development and characterization of electrically...

Indian Journal of Chemical Technology

Vol. 19, November 2012, pp. 434-441

Development and characterization of electrically conductive polyaniline

coated fabrics

N Muthukumar1,

* & G Thilagavathi 2

1Department of Fashion Technology, 2Department of Textile Technology, PSG College of Technology, Coimbatore 641 004, India

Received 25 August 2011; accepted 18 January 2012

Electrically conductive cotton, polyester and nylon fabrics have been prepared from conductive polyaniline (PANI)

polymer by in situ chemical oxidative polymerization of aniline using ammonium persulphate as the oxidant by a process of

diffusion polymerization in a mixed bath. These fabrics are then characterized by ATR-FTIR, WAXD, SEM and DSC. The

tensile strength, stiffness and electrical and electromagnetic measurements of the fabric samples are also studied. The

structural studies show that the crystalline region of cotton, polyester and nylon is not affected by the polyaniline and the

interaction of polyaniline with the fabrics. The SEM studies reveal a very uniform deposition of polyaniline on the fabrics.

The thermal studies show that the PANI-treated fabrics have better thermal stability. The intact textile characteristics of the

polyester and nylon fabrics coated with PANI are found to be protected, whereas the characteristics of the cotton fabric

coated with PANI become inferior. The conductivity studies show that the treated fabrics have good electrical conductivity.

The electromagnetic shielding tests show that the cotton, polyester and nylon fabrics have the electromagnetic interference

values of -1.62, -2.78 and -1.5 dB respectively in the frequency range 8-12 GHz.

Keywords: Conductive fabrics, Cotton, EMI shielding, Polymerization, Nylon, Polyaniline, Polyester, Surface resistance

With the advent of electrical and electronic devices

worldwide, electromagnetic interference among the

appliances is one of the major problems to be resolved.

Various researches and industrial companies have

shown keen interest in providing solutions to overcome

this problem. Among the various solutions offered,

textile products have caught the attention of researchers

owing to their versatility and conformability to different

structures. Conductive fabrics based on incorporation of

metals (such as copper, stainless steel and aluminum),

electroplating of metal on the fabric and deposition of

conducting polymers have been widely used for

electromagnetic shielding. The incorporation of metal

wires and electroplating of metal is likely to affect the

pliability of material and moreover corrosion of these

metals in hostile environments is likely to hamper their

shielding properties.

The deposition of conducting polymers such as

polyaniline, polypyrrole, and polythiophene on textile

fabrics is likely to overcome the disadvantages

mentioned above. Among the various classes of

conductive polymers, polyaniline has attracted great

attention as a conducting material due to its ease in

synthesis, low cost and good environmental stability.

Polyaniline can be coated on various substrates like

plastics, glass and ceramic materials and it can also be

coated on the surface of the textile materials by

chemical or electrochemical method. The electrical

conductivity of polyaniline coated fabric is higher

than the other conventional textile fabrics and lower

than the metal coated fabrics1.

Das et al.2

reported the effects of type of material,

yarn count, type of moderant and number of layers of

fabrics on the electromagnetic shielding properties of

textile materials. Dhawan et al.3 reported that the fabrics

coated with PANI has -3 to -11 dB of electromagnetic

shielding efficiency in the frequency range 8-12 GHz. In

their other study, these authors4 determined that the

shielding efficiency values of silica and polyester fabrics

coated with PANI are 35 and 21 dB at 101 GHz

respectively. Sudha and Sivakala5 developed electrically

conducting polystyrene (PS)/polyaniline blends with

electro-magnetic interference shielding efficiency of

1-10 dB and reported the polystyrene (PS)/polyaniline

blends suitable for EMI shielding and anti static

discharge matrix for the encapsulation of micro-

electronic devices.

Neelakandan and Madhusoothanan6

reported in

their study that in any coating process, apart from the

chemical concentrations, the nature of the substrate

and the method of coating have a direct influence on

______________________

*Corresponding author.

E-mail: [email protected]

MUTHUKUMAR & THILAGAVATHI: ELECTRICALLY CONDUCTIVE POLYANILINE COATED FABRICS

435

the polymer deposition. They also showed that the

electrical resistivity of polyaniline coated fabrics is

greatly influenced by the nature of fabric structure

and the amount of yarns in the fabric. The aim of our

work is to study about how the nature of substrate

influences the polymer deposition. Hence, 100%

cotton, polyester, nylon fabrics have been taken

instead of taking blends. In this study, the 100%

cotton, polyester and nylon fabrics are coated with

polyaniline with the chemical oxidative in situ

polymerization method. After the production process,

these fabrics are characterized by ATR-FTIR,

WAXD, SEM, and DSC. Moreover, the tensile

strength, stiffness, the electrical resistivity, and EMI

shielding efficiency measurements of the fabric

samples are also carried out.

Experimental Procedure

Materials

Aniline, concentrated HCl, and ammonium

persulfate (APS), all of A R grade and obtained from

S.D. Fine Chemicals Ltd., India, were used. Aniline

was distilled twice before use. 100% cotton plain

woven fabrics (GSM 93), polyester fabric (GSM 86)

and nylon fabric (GSM 50) were used.

Synthesis of conductive fabrics

Conductive fabrics were developed by in situ

chemical polymerization of aniline on the fabrics. In

this process, freshly distilled 0.5 M aniline was

dissolved in the bath containing 0.35 N HCL solution

for diffusion. A vigorous stirring was given to the

bath containing mixtures of aniline and aqueous acid

to attain the homogeneous mixing. Dry pre-weighed

fabric sample was placed in the above solution at

40°C and allowed for 2 h to soak well with the

monomer and dopant solution. 0.25 M ammonium per

sulfate was separately dissolved in 0.35 N HCL

solution for polymerization. The aqueous oxidizing

agent in the separate bath was then slowly added in to

the diffusion bath to initiate the polymerization

reaction. The oxidant to aniline ratio was kept at

around 1.25. The whole polymerization reaction was

carried out at 5°C for 1hour. After completing the

polymerization process, the coated fabric was taken

out and washed in distilled water containing 0.35 N

HCL and dried at 60°C (refs 1, 6 – 11).

Characterization

The infrared absorption spectra of the control and

polyaniline treated samples were recorded in

the range 400-4000 cm-1

using a Shimadzu FTIR

spectrophotometer at a resolution of 2 cm-1

with

background correction for 350 scans in the ATR

mode. The XRD patterns were recorded by Shimadzu

XRD- 6000 X-ray diffractometer unit. The SEM

images were recorded by JEOL SEM (model JSM-

6360) to study the surface morphology of the control

and polyaniline treated samples in the longitudinal

view. The thermal studies of the control and

polyaniline coated fabrics were made with a Perkin

Elmer differential scanning calorimeter (Model DSC 7).

The tensile properties (in warp direction) of the fabric

samples were determined with an Instron (USA) 4411

tester according to ASTM D 5035-90 (strap test). The

fabric bending properties (in warp direction) of the

fabric samples were determined with Shirley stiffness

tester according to BS 3356:1990.

Electrical resistance measurements

Electrical resistance measurements were performed

on all samples after conditioning the samples in a

standard atmosphere. The resistance was measured

ten times on each side of the sample and the average

values were taken. The American Association of

Textile Chemists and Colourists (AATCC) test

method 76-1995 was used to measure the resistance

of the samples and the surface resistivity of the fabric

was calculated as follows:

R = Rs (l / w)

where R is the resistance in ohms; Rs, the sheet

resistance or surface resistivity in ohms/square; l, the

distance between the electrodes; and w, the width of

each electrode1,12

. Measurement of electromagnetic shielding efficiency

EMI shielding efficiency of polyaniline treated

cotton, polyester and nylon fabrics was measured as

per ASTM D4935 standards using Agilent E5061 A/E

5062A ENA series of RF net work analyzer2,13

. The

instrument consists of a signal generator and a signal

receiver to measure various properties associated with

the device under test. The instrument is able to

measure both the near field and far field shielding

effectiveness of all planer materials (mainly textile

fabrics). EMI SE was studied with electromagnetic

waves having frequency in the range 8-12 GHz.

Results and Discussion

FTIR analysis

Figure 1 shows the ATR-FTIR spectra of the

control cotton and cotton + PANI fabric. The bands at

INDIAN J. CHEM. TECHNOL., NOVEMBER 2012

436

1579 and 1271 cm-1

in the PANI coated cotton fabric

are attributed to the C=N stretching modes of quinoid

rings and C-N stretching modes of benezenoid rings.

The N=Q=N stretching of the quinonoid units of

PANI due to electron delocalization of PANI are

observed in the coated fabric as peak at 1146 cm-1

.

The peak at 2928 cm-1

in the bare fabric is due to the

CH2 anti symmetric stretching vibrations of secondary

CH2OH groups in the glucose units of cellulose. The

peak is removed in spectra of the PANI coated fabric

because of the interaction of PANI with CH2OH

groups in the glucose units of cellulose8-10

. Hence, it is

deduced that PANI is attached to cellulose by

hydrogen bridges over OH of CH2OH.

Figure 2 shows ATR-FTIR spectra of control

polyester and polyester + PANI fabric. The band at

3437 cm-1

in the PANI coated fabric is attributed to

OH stretching. The bands at 1813, 1732 and 1705 cm-1

are attributed to C=O stretching (carboxyl group). The

bands at 1464, 1504 and 1576 cm-1

are attributed to

benzene ring, CH out of plane vibrations; this

observation is in line with earlier data1,10,15,16

. Hence,

it is inferred that PANI is attached to polyester fabric.

Figure 3 shows ATR-FTIR spectra of control nylon

and nylon + PANI fabric. In the spectra of PANI

coated nylon fabric, the intense absorption bands at

1552 and 1508 cm-1

correspond to the plane stretching

vibrations of the C=C bonds in quinine diimine

fragments of PANI. The intense bands at 1170 cm-1

can be assigned to the stretching and symmetric

bending vibrations of the CN bonds in the aromatic

amines, whose structure can be presented as B-N=Q,

where Q and B stand for quinoid and benzene rings.

The above spectral changes indicate the formation of

hydrogen bonds between PANI and nylon. This

spectral evidence suggests that polymerization leads

to the formation of the emaraldine form of

polyaniline15,17

.

WAXD analysis

The XRD patterns for the control cotton and the

cotton + PANI fabrics are shown in Fig 4. The X-ray

diffraction pattern of control cotton shows maxima at

2θ values of 14.9 and 22.77. The peak maxima of

cotton + PANI composite fabrics are found to be

located at 2θ =15.3 and 22.97, and the values are

slightly shifted towards higher side. From this, we can

conclude that the PANI molecules were diffused into

cotton fabric. In the cotton + PANI composite fabrics

the peak at 22.97 has a hump like shape probably due

Fig. 1 FTIR pattern of cotton (a) and polyaniline treated cotton (b)

Fig. 2 FTIR pattern of polyester control (a), and polyaniline

treated polyester (b)

Fig. 3 FTIR pattern of nylon control (a), and polyaniline

treated nylon (b)


437

to the presence of the PANI. Further, additional peaks

appear at 37.79 and 44.02, corresponding to pure

PANI crystals as reported earlier8,9

. This reveals the

presence of PANI in the cotton fabric.

The XRD patterns for the control polyester and the

polyester + PANI fabrics are shown in Fig. 5. The

X-ray diffraction pattern of the control polyester fabric

shows maxima at 2θ values of 17.5,23 and 25.7. The

peak maxima of PANI + polyester fabrics are found to

be located at 2θ =17.32, 22.6 and 25.7. The 2θ values

in PANI + polyester fabric are slightly decreased. It

indicates the reaction of polyaniline on polyester fabric.

The XRD patterns for the control nylon and the

nylon + PANI fabrics are shown in Fig. 6. The X-ray

diffraction pattern of control nylon fabric shows maxima

at 2θ values of 20.4 and 23.7, which are reasonably

close to the values assigned by previous researchers7 for

the α1 and α2 peaks respectively. Peak maxima of PANI

+ nylon composite fabrics are located at 2θ = 20.5 and

24.2. The α2 values are slightly shifted towards higher

side. It is supposed that ordered hydrogen bonding are

formed between polyaniline and nylon7.

SEM studies

The surface views of SEM micrographs of the control

cotton and cotton + PANI, control polyester and polyester

+ PANI and control nylon and nylon + PANI are shown

in Fig. 7. Just a glance at the fabrics with the naked eye

shows a uniform color (in this case, green), indicating that

PANI has penetrated into the fabrics. However, the SEM

studies reveal how evenly the surface has been coated as

well as the depth of penetration.

From these SEM studies, it is clear that the PANI

particles are very evenly deposited on the fabric, and are

seen as small globules. The surface studies clearly reveal

uniform distribution even at the microscopic level,

which is necessary for the reproducibility and reliability

of applications. The diffusion and polymerization of

aniline in the fabric is evident at the macroscopic level in

terms of the increased thickness of the fabric, as shown

in Table 1. The fibres are swelled due to polyaniline

impregnation. Because of this swelling of fibres, the

thickness of PANI coated fabrics increases8,17

.

Fig. 4 XRD pattern of cotton control and polyaniline

treated cotton

Table 1 Fabric thickness

Material Thickness, mm

Control PANI treated

Cotton 0.30 0.31

Polyester 0.19 0.20

Nylon 0.09 0.10

Fig. 5 XRD pattern of polyester control and polyester

treated polyester

Fig. 6 XRD pattern of nylon control and polyaniline

treated nylon


438

Thermal studies

The thermograms of the cotton control and

polyaniline treated fabrics are shown in Fig. 8.

Thermograms show that there is a lot of moisture

present in the control cotton, where the fabric treated

with PANI shows a much suppressed peak due to

moisture at a lower temperature (78°C). This is

because the PANI molecules occupy about 50% of the

region available for moisture absorption, leaving little

space for actual moisture to be absorbed. The

thermogram of the composite fabrics shows more

stability in the heat uptake, and is steadier up to

210°C, whereas the control cotton fabric sample loses

its stability from 150°C onwards8,9

. This suggests that

the composite fabric samples are more thermally

stable after the incorporation of PANI.

The thermograms of the control and polyaniline

treated polyester and nylon fabrics are shown in

Fig. 7 SEM image of control and polyaniline coated fabrics: (a) Control cotton; (b) Polyaniline coated cotton; (c) Control polyester;

(d) Polyaniline coated polyester; (e) Control nylon and (f) Polyaniline coated nylon


439

Figs 9 and 10. The thermal properties of both the control

and polyaniline treated polyester and nylon fabrics are

analyzed and compared (Table 2). The heat of fusion

and degree of crystallinity of PANI + nylon fabric are

slightly reduced as compared to that of the control

nylon. The melting point of PANI + nylon fabric also

tends to be at a slightly lower temperature. But the

changes in thermal properties are very minor. The

overall results indicate that the crystal structures of

nylon in the PANI + nylon composite fabrics are not

greatly affected by the presence of polyaniline7,10

.

The heat of fusion and degree of crystallinity of

PANI + polyester fabric are slightly at higher

temperature. The overall results indicate that the

crystal structures of polyester in the PANI + polyester

fabrics are improved by the presence of polyaniline.

Tensile properties

The tensile strength and elongation values of control

and PANI coated cotton, polyester and nylon fabrics are

shown in Table 3. After coating with PANI, the tensile

strength and elongation values of cotton fabrics decrease

from 18.46 kgf to 10.83 kgf and from 11.53 mm to

8.76 mm respectively. This significant decrease in the

tensile strength of PANI coated cotton fabric samples is

resulted from very low pH values of the process

(pH 0.15). Because cotton is very sensitive to the dilute

mineral acids such as hydrochloric acid and is degraded

by acid with the hydrolysis of glycosidic linkages, hydro

celluloses cause the losses in weight and tensile strength

in the cotton8,9

. In case of polyester fabrics, the tensile

strength decreases due to PANI coating but the changes in

tensile strength of polyester fabric due to PANI coating is

not significant. The tensile strength of nylon fabric

increases due to PANI coating.

Fig. 9 DSC thermogram of polyester control (a), and polyaniline

treated polyester (b)

Fig. 10 DSC thermogram of nylon control (a), and polyaniline

treated nylon (b)

Table 2 Thermal properties of PANI treated and untreated

fabrics

Material Melt on set

temperature

Melt peak

temperature

Enthalpy

J/g

Per cent

crystallinity

°C °C

Polyester

(control)

253.74 258.91 51.87 17.70

Polyester

(treated)

251.89 259.64 55.81 19.05

Nylon

(control)

217.10 222.33 80.16 27.36

Nylon

(treated)

213.87 221.79 79.60 27.16

Fig. 8 DSC thermogram of cotton control (a), and polyaniline

treated cotton (b)


440

Bending properties

The results of bending property testing are shown

in Table 3. In general, the treatment has surprisingly

little effect on the fabric bending length. For the

synthetic fabrics (polyester and nylon) there is a

general increase in bending length due to PANI

coating. For cotton, PANI treated fabric has lower

bending length (or stiffer) than control fabric. In

PANI treated cotton fabrics, the polymer accumulates

in fibre interstices, or if the polymer coating is thick

enough it causes fibres to make contact with each

other over a longer length (or even become ‘glued’

together). Because of this, fibres are less able to

behave independently of each other during bending

and other deformation, and the cotton fabric becomes

stiffer and less extensible18

.

Electrical properties

Surface resistivity is a material property that is

normally considered constant and ideally independent

of measurement technique. Surface resistivity

measurement is often used to characterize fabric

resistivity and is typically reported as ohm/square12

.

We studied the electrical resistivity of the polyaniline

coated fabrics by two probe resistivity measurement

in a normal environment at 65% RH. The surface

resistivity values of the fabrics coated with

polyaniline are shown in Table 4. Lekpittaya et al.19

developed electrically conductive polyester and cotton

fabrics using conductive polymers (polypyrole,

polyaniline and polythiophene) by admicellar

polymerization. They reported in their study that the

conductive polymers can coat polyester fibre better

than cotton. Our results are in good agreement with

Lekpittaya et al.19

and the polyaniline can coat

polyester and nylon fabrics than cotton fabric because

the surface resistivity values of polyaniline coated

polyester and nylon fabrics are lower than that of

polyaniline coated cotton.

In order to determine the influence of the

temperature on surface resistivity of the PANI coated

fabrics, we measured the resistance of PANI coated

fabrics at different temperatures and the results are

shown in Fig. 11. The important point noted is that in

all the PANI coated fabrics, the conduction

mechanism of the composite is similar to that of

virgin conducting polymer. The surface resistivity

increases with increasing temperature up to 70°C,

above which the resistivity steadily decreases with

temperature. Hence, this behavior might be

characteristic of PANI and is probably due to the

increased chain mobilities8,10

. This leads to a greater

number of charge carriers in the conduction band at

higher temperatures and hence shows the semi-

conductor like behavior at such temperatures.

Electromagnetic properties

EMI shielding efficiency of polyaniline treated

cotton, polyester and nylon fabrics is measured as per

ASTM D4935 standards using Agilent E5061 A/E

5062A ENA series of RF net work analyzer. EMI

shielding efficiency is studied with electromagnetic

waves having frequency in the range 8-12 GHz as per

procedure reported earlier 2,13,20

. The tests are carried

Table 3 Physical properties of PANI treated fabrics

Property Cotton Polyester Nylon

Control Treated Control Treated Control Treated

Tensile strength, kgf 18.46 10.83 46.80 46.56 33.03 38.60

Elongation, mm 11.53 8.76 65.27 57.23 36.93 35.25

Bending length, cm 1.90 1.70 1.57 1.63 1.90 1.95

Table 4 Surface resistivity of control and PANI treated fabrics

Material Surface resistivity, ohm/square

Control PANI treated

Cotton 1 × 109 7 × 103

Polyester 1 × 1012 5 × 103

Nylon 1 × 1012 5 × 103

Fig. 11 Surface resistivity versus temperature of PANI

coated fabrics


441

out to measure the electromagnetic shielding

effectiveness in terms of S11 (reflected/incident) and

S21 (transmitted/incident) values. The actual

shielding effectiveness is the only transmitted/incident

values (primarily S21 values). Table 5 shows both

S11 and S21 parameters.

In general EMI shielding efficiency increases with

decrease in the surface resistivity. In this study, the

surface resistivity of polyester and nylon fabrics is

same but nylon fabric has lower EMI shielding

efficiency compared to polyester fabric. This is due to

the lower GSM of nylon fabric compared to polyester

and is explained by the following equation:

A=1.314×t Y Yµ Gf

where A is the absorption loss in dB; t, the

thickness of shield in mm; f, the frequency in MHz;

and µγ & Gγ, the constants specific to a particular

material.

According to the above equation the shielding due

to any material is directly proportional to the

thickness of the material apart from the other

parameters that are related2. Our observations are in

good agreement with Sudha et al.5

result and the

developed polyaniline coated cotton, polyester and

nylon fabrics can be used for EMI shielding and anti

static discharge matrix for the encapsulation of the

microelectronic devices.

Conclusion

It is inferred that the crystalline region of cotton,

polyester and nylon is not affected due to PANI coating

and the fabrics interact with the polyaniline. SEM

studies reveal a very uniform and dense deposition of

the polyaniline on the fabrics. The thermal studies

show that the PANI impregnated fabrics have better

thermal stability. Moreover, tensile strength property of

cotton fabric significantly decreases after PANI

coating, whereas tensile strength of PANI coated

polyester and nylon fabrics are not changed. There is

no significant change in stiffness of polyester and

nylon fabrics due to PANI coating, whereas the

stiffness PANI coated cotton fabric increases.

The conductivity studies clearly show that the

conduction mechanism of PANI coated fabrics is

same as that of the polyaniline polymer. The EMI

shielding effectiveness tests show that the cotton,

polyester and nylon fabrics have the electromagnetic

interference values of -1.62, -2.78 and -1.5 dB

respectively in the frequency range 8-12 GHz, and

EMI shielding due to any material is directly

proportional to the thickness of the material apart

from the other parameters that are related.

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Table 5 EMI shielding effectiveness of PANI treated fabrics

in frequency range of 8-12 GHZ

Material S11 (dB) S21 (dB)

Cotton -18.392 -1.6185

Polyester -9.020 -2.7799

Nylon -21.198 -1.5001

development and characterization of electrically...

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