ORIGINAL PAPER

Sisal/Carbon Fibre Reinforced Hybrid Composites: Tensile,Flexural and Chemical Resistance Properties

P. Noorunnisa Khanam • H. P. S. Abdul Khalil •

M. Jawaid • G. Ramachandra Reddy •

C. Surya Narayana • S. Venkata Naidu

� Springer Science+Business Media, LLC 2010

Abstract The variation of mechanical properties such as

tensile and flexural properties of randomly oriented

unsaturated polyester based sisal/carbon fibre reinforced

hybrid composites with different fibre weight ratios have

been studied. The chemical resistance test of these hybrid

composites to various solvents, acids and alkalies were

studied. The effect of NaOH treatment of sisal fibres on the

tensile, flexural and chemical resistance properties of these

sisal/carbon hybrid composites has also been studied. The

hybrid composites showed an increase in tensile and flex-

ural properties with increase in the carbon fibre loading.

The tensile properties and flexural properties of these

hybrid composites have been found to be higher than that

of the matrix. Significant improvement in tensile properties

and flexural properties of the sisal/carbon hybrid compos-

ites has been observed by alkali treatment. The chemical

resistance test results showed that these untreated and

alkali treated hybrid composites are resistance to all

chemicals except carbon tetra chloride. Hand lay-up tech-

nique was used for making the composites and tests are

carried out by using ASTM methods.

Keywords Sisal fibre � Carbon fibre �Unsaturated polyester resin � Hybrid composites �Tensile properties � Flexural properties

Introduction

Now a days fibre reinforced composites are in use in a

variety of structures, ranging from space craft and aircraft

to buildings and bridges. This wide use of composites has

been facilitated by the introduction of new materials,

improvement in manufacturing processes and develop-

ments of new analytical and testing methods. Fiber-rein-

forced materials have high mechanical properties, and their

strength-to-weight ratios are superior to those of most

alloys. When compared to metals they offer many other

advantages as well as including non-corrosiveness, trans-

lucency good bonding properties, and ease of repair.

The performance of a polymer composite depends not

only on the selection of their components, but also on the

interface between them. In order to meet the specific needs,

sometimes it is necessary to modify the matrix, and the

reinforcement. Natural fibres play an important role in

developing high performing fully biodegradable ‘green’

composites which will be a key material to solve the

environmental problems. Natural fibres offer many attrac-

tive technical and environmental qualities when used

as reinforcements in polymer composites. Natural fibers

are largely divided into two categories depending on their

origin: plant based and animal based. In general plant

based fibers are lignocellulose in nature composed of cel-

lulose, hemicellulose and lignin eg. jute, coir, sisal, cotton

etc. [1–6], whereas animal based fibers are composed of

proteins e.g. silk and wool [7, 8]. Natural fibres are low-

cost fibres, highly available and renewable, with low

P. Noorunnisa Khanam � H. P. S. Abdul Khalil � M. Jawaid

School of Industrial Technology, Universiti Sains Malaysia,

11800 Penang, Malaysia

G. Ramachandra Reddy � C. Surya Narayana � S. Venkata Naidu

Department of Polymer Science & Technology, Sri Krishna

Devaraya University, Anantapur 515001, Andhra Pradesh, India

P. Noorunnisa Khanam (&)

Division of Bioresource Technology, School of Industrial

Technology, University Science Malaysia, 11800 Penang,

Malaysia

e-mail: pnkhanam_phd@yahoo.com

123

J Polym Environ

DOI 10.1007/s10924-010-0210-3

density and high specific properties as well as they are

biodegradable and less abrasive to expensive molds and

mixing equipments. However, their potential use as rein-

forcement is greatly reduced because of their incompati-

bility with the hydrophobic polymer matrix, their poor

resistance to moisture and their tendency to form aggregate

during processing. The mechanical properties of natural

fibre composites are much lower than those of the synthetic

fibre composites. To produce the reactive hydroxyl groups

and the rough surface for adhesion with polymeric mate-

rials, plant fibres need to undergo physical and/or chemical

treatment to modify the surface and structure. Though the

synthetic fibres have very good mechanical properties, their

disadvantage is difficult recycling. Another advantage of

synthetic fibre is their moisture repellency, whereas poor

resistance to moisture absorption made the use of natural

fibre reinforced composites less attractive.

To take advantage of both natural and synthetic fibres,

they can be combined in the same matrix to produce hybrid

composites that take full advantage of the best properties of

the constituents. Incorporation of fibres (man made or

natural) into a polymer is known to cause substantial

changes in the mechanical properties of composites.

Hybrid composites offers a attractive mode for fabricating

products with reduced cost, high specific modulus,

strength, corrosion resistance and in many cases excellent

thermal stability [9–13].

Suhara Panthpulakkal et al. [14] studied the mechanical,

water absorption and thermal properties of injection-mol-

ded short hemp fibre/glass fibre reinforced poly propylene

hybrid composites. Results showed that hybridization with

glass fibre enhanced the performances properties, thermal

properties and resistance to water absorption properties of

the hemp fibre composites were improved by hybridization

with glass fibres. Abdul Khalil et al. [15] studied the

mechanical and physical properties of oil palm empty fruit

bunch/glass hybrid reinforced polyester composites. Va-

radarajulu et al. [16] studied the tensile properties of ridge

gourd/glass fibre reinforced phenolic composites. They

observed that tensile properties are increased with

increasing glass fibre in the hybrid composites. Padma

priya et al. [17] studied the mechanical performance of bio

fibre/glass reinforced epoxy hybrid composites and they

observed that flexural properties of silk fibre reinforced

composites are improved by the incorporation of glass fibre

in it. John et al. [18–20] studied the tensile, flexural, impact

and compressive properties of sisal/glass fibre hybrid

composite. They observed that these properties were

increases with glass fibre loading. Singha et al. [21] studied

the chemical resistance, mechanical and physical proper-

ties of bio fibre based polymer composites. Srinivasulu

et al. [22] studied the chemical resistance and tensile

properties of short bamboo fibre reinforced epoxy/poly

carbonate composites. Raghu et al [23] studied the chem-

ical resistance properties of sisal/silk hybrid composites.

Varada Rajulu et al [24] studied the chemical resistance,

void contents and morphological properties of Hildegardia

fabric/polycarbonate toughened epoxy composites. Anup-

ama Kaushic et al. [25] studied the mechanical properties

and chemical resistance of short glass fibre reinforced

epoxy composites

In the present work the author prepared the untreated

and alkali treated sisal/carbon hybrid composites with

different weight ratios i.e. 100:0, 75:25, 50:50, 25:75 and

0:100. Interface plays an important role in the physical and

mechanical properties of composites. To make good use of

sisal-fibre reinforcement in composites, fibre-surface

treatment must be carried out to obtain an enhanced

interface between the hydrophilic sisal fibre and the

hydrophobic polymer matrices. Alkali treatment can

remove natural and artificial impurities and produce a

rough surface topography. In addition, alkali treatment

leads to fibre/fibre fibrillation, i.e. breaking down the fibre

bundle into smaller fibres. This increases the effective

surface area available for wetting by the matrix resin.

Hence, increasing the fibre aspect ratio caused by reduced

fibre diameter and producing a rough surface topography

offer better fibre/matrix interface adhesion and increase in

mechanical properties. Unsaturated polyester resin was

used as matrix for preparing the composites. Some

mechanical properties such as tensile and flexural

properties and chemical resistance properties were stud-

ied for these sisal/carbon fibre reinforced hybrid

composites.

Materials

Sisal fibres were collected from local sources. Woven cloth

of carbon was used for the present study. Unsaturated

polyester resin was used as matrix and this was taken from

Allied Marketing Ltd, Hyderabad, India. Methyl ethyl

ketone peroxide was used as a catalyst and cobalt naph-

thenate was used as an accelerator. These were taken from

M/S Bakelite Hylam, Hyderabad. The styrene monomer,

PVA, NaOH, toluene, benzene, carbon tetra chloride, nitric

acid, hydro chloric acid, and nitric acid, NaOH, Na2CO3

and NH4OH were purchased from SD Fine chemicals Ltd.

Methods

Sisal Fibre Treatment

The fibers were boiled in aqueous 18% NaOH solution for

30 min to remove the soluble greasy material in order to

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enhance the adhesion characteristics between the fibre and

the matrix. The treated fiber was washed with water to

remove the excess of NaOH sticking to the fibres. Final

washing was carried out with distilled water and the fibres

were dried in hot air oven. The fibres were cut into 2 cm

length for molding the composites.

Preparation of Hybrid Composite

The different combinations (100/0, 75/25, 50/50, 25/75,

0/100) were selected to do hybrid sisal/carbon /polyester

laminates by fixing the fibre length i.e. 2 cm. Unsatu-

rated polyester resin and styrene are mixed in the ratio

100:25 parts by weight respectively. Later, 1 wt% methyl

ethyl ketone peroxide and 1 wt% cobalt naphthenate

were added and mixed thoroughly. This system was

processed by hand lay-up technique for making test

specimens. In order to make the test specimens, the

matrix system is poured into a mould made of glass

plates. The mould was coated with a thin layer of

aqueous solution of poly vinyl alcohol (10 wt%), which

acts as a good releasing agent. Excess resin and air

bubbles were removed carefully with a roller, and a glass

plate was placed on top. The castings were allowed to

24 h at room temperature and post cured at 80�C for 4 h.

Test specimens of the required size followed by ASTM

standards were cut out from sheets.

Mechanical Tests

The tensile test specimens were cut as per ASTM D 638

and flexural test specimens were cut as ASTM D 618

specifications. The tests were measured by employing a

Universal Testing Machine (INSTRON model 3369). Five

samples were tested in each case and the average value is

reported.

Chemical Resistance Test

The chemical resistance tests of untreated and 18% NaOH

boiled sisal/carbon hybrid composites have been tested by

using the ASTM D 543-87 [26]. The effect of solvents

(benzene, toluene, carbon tetra chloride and distilled

water), acids (hydrochloric acid (10%), acetic acid (5%)

and nitric acid 40%) and alkalies (sodium hydroxide,

sodium carbonate and ammonium hydroxide) on matrix

and sisal/carbon hybrid composites In each case five pre

weighed samples were dipped in the respective chemical

reagents for 24 h. They were then removed and immedi-

ately washed in distilled water and dried by pressing them

on both sides with a filter paper at room temperature. The

samples were then weighed and the percentage weight loss/

gain was determined.

Results and Discussions

Tensile Properties

Tensile strength and tensile modulus measurements are

among the most important indications of strength in a

material and are most widely specified property. Tensile

test is a measurement of the ability of a material to with-

stand forces that tend to pull it apart and to determine to

what extent the material stretches before breaking. Tensile

modulus, an indication of the relative stiffness of a mate-

rial, can be determined from a stress strain diagram. Ten-

sile strength and tensile modulus of matrix and randomly

oriented untreated sisal/carbon fibre reinforced hybrid

composites and 18% aqueous NaOH boiled sisal/carbon

fibre hybrid composites with different fibre weight ratios

i.e. 100:0, 75:25, 50:50, 25:75 and 0:100 were presented in

the Table 1. From the table, it was observed that tensile

strength and tensile modulus increases with carbon fibre

loading. It was also seen that tensile strength and modulus

of matrix is lower than the hybrid composites. This

enhancement indicates the effectiveness of the reinforce-

ment. It was also observed from the table that 18% aqueous

boiled sisal/carbon hybrid composites have higher tensile

strength and tensile modulus than untreated sisal/carbon

hybrid composites. Improvement of tensile properties are

due to the surface modification of sisal fibres boiled with

18% aqueous NaOH. Boiling the fibre with 18% aqueous

NaOH gives the surface of the fibre more roughness due to

the removal of lignin and hemi cellulose. This increases the

interface bonding between the fibre and the matrix.

Figures 1 and 2 shows the variation of tensile strength

and tensile modulus of untreated and 18% aqueous NaOH

boiled sisal /carbon fibre reinforced hybrid composites with

different fibre weight ratios. From the figures it was

observed that tensile strength and tensile modulus increases

with increase in the carbon fibre content in hybrid com-

posites. It was also observed that carbon fibre composites

have higher tensile strength than these hybrid composites.

It was seen that 18% aqueous NaOH boiled sisal fibre/

carbon fibre composites possess higher tensile strength than

untreated sisal/carbon fibre hybrid composites, because of

the rough surface topography of the sisal fibre after alkali

treatment.

Flexural Properties

Flexural strength is one of the important mechanical

properties of the composites. For a composite to be used as

the structural materials it must possess higher flexural

strength. The flexural strength and modulus values for

different weight ratios of (i.e. 100:0, 75:25, 50:50, 25:75

and 0:100) untreated and 18% NaOH boiled sisal /carbon

J Polym Environ

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hybrid composites are presented in Table 2. For compari-

son these values for the matrix are also presented in the

same table. It is observed that the flexural strength and

modulus for different fibre weight ratios of the composites

are more when alkali boiled fibre was used in the com-

posites. From table it is clearly evident that the flexural

strength and modulus of the hybrid composites are higher

than those of the matrix. From the table it is also observed

that the flexural strength and flexural modulus increases

with increase the carbon fibre content in the hybrid

composite.

The variation of flexural strength and flexural modulus

of untreated and 18% aqueous NaOH boiled sisal /carbon

hybrid composites with different weight ratios of fibres in

hybrid composites are presented in Figs. 3 and 4. It is

clearly seen in the figures that flexural strength and flexural

modulus increases with carbon fibre content. From the

figures it is observed that the flexural properties of the sisal

fibre reinforced composites were considerably lower than

those for the carbon fibre reinforced composites and hence,

as the carbon fibre is added to the sisal in the hybrid

composite, the properties were improved. From the figures

it is also observed that 18% aqueous NaOH boiled sisal /

carbon hybrid composites have higher flexural strength

than untreated sisal/carbon hybrid composites. A possible

enhancement of the bonding between the reinforcement

Table 1 Tensile strength and modulus of different weight ratios of untreated and 18% NaOH boiled sisal/carbon fibre reinforced hybrid

composites

S.No Fibre weight

ratios sisal/carbon

Tensile strength (MPa) Tensile modulus (GPa)

Untreated 18% aqueous

NaOH boiled

Untreated 18% aqueous

NaOH boiled

1 100:0 24.16 78.22 1.37 1.96

2 75:25 31.35 84.74 1.68 1.99

3 50:50 38.3 93.97 1.97 2.17

4 25:75 50.85 107.51 2.37 2.78

5 0:100 122.11 122.11 2.98 2.98

6. Matrix 22.42 983.98

Fig. 1 Variation of tensile strength of different weight ratios of

untreated and 18% NaOH boiled sisal/carbon hybrid compositesFig. 2 Variation of tensile modulus of different weight ratios of

untreated and 18% NaOH boiled sisal/carbon hybrid composites

J Polym Environ

123

and the matrix by the alkali treatment responsible for the

increased flexural properties. This is due to the fact that

alkali treatment improves the adhesive characteristics of

sisal fibre surface by removing hemi cellulose, thereby

producing rough surface topography. This topography

offers better fibre matrix interface adhesion and an increase

in mechanical properties.

Chemical Resistance Properties

The chemical resistance study was to test the composites

were capable of withstanding exposure to a variety of

chemicals. The percent weight gain (?) or loss (-) values

when the composites and matrix materials are immersed in

solvents, acids and alkalis are presented in Table 3. From

the table, it is clearly evident that weight gain is observed

for almost all chemical reagents used when the fibre of the

composites were untreated and 18% NaOH boiled sisal

fibres. But the weight loss was observed when the samples

were immersed in carbon tetra chloride, because the cross

linked polyesters are easily attracted by chlorinated

hydrocarbons. The ester groups in the polymer provide

sites for hydrolytic attack and the strong alkalis cause

appreciable degradation.

Conclusions

The mechanical properties such as tensile and flexural

properties of untreated and 18% NaOH boiled sisal/carbon

Table 2 Flexural strength and modulus of different weight ratios of untreated and 18% NaOH boiled sisal/carbon fibre reinforced hybrid

composites

S.No Fibre weight

ratios sisal/carbon

Flexural strength (MPa) Flexural modulus (GPa)

Untreated 18% aqueous NaOH boiled Untreated 18% aqueous NaOH boiled

1 100:0 63.87 138.78 3.79 5.32

2 75:25 90.55 140.89 4.25 6.52

3 50:50 131.48 158.31 7.97 8.69

4 25:75 148.78 169.14 9.35 11.33

5 0:100 176.53 176.53 13.47 13.47

6 Matrix 58.11 – 1.02 –

Fig. 3 Variation of flexural strength of different weight ratios of

untreated and 18% NaOH boiled sisal/carbon hybrid compositesFig. 4 Variation of flexural modulus of different weight ratios of

untreated and 18% NaOH boiled sisal/carbon hybrid composites

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hybrid composites were studied. The variation of tensile

and flexural properties of these hybrid composites were

studied by different weight ratios. The chemical resistance

tests of these hybrid composites were also studied. It is

observed that their has been enhancement in these tensile

and flexural properties with increases carbon fibre content

in the hybrid composites. The effect of alkali treatment of

sisal fibres on the tensile and flexural properties have also

been studied and found that increase in properties by alkali

treatment. It was observed that 18% NaOH boiled sisal/

carbon fibre reinforced hybrid composites showed superior

tensile and flexural properties than untreated sisal/carbon

hybrid composites. This is due to the fact that alkali

treatment improves the fibre surface adhesion characteris-

tics by removing hemicellulose, thereby producing rough

surface topography. This topography offers better fibre-

matrix interface adhesion and an increase in mechanical

properties. The chemical resistance study clearly indicates

that the untreated and treated composites are strongly

resistant to all chemicals except carbon tetra chloride.

Acknowledgements The researchers would like to thank the Uni-

versity Sains Malaysia, Penang for providing Post doctoral fellow-

ship, USM fellowship and research Grant 1001/PTEKIND/841020

that has made this work possible. Author also thankful to Department

of Polymer science and technology, Sri Krishna Deva raya University,

Anantapur, India.

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Table 3 Chemical resistance properties of untreated and 18% NaOH boiled sisal/carbon hybrid composites for different chemicals

Chemicals Matrix Different weight ratios of untreated sisal/carbon hybrid

composites

Different weight ratios of 18% NaOH boiled sisal/carbon

hybrid composites

100:0 75:25 50:50 25:75 0:100 100:0 75:25 50:50 25:75 0:100

Toluene 0.73 1.234 3.854 3.860 3.658 4.95 0.224 3.422 4.031 1.941 4.951

Benzene 0.618 5.172 0.813 2.583 4.314 3.833 0.492 0.056 4.593 5.063 3.833

ccl4 -0.55 -1.218 -1.116 -0.351 -1.012 -0.354 -0.363 -0.185 -0.731 -0.359 -0.354

H2O 0.618 1.982 2.082 1.481 1.377 0.415 6.828 1.577 1.408 0.607 0.415

CH3COOH (5%) 0.532 0.121 3.705 1.203 1.220 0.467 0.287 1.640 0.850 0.558 0.467

HCL (10%) 0.235 0.543 1.620 1.299 1.072 0.314 0.543 0.643 0.497 0.648 0.314

HNO3 (40%) 0.323 0.320 2.021 1.481 1.964 0.518 0.760 0.673 0.780 0.868 0.518

NaOH (10%) 0.44 0.721 1.369 0.089 1.686 1.365 1.993 3.742 0.028 2.821 1.365

Na2CO3 (20%) 0.02 0.325 1.600 1.731 1.463 0.179 0.314 0.762 0.456 0.146 0.179

NH4OH (10%) 0.650 0.765 5.448 4.093 3.831 2.069 0.483 1.754 2.997 3.358 2.069

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