Advanced Materials Research Vols. 87-88 (2010) pp 363-368 © (2010) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.87-88.363
Preparation and electrical conductivity of composites of PA66 filled with carbon nanotubes Fang-Chang Tsai1,2,a*, Peng Li1,2,b, Xiao-Peng Shang1,2,c, Ning Ma1,2,d, Lung-Chang Tsai3,e and Jen-Taut Yeh1,2,f 1
Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, Wuhan, China 2
Faculty of Material Science and Engineering, Hubei University, Wuhan 430062, China
3
Graduate School of Environment and Safety Engineering, National Yunlin University of Science and Technology, Yunlin 640, Taiwan, China a*
[email protected],
[email protected],
[email protected], d
[email protected],
[email protected],
[email protected]
Keywords: multi-walled carbon nanotubes; PA66; carboxyl-modified; electrical conductivity
Abstract. An investigation of the blend of PA66 / organic modified multi-wall carbon nanotubes (MWNT) is reported. The MWNT was carboxylated in a sulfuric and nitric mixed acid under ultrasonic vibration. In fact, the electrical conductivity of these composites is analyzed. The MWNT-filled PA66 shows percolation point of the electrical conductivity at low filler loadings (0.5-12wt%). Presumably, the carboxylated MWNT was reacted with PA66. The neat MWNT, carboxlyated MWNT, and PA66/MWNT composites were characterized with FTIR, polarity, DSC, and electrical conductivity. Introduction Interest in clusters or nanoparticles with properties distinct from those of individual atoms and molecules or bulk matter has been widespread [1]. Polyamide resin, regarded as the most widely used engineering plastics, has advantages of excellent mechanical properties, wear resistance, acid and alkaline resistance, self-lubricity. Polyamide resin is used as injection and extrusion molding material, mainly in machinery, instrument, automobile, and textile industries. Polyamide will also play an important role in bearings, gears, fan blades, automobile components, medical appliance, oil pipes, gasoline tanks, electronics and electrical products. Due to disadvantages of bad water resistance and dimensional stability, its application is badly limited. However, few studies have probed the composition of two kinds of all-organic composite approaches were used to fabricate high dielectric constant polymer composites [2]. One approach is to use the percolation phenomena observed in polymer/conductive polymer composites [2-4]. Carbon nanotubes are theoretically ideal reinforcing materials for high-performance composites and own a range of potential application due to its extraordinary structure and performance. Carbon nanotubes have superior mechanical properties. In carbon nanotubes, there are three basic forces between carbon atoms, including: strong δ bonds; π bonds between C-C; interaction forces between
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the different layers of multi-walled nanotubes. All of these forces play an important role in the mechanical properties of carbon nanotubes. Theories and experiment results show that carbon nanotubes have really high plastic modulus (up to 1 TPa, 10-100 times of strengths of steel). The axial young's modulus experimental value of multi-walled carbon nanotubes is up to 200~4000 GPa. Extensive work has been done to characterize CNTs, including their exceptional mechanical [5-7], thermal [8-10] and electrical characteristics [11-13]. The main objective of this study is to investigate the blending, rheological and tensile properties of PA 66/MWNT blends. The blending properties of PA 66/ MWNT blends prepared with varying compositions were investigated. In fact, by using proper PA66/ MWNT compositions, PA 66/MWNT series specimens exhibit significantly better electrical conduction than PA 66 specimen. Materials and sample preparation The PA 66 and multi-wall carbon nanotube (MWNT) used in this study was obtained from DuPont and Nanotechnologies Port Co., Ltd, Shenzhen, China wherein PA66 and MWNT had a trade name of 101L and MWNT is an S.MWNTs-4060. The modified MWNT was prepared by sulfuric and nitric mixed acid under ultrasonic vibration. The compositions of the modified MWNT and PA 66/MWNT series specimens prepared in this study are summarized in Table 1 and 2, respectively. Table 1 Compositions of modified MWNT specimens MWNT Compositions B0 B1 B2 B3 B4 B5
Treated by mixed acid (hours) 0 1 2 4 6 8
Treated by mixed acid and H2O2 (hours) 0 0.5 1 2 3 4
Table 2 Compositions of PA 66/ MWNT film specimens Compositions PA66 PA6699.5/CNTb30.5 PA6699.0/CNTb31 PA6697.0/CNTb33 PA6695.0/CNTb35 PA6688.0/CNTb312 MWNT
PA66 (wt%) 100.0 99.5 99.0 97.0 95.0 88.0 0.0
CNTs (wt%) 0.0 0.5 1.0 3.0 5.0 12.0 100.0
Fourier transform infrared spectroscopy (FT–IR) Typical Fourier transform infrared spectra (FT-IR) of PA66 and PA66/MWNT series specimens were recorded on a Nicolet Avatar 320 FT-IR spectrophotometer at 25°C, wherein 32 scans with a spectral resolution 1 cm-1 were collected during each spectroscopic measurement. Infrared spectra of the film specimens were determined by using the conventional KBr pellet technic.
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Polarity The polarity of pure MWNT and modified MWNT specimens were determined at 25 °C and 50% relative humidity for 30 minutes using by ultrasonic vibration with toluene/pure water solution, and then, the solution standing storage for 12 hours. Thermal properties The thermal properties of PA66 and PA66/MWNT series samples were determined at 25 °C and 50% relative humidity using a TA Q100 differential scanning calorimetry (DSC), respectively. All scans were carried out at a heating rate of 10°C/min and under flowing nitrogen of a flow rate of 50ml/min. The instrument was calibrated using pure indium. Samples weighing about 10mg were placed in standard aluminum sample pans for each DSC experiment. The samples were rapidly heated at a heating rate of 40°C/min and kept at 250°C for 3 minutes in order to eliminate any residual crystals. The fully melted samples were then cooled at a rate of 10°C/min, until the crystallization was completed. The melting temperatures of the samples were determined by heating the specimens to 250°C at a rate of 10°C/min. Surface resistivity properties Results and Discussion Fourier transform infrared spectroscopy (FT–IR) Typical FT-IR spectra of modified MWNT samples are shown in Fig. 1. The distinguished absorption bands of modified MWNT specimens centered at 960 and 1645 cm-1, are most likely corresponding to the motions of O-H out-of-plane bending and C(=O)-O stretching, respectively. Presumably, this formation of carboxylated-grafted-MWNT copolymers through the reaction of carboxylate anion groups of MWNT molecules during the reactive extrusion of carboxylated MWNT.
Fig. 1 FT-IR spectra of modified MWNT specimens determined at 25 °C Polarity Typical photograph of the polarity of pure MWNT and modified MWNT specimens are summarized in Fig. 2. As a result of these specimens was suspension in the water. Apparently, these specimens are hydrophilic group. However, as shown in Fig. 2c, more clearly photograph of MWNT specimens were suspension in the toluene/pure water solution. Presumably, the CNTb3
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specimens of modified MWNT specimens can be even smaller than that of the other modified MWNT specimens, because their carboxyl structures are more symmetric and perfect for the formation of inter- and intramolecular hydrogen bonding in their amorphous regions. It is interesting to note that the results suggest that CNTb3 specimens are advantageous in the disperser PA66 resin. It is, therefore, the compositions of the PA66/MWNT series specimens prepared in this study are summarized in table 2.
Fig. 2 The photograph of the polarity of pure MWNT and modified MWNT specimens Thermal properties DSC thermograms of isothermally crystallized PA66 and PA66x/CNTb3y resins are summarized in Fig. 3. Only a single exothermic was found on each DSC thermogram of PA66, PA6699.5/CNTb30.5, PA6699.0/CNTb31,PA6697.0/CNTb33, and PA6695.0/CNTb35 specimens. A main crystallization exothermic with the peak temperature at around 209.62°C was found on the DSC thermograms of PA66 resins. After reactive extrusion with the CNTb3 resin, the peak crystallization temperature corresponding to the main crystallization exothermic of MWNT increase slightly to about 234.86 °C (see Fig. 3b). In fact, the peak temperature of the MWNT increases significantly from 209.62 to 237.95°C as the weight ratios of MWNT to PA66 increase. Table 3 summarized the peak crystallization temperatures and melting temperatures of these isothermally crystallized specimens. For instance, the supercooling degree values (△T) of PA66x/CNTb3y specimens increase only slightly from 1 to 3wt% as their MWNT contents decreasing from 29.84 to 23.34°C. However, the melting endotherm of MWNT present in PA66x/CNTb3y specimens can be attributed to the decreasing as their MWNT contents increase (see Fig. 4). The isotherms observed for PA66, PA6699.5/CNTb30.5, PA6699.0/CNTb31, PA6697.0/CNTb33, and PA6695.0/CNTb35 specimens are attributed to the crystallization exothermic and melting endothermic of PA66 crystals crystallized during their isothermally crystallization pr°Cesses.
Fig. 3 DSC thermograms of non-isothermal crystallization of (a) PA66, (b) PA6699.5/CNTb30.5, (c) PA6699.0/CNTb31, (d) PA6697.0/CNTb33 and (e) PA6695.0/CNTb35
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Table 3
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Values of crystallization and melting temperatures of PA66 and PA66x/CNTb3y specimens
Compositions PA66 PA6699.5/CNTb30.5 PA6699.0/CNTb31 PA6697.0/CNTb33 PA6695.0/CNTb35
Crystallization temperature (°C) 209.62 234.86 234.10 237.95 234.96
Melting temperatures (°C) 264.25 262.17 263.94 261.29 263.51
Supercooling degree (°C) 54.63 27.31 29.84 23.34 28.55
Fig. 4 DSC thermograms of non-isothermal melting of (a) PA66, (b) PA6699.5/CNTb30.5, (c) PA6699.0/CNTb31, (d) PA6697.0/CNTb33 and (e) PA6695.0/CNTb35. Surface resistivity properties Fig. 5 summarized the evaluated surface resistivity properties of PA66x/CNTb3y specimens. The surface resistivity values of PA66x/CNTb3y specimens tend to increasing with increasing treated by CNTs contents.
Fig. 5 Surface resistivity of PA66x/CNTb3y specimens determined at 25 °C Summary (1) The results obtained from Fourier transform infrared spectroscopy (FT–IR) proved that the MWNT can be effectively carboxylated in a sulfuric/ nitric mixed acid system. (2) The PA66x/CNTb3y crystallization and the fusing curve indicated that, carboxylation MWNTs joins may enhance PA66 the crystallizing point, and reduced the PA66 fusing temperature, enhanced the crystallization integrity and the crystal speed. (3) The PA66x/CNTb3y surface resistance curve indicated that, carboxyl group MWNTs may improve PA66 the electrical conductivity. The pure PA66 surface resistance for 1013Ω, after joins 12% MWNTs the surface resistance to drop 109Ω, dropped 4 magnitudes.
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