Journal of Minerals & Materials Characterization & Engineering, Vol. 11, No.2 pp.169-181, 201 2 Printed in the USA. All rights reserved
Mica Filled PVC Composites: Performance Enha ncement in Dielectric
and Mech anical Properties with Treated/Untreated Mica of
Different Particle Size and Different Concentration
S. P. Deshmukh and A. C. Rao
General Engineering Department,Institute of Chemical TechnologyMatunga, Mumbai
400019, India.
Polyvinyl chloride (PVC) of different grades is the second most commonly used polymer for
fabrication of electric cables and wires after polyethylene. Cables of domestic and industrial
use of various capacities are fabricated using different compounds of PVC. Mica is useful
particulate filler extensively used to enhance the performance of many polymeric materials. It
surface resistance and arc resistance improving its mechanical properties. In the present
research work mica filled PVC composites of different concentrations were prepared using
untreated and surface treated water ground mica of different particle size. Mica filled PVC
composites were compounded for various compositions and test samples were prepared
using compression moulding process. These samples were tested fo r electrical insulation and
mechanical properties. The results shows enhancement in dielectric properties with
improvement in Young’s modulus, stiffness, reduction in elongation at break and slight
increase in shore D hardness of composites. Scanning electron microscopy was used to test
the morphology of the samples which has shown proper distributions and adhesion of the
filler mica in PVC matrix. There was some effect of surface treatment of mica on its
mechanical and dielectric properties of the composite.
Key words: Polyvinyl chloride (PVC), Water ground mica (WGM), Scanning electron
microscope (SEM), PVC composite
PVC is the most used polymer for general purpose domestic and industrial wiring, cable
insulation and sheathing, taking about 70% of the compounded polymers used by the industry
and it is likely to retain its importance among thermoplastic compounds [1,2]. It is readily
170 S. P. Deshmukh and A. C. Rao Vol.11, No.2
miscible and compatible polymer with large number of molecular weight compounds to give
vide differing mechanical and electrical properties from rigid to flexible compounds.
Compounded PVC, more than any other plastic material, is considered most versatile plastic.
It can be formulated to be non-toxic, nonflammable, light, stable and stain resistance through
proper formulations. As material for ultimate product, compounded PVC cables and sheets
are manufactured by extrusion process. Mica is extensively used as reinforcing filler for
plastic composites because of its influence on the physical, mechanical and electrical
properties of composites [3-6]. Mica has the modulus of 172 GN/m2 against 73 GN/ m2 of the
glass flakes, hence its choice and is used as particulate filler for reinforced composite. Mica
has excellent chemical and corrosion resistance, good electric properties, low thermal
expansion and cause less wear and abrasion to the processing equipment.
Gupta et al [7] has found in their studies that microcracks resulted from internal stresses of
mica filled composites have adequate strength and electrical properties. High modulus mica
fillers does not distort during cooling of the composite and consequently leads to brittle
matrix cracks. These microcracks in composite materials arise mainly from debonding of the
interface between mica and resin. It has been found that dimensional stability of the mica
filled composites was more compared to wood and glass filled composites [8,9]. The
properties of the mica filled composites are determined by component properties,
composition, structure, particle-particle i nteraction, and particle matrix interaction [10]. Mica
agglomeration, distribution, wetting and adhesion with polymer resin determine the
composite properties. Upgrading mica by increasing aspect ratio and coupling efficiency and
combining mica with other fibres can improve the reinforcing effect of the composites [11].
Studies by P.Bajaj et al [12], reveals that mica filled composite sheets can utilize the planner
reinforcing properties of mica, although other fabrication techniques are also used in
fabrication of part of these composite. Processin g, applications, and properties of mica filled
compos it es h as b een rev iewed ex t ens iv el y in many references (12,13). Use o f m ica as a fil l er
in composite leads to initial breakage and delamination of it’s particles during processing,
changing it’s size significantly influence the final properties of the composites.
Mica filled polymer composite materials shows significant improvement in dielectric
properties of the plastics [14]. These changes in the electrical properties of the mica filled
polymer composites make them suitable for their use in electrical insulation applications on
large extent. The study carried out on the mica filled PVC composites of varying size and
different fill er conc entrat ion reveals ch anges of the m echanical and ele ctri cal p roperti es such
as stiffness, tensile strength, dielectric strength, surface resistance etc. of the composites
2.1 Material s
Different PVC mica composites were prepared for research work to develop the final
compression moulded sheets. PVC resin of k 57 grade of Reliance Industries ltd., India was
Vol.11, No.2 Mica Filled PVC composites: Performance enhancement 171
used for the research work. INSTABEX C-11, one pack stabilizer ( 66-72% Pb, 71.1
77.55% PbO, 3.2 3.8 Sp. gr. and 1% maximum moisture) supplied by m/s Aryavart
Chemicals Pvt. Ltd India was used as the stabilizer. Stearic acid supplied by m/s Godrej
Industries ltd was used as lubricant. DOP was used as a plasticizer for compounding. Water
ground high aspect ratio( 20 -40) lustrous filler mica of WGM 101, WGM 202, and WGM
SIL supplied by M/s Galaxy Corporation, Mumbai, India was used in different proportions
starting from 10 grams to maximum 50grams in the range of 10grams in every stage. Virgin
test samples without filler were prepared with the PVC and additives such as stabilizer,
lubricant and plasticizer. . Silquest 11009(3-aminopropyltriethoxysilane) silane coupling
agent, supplied by Crompton specialties Purto Rico, USA was used for Surface treatment of
2.2 Compounding
For all composite formulations weight of resin, stabilizer, lubricant and plasticizer were kept
uniform and mica was added as filler to this mix in different weight proportions. The
research work was aimed to determine use of mica as filler in PVC to develop composite with
improved mechanical and electrical properties. The weight proportions of the resin,
lubri cant, stabi lizer an d plas ticizer were select ed based o n the PVC cable formulat ions and is
given in Table 1. Water grou nd mica WGM 101, WGM202 and WGM SIL of 150, 74 and 44
micron particle size and surface area of 1.4, 2 and 4.8 m2/gm respectively was used in
Table 1. Mica PVC Composite formulation for study
Weight in
10 to 50
PVC Resin
Liquid DOP
Stearic Acid
PVC resin, INSTABEX C-11, mica, and stearic acid were dry blended using high-speed
mixer for five minutes. Liquid DOP was added in two to three stages during dry blending.
The dry blending process was carried out at 1050C.
172 S. P. Deshmukh and A. C. Rao Vol.11, No.2
Dry blended mixtures were melt compounded using Haake Rheocord 9000 batch
compounder. Roller blades Rheomix 600 were used for compounding of the mix. Dry
blended PVC mix of 60-gram weight was compounded at 1800C temperature for 5minutes
with 60r.p.m. roller speed in different batches. Ten batches of such compound were
processed with this machine for each formulation of composite. Processed PVC mix was
found non stick y and was able to remove from blades easil y. The compounded mix was then
cooled to room temperature before it was packed and labelled.
2.2.1 Compression molding
The compounded PVC composite was dried in oil heated electric oven at 1050C for the
period of one hour to remove the moisture before it is compression moulded making test
sheets. The compression-moulded sheets of 90 gm weight and 180x180mm size with 2mm
thickness were fabricated. The hydraulic compression-moulding machine was used for the
study. The compression moulds were heated to temperature of 1800C for moulding of the test
samples. After the molding of sheet the mold and sheet were cooled to the 400C at the process
pressure of 130kg/cm2 allowing curing of sheets. These sheets wer e t hen us ed for det ermi ning
mechanical and electrical properties of the PVC composites.
2.2.2 Surface treatment of filler
Diluted solution of ethanol/water (90%/10%) and Silquest A-1100 in 80/20 weight proportion
was prepared. 200gm WGM 101, WGM 202 and WGM SIL mica were prewetted with 16
ml, 12 ml, and 8 ml of ethanol and silquest solution respectivel y and thoroughly mixed and
dried at 1050C at 2400 rpm for 10 minutes. The treated mica was dried in air circulating oven
at 1050C to remove diluent for one hour before m ixing with PVC resin and other ingredients
of composites.
2.2.4 Mechanical pr operties
Mechanical properties of the test specimen were evaluated ae per ASTM D 638 using
Universal Testing Machine LR 50K from Lloyd Instruments Ltd., U.K. at cross head speed of
50mm/min. Five test samples of each composite were tested for finding average values of
mechanical properties. Shore D hardness test was carried out on test samples and results are
2.2.5 Electrical properties
The dielectric strength was investigated as per ASTM D 149 usin g Zaran Instruments (India)
with 2mm thick test samples of the composites. The voltage for this test was slowly increased
to penetrate the sample and its maximum values were noted. The instrument was having input
configuration of 240 V, 50 Hz, 1 PH with 0-50 K V output at 100 mA with 15 minutes rating.
Arc resistance of test specimen was carried out as per ASTM D 495-89, which is high
voltage, low current test. Arc resistance was determined using Zaran Instrument with 2mm
Vol.11, No.2 Mica Filled PVC composites: Performance enhancement 173
thick composite sheets. Surface resistance tests were carried out as per ASTM D 257 using
HP 4339 B high resist ance met er of Hewlet t Pack ard, surfa ce testin g machin e. The Electro de
diameter machine was 2.5 cm with output voltage of 500V and the current limit of 500µA.
Dielectric constant of the composites were measured using Precision impedance analyze of
Wayne Kerr. U.K. with Dc current with voltage range of 0 to 40 V and frequency of 20Hz to
20MHz as per ASTM D150.
2.2.6 Morphological properties
SEM was used to study morphology of the mica P VC composites. SEM st udies of tensil e test
fractured and liquid nitrogen fractured samples were carried out using JSM-6380LA
Analytical Scanning microscope of Joel make, Japan. The Samples were sputter coated with
platinum to increase the surface conductivity using JFC-1600 auto fine coater of Joel Make
Japan.. The digitized images of the samples were recorded and studied.
3.1 Elongation at Break
It is observed that elongation at break of test samples decreases with increasing concentration
of filler loading of each type of PVC composite. This decrease in elongation is attributed to
restriction of polymer chain movements. The extent of filler dispersion plays an important
role in changing properties of mica filled composite. Even though, there was proper filler and
matrix bonding, this bonding appeared unable to withstand shear strain and elongations at
rupture of mica filled composites failing it catastrophically.
The trend of elongation of the PVC composite is shown in figure 1. It shows that, as the
concentration of filler increases the polymer chain moment and displacement due to applied
force reduces. From the figure it is found that in reinforcement matrix there will be a
distribution of tensile and compressive micro stresses. Tensile stresses more likely at low
volume fractions, and it i s pos sible th at these st resses m ay generat e int erface cr acking. In the
flakes, the possibility of a tensile stress near the periphery of the flakes is low. However,
between two neighbouring flakes and away from the edges, a tensile stress is likely to
develop to maintain overall equilibrium. Strength reduction in mica filled PVC composite in
relation with virgin (neat) PVC could be attributed to formation of micro cracks in the resin
matrix due to the internal stresses developed during curing and difference in the thermal
shrinkage of PVC and mica.
The lowering of extension of the Mica filled PVC composite may be associated with weak
fibre matrix adhesion. The weak filler polymer matrix has less elongation at break as
compared neat polymer. More filler content of the polymer matrix reduces its elongation
considerably. The reduction in elongation improves the Young’s modulus and stiffness of the
composite which will be beneficial for use of this materials in wire and cable applications for
outdoor applications improving the life of the insulation.
174 S. P. Deshmukh and A. C. Rao Vol.11, No.2
Figure 1. Elongation of Mica Filled PVC Composites
3.2 Electrica l Prop e rti e s
The results obtained for the dielectric strength, surface resistance and arc resistance and
dielectric constant for test specimens with increasing mica content in PVC are shown in
figure 2 to 4. Small mica addition in PVC acts as a intermolecular plasticizer and is able to
penetrat e the molecules of the PVC , leading to chain s eparation. Thi s leads to th e increase in
the some of the dielectric properties of the materials. At higher loading of mica, it acts as an
intramolecular plasticizer, where the mica molecules distributed in a inner aggregate space.
This hinders the polymer chain elongation and consequently reduces some the dielectric
Figure 2 Dielectric Strength of Mica filled PVC composites.
Vol.11, No.2 Mica Filled PVC composites: Performance enhancement 175
The surface resistance, dielectric strength and arc resistance, and dielectric constant of the
untreated and surface treated mica filled PVC composites containing 10 to 50 parts by
weight of mica flakes of different sizes were measured on five samples of each composition
and average of the reading are tabulated for analysis purpose. Form the figure 2 it has been
shown clearly that the dielectric strength of the mica filled PVC composite has been
increasi ng as ex pected from the vi rgin ( neat ) PVC mat rix witho ut any fill er contai n as mi ca
has good electric resistance. For WGM SIL mica of 44 µm the percent increase was as high
as 187.5% as against the reduction b y 17 % for t he same type of mica. For other mica fillers
the dielectric strength has been found increased considerably. This may be explained as
follows. As the SEM micrographs (figures 7-11) shows, the resin is more densely packed in
the sample containing 30 and 40 parts by weight of mica filler, while in the samples of low
loading of mica , the resin is relatively loosely packed . Since dense packing will hinder
displacement of the dipoles and also hinder the accumulation of charges at the filler resin
interphase, and since dielectric strength is directly related to these two factors the rate of
increase is observed.
Presence of chlorine atoms in the polyvinyl chloride molecules determines an increased
polarity in comparison with other polymers such as polyolefin. Electrical resistivity is the
most important representative characteristic for cable insulation. It depicts the structural
integrity under the action of the electrical field, and electron availability as charge carrier. For
PVC the energy transfer from it is consumed for bond scission which is followed by the
remote of hydrochloric acid, and the increase in the unsaturation level, or by cross linking.
Consequently the electrical resistance will take certain values according to the modifications
of the composition of the insulating material.
Fig. 3 Surface Resistance for Mica filled PVC Composites
It has been observed from fig.3, that there is variation in surface resistance of the composit e.
For the WGM SIL mica of 44 µm th e increase in s urface resist ance is 10 times more surface
176 S. P. Deshmukh and A. C. Rao Vol.11, No.2
resistance of neat PVC matrix and also more as compared to mica PVC composites with
mica with bigger particle size i.e. WMG 101 and WGM 202.
Arc resistance of the composite also shows variation for the 10 and 40 and 50 parts by
weight(fig.4). For the 10gm weight for the WGM 101 mica filled PVC composite the
reduction in the arc resistance was 40 percent The maximum rate of reduction in arc
resistance is observed for the composite with 20 parts per weight for WGM 202 type mica
with reduction of 45 percent compared to neat PVC matrix without filler.
Fig. 4 Arc Resistance for Mica filled PVC Composite`
Dielectric constant defines ratio of the capacitance induced by the metallic plates with the
insulator placed between them and the capacitance of the plates with vacuum between them
and indicates the ability of the insulator to store electric energy. Figure 5 shows that the
dielectric constant for the test pieces lies between 11 and 16 for the test samples with
different concentration of untreated and treated mica PVC composites. This indicates that
there is small variat ion in values of capacitan ce of the test materials making more suitable to
be used as electric insulating material.
3.3 Shore D Hardness of Test Samp les
The compression molded test samples were tested for the shore D hardness as per ASTM .
The figure 6 shows that, there is about 4percent rise in the hardness of the WGM 101 mica
filled PVC composite for its 10 weight percent addition where as it reduces by 14 percent
when same mica is added up-to 30 weight percent in the PVC composite. For the WGM SIL
mica incorporation in the PVC composite in dif ferent concentration the ha rdness incr eases by
26 percent for 30 weight percent addition where it reduces a fter for more filler concentration.
For the WGM 202 mica addition in the composite there was marginal increase in the
hardness when concentration is above 40 weight percent. In all for the untreated mica
addition of different particle size and different filler concentration small increase in the shore
Vol.11, No.2 Mica Filled PVC composites: Performance enhancement 177
D hardness indicates that the even after filler addition up-to 50 weight percent the PVC
composite remains comparatively soft so can be used for cable and sheathing application.
The effect of high amount of plasticizer (50grams) in the composite clearly indicates that
flexibility and ductility of the composite is not affected drastically without much increase in
hardness of the mica filled PVC composites. This will make it possible to use these
composites for fabrication of cables and wire with affordable cost and improvement of
mechanical and electrical properties.
Fig. 5 Dielectric constant of mica filled PVC composites.
Fig.6 Shore D hardness of Mica filled PVC Composites
3.4 Fracture Morphology
Liquid nitrogen fractured and tensile test fractured surfaces of the mica filled PVC
178 S. P. Deshmukh and A. C. Rao Vol.11, No.2
composites are shown in figure 7 to 11. The possible origins of the crack in these composites
are voids or air bubbles, resin rich areas, particle size of the fillers and poor mica and matrix
adhesion. The figures 7 to 9 shows brittle fractures of the composites. For the tensile tested
compos ite specim ens (Fig. 10,11) the d ebonding at the interface of the mica and PVC matrix
shows pullout of the mica particles showing voids of bigger size. This mainl y happens due to
lack of proper interfacial adhesion.
Fig. 7 SEM:SPD 11, 1K, Liquid Nitrogen Fractured, 10 phr WGM SIL mica filled PVC
Fig. 8 SEM:SPD 13, 1K, Liquid Nitrogen Fractured,, 30 phr WGM SIL mica filled PVC
The micrographs clearly shows that the mica particles are randomly oriented and large
number of particles are subjected to tensile stresses acting on the planes perpendicular to
them where crack propagation takes place. As the mica is having low splitting energy it
undergoes delamination. The high levels of particle pull out occur due to the low strength
values and low elongation at break.
Vol.11, No.2 Mica Filled PVC composites: Performance enhancement 179
Fig. 9 SEM: SPD 15, 1K, Liquid Nitrogen Fracture d, 50 phr WGM SIL Mica filled PVC
Fig. 10 SEM: SPD 13-1K Tensile tested Specimen , with 30 phr WGM SIL Mica filled PVC
Fig. 11 SEM SPD 15 1K Tensile Tested Specimen with 50phr WGM SIL Mica Filled
PVC Composite
180 S. P. Deshmukh and A. C. Rao Vol.11, No.2
Elongation at break of the composite reduces with higher loading of mica for treated
and untreated mica filled composites. This is primarily because of interfacial stresses
developed between filler and matrix at the time of curing and stressing of composite leads to
micro-cracks reducing its tensile properties. This happens also because of weak filler matrix
Dielectric strength and surface resistance of composite increases up to 30 gram mica
addition. Increase in these properties was slightly more for surface treated mica filled PVC
composites as it improves surface treatment improves filler adhesion with polymer matrix.
Higher loading of mica changes the structure of polymer matrix reducing its insulation
Surface treatment of mica improves an arc resistance of composite which increases
for the higher loadin g of t reated and un treat ed mi ca in PVC m atrix . It has b een als o ob serv ed
that values of dielectric constant does not changes drastically as there is small variation in
capacitance of the material.
Shore D hardness of test composite shows that even for higher loading of mica
polymer retains its softness and can be used for wire and cable applications.
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