Journal of Minerals & Materials Characterization & Engineering, Vol. 9, No.9, pp.831-844, 2010 Printed in the USA. All rights reserved
Effect of Particle Size and Concentration on Mechanical and Electrical
Properties of the Mica Filled PVC
S.P. Deshmukh
, A.C. Rao
, V. R. Gaval
, Seena Joseph
, P.A. Mahanwar
Department of General Engineering, Institute of Chemical Technology,
Matunga, Mumbai-400019, India.
Department of Polymer engineering and and Surface Coating
Institute of Chemical Technology, Matunga, Mumbai-400019, India.
* Corresponding Author:
The performance of the composites is determined on the basis of the interface bonding of the
filler and the polymer matrix. Particulate filled polymer composites are used extensively for their
wide range of applications at low cost. In this study, the effect of the mica with different particle
size and different filler concentration (10 to 50 weight percent) on the mechanical and electrical
properties of the polyvinyl chloride (PVC) was investigated. The PVC composites of water
ground mica were prepared by Haake Rheocord 9000 machine, with Rheomix 600 using rotor
type roller blades. Mechanical properties such as stiffness, and Young’s modulus of the PVC
mica composites were found increasing with increase in mica loading, whereas elongation at
break and tensile strength was found to be decreasing with the mica loading. Dielectric
strength and surface resistance were found increasing with increasing mica loading whereas
there was no significant increase of arc resistance of the composites. Morphological studies
revealed that there is good dispersion and wetting of the mica with PVC matrix. SEM
micrographs of the composites were studied for finding the filler dispersion and fracture analysis
of the test samples.
Keywords: PVC composite, mica, Scanning Electron Microscope (SEM), Water Ground Mica
S.P. Deshmukh, A.C. Rao, V. R. Gaval, S. Joseph, P.A. Mahanwar Vol.9, No.9
PVC is the most used polymer for variety of general purpose domestic, industrial applications
and for wiring and 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. It is much more readily miscible and compatible than other polymers with large
number of molecular weight compounds to give wide differing mechanical properties from rigid
to flexible. Compounded PVC, more than any other plastic material, is considered most versatile
plastic. It can be formulated to be non-toxic, nonflammable, light, and stable and stain resistance
through proper formulations. Mica has been extensively used as reinforcing filler for thermosets
and thermoplastics because of its influence on the physical, mechanical and electrical properties
of composites. Mica has the modulus of 172 GN/m
against 73 GN/ m
of the glass flakes; hence
its choice as filler for reinforced composite is obvious. Mica has excellent chemical and
corrosion resistance, good electric properties, low thermal expansion and cause less wear and
abrasion to the processing equipment
Maine et al.
has suggested that the most promising area of full utilization of the planner
reinforcing properties of mica is in sheet materials, although other fabrication techniques can be
used. Processing, applications, and properties of mica filled composites have been reviewed in
many references. The notable nature of mica leads to the initial breakage and delamination of the
mica particles during processing, such that the initial dimensions of the mica changes
significantly influencing the properties of the composites.
There is extensive literature explaining changes in the mechanical properties of the mica filled
composites. In all the studies it has been clearly demonstrated that the modulus and the stiffness
are the easiest mechanical properties to estimate, since these properties largely depends on
particle size, modulus, geometry, distribution and filler loading
. The tensile strength of the
filled polymer is difficult to predict as it depends on the interfacial bonding of the filler and
polymer in addition to the above.
A number of investigations has shown that modulus and the stiffness of the mica filled
composites increase with the filler concentration irrespective of the particle size of the mineral
filler. The tensile strength of the composite totally depends on the strong adhesion of filler and
polymer and the wetting ability of the polymer. For good wetting low surface tension, low
viscosity of the polymer matrix and similar polarities of both the phases are essential
Normally thermosetting polymers are low viscous liquids and are converted to solids by cross-
linking and many of thermosetting polymers are polar in nature.
Mica addition to polymers also shows significant changes in dielectric properties of the plastics
. These changes in the electrical properties of the mica filled polymer composites make them
Vol.9, No.9 Effect of Particle Size and Concentration 833
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 filler concentration reveals
changes of the mechanical and electrical properties of the composites
2.1 Materials
PVC mica composites of different formulations were prepared for research work to develop the
final compression molded sheets. PVC resin of k 67 grade, manufactured by Reliance Industries
Ltd., India was used for this 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 for the experimental work. Stearic acid was used as
lubricant and was supplied by m/s Godrej Industries Ltd. Dioctyl phthalate (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 of 10phr to 50phr in the range of 10phr in every stage. The particle
size and surface area of different types of mica used in this study are given in Table 1. Virgin test
samples were prepared with the PVC with all the additives such as stabilizer, lubricant and
plasticizer but without filler.
2.2 Preparation of the Test Specimens
2.2.1 Dry blending
For different composite formulations weight of resin, stabilizer, lubricant and plasticizer were
kept uniform and mica was added in different weight proportions. The aim of this research study
was to determine use of mica as filler in PVC to develop composite with improved mechanical
and electrical properties. The weight proportions of the resin, lubricant, stabilizer and plasticizer
were selected based on the PVC cable formulations reported and the formulation is given in
Table 2. Water ground mica of different particle sizes and different surface area was used in
these formulations.
Table 1. Size of water ground mica used for formulations.
Wet Ground Mica Type Particle size (microns) Surface area (m
WGM 202 74 2
WGM SIL 44 4.8
WGM 101 150 1.4
S.P. Deshmukh, A.C. Rao, V. R. Gaval, S. Joseph, P.A. Mahanwar Vol.9, No.9
Table 2. PVC formulation for study.
PVC Resin 100gm
Liquid DOP 50gm
Stearic Acid 1gm
Mica 10 to 50gm
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 105
2.2.2 Melt compounding
Dry blended mixtures of different formulations were melt compounded using Haake Rheocord
9000 batch compounding machine. Roller blades Rheomix 600 were used for compounding of
the mix. Dry blended PVC mix of 60-gram weight was added to the machine to compound it in
different batches. Ten batches of each such compound were processed as per the processing
parameters given in Table 3. During compounding it was observed that the, processed PVC mix
was non sticky and was able to remove from blades easily. The compounded mix was then
allowed to cool to room temperature before it was packed in labeled plastic packets.
Table 3. Process parameters for Haake Rheomix 600.
Processing Temperature Roller Speed (r.p.m) Processing time (Minutes)
C 60 5
2.2.3 Compression molding
The compounded PVC composite was dried in oil heated electric oven at 105
C for the period of
one hour to remove the moisture present in the material before it was compression molded in test
sheets at 180
C temperature and 130kg/cm
mold pressure. The compression-molded sheets of
90 gm weight and 180x180mm size with 2mm thickness were made. The hydraulic compression-
molding machine was used for the study. The die was cooled to 40
C at the process pressure of
. These sheets were then used for determining mechanical and electrical properties of
the PVC composites.
Vol.9, No.9 Effect of Particle Size and Concentration 835
2.2.4 Mechanical properties
Mechanical properties of the test specimen were evaluated as per ASTM D 638 using Universal
Testing Machine LR 50K from Lloyd Instruments Ltd., U.K. at cross head speed of 50mm/min.
Five samples of each composite were tested for finding average values of mechanical properties.
2.2.5 Electrical properties
The dielectric strength was investigated as per ASTM D 149 using 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.
The 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 thick
composite sheets.
The surface resistance tests were carried out as per ASTM D 257 using HP 4339 B high
resistance meter of Hewlett Packard, surface testing machine. The Electrode diameter machine
was 2.5 cm with output voltage of 500V and the current limit of 500µA.
2.2.6 Morphological properties
SEM was used to study morphology of the mica PVC composites. SEM studies of tensile 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. Stiffness and Young’s Modulus
The effects of concentration of mica and its size on the mechanical properties of the PVC
composites are presented in Figures 1 and 2. From the results it is found that stiffness and
Young’s modulus of the composite was increasing with increase of the filler content. It was
observed that the increase in stiffness as well as Young’s modulus of the composite is attributed
to the platy structure of the mica. The rate of increment of stiffness as well as Young’s modulus
varies with varying particle size of mica. The stiffness and the Young’s modulus variation and its
S.P. Deshmukh, A.C. Rao, V. R. Gaval, S. Joseph, P.A. Mahanwar Vol.9, No.9
percent increment with increase in concentration clearly indicate the dependence of particle size
and its dispersion. Shepherd et al
have found that the use of mica increase stiffness, Young’s
modulus and dimensional stability of some common polymers. Addition of mica in polymer
influences filler matrix which is responsible for variation in mechanical properties of composites.
It is observed that at 30 weight percent filler loading of each type of mica showed stiffness
increase above 300%, indicating maximum level of dispersion whereas the Young’s modulus is
higher at 50 weight % loading of WGM SIL mica having 44 µm size. At this loading the
Young’s modulus is same for WGM 101 mica and WGM 202 mica indicating optimum level of
dispersed platelets. It clearly indicates that stiffness and Young’s modulus depends on extent of
dispersion as well as dispersion of agglomerates.
020 40 60
% Mica
WGM 6030TWGM 101T
Figure1. Stiffness of mica filled PVC composites.
Figure 2. Young’s modulus for mica filled PVC composite.
It is also indicated that the agglomerates at 30 and 50 weight % also support the extent of
dispersion and property variation. Figures 3, 4, and 5 show SEM of the liquid N
surfaces of 10%, 30% and 50% mica filled PVC composites. It is observed from the SEM
02040 60
% Mica
Young's modulus (MP)
WGM 101WGM202
Vol.9, No.9 Effect of Particle Size and Concentration 837
photographs that, at 30 weight % mica, the agglomeration is started due to which poor dispersion
of mica in polymer matrix has been observed, whereas at 50 weight % mica agglomerates are
observed but these agglomerates are in dispersed form as compared to 30 weight % mica PVC
composite. Thus the trend in increment in stiffness and Young’s modulus is clearly dependent on
the extent of dispersion of the particles of mica in polymer. As the maximum increase in the
Young’s modulus of test composite is found to be over 300 percent, it suggests that there was
proper bonding between filler and matrix.
Figure 3. SEM: Liquid nitrogen fractured, 10 phr WGM SIL mica filled PVC composite.
Figure 4. SEM Liquid nitrogen fractured, 30 phr WGM SIL mica filled PVC Composite.
S.P. Deshmukh, A.C. Rao, V. R. Gaval, S. Joseph, P.A. Mahanwar Vol.9, No.9
Figure 5. SEM: Liquid nitrogen fractured, 50 phr WGM SIL Mica filled PVC Composite.
3.2. Tensile Strength and Extension at Break
The elongation at break and tensile strength values of mica filled PVC composites at different
filler content are given in Figures 6 and 7. It is observed that the tensile strength and elongation
at break decrease with increasing concentration of filler loading of each type of PVC composite.
The decrease in tensile strength as well as elongation attributes to restriction of polymer chain
movements. It is also supported by variation in rate of change of tensile strength with increase in
concentration of filler. The rate of decrease in tensile strength is higher at higher filler loading.
This rate of decrease in tensile strength is higher for higher particle size as compared to smaller
particle size of mica. Raj et al.
in their studies have found that elongation and tensile strength
of composite decreases with increase in particulate filler concentration. The extent of dispersion
also plays an important role in varying the 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.
Vol.9, No.9 Effect of Particle Size and Concentration 839
1 00
020 4060
% Mica
Extension at break (mm)
WGM 101WGM202
Figure 6. Extension at break for mica filled PVC composite.
From the trend in variation in mechanical properties of the PVC composite, it is clear that, as the
concentration of filler increases the polymerr chain moment and displacement due to applied
force is reduced. It has been shown Figure 7 that in the fiber reinforced matrix there will be a
distribution of tensile and compressive micro stresses present in the matrix with tensile stresses
more likely at low volume fractions, and it is possible that these stresses may generate interface
cracking. In the flakes, the possibility of a tensile stress near the periphery of the flakes is low.
However, between two neighboring flakes and away from the edges, a tensile stress is likely to
develop to maintain overall equilibrium. As indicated by Gupta et al.
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.
020 40 60
% Mica
Tensile strength (MP)
WGM 101WGM202
Figure 7. Tensile strength for mica filled PVC composites.
S.P. Deshmukh, A.C. Rao, V. R. Gaval, S. Joseph, P.A. Mahanwar Vol.9, No.9
It is most likely that the addition of the mica influence fiber/matrix adhesion, which is
responsible for the mechanical property variation with mica content
. The interfacial shear
strength is one of the most important parameter controlling strength and toughness of
The lowering of the extension of the mica filled PVC composite may be associated with weak
fiber/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.
3.4. Electrical Properties
The dielectric strength, surface resistance and arc resistance for test specimens with increasing
mica content in PVC are shown in Figures 8, 9 and 10. Small mica addition in PVC acts as a
intermolecular plasticizer and is able to penetrate the molecules of the PVC, leading to chain
separation. This leads to the 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 inter aggregate space. This hinders the polymer chain elongation and consequently
reduces some dielectric properties
020 40 60
% Mica
Dielectric strength (KV/mm)
WGM 101WGM202
Figure 8. Dielectric strength for mica filled PVC composite.
Vol.9, No.9 Effect of Particle Size and Concentration 841
020 4060
% Mica
Surface resist. (X1014)
WGM 101WGM202
Figure 9. Surface resistance for mica filled PVC composites.
From the Figure 8, it has been shown clearly that the dielectric strength of the mica filled PVC
composite has been increasing with mica content up to 30 weight percent, as mica has good
electric resistance and it slightly reduces after it. For WGM SIL mica of 44 µm particle size, the
percent increase was as high as 180.8%. For other mica fillers the dielectric strength has been
found increased considerably. This may be explained as follows. As the SEM micrographs
(Figures 3, 4, and 5) 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
020 40 60
% Mica
Arc resistance time
WGM 101WGM202
Figure 10. Arc resistance for mica filled PVC composite.
S.P. Deshmukh, A.C. Rao, V. R. Gaval, S. Joseph, P.A. Mahanwar Vol.9, No.9
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.
Arc resistance of the composite also shows variation for the 10 and 40 and 50 parts by weight
(Figure 9). For the 10gm weight for the WGM SIL mica filled PVC composite the reduction in
the arc resistance was 24 percent. It has been observed in Figure 10, that there is variation in
surface resistance of the composite. For the WGM SIL mica of 44 µm the increase in surface
resistance is 3 times more surface resistance of neat PVC matrix and also more as compared to
mica PVC composites with bigger mica particle size i.e. WMG 101 and WGM 202.
3.5. Fracture Morphology
Liquid nitrogen fractured and tensile test fractured surfaces of the mica filled PVC composites
are shown in Figures 3, 4, 5, 11 and 12. 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. Figures 3, 4 and 5 show brittle fractures of the composites. For the tensile tested
composite specimens the debonding at the interface of the mica and PVC matrix shows pullout
of the mica particles showing voids of bigger size. This mainly happens due to lack of proper
interfacial adhesion.
Figure 11. SEM of tensile fractured surface, 30 phr WGM SIL mica filled PVC composite.
Vol.9, No.9 Effect of Particle Size and Concentration 843
Figure12. SEM of tensile fractured surface with 50phr WGM SIL mica filled PVC composite.
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.
High levels of particle pull out; occur due to low strength values and low elongation at break.
From the study of the mica filled PVC composites prepared from mica of different particle size
and with different filler concentration following results can be concluded:
Stiffness and Young’s modulus of the mica filled composite have been found increasing with the
higher percent of mica content in the composite. For composites of mica with small particle size
the rate of increase was slightly more as compared mica with higher particle size. This has been
mainly observed because the filler was properly dispersed in the matrix and there was good
bonding of filler and PVC matrix.
Extension at break and tensile strength of the composite was found reducing with increase in
filler concentration. This is due to the fact that the strength of filler is higher than the strength of
PVC matrix which leads to decrease in adhesion between filler and matrix.
Dielectric strength of the mica filled PVC composite was found increasing up to 30 percentage
filler concentration and then reduced marginally for further increase in filler concentration.
Surface resistance was found increasing with increase in filler concentrations for mica of all
particle sizes where as there was no significant change in the arc resistance of the composite
irrespective of filler concentration and particle size of the mica.
S.P. Deshmukh, A.C. Rao, V. R. Gaval, S. Joseph, P.A. Mahanwar Vol.9, No.9
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