- Email: [email protected]
Nanocomposites with enhanced electrical properties based on biodegradable poly(butylene succinate) and polyetheramine modified carbon nanotube
Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
Contents lists available at SciVerse ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice
Nanocomposites with enhanced electrical properties based on biodegradable poly(butylene succinate) and polyetheramine modified carbon nanotube Chin-Sheng Lin a, Yeng-Fong Shih b,*, Ru-Jong Jeng c, Shenghong A. Dai a, Jiang-Jen Lin c, Chuan-Chen Lee d a
Department of Chemical Engineering, National Chung Hsing University, Taichung 40227, Taiwan Department of Applied Chemistry, Chaoyang University of Technology, Wufeng District, Taichung 41319, Taiwan c Institute of Polymer Science and Engineering, National Taiwan University, Taipei 10617, Taiwan d Department of Health and Nutrition Biotechnology, Asia University, Wufeng, Taichung 41354, Taiwan b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 7 August 2011 Received in revised form 5 October 2011 Accepted 10 October 2011 Available online 13 November 2011
In order to improve the compatibility between the poly(butylene succinate) (PBS) and multi-walled carbon nanotubes (MWNTs), Jeffamine1 Polyetheramines were grafted onto MWNTs. The results show that excellent dispersion of nanotubes in the PBS matrices was achieved. An improvement in thermal properties of the PBS/MWNTs nanocomposites was also observed. With the addition of 3.0 wt% MWNT2070D, the Td of the nanocomposite was 10.1 8C higher than that of the pristine PBS sample. Apart from that, the increments of E0 and E00 of the nanocomposite at 25 8C were 113 and 116%, respectively. In the aspect of conductivity, the surface resistivity decreased from 2.35 1014 V/& for neat PBS to 5.88 103 V/& for the nanocomposites with a 3.0 wt% of MWNT-2070D. Such PBS/MWNT-2070D nanocomposites are potentially efficient for anti-static purposes, even electrostatic discharge and EMI shielding, which can be applied in electronic materials. ß 2011 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Carbon nanotube Poly(butylene succinate) Nanocomposite Electrical property
1. Introduction The development of biodegradable polymers has been a subject of great interest in materials science from both ecological and biomedical perspectives [1]. Due to the problems of worsening environmental pollution, increasing awareness of environmental damage caused by plastic materials over the last few decades has led to research aimed at producing eco-friendly versions of those plastics. One of these biodegradable polymers is poly(butylene succinate) (PBS). PBS is synthesized through the polycondensation reaction of glycols, such as ethylene glycol and 1,4-butanediol, and aliphatic dicarboxylic acids, such as succinic acid and adipic acid. This biodegradable polymer exhibits a melting point similar to low-density polyethylene (LDPE), a glass transition temperature and tensile strength between polyethylene (PE) and poly(propylene) (PP), and a stiffness between LDPE and high-density polyethylene (HDPE). PBS possesses satisfactory strength and toughness, close to that of LDPE [2–5], which is considered highly promising as a commercial commodity polymer. Since the first observation of carbon nanotubes in 1991 by Iijima [6] and the awareness of their distinctive mechanical, thermal and electrical properties, extensive research in the field of
* Corresponding author. Tel.: +886 4 233230004586; fax: +886 4 23742341. E-mail address: [email protected] (Y.-F. Shih).
CNT/polymer nanocomposites has been conducted. However, the optimal amount of multi-walled carbon nanotubes (MWNT) is only 1 wt% because excessive MWNT would cause separation of the organic and inorganic phases and lower their compatibility [7,8]. Therefore, organic modification of MWNTs to increase their organophilic properties is required for many industrial applications. One approach is to take advantage of the oxidative formation of carboxyl functionalities and subsequently to graft organic moieties onto the tubes. A great deal of research effort followed this route to the preparation of soluble nanotubes [9–12]. Even though research on polymer/CNT composites is growing rapidly, biodegradable polymer/CNT composites are seldom prepared. Additionally, most biodegradable polymer/CNT composites have been prepared directly by mixing the biodegradable polymer with acidified CNT [13,14], or by in situ polymerization [15,16], and the CNTs therein are not modified chemically to improve their dispersion in the polymer matrix. Lin et al. [17] demonstrated the feasibility of functionalizing MWNTs with carbonyl derivatives through oxidation. Subsequently, the poly(oxyalkylene)-amine (POA-amine) pendants were grafted onto MWNTs via amide linkages. Three different amidation routes (direct thermal amidation, acylation-mediated amidation and N,N0 -dicyclohexylcarbodiimide (DCC)-coupling amidation for grafting POA-amines onto MWNTs were investigated. The results reveal that the DCCcoupling method is more effective for grafting diamines onto MWNT-COOH via amide linkages. In our previous study [18], we
1876-1070/$ – see front matter ß 2011 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jtice.2011.10.009
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
323
Scheme 1. Surface modification of MWNTs.
modified the MWNTs with stearyl alcohol via the DCC-coupling method to establish a long alkyl chain on the MWNTs, so as to reduce the aggregation of MWNTs, and improve the compatibility between MWNTs and polymers. As a result, the PBS/MWNTs-C18 nanocomposites exhibited not only a good dispersion of nanotubes in the PBS matrices, but an improvement in thermal and mechanical properties as well. Moreover, a decrease of over 109fold in value of the electrical resistivity and an excellent anti-static capacity were found for the composite with 3 wt% MWNTs-C18. In this study, the surfaces of multi-walled carbon nanotubes (MWNTs) were chemically modified to enhance the compatibility between PBS and MWNTs. MWNTs were first pre-treated using acid solution to obtain functionalized carboxylic groups. Next, Jeffamine1 Polyetheramines were grafted onto MWNTs with the assistance of a dehydrating agent. Jeffamine1 Polyetheramines possess ethylene oxide (EO) and propylene oxide (PO) groups. It is expected that the more similar structure of PBS to Jeffamine1 Polyetheramines than stearyl alcohol would be more effective in improving the compatibility between the PBS and the modified MWNTs. Subsequently, the PBS/MWNT nanocomposites were prepared through melt-blending. As a result, the mechanical properties, thermal behavior and conductivity of these resultant polymer/MWNT composites can be further enhanced.
Chemical Perfomance Polymers Inc., Japan. The Jeffamine1 Polyetheramines (M2005 (EO/PO = 6/29, M.W. = 1977) and M2070 (EO/ PO = 31/10, M.W. = 2063)), supplied by Huntsman Co., were used to modify the multi-walled carbon nanotubes (purity > 95%, obtained from Scientech Co., Taiwan). 2.2. Surface modification of MWNTs The surface modification of MWNTs was achieved by the following. First, purified MWNTs were dispersed in HNO3 and kept at 120 8C for 60 min in the reflux system for introducing carboxyl groups at their opening ends and defect locations on their walls. The obtained MWNT-COOH was dispersed in dry DMF and mixed with Jeffamine1 Polyetheramines (M2005 (EO/PO = 6/29), M2070 (EO/ PO = 31/10)) and N,N0 -dicyclohexylcarbodiimide (DCC), and reacted at room temperature for 48 h, to graft the Jeffamine1 Polyetheramines onto MWNTs (MWNT-2005D, MWNT-2070D (with DCC), MWNT-2005, MWNT-2070 (without DCC)) (Scheme 1). 2.3. Preparation of PBS/MWNT nanocomposites
2. Experimental
The PBS/MWNT nanocomposites were prepared through meltblending at 120 8C with a rotor speed of 60 rpm for 5 min (Scheme 2). The mixed samples were then compressed under a pressure of about 200 kgf/cm2 at 140 8C for 3 min using a hot press.
2.1. Materials
2.4. Characterizations
Polybutylene succinate (PBS, GS Pla1 AZ91 T) with a melting point of 110 8C and a density of 1.26 g/m3 was supplied by Mitsubishi
Thermogravimetric analyses (TGA) were performed using a ThermoCahn VersaTherm analyzer. Samples were heated from
Scheme 2. Illustration of the melt-blending process.
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
324
Fig. 1. Dispersion of (a) pristine MWNT, (b) MWNT-COOH, (c) MWNT-2005D, (d) MWNT-2005, (e) MWNT-2070D, (f) MWNT-2070 in water and chloroform.
room temperature to 800 8C at a heating rate of 10 8C/min under a nitrogen purge. Raman Spectrum (TRIAX 550 Jobin-Yvon) was used to analyze the structure of MWNTs after modification. Dynamic mechanical behaviors of the nanocomposites were measured by a Perkin Elmer DMA 7E. The dimensions of samples were 2 mm 18 mm 10 mm and the tests were performed in a three-point bending mode at a frequency of 1 Hz. Surface resistivities of the nanocomposites were measured using a Hioki SM-8220 Ultra Megohmmeter and a GWInstek GOM-802 DC MilliOHM Meter. Scanning electron microscopy (SEM) (JEOL JSM6700F) was used to observe the fractured surface of PBS/MWNT nanocomposites with different MWNT contents. 3. Results and discussion 3.1. Characterization of Jeffamine1 Polyetheramine grafted MWNTs Fig. 1(a) shows that the pristine carbon nanotubes (p-MWNT) do not exhibit either hydrophilicity or hydrophobicity. The dispersibility of MWNT-COOH is remarkably changed after modification. MWNT-COOH is hydrophilic and well dispersed in water (Fig. 1(b)). It was found that the presence of EO or PO chains plays a critical role in the solubilization process. MWNT-2005D and MWNT-2005 possess more hydrophobic PO chains, which are well dispersed in chloroform (Fig. 1(c) and (d)). Otherwise, MWNT2070D and MWNT-2070 possess more hydrophilic EO chains, which are well dispersed in water (Fig. 1(e) and (f)). After modification, the thermal stability of carbon nanotubes is decreased due to organic attachment (Fig. 2). The attached
Fig. 2. TGA curves for MWNTs.
Fig. 3. (a) Raman spectrum and (b) the value of ID/IG for MWNTs.
organic content [19] was estimated according to the residual weight of the functionalized MWNTs at 500 8C. The estimated organic attachment content of MWNT-2005D, MWNT-2070D, MWNT-2005 and MWNT-2070 are 11.7, 10.6, 9.5 and 6.8 wt%, respectively. The results reveal that DCC promoted the grafting reaction effectively. Raman spectroscopy is a powerful technique to evaluate the quality of modified MWNT products. The G band located around 1586 cm1 is assigned to the C–C bond motions for a perfect hexagonal structure. On the other hand, the D band centered around 1340 cm1 is usually ascribed to the existence of disordered carbon in bulk carbon. It is attributed to lattice defects, which induce a breaking of the 2D translational symmetry [20]. The intensity ratio of the G and D modes (IG/ID) is often regarded as an indicator of the purity of modified MWNT products [21]. Generally, low ID/IG corresponds to high-purity tube products. As shown in Fig. 3, it was found that the ID/IG value of MWNTCOOH was greater than that of original MWNTs due to the breaking of the 2D translational symmetry of MWNTs after acid treatment. Moreover, the ID/IG values of Jeffamine1 Polyetheramine modified MWNTs were all larger than that of MWNT-COOH. This indicates that the 2D translational symmetry of MWNTs subsequently decreased after the alkylation process. The results also reveal that the ID/IG values of the alkylated MWNTs using a DCC agent (MWNT-2005D and MWNT-2070D) were larger than those of the ones without a DCC agent (MWNT-2005 and MWNT-2070). This is consistent with the TGA results (Fig. 2) showing that DCC promoted the grafting reaction effectively.
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
325
Table 1 Td5 of PBS/MWNTs nanocomposites. Sample
Td5 (8C)
PBS PBS + 3.0%p-MWNT PBS + 3.0%MWNT-2005D PBS + 3.0%MWNT-2005 PBS + 3.0%MWNT-2070D PBS + 3.0%MWNT-2070
352.7 350.3 354.5 351.3 362.8 357.2
3.2. Thermal properties of PBS/MWNT nanocomposites Table 1 shows the thermal decomposition temperature (Td) of the nanocomposite at a 5 wt% weight loss, exhibiting that the addition of MWNT-2070, MWNT-2070D and MWNT-2005D enhanced the Tds for the PBS/MWNT nanocomposites. This was due to the fact that the structure of nanotubes retards organic combustion and acts as a gas barrier that prevents the permeation of volatile gas out of the nanocomposites during thermal decomposition [22]. Enhancement of the thermal stability of M2070-modified MWNTs containing a nanocomposite is more remarkable than that of p-MWNT containing one. With the addition of 3 wt% MWNT-2070D, the Td of the nanocomposite was increased as much as 10.1 8C. This suggests that MWNT-2070D can be dispersed more homogenously than the other modified MWNTs in PBS, providing a good interfacial adhesion with the PBS matrices [23]. The results also reveal that the Tds of the nanocomposites containing alkylated MWNTs using a DCC agent (PBS + 3.0%MWNT-2005D and PBS + 3.0%MWNT-2070D) were larger than those of the ones containing alkylated MWNTs without a DCC agent (PBS + 3.0%MWNT-2005 and PBS + 3.0%MWNT-2070). This is consistent with the Raman Analysis (Fig. 3) that DCC can promote the grafing reaction. Subsequently, the interfacial adhesion between MWNTs and the PBS matrices was improved and led to better thermal stability of the nanocomposites. 3.3. Mechanical properties of PBS/MWNT nanocomposites Fig. 4 shows variations of the storage modulus (E0 ) with MWNT content for PBS/MWNT nanocomposites at 25 8C, and the results show that E0 increased with the increase in the nanotube content. This implies that nanotubes could enhance the rigidity of nanocomposites. The enhancement of the mechanical properties of the MWNT-2070D system was more remarkable than that of the p-MWNT system. With the addition of 3 wt% MWNT-2070D, the increment of E0 for the nanocomposite increased up to 113% (from 191 to 407 MPa). This is consistent with the results of a TGA
Fig. 5. Loss modulus of PBS/MWNT nanocomposites at 25 8C.
analysis that showed interfacial adhesion between MWNT-2070D and the PBS matrices was better than those of the other modified MWNTs in PBS. Moreover, the results also reveal that the E0 s of the nanocomposites containing alkylated MWNTs using a DCC agent (PBS/MWNT-2005D and PBS/MWNT-2070D) were larger than those of the ones containing alkylated MWNTs without a DCC agent (PBS/ MWNT-2005 and PBS/MWNT-2070). This is consistent with the results from the thermal analysis (Fig. 2 and Table 1) that showed that the higher grafing ratio via DCC led to better compatibility and better mechanical properties for nanocomposites. Fig. 5 shows variations of the loss modulus (E00 ) with MWNT content for PBS/MWNTs nanocomposites at 25 8C, and the results show that E00 increased with the increase in the nanotube content. The enhancement of the mechanical properties of the MWNT2070D system was more remarkable than that of the p-MWNT system. With the addition of 3 wt% MWNT-2070D, the increment of E00 for the nanocomposite increased up to 116% (from 15.4 to 33.3 MPa). Moreover, the E00 s of the nanocomposites containing alkylated MWNTs using a DCC agent (PBS/MWNT-2005D and PBS/ MWNT-2070D) were larger than those of the ones containing alkylated MWNTs without a DCC agent (PBS/MWNT-2005 and PBS/ MWNT-2070). This is identical to the results of the storage modulus. Table 2 shows the Tgs of PBS/CNTs nanocomposites from the E00 peak. The Tgs of the nanocomposites containing alkylated MWNTs
Table 2 Tgs (8C, from E00 peak) of PBS/CNTs nanocomposites. PBS/MWNTs
0 wt%
0.5 wt%
1.5 wt%
3.0 wt%
PBS/p-MWNT PBS/MWNT-2005D PBS/MWNT-2005 PBS/MWNT-2070D PBS/MWNT-2070
36.7 36.7 36.7 36.7 36.7
36.0 35.5 36.0 34.5 35.8
35.4 33.1 35.2 32.9 34.8
34.6 31.5 35.0 31.1 34.1
Table 3 Surface resistivity of PBS/MWNTs nanocomposites.
Fig. 4. Storage modulus of PBS/MWNT nanocomposites at 25 8C.
MWNTs
0.5 wt%
1.5 wt%
3.0 wt%
PBS/p-MWNT PBS/MWNT-2005D PBS/MWNT-2005 PBS/MWNT-2070D PBS/MWNT-2070
1.55 1011 4.59 109 8.64 1010 4.78 109 9.58 1010
3.63 108 8.12 105 1.73 107 5.65 105 6.01 105
8.71 105 4.68 104 8.40 105 5.88 103 1.08 104
326
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
Fig. 6. SEM micrographs of the fracture surface of (a) PBS, (b) PBS + 0.5%p-MWNT, (c) PBS + 1.5%p-MWNT and (d) PBS + 3.0%p-MWNT.
Fig. 7. SEM micrographs of the fracture surface of (a) PBS + 0.5%MWNT-2005D, (b) PBS + 1.5%MWNT-2005D, (c) PBS + 3.0%MWNT-2005D, (d) PBS + 0.5%MWNT-2005, (e) PBS + 1.5%MWNT-2005 and (f) PBS + 3.0%MWNT-2005.
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
using a DCC agent (PBS/MWNT-2005D and PBS/MWNT-2070D) was larger than that of ones containing alkylated MWNTs without a DCC agent (PBS/MWNT-2005 and PBS/MWNT-2070). The Tgs of the nanocomposites can be elevated about 5 8C with the addition of 3 wt% MWNT-2005D or MWNT-2070D. This indicates that better adhesion between MWNTs and PBS matrices via Jeffamine1 Polyetheramines modification by DCC can obviously influence the mobility of the PBS chain and lead to a higher transition temperature. From the results of the DMA, the enhanced mechanical properties confirm that the Jeffamine1 Polyetheramine modified carbon nanotubes were well dispersed in PBS matrices and interaction was greatly increased between the PBS and modified carbon nanotubes. 3.4. Electrical properties of PBS/MWNT nanocomposites Table 3 shows the effect of MWNT content on surface resistivity for PBS/MWNT composites. At a very low content of MWNTs, the surface resistivity gradually decreased with increasing nanotube content. MWNTs in the polymer matrices would intertwine with each other and then form an interconnecting conductive pathway: an electrical percolation threshold [24–26]. The surface resistivity of the PBS/MWNT composites decreased from >1014 V/& (pristine
327
PBS: 2.35 1014) to 103 V/& (for PBS/MWNT-2070D), a decrease of about 1011-fold in the value of the electrical resistivity. In comparison to our previous study [18], a decrease of about 109fold in the value of the electrical resistivity was achieved for the composite with 3 wt% MWNT-C18 (the MWNT modified by stearyl alcohol via the DCC-coupling method). The decrease of surface resistivity of PBS/MWNT-2070D composites was obviously larger than that of the other composites and PBS/MWNTs-C18 system, indicating a better dispersion of MWNT-2070D in the polymer matrices compared with those of other MWNTs. This implies that the percolation thresholds of electrical conductivity were depressed. For this reason, the well-dispersed MWNT-2070D in the PBS matrices could easily connect with each other. Therefore, the amount of MWNTs needed to construct a conductive pathway was reduced. In general, electric resistance between 108 and 1012 V would be capable of handling the anti-static function [27]. Therefore, the PBS/MWNT nanocomposites can serve the purpose of electrostatic discharge as electronic packing materials. 3.5. SEM analysis The SEM photographs of the fracture surface of PBS/MWNT nanocomposites are shown in Figs. 6–8. Fig. 6 reveals that many
Fig. 8. SEM micrographs of the fracture surface of (a) PBS + 0.5%MWNT-2070D, (b) PBS + 1.5%MWNT-2070D, (c) PBS + 3.0%MWNT-2070D, (d) PBS + 0.5%MWNT-2070, (e) PBS + 1.5%MWNT-2070 and (f) PBS + 3.0%MWNT-2070.
328
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
entangled clusters of MWNT in PBS matrices were observed for the p-MWNT system. Apparently, the modified MWNTs dispersed homogenously both in the 2005D (Fig. 7(a)–(c)) and 2070D (Fig. 8(a)–(c)) systems, which indicates that the modified MWNTs are more compatible with the PBS matrices as compared with pMWNTs. Better dispersion of the modified MWNTs in PBS/MWNT nanocomposites was due to the chemical modification of the MWNT, which would bring about better compatibility with PBS. On the other hand, some entangled clusters of MWNT in PBS matrices were still found for 2005 (Fig. 7(d)–(f)) and 2070 (Fig. 8(d)–(f)) systems. This is consistent with the results from the thermal analysis, indicating that the higher grafting ratios via DCC led to better compatibility and better mechanical properties for nanocomposites. The results of SEM show that the nanotubes were more compatible with the PBS matrices after the chemical modification, leading to better thermal, mechanical and electrical properties. 4. Conclusions We have successfully modified MWNTs by using Jeffamine1 Polyetheramines and DCC dehydrating agents. The modified MWNT-2005D and MWNT-2070D samples can be well dispersed in organic solvents and incorporated into the PBS matrices through simple melt-blending. The results obtained show that thePBS/ MWNT-2005D and PBS/MWNT-2070D nanocomposites exhibited not only good dispersion of nanotubes in the PBS matrices, but an improvement in thermal and mechanical properties as well. The enhancements of the thermal, mechanical and electrical properties of the MWNT-2070D system were more remarkable than for the MWNT-2005D system. The decomposition temperature of the nanocomposite increased up to 10.1 8C, and the increment of E0 for the nanocomposite at 25 8C amounted to 113%, compared with the neat PBS sample. Moreover, a decrease of about 1011-fold in value of the electrical resistivity and an excellent anti-static capacity were found for the composite with 3 wt% MWNT-2070D. References [1] Ikada Y, Tsuji H. Biodegradable polyesters for medical and ecological applications. Macromol Rapid Commun 2000;21:117–32. [2] Fujimaki T. Processability and properties of aliphatic polyesters, ‘BIONOLL E’, synthesized by polycondensation reaction. Polym Degrad Stab 1998;59: 209–14. [3] Mani R, Bhattacharya M. Properties of injection moulded blends of starch and modified biodegradable polyesters. Eur Polym J 2001;37:515–26. [4] Lim ST, Hyun YH, Choi HJ, Jhon MS. Synthetic biodegradable aliphatic polyester/montmorillonite nanocomposites. Chem Mater 2002;14:1839–44.
[5] Shih YF, Chieh YC. Thermal degradation behavior and kinetic analysis of biodegradable polymers using various comparative models, 1: poly(butylene succinate). Macromol Theor Simul 2007;16:101–10. [6] Iijima S. Helical microtubules of graphitic carbon. Nature 1991;354:56–8. [7] Cheah K, Simon GP, Forsyth M. Effects of polymer matrix and processing on the conductivity of polymer blends. Polym Int 2001;50:27–36. [8] Hussain F, Hojjati M, Okamoto M, Gorga RE. Polymer–matrix nanocomposites, processing, manufacturing, and application: an overview. J Compos Mater 2006;40:1511–75. [9] Hong CY, You YZ, Pan CY. Synthesis of water-soluble multiwalled carbon nanotubes with grafted temperature-responsive shells by surface RAFT polymerization. Chem Mater 2005;17:2247–54. [10] Gao C, Jin YZ, Kong H, Whitby RLD, Acquah SFA, Chen GY, et al. Polyureafunctionalized multiwalled carbon nanotubes: synthesis, morphology, and Raman spectroscopy. J Phys Chem B 2005;109:11925–32. [11] Chen J, Hamon MA, Hui H, Chen Y, Rao AM, Eklund PC, et al. Solution properties of single-walled carbon nanotubes. Science 1998;282:95–8. [12] Chen C, Zhang Y. Manipulation of single-wall carbon nanotubes into dispersively aligned arrays between metal electrodes. Phys D Appl Phys 2006;39: 172–6. [13] Song L, Qiu Z. Crystallization behavior and thermal property of biodegradable poly(butylene succinate)/functional multi-walled carbon nanotubes nanocomposite. Polym Degrad Stab 2009;94:632–7. [14] Sanchez-Garcia MD, Lagaron JM, Hoa SV. Effect of addition of carbon nanofibers and carbon nanotubes on properties of thermoplastic biopolymers. Compos Sci Technol 2010;70:1095–105. [15] Chakoli AN, Wan J, Feng JT, Amirian M, Sui JH, Cai W. Functionalization of multiwalled carbon nanotubes for reinforcing of poly(L-lactide-co-e-caprolactone) biodegradable copolymers. Appl Surface Sci 2009;256:170–7. [16] Kim HS, Chae YS, Park BH, Yoon JS, Kang M, Jin HJ. Thermal and electrical conductivity of poly(L-lactide)/multiwalled carbon nanotube nanocomposites. Curr Appl Phys 2008;8:803–6. [17] Lin ST, Wei KL, Lee TM, Chiou KC, Lin JJ. Functionalizing multi-walled carbon nanotubes with poly(oxyalkylene)-amidoamines. Nanotechnology 2006;17: 3197–203. [18] Shih YF, Chen LS, Jeng RJ. Preparation and properties of biodegradable PBS/ multi-walled carbon nanotube nanocomposites. Polymer 2008;49:4602–11. [19] Zhao C, Ji L, Liu H, Hu G, Zhang S, Yang M, et al. Functionalized carbon nanotubes containing isocyanate groups. J Solid State Chem 2004;177:4394–8. [20] Yan H, Li Q, Zhang J, Liu Z. Possible tactics to improve the growth of single-walled carbon nanotubes by chemical vapor deposition. Carbon 2002;40:2693–8. [21] Duesberg GS, Blau WJ, Byrne HJ, Muster J, Burghard M, Roth S. Experimental observation of individual single-wall nanotube species by Raman microscopy. Chem Phys Lett 1999;310:8–14. [22] Tseng CH, Wang CC, Chen CY. Functionalizing carbon nanotubes by plasma modification for the preparation of covalent-integrated epoxy composites. Chem Mater 2007;19:308–15. [23] Ray SS, Vaudreuil S, Maazouz A, Bousmina M. Dispersion of multi-walled carbon nanotubes in biodegradable poly(butylenes succinate) matrix. J Nanosci Nanotechnol 2006;6:2191–5. [24] Sandlera J, Shaffera MSP, Prasseb T, Bauhoferb W, Schultea K, Windlea AH. Development of a dispersion process for carbon nanotubes in an epoxy matrix and the resulting electrical properties. Polymer 1999;40:5967–71. [25] Bai JB, Allaoui A. Effect of the length and the aggregate size of MWNTs on the improvement efficiency of the mechanical and electrical properties of nanocomposites-experimental investigation. Composites Part A 2003;34:689–94. [26] Hu G, Zhao C, Zhang S, Yang M, Wang Z. Low percolation thresholds of electrical conductivity and rheology in poly(ethylene terephthalate) through the networks of multi-walled carbon nanotubes. Polymer 2006;47:480–8. [27] Harry SK, John VM. Handbook of fillers for plastics. New York: Van Nostrand Reinhold Co; 1987.
Contents lists available at SciVerse ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice
Nanocomposites with enhanced electrical properties based on biodegradable poly(butylene succinate) and polyetheramine modified carbon nanotube Chin-Sheng Lin a, Yeng-Fong Shih b,*, Ru-Jong Jeng c, Shenghong A. Dai a, Jiang-Jen Lin c, Chuan-Chen Lee d a
Department of Chemical Engineering, National Chung Hsing University, Taichung 40227, Taiwan Department of Applied Chemistry, Chaoyang University of Technology, Wufeng District, Taichung 41319, Taiwan c Institute of Polymer Science and Engineering, National Taiwan University, Taipei 10617, Taiwan d Department of Health and Nutrition Biotechnology, Asia University, Wufeng, Taichung 41354, Taiwan b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 7 August 2011 Received in revised form 5 October 2011 Accepted 10 October 2011 Available online 13 November 2011
In order to improve the compatibility between the poly(butylene succinate) (PBS) and multi-walled carbon nanotubes (MWNTs), Jeffamine1 Polyetheramines were grafted onto MWNTs. The results show that excellent dispersion of nanotubes in the PBS matrices was achieved. An improvement in thermal properties of the PBS/MWNTs nanocomposites was also observed. With the addition of 3.0 wt% MWNT2070D, the Td of the nanocomposite was 10.1 8C higher than that of the pristine PBS sample. Apart from that, the increments of E0 and E00 of the nanocomposite at 25 8C were 113 and 116%, respectively. In the aspect of conductivity, the surface resistivity decreased from 2.35 1014 V/& for neat PBS to 5.88 103 V/& for the nanocomposites with a 3.0 wt% of MWNT-2070D. Such PBS/MWNT-2070D nanocomposites are potentially efficient for anti-static purposes, even electrostatic discharge and EMI shielding, which can be applied in electronic materials. ß 2011 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Keywords: Carbon nanotube Poly(butylene succinate) Nanocomposite Electrical property
1. Introduction The development of biodegradable polymers has been a subject of great interest in materials science from both ecological and biomedical perspectives [1]. Due to the problems of worsening environmental pollution, increasing awareness of environmental damage caused by plastic materials over the last few decades has led to research aimed at producing eco-friendly versions of those plastics. One of these biodegradable polymers is poly(butylene succinate) (PBS). PBS is synthesized through the polycondensation reaction of glycols, such as ethylene glycol and 1,4-butanediol, and aliphatic dicarboxylic acids, such as succinic acid and adipic acid. This biodegradable polymer exhibits a melting point similar to low-density polyethylene (LDPE), a glass transition temperature and tensile strength between polyethylene (PE) and poly(propylene) (PP), and a stiffness between LDPE and high-density polyethylene (HDPE). PBS possesses satisfactory strength and toughness, close to that of LDPE [2–5], which is considered highly promising as a commercial commodity polymer. Since the first observation of carbon nanotubes in 1991 by Iijima [6] and the awareness of their distinctive mechanical, thermal and electrical properties, extensive research in the field of
* Corresponding author. Tel.: +886 4 233230004586; fax: +886 4 23742341. E-mail address: [email protected] (Y.-F. Shih).
CNT/polymer nanocomposites has been conducted. However, the optimal amount of multi-walled carbon nanotubes (MWNT) is only 1 wt% because excessive MWNT would cause separation of the organic and inorganic phases and lower their compatibility [7,8]. Therefore, organic modification of MWNTs to increase their organophilic properties is required for many industrial applications. One approach is to take advantage of the oxidative formation of carboxyl functionalities and subsequently to graft organic moieties onto the tubes. A great deal of research effort followed this route to the preparation of soluble nanotubes [9–12]. Even though research on polymer/CNT composites is growing rapidly, biodegradable polymer/CNT composites are seldom prepared. Additionally, most biodegradable polymer/CNT composites have been prepared directly by mixing the biodegradable polymer with acidified CNT [13,14], or by in situ polymerization [15,16], and the CNTs therein are not modified chemically to improve their dispersion in the polymer matrix. Lin et al. [17] demonstrated the feasibility of functionalizing MWNTs with carbonyl derivatives through oxidation. Subsequently, the poly(oxyalkylene)-amine (POA-amine) pendants were grafted onto MWNTs via amide linkages. Three different amidation routes (direct thermal amidation, acylation-mediated amidation and N,N0 -dicyclohexylcarbodiimide (DCC)-coupling amidation for grafting POA-amines onto MWNTs were investigated. The results reveal that the DCCcoupling method is more effective for grafting diamines onto MWNT-COOH via amide linkages. In our previous study [18], we
1876-1070/$ – see front matter ß 2011 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jtice.2011.10.009
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
323
Scheme 1. Surface modification of MWNTs.
modified the MWNTs with stearyl alcohol via the DCC-coupling method to establish a long alkyl chain on the MWNTs, so as to reduce the aggregation of MWNTs, and improve the compatibility between MWNTs and polymers. As a result, the PBS/MWNTs-C18 nanocomposites exhibited not only a good dispersion of nanotubes in the PBS matrices, but an improvement in thermal and mechanical properties as well. Moreover, a decrease of over 109fold in value of the electrical resistivity and an excellent anti-static capacity were found for the composite with 3 wt% MWNTs-C18. In this study, the surfaces of multi-walled carbon nanotubes (MWNTs) were chemically modified to enhance the compatibility between PBS and MWNTs. MWNTs were first pre-treated using acid solution to obtain functionalized carboxylic groups. Next, Jeffamine1 Polyetheramines were grafted onto MWNTs with the assistance of a dehydrating agent. Jeffamine1 Polyetheramines possess ethylene oxide (EO) and propylene oxide (PO) groups. It is expected that the more similar structure of PBS to Jeffamine1 Polyetheramines than stearyl alcohol would be more effective in improving the compatibility between the PBS and the modified MWNTs. Subsequently, the PBS/MWNT nanocomposites were prepared through melt-blending. As a result, the mechanical properties, thermal behavior and conductivity of these resultant polymer/MWNT composites can be further enhanced.
Chemical Perfomance Polymers Inc., Japan. The Jeffamine1 Polyetheramines (M2005 (EO/PO = 6/29, M.W. = 1977) and M2070 (EO/ PO = 31/10, M.W. = 2063)), supplied by Huntsman Co., were used to modify the multi-walled carbon nanotubes (purity > 95%, obtained from Scientech Co., Taiwan). 2.2. Surface modification of MWNTs The surface modification of MWNTs was achieved by the following. First, purified MWNTs were dispersed in HNO3 and kept at 120 8C for 60 min in the reflux system for introducing carboxyl groups at their opening ends and defect locations on their walls. The obtained MWNT-COOH was dispersed in dry DMF and mixed with Jeffamine1 Polyetheramines (M2005 (EO/PO = 6/29), M2070 (EO/ PO = 31/10)) and N,N0 -dicyclohexylcarbodiimide (DCC), and reacted at room temperature for 48 h, to graft the Jeffamine1 Polyetheramines onto MWNTs (MWNT-2005D, MWNT-2070D (with DCC), MWNT-2005, MWNT-2070 (without DCC)) (Scheme 1). 2.3. Preparation of PBS/MWNT nanocomposites
2. Experimental
The PBS/MWNT nanocomposites were prepared through meltblending at 120 8C with a rotor speed of 60 rpm for 5 min (Scheme 2). The mixed samples were then compressed under a pressure of about 200 kgf/cm2 at 140 8C for 3 min using a hot press.
2.1. Materials
2.4. Characterizations
Polybutylene succinate (PBS, GS Pla1 AZ91 T) with a melting point of 110 8C and a density of 1.26 g/m3 was supplied by Mitsubishi
Thermogravimetric analyses (TGA) were performed using a ThermoCahn VersaTherm analyzer. Samples were heated from
Scheme 2. Illustration of the melt-blending process.
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
324
Fig. 1. Dispersion of (a) pristine MWNT, (b) MWNT-COOH, (c) MWNT-2005D, (d) MWNT-2005, (e) MWNT-2070D, (f) MWNT-2070 in water and chloroform.
room temperature to 800 8C at a heating rate of 10 8C/min under a nitrogen purge. Raman Spectrum (TRIAX 550 Jobin-Yvon) was used to analyze the structure of MWNTs after modification. Dynamic mechanical behaviors of the nanocomposites were measured by a Perkin Elmer DMA 7E. The dimensions of samples were 2 mm 18 mm 10 mm and the tests were performed in a three-point bending mode at a frequency of 1 Hz. Surface resistivities of the nanocomposites were measured using a Hioki SM-8220 Ultra Megohmmeter and a GWInstek GOM-802 DC MilliOHM Meter. Scanning electron microscopy (SEM) (JEOL JSM6700F) was used to observe the fractured surface of PBS/MWNT nanocomposites with different MWNT contents. 3. Results and discussion 3.1. Characterization of Jeffamine1 Polyetheramine grafted MWNTs Fig. 1(a) shows that the pristine carbon nanotubes (p-MWNT) do not exhibit either hydrophilicity or hydrophobicity. The dispersibility of MWNT-COOH is remarkably changed after modification. MWNT-COOH is hydrophilic and well dispersed in water (Fig. 1(b)). It was found that the presence of EO or PO chains plays a critical role in the solubilization process. MWNT-2005D and MWNT-2005 possess more hydrophobic PO chains, which are well dispersed in chloroform (Fig. 1(c) and (d)). Otherwise, MWNT2070D and MWNT-2070 possess more hydrophilic EO chains, which are well dispersed in water (Fig. 1(e) and (f)). After modification, the thermal stability of carbon nanotubes is decreased due to organic attachment (Fig. 2). The attached
Fig. 2. TGA curves for MWNTs.
Fig. 3. (a) Raman spectrum and (b) the value of ID/IG for MWNTs.
organic content [19] was estimated according to the residual weight of the functionalized MWNTs at 500 8C. The estimated organic attachment content of MWNT-2005D, MWNT-2070D, MWNT-2005 and MWNT-2070 are 11.7, 10.6, 9.5 and 6.8 wt%, respectively. The results reveal that DCC promoted the grafting reaction effectively. Raman spectroscopy is a powerful technique to evaluate the quality of modified MWNT products. The G band located around 1586 cm1 is assigned to the C–C bond motions for a perfect hexagonal structure. On the other hand, the D band centered around 1340 cm1 is usually ascribed to the existence of disordered carbon in bulk carbon. It is attributed to lattice defects, which induce a breaking of the 2D translational symmetry [20]. The intensity ratio of the G and D modes (IG/ID) is often regarded as an indicator of the purity of modified MWNT products [21]. Generally, low ID/IG corresponds to high-purity tube products. As shown in Fig. 3, it was found that the ID/IG value of MWNTCOOH was greater than that of original MWNTs due to the breaking of the 2D translational symmetry of MWNTs after acid treatment. Moreover, the ID/IG values of Jeffamine1 Polyetheramine modified MWNTs were all larger than that of MWNT-COOH. This indicates that the 2D translational symmetry of MWNTs subsequently decreased after the alkylation process. The results also reveal that the ID/IG values of the alkylated MWNTs using a DCC agent (MWNT-2005D and MWNT-2070D) were larger than those of the ones without a DCC agent (MWNT-2005 and MWNT-2070). This is consistent with the TGA results (Fig. 2) showing that DCC promoted the grafting reaction effectively.
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
325
Table 1 Td5 of PBS/MWNTs nanocomposites. Sample
Td5 (8C)
PBS PBS + 3.0%p-MWNT PBS + 3.0%MWNT-2005D PBS + 3.0%MWNT-2005 PBS + 3.0%MWNT-2070D PBS + 3.0%MWNT-2070
352.7 350.3 354.5 351.3 362.8 357.2
3.2. Thermal properties of PBS/MWNT nanocomposites Table 1 shows the thermal decomposition temperature (Td) of the nanocomposite at a 5 wt% weight loss, exhibiting that the addition of MWNT-2070, MWNT-2070D and MWNT-2005D enhanced the Tds for the PBS/MWNT nanocomposites. This was due to the fact that the structure of nanotubes retards organic combustion and acts as a gas barrier that prevents the permeation of volatile gas out of the nanocomposites during thermal decomposition [22]. Enhancement of the thermal stability of M2070-modified MWNTs containing a nanocomposite is more remarkable than that of p-MWNT containing one. With the addition of 3 wt% MWNT-2070D, the Td of the nanocomposite was increased as much as 10.1 8C. This suggests that MWNT-2070D can be dispersed more homogenously than the other modified MWNTs in PBS, providing a good interfacial adhesion with the PBS matrices [23]. The results also reveal that the Tds of the nanocomposites containing alkylated MWNTs using a DCC agent (PBS + 3.0%MWNT-2005D and PBS + 3.0%MWNT-2070D) were larger than those of the ones containing alkylated MWNTs without a DCC agent (PBS + 3.0%MWNT-2005 and PBS + 3.0%MWNT-2070). This is consistent with the Raman Analysis (Fig. 3) that DCC can promote the grafing reaction. Subsequently, the interfacial adhesion between MWNTs and the PBS matrices was improved and led to better thermal stability of the nanocomposites. 3.3. Mechanical properties of PBS/MWNT nanocomposites Fig. 4 shows variations of the storage modulus (E0 ) with MWNT content for PBS/MWNT nanocomposites at 25 8C, and the results show that E0 increased with the increase in the nanotube content. This implies that nanotubes could enhance the rigidity of nanocomposites. The enhancement of the mechanical properties of the MWNT-2070D system was more remarkable than that of the p-MWNT system. With the addition of 3 wt% MWNT-2070D, the increment of E0 for the nanocomposite increased up to 113% (from 191 to 407 MPa). This is consistent with the results of a TGA
Fig. 5. Loss modulus of PBS/MWNT nanocomposites at 25 8C.
analysis that showed interfacial adhesion between MWNT-2070D and the PBS matrices was better than those of the other modified MWNTs in PBS. Moreover, the results also reveal that the E0 s of the nanocomposites containing alkylated MWNTs using a DCC agent (PBS/MWNT-2005D and PBS/MWNT-2070D) were larger than those of the ones containing alkylated MWNTs without a DCC agent (PBS/ MWNT-2005 and PBS/MWNT-2070). This is consistent with the results from the thermal analysis (Fig. 2 and Table 1) that showed that the higher grafing ratio via DCC led to better compatibility and better mechanical properties for nanocomposites. Fig. 5 shows variations of the loss modulus (E00 ) with MWNT content for PBS/MWNTs nanocomposites at 25 8C, and the results show that E00 increased with the increase in the nanotube content. The enhancement of the mechanical properties of the MWNT2070D system was more remarkable than that of the p-MWNT system. With the addition of 3 wt% MWNT-2070D, the increment of E00 for the nanocomposite increased up to 116% (from 15.4 to 33.3 MPa). Moreover, the E00 s of the nanocomposites containing alkylated MWNTs using a DCC agent (PBS/MWNT-2005D and PBS/ MWNT-2070D) were larger than those of the ones containing alkylated MWNTs without a DCC agent (PBS/MWNT-2005 and PBS/ MWNT-2070). This is identical to the results of the storage modulus. Table 2 shows the Tgs of PBS/CNTs nanocomposites from the E00 peak. The Tgs of the nanocomposites containing alkylated MWNTs
Table 2 Tgs (8C, from E00 peak) of PBS/CNTs nanocomposites. PBS/MWNTs
0 wt%
0.5 wt%
1.5 wt%
3.0 wt%
PBS/p-MWNT PBS/MWNT-2005D PBS/MWNT-2005 PBS/MWNT-2070D PBS/MWNT-2070
36.7 36.7 36.7 36.7 36.7
36.0 35.5 36.0 34.5 35.8
35.4 33.1 35.2 32.9 34.8
34.6 31.5 35.0 31.1 34.1
Table 3 Surface resistivity of PBS/MWNTs nanocomposites.
Fig. 4. Storage modulus of PBS/MWNT nanocomposites at 25 8C.
MWNTs
0.5 wt%
1.5 wt%
3.0 wt%
PBS/p-MWNT PBS/MWNT-2005D PBS/MWNT-2005 PBS/MWNT-2070D PBS/MWNT-2070
1.55 1011 4.59 109 8.64 1010 4.78 109 9.58 1010
3.63 108 8.12 105 1.73 107 5.65 105 6.01 105
8.71 105 4.68 104 8.40 105 5.88 103 1.08 104
326
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
Fig. 6. SEM micrographs of the fracture surface of (a) PBS, (b) PBS + 0.5%p-MWNT, (c) PBS + 1.5%p-MWNT and (d) PBS + 3.0%p-MWNT.
Fig. 7. SEM micrographs of the fracture surface of (a) PBS + 0.5%MWNT-2005D, (b) PBS + 1.5%MWNT-2005D, (c) PBS + 3.0%MWNT-2005D, (d) PBS + 0.5%MWNT-2005, (e) PBS + 1.5%MWNT-2005 and (f) PBS + 3.0%MWNT-2005.
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
using a DCC agent (PBS/MWNT-2005D and PBS/MWNT-2070D) was larger than that of ones containing alkylated MWNTs without a DCC agent (PBS/MWNT-2005 and PBS/MWNT-2070). The Tgs of the nanocomposites can be elevated about 5 8C with the addition of 3 wt% MWNT-2005D or MWNT-2070D. This indicates that better adhesion between MWNTs and PBS matrices via Jeffamine1 Polyetheramines modification by DCC can obviously influence the mobility of the PBS chain and lead to a higher transition temperature. From the results of the DMA, the enhanced mechanical properties confirm that the Jeffamine1 Polyetheramine modified carbon nanotubes were well dispersed in PBS matrices and interaction was greatly increased between the PBS and modified carbon nanotubes. 3.4. Electrical properties of PBS/MWNT nanocomposites Table 3 shows the effect of MWNT content on surface resistivity for PBS/MWNT composites. At a very low content of MWNTs, the surface resistivity gradually decreased with increasing nanotube content. MWNTs in the polymer matrices would intertwine with each other and then form an interconnecting conductive pathway: an electrical percolation threshold [24–26]. The surface resistivity of the PBS/MWNT composites decreased from >1014 V/& (pristine
327
PBS: 2.35 1014) to 103 V/& (for PBS/MWNT-2070D), a decrease of about 1011-fold in the value of the electrical resistivity. In comparison to our previous study [18], a decrease of about 109fold in the value of the electrical resistivity was achieved for the composite with 3 wt% MWNT-C18 (the MWNT modified by stearyl alcohol via the DCC-coupling method). The decrease of surface resistivity of PBS/MWNT-2070D composites was obviously larger than that of the other composites and PBS/MWNTs-C18 system, indicating a better dispersion of MWNT-2070D in the polymer matrices compared with those of other MWNTs. This implies that the percolation thresholds of electrical conductivity were depressed. For this reason, the well-dispersed MWNT-2070D in the PBS matrices could easily connect with each other. Therefore, the amount of MWNTs needed to construct a conductive pathway was reduced. In general, electric resistance between 108 and 1012 V would be capable of handling the anti-static function [27]. Therefore, the PBS/MWNT nanocomposites can serve the purpose of electrostatic discharge as electronic packing materials. 3.5. SEM analysis The SEM photographs of the fracture surface of PBS/MWNT nanocomposites are shown in Figs. 6–8. Fig. 6 reveals that many
Fig. 8. SEM micrographs of the fracture surface of (a) PBS + 0.5%MWNT-2070D, (b) PBS + 1.5%MWNT-2070D, (c) PBS + 3.0%MWNT-2070D, (d) PBS + 0.5%MWNT-2070, (e) PBS + 1.5%MWNT-2070 and (f) PBS + 3.0%MWNT-2070.
328
C.-S. Lin et al. / Journal of the Taiwan Institute of Chemical Engineers 43 (2012) 322–328
entangled clusters of MWNT in PBS matrices were observed for the p-MWNT system. Apparently, the modified MWNTs dispersed homogenously both in the 2005D (Fig. 7(a)–(c)) and 2070D (Fig. 8(a)–(c)) systems, which indicates that the modified MWNTs are more compatible with the PBS matrices as compared with pMWNTs. Better dispersion of the modified MWNTs in PBS/MWNT nanocomposites was due to the chemical modification of the MWNT, which would bring about better compatibility with PBS. On the other hand, some entangled clusters of MWNT in PBS matrices were still found for 2005 (Fig. 7(d)–(f)) and 2070 (Fig. 8(d)–(f)) systems. This is consistent with the results from the thermal analysis, indicating that the higher grafting ratios via DCC led to better compatibility and better mechanical properties for nanocomposites. The results of SEM show that the nanotubes were more compatible with the PBS matrices after the chemical modification, leading to better thermal, mechanical and electrical properties. 4. Conclusions We have successfully modified MWNTs by using Jeffamine1 Polyetheramines and DCC dehydrating agents. The modified MWNT-2005D and MWNT-2070D samples can be well dispersed in organic solvents and incorporated into the PBS matrices through simple melt-blending. The results obtained show that thePBS/ MWNT-2005D and PBS/MWNT-2070D nanocomposites exhibited not only good dispersion of nanotubes in the PBS matrices, but an improvement in thermal and mechanical properties as well. The enhancements of the thermal, mechanical and electrical properties of the MWNT-2070D system were more remarkable than for the MWNT-2005D system. The decomposition temperature of the nanocomposite increased up to 10.1 8C, and the increment of E0 for the nanocomposite at 25 8C amounted to 113%, compared with the neat PBS sample. Moreover, a decrease of about 1011-fold in value of the electrical resistivity and an excellent anti-static capacity were found for the composite with 3 wt% MWNT-2070D. References [1] Ikada Y, Tsuji H. Biodegradable polyesters for medical and ecological applications. Macromol Rapid Commun 2000;21:117–32. [2] Fujimaki T. Processability and properties of aliphatic polyesters, ‘BIONOLL E’, synthesized by polycondensation reaction. Polym Degrad Stab 1998;59: 209–14. [3] Mani R, Bhattacharya M. Properties of injection moulded blends of starch and modified biodegradable polyesters. Eur Polym J 2001;37:515–26. [4] Lim ST, Hyun YH, Choi HJ, Jhon MS. Synthetic biodegradable aliphatic polyester/montmorillonite nanocomposites. Chem Mater 2002;14:1839–44.
[5] Shih YF, Chieh YC. Thermal degradation behavior and kinetic analysis of biodegradable polymers using various comparative models, 1: poly(butylene succinate). Macromol Theor Simul 2007;16:101–10. [6] Iijima S. Helical microtubules of graphitic carbon. Nature 1991;354:56–8. [7] Cheah K, Simon GP, Forsyth M. Effects of polymer matrix and processing on the conductivity of polymer blends. Polym Int 2001;50:27–36. [8] Hussain F, Hojjati M, Okamoto M, Gorga RE. Polymer–matrix nanocomposites, processing, manufacturing, and application: an overview. J Compos Mater 2006;40:1511–75. [9] Hong CY, You YZ, Pan CY. Synthesis of water-soluble multiwalled carbon nanotubes with grafted temperature-responsive shells by surface RAFT polymerization. Chem Mater 2005;17:2247–54. [10] Gao C, Jin YZ, Kong H, Whitby RLD, Acquah SFA, Chen GY, et al. Polyureafunctionalized multiwalled carbon nanotubes: synthesis, morphology, and Raman spectroscopy. J Phys Chem B 2005;109:11925–32. [11] Chen J, Hamon MA, Hui H, Chen Y, Rao AM, Eklund PC, et al. Solution properties of single-walled carbon nanotubes. Science 1998;282:95–8. [12] Chen C, Zhang Y. Manipulation of single-wall carbon nanotubes into dispersively aligned arrays between metal electrodes. Phys D Appl Phys 2006;39: 172–6. [13] Song L, Qiu Z. Crystallization behavior and thermal property of biodegradable poly(butylene succinate)/functional multi-walled carbon nanotubes nanocomposite. Polym Degrad Stab 2009;94:632–7. [14] Sanchez-Garcia MD, Lagaron JM, Hoa SV. Effect of addition of carbon nanofibers and carbon nanotubes on properties of thermoplastic biopolymers. Compos Sci Technol 2010;70:1095–105. [15] Chakoli AN, Wan J, Feng JT, Amirian M, Sui JH, Cai W. Functionalization of multiwalled carbon nanotubes for reinforcing of poly(L-lactide-co-e-caprolactone) biodegradable copolymers. Appl Surface Sci 2009;256:170–7. [16] Kim HS, Chae YS, Park BH, Yoon JS, Kang M, Jin HJ. Thermal and electrical conductivity of poly(L-lactide)/multiwalled carbon nanotube nanocomposites. Curr Appl Phys 2008;8:803–6. [17] Lin ST, Wei KL, Lee TM, Chiou KC, Lin JJ. Functionalizing multi-walled carbon nanotubes with poly(oxyalkylene)-amidoamines. Nanotechnology 2006;17: 3197–203. [18] Shih YF, Chen LS, Jeng RJ. Preparation and properties of biodegradable PBS/ multi-walled carbon nanotube nanocomposites. Polymer 2008;49:4602–11. [19] Zhao C, Ji L, Liu H, Hu G, Zhang S, Yang M, et al. Functionalized carbon nanotubes containing isocyanate groups. J Solid State Chem 2004;177:4394–8. [20] Yan H, Li Q, Zhang J, Liu Z. Possible tactics to improve the growth of single-walled carbon nanotubes by chemical vapor deposition. Carbon 2002;40:2693–8. [21] Duesberg GS, Blau WJ, Byrne HJ, Muster J, Burghard M, Roth S. Experimental observation of individual single-wall nanotube species by Raman microscopy. Chem Phys Lett 1999;310:8–14. [22] Tseng CH, Wang CC, Chen CY. Functionalizing carbon nanotubes by plasma modification for the preparation of covalent-integrated epoxy composites. Chem Mater 2007;19:308–15. [23] Ray SS, Vaudreuil S, Maazouz A, Bousmina M. Dispersion of multi-walled carbon nanotubes in biodegradable poly(butylenes succinate) matrix. J Nanosci Nanotechnol 2006;6:2191–5. [24] Sandlera J, Shaffera MSP, Prasseb T, Bauhoferb W, Schultea K, Windlea AH. Development of a dispersion process for carbon nanotubes in an epoxy matrix and the resulting electrical properties. Polymer 1999;40:5967–71. [25] Bai JB, Allaoui A. Effect of the length and the aggregate size of MWNTs on the improvement efficiency of the mechanical and electrical properties of nanocomposites-experimental investigation. Composites Part A 2003;34:689–94. [26] Hu G, Zhao C, Zhang S, Yang M, Wang Z. Low percolation thresholds of electrical conductivity and rheology in poly(ethylene terephthalate) through the networks of multi-walled carbon nanotubes. Polymer 2006;47:480–8. [27] Harry SK, John VM. Handbook of fillers for plastics. New York: Van Nostrand Reinhold Co; 1987.