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

1
The Effect of Nanofiller on Polyethylene
SystemK. Y. Lau1, 2, , A. S. Vaughan1, G. Chen1
and I. L. Hosier11University of Southampton,
Southampton, UK2Universiti Teknologi Malaysia,
Johor Bahru, Malaysia
Morphological Analysis
Introduction
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. 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.

• Figure 2 illustrates the morphological structure
  for the materials investigated.
• 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.
• 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 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.
• 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.

(a) PEA/0/115 (b) PEA/0/113 (c)
PEA/0/117
(d) PEA/5S1M/115 (e) PEA/0/Q (f)
PEA/5S1M/Q
Table 1 Materials investigated
Figure 2 Optical micrographs taken under crossed
polarisers
Designation 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/0/115 Polyethylene system type A (20 wt of HDPE and 80 wt of LDPE), without nanofiller, and being isothermally crystallised at 115 ºC.
PEA/5S1M/115 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.
Breakdown Strength Analysis
Table 3 Weibull parameters

• 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.
• Table 2 shows the Weibull parameters obtained
  from the breakdown test conducted for each of the
  materials.

Sample Scale parameter (kV/mm) Shape parameter
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

• 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.
• 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.

• Therefore, in this preparation route, the
  addition of nanosilica caused reduced breakdown
  strength in both quenched and isothermally
  crystallised polyethylene systems.

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 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.
• 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.

Figure 3 Breakdown strength of PEA/5S1M/Q and
PEA/0/Q
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.
• In the isothermally crystallised polyethylene
  systems, the addition of nanosilica disrupted
  spherulitic development, as observed by POM.
• 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.

kyl1g10_at_ecs.soton.ac.uk University of
Southampton, Highfield, Southampton, SO17 1BJ, UK
Figure 1 DSC melting traces
Contact details
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.