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DOI : 10.2240/azojono0106

Multi-Wall Carbon Nanotubes/Natural Rubber Nanocomposite

Muataz Ali Atieh, Nazlia Girun, Fakhru’l-Razi Ahmadun, Chuah Teong Guan, El-Sadig Mahdi and Dayang Radia Baik

Submitted: August 5th, 2005

Posted: November 29th, 2005

Topics Covered

Abstract

Introduction

Carbon Nanotubes

Carbon Nanotubes as Reinforcements in Composite Materials

Multi-Walled Carbon Nanotube-Based Nanocomposites in This Study

Experimental

Dispersion of Nanotubes

Dissolution of the Rubber

Mixing of Rubber with Nanotube Solution

Pressing and Testing The Sample

Results and Discussion

Production of Multi Wall Carbon Nanotubes (MWCNTs)

SEM Characterization

TEM Characterization

Carbon Nanotube/Natural Rubber Nanocomposites

TEM Observations

Effect of CNTs on the Stress-Strain value of Natural Rubber

Effect of CNTs on the Young’s modulus of SMR CV 60.

Effect of CNTs on the Energy Absorption of SMR CV 60

Conclusion

Acknowledgement

References

Contact Details

Abstract

A floating catalyst chemical vapor deposition (FC-CVD) method was designed and fabricated to produce high quality and quantity carbon nanotubes. The design parameters like the hydrogen flow rate; reaction time and reaction temperature were optimized to produce high yield and purity of Multi Wall Carbon Nanotubes (MWCNTs). Multi-Walled Carbon Nanotubes (MWNTs) were used to prepare natural rubber (NR) nanocomposites. Our first efforts to achieve nanostructures in MWNTs/NR nanocomposites were formed by incorporating carbon nanotubes in a polymer solution and subsequently evaporating the solvent. Using this technique, nanotubes can be dispersed homogeneously in the NR matrix in an attempt to increase the mechanical properties of these nanocomposites. The properties of the nanocomposites such as tensile strength, tensile modulus, elongation at break and hardness were studied.  Mechanical test results show an increase in the initial modulus for up to 12 times in relation to pure NR. In addition to mechanical testing, the dispersion state of the MWNTs into NR were studied by Transmission Electron Microscopy (TEM) in order to understand the morphology of the resulting system.

Introduction

Research on new materials technology is attracting the attention of studies all over the world. Developments are being made to improve the properties of the materials and also to find alternative precursors that can bestow desirable properties on materials. Great interest has recently developed in the area of nanostructured carbon materials. Carbon nanostructures are becoming of considerable commercial importance with interest growing increasingly rapidly over the decade or so since the discovery of buckminsterfullerene, carbon nanotubes, and carbon nanofibers.

Carbon Nanotubes

Carbon nanotubes (CNTs) exhibit unique mechanical, electronic and magnetic properties, which have caused them to be widely studied [1-3]. CNTs are probably the strongest substances that will ever exist with a tensile strength greater than steel, but only one sixth the weight of steel [4].  Iijima (1991) first discovered carbon nanotubes (CNTs) using arc discharge method [5,6]. Following this discovery, a number of scientific research projects have been initiated and a variety of methods have been used to synthesize CNTs, namely, arc discharge, laser vaporization [7] and catalytic chemical vapor deposition of hydrocarbons [8-10]. Since carbon–carbon covalent bonds are one of the strongest in nature, a structure based on a perfect arrangement of these bonds oriented along the axis of nanotubes would produce an exceedingly strong material. Nanotubes are strong and resilient structures that can be bent and stretched into shapes without catastrophic structural failure in the nanotube [11, 12].  The Young's modulus and tensile strength rival that of diamond (1 Tera Pascal and ~200 Giga Pascal, respectively) [13].

Carbon Nanotubes as Reinforcements in Composite Materials

This fantastic property of mechanical strength allows these structures to be used as possible reinforcing materials. Just like current carbon fiber technology, these nanotubes reinforce would allow very strong and light materials to be produced. These properties of CNTs attracted the attention of scientists in all over the world because their high ability for absorbing the load which is applied to nanocomposite materials [11-13].

Multi-Walled Carbon Nanotube-Based Nanocomposites in This Study

Multi-walled carbon nanotubes (MWNTs) will be used to prepare natural rubber (NR) nanocomposites. Our first effort to achieve nanostructures in MWNTs/NR nanocomposites will be formed by incorporating nanotubes in a polymer solution and subsequently evaporating the solvent. Using this technique, nanotubes will be dispersed homogeneously in the NR matrix in an attempt to increase the mechanical properties of these nanocomposites. The properties of the composites such as tensile strength, tensile modulus and elongation at break were studied.

Experimental

The FC-CVD reactor has been designed to produce CNF & CNT. The production of carbon nanofibers/ nanotube in the present work has been conducted in a horizontal tubular reactor. The horizontal reactor is a quartz tube of 50 mm in diameter and 900 mm in length, heated by silicon carbide heating element. Two conical flasks connected to each other with an insulated plastic tube, one of them for the hydrocarbon source and the other one for the catalyst source were placed before the tubular reactor. They were connected to the reactor through a stainless steal pipe. The flask, which contains the catalyst, was placed on a heating mantel with a temperature controller. Two types of gases were used in this system, hydrogen was used as a reacting gas and the argon for flashing the air from the system, and both of them were controlled by a flow meter. One condenser was placed after the reactor to cool down the gas outlet temperature and entrapped materials as shown in the schematic diagrams and picture in figure 1.

AZoNano - Nanotechnology - Schematic diagram of modified FC-CVD.

Figure 1. Schematic diagram of modified FC-CVD.

The carbon nanotubes were added to natural rubber as a filler. The natural rubber, which was used in this study, is a Standard Malaysian Rubber Constant Viscosity 60 (SMR CV 60). The preparation of the nanocomposites was carried out by using a solvent casting method using toluene as a solvent. The added amounts of the carbon nanotubes were 1, 3, 5, 7 and 10 wt % of 10 grams of the total weight.

The process of making natural rubber/nanotubes as nanompcosite material divided into the four following processes.

Dispersion of Nanotubes

This phase involves the dissolution/dispersion of CNTs in a solvent (in this case, toluene) in order to disentangle the nanotubes that typically tend to cling together and form lumps, which become very difficult to process.  For this, a certain quantity of carbon nanotubes or nanofibers was added to a specific amount of toluene solution after carefully weighing (in order to maintain a specific weight ratio of nanotubes in the solution). This solution was further sonicated using a mechanical probe sonicator (Branson sonifier), capable of vibrating at ultrasonic frequencies in order to induce an efficient dispersion of nanotubes or nanofibers. For this study, different CNT solutions were prepared (containing CNTs in various weight ratios):

i)        1 wt% CNTs containing in 10ml of toluene solution

ii)      3 wt% CNTs in 10ml of toluene solution

iii)     5 wt% of CNTs in 10ml of toluene solution

iv)    7 wt% CNTs in 10ml of toluene solution

v)     10 wt % CNTs in 10ml of toluene solution.

Dissolution of the Rubber

This stage involves the dissolution of the Rubber in a suitable organic solvent (toluene). A specific amount of rubber (in this case, 10 gms) weighed using a balance was added to a certain quantity of organic solvent (500 ml of toluene) thereby maintaining a desired rubber weight ratio. This mixture was stirred and kept for certain duration of time until the rubber became uniformly dissolved in the solvent. 

Mixing of Rubber with Nanotube Solution

This is the final step in the melt preparation process and basically involves thorough mixing of the solutions prepared in the first and second stages, resulting in a solution that consists of a good blend of nanotubes in the rubber.

Pressing and Testing The Sample

The nancomposite material (rubber with CNTs) was pressed using hot press and cut into standard shapes. The samples were then characterized and mechanical properties measured.

Results and Discussion

Production of Multi Wall Carbon Nanotubes (MWCNTs)

In this research work, MWCNTs were produced by using floating catalyst chemical vapor deposition (FC-CVD). To produce these carbon materials, carbon atoms bond together in the presence of iron (Fe) catalyst.

The iron (Fe) catalyst, in particle form was obtained from decomposition of the ferrocene. The carbon atoms produced from the cracking of benzene C6H6 served as the raw materials. The product was collected from the wall of the reactor and the ceramic boats, which were placed at the center of the reaction chamber. The study of the effects of each key parameter on the yield, purity, average diameter and distribution of the carbon material are discussed, however greater emphasis were placed on CNTs and to a lesser extent CNFs because of their industrial importance and wider applicability. The production conditions of pure CNTs have been fixed at reaction temperature 850°C, hydrogen flow rate 300 ml/min and reaction time 45min. The diameters of the CNTs were varied from 2 nm to 30 nm and the average length was at 70 µm.

SEM Characterization

The resultant carbon nanotubes were characterized extensively using SEM. Figure 1 shows typical SEM images of carbon nanotubes. High purity, carbon nanotube array were observed in figure 1. The SEM observation shows that these carbon nanotubes are tens of microns long (up to 50 micron) with uniform diameters. The bulk morphology of the long carbon nanotubes are film like and oriented. However, the images indicate that the products are clean except for some nanoparticle impurities.

AZoNano - Nanotechnology - SEM Images of carbon nanotubes reaction temperature 850°C, hydrogen flow rate 300 ml/min and reaction time 45min.

AZoNano - Nanotechnology - SEM Images of carbon nanotubes reaction temperature 850°C, hydrogen flow rate 300 ml/min and reaction time 45min.

Figure 2. SEM Images of carbon nanotubes reaction temperature 850°C, hydrogen flow rate 300 ml/min and reaction time 45min.

TEM Characterization

TEM was carried out to characterize the structure of nanotubes (Figure 2). To prepare TEM samples, some alcohol was dropped on the nanotubes film, then, these films were transferred with a pair of tweezers to a carbon-coated copper grid.

The TEM images of nanotubes are presented in figure 3(a). It is obvious, from the images that all the nanotubes are hollow and tubular in shape. In some of the images, catalyst particles can be seen inside the nanotubes. TEM images indicate that the nanotubes are high purity, with uniform diameter distribution and contain no deformity in the structure. While figure 3(b) shows the High Resolution Transmission Electron Microscope (HRTEM) of the carbon nanotubes. It shows that a highly ordered crystalline structure of CNT is present. The clear fringes of graphitic sheets are well separated by 0.34 nm and aligned with a tilted angle of about 2° toward the tube axis.

AZoNano - Nanotechnology - TEM images of CNTs at Low resolution

AZoNano - Nanotechnology - TEM images of CNTs at High resolution.

Figure 3. TEM images of CNTs (a) Low resolution (b) High resolution.

Carbon Nanotube/Natural Rubber Nanocomposites

In this research work, carbon nanotubes were employed as an interface nano-reinforcement in an advanced commercial carbon/rubber composite and this is the first time such work has been reported. Theoretical predictions of the mechanical properties of carbon nanotubes as described above, in particular their predicted high strengths (of the order of 60 GPa) and modules (~1 TPa), make them attractive candidates as a reinforcement filler material in polymer based structural composites. Initial experimental work on carbon nanotube-reinforced CNT-NR has demonstrated that large increase in effective modulus and strength can be obtained with the addition of small amounts of carbon nanotubes.

TEM Observations

The dispersion of CNTs in the SMR CV60 was characterized by using Transmission Electron Microscopy (TEM). A thin section of about 100 nm was cut with a diamond knife at -120°C to observe the dispersion of CNTs inside the rubber. In figure, 4(a) short and long CNTs are seen. It was shown in this figure that the CNTs are homogenously distributed in the SMR CV60 matrix. However, the CNTs are open at both ends during the dispersion of the CNTs into the toluene, using ultrasonic frequency vibration and during the mixing of CNTs in the SMR CV60 by mechanical stirring. The distance between the CNTs in the matrix is wide and that makes them well oriented with little interface interaction between them. The size of the CNTs in the TEM shows varying diameter from 2-20nm and varying length, which can be either short or long. Figure 4(b) shows the image of a 3 wt % CNTs, dispersed in the matrix, the orientations of the CNTs in the SMR CV60 had become less oriented and more random. The figure also shows that the CNTs are open at the end. Figure 4(c, d and e) shows the CNTs in the SMR CV 60 at 5, 7, and 10 wt % respectively. The figures also indicate that the orientation of the CNTs plays a very important role in the stress and strain of the matrix. Another factor considered important on the mechanical properties is the aspect ratio; if the aspect ratio is high the strength of the material will increase.

AZoNano - Nanotechnology - TEM image of CNTs in SMR CV60,  1 wt % of CNTs and 3 wt % of CNTs.

AZoNano - Nanotechnology - TEM image of CNTs in SMR CV60 at 5 wt % of CNTs and 7 wt % of CNTs.

AZoNano - Nanotechnology - TEM image of CNTs in SMR CV60 with 10 wt % of CNTs.

Figure 4. TEM image of CNTs in SMR CV60 (a) 1 wt % of CNTs (b) 3 wt % of CNTs (c) 5 wt % of CNTs (d) 7 wt % of CNTs and (e) 10 wt % of CNTs.

The stress-strain curve of different percentages of pure carbon nanotube (1, 3, 5, 7 and 10 wt % of CNTs) with SMR CV60 is presented in figure 5. The tensile strength radically increases as the amount of CNTs concentration increases.  The general tendency is that the stress level is increased by the addition of CNTs which plays the role of reinforcement. From these results, it is deduced that the reinforcing effect of CNTs is very marked. As the CNT content in the rubber increases, the stress level gradually increases but at the same time the strain of the nanocomposites decreases.

AZoNano - Nanotechnology - Stress-strain of SMR CV60 with different percentage of CNTs.

Figure 5. Stress-strain of SMR CV60 with different percentage of CNTs.

The increased level of stress was due to the interaction between the CNTs and the rubber. A good interface between the CNTs and the rubber is very important for a material to withstand the stress. As described above CNTs are extremely strong materials compared to other types of fillers, thus making them good candidates as nanofillers. Under load, the matrix distributes the force to the CNTs which carry most of the applied load.

Effect of CNTs on the Young’s modulus of SMR CV 60.

The same phenomenon was observed for Young’s Modulus. The young’s modulus of the composites normalized with that of the pure matrix is presented in figure 6. The result indicated that the Youngs Modulus increased with an increase in the amount of the CNTs in the formulation. However, at 1 and 3 wt % of CNTs, the increment of the modulus is not as high as that of the tensile strength. The same value of the modulus and the tensile strength were observed at 5 wt % of CNTs. While at 7 and 10 wt % the modulus was higher than the tensile strength.

AZoNano - Nanotechnology - Young Modulus of SMR CV60 at different percentage of CNTs.

Figure 6. Young Modulus of SMR CV60 at different percentage of CNTs.

Effect of CNTs on the Energy Absorption of SMR CV 60

Figures 7 shows the toughness of the nanocomposite and considers the amount of energy required to fracture a material. The figure shows that, by increasing the amount of CNTs into the SMR CV60 the energy of absorption needed to fracture the material increases. Since strength is proportional to the force needed to break the sample, and strain is measured in units of distance (i.e., the distance the sample is stretched), then strength times strain is proportional to force times distance which in turn equals to energy i.e.:

Strength × strain ~ force × distance = energy

AZoNano - Nanotechnology - Shows the toughness as function of wt % of CNTs.

Figure 7. Shows the toughness as function of wt % of CNTs.

In general, stress increases with the amount of CNTs from 1-10 wt %. This therefore implies an increase in the energy required to fracture the material. However there was an insignificant decrease in strain at 1 and 3 wt % implying that the ductility was virtually preserved at these percentages. The observed decrease in strain shown in the figure from 5-10 wt % has no effect on the overall strength of the carbon nanotubes due to the much higher increase in stiffness. As shown in the figure the energy of absorption at 1,3,5,7 and 10 wt % shows a general trend of increase in stiffness with increase in energy, which is 0.24, 0.38, 4.7, 10 and 24 J respectively compared to the pure which is 0.12 J. This increase can be attributed to the reinforcing property of carbon nanotubes which in turn increases the strength of the rubber.

Conclusion

In summary, we have demonstrated the successful fabrication of nanocomposite consisting of Natural Rubber matrix with 1-10 wt % Multi walled carbon nanotubes (MWCNTs). Carbon nanotubes were applied for interface nano-reinforcement in advanced commercial carbon/rubber composite and this is the first attempt such a work is reported. The preparation of the nanocomposites was carried out by a solvent casting method using toluene as a solvent. It is clear from the figure that the maximum stress of pure SMR CV60 is 0.2839 MPa. When 1wt % of CNTs were added to the rubber the stress level for the nanocomposite material increased from 0.2839 MPa to 0.56413 MPa. Addition of the wt % CNTs to the natural rubber increased the stress level gradually as shown in figure 5. At 10 wt % of CNTs the stress value obtained reached 2.55 MPa which is 9 times that of pure natural rubber. The result indicates that, by increasing the amount of CNTs added into the rubber the ductility decreased and the material become stronger and tougher but at the same time more brittle. The clear trend observed here is that as nanotube load increases, the fiber breaking strain decreases. It also shows that the highest strain value was obtained for the nanocomposite at 1wt % of the CNTs. This composite at this percentage is more ductile and more elastic compared to other percentages of CNTs. The strain value at 1wt % was almost the same as for pure rubber. Minimum strain value was obtained at 10 wt % of CNTs; the strain value decreased almost 2.5 times i.e.  2.94 compared to pure rubber which was 7.34.

Acknowledgement

The authors gratefully acknowledge the national intensification of research in priority areas (IRPA) for their financial support of this research. 

References

1.       Dresselhaus, M. S., Dresselhaus, G., Eklund, P. C. Science of fullerenes and carbon nanotubes; Academic Press: San Diego, (1996).

2.       Wong, E. W.; Sheehan, P. E., Lieber, C. M. Nanobeam mechanics: Elasticity, strength, and toughness of nanorods and nanotubes. Science 277, 1971-1975, (1997).

3.       Treacy M.M.J., Ebbesen T.W. and Gibson J.M., “Exceptionally high Young's modulus observed for individual carbon nanotubes”, Nature 381, 678, (1996).

4.       Iijima S., Helical microtubules of graphitic carbon. (1991) Nature 354 p.56.

5.       Saito R., Dresselhaus G., and Dresselhaus M.S. Physical Properties of Carbon Nanotubes, London: Imperial College Press, 1-4 (1999).

6.       Scott C.D., Arepalli S., Nikolaev P. and Smalley R.E., “Growth Mechanisms for Single-Wall Carbon Nanotubes in a Laser-Ablation Process”, Applied Physics A 72, 573-80 (2001).

7.       Ebbesen, T. W.; Ebbesen, T. W., Ed, In Carbon nanotubes: Preparation and properties, CRC Press: Boca Raton, p. 139-162 (1997).

8.       Andrews R., Jacques D., Rao A. M., Derbyshire F., Qian, D., Fan, X., Dickey E. C. and Chen J., Continuous production of aligned carbon nanotubes: A step closer to commercial realization, Chem.Phys. Lett. 303, p. 467-474 (1999).

9.       Falvo M.R., Clary G.J., Taylor II R.M., Chi V., Brooks Jr F.P., Washburn S. and Superfine R., “Bending and buckling of carbon nanotubes under large strain”, Nature 389  582-84, (1997).

10.    Dalton A.B., Collins S., Munoz E., Razal J.M., Ebron V.H., Ferraris J.P., Coleman J.N., Kim B.G. and Baughman R.H., “Super-tough carbon-nanotube fibres”, Nature 423, p. 703 (2003).

11.    Dujardin E., Ebbesen T. W., Krishnan A., Yianilos P. N., and, Treacy M. J., “Young's Modulus of Single-Walled Nanotubes”, Physical Review B 58(20)  14013-14019 (1998).

12.    Baughman R.H., Zakhidov A.A. and Heer W.A. “Carbon nanotubes - The route toward applications”, Science 279, 787-92 (2002).

13.    Qian, D., Dickey, E. C., Andrews, R., Rantell, T., “Load transfer and deformation mechanisms in carbon nanotube-polystyrene composites”,. Appl. Phys. Lett. 76, 2868-2870 (2000).

Contact Details

Muataz Ali Atieh
Department of Chemical and Environmental Engineering
University Putra Malaysia
43400, UPM, Serdang
Malaysia

motazali@hotmail.com

Nazlia Girun
Department of Chemical and Environmental Engineering
University Putra Malaysia
43400, UPM, Serdang
Malaysia

Fakhru’l-Razi Ahmadun
Department of Chemical and Environmental Engineering
University Putra Malaysia
43400, UPM, Serdang
Malaysia

Chuah Teong Guan
Department of Chemical and Environmental Engineering
University Putra Malaysia
43400, UPM, Serdang
Malaysia

El-Sadig Mahdi
Department of
Aerospace Engineering
University Putra Malaysia
43400, UPM, Serdang
Malaysia

Dayang Radia Baik
Department of Chemical and Environmental Engineering
University Putra Malaysia
43400, UPM, Serdang
Malaysia

 

Date Added: Nov 29, 2005 | Updated: Jun 11, 2013
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