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Journal of Minerals & Materials Characterization & Engineering, Vol. 8, No.4, pp 271-282, 2009
Printed in the USA. All rights reserved
Effect of Concentration of Mica on Properties of Polyester Thermoplastic
M. S. Sreekanth
, 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
*Corresponding Author, contact: email@example.com
Phone: +91-22-24145616, Fax: +91-22-24145616
Particulate filled polymer composites are becoming attractive because of their wide applications
and low cost. In this study the effects of mica with varying concentration on the mechanical,
thermal, electrical, rheological and morphological properties of polyester thermoplastic
) was investigated. Composites of Hytrel
with varying concentrations (viz. 5
to 40 weight %) of mica were prepared by twin screw extrusion. Mechanical properties such as
flexural strength and modulus were found to increase with mica concentration, whereas tensile
strength was found to decrease at higher concentrations. Electrical and thermal properties of
composite were found to increase with filler concentration. Morphological studies revealed that
there is a good dispersion of filler in the polymer matrix at lower concentrations.
The performance of filled polymers is generally determined on the basis of the interface
attraction of filler and polymers. 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
on size, shape and distribution of filler particles in the polymer matrix and extent of interfacial
adhesion between filler and matrix.
272 M. S. Sreekanth, V. A. Bambole, S. T. Mhaske, P. A. Mahanwar
Thermoplastic elastomers  are an important class of engineering thermoplastic elastomers,
combines the physical properties of elastomers with the excellent processing characteristics of
thermoplastics. A family of novel segmented polyester thermoplastic elastomer has been
developed by du Pont under the trade-mark Hytrel
. 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
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 elastomers , particulate fillers such as alumina trihydrate, montmorillonite,
clays, talc, mica, silica, flyash, wollastonite, kaolin etc are incorporated. Flakes or platelets
represent a special class of reinforcing fillers for thermoplastics and thermosets. Mica  is one
such type of filler and is a particularly abundant mineral. Mica  had been a widely studied
filler due to its unique set of properties.
Structure of Hytrel
Recently the effect of mica on properties of thermoplastic elastomers [9-10] and engineering
thermoplastics [11-13] have been investigated extensively. Mica has an outstanding mechanical,
thermal, electrical and chemical properties rarely found in any other products. Mica  provides
cost effective improvements in the critical properties for a wide range of thermoplastic and
thermoset 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 shock damping applications In the present work
we studied the effect of mica of varying concentration  on the properties of polyester
thermoplastic elastomer. The detail list of materials used is given in Table 1.
The matrix and filler were predried prior to the compounding. Polyester thermoplastic elastomer
and mica were dried at 80
C for 6 hours in an air circulated oven and both of them are dry
blended to a uniform physical dispersion of polymer and filler. The following composition of
Vol.8, No.4 Effect of Concentration of Mica on Properties of Polyester Composites 273
filler (viz. 5 to 40 weights %) 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-
C and then pelletized. For the melt blending the temperature profile of the extrusion were as
follows: Zone 1 (120
C), Zone 2 (180
C), Zone 3 (210
C), Zone 4 (225
C) and Die (240
The extrudates of the compositions were palletized in Boolani’s pelletizing machine. The speed
of the pelletizer was maintained between the ranges of 2-3 rpm.
Table 1 Materials used
Materials used Function Grade Suppliers
M/S Rupal Plastics
Ltd, Mumbai, India
2.2. 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) and Zone 3 (245
2.3.1. Mechanical properties
Tensile strength as per ASTM D638 M91 was evaluated using universal tensile 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 tests were carried out using an Avery Denison impact tester (ASTM D256-92).
A 5.0 J 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 unit
of expression is J/m
274 M. S. Sreekanth, V. A. Bambole, S. T. Mhaske, P. A. Mahanwar
2.3.2. 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.
2.3.3. 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.
2.3.4. 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 250°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.
2.3.1. 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
3. RESULTS AND DISCUSSION
3.1. Tensile Properties
Fig. 1 shows the variation of tensile strength  as a function of mica in wt%. After a moderate
increment in the initial concentration of mica, the tensile strength decreases at higher filler
concentrations. The increment  may be due to the platy structure of the mica providing good
reinforcement. As the filler concentration increases mica platelets tend to aggregate and the
tensile strength decreases. Elongation properties as seen from Fig. 2 decreased with the addition
of filler indicating interference
by the filler in the mobility
or deformability of the matrix. This
interference is created through the physical interaction and immobilization
of the polymer matrix
by the presence of mechanical restraints. So as the filler concentration increases the elongation at
break get reduced.
Vol.8, No.4 Effect of Concentration of Mica on Properties of Polyester Composites 275
Figure 1. Variation of the Tensile Strength of Polyester Thermoplastic Elastomer with Mica
Figure 2. Variation of the Elongation at break of Polyester Thermoplastic Elastomer with Mica
276 M. S. Sreekanth, V. A. Bambole, S. T. Mhaske, P. A. Mahanwar
3.2. Flexural Properties
Fig. 3 shows the variation in flexural strength with varying concentration of mica. The flexural
strength of composites increases with increase in concentration of mica. There is a significant
increase in the flexural strength with increasing concentration of mica as shown in the figure. It
is worth pointing out that the total area for deformation stress also has an important role in
flexural properties. Flexural modulus  as shown in Fig. 4 is found to increase with increase in
concentration of mica.
Figure 3. Variation of the Flexural strength of Polyester Thermoplastic Elastomer with Mica
3.3. Impact Strength
Fig. 5 illustrates the variation of impact strength with mica 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 thereby reducing the deformability of matrix
and in turn the ductility in the skin area, so that the composite tend to form a weak structure. An
increase in concentration of filler reduces the ability of matrix to absorb energy and thereby
reducing the toughness, so impact strength decreases.
Vol.8, No.4 Effect of Concentration of Mica on Properties of Polyester Composites 277
Figure 4. Variation of the Flexural modulus of Polyester Thermoplastic Elastomer with Mica
Figure 5. Variation of the Impact Strength of Polyester Thermoplastic Elastomer with Mica
278 M. S. Sreekanth, V. A. Bambole, S. T. Mhaske, P. A. Mahanwar
3.4. Dielectric Strength
It is clear from Fig. 6 that the dielectric strength increased with the increase in mica
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 mica is attributed to the total surface area available from the filler as well as its
continuity. The dielectric strength values showed better for higher particle size of mica.
Figure 6. Variation of the Dielectric Strength of Polyester Thermoplastic Elastomer with Mica
3.5. Thermal Properties
The melting and the crystallization temperature of the composites were studied by using DSC.
Fig. 7 shows the variation of melting temperature with filler addition. The matrix polymer
showed a melting temperature around 211.95 °C. With the addition of filler the melting point of
composites increased up to 3 to 4 °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 crystallization temperature around 170.05 °C.
Further, mica acts as a nucleating agent manifesting in higher crystallization temperature in the
composites. The increment is due to the small and uniform crystallite size distribution.
Vol.8, No.4 Effect of Concentration of Mica on Properties of Polyester Composites 279
Figure 7. Variation of Melting Temperature of Polyester Thermoplastic Elastomer with Filler
Figure 8. Variation of Crystallisation Temperature of Polyester Thermoplastic Elastomer with
280 M. S. Sreekanth, V. A. Bambole, S. T. Mhaske, P. A. Mahanwar
3.6. Rheological Properties
Fig. 9 illustrates the variation of shear viscosity at 250
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 (
= vol. fraction of the filler and
µ = Max. packing
fraction. Rheological study shows that with an increase in filler content the viscosity of the
3.7. Morphological Properties
SEM is used to study the morphology of composites. Fig. 10 shows the SEM micrographs of
composites with 10% concentration of mica. Improved interaction between the filler and the
matrix is inferred at lower concentration of filler (Fig.10). However, at higher concentrations, the
interaction between the filler and the polymer gets reduced due to aggregation of the filler
particles. The SEM images further exhibits that the mica platelets are aligned parallel to each
Figure 9. Variation of Shear Viscosity at 0.1 Shear rate at 245°C of Polyester Thermoplastic
Elastomer with Mica Concentration
Vol.8, No.4 Effect of Concentration of Mica on Properties of Polyester Composites 281
Figure10. SEM micrograph of Polyester Thermoplastic Elastomer with 10% Concentration of
Inorganic fillers viz. mica 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 mica improved the thermal properties of
the composites due to small and uniform crystallite size distribution. Morphological studies
showed that there is a better interaction between filler and the matrix at lower filler concentration
and platelets are aligned parallel to each other. 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. Platy structured filler such
as mica gave significant improvement in stiffness. It is concluded that the composite showed
improved mechanical (flexural), thermal as well as electrical properties on addition of filler.
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