Nucleation Ability of Multiwall Carbon Nanotubes in
Polypropylene Composites
E. ASSOULINE,
1
A. LUSTIGER,
2
A. H. BARBER,
1
C. A. COOPER,
1
E. KLEIN,
3
E. WACHTEL,
3
H. D. WAGNER
1
1
Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel
2
ExxonMobil Research and Engineering, Route 22 East, Annandale, New Jersey 08801
3
Chemical Services Unit, Weizmann Institute of Science, Rehovot 76100, Israel
Received 1 July 2002; revised 30 October 2002; accepted 20 November 2002
ABSTRACT: The nonisothermal crystallization of multiwall carbon nanotube (MWNT)/
isotactic polypropylene (iPP) nanocomposites was investigated. The results derived
from the differential scanning calorimetry curves (onset temperature, melting point,
supercooling, peak temperature, half-time of crystallization, and enthalpy of crystalli-
zation) were compared with those of neat iPP. The data were also processed according
to Ozawa’s theory and Dobreva’s approach. These results and X-ray diffraction data
showed that the MWNTs acted as -nucleating agents in iPP. Accordingly, MWNT/iPP
was significantly different from neat iPP: A fibrillar morphology was observed instead
of the usual spherulites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41:
520 –527, 2003
Keywords: poly(propylene) (PP); carbon nanotubes; nanocomposites; crystallization;
morphology
INTRODUCTION
Nanometer-scale reinforcing particles have stim-
ulated great interest in the field of composite ma-
terials, and they may replace traditional fibers as
fillers in polymer matrices because of their high
aspect ratio (surface/area ratio) and low density.
The most common nanoreinforcements are inor-
ganic clay minerals consisting of silicate lay-
ers.
1–4
The favorable mechanical properties of
multiwall carbon nanotubes (MWNTs; tensile
modulus 1 TPa,
5,6
compressive strength 150
GPa
5,7
and tensile strength = 11– 63 GPa
6
) have
made them very attractive for use in nanocompos-
ites. Their influence on macroscopic mechanical
properties is still controversial. For instance, in
the case of poly(methyl methacrylate),
8
the im-
pact strength was significantly improved by even
small amounts of single-wall nanotubes (SWNTs),
whereas the tensile modulus was insensitive to
their presence and to that of MWNTs. Conversely,
the tensile modulus of polystyrene,
9
isotactic
polypropylene (iPP),
10
and polypropylene fibers
11
was shown to increase when reinforced with
MWNTs.
The mechanical properties of a crystalline poly-
mer are affected by its morphology, which is itself
influenced by the kinetics of crystallization.
Therefore, the kinetics of crystallization of iPP
were studied under nonisothermal conditions as a
function of the cooling rate and the presence or
absence of MWNTs. Because of the nanoscale size
of the filler, the growth rate could not be esti-
mated as for microscopic fibers.
12
Therefore, over-
all measurements were performed, as for other
Correspondence to: H. D. Wagner (E-mail: daniel.wagner@
weizmann.ac.il)
Journal of Polymer Science: Part B: Polymer Physics, Vol. 41, 520 –527 (2003)
© 2003 Wiley Periodicals, Inc.
520