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Electrically conducting-adhesive coating on polyamide fabrics
Synthetic Metals 160 (2010) 1683–1687
Contents lists available at ScienceDirect
Synthetic Metals journal homepage: www.elsevier.com/locate/synmet
Electrically conducting-adhesive coating on polyamide fabrics Alessio Varesano, Barbara Antognozzi, Claudio Tonin ∗ CNR-ISMAC, Institute for Macromolecular Studies, C.so G. Pella, 16–13900 Biella, Italy
a r t i c l e
i n f o
Article history: Received 23 March 2010 Received in revised form 7 May 2010 Accepted 28 May 2010 Available online 25 June 2010 Keywords: Electrically conductive textiles Polypyrrole Polyamide Adhesion
a b s t r a c t Solvent-based preliminary treatments were carried out on polyamide fabrics to be coated with a thin layer of electrically conducting doped polypyrrole, with the aim of improving the adhesion of the conducting layer to the fibre substrate. Polyamide fabrics were treated with dilute formic acid, pure tetrachloroethylene and ethanol/water at different temperatures and times. After the treatments, the fabrics were coated with polypyrrole by in situ chemical oxidative polymerisation. The adhesion of the PPy layer was evaluated by means of surface resistivity measurements, SEM investigation and ATR FT-IR analysis after Martindale abrasion tests. The adhesion of PPy layer on the fibre surface was strongly improved by the solvent treatments, in particular with ethanol and tetrachloroethylene. The surface resistivity of the ethanol-treated fabrics did not change after more than 200 abrasion cycles and the PPy layer linked to the fibre surface was observed by SEM and ATR FT-IR also after 4000 abrasion cycles. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Electrically conducting fabrics produced by deposition of thin layers of inherently conducting polymers (ICPs) on the fibre surface of fabrics and yarns have recently been proposed for microwave attenuation and EMI shielding [1–5], static electric charge dissipation and resistive heating [6,7], and sensors [8–11]. Among the ICPs, including polyaniline, and polythiophene and polyethylendioxithiophene, polypyrrole (PPy) is one of the most promising candidates for producing electrically conducting fabrics in the range of surface resistivities from 10 to millions /square. PPy-based fabrics with good electrical properties were produced by in situ polymerisation of pyrrole on the surface of many kind of textile materials such as wool [12–15], silk [16–19], cotton and cellulose-based fibres [16,20–24], polyesters [25–29], polyamides [25,26], polypropylene [26], and acrylic [26]. One of the most important problems that encumber the diffusion of this technology concerns the low adhesion of the PPy layer to the fibre surface. PPy shows excellent affinity to man-made cellulose-based fibres (PPy polymerises also inside the fibre bulk of viscose, lyocell, tencel) [21,22] and to treated animal fibres (e.g. Hercosett wool, Basolan wool) [15]. On the contrary, the adhesion to synthetic fibres is poor, and few are reported in the literature about the improvement of adhesion. In particular, plasma-modified (–OH groups) polypropylene fabrics and viscose fabrics were treated with pyrrole-functionalized triethoxysilane before PPy deposition in order to improve fastness to washing [30]. Adhesion of PPy
∗ Corresponding author. Tel.: +39 0158493043; fax: +39 0158408387. E-mail address: [email protected] (C. Tonin). 0379-6779/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2010.05.041
on wool and polyester fabrics was improved using atmospheric pressure glow discharge plasma treatments [31]. Alkali treatments carried out on polyester fibres before PPy deposition showed an increase in the amount of deposited PPy, but fastness to rubbing slightly decreased because of the resulting surface roughness [32]. Moreover, prolonged immersion time of polyester fabrics in the reactants did not improve abrasion fastness [33]. In this work, solvent-based treatments were carried out on polyamide-66 fabrics with the aim of improving the adhesion between fibres and the PPy layer produced by in situ chemical oxidative polymerisation.
2. Experimental 2.1. Materials Polyamide-66 (PA66) fabrics were Spun Nylon 66 DuPont Type 200 Woven Fabris, 124 g/m2 from Testfabrics (USA). The chemicals were: pyrrole (97%) by Fluka; iron (III) sulphate hydrate (humidity 21%, Fe 21–23%) by Riedel-de Haën, Ethanol (ACS reagent grade) by Sigma–Aldrich, Tetrachloroethylene extra pure by Riedel-de Haën, Formic acid (reagent grade, ≥95%) by Sigma–Aldrich. All chemicals were used without further purifications.
2.2. Methods PA66 fabric samples (20 cm × 20 cm) were treated with (1) ethanol, (2) tetrachloroethylene and (3) formic acid with different procedures.
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(1) Samples were plugged in flasks containing ethanol (80% v/v) and demineralised water at the boiling point (79.4 ◦ C) [34,35] connected to a coiled condensers for 30 min, 1 and 2 h. For comparison, tests were carried out at 40 ◦ C using an Original Hanau Linitest apparatus for 30 min. For both the procedure the liquor ratio was set to 80:1 ml/g. The samples were dried at room temperature. (2) Samples were plugged in sealed vessels containing pure tetrachloroethylene with a liquor ratio of 40:1 ml/g at room temperature, and stirred for 30 min, 1 and 2 h. The samples were dried at room temperature. (3) Formic acid was added to the PPy polymerisation bath solutions during the impregnation step before the addition of the monomer (see the PPy deposition procedure described below) at final concentrations of 5, 10 and 20% v/v. In this case the duration of the impregnation step was 1 h. PPy depositions on PA 66 fabric samples of were carried out at room temperature by plunging the samples in stirred solutions of ferric sulphate (0.082 M) with a liquor ratio of 50:1 ml/g. After an impregnation of 15 min, pyrrole was added drop wise to the solution, up to the final concentration (0.073 M). The samples were pulled out from the polymerisation bath after 4 h, rinsed in cold water, dried at room temperature and stored at 20 ◦ C at 65% RH for at least 24 h before tests. Abrasion tests (based on EN ISO 12947-1) were performed against standard wool abrading fabric using a Nu-Martindale Abrasion and Pilling Tester from James Heal & Co. Two kinds of abrasion tests were performed on each conductive coated fabrics: (1) for electrical measurements, round specimens with diameter of 15 cm were cut from the PPy-coated samples, mounted on the bottom holder of the Martindale and subjected to abrasion cycles with a pressure of 12 kN; (2) for other analysis (i.e. SEM, ATR FT-IR), round specimens with diameter of 3.9 cm were placed in the top holder of the Martindale and submitted to abrasion without any load. The procedures were previously described in several papers [13,31,33]. Electrical measurements were performed in a conditioned laboratory at 20 ◦ C and 65% RH by means of an electrical circuit composed of a Metrel potentiometer, a digital Multimeter Escort 170 used as a voltmeter and a Supertester 680G ammeter. The electrical measurements were carried out on samples (abraded or not) cut in squares of 10 cm × 10 cm, and the value of surface resistivity was calculated by the Ohm’s law. Scanning electron microscopy (SEM) investigations were performed on the samples without sputtering preparation, with a LEO (Leica Electron Optics) 435 VP SEM, at an acceleration voltage of 15 kV and a 20 mm working distance. ATR FT-IR spectra were acquired in the range from 4000 to 600 cm−1 with 100 scansions and 4 cm−1 of band resolution by means of a Thermo Nicolet Nexus spectrometer with attenuated total reflection (ATR) technique using a Smart Endurance accessory equipped with a diamond crystal ZnSe focusing element. 3. Results and discussion 3.1. Solvent treatments and PPy deposition The solvent treatments studied in this work should have two main effects on the PA66 fabrics: cleaning of the surface and fibre swelling. Cleaning could have positive effects such as an improvement of the adhesion of the following PPy deposition; on the contrary fibre swelling could have negative effects on the electrical conductivity especially if swelling modifies the structure of the fabric, thus reducing the density of contact point between yarns and fibres.
Table 1 Initial surface resistivity and weight uptake after PPy-coating of treated and untreated PA66 fabrics. Treatment
Surface resistivity (/sq.)
Weight uptake (%)
Untreated
407 ± 32
13.3
Ethanol Boiling, 30 min 1h 2h 40 ◦ C, 30 min
301 294 291 401
± ± ± ±
49 31 29 45
16.9 17.0 17.8 13.6
Tetrachloroethylene 30 min 1h 2h
536 ± 67 450 ± 40 408 ± 27
14.4 15.3 15.5
Formic acid 20 vol.% 10 vol.% 5 vol.%
801 ± 87 574 ± 60 520 ± 47
16.3 16.5 16.7
The surface resistivities of fresh PPy-coated fabrics are reported in Table 1 for each solvent treatment. Table 1 also reports the weight uptake of the PPy-coating. There are no direct correlations between resistivity and weight uptake when comparing the different treatments, although a higher weight uptake is generally connected to a lower surface resistivity for the same treatment. In particular, treatments at the boiling point of ethanol (80% v/v.) improve significantly both the conductivity and the weight uptake in the resulting PPy-coated fabrics, and the effect is slightly enhanced by the duration of the treatment. On the other hand, at temperature of 40 ◦ C the treatment with ethanol seems to have no influence on the electrical performances and PPy uptake with respect to untreated fabric. Treatments with tetrachloroethylene at room temperature increase the weight uptake, but worsen the electrical performances. A treatment of 2 h in tetrachloroethylene leads to the same electrical surface resistivity of untreated fabric with a significant increase of the weight uptake. Finally, formic acid-treatments increase the surface resistivity with respect the untreated fabrics, although the weight uptakes are greater. Moreover, the increase in surface resistivity is higher with increasing the acid concentration. It is worth to note that in this case, formic acid is present in the polymerisation bath during the synthesis of PPy. Therefore it is possible that at higher concentration (particularly at 20% v/v) formic acid interferes with the reaction between the monomer and the oxidant leading to poor conducting PPy. 3.2. Abrasion tests Due to the colour of PPy, the fabrics turn black after coating. The pictures in Fig. 1 show PPy-coated fabrics after the abrasion tests. On untreated fabrics (a) the action of abrasion is noticeable already after 200 cycles, and becomes evident after 1000 cycles. The adhesion is poor also on the fabrics treated with formic acid (d). On the contrary, ethanol-treated (b) and tetrachloroethylenetreated (c) fabrics show an improved adhesion of the PPy layer on the textile substrate: also after 2000 cycles both the samples show a black colour (excepting for the presence of some pills). 3.3. SEM observations In order to demonstrate the presence of an even layer of electrically conducting polymer on the fibre surface after the abrasion tests, samples of abraded fabrics were investigated by SEM without sputter-coating of metals (metallisation) usually needed for good quality SEM imagines. Fig. 2 reports the SEM pictures of PPy-
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Moreover aggregates of PPy synthesised in the bulk solution are also present on the fabrics. Images (b) and (c) in Fig. 2 reports the SEM pictures of untreated samples after 1000 and 2000 abrasion cycles. It is evident that wide parts of the conductive coating are completely worn out reaching the non-conductive substrate (white zones). Due to the low conductivity of the abraded fabrics not subjected to solvent treatments, it was impossible to take pictures of the samples after 4000 abrasion cycles. On the contrary, ethanol-treated fabrics still show a uniform conductive layer on every fibres after 2000 (e) and 4000 (f) abrasion cycles. The PPy layer is strongly linked to the fibres surface. It is worth to note that the surfaces after abrasion appear smooth, that is the abrasion action removed roughness and the nodules of PPy, but not the PPy layer directly linked to the fibre surface.
3.4. FT-IR analysis
Fig. 1. Pictures of PPy-coated fabrics after abrasion cycles: (a) untreated fabric, (b) ethanol-treated fabric, (c) tetrachloroethylene-treated fabric, and (d) formic acidtreated fabric.
coated fabrics before and after the abrasion tests of untreated and ethanol-treated fabrics. Before abrasion, the fibres of both the untreated (a) and ethanoltreated (d) fabrics are coated with an even layer of conducting polymer directly grown on the fibre surface during the PPy synthesis (in situ). The polymer also synthesises in the solution bulk forming aggregates of particles weakly linked to the fibre surface.
Attenuated total reflection (ATR) technique is a powerful tool for investigating evenness, thickness and degree of coating since the infrared beam analyses only a thin layer (1–2 m) of the fibre surface. Fig. 3 shows ATR FT-IR spectra of PPy-coated and uncoated fabrics. The spectrum (a) related to PPy-coated PA66 fabric before abrasion is characterized by the typical features of PPy. In the region between 4000 and 2000 cm−1 there is the tail of the electronic absorption band characteristic of conducting PPy [36]. The spectrum also shows the weak and broad absorption band at 1538 cm−1 attributed to the C–C stretching, the band at 1473 cm−1 assigned to C–N stretching, and the weak band at 1294 cm−1 assigned to C–H and C–N in-plane deformation modes [37,38]; the peaks at 1178 and 1043 cm−1 is attributed to PPy ring breathing and C–H deformation, respectively [38,39]. Moreover, the absence of the any other peaks attributable to PA66 suggests the fibres are completely coated by an even layer of PPy. The spectrum (g) related to the uncoated PA66 fabric shows typical absorption bands of the peptide bond (–CONH–). In particular, the absorption band at 3310 cm−1 is attributed to N–H stretching, the strong peak at 1637 cm−1 to C O stretching, the band at 1533 cm−1 mainly to N–H bending and C–N stretching, and the band at 1276 cm−1 to combinations of N–H in-plane bending and C–N stretching. Other absorption bands are related to aliphatic seg-
Fig. 2. SEM pictures of PPy-coated fabrics (without further conductive sputter-coating) of untreated fabric: (a) before abrasion, (b) after 1000 abrasion cycles, (c) after 2000 abrasion cycles; and ethanol-treated fabric: (d) before abrasion, (e) after 2000 abrasion cycles, and (f) after 4000 abrasion cycles.
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abrasion test) the increments in resistivities are: 35.4% after 200 abrasion cycles, 60.2% after 1000, 89.4% after 2000 and 93.6% after 4000. On the contrary, ethanol-treated and tetrachloroethylenetreated fabrics showed a different behaviour to abrasion. After an initial increase (up to 25.8% after 200 abrasion cycles for ethanol-treated fabric and 31.4% after 1000 abrasion cycles for tetrachloroethylene-treated fabric) the resistivities are substantially constant with further abrasion cycles (Fig. 4). Probably, after an initial removal of unlinked or weakly linked PPy to the fibres, the residual PPy layer strongly linked to the fibres surface (observed by SEM in Fig. 2) still gives good electrical properties to the fabrics. 4. Conclusion
Fig. 3. ATR FT-IR spectra of PPy-coated and uncoated fabrics: (a) PPy-coated PA66 fabric before abrasion, (b) ethanol-treated fabric after 2000 abrasion cycles, (c) ethanol-treated fabric after 4000 abrasion cycles, (d) tetrachloroethylene-treated fabric after 2000 abrasion cycles, (e) formic acid-treated fabric after 2000 abrasion cycles, (f) untreated fabric after 2000 abrasion cycles, and (g) uncoated PA66 fabric.
ments of the backbone chain: the bands at 2937 and 2877 cm−1 to C–H stretching and the bands at 1475, 1436 and 1380 cm−1 to –CH2 vibration modes. After abrasion, the features of the spectra (b)–(f) in Fig. 3 are related to both PPy and PA66. In the spectra (b), (c) and (d) related to ethanol-treated fabric after 2000 and 4000 abrasion cycles, and tetrachloroethylene-treated fabric after 2000 abrasion cycles, the absorption bands assigned to PPy are stronger with respect to those assigned to PA66. On the contrary, the bands assigned to PA66 are stronger than those of PPy in the spectra (e) and (f) related to the formic acid-treated fabric and the untreated fabric, both after 2000 abrasion cycles. Therefore, the ATR FT-IR analysis supports the SEM observations. 3.5. Surface resistivity In order to further assess the improvement of the adhesion of the PPy layer onto ethanol-treated and tetrachloroethylene-treated fabrics in comparison with the untreated PA66 fabric, surface resistivity measurements were carried out after 200, 1000, 2000 and 4000 abrasion cycles. Fig. 4 reports the surface resistivity values versus the abrasion cycles. The surface resistivity of the untreated fabric increases during the abrasion test. With respect to the initial value (before the
Fig. 4. Surface resistivity vs. abrasion cycles of untreated, ethanol-treated and tetrachloroethylene-treated PPy-coated fabrics.
PA66 fabrics were subjected to solvent treatments (with ethanol, pure tetrachloroethylene and formic acid) before a PPy deposition in order to improve the adhesion of the conductive layer onto the fibre surface. The adhesion was evaluated measuring the fastness to abrasion and by SEM and ATR FT-IR analyses. The treatment efficiencies are in the order: ethanol ≈ tetrachloroethylene > formic acid > no treatment. The untreated fabric almost double the surface resistivity after 4000 abrasion cycles, whereas for ethanol- and tetrachloroethylene-treated fabrics the surface resistivities increase of about a quarter and a third, respectively. SEM observations revealed that the PPy layer grown on the fibre surface of ethanol- and tetrachloroethylene-treated fabrics during the in situ chemical polymerisation is strongly linked to the PA66 fibres. ATR FT-IR analysis also showed that the presence of a layer of PPy covers the typical IR features of the PA66 suggesting that the fibres of the abraded fabrics are still evenly coated by a layer of the conducting polymer. Acknowledgement Regione Piemonte is gratefully acknowledged for supporting this research through the project “HI-TEX” (D.G.R. n. 227-4715, 27/11/2006). References [1] Y.K. Hong, C.Y. Lee, C.K. Jeong, J.H. Sim, K. Kim, J. Joo, M.S. Kim, J.Y. Lee, S.H. Jeong, S.W. Byun, Current Applied Physics 1 (2001) 439. [2] M.S. Kim, H.K. Kim, S.W. Byun, S.H. Jeong, Y.K. Hong, J.S. Joo, K.T. Song, J.K. Kim, C.J. Lee, J.Y. Lee, Synthetic Metals 126 (2002) 233. [3] S.K. Dhawan, N. Singh, S. Venkatachalam, Synthetic Metals 129 (2002) 261. [4] E. Håkansson, A. Amiet, A. Kaynak, Synthetic Metals 156 (2006) 917. [5] A. Kaynak, E. Håkansson, A. Amiet, Synthetic Metals 159 (2009) 1373. [6] E. Håkansson, A. Kaynak, T. Lin, S. Nahavandi, T. Jones, E. Hu, Synthetic Metals 144 (2004) 21. [7] A. Varesano, A. Ibarzabal Ferrer, C. Tonin, e-Polymers 022 (2007). [8] D. Kincal, A. Kumar, A. Child, J. Reynolds, Synthetic Metals 92 (1998) 53. [9] Y. Li, M.Y. Leung, X.M. Tao, X.Y. Cheng, J. Tsang, M.C.W. Yuen, Journal of Materials Science 40 (2005) 4093. [10] B.J. Munro, J.R. Steele, T.E. Campbell, G.G. Wallace, in: A. Lymberis, D. de Rossi (Eds.), Wearable eHealth Systems for Personalised Health Management, IOS Press, Amsterdam, 2004, pp. 271–277. [11] J. Wu, D. Zhou, C.O. Too, G.G. Wallace, Synthetic Metals 155 (2005) 698. [12] A. Kaynak, L. Wang, C. Hurren, X. Wang, Fibers and Polymers 3 (2002) 24. [13] A. Varesano, L. Dall’Acqua, C. Tonin, Polymer Degradation and Stability 89 (2005) 125. [14] L. Wang, T. Lin, X. Wang, A. Kaynak, Fibers and Polymers 6 (2005) 259. [15] A. Varesano, A. Aluigi, C. Tonin, F. Ferrero, Fibers and Polymers 7 (2006) 105. [16] S.H. Hosseini, A. Pairovi, Iranian Polymer Journal 14 (2005) 934. [17] A. Boschi, C. Arosio, I. Cucchi, F. Bertini, M. Catellani, G. Freddi, Fibers and Polymers 9 (2008) 698. [18] Y. Xia, Yun Lu, Composites Science and Technology 68 (2008) 1471. [19] I. Cucchi, A. Boschi, C. Arosio, F. Bertini, G. Freddi, M. Catellani, Synthetic Metals 159 (2009) 246. [20] S.N. Tan, H. Ge, Polymer 37 (1996) 965. [21] L. Dall’Acqua, C. Tonin, R. Peila, F. Ferrero, M. Catellani, Synthetic Metals 146 (2004) 213.
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[30] M. Miˇcuˇsík, T. Nedelˇcev, M. Omastová, I. Krupa, K. Olejníková, P. Fedorko, M.M. Chehimi, Synthetic Metals 157 (2007) 914. [31] S. Garg, C. Hurren, A. Kaynak, Synthetic Metals 157 (2007) 41. [32] H. Tavanai, A. Kaynak, Synthetic Metals 157 (2007) 764. [33] T. Lin, L. Wang, X. Wang, A. Kaynak, Thin Solid Films 479 (2005) 77. [34] R.H. Perry, D.W. Green (Eds.), Perry’s Chemical Engineers’ Handbook, 7th ed., McGraw-Hill, New York, 1998, pp. 12–13. [35] J.S. Carey, W.K. Lewis, Industrial and Engineering Chemistry 24 (1932) 882. [36] N. Toshima, O. Ihata, Synthetic Metals 79 (1996) 165. [37] Y. Tian, F. Yang, W. Yang, Synthetic Metals 156 (2006) 1052. [38] M. Omastová, M. Trchová, J. Kovárová, J. Stejskal, Synthetic Metals 138 (2003) 447. [39] R.G. Davidson, T.G. Turner, Synthetic Metals 72 (1995) 121.
Contents lists available at ScienceDirect
Synthetic Metals journal homepage: www.elsevier.com/locate/synmet
Electrically conducting-adhesive coating on polyamide fabrics Alessio Varesano, Barbara Antognozzi, Claudio Tonin ∗ CNR-ISMAC, Institute for Macromolecular Studies, C.so G. Pella, 16–13900 Biella, Italy
a r t i c l e
i n f o
Article history: Received 23 March 2010 Received in revised form 7 May 2010 Accepted 28 May 2010 Available online 25 June 2010 Keywords: Electrically conductive textiles Polypyrrole Polyamide Adhesion
a b s t r a c t Solvent-based preliminary treatments were carried out on polyamide fabrics to be coated with a thin layer of electrically conducting doped polypyrrole, with the aim of improving the adhesion of the conducting layer to the fibre substrate. Polyamide fabrics were treated with dilute formic acid, pure tetrachloroethylene and ethanol/water at different temperatures and times. After the treatments, the fabrics were coated with polypyrrole by in situ chemical oxidative polymerisation. The adhesion of the PPy layer was evaluated by means of surface resistivity measurements, SEM investigation and ATR FT-IR analysis after Martindale abrasion tests. The adhesion of PPy layer on the fibre surface was strongly improved by the solvent treatments, in particular with ethanol and tetrachloroethylene. The surface resistivity of the ethanol-treated fabrics did not change after more than 200 abrasion cycles and the PPy layer linked to the fibre surface was observed by SEM and ATR FT-IR also after 4000 abrasion cycles. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Electrically conducting fabrics produced by deposition of thin layers of inherently conducting polymers (ICPs) on the fibre surface of fabrics and yarns have recently been proposed for microwave attenuation and EMI shielding [1–5], static electric charge dissipation and resistive heating [6,7], and sensors [8–11]. Among the ICPs, including polyaniline, and polythiophene and polyethylendioxithiophene, polypyrrole (PPy) is one of the most promising candidates for producing electrically conducting fabrics in the range of surface resistivities from 10 to millions /square. PPy-based fabrics with good electrical properties were produced by in situ polymerisation of pyrrole on the surface of many kind of textile materials such as wool [12–15], silk [16–19], cotton and cellulose-based fibres [16,20–24], polyesters [25–29], polyamides [25,26], polypropylene [26], and acrylic [26]. One of the most important problems that encumber the diffusion of this technology concerns the low adhesion of the PPy layer to the fibre surface. PPy shows excellent affinity to man-made cellulose-based fibres (PPy polymerises also inside the fibre bulk of viscose, lyocell, tencel) [21,22] and to treated animal fibres (e.g. Hercosett wool, Basolan wool) [15]. On the contrary, the adhesion to synthetic fibres is poor, and few are reported in the literature about the improvement of adhesion. In particular, plasma-modified (–OH groups) polypropylene fabrics and viscose fabrics were treated with pyrrole-functionalized triethoxysilane before PPy deposition in order to improve fastness to washing [30]. Adhesion of PPy
∗ Corresponding author. Tel.: +39 0158493043; fax: +39 0158408387. E-mail address: [email protected] (C. Tonin). 0379-6779/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2010.05.041
on wool and polyester fabrics was improved using atmospheric pressure glow discharge plasma treatments [31]. Alkali treatments carried out on polyester fibres before PPy deposition showed an increase in the amount of deposited PPy, but fastness to rubbing slightly decreased because of the resulting surface roughness [32]. Moreover, prolonged immersion time of polyester fabrics in the reactants did not improve abrasion fastness [33]. In this work, solvent-based treatments were carried out on polyamide-66 fabrics with the aim of improving the adhesion between fibres and the PPy layer produced by in situ chemical oxidative polymerisation.
2. Experimental 2.1. Materials Polyamide-66 (PA66) fabrics were Spun Nylon 66 DuPont Type 200 Woven Fabris, 124 g/m2 from Testfabrics (USA). The chemicals were: pyrrole (97%) by Fluka; iron (III) sulphate hydrate (humidity 21%, Fe 21–23%) by Riedel-de Haën, Ethanol (ACS reagent grade) by Sigma–Aldrich, Tetrachloroethylene extra pure by Riedel-de Haën, Formic acid (reagent grade, ≥95%) by Sigma–Aldrich. All chemicals were used without further purifications.
2.2. Methods PA66 fabric samples (20 cm × 20 cm) were treated with (1) ethanol, (2) tetrachloroethylene and (3) formic acid with different procedures.
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A. Varesano et al. / Synthetic Metals 160 (2010) 1683–1687
(1) Samples were plugged in flasks containing ethanol (80% v/v) and demineralised water at the boiling point (79.4 ◦ C) [34,35] connected to a coiled condensers for 30 min, 1 and 2 h. For comparison, tests were carried out at 40 ◦ C using an Original Hanau Linitest apparatus for 30 min. For both the procedure the liquor ratio was set to 80:1 ml/g. The samples were dried at room temperature. (2) Samples were plugged in sealed vessels containing pure tetrachloroethylene with a liquor ratio of 40:1 ml/g at room temperature, and stirred for 30 min, 1 and 2 h. The samples were dried at room temperature. (3) Formic acid was added to the PPy polymerisation bath solutions during the impregnation step before the addition of the monomer (see the PPy deposition procedure described below) at final concentrations of 5, 10 and 20% v/v. In this case the duration of the impregnation step was 1 h. PPy depositions on PA 66 fabric samples of were carried out at room temperature by plunging the samples in stirred solutions of ferric sulphate (0.082 M) with a liquor ratio of 50:1 ml/g. After an impregnation of 15 min, pyrrole was added drop wise to the solution, up to the final concentration (0.073 M). The samples were pulled out from the polymerisation bath after 4 h, rinsed in cold water, dried at room temperature and stored at 20 ◦ C at 65% RH for at least 24 h before tests. Abrasion tests (based on EN ISO 12947-1) were performed against standard wool abrading fabric using a Nu-Martindale Abrasion and Pilling Tester from James Heal & Co. Two kinds of abrasion tests were performed on each conductive coated fabrics: (1) for electrical measurements, round specimens with diameter of 15 cm were cut from the PPy-coated samples, mounted on the bottom holder of the Martindale and subjected to abrasion cycles with a pressure of 12 kN; (2) for other analysis (i.e. SEM, ATR FT-IR), round specimens with diameter of 3.9 cm were placed in the top holder of the Martindale and submitted to abrasion without any load. The procedures were previously described in several papers [13,31,33]. Electrical measurements were performed in a conditioned laboratory at 20 ◦ C and 65% RH by means of an electrical circuit composed of a Metrel potentiometer, a digital Multimeter Escort 170 used as a voltmeter and a Supertester 680G ammeter. The electrical measurements were carried out on samples (abraded or not) cut in squares of 10 cm × 10 cm, and the value of surface resistivity was calculated by the Ohm’s law. Scanning electron microscopy (SEM) investigations were performed on the samples without sputtering preparation, with a LEO (Leica Electron Optics) 435 VP SEM, at an acceleration voltage of 15 kV and a 20 mm working distance. ATR FT-IR spectra were acquired in the range from 4000 to 600 cm−1 with 100 scansions and 4 cm−1 of band resolution by means of a Thermo Nicolet Nexus spectrometer with attenuated total reflection (ATR) technique using a Smart Endurance accessory equipped with a diamond crystal ZnSe focusing element. 3. Results and discussion 3.1. Solvent treatments and PPy deposition The solvent treatments studied in this work should have two main effects on the PA66 fabrics: cleaning of the surface and fibre swelling. Cleaning could have positive effects such as an improvement of the adhesion of the following PPy deposition; on the contrary fibre swelling could have negative effects on the electrical conductivity especially if swelling modifies the structure of the fabric, thus reducing the density of contact point between yarns and fibres.
Table 1 Initial surface resistivity and weight uptake after PPy-coating of treated and untreated PA66 fabrics. Treatment
Surface resistivity (/sq.)
Weight uptake (%)
Untreated
407 ± 32
13.3
Ethanol Boiling, 30 min 1h 2h 40 ◦ C, 30 min
301 294 291 401
± ± ± ±
49 31 29 45
16.9 17.0 17.8 13.6
Tetrachloroethylene 30 min 1h 2h
536 ± 67 450 ± 40 408 ± 27
14.4 15.3 15.5
Formic acid 20 vol.% 10 vol.% 5 vol.%
801 ± 87 574 ± 60 520 ± 47
16.3 16.5 16.7
The surface resistivities of fresh PPy-coated fabrics are reported in Table 1 for each solvent treatment. Table 1 also reports the weight uptake of the PPy-coating. There are no direct correlations between resistivity and weight uptake when comparing the different treatments, although a higher weight uptake is generally connected to a lower surface resistivity for the same treatment. In particular, treatments at the boiling point of ethanol (80% v/v.) improve significantly both the conductivity and the weight uptake in the resulting PPy-coated fabrics, and the effect is slightly enhanced by the duration of the treatment. On the other hand, at temperature of 40 ◦ C the treatment with ethanol seems to have no influence on the electrical performances and PPy uptake with respect to untreated fabric. Treatments with tetrachloroethylene at room temperature increase the weight uptake, but worsen the electrical performances. A treatment of 2 h in tetrachloroethylene leads to the same electrical surface resistivity of untreated fabric with a significant increase of the weight uptake. Finally, formic acid-treatments increase the surface resistivity with respect the untreated fabrics, although the weight uptakes are greater. Moreover, the increase in surface resistivity is higher with increasing the acid concentration. It is worth to note that in this case, formic acid is present in the polymerisation bath during the synthesis of PPy. Therefore it is possible that at higher concentration (particularly at 20% v/v) formic acid interferes with the reaction between the monomer and the oxidant leading to poor conducting PPy. 3.2. Abrasion tests Due to the colour of PPy, the fabrics turn black after coating. The pictures in Fig. 1 show PPy-coated fabrics after the abrasion tests. On untreated fabrics (a) the action of abrasion is noticeable already after 200 cycles, and becomes evident after 1000 cycles. The adhesion is poor also on the fabrics treated with formic acid (d). On the contrary, ethanol-treated (b) and tetrachloroethylenetreated (c) fabrics show an improved adhesion of the PPy layer on the textile substrate: also after 2000 cycles both the samples show a black colour (excepting for the presence of some pills). 3.3. SEM observations In order to demonstrate the presence of an even layer of electrically conducting polymer on the fibre surface after the abrasion tests, samples of abraded fabrics were investigated by SEM without sputter-coating of metals (metallisation) usually needed for good quality SEM imagines. Fig. 2 reports the SEM pictures of PPy-
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Moreover aggregates of PPy synthesised in the bulk solution are also present on the fabrics. Images (b) and (c) in Fig. 2 reports the SEM pictures of untreated samples after 1000 and 2000 abrasion cycles. It is evident that wide parts of the conductive coating are completely worn out reaching the non-conductive substrate (white zones). Due to the low conductivity of the abraded fabrics not subjected to solvent treatments, it was impossible to take pictures of the samples after 4000 abrasion cycles. On the contrary, ethanol-treated fabrics still show a uniform conductive layer on every fibres after 2000 (e) and 4000 (f) abrasion cycles. The PPy layer is strongly linked to the fibres surface. It is worth to note that the surfaces after abrasion appear smooth, that is the abrasion action removed roughness and the nodules of PPy, but not the PPy layer directly linked to the fibre surface.
3.4. FT-IR analysis
Fig. 1. Pictures of PPy-coated fabrics after abrasion cycles: (a) untreated fabric, (b) ethanol-treated fabric, (c) tetrachloroethylene-treated fabric, and (d) formic acidtreated fabric.
coated fabrics before and after the abrasion tests of untreated and ethanol-treated fabrics. Before abrasion, the fibres of both the untreated (a) and ethanoltreated (d) fabrics are coated with an even layer of conducting polymer directly grown on the fibre surface during the PPy synthesis (in situ). The polymer also synthesises in the solution bulk forming aggregates of particles weakly linked to the fibre surface.
Attenuated total reflection (ATR) technique is a powerful tool for investigating evenness, thickness and degree of coating since the infrared beam analyses only a thin layer (1–2 m) of the fibre surface. Fig. 3 shows ATR FT-IR spectra of PPy-coated and uncoated fabrics. The spectrum (a) related to PPy-coated PA66 fabric before abrasion is characterized by the typical features of PPy. In the region between 4000 and 2000 cm−1 there is the tail of the electronic absorption band characteristic of conducting PPy [36]. The spectrum also shows the weak and broad absorption band at 1538 cm−1 attributed to the C–C stretching, the band at 1473 cm−1 assigned to C–N stretching, and the weak band at 1294 cm−1 assigned to C–H and C–N in-plane deformation modes [37,38]; the peaks at 1178 and 1043 cm−1 is attributed to PPy ring breathing and C–H deformation, respectively [38,39]. Moreover, the absence of the any other peaks attributable to PA66 suggests the fibres are completely coated by an even layer of PPy. The spectrum (g) related to the uncoated PA66 fabric shows typical absorption bands of the peptide bond (–CONH–). In particular, the absorption band at 3310 cm−1 is attributed to N–H stretching, the strong peak at 1637 cm−1 to C O stretching, the band at 1533 cm−1 mainly to N–H bending and C–N stretching, and the band at 1276 cm−1 to combinations of N–H in-plane bending and C–N stretching. Other absorption bands are related to aliphatic seg-
Fig. 2. SEM pictures of PPy-coated fabrics (without further conductive sputter-coating) of untreated fabric: (a) before abrasion, (b) after 1000 abrasion cycles, (c) after 2000 abrasion cycles; and ethanol-treated fabric: (d) before abrasion, (e) after 2000 abrasion cycles, and (f) after 4000 abrasion cycles.
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abrasion test) the increments in resistivities are: 35.4% after 200 abrasion cycles, 60.2% after 1000, 89.4% after 2000 and 93.6% after 4000. On the contrary, ethanol-treated and tetrachloroethylenetreated fabrics showed a different behaviour to abrasion. After an initial increase (up to 25.8% after 200 abrasion cycles for ethanol-treated fabric and 31.4% after 1000 abrasion cycles for tetrachloroethylene-treated fabric) the resistivities are substantially constant with further abrasion cycles (Fig. 4). Probably, after an initial removal of unlinked or weakly linked PPy to the fibres, the residual PPy layer strongly linked to the fibres surface (observed by SEM in Fig. 2) still gives good electrical properties to the fabrics. 4. Conclusion
Fig. 3. ATR FT-IR spectra of PPy-coated and uncoated fabrics: (a) PPy-coated PA66 fabric before abrasion, (b) ethanol-treated fabric after 2000 abrasion cycles, (c) ethanol-treated fabric after 4000 abrasion cycles, (d) tetrachloroethylene-treated fabric after 2000 abrasion cycles, (e) formic acid-treated fabric after 2000 abrasion cycles, (f) untreated fabric after 2000 abrasion cycles, and (g) uncoated PA66 fabric.
ments of the backbone chain: the bands at 2937 and 2877 cm−1 to C–H stretching and the bands at 1475, 1436 and 1380 cm−1 to –CH2 vibration modes. After abrasion, the features of the spectra (b)–(f) in Fig. 3 are related to both PPy and PA66. In the spectra (b), (c) and (d) related to ethanol-treated fabric after 2000 and 4000 abrasion cycles, and tetrachloroethylene-treated fabric after 2000 abrasion cycles, the absorption bands assigned to PPy are stronger with respect to those assigned to PA66. On the contrary, the bands assigned to PA66 are stronger than those of PPy in the spectra (e) and (f) related to the formic acid-treated fabric and the untreated fabric, both after 2000 abrasion cycles. Therefore, the ATR FT-IR analysis supports the SEM observations. 3.5. Surface resistivity In order to further assess the improvement of the adhesion of the PPy layer onto ethanol-treated and tetrachloroethylene-treated fabrics in comparison with the untreated PA66 fabric, surface resistivity measurements were carried out after 200, 1000, 2000 and 4000 abrasion cycles. Fig. 4 reports the surface resistivity values versus the abrasion cycles. The surface resistivity of the untreated fabric increases during the abrasion test. With respect to the initial value (before the
Fig. 4. Surface resistivity vs. abrasion cycles of untreated, ethanol-treated and tetrachloroethylene-treated PPy-coated fabrics.
PA66 fabrics were subjected to solvent treatments (with ethanol, pure tetrachloroethylene and formic acid) before a PPy deposition in order to improve the adhesion of the conductive layer onto the fibre surface. The adhesion was evaluated measuring the fastness to abrasion and by SEM and ATR FT-IR analyses. The treatment efficiencies are in the order: ethanol ≈ tetrachloroethylene > formic acid > no treatment. The untreated fabric almost double the surface resistivity after 4000 abrasion cycles, whereas for ethanol- and tetrachloroethylene-treated fabrics the surface resistivities increase of about a quarter and a third, respectively. SEM observations revealed that the PPy layer grown on the fibre surface of ethanol- and tetrachloroethylene-treated fabrics during the in situ chemical polymerisation is strongly linked to the PA66 fibres. ATR FT-IR analysis also showed that the presence of a layer of PPy covers the typical IR features of the PA66 suggesting that the fibres of the abraded fabrics are still evenly coated by a layer of the conducting polymer. Acknowledgement Regione Piemonte is gratefully acknowledged for supporting this research through the project “HI-TEX” (D.G.R. n. 227-4715, 27/11/2006). References [1] Y.K. Hong, C.Y. Lee, C.K. Jeong, J.H. Sim, K. Kim, J. Joo, M.S. Kim, J.Y. Lee, S.H. Jeong, S.W. Byun, Current Applied Physics 1 (2001) 439. [2] M.S. Kim, H.K. Kim, S.W. Byun, S.H. Jeong, Y.K. Hong, J.S. Joo, K.T. Song, J.K. Kim, C.J. Lee, J.Y. Lee, Synthetic Metals 126 (2002) 233. [3] S.K. Dhawan, N. Singh, S. Venkatachalam, Synthetic Metals 129 (2002) 261. [4] E. Håkansson, A. Amiet, A. Kaynak, Synthetic Metals 156 (2006) 917. [5] A. Kaynak, E. Håkansson, A. Amiet, Synthetic Metals 159 (2009) 1373. [6] E. Håkansson, A. Kaynak, T. Lin, S. Nahavandi, T. Jones, E. Hu, Synthetic Metals 144 (2004) 21. [7] A. Varesano, A. Ibarzabal Ferrer, C. Tonin, e-Polymers 022 (2007). [8] D. Kincal, A. Kumar, A. Child, J. Reynolds, Synthetic Metals 92 (1998) 53. [9] Y. Li, M.Y. Leung, X.M. Tao, X.Y. Cheng, J. Tsang, M.C.W. Yuen, Journal of Materials Science 40 (2005) 4093. [10] B.J. Munro, J.R. Steele, T.E. Campbell, G.G. Wallace, in: A. Lymberis, D. de Rossi (Eds.), Wearable eHealth Systems for Personalised Health Management, IOS Press, Amsterdam, 2004, pp. 271–277. [11] J. Wu, D. Zhou, C.O. Too, G.G. Wallace, Synthetic Metals 155 (2005) 698. [12] A. Kaynak, L. Wang, C. Hurren, X. Wang, Fibers and Polymers 3 (2002) 24. [13] A. Varesano, L. Dall’Acqua, C. Tonin, Polymer Degradation and Stability 89 (2005) 125. [14] L. Wang, T. Lin, X. Wang, A. Kaynak, Fibers and Polymers 6 (2005) 259. [15] A. Varesano, A. Aluigi, C. Tonin, F. Ferrero, Fibers and Polymers 7 (2006) 105. [16] S.H. Hosseini, A. Pairovi, Iranian Polymer Journal 14 (2005) 934. [17] A. Boschi, C. Arosio, I. Cucchi, F. Bertini, M. Catellani, G. Freddi, Fibers and Polymers 9 (2008) 698. [18] Y. Xia, Yun Lu, Composites Science and Technology 68 (2008) 1471. [19] I. Cucchi, A. Boschi, C. Arosio, F. Bertini, G. Freddi, M. Catellani, Synthetic Metals 159 (2009) 246. [20] S.N. Tan, H. Ge, Polymer 37 (1996) 965. [21] L. Dall’Acqua, C. Tonin, R. Peila, F. Ferrero, M. Catellani, Synthetic Metals 146 (2004) 213.
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