Transcript The importance and methods of dispersing fillers into epoxy resin

The importance and methods of dispersing fillers into epoxy resin
M
*
Reading ,
Z. Xu, A S Vaughan and P L Lewin
University of Southampton, Southampton, UK
Results
Dispersion methods and materials
 Approximately 12-15 breakdown sites were performed for each sample using 6.3 mm ball
bearing electrodes covered in silicone oil to prevent flashover.
Unfilled epoxy
99.9
99.0
95.0
99.9
99.0
95.0
70.0
70.0
70.0
50.0
50.0
50.0
20.0
10.0
5.0
Unmixed
Hand mixed
Magnetically stirred
Ultrasound
Sonication
1.0
 Samples produced using a previously established gravity fed pre-made mould technique
using a QZ13 release agent. This method produced thin film samples of ~ 80 µm.
 Samples were de-gassed at 50
for 20 minutes before being cured at 100
hours followed by a gradual cool over 10 hours.
0C
120
140
160
Breakdown Strength / kVmm-1
MMT filled
Weibull Probability / %
50.0
20.0
10.0
5.0
Unmixed
Hand mixed
Magnetically stirred
Ultrasound
Sonication
1.0
0.0
100
120
140
160
Breakdown Strength / kVmm-1
 0.25 g of MMT, SD and NSD added pre-curing and 5 different mixing regimes employed
to create 20 samples, detailed in Table 1 with the mixing regimes detailed in Table 2.
Samples were de-gassed for 20 minutes prior to mould introduction.
Table 1. Samples generated
Sample
Filler
Mixing
regime
SD NM
5% micro SD
A
Mixing
regime
A
Unmixed
Hand mixed
Magnetically stirred
Ultrasound
Sonication
1.0
20.0
10.0
5.0
Unmixed
Hand mixed
Magnetically stirred
Ultrasound
Sonication
1.0
0.1
0.0
100
120
140
160
Breakdown Strength / kVmm-1
99.9
99.0
95.0
0.1
Figure 2. An example thin film sample
5.0
Sample
70.0
Figure 1. Pre-made mould
10.0
0.0
100
for 4
20.0
0.1
0.0
0C
NSD filled
99.9
99.0
95.0
0.1
 DER 332 epoxy resin cured using a Jeffamine D-230 hardener chosen as the host
polymer matrix. The stoichiometric ratio was calculated to be 1000:344 for resin:hardener.
SD filled
Weibull Probability / %
For this investigation an epoxy system (EP) was chosen as the host polymer with
aluminium pillared montmorillonite (MMT), micro spheres of silicon dioxide (SD) and nano
spheres of silicon dioxide (NSD) as fillers. The dispersion of the fillers was quantified by
use of a scanning electron microscope (SEM) and inferred by use of electrical breakdown
tests, which also revealed any effect on the electrical breakdown strength of the materials.
 For electrical breakdown characterisation a custom built AC breakdown kit was used
following the ASTM D149 standard (50 Hz, 50 V/s).
Weibull Probability / %
There are many methods available to achieve a good dispersion of fillers, however it is
important to ensure that these methods do not alter the polymer matrix resulting in
misleading results. This investigation looks at several methods of dispersing three chosen
fillers within a polymer matrix and the resulting electrical properties with regard to the
dispersion state of the fillers. Also, the same processes will be performed on unfilled
materials to investigate any effects they may have on the host material.
Weibull Probability / %
Introduction
Weibull
Parameter
α
β
100
120
160
Breakdown Strength / kVmm-1
Sample
Weibull
Parameter
α
EP NM
EP HM
EP MS
EP US
EP SON
MMT NM
MMT HM
MMT MS
MMT US
135.8
141.3
143.8
147.5
152
128.9
137.8
139.2
138.5
9.1
14.3
26.5
21.9
22.17
6.1
7.52
14.9
29.9
SD NM
SD HM
SD MS
SD US
SD SON
NSD NM
NSD HM
NSD MS
NSD US
129.8
127
132.5
138.3
141.5
129.2
135.3
139.5
145.9
MMT SON
141.8
11.52
NSD SON
138.5
Figures 3-6. Weibull plots of Eb data
for samples containing no filler (top left),
SD filler (top centre), NSD filler (top right)
and MMT filler (bottom left)
140
β
9.88
14.62
16.2
13.1
15.7
5.6
10.18
12.3
18.4
19.9
Table 3. Weibull parameters for samples
 For scanning electron microscope (SEM) a Carl Zeiss AG Evo 50 was used
Sample
Filler
EP NM
-
EP HM
-
B
SD HM
5% micro SD
B
EP MS
-
C
SD MS
5% micro SD
C
EP US
-
D
SD US
5% micro SD
D
EP SON
-
E
SD SON
5% micro SD
E
MMT NM
5% MMT
A
NSD NM
5% nano SD
A
MMT HM
5% MMT
B
NSD HM
5% nano SD
B
MMT MS
5% MMT
C
NSD MS
5% nano SD
C
MMT US
5% MMT
D
NSD US
5% nano SD
D
MMT SON
5% MMT
E
NSD SON
5% nano SD
E
Figures 7-8. SEM images of unfilled epoxy (left) and a single SD particle in SD-SON (right)
 Magnetic stirring was performed on a standard Heat stirrer plate at 50 0C using a
magnetic stirrer bar
 For Ultrasound an UltraWave DP201 Precision Ultrasonic bath was used at 50 0C
 For Sonication a Hielscher UP200S Ultrasonic processor was used at 50 % amplitude.
Regime
Table 2. Mixing regimes
Details
A
Resin, hardener and filler combined with no mixing
B
Hand mixed for 20 minutes
C
Hand mixed for 20 minutes followed by
D
magnetic stirring for 20 minutes
Hand mixed for 20 minutes, magnetically stirred
E
for 20 minutes and ultrasound for 20 minutes
Hand mixed for 20 minutes, magnetically stirred
for 20 minutes and sonicated for 20 minutes
Contact details :
M Reading, [email protected]
University of Southampton, Highfield, Southampton, SO17 1BJ, UK
Figures 9-10. A standard SEM image of the MMT-SON sample (left) and a backscattered image
highlighting the highly dispersed MMT particles (right)
Conclusions
 It is clear from SEM that regimes A and B produce poorly dispersed composites resulting
in low β values and agglomeration of the fillers, as expected.
 Magnetic stirring is seen to improve the dispersion of the fillers within the host polymer,
achieving an acceptable level of dispersion seen by SEM and higher β values.
 Ultrasound and Sonication methods are both seen to further improve the dispersion of the
materials by use of SEM, with sonication found to produce particularly uniform materials
having broken up the larger agglomerations of filler. However β values do not appear to
reflect this.
 Ultrasound and Sonication were actually seen to act to increase the breakdown strength
of the unfilled epoxy slightly, an effect worth investigating.