Journal of Minerals & Materials Characterization & Engineering, Vol. 2, No.1, pp11-31, 2003
http://www.jmmce.org, printed in the USA. All rights reserved
11
Processed Low NO
x
Fly Ash as a Filler in Plastics
X. Huang, J.Y. Hwang, and J.M. Gillis
Institute of Materials Processing
Michigan Technological University
1400 Townsend Drive
Houghton, Michigan 49931-1295
Fly ash generated from low NO
x
burners at American Electric Power's Glen Lyn
facility was beneficiated to remove residual carbon, magnetic particles, and
cenospheres. The clean fly ash had a mean particle size of about 30 microns,
which is coarser than typical commercial fillers used in plastics. To obtain a finer
sized fly ash, air classification was used to separate the clean fly ash into its
coarse and fine fractions. The resulting fine fraction had a mean particle size of
4.13 microns and accounted for 16.7 wt% of the total clean ash. The brightness of
the clean ash was also less than that of typical commercial fillers and efforts to
improve the brightness proved unsuccessful. The resulting fine ash was then
coated with a silane coupling agent and then added to polypropylene, low density
polyethylene, and high density polyethylene at various levels. These mixtures
were in turn used to make tensile test specimens by injection molding. For
comparison, a commercial CaCO
3
filler was also tested under the same
conditions. The mechanical properties of these specimens were determined and
the results show that the polymers containing fly ash as a filler have equivalent
properties to those same polymers when commercial fillers are used in most
cases.
Keywords: Fly ash, filler, plastics, injection molding.
Introduction
The 1990 Clean Air Act Amendments has forced many utilities to retrofit with low NO
x
burners
to meet the new standards. One side effect of low NO
x
burners is that a fly ash with higher
carbon content is created, which prohibits its use in cement and concrete products and its
potential penetration into a number of other markets.
The Institute of Materials Processing at Michigan Technological University (IMP/MTU) has
used its patented beneficiation process to remove the residual carbon, magnetic particles, and
cenospheres from low NO
x
fly ash at pilot plant scale. As a result the loss on ignition (LOI) of
the fly ash received from American Electric Power Company (AEP) has been reduced from
23.3% to 1.2%.
A potential application for fly ash, other than as a substitute for cement, is to use the resulting
clean ash as a plastic filler. Mineral fillers are widely used in plastic products to improve

12 X. Huang, J. Y. Hwang, and J. M. Gillis Vol.2, No.1
performance and reduce the costs. The minerals commonly used for plastic fillers include
calcium carbonate, kaolin, aluminum trihydrate, talc and titanium dioxide. Yet calcium carbonate
accounts for about 70% of the fillers used.
Fly ash can also be classified as a mineral based on its chemistry and physical properties. The
characteristics of fly ash are very close to a number of commercial fillers. Previous studies have
indicted that the use of fly ash as a plastic filler has shown promising results
[1-3]
. However, the
particle size and brightness of fly ash are still less desirable than those of a typical commercial
filler. The objective of this research is to further process the clean fly ash by separating the finest
fraction and improving its brightness while evaluating its performance as a plastic filler.
Most commercial plastic fillers have a mean diameter of only a few microns. The average
particle size of the clean AEP ash is about 30 microns with about 15% having a mean diameter
of less than 5 microns. Based on the clean ash size distribution and commercial filler
specification, clean ash with a maximum particle size of 5 microns seems an appropriate choice
to satisfy the basic plastic filler requirements. Both a hydrocyclone and an air classification
system offer a potential means for the separation of fly ash into two fractions using 5 microns as
the cut. In this study an air classifier was used for the separation.
The approach adopted in this study to improve brightness was to control the precipitation of
TiO
2
, CaCO
3
or ZnO onto the clean ash surface. The evaluation of the fine clean ash coated with
a coupling agent as a plastic filler was conducted by comparing it to three polymers,
polypropylene, low density polyethylene and high density polyethylene, compounded with a
commercial CaCO
3
filler under the same conditions. At the end of the study, a plastic company
was invited to try the resulting polymers, compounded with the clean ash, to produce two
commercial auto parts.
Experimental
Beneficiation
Ash beneficiation on a pilot plant level was conducted at the IMP with a feed rate of about 90
kg/hr. The as-received fly ash was mixed with water to form a slurry and pumped into a
magnetic separator. After the magnetic fraction had been removed, the slurry was fed into a
settling tank to capture the cenospheres and provide a uniform feed to a flotation circuit. The
cenospheres that floated were in turn recovered by skimming the surface of the water. The under
flow material was then pumped into a conditioning tank, where reagents were added into the
slurry and then routed to the first tank, or rougher stage, of the flotation phase of the process. A
more detailed description on the beneficiation can be found in reference
[4]
.
Classification
An Acucut air classifier was used for the air classification task. The classification tests initiated
with the runs being conducted under different operating parameters to determine the optimum
conditions for the cut desired. After each test, the resulting coarse and fine fractions had their

Vol. 2. No. 1 Processed Low NO
x
Fly Ash as a Filler in Plastics 13
particle size distributions and yields established using a Leeds & Northrup Microtrac. After 12
tests, it was found that Test #10 offered the most favorable results. These parameters were then
used to produce more than 3 kg of clean AEP ash with a particle size of less than 5 microns.
Characterization
The most important characteristics for a plastic filler are mean particle size, size distribution,
shape, oil absorption, loose density, tap density, brightness, pH, and composition. After air
classification had been used to make a cut at 5 microns with the clean AEP ash the resulting fine
fraction was characterized according to these properties. The particle size and size distribution
was analyzed using a Leeds & Northrup Microtrac analyzer. The particle shape was established
using a JEOL JSM 820 scanning electron microscope (SEM). The loose density was measured
by charging the ash into a 100 ml graduated cylinder weighing the 100 ml ash, and simply
dividing the weight by the 100 ml. The tap density was measured by charging ash into a 100 ml
graduated cylinder, taping the cylinder 100 times on a Stave 2003 stamp volumeter, measuring
the weight and volume, and again simply dividing the weight by the volume. The oil absorption
was determined by following the ASTM standard D281. Brightness was determined using a
ZEISS photoelectric reflectance photometer with a swing-in brightness standard at brightness of
95.9%. The pH was measured following the ASTM standard D4972.
Brightness Improvement Test
It was intended to produce TiO
2
, CaCO
3
or ZnO coating on fly ash surfaces by controlling their
precipitations. The principle involved is to control the reaction between two materials so that the
resulting product will only nucleate and grow on fly ash surface. The TiO
2
, CaCO
3
and ZnO
precipitations were produced according to the following reactions:
TiCl
4
+ 4NaOH = TiO
2
+ 2H
2
O + 4NaCl (1)
CaCl
2
H
2
O + Na
2
CO
3
= 2NaCl + CaCO
3
+ 2H
2
O (2)
ZnCl
2
+ 2NaOH = Zn(OH)
2
+ 2NaCl (3)
Zn(OH)
2
150EC ZnO + H
2
O (4)
A slurry with 5% clean ash and two reactant solutions with low concentration but proper ratios
based on the above reactions were prepared. The two reactant solutions were charged into 250 ml
burets and very slowly fed into a beaker containing the fly ash slurry while being stirred.
Polymers
In order to promote industrial application, Soo Plastics in Sault Ste. Marie, Michigan was been
contacted. This company donated polypropylene, low density polyethylene, and high density

14 X. Huang, J. Y. Hwang, and J. M. Gillis Vol.2, No.1
polyethylene, which are currently being used by Soo Plastics, to IMP/MTU for this research.
These polymers are polypropylene homopolymer T-3922 nat., Escorene LL 6407.67 nat. linear
low density polyethylene, and HXM 50100 nat. high density polyethylene. These polymers were
produced by Fina Oil & Chemical Company, Exxon Chemical Americas, and Phillips Petroleum,
respectively.
Filler Surface Treatment
A Silane coupling agent was coated on the filler surface to improve bonding between the filler
surface and the matrix of the polymer. Silane is a series of products formulated for different filler
and polymer systems and is one of the most commonly used coupling agents. After consulting
with the Dow Corning Corporation, a silane manufacturer, Dow Corning Z-6032 was selected
for testing. This silane is suitable for fly ash and compatible with the three polymer systems
selected, with properties as outlined in Table 1. Dow Corning donated the Z-6032 for this
project. The fine ash was in turn coated with the silane, using the procedure given in Table 2.
Table 1. Typical Properties of Dow Corning Z-6032 Silane
Functionality vinylbenzyl-amine-methoxy
Percent Solids 40
Solvent Methanol
Specific Gravity at 25°C 0.900
Flash Point, closed cup, °C 13
Viscosity, at 25°C, cSt 2
Suitable diluents alcohols, water
Shelf life (from date of shipment), months 6
Table 2. Silane Coating Procedure
Step Activity
Silane amount = 0.5 weight percent of ash
Silane dilution: add 100 times by weight distilled water
Mix the silane solution with ash for 10 minutes
Oven dry the slurry
Crush the coated ash powder through a 100 mesh screen
Commercial Calcium Carbonate Filler
A commercial CaCO
3
filler commonly used with polymers, Gama-Sperse CS-11, was acquired
from the Georgia Marble Company. This filler has been precoated with 1% stearate by the
manufacturer and no additional coupling agents were added to the calcium carbonate in this
study.
Polymer and Filler Mixing
Polypropylene, low density polyethylene, and high density polyethylene were each compounded
with the fine ash fraction and the commercial calcium carbonate filler. Each polymer was
compounded with ash and then compounded with calcium carbonate at concentrations of 0, 10,

Vol. 2. No. 1 Processed Low NO
x
Fly Ash as a Filler in Plastics 15
20, 40 and 80 parts per hundred parts of resin (phr). Each of the batches were mixed for 30
minutes in a Brabender Plasti-Corder torque-rheometer at 50 RPM. The mixing temperatures
were 250°C, 190°C and 200°C for polypropylene, low density polyethylene, and high density
polyethylene respectively.
Injection Molding Test
Injection molding is one of the primary forming processes used by the plastic industry to produce
various products. In this research, an Arburg 221-75-350 injection molding machine with a four-
cavity standard tensile specimen mold was used for the forming of the test specimens. This
machine is capable of providing 35 tons of clamping force and 7.5 tons of injection force. The
multi-cavity mold is jacketed with water being used for the heating or cooling of the mold. The
water temperature was in turn controlled by a Model TDW-INX conditioner, manufactured by
Application Engineering Corporation. If a polymer and filler mixture proved to be injection
moldable, ten tensile specimens were produced from each batch for mechanical testing.
Mechanical Testing
The modules of elasticity, elongation, yield and ultimate strengths of the specimens produced by
injection molding were determined using an Instron testing system following the ASTM standard
D638. If the elongation of a specimen was less than 40%, the elongation was measured by an
extensometer automatically. If the elongation of a specimen was greater than 40%, the
elongation was measured manually.
Fracture Surface Examinations
Observations were made with the assistance of SEM on the fracture surfaces of the broken
tensile specimens to examine the bonding between the polymers and the fillers.
Demonstration of Commercial Manufacturing
Arrangements were made with a local plastics firm that would allow for the injection molding of
various commercial products using the compounds produced. These compounds were in-turn
granulated down to a size that would flow freely from the feed hopper through the feed chute and
into the barrel of a commercial injection molding machine.
The three polymers used in this project were compounded with the fine fraction of the clean AEP
ash. The resulting three compounds were used to produce two different automotive parts, a trim
clip being used by Chrysler and a component to support an under the hood wiring harness used
by General Motors. The trim clip was chosen as a result of the symmetrical cavity layout and
because the major surfaces were parallel and perpendicular to the runner. In addition the GM part
contained large radii and smooth surfaces that would provide a good indication of the surface
quality that could be expected from compounds containing fly ash.

16 X. Huang, J. Y. Hwang, and J. M. Gillis Vol.2, No.1
Results and Discussion
Beneficiation
The chemical compositions and LOIs of the AEP fly ash before and after the beneficiation are
compared in Table 3. This table shows that the LOI of the AEP fly ash has been reduced from
23.3% to 1.2%, an indication of the effectiveness of the MTU's beneficiation process in removal
of residual carbon. As indicated in the table concentrations of the components other than carbon
have increased considerably as a result of the large amount carbon removed using the MTU
process. However, it should be noted that Fe
2
O
3
had not increased as much, which is due to the
removal of magnetic particles during the magnetic separation phase of the process.
Table 3. Chemical compositions of as-received and clean AEP fly ash
Components
As
-
Received AEP Fly Ash, %
Clean AEP Fly Ash, %
SiO
2
44
58.25
Al
2
O
3
22.35
28.57
Fe
2
O
3
5.29
5.32
MgO
0.86
1.06
CaO
0.76
0.9
Na
2
O
0.32
0.43
K
2
O
2
.35
2.98
TiO
2
1.11
1.21
P
2
O
5
0.03
0.28
MnO
0.01
0.02
Cr
2
O
3
0.017
0.015
Ba, ppm
1223
1511
Sr, ppm
978
1129
Zr, ppm
194
278
Y, ppm
63
82
LOI, %
23.3
1.2
Sum, %
100.75
100.67
Classification
Table 4 presents the air classification results of a few tests. As indicated test #10 resulted in the
most favorable separation with a 16.7% yield and a mean particle size of 4.13 microns. In turn
the operating parameters associated with this test were used to produce more than 3 kg of fine
ash. Table 5 shows two particle size distribution analyses of the samples taken from the bottom
and top of the 3 kg batch. The two analyses results are very close and show a relatively narrower

Vol. 2. No. 1 Processed Low NO
x
Fly Ash as a Filler in Plastics 17
size distribution of the fine ash. The mean particle sizes of the bottom and top samples are 3.96
and 4.19 microns respectively.
Table 4. Air classification results
Test No. Coarse Fraction Fine Fraction
Mean Size(µ)
Yield %
Mean Size(µ)
Yield %
4
28.11
95.4
3.46
4.6
5
35.12
94.6
2.95
5.4
6
33.10
92.2
3.13
7.8
7
39.59
86.1
4.25
13.9
8
36.20
97.9
2.61
2.1
9
29.04
99.3
2.71
0.7
10
38.27
83.3
4.13
16.7
11
37.69
82.3
4.65
17.7
12
37.33
88.9
21.18
11.1
Table 5. Particle size distribution of fine clean AEP ash
Bottom Sample Top Sample
Particle Size
Microns
Cumulative, % Volume, % Cumulative, % Volume, %
22
100.0
0.0
100.0
0.0
16
100.0
0.8
100.0
1.6
11
99.2
5.1
98.4
6.1
7.8
94.2
13.8
92.4
15.3
5.5
80.4
21.0
77.1
22.1
3.9
59.4
24.0
55.0
22.3
2.8
35.4
19.9
32.7
18.2
1.9
15.4
8.3
14.5
7.8
1.4
7.1
5.2
6.7
4.9
0.9
1.9
1
.9
1.8
1.8
Characterization
The particle shape associated with the fine fraction of the clean AEP ash is shown in Figure 1.
They are all spherical except a very few irregular shaped impurities. The particle size distribution
has been given in Table 5. The mean particle size, loose and tap densities, brightness, pH, and oil
absorption of this ash are presented in Table 6. Table 7 shows the characterization of a
commercial calcium carbonate filler and a commercial alumino-silicate filler. Table 8 gives the
particle size distribution information of the two fillers. Figure 2 shows the alumino-silicate

18 X. Huang, J. Y. Hwang, and J. M. Gillis Vol.2, No.1
filler's shape. In comparison with the commercial fillers, the fly ash filler has similar mean
particle size, narrower size distribution, a reduced variation in the loose and tap densities, and
similar oil absorption to that of alumino-silicate filler. The pH of the fly ash filler also falls
between the two commercial fillers. The major differences are the lower brightness and spherical
shape of the fly ash filler. While the lower brightness of the ash may slightly reduce the potential
spectrum of applications the spherical shape of the ash particle could improve the structural
characteristics of polymers compounded with ash resulting in a very broad spectrum of
industrial or "under the hood" applications where brightness is not a factor.
Figure 1. SEM micrograph of the fine fraction of the clean AEP ash
Figure 2. Alumino-silicate filler’s shape
Table 6. Characteristics of fine clean AEP ash as a plastic filler

Vol. 2. No. 1 Processed Low NO
x
Fly Ash as a Filler in Plastics 19
Properties
AEP
-
C
-
4M
Mean particle size, microns
4.13
Loose density, g/cc
0.804
Tap density, g/cc
0.874
Brightness
24.2
PH
6.6
Oil absorption
30
Table 7. Characteristics of Commercial Calcium Carbonate and Alumino-Silicate Fillers
Properties
Calcium carbonate filler
Alumino
-
silicate filler
Mean particle size(
µ
)
3.0
4.8
Loose density, g/cc
0.56
0.38
Tap density, g/cc
n/a
0.72
Brightness
94
79
-
82
PH
9.5
3.5
-
5.0
Oil absorption
16
30
-
35
Table 8. Particle Size Distributions of Calcium Carbonate and Alumino-Silicate Fillers
Gama
-
Sperse CS
-
11
ASP 400P
Particle Size
(µ)
Cumulative, %
Volume, %
Cumulative, %
Volume, %
22
100.0
0.0
100.0
6
16
100.0
4.5
94
7
11
95.5
9.5
87
10
7.8
86.0
13.5
77
21
5
.5
72.5
15.0
56
14
3.9
57.5
17.5
42
12
2.8
40.0
12.0
30
10
1.9
28.0
6.0
20
6
1.4
22.0
7.5
14
7
0.9
14.5
14.5
7
7

20 X. Huang, J. Y. Hwang, and J. M. Gillis Vol.2, No.1
Brightness Improvement Test
It has been established in our studies that TiO
2
and CaCO
3
crystals formed by very slow
precipitation are transparent and have tendency not to nucleate on the fly ash surfaces. Figure 3
is an example of the CaCO
3
precipitation coating. The cubic particles are CaCO
3
crystals and the
spheres are fly ash. Both the TiO
2
and CaCO
3
coating tests have not been able to improve the
brightness of fly ash. While the precipitated ZnO/ZnO(OH)
2
, as indicated in the SEM image
(Figure 4), surrounds the entire fly ash surfaces with the intent to nucleate on the surface. Yet the
brightness of fly ash has not been improved. The precipitation of pure ZnO/Zn(OH)
2
without fly
ash as nuclei was also conducted and resulted in a very white surface. One possible reason for
the large brightness difference would possibly be attributed to the contamination from the
various fly ash impurities leaching out and affecting the reaction. Another possible reason could
be that the coating was too thin.
In an attempt to identify the problem a multilayer coating was tried. The resulting fly ash
particles had grown from an initial size of about twenty microns to a few hundred microns with
additional coatings, yet the brightness showed no improvement. A comparison test was also
made using a steel stirrer and a polymer coated magnetic bar stirring the pure ZnO precipitation.
The ZnO precipitation particles using a magnetic bar as a stirrer were brighter than that using a
steel stirrer, which indicated iron contamination from the steel. A leaching test, adding different
amount of HCl in fly ash slurry resulted a yellowish solutions. ICP analyses of these solutions
revealed that many elements are leachable from fly ash when the fly ash is slurred in an acid
solution. Table 9 shows the ICP analysis results. The current pH of the coating slurry is about 6.
We also found that a longer settling time resulted in a darker appearance. These results indicate
that the elements being leached out from fly ash during a coating test caused contamination,
resulting in an off-white color.
Figure 3. SEM micrograph of CaCO
3
precipitation coating on fly ash

Vol. 2. No. 1 Processed Low NO
x
Fly Ash as a Filler in Plastics 21
Figure 4. SEM micrograph of ZnO/ZnO(OH)
2
precipitation coating on fly ash
Table 9. Chemical composition of the solution after fly ash leaching
Leaching Test Results
Content in Leaching Solution, ppm
Element
X1FLY
X2FLY
X3FLY
Si
66.39
65.2
66.9
Mg
23.74
28.23
25.44
Mn
0.7236
0.7432
0.7566
Pb
1.206
1.201
1.233
Ba
8.077
8.338
8.841
K
32.79
35.05
37.04
Na
6.458
6.831
7.83
Ni
0.7788
0.7787
0.896
Al
273.9
285.6
288.6
Ca
88.54
95.32
89.07
Fe
84.79
91.86
86.51
Zn
3.875
3.867
2.046
Cu
1.419
1.522
1.45
P
10
.3
10.27
10.63

22 X. Huang, J. Y. Hwang, and J. M. Gillis Vol.2, No.1
Injection Molding Tests
The addition of a filler to a polymer increases the viscosity of the resulting compound when the
polymer is melted by the addition of heat. This increase in viscosity decreases the polymers
moldability. If the addition of filler is over a certain level, the compound may become so viscous
that it cannot be injection-molded. In some applications, higher filler loading is required to
achieve the targeted properties. In turn it would be desirable to have a filler that would be
capable of higher loading for wider applications. In this study, the resulting compounds were
injection-molded at the conditions of intentionally lower temperature and lower pressure. If the
polymer compounds could not be injected, the injection pressure was gradually increased until
the compound could be injected fully into the mold. If the maximum pressure could not inject the
compound, the mold temperature was increased gradually without surpassing the upper limit of
the suggested injection temperature for the polymer. Table 10, 11 and 12 list the injection
molding parameters for the polypropylene, low density polyethylene, and high density
polyethylene compounds as well as the various concentrations of fine AEP ash and the
commercial calcium carbonate fillers used.
Filler levels, using either AEP ash or calcium carbonate, at or below 80 phr in polypropylene did
not result in any difficulties in the injection molding of the compounds. Each was injection-
molded under the conditions listed in Table 10.
The addition of fillers in the low density polyethylene decreased the moldability of the
compound more significantly. The injection pressure had to be increased to overcome the
increase in viscosity as the filler content increased. The low density polyethylene with 40 phr fly
ash required 700 psi injection pressure, while the same polymer with 40 phr calcium carbonate
filler required 900 psi pressure, as shown in Table 11. When the loading level increased to 80
phr, the low density polyethylene with fly ash was still moldable but the same polymer with
calcium carbonate filler was not even though the injection pressure had been increased to the
maximum 2200 psi.
The high density polyethylene proved more difficult to inject because of its higher viscosity. The
injection pressure had to be greater than 1200 psi in order to fully fill the mold cavity even for
the pure polymer. The addition of fly ash filler in the levels below or equal 40 phr did not cause
any injection problems, but the addition of calcium carbonate filler in the amount of 40 phr
introduced a significant increase in viscosity. The injection pressure had to be adjusted to the
maximum of 2200 psi, the mold temperature was raised from 100°F to 140°F, and the injection
temperatures had to be increased to the highest suggested temperatures for this polymer, but this
compound still could not be injected into the cavity fully.
These injection molding tests indicated that polypropylene, low and high density polyethylenes
compounded with fine AEP ash have similar or better moldability than their counterparts when
compounded with a commercial calcium carbonate filler.

Vol. 2. No. 1 Processed Low NO
x
Fly Ash as a Filler in Plastics 23
Table 10. Injection Molding Test of Polypropylene with Fillers
Fillers
Filler
Content
phr
Zone I
Temp.
°C
Zone II
Temp.
°C
Zone III
Temp.
°C
Zone IV
Temp.
°C
Injection
Velocity
Dial*
Injection
Pressure
Psi
Holding
Pressure
psi
Mold
Temp.
EF
None 0 210 220 210 200 5.0 400 100 100
Fly Ash
CaCO
3
10
10
210
210
220
220
210
210
200
200
5.0
5.0
400
400
100
100
100
100
Fly Ash
CaCO
3
20
20
210
210
220
220
210
210
200
200
5.0
5.0
400
400
100
100
100
100
Fly Ash
CaCO
3
40
40
210
210
220
220
210
210
200
200
5.0
5.0
400
400
100
100
100
100
Fly Ash
CaCO
3
80
80
210
210
220
220
210
210
200
200
5.0
5.0
400
400
100
100
100
100
* Dial 5.0 is the maximum injection velocity of the machine.
Table 11.Injection molding test of low density polyethylene with fillers
Fillers
Filler
Content
phr
Zone I
Temp.
°C
Zone II
Temp.
°C
Zone III
Temp.
°C
Zone IV
Temp.
°C
Injection
Velocity
Dial*
Injection
Pressure
psi
Holding
Pressure
psi
Mold
Temp.
EF
None 0 210 220 210 200 5.0 500 100 100
Fly Ash
CaCO
3
10
10
210
210
220
220
210
210
200
200
5.0
5.0
500
500
100
100
100
100
Fly Ash
CaCO
3
20
20
220
220
230
230
220
220
210
210
5.0
5.0
700
700
100
100
100
100
Fly Ash
CaCO
3
40
40
220
220
230
230
220
220
210
210
5.0
5.0
700
900
100
100
100
100
Fly Ash
CaCO
3
*
80
80
220
240
230
250
220
240
210
230
5.0
5.0
900
2200
150
150
100
120
* This material can't be injected even at the maximum pressure 2200 psi.
Table 12. Injection molding test of high density polyethylene with fillers
Fillers
Filler
Content
phr
Zone I
Temp.
°C
Zone II
Temp.
°C
Zone III
Temp.
°C
Zone IV
Temp.
°C
Injection
Velocity
Dial*
Injection
Pressure
psi
Holding
Pressure
psi
Mold
Temp.
EF
None 0 260 260 250 250 5.0 1200 100 100
Fly Ash
CaCO
3
10
10
260
260
260
260
250
250
250
250
5.0
5.0
1200
1200
100
100
100
100
Fly Ash
CaCO
3
20
20
260
260
260
260
250
250
250
250
5.0
5.0
1200
1200
100
100
100
100
Fly Ash
CaCO
3
*
40
40
260
290
260
290
250
270
250
270
5.0
5.0
1200
2200
100
100
100
140
* This material can't be injected even at the maximum pressure 2200 psi.

24 X. Huang, J. Y. Hwang, and J. M. Gillis Vol.2, No.1
Mechanical Properties
The ultimate tensile strength, yield strength, elongation and Young's modules are the most
important mechanical properties for polymer materials. Filler content, filler particle size, size
distribution, shape, mixing quality, and bonding between filler and polymer matrix all affect the
mechanical properties. As a rule, higher filler content leads to higher yield strength and an
increase in the Young's modules while a lower elongation would be expected because the filler
particles restrict deformation of the polymers. The fillers also affect the ultimate tensile strength
(UTS) in two ways. First, the filler particles cause stress concentration and initiate cracks, lowing
UTS. Second, if the particles have the proper shape and a strong bonding between the particles
and the polymer matrix, the particles may serve to reinforce the polymer, resulting in higher
UTS. With regard to size the larger particles usually reduce the UTS and elongation.
Table 13 represents the mechanical properties of polypropylene with fly ash and calcium
carbonate fillers. This table indicates that the yield strength and Young's modules increase and
UTS and elongation decrease as the filler content increases, except when calcium carbonate
content is over 40 phr. At this level the calcium carbonate filler begins to decrease the yield
strength as well as the Young's modules. With lower calcium carbonate contents of 10 and 20
phr, the polypropylene compound shows higher UTS than those of the polymers with fly ash
filler. When the calcium carbonate content exceeds 40 phr, the UTS of the compound is lower
than that of the compounds with ash as the filler. The yield strength and Young's modules of the
polypropylene with an ash filler are higher than those of the polypropylene with calcium
carbonate filler, but the elongation is lower than that of the counterpart. In general, ash filler can
replace calcium carbonate filler to reach the equivalent mechanical properties when the filler
content is less than or equal to 20 phr.
Table 14 shows the results of the mechanical tests for the low density polyethylene with ash and
calcium carbonate fillers. The low density polyethylene with ash filler have better mechanical
properties than those of the same polymer with calcium carbonate filler. This superiority is more
obvious at the higher loading level of 40 phr.
Table 15 gives the mechanical properties for the high density polyethylene with ash and calcium
carbonate fillers. The noticeable phenomenon is that the UTS increases when filler content
reaches 40 phr for the polymer with ash filler. This indicates that the ash filler may reinforce the
polymer matrix. Over all, the high density polyethylene with an ash filler has better strengths and
Young's modules than those of the polymer with calcium carbonate filler, but the elongation is
not as good as its counterpart.

Vol. 2. No. 1 Processed Low NO
x
Fly Ash as a Filler in Plastics 25
Table 13. Mechanical properties of polypropylene with fillers
Fillers
Filler Content
phr
Ultimate
Tensile
Strength, psi
Yield Strength
psi
Elongation
%
Young's
Modules, ksi
None 0 6666 1728 650 185
Fly Ash
CaCO
3
10
10
4724
5024
2199
1880
630
650
189
164
Fly Ash
CaCO
3
20
20
4378
4928
2340
2114
467
600
211
178
Fly Ash
CaCO
3
40
40
4267
3850
2416
1738
32
367
237
125
Fly Ash
CaCO
3
80
80
3953
2900
2474
1480
1.3
41.7
314
217
Table 14. Mechanical properties of low density polyethylene with fillers
Fillers
Filler Content
phr
Ultimate Tensile
Strength, psi
Yield Strength
psi
Elongation
%
Young's
Modules, ksi
None 0 3336 485 467 27.5
Fly Ash
CaCO
3
10
10
3463
3255
557
545
467
467
36.0
33.4
Fly Ash
CaCO
3
20
20
2635
2563
560
573
462
483
39.4
33.6
Fly Ash
CaCO
3
40
40
2449
1905
738
574
450
442
47.3
33.6
Fly Ash
CaCO
3
80
80
2377
-
888
-
46.6
-
90.5
-
Table 15. Mechanical properties of high density polyethylene with fillers
Fillers
Filler Content
phr
Ultimate Tensile
Strength, psi
Yield
Strength psi
Elongation
%
Young's
Modules, ksi
None 0 5040 1016 60 79.4
Fly Ash
CaCO
3
10
10
4843
3807
1192
940
45
83
73.2
45.2
Fly Ash
CaCO
3
20
20
4823
3698
1160
1089
50
84
81.6
56.6
Fly Ash
CaCO
3
40
40
5219
-
1279
-
28
-
96.4
-

26 X. Huang, J. Y. Hwang, and J. M. Gillis Vol.2, No.1
Fracture Surface Examinations
SEM images indicate that in general, fillers have been homogeneously mixed with the polymers.
Figure 5 to 10 show the fracture surfaces of the polypropylene, low density polyethylene and
high density polyethylene with 40 phr of ash filler and calcium carbonate filler respectively.
Good bonding between the ash filler and the three polymers can be seen in Figure 5, 7, and 9.
Figure 6, 8 and 10 give examples of calcium carbonate filler and polymer bonding. It appears
that fly ash, along with the silane coupling agent, has better bonding with the three polymers than
the calcium carbonate does.
Figure 5. SEM micrograph of the fracture surface of ash fillers in polypropylene
Figure 6. SEM micrograph of the fracture surface of
CaCO
3
fillers in polypropylene

Vol. 2. No. 1 Processed Low NO
x
Fly Ash as a Filler in Plastics 27
Figure 7. SEM micrograph of the fracture surface of ash
fillers in low density polyethylene
Figure 8. SEM micrograph of the fracture surface of CaCO
3
fillers in low density polyethylene

28 X. Huang, J. Y. Hwang, and J. M. Gillis Vol.2, No.1
Figure 9. SEM micrograph of the fracture surface of ash fillers
in high density polyethylene
Figure 10. SEM micrograph of the fracture surface of CaCO
3
fillers in high density polyethylene

Vol. 2. No. 1 Processed Low NO
x
Fly Ash as a Filler in Plastics 29
Demonstration of Commercial Manufacturing
A VanDorn, Model #75-RS-4F, injection machine was used to process the ash filled compounds.
With VanDorn being a large and well established producer of injection molding machines, the
use of this machine would provide a very good representation of the typical injection molding
machine used today. Injection of the trim clip was carried out first because it was a much smaller
component and in-turn would not be as difficult as to clean up should the experimental materials
prove difficult to inject. Yet all went smoothly, material flowed well, cavities were filled
uniformly, lines were well defined and parting of the product was realized without the addition
of a mold release. The operators, as well as the owner of the business went on to say that they
could not distinguish between the operation of the machine using the experimental compounds
and the commercial materials typically used to produce the trim clips. Figure 11 shows the parts
produced from one of the polymers with ash filler. The injection of the GM wiring harness
support proceeded just as smoothly. Though the shape was of a nature that considerably more
resistance would be encountered, the material readily filled the cavities. Adjustments were made
to the injection pressure, holding pressure and back pressure yet the new settings were typical of
what would be expected given the nature of the die and not a result of the variation in the
compound being injected. Figure 12 presents the GM wiring harness supports produced from one
of the ash filled polymers.
Figure 11. Parts produced from the polymer with ash filler

30 X. Huang, J. Y. Hwang, and J. M. Gillis Vol.2, No.1
Figure 12. GM wiring harness supports produced from one of ash filled polymers
With the mechanical testing of the tests specimens, produced in the lab, serving to establish the
physical properties of the compounds, the primary concern with regard to quality of the products
produced was the resulting surface finish. Those materials containing 10 phr displayed very
smooth somewhat glossy surfaces. Injection of those compounds containing 20 phr produced
parts that had a somewhat opaque finish, yet it was still a very smooth surface. The parts coming
out of the mold as the compounds containing 40 phr were feed to the barrel displayed an uneven
surface that was dull in nature and revealed flow patterns in many cases. An operator was quick
to point out that this was not at all uncommon with compounds containing a considerable amount
of filler. He even produced parts that they regularly manufacture for comparison, which, from
the surface, displayed the same characteristics with regard to the surface quality.
Overall the injection of the ash filled compounds went very smoothly. There were no major
problems encountered and the resulting products indicated that a quality finish could be expected
when using these materials in the injection molding of commercial products. Which polymers
would be best suited for compounding with ash would still need additional study, yet as indicated
by this preliminary study, their use as a filler in both high and low density polyethylene as well
as polypropylene would certainly be expected to yield considerable benefit.
Conclusions
AEP as-received low NO
x
ash can be processed to produce fine clean powders with the
characters suitable for plastic filler application. The particle size distribution is narrower than
that of two comparable commercial fillers. However, the brightness is about 24, much lower than
that of commercial calcium carbonate filler and alumino-silicate filler, which limits its uses to
darker color applications. The unique spherical shape can be an advantage over most existing
commercial fillers.

Vol. 2. No. 1 Processed Low NO
x
Fly Ash as a Filler in Plastics 31
The polypropylene, low density and high density polyethylene compounds with fine clean ash
filler have equivalent or better moldability for producing articles in comparison with the
commercial calcium carbonate filler, Gama-Sperse CS-11.
In general, the polypropylene and high density polyethylene with fine clean ash filler show
equivalent or better strengths and Young's modules, but the elongation is not as good as those of
the same polymers with the commercial calcium carbonate filler, Gama-Sperse CS-11. The low
density polyethylene with the fine clean ash filler shows superiority over the same polymer with
calcium carbonate filler in all measured mechanical properties at various loading levels.
The ash filler coated with Dow Corning Z-6032 silane appear to offer very good bonding with
the polypropylene as well as the low density and high density polyethylene matrixes.
The polymers with ash filler can be used to produce commercial automotive parts with no
difference in injection moldability, dimension accuracy and surface quality in comparison with
the commercially filled polymer compounds.
Acknowledgement
Funding for this project has been provided by a grant from the U.S. Department of Energy under
contract PRDA No. DE-RA21-93MC30056.
References
1. C. Plowman and N.B. Shaw, "Use of Pulverized Fuel Ash as a Filler in Plastics,"
AshTech'84 - Conference Proceedings, London, England: Central Electricity Generating
Board, 1984, pp.663-670; Conference: 2. International Conference on Ash Technology
and Marketing, London, UK, 17 Sept. 1984.
2. G. J. Jablonshi, "Fly Ash Utilization as an Extender in Plastics and Paints," Proceedings:
Eighth International Ash Utilization Symposium: Volume 2; Oct. 1987, pp. 38.1-38.15;
Availability: NTIS, PC A20-Research Reports Center, Box 50490, Palo Alto, CA.
3. X. Huang, J.Y. Hwang and R. Tieder, "Clean Fly Ash as Fillers in Plastics," Proceedings:
11th International Symposium on Use and Management of Coal Combustion By-Products
(CCBs), Volume 1, January 1995, pp33-1.
4. Final Report - Utilization of Low NO
x
Coal Combustion By-Products. Houghton, Mich.:
Institute of Materials Processing at Michigan Technological University, funded by U.S.
Department of Energy, PRDA No. DE-RA21-93MC30056, 1996.