Influence of Pre-Impregnation Treatment on Bamboo Reinforced Epoxy/UPE Resin Composites

doi:10.4236/ojcm.2012.24017

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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.

Email: [email protected]

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

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

Increase in Weight(%)

Time1/2, (h1/2)

BPIE

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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