Multiwalled carbon nanotubes-magnetite reinforced

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on the magnetic and dynamic mechanical properties of thermoplastic polypropylene-natural rubber (TPNR) nanocomposites was evaluated. The effect of acid ...
Multiwalled carbon nanotubes-magnetite reinforced thermoplastic polypropylenenatural rubber blends by Ing Kong, Robert Shanks, Sahrim Ahmad and Lih-Jiun Yu reprinted from

WORLD JOURNAL OF ENGINEERING VOLUME 9 NUMBER 6 2012

MULTI-SCIENCE PUBLISHING COMPANY LTD.

World Journal of

World Journal of Engineering 9(6) (2012) 463-468

Engineering

Multiwalled carbon nanotubes-magnetite reinforced thermoplastic polypropylenenatural rubber blends Ing Kong1,*, Robert Shanks1, Sahrim Ahmad2 and Lih-Jiun Yu2 1School

of Applied Sciences, RMIT University, GPO BOX 2476, Melbourne, VIC 3001, Australia 2School of Applied Physics, Faculty of Science and Technology, UKM, 43600 Bangi, Selangor, Malaysia *E-mail: [email protected] (Received 28 January 2012; accepted 19 October 2012)

Abstract The effect of multiwalled carbon nanotubes (MWCNTs)-magnetite (Fe3O4) hybrid content on the magnetic and dynamic mechanical properties of thermoplastic polypropylene-natural rubber (TPNR) nanocomposites was evaluated. The effect of acid treatment of MWCNTs on the properties of nanocomposites has also been examined. TPNR/fillers nanocomposites were prepared via a Thermo Haake internal mixer using melt blending method with ball-milling technique as a pre-mixed process. The acid treatment successfully shortened the lengths and disentangled the crowds of MWCNTs. The improved dispersion of acid-treated MWCNTsFe3O4 in TPNR matrix and the enhanced interfacial adhesion between acid-treated MWCNTs-Fe3O4 and TPNR matrix increased the magnetic and dynamic mechanical properties. Acid-treated MWCNTs-Fe3O4 filled TPNR shows 10% improvement in storage modulus over neat TPNR due to the fine dispersion of MWCNTs in the TPNR matrix. Key words: Carbon nanotubes, Magnetite, Dynamic mechanical properties, Magnetic properties

1. Introduction Carbon nanotubes (CNTs) applications have received continuous growing interest since CNTs were discovered in 1991 (Iijima, 1991). In recent years, many efforts have been made towards decorating CNTs with different materials (Aderemi et al., 2010; Jain and Wilhelm, 2007; Lin et al., 2007; Zhang et al., 2008; Lv et al., 2008). Especially CNTs coated or filled with magnetic nanoparticles have recently attracted considerable interest due to their excellent microwave absorbing characteristics. The

ISSN:1708-5284

microwave absorbance of MWCNTs 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 (Haiyan et al., 2008). However, most recent research has focused on CNTs-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 TPNR and MWCNTs-Fe3O4 hybrids

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Ing Kong et al./World Journal of Engineering 9(6) (2012) 463-468

using a combined ball-milling and melt-blending technique. Objectives included functionalizing the MWCNTs with Fe3O4, preparing TPNR-MWCNTsFe3O4 composites and determining the contribution of acid treatment of MWCNTs to microstructure, magnetic and dynamic mechanical properties of the nanocomposites.

2. Experimental 2.1. Materials MWCNTs 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 commercial suppliers in powder form (Nanostructured and Amorphous Materials, Inc., USA). The TEM micrograph of Fe3O4 nanoparticles is shown in Figure 2. These (a)

Closed end

100 nm

(b)

Open end

100 nm

Fig. 1. TEM micrographs of (a) pristine MWCNTs and (b) acid-treated MWCNTs.

100 nm

Fig. 2. TEM micrograph of the Fe3O4 nanoparticles.

particles are polydisperse and some of them agglomerated due to magneto-dipole interactions between particles. 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. 2.2. Preparation of nanocomposites MWCNTs 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 stirring for 24 h. The acid-treated MWCNTs 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 MWCNTs were mixed with Fe3O4 nanoparticles at a weight ratio of 1:1 for 1 h in a ball-milling 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 MWCNTs-Fe3O4 hybrid in the polymer matrix, MWCNTs-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 600 p). 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.

Ing Kong et al./World Journal of Engineering 9(6) (2012) 463-468

2.3. Characterization The microstructure of the samples was measured using an X-ray diffraction (XRD) technique (Bruker D8 Advance) with CuKa1 radiation (λ = 1.41Å) 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. Dynamic mechanical analysis (DMA) properties were measure with Perkin Elmer Pyris Diamond DMA. DMA tests were carried out in tensile mode at a fixed frequency of 1 Hz. A rectangular sample with a dimension of 10 mm × 10 mm × 0.7 mm was cut and submitted to a temperature sweep from −120° to 100°C at 2°C · min−1.

3. Results and discussion 3.1. Structure The XRD patterns of TPNR containing 2%·w/w filler with different formulations are shown in Figure 3. Comparison of the XRD patterns reveals no significant difference between TPNR filled with untreated and acid-treated MWCNTs. The XRD patterns of the composites comprise of two phases,

10

(511)

(311) (311)

TCNT TCNT/Magnetite

(511)

(220) (220)

Intensity (a.u.)

UCNT UCNT/Magnetite

20

30 40 2 Theta (degree)

50

60

Fig. 3. XRD patterns of TPNR containing 2%·w/w filler with different formulations.

465

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 (110), (040), (130) and (111) 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. For the TPNR filled with untreated and acid-treated MWCNTsFe3O4, there are characteristic peaks at 2θ = 30.3° , 35.6° and 57.2°, which can be assigned to (220), (311) and (511) planes of Fe3O4 respectively (JCPDS 01-1111). This also indicates that the structure of Fe3O4 in the nanocomposites is maintained. 3.2. Dynamic mechanical analysis Figure 4(a) and (b) show the storage modulus (E′) and loss modulus (E″) versus temperature for nanocomposites with 2%·w/w filler at a frequency of 1 Hz. With increasing temperature, all the curves show three distinct regions: a glassy high modulus region where the segmental mobility is restricted at very low temperature, a transition zone where a substantial decrease in the E′ values and the physical properties change drastically and a rubbery region where a drastic decay in the modulus with temperature. It can be noted that, at low temperature, modulus of the nanocomposites is high. All samples show transition and a plateau region corresponding to NR and PP. The storage modulus then decreases with increasing temperature and levels off at high temperature. The two-step curves are due to two-phase morphology indicating the blend between the phases is incompatible. The results are in agreement with those of systems based on blends of nylon copolymer-EPDM rubber and blends of PP-EPDM (Komalan et al., 2007; KargerKocsis and Kiss, 1987). The storage modulus at −90°C is summarized in Table 1. TPNR filled with acid-treated MWCNTs has the highest storage modulus while the TPNR containing untreated MWCNTs has the lowest. This is probably due to the fine dispersion of the acidtreated MWCNTs in the TPNR matrix which enhanced the interaction between functional groups of MWCNTs and the polymer chains. The storage modulus for TPNR containing untreated MWCNTs-

Ing Kong et al./World Journal of Engineering 9(6) (2012) 463-468

466 (a)

Table 1. Dynamic mechanical parameters of nanocomposites at 1 Hz

20 18

Storage modulus (GPa)

16

UCNT UCNT/Magnetite TCNT TCNT/Magnetite

Tg (°C) NR phase PP phase

Samples UCNT TCNT UCNT-Magnetite TCNT-Magnetite

14 12 10

–77.0 –75.8 –75.1 –76.8

E′ at −90°C (GPa)

–3.63 –5.65 –5.99 –6.69

16.3 18.5 16.5 17.7

8 6

0.7 UCNT UCNT/Magnetite 0.6 TCNT 0.5 TCNT/Magnetite

4 2

0.4 0

20

40

60

80 100

Temperature (°C) (b)

1.6 1.4

0.3 Magnetization (emu/g)

0 −120−100 −80 −60 −40 −20

0.2 0.1 −12 −10 −8

Loss modulus (GPa)

1.2

−6

−1E−15 −4 −2 0 −0.1

4

2

6

8

10

12

−0.2 −0.3 −0.4

1

−0.5 −0.6

0.8

−0.7 Field (kOe)

0.6

Fig. 5. Hysteresis loops of TPNR containing 2%·w/w filler with different formulations.

0.4 0.2 0 −120−100 −80 −60 −40 −20

0

20

40

60

80 100

Temperature (°C)

Fig. 4. Dynamic mechanical analysis of nanocomposites: (a) storage modulus and (b) loss modulus versus temperature.

Fe3O4 is relatively low. This can be attributed by the agglomeration tendency of Fe3O4 nanoparticles due to the strong magneto-dipole interactions between particles (Kong et al., 2010), which weaken the adhesion of polymer molecules on nanofillers surface. 3.3. Magnetic properties Figure 5 depicts the hysteresis loops of the nanocomposites, 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 2. Generally, the MS of

composites decreases while the HC of composites increases with increasing the MWCNTs content. The MS of composites filled with MWCNTs is almost negligible. Hence, the MS of the composites with MWCNTs- Fe3O4 hybrid is mainly attributed to the existence of Fe3O4 nanoparticles. In addition, the effect of acid treatment of MWCNTs on the magnetic property of MWCNTs and MWCNTsFe3O4 was studied. As can be seen from Figure 5, samples with acid-treated MWCNTs show higher

Table 2. Magnetic properties of nanocomposites Samples UCNT TCNT UCNT-Magnetite TCNT-Magnetite

MS (emu/g)

MR (emu/g)

HC (Oe)

0.027 0.038 0.581 0.622

0.004 0.006 0.082 0.088

126.90 111.68 99.015 95.019

Ing Kong et al./World Journal of Engineering 9(6) (2012) 463-468

MS and MR than those with untreated MWCNTs. This phenomenon can be explained by the agglomerations of untreated MWCNTs, which results in decreasing magnetic property of the composite.

4. Conclusions The TPNR-MWCNTs-Fe3O4 composites were successfully prepared by a combined ball-milling and melt-blending technique. The XRD results reveal that the acid treatment of MWCNTs does not influence the structure of TPNR and Fe3O4 nanoparticles, while the acid-treated MWCNTs alter the magnetic and dynamic mechanical properties of the nanocomposites. This can be attributed to the disentanglements of MWCNTs by acid treatment that results in uniform dispersion and strong interaction between acid-treated MWCNTs and polymer chains.

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