1. ORIGINAL PAPER
Effect of silver coating on electrical properties of sisal
fibre-epoxy composites
Manindra Trihotri • Deepak Jain • U. K. Dwivedi •
Fozia Haque Khan • M. M. Malik • M. S. Qureshi
Received: 6 March 2013 / Revised: 6 June 2013 / Accepted: 19 August 2013
Ó Springer-Verlag Berlin Heidelberg 2013
Abstract In this paper, the effect of silver coating and size of fibre on electrical
properties of sisal fibre-reinforced epoxy composites has been reported. For this
purpose, epoxy composites reinforced with silver-coated sisal (of 5 and 10 mm
length) prepared by hand moulding and samples were characterized for their elec-
trical properties, such as dielectric constant (e0
), dielectric dissipation factor (tan d)
and AC conductivity (rac), at different temperatures and frequencies. It was
observed that dielectric constant increases with increase in temperature and
decreases with increase in frequency from 500 Hz to 5 kHz. The peak height at the
transition temperature decreases with increasing frequency. Interestingly, sample
having silver-coated fibre of 5 mm length exhibited higher value of dielectric
constant as compared to the sample having 10 mm of fibre length, which is
attributed to the increased surface area of coated fibre. This behaviour of the
material can be explained in terms of interfacial polarization. At a constant volume
of fibres and at a length of 5 mm, the number of interfaces per unit volume element
is high and this results in high interfacial polarization. The number of interfaces
decreases as the fibre length increases and therefore the value of e0
decreases at
10 mm fibre length. To study the changes in structure of samples, Fourier transform
infrared spectrometry and scanning electron microscopy of the samples were carried
out.
M. Trihotri (&) Á F. H. Khan Á M. M. Malik Á M. S. Qureshi
Department of Physics, Maulana Azad National Institute of Technology, Bhopal 462051, MP, India
e-mail: manindratrihotri@yahoo.com
D. Jain
Department of Research and Development, Permali Wallace Pvt. Ltd., Bhopal 462023, MP, India
U. K. Dwivedi
Department of Physics, Amity University, Jaipur 302006, Rajasthan, India
123
Polym. Bull.
DOI 10.1007/s00289-013-1036-7

2. Keywords Electrical properties Á Interfacial polarization Á Interface Á
Fibre-epoxy composite
Introduction
Study of the properties and applications of fibre-reinforced polymer composite
materials is a very fast growing area of research nowadays. With natural fibres, the
interest arises due to high performance in electrical properties, mechanical
properties, low cost and significant processing advantages of the composite material
[1–5]. The reason is, natural fibres are cheaper, renewable, environment friendly,
light in weight and possess no health hazards, which makes them smart materials
with versatile applications in different areas like aerospace, automobile, electro-
magnetic shielding etc. In recent years, natural fibre-reinforced polymer composites
have attracted more and more research interests. As a result, natural fibres are
considered as replacements in place of glass or carbon fibres [6].
Compared to other lignocellulosic fibres sisal is of particular interest because its
composites have high impact strength with moderate tensile and flexural
properties. Figure 1 shows the chemical structure of sisal fibre. The electrical
properties such as dielectric constant (e0
), dielectric dissipation factor (tan d), AC
conductivity (rac) of sisal fibre-reinforced polymer composites have also been
studied by several researchers. The electrical properties of the composites have
been analysed with special reference to the effect of fibre length, fibre
concentration and fibre treatment. Properties of natural fibre-reinforced polymer
composites like fibre length, dispersion; fibre loading and fibre to matrix adhesion
are, changed by many factors [1, 7–13]. The study of dielectric constant and
dielectric loss as a function of temperature and frequency, is one of the most
convenient and sensitive methods of studying polymeric structure. The electrical
Fig. 1 Chemical structure of sisal
Polym. Bull.
123

3. properties of sisal fibre-reinforced composites showed that the composite has
electric anisotropic behaviour [14]. The electrical properties of sisal fibre-
reinforced, low-density polyethylene composite have been compared with those of
carbon black and glass fibre filled low-density polyethylene composites. Paul et al.
in their study considered the effect of frequency, fibre content and fibre length on
various electrical properties [15]. They have also noted that dielectric constant
decreased with increase of fibre length and frequency. The composite with 1 mm
fibres and 30 % fibre content had the highest value of dielectric constant at all
frequencies. Paul et al. did the investigation on the effect of surface treatment on
electrical properties of low-density polyethylene composite reinforced with short
sisal fibres. The dielectric strength of composite materials is found to decrease
with decrease in hydrophilicity of the composite, when the samples are treated
with alkali, steric acid, peroxide, acetylation and permanganate [10]. Li et al. [7]
observed in their study that sisal/low-density polyethylene composites containing
5 % carbon black could be used in antistatic applications to dissipate static charge.
The studies on dewaxed sisal fibre-reinforced epoxy composite (DSFREC) and raw
sisal fibre-reinforced epoxy composite (RSFREC) indicate that there exists a good
correlation between dielectric behaviour and mechanical properties of epoxy
reinforced by sisal fibre. Beside this, both electrical and mechanical properties of
the composites have been correlated with the structural parameters of the
reinforced fibre [16]. Frequency and temperature dependence of dielectric constant
(e0
), dielectric loss (tan d), AC conductivity (rac) and complex impedance
spectroscopy studies on cured polyester matrix and sisal fibre-reinforced polyester
composites (SFRPC) have been investigated in the frequency range from 180 Hz
to 1 MHz and temperature range from room temperature to 200 °C. The
experimental results showed that with the incorporation of sisal fibre, the values
of e0
, tan d and rac are found to increase. It is also found that the values of e0
and
tan d for both cured polyester matrix and SFRPC are decreased with increasing
frequency, which indicate that the major contribution to the polarization may come
from interfacial polarization and orientation polarization [17]. There has been a
growing interest in utilizing natural fibres in polymer composite for making low
cost construction materials, in recent years. Natural fibres are prospective
reinforcing materials and their use, until now, has been more traditional than
technical. They have long served many useful purposes but the application of the
material technology for the utilization of natural fibres as reinforcement in polymer
matrix took place in comparatively recent years [2].
Researchers investigated the electrical properties of sisal fibre-reinforced epoxy
composite, but they never studied the effect of the silver-coated sisal fibre-
reinforced epoxy composite with different lengths and at different parameters. The
aim of this work is to analyse the electrical properties of silver-coated sisal epoxy
composites at different temperatures and frequencies. In this study, the length of the
silver-coated sisal fibre was 5 and 10 mm. The effect of length of the sisal fibre and
temperature on the dielectric constant (e0
), dielectric dissipation factor (tan d) and
AC conductivity (rac) has been studied and reported here.
Polym. Bull.
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4. Experimental
Materials
The thermosetting matrix used in this study was unmodified epoxy resin provided
by Atul Pvt. Ltd. Valsad India cured at room temperature. Figure 2a and b shows
the structure of unmodified epoxy pre-polymer resin and structure of a hardener.
The density of the resin, cured at room temperature was 1.15 g/cm3
. The sisal fibres
used in the present study were collected from Bilaspur, India. Density of the sisal
fibre was 1.45 g/cm3
. Fibre diameter used in this study was 100–200 mm.
Composite preparation
Composite is prepared using a resin/hardener ratio of 10:1. Sisal fibres were first
coated with silver conducting paint and the coated fibres were dried at 80 °C for 2 h
in an air-circulating oven. In the coated fibres, weight fractions in the composites
were kept in the ratio of 10:90. The pressure applied was 1 MPa. Table 1 lists the
density and types of composites prepared.
Preparation of test sample
Sample sheets having two different lengths of randomly oriented sisal fibre with
epoxy were prepared. Test samples were cut from the sheets in the form of circular
Fig. 2 a Structure of unmodified epoxy pre-polymer resin. b Structure of a hardener
Table 1 Types of composites
S. no. Samples Density
(g/cm3
)
1 Pure epoxy resin (EP-00) 1.15
2 Epoxy composites filled with silver-coated
sisal of length 5 mm (EP-05)
1.22
3 Epoxy composites filled with silver-coated
sisal of length 10 mm (EP-10)
1.30
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5. discs of 1 mm thickness and 10 mm diameter. Uniformity of surface was obtained
by polishing the sample. Both sides of the sample were coated using air-drying
conducting paint such that both the surfaces should not connect electrically with
each other. The test samples were then heated at 60 °C for 10 min, to remove the
solvent of the silver conducting paste, and then kept in between the electrodes of the
sample holder, for various measurements.
Characterization
Fourier transform infrared spectroscopy (FTIR) analysis
FTIR analysis of the sample was carried out using Bruker ALPHA FT-IR
Spectrometer.
Scanning electron microscope (SEM) analysis
SEM images of the prepared samples were taken by JSM 6390A (JEOL Japan) at
different magnifications. The prepared samples were coated with gold in a vacuum
coating unit prior to the examination. Images of the samples were taken along the
two surfaces, fractured surfaces of the samples and plane polished surfaces of the
sample pellets.
Electrical measurements
The dielectric properties of materials play a key role on the practical performances
of integrated circuits. A basic understanding of dielectric properties is therefore
needed for engineers and scientists working in semiconductor industries. One
important property of dielectric materials is the dielectric constant (permittivity).
Dielectric constant (e0
) is a measure of the ability of a material to be polarized by an
electric field, and is closely related to the capacitance (C) i.e. the ability to store
electric charge.
Capacitance (C) and tan d values were measured using a Wayne Kerr 6500B
Impedance Analyzer in the temperature range from 35 to 180 °C at different
frequencies (0.5–5 kHz) keeping the heating rate constant at 2 °C/min. Dielectric
constant (e0
) of the composite has been calculated using the following relation
e0
¼
C
Co
ð1Þ
where C and CO are the capacitance with and without dielectric, respectively; CO in
pF is given by
Co ¼
ð0:08854ÞA
d
pF
where A (cm2
) is the area of the electrodes and d (cm) the thickness of the sample.
Dielectric dissipation factor (tan d) is defined as follows
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6. tan d ¼
e00
e0
ð2Þ
where e00
is the dielectric loss.
In dielectric analysis, the sample is placed between two parallel electrodes. By
applying a sinusoidal voltage, an alternating electric field is created, due to which
polarization is produced in the sample, which oscillates at the same frequency as the
electric field, but has a phase angle shift. The phase angle shift is measured by
comparing the applied voltage, with the measured current, which is separated into
capacitive and conductive components [18]. Measurements of capacitance and
conductance are used to calculate, (1) real part of permittivity (apparent
permittivity) e0
, which is proportional to the capacitance and measures the
alignment of dipoles, (2) dielectric dissipation factor, tan d = e00
/e0
and (3) AC
conductivity (rac) calculated from the relation
rac ¼ e0xe0
tan d ð3Þ
where e0 is the permittivity of free space, tan d the dielectric dissipation factor and
x the angular frequency of the applied electric field.
At lower and intermediate frequencies e0
and tan d values in sisal fibre-reinforced
composites are due to the contributions of orientation, space charge and interfacial
polarization. Contribution of orientation polarization decreases at high frequency
because molecules do not have time for orientation which is indicated by the
decrease in e0
and tan d of composites with frequency.
Results and discussions
Generally, the dielectric constant of a composite material depends on polarization of
molecules and the dielectric constant increases with increase in polarizability. The
different types of polarizations possible in a composite material are (a) Electronic
polarization (b) Atomic polarization and (c) Orientation polarization due to the
orientation of dipoles parallel to the applied field [18].
The prepared samples contain pure epoxy with sisal fibres embedded in it. Epoxy
is also known as polyepoxide. Epoxy is a copolymer; that is, it is formed from two
different chemicals. These are referred to as the ‘‘resin’’ or ‘‘compound’’ and the
‘‘hardener’’ or ‘‘activator’’. The resin consists of monomers or short chain polymers
with an epoxide group at either end. The hardener consists of polyamine monomers.
When these compounds are mixed, the amine groups react with the epoxide groups
to form a covalent bond. Each NH group can react with an epoxide group from
distinct pre-polymer molecules, so that the resulting polymer is heavily cross-
linked, and is thus rigid and strong.
Sisal fibre is obtained from the leaves of the plant Agave Sislana. The chemical
constituents of the sisal fibre are cellulose 66–72 %, lignin 10–14 %, hemicellulose
12 % and moisture 10 %. The FTIR spectra of the three samples are shown in Fig. 3a
pure epoxy (EP-00), Fig. 3b 5 mm sisal epoxy composite (EP-05) and Fig. 3c 10 mm
sisal epoxy composite (EP-10). It shows the peaks at 3,628, 3,224 cm-1
in EP-00,
Polym. Bull.
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7. Fig. 3 a FTIR spectra of pure epoxy (EP-00). b FTIR spectra of 5 mm length silver-coated sisal epoxy
composite (EP-05). c FTIR spectra of 10 mm length silver-coated sisal epoxy composite (EP-10)
Polym. Bull.
123

8. 3,683, 3,261 cm-1
in EP-05 and 3,639, 3,210 cm-1
in EP-10 correspond to
characteristic OH stretching vibration of the water, and alcohol group in epoxy which
form the polymer base in case of all the three samples. Peaks at 3,318 cm-1
in EP-00,
3,330 cm-1
in EP-05 and 3,306 cm-1
in EP-10 correspond to the NH stretching of
primary amine. The peaks at 1,699 cm-1
in EP-00, 1,648 cm-1
in EP-05 and at
1,643 cm-1
in EP-10 can be attributed to stretching of carbonyl group of lignin and the
peaks at 1,457 cm-1
in EP-00, 1,459 cm-1
in EP-05 and at 1,437 cm-1
in EP-10
corresponds to aromatic ring skeletal vibrations. There are peaks at 1,026 cm-1
in EP-
00, 1,024 cm-1
in EP-05 and 996 cm-1
in EP-10, which are from the stretching of
methyl groups and vibrations of the benzene structure. Stretching of C–O–C of oxirane
group is seen at peak 822 cm-1
in EP-00, 822 cm-1
in EP-05 and 818 cm-1
in EP-10.
Stretching bands in the region of 1,024–1,232 cm-1
, in all the three samples, belong to
C–O–C functionalgroup.Thebands observedaround 2,366 cm-1
in EP-10,2,365 cm-1
in EP-05 and 2,340 cm-1
in EP-00 are might be due to the presence of double CO2 band.
The peaks at 1,510, 1,511 and 1,541 cm-1
in all the three samples EP-00, EP-05 and EP-
10 ,respectively, shows the N–H deformation of primary amine and denotes the presence
of primary amine due to hardener used in pure epoxy. All these findings in the FTIR
spectra lead to the conclusion of the use of pure epoxy in the samples.
Fig. 4 a, b Fractured surface of EP-00
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9. A Peak at 2,860 and 2,860 cm-1
that is present in the EP-05 and EP-10
respectively corresponds to CH stretching in cellulose and hemicelluloses of sisal
fibres. Peaks observed in the frequency range of 540–657 cm-1
correspond to C–C
bond due to aromatic rings in sisal fibre, which are again not present in the case of
sample EP-00 pure epoxy. This confirms the presence of sisal fibres in case of EP-05
and EP-10 and absence of these peaks confirms absence of sisal fibres in EP-00.
Figures 4, 5 and 6 show the SEM micrographs of pure epoxy and silver-coated
sisal epoxy composites. Fractured surface of EP-00 sample can be seen in Fig. 4a, b.
SEM micrographs shown in Figs. 5a–d and 6a–c for Sisal epoxy sample exhibit the
gap between sisal fibre and epoxy matrix interface due to silver coating which
shows the hydrophobic nature of coated sisal fibre surface. Fibre is not completely
debonded but is in poor contact with the matrix. Silver-coated sisal fibre surface
could not adhere well with epoxy matrix, hence interfacial bonding is poor.
The conductivity of fibre-reinforced composites depends on many factors such as
the moisture content, crystalline and amorphous component present, chemical
composition, cellular structure etc. Fibres having elongated shapes affect the
electrical conductivity due to the contact surface area. The moisture content present
in the fibre results in the increase of the conductivity of composite. The hydrophilic
property of cellulose fibre is the main cause for greater conductivity of the
composite. An increase in the conductivity of the resin is due to the hydroxyl groups
in the hydrophilic fibre, which can absorb moisture. The dielectric constant of
polymeric materials depends on the contribution of interfacial, dipole, electronic
and atomic polarizations. The interfacial polarization can explain the behaviour at
low frequencies. This type of polarization is present due to the heterogeneity present
Fig. 5 a–d SEM micrographs of silver-coated sisal epoxy composites (EP-05)
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10. as impurity in the composite material. Interfacial relaxation occurs when charge
carriers are trapped at the interfaces of heterogeneous systems. Interfacial
polarization decreases with increasing frequency and it influences the low frequency
dielectric properties. The dielectric constant of the material directly depends upon
the polarizability. The greater the polarizability of the molecule, the higher the
dielectric constant. Therefore, the polarizability decreases with increase in volume
of fibres, i.e. due to the decreased number of polar groups [2].
Figure 7a–c shows the variation of dielectric constant (e0
) with temperature
(T) for pure epoxy (EP-00), epoxy composite filled with 5 mm length silver-coated
sisal fibre (EP-05) and epoxy composite filled with 10 mm length silver-coated sisal
fibre (EP-10) measured at 0.5, 1, 2, 4 and 5 kHz, respectively. Figure 7a shows that
dielectric constant increases with increase of temperature from 35 to 185 °C and it
decreases with increase in frequency from 0.5 to 5 kHz. The peak height at the
transition temperature decreases with increasing frequency. At low frequencies, all
the dipole groups in the epoxy molecular chains can orient themselves, resulting in
higher dielectric constant. When the frequency of ac voltage increases, the
polarization fails to settle itself completely and the values of dielectric constant of
epoxy resin begin to drop, when approaching at the higher frequencies. At lower
temperatures, e0
values at different frequencies have merged. Figure 7b shows that
dielectric constant increases with increase in temperature and decreases with
increase of frequency from 0.5 to 5 kHz. In this case, the dielectric constant (e0
) is
greater than that of pure epoxy. This increase in e0
is due to the incorporation of
silver conducting coated sisal fibre in the epoxy matrix. It is also observed that the e0
Fig. 6 a–c SEM micrographs of silver-coated sisal epoxy composites (EP-10)
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123

11. Fig. 7 a–c Shows the variation
of dielectric constant (e0
) with
temperature (T) for pure epoxy
(EP-00), epoxy composite filled
with 5 mm length silver-coated
sisal fibre (EP-05) and epoxy
composite filled with 10 mm
length silver-coated sisal fibre
(EP-10) measured at 0.5, 1, 2, 4
and 5 kHz respectively
Polym. Bull.
123

12. increases initially with temperature up to 120 °C after that it decreases up to 150 °C
and again increases up to 185 °C. Fig. 7c shows that the dielectric constant (e0
)
increases initially with temperature up to 115 °C and then decreases with
temperature until it increased to 140 °C. Dielectric constant (e0
) decreases with
increase of frequency from 0.5 to 5 kHz. This initial increase of e0
is due to the
increased mobility of water dipoles. When the water content reduced, the value of e0
decreased. The dielectric constant of 5 mm length of sisal epoxy composite (EP-05)
was observed higher than that of 10 mm length sisal epoxy composite (EP-10). This
is because of the higher concentration of silver particles in form of coating
presented in the 5 mm length composite specimen than the 10 mm length sisal
epoxy composite. It is well understood that, surface area of the smaller size sisal
fibre (5 mm length sisal fibre) will be more compared to larger size sisal fibre
(10 mm length sisal fibre) in case of constant volume (%) of sisal fibre present in
fibre-epoxy composite. This behaviour of the material can be explained in terms of
interfacial polarization. At a constant volume (%) of fibres and at a length of 5 mm,
the number of interfaces per unit volume element is high and this results in high
interfacial polarization. The number of interface decreases as the fibre length
increases and therefore the value of e0
decreases at 10 mm fibre length. This
observation is similar to the work of Prasantha et al. [19] in which they have shown
that the surface area of the smaller size sisal fibre will be more compared to larger
size sisal fibre in case of constant volume (%) of sisal fibre present in composite. We
have observed the similar trend in dissipation factor (tan d) and AC conductivity
(rac).
Figure 8a–c shows the plots of tan d with temperature for pure epoxy, 5 and
10 mm length silver-coated sisal epoxy composite measured at 0.5, 1, 2, 4 and
5 kHz, respectively. Dissipation factor (tan d) increases with increase in temper-
ature. Dissipation factor (tan d) is the ratio of the electrical power dissipated in a
material to the total power circulating in the circuit. In polymers or their composites,
tan d is a function of the electrical conductivity (which depends on the charge
carrier mobility) and the applied excitation frequency. There are two different
interacting processes, which might influence tan d behaviour in composites. The
first one is the number of charge carriers available for electrical conduction and the
other is the number of interfaces and polymer chain entanglements in the bulk [20].
The plots show that in all the three samples, there is a continuous decrease in tan d
values with increasing frequency for all filler lengths and at lower temperatures the
values of tan d is approximately same, there is an increase in the values of tan d with
increase in temperature. The most likely reason for this observation is a decrease in
electrical conductivity in the epoxy composites with increasing frequency, which
may be caused by the inability of the charge carriers to traverse the thickness of the
material at the higher frequencies. At high frequencies, the motion of charge carriers
contributing to the conductivity primarily occurs along polymer chains [21]. A
barrier to the charge transport in polymers (causing reduction in electrical
conductivity) can occur due to defects, inter-chain charge transport and transport
through interfaces. The influence of temperature on conductivity has been explained
by considering the mobility of charge carriers responsible for hopping. As
temperature increases, the mobility of hopping ions also increases thereby
Polym. Bull.
123

13. increasing conductivity. The electrons that are involved in hopping are responsible
for electronic polarization in these composites. The conductivity increases up to a
temperature and further increase of temperature reduces the conductivity. This
decrease in conductivity at higher temperature is based on the thermal expansion of
polymer. At higher temperatures, the polymer density reduced by thermal
expansion, reduces the conductivity [22]. Probably, in composites, the presence
of a large number of interfaces and polymer chain entanglements inhibit the motion
of charges in the system, which in turn causes a reduction in the electrical
conductivity (hence a lower tan d value).
Figure 9a–c show the plots of AC conductivity (rac) with Temperature (T) for
pure epoxy, 5 and 10 mm length sisal epoxy composite measured at 0.5, 1, 2, 4
and 5 kHz, respectively. These plots show that the AC conductivity increased with
Fig. 8 a–c Shows the plots of tan d with temperature for pure epoxy (EP-00), 5 mm length silver-coated
sisal epoxy composite (EP-05) and 10 mm length silver-coated sisal epoxy composite (EP-10) measured
at 0.5, 1, 2, 4 and 5 kHz respectively
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14. increasing temperature. The AC conductivity for 5 mm length sisal epoxy
composite and 10 mm length sisal fibre-epoxy composites is higher than that of
pure epoxy at all frequencies. This is due to hydrophilicity of the lignocellulosic
sisal fibres present in the composites. It was observed that AC conductivity (rac) of
all the three samples increases with the increase in temperature and this confirms
the positive coefficient of conductivity with temperature. This behaviour also
suggests that the electrical conduction increases at the higher temperature, which
may be again due to the increase in the segmental mobility of the polymer
molecules.
Figure 10a–c show the variation of e0
, tan d and (rac) with log f (frequency) for
pure epoxy, 5 and 10 mm length sisal epoxy composite measured at 35 °C. It was
Fig. 9 a–c Shows the plots of AC conductivity (rac) with Temperature (T) for pure epoxy (EP-00),
5 mm length silver-coated sisal epoxy composite (EP-05) and 10 mm length silver-coated sisal epoxy
composite (EP-10) measured at 0.5, 1, 2, 4 and 5 kHz respectively
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15. Fig. 10 a–c Shows the variation of e0
, tan d and (rac) with log f (frequency) for pure epoxy (EP-00),
5 mm length silver-coated sisal epoxy composite (EP-05)and 10 mm length silver-coated sisal epoxy
composite (EP-10) measured at 35 °C
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16. observed that the e0
and tan d decreased with increasing frequency and a.c.
conductivity increased with increasing frequency. The change of e0
at lower
frequency region is higher than that of at high frequency. The atomic and electronic
polarizations are instantaneous polarization components, the effect of which is seen
only at high frequencies. The dipole or orientation polarization occurs due to the
presence of polar groups in the material. The interfacial polarization arises due to
heterogeneity, which is highest at lower frequency. Hence, the higher values of e0
at
low frequency can be explained in terms of interfacial polarization. The behaviour
of tan d with frequency is very much similar to e0
, i.e. with increase in frequency tan
d value also decreases. The value of tan d in all the three samples at low frequency
region becomes high due to free motion of dipoles within the material. This value of
tan d is very high for the EP 10 sample. The behaviour of frequency dependence of
a.c. conductivity (rac) of sisal epoxy composite (EP 05, EP 10) is similar to pure
epoxy sample (EP 00) i.e. with increase in temperature, rac increases and frequency
independent plateau is observed at lower frequency. It is clear from the Fig. 10c that
the rac of EP 05 and EP 10 is higher than the EP 00, and that may be due to the
incorporation of more polar molecules because of hydroxyl groups present in the
fibre. Again, the addition of fibres enhances the flow of current through the
amorphous region due to their ability to absorb moisture. Paul et al. [10] reported
that the dielectric constant of sisal fibre LDPE composite increased with increase in
fibre loading. The increase is higher at low and medium frequencies and lower at
higher frequencies, which has been explained by considering the interfacial
polarization and orientation polarization.
Conclusions
The study concludes that the incorporation of conducting silver coating in sisal
epoxy composite significantly enhances the dielectric properties. Sample having
silver-coated fibre of 5 mm length exhibited higher value of dielectric constant as
compared to the sample having 10 mm of fibre length, which is attributed to the
increased surface area of coated fibre. The dielectric constant increases with
increase of temperature and decreases with increase of frequency from 0.5 to 5 kHz.
The peak height at the transition temperature decreases with increasing frequency.
A continuous decrease in tan d values with increasing frequency for all fibre lengths
and at lower temperatures the values of tan d is approximately same. The AC
conductivity for 5 mm length sisal epoxy composite and 10 mm length sisal fibre-
epoxy composites is higher than that of pure epoxy at all frequencies. FTIR results
confirm the structure present in the samples. Silver-coated sisal fibre surface could
not adhere with epoxy matrix, which is observed in SEM micrographs.
Acknowledgments The author would like to acknowledge the support of the Director (Dr. Appu Kuttan
K.K.), Maulana Azad National Institute of Technology Bhopal-462051(M.P.) India for providing basic
facilities in the institute. The support of the Dr. Rajnish Kurchania (Head) Department of Physics,
Maulana Azad National Institute of Technology Bhopal-462051(M.P.) India is kindly acknowledged.
Polym. Bull.
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