Open Journal of Composite Materials, 2012, 2, 139-141
http://dx.doi.org/10.4236/ojcm.2012.24017 Published Online October 2012 (http://www.SciRP.org/journal/ojcm)
139
Influence of Pre-Impregnation Treatment on Bamboo
Reinforced Epoxy/UPE Resin Composites
Pradeep Kr. Kushwaha1, Rakesh Kumar2
1Indian Plywood Industries Research and Training Institute, Mohali, India; 2Indian Institute of Technology, New Delhi, India.
Received July 25th, 2012; revised August 24th, 2012; accepted September 7th, 2012
ABSTRACT
Bamboo based biocomposites were made with woven bamboo mats and epoxy/unsaturated polyester (UPE) resins. The
effects of pre-impregnation on the mechanical and water resistant properties of composites were studied. An alkaline
treatment was used to enhance the fiber wetting so as to achieve complete pre-impregnation with epoxy and unsaturated
polyester resins. A combined treatment of alkali and dilute epoxy/polyester gives the best result. Bending strength,
modulus of elasticity, tensile strength, tensile modulus, impact strength, water absorption were evaluated and compared
for all composites. Scanning electron microscopy (SEM) studies of the composites tensile fracture surface also indi-
cated that there is an improved adhesion between fiber and matrix. The mechanical as well as water resistant properties
of the biocomposites improved after pre-impregnation treatment.
Keywords: Biocomposites; Pre-Impregnation; Epoxy Resin; Polyester Resin; Mechanical Properties
1. Introduction
Many papers are published about the pre-impregnated
natural fiber reinforced composites [1-4]. A combined
treatment of alkali and dilute epoxy gives the best result.
The epoxy has been diluted in acetone, and tests show
that this has a significant effect on the mechanical prop-
erties of the composite [1]. The adhesion between indus-
trial hemp fibers and UPE matrix was increased by
treatment of hemp fiber surface with UPE (matrix). The
surface treatment of hemp mats also resulted in higher
mechanical and thermal properties [2]. Henequen fiber
surface preimpregnation with dilute polyethylene di-
lute solution results in composite with increased tensile
strength and interfacial shear strength [3,4].
In this study, resin pre-impregnation of bamboo mat-
ting was carried out by dilute epoxy and polyester resins.
Pre-treated bamboo reinforced epoxy and polyester com-
posites were prepared and the properties were measured.
The effect of treatment on tensile, flexural and water
absorption properties were examined.
2. Experimental
Orthogonal bamboo strip mats were acquired from the
local market. The cross-section of the strip used in the
mats is 4.25 mm × 0.5 mm. Bamboo mats cut to size
300 × 200 mm2 were cleaned with washing powder and
washed in running water thoroughly to remove dust and
other deposits from the surface. They were left in the
open to dry out for 4 h. Epoxy resin (CY-230) and hard-
ener (HY-951) were purchased from CIBA-GEIGY. Ep-
oxy resin was heated in oven for 10 min to remove the
moisture and air bubbles. After cooling the resin to room
temperature, hardener, 10% by weight, was added, stirred
to mix thoroughly and subsequently applied on the bam-
boo mats. Piled one over another to seven layers. Placed
in between two Perspex sheets, 300 × 200 mm2, and
pressed in the hydraulic press under a pressure of 170
KN for 24 h. Then the composites were cured at 80˚C for
4 h in oven.
The bamboo mats were alkali treated before preim-
pregnation. The fiber mats were completely immersed in
five percent solution of sodium hydroxide solution for
half an hour at room temperature. Then the fiber mats
were washed with tap water until adhered alkali was re-
moved from their surface. The fiber mats were then neu-
tralized in distilled water with 2% glacial acetic acid.
This solution was then drained and the fibers were
washed with distilled water and kept for drying in the
open. After room drying, they were oven dried at 80˚C
for 8 h.
For the pre-impregnation with dilute epoxy, the alkali
treated fibres were immersed in 2% solution of epoxy
which was dissolved in acetone for 2 h at room tempera-
ture. After removal, the fibers were dried and cured in an
oven at 80˚C for 8 h. These surface-treated fiber mats

Influence of Pre-Impregnation Treatment on Bamboo Reinforced Epoxy/UPE Resin Composites
140
were then used for fabricating composites with epoxy.
Five percent solution of UPE and MEKP (99:1) was
made in 95% acetone. The alkali treated fibers were
soaked in the UPE-MEKP solution for 30 min. The ex-
cess solution was drained off from their surface and they
were dried overnight under the hood. The treated mats
were oven dried at 80˚C for 8 h. These surface-treated
fiber mats were then used for fabricating composites with
polyester. A number of composites were fabricated as
tabulated in Table 1.
The tensile test was performed according to the ASTM
D638. Dog bone shaped specimens of the composites
were cut. At least five replicate specimens were tested
for each formulation. Each specimen was tested to failure
under tension at a cross-head speed of 2 mm/min on IN-
STRON 3369. Three-point bending test was performed
according to ASTM D790. Specimens of dimension 96 ×
13 mm2 were prepared. Support separation was 70 mm
and test speed was 5 mm/min on ZWICK Z010. Notched
Izod impact test samples with dimensions of 63.5 × 12.5
mm2 by the thickness were cut from the laminate com-
posites. The testing was conducted according to ASTM
D256 on a Zwick model 5101 with a pendulum weight of
25 J. Five samples were tested and the average value was
taken as the Izod impact strength. The Izod impact
strength was calculated using the formula given below:
Impact strength (kJ/m2) = [Impact energy (J)/Cross
sectional area] × 103.
Tensile fracture surface of the composite samples were
coated with silver and then analyzed using CARL ZEISS
EVO 50 scanning electron microscope.
Water absorption studies were performed following
the ASTM D570-98 method at room temperature (25˚C).
The samples were taken out periodically and weighed
immediately, after wiping out the water on the surface of
the sample, to find out the content of water absorbed.
The amount of water absorbed in the composites was
calculated by the weight difference between the samples
exposed to water and the dried samples.
3. Results and Discussions
The alkali treatment removes the hemicellulose, lignin
and pectins. The impregnation with dilute epoxy presents
an optimum improvement of the longitudinal properties.
In this case, the low-viscous resin can already fill the
micro-pores and flow in between the elementary fibers,
which is beneficial for the impregnation afterwards. In
fact, this treatment is the combined effect of three solu-
tions, namely alkali, epoxy and acetone, in which the
epoxy has been diluted.
As shown in Figure 1, the tensile strength of treated
bamboo epoxy composite is 40% higher, and the elastic
modulus is 35% higher as compared with that of un-
Table 1. Nomenclature of water modified composites.
MaterialSpecification
BE Untreated bamboo epoxy composite
BPIE Epoxy pre-impregnated bamboo epoxy composite
BP Untreated bamboo polyester composite
BPIP Polyester pre-impregnated bamboo polyester composite
BE BPIE BP BPIP
70
80
90
100
110
120
Tensile Strength
Elastic Modulus
Composite
Tensile Strength(MPa)
4000
5000
6000
7000
8000
9000
Elastic Modulus(MPa)
Figure 1. Tensile properties of water treated bamboo com-
posites.
treated bamboo-epoxy composite. The treated bamboo
polyester composite has an increment of 54% in tensile
strength, and 95% in elastic modulus compared with that
of untreated bamboo based polyester composite. Ac-
cording to Weyenberg et al. [2], the increase in tensile
strength and modulus of the treated hemp fibers-based
composites may be an outcome of the improved adhesion
between the fiber and the matrix. This improved adhe-
sion might have enhanced the interfacial bonding and
thus made it easier for the stress to be effectively trans-
ferred from the matrix to the fiber. The adhered matrix
over the fiber can be observed from the Figures 2(a) and
(b).
As shown in Figure 3, the flexural strength of treated
bamboo epoxy composite is 39% higher, and the flexural
modulus show a decrement from 11.9 GPa to 9.8 GPa
compared with that of untreated bamboo epoxy compos-
ite. The treated bamboo polyester composite has an in-
crement of 20% in flexural strength, and 116% in flex-
ural modulus compared with that of untreated bamboo
based polyester composite.
Figure 4 shows the water absorption behavior of
pre-impregnated bamboo epoxy and polyester compos-
ites. The water absorption for all the composites in-
creased up to 5th or 7th week and then leveled-off. In both
the procedure of water absorption test, composites rein-
forced with chemically treated fibers absorb less water

Influence of Pre-Impregnation Treatment on Bamboo Reinforced Epoxy/UPE Resin Composites
141
(a) (b)
Figure 2. SEM micrograph of tensile fracture surfaces of (a)
BPIE & (b) BPIP.
BE BPIE BP BPIP
100
110
120
130
140
150
160
170
Flexural Strength
Flexural Modulus
Composite
Flexural Strength (MPa)
4000
5000
6000
7000
8000
9000
10000
11000
12000
13000
Flexural Modulus (MPa)
Figure 3. Flexural properties of water treated bamboo com-
posites.
0 10203040
0
10
20
30
40
50
60
Increase in Weight(%)
Time1/2, (h1/2)
BE
BPIE
BP
BPIP
Figure 4. Water absorption curve for water treated bamboo
composites.
than the untreated fibers. For the long term water immer-
sion test, percent increase in water absorption for un-
treated bamboo polyester and epoxy composites are
52.26 and 41.43 respectively. The water absorption by
the treated composites has decreased. Water absorption
at saturation was 23.80% and 22.68% for the epoxy and
polyester based composites respectively. This is due to
improved adhesion between the fibers and matrix. In this
case, the low-viscous resin can already fill the micro-
pores and flow in between the elementary fibers, which
is beneficial for the impregnation afterwards.
As shown in Figure 4, where percentage moisture ab-
sorption increases steadily with t1/2 in the initial stage and
then tend to level off following the saturation point, in-
dicating a Fickian mode of diffusion.
4. Conclusion
Preimpregnation has improved the mechanical and water
resistant properties of the both epoxy and polyester based
composites. The tensile strength of preimpregnated bam-
boo epoxy composite is increased by 40% and the elastic
modulus by 35%. The treated bamboo polyester compos-
ite has an increment of 54% in tensile strength and 95%
in elastic modulus. The treated bamboo polyester com-
posite has an increment of 20% in flexural strength, and
116% in flexural modulus. The percentage improvement
was more for treated bamboo polyester composite. Water
absorption at saturation was 23.80% and 22.68% for the
epoxy and polyester based composites respectively.
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