ELECTRICALLY CONDUCTIVE EXTRUDED FILAMENTS OF …meitalz/Articles/C9.pdfVol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments of PS/PAN I Blends and 150°C Fla. plaquest

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

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Vol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments of PS/PANI Blends

I N T R O D U C T I O N

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 Vers icon r M (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

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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.

E X P E R I M E N T A L

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

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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/cm2.

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 0.127 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 991-89), for the 12x1.2x0.3 cm3 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 60-1.5 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.




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(T4

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

i o , u 1 1 '

0 5 10 15 '20 25 30 35

PANI Content (wt%) Fig. 1: Electrical conductivity vs. PANI content for compression molded plasticized

PS / PANI blends.



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.




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 C M = 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, under-

goes 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



Vol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments of PS/PAN I Blends

10 ο =-

10' 3 · · · ο ο

CJ CO >>

> Ο

•Ό C C

U

10

Γ σ = 0.05 CM

2 t

10 3 ί

1 0 - 4 i

10 ο 10 10 ' 10 10" 10H

Shear Rate (sec" ) Fig. 3: Electrical conductivity vs. shear rate for 20 wt % PANI blend filaments

produced at (*)=170oC and (0)=I50°C. a c o m p r e s s i o n raoided=0.05 S/cm.

10

_ 10"1

Ρ •Ü 1 0 " ]

C/j

10"3

t l ΙΟ""1 3

5 10

ΙΟ"7

1 0 °

σ = 0.05 CM

σ = 2.5*10 C M

10 10

- L

10H 10 10-

Shear Rate (sec") Fig. 4: Electrical conductivity vs. shear rate for 170°C plasticized PS/PANI

filaments: ( · ) = 2 0 wt% PANI blend; ( · )=15 wt% PANI blend.




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).



Vol. 20, No. 2, 2000 Electrically Conductive Extruded Filaments of PS/PANI Blends

Fig. 6: Fracture surface morphology (parallel to flow direction) of 20 w t % PANI

blend produced at 150°C: (a) = 8 s e c o u t e r surface, (b) = 8 s e c c e n t e r ,

(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 4200




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.

ο υ C/3 Λ

CL

Ο ο ΙΛ

Μ ω χ: οο

10 Ε (a)

,3 -10

ΙΟ2 γ

10ίο°

ο · ο ·

ο

ο · ο

Ο · ο

ΙΟ1 102 ΙΟ3

Shear Rate (sec-1)

ΙΟ4

ο ω α

CU

ο υ on

03 <υ -C οη

Fig. 7:

ΙΟ1 10ζ 10J

Shear Rate (sec1) Shear viscosity curves, (O) = plasticized PS matrix and ( · ) = 20 wt% PANI

blend: (a) = 170°C, (b) = 150°C.



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, 1990.




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).



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