Indian Journal of Fibre & Textile Research
Vol. 41, September 2016, pp. 235-241
Properties of sisal fibre reinforced epoxy composite
M K Gupta
a
& R K Srivastava
Department of Mechanical Engineering, Motilal Nehru National Institute of Technology, Allahabad 211 004, India
Received 12 February 2015; revised received and accepted 15 May 2015
Sisal fibre reinforced epoxy composites have been prepared by hand lay-up technique followed by static compression,
using various fibre weight fractions (15, 20, 25 and 30%). Mechanical properties, thermal properties, water absorption
properties and dynamic mechanical analysis of sisal composites are investigated. The results show that the addition of sisal
fibres in epoxy matrix up to 30 wt. % increases the mechanical, thermal and water absorption properties. The values of
storage modulus and loss modulus increase with the increase in fibre content up to 25 wt. % and then decrease. The glass
transition temperature (T
g
)
is obtained from loss modulus and tan delta curve. The value of T
g
obtained from loss modulus
curve is found to be lower than that obtained from tan delta curve.
Keywords: Dynamic mechanical analysis, Mechanical properties, Sisal fibre, Thermal properties, Water absorption properties
1 Introduction
There is a rising interest of researchers in the use of
natural fibres as reinforcement for polymer
composite. Natural fibres have many advantages, such
as low cost, low density, availability in abundance,
eco-friendliness, non-toxicity, high flexibility,
renewability, biodegradability, relative non-
abrasiveness, and high specific strength and modulus
1-4
.
However, natural fibres suffer from some
disadvantages also, like low impact strength, high
brittleness and higher moisture absorption properties
5
.
Nowadays, natural fibre reinforced polymer
composites are being used in automotive parts,
aerospace and constructions industries
5, 6
.
Kaewkuk et al
7
. studied the physical properties of
sisal fibre reinforced polypropylene composite and
found that on increasing the sisal fibre content, the
tensile strength, tensile modulus and water absorption
properties of sisal polypropylene composite increase
but impact strength and elongation–at-break decrease.
Mohanthy et al
8
. studied the mechanical and
viscoelastic behavior of jute fibre reinforced high
density polyethylene composites and observed that
the tensile, flexural and impact strength are found to
be increased with the increase in fibre loading up to
30 %. Storage modulus was increased on increasing
fibre loading, whereas damping parameters are
decreased as compared to epoxy. Cheng et al
9
.
presented studies on mechanical and thermal
properties of chicken feather reinforced PLA
composites. They observed that the addition of
chicken feather as reinforcement into PLA, enhanced
the tensile moduli and thermal stability of composites
as compared to pure PLA. Girisha et al
10
. reported
study on the mechanical properties and water
absorption behavior of sisal and coconut coir fibre
reinforced epoxy composite. They highlighted that as
a result of hybridization of sisal fibre with coconut
coir epoxy composite, the mechanical properties were
improved and water absorption property was reduced.
Venkateshwaran et al
11
. investigated the effect of sisal
fibre loading on mechanical and water absorption
properties of banana fibre reinforced epoxy composite
and reported that the addition of sisal fibre results in
increased mechanical properties and decreased water
absorption properties of banana fibre reinforced
epoxy composite.
The present study aims at investigating the
mechanical properties, thermal property, water
absorption properties and dynamic mechanical
analysis of sisal fibre reinforced epoxy composite.
The proposed sisal composites found are suitable in
light weight automotive parts application.
2 Materials and Methods
2.1 Materials
Sisal fibres were used as reinforcement and epoxy
AY 105 as a matrix in this study. Sisal fibres and
epoxy matrix were purchased from local resource.
____________
a
Corresponding author.
E-mail: mkgupta@mnnit.ac.in/mnnit.manoj@gmail.com
INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2016
236
Epoxy is a thermosetting polymer and hence
requires a hardener for curing; HY951 hardener was
used. Density and dynamic viscosity of epoxy resin
are 1.108 g/cm
3
and 11.789 Pa.s respectively. The
matrix material was prepared by using epoxy and
hardener in the ratio 10:1, as recommended
11
.
Sisal fibre (Agave sisalana) was extracted by
decortication, wherein leaves were crushed and beaten
by a rotating wheel set with blunt knives. The
properties of sisal fibre have been reported earlier
12, 13
.
2.2 Fabrication of Composites
Hand lay-up technique was used to fabricate the
composites by reinforcing sisal fibres into epoxy
matrix. Composites were prepared using various fibre
weight fractions (15, 20, 25 and 30 wt. %) with
unidirectional alignment of sisal fibres. A stainless
steel mould having dimensions of 500 × 300 × 3 mm
3
was used for casting of composites. Silicon spray was
used to facilitate easy removal of the composite from
the mould after curing. The cast of each composite was
cured under a load of 50 kg for 24 h before its removal
from the mould. Dimension of specimens were cut as
per ASTM standard using a diamond cutter. The
composites manufactured with varying wt. % of fibres
are designated as S15 (15 wt. % of sisal fibre), S20
(20 wt. % of sisal fibre), S25 (25 wt. % of sisal fibre)
and S30 (30 wt. % of sisal fibre).
2.3 Testing and Characterizations of Composites
The fabricated sisal fibre reinforced epoxy
composites were tested for mechanical, thermal, water
absorption properties and dynamic mechanical
analysis.
2.3.1 Tensile Test
Tensile properties tests of the composite samples
were performed on Tinius Olsen H 10 K-L (Bi-axial
testing machine) with a crosshead speed of 2 mm/min
and temperature of 30 °C. Tests were conducted as
per ASTM D638, using sample of dimension 165 mm
× 13 mm × 3 mm. Five specimens of each composite
were tested and average values are reported.
2.3.2 Flexural Test
Flexural properties of the composite were
determined using a three point bending test on Tinius
Olsen H10 K-L (Bi-axial testing machine). The
dimension of the sample used for the flexural test was
taken as 80 mm × 12.7 mm × 3 mm as per ASTM
D790. The flexural test was carried out at 30 °C
temperature and 2 mm/min crosshead speed. Flexural
strength and flexural modulus were calculated using
the following equations
14
:
Flexural strength=
2
2
3
bd
FL
and ... (1)
Flexural modulus=
3
3
4
bd
mL
... (2)
where
F
is the ultimate failure load (N);
L
, the span
length (mm); b and d , the width and thickness of
specimen in (mm) respectively; and
m
, the slope of
the tangent to the initial line portion of the load-
displacement curve. Five specimens of each
composite were tested and average values are
reported.
2.3.3 Impact Test
Impact test of composite was performed on Tinius
Olsen Impact 104 machine. The dimension of the
sample used for the impact test was taken as 65 mm ×
12.7 mm × 3 mm, with notch thickness of 2.5 mm, as
per ASTM D 256. Five specimens of each composite
were tested and average values are reported.
2.4 Water Absorption Behavior
Behavior of water absorption by sisal fibre
reinforced epoxy composites has been studied. The
water absorption causes the degradation of fibre-
matrix interface region, resulting in reduction of
mechanical properties along with the change in
dimensions of composites. Water absorption by
natural fibre reinforced polymer composite is very
similar to Fickian diffusion process
15
. Diffusion is
defined as the mass flow process by which molecules
change their position under the influence of thermal
energy and gradient (concentration, electrical, magnetic
and stress). Under the steady state condition and
unidirectional flow of matter, Fick’s first law states
15
:
D
C
x
ϕ
∂
= −
∂
… (3)
where
φ
is the flux (flow of matter per unit area and
per unit time);
D
, the diffusion coefficient; and
c
x
δ
δ
,
the concentration gradient
15
.
Under the non steady state condition and
unidirectional flow of matter, Fick’s second law
states
16
.
GUPTA & SRIVASTAVA: PROPERTIES OF SISAL FIBRE REINFORCED EPOXY COMPOSITE
237
2
2
x
C
x
C
D
∂
∂
=
∂
∂
… (4)
Water absorption behavior of sisal fibre reinforced
polymer composite was investigated as per ASTM D
570. The specimens were submerged in water at
30 °C temperature to study the kinetics of water
absorption. The samples were taken out periodically
and weighed immediately after wiping out the water
from the surface of samples. Water absorption by the
sample was measured using a precise 4-digit balance.
The percentage of water absorption was calculated
using the following equation
16
:
Water absorption (%) =
1
12
W
WW
−
× 100 … (5)
where W
1
is the weight before soaking into water (g);
and W
2
, the weight after soaking into water (g). The
higher diffusivity of one substance with respect to
another shows that they diffuse into each other faster.
The kinetic parameter, diffusion coefficient (mm
2
/s),
was calculated using the following equation
16
:
Diffusion coefficient
(
)
D =
π
2
22
16
s
M
mt
… (6)
where
m
is the slope of linear portion of the sorption
curve; and
t
, the initial sample thickness in (mm).
The permeability of water molecules through the
composite sample depends on the sorption of water by
the fibres. Therefore, the sorption coefficients (related
to the saturation sorption) was calculated using the
following equation
16
:
Sorption coefficient
s
MS = /
t
M … (7)
where M
s
and M
t
are the percentage of water uptake at
saturation time and at a specific time t respectively.
The permeability coefficient
P
(mm
2
/s), which
implies the net effect of sorption and diffusion
coefficient was calculated using the following
equation
16
:
Permeability coefficient SDP
×
=
… (8)
2.5 Thermogravimetric Analysis
Thermal stability of the composites was assessed
by thermogravimetric Perkin Elmer TGA 4000
apparatus. TGA measurements were carried out on
15-25 mg sample placed in a platinum pan, heated
from 30 ºC to 800 ºC at a heating rate of 10 ºC/min in
a nitrogen atmosphere with a flow rate of 20 mL/min
to avoid unwanted oxidation.
2.6 Dynamic Mechanical Analysis
Viscoelastic properties of fibre reinforced polymer
composites depend on the nature of the matrix,
reinforcement and fibre–matrix interfaces. The
viscoelastic properties of epoxy and sisal composites
were studied by using the dynamic mechanical
analyzer (Seiko instruments DMA 6100). The
viscoelastic properties were determined in 3 point
bending test at 1 Hz frequency as a function of
temperature. The composites were cut into samples of
dimensions 50 mm ×13 mm × 3 mm according to
ASTM D 5023. Experiments were carried out in the
temperature range 30°–200°C at a heating rate of
10°C/min. The viscoelastic properties such as storage
modulus, loss modulus and damping parameter of the
specimens were measured.
3 Results and Discussion
3.1 Mechanical Properties
The tensile, flexural and impact properties of epoxy
and sisal fibre reinforced epoxy composite are given
in Table 1.
3.1.1 Tensile Properties
Table 1 shows the tensile strength and tensile
modulus of epoxy and sisal fibre reinforced epoxy
composites. The tensile strength and tensile modulus
of sisal composites are found to be increased with
increasing sisal fibre content up to 30 wt. %. The
maximum values of tensile strength and tensile
Table 1— Mechanical properties of epoxy and sisal composites
Composite Tensile strength
MPa
Tensile modulus
GPa
Flexural strength
MPa
Flexural modulus
GPa
Impact strength
kJ/m
2
Impact energy
J
Epoxy
33.86±2.59 0.712±0.01 118.73±10.49 5.781±0.60 5.67±0.35 0.14±0.01
S15
44.93±3.80 0.905±0.07 155.99±12.99 7.584±0.83 16.84±1.46 0.55±0.07
S20
47.01± 2.40 1.205±0.10 169.99±12.19 9.174±1.08 18.01±1.83 0.65±0.12
S25
61.46± 4.59 1.222±0.10 180.57±17.25 9.445±1.14 19.96±2.86 0.87±0.17
S30
83.96± 6.94 1.58±0.08 252.39±12.11 11.316±1.02 22.03±1.74 1.09±0.10
INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2016
238
modulus are found for the composite S30 due to
strong adhesion between sisal fibres and epoxy matrix
which allows a uniform transfer of stress from matrix
to fibres. Tensile strength and tensile modulus of the
composite S30 are found 83.96 MPa and
1.580 GPa, which are 148% and 122% more than that
of epoxy. It is observed that tensile strength of
composite S30 is 87, 79 and 37% more than those of
composites S15, S20 and S25 respectively, and tensile
modulus is 75, 31 and 29% more than those of
composites S15, S20 and S25 respectively.
3.1.2 Flexural Properties
The flexural strength and flexural modulus of
epoxy and sisal fibre reinforced epoxy composites are
shown in Table 1. The flexural strength and flexural
modulus of sisal composite are also found to be
increased with increasing sisal fibre content up to
30 wt.%. The composite S30 offers the maximum
value of flexural strength and flexural modulus due to
strong fibre-matrix adhesion. Flexural strength and
flexural modulus are found maximum for composite
S30 such as 252.39 MPa and 11.316 GPa
respectively, which are 113% and 96% more than that
of epoxy. It is observed that the flexural strength of
composite S30 is 62, 48 and 40% more than those of
composites S15, S20 and S25 respectively, and
flexural modulus is 49, 23 and 20% more than those
of composites S15, S20 and S25 respectively.
3.1.3 Impact Properties
Table 1 shows the Impact strength and impact
energy of epoxy and sisal fibre reinforced epoxy
composites. The similar trend of tensile and flexural
properties is seen for impact properties of sisal fibre
reinforced epoxy composites. Impact properties are
found to be increased with increasing sisal fibre
content up to 30 wt. % in epoxy matrix. Impact
strength and impact energy are found to be maximum
for composite S30 such as 22.03 kJ/m
2
and 1.0909 J
respectively, which are very high than those of epoxy.
The impact strength is found 31, 22 and 10% higher
than those of composites S15, S20 and S25
respectively, and impact energy is 99, 68 and 26 %
higher than those of composites S15, S20 and S25
respectively.
3.2 Water Absorption Behaviour
The percentage water absorption of sisal fibre
reinforced epoxy composites is plotted against the
square root of time (Fig. 1). It is found that the initial
rate of water absorption and maximum water uptake
increase with the increase in fibre content up to
30 wt.%. This may be due to the presence of micro-
voids in matrix; water molecules start diffusing into
micro-voids till saturation state. The composite S30
shows the higher water absorption, which is 13, 10
and 4% more than those of composites S15, S20 and
S25 respectively. The increase in water absorption is
due to the hydrophilic nature of sisal fibre and greater
interfacial area between fibre and matrix
16
. Sisal fibre
shows the hydrophilic nature due to presence of
cellulose. On increasing the sisal fibre content, weight
fraction of fibres is increased which causes increase in
amount of cellulose, micro voids and interface surface
area. The water absorption by epoxy is almost
negligible due to its hydrophobic nature. The sorption,
diffusion and permeability coefficient of sisal fibre
reinforced epoxy composites are given in Table 2.
The composite S15 shows the higher values of
diffusion and permeability coefficient than all other
composites, due to lower fibre loading.
3.3 Thermogravimetric Analysis (TGA)
Figure 2 shows the variation in percentage weight
loss of epoxy and sisal composites with temperature.
It is observed that there are three significant regions
Fig. 1—W
ater absorption of sisal composites as a function of
square root of time
Table 2—Sorption, diffusion and permeability coefficient of sisal
composites
Composites % water
uptake at
saturation
time (M
∞
)
Sorption
coefficient
(S)
Diffusion
coefficient
(D)
mm
2
/s × 10
-5
Permeability
coefficient
(P)
mm
2
/s × 10
-5
S15 3.32 1.54 1.71 2.63
S20 3.41 2.93 0.48 1.41
S25 3.60 1.96 1.06 2.07
S30 3.76 2.53 0.64 1.62
GUPTA & SRIVASTAVA: PROPERTIES OF SISAL FIBRE REINFORCED EPOXY COMPOSITE
239
of weight loss due to rise in temperature. The initial
weight losses (~ 5%) of epoxy and sisal composites
S15, S20, S25 and S30 are obtained at 330º and, 317º,
306º, 310º and 279ºC respectively. The initial low
temperature weight losses of composites are due to
the removal of solvent from composites
17
. The major
weight losses (~75%) of epoxy and sisal composites
S15, S20, S25 and S30 are obtained at 450º and, 470º,
502º, 460º and 508ºC respectively. The major weight
loss is due to degradation and volatization of epoxy
along with the fibres present in composites
17
. The
residue formed after degradation requires higher
temperature for subsequent degradation. The final
weight losses of epoxy and sisal composites S15,
S20, S25 and S30 are obtained at 679º and, 688º,
680º, 672º and 694ºC respectively. The major weight
loss of the composite S30 occurs at 508ºC. Here,
degradation is shifted towards higher temperature
which shows increased thermal stability of the
composite S30 due to stronger interface between
fibres and matrix as compared to the all other
composites.
3.4 Dynamic Mechanical Analysis
The dynamic mechanical analysis (DMA) of
composite samples was performed to study their
viscoelastic properties. shows the variation in
'
E
,
"
E
and Tanδ of the epoxy and sisal composites as a
function of temperature at a frequency of 1 Hz.
3.4.1 Storage Modulus
Storage modulus (
'
E
) is amount of energy stored
by materials during one cycle of oscillation.
Figure 3(a) shows the variation in storage modulus of
epoxy and sisal composites as a function of
temperature at a frequency of 1 Hz. On comparing the
different composites, it is found that the value of
'
E
increases with an increase in weight fraction of
sisal fibres up to 25 wt. %. The value of
'
E
is found
3.6532 GPa for epoxy in the glassy region, but this
value reaches up to 4.4172 GPa for the composite S25
due to reinforcement of sisal fibres in epoxy matrix.
The storage modulus of the epoxy and sisal
composites decrease as temperature is increased due
to the loss in stiffness of fibres. Epoxy has a very
sudden fall in the value of
'
E
,
whereas sisal
Fig. 2—
Variation in weight loss of epoxy and sisal composites
with temperature
Fig. 3— Variation in (a) storage modulus, (b) loss m
odulus and
(c) Tan δ with temperature of epoxy and sisal composites