Effect of cenosphere on mechanical prope
Original Article
Effect of cenosphere on mechanical
properties of bamboo–epoxy composites
Journal of Reinforced Plastics
and Composites
32(11) 794–801
! The Author(s) 2013
Reprints and permissions:
sagepub.co.uk/journalsPermissions.nav
DOI: 10.1177/0731684413476925
jrp.sagepub.com
Hemalata Jena, Mihir Kumar Pandit and Arun Kumar Pradhan
Abstract
Cenosphere is a ceramic-rich industrial waste produced during burning of coal in thermal power plants. This study deals
with the effect of cenosphere as particulate filler on mechanical behaviour of natural fibre composites. The natural fibre
composite consists of bamboo fibre as reinforcement and epoxy as matrix. The bamboo fibre is treated with alkali to
improve its surface properties. The conventional hand lay-up technique is used to prepare different composite specimens. Twenty numbers of different composite specimens are prepared with varying number of laminae and filler content.
The samples are analysed for their mechanical properties to establish the effect of varying filler content and the number
of laminae. It is found that the mechanical properties are significantly influenced by addition of this waste-based ceramic
filler.
Keywords
Cenosphere, bamboo fibre, alkali treatment, epoxy resin, mechanical properties
Introduction
Nowadays natural fibres have gained wide popularity
as reinforcements in polymer composites for various
applications. Due to its eco-friendly nature and good
mechanical properties, it offers a promising alternative
to glass, carbon, and other synthetic fibres used for the
manufacture of composites.1 The potential of natural
fibres such as abaca, sisal, pineapple, flax and coir as
reinforcement in composites is now becoming a popular
area of research.2–6 Among these available natural
fibres, bamboo has many advantages, such as ample
availability, fast growth rate, lightweight, low cost
and low energy consumption in processing and biodegradability.7 It is becoming very popular as one of
the most useful non-timber forest resources due to its
high socio-economic benefits. It possess very good
mechanical properties due to its longitudinally oriented
fibres. Using bamboo fibre one can reduce the demand
for wood fibre and environmental impacts associated
with wood fibre harvesting. Hence, bamboo fibre
appears to be one of the most promising candidates
as natural fibres for polymer composites. It is reported
that bamboo composite possesses specific strength
superior to that of ordinary glass fibre reinforced
composites.8 But the presence of hydroxyl and other
polar groups in the natural fibres leads to the weak
interfacial bonding between fibres and matrix. The
fibre surface properties can be improved substantially
by different chemical treatments.9 Alkaline treatment is
one of the most used chemical treatments of natural
fibres when used to reinforce in thermoplastics or
thermosets. Mishra et al.10 while working with sisal
fibre found that the mechanical properties of the composite improved by treating the fibre with alkali. The
improvement was found to be highest for 5% NaOH
concentration.11–13
Further, the physical and mechanical characteristics
of composites can be modified by adding a suitable
filler phase to the matrix during their fabrication.
Addition of filler in composites not only improves its
School of Mechanical Sciences, Indian Institute of Technology,
Bhubaneswar, India
Corresponding author:
Hemalata Jena, School of Mechanical Sciences, IIT Bhubaneswar,
Samantapuri, Bhuabeneswar 751013, India.
Email: [email protected]
795
Jena et al.
mechanical properties but also reduces its cost.14
Therefore, the use of inorganic fillers in the composites
is gaining popularity. There are a number of literatures
available on the use of ceramics as filler in composite
materials.15–18 Cenosphere, which is one of the industrial wastes produced during burning of coal in thermal
power plants,19 could be a unique class of filler in polymer matrix composite due to its fine dispersion, homogeneity, inertness and chemical stability. Though the
literature is rich with the studies on the mechanical
properties of the cenosphere filled polymer composites,20–23 no attempt has been reported till date to critically analyse the mechanical characterisation of
cenosphere filled bamboo–fibre composites.
It is proved that the mechanical properties of
bamboo–epoxy composites under different loading conditions can be modified by changing the number of
laminae and configuration of laminae in resin.8,24 And
also hybridisation of natural fibre with different fillers25
or synthetic fibres like carbon, aramid, glass, etc., can
improve the stiffness, strength, as well as moisture
resistance of the composites.26–28
The present study attempts to investigate a new class
of natural fibre composite in which bamboo fibre is
used as reinforcement, epoxy as matrix and cenosphere
as particulate microsphere filler. The mechanical properties of these bamboo fibre reinforced composites are
evaluated. The effect of adding cenosphere to matrix
phase aims at improving their mechanical properties.
The effects of number of laminae and varying weight
percent of cenosphere have also been studied for this
purpose.
Table 1. Raw materials and their physical characteristics.
Raw materials
Grade
Characteristics
Cenosphere
CS 300
Epoxy
LAPOX L-12
Hardener
K-6
Bamboo fibre
–
Particle density ¼ 0.45–
0.80 g/mL, particle
size ¼ 60–94 mm, light
grey powder,
non-soluble in water,
melting temperature ¼ 1300–1500 C
Viscosity ¼ 9000–12,000
mPa.s,
density ¼ 1.1 g/cc
Refractive index at
25 C ¼ 1.4940–1.5000
Weave type, density ¼ 0.95 g/cc,
width ¼ 4.5 mm,
thickness ¼ 1.5 mm
Table 2. Designation of composite specimens.
Group
Designation
A
A0
A2
A4
A6
A8
B
B0
B2
B4
B6
B8
C
C0
C2
C4
C6
C8
D
D0
D2
D4
D6
D8
Fabrication procedure
In the present work, the composite consists of bamboo
fibre as reinforcement and cenosphere as filler material
in the epoxy matrix. The properties of these constituents are given in Table 1.
Initial step of fabricating the composite is alkali
treatment of bamboo mats to improve their mechanical
properties. The bamboo mats are cleaned and dried
before dipping into NaOH solution of 5% concentration for 30 min at room temperature (20 C).13 These
mats are thoroughly washed in distilled water and
then neutralised in 2% HCl solution. The neutralised
mats are then dried in an oven at 60 C for 24 h. The
fabrication of the composite is done by conventional
hand lay-up technique at room temperature. Low temperature cured epoxy resin (L12) and corresponding
hardener (K6) are mixed in a ratio of 10:1 by weight.
A number of composite specimens are prepared using
different number of laminae and varying weight percent
of cenosphere as filler. The composite specimens
Composite
with varying
laminae
3-layered bamboo–
epoxy composite
5-layered bamboo–
epoxy composite
7-layered bamboo–
epoxy composite
9-layered bamboo–
epoxy composite
Composite
with varying
wt% of
23cenosphere
0.0
1.5
3.0
4.5
6.0
0.0
1.5
3.0
4.5
6.0
0.0
1.5
3.0
4.5
6.0
0.0
1.5
3.0
4.5
6.0
796
so made with varying number of layers and weight
percent of cenosphere are designated as shown
in Table 2.
Journal of Reinforced Plastics and Composites 32(11)
10mm
170mm
250mm
Mechanical tests
In order to study the mechanical properties of the prepared composite specimens with different compositions,
the following tests are conducted.
Figure 1. Tensile test specimen.
Scanning electron microscopy
The surfaces of the specimens are examined directly
under scanning electron microscope (SEM) JEOL
JSM-6480LV. The composite samples are mounted on
carbon stubs. To enhance the conductivity of the samples, a thin film of gold is vacuum-evaporated on them
before the photomicrographs are taken.
Span L/t=10
Micro-hardness test
Micro-hardness measurement is done using a Zwick/
Roell micro-hardness tester as per ASTM E92. A diamond indenter, in the form of a right pyramid with a
square base and an angle 136 between opposite faces,
is used with load.
Figure 2. Flexural test specimen.
Tensile test
The tensile test is performed in the universal testing
machine (UTM) Instron 3382 as per ASTM D303976. The geometry of the test specimen is shown in
Figure 1. At a grip pressure of 4.2 MPa, the rate of
loading 2 mm/min is used for testing. During the test
a uni-axial load is applied through both the ends of the
specimen. The results are analysed to calculate the tensile strength of the composite samples.
2.54mm
64mm
Figure 3. Impact test specimen.
Flexural test and interlaminar shear strength test
The data recorded during the 3-point bend test is used
to evaluate the flexural strength and interlaminar shear
strength (ILSS). The test is conducted as per ASTM
standard (D2344-84) using the same UTM with bend
test fixtures. The cross head speed of 10 mm/min is
maintained. Geometry configuration for flexural test
specimen is shown in Figure 2.
Impact test
Impact test is performed on the pendulum impact testing machine as per ASTM D256. A ‘V’ notch is created
at the centre of the specimen having notch depth of
2.54 mm and notch angle of 45 , using Impactometer
Figure 4. SEM image of untreated fibre.
797
Jena et al.
6545 (Ceast, Italy) as shown in Figure 3. A 10 mm
hemispherical head impacts a test specimen at a
constant velocity of 1.06 m/s at impact energy of
15.26 J. The respective values of impact energy of different specimens are recorded directly from the dial
indicator.
Figure 5. SEM image of treated fibre.
Results and discussion
The morphology of the composite reinforced with
untreated and treated fibre surfaces have been studied
using an SEM. The surfaces of untreated fibre appear
to be rough as shown in Figure 4. This may be due to
the presence of lignin, wax, oil and other surface impurities which are removed with alkali treatment. The surfaces of the treated fibre are shown in Figure 5. These
clean surfaces are expected to provide direct bonding
between the fibre and matrix.
The hardness test results as shown in Figure 6 indicate that the hardness increases with the increase in
weight percent of cenosphere for the composites of
type A, B and C. The increase in hardness value may
be due to the fact that the outer shell of the cenosphere
made of ceramic particles enhances the hardness.
However, hardness value for type D composite
decreases after a certain number of layers for the
same weight percent of cenosphere. The maximum
hardness value is found in the C6 composite, which
is 16% higher as compared to unfilled composite
of type C0.
The values of tensile strength of different bambooepoxy composites are given in Figure 7. A marginal
increase in strength is observed for A2, B2 and C2 as
compared to A0, B0 and C0 composites, respectively.
The results indicate that cenosphere can increase the
tensile strength by 25.4%, 6.50% and 4.10% for
40
35
Hardness (Hv)
30
25
20
15
10
5
0
A0 A2 A4 A6 A8 B0 B2 B4 B6 B8 C0 C2 C4 C6 C8 D0 D2 D4 D6 D8
Composite Type
Figure 6. Micro-hardness of the laminates.
798
Journal of Reinforced Plastics and Composites 32(11)
composites A, B and C, respectively. It is observed that
the influence of filler addition is more in case of composite type A which is having a lower weight fraction of
fibre i.e. 18%. Laminates B and C, which have more
number of layers, are accompanied by less change in
maximum tensile strength with the addition of filler,
whereas in case of laminate D there is no improvement
of strength. During the preparation of laminate D
having 43% fibre weight fraction, it is observed that
the quantity of resin is insufficient to impregnate the
fibres. This, subsequently, influences the wettability of
the fibre and fibre matrix adhesion which, in turn,
increases the void content in the composite. As a
result, the crack initiation and its propagation will be
easier in these composites. Though the strength of the
composites A, B and C are observed to increase with
the addition of cenosphere filler due to better adhesion
and wettability, there is a limitation to addition of filler.
Too higher filler content leads to discontinuous phase
of resin and this develops clusters of filler, which results
in local phase inversion leading to failure. SEM micrographs are taken for surface failed sample as shown in
Figure 8. From the figure a clear evidence of brittle
failure is observed within the composites.
Fractographs of these samples show fibre pull-out
from the matrix with fairly clean and recognisable
fibres without matrix adherence.
Figure 9 shows the results of flexural test of prepared
composite samples. For same weight percent of cenosphere filler the flexural strength increases with increase
in number of layers. If the number of layers is increased
Figure 8. SEM image of tensile fracture of laminate.
120
Tensile strength (MPa)
100
80
60
40
20
0
A0 A2 A4 A6 A8 B0 B2 B4 B6 B8 C0 C2 C4 C6 C8 D0 D2 D4 D6 D8
Composite type
Figure 7. Tensile strength of the laminates.
799
Jena et al.
160
140
Flexural strength (MPa)
120
100
80
60
40
20
0
A0 A2 A4 A6 A8 B0 B2 B4 B6 B8 C0 C2 C4 C6 C8 D0 D2 D4 D6 D8
Composite type
Figure 9. Flexural strength of the laminates.
Figure 10. SEM image of tensile fracture surface of laminate
under flexural load.
more than seven there is a decrease in strength. It is also
seen that the addition of cenosphere increases their flexural strength except for the case of laminate of type D.
The improvement of strength in laminates A, B and C
are observed when the cenosphere content is increased
up to 3 wt%. Further increase in cenosphere deteriorates the laminate strength. One of the broken samples is
observed under SEM. Figure 10 shows the SEM image
of that fractured surface where failure initiated
from the tensile region of the flexural specimen. Fibre
bending and matrix failure are observed from the
figure.
The ILSS results as shown in Figure 11 follow the
similar trend as that of flexural strength. The maximum
ILSS is recorded for the composite of type C4. It is
observed that the ILSS value of C4 is increased by
90.6% as compared to composite of type A0.
The results of the impact tests for different composites are shown in Figure 12. The figure indicates
that with number of laminae remaining same, the
addition of cenosphere improves the impact strength
of the composite. This may be due to the reason
that cenosphere particles are rigid and have much
higher fracture strength as compared to epoxy
resin. Additionally, the increase in cenosphere content increases the strength up to certain limit after
which the impact strength is decreased on further
addition. For 3-layered laminate, the impact strength
increases with the increase content of cenosphere and
maximum energy is recorded in A6 composite,
which is 56.82% more as compared to A0. For
5 -, 7 - and 9-layered laminates, the maximum
impact strength is recorded for B2, C2 and D2 composites, which increase by 61.49%, 31.7% and
19.35% as compared to B0, C0 and D0, respectively.
800
Journal of Reinforced Plastics and Composites 32(11)
12
Interlaminar shear strength (MPa)
10
8
6
4
2
0
A0 A2 A4 A6 A8 B0 B2 B4 B6 B8 C0 C2 C4 C6 C8 D0 D2 D4 D6 D8
Composite type
Figure 11. Interlaminar shear strength of the laminates.
20
18
Imapact strength (KJm–2)
16
14
12
10
8
6
4
2
0
A0 A2 A4 A6 A8 B0 B2 B4 B6 B8 C0 C2 C4 C6 C8 D0 D2 D4 D6 D8
Composite type
Figure 12. Impact strength of the laminates.
For higher weight percent of cenosphere the impact
strength is reduced. This may be due to the inclusion of more voids and dispersion problem in larger
cenosphere content composite. Among all compositions, type C2 composite has maximum impact
strength of 18.132 kJ/m2.
Conclusion
In the presented work, the mechanical properties of
bamboo–fibre reinforced composites are studied with
varying weight percent of cenosphere and number of
layers. Inclusion of fibre and filler in matrix improves
Jena et al.
the load-carrying capacity (tensile strength), the ability
to withstand bending (flexural strength) and shearing of
lamina (ILSS) of the composites. Hardness and impact
values also have been found to have improved invariably for all the composite types considered on addition
of particulate filler. The addition of cenosphere
improves the mechanical properties of the composites,
but it depends upon the amount of cenosphere and fibre
content in the composite. The composite strength can
be effectively tailored by varying weight fraction of
filler and number of layers.
Funding
This research received no specific grant from any funding
agency in the public, commercial, or not-for-profit sectors.
References
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agents. J Appl Polym Sci 2003; 88: 278–286.
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polyester composites reinforced with short abaca fibre.
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3. Bisanda ETN. The effect of alkali treatment on the adhesion characteristics of sisal fibres. Appl Compos Mater
2000; 7: 331–339.
4. Luo S and Netravali AN. Interfacial and mechanical
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7. Mohanty AK, Misra M and Drzal TL. Natural fibres,
biopolymers, and bio composites. Boca Raton: CRC
Press, 2005, pp.181–183.
8. Shin FG, Xian XJ, Zheng WP, et al. Analyses of the
mechanical properties and microstructure of bambooepoxy composites. J Mater Sci 1989; 24: 3483–3490.
9. Xue L, Lope GT and Panigrahi S. Chemical treatments
of natural fibre for use in natural fibre-reinforced composites: a review. J Polym Environ 2007; 15: 25–33.
10. Mishra M, Misra SS, Tripathy SK, et al. The influence of
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164–170.
11. Jacob M, Thomas S and Varughese KT. Mechanical
properties of sisal/oil fibre reinforced natural rubber
composites. Compos Sci Technol 2004; 64: 955–965.
12. Ray D, Sarkar BK, Rana AK, et al. Effect of alkali treated jute fibres on composite properties. Bull Mater Sci
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13. Kushwaha P and Kumar R. Enhanced mechanical
strength of BFRP composite using modified bamboos.
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epoxy composites. Polym Compos 2008; 29: 239–344.
16. Velmurugan R, Jeyaprakash P and Balaganesan G.
Damping study of hybrid nano composites by low velocity impact. In: International conference on aerospace
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hybrid composites. J Mater Sci Eng 1992; 27: 3827–3834.
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Effect of cenosphere on mechanical
properties of bamboo–epoxy composites
Journal of Reinforced Plastics
and Composites
32(11) 794–801
! The Author(s) 2013
Reprints and permissions:
sagepub.co.uk/journalsPermissions.nav
DOI: 10.1177/0731684413476925
jrp.sagepub.com
Hemalata Jena, Mihir Kumar Pandit and Arun Kumar Pradhan
Abstract
Cenosphere is a ceramic-rich industrial waste produced during burning of coal in thermal power plants. This study deals
with the effect of cenosphere as particulate filler on mechanical behaviour of natural fibre composites. The natural fibre
composite consists of bamboo fibre as reinforcement and epoxy as matrix. The bamboo fibre is treated with alkali to
improve its surface properties. The conventional hand lay-up technique is used to prepare different composite specimens. Twenty numbers of different composite specimens are prepared with varying number of laminae and filler content.
The samples are analysed for their mechanical properties to establish the effect of varying filler content and the number
of laminae. It is found that the mechanical properties are significantly influenced by addition of this waste-based ceramic
filler.
Keywords
Cenosphere, bamboo fibre, alkali treatment, epoxy resin, mechanical properties
Introduction
Nowadays natural fibres have gained wide popularity
as reinforcements in polymer composites for various
applications. Due to its eco-friendly nature and good
mechanical properties, it offers a promising alternative
to glass, carbon, and other synthetic fibres used for the
manufacture of composites.1 The potential of natural
fibres such as abaca, sisal, pineapple, flax and coir as
reinforcement in composites is now becoming a popular
area of research.2–6 Among these available natural
fibres, bamboo has many advantages, such as ample
availability, fast growth rate, lightweight, low cost
and low energy consumption in processing and biodegradability.7 It is becoming very popular as one of
the most useful non-timber forest resources due to its
high socio-economic benefits. It possess very good
mechanical properties due to its longitudinally oriented
fibres. Using bamboo fibre one can reduce the demand
for wood fibre and environmental impacts associated
with wood fibre harvesting. Hence, bamboo fibre
appears to be one of the most promising candidates
as natural fibres for polymer composites. It is reported
that bamboo composite possesses specific strength
superior to that of ordinary glass fibre reinforced
composites.8 But the presence of hydroxyl and other
polar groups in the natural fibres leads to the weak
interfacial bonding between fibres and matrix. The
fibre surface properties can be improved substantially
by different chemical treatments.9 Alkaline treatment is
one of the most used chemical treatments of natural
fibres when used to reinforce in thermoplastics or
thermosets. Mishra et al.10 while working with sisal
fibre found that the mechanical properties of the composite improved by treating the fibre with alkali. The
improvement was found to be highest for 5% NaOH
concentration.11–13
Further, the physical and mechanical characteristics
of composites can be modified by adding a suitable
filler phase to the matrix during their fabrication.
Addition of filler in composites not only improves its
School of Mechanical Sciences, Indian Institute of Technology,
Bhubaneswar, India
Corresponding author:
Hemalata Jena, School of Mechanical Sciences, IIT Bhubaneswar,
Samantapuri, Bhuabeneswar 751013, India.
Email: [email protected]
795
Jena et al.
mechanical properties but also reduces its cost.14
Therefore, the use of inorganic fillers in the composites
is gaining popularity. There are a number of literatures
available on the use of ceramics as filler in composite
materials.15–18 Cenosphere, which is one of the industrial wastes produced during burning of coal in thermal
power plants,19 could be a unique class of filler in polymer matrix composite due to its fine dispersion, homogeneity, inertness and chemical stability. Though the
literature is rich with the studies on the mechanical
properties of the cenosphere filled polymer composites,20–23 no attempt has been reported till date to critically analyse the mechanical characterisation of
cenosphere filled bamboo–fibre composites.
It is proved that the mechanical properties of
bamboo–epoxy composites under different loading conditions can be modified by changing the number of
laminae and configuration of laminae in resin.8,24 And
also hybridisation of natural fibre with different fillers25
or synthetic fibres like carbon, aramid, glass, etc., can
improve the stiffness, strength, as well as moisture
resistance of the composites.26–28
The present study attempts to investigate a new class
of natural fibre composite in which bamboo fibre is
used as reinforcement, epoxy as matrix and cenosphere
as particulate microsphere filler. The mechanical properties of these bamboo fibre reinforced composites are
evaluated. The effect of adding cenosphere to matrix
phase aims at improving their mechanical properties.
The effects of number of laminae and varying weight
percent of cenosphere have also been studied for this
purpose.
Table 1. Raw materials and their physical characteristics.
Raw materials
Grade
Characteristics
Cenosphere
CS 300
Epoxy
LAPOX L-12
Hardener
K-6
Bamboo fibre
–
Particle density ¼ 0.45–
0.80 g/mL, particle
size ¼ 60–94 mm, light
grey powder,
non-soluble in water,
melting temperature ¼ 1300–1500 C
Viscosity ¼ 9000–12,000
mPa.s,
density ¼ 1.1 g/cc
Refractive index at
25 C ¼ 1.4940–1.5000
Weave type, density ¼ 0.95 g/cc,
width ¼ 4.5 mm,
thickness ¼ 1.5 mm
Table 2. Designation of composite specimens.
Group
Designation
A
A0
A2
A4
A6
A8
B
B0
B2
B4
B6
B8
C
C0
C2
C4
C6
C8
D
D0
D2
D4
D6
D8
Fabrication procedure
In the present work, the composite consists of bamboo
fibre as reinforcement and cenosphere as filler material
in the epoxy matrix. The properties of these constituents are given in Table 1.
Initial step of fabricating the composite is alkali
treatment of bamboo mats to improve their mechanical
properties. The bamboo mats are cleaned and dried
before dipping into NaOH solution of 5% concentration for 30 min at room temperature (20 C).13 These
mats are thoroughly washed in distilled water and
then neutralised in 2% HCl solution. The neutralised
mats are then dried in an oven at 60 C for 24 h. The
fabrication of the composite is done by conventional
hand lay-up technique at room temperature. Low temperature cured epoxy resin (L12) and corresponding
hardener (K6) are mixed in a ratio of 10:1 by weight.
A number of composite specimens are prepared using
different number of laminae and varying weight percent
of cenosphere as filler. The composite specimens
Composite
with varying
laminae
3-layered bamboo–
epoxy composite
5-layered bamboo–
epoxy composite
7-layered bamboo–
epoxy composite
9-layered bamboo–
epoxy composite
Composite
with varying
wt% of
23cenosphere
0.0
1.5
3.0
4.5
6.0
0.0
1.5
3.0
4.5
6.0
0.0
1.5
3.0
4.5
6.0
0.0
1.5
3.0
4.5
6.0
796
so made with varying number of layers and weight
percent of cenosphere are designated as shown
in Table 2.
Journal of Reinforced Plastics and Composites 32(11)
10mm
170mm
250mm
Mechanical tests
In order to study the mechanical properties of the prepared composite specimens with different compositions,
the following tests are conducted.
Figure 1. Tensile test specimen.
Scanning electron microscopy
The surfaces of the specimens are examined directly
under scanning electron microscope (SEM) JEOL
JSM-6480LV. The composite samples are mounted on
carbon stubs. To enhance the conductivity of the samples, a thin film of gold is vacuum-evaporated on them
before the photomicrographs are taken.
Span L/t=10
Micro-hardness test
Micro-hardness measurement is done using a Zwick/
Roell micro-hardness tester as per ASTM E92. A diamond indenter, in the form of a right pyramid with a
square base and an angle 136 between opposite faces,
is used with load.
Figure 2. Flexural test specimen.
Tensile test
The tensile test is performed in the universal testing
machine (UTM) Instron 3382 as per ASTM D303976. The geometry of the test specimen is shown in
Figure 1. At a grip pressure of 4.2 MPa, the rate of
loading 2 mm/min is used for testing. During the test
a uni-axial load is applied through both the ends of the
specimen. The results are analysed to calculate the tensile strength of the composite samples.
2.54mm
64mm
Figure 3. Impact test specimen.
Flexural test and interlaminar shear strength test
The data recorded during the 3-point bend test is used
to evaluate the flexural strength and interlaminar shear
strength (ILSS). The test is conducted as per ASTM
standard (D2344-84) using the same UTM with bend
test fixtures. The cross head speed of 10 mm/min is
maintained. Geometry configuration for flexural test
specimen is shown in Figure 2.
Impact test
Impact test is performed on the pendulum impact testing machine as per ASTM D256. A ‘V’ notch is created
at the centre of the specimen having notch depth of
2.54 mm and notch angle of 45 , using Impactometer
Figure 4. SEM image of untreated fibre.
797
Jena et al.
6545 (Ceast, Italy) as shown in Figure 3. A 10 mm
hemispherical head impacts a test specimen at a
constant velocity of 1.06 m/s at impact energy of
15.26 J. The respective values of impact energy of different specimens are recorded directly from the dial
indicator.
Figure 5. SEM image of treated fibre.
Results and discussion
The morphology of the composite reinforced with
untreated and treated fibre surfaces have been studied
using an SEM. The surfaces of untreated fibre appear
to be rough as shown in Figure 4. This may be due to
the presence of lignin, wax, oil and other surface impurities which are removed with alkali treatment. The surfaces of the treated fibre are shown in Figure 5. These
clean surfaces are expected to provide direct bonding
between the fibre and matrix.
The hardness test results as shown in Figure 6 indicate that the hardness increases with the increase in
weight percent of cenosphere for the composites of
type A, B and C. The increase in hardness value may
be due to the fact that the outer shell of the cenosphere
made of ceramic particles enhances the hardness.
However, hardness value for type D composite
decreases after a certain number of layers for the
same weight percent of cenosphere. The maximum
hardness value is found in the C6 composite, which
is 16% higher as compared to unfilled composite
of type C0.
The values of tensile strength of different bambooepoxy composites are given in Figure 7. A marginal
increase in strength is observed for A2, B2 and C2 as
compared to A0, B0 and C0 composites, respectively.
The results indicate that cenosphere can increase the
tensile strength by 25.4%, 6.50% and 4.10% for
40
35
Hardness (Hv)
30
25
20
15
10
5
0
A0 A2 A4 A6 A8 B0 B2 B4 B6 B8 C0 C2 C4 C6 C8 D0 D2 D4 D6 D8
Composite Type
Figure 6. Micro-hardness of the laminates.
798
Journal of Reinforced Plastics and Composites 32(11)
composites A, B and C, respectively. It is observed that
the influence of filler addition is more in case of composite type A which is having a lower weight fraction of
fibre i.e. 18%. Laminates B and C, which have more
number of layers, are accompanied by less change in
maximum tensile strength with the addition of filler,
whereas in case of laminate D there is no improvement
of strength. During the preparation of laminate D
having 43% fibre weight fraction, it is observed that
the quantity of resin is insufficient to impregnate the
fibres. This, subsequently, influences the wettability of
the fibre and fibre matrix adhesion which, in turn,
increases the void content in the composite. As a
result, the crack initiation and its propagation will be
easier in these composites. Though the strength of the
composites A, B and C are observed to increase with
the addition of cenosphere filler due to better adhesion
and wettability, there is a limitation to addition of filler.
Too higher filler content leads to discontinuous phase
of resin and this develops clusters of filler, which results
in local phase inversion leading to failure. SEM micrographs are taken for surface failed sample as shown in
Figure 8. From the figure a clear evidence of brittle
failure is observed within the composites.
Fractographs of these samples show fibre pull-out
from the matrix with fairly clean and recognisable
fibres without matrix adherence.
Figure 9 shows the results of flexural test of prepared
composite samples. For same weight percent of cenosphere filler the flexural strength increases with increase
in number of layers. If the number of layers is increased
Figure 8. SEM image of tensile fracture of laminate.
120
Tensile strength (MPa)
100
80
60
40
20
0
A0 A2 A4 A6 A8 B0 B2 B4 B6 B8 C0 C2 C4 C6 C8 D0 D2 D4 D6 D8
Composite type
Figure 7. Tensile strength of the laminates.
799
Jena et al.
160
140
Flexural strength (MPa)
120
100
80
60
40
20
0
A0 A2 A4 A6 A8 B0 B2 B4 B6 B8 C0 C2 C4 C6 C8 D0 D2 D4 D6 D8
Composite type
Figure 9. Flexural strength of the laminates.
Figure 10. SEM image of tensile fracture surface of laminate
under flexural load.
more than seven there is a decrease in strength. It is also
seen that the addition of cenosphere increases their flexural strength except for the case of laminate of type D.
The improvement of strength in laminates A, B and C
are observed when the cenosphere content is increased
up to 3 wt%. Further increase in cenosphere deteriorates the laminate strength. One of the broken samples is
observed under SEM. Figure 10 shows the SEM image
of that fractured surface where failure initiated
from the tensile region of the flexural specimen. Fibre
bending and matrix failure are observed from the
figure.
The ILSS results as shown in Figure 11 follow the
similar trend as that of flexural strength. The maximum
ILSS is recorded for the composite of type C4. It is
observed that the ILSS value of C4 is increased by
90.6% as compared to composite of type A0.
The results of the impact tests for different composites are shown in Figure 12. The figure indicates
that with number of laminae remaining same, the
addition of cenosphere improves the impact strength
of the composite. This may be due to the reason
that cenosphere particles are rigid and have much
higher fracture strength as compared to epoxy
resin. Additionally, the increase in cenosphere content increases the strength up to certain limit after
which the impact strength is decreased on further
addition. For 3-layered laminate, the impact strength
increases with the increase content of cenosphere and
maximum energy is recorded in A6 composite,
which is 56.82% more as compared to A0. For
5 -, 7 - and 9-layered laminates, the maximum
impact strength is recorded for B2, C2 and D2 composites, which increase by 61.49%, 31.7% and
19.35% as compared to B0, C0 and D0, respectively.
800
Journal of Reinforced Plastics and Composites 32(11)
12
Interlaminar shear strength (MPa)
10
8
6
4
2
0
A0 A2 A4 A6 A8 B0 B2 B4 B6 B8 C0 C2 C4 C6 C8 D0 D2 D4 D6 D8
Composite type
Figure 11. Interlaminar shear strength of the laminates.
20
18
Imapact strength (KJm–2)
16
14
12
10
8
6
4
2
0
A0 A2 A4 A6 A8 B0 B2 B4 B6 B8 C0 C2 C4 C6 C8 D0 D2 D4 D6 D8
Composite type
Figure 12. Impact strength of the laminates.
For higher weight percent of cenosphere the impact
strength is reduced. This may be due to the inclusion of more voids and dispersion problem in larger
cenosphere content composite. Among all compositions, type C2 composite has maximum impact
strength of 18.132 kJ/m2.
Conclusion
In the presented work, the mechanical properties of
bamboo–fibre reinforced composites are studied with
varying weight percent of cenosphere and number of
layers. Inclusion of fibre and filler in matrix improves
Jena et al.
the load-carrying capacity (tensile strength), the ability
to withstand bending (flexural strength) and shearing of
lamina (ILSS) of the composites. Hardness and impact
values also have been found to have improved invariably for all the composite types considered on addition
of particulate filler. The addition of cenosphere
improves the mechanical properties of the composites,
but it depends upon the amount of cenosphere and fibre
content in the composite. The composite strength can
be effectively tailored by varying weight fraction of
filler and number of layers.
Funding
This research received no specific grant from any funding
agency in the public, commercial, or not-for-profit sectors.
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