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Co-PAN composite fibers prepared by wet spinning
Synthetic Metals 149 (2005) 181–186
Electrically conductive PANI-DBSA/Co-PAN composite fibers prepared by wet spinning Jiang Jianminga , Pan Weia,b , Yang Shenglina , Li Guanga,∗ a
State Key Laboratory for Modification of Chemical Fibers and Polymer Material, Donghua University, Shanghai 200051, PR China b Zhongyuan Institute of Technology, Zhengzhou 450007, PR China Received 16 September 2004; received in revised form 14 December 2004; accepted 30 December 2004 Available online 1 February 2005
Abstract Conductive composite fibers of polyaniline doped with dodecylbenzene sulfonic acid (PANI-DBSA) and polyacrylonitrile containing methylacrylate (Co-PAN) were prepared via a conventional wet spinning process. The influences of PANI-DBSA content on the electrical conductivity, thermal stability and mechanical properties of the composite fibers were investigated. The fiber with 7 wt% PANI-DBSA showed its conductivity of an order of 10–3 S/cm. The tensile strength of the fibers was in the range of 2.5–3.5 cN/dtex. The thermal stability of the composite fiber was superior to both pure Co-PAN and PANI-DBSA. It was observed through scanning electron microscope (SEM) and transmission electron microscope (TEM) that nanosized dot-like PANI-DBSA was well dispersed within Co-PAN matrix. © 2005 Elsevier B.V. All rights reserved. Keywords: Polyaniline; Polyacrylonitrile; Conductivity; Composite fiber; Wet spinning
1. Introduction Polyaniline (PANI) is one of the most promising conducting polymers due to its straightforward polymerization and excellent chemical stability combined with relatively high levels of conductivity. Volumes of researches focusing on conducting PANI have been made in developing soluble or melt-processable PANI [1–3], and significant progresses have been made in this area since the last decades [4–6]. The counter-ion induced solubility of PANI is a successful attempt to solve the processing problem of PANI. For example, PANI doped with organic acids containing long alkyl chains, such as camphor sulfuric acid (CSA) or dodecylbenzene sulfonic acid (DBSA), could be soluble in some common solvents. The soluble PANI was then usually blended with some insulative polymers to prepare conducting polymer composites to explore the possibilities of applications [7–9]. The conductivities and morphologies of these com∗
Corresponding author. E-mail address: [email protected] (G. Li).
0379-6779/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2004.12.008
posites are varied with different components [10]. Roichman et al. studied PANI-DBSA/PS blends cast from xylene, and found that the conductivity of the blends depended on the dispersion of PANI-DBSA in PS matrix. Under the same content of 10% PANI-DBSA, the conductivity of the blends could be from 10−7 to 10−1 S/cm. Furthermore, the dispersion of PANI-DBSA in PS was strongly related to the rate of oxidant addition while PANI was synthesized by chemical oxidation polymerisation [11]. Polycarbonate (PC) was also used as a matrix to prepare PANI-DBSA/PC composites. PANI-DBSA was produced at the presence of PC in chloroform by emulsion polymerization in which DBSA played as both surfactant and dopent. The PANI-DBSA/PC composite with 13 wt% PANI has an electrical conductivity of 10−2 S/cm [12]. Except for solution mixing, Zilberman et al. prepared conductive PANI-DBSA/PS, PANI-DBSA/PE and PANI-DBSA/Co-PA blends by melt processing. It was found that for a given 20 wt% PANI-DBSA and 80 wt% matrix polymer, the electrical conductivities of the blends varied different polymer matrix, in which the PANI-DBSA/PS exhibited the highest conductivity while the PANI-DBSA/Co-PA showed
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lowest conductivity, which was consistent with their morphology observation via SEM [13]. It should be noticed most publications about conductive polymer composites concern their film materials, and only a few papers are related to conductive fibers. Zhang et al. prepared conductive polyaniline/poly-anioundecanoyle blending fiber by dissolving polyaniline and poly--anioundecanoyle in sulfonic acid, then via wet spinning [14]. Electrostatic fabrication technology was employed by Norris et al. [15] to prepare ultra fine conducting polyaniline/polyethylene oxide blend fibers. Passiniemi reported that the polyaniline/PP blending conductive fiber with an electrical conductivity of up to 10−3 S/cm were prepared by melt spinning [16], where a proprietary plasticizer which was used to make PANI fusible. In this work, soluble polyaniline doped with dodecylbenzene sulfonic acid (PANI-DBSA) was used to blend with co-polyacrylonitrile (Co-PAN) containing methylacrylate via solution mixing. The blend solution was spun into the composite fiber via wet spinning technique. The conductivity, property as well as morphology of the PANI-DBSA/Co-PAN composite fibers were investigated.
2. Experimental 2.1. Preparation of samples The soluble polyaniline doped with dodecylbenzene sulfonic acid (PANI-DBSA) was prepared by emulsion polymerization according to the procedure described in literature [17]. PANI-DBSA was dissolved in chloroform and Co-PAN containing 10 wt% methylacrylate component (supplied by Shanghai Petroleum Chemical Company) was dissolved in DMSO. Then these two solutions were mixed together according to the desired compositions; the total concentration of PANI-DBSA and Co-PAN was kept as 17 wt%. To prepare PANI-DBSA/Co-PAN composite film samples, the blend solutions were cast into a film and left to dry at room temperature for 24 h, and then dried in vacuum at 60 ◦ C for 48 h. To prepare fiber samples, the blend solutions were first filtered and degassed under a reduce pressure at room temperature, and then spun into fibers via conventional wet spinning technique. 2.2. Measurements Electrical conductivities of the samples were measured by the usual four-probe method. JSM-5600LV scanning electron microscope (SEM) and JEM-200CX transmission electron microscope (TEM) were employed to observe the morphology of the fibers and films. DSC thermograms of various samples were obtained at heating rate of 20 ◦ C/min in the range of 40–180 ◦ C under N2 atmosphere by Perkin-Elmer differential scanning calorimeter. The thermal stability of composite fibers was investigated by TGA (Du Pont l090)
Fig. 1. Schematic diagram of wet spinning process.
under air atmosphere. The mechanical properties were measured by means of AGS-500ND tensile tester at 20 ◦ C, 65% R.H. The gauge length was 20 mm, and crosshead speed was 20 mm/min.
3. Results and discussion 3.1. Wet spinning of PANI-DBSA/Co-PAN composite fibers The schematic diagram for wet spinning of PANIDBSA/Co-PAN composite fibers is shown in Fig. 1, which included spinning, coagulating, drawing, washing, oiling, drying and winding procedures. There were 210 spinneret holes in the adopted spinning head, and the diameter of each hole was 0.08 mm. The dope solution was spun into a coagulation bath (50% DMSO in water) at 20 ◦ C with a spinning speed of 15 mm/min. The as-spun fibers were continually drawn in warm water bath at 90 ◦ C at a draw ratio of 6. The color of resultant composite fibers was green or deep green when more PANI-DBSA content was applied. It should be noticed that the PANI-DBSA/Co-PAN blend dope showed as good spinnability as usual Co-PAN dope. 3.2. Conductivity of PANI-DBSA/Co-PAN composite fibers The effect of PANI-DBSA content on the electrical conductivity of the PANI-DBSA/Co-PAN fibers is shown in Fig. 2. It could be seen that with 5 wt% PANI-DBSA the composite fiber exhibits a conductivity value of 10−3 S/cm, which is a little lower than their corresponding film [11]. Norris et al. found the similar result that the conductivity of polyaniline doped with camphor sulfonic acid, and polyethylene oxide blend film was higher than that of the corresponding electro-spun fibers [15]. But Wang et al. reported that the conductivity of composite fibers spun from PANI/SBS complex was higher than that of films [17], and they regarded that the orientation of the polymer chains could improve the electrical conductivity of the complex. As a matter of fact, many factors, such as doped extent of PANI, dispersion and distribution of PANI in polymer matrix, as well as measuring technique will influence the conductivity of the blends. In the present case, lower electrical conductivity obtained for PANI-DBSA/Co-PAN composite fiber may be caused by strong washing during fiber formation, which will result in
J. Jianming et al. / Synthetic Metals 149 (2005) 181–186
Fig. 2. Electrical conductivity of PANI-DBSA/Co-PAN fibers (lower) and films (upper).
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sample is less homogeneous than in film samples. From TEM micrographs of cross sections of composite fibers at higher magnification (Fig. 5), it is clear that PANI-DBSA dispersed as a lot of separated dots and showed a tendency to form nonhomogeneous clusters. The average diameter of those dots was in the nanometer range. Although electrically conductive path could be formed by connection of dots at higher PANIDBSA content, it is less efficient as compared with the case of PANI-DBSA/Co-PAN film. Like Co-PAN matrix, PANIDBSA was orientated along axial direction of fibers under spinning and drawing. While film was formed via casting, no obviously directional force was applied in the sample. In fact, it is possible to form a random three-dimensional network of PANI-DBSA in film samples. Anyway, PANI-DBSA can disperse well in Co-PAN matrix as compared with in other polymer matrix such as in PS, EPDM, PE, etc. [11,18,19]. 3.4. Compatibility of PANI-DBSA and Co-PAN
the dedoping of PANI-DBSA from the fibers or by drawing along fiber axis during fiber production, which can disturb the network formation of PANI-DBSA in Co-PAN matrix. 3.3. The morphology of PANI-DBSA/Co-PAN fibers The surface and cross section of PANI-DBSA/Co-PAN composite fibers are shown in Fig. 3. The composite fiber still appears the characteristic kidney-shaped cross section. As compared with the SEM micrograph of the cross section of PANI-DBSA/Co-PAN composite films showed in Fig. 4, it is easy to see that the dispersion of PANI-DBSA in fiber
The good dispersion of PANI-DBSA in Co-PAN matrix should be ascribed to their better compatibility. DMA curves of both PANI-DBSA/Co-PAN (10 wt% PANI-DBSA) and pure Co-PAN are shown in Fig. 6. There is only one Tg for PANI-DBSA/Co-PAN, which is a little lower than that of pure Co-PAN. When PANI doped with p-toluene sulfuric acid (PANI-TSA) was employed to blend with EPDM, the systems with different content of PANI-TSA always appeared the same Tg as that of EPDM itself [19], which meant that PANI was not compatible with EPDM. From FT-IR spectra of PANI-DBSA/Co-PAN composite (Fig. 7), it could be
Fig. 3. Surface and cross section of PANI-DBSA/Co-PAN composite fiber.
Fig. 4. Cross section of PANI-DBSA/Co-PAN composite.
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Fig. 5. Cross section TEM micrographs of PANI-DBSA/Co-PAN composite fibers with different PANI-DBSA contents: (a) 0 wt%, (b) 2.5 wt%, (c) 5 wt% and (d) 10 wt%.
elucidated why PANI is compatible with Co-PAN. It was mentioned in previous context that Co-PAN used in this study contains methylacrylate segments. The absorption band at 1740 cm−1 is assigned to free carbonyl group absorption of pure Co-PAN. Furthermore, upon mixing Co-PAN with PANI-DBSA, the band is observed to slightly shift to lower wave numbers. The more the PANI-DBSA content, the lower the wave numbers. For PANI-DBSA 10 wt% blend, the carbonyl band is observed to be at 1731 cm−1 , 9 cm−1 lower than the band of free carbonyl. Whether hydrogen bonding
Fig. 6. DMA curves of (a) PAN and (b) PAN/PANI-DBSA (10 wt% PANIDBSA).
Fig. 7. FT-IR curves of carbonyl group in PAN/PANI-DBSA blend film (PANI-DBSA/PAN: (a) 0/100; (b) 2.5/97.5; (c) 5/95; (d) 10/90).
and is responsible for the shifts of between carbonyl group band in this composites? Fig. 8 shows the corresponding imine stretching bands of PANI-DBSA and PANI-DBSA/Co-PAN blends. The peak around 3450 cm−1
Fig. 8. FT-IR curves of imide group in PAN/PANI-DBSA blend film (PANIDBSA/PAN: (a) 0/100; (b) 2.5/97.5; (c) 5/95; (d) 10/90).
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Fig. 9. Proposed scheme of the hydrogen bonding between PANI-DBSA and Co-PAN.
comes from free imine groups (–NH–) of PANI-DBSA; at the same time, a shoulder at lower wave number (3285 cm−1 ) appears for PANI-DBSA/Co-PAN blends, and the intensity of this shoulder increases with the increasing PANI-DBSA content. Integrating the shift of carbonyl groups in Co-PAN sample, this shoulder peak should be attributed to the hydrogen bonding between imine and carbonyl group. The proposed scheme of the hydrogen bonding between PANI-DBSA and Co-PAN is given in Fig. 9. 3.5. Thermal stability of composite fibers TGA and DTG curves in Fig. 10 show the dependence of thermal stabilities of composites on PANI-DBSA content. There are two obvious weight loss peaks at 250–270 ◦ C and 550–580 ◦ C in the TGA curves. The first weight loss is caused by decarboxylation of the methylacrylate in Co-PAN, and the second weight loss is due to thermo-oxidative degradation of PAN macromolecular chains. For PANI-DBSA/CoPAN composite, the temperature of the first weight loss peak becomes higher when with more content of PANIDBSA, while the temperature of the second weight loss decreased with increasing PANI-DBSA content. The better thermal stability of the blend than either of pure PANIDBSA and pure Co-PAN before 500 ◦ C could be considered as additional evidence of interactions between PANIDBSA and Co-PAN. However, the hydrogen bonding will be destroyed at higher temperature and the decomposition of PANI-DBSA may accelerate the degradation of PANIDBSA/Co-PAN composite. This may be the reason that the peak temperature of thermo-oxidative degradation of the
Fig. 11. Tensile strength and elongation at break of the composite fibers.
blends gets a little lower with the increasing component of PANI-DBSA. 3.6. Mechanical properties The mechanical properties of the composite fibers with different PANI-DBSA contents are showed in Fig. 11. The tensile strength first increases, and then declines when the PANI-DBSA content changes from 0 to 10 wt%, the composite fiber with 5 wt%, and PANI-DBSA shows higher tensile strength than other composite fibers. On the other hand, the elongation at break reduces with the increase of PANIDBSA content. It could be considered that PANI-DBSA in the composites behaves as both an enhancing filler and a defect in the matrix polymer. With low adding of PANI-DBSA, the dispersion of PANI-DBSA in Co-PAN is well and homogeneous, and enhancing is predominant. More addition of PANI-DBSA may make defects in the matrix greatly or more, which will decrease the tensile strength (Fig. 11). 4. Conclusion The PANI-DBSA/Co-PAN composite fiber was firstly successfully prepared via conventional wet spinning technique. The fiber with 7 wt% showed it conductivity of an order of 10−3 S/cm, and showed suitable mechanical properties as well as better thermal stability as compared with the pure Co-PAN fibers.
Fig. 10. TGA and DTG curves of (a) PANI-DBSA, (b) Co-PAN and PANI-DBSA/Co-PAN composites with (c) 2.5%, (d) 5%, (e) 10% PANI-DBSA content.
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[9] E. Ruckenstein, S.A. Yang, Synth. Met. 53 (1993) 283. [10] H. Morgan, P.J. Foot, N.W. Brooks, J. Mater. Sci. 36 (2001) 5369. [11] Y. Roichman, G.I. Titelman, M.S. Silverstein, Synth. Met. 98 (1999) 201. [12] B.H. Jeon, S. Kim, M.H. Choi, Synth. Met. 104 (1999) 95. [13] M. Zilberman, G.I. Titelman, A. Siegmann, J. Appl. Polym. Sci. 66 (1997) 243. [14] Q. Zhang, X. Wang, D. Chen, J. Appl. Polym. Sci. 85 (2002) 1458. [15] I.D. Norris, M.M. Shaker, F.K. Ko, Synth. Met. 114 (2000) 109. [16] P. Passiniemi, Synth. Met. 101 (1999) 677. [17] H.L. Wang, R.J. Romero, B.R. Mattes, J. Polym. Sci., Part B: Polym. Phys. 38 (2000) 194. [18] G.R. Valenciano, A.E. Job, L.H. Mattoso, Polymer 41 (2000) 4757. [19] F. Roselena, A.G. Wilson, D.P. Marco-A, Polymer 40 (1999) 5497.
Electrically conductive PANI-DBSA/Co-PAN composite fibers prepared by wet spinning Jiang Jianminga , Pan Weia,b , Yang Shenglina , Li Guanga,∗ a
State Key Laboratory for Modification of Chemical Fibers and Polymer Material, Donghua University, Shanghai 200051, PR China b Zhongyuan Institute of Technology, Zhengzhou 450007, PR China Received 16 September 2004; received in revised form 14 December 2004; accepted 30 December 2004 Available online 1 February 2005
Abstract Conductive composite fibers of polyaniline doped with dodecylbenzene sulfonic acid (PANI-DBSA) and polyacrylonitrile containing methylacrylate (Co-PAN) were prepared via a conventional wet spinning process. The influences of PANI-DBSA content on the electrical conductivity, thermal stability and mechanical properties of the composite fibers were investigated. The fiber with 7 wt% PANI-DBSA showed its conductivity of an order of 10–3 S/cm. The tensile strength of the fibers was in the range of 2.5–3.5 cN/dtex. The thermal stability of the composite fiber was superior to both pure Co-PAN and PANI-DBSA. It was observed through scanning electron microscope (SEM) and transmission electron microscope (TEM) that nanosized dot-like PANI-DBSA was well dispersed within Co-PAN matrix. © 2005 Elsevier B.V. All rights reserved. Keywords: Polyaniline; Polyacrylonitrile; Conductivity; Composite fiber; Wet spinning
1. Introduction Polyaniline (PANI) is one of the most promising conducting polymers due to its straightforward polymerization and excellent chemical stability combined with relatively high levels of conductivity. Volumes of researches focusing on conducting PANI have been made in developing soluble or melt-processable PANI [1–3], and significant progresses have been made in this area since the last decades [4–6]. The counter-ion induced solubility of PANI is a successful attempt to solve the processing problem of PANI. For example, PANI doped with organic acids containing long alkyl chains, such as camphor sulfuric acid (CSA) or dodecylbenzene sulfonic acid (DBSA), could be soluble in some common solvents. The soluble PANI was then usually blended with some insulative polymers to prepare conducting polymer composites to explore the possibilities of applications [7–9]. The conductivities and morphologies of these com∗
Corresponding author. E-mail address: [email protected] (G. Li).
0379-6779/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2004.12.008
posites are varied with different components [10]. Roichman et al. studied PANI-DBSA/PS blends cast from xylene, and found that the conductivity of the blends depended on the dispersion of PANI-DBSA in PS matrix. Under the same content of 10% PANI-DBSA, the conductivity of the blends could be from 10−7 to 10−1 S/cm. Furthermore, the dispersion of PANI-DBSA in PS was strongly related to the rate of oxidant addition while PANI was synthesized by chemical oxidation polymerisation [11]. Polycarbonate (PC) was also used as a matrix to prepare PANI-DBSA/PC composites. PANI-DBSA was produced at the presence of PC in chloroform by emulsion polymerization in which DBSA played as both surfactant and dopent. The PANI-DBSA/PC composite with 13 wt% PANI has an electrical conductivity of 10−2 S/cm [12]. Except for solution mixing, Zilberman et al. prepared conductive PANI-DBSA/PS, PANI-DBSA/PE and PANI-DBSA/Co-PA blends by melt processing. It was found that for a given 20 wt% PANI-DBSA and 80 wt% matrix polymer, the electrical conductivities of the blends varied different polymer matrix, in which the PANI-DBSA/PS exhibited the highest conductivity while the PANI-DBSA/Co-PA showed
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lowest conductivity, which was consistent with their morphology observation via SEM [13]. It should be noticed most publications about conductive polymer composites concern their film materials, and only a few papers are related to conductive fibers. Zhang et al. prepared conductive polyaniline/poly-anioundecanoyle blending fiber by dissolving polyaniline and poly--anioundecanoyle in sulfonic acid, then via wet spinning [14]. Electrostatic fabrication technology was employed by Norris et al. [15] to prepare ultra fine conducting polyaniline/polyethylene oxide blend fibers. Passiniemi reported that the polyaniline/PP blending conductive fiber with an electrical conductivity of up to 10−3 S/cm were prepared by melt spinning [16], where a proprietary plasticizer which was used to make PANI fusible. In this work, soluble polyaniline doped with dodecylbenzene sulfonic acid (PANI-DBSA) was used to blend with co-polyacrylonitrile (Co-PAN) containing methylacrylate via solution mixing. The blend solution was spun into the composite fiber via wet spinning technique. The conductivity, property as well as morphology of the PANI-DBSA/Co-PAN composite fibers were investigated.
2. Experimental 2.1. Preparation of samples The soluble polyaniline doped with dodecylbenzene sulfonic acid (PANI-DBSA) was prepared by emulsion polymerization according to the procedure described in literature [17]. PANI-DBSA was dissolved in chloroform and Co-PAN containing 10 wt% methylacrylate component (supplied by Shanghai Petroleum Chemical Company) was dissolved in DMSO. Then these two solutions were mixed together according to the desired compositions; the total concentration of PANI-DBSA and Co-PAN was kept as 17 wt%. To prepare PANI-DBSA/Co-PAN composite film samples, the blend solutions were cast into a film and left to dry at room temperature for 24 h, and then dried in vacuum at 60 ◦ C for 48 h. To prepare fiber samples, the blend solutions were first filtered and degassed under a reduce pressure at room temperature, and then spun into fibers via conventional wet spinning technique. 2.2. Measurements Electrical conductivities of the samples were measured by the usual four-probe method. JSM-5600LV scanning electron microscope (SEM) and JEM-200CX transmission electron microscope (TEM) were employed to observe the morphology of the fibers and films. DSC thermograms of various samples were obtained at heating rate of 20 ◦ C/min in the range of 40–180 ◦ C under N2 atmosphere by Perkin-Elmer differential scanning calorimeter. The thermal stability of composite fibers was investigated by TGA (Du Pont l090)
Fig. 1. Schematic diagram of wet spinning process.
under air atmosphere. The mechanical properties were measured by means of AGS-500ND tensile tester at 20 ◦ C, 65% R.H. The gauge length was 20 mm, and crosshead speed was 20 mm/min.
3. Results and discussion 3.1. Wet spinning of PANI-DBSA/Co-PAN composite fibers The schematic diagram for wet spinning of PANIDBSA/Co-PAN composite fibers is shown in Fig. 1, which included spinning, coagulating, drawing, washing, oiling, drying and winding procedures. There were 210 spinneret holes in the adopted spinning head, and the diameter of each hole was 0.08 mm. The dope solution was spun into a coagulation bath (50% DMSO in water) at 20 ◦ C with a spinning speed of 15 mm/min. The as-spun fibers were continually drawn in warm water bath at 90 ◦ C at a draw ratio of 6. The color of resultant composite fibers was green or deep green when more PANI-DBSA content was applied. It should be noticed that the PANI-DBSA/Co-PAN blend dope showed as good spinnability as usual Co-PAN dope. 3.2. Conductivity of PANI-DBSA/Co-PAN composite fibers The effect of PANI-DBSA content on the electrical conductivity of the PANI-DBSA/Co-PAN fibers is shown in Fig. 2. It could be seen that with 5 wt% PANI-DBSA the composite fiber exhibits a conductivity value of 10−3 S/cm, which is a little lower than their corresponding film [11]. Norris et al. found the similar result that the conductivity of polyaniline doped with camphor sulfonic acid, and polyethylene oxide blend film was higher than that of the corresponding electro-spun fibers [15]. But Wang et al. reported that the conductivity of composite fibers spun from PANI/SBS complex was higher than that of films [17], and they regarded that the orientation of the polymer chains could improve the electrical conductivity of the complex. As a matter of fact, many factors, such as doped extent of PANI, dispersion and distribution of PANI in polymer matrix, as well as measuring technique will influence the conductivity of the blends. In the present case, lower electrical conductivity obtained for PANI-DBSA/Co-PAN composite fiber may be caused by strong washing during fiber formation, which will result in
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Fig. 2. Electrical conductivity of PANI-DBSA/Co-PAN fibers (lower) and films (upper).
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sample is less homogeneous than in film samples. From TEM micrographs of cross sections of composite fibers at higher magnification (Fig. 5), it is clear that PANI-DBSA dispersed as a lot of separated dots and showed a tendency to form nonhomogeneous clusters. The average diameter of those dots was in the nanometer range. Although electrically conductive path could be formed by connection of dots at higher PANIDBSA content, it is less efficient as compared with the case of PANI-DBSA/Co-PAN film. Like Co-PAN matrix, PANIDBSA was orientated along axial direction of fibers under spinning and drawing. While film was formed via casting, no obviously directional force was applied in the sample. In fact, it is possible to form a random three-dimensional network of PANI-DBSA in film samples. Anyway, PANI-DBSA can disperse well in Co-PAN matrix as compared with in other polymer matrix such as in PS, EPDM, PE, etc. [11,18,19]. 3.4. Compatibility of PANI-DBSA and Co-PAN
the dedoping of PANI-DBSA from the fibers or by drawing along fiber axis during fiber production, which can disturb the network formation of PANI-DBSA in Co-PAN matrix. 3.3. The morphology of PANI-DBSA/Co-PAN fibers The surface and cross section of PANI-DBSA/Co-PAN composite fibers are shown in Fig. 3. The composite fiber still appears the characteristic kidney-shaped cross section. As compared with the SEM micrograph of the cross section of PANI-DBSA/Co-PAN composite films showed in Fig. 4, it is easy to see that the dispersion of PANI-DBSA in fiber
The good dispersion of PANI-DBSA in Co-PAN matrix should be ascribed to their better compatibility. DMA curves of both PANI-DBSA/Co-PAN (10 wt% PANI-DBSA) and pure Co-PAN are shown in Fig. 6. There is only one Tg for PANI-DBSA/Co-PAN, which is a little lower than that of pure Co-PAN. When PANI doped with p-toluene sulfuric acid (PANI-TSA) was employed to blend with EPDM, the systems with different content of PANI-TSA always appeared the same Tg as that of EPDM itself [19], which meant that PANI was not compatible with EPDM. From FT-IR spectra of PANI-DBSA/Co-PAN composite (Fig. 7), it could be
Fig. 3. Surface and cross section of PANI-DBSA/Co-PAN composite fiber.
Fig. 4. Cross section of PANI-DBSA/Co-PAN composite.
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Fig. 5. Cross section TEM micrographs of PANI-DBSA/Co-PAN composite fibers with different PANI-DBSA contents: (a) 0 wt%, (b) 2.5 wt%, (c) 5 wt% and (d) 10 wt%.
elucidated why PANI is compatible with Co-PAN. It was mentioned in previous context that Co-PAN used in this study contains methylacrylate segments. The absorption band at 1740 cm−1 is assigned to free carbonyl group absorption of pure Co-PAN. Furthermore, upon mixing Co-PAN with PANI-DBSA, the band is observed to slightly shift to lower wave numbers. The more the PANI-DBSA content, the lower the wave numbers. For PANI-DBSA 10 wt% blend, the carbonyl band is observed to be at 1731 cm−1 , 9 cm−1 lower than the band of free carbonyl. Whether hydrogen bonding
Fig. 6. DMA curves of (a) PAN and (b) PAN/PANI-DBSA (10 wt% PANIDBSA).
Fig. 7. FT-IR curves of carbonyl group in PAN/PANI-DBSA blend film (PANI-DBSA/PAN: (a) 0/100; (b) 2.5/97.5; (c) 5/95; (d) 10/90).
and is responsible for the shifts of between carbonyl group band in this composites? Fig. 8 shows the corresponding imine stretching bands of PANI-DBSA and PANI-DBSA/Co-PAN blends. The peak around 3450 cm−1
Fig. 8. FT-IR curves of imide group in PAN/PANI-DBSA blend film (PANIDBSA/PAN: (a) 0/100; (b) 2.5/97.5; (c) 5/95; (d) 10/90).
J. Jianming et al. / Synthetic Metals 149 (2005) 181–186
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Fig. 9. Proposed scheme of the hydrogen bonding between PANI-DBSA and Co-PAN.
comes from free imine groups (–NH–) of PANI-DBSA; at the same time, a shoulder at lower wave number (3285 cm−1 ) appears for PANI-DBSA/Co-PAN blends, and the intensity of this shoulder increases with the increasing PANI-DBSA content. Integrating the shift of carbonyl groups in Co-PAN sample, this shoulder peak should be attributed to the hydrogen bonding between imine and carbonyl group. The proposed scheme of the hydrogen bonding between PANI-DBSA and Co-PAN is given in Fig. 9. 3.5. Thermal stability of composite fibers TGA and DTG curves in Fig. 10 show the dependence of thermal stabilities of composites on PANI-DBSA content. There are two obvious weight loss peaks at 250–270 ◦ C and 550–580 ◦ C in the TGA curves. The first weight loss is caused by decarboxylation of the methylacrylate in Co-PAN, and the second weight loss is due to thermo-oxidative degradation of PAN macromolecular chains. For PANI-DBSA/CoPAN composite, the temperature of the first weight loss peak becomes higher when with more content of PANIDBSA, while the temperature of the second weight loss decreased with increasing PANI-DBSA content. The better thermal stability of the blend than either of pure PANIDBSA and pure Co-PAN before 500 ◦ C could be considered as additional evidence of interactions between PANIDBSA and Co-PAN. However, the hydrogen bonding will be destroyed at higher temperature and the decomposition of PANI-DBSA may accelerate the degradation of PANIDBSA/Co-PAN composite. This may be the reason that the peak temperature of thermo-oxidative degradation of the
Fig. 11. Tensile strength and elongation at break of the composite fibers.
blends gets a little lower with the increasing component of PANI-DBSA. 3.6. Mechanical properties The mechanical properties of the composite fibers with different PANI-DBSA contents are showed in Fig. 11. The tensile strength first increases, and then declines when the PANI-DBSA content changes from 0 to 10 wt%, the composite fiber with 5 wt%, and PANI-DBSA shows higher tensile strength than other composite fibers. On the other hand, the elongation at break reduces with the increase of PANIDBSA content. It could be considered that PANI-DBSA in the composites behaves as both an enhancing filler and a defect in the matrix polymer. With low adding of PANI-DBSA, the dispersion of PANI-DBSA in Co-PAN is well and homogeneous, and enhancing is predominant. More addition of PANI-DBSA may make defects in the matrix greatly or more, which will decrease the tensile strength (Fig. 11). 4. Conclusion The PANI-DBSA/Co-PAN composite fiber was firstly successfully prepared via conventional wet spinning technique. The fiber with 7 wt% showed it conductivity of an order of 10−3 S/cm, and showed suitable mechanical properties as well as better thermal stability as compared with the pure Co-PAN fibers.
Fig. 10. TGA and DTG curves of (a) PANI-DBSA, (b) Co-PAN and PANI-DBSA/Co-PAN composites with (c) 2.5%, (d) 5%, (e) 10% PANI-DBSA content.
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