Title should be like this A P Robinson1, P L Lewin1, S

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Transcript Title should be like this A P Robinson1, P L Lewin1, S

The Effect of Nanofiller on Polyethylene System
K. Y. Lau1, 2, *, A. S. Vaughan1, G. Chen1 and I. L. Hosier1
1University of Southampton, Southampton, UK
2Universiti Teknologi Malaysia, Johor Bahru, Malaysia
Introduction
Morphological Analysis
The topic of polymer nanocomposites remains an active area of research in terms of its
potential applications in dielectric and electrical insulation applications. Although more than
a decade has passed since Lewis first considered these systems as dielectric materials, the
precise effects of incorporating nanofillers into different polymers are yet to be confirmed.
 Figure 2 illustrates the morphological structure for the materials investigated.
This paper reports on an investigation into nano-filled polyethylene system prepared via a
solution blending route. A blend of polyethylene containing both high and low density
polyethylene was used as the base polymer, with nanosilica as the filler. The strategy
employed for material preparation involves the initial dissolution of the polymer in nonpolar
xylene and the dispersion of the nanosilica in relatively polar methanol – a non-solvent for
polyethylene. Mixing together the two components results in the rapid gelation of the
polymer, including the nanoparticles. The crystallisation behaviour and morphology of
differently processed materials have been evaluated by differential scanning calorimetry
(DSC) and polarised optical microscopy (POM). The influence of nanofiller dispersion on
breakdown behaviour is also described.
 However, as shown in Figure 2(d), the observation of spherulites was less pronounced
due to nano-inclusion. Therefore, the addition of nanosilica appears to have dramatically
perturbed spherulitic development.
 In the unfilled polyethylene system that has been isothermally crystallised at 115 ºC
(Figure 2(a)), spherulites can be clearly observed through POM. Crystallisation at 113 ºC
(Figure 2(b)) and 117 ºC (Figure 2(c)) also show clear evidence of spherulites in this system.
 In both unfilled (Figure 2(e)) and nano-filled (Figure2(f)) systems that have been
quenched, no spherulites can be observed by POM.
Materials Preparation and Experimental Setup
 The desired amount of nanosilica was added into methanol and sonicated. Concurrently,
the proper amount of high density polyethylene (HDPE) and low density polyethylene
(LDPE) were dissolved in xylene under heating and stirring.
(a) PEA/0/115
(b) PEA/0/113
(c) PEA/0/117
 The hot xylene/polyethylene mixture was poured onto the methanol/nanosilica mixture
quickly with vigorous stirring. The nanocomposites precipitated out as a white mass.
 Upon filtering and drying, the resulting nanocomposite was melt pressed at 150 ºC and
vacuum dried at 100 ºC.
 Samples for different tests were prepared by melt pressing at a temperature of 150 ºC,
followed by direct quenching into water or isothermal crystallisation.
 For comparison purpose, unfilled polyethylene system were prepared in the same way.
 The types of materials investigated are summarised as in Table 1.
(d) PEA/5S1M/115
Table 1: Materials investigated
Description
PEA/0/Q
Polyethylene system type A (20 wt% of HDPE and 80 wt% of LDPE), without
nanofiller, and being quenched directly into water.
PEA/5S1M/Q
Polyethylene system type A (20 wt% of HDPE and 80 wt% of LDPE), with 5 wt%
of nanosilica being sonicated for 1 hour in methanol, and being quenched directly
into water.
PEA/5S1M/115
(f) PEA/5S1M/Q
Figure 2: Optical micrographs taken under crossed polarisers
Designation
PEA/0/115
(e) PEA/0/Q
Breakdown Strength Analysis
 Figure 3 and Figure 4 show that the breakdown
strength of PEA/5S1M/Q and PEA/5S1M/115 were
significantly lower than that of PEA/0/Q and
PEA/0/115, respectively.
Polyethylene system type A (20 wt% of HDPE and 80 wt% of LDPE), without
nanofiller, and being isothermally crystallised at 115 ºC.
Polyethylene system type A (20 wt% of HDPE and 80 wt% of LDPE), with 5 wt%
of nanosilica being sonicated for 1 hour in methanol, and being isothermally
crystallised at 115 ºC.
 Table 2 shows the Weibull parameters obtained
from the breakdown test conducted for each of the
materials.
 Polarised optical microscopy was used to evaluate the morphology of the materials.
 Differential scanning calorimetry was used to determine the thermal behaviour of the
materials. The experiment was performed in a nitrogen atmosphere at a scan rate of
10 ºC/min, with sample weight of about 5 mg.
Table 3: Weibull parameters
Scale
Shape
Sample
parameter
parameter
(kV/mm)
PEA/0/Q
148 ± 4
16 ± 5
PEA/5S1M/Q
132 ± 4
13 ± 4
PEA/0/115
152 ± 3
19 ± 6
PEA/5S1M/115
138 ± 6
9±3
 Therefore, in this preparation route, the addition of nanosilica caused reduced breakdown
strength in both quenched and isothermally crystallised polyethylene systems.
 Dielectric breakdown strength measurements were conducted based upon the general
consideration laid down in the ASTM Standard D149-87. The sample thickness was about
85 µm. An AC voltage of 50 Hz and a ramp rate of 50 V/s was applied until failure. The
breakdown data were statistically analysed using the two-parameter Weibull distribution
analysis.
Thermal Analysis
 The DSC melting behaviour for the materials
investigated is shown in Figure 1.
 There are two melting peaks observed in
each material, with the lower peak associated
with the LDPE-rich phase and the upper peak
associated with the HDPE-rich phase.
 The lower and upper melting peaks of
PEA/5S1M/115 were ~105 ºC and ~124 ºC,
respectively, with no significant difference from
PEA/0/115.
 The DSC thermal traces indicate that there
were no thermal changes caused by nanosilica
inclusion.
Endothermic
 The melting behaviour of PEA/5S1M/Q is
similar to PEA/0/Q, with a lower peak of ~114 ºC
and an upper peak of ~124 ºC.
Figure 3: Breakdown strength of PEA/5S1M/Q and
PEA/0/Q
PEA/5S1M/115
Figure 4: Breakdown strength of PEA/5S1M/115 and
PEA/0/115
Summary and Future Work
 The melting behaviour of both the quenched and isothermally crystallised polyethylene
systems was not altered by nano-inclusion.
PEA/0/C
PEA/5S1M/Q
 In the isothermally crystallised polyethylene systems, the addition of nanosilica disrupted
spherulitic development, as observed by POM.
PEA/0/Q
 The breakdown strength was significantly reduced due to nano-inclusion. It could be
related to the preparation or morphology of the materials, but more detailed analysis, such as
the use of scanning electron microscopy, is required to provide such understanding.
60
80
100
120
140
Temperature / °C
Figure 1: DSC melting traces
* Contact details :
[email protected]
University of Southampton, Highfield, Southampton, SO17 1BJ, UK
Acknowledgements
One of the authors (K. Y. Lau) would like to acknowledge Ministry of Higher Education, Malaysia and Universiti Teknologi Malaysia for the financial sponsorship.