polymerization of bisphenol-A ethoxy diacrylate after centrifugating produced biomimetic composites with 74–86 % filler content. The filler space was efficiently filled by using a combination of nano and microsize fillers, especially in the nanosilica-CaCO3 composite. The morphology of the composites indicates that the fillers were well dispersed and embedded in the polymer matrix. The etched surface of the nanosilica-talc composite reveals that the combination of talc and nanosilica formed a biomimetic composite that displayed an ordered brick-and-mortar nacre-like structure. The wide-angle X-ray diffraction patterns indicate the crystal structure of CaCO3 and talc were maintained in the composit

Daud, N

Kong, I

Shanks, R

RMIT Research Repository

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Daud, N, Shanks, R and Kong, I 2012, 'Compacted nanosilica-talic/calcium carbonate
polyacrylate composites prepared using accelerated sedimentation', World Journal of
Engineering, vol. 9, no. 5, pp. 385-389.
http://researchbank.rmit.edu.au/view/rmit:17702
Published Version
2012 Multi-Science Publishing Co. Ltd
http://dx.doi.org/10.1260/1708-5284.9.5.385
World Journal of
EngineeringWorld Journal of Engineering 9(5) (2012) 385-390
1. Introduction
Biomimetic approaches to materials design have
rapidly grown as has the potential to be explored
and expanded scientifically and technologically.
The term biomimetic is used to describe
engineering design that mimics or imitates nature.
Biomimetic materials are those where the
component materials, technique of preparation or
the microstructure are based upon naturally
occurring materials.
Compacted nanosilica-talc /calcium carbonate
polyacrylate composites prepared using
accelerated sedimentation
Norlinda Daud1,2, Robert A. Shanks1 and Ing Kong1,*
1School of Applied Sciences, RMIT University Box 2476 GPO, Melbourne, VIC 3001,
Australia
2Department of Chemistry, Faculty of Science and Mathematics, UPSI, 35900 Tg Malim,
Perak, Malaysia
*E-mail: ing.kong@rmit.edu.au
(Received 17 November 2011; accepted 12 August 2012)
Abstract
The effectiveness of centrifugation as the compacting method in preparing high filler
composites has been investigated. Different size and shape of fillers were used to ensure
efficient filler space filling. In situ polymerization of bisphenol-A ethoxy diacrylate after
centrifugating produced biomimetic composites with 74–86 % filler content. The filler space
was efficiently filled by using a combination of nano and microsize fillers, especially in the
nanosilica-CaCO3 composite. The morphology of the composites indicates that the fillers
were well dispersed and embedded in the polymer matrix. The etched surface of the
nanosilica-talc composite reveals that the combination of talc and nanosilica formed a
biomimetic composite that displayed an ordered brick-and-mortar nacre-like structure. The
wide-angle X-ray diffraction patterns indicate the crystal structure of CaCO3 and talc were
maintained in the composite.
Key words: Centrifugation; Composite, Nanosilica, Accelerated sedimentation
High performance natural composites, such as
nacre, demonstrate unparalleled combination of
strength, stiffness and toughness, which are attributed
to their intricate architectures. The excellent
mechanical properties of nacre originate from its
unique microstructure consisting of 95%·w/w
aragonite (CaCO3) platelets and interfacial organic
phase (Tushtev et al., 2008). The mineral platelets
are arranged layer-by-layer separated by thin layers
of biopolymer in a highly order brick-and-mortar
ISSN:1708-5284
386 Norlinda Daud et al./World Journal of Engineering 9(5) (2012) 385-390
structure. Artificial nacre-like layered organic-
inorganic composites have been prepared by several
techniques such as biomineralization, layer-by-layer
deposition, hot-press assisted slip casting (HASC)
and roll compaction (Luz and Mano, 2010; Chen et al.,
2008). Platelet fillers, for instance clay and talc are
often chosen because they consist of crystal sheets
of similar dimension as aragonite tablets.
Fabrication of high volume fraction mineral
composites usually results in a non-uniform
reinforcement distribution and porosity in the
matrix. The addition of nanoparticles to composites
generally improves their strength, modulus,
toughness, heat resistance and dimensional
stability. However, dispersion of the nanoparticles
can be problematic due to their tendency to remain
as aggregates or agglomerate, resulting in none of
the anticipated enhancement in mechanical
properties (Oberdisse, 2006).
The aim is to prepare and characterise,
nanoscopic silica and micro-size CaCO3 and talc
that are dispersed by ultrasonication. The filled pre-
polymer was very viscous, however centrifuging the
dispersion, including the initiator, maximized the
filler concentration.
2. Experimental study
2.1. Materials
Bisphenol-A ethoxy diacrylate (Ebecryl 150 from
UCB Chemicals) was used as received. The
amorphous fumed silica Aerosil 300 (Degussa,
Germany) used in this work has a silica content of 
> 99.8 %⋅w/w and average primary particle size of 7
nm. Calcium carbonate, CaCO3 (Omyacarb) with an
average particle size of 1.7 µm was obtained from
OMYA (Australia). Talc (T63A) was supplied by
Orica Chemicals (Australia). All fillers were dried in
an oven prior to use. Benzoyl peroxide and toluene
were used as received from Merck, Germany.
2.2. Composites preparation
A nanosilica (1 %⋅w/w) was mixed in the monomer
resin using impeller blade mechanical stirrer at 
300 rpm for 15 min, followed by dispersion using
ultrasonication for 15 min. CaCO3 or talc (24 %⋅w/w)
was then added and the dispersion was stirred for 
15 min at 300 rpm with ultrasonication for 15 min.
The suspension was degassed in vacuum until
entrapped bubbles were removed completely. An
initiator, benzoyl peroxide, (1 %⋅w/w), was dissolved
in toluene and mixed at 100 rpm for 2 min.
Immediately after mixing, the mixture was
centrifuged at 10,000 rpm for 15 min. The dispersion
was cured by slowly heating to 90 °C for 6 h in a
vacuum oven. The cured composite was removed
from the centrifuge tube and cut using a diamond saw
to form test specimens from the lower part of the cured
resin. The upper fraction contained less filler since the
filler had been compacted at the bottom of the tube
during centrifuging.
2.3. Characterization
The thermal decomposition temperature was
determined by thermogravimetry (TGA) using
Perkin-Elmer Pyris 1 thermogravimetric analyzer.
Samples of about 3.0 mg were heated from 50 to
850 °C at a heating rate of 10 K⋅min–1. The purging
gas (flow rate: 20 mL⋅min–1) was nitrogen from
50–700 °C, then it was changed to air at 700 °C. 
The surface morphology of the fractured and
etched composites was examined under a scanning
electron microscope (SEM), specifically a FEI Nova
NanoSEM (2007). A fractured sample was prepared
by submerging it in liquid nitrogen for 1 min and
then breaking it transversely with a rapid impact.
For the etched sample, the cross-sections of the
composites were cut, polished and then etched in a
solvent mixture of 8 mol⋅L−1 NaOH and methanol
(3:2 volume ratio) and stirred for 2 h. All samples
were gold-coated prior to scanning.
Wide-angle X-ray diffraction (WAXD) patterns
were recorded with a Bruker D8 Advance 
X-ray diffractometer with Cu Kα1 radiation (λ =
1.541 Å) in the 2θ range from 5° to 60°, in steps
of 0.02°.
3. Results and discussion
The composites were prepared by in situ
polymerization, in which the monomer was
polymerized in the presence of different filler
combinations. Given the preparation route, the
final filler composition in the prepared composites
had to be verified by TGA (Figure 1). The
degradation of the polymer occurred in two stages.
In the first stage, at temperatures between 50 to
700 °C, the weight loss of polymer (95.9%) is
attributed to the evaporation of moisture and
organic solvent, volatilization of low molecular
weight fragments and cleavage of the main chain
accompanied by the combustion of the cleaved
Norlinda Daud et al./World Journal of Engineering 9(5) (2012) 385-390 387
products. The second decomposition (4.1%) at
temperature > 700 °C is ascribed to the further
combustion or carbonization of organic compound
when air was introduced at 700 °C. No residue
remained at 850 °C.
Similarly, nanosilica- CaCO3 composite
decomposed in a two-stage process. The first stage of
weight loss in the composite (13.6%) at 50 to 650 °C
is attributed to the degradation of the polymer matrix
and the second weight loss (37.0%) is mainly due to
the loss of CO2 from the CaCO3 filler. The residue
remaining at 850 °C mainly contained CaO and silica.
Hence, the first weight loss was used to determine the
weight fraction of filler in the composites.
The nanosilica-talc composite decomposed in a
one-stage process. The decomposition is attributed
to the degradation of the polymer matrix. The
residue remaining at 850 °C (74.4%) contains talc
and nanosilica and was used to determine the
weight fraction of fillers in the composite. The
weight fraction of fillers in nanosilica-talc and
nanosilica-CaCO3 composites are 74.4% and 86.4%
respectively.
Thermal stability of the cured resin and its
composites were measured as the decomposition
at temperature of 10% weight loss (Td, 10%). The
Td, 10% for polymer, nanosilica-CaCO3 and
nanosilica-talc composites are 418 °C, 443 °C and
448 °C respectively. The high Td, 10% observed for
the composites is considered to be related to the
tortuous path of degradation products, which is
strongly related to the distribution of filler particles
in the resin. In addition, this increase in the thermal
stability could be attributed to the high thermal
stability of the fillers and the interaction between
the fillers and the polymer matrix. The fillers were
considered to be acting as a thermal barrier,
thereby protecting the polymer from degradation.
The effective barrier action of the talc layers
further enhances the thermal stability of the
composites.
The morphology of the nanosilica-CaCO3 and
nanosilica-talc composites are shown in Figure 2
0
20
40
60
80
100
50 250 450 650 850
Temperature/°C
W
ei
gh
t f
ra
ct
io
n/
%
(a)
(b)
(c)
Fig. 1. TGA curve of (a) polymer, (b) nanosilica-CaCO3
composite and (c) nanosilica-talc composite.
(a) Fractured surface
HV
10.0 kV
spot
3.5
WD
5.1 mm
mag
72 447 ×
det
TLD
2 µm
(b) Etched surface
HV
15.0k V
spot
3.5
WD
5.1 mm
mag
115 507 ×
det
TLD
1 µm
Fig. 2. SEM image of the nanosilica-CaCO3 composite.
Nanosilica CaCO3
Fig. 3. Schematic drawing of nanosilica and CaCO3 dispersion
in polymer matrix.
388 Norlinda Daud et al./World Journal of Engineering 9(5) (2012) 385-390
and Figure 4, respectively. The SEM micrograph
on Figure 2(a) confirms uniform distribution of the
nanosilica and CaCO3 particles in the composite.
The surface fracture of the nanosilica-CaCO3
composite shows that the fillers were well
dispersed and embedded in the polymer matrix.
The etched surface of the composite (Figure 2(b))
reveals small pores scattered evenly indicating that
the composite was effectively compacted. The
nanosilica is expected to fill the empty space
between the micro-size filler particles as illustrated
in Figure 3. Judging from the surface morphology,
sonication led to a good dispersion of fillers in
polymer matrix.
The SEM micrographs in Figure 4 reveal the
distribution and orientation of talc platelets in the
polyacrylate composite. Interestingly, the flake-
like talc particles were dispersed and oriented in
planes rather than randomly. The etched surface of
the composite exhibits a layered structure,
analogous to the nacre brick-and-mortar structure
as illustrated in Figure 5.
The results confirm that the talc platelets were
preferentially aligned in the centrifugal deposition
process, hence efficiently compacting the composite.
This finding is in agreement with another study that
discovered the automatic alignment of clay platelets
under centrifugal force (Chen et al., 2008). The
centrifugation technique is similar to natural
deposition of mineral in natural composites, except
that instead of gravity, centripetal force was used to
accelerate the sedimentation process.
Figure 6 shows the wide-angle X-ray diffraction
(WAXD) patterns of the polymer, CaCO3 and
nanosilica-CaCO3 composite. A large halo
obtained in polymer pattern at around 2θ = 20°
indicates the amorphous state of the cured resin.
The relatively high intensity of the Bragg
reflections is presented at the (104) plane (2θ = 29.5°)
for CaCO3 and nanosilica-CaCO3 composites,
which indicates that the CaCO3 is in the calcite form.
The position of the peaks in the composite did not
change, indicating the structure of the CaCO3
crystal was maintained in the composite. Similarly,
the structure of the talc crystal in the composite did
not change (Figure 7).
(a) Fractured surface.
HV
15.0 kV
spot
3.5
WD
5.0 mm
mag
65 944 ×
det
TLD
2 µm
(b) Etched surface.
HV
10.0 kV
spot
3.5
WD
5.0 mm
mag
90 786 ×
det
TLD
1 µm
Fig. 4. SEM image of the nanosilica-talc composite.
Nanosilica Talc
Fig. 5. Schematic drawing of ordered layered of nanosilica-talc
composite.
0 10 20 30 40 50 60
Scattering angle, 2θ/°
R
el
at
iv
e 
in
te
ns
ity
(a)
10
4
(b)
(c)
Fig. 6. Wide-angle X-ray diffraction (WAXD) pattern of 
(a) polymer, (b) nanosilica-CaCO3 composite and (c) CaCO3.
Norlinda Daud et al./World Journal of Engineering 9(5) (2012) 385-390 389
4. Conclusions
Centrifugation was applied to the fabrication of
nanosilica-talc and nanosilica-CaCO3 nanocomposites
as a compacting method. The filler space was
efficiently filled by using a combination of nano- and
micro-size fillers, especially in the nanosilica-CaCO3
composite. Centrifugation did not form layer-by-layer
structure. However due to the talc platelet crystals, the
nanosilica-talc composite displayed an ordered brick-
and-mortar nacre-like structure. The wide-angle 
X-ray diffraction pattern of nanosilica-CaCO3 and
nanosilica-talc composites confirmed that the
structure of talc and CaCO3 crystals were maintained
in the composite.
References
Chen R., Wang C., Huang Y. and Le Huirong, 2008. An
accelerated biomimetic process for artificial nacre with
ordered-nanostructure. Mater. Sci Eng., C 28, 218–222.
Luz G.M. and Mano J.F. 2010. Mineralized structures in nature:
examples and inspirations for the design of new composite
materials and biomaterials. Comp. Sci. Tech., 70: 1777–1788.
Oberdisse J., 2006. Aggregation of colloidal nanoparticles in
polymer matrices. Soft Matter 2, 29–36.
Tushtev K., Murck M. and Grathwohl G., 2008. .On the nature
of the stiffness of nacre. Mater. Sci. Eng., C 28, 1164–1172.
0 10 20 30 40 50 60
Scattering angle, 2θ/°
R
el
at
iv
e 
in
te
ns
ity
(a)
(b)
00
2
00
4
00
6
Fig. 7. Wide-angle X-ray diffraction (WAXD) pattern of 
(a) nanosilica-talc composite and (b) talc.



Compacted nanosilica-talic/calcium carbonate polyacrylate composites prepared using accelerated sedimentation

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