awang2017

International Conference on Electrical Engineering and Computer Science (ICECOS) 2017
AC Breakdown Strength Enhancement of LDPE
Nanocomposites Using Atmospheric Pressure Plasma
N.A.Awang1, M.H.Ahmad1, Z.A.Malek1, M.A.B. Sidik2, Z. Nawawi2, M. I. Jambak2, E. P. Waldi3, Aulia3
1
Institute of High Voltage & High Current, Faculty of Electrical Engineering
Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia
2
Department of Electrical Engineering, Faculty of Engineering
Universitas Sriwijaya, Ogan Ilir, South Sumatra, Indonesia.
3
Department of Electrical Engineering, Faculty of Engineering
Universitas Andalas, 25163, Padang, West Sumatra, Indonesia.
[email protected]
the polymer matrix and the nanoparticles [7–10]. This method
had increased the breakdown strength as reported by Lau et al.
[5]. Similarly, Tagami et al. [11] reported that the coupling
agent produced stronger effect on the dielectric properties as
compared to other method which has the poorer effect.
However, this method did not solve the issue of nanoparticle
agglomeration and high water uptake. Also, this method was
not suitable for mass production and high toxicity due to
involvement of solvent [12].
Recently, atmospheric pressure plasma treatment (APP)
was introduced to treat the nanoparticle surfaces in order to
enhance
the
dielectric
performance
of
polymer
nanocomposites. This treatment has been reported to reduce the
nanoparticle agglomeration and improved the chemical bonds
thereby leading to the improvement of the electrical insulation
properties [13]. Yan et al. [14] used APP to treat the surface of
silica nanofillers, but in this study, similar APP was used to
treat BN nanofillers to improve the surface compatibility and
the interfacial zone. The APP treatment on BN nanofillers and
its effect on AC breakdown strength of LDPE nanocomposites
have never been reported previously. Therefore, this technique
was employed to increase the breakdown strength of the LDPE
nanocomposites.
Abstract—Polymer nanocomposites have been identified to
possess superior electrical insulation properties compared to its
base polymer. However, weak interfacial interaction between the
nanoparticles and the host polymer matrices would result in poor
insulation properties. In this study, the surfaces of Boron Nitride
(BN) nanoparticles were treated with atmospheric pressure
plasma discharge to strengthen the interface between the low
density polyethylene (LDPE) matrices and BN nanoparticles.
Furthermore, AC breakdown strengths of the untreated and
treated LDPE nanocomposites were measured according to
ASTM D149 standard. The obtained results were analyzed with
2-parameter Weilbull distribution. Moreover, the treated and
untreated nanocomposites were characterized using Fourier
Transform Infrared (FTIR) Spectroscopy in order to
characterize the functional groups in LDPE nanocomposite
samples after subjected to plasma discharges. It is shown that
hydrogen bonds are created in the functional groups of the
plasma treated LDPE nanocomposites. The results also show that
the AC breakdown strength of plasma treated LDPE
nanocomposites sample was improved compared with the
untreated LDPE nanocomposites.
Keywords—Atmospheric pressure plasma; breakdown strength;
Boron Nitride; Low Density Polyethylene
I. INTRODUCTION
Nanocomposites become a main topic to be published in
many publications as it has been reported to possess excellent
electrical properties such as high partial discharge resistance,
electrical treeing suppression, reduced space charge
accumulation, low tangent delta and reduced permittivity [1–
3]. Also, the nanocomposites have been reported to possess
higher breakdown strength compared to microcomposites and
its host polymer [4]. In spite of the positive feedbacks, many
researchers have also reported that the nanocomposites have
resulted in reduced breakdown strength especially in DC
breakdown test [4–6]. This issue is identified to be caused by
the factors of filler/matrix incompatibility, nanoparticle
agglomeration, weak filler/matrix interfacial interaction and
high water uptake [4],[6],[7]. Many researchers have proposed
a method to solve this issue known as surface treatment by
using silane coupling agent to strengthen the interface between
978-1-4799-7675-1/17/$31.00 ©2017 IEEE
II. EXPERIMENTAL
A. Materials
The base material of the polymer nanocomposite sample
used in this study was low density polyethylene (LDPE) by
Titan Chemical, Malaysia. It has density of 0.922 g/cm3 and
the melting index of 25 g/10min. The hexagonal Boron Nitride
(BN) was used as nanofiller with an average particle size of
137 nm supplied by Nanostructured and Amorphous
Materials, USA.
B. Plasma Treatment
The treatment of BN nanofillers was done in the plasma
chamber which applied the concept of dielectric barrier
discharge (DBD) configuration system. The dimension of the
plasma chamber in this study was 180mm × 180mm × 100mm
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International Conference on Electrical Engineering and Computer Science (ICECOS) 2017
TABLE I.
and the stainless steel electrodes were attached with the wire
mesh. Two quartz glass with 1mm thick in between of the
high voltage electrode used as dielectric barrier to avoid from
flashover.
The gap spacing was kept at 3mm and it was generated by
a 50 Hz of AC power supply with a maximum applied voltage
between 7 to 8.5 kVrms. Helium gas was used as discharge
gas with a flow rate of 1 l/min which applied inside the plasma
chamber. The plasma power was consumed at 3 to 15 W.
The nanoparticles were placed between DBD’s plate in the
plasma chamber and treatment time was performed for 15
minutes. To obtain a homogenous exposure, the nanoparticles
were placed between DBD’s plate in the plasma chamber and
treatment time was performed at every 5 minutes then it were
stirred for 30 seconds of surface treatment [13]. The process
was repeated for 3 times and 6 times to get the total treatment
time of 15 minutes and 30 minutes. Fig. 1 shows a schematic
diagram of the setup for the plasma treatment of the BN
nanoparticles.
CODE AND COMPOSITION OF EACH SAMPLE
Sample code
PL
Composition
Pure Low Density Polyethylene
LB1
Low Density Polyethylene/1wt% Untreated Boron
Nitride Nanocomposite
Low Density Polyethylene/3wt% Untreated Boron
Nitride Nanocomposite
Low Density Polyethylene/5wt% Untreated Boron
Nitride Nanocomposite
Low Density Polyethylene/1wt% of 15 minutes
Plasma Treated Boron Nitride Nanocomposite
Low Density Polyethylene/3wt% of 15 minutes
Plasma Treated Boron Nitride Nanocomposite
Low Density Polyethylene/5wt% of 15 minutes
Plasma Treated Boron Nitride Nanocomposite
Low Density Polyethylene/1wt% of 30 minutes
Plasma Treated Boron Nitride Nanocomposite
Low Density Polyethylene/3wt% of 30 minutes
Plasma Treated Boron Nitride Nanocomposite
Low Density Polyethylene/5wt% of 30 minutes
Plasma Treated Boron Nitride Nanocomposite
LB3
LB5
LBA1
LBA3
LBA5
LBB1
LBB3
LBB5
D. Experimental Setup
The AC breakdown tests were conducted based on ASTM
D149-87 standard. The breakdown strength of LDPE
nanocomposites thin films was measured by placing in
between two 6.3 mm diameter steel ball bearing electrodes
immersed in mineral oil to prevent from flashover. A 50 Hz of
AC voltage with a ramp rate of 50 Vrms/s was applied to the
sample until its failure. The total test points of 15 breakdown
measurements were collected for each sample. Fig. 2 shows
the experimental setup of AC breakdown tests.
Fig. 1. Schematic diagram of a setup for plasma treatment
C. Sample Preparation
The compounding process of LDPE and BN filler was
performed using a Brabender mixer with the chamber size of
50 cm3 by melt mixing at 165 °C. The electrode speed mixer
has a high shear force and it was controlled at 35 rpm to
ensure the mixing process was mixed homogenously between
polymer and the nanofillers. The mixing time of LDPE
nanocomposites was kept constant at 2 minutes for each
sample.
The samples of LDPE nanocomposites were prepared with
thickness of 100μm±0.5mm are used for breakdown
measurements by hot pressing at 160 °C. Preheating process
was conducted for 3 minutes followed by 3 minutes of
compression. After that, the molded sample was kept 3
minutes for cooling process. Table I shows the sample code
and composition of each sample.
Fig. 2. Experimental setup of AC breakdown tests
All breakdown voltage data were analysed using Weilbull
analysis with 2-parameter function [5]:
ܲሺ‫ܧ‬ሻ ൌ ͳ െ Ղ
ಶ ഁ
ഀ
ቈିቀ ቁ ቉
(1)
where ܲሺ‫ܧ‬ሻ is the cumulative probability of the electrical
failure at E which is the experimental breakdown strength.
Where Į and ȕ are referred to the scale and shape parameters.
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International Conference on Electrical Engineering and Computer Science (ICECOS) 2017
TABLE II.
The experimental cumulative probability of failure, ܲሺ‫ܧ‬ሻ was
estimated using median rank function:
௜ି଴Ǥଷ
(2)
ܲሺ‫ܧ‬ሻ ൌ Sample
PL
LB1
LB3
LB5
LBA1
LBA3
LBA5
LBB1
LBB3
LBB5
௞ା଴Ǥସ
where ݅ and ݇ are respectively to the progressive order of
failure tests and the total number of tests.
III. RESULT AND DISCUSSION
A. AC Breakdown Strength
Figs. 3, 4 and 5 represented Weibull analysis plots of the
AC breakdown strength for LDPE containing 1, 3 and 5wt%
of untreated, 15 minutes and 30 minutes of plasma treated BN
nanofiller. The breakdown strength and shape parameter for
all the AC breakdown results are summarized in the Table II.
It can be observed that all the AC breakdown performance of
the addition of BN nanofiller slightly decreased for as
compared to the unfilled samples which were 145.01, 132.96
and 130.07 kV/mm for 1, 3 and 5wt% respectively. AC
breakdown strength result of PL sample is 155.47 kV/mm.
With the addition of BN filler, the results of AC breakdown
strength were significantly lower than PL sample. At high
filler loading, LB5 sample has the lowest results in breakdown
strength compared to other sample.
However, the AC breakdown strength for 15 minutes of
plasma treated BN filler sample shows an increment values
which were 145.54, 149.66 and 145.32 kV/mm for LBA1,
LBA3 and LBA5 sample respectively. However, LBP3 sample
has the highest value of breakdown strength compared to
LBA1 and LBA5 it may be caused by the stronger chemical
bonds strength between nanofiller and polymer matrices after
plasma treatment [15]. Thus, it attributes to the improvement
in AC breakdown strength. In contrast, the AC breakdown
strength for 30 minutes of plasma treated BN nanofiller were
improved compared to others sample with results of 171.66,
157.95 and 155.93 kV/mm for LBB1, LBB3 and LBB5
respectively. Meanwhile, AC breakdown strength has slightly
increased when the plasma treatment time was prolonged to 30
minutes. The LBB1 sample shows the highest result compared
to LBB3 and LBB5 samples.
It can be observed that all the nanocomposite samples for
untreated and 15 minutes of plasma treated BN nanofillers
show a reduction of breakdown strength results compared to
PL sample. This happens because of the average particles size
of BN (137 nm) is larger than 100 nm in which may cause the
reduction of AC breakdown strength values. The shape
parameter, ȕ of all LDPE nanocomposite samples range
between 9.66 and 18.41. For the LB3 sample has the largest
shape which presents a very good repeatability of the data.
AC BREAKDOWN STRENGH RESULTS FROM WEIBULL
ANALYSIS
Scale, Į (kV/mm)
155.47
145.01
132.96
130.07
145.54
149.66
145.32
171.66
157.96
155.93
Shape, ȕ
10.11
11.19
18.41
12.92
16.02
13.01
9.66
14.03
17.43
17.77
Fig. 3. Weibull analysis of AC breakdown strength for untreated BN
nanofiller
Fig. 4. Weibull analysis of AC breakdown strength for 15 minutes of plasma
treated BN nanofiller
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International Conference on Electrical Engineering and Computer Science (ICECOS) 2017
to the surface and it may increase the number of O-H groups
in the sample during the addition of nanoparticles to the base
polymer. In contrast, results showed that the peak of O-H
groups increased from the spectrum of the LBP5 sample. This
result indicates that the more intensity of O-H group on its
surface are produced after plasma treatment [15–17] . It
happens because of plasma discharges contained many
reactive species such as ion, electron and proton. While, O-H
group contributes in increasing the number of hydrogen bond
(H+) proton which is covalently bound. The positive charge of
the proton is not attached with other electrons which strongly
attract the electrons from another atom [18]. These effects
may lead to the enhancement of the interfacial interaction
between the nanofiller and the polymer matrices [19]. Thus,
the increase in hydroxyl groups in LDPE nanocomposites has
resulted in enhancement of AC breakdown strength which in
line with Ko et al [20]. In addition, it can be found that the
peak located at 795.28 cm-1 for untreated (LB5) sample has
reduced to 789.24 cm-1 from the spectrum of the plasma
treated (LBA5and LBB5) sample. This result indicates the
B-N-B bonds for both spectrum [16].
Fig. 5. Weibull analysis of AC breakdown strength for 30 minutes of plasma
treated BN nanofiller
B. Characterization of Nanoparticles
The functional groups of LDPE, untreated and plasma
treated LDPE nanocomposites were characterized using
Fourier Transform Infrared (FTIR). The results in Fig. 6
depict the spectrum of functional groups for each sample. It
shows that the characteristics of transmittance bands for each
sample started to change at 3000-3750 cm-1, 1250-1750 cm-1
and 800-600 cm-1 that referred to the PL sample. The
absorption peak for pure polyethylene sample located at
3395.00 cm-1, 2848.25-2916.02 cm-1, 1645.69 cm-1 and 719.10
cm-1. Then, the peaks at 2848.25-2916.02 cm-1 represented the
CH2 stretching vibrations due to polyethylene characteristics
itself for all spectrums. After the addition of BN nanoparticles,
new additional peaks are found at 1462.41cm-1, 1462.40 cm-1,
795.28 cm-1 and 789.24 cm-1.
IV. CONCLUSION
The AC breakdown strength was investigated in LDPE
filled with 1, 3 and 5wt% of untreated, 15 minutes and 30
minutes of plasma treated BN nanofillers. The AC breakdown
strength of the LDPE nanocomposites has been found to be
improved when the nanofillers were modified using plasma
treatment as compared to the untreated samples. The addition
of untreated BN filler in LDPE caused the AC breakdown
strength to reduce compared to PL sample. However, it was
observed that the improvements of AC breakdown strength
values after plasma treatment which indicating that the
breakdown strength of pure LDPE was better than untreated
and 15 minutes of plasma treated sample. However, the AC
breakdown strength of LDPE nanocomposites were
significantly improved when the treatment time was prolonged
to 30 minutes. The FTIR analysis clearly showed that the
plasma treatment produced hydroxyl group in the LDPE
nanocomposites which thereby contributing to the improved of
interfacial interaction between the nanofillers and the polymer
matrices of the LDPE sample.
ACKNOWLEDGMENT
The authors would like to acknowledge Universiti Teknologi
Malaysia, and Universitas Sriwijaya for providing research
grants under vote numbers 13H98, 11H21, 4B278 and 4B279.
Also, authors acknowledge Dr. Lau Kwan Yiew for providing
AC breakdown voltage facilities.
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