Journal of Minerals & Materials Characterization & Engineering, Vol. 11, No.2 pp.193-210, 2012 Printed in the USA. All rights reserved
Mech an ic al Pr op ert ie s of Pot assiu m Titanat e Wh isker Reinforced Epoxy
Resin Composites
M. Sudheer1*, K. M. Subbaya 2, Dayananda Jawali 3, Thirumaleshwara Bhat 1
1 Department of Mechanical Engineering,St. Joseph Engineering College, Mangalore-575 028,
Karnatak a, IND IA.
2 Department of Industrial Production Engineering,National Institute of Engineering, Mysore-
570 008, Karnataka, INDIA.
3 Department of Mechanical Engineering,Sri Jayachamarajendra College of Engineering,
Mysore-575 006. Karnataka, INDIA
* Corresponding author:
This paper deals with the study of mechanical properties of Potassium Titanate Whisker (PTW)
reinforced epoxy based Polymer Matrix Composites (PMCs). Epoxy composites filled with PTW
in various content of 0-20 wt% were prepared using the casting technique. Data on neat epoxy is
also included for comparison. All tests were conducted at room temperature and as per ASTM
standards. It was observed that inclusion of PTW affected most of the mechanical properties of
neat epoxy. Density, hardness and heat deflection temperature of neat epoxy were found to
increase with the PTW content. However tensile and flexural properties of the developed
composites exhibited a varying trend with respect to PTW content. Epoxy filled with 10 wt%
PTW showed good improvement in tensile strength and flexural strength of neat epoxy. It was
observed that PTW is not beneficial in improving the impact strength of n eat epoxy. Composites
194 M. Sudheer, K. M. Subbaya, Dayananda Jawali Vol.11, No.2
with 20 wt% PTW exhibited least impact strength. This paper also highlights the possible
reasons for variation in the mechanical properties of developed polymer composites.
Key words: Epoxy, PTW, PMCs, Mechanical Properties.
It is a common practice in the plastics industry to compound homo-polymers with fillers and
fibers to dilute the manufacturing cost and/or attain desired properties [1]. By combining
different fillers or fibers with various polymer matrices, polymer composites can be tailored to
achieve propert y combinations which cannot easily be obtained from either the polymer matrices
or the reinforcements alone. In past decades, many different substances have been used as
reinforcements in composite preparation, although short fibers have attracted much more
attention than other materials because of their low price and effectiveness in reinforcing
polymers [2].
Whiskers are short fiber-shaped single crystals with high perfection and very large length-to-
diameter ratios. According to theories of short fiber composites, the composites reinforced with
thinner and stronger fibers can be anticipated to achieve much higher mechanical properties.
Generally whiskers possess high strength and stiffness due to their nearly perfect crystal
structure [3]. Therefore whiskers are reckoned as more effective reinforcements than traditional
fibers such as carbon fiber and glass fiber. Recentl y various inorganic whiskers such as Calcium
Carbonate (CaCO3), Alumina (Al2O3), Silicon Carbide (SiC) and Potassium Titanate
(K2Ti6O13) were prepared and employed in the manufacturing of composites with different
polymer matrices.
Several researchers have observed the significant changes in the mechanical properties of
polymers reinforced with different kind of whiskers [4-19]. Youxi et al. [4] reported that optimal
content of CaCO 3 whisker in PEEK composites is 15% to 20% combining both mechanical and
Vol.11, No.2 Mechanical Properties of Potassium Titanate 195
tribological properties. The reinforcing effectiveness of CaCO 3 whisker contributing to increase
in thermal stability, stiffness and load carrying capacity of PEEK was also reported by same
investigators in another study [5]. Zhang et al. [6] investigated the mechanical and wear
properties of silicon carbide and alumina whisker reinforced epoxy composites. It was observed
in their study that both those whiskers significantly improved the flexural modulus and wear
resistance of epoxy composites. However, Avella et al. [7] reported that addition of untreated
SiC whisker into polypropylene lead to an enhancement of the modulus, but a decrease in the
tensile strength.
Wang et al. [ 8] reveal ed t hat ZnO whisk ers h ave bett er rein forcin g ef fect wit h the nylon t han th e
ZnO particles. ZnO whisker reinforced nylon exhibited higher tensile strength and hardness for
most of the material combinations developed. Jang et al. [9] proposed modifications of matrix
resin with thermoplastic particulates or ceramic whiskers as an alternative to rubber-toughening
for improving the impact resistance of epoxy resins. They observed that dispersion of 10% of
ceramic whiskers in an epoxy resin improved appreciably the impact energy, flexural strength
and modulus of the epoxy.
Among the numerous inorganic fillers, potassium titanate whiskers (PTW, K2O.6TiO2) has been
found to be a promising reinforcer for the wear resistant composites due to its unique properties,
such as outstanding mechanical performance, low hardness (Mohs hardness 4) and excellent
chemical stability. PTW is a kind of very fine micro-reinforcing material and it is suitable to
reinforce the very narrow space in composites that conventional fillers are unable to do. In
practice, it is an ex cellent fi t for makin g products that have a complex shape, great precision and
high polished surface. The price of the PTW ranges from one-tenth to one-twentieth of the cost
of SiC whiskers [10]. In this regard, PTW have been used to reinforce most of the polymers.
Many studies on PTW reinforced polymer composites have been carried out [11-19]. Generally
Young’s moduli of the PTW reinforced composites increase with increasing whiskers content
and impact strengths of the composites have opposite variation. But the tensile strengths of
composites exhibit complicated variation.
196 M. Sudheer, K. M. Subbaya, Dayananda Jawali Vol.11, No.2
Xing et al. [11] studied the effects of PTW on mechanical properties of PTW/PTFE composites
and observed that PTW improved the properties of neat pol ymer. The range of PTW in PTFE fo r
optimal integrative properties was found to be 5-10 wt%, which is similar to the behavior of
nanoparticles. Chen et al. [ 12] fabricated PVC rei nforced wit h controllably oriented PTW by hot
pressing the precursor fibers that contained the whiskers. An increase of over 250% in tensile
strength and 300% in flexural strength was observed for the composite containing 40% PTW.
Shoubing et al. [1 3] s ystemat icall y evaluated the tensile strength of a series of PTW filled castor
oil-based polyurethane/epoxy resin interpenetrating polymer network and found an optimum
increase in the tensile strength (25.5 MPa) of the composites at 3% of PTW. Demei et al. [14]
reported a maximum PTW content limit of 20 wt% in polypropylene/polyamide blend matrix
when the tensile strength of the composite increased with the increasing whisker content.
Tjong and Meng [15,16] observed increase in the tensile strength and modulus and decrease in
strain at break and impact strength of PTW reinforced polyamide composites. Their study also
reveal ed that sur face treat ed PTW has b etter reinf orcing effect with po lymer matric es and henc e
enhance most of the mechanical properties. Increase in tensile strength and tensile modulus of
PTW reinforced PEEK composites was also repo rted by Zhaun g et al. [17]. It was revealed that
compounding processes exhibit great influence on reinforcement efficiency of PTW. The
composites pre-compounded with rheometer possessed higher mechanical performance than
those pre-compounded with the extruder.
Zhu et al. [18] compared the effect of various whiskers on the performance of non-metallic
(phenolic resin based) friction materials. The results showed that addition of the whiskers
decreased the hardness of unmodified material and greatly improved its mechanical properties.
Among them, magnesium borate whisker composite exhibited highest tensile strength and
poorest Young’s modulus, calcium sulfate whisker composite exhibited best thermal stability and
PTW imparted highest wear resistance to the composite. In a recent study on hybrid polymer
composite friction materials, Mukesh et al. [19] observed that absolute friction effectiveness
remained higher in the composites with ≥ 25wt% of PTW.
Most of the researches paid attention towards studying the influence of whiskers on
thermoplastic materials and less work has been done by reinforcing the PTW with thermoset
Vol.11, No.2 Mechanical Properties of Potassium Titanate 197
matrices. Epoxy resin is a well known thermoset polymer matrix as they possess better
mechanical and thermal properties. The y wet many substrate materials, absorb less moisture and
can be processed with considerable degree of ease. The other advantages include excellent
chemical resistance coupled with good electrical properties [20]. In this paper, study is focused
on processing and mechanical characterization of PTW reinforced epoxy resin composites. The
different mechanical properties such as density, hardness, tensile, flexural, impact properties and
heat deflection temperature of the developed composites as a function of PTW content is
measured to investigate the effect of PTW on epoxy resin system.
2.1 Materials Used
Room temperature curing Epoxy resin system (LY556 + HY951 of M/s Hindustan Ciba Geigy
Ltd, Mumbai) was used as the host matrix material. Potassium Titanate Whiskers (PTW,
K2Ti6O13) are ceramic micro- fillers and were used as the reinforcement. These ceramic
whiskers are of splinter shape and properties are listed in Table 1.
Table 1. Properties of PTW
Densi t y
Tensile strength
(G Pa)
Tensile Modulus
(G Pa)
0.5 - 2.5
10 - 100
2.2 Fabrication of Composite Specimens
An open mold with cavity dimensions 300×300×6 mm was fabricated to cast polymer
composites. The fillers were preheated to remove any moisture present and cooled to ambient
temperature. The required quantities of filler were stirred gently into liquid epoxy resin, taking
care to avoid the introduction of air bubbles. Hardener was then added to the resin in the ratio of
1:10 and then stirred to ensure complete mixing. The mixture was then poured into an open
198 M. Sudheer, K. M. Subbaya, Dayananda Jawali Vol.11, No.2
metallic mold coated with release agent to yield specimens of 300×300×3 mm upon curing and
released from mold after 24 hrs.
Composition of the test specimens was varied up to 20% of filler loading at intervals of 5%.
Extreme care was taken to avoid any undesirable filler settling effect by casting the slurry just
prior to its gelling stage, all time keeping it in a stirred condition. This was done to ensure the
uniform composition of cast specimens across its volume. Fig.1 outlines the casting procedure.
2.3 Mechanical Characterization
All tests were performed at room temperature and as per ASTM standards. The standards used
are list ed in the T abl e 2. All the repo rted val ues w ere cal cul ated as aver age s over five s peci mens
for each composition.
2.3.1 Density
Density is mass per unit volume and is usually expressed in g/cc. Densities of the composite
were determined using the Archimedes principle. Distilled water at room temperature was used
as the immersion fluid and the mass was measured using the high precision digital weighing
balance (Shimadzu Japan, 0.1mg Accuracy). Mass of the specimen divided by the difference in
the readi ng before an d aft er the imm ersion of t he compos ite specim en in the m easurin g jar gives
density values for the specimens.
2.3.2 Hardness
Hardness of material is defined as the resistance to deformation, particularly permanent
deformation, indentation or scratching. Hardness of developed composite samples was measured
using Rockwell’s Hardness Tester on M-Scale.
2.3.3 Tensile Properties
Vol.11, No.2 Mechanical Properties of Potassium Titanate 199
The tensile properties namely Tensile Strength, Tensile Modulus and Elongation at Break were
investigated using Universal tensile testing machine (JJ Lloyd, London, United Kingdom,
capacity 1–20 kN). The tensile test was performed at a crosshead speed of 10 mm/min
considering a gauge length of 50 mm.
Figure 1. Schematic representation of the casting procedure
2.3.4 Flexural Properties
The flexural properties were investigated using Universal testing machine (JJ Lloyd, London,
United Kingdom, capacity 1–20 kN). Three-point bending test was performed at a crosshead
speed of 13 mm/min considering a beam span of 50 mm.
2.3.5 Impact Strength
200 M. Sudheer, K. M. Subbaya, Dayananda Jawali Vol.11, No.2
Impact strength refers to ability of material to absorb the energy. Izod impact testing was done
using CEAST pendulum impact testing machine (Max. capacity 25J). Unnotched specimens
were fractured by impact input energy of 5.5 J.
2.3.6 Heat Deflection Temperature
Heat deflection temperature corresponds to the temperature that results in a deflection of 0.25mm
at the mid span of the composite specimen during the three point bending conditions. This
temperature was measured using a custom built set up.
Table 2. Standards used for Mechanical Test i ng
Mechanical Properties
Hardness (Rockwell M scale)
Tensile properties
ASTM D3039
Flexural properties
Impact strength (Izod test)
Heat deflection temperature
PTW has modified the properties of neat epoxy in many ways. Significant improvements have
been achieved by incorporating few wt% of PTW into epoxy matrix. Mechanical properties of
filled polymer composites depend strongly on three important factors namely filler size, filler-
matrix interface adhesion and filler loading [21]. Various trends of effect of PTW on composite
properties have been observed due to interplay between these three factors which cannot be
3.1 Density
Density of a composite depends on the relative proportion of matrix and reinforcing materials
and is one of the most important factors determining the properties of the composites. Many
Vol.11, No.2 Mechanical Properties of Potassium Titanate 201
mathematical models are developed for determining the densities of polymer composites. Rule of
mixture [20] is one such simplest and widely used model for determining the theoretical densities
of polymer composites. The variation in the density with respect to PTW content is reported in
the Figure 2. It was observed that incorporation of PTW into epoxy matrix has increased the
density of composites. This is mainly because of highly dense PTW fillers. Figure 2 also
compares theoretical density values and experimental results. It was observed that experimental
values are slightly lesser than that predicted by Rule of mixture. This was mainly because of
micro voids present in the composite which was not considered in theoretical calculations.
The voids significantly affect some of the mechanical properties and even the performance of
composites in the place of use. Higher void contents usually mean lower fatigue resistance,
greater susceptibility to water penetration and weathering. The knowledge of void content was
desirable for estimation of the quality of the composites. It was understandable that a good
composite should have fewer voids. However, presence of void was unavoidable in composite
making particularly through hand-lay-up route.
Figure 2. Effect of PTW content on the Density of neat Epoxy
202 M. Sudheer, K. M. Subbaya, Dayananda Jawali Vol.11, No.2
3.2 Hardness
PTW was found to increase the hardness of neat epoxy (Table 3). Increase in hardness of neat
epoxy with the increase in the content of PTW can be attributed to uniform dispersion of the
harder PTW phase in epox y matrix. A significant improvement in hardnes s was observed for 10
wt% PTW and hardness used to increase by small value at higher PTW contents. High strength
PTW reinforcements may result in forming a network structure that improves the hardness of the
composites. Whisker reinforcements such as SiC, Al2O3, CaCO3 and PTW generally impart
higher hardness to base polymer matrix [4,6,1 1].
3.3 Tensile Properties
Effect of PTW on tensile strength of the composites is depicted in Figure 3. Optimal increase in
the tensile strength was observed at 10% PTW (50.94 MPa) compared to neat epoxy (44.65
MPa) which indicates a gain of nearly 14% in tensile strength. Reduction in the tensile strength
at higher whisker loadings is explained by poor polymer-whisker interaction.
Ultimate strength of a composite depends upon weakest fracture path through t he material. Hard
particl es such as PTW affect the st rength in t wo ways. One i s the weaken ing effect due to stress
concentrations they cause and another is the reinforcing effect since they serve as barriers to
crack growth [21]. In some cases, the weakening effect is predominant and thus composite
strength is lower than matrix and in other cases reinforcing effect is more significant and then
composites have higher strength than the base matrix.
Table 3. Hardness properties of Epoxy/PTW composites
Hardness (Rockwell M Scale)
Neat Epoxy
Epoxy + 5% PTW
Epoxy + 10% PTW
Epoxy + 15% PTW
Epoxy + 20% PTW
Vol.11, No.2 Mechanical Properties of Potassium Titanate 203
Tensile modulus and percentage elongation variation with PTW loading is illustrated in Figure 4.
Tensile modulus is found to decrease at 5 wt% of PTW and later increased considerably at higher
filler loadings. It indicated that the composite has achieved superior stiffness at higher PTW
content. Highest composite stiffness was observed at 20 wt% PTW which is a gain of 15% over
neat Epoxy. Improvement in tensile modulus is an obvious effect of stiffer PTW particles.
However elongation was reduced with the increase in the filler content. This indicated the loss in
the ductility of the composite at higher PTW contents.
Figure 3. Effect of PTW content on the Tensile Strength of neat Epoxy
204 M. Sudheer, K. M. Subbaya, Dayananda Jawali Vol.11, No.2
Figure 4. Effect of PTW on (a) Tensile Modulus (b) Percentage Elongation of neat Epoxy
Similar trend in the tensile behavior of PTW reinforced polymer composites with PEEK as
matrix material [22, 23] and PP/PA blend [24] has been reported by previous researchers.
3.4 Flexural Properties
Flexural strength indicates ability of material to withstand bending forces applied
perpendicularly to its longitudinal axis. In the present investigation a maximum strength of 72.48
MPa was observed for 10 wt% PTW which is an improvement of nearly 24% over the neat
epoxy (Fig. 5a). However maximum flexural modulus of 4.30 GPa was observed at 5 wt% of
PTW which is a gain of 13% over that of neat Epoxy (Fig. 5b).
Flexural strength was found to decrease at higher PTW content. Interfacial adhesion between
PTW and epoxy molecules might be weaker than the intermolecular forces of epoxy and the
micro-porosities of PTW/Epoxy composites tends to increase with the increasing PTW content,
thus the flexural strength of composites was decreased at higher PTW content. In the present
study flexural modulus obtained for composites are higher than that for neat epoxy for all
material combinations. However at higher PTW contents, compatibility between the polymer
matrix and PTW became poor and flexural modulus found to decrease. In t he experim ent al ran g e
the best flexural properties were obtained with the composite with 10% PTW.
Vol.11, No.2 Mechanical Properties of Potassium Titanate 205
Figure 5. Effect of PTW content on (a) Flexural Strength (b) Flexural Modulus of Epoxy
Figure 6. Effect of PTW content on the Impact Strength of neat Epoxy
3.5 Impact Strength
206 M. Sudheer, K. M. Subbaya, Dayananda Jawali Vol.11, No.2
The impact property of polymeric materials is directly related to the overall toughness of the
material. The objective of Izod impact test is to measure the relative susceptibility of a standard
test specimen to the pendulum type impact load. The results are expressed in terms of kinetic
energy consumed by the pendulum in order to break the specimen. The impact resistance results
were very striking (Fig. 6). It was observed that impact strength of all materials combinations are
less than that of neat epoxy. Composite with PTW content of 20 wt% exhibited the least impact
strength (63.33 J/m) compared to neat epoxy (73.33 J/m) which is reduction of nearly 14%. It is
obvious that PTW is not beneficial in improving the impact properties of neat epoxy.
Polymer based composite materials when subjected to impact type of loading conditions, energy
is absorbed in the process of plastic deformation of matrix material, debonding at
matrix/reinforcement interface and in the fracture of reinforcing material. The phenomena that
absorbs least energy for its occurrence become prominent and leads to fracture [25]. In the
present study, plastic deformation of epoxy matrix and debonding at interface could be the
reason for decrease in impact properties of composites. However impact strength can be
enhanced by proper surface treatment of whiskers resulting in improved adhesion between
polymer and PTW and also by using suitable toughners for epoxy [15,16].
Vol.11, No.2 Mechanical Properties of Potassium Titanate 207
Figure 7. Effect of PTW content on the Heat Deflection Temperature of neat Epoxy
The decline in the impact strength with the increase in the PTW content was reported b y Zhuang
et al. [22] and Long et al. [26] also observed same trend of impact strength with the PTW
loading in case of Polypropylene composites.
3.6 Heat Deflection Temperature
Heat deflection temperature is an indicator of general short term temperature resistance of
materials. PTW was found to have positive influence on the distortion temperature of neat epoxy.
An increase in the distortion temperature was observed with the PTW loading (Fig.7). At 20 wt%
loading of PTW, a gain of 23% in deflection temperature was observed compared to the
performance of neat epoxy. Increase in the deflection temperature is an obvious result of high
thermal stability (1200°C in air) of PTW.
208 M. Sudheer, K. M. Subbaya, Dayananda Jawali Vol.11, No.2
The effect of content of PTW on the properties of epoxy resin system was carefully studied.
Study revealed a direct correspondence between the content of PTW and mechanical properties
of composites and following conclusion were drawn.
1. PTW is an excellent performance whisker; it can improve density, hardness and heat
deflection temperature of neat epoxy.
2. PTW filler addition shows significant improvement in tensile and flexural properties only at
certain co nt ent (5 -10 wt %). This per formance is si milar to that of nano-particles. Thus PTW can
be an effective strengtheners and stiffners for thermosetting resins like epoxy.
3. Addition of PTW indicated a detrimental effect on impact strength of epoxy and it cannot be
an effective toughners for epoxy.
PTW has immense scope on the fabrication of whisker reinforced polymer composites having
vast number of industrial applications.
The authors would like to thank Director Fr. Valerian D’souza and Principal Dr. Joseph
Gonsalvis, St. Joseph Engineering College Mangalore, for their cooperation and encouragement
to carry out research work. Financial assistance provided by Sriram Charitable Trust Mudradi is
highly acknowledged. Authors also express their sincere thanks to M/s. GTTC Mangalore for
technical help and M/s. Brakes India Ltd. Mysore for providing testing facilities.
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