폴리프로필렌 나노 복합체의 제조와 점탄성에 관한 연구
김종관, 이승종
서울대학교 응용화학부
A study on the preparation of polypropylene nanocomposite and its
viscoelastic properties.
Jongkwan Kim and Seung Jong Lee
School of Chemical Engineering, Seoul National University
Introduction
Recently the nanocomposites prepared from polymer and inorganic clay have attracted
interest from researchers since they frequently exhibit unexpected hybrid properties
synergistically derived from two components. To prepare the nanocomposite, we need to get
homogeneous dispersion of clay layers in polymer matrix. Since the silicate layers of clay
have polar hydroxy group, polymer matrix also should have polar group which interact with
silicate layer to make clay dispersed in polymer. However, polypropylene (PP) does not
include any polar group in its backbone, copolymer with polar OH groups as a compatibilizer
is necessary for making PP nanocomposite. Kawasumi et al.[1] have recently reported a
method to prepare a PP nanocomposite using maleated polypropylene. From processing and
application points of view, the rheological properties of these nanocomposites are very
important. In this paper, we focus on the thermal stability and the viscoelastic behavior of the
nanocomposite.
Experimental Section
Organically modified montmorillonite, Cloisite 20A that has an organic salt: dimethyl
dihydrogenated tallow ammonium was provided by Southern Clay Products. PP was supplied
by Daelim Industrial Company, has a melt flow rate of 6.0 g/min, Mw of 127000, and Mn of
13000. MAPP, Polybond 3150 (melting point 160 oC, melt flow rate 5 g/min at 230oC) from
Uniroyal chemical is also used to prepare the nanocomposite.
1 wt % nanocomposite was prepared by mixing 28 g of PP, 12 g of MAPP and 0.41 g
of clay in a Haake mixer for 10 minutes at 180oC and 50 RPM. The compositions of samples
prepared in this study were provided in Table 1. X-ray diffraction (XRD) was carried out
using a Rigaku D/MAX-IIIC X-ray diffractometer. Thermogravimetric analysis (TGA) of
unfilled polymer blend and nanocomposites was performed with TGA 2050 of TA
Instruments. Oscillatory shear measurements and steady shear tests were performed on an
Advanced Rheometrics Mechanical Spectrometer (ARES) with a parallel plate fixture.
Result and Discussion
Clay powder shows a 001 peak at 2=3.6o corresponding to an interlayer spacing of
d=24.1Å (Figure 1). The nanocomposites show no clay peak. Absence of 001 and
subsequent peaks is interpreted as defoliation of clay layers into the polypropylene matrix.
From TGA analysis (Figure 2) the nanocomposite shows delayed decomposition
compared to the unfilled polymer blend. From the TGA data, it is clear that the
nanocomposite exhibits higher thermal stability compared to unfilled polymer blend. Some
works[2-4] attributed the increased thermal stability to hindered out-diffusion of the volatile
decomposition products. It may be attributed to the nanometer level dispersion and special
geometry (high aspect ratio) of the clay nanocomposite[4].
The steady shear viscosity (Figure 3) is enhanced considerably at low shear rates, and
increases with clay loading. Furthermore, the nanocomposites display a shear thinning
behavior at low shear rates while the polymer wherein a low shear rate Newtonian plateau is
observed. The onset of shear thinning in viscosity shifts to lower shear rate at higher clay
loading. It thus appears that the interaction between the polymer and the silicate sheets alters
the relaxation dynamics of the polymer[5].
The linear viscoelastic response was measured by the storage and loss moduli (G’ and
G’’, respectively) for the unfilled polymer blend and nanocomposites. Both G’ (Figure 4) and
G’’ (not shown here) show an increase with clay loading at all frequencies. Terminal zone
slopes were estimated for all samples at frequencies below 10 rad/s and reported Table 2. The
terminal zone dependence of G’ and G’’ for nanocomposites shows nonterminal behavior
with power law dependencies for G’ and G’’ much smaller than the usual 2 and 1,
respectively. Furthermore, there also appears to be a gradual decrease in the power law
dependence of G’ and G’’ with increasing clay loading. The nonterminal behavior at lower
frequency observed in nanocomposite could be attributed to the retardation of molecular
relaxation process produced by the tethering of one end of polymer chain and clay surface[6].
Nonterminal low frequency rheological behavior has also been observed in ordered
block copolymers and smetic liquid crystalline polymer[7,8]. Larson et al.[8] in the study on
smectic small molecules and ordered block copolymers has suggested that the nonterminal
low frequency response is due to the ordered structure and the presence of defects. Thus, it
can be expected that a certain relation between the nanocomposite and the block copolymer
exist. The study on analogy between the microstructure of nanocomposite and that of block
copolymer is still our on-going project.
Conclusions
The nanocomposite offers an improved thermal stability compared to unfilled polymer.
This improvement arises due to the molecular level dispersion of clay in polymer matrix and
the unique geometry of clay. The end-tethered structure of the nanocomposite also increases
the steady shear viscosity. The power law dependence in the low frequency region decreases
as the concentration of the clay increases. Similarities of the rheological response of the
nanocomposite and block copolymer and liquid crystalline polymer are also introduced.
References
(1) Kawasumi, M.; Hasegawa N.; Kato, M.; Usuki, A.; Okada, A. Macromolecules 1997, 30,
6333.
(2) Burnside, S. D.; Giannelis, E. P. Chem. Mater. 1995, 7, 1597.
(3) Yano, K.; Usuki, A.; Okada, A.; Kurauchi, T.; Kamigaito, O. J. Polym. Sci., Part A:
Polym. Chem. 1993, 31, 2493.
(4) Doh, J. G.; Cho, I. Polym. Bulletin 1998, 41, 511.
(5) Krishnamoorti, R.; Vaia, R. A.; Giannelis, E. P. Chem. Mater. 1996, 8, 1728.
(6) Krishnamoorti, R.; Giannelis, E. P. Macromolecules 1997, 30, 4097.
(7) Koppi, K. A.; Tirrell, M.; Bates, F. S.; Almdal, K.; Colby, R. H. J. Phys. II (Paris) 1993, 2,
1941.
(8) Larson, R. G.; Winey, K. I.; Patel, S. S.; Watanabe, H.; Bruinsma, R. Rheol. Acta 1993, 32,
245.
Table 1. Compositions of the prepared hybrids
1
w
t
%
C
l
a
y
3
w
t
%
C
l
a
y
Intesiy
sample
PP/MAPP
blend
1 wt % Clay
3 wt % Clay
5 wt % Clay
C
l
o
i
s
i
t
e
2
0
A
Composition, weight (g)
PP
MAPP
Clay
28
12
0
28
28
28
12
12
12
0.41
1.24
2.11
5
w
t
%
C
l
a
y
1
2
3
4
5
6
7
8
9
1
0
2



d
e
g
r
e
e

Figure 1. XRD curves for clay and
nanocomposites.
1
2
0
1
0
0
Table 2. Terminal slopes of G’ and G’’ vs. 
8
0
G’
1.46
G’’
0.94
1.23
0.79
0.55
0.90
0.78
0.67
6
0
Weight(%)
sample
PP/MAPP
blend
1 wt % Clay
3 wt % Clay
5 wt % Clay
4
0
U
n
f
i
l
l
e
d
P
o
l
y
m
e
r
5
w
t
.
%
C
l
a
y
2
0
0
2
0
0
1
0
0 2
0
0 3
0
0 4
0
0 5
0
0 6
0
0
o
T
e
m
p
e
r
a
t
u
r
e
(
C
)
Figure 2. TGA traces for unfilled polymer
blend and 5wt% clay nanocomposites.
4
1
0
5
1
0
U
n
f
i
l
l
e
d
P
o
l
y
m
e
r
1
w
t
%
C
l
a
y
3
w
t
%
C
l
a
y
5
w
t
%
C
l
a
y
3
1
0
4
1
0
Viscoty(Pa.S)
3
1
0
2
1
0
U
n
f
i
l
l
e
d
P
o
l
y
m
e
r
1
w
t
%
C
l
a
y
3
w
t
%
C
l
a
y
5
w
t
%
C
l
a
y
StorageMdulsG'(Pa)
2
1
0
1
1
0
1
1
0
1
1
0
0
1
0
1
1
0
1
1
0
1
S
h
e
a
r
R
a
t
e
(
S
)
0
1
0
1
1
0
2
1
0
3
1
0
F
r
e
q
u
e
n
c
y
(
r
a
d
/
s
e
c
)
Figure 3. Steady shear viscosity
Figure 4. Storage modulus (G’) for unfilled
as a function of shear rate for
polymer blend and nanocomposites. All
unfilled
measurements were carried out at 200oC
polymer
blend
nanocomposites at 200oC
and
with 4% of strain