Synthetic Metals 144 (2004) 29–49

Composites of polyaniline and cellulose acetate: preparation,characterization, thermo-oxidative degradation and stability

in terms of DC electrical conductivity retention

Amir Al-Ahmeda, Faiz Mohammada,∗, M. Zaki Ab. Rahmanba Department of Applied Chemistry, Aligarh Muslim University, Aligarh, India

b Department of Chemistry, University Putra Malaysia, Selangor, Malaysia

Received 12 December 2003; accepted 26 January 2004

Available online 1 April 2004

Abstract

The composite films of polyaniline and cellulose acetate have been prepared by using two slightly different techniques. Thus-preparedpolyaniline:celluloseacetate (PANI:CA) composite films were characterized by FTIR and SEM. The thermo-oxidative degradation wasstudied by thermogravimetric analysis (TGA) while the stability in terms of retention of DC electrical properties was studied in an oxidativeenvironment by two slightly different techniques.© 2004 Elsevier B.V. All rights reserved.

Keywords: Thermo-oxidative degradation; Stability in terms of DC electrical conductivity retention; Conducting polyaniline:celluloseacetate composites

1. Introduction

With the advent of newer and newer technologies, thedemand for materials possessing a combination of a widerange of desirable properties is increasing day by day. Oneof the techniques to develop such materials is the formula-tion of composites from compatible materials individuallypossessing the desirable properties. In view of lightweight,low cost, low temperature fabrication as well as good me-chanical strength and environmental stability, electricallyconducting composites based on an electrically conductingpolymer, polyaniline (PANI) with an insulating polymer, cel-lulose acetate (CA), were selected for this study. High inter-molecular forces and the regular structure of the celluloseacetate result in its having an unusually high degree of crys-tallinity and a very high melting point—it decomposes be-fore beginning to melt[1–4]. Cellulose acetate is preparedby reacting natural cellulose with acetic anhydride or glacialacetic acid in the presence of a catalyst, such as sulfuric acidor perchloric acid. This is followed by partial hydrolysisto get 2–2.5 acetate group per C6H10O5 unit, after this theproduct becomes soluble in common organic solvents likeacetone. Cellulose acetate is a colorless, odorless, tasteless,

∗ Corresponding author. Present address: Department of Chemistry,Mekelle University, P.O. Box: 231, Mekelle, Ethiopia.E-mail address: faiz@freemail.et (F. Mohammad).

tough, and durable plastic with a density of 1.2–1.4 g cm−3.It has good impact strength and can easily be machined andmolded. It is widely used in the manufacture of commodityas well as engineering articles[2,3,5,6]. Polyaniline occu-pies a high place among intrinsically conducting polymersbecause of its very simple preparation, good environmentalstability and the fact that it can be doped by protonic acidsto high electrical conductivities[7–14].

2. Experimental

2.1. Materials

The materials used included aniline (99%, Qualigens, In-dia), cellulose acetate (CDH, India), acetone (CDH, India),hydrochloric acid (35%, E. Merck, India), potassium per-sulphate (98%, CDH, India) and ammonia solution (Quali-gens). Aniline was doubly distilled prior to use and all othermaterials were used as received.

2.2. Synthesis of polyaniline

Polyaniline was synthesized by oxidative polymerizationof doubly distilled aniline dissolved in aqueous HCl (1 M),using potassium persulphate (K2S2O8) in aqueous HCl (1 M)as an oxidant at ice temperature. Aniline (0.2 mol) was dis-

0379-6779/$ – see front matter © 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.synthmet.2004.01.007

30 A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49

solved in 1000 ml of aqueous solution of HCl (1 M) andpotassium persulphate (0.25 mol) was dissolved in 1000 mlHCl (1 M). The oxidant solution was then added slowly tothe aniline solution with continuous stirring at ice tempera-ture. The reaction mixture was kept under continuous stir-ring for an hour and then kept in a refrigerator overnight. Thereaction mixture was filtered and washed with HCl (1 M) tillthe filtrate became colorless and then with doubly distilledwater until the filtrate became acid free. Thus synthesizedpolyaniline was undoped by treatment with excess of aque-ous ammonia (1 M) and repeatedly washed with distilledwater until the filtrate became neutral. The polymer wasground to fine powder and low molecular weight oligomerswere removed from polyaniline by soxhalation with acetone[15–19]. As-prepared polyaniline was dried at 60◦C in anair oven for 48 h and stored in a dessicator for further ex-perimentation.

2.3. Preparation of polyaniline:celluloseacetate(PANI:CA) composites

Finely ground, as-prepared and undoped polyaniline wasadded to the solution of cellulose acetate in acetone. Thesolution mixture was shaken well to get a homogeneous sus-pension. The films of composites were casted on glass plateswith extremely flat surfaces by solvent evaporation. Thefilms were dried at 60◦C for 48 h in an air oven and storedin a dessicator for experiments. The details of the prepara-tion of polyaniline:celluloseacetate-1 (PANI:CA1) compos-ites are given inTable 1.

In another technique, a viscous solution of celluloseacetate (4.5 g) in aniline (10 g) was prepared by slowlyadding portions of cellulose acetate in aniline at the roomtemperature. Films were casted from the solution of cel-lulose acetate in aniline on the flat glass plates by dryingin a closed container. The polymerization of aniline withinthe cellulose acetate matrix was effected by treatment withpotassium persulphate (K2S2O8) solution in HCl (1 M).The composite films were washed with aqueous HCl (1 M)followed by doubly distilled water till the filtrate becameacid free. Thus-prepared composite films were undoped

Table 1Preparation of polyaniline:celluloseacetate-1 (PANI:CA1) composites

Sample ID Quantity ofcelluloseacetate (g)

Quantityof acetone(ml)

Quantity ofpolyanilinepowder (g)

PANI:CA1-1 1 30 0.1PANI:CA1-2 1 30 0.2PANI:CA1-3 1 30 0.3PANI:CA1-4 1 30 0.4PANI:CA1-5 1 30 0.5PANI:CA1-6 1 30 0.6PANI:CA1-7 1 30 0.7PANI:CA1-8 1 30 0.8PANI:CA1-9 1 30 0.9PANI:CA1-10 1 30 1.0

by treatment with excess of aqueous ammonia (1 M) andrepeatedly washed with distilled water until the filtrate be-came neutral. The films of polyaniline:celluloseacetate-2(PANI:CA2) were dried at 60◦C for 48 h in an air oven andstored in a dessicator for experiments.

2.4. Characterization

The FTIR spectra of polyaniline:celluloseacetate-1 com-posites were recorded by a Perkin-Elmer 1725 while theFTIR spectra of polyaniline and polyaniline:cellulose-acetate-2 composites were recorded by Perkin-Elmer (Spec-trum BX) instrument. The FTIR spectra of cellulose acetatewere recorded by Nicolete-Protége 460. The SEM studieswere performed on a LEO 435 VP SEM instrument to ex-amine the surface morphologies of the composites and theircomponents. Simultaneous differential thermal analysis(DTA) and thermogravimetric analysis (TGA) were per-formed on some selected composites by using Perkin-Elmer(Pyris Dimond) instrument from∼25 to ∼600◦C at aheating rate of 10◦C min−1 with a dry air flow rate of200 ml min−1.

2.5. Thermal stability in terms of DC electricalconductivity retention

DC electrical conductivity of the doped composite filmswas measured with increasing temperature (35–100◦C) byusing a four-in-line probe DC Electrical Conductivity Mea-suring Instrument (Scientific Equipments, Roorkee). DCelectrical conductivity (σ) was calculated using followingequations:

ρ = G7(W/S)

ρo(1)

G7

(W

S

)=

(2S

W

)ln 2 (2)

ρo =(

V

I

)2πS (3)

σ = 1

ρ(4)

whereG7(W/S) is a correction divisor which is a functionof thickness of the sample as well as probe-spacing whereI, V, W, andS are current (A), voltage (V), thickness of thefilm (cm) and probe spacing (cm), respectively[20].

The isothermal stability of composite samples in terms ofDC electrical conductivity retention was carried out on theselected composites at 50, 70, and 90◦C in an air oven. Theelectrical conductivity measurements were carried out at in-tervals of 15 min. The thermal stability of the composites interms of DC electrical conductivity retention was also stud-ied by repeatedly measuring four-in-line probe DC electri-cal conductivity on films with increasing temperature from35 to 100◦C. The measurements were repeated in this tem-perature range for five times at intervals of 45 min.

A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49 31

3. Results and discussion

3.1. Preparation of materials

When aniline is oxidized in an acidic (HCl) aqueousmedium with potassium persulphate (K2S2O8), the proto-nated conducting form of polyaniline (PANI:HCl) is pro-duced as given in the following unbalanced redox reaction

Ph–NH3+Cl− + S2O8

2−

→ –[–Ph–NH–Ph–NH•+(Cl−)–]n– + SO42− (5)

Thus-prepared dark green polyaniline was of high molec-ular weight as very little (<0.5%) oligomers could be ex-tracted from it on soxhalation for 24 h. The yield of polymerwas more than 50% after washing and drying.

The color change from dark green to sky blue is asso-ciated with the neutralization of positive charges on pro-tonated polyaniline chains. The process may be treated asn-type doping of a p-type doped polymer in which the poly-mer passes through an insulating state. Schöllhörn and Za-gefka[21] have suggested a redox reaction for ammonia oramine intercalation into layered metal chalcogenides whichhas been further supported by the work of Foot and Shaker[22]. On the basis of the disproportionation reaction of am-monia as suggested by above workers, an analogous reac-tion was suggested by Mohammad[23] for the undoping ofpolythiophene (PTH) by water. The overall chemical reac-

Table 2FTIR peak positions (cm−1) of polyaniline (PANI), cellulose acetate (CA), and polyaniline:celluloseacetate (PANI:CA) composites

PANI CA PANI:CA1-1

PANI:CA1-2

PANI:CA1-3

PANI:CA1-4

PANI:CA1-5

PANI:CA1-6

PANI:CA1-7

PANI:CA1-8

PANI:CA1-9

PANI:CA1-10

PANI:CA2

3259 3750 3436 3438 3436 3438 3436 3438 3438 3438 3438 3436 34363035 3494 2926 2920 2914 2920 2920 2920 2922 2926 2918 2916 29182846 2961 1738 1742 1732 1730 1732 1732 1738 2856 1726 1740 17382354 2926 1630 1726 1634 1644 1634 1634 1728 1746 1666 1728 15881587 2730 1552 1630 1434 1634 1590 1590 1694 1664 1642 1692 15001497 2469 1442 1550 1374 1556 1434 1456 1582 1642 1632 1680 13761377 2359 1384 1442 1318 1446 1372 1374 1556 1632 1584 1666 13081302 2122 1240 1382 1238 1434 1316 1236 1494 1584 1554 1642 12421241 1943 1032 1234 1164 1234 1234 1034 1484 1554 1482 1632 11461143 1723 668 1034 1114 1162 1164 900 1470 1466 1468 1584 10341008 1634 598 670 1034 1116 1114 796 1370 1452 1441 1554 830954 1374 466 600 900 1034 1034 668 1296 1372 1370 1482 696824 906 408 662 796 670 598 1214 1294 1294 1468 600728 838 600 668 602 470 1116 1212 1214 1444 508505 602 560 600 562 1030 1162 1116 1370 424

559 474 492 468 794 1116 1034 1294 412457 412 408 694 1032 796 1228

598 794 694 1038490 698 596 792404 662 494 690

598 406 668478 598450 480

436408

tions are given in following equations:

8NH3 → 6NH4+ + 6e− + N2 (6)

PTH+–BF4− + NH4

+ + e− → PTH+ NH4BF4 (7)

6H2O → 4H3O+ + 4e− + O2 (8)

PTH+–BF4− + H3O+ + e− → PTH+ HBF4 · H2O (9)

HBF4 · H2O → HF + BF3 + H2O (10)

The charge neutralization reaction depends on the rate ofchemical reaction between the polymer and dopant whichin turn will depend upon the reactivity of the polymer chainand the basic strength of dopant[23]. The basic strengthof water is very low, hence it does not act as an effectiveundoping agent in the case of polyaniline, however, ananalogous neutralization reaction for the undoping of thepolyaniline component of the composites by ammonia maybe suggested as under

[PANI(CA)]n+(nCl−) + nNH4+ + ne−

→ PANI(CA) + nNH4Cl (11)

The method of preparation of polyaniline:celluloseace-tate-1 composite films by mixing undoped polyanilinepowder with the cellulose acetate dissolved in acetone issuccessfully demonstrated. A gradual change in film thick-ness from PANI:CA1-1 to PANI:CA1-10 is essentiallydue to the increase in polyaniline content in the compos-

32 A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49

Fig. 1. FTIR spectra of polyaniline:celluloseacetate (PANI:CA) composites: (a) PANI:CA1-1, (b) PANI:CA1-2, (c) PANI:CA1-3, (d) PANI:CA1-4, (e)PANI:CA1-5, (f) PANI:CA1-6, (g) PANI:CA1-7, (h) PANI:CA1-8, (i) PANI:CA1-9, (j) PANI:CA1-10, (k) PANI:CA2, (l) CA, and (m) PANI.

A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49 33

ites. Polyaniline:celluloseacetate-2 composite was preparedsuccessfully by dissolving the cellulose acetate in anilinefollowed by the polymerization of aniline within celluloseacetate matrix in the form of dark black films with almostuniform thickness.

3.2. FTIR studies

The bands around 1146, 1300, 1370, 1490, 1584 cm−1

correspond to polyaniline in the composites. The band cor-responding to out of plane bending vibration of C–H bond

Fig. 2. SEM photographs of (a) polyaniline and (b) cellulose acetate film.

of p-disubstituted benzene ring appears at 824 cm−1. Thebands corresponding to stretching vibrations of N–B–N andN=Q=N structures appear around 1490 and 1584 cm−1,respectively (where –B– and=Q= stand for benzenoid andquinoid moieties in the polyaniline backbone). The band cor-responding to vibration mode of N=Q=N ring and stretchingmode of C–N bond appear at 1146 and 1300 cm−1, respec-tively. The characteristic broad band for O–H group of cel-lulose acetate appears around 3436 cm−1 and a band around2961 cm−1 because of C–H present in CH2OH group hasbeen observed. A broad band around 1034 cm−1 for the

34 A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49

–C–O–C– and the band corresponding to C=O of the acetateappears around 1723 cm−1. In polyaniline:celluloseacetate-1composites, the gradual increase in the intensities in thebands corresponding to polyaniline and decrease in thebands corresponding to cellulose acetate support the gradualchange in the composition of the composite formulations.In polyaniline:celluloseacetate-2 composite, all the charac-teristic peaks of polyaniline and cellulose acetate has beenobserved[24–29]. The FTIR spectra of polyaniline, cel-lulose acetate and polyaniline:celluloseacetate (PANI:CA)

Fig. 3. SEM photograph of polyaniline:celluloseacetate composites: (a) PANI:CA1-1, (b) PANI:CA1-3, (c) PANI:CA1-5, (d) PANI:CA1-7, (e) PANI:CA1-9,and (f) PANI:CA2.

composites are shown inFig. 1 and the peak positions ofthe FTIR spectra are presented inTable 2.

3.3. SEM studies

The percolation threshold in composites is related to thehomogeneousness of the mixing of individual componentsof the composites, hence, the SEM studies were performed.Besides the little difference in the surface morphologies ofthe two composites viz. PANI:CA1 and PANI:CA2, the SEM

A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49 35

Fig. 3. (Continued )

photographs of the composites support the homogeneity ofthe composites and uniformity of film surface as evidentfrom Figs. 2 and 3.

3.4. TGA studies

In case of undoped polyaniline, the initial weight loss of∼4.4% up to 100◦C is due to the removal of moisture presentin the polymer. An extremely small weight loss of∼2.3%up to 275◦C suggests that the polyaniline still contains somevolatile material, most probably the doping agent, HCl, and

that it is thermally stable up to 275◦C under oxidative con-ditions. The onset temperature of thermo-oxidative degra-dation of polyaniline is observed at 275◦C, accompaniedwith a massive weight loss of 93.3% up to∼650◦C leav-ing behind no residue. A strong exothermic peak in DTA at512◦C corresponds to this degradation. In the case of cel-lulose acetate, the small weight loss of 4.8% up to 286◦Cindicates its good thermal stability. The weight loss in thisstep may be attributed to the removal of water and othervolatile constituents present in the polymer. The onset tem-perature of thermo-oxidative degradation is 286◦C associ-

36 A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49

Fig. 3. (Continued ).

ated with a massive weight loss beyond this temperature andthree simultaneous exothermic peaks in DTA. The detailsof the TGA and DTA analysis of undoped polyaniline andcellulose acetate are presented inTable 3andFig. 4.

In case of PANI:CA1 composite, the initial weight loss of2.7–4.1% up to 100◦C may be associated with the loss ofwater. Beyond this temperature, an extremely small weightloss of 1.5–2.3% up to 267–284◦C suggests that the com-posites still contain some volatile material, most probablythe doping agent, HCl, and that the mechanically prepared

composites are thermo-oxidatively as stable as their compo-nents. In the last step, some simultaneous exothermic peaksin DTA appear while the TGA curve indicates a massiveweight loss in two parts. The initial part of the weight lossmay be associated with the thermo-oxidative degradation ofthe composites while the last part may be associated withthe thermo-oxidative degradation exclusively of polyanilineas the weight loss percentage in the last part of the thirdstep gradually increases with the increase in polyanilinecontent in the composites. The extent of∼100% weight

A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49 37

Table 3DTA and TGA studies of polyaniline (PANI) and cellulose acetate (CA)

SampleID

DTA TGA

Peaktemperature(◦C)

Comment Temperaturerange (◦C)

Loss(wt.%)

PANI – – 0–92 4.42– – 92–275 2.25– – 275–475 44.53512 Exo 475–658 48.77

0–62 3.1CA 257 Exo 62–286 1.7

305 Exo 286–381 77.0380 Exo 381–545 17.7525 Exo – –

Endo, endothermic peak; Exo, exothermic peak.

Fig. 4. TGA and DTA of (a) polyaniline and (b) cellulose acetate.

loss up to∼600◦C leaving behind no residue suggests thatthere is no chemical reaction between the components ofthe composite during thermo-oxidative degradation leadingto the formation of thermally stable organics. In the caseof PANI:CA2 composite, three step weight loss similar toPANI:CA1 composite is observed. The initial weight loss of6.5% up to 95◦C is due to the removal of moisture whilea further weight loss of 2.4% up to 250◦C may be asso-ciated with the removal of other volatile substances, mostprobably the doping agent, HCl, trapped within the compos-ite. Like PANI:CA1 and its components, PANI:CA2 is alsofound to be stable up to 250◦C and thermo-oxidative degra-dation starts beyond this temperature in two parts associatedwith three simultaneous DTA peaks[30–33]. The moisturecontent in PANI:CA2 is comparatively more than that inPANI:CA1 while the onset temperature of thermo-oxidativedegradation of PANI:CA2 is lower than that of PANI:CA1by about 17◦C. TGA and DTA data of PANI:CA1 andPANI:CA2 is presented inTable 4and the thermograms aregiven inFig. 5.

38 A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49

Fig. 5. TGA and DTA of polyaniline:celluloseacetate (PANI:CA) composites: (a)PANI:CA1-1, (b) PANI:CA1-3, (c) PANI:CA1-5, (d) PANI:CA1-7, (e)PANI:CA1-9, and (f) PANI:CA2.

3.5. Stability in terms of DC electrical conductivityretention

It was observed that the PANI:CA composites showedan enhanced electrical conductivity on exposure to HCl,due to the involvement of charge-transfer reaction between

polyaniline component of the composites and the dopingagent[34,35].

n[PANI(CA)] + nHCl → n[PANI–H(CA]+(Cl−) (12)

The electrical conductivity of the composite films weremeasured from 35 to 130◦C and found to be in the semi-

A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49 39

Fig. 5. (Continued).

conducting region as presented inTable 5. All the PANI:CAcomposite samples, in principle, follow Arrhenius equationfor temperature dependence of electrical conductivity, as ev-ident fromFig. 6, that supports the semiconducitng natureof the HCl doped composites. No semiconductor to metal

transition is observed in the Arrhenius plots even at highertemperature.

Six composite samples (PANI:CA1-1, PANI:CA1-3,PANI:CA1-5, PANI:CA1-7, PANI:CA1-9, and PANI:CA2)were selected for study the stability in terms of DC electri-

40 A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49

cal conductivity retention under isothermal conditions at 50,70, 90, 110, and 130◦C. The temperature of the compositefilms was maintained at the temperature of study and the DCelectrical conductivity was measured after every 15 min inthe accelerated ageing experiments. The electrical conduc-tivity measured with respect to the time of accelerated age-

Fig. 6. Temperature dependence of DC electrical conductivity of polyaniline:celluloseacetate (PANI:CA) composites: (a) PANI:CA1-1, (b) PANI:CA1-2,(c) PANI:CA1-3, (d) PANI:CA1-4, (e) PANI:CA1-5, (f) PANI:CA1-6, (g) PANI:CA1-7, (h) PANI:CA1-8, (i) PANI:CA1-9, (j) PANI:CA1-10, and (k)PANI:CA2.

ing is presented inTable 6andFig. 7. It has been observedthat the DC electrical conductivity is quite stable at 50, 70,and 90◦C—this supports the fact that the electrical prop-erties of the composites are sufficiently stable below 90◦Cunder thermo-oxidative atmosphere as was also observed inthe TGA studies that doping agent does not volatilizes below

A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49 41

Fig. 6. (Continued )

42 A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49

Fig. 6. (Continued )

A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49 43

Fig. 6. (Continued ).

Table 4DTA and TGA studies of polyaniline:celluloseacetate (PANI:CA) com-posites

Sample ID DTA TGA

Peaktemperature(◦C)

Comment Temperaturerange (◦C)

Loss(wt.%)

PANI:CA1-1 0–88 3.288–284 1.7

389 Exo 284–388 68.8501 Exo 388–562 25.4

PANI:CA1-3 0–86 3.686–278 2.2

389 Exo 278–381 53.6491 Exo 381–584 39.5

PANI:CA1-5 0–82 2.782–271 2.0

383 Exo 271–381 53.3469 Exo 381–589 41.9

Table 4 (Continued )

Sample ID DTA TGA

Peaktemperature(◦C)

Comment Temperaturerange (◦C)

Loss(wt.%)

PANI:CA1-7 0–87 4.187–280 2.3

377 Exo 280–368 45.1464 Exo 368–591 48.0

PANI:CA1-9 0–81 3.481–267 1.5

383 Exo 267–376 49.7462 Exo 376–598 44.8

PANI:CA2 0–95 6.52307 Exo 95–250 2.42325 Exo 250–328 38.88472 Exo 328–571 51.96

Endo, endothermic peak; Exo, exothermic peak.

44A

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al./SyntheticM

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(2004)29–49

Table 5Temperature dependence of DC electrical conductivity (S cm−1) of HCl doped polyaniline:celluloseacetate (PANI:CA) composites

Temperature(◦C)

Sample ID

PANI:CA1-1 ×10−6

PANI:CA1-2 ×10−5

PANI:CA1-3 ×10−5

PANI:CA1-4 ×10−4

PANI:CA1-5 ×10−4

PANI:CA1-6 ×10−4

PANI:CA1-7 ×10−4

PANI:CA1-8 ×10−4

PANI:CA1-9 ×10−4

PANI:CA1-10× 10−4

PANI:A2 ×10−4

35 2.0779 0.5398 3.1844 0.4716 0.4822 0.6841 0.5497 0.5970 0.5898 0.7020 3.702440 2.2475 0.5436 3.3478 0.4916 0.5095 0.7035 0.5872 0.6378 0.6032 0.7387 3.817645 2.4761 0.6146 3.5214 0.5400 0.5502 0.7401 0.6169 0.6701 0.6220 0.7627 4.004350 2.6634 0.6264 3.7395 0.5573 0.5716 0.7829 0.6527 0.7090 0.6419 0.8667 4.186355 2.7173 0.6545 3.9382 0.5790 0.5948 0.8149 0.6865 0.7456 0.6578 0.8946 4.359760 2.8135 0.6799 4.1486 0.5922 0.6168 0.8671 0.7274 0.7901 0.6773 0.9209 4.548165 2.8642 0.6907 4.3247 0.6204 0.6474 0.9011 0.7615 0.8272 0.6948 0.9686 4.723070 2.9768 0.7132 4.4669 0.6473 0.6853 0.9469 0.7777 0.8448 0.7165 0.9741 4.944975 3.1169 0.7929 4.6187 0.6768 0.7189 1.0215 0.8308 0.9024 0.7362 1.0068 5.152480 3.2508 0.8359 4.7953 0.7042 0.7464 1.0577 0.8551 0.9287 0.7602 1.0892 5.339185 3.4199 0.9961 4.9257 0.7392 0.7812 1.0886 0.8808 0.9567 0.8205 1.1448 5.539890 3.4673 1.0882 5.1271 0.7720 0.8138 1.1385 0.9254 1.0052 0.8735 1.2164 5.847595 3.8030 1.1178 5.2764 0.8017 0.8492 1.1697 0.9485 1.0313 0.9338 1.2236 5.9902

100 4.0826 1.1436 5.4347 0.8473 0.8811 1.2857 0.9813 1.0659 0.9827 1.2570 6.1399105 4.1740 1.1763 5.5836 0.8833 0.9084 1.3558 1.0084 1.0953 1.0118 1.3178 6.3516110 4.2054 1.1991 5.7409 0.9142 0.9375 1.3938 1.0444 1.1344 1.0363 1.4854 6.5203115 4.3358 1.2290 5.9288 0.9390 0.9931 1.4204 1.0751 1.1678 1.0620 1.6792 6.6378120 4.4986 1.2603 6.0836 1.0319 1.0371 1.4989 1.1162 1.2123 1.0822 1.7934 6.7596125 4.6610 1.2866 6.2468 1.0635 1.0654 1.6036 1.1698 1.2705 1.1103 1.8406 6.9509130 4.6352 1.2866 6.3938 1.1329 1.0952 1.6852 1.1888 1.2912 1.1249 1.8904 7.0171

A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49 45

Fig. 7. Isothermal stability of (a) PANI:CA1-1, (b) PANI:CA1-3, (c) PANI:CA1-5, (d) PANI:CA1-7, (e) PANI:CA1-9, and (f) PANI:CA2 composites interms of retention of DC electrical conductivity with respect to time at 50, 70, 90, 110, 130◦C.

46 A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49

Fig. 7. (Continued ).

A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49 47

Table 6Stability of DC electrical conductivity of polyaniline:celluloseacetate (PANI:CA) composites (under isothermal conditions)

Temperature(◦C)

Time(min)

DC electrical conductivityσ (S cm−1)

PANI:CA1-10× 10−6

PANI:CA1-3 ×10−5

PANI:CA1-5 ×10−5

PANI:CA1-7 ×10−5

PANI:CA1-9 ×10−5

PANI:CA2 ×10−4

50 0 1.8666 3.1681 3.2717 5.2451 5.9656 4.671015 2.0331 3.2578 3.5780 5.2674 6.3256 4.923430 1.7640 3.6255 3.4611 5.1793 6.4345 3.787345 2.0331 3.7741 3.6730 5.5261 6.6116 3.824460 2.7278 4.0747 4.1090 5.7574 6.8635 3.8244

70 0 1.7685 3.8453 6.2276 5.8945 6.7173 6.817115 1.7359 4.2021 6.4049 6.0383 6.8474 6.015130 2.7652 4.7122 6.4916 6.2835 6.8918 3.620545 2.8720 5.4712 7.3460 6.1584 6.6751 3.762560 3.3804 6.3688 8.1071 6.4137 6.9825 3.69010 2.6711 5.7816 6.8519 7.1968 7.7427 6.8263

90 15 3.1192 6.2468 7.0303 6.4471 8.7105 6.392330 2.3629 6.1525 6.7155 6.0383 8.9131 7.102545 2.4446 5.8648 7.1799 6.2517 8.7105 7.102560 2.3788 6.0386 8.4364 6.8796 9.1253 7.1025

110 0 2.9561 6.1064 8.6527 9.6707 8.2896 6.308115 2.8955 5.8022 7.9636 8.7682 7.4874 6.308130 2.6362 4.9109 6.3150 7.8345 6.1904 3.435745 2.1705 4.0130 5.6419 6.4646 5.6560 2.959960 1.8865 3.6851 5.4719 5.9129 5.2412 2.2445

130 0 3.0128 6.2708 8.9988 10.315 9.0439 6.055815 2.3394 5.3987 7.0303 7.9910 8.4624 4.780930 2.0568 3.7545 5.9793 4.7865 8.0087 3.348745 1.8069 3.2567 4.5227 2.8544 6.1195 2.558960 1.5177 2.0531 3.5090 1.4766 4.0135 1.8707

Table 7Stability of DC electrical conductivity of polyaniline:celluloseacetate(PANI:CA1-9) composite (cyclic technique)

Temperature(◦C)

DC electrical conductivityσ × 10−5 (S cm−1)

Cycle-1 Cycle-2 Cycle-3 Cycle-4 Cycle-5

35 6.5822 5.9357 4.8588 4.0676 3.021840 6.7082 5.9581 5.3108 4.3439 3.203545 6.8059 5.9807 5.7502 4.6201 3.475150 7.1168 6.0962 6.1248 4.9036 3.708955 7.4181 6.2905 6.4982 5.1401 3.966660 7.7460 6.4445 6.8325 5.3643 4.169265 8.0576 6.8056 7.1047 5.5506 4.320470 8.3454 6.9555 7.3329 5.7296 4.465275 8.6544 7.7020 7.5404 5.8771 4.674180 8.8736 8.4888 7.7600 6.0323 4.771885 9.2849 8.7717 8.1145 6.1483 4.995590 9.7363 8.8703 8.2827 6.2444 5.190195 9.8043 9.0742 8.4580 6.3435 5.3643

100 10.014 9.3427 8.6409 6.4458 5.4933105 9.6029 9.8069 8.7833 6.5515 5.6090110 9.5376 9.7464 8.9305 6.6330 5.6888115 9.4731 9.6866 9.0828 6.6885 5.7710120 9.3468 9.6275 9.1872 6.7450 5.8342125 8.9873 9.5115 9.2403 6.8024 5.8771130 8.2472 9.0742 9.2940 6.8608 5.9206

Table 8Stability of DC electrical conductivity of polyaniline:celluloseacetate(PANI:CA2) composite (cyclic technique)

Temperature(◦C)

DC electrical conductivityσ × 10−4 (S cm−1)

Cycle-1 Cycle-2 Cycle-3 Cycle-4 Cycle-5

35 1.9635 2.3709 3.0439 2.1989 2.525540 2.0501 2.4894 3.1829 2.2558 2.600945 2.1514 2.6205 3.3351 2.3709 2.670750 2.2485 2.7994 3.4852 2.4544 2.788255 2.3157 2.9288 3.6495 2.6009 2.880360 2.3628 3.1118 3.8090 2.7122 2.885965 2.4544 3.2725 3.9831 2.8335 3.017570 2.6009 3.4169 4.1491 2.9411 3.162775 2.6809 3.5383 4.3295 3.0572 3.346080 2.8335 3.6687 4.4683 3.1540 3.485285 2.9788 3.7678 4.6162 3.2421 3.551990 3.1118 3.8725 4.7418 3.3512 3.664795 3.2271 3.9605 7.8745 3.4337 3.7849

100 3.3351 4.0292 5.0147 3.5027 3.8479105 3.4169 4.1245 5.1254 3.5746 3.9132110 3.4852 4.1991 5.2410 3.6304 3.9806115 3.5564 4.2764 5.3210 3.6881 3.9915120 3.6116 4.3295 5.4035 3.7275 4.0615125 3.6687 4.3839 5.4886 3.7678 4.0726130 3.7275 4.4398 5.5321 3.8090 4.0726

48 A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49

Fig. 8. Stability of DC electrical conductivity of PANI:CA1-9 composite (cyclic technique).

Fig. 9. Stability of DC electrical conductivity of PANI:CA2 composite (cyclic technique).

∼100◦C. The decrease in electrical conductivity at highertemperatures may be attributed to the loss of dopant.

Two composite samples (PANI:CA1-9 and PANI:CA2)were selected to study the stability in terms of the DCelectrical conductivity retention by cyclic technique. Thecomposite PANI:CA1-9 shows a minor but gradual de-crease of electrical conductivity up to the cycle-5 whichmay be attributed to the volatilization of dopant along withmoisture as evident fromTable 7andFig. 8. While in thecase of PANI:CA2, the DC electrical conductivity graduallyincreases with the cycle number. The increase in the DCelectrical conductivity may be attributed to the removal ofmoisture, annealing and crystallization of the polymer whichcreates a homogeneous doping of the polymer and decreasesthe percolation threshold, as evident fromTable 8 andFig. 9.

4. Conclusions

Chemically prepared conducting polymers are difficult toprocess by solution or melt technique because they are in-tractable and degrade below their melting points. We havesuccessfully prepared the conducting composite in the formof films by using polyaniline, an electrically conductingpolymer within an insulating polymer matrix of celluloseacetate. The insulating polymer used in this study has goodfilm-forming properties along with several other individualmerits.

The electrical properties of the composites were observedto be of good quality as almost all the composites showedan increase in their electrical conductivity from insulator tosemiconductor region after doping with hydrochloric acid.All the composite materials were successfully characterized

A. Al-Ahmed et al. / Synthetic Metals 144 (2004) 29–49 49

for their electrical properties and by using FTIR, SEM, andTGA and it was found that the materials are of good standardand of uniform morphology.

Thermo-oxidative as well as stability in terms of reten-tion of DC electrical conductivity were also observed to befairly good, as studied by several experimental techniquesand most of the formulations of the composites so preparedare found to be suitable for use in electrical and electronicapplications below 100◦C after annealing.

Acknowledgements

One of us (FM) thankfully acknowledges the financialassistance given by the University Grants Commission underUGC Project No. F.12-7/98(SR-I).

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