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)
MUTHUKUMAR & THILAGAVATHI: ELECTRICALLY CONDUCTIVE POLYANILINE COATED FABRICS
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
INDIAN J. CHEM. TECHNOL., NOVEMBER 2012
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
MUTHUKUMAR & THILAGAVATHI: ELECTRICALLY CONDUCTIVE POLYANILINE COATED FABRICS
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)
INDIAN J. CHEM. TECHNOL., NOVEMBER 2012
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
MUTHUKUMAR & THILAGAVATHI: ELECTRICALLY CONDUCTIVE POLYANILINE 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