ELECTRICALLY CONDUCTIVE EXTRUDED FILAMENTS OF POLY ANILINE/POLYMER BLENDS. Department of Materials Engineering

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ELECTRICALLY CONDUCTIVE EXTRUDED FILAMENTS OF POLY ANILINE/POLYMER BLENDS M. Zilberman and A. Siegmann Department of Materials Engineering M.

1 ELECTRICALLY CONDUCTIVE EXTRUDED FILAMENTS OF POLY ANILINE/POLYMER BLENDS M. Zilberman and A. Siegmann Department of Materials Engineering M. Narkis* Department of Chemical Engineering Technion - Israel Institute of Technology Haifa 32000, Israel ABSTRACT Blends of plasticized polystyrene and conductive polyaniline (PANI) were prepared by melt processing, and extruded filaments were obtained by using a capillary rheometer. The effect of flow conditions, including temperature and shear rate, on the morphology of the blends and on the resulting electrical conductivity were investigated. Under a combination of specific processing and given blend compositions, the electrical conductivity was found to be independent of shear level over a wide range of shear rates. Thus, conductive melt processible PANI-based blends can be designed, however relatively high PANI concentrations (well above percolation) are required. Blend systems can be developed to further reduce the PANI concentration in ternary component blends. KEYWORDS polyaniline blends, melt processing, binary polymer blends. * Corresponding author 97

$Intrinsically conductive polymers (ICPs), recently making their first appearance in the market, are expected to yield a good balance of properties l\l.$

2 Vol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments of PS/PANI Blends INTRODUCTION There is an increasing interest in electrically conductive polymeric materials, combining electrical conductivity and desired physical properties, processed by conventional methods. Intrinsically conductive polymers (ICPs), recently making their first appearance in the market, are expected to yield a good balance of properties l\l. Polyaniline (PANI) is a promising ICP because of its relatively high environmental and thermal stability and its simple and economical production 121. The main disadvantage of PANI, like other ICPs, is its limited thermal processability. One method, still in the development stages, is blending with conventional polymers. Such blends should combine the desired properties of each component, namely, the electrical conductivity of PANI together with the physical and mechanical properties of the matrix polymer. The morphology of such immiscible blends has a dominant effect on their properties. In most studies of PANI-containing polymer blends, blending was performed in solution (for example see 12-41). Only a few studies have reported on blends prepared via melt processing /1, 5-8/. Shacklette et al. /5/ reported that Versicon rm (Allied-Signal Inc., p-toluene sulfonic acid [ptsa]- doped PANI), a conductive form of polyaniline, is dispersible in polar thermoplastic matrix polymers, such as polycaprolactone and poly (ethyleneterephthalate glycol). The conductivity percolation threshold in such blends was observed in the range of 6 to 10 v/v% of Versicon. Ikkala et al. /1 / described melt-mixed conductive polymer blends with a Neste Complex (PANI doped with dodecyl-benzene sulfonic acid (DBSA) prepared by thermal doping), using conventional melt processing techniques. That study mainly addressed the electrical and mechanical properties of the blends. Passiniemi et al. Ill reported on certain blends with PANI, processed by methods such as injection molding, film blowing, and fiber spinning. The authors suggested that the key feature for successful processing is using a plasticizer, developed by Neste (Finland). In addition, the authors reported the existence of a through-the-thickness conductivity profile in injection molded sheets of PP and PANI. Tanner et al. /8/ reported that Neste (Finland), in cooperation with Uniax (U.S.A), have developed fusible PANI- DBSA complexes by the application of the proprietary additives. These investigators showed that such PANI-compIexes exhibited conventional 98

3 Μ. Zilberman, Α. Siegmann, Μ. Narkis Journal of Polymer Engineering polymer rheology. The phase continuity of a fusible PANI-compiex should be tailored by controlling its viscosity, relative to the matrix polymer, to obtain polyolefin-based conducting blends. The present authors recently reported on several conductive blends, consisting of thermoplastic polymers and various types of conducting polyaniline, prepared by melt mixing in a Brabender mixer /9-11/. We suggested that the interaction level between doped PANI and a matrix polymer affects the morphology of the blend and thus, its electrical conductivity. Similar solubility parameters of PANI and a matrix were found to be essential for an effective PANI dispersion, within the matrix polymer, for the formation of conducting paths at low PANI content. Deformation and orientation of immiscible polymer blends are common results of the effective flow fields during polymer melt processing /12/. A convenient method to study the relation between flow conditions, morphology, and conductivity /13,14/ is the use of a capillary rheometer under controlled flow conditions. The elongational flow at the capillary entrance and the shear flow along the capillary may induce morphological orientational and radial profiles in the extrudates. In the present study, conductive blends (plasticized PS/PAN I) were melt mixed and subsequently used to produce capillary extrudates. The effect of flow conditions on the morphology of the blends and the associated electrical conductivity was investigated. EXPERIMENTAL Materials Versicon, a conductive ptsa-doped polyaniline (σ = 6 S/cm); Zipperling Kessler & Co, Germany. Polystyrene (PS); Galirene HH-102-E (MFI=4, 200 C, 5 kg), Carmel Olefins, Israel. The PS was plasticized with dioctyl phthalate (DOP); PS:DOP = 85:15 wt. ratio. Blend Preparation Binary polymer blends, consisting of plasticized PS matrix and PANI, were prepared by melt mixing for 12 min in a Brabender mixing head, at 50 rpm 99

4 Vol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments of PS/PAN I Blends and 150 C. Flat plaques, 3 mm thick, for conductivity measurement were prepared by compression molding at 150 C, under a pressure of 280 Kg/cm 2. Capillary rheometry An MCR capillary rheometer, mounted on an Instron TT-D, was used for processing the Brabender-produced blends and for the shear viscosity measurements. A capillary, 5cm long and cm diameter (L/D = 40), was used at various processing temperatures. The rheometer was operated at 0.1 to 50 cm min-1, yielding an apparent shear-rate range of 3 to 2935 sec-1. The shear viscosity of the blends and of the matrix polymer was determined. The Rabinowitsch correction for the non-newtonian behavior was applied, whereas the Bagley end correction was neglected because of the relatively high capillary L/D ratio. The capillary extrudates, produced at different rheometer operating conditions, were collected, and their room temperature conductivity and morphology were determined. Conductivity Measurements Electrical conductivity measurements were performed, using the "four probe technique" (ASTM-D ), for the 12x1.2x0.3 cm 3 plaques and for the extruded filaments. The filaments were first coated with a silver paint at the two contact zones with the metal electrodes to reduce sample-electrode contact resistance. A Keithley 240 A high voltage supply or a Sorensen model QRD were used as power suppliers, Keithley 614 or 175 electrometers were used as amperemeters, and a Keithley 610C electrometer was used as a voltmeter. Morphological Characterization Scanning Electron Microscopy (SEM) of cryogenically fractured (parallel to flow direction) surfaces of the extrudates was performed using a Jeol JSM- 840 at an accelerating voltage of 10 kv. The SEM samples were gold sputtered before observation. 100

Μ. Zilberman, Α. Siegmann, Μ. Narkis Journal of Polymer Engineering RESULTS AND DISCUSSION The electrical conductivity vs. PANI content for compression-molded plaques is presented in Fig. 1.

5 Μ. Zilberman, Α. Siegmann, Μ. Narkis Journal of Polymer Engineering RESULTS AND DISCUSSION The electrical conductivity vs. PANI content for compression-molded plaques is presented in Fig. 1. The percolation threshold occurs at about 12 wt% PANI. The blend containing 15 vvt% PANI has a conductivity of 2.5*1(T 4 S/cm. Beyond percolation, the conductivity level slowly increased with PANI content, due to further generation of a conductive network of an improved quality, attaining 0.23 S/cm for the 30 wt% PANI blend. Most of the present study was performed on the 20 wt% PANI blend (0.05 S/cm). The morphology of this blend and that of the matrix polymer, PS/DOP, is presented in Fig. 2. In general, the characteristic features of the plasticized PS fracture surface were not observed upon the addition of PANI, and very small, 0.1 to 0.2 μπι, particles were observed on the fracture surface of the blend. These very fine particles are generated during melt blending, due to the severe fracturing process of the original, as the prepared PANI aggregates. Earlier studies /9-11/ had suggested that the conductive blend's morphology could be described by a two-level hierarchy: a primary structure composed of io,u 1 1 ' Fig. 1: ' PANI Content (wt%) Electrical conductivity vs. PANI content for compression molded plasticized PS / PANI blends. 101

$The fibrillar network structure is formed, upon cooling the blend, by precipitation from the melt of a dissolved PANI fraction (the lower molecular weight fraction).$

6 Vol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments ofps/pani Blends Fig. 2: Fracture surface morphology of: (a) 20 wt% PANI blend, (b) plasticized matrix without PANI. the small dispersed PANI particles, and a short range, very fine fibrillar structure interconnecting the small dispersed particles. The fibrillar network structure is formed, upon cooling the blend, by precipitation from the melt of a dissolved PANI fraction (the lower molecular weight fraction). The plasticized PS/PANI blends were also studied as extruded filaments prepared by the Instron capillary rheometer. The electrical conductivity was investigated as function of the shear rate. 102

The 170 C extrudates exhibited a conductivity that was practically independent of the shear rate and somewhat higher than that of the respective compression molded blend (a CM = 0.05 S/cm).

7 Μ. Zilberman, Α. Siegmann, Μ. Narkis Journal of Polymer Engineering Extruded Filaments Electrical Conductivity The electrical conductivity vs. the extrusion shear rate of extruded 20 wt% PANI filaments, prepared at 150 C and 170 C, is presented in Fig. 3. The 170 C extrudates exhibited a conductivity that was practically independent of the shear rate and somewhat higher than that of the respective compression molded blend (a CM = 0.05 S/cm). A similar behavior was observed for the low shear rate (below 100 sec" 1 ), 150 C extrudates. At higher shear rates, however, the conductivity at 150 C significantly decreased with shear rate, becoming about 10" 5 S/cm at 3000 sec" 1. Recall that the blending step in the Brabender mixing cell took place at 150 C at an effective shear-rate level of roughly 50 sec" 1 (approximated for 50 rpm). Thus, at 150 C the conductive network structure present is preserved up to a certain level of shear stress field and subsequently undergoes gradual destruction. In fact, in capillary extrusion, deterioration of the conducting network occurs mainly at the die entry /13/. A higher extrusion temperature of 170 C (20 C above the preparation temperature in the Brabender mixing cell) is actually beneficial for preserving the original structure of the conducting network because lower shear stress levels are developed at 170 C. Thus, the quality of the conducting network is not only preserved at 170 C but also may even be improved 19/, as long as the higher temperature by itself (namely, under static conditions) does not cause structural changes with an associated conductivity reduction. Indeed, the same electrical conductivity was measured on compression-molded plaques that were produced at 150 C, 170 C, and 180 C; namely, proof of thermal stability up to 180 C. Thus, the data shown in Fig. 3 reflect the significant stability of the conducting network at 170 C up to shear-rate levels of at least 4000 sec" 1. At 170 C, the conducting network structure of the blend containing 15 wt% PANI, close to the percolation concentration as shown in Fig. 4, undergoes gradual destruction with increasing shear level. The conductivity vs. shear rate curves clearly indicate that melt processible PANI/polymer blends are feasible under certain conditions, but the 20 wt% PANI loading that is required is high. Nevertheless, this obstacle can be largely heeled by using 103

Vol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments of PS/PAN I Blends 10 =- CJ CO >> > Ο Ό C U 10' 2 t 10 10 3 ί 10-4 i Γ σ = 0.

shear rate for 20 wt % PANI blend filaments produced at (*)=170 o C and (0)=I50 C. a compression rao i ded =0.05 S/cm.

8 Vol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments of PS/PAN I Blends 10 =- CJ CO >> > Ο Ό C U 10' 2 t ί 10-4 i Γ σ = 0.05 CM ' 10 10" 10 H Shear Rate (sec" ) Fig. 3: Electrical conductivity vs. shear rate for 20 wt % PANI blend filaments produced at (*)=170 o C and (0)=I50 C. a compression rao i ded =0.05 S/cm. 10 _ 10" 1 Ρ Ü 10" ] C/j 10" 3 σ = 0.05 CM σ = 2.5*10 CM tl ΙΟ"" ΙΟ" H -L Shear Rate (sec") Fig. 4: Electrical conductivity vs. shear rate for 170 C plasticized PS/PANI filaments: ( )=20 wt% PANI blend; ( )=15 wt% PANI blend. 104

Μ. Zilberman, Α. Siegmann, Μ. Narkis Journal of Polymer Engineering ternary immiscible polymer blends, in which the PANI concentration can be greatly reduced /15,16/.

This similarity indirectly supports the similar conductivity levels that were Fig.

9 Μ. Zilberman, Α. Siegmann, Μ. Narkis Journal of Polymer Engineering ternary immiscible polymer blends, in which the PANI concentration can be greatly reduced /15,16/. Morphology The extrudates prepared at 170 C and 4200 sec -1 showed morphological behavior similar to those prepared at 170 C and 8 sec' 1 (Fig. 5). This similarity indirectly supports the similar conductivity levels that were Fig. 5: Fracture surface morphology (parallel to flow direction) of 20 wt% PANI blend produced at 170 C: (a) = 8 sec - ', outer surface, (b)= 8 sec -1, center, (c) = 4200 sec - ', outer surface, (d) = 4200 sec -1, center. observed at 170 C for these two extreme shear-rate levels (Fig. 3). A similar morphology was also observed for blend extrudates prepared at 150 C and 8 sec" 1, whereas different fracture surface characteristics were observed for blend extrudates prepared at 150 C and the high shear rate of 4000 sec -1 (Fig. 6). 105

outer surface, (d) = 4200 sec -1, center.

The viscosity of the plasticized matrix increased upon the addition of PANI, but differently at 170 C when compared with 150 C (Fig. 7). At 170 C (Fig.

10 Vol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments of PS/PANI Blends Fig. 6: Fracture surface morphology (parallel to flow direction) of 20 wt% PANI blend produced at 150 C: (a) = 8 secouter surface, (b) = 8 seccenter, (c) = 4200 sec -1, outer surface, (d) = 4200 sec -1, center. Rheological Behavior The rheological behavior of the 20 wt% PANI blend and the plasticized matrix without PANI is presented in Fig. 7. The viscosity of the plasticized matrix increased upon the addition of PANI, but differently at 170 C when compared with 150 C (Fig. 7). At 170 C (Fig. 7a) the shear viscosity curve of the blend is almost parallel to that of the matrix polymer, over the entire shear rate range studied. This behavior may indicate that at 170 C, the original network structure of the blend is virtually preserved. In contrast, at 150 C (Fig. 7b), the difference between the shear viscosity of the blend and that of the matrix gradually decreased with shear rate, becoming similar at

IMI suggested a similar interpretation for conductive polymer blends containing carbon black particles.

11 Μ. Zilberman, Α. Siegmann, Μ. Narkis Journal of Polymer Engineering sec" 1. This result may indicate that at this temperature, the network structure is gradually destroyed with increasing shear rate levels. Zhu et al. IMI suggested a similar interpretation for conductive polymer blends containing carbon black particles. 10 Ε (a) υ C/3 Λ CL,3-10 Ο ΙΛ Μ ω χ: ΙΟ 2 γ Ο 10 ί ΙΟ ΙΟ 3 Shear Rate (sec -1 ) ΙΟ 4 ω α CU υ on 03 <υ -C η Fig. 7: ΙΟ 1 10 ζ 10 J Shear Rate (sec 1 ) Shear viscosity curves, (O) = plasticized PS matrix and ( ) = 20 wt% PANI blend: (a) = 170 C, (b) = 150 C. 107

12 Vol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments of PS/PAN 1 Blends In summary, the results presented in this paper indicate that polymer/ PANI blends, such as the plasticized PS/PANI blend described here, can be designed as melt processible materials. Nevertheless, the PANI concentration that is required to preserve conductivity is well above the PANI percolation concentration that has been determined on compression molded specimens. Melt processible blends at lower PANI concentrations can be developed, based on multi-component blend concepts, such as polymer/polymer/pani systems. REFERENCES 1. O.T. Ikkala, J. Laakso, K. Vakiparta, E. Virtanen, H. Ruohnen, H. Jarvinen, T. Taka, P. Passiniemi and J.E. Osterholm., Synthetic Metals, 69, 97 (1995). 2. A.J. Heeger, Synthetic Metals, 57, 3471 (1993). 3. Y. Cao, P. Smith and A.J. Heeger, Synthetic Metals, 57, 3514 (1993). 4. C.Y. Yang, Y. Cao, P. Smith and A.J. Heeger, Synthetic Metals, 53, 293 (1993). 5. L.W. Shacklette, C.C. Han and M.H. Luly, Synthetic Metals, 57, 3532 (1993). 6. S.J. Davides, T.G. Ryan, C.J. Wilde and G. Beyer, Synthetic Metals, 69, 209(1995). 7. P. Passiniemi, J. Laakso, H. Ruohnen and K. Vakiparta, Mat. Res. Soc. Symp. Proc., Vol. 413, 577 (1996). 8. J.O. Tanner, O.T. Ikkala, J. Laakso and P. Passiniemi, Mat. Res. Soc. Symp. Proc., Vol. 413, 565 (1996). 9. M. Narkis, M. Zilberman and A. Siegmann, Polym. Adv. Tech., 8, 525 (1997). 10. M. Zilberman, G.I. Titelman, A. Siegmann, Y. Haba, and M. Narkis, J. Appl. Polym. Sei., 66, 2199 (1997). 11. Μ. Zilberman, Α. Siegmann and M. Narkis, J. Macromol. Sei. (Phys.), B37, 301 (1998). 12. L.A. Utracki, "Polymer Alloys and Blends", Hauser publishers, New York,

15. M. Zilberman, A. Siegmann and M. Narkis, Polym. Adv. Tech., in press. 16. M. Zilberman, A. Siegmann and M. Narkis,, J.

13 Μ. Zilberman, Α. Siegmann, Μ. Narkis Journal of Polymer Engineering 13. Ο. Breuer, R. Tchoudakov, M. Narkis and A. Siegmann. Polym. Eng. Sei., 38, 1898 (1998). 14. O. Breuer, R. Tchoudakov, M. Narkis and A. Siegmann, J. Appl. Polym. Sei., in press. 15. M. Zilberman, A. Siegmann and M. Narkis, Polym. Adv. Tech., in press. 16. M. Zilberman, A. Siegmann and M. Narkis,, J. Macromol. Sei. (Phys.), in press. 17. J. Zhu, Y.C. Ou and Y.P. Feng, Polymer International, 37, 105 (1995). 109

Melt-Processed, Electrically Conductive Ternary Polymer Blends Containing Polyaniline

Journal of Macromolecular Science, Part B Physics ISSN: 0022-2348 (Print) 1525-609X (Online) Journal homepage: http://www.tandfonline.com/loi/lmsb20 Melt-Processed, Electrically Conductive Ternary Polymer