World Journal Of Engineering
PREPARATION AND PROPERTIES OF MAGNETITE–CARBON NANOTUBE
REINFORCED POLYPROPYLENE–NATURAL RUBBER BLENDS
Ing KONGa, Robert SHANKSa, Sahrim AHMADb, Lih-Jiun YUb
School of Applied Sciences, RMIT University, PO BOX 2476V, Melbourne, VIC 3001, Australia
b
School of Applied Physics, Faculty of Science and Technology, UKM, 43600 Bangi, Selangor, Malaysia
*Email: [email protected]
a
commercial suppliers in powder form (Nanostructured &
Amorphous Materials, Inc., USA). Natural rubber (NR)
and polypropylene (PP) were supplied by Rubber
Research Institute of Malaysia (RRIM) and Mobile (M)
Sdn Bhd, respectively. Liquid natural rubber (LNR) was
prepared by the photosynthesized degradation of NR in
visible light.
Introduction
Carbon nanotube (CNT) applications have received
continuous growing interest since CNT were discovered
in 1991 [1]. In recent years, many efforts have been
made towards decorating CNTs with different materials.
Especially CNTs coated or filled with magnetic
nanoparticles have recently attracted considerable
interest due to their excellent microwave absorbing
characteristics. The microwave absorbance of CNTs has
been limited by its small magnetic loss. To optimize the
performance of CNTs in radar absorbing materials, it is
important to create hybrid CNTs with magnetic
nanoparticles, which display both dielectric and
magnetic losses [2]. However, most recent research has
focused on CNT–magnetic materials hybrids, and few
studies are reported on the properties of CNT–magnetic
material hybrid reinforced polymer composites.
The aim was to prepare composites of thermoplastic
polypropylene–natural rubber (TPNR) and CNT–Fe3O4
hybrids using a combined ball-milling and melt-blending
technique. Objectives included functionalizing the CNTs
with Fe3O4, preparing TPNR-CNTs/Fe3O4 composites
and determining the contribution of acid treatment of
CNTs to microstructure and magnetic properties of the
composites.
Preparation of nanocomposites
CNTs were dispersed in a round-bottomed flask
containing HNO3 solution with the aid of ultrasonic
water bath for 1 h. The solution was refluxed at 80 °C
with vigorous mixing for 24 h. The acid-treated CNTs
were collected by centrifugation, and then they were
dried at 80 °C for 24 h. From the treatment in boiling
nitric acid, the MWCNTs were broken into shorter and
straighter forms with open ends, as presented in Figure
1(b). The acid-treated CNTs were mixed with Fe3O4
nanoparticles at a weight ratio of 1:1 for 1 h in a ballmilling apparatus. The porcelain balls in the mill were
15 mm in diameter and 11 g in mass. The ball to powder
weight ratio was 10:1. To further disperse the CNTs–
Fe3O4 hybrid in the polymer matrix, CNTs–Fe3O4 hybrid
and PP pellets were pre-treated prior to a melt-blending
process. After that, the mixture was melt-blended by
using laboratory mixer (Model Thermo Haake 600p).
The weight ratio of PP, NR and LNR was 70:20:10 with
the LNR as the compatibilizer for the mixture. Blending
was carried out with a mixing speed of 100 rpm at
180 °C for 13 min.
Experimental
(a)
Characterization
The microstructure of the samples was measured using
an X-ray diffraction (XRD) technique (Bruker D8
Advance) with CuKα1 radiation (λ = 1.541 Å) in the 2θ
range from 5° to 80°, in steps of 0.02°. The samples for
the magnetic measurements were made into a disc shape
5 mm in diameter. The magnetic properties were
measured by using a vibrating sample magnetometer
(Model VSM 7404) at room temperature. The
measurements were carried out in a maximum external
field of 12 kOe. The external field was applied parallel
to the sample.
(b)
Figure 1 Images of (a) pristine CNTs and (b) acid-treated CNTs.
Materials
CNTs with an average diameter 9.5 nm, average length
1.5 μm and purity of 90 % were provided by Nanocyl, as
shown in Figure 1(a). Fe3O4 nanoparticles, with particle
size ranging from 20-30 nm, were obtained from
591
World Journal Of Engineering
the MS of the composites with CNTs Fe3O4 hybrid is
mainly attributed to the existence of Fe3O4 nanoparticles.
In addition, the effect of acid treatment of CNTs on the
magnetic property of CNTs and CNT Fe3O4 was studied.
As can be seen from Figure 3, samples with acid-treated
CNTs show higher MS and MR than those with untreated
CNTs. This phenomenon can be explained by the
agglomerations of untreated CNTs, which results in
decreasing magnetic property of the composite.
Results and Discussion
(511)
Figure 3 Hysteresis loops of TPNR containing 2 %·w/w filler with
different formulations.
(511)
(311)
(311)
(220)
(220)
The XRD patterns of TPNR containing 2 %·w/w filler
with different formulations are shown in Figure 2.
Comparison of the XRD patterns reveals no significant
difference between TPNR filled with untreated and acidtreated CNTs. The XRD patterns of the composites
comprise of two phases, which are the semi-crystalline
and crystalline phases. The semi-crystalline TPNR phase
for all the composites display characteristic diffraction
peaks at 2θ= 14.1°, 16.7°, 18.5° and 21.8°, which can be
assigned to the respective (1 1 0), (0 4 0), (1 3 0) and
(1 1 1) planes of the α-phase crystals of polypropylene.
This implies that the addition of filler in TPNR matrix
does not change the crystal structure of the neat TPNR.
Similar results have been reported by other researchers
[3]. For the TPNR filled with untreated and acid-treated
CNTs–Fe3O4, there are characteristic peaks at 2θ= 30.3°,
35.6° and 57.2°, which can be assigned to (2 2 0), (3 1 1)
and (5 1 1) planes of Fe3O4, respectively (JCPDS 011111). This also indicates that the structure of Fe3O4 in
the nanocomposites is maintained.
Table 1 Magnetic properties of nanocomposites.
Samples
UCNT
TCNT
UCNT–Magnetite
TCNT–Magnetite
MS
(emu/g)
0.027
0.038
0.581
0.622
MR
(emu/g)
0.004
0.006
0.082
0.088
HC
(Oe)
126.90
111.68
99.015
95.019
Conclusion
Figure 2 XRD patterns of TPNR containing 2wt% filler with different
formulations.
The TPNR-CNTs–Fe3O4 composites were successfully
prepared by a combined ball-milling and melt-blending
technique. The XRD results reveal that the acid
treatment of CNTs does not influence the structure of
TPNR and Fe3O4 nanoparticles, while the acid-treated
CNTs alter the magnetic property of the composites.
This can be attributed to the disentanglements of CNTs
by acid treatment that results in better magnetic property.
Figure 3 depicts the hysteresis loops of the samples,
which are the typical loops of a soft magnet. Saturation
magnetization (MS), remanence (MR) and coercive force
(HC) for all samples are listed in Table 1. Generally, the
MS of composites decreases while the HC of composites
increases with increasing the CNTs content. The MS of
composites filled with CNTs is almost negligible. Hence,
592
World Journal Of Engineering
References
[1] Iijima, S. "Helical microtubules of graphitic carbon",
Nature 354 (1991): 56-58.
[2] Haiyan Lin, Hong Zhu, Hongfan Guo, Liufang Yu.
“Microwave-absorbing properties of Co-filled
carbon nanotubes”, Materials Research Bulletin 43
(2008): 2697-2702.
[3] S.P.Bao, S.C. Tjong. "Mechanical behaviors of
polypropylene/carbon nanotube nanocomposites:
The effects of loading rate and temperature."
Materials Science and Engineering A 485 (2008):
508-516.
593