A new nano ceria reinforced epoxy polymer composite

INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME
ENGINEERING AND TECHNOLOGY (IJARET)

ISSN 0976 - 6480 (Print) IJARET
ISSN 0976 - 6499 (Online)
Volume 3, Issue 2, July-December (2012), pp. 248-256
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©IAEME
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A NEW NANO-CERIA REINFORCED EPOXY POLYMER COMPOSITE
WITH IMPROVED MECHANICAL PROPERTIES

Siddhant Datta1*, B.M. Nagabhushana2, R. Harikrishna2
1
Department of Mechanical Engineering, RV College of Engineering. Bangalore. India-560 059
2
Department of Chemistry, MS Ramiah Institute of Technology. Bangalore. India-560 054

(*Corresponding author: email-siddhant.datta@gmail.com)

ABSTRACT

This study deals with enhancement of mechanical properties of Epoxy matrix using nano-
Ceria (CeO2) as particulate reinforcement. Nano-Ceria with 10-20nm crystallite size was
prepared by solution combustion method using Citric acid as fuel. Epoxy matrix was a standard
diglycidyl ether of bis-phenol A (DGEBA) cured with aliphatic amine hardner. Nano-Ceria was
dispersed in epoxy resin by manual stirring followed by sonication at 20 Khz for 15 minutes.
Amine hardner was added to the sonicated mixture and rectangular polymer composite slabs of
10x8x1.5 cm3 were cast using releasing agent coated glass moulds. Effect of varying wt% of
nano-ceria filler on mechanical properties of the matrix was studied. Flexural strength,
Compressive strength, Vicker’s Microhardness and Density were tested for polymer slabs
varying in wt% of nano-ceria filler from 0 to 3 wt%. Polymer nano-composite sample containing
0.25 wt% nano-ceria exhibits 42% increase in flexural strength. Sample with 0.5 wt% nano-ceria
shows increase of 42.7% in compressive strength. Microhardness increased by 29% for the
sample with 1 wt% of nano-ceria. All tests were carried out according to ASTM standards. As
the wt% of nano-ceria increased the mechanical properties showed improvement till a maximum
value and then these properties deteriorated with further increase in nano filler content. However,
density continued to increase with increase in wt% of nano-Ceria.

Keywords: Epoxy, Nano-ceria, Sonication, Mechanical properties, Nano-composite.

1. INTRODUCTION

Epoxy resins are well established thermosetting matrices of advanced composites, displaying
a series of interesting characteristics like good stiffness and specific strength, dimensional
stability, chemical resistance, ease of processing and also strong adhesion to the embedded

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reinforcement [1]. Epoxy resin is widely used as host matrix for fabricating Fiber Reinforced
Polymers (FRP) with higher strength to weight ratio than steel. Commonly used Fibers in epoxy
based FRPs are glass fiber, kevlar fiber, carbon fiber etc. The use of particulate fillers has been
proven to improve the material properties of epoxy resins. Building on the fact that the micro-
scaled fillers have successfully been synthesized with epoxy resin, the nano-scaled fillers are
now being considered to produce high performance composite structures with further enhanced
properties. Nano filler reinforced epoxy matrix can also provide superior host matrix for FRP
composites. Improvements in mechanical, electrical, and chemical properties have resulted in
major interest in nanocomposite materials in numerous automotive, aerospace, electronics and
biotechnology applications [2].
Various kinds of ceramic materials, e.g. SiC, Montmorillonite clay, Al2O3, SiO2, WO3 and
ZrO2, have been used to reinforce polymers. Superior properties of metal oxides such as high
refractoriness, hardness, compressive strength, modulus of elasticity, thermal resistance and wear
resistance make them suitable for use as reinforcement material in polymer matrices [3,4].
Incorporating ultra-fine particles of metal oxides can significantly improve mechanical properties
of the host matrix by getting uniformly embedded in the thoroughly cross linked chains of the
thermoset-polymer. Metal oxide nanoparticles possess high surface area to volume ratio which
increases interfacial interaction between nano-reinforment and host polymer matrix, thus better
adhesion between resin and filler is achieved. These nanoparticles present good wettabilty with
the thermoset-polymer and fill in the small gaps between cross-linked polymer chains providing
the chains with high resistance to deformation under stress. Nanoparticle reinforcements can
reduce thermal expansion coefficient and increase thermal and wear resistance of the host matrix.
By uniformly distributing these nano-reinforcement particles in epoxy resin the reinforcement
material can impart superior mechanical properties to every region of the host matrix in a
uniform manner [5,6].

The nanoparticles present high tendency to agglomerate under the influence of Vander Val’s
forces. Agglomeration of these particle in the host matrix can result to reduced interfacial
interaction between resin and reinforcement. Non uniform dispersion of the reinforcement causes
thermal stresses in the matrix around agglomerated nano particles due to unevenly distributed
coefficient of thermal expansion within the composite matrix. Many methods can be used to
infuse nanoparticles inside polymers including ultra-sonication bath, probe sonicator, high shear
mixing by ball milling, high speed stirrer etc [7].

In this study the nano-CeO2 reinforced epoxy slabs were fabricated and fiber reinforcements
were not added in order to clearly analyze the effect of lab synthesized nano-CeO2 particles
(crystsllite size 10-20nm) on mechanical properties of epoxy resin matrix. Sample slabs with
wt% of nano-CeO varying from 0 to 3wt% were fabricated and mechanical properties namely
flexural strength, compressive strength, microhardness and density were tested.

2. EXPERIMENTAL

2.1 Materials used
The matrix used in this work is a commercially available analar grade of diglycidyl ether of
bis-phenol A ((4-(2,3 epoxypropoxy) phenyl) propane), abbreviated as DGBEA, was obtained
from Huntsman Advanced Materials under the commercial name Araldite AY 105. Along with

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epoxy resin an aliphatic polyamine hardner commercially known as Aradur HY 951 was also
obtained from the same company. Nano-CeO2 powder synthesized by Solution Combustion
method was used as reinforcement material.

2.2 Synthesis of nano-CeO2 particles.
Nano-CeO2 particles were synthesized by dissolving cerium nitrate (Ce(NO3)3.6H2O) and
citric acid (C6H8O7) in minimum quantity of double distilled water in a pyrex dish. The solution
is then placed in a pre-heated Muffle furnace maintained at 400±10°C. Solution boils and
dehydration takes place followed by decomposition and evolution of gases. Then spontaneous
combustion occurs with enormous swelling and porous product, CeO2 is obtained. Solution takes
5mins in Muffle furnace till the bright sparks throughout the pyrex dish are seen which indicate
the occurrence of spontaneous combustion and formation of nano-Ceria. The theoretical equation
of the combustion of redox mixture for the formation of CeO2 nanopowder using citric acid fuel
can be represented by:

2Ce(NO3)3 (aq) + C6H8O7 (aq) → 2 CeO2 + 6CO2 (g) + 4H2O (g) + 9 N2 (g)........................ (1)
2.3 Characterization of nano-CeO2 by PXRD, FTIR and SEM.
The powder XRD patterns of CeO2 samples were obtained using a Philips PW/1050/70/76 X-
ray diffractometer which was operated at 30 kv and 20 mA using CuKa radiation with nickel
filter at a scan rate of 20/min. The surface morphology of the powders was examined using
JEOL (JSM-840A) scanning electron microscopy (SEM). FTIR spectra were recorded using a
Nicollet IMPACT 400 D FTIR spectrometer in the range 4000-400 cm-1 using KBr pellet.

2.4 Fabrication of polymer nano composite slabs.
Nano-Ceria filler was added to epoxy resin and stirred manually in a beaker using a glass rod
followed by Sonication. Sonication of the mixture was done using a Probe-type Ultrasonic
processor at 20 Khz frequency for a duration of 15 minutes. On/Off pulse was set to 10s to avoid
over heating of the resin. Sonicated mixture was allowed to cool down following which
polyamine hardner was added to cure the resin. This mixture was poured into rectangular moulds
of dimension 10x8x1.5 cm3 and allowed to cure at room temperature for 48 hours. Resin to
hardner weight ratio was kept 10:1 as specified.

2.5 Flexural test.
Three Point Bending test was used to determine the flexural strength of the polymer
composites containing different wt% of nano-ceria. Specimens with dimensions 80x10x4 mm3
were prepared for Three point bending test according to ASTM D-790-2010 standard.

2.6 Compression test.
Compressive strength of the polymer composite samples was determined using Universal
Testing Machine (UTM). Compression test was carried our according to ASTM D-695-2002
standard and specimens of dimensions 10x10x4 mm3 were prepared for this test.

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6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July December (2012), © IAEME
July-December

2.7 Microhardness test.
Microhardness of polymer composites was determined using Vicker’s Microhardness tester
with a diamond pyramid indenter. Load of 300g was applied for a duration of 20s and diagnols
d 20
of the indentation were measured with an Optical Microscope with a Micrometer attachment in
Microscope
the eye piece.

Formula used: …………………………......(2)
………………………….....
Where ‘F’ is Load applied in N, ‘d’ is the average diagonal of indentation and ‘HV’
represents Vickers Hardness Number.

2.8 Density test.
Density was determined using displacement method with distilled water at 23°C. Test was
performed according to ASTM DD-792-1998 standard.

3. RESULTS AND DISCUSSIONS

3.1 Characterization
3.1.1 Powder X-Ray Diffraction of nano
Ray nano-CeO2 powder.

Figure 1 PXRD pattern for as-formed nano-ceria

Fig. 1 gives the PXRD patterns of the as as-prepared CeO2 sample, diffraction peaks,
d
corresponding to cubic fluorite structure (JCPDS: 43 1002) are clearly observed. By applying the
43-1002)
Scherrer’s formula [8] to the full width at half maximum of the diffraction pe peaks, the mean
crystallite sizes was calculated as 10
10-20 nm.

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3.1.2 Scanning Electron Microscopy of nano-CeO2 powder.

Figure 2 SEM image of nano-ceria

Fig 2 shows the SEM photographs of as prepared CeO2. The nano particles are agglomerated,
and fluffy with porous morphology. The agglomeration of nanoparticles is usually explained as a
common way to minimize their surface free energy. The voids and pores present in the sample
are due to large amount of gases produced during the combustion synthesis.

3.1.3 FTIR analysis of nano-CeO2.

Figure 3 FTIR spectra of nano-ceria

Fig. 3 shows the FTIR spectra of as formed CeO2 nanopowder. The peak appearing at 400
-1
cm , can be ascribed to the Ce-O vibration of the CeO2 nanopowder. The weak absorption peak
at 3421 cm-1 corresponds to the -OH group of water adsorbed on the surface of the CeO2 powder.

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3.2 Mechanical properties
3.2.1 Flexural test
Flexural tests of the samples reveal improvement in the bending strength of epoxy matrix due
to addition of nano-ceria. Maximum increase of 42% in bending strength was shown by the
sample containing 0.25 wt% of nano-ceria. Flexural strength of pure epoxy sample was 64.4
Mpa and increased with increase in wt% of nano-ceria till a maximum value of 91.5 Mpa was
obtained for 0.25 wt% sample. Increase in wt% nano-ceria beyond 0.25% resulted in decrease in
flexural strength and sample with 3 wt% ehibited lowest flexural strength of 57.6 Mpa.
Relation of flexural strength to wt% of nano-ceria is shown in Fig4. Increase in flexural
strength due to addition of nano-CeO2 till 0.25wt% can be attributed to resistance to crack
initiation and crack growth offered by nano-ceria particles bonded strongly in the spaces between
polymer chains. Due to extremely high surface area of nano-particles they adhere strongly to the
epoxy matrix and fill in extremely small gaps between polymer chains owing to their nano size.
The high strength of ceramic reinforcement is transmitted uniformly throughout the matrix when
reinforcement is dispersed uniformly at nano scale level.[4] Presence of air bubbles in matrix can
form crack initiation sites under bending stresses, formation of these air bubbles can be reduced
by addition of reinforcement since reinforcement material can fill in void spaces.

Figure 4 Flexural strength vs Wt% of nano-ceria

The decrease in flexural strength when wt% is increased beyond 0.25% is due to absence of
enough resin in some regions to bond with surplus reinforcement material which results in
weaker regions in the matrix. Higher content of nanoparticles can hinder uniform curing of the
resin and result in non uniform cross linking of the epoxy network. At higher wt% there is a
possibility of agglomeration of nano-reinforcement in different regions of the matrix resulting in
non uniform dispersion of reinforcement material [7,9]. Thermal stresses can be induced in
regions around agglomerated nano-particles at the time of curing since there is a mismatch of
thermal expansion coefficient of nano-ceria reinforcement and epoxy matrix.

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3.2.2 Compression test
Compression tests reveal increase in compressive strength of epoxy matrix with increase in
wt% of nano-ceria from 0 to 0.5 %. Compressive strength of pure-epoxy sample was 368 Mpa
which increased to a maximum value of 525 Mpa for 0.5wt% sample. Increase in wt% beyond
0.5% caused decrease in compressive strength and 3 wt% showed compressive strength of 406
Mpa. This trend is shown in Fig 5.

Figure 5 Compressive strength vs Wt% of nano-ceria

Increase in compressive strength with increase in wt% of nano-ceria till 0.5wt% is a result of
high strength of CeO2 nanoparticles which is transmitted uniformly to the host matrix due to
very high interfacial area between resin matrix and nanoparticles assists in transfer of physical
stress. Nanoparticles are uniformly dispersed in the matrix and occupy spaces between polymer
chains decreasing mobility of the chains and increasing resistance of matrix to deformation and
crack growth. Possibility of air bubbles reduces by addition of nano-ceria filler thus preventing
crack initiation due to void spaces in the matrix. Decrease in compressive strength on increasing
wt% beyond 0.5% was observed. This decrease can be due to agglomeration of nanoparticles and
lack of resin material to accommodate high content of nano-ceria. Region around agglomerated
nanopaticles develops thermal stresses during curing cycle due to mismatch of thermal expansion
coefficient between resin host matrix and nano-ceria aggregate [11]. Cracks can initiate in such
regions with stress concentrations present due to poorly dispersed reinforcement or lack of resin
material to bond high content of reinforcement.

3.2.3 Vicker’s Microhardness test
Microhardness of pure epoxy slab was 268.66 HV/0.3Kg and increased to a maximum value
of 347.62 HV/0.3Kg for 1 wt% slab. Composite slabs with low filler content (0.1 and 0.25 wt%)
do not exhibit considerable change in microhardness. Increase in nano-ceria content above 0.25
wt% showed increment in microhardness till maximum value was achieved at filler loading of 1
wt%. When filler loading was increased beyond 1 wt% a decrease in microhardness is observed
and value drops down to 319.85 HV/0.3Kg for 1.5 wt% slab. Decreased mobility of polymer
chains due to hard ceramic nano filler can be the reason for high microhardness exhibited by
slabs at high filler content [10,12]. Higher surface area of nano-ceria reinforces larger volume of
resin matrix and stress can be transferred to nanoparticles more efficiently owing to high

254


interfacial area between resin and nano-Ceria. Trend of Microhardness with wt% of nano-ceria is
given in Fig 6.

Figure 6 Vickers Microhardness vs Wt% of nano-ceria

More than 1 wt% nano-ceria content resulted in drop in microhardness value but still slabs with
1.5 and 3 wt% possessed significantly higher microhardness than pure epoxy slab. High hardness
of ceramic filler contributes to the increase in microhardness but high content of nano-ceria
results in its non uniform distribution and formation of aggregates. This can lead to non uniform
reinforcement of host matrix and hindrance in curing of matrix in regions where nano-ceria
aggregates are present.
3.2.4 Density test
Minute increase in density was observed with increment in wt% of nano-CeO2 due to high
density of Ceria particles. Density of pure epoxy casting was 1.19g/cm3 and sample with 3wt%
of nano-CeO2 exhibited a density of 1.22g/cm3. Table 1 shows the trend of density of polymer
castings with variation in wt% of nano-ceria.

Table 1 Density with varying Wt% of nano-ceria

Wt% of 0% 0.10% 0.25% 0.50% 1.0% 1.50% 3.0%
nano-CeO2
Density 1.19 1.19 1.20 1.20 1.20 1.21 1.22
(g/cm3)

4. CONCLUSION

Nano-ceria reinforcement synthesized by combustion method significantly improved the
mechanical properties of epoxy matrix. 42.6% increase in compressive strength, 42% increase in
flexural strength and 29% increase in microhardness suggest that this nano-ceria reinforced
epoxy can be used as host matrix for fabricating better FRPs. Enhancement of mechanical
properties uniformly throughout the polymer composite slabs at filler content lower than 1 wt%

255


suggests that sonication process successfully dispersed the nano-ceria particles in the resin
matrix. Negligible increase in density was observed when filler content increased from 0 to 3
wt%. Since low nano-ceria content is needed to achieve this improvement in properties there is
scope of accommodating additional reinforcement materials, e.g. carbon fiber, glass fiber, carbon
nanotubes, into the epoxy host matrix.

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