- Email: [email protected]
A novel approach to preparing carbon nanotube reinforced thermoplastic polymer composites
Letters to the Editor / Carbon 43 (2005) 2397–2429
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A novel approach to preparing carbon nanotube reinforced thermoplastic polymer composites Zhong-Ming Li *, Sha-Ni Li, Ming-Bo Yang, Rui Huang College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, Sichuan, PeopleÕs Republic of China Received 10 November 2004; accepted 13 April 2005 Available online 1 July 2005
Keywords: Carbon nanotubes; Chemical treatment; Mixing; Microstructure; Mechanical properties
In order to optimize the performance of the carbon nanotubes (CNTs) reinforced polymer composites, many efforts have been made to produce alignment of CNTs in the matrix, such as spinning CNT gel fibers [1,2], mechanical stretching of a polymer/nanotubes composite [3] and synthesis of aligned nanotubes by deposition of nanotubes onto chemically modified substrate [4]. Dalton et al. [1] showed that their resulting composite fibers obtained by a type of coagulationbased CNT spinning method, which were about 50 lm in diameter and contained around 60% SWNTs by weight, had a tensile strength of 1.8 gigapascals (GPa). Although using spinning technique to prepare alignment of CNTs in the matrix would greatly increase the mechanical (and other physical) properties of the CNT/polymer composites, CNT only oriented in x- or y-direction and hardly facilitated isotropic materials. Moreover, for most CNT filled polymer composite, the increases in strength and modulus are on sacrifice of toughness and ductility, due to embrittlement [5]. In this communication, we report a novel approach to preparing carbon nanotube reinforced thermoplastic polymer composites by the following three steps: (1) preparation of CNT-polymer a compound by solution processing and/or melt mixing, (2) melt extrusion and hot stretching of CNT-polymer a compound and matrix polymer b to generate in-situ CNT-polymer a microfibrils at a processing temperature of the higher melting component (usually polymer a, and (3) isotropization of the microfibrillar composite by melt mixing, extrusion, injection molding, and/or compressive molding at a processing temperature of the lower processing-
*
Corresponding author. Tel.: +8685405324; fax: +8685401988. E-mail address: [email protected] (Z.-M. Li).
0008-6223/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2005.04.037
temperature component (usually polymer b). A CNTreinforced microfibrillar composite (CNT-MRC) based on polycarbonate (PC) and polyethylene (PE) was fabricated by this way in this study. In this material, well-defined CNT/PC microfibrils were generated in PE matrix, and almost all CNTs were preferably localized in the PC microfibrils. There was simultaneously an increase in the strength, modulus, and elongation at break of the CNT-MRC in two directions (horizontal and vertical), which defined this new CNT reinforced composite to be isotropic. The starting CNTs in our experiment are MWNTs with a purity of 80% (obtained by thermal gravimetric analysis, TGA), purchased from Nano Harbor Co. Ltd. (China), with 20–40 nm in diameter and 0.5– 500 lm in length. A commercially available ethyleneco-vinyl acetate copolymer (EVA) (Model Evaflex) with 28 wt% of vinyl acetate was purchased from Du PontMistsui Poly Chemicals Co. Ltd, Japan. It was used as the carrier polymer of CNTs. In order to eliminate non-nanotube carbon and metallic oxide, MWNTs were treated by immersing in 3 mol/l (approximately 13.3 wt%) nitric acid and refluxing for 8 h, subsequently washed with distilled water until the pH of the solution approached 7. This purification hardly gave any damage to MWNTs [6]. The MWNTs with a purity of 95% (shown by TGA) were thus obtained after being dried in a vacuum oven at 90 C for 24 h. Solution-phase processing was used to prepare the CNT/EVA masterbatch with a high CNT content, as reported earlier [7]. It showed homogeneously dispersed 20 wt% MWNTs in EVA copolymer as verified in scanning electron micrographs (Fig. 1a). From Fig. 1a, individual MWNT was randomly dispersed (without preferred alignment or orientation after dispersion) within the matrix, and no obvious MWNTs aggregation was observed at such high
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Letters to the Editor / Carbon 43 (2005) 2397–2429
concentration. After CNT/EVA masterbatch was melt mixed with PC by a Haake Rheomixer mixer at 270 C, with a speed of 30 rpm and a mixing time of 15 min, MWNTs were still in homogeneous dispersion in PC phase, as shown in Fig. 1b where the MWNTs content was 5 wt% in CNT/EVA/PC compound (5/20/ 75 CNT/EVA/PC by weight). This not only gives evidence that EVA and PC were very compatible, but also showed that MWNTs have negatively changed even after melt processing, with many intact MWNTs being seen. Therefore, uniform dispersion of MWNTs in polymer a and good compatibility between polymer a and b are important to make new well dispersed composites. This indicates that the present way, which combines solution processing and melt mixing, is very effective and applicable for CNTs dispersion in polymer matrix since the former is capable of homogeneous dispersion of high concentration CNTs while the latter usually applies to high volume production. After slit die extrusion and hot-stretching of CNT/ EVA/PC compound and matrix PE mixture at a processing temperature (275 C) of PC (see the detailed processing operation in [7]), CNT filled PC microfibrils had been successfully formed in the PE matrix. Fig. 1c con-
firmed that the diameter of most microfibrils in the micrograph was under 5 lm (the lowest only 0.5 lm, as the hot stretch ratio (the area of the transverse section of the die to the area of the transverse section of the extrudate) was 8.9. And all microfibrils had been oriented along the draw direction since they left a long section being vertical to the fracture surface. More attractively, at higher magnification (Fig. 1d) one could notice that MWNTs predominantly localize in the PC microfibrils without obvious migration to PE matrix. These phenomena imply that there is strong interfacial bonding between CNTs and EVA copolymer, which were presumably due to the fact the functionalization of the MWNTs with –COOH groups increases the anchoring (or interacting) sites along the nanotubes with EVA copolymer [6,7]. Moreover, the fracture surface of composites clearly showed none of nanotube ropes (white spots in the micrograph) have been pulled out from the microfibrils. Most nanotubes were embedded and tightly held to the matrix. This once again indicated the existence of strong interfacial bonding between the nanotubes and EVA, capable of transferring the stress load and preventing the sliding of nanotubes during tension (the fracture surfaces were obtained under tension
Fig. 1. (a) SEM image of the CNT/EVA composite containing 20 wt% CNT, prepared by solution-phase processing techniques; (b) SEM image of the CNT/EVA/PC composite containing 5 wt% CNT, prepared by melt blending techniques; (c) SEM image of the CNT filled PC/PE microfibrillar composite prepared by slit die extrusion and hot-stretching and (d) SEM image of CNT dispersion in PC microfibrils (the bright white spots show the broken fragment of CNT).
Letters to the Editor / Carbon 43 (2005) 2397–2429
in liquid nitrogen). On the other hand, the interfacial adhesion between the CNT/PC microfibrils and PE matrix was also perfect, which could be partly confirmed by comparing with the pure PC/PE MRC without EVA. In the pure PC/PE MRC as shown in Fig. 2, the majority of the PC microfibrils were pulled out from the PE matrix. It was interesting that the surfaces of the pure PC microfibrils were very smooth, while those of the CNTs filled PC ones were coarse and irregular caused by incorporation of a solid heterogeneous phase [8]. This might be conducive to load transfer by interfacial friction between CNTs and host polymer [9]. In order to yield isotropic mechanical properties in xand y-direction, the CNT-MRC sheets were cut into small pellets. After homogeneous melt mixing, the materials were hot pressed at the processing temperature (150 C) of PE matrix, far below the processing temperature (usually above 230 C) of PC. The earlier studies had shown that such a processing operation could successfully preserve the previously formed PC microfibrils in the composite [10]. The dog-bone shape samples for mechanical testing, machined from the compressive molded plates, had a length of 60 mm, a width of 10 mm and a thickness of about 0.5 mm. The tensile tests were carried out using an Instron universal material testing system at 25 C with gauge length of 25 mm and crosshead speed of 50 mm/min. To ensure data accuracy and repeatability, a minimum of six and up to nine specimens from different batches of samples were tested. The typical stress–strain curves of 0.5 wt% CNT-MRC were shown in Fig. 3, and the average ten-
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Fig. 2. SEM micrograph of the cryofracture surface for the extruded and stretched pure PC/PE microfibrillar composite where a great amount of PC microfibrils were pulled out from the PE matrix.
sile properties including elastic modulus, ultimate tensile strength, failure strain and toughness (characterized by area under the stress–strain curve) were summarized in Table 1. As shown in Table 1, tensile strength, elastic modulus, failure strain and toughness of CNT-MRC in both two (x- and y-) directions were increased at least 13% from 20.0 to 22.6 MPa, 56% from 766 to 1197 MPa, 13% from 707% to 796% and 28% from 25.9 to 33.1 kJ/m2 compared to those of pure PC/PE MRC, respectively. All curves in Fig. 3 displayed a typical ductile fracture behavior, similar to pure PE. The post-yield stress of CNT-MRC was constantly higher than those of pure PE and MRC. Besides, the ductibility
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Fig. 3. Typical strain–stress curves for all microfibrillar composite and pure PE at a crosshead speed of 50 mm/min and at 25 C: (a) pure PE; (b) pure PC/PE microfibrillar composite; (c) CNT filled PC/PE microfibrillar composite (x-direction) and (d) CNT filled PC/PE microfibrillar composite (y-direction).
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Table 1 Mechanical properties of CNT filled microfibrillar PC/PE blend and its corresponding pure MRC Sample
Tensile strength (MPa)
Elastic modulus (MPa)
Failure strain (%)
Toughness (kJ/m2)
Pure PE Pure MRC CNT filled MRC (x-direction) CNT filled MRC (y-direction)
20.97 20.00 23.87 22.62
836.1 766.6 1196.0 1197.0
766.70 707.60 817.70 796.80
27.2 25.9 35.2 33.1
and toughness of CNTs filled MRC increased, rather than decreased, with respect to pure MRC. We believe these enhancements in tensile modulus, strength, and toughness of CNT-MRC were due to effective load transfer from microfibrillar network to CNTs through strong interfacial bonding between nanotubes and EVA matrix, and between EVA and PC, and between PC microfibrils and PE matrix where EVA acted as a successful compatibilizer, which could help more strain energy absorption before fracture. The orientation of CNTs in PC microfibrils might be another factor bringing out property enhancement [3]. During hot stretching, the CNTs can also have some orientation along with PC droplets while they are elongated into microfibrils. Quite possibly, high orientation of CNTs in PC microfibrils (entangled non-oriented nanotubes were usually incorporated as dense aggregates, which are not able to slow down the crack propagation process during tensile test), and generation of much finer PC microfibrils can result in CNTs filled PC microfibrils with higher mechanical properties, and hence it is believed that the overall mechanical properties of the CNTs filled microfibrillar polymer composites can be further improved in the next work. On the other hand, due to high thermal and electrical conductivity, the CNTs filled polymer micofibrils may be highly conductive. As long as the long and fine CNTs filled microfibrils can form a network path, the whole composite system is also conductive with a very low percolation threshold [10]. It can be expected that the approach to preparing CNT reinforced microfibrillar composites has the potential to make a new type of functional materials. In summary, we have reported here a novel approach to preparing the CNTs reinforced isotropic polymer composites, which facilitate simultaneous increasing tensile strength, modulus and toughness. Moreover, the oriented CNTs are almost localized in the continuous PC microfibrils networks. Considering whether there are some other factors making the nanotubes only localized in one phase, further substantial works are expected.
Acknowledgements The authors gratefully acknowledge the financial support by Program for New Century Excellent Talents in University (NCET) and Sichuan Youth Science and Technology Foundation (Contract number: 04ZQ026037).
References [1] Dalton AB, Collins S, Munˇoz E, Razal JM, Ebron VH, Ferraris JP, et al. Super-tough carbon-nanotube fibres. Nature. 2003;423(12):703. [2] Sen R, Zhao B, Perea D, Itkis ME, Hu H, Love J, et al. Preparation of single-walled carbon nanotube reinforced polystyrene and polyurethane nanofibers and membranes by electrospinning. NanoLett 2004;4(3):459–64. [3] Jin L, Bower C, Zhou O. Alignment of carbon nanotubes in a polymer matrix by mechanical stretching. Appl Phy Lett 1998;73(9):1197–9. [4] Terrones M, Grobert N, Olivares J, Zhang JP, Terrones H, Kordatos K, et al. Controlled production of aligned-nanotube bundles. Nature. 1997;388(3):52–5. [5] Olaf M, Dirk K, Hans W, Christian F, Marc V, Holger W. Mechanical properties and electrical conductivity of carbonnanotube filled polyamide-6 and its blends with acrylonitrile/ butadiene/styrene. Polymer 2004;45(3):739–48. [6] Kim YJ, Shin TS, Choi HD, Kwon JH, Chung YC, Yoon HG. Electrical conductivity of chemically modified multiwalled carbon nanotube/epoxy composites. Carbon 2005;43:23–30. [7] Li SN, Li ZM, Yang MB, Hu ZQ, Xu XB, Huang R. Carbon nanotubes induced nonisothermal crystallization of ethylene– vinyl acetate copolymer. Mater Lett 2004;58:3967–70. [8] Xu XB, Li ZM, Jiang S, Lu A, Yang MB, Huang R. The role of the surface microstructure of the microfibrils in the electrically conductive microfibrillar CB/PET/PE composite. Carbon 2005;43: 1479–87. [9] Ye HH, Lam H, Titchenal N, Gogotsi Y, Ko F. Reinforcement and rupture behavior of carbon nanotubespolymer nanofibers. Appl Phys Lett 2004;85(10):1775–7. [10] Li ZM, Xu XB, Lu A, Shen KZ, Huang R, Yang MB. Carbon black/poly(ethylene terephthalate)/polyethylene composite with electrically conductive in situ microfiber network. Carbon 2004;42:428–32.
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A novel approach to preparing carbon nanotube reinforced thermoplastic polymer composites Zhong-Ming Li *, Sha-Ni Li, Ming-Bo Yang, Rui Huang College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, Sichuan, PeopleÕs Republic of China Received 10 November 2004; accepted 13 April 2005 Available online 1 July 2005
Keywords: Carbon nanotubes; Chemical treatment; Mixing; Microstructure; Mechanical properties
In order to optimize the performance of the carbon nanotubes (CNTs) reinforced polymer composites, many efforts have been made to produce alignment of CNTs in the matrix, such as spinning CNT gel fibers [1,2], mechanical stretching of a polymer/nanotubes composite [3] and synthesis of aligned nanotubes by deposition of nanotubes onto chemically modified substrate [4]. Dalton et al. [1] showed that their resulting composite fibers obtained by a type of coagulationbased CNT spinning method, which were about 50 lm in diameter and contained around 60% SWNTs by weight, had a tensile strength of 1.8 gigapascals (GPa). Although using spinning technique to prepare alignment of CNTs in the matrix would greatly increase the mechanical (and other physical) properties of the CNT/polymer composites, CNT only oriented in x- or y-direction and hardly facilitated isotropic materials. Moreover, for most CNT filled polymer composite, the increases in strength and modulus are on sacrifice of toughness and ductility, due to embrittlement [5]. In this communication, we report a novel approach to preparing carbon nanotube reinforced thermoplastic polymer composites by the following three steps: (1) preparation of CNT-polymer a compound by solution processing and/or melt mixing, (2) melt extrusion and hot stretching of CNT-polymer a compound and matrix polymer b to generate in-situ CNT-polymer a microfibrils at a processing temperature of the higher melting component (usually polymer a, and (3) isotropization of the microfibrillar composite by melt mixing, extrusion, injection molding, and/or compressive molding at a processing temperature of the lower processing-
*
Corresponding author. Tel.: +8685405324; fax: +8685401988. E-mail address: [email protected] (Z.-M. Li).
0008-6223/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2005.04.037
temperature component (usually polymer b). A CNTreinforced microfibrillar composite (CNT-MRC) based on polycarbonate (PC) and polyethylene (PE) was fabricated by this way in this study. In this material, well-defined CNT/PC microfibrils were generated in PE matrix, and almost all CNTs were preferably localized in the PC microfibrils. There was simultaneously an increase in the strength, modulus, and elongation at break of the CNT-MRC in two directions (horizontal and vertical), which defined this new CNT reinforced composite to be isotropic. The starting CNTs in our experiment are MWNTs with a purity of 80% (obtained by thermal gravimetric analysis, TGA), purchased from Nano Harbor Co. Ltd. (China), with 20–40 nm in diameter and 0.5– 500 lm in length. A commercially available ethyleneco-vinyl acetate copolymer (EVA) (Model Evaflex) with 28 wt% of vinyl acetate was purchased from Du PontMistsui Poly Chemicals Co. Ltd, Japan. It was used as the carrier polymer of CNTs. In order to eliminate non-nanotube carbon and metallic oxide, MWNTs were treated by immersing in 3 mol/l (approximately 13.3 wt%) nitric acid and refluxing for 8 h, subsequently washed with distilled water until the pH of the solution approached 7. This purification hardly gave any damage to MWNTs [6]. The MWNTs with a purity of 95% (shown by TGA) were thus obtained after being dried in a vacuum oven at 90 C for 24 h. Solution-phase processing was used to prepare the CNT/EVA masterbatch with a high CNT content, as reported earlier [7]. It showed homogeneously dispersed 20 wt% MWNTs in EVA copolymer as verified in scanning electron micrographs (Fig. 1a). From Fig. 1a, individual MWNT was randomly dispersed (without preferred alignment or orientation after dispersion) within the matrix, and no obvious MWNTs aggregation was observed at such high
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Letters to the Editor / Carbon 43 (2005) 2397–2429
concentration. After CNT/EVA masterbatch was melt mixed with PC by a Haake Rheomixer mixer at 270 C, with a speed of 30 rpm and a mixing time of 15 min, MWNTs were still in homogeneous dispersion in PC phase, as shown in Fig. 1b where the MWNTs content was 5 wt% in CNT/EVA/PC compound (5/20/ 75 CNT/EVA/PC by weight). This not only gives evidence that EVA and PC were very compatible, but also showed that MWNTs have negatively changed even after melt processing, with many intact MWNTs being seen. Therefore, uniform dispersion of MWNTs in polymer a and good compatibility between polymer a and b are important to make new well dispersed composites. This indicates that the present way, which combines solution processing and melt mixing, is very effective and applicable for CNTs dispersion in polymer matrix since the former is capable of homogeneous dispersion of high concentration CNTs while the latter usually applies to high volume production. After slit die extrusion and hot-stretching of CNT/ EVA/PC compound and matrix PE mixture at a processing temperature (275 C) of PC (see the detailed processing operation in [7]), CNT filled PC microfibrils had been successfully formed in the PE matrix. Fig. 1c con-
firmed that the diameter of most microfibrils in the micrograph was under 5 lm (the lowest only 0.5 lm, as the hot stretch ratio (the area of the transverse section of the die to the area of the transverse section of the extrudate) was 8.9. And all microfibrils had been oriented along the draw direction since they left a long section being vertical to the fracture surface. More attractively, at higher magnification (Fig. 1d) one could notice that MWNTs predominantly localize in the PC microfibrils without obvious migration to PE matrix. These phenomena imply that there is strong interfacial bonding between CNTs and EVA copolymer, which were presumably due to the fact the functionalization of the MWNTs with –COOH groups increases the anchoring (or interacting) sites along the nanotubes with EVA copolymer [6,7]. Moreover, the fracture surface of composites clearly showed none of nanotube ropes (white spots in the micrograph) have been pulled out from the microfibrils. Most nanotubes were embedded and tightly held to the matrix. This once again indicated the existence of strong interfacial bonding between the nanotubes and EVA, capable of transferring the stress load and preventing the sliding of nanotubes during tension (the fracture surfaces were obtained under tension
Fig. 1. (a) SEM image of the CNT/EVA composite containing 20 wt% CNT, prepared by solution-phase processing techniques; (b) SEM image of the CNT/EVA/PC composite containing 5 wt% CNT, prepared by melt blending techniques; (c) SEM image of the CNT filled PC/PE microfibrillar composite prepared by slit die extrusion and hot-stretching and (d) SEM image of CNT dispersion in PC microfibrils (the bright white spots show the broken fragment of CNT).
Letters to the Editor / Carbon 43 (2005) 2397–2429
in liquid nitrogen). On the other hand, the interfacial adhesion between the CNT/PC microfibrils and PE matrix was also perfect, which could be partly confirmed by comparing with the pure PC/PE MRC without EVA. In the pure PC/PE MRC as shown in Fig. 2, the majority of the PC microfibrils were pulled out from the PE matrix. It was interesting that the surfaces of the pure PC microfibrils were very smooth, while those of the CNTs filled PC ones were coarse and irregular caused by incorporation of a solid heterogeneous phase [8]. This might be conducive to load transfer by interfacial friction between CNTs and host polymer [9]. In order to yield isotropic mechanical properties in xand y-direction, the CNT-MRC sheets were cut into small pellets. After homogeneous melt mixing, the materials were hot pressed at the processing temperature (150 C) of PE matrix, far below the processing temperature (usually above 230 C) of PC. The earlier studies had shown that such a processing operation could successfully preserve the previously formed PC microfibrils in the composite [10]. The dog-bone shape samples for mechanical testing, machined from the compressive molded plates, had a length of 60 mm, a width of 10 mm and a thickness of about 0.5 mm. The tensile tests were carried out using an Instron universal material testing system at 25 C with gauge length of 25 mm and crosshead speed of 50 mm/min. To ensure data accuracy and repeatability, a minimum of six and up to nine specimens from different batches of samples were tested. The typical stress–strain curves of 0.5 wt% CNT-MRC were shown in Fig. 3, and the average ten-
2415
Fig. 2. SEM micrograph of the cryofracture surface for the extruded and stretched pure PC/PE microfibrillar composite where a great amount of PC microfibrils were pulled out from the PE matrix.
sile properties including elastic modulus, ultimate tensile strength, failure strain and toughness (characterized by area under the stress–strain curve) were summarized in Table 1. As shown in Table 1, tensile strength, elastic modulus, failure strain and toughness of CNT-MRC in both two (x- and y-) directions were increased at least 13% from 20.0 to 22.6 MPa, 56% from 766 to 1197 MPa, 13% from 707% to 796% and 28% from 25.9 to 33.1 kJ/m2 compared to those of pure PC/PE MRC, respectively. All curves in Fig. 3 displayed a typical ductile fracture behavior, similar to pure PE. The post-yield stress of CNT-MRC was constantly higher than those of pure PE and MRC. Besides, the ductibility
24 22 20
c
18 d
14 12
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10
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Stress (MPa)
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6
a
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b
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0
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20
30
40
50
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70
Strain (%)
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100
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300
400 500 Strain (%)
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700
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900
Fig. 3. Typical strain–stress curves for all microfibrillar composite and pure PE at a crosshead speed of 50 mm/min and at 25 C: (a) pure PE; (b) pure PC/PE microfibrillar composite; (c) CNT filled PC/PE microfibrillar composite (x-direction) and (d) CNT filled PC/PE microfibrillar composite (y-direction).
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Table 1 Mechanical properties of CNT filled microfibrillar PC/PE blend and its corresponding pure MRC Sample
Tensile strength (MPa)
Elastic modulus (MPa)
Failure strain (%)
Toughness (kJ/m2)
Pure PE Pure MRC CNT filled MRC (x-direction) CNT filled MRC (y-direction)
20.97 20.00 23.87 22.62
836.1 766.6 1196.0 1197.0
766.70 707.60 817.70 796.80
27.2 25.9 35.2 33.1
and toughness of CNTs filled MRC increased, rather than decreased, with respect to pure MRC. We believe these enhancements in tensile modulus, strength, and toughness of CNT-MRC were due to effective load transfer from microfibrillar network to CNTs through strong interfacial bonding between nanotubes and EVA matrix, and between EVA and PC, and between PC microfibrils and PE matrix where EVA acted as a successful compatibilizer, which could help more strain energy absorption before fracture. The orientation of CNTs in PC microfibrils might be another factor bringing out property enhancement [3]. During hot stretching, the CNTs can also have some orientation along with PC droplets while they are elongated into microfibrils. Quite possibly, high orientation of CNTs in PC microfibrils (entangled non-oriented nanotubes were usually incorporated as dense aggregates, which are not able to slow down the crack propagation process during tensile test), and generation of much finer PC microfibrils can result in CNTs filled PC microfibrils with higher mechanical properties, and hence it is believed that the overall mechanical properties of the CNTs filled microfibrillar polymer composites can be further improved in the next work. On the other hand, due to high thermal and electrical conductivity, the CNTs filled polymer micofibrils may be highly conductive. As long as the long and fine CNTs filled microfibrils can form a network path, the whole composite system is also conductive with a very low percolation threshold [10]. It can be expected that the approach to preparing CNT reinforced microfibrillar composites has the potential to make a new type of functional materials. In summary, we have reported here a novel approach to preparing the CNTs reinforced isotropic polymer composites, which facilitate simultaneous increasing tensile strength, modulus and toughness. Moreover, the oriented CNTs are almost localized in the continuous PC microfibrils networks. Considering whether there are some other factors making the nanotubes only localized in one phase, further substantial works are expected.
Acknowledgements The authors gratefully acknowledge the financial support by Program for New Century Excellent Talents in University (NCET) and Sichuan Youth Science and Technology Foundation (Contract number: 04ZQ026037).
References [1] Dalton AB, Collins S, Munˇoz E, Razal JM, Ebron VH, Ferraris JP, et al. Super-tough carbon-nanotube fibres. Nature. 2003;423(12):703. [2] Sen R, Zhao B, Perea D, Itkis ME, Hu H, Love J, et al. Preparation of single-walled carbon nanotube reinforced polystyrene and polyurethane nanofibers and membranes by electrospinning. NanoLett 2004;4(3):459–64. [3] Jin L, Bower C, Zhou O. Alignment of carbon nanotubes in a polymer matrix by mechanical stretching. Appl Phy Lett 1998;73(9):1197–9. [4] Terrones M, Grobert N, Olivares J, Zhang JP, Terrones H, Kordatos K, et al. Controlled production of aligned-nanotube bundles. Nature. 1997;388(3):52–5. [5] Olaf M, Dirk K, Hans W, Christian F, Marc V, Holger W. Mechanical properties and electrical conductivity of carbonnanotube filled polyamide-6 and its blends with acrylonitrile/ butadiene/styrene. Polymer 2004;45(3):739–48. [6] Kim YJ, Shin TS, Choi HD, Kwon JH, Chung YC, Yoon HG. Electrical conductivity of chemically modified multiwalled carbon nanotube/epoxy composites. Carbon 2005;43:23–30. [7] Li SN, Li ZM, Yang MB, Hu ZQ, Xu XB, Huang R. Carbon nanotubes induced nonisothermal crystallization of ethylene– vinyl acetate copolymer. Mater Lett 2004;58:3967–70. [8] Xu XB, Li ZM, Jiang S, Lu A, Yang MB, Huang R. The role of the surface microstructure of the microfibrils in the electrically conductive microfibrillar CB/PET/PE composite. Carbon 2005;43: 1479–87. [9] Ye HH, Lam H, Titchenal N, Gogotsi Y, Ko F. Reinforcement and rupture behavior of carbon nanotubespolymer nanofibers. Appl Phys Lett 2004;85(10):1775–7. [10] Li ZM, Xu XB, Lu A, Shen KZ, Huang R, Yang MB. Carbon black/poly(ethylene terephthalate)/polyethylene composite with electrically conductive in situ microfiber network. Carbon 2004;42:428–32.