Physical, mechanical, and water absorption behavior of coir/glass fiber reinforced epoxy based...

Physical, Mechanical, and Water Absorption Behaviorof Coir/Glass Fiber Reinforced Epoxy Based HybridComposites

Vineet Kumar Bhagat, Sandhyarani Biswas, Janaki DehuryMechanical Engineering Department, N.I.T., Rourkela, India

Fiber reinforced polymer composites has been used ina variety of application because of their many advan-tages such as relatively low cost of production, easyto fabricate, and superior strength compare to neatpolymer resins. Reinforcement in polymer is either syn-thetic or natural. Synthetic fiber such as glass, carbon,etc. has high specific strength but their fields of appli-cation are limited due to higher cost of production.Recently there is an increase interest in natural com-posites which are made by reinforcement of naturalfiber. In this connection, an investigation has been car-ried out to make better utilization of coconut coir fiberfor making value added products. The objective of thepresent research work is to study the physical,mechanical, and water absorption behavior of coir/glass fiber reinforced epoxy based hybrid composites.The effect of fiber loading and length on mechanicalproperties like tensile strength, flexural strength, andhardness of composites is studied. The experimentalresults reveal that the maximum strength properties isobserved for the composite with 10 wt% fiber loadingat 15 mm length. The maximum flexural strength of 63MPa is observed for composites with 10 wt% fiberloading at 15 mm fiber length. Similarly, the maximumhardness value of 21.3 Hv is obtained for compositeswith 10 wt% fiber loading at 20 mm fiber length. Also,the surface morphology of fractured surfaces after ten-sile testing is examined using scanning electron micro-scope (SEM). POLYM. COMPOS., 35:925–930, 2014. VC 2013Society of Plastics Engineers

INTRODUCTION

The interest in natural fiber based polymer composites

is rapidly increasing both in terms of their industrial

applications and fundamental research. Their availability,

renewability, low density, and price as well as satisfactory

mechanical properties make them an attractive ecological

alternative to glass, carbon, and other man-made fibers.

Many investigations have been made on the potential of

the natural fibers such as flax, kenaf, and jute as rein-

forcements for polymer composites. Among various natu-

ral fibers, coconut coir fibers are getting acceptance from

many researchers and it can be used as an alternative

reinforcement in composite materials [1]. Coir is a natural

fiber extracted from the husk of coconut fruit. The husk

contains coir fiber and a corky tissue called pith. It is a

fiber which is highly available in India the second highest

in the world after Philippines. It consists of water, fibers,

and small amounts of solvable solids. Because of the high

lignin content coir is more long-lasting when compared to

other natural fibers [2]. Natural fibers such as coir based

composites enjoying broader applications in automobiles

and railway coaches and buses for public transport sys-

tem. In view of this, the present research work is under-

taken to study the reinforcement potential of coir fibers in

polymer composites. Another possibility that the incorpo-

ration of different types of fibers in polymer could pro-

vide a synergism in terms of improved properties has not

been adequately explored so far. However, some recent

reports suggest that by both natural and synthetic fibers in

the polymer matrix composites, synergistic effects may be

achieved in the form of higher mechanical properties and

reduced material cost. Such multi-component composites

consisting of a matrix phase reinforced with a fiber and

filled with particulates are termed as hybrid composites.

The properties of the natural fiber reinforced composites

can be improved by hybridizing with high strength syn-

thetic fibers. Interspersing the two or more kinds of fiber

in a common matrix forms hybrid composites. The con-

cept of hybridization gives flexibility to the design engi-

neer to tailor the material properties according to the

requirements, which is one of the major advantages of

composites. Glass fibers are most commonly used in rein-

forcing both thermoplastics and thermosets. They have

high tensile strength, high chemical resistance, high

dimensional stability, and has excellent insulation proper-

ties. Hybridization of natural fiber with synthetic fiber

can improve the mechanical properties as well as mois-

ture resistance behavior of the composites and hence a

balance between environmental impact and performance

Correspondence to: Sandhyarani Biswas; e-mail: sandhya_biswas@

yahoo.co.in

DOI 10.1002/pc.22736

Published online in Wiley Online Library (wileyonlinelibrary.com).

VC 2013 Society of Plastics Engineers

POLYMER COMPOSITES—2014

could be achieved with optimum cost. Many researchers

have studied on various aspects of hybrid fiber based

polymer composites. Thew and Liao [3] informed that

mechanical properties of bamboo/glass fiber reinforced

hybrid composites depends on fiber length, fiber weight

ratio and adhesion characteristics between the matrix and

the fiber. Velmurugan et al. [4] studied the tensile, shear,

impact and flexural properties of the Palmyra/glass fiber

hybrid composites. Goud and Rao [5] found a consider-

able increase in the tensile, flexural, impact, and hardness

properties of Roystonearegia/glass fiber hybrid compo-

sites with the increase in glass fiber loading. Pothan et al.

[6] studied on the banana-glass hybrid composites and

found layering pattern or the geometry of the composites

has a profound effect on the dynamic behavior of the

composites. There are many factors influencing the vari-

ous properties of composites such as fiber loading, orien-

tation, length, types, properties of the matrix, fiber–matrix

interface strength etc. A great deal of work has already

been reported on the effect of various parameters on the

performance of composites. Basiji et al. [7] studied the

effects of fiber length and fiber loading on the mechanical

properties of wood-plastic (polypropylene) composites.

Vilay et al. [8] studied the effect of fiber surface treat-

ment and fiber loading on the properties of bagasse fiber

reinforced unsaturated polyester composites. Alamri and

Low [9] studied the mechanical and water absorption

behavior of recycled cellulose fiber reinforced epoxy

composites. To this end, this study is undertaken to

develop a new class of hybrid polymer composites rein-

forced with both coir and glass fiber and study their phys-

ical, mechanical, and water absorption behavior.

EXPERIMENTAL DETAILS

Composite Fabrication

The short coir fiber and E-glass fiber is taken as rein-

forcement and epoxy as matrix material. The composites

are fabricated by using simple hand lay-up technique. A

stainless steel mould having dimension of 180 3 180 3

40 mm3 is used for composite fabrication. The short coir

fiber and glass fiber are mixed with epoxy resin by the

simple mechanical stirring and the mixture is poured into

various moulds conforming to the requirements of various

testing conditions and characterization standards. Compo-

sites of eight different compositions reinforced with two

different weight percentage of coir fiber loading (5 and

10 wt%) with four different fiber lengths (5, 10, 15, and

20 mm) are made keeping glass fiber loading constant

(20 wt%) with fiber length of 10 mm. The detailed com-

position and designation of the composites are presented

in Table 1. Figure 1a and b shows coir fiber and glass

fiber respectively. Similarly, Fig. 2 shows coir/glass fiber

reinforced epoxy based hybrid composite. The cast of

each composite is cured under a load of about 50 kg for

24 h. Specimens of suitable dimension are cut with the

help of hack saw for mechanical and water absorption

tests.

Physical and Mechanical Tests

The theoretical density of composite material is calcu-

lated as per the formula given by Agarwal and Broutman

[10].

qct 51

Wf=qf

� �1 Wm=qmð Þ

(1)

where W and q represent the weight fraction and density

respectively. The suffix f, m, and ct stand for the fiber,

matrix, and the composite materials respectively.

The actual density (qce) of the composite, however,

can be determined experimentally by simple water

immersion technique. The volume fraction of voids (Vv)

in the composites is calculated using the following

equation:

Vv5qct 2qce

qct

(2)

The tensile test is done using Universal Testing

Machine Instron 1195 as per ASTM D3039-76 test stand-

ards. A uniaxial load was applied both the ends of com-

posite specimens for the test. The test is repeated two

times on each composite of same composition and the

mean value is considered. A three point bend test is done

to evaluate the flexural strength. For the test, the cross

head speed is taken as 2 mm/min and a span of 40 mm is

maintained. Micro-hardness test of composite specimens

is done using Leitz micro-hardness tester. The fractured

surfaces after tensile testing are examined using scanning

electron microscope (SEM) JEOL JSM-6480LV.

TABLE 1. Designation of composites.

Composites Compositions

C1 Epoxy (75 wt%) 1Glass Fiber (20 wt%) 1Coir Fiber

(Fiber length 5 mm) (5 wt%)















926 POLYMER COMPOSITES—2014 DOI 10.1002/pc

Water Absorption Test

Water absorption studies were performed according to

ASTM D 570-98 standard test method using the formula

%W5Wt2Woð Þ

Wo

3100

where Wt is the weight of specimen at a given immer-

sion time and Wo is the oven-dried weight.

RESULTS AND DISCUSSION

Physical and Mechanical Characteristics of Composites

Effect of Fiber Loading and Length on Density of

Composites. Density of a composite depends on the rela-

tive proportion of matrix and reinforcing materials and this

is one of the most important factors determining the proper-

ties of the composites. The void content is the cause for the

difference between the values of true density and the theo-

retically calculated one. The difference in theoretical and

experimental densities is mainly due to the presence of

voids in the composite. Hence, it becomes essential to

determine the percentage of voids in the samples prepared.

Table 2 shows the theoretical density, experimental density,

and the corresponding void content. It can be seen that the

void fraction in the composites increases with the fiber

loading. Natural fibers generally contain large amounts of

the hydroxyl group, which makes them polar and hydro-

philic in nature. However, most plastics are hydrophobic in

nature. This polar nature also results in high moisture sorp-

tion in natural fiber based composites, leading to fiber

swelling and voids in the fiber–matrix interface [11]. The

void fraction increases with fiber loading and this may be

attributed to poor interaction/adhesion between fiber and

matrix materials. The similar trend of increase in void frac-

tion with increase in fiber loading is also reported by previ-

ous researchers [12].

Effect of Fiber Loading and Length on Hardness of

Composites. The effect of fiber loading and length on

the coir/glass fiber reinforced epoxy based hybrid compo-

sites is shown in Fig. 3. The test results show that with

FIG. 2. Short coir/glass fiber reinforced epoxy based hybrid composite.

[Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]

TABLE 2. Void fraction of composites.

Composites

Theoretical

density(gm/cc)

Experimental

density (gm/cc)

Volume fraction

of voids (%)

C1 1.2489 1.1975 4.11562

C2 1.2489 1.178 5.67699

C3 1.2489 1.177 5.75706

C4 1.2489 1.174 5.99727

C5 1.2548 1.1775 6.16303

C6 1.2548 1.17 6.76072

C7 1.2548 1.149 8.43424

C8 1.2548 1.135 9.54993

FIG. 1. Short coir fiber and glass fiber. [Color figure can be viewed in the online issue, which is available

at wileyonlinelibrary.com.]

DOI 10.1002/pc POLYMER COMPOSITES—2014 927

wileyonlinelibrary.com

wileyonlinelibrary.com

the increase in fiber length, the micro-hardness value of

the composites is increases. Similar trend of increase in

hardness value with the increase in fiber length is also

observed in case of bamboo/glass fiber reinforced epoxy

composites [13]. It is also evident from the Fig. 3 that

with the increase of fiber loading, micro-hardness value

decreases. Composites with 5 wt% fiber loading shows

better hardness value as compared to 10 wt% irrespective

of fiber length except for composites with coir fiber of 20

mm length. Similar trend of decrease in hardness value

with the increase in fiber loading is also observed in case

of glass fiber reinforced epoxy composites [14].

Effect of Fiber Loading and Length on Tensile

Properties of Composites. The influence of fiber load-

ing on the tensile strength and tensile modulus of the com-

posites is shown in Figs. 4 and 5 respectively. A gradually

increase in tensile strength can be observed with the

increase in the fiber length up to 15 mm of coir/glass epoxy

based hybrid composites. This is due to the proper adhesion

between the both types of fiber and the matrix. However,

further increase in fiber length, i.e., 20 mm, there is a

decrease in the tensile strength. The reason may be due to

the curling effect of the long coir fiber [15]. The curly

nature of fibers prevents the proper alignment of fibers in

the (longitudinal direction) composites. The maximum ten-

sile strength is observed for the composite with 10 wt%

fiber loading at 15 mm length. Similarly, the tensile modu-

lus of composites is found to be increasing with increase in

fiber length irrespective of fiber loading as observed in Fig.

5. However, with increased in fiber loading the tensile

modulus gradually goes on increasing irrespective of fiber

length. The increase of the tensile modulus may be highly

related to the increase of stiffness of the composites by vir-

tue of coir fiber loading. The similar trend of increase in

tensile modulus with increase in fiber loading is also

observed by past researchers [16].

Effect of Fiber Loading and Length on Flexural Prop-

erties of Composites. The effect of fiber loading and

length on the flexural strength of coir/glass fiber reinforced

epoxy based hybrid composites is shown in Fig. 6. The

flexural strength of composite increases, with increase in

fiber length up to 15 mm. However, further increase in fiber

length (up to 20 mm) the value decreases. The reason may

be due to the longer fibers tend to ball up resulting in low

workability and decline in strength. The similar trend is

also observed by previous researchers [17]. As far as the

effect of fiber loading is concerned, composites with 10

wt% fiber loading shows better flexural strength value as

compared to 5 wt% fiber loading. The maximum flexural

strength of 63 MPa is observed for composites with 10 wt%

fiber loading at 15 mm length.

Surface Morphology

Figure 7a and b shows the fracture surfaces of coir/

glass fiber reinforced epoxy based hybrid composite after

FIG. 3. Effect of fiber loading and length on Micro-hardness of

composites.

FIG. 4. Effect of fiber loading and length on tensile strength of

composites.

FIG. 5. Effect of fiber loading and length on tensile modulus of

composites.


the tensile test with different fiber loading and fiber

length. Figure 7a shows the tensile fracture of composite

with 10 wt% coir fiber loading and 20 mm fiber length.

It can be clearly observed from the Fig. 7a that the fibers

pull out from the resin surface due to poor interfacial

bonding. Figure 7b shows the tensile fracture surface of

composites reinforced with 10 wt% coir fiber loading at

15 mm fiber length. It is evident from the Fig. 7b that

surface without much fiber pull out is clearly visible may

be due to the better adhesion fiber and matrix which leads

to better of strength properties of composites. The frac-

ture surfaces study of coir fiber reinforced epoxy compos-

ite after the tensile test and flexural test is done by

Biswas et al. [18].

Water Absorption Behavior of Composites

The effect of fiber loading and length on the water

absorption of the coir/glass fiber reinforced composites

with increase in immersion time is shown in Fig. 8. It is

evident from the figure that the rate of moisture absorption

increases with increase in fiber lengths. Generally, the rate

of water absorption is greatly influenced by the materials

density and void content. It has been reported by earlier

researchers that the incorporation of long coir fibers into

the matrix decreased workability and increased the void

space [19]. Consequently, the longer the fiber, the higher is

the water absorption. As far as effect of fiber loading is

concerned composites with 10 wt% coir fiber loading

shows higher water absorption rate as compared to 5 wt%

fiber loading. The reason may be due to the coir fibers con-

tain abundant polar hydroxide groups, which result in a

high moisture absorption level of natural fiber reinforced

polymer matrix composites and are a major obstacle for

preventing extensive applications of these materials. The

minimum water absorption rate is observed for composites

with 5 wt% fiber loading and at 5 mm fiber length. It is

also observed from the figure that the water absorption rate

generally increases with immersion time, reaching a certain

value at a saturation point where no more water is

FIG. 7. Scanning electron micrographs of coir/glass fiber reinforced epoxy composite specimens after ten-

sile test at different fiber loading and length.

FIG. 8. Effect of immersion time on water absorption properties of

composites.

FIG. 6. Effect of fiber loading and length on flexural strength of

composites.

DOI 10.1002/pc POLYMER COMPOSITES—2014 929

absorbed. The maximum weight gain from 3.340% to

7.250% (weight fraction) is observed by the composite

specimens at room temperature.

CONCLUSIONS

The experimental investigation on the physical,

mechanical, and water absorption behavior of coir/glass

fiber reinforced epoxy based hybrid composites lead us to

the following conclusions obtained from this study:

� Successful fabrication of coir/glass fiber reinforced epoxy

based hybrid composites is possible by simple hand lay-up

technique.

� It has been noticed that the various properties of the com-

posites are greatly influenced by the fiber loading and

fiber length. The void content of composites increases

with increase in both the fiber loading and fiber length.

� The experimental results reveal that the maximum strength

properties is observed for the composite with 10 wt% fiber

loading at 15 mm length. The maximum flexural strength

of 63 MPa is observed for composites with 10 wt% fiber

loading at 15 mm fiber length. It can be observed that

with the increase of fiber length, the tensile modulus

increases irrespective of fiber loading. Similarly, the maxi-

mum hardness value of 21.3 Hv is obtained for composites

with 10 wt% fiber loading at 20 mm fiber length.

� SEM images of the fracture surfaces of composites after

the tensile test shows that the increase in strength proper-

ties of composites at 10 wt% fiber loading and 15 mm

length is due to the better adhesion between fiber and

matrix.

� The rate of moisture absorption increases with increase in

both fiber loading and fiber lengths. The minimum water

absorption rate is observed for composites with 5 wt%

fiber loading and at 5 mm fiber length.

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