preparation and characterisation of nizn ferrite/multiwalled nanotubes thermoplastic natural rubber...

214 Int. J. Materials Engineering Innovation, Vol. 4, Nos. 3/4, 2013

Copyright © 2013 Inderscience Enterprises Ltd.

Preparation and characterisation of NiZn ferrite/multiwalled nanotubes thermoplastic natural rubber composite

Lih-Jiun Yu* and Sahrim Hj. Ahmad School of Applied Physics, Faculty of Science and Technology, University Kebangsaan Malaysia, 43600, Bangi, Selangor Darul Ehsan, Malaysia E-mail: [email protected] E-mail: [email protected] *Corresponding author

Ing Kong School of Applied Sciences, RMIT University, G.P.O. Box 2476, Melbourne, VIC 3001, Australia E-mail: [email protected]

Mouad A. Tarawneh and Moayad Husein Flaifel School of Applied Physics, Faculty of Science and Technology, University Kebangsaan Malaysia, 43600, Bangi, Selangor Darul Ehsan, Malaysia E-mail: [email protected] E-mail: [email protected]

Abstract: The NiZn ferrite and multiwalled nanotubes were mixed by the weight ratio of 1:1, then the mixture were incorporated into the thermoplastic natural rubber nanocomposite by melt blending process. The physical properties: thermal stability, magnetic properties, dynamic mechanical properties, and morphology of the obtained composites were investigated in the aspect of filler loadings effects. It was found that both NiZn ferrite and multiwalled nanotubes are well dispersed in the thermoplastic natural rubber matrix. The thermogravimetric analysis and vibrating sample magnetometer results indicate that the filler loading has improved the thermal stability and the magnetic properties of the composite. The dynamic mechanical test shows that the highest storage modulus was achieved by 8 wt% filler. Any further increment of the filler content leads to the formation of agglomerate, hence, affecting the dynamic mechanical properties.

Preparation and characterisation of NiZn ferrite/multiwalled nanotubes 215

Keywords: thermoplastic natural rubber; TPNR; polymer matrix composite; thermal stability; dynamic mechanical properties; magnetic properties; NiZn ferrite; multiwalled nanotubes; materials engineering.

Reference to this paper should be made as follows: Yu, L-J., Ahmad, S.H., Kong, I., Tarawneh, M.A. and Flaifel, M.H. (2013) ‘Preparation and characterisation of NiZn ferrite/multiwalled nanotubes thermoplastic natural rubber composite’, Int. J. Materials Engineering Innovation, Vol. 4, Nos. 3/4, pp.214–224.

Biographical notes: Lih-Jiun Yu is a PhD candidate in Materials Science from National University of Malaysia (UKM). She holds a BSc (Hons.) in Materials Science from National University of Malaysia in 2008. Her research interests during her Bachelor degree were in metallurgy, focused in the metallurgical polishing and stereology of the materials. At present, her current research interests are preparation and characterisation of polymeric materials, focusing in the polymer blends and nanocomposites, containing: magnetic nanoparticles, carbon nanotubes and the hybrids materials.

Sahrim Hj. Ahmad obtained his PhD from Loughborough University of Technology, UK in 1988 in Materials Physics. He was appointed as a Professor of Polymer and Composites in the School of Applied Physics, Faculty of Science and Technology, National University of Malaysia in 2002, and currently is the Dean of Faculty of Science and Technology. He has been involved as Head and Researcher in more than 27 research project funded by UKM, IRPA, MOSTE, ScienFund-MOSTI, FRGS-MOHE, MTSF, Yayasan Felda and SAGA-Akademi Sains Malaysia in the area of materials physics, polymer composites, polymer physics, advanced semiconductor packaging, and smart magnetic paper. So far he has published more than 100 papers in local and international journals. He also won three gold and seven silver medals at local and international exhibitions/competitions. He has supervised more than 50 Master and PhD students. His research interests are polymer physics, nanocomposites, magnetic polymer and polymer composite.

Ing Kong is a Postdoctoral Fellow of Polymer Science in School of Applied Science, RMIT University. She received both her BSc (Hons.) and PhD in Materials Science from National University of Malaysia in 2005 and 2009. Her research interests focus primarily on the processing and properties (mechanical, thermal, etc.) of polymeric materials, preparation and characterisation of functional polymer composites and nanocomposites containing magnetic nanoparticles, carbon nanotubes and graphene, natural fibre reinforced polymer composites and biodegradable polymer.

Mouad A. Tarawneh is working in the Department of Material Science, School of Applied Physics, Faculty of Science and Technology, The National University of Malaysia as a Research Assistant. He received his PhD in Material Science from National University of Malaysia, Malaysia 2010 and his Masters in Material Science from Mu’tah University, Jordan in 2002 and Bachelors in Physics from Mu’tah University, Jordan in 2002, and he has published papers in many national and international journals and his research interests are thermoplastic natural rubber, natural rubber, liquid natural rubber, mechanical and thermal properties of nanocomposites, nanoclay, nanoparticles, carbon nanotube also graphene.

Moayad Husein Flaifel is currently a PhD student in the Department of Material Science, School of Applied Physics, Faculty of Science and Technology, National University of Malaysia (UKM). He obtained his BSc and MSc in Physics from Aligarh Muslim University (AMU), India in 2001 and

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2003, respectively. He taught material science subject to undergraduate students for two years. His research interest is in the preparation, characterisation and applications of magnetic nanomaterials, polymer nanocomposite materials and magnetic polymer nanocomposite materials.

This paper is a revised and expanded version of a paper entitled ‘Morphology, thermal stability, and dynamic mechanical properties of NiZn ferrite/MWNT thermoplastic natural rubber composite’ presented at the 2nd Malaysia Polymer International Conference 2011 (MPIC2011), Universiti Kebangsaan Malaysia (UKM), 18–20 October 2011.

1 Introduction

The carbon nanotubes (CNTs) are allotropes of carbon. They look similar to the graphene sheets that are rolled into cylindrical shape. Multiwalled carbon nanotubes (MWNT) are formed when they are wrapped by layers of CNTs. The unique structure of CNTs and their outstanding mechanical and electrical properties have been extensively studied and reported since the discovery of CNTs in 1991. At present, there are various properties of CNTs and applications being explored, such as field emission properties (Darsono et al., 2008), thermal conducting properties (Che et al., 2000) and microwave absorbing properties (Kim et al., 2008). CNTs are used as a reinforcement filler, incorporated into various polymer matrices to enhance the mechanical properties and microwave absorbing properties (Ma et al., 2007; Makeiff and Huber, 2006). However, the microwave absorbing properties of CNTs are limited due to the absence of or very low magnetic loss mechanism in the CNTs. Thus, various strategies have been applied to the CNTs, in order to achieve the desired property. Surface modification of CNTs, coating CNTs with a metallic layer, and insertion of magnetic inclusion are the common strategies which have been done by the researchers (Harris, 1999).

NiZn ferrite, which has been extensively used in the electronics industry as electromagnetic suppression devices and transformers, was selected to be mixed with CNTs due to its excellent chemical and thermal stability as well as its high magnetisation property. The compounding of natural rubber (NR) and thermoplastic polyolefin, produced thermoplastic natural rubber (TPNR) composite. This TPNR, which exhibits intermediate properties between the NR and polyolefin, offers great reproducibility, flexibility in shaping and low production cost. In our study, TPNR was used as a matrix, and blended the hybrid fillers (magnetic nanoparticles and multiwalled nanotubes).

Apart from the microwave absorbing properties, the overall properties such as mechanical properties and thermal properties, should not be neglected. The dispersion behaviour of the nanofillers in the polymer matrices has become a crucial factor to achieve its optimum properties. The mechanical properties of nanocomposite reinforced by CNTs might be affected due to the entanglement of CNTs in its nature, which restricts the dispersion ability in the polymer matrices. In addition, the magnetic nanoparticles tend to agglomerate due to the magnetic interaction between them. Therefore, the difficulties in controlling the filler dispersion have increased, when producing a nanocomposite which consists both of CNTs and magnetic nanoparticles. In our study, we succeeded in producing a new nanocomposite with good filler dispersion. The effects of filler loading on thermal stability, magnetic properties and dynamic mechanical properties were investigated and reported.


2 Materials and methods

The powder form nickel zinc ferrite nanoparticles (Ni0.5Zn0.5Fe2O4), with 98.5% purity, average particle size 10–30 nm were supplied by the Nanostructured and Amorphous Materials Inc., USA. MWNT with 90% purity, average diameter 9.5 nm, and average length 1.5 μm were obtained from Nanocyl. The NR and polypropylene (PP) were supplied by the Rubber Research Institute of Malaysia (RRIM) and Mobile (M) Sdn. Bhd, respectively. Liquid natural rubber (LNR) was prepared by photosynthesised degradation of NR in visible light.

The TPNR was prepared by blending PP, NR, and LNR according to the weight ratio of 70:20:10, respectively. LNR was used as a compatibiliser in the mixture. The hybrid fillers of NiZn ferrite and MWNT were prepared according to the weight ratio 1:1. The powder to porcelain balls weight ratio of 1:10 for the hybrid fillers was mixed and ball-milled in a tubular mixing machine for 1 hour. The mixture of NiZnFe2O4/MWNT (H0) was then incorporated into the TPNR matrix by the melt blending technique. Various fillers loading (2–10 wt%) were incorporated into the TPNR by Thermo Haake internal mixer with a mixing speed of 100 r.p.m., at 180°C for 13 minutes. The outputs were then hot-pressed into a thin sheet using a hydraulic press at 185°C.

Field emission scanning electron microscopy (FESEM, Model: ZEISS-SUPRA 55V) was used to examine the fractured morphology of samples. Magnetisation measurements were carried out using a vibrating sample magnetometer, VSM (Model 7404), to obtain the M-H loop at room temperature (25°C). The thermal stability of the nanocomposites was measured by a thermal degradation analyser, TGA/STDA 581 (Mettler Toledo). The samples were degraded under a nitrogen flow at the heat rate of 20°C/min from 30–500°C. The storage modulus and tan δ were determined using a dynamic mechanical analyser (DMA-Perkin Elmer Pyris Diamond). The samples with the dimensions of 10 mm (l) × 10 mm (w) × 0.7 mm (t) were tested in a tensile mode from –100 to 100°C at a heating rate of 2°C/min and a frequency of 1 Hz.

3 Results and discussion

3.1 Morphological characterisation

Figures 1 and 2 show the fractured images of 2 wt% H0 nanocomposite and 10 wt% H0 nanocomposite, respectively. Both images reveal a good dispersion of hybrid fillers in the TPNR matrix. However, it is hard to distinguish the short protruding part of MWNTs with sphere shape NiZn ferrite nanoparticles as both look identical in Figure 1. Hence, the EDX characterisation was used to confirm the existence of the NiZn ferrite and MWNTs on the fractured surface. In Figure 2, it is clearly seen that the interparticle distance of fillers was minimised at high filler content (10 wt%), as compared to 2 wt% fillers in Figure 1. This indicates that the ability of nanofillers to disperse in TPNR matrix is reduced when the filler content increases. In Figure 2, there are a large amount of long cylinder shape MWNT fibres being pulled out from the TPNR matrix. It is possibly caused by the interfacial structural relaxation, due to the poor interfacial adhesion (poor

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wetting process) between MWNTs and TPNR matrix. The weakening of interfacial adhesion attributed to the entanglement of MWNTs by its Van der Waals forces, tending to reduce its in-contact surface area with TPNR matrices.

Figure 1 FESEM micrograph of 2 wt% H0 nanocomposite

Figure 2 FESEM micrograph of 10 wt% H0 nanocomposite


3.2 Magnetic properties

Saturation of magnetisation is achieved when all magnetic dipoles align in the direction of the magnetic field. The relationship between the saturation magnetisation of composite (MS) and weight fraction of magnetic fillers (Wf) has been studied by Makled et al. (2005) and Ramajo et al. (2009). They concluded that saturation magnetisation (MS) of the nanocomposite depends on the content of the filler with magnetic moments in a given mass fraction. The theoretical Ms values were calculated according to the equation: MS = MfWf, where Mf is the saturation magnetisation of ferrite. In Figure 3, the theoretical Ms values were compared with the experimental Ms values. The results indicate that both experimental and theoretical MS values are similar. Hence, we can consider that the overall distribution of fillers is good in the TPNR matrix, whereby consistent with the observation obtained in morphology characterisation.

Figure 3 Theoretical and experimental Ms values obtained from VSM (see online version for colours)

3.3 Thermal degradation

The thermal stability of H0 composites was studied by thermogravimetric analysis (TGA) as shown in Figure 4. The weight loss below 110°C is due to the water absorption of the fillers and TPNR matrix during the sample preparation process. It was found that the thermal degradation of TPNR and its nanocomposites takes place through a two-step process, significantly at decomposition temperatures of around 360°C and 440°C. The first decomposition temperature was attributed to the decomposition of the NR phases while the latter was attributed to the decomposition of the PP phases (Puryanti et al., 2007). The decomposition temperature of the TPNR affected the degree of crystallinity of the phases, whereas the amorphous phase (NR) provided more free volume to enable the molecules movement during the heating process. According to Menard (1999), as the temperature increases, the vibration of molecule chains increases, as does the kinetic energy. Subsequently, it has reduced the chain breaking activation energy. Therefore, the

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amorphous phases (NR) have a lower decomposition temperature as compared to the PP phases which are semi-crystalline. A previous report by Yu et al. (2012) has shown the degree of crystallinity of PP phase in TPNR is 0.47. In contrast, the relatively high crystalline oriented order molecules (H0 fillers), starts to decompose at a higher temperature, when the temperature exceeds 600°C (Datsyuk et al., 2008).

Figure 4 TGA curve for various filler content of TPNR and H0 nanocomposites (see online version for colours)

The thermal decomposition temperature of NR phases and PP phases of the nanocomposites was studied at the 10% weight loss and 50% weight loss of samples, denoted by T10 and T50, respectively (Table 1). The results revealed that the T10 and T50 shifted slightly towards the higher value, indicated that the addition of H0 fillers has increased in the thermal stability of the TPNR. A similar increasing trend of thermal stability behaviour upon the addition of fillers has been reported by Bikiaris et al. (2008), Chae and Kim (2007), Datsyuk et al. (2008) and Puryanti et al. (2007). According to Yang et al. (2005), the thermal stability depends on the physical-chemical adsorption between fillers and polymer decomposition products. The reactivity of polymer molecules chains is decreased when adsorption occurs between the fillers surface and the nearby polymer molecule chains. Since no surface treatment was done prior to the sample preparation process, the interfacial adsorption between the H0 fillers and TPNR was mainly contributed by the dispersive adhesion (Van der Waals forces). During the heating process, the existent of physical adhesion has reduced the polymer molecule chains vibration, thus delaying the releasing of TPNR decomposition products. As seen in the micrograph images in Figure 1 and 2, TPNR matrices surrounded by large number of MWNTs fibres at a higher filler content (10 wt% fillers), lead to a better barrier formation. The barrier effect hindered the degradation products to diffuse from the bulk of the polymer onto the gas phases (Bikiaris et al., 2008), thus improving the thermal stability of the nanocomposites. Furthermore, the role of MWNTs acts as a radical scavenger to terminate the free radical propagation, retarding the chain scissoring of the polymer upon thermal decomposition, hence, delaying the decomposition process (Zeng et al., 2006).


The weight loss of samples becomes uniform at the endset temperature (TT). At this temperature, most of the hydrocarbon molecules were decomposed into volatile products while some carbonised polymer fragment remained (Saini et al. 2009). The H0 nanocomposites with high TPNR content (low filler content) exhibits higher TT, due to more thermal energy being required to decompose the larger amount of TPNR hydrocarbon molecules. The remaining residual at 500°C is a mixture of the non-combustible fillers and leftover polymer fragments that are inert to the thermal decomposition. The residual weight percentage as shown in Table 1, is similar to the initial filler loading weight percentage, further supporting the point of overall good H0 fillers distribution in TPNR matrix, as discussed in morphology characterisation. Table 1 Characteristic temperatures obtained from TGA analysis

Nanocomposite T10 (°C) T50 (°C) TT (°C) Residual weight (%)

TPNR 365.5 441.5 483.0 0.97 2wt% H0 367.0 442.5 482.5 2.05 4wt% H0 368.0 445.5 481.0 4.06 6wt% H0 368.0 447.0 480.5 5.55 8wt% H0 369.0 448.0 480.5 7.74 10wt% H0 370.5 450.5 480.0 9.83

3.4 Dynamic mechanical properties

The temperature dependence of storage modulus (E’) of H0 nanocomposite was showed in Figure 5. It can be observed that, at a fixed temperature (–80°C), the addition of H0 fillers (with high aspect ratio of MWNTs and large surface area of the NiZn ferrite) has induced higher E’ values, except for 10 wt%. The increment stiffness of the nanocomposite is attributed to the effective load transfer from the TPNR matrices to the fillers, resulting from the good dispersion of fillers in the matrix (Diez-Pascual et al., 2009). The E’ value of 10 wt% H0 nanocomposite did not present the highest among the samples, its E’ value is approaching the E’ value of 2 wt% nanocomposite. This phenomenon could be explained by the formation of large aggregate fillers at very high filler content, causing phase separation and hence reducing the interfacial area which enables effective load to transfer from the TPNR matrix to the filler.

The tan δ is a ratio of loss modulus and storage modulus, showed in Figure 6. Along the studied temperature (–100 to 100°C), the tan δ peak value of the H0 nanocomposites is higher than the corresponding tan δ peak value of TPNR. This indicates that the H0 filler addition to the TPNR matrices has increased the hysteresis loss of the TPNR. The applied energy was dissipated via particle-particle friction, fibre-fibre friction and fibre-matrix interaction, and finally, dissipated as heat energy. The corresponding glass transition temperature (Tg) of the TPNR and the H0 nanocomposites was identified from the tan δ peak position, as listed in Table 2. It can be seen that there are two glass transition temperatures shown by TPNR. The first Tg (–59.80°C) is the Tg for NR, while the latter (11.43°C) is the Tg for PP. Similar observation was reported by Ibrahim and Dahlan (1998), where TPNR consists of two glass transition temperatures. The shifting of both Tg values to the lower temperature when H0 fillers were first incorporated into the TPNR implies the increment of the TPNR chain segment mobility. The TPNR chain

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segment, which adsorbs near to the surface of the filler, tends to move relative to the filler’s surface upon the applied stress. This slippery effect helps to distribute the stress to the neighbouring molecules, and hence, strengthens the matrices phases (Hanafi, 2000). However, the increment of H0 filler loading led to the increment of Tg values. This indicated that the addition of fillers loading has reduced the free volume of the TPNR molecule chains, restricting the molecular mobility (Sui et al., 2008).

Figure 5 Temperature dependence of storage modulus of TPNR and H0 nanocomposites (see online version for colours)

Figure 6 Temperature dependence of tan delta of TPNR and H0 nanocomposites (see online version for colours)


Table 2 Characteristic temperatures obtained from Tan δ peak

Nanocomposite Tg1 (°C) Tg2 (°C)

TPNR –59.80 11.43 2wt%H0 –73.82 –1.58 4wt% H0 –73.08 –0.92 6wt% H0 –70.17 1.09 8wt% H0 –68.80 5.34 10wt% H0 –68.80 8.27

4 Conclusions

The TPNR nanocomposites with pre-mixed H0 filler (NiZn ferrite and MWNTs) were prepared by the melt blending process. The addition of the filler had a positive impact on the thermal stability, magnetic properties, and enhanced the stiffness of the nanocomposites. From the observation of morphology, the fillers were well dispersed in the TPNR matrix at 2 wt% filler. Larger filler aggregation occurs at higher filler content and leads to the degradation of the dynamic mechanical properties, once the filler content exceeds 8 wt%.

Acknowledgements

The authors would like to thank the Ministry of Science, Technology and Innovation (MOSTI) for the National Science Fund (NSF) scholarship and the Polymer Research Group from RMIT University for technical support.

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preparation and characterisation of nizn ferrite/multiwalled nanotubes thermoplastic natural rubber...

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