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Journal of Minerals & Materials Characterization & Engineering, Vol. 8, No.3, pp 237-248, 2009
jmmce.org Printed in the USA. All rights reserved
Effect of Particle Size and Concentration of Flyash on Properties of Polyester
Thermoplastic Elastomer Composites
, V.A. Bambole
, S.T. Mhaske
, P.A. Mahanwar
1. Department Polymer Engineering & Technology
2. Department of Applied Physics
Institute of Chemical Technology, Matunga, Mumbai-400019, India
The performance of filled polymers is generally determined on the basis of the interface
attraction of filler and polymers. Particulate filled polymer composites are becoming attractive
because of their wide applications and low cost. In this study the effects of flyash with three
varying particle size and filler concentrations (viz. 5 to 40 weight %) on the mechanical,
thermal, electrical, rheological and morphological properties of polyester thermoplastic
) was investigated. Composites of polyester thermoplastic elastomer with
varying concentrations of flyash were prepared by twin screw extrusion. Mechanical properties
such as flexural strength and modulus increases with filler loading, where as tensile strength is
found to be decrease with increase in flyash loading. Dielectric strength of composites also
increases with flyash loading. Morphological studies revealed that there is good dispersion of
filler in the polymer matrix. Thermal properties were found to be improved with flyash addition.
Further, it was observed that the mechanical (flexural), thermal as well as electrical properties
of composites improved with decrease in particle size of filler.
Key Words: Particulate composites, thermoplastic elastomers, hytrel, flyash.
Fillers are used along with various commodity as well as engineering polymers to improve the
properties  and reduce the cost. Incorporating inorganic mineral fillers into plastic resin
improves various physical properties of the materials such as mechanical strength, modulus etc.
In general the mechanical properties  of particulate filled polymer composites depend strongly
238 M.S. Sreekanth, V.A. Bambole, S.T. Mhaske, P.A. Mahanwar Vol.8, No.3
on size, shape and distribution of filler particles in the polymer matrix and extend of interfacial
adhesion between filler and matrix.
Polyester thermoplastic elastomer (Hytrel
) is an important engineering thermoplastic elastomer,
combines the physical properties of elastomer with the excellent processing characteristics of
thermoplastic. Polyester thermoplastic elastomer  consisting of poly(butylene terephthalate)
(PBT), as hard segments and poly(tetramethylene ether glycol terephthalate) as soft segments.
The basic structure of polyester thermoplastic elastomer
is shown in scheme 1. Polyester
thermoplastic elastomer shows outstanding mechanical properties [4, 5] at temperatures up to
130°C coupled with very good low temperature flexibility. It shows good resistance to tear,
impact, abrasion and creep and excellent oil, hydraulic fluids and grease resistance. In order to
improve thermal, mechanical and electrical properties of polyester thermoplastic elastomer,
particulate fillers such as aluminatrihydrate, montmorillonite, clays, talc, mica, silica, flyash,
wollastonite, kaolin etc are incorporated . Flyash had been one of the widely studied filler due
to its unique set of properties [2, 7].
Scheme 1: Structure of Hytrel
In this investigation we studied the effect of flyash with three varying particle sizes and
concentration on properties Hytrel
. Recently many investigators studied the effect of flyash on
properties of thermoplastics and thermosets [8-13]. Flyash is the finely divided mineral residue
resulting from the burning of pulverised coal in thermal power stations. Flyash has been used in
industry because of such advantages as low density, low cost, strong filling ability, smooth
spherical surface, small and well distributed internal stress in the products and good
processability of the filled materials. Flyash provides cost effective improvements in the critical
properties for a wide range of polymer composites. Polyester thermoplastic elastomer composites
are mainly used in a wide variety of automotive parts such as gears and sprockets . It is also
used in high strength industrial hoses and tubing [14, 15] and also in vibration damping
The matrix polyester thermoplastic elastomer with 1.22 g/cc density was procured from Rupal
Plastics Ltd (Mumbai, India). The filler flyash of three different particle sizes (25-45µm, 90-
105µm & 150-180µm) was obtained from Pozocrete Minerals (Mumbai, India). The detail list of
materials used is given in Table 1 below.
Vol.8, No.3 Effect of Particle Size and Concentration of Flyash 239
Table 1. Materials used.
Polyester TPE Polymer matrix Hytrel 6356
M/S Rupal Plastics
Ltd, Mumbai, India
The matrix and filler was predried prior to the compounding. Polyester thermoplastic elastomer
and flyash were dried at 80
C for 6 hours in an air circulated oven and then both of them are dry
blended to a uniform physical dispersion of polymer and filler. The following composition of
filler (viz. 5 to 40 weights %) shown in the table was mixed and extruded in a co-rotating twin
extruder (APV Baker Ltd. England, Model: MP19PC). The L/D ratio of the screw is 25:1.
Mixing speed of 60 rpm was maintained for all the compositions. The extrudates from the die
were quenched in a tank at 20-25
C and then palletized. For the melt blending the temperature
profile of the extrusion were as follows, Zone 1: (120
C), Zone 2: (180
C), Zone 3: (210
Zone 4: (225
C) and Die (240
C). The extrudates were pelletised in Boolani’s pelletizing
machine. The speed of the pelletizer was maintained between the ranges of 2-3 rpm.
2.3. Injection Molding
The granules of the extrudates were predried in an air circulated oven at 80
C for 8 hours and
injection molded in a microprocessor based Boolani’s injection moulding machine fitted with a
master mould containing the cavity for tensile strength, flexural and impact specimens. After its
ejection from the mould, specimens were cooled in ice–water. Processing parameters are Zone 1:
C), Zone 2: (225
C), Zone 3: (245
3.1. Mechanical Properties
Tensile strength as per ASTM D638 M91 was evaluated using Universal Testing Machine
LR50K from Lloyd instruments Ltd.,U.K at a crosshead speed of 50mm/min. Flexural properties
according to ASTM D790 were tested using LR 50K from Lloyd instruments Ltd., U.K. Izod
impact test were carried out using an Avery Denison impact tester (ASTM D256-92). A 5.0 J
240 M.S. Sreekanth, V.A. Bambole, S.T. Mhaske, P.A. Mahanwar Vol.8, No.3
energy hammer was used and the striking velocity was 3.46 m/sec. For Izod impact test
specimens the notch was cut using a motorized notch- cutting machine (Rayran U.K). The
impact strength is expressed in J/m
3.2. Electrical Properties
The Dielectric Strength, according to ASTM D 149, was measured using Zaran Instruments
(India) with a 2 mm thick composite disc. The voltage was increased slowly and the voltage at
which the current penetrated the sample was noted. The configurations of the instruments were:
input: 240 V, 50 Hz, 1 PH; output: 0–50 kV; capacity: 100 mA; rating: 15 min.
3.3. Thermal Properties
DSC is used to study the thermal properties of the composites. DSC measurements were
performed using TA Q100 analyzer (TA Instruments, U.S.). The weight of sample was between
6 to 9 mg in a standard aluminium pan.
3.4. Rheological Properties
The melt rheology of the polymer and the composites were studied using a rotational rheometer
(Haake RT 10, Germany), employing a parallel plate assembly, diameter 35 mm, at 245°C. The
samples were predried before analysis. The shear rate range was varied from 1 – 100 s
viscosity, η (Pa s) as a function of shear rate, γ (1/s) was recorded.
3.5. Morphological Properties
SEM is used to study the morphology of the composites. SEM studies of fractured impact
samples were carried out on a Cameca SU-SEM probe. The accelerated voltage used was 15 kV.
Samples were sputter-coated with gold to increase surface conductivity. The digitized images
4. RESULTS AND DISCUSSION
4.1. Tensile Properties
Fig. 1 shows the variation of tensile strength as a function of flyash in wt%. Tensile strength of
composites was found to decreases with the addition of filler. The rate of decrease of tensile
strength is higher in the case of larger particle size of flyash. It is observed that flyash with
smaller particles showed higher value of tensile strength. The percentage elongation at break is
also decreases  on addition on filler as shown in Fig. 2. This is due to the interference of
filler in the mobility or deformability of the matrix. This interference is created through the
physical interaction and immobilisation of the polymer matrix by the presence of mechanical
restraints, there by reducing the elongation at break. Flyash with smaller particle size show
higher values of elongation at break.
Vol.8, No.3 Effect of Particle Size and Concentration of Flyash 241
Figure 1. Variation of Tensile Strength of Polyester Thermoplastic Elastomer with Filler
Figure 2. Variation of Elongation at break of Polyester Thermoplastic Elastomer with Filler
4.2. Flexural Properties
The variation of flexural strength with filler addition is shown in Fig. 3. The flexural strength of
composites increases with increase in concentration of flyash. Composites with flyash at smaller
particle size show higher value of flexural strength. The increment in flexural strength is due to
242 M.S. Sreekanth, V.A. Bambole, S.T. Mhaske, P.A. Mahanwar Vol.8, No.3
the better increased surface area of filler in the matrix. It is worth pointing out that the total area
for deformation stress also has an important role to play. Flexural modulus  as shown in Fig.
4 is found to increase with increase in concentration of flyash. The rate of increase of flexural
modulus is higher in the case of smaller particle size of flyash. Composites with flyash at smaller
particle size show consistant and better values of flexural properties.
Figure 3. Variation of Flexural strength of Polyester Thermoplastic Elastomer with Filler
Figure 4. Variation of Flexural modulus of Polyester Thermoplastic Elastomer with Filler
Vol.8, No.3 Effect of Particle Size and Concentration of Flyash 243
4.3. Impact Strength
Fig. 5 illustrates the variation of impact strength with filler loading. It is clear from the figure
that the impact strength decreases with filler addition. This is mainly due to the reduction of
elasticity  of material due to filler addition and there by reducing the deformability of matrix.
An increase in concentration of filler reduces the ability of matrix to absorb energy and there by
reducing the toughness, so impact strength decreases. It is observed that the flyash with smaller
particle size showing higher increment of impact strength. The rate of decrease of impact
strength is higher in the case of smaller particle size of flyash.
Figure 5. Variation of Impact Strength of Polyester Thermoplastic Elastomer with Filler
4.4. Dielectric Strength
It is clear from Fig. 6 that the dielectric strength increased with the increase in filler
concentration and attained maxima. At higher filler loading the dielectric strength values
remained almost constants with the increase in filler. This trend in variation of dielectric
strength in flyash is attributed to the total surface area available from the filler as well as its
continuity. The dielectric strength is higher for smaller particle size of flyash.
244 M.S. Sreekanth, V.A. Bambole, S.T. Mhaske, P.A. Mahanwar Vol.8, No.3
Figure 6. Variation of Dielectric Strength of Polyester Thermoplastic Elastomer with Filler
4.5. Thermal Properties
The melting and the crystallisation temperature of the composites were studied by using DSC.
Fig. 7 shows the variation of melting temperature with filler addition. The polymer matrix
showed a melting temperature around 211.95 °C. Addition of filler increases the melting point of
composites up to 3 °C manifesting the fact that the addition of filler improves the thermal
stability of composites. Fig. 8 shows the variation of crystallisation temperature with filler
addition. The matrix polymer shows a crystallisation temperature around 170.05 °C. Further,
flyash acts as a nucleating agent manifesting in higher crystallisation temperature in the
composites. The crystallisation temperature is shifted right to around 8 °C with the addition of
filler from 5 to 40 wt%. The increment is due to the small and uniform crystallite size
distribution. There is no significant variation of thermal properties with particle size of filler.
4.6. Rheological Properties
Fig. 9 illustrates the variation of shear viscosity at 245
C (in Pascal sec) with filler concentration
at a shear rate at 0.1 sec
. Increase in the viscosity may be attributed to the properties of the filler
such as maximum packing fraction. The increase in viscosity  was due to the ability of fine
particles of filler particle to form a tight packing network. Rate of increase in the viscosity
depended upon the ratio (ø/ øµ), where ø = vol. fraction of the filler and øµ = Max. packing
fraction. With an increase in filler content the viscosity of the component increased. Rheological
study showed that smaller particle size of flyash giving higher value of viscosity.
Vol.8, No.3 Effect of Particle Size and Concentration of Flyash 245
Figure 7. Variation of Melting Temperature of Polyester Thermoplastic Elastomer with Filler
Figure 8. Variation of Crystallisation Temperature of Polyester Thermoplastic Elastomer with
246 M.S. Sreekanth, V.A. Bambole, S.T. Mhaske, P.A. Mahanwar Vol.8, No.3
Figure 9. Variation of Shear Viscosity at 0.1 Shear rate at 245°C with filler loading.
4.7. Morphological Properties
SEM is used to study the morphology of composites. Fig. 10 shows the SEM micrographs of
composites with 20% loadings of flyash. Morphological study shows that flyash having smooth
spherical surface having more surface area for interaction. There is a good dispersion of filler
particle in the polymer matrix. The interaction between the filler and the matrix is also good as
shown in the SEM micrograph.
Figure10. SEM micrograph of Polyester Thermoplastic Elastomer with 10% Flyash of 25-45
µm particle size.
Vol.8, No.3 Effect of Particle Size and Concentration of Flyash 247
Inorganic fillers viz. flyash added to the polymer improved its rigidity, strength, and thermal
stability, but dramatically decreased the elongation at break. There is a significant increment in
the flexural strength and modulus with an increase in the filler concentration. The impact
strength decreases with concentration of filler due to the reduction of elasticity of material due to
filler addition and there by reducing the deformability of matrix. There is a significant increase in
the dielectric strength with filler addition. Addition of flyash improved the thermal properties of
the composites due to small and uniform crystallite size distribution. Morphological studies
showed that there is a better dispersion of filler in the matrix. The mechanical properties of the
composite were found to be a function of the particle size, aspect ratio, the dispersion, the
particle orientation, the interfacial interaction between the minerals and the polymer matrix.
Spherical shaped filler, such as flyash gave significant improvement in stiffness due to better
surface area for interaction. It is concluded that composites with flyash at smaller particle size
showed significant improvement in the overall (mechanical and electrical) properties of
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