TY - JOUR
AU1 - Afzal, Asma, Binat
AU2 - Akhtar, Muhammad, Javed
AU3 - Ahmad,, Maqsood
AB - Abstract Solution blending technique has been used to synthesize dodecylbenzenesulfonic acid (DBSA)-doped polyaniline (PAND)/poly-vinyl chloride (PVC) blends by two methods, namely redoping method (PANDR/PVC blends) and aqueous polymerization method (PANDA/PVC blends). PANDR/PVC blends show improved mechanical properties as compared to PANDA/PVC blends, which show brittle nature of the films. However, by increasing concentration of PANDR in the PVC matrix, PANDR/PVC blend films are becoming more rigid due to increases in the modulus of elasticity. Irradiation of blend samples by electron beam used during scanning electron microscopy (SEM) analyses has changed the morphology of PANDA/PVC blend films due to dehydrochlorination of free PVC, whereas PANDR/PVC blends remain unaffected during irradiation by electron beam. polyaniline, blends, DBSA, PVC, electron microscopy, mechanical properties Introduction Polymer blends are synthesized to form new materials from already existing materials with a wide variety of properties and reduced development costs [1]. Among polymers, conducting polymers are generally prepared in powder form with poor mechanical properties. Thus, a large number of applications of conducting polymers, especially for polyaniline (PANI), are limited by its insolubility, infusibility and poor processability [2]. Various procedures have been adopted to overcome these shortcomings [3]. Among them, the most important is blending of PANI with other commercial polymers in a co-solvent using solution casting technique [4]. The key features of solution blending are the solubility of both polymers in a common solvent, compatibility and miscibility, with enhanced electrical properties and better performance of the end products. Doping of PANI by functionalized protonic acids such as dodecylbenzenesulfonic acid (DBSA) [5] or camphorsulfonic acid (CSA) [6] increases its solubility in common organic solvents in which other co-polymers can be dissolved. Solution blending of acid-doped PANI with various types of polymers have been reported in literature [7–9]. It has been investigated that properties of PANI/poly-vinyl chloride (PVC) blends are modified by exposure to energetic radiations like gamma rays and accelerated electrons [10–13]. Srivastava et al. [10] studied the physico-chemical changes brought about by swift heavy ions of silicon and nickel in PVC/PANI films in terms of optical, electrical and chemical modifications. Bodugoz et al. [11,12] have shown that acid doping in PANI/PVC blends can be achieved by radiation-induced HCl release from PVC parts. Sevil et al. [13] determined the dose response of PANI samples blended with PVC and chlorinated poly-propylene (PPCl) by measuring the high frequency conductance of these blends irradiated with different doses. In the present study, DBSA-doped PANI (PAND)/PVC blends have been prepared by solution blending technique using tetrahydrofuran (THF) as a solvent, although DBSA-doped PANI can be prepared by three methods: (i) redoping, (ii) aqueous polymerization and (iii) emulsion polymerization [14]. In this study, redoping and aqueous polymerization methods have been employed to synthesize PAND. PVC has been selected for blending because of its compatibility with a variety of additives and can be plasticized to make it flexible for use in desirable applications. In this manuscript, we explore the effect of electron beam used during scanning electron microscopy (SEM) analysis on morphology of the synthesized blends. The mechanical properties of these blends are also investigated. Experimental Aniline, ammonium peroxy disulfate (APS) and THF were purchased from Riedel-de-Haën and DBSA from Fluka (Italy). Aniline was distilled under vacuum before use, while all other chemicals were used as received without further purification. Deionized water was used during the experimentation. Polyaniline emeraldine base (PANIEB) was prepared by chemical oxidative polymerization of aniline in aqueous acidic medium (1 M HCl) using APS as an oxidant, followed by deprotonation; details of the procedure have been described elsewhere [15–17]. In redoping method, PANIEB powder was mechanically mixed with DBSA in an agate mortar, having PANIEB/DBSA = 1:3 (by weight) to obtain the PAND named as PANDR, according to the procedure reported by Cao et al. [18]. Aqueous dispersion of PANI–DBSA complex was synthesized by oxidative polymerization of aniline in the presence of DBSA in aqueous media, using APS as an oxidant according to previously described Gospodinova’s procedure [19]. The aqueous dispersion was poured in methanol and filtered to get PAND referred to as PANDA. PANDA and PANDR are collectively called as PAND in this manuscript. The solutions of PVC, PANDA and PANDR were prepared separately in THF. The PAND was added to the PVC solution at different proportions to prepare 5% PAND (PANDR5/PANDA5), 10% PAND (PANDR10/PANDA10), 15% PAND (PANDR15/PANDA15), 20% PAND (PANDR20/PANDA20) and 40% PAND (PANDR40/PANDA40). After stirring for 2 h at room temperature, the mixed solutions were poured into the Petri dishes. The solvent was allowed to evaporate at room temperature to get PANDR/PVC and PANDA/PVC blend films; the thicknesses of these films were 60 ± 5 μm and 17 ± 5 μm, respectively. A scanning electron microscope (LEO 440i) was used to examine the morphology of PAND/PVC blends of various compositions. In order to investigate the mechanical properties of PAND/PVC blends, Shenzhen Sans Testing Machine Co. Ltd. was used. Measurements were done on rectangular film samples (26 mm × 5 mm) at a strain rate of 10 mm/min at room temperature. Results and discussion Mechanical properties In the present study, mechanical properties of PAND/PVC blends have been investigated; it has been observed that all compositions of PANDA/PVC blends are brittle in nature. The stress–strain curves for these films could not be established as the films break with the application of force, which clearly indicates the brittle nature of the films. In PANDR/PVC blends, the tensile strength of the blend increases continuously up to 20% addition of PANDR designating that PANI content is uniformly distributed in the PVC matrix; these results are shown in Table 1. Similar findings have been reported by Thanpitcha et al. [20] for PANI/chitosan blend film. Additional increase in concentration of PANDR decreases the tensile strength, pointing out that insertion of higher content of PANDR (40%) causes the formation of weak points or defects in the PVC matrix. The increase in the concentration of PANDR increases the modulus of elasticity, indicating that films are becoming more rigid [21]. Elongation at break decreases substantially upon addition of PANDR, suggesting that blend films are becoming brittle with an increase in concentration of PANDR. In the present study, pure PVC was taken as a reference material and has 180% elongation at break. Table 1 Mechanical properties of PANDR/PVC blends Samples . Tensile strength (MPa) . Modulus of elasticity (MPa) . Elongation at break (%) . PANDR5 16.4 212 176.3 PANDR10 16.4 467 157.5 PANDR15 20.6 525 70 PANDR20 37.7 589.8 42.7 PANDR40 10.0 672 5.2 Samples . Tensile strength (MPa) . Modulus of elasticity (MPa) . Elongation at break (%) . PANDR5 16.4 212 176.3 PANDR10 16.4 467 157.5 PANDR15 20.6 525 70 PANDR20 37.7 589.8 42.7 PANDR40 10.0 672 5.2 Open in new tab Table 1 Mechanical properties of PANDR/PVC blends Samples . Tensile strength (MPa) . Modulus of elasticity (MPa) . Elongation at break (%) . PANDR5 16.4 212 176.3 PANDR10 16.4 467 157.5 PANDR15 20.6 525 70 PANDR20 37.7 589.8 42.7 PANDR40 10.0 672 5.2 Samples . Tensile strength (MPa) . Modulus of elasticity (MPa) . Elongation at break (%) . PANDR5 16.4 212 176.3 PANDR10 16.4 467 157.5 PANDR15 20.6 525 70 PANDR20 37.7 589.8 42.7 PANDR40 10.0 672 5.2 Open in new tab Scanning electron microscopy Figure 1 represents the SEM micrographs of the PANDA/PVC blends and the line scan corresponding to image of PANDA20. The line scan indicates the presence of bright regions containing higher concentration of sulfur and less chlorine content which are related to conductive PAND phase, whereas black regions rich in chlorine and having less amount of sulfur represent the PVC phase. In all compositions of PANDA/PVC blends, both phases are well separated with more defects and weak points, thereby making them brittle as discussed in the previous section. Figure 1 shows that clusters of PANDA agglomerates are dispersed in the PVC matrix. By increasing the concentration of PANDA from 5% to 40%, the aggregates of the conducting phase form a continuous macroscopic network which may cause an increase in the conductivity of the blend [17]. It has been observed that, during SEM measurements, the structure of PANDA/PVC blends is being changed, indicating the degradation of PVC in the blend. It is a well-known fact that the prevailing side reaction caused by irradiation of PVC is dehydrochlorination [10,11]. Fig. 1 Open in new tabDownload slide SEM images of (a) PANDA5, (b) PANDA10, (c) PANDA15, (d) PANDA20, (e) PANDA40; (f) a typical EDS scan of PANDA/PVC blends; (g) the SEM micrograph of PANDA20 showing the reference line scans; (h), (i) and (j) are the EDS line scans for C, S and Cl, respectively. Fig. 1 Open in new tabDownload slide SEM images of (a) PANDA5, (b) PANDA10, (c) PANDA15, (d) PANDA20, (e) PANDA40; (f) a typical EDS scan of PANDA/PVC blends; (g) the SEM micrograph of PANDA20 showing the reference line scans; (h), (i) and (j) are the EDS line scans for C, S and Cl, respectively. Figure 2 shows the SEM images of PANDA10 recorded by using an electron beam of energy 5 kV and 70 pico-ampere probe current after a few seconds, 2, 5 and 12 min; the image after 12 min is taken at 20 kV to see the maximum damage to the film. From these images, it is illustrated that, during SEM analysis, as the time of exposure of the sample to the electron beam is increased, more and more phase separation occurs due to degradation of PVC by dehydrochlorination. Fig. 2 Open in new tabDownload slide SEM images of PANDA10 after (a) a few seconds, (b) 2 min, (c) 5 min and (d) 12 min. Fig. 2 Open in new tabDownload slide SEM images of PANDA10 after (a) a few seconds, (b) 2 min, (c) 5 min and (d) 12 min. SEM images of PANDR/PVC blends and line scan of PANDR20 are shown in Fig. 3. It has been observed that bright and dark regions correspond to PANDR and PVC contents, respectively, similar to PANDA/PVC blends. From Fig. 3, we note that blends having lower concentration of PANDR (PANDR5 and PANDR10) exhibit a single-phase, smooth, compact and continuous structure in contrast to PANDA/PVC blends, where two distinguished phases were observed. Further increase in concentration of PANDR indicates its uniform distribution in the PVC matrix. These blends are stable when exposed to electron beam irradiation during SEM analysis contrary to PANDA/PVC blends. It has been suggested that greater stability of PANDR/PVC blends to irradiation can be due to the fact that chains of PANDR and PVC are entangled into each other due to large interactions, leading to single-phase structure. Therefore, no free PVC is available for dehydrochlorination during irradiation, thereby making these blends stable as compared to PANDA/PVC blends. The interaction energies between PAND and PVC components are higher in PANDR/PVC blends than PANDA/PVC blends as indicated by heatflow microcalorimetry technique [22]. Energy dispersive spectroscopy (EDS) analysis of both types of blends confirm the presence of DBSA and PVC in it. Fig. 3 Open in new tabDownload slide SEM images of (a) PANDR5, (b) PANDR10, (c) PANDR15, (d) PANDR20, (e) PANDR40; (f) a typical EDS spectrum of PANDR/PVC blends; (g) the SEM micrograph of PANDR20 showing the reference line scans; (h), (i) and (j) are the EDS line scans for C, S and Cl, respectively. Fig. 3 Open in new tabDownload slide SEM images of (a) PANDR5, (b) PANDR10, (c) PANDR15, (d) PANDR20, (e) PANDR40; (f) a typical EDS spectrum of PANDR/PVC blends; (g) the SEM micrograph of PANDR20 showing the reference line scans; (h), (i) and (j) are the EDS line scans for C, S and Cl, respectively. Conclusions The PAND/PVC blends were synthesized by solution blending techniques. All compositions of PANDA/PVC blends are brittle in nature, whereas PANDR/PVC blend films are becoming more rigid by increasing concentration of PANDR in the PVC matrix. The change in morphology for PANDA/PVC blends has been observed by SEM with the increase in irradiation time. EDS analysis confirmed that the changes have been found in the composition with the increase in irradiation time. Electron beam used during SEM analysis has changed the morphology of PANDA/PVC blend films due to dehydrochlorination of PVC; however, PANDR/PVC blends remain unaffected, as no free PVC is available for dehydrochlorination. We are grateful to the Higher Education Commission (HEC) of Pakistan for the financial support through indigenous scholarship scheme for Ph. D. studies of A.B.A. in science and technology (Batch II). References 1 Pielichowski K . Thermal degradation of poly (vinyl chloride)/polyaniline conducting blends , J. Therm. Anal. Cal. , 1998 , vol. 54 (pg. 171 - 175 ) Google Scholar Crossref Search ADS WorldCat 2 Anand J , Palaniappan S , Sathyanarayana D N . Conducting polyaniline blends and composites , Prog. Polym. Sci. , 1998 , vol. 23 (pg. 993 - 1018 ) Google Scholar Crossref Search ADS WorldCat 3 Thangarathinavelu M , Tripathi A K , Goel T C , Varma I K . Preparation and characterization of polyaniline-PVC polymer composite films , J. Appl. Polym. Sci. , 1994 , vol. 51 (pg. 1347 - 1349 ) Google Scholar Crossref Search ADS WorldCat 4 Andreatta A , Heager A J , Smith P . Electrically conductive polyblend fibres of polyaniline and poly-(p-phenylene terephthalamide) , Polym. Commun. , 1990 , vol. 31 (pg. 275 - 278 ) OpenURL Placeholder Text WorldCat 5 Cao Y , Smith P , Heeger A J . Counter-ion induced processibility of conducting polyaniline and of conducting polyblends of polyaniline in bulk polymers , Synth. Met. , 1992 , vol. 48 (pg. 91 - 97 ) Google Scholar Crossref Search ADS WorldCat 6 Cao Y , Smith P . Liquid-crystalline solutions of electrically conducting polyaniline , Polymer , 1993 , vol. 34 (pg. 3139 - 3143 ) Google Scholar Crossref Search ADS WorldCat 7 Zhang L , Long Y , Chen Z . The effect of hydrogen bonding on self-assembled polyaniline nanostructures , Adv. Funct. Mater. , 2004 , vol. 14 (pg. 693 - 698 ) Google Scholar Crossref Search ADS WorldCat 8 Yoon C O , Reghu M , Moses D , Heeger A J . Electrical transport in conductive blends of polyaniline in poly (methyl methacrylate) , Synth. Met. , 1994 , vol. 63 (pg. 47 - 52 ) Google Scholar Crossref Search ADS WorldCat 9 Gupta R K , Singh R A . Preparation and characterization of polymer composites of polyaniline with poly (vinyl chloride) and polystyrene , J. Non-Cryst. Solids , 2005 , vol. 351 (pg. 2022 - 2028 ) Google Scholar Crossref Search ADS WorldCat 10 Srivastava A , Singh V , Chandra A , Witte K , Scherer U W , Singh T V . Electrical conductivity studies of swift heavy ion modified PVC and PVC PANI composites , Nucl. Instrum. Meth. B , 2006 , vol. 245 (pg. 277 - 280 ) Google Scholar Crossref Search ADS WorldCat 11 Bodugoz H , Guven O . Radiation induced dehyrochlorination as an in-situ doping technique for enhancement of the conductivity of polyaniline blends , Nucl. Instrum. Meth. B , 2005 , vol. 236 (pg. 153 - 159 ) Google Scholar Crossref Search ADS WorldCat 12 Bodugoz H , Sevil U A , Guven O . Radiation-induced conductance in the blends of poly(aniline-base) with poly(vinyl chloride) and poly[(vinylidene chloride)-co-(vinyl acetate)] , Macromol Symp. , 1998 , vol. 169 (pg. 289 - 295 ) Google Scholar Crossref Search ADS WorldCat 13 Sevil U A , Guven O , Kovacs A , Slezsak I . Gamma and electron dose response of the electrical conductivity of polyaniline based polymer composites , Radiat. Phys. Chem. , 2003 , vol. 67 (pg. 575 - 580 ) Google Scholar Crossref Search ADS WorldCat 14 Barra G M O , Leyva M E , Soares B G , Sens M . Solution-cast blends of polyaniline-DBSA with EVA copolymers , Synth. Met. , 2002 , vol. 130 (pg. 239 - 245 ) Google Scholar Crossref Search ADS WorldCat 15 Afzal A B , Akhtar M J , Nadeem M , Ahmad M , Hassan M M , Yasin T , Mehmood M . Structural and electrical properties of polyaniline/silver nanocomposites , J. Phys. D Appl. Phys. , 2009 , vol. 42 (pg. 015411 - 18 ) Google Scholar Crossref Search ADS WorldCat 16 Afzal A B , Akhtar M J , Nadeem M , Hassan M M . Investigation of structural and electrical properties of polyaniline/gold nanocomposites , J. Phys. Chem. C , 2009 , vol. 113 (pg. 17560 - 17565 ) Google Scholar Crossref Search ADS WorldCat 17 Afzal A B , Akhtar M J , Nadeem M , Hassan M M . Dielectric and impedance studies of DBSA doped polyaniline/PVC composites , Curr. Appl. Phys. , 2010 , vol. 10 (pg. 601 - 606 ) Google Scholar Crossref Search ADS WorldCat 18 Cao Y , Smith P , Heeger A J . Counter-ion induced processibility of conducting polyaniline , Synth. Met. , 1993 , vol. 57 (pg. 3514 - 3519 ) Google Scholar Crossref Search ADS WorldCat 19 Gospodinova N , Mokreva P , Tsanov T , Terlemezyan L . A new route to polyaniline composites , Polymer , 1997 , vol. 38 (pg. 743 - 746 ) Google Scholar Crossref Search ADS WorldCat 20 Thanpitcha T , Sirivat A , Jamieson A M , Rujiravanit R . Preparation and characterization of polyaniline/chitosan blend film , Carbohyd. Polym. , 2006 , vol. 64 (pg. 560 - 568 ) Google Scholar Crossref Search ADS WorldCat 21 Faez R , Gazotti W A , De Paoli M -A . An elastomeric conductor based on polyaniline prepared by mechanical mixing , Polymer , 1999 , vol. 40 (pg. 5497 - 5503 ) Google Scholar Crossref Search ADS WorldCat 22 Afzal A B , Akhtar M J , Svensson L G . Thermal studies of DBSA-doped polyaniline/PVC blends by isothermal microcalorimetry , J. Therm. Anal. Calorim. , 2010 , vol. 100 (pg. 1017 - 1025 ) Google Scholar Crossref Search ADS WorldCat © The Author 2010. Published by Oxford University Press on behalf of Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org Oxford University Press
TI - Morphological studies of DBSA-doped polyaniline/PVC blends
JF - Journal of Electron Microscopy
DO - 10.1093/jmicro/dfq050
DA - 2010-10-01
UR - https://www.deepdyve.com/lp/oxford-university-press/morphological-studies-of-dbsa-doped-polyaniline-pvc-blends-CCg15J1s4z
SP - 339
EP - 344
VL - 59
IS - 5
DP - DeepDyve
ER -