Preparation of Polypropylene Fiber Banana Fiber

Preparation of Polypropylene Fiber/Banana FiberComposites by Novel Commingling Method

Sherely Annie Paul,1 Kuruvilla Joseph,2 Gem Mathew,3 Laly A. Pothen,1 Sabu Thomas41Department of Chemistry, Bishop Moore College, Mavelikara, Kerala, India

2Department of Chemistry, Indian Institute of Space Science and Technology, ISRO P.O,Thiruvananthapuram, Kerala, India

3Department of Chemistry, St. Thomas College, Pala, Kerala, India

4School of Chemical Sciences, Mahatma Gandhi University, Priyadharshini Hills P.O, Kottayam, Kerala, India

Short natural fiber thermoplastic composites are usuallyfabricated by melt mixing or solution mixing followed byconventional methods like injection molding or com-pression molding. In melt mixing, the fibers are sub-jected to high shear and this damage the natural fiber.In solution mixing, the use of the organic solvent isessential and its use is hazardous. Development of anovel method commingling to prepare polypropylene(PP)/short natural fiber composite is the main objectiveof this study. The influence of fiber loading on themechanical properties of the composites prepared bythe above method has been evaluated. The applicationsand limitations of several equations to predict physicalproperties such as tensile strength and modulus of thecomposites have been described. POLYM. COMPOS.,31:816–824, 2010. ª 2009 Society of Plastics Engineers

INTRODUCTION

The interest in natural fiber reinforced polymer com-

posite is rapidly growing both in terms of industrial

applications and basic research. The availability, renew-

ability, biodegradability, low density, low cost and satis-

factory mechanical properties of the natural fibers make

them an attractive ecological alternative to glass, carbon

and man-made fibers used for the manufacturing of com-

posites [1–3]. High performance thermoplastic/natural

fiber composite materials offer significant potential

advantages than thermosets including higher damage tol-

erance, unlimited shelf life, faster component manufactur-

ing time and greater recyclability. The main attraction of

thermoplastic composite materials lies in the possibility

of achieving very short remolding times as no chemical

reaction is required. Because of the high viscosity of the

thermoplastic matrix material, it is generally not easy to

properly impregnate a fiber reinforcement lay up during

the manufacturing process. Due to these difficulties in

resin impregnation, intermediate materials that are par-

tially impregnated have been developed which offer a

route to more efficient manufacturing of thermoplastic

composites [4, 5].

In general, the processing of thermoplastic composites

is classified into two categories: pre-impregnation and

post impregnation. In the former case, the fibers are wet-

ted and impregnated by the polymer in one step. The pre-

impregnated fibers can be prepared by solution mixing or

melt mixing. In post-impregnation, the polymers are

available in the forms of film, filaments, or powder [6].

The fibers and the polymer are mixed in a desired manner

without any adhesion or bonding. Impregnation takes

place during part fabrication. The polymeric fibers can

also be mixed with reinforcing fibers to form a com-

mingled bundle, which can be used in various applica-

tions. With commingling a good blending of matrix and

reinforcement fibers is possible [6].

R. Alagirusamy [7] studied the effect of the commin-

gling process variables, namely air pressure and volume

fraction of the matrix forming fibers on the structure and

properties of Glass/polypropylene, Glass polyester and

Glass nylon commingled yarns. Dubouloz-Monnet et al.

[8] reported the viscoelastic behavior of commingled

composites of polypropylene reinforced by 22, 35, and

50 vol% of unidirectional glass fibers, by taking into

account qualitative and quantitative morphological analy-

sis. The aim was to separate the mechanical properties of

Correspondence to: S. Thomas; e-mail: [email protected]

DOI 10.1002/pc.20864

Published online in Wiley InterScience (www.interscience.wiley.com).

VVC 2009 Society of Plastics Engineers

POLYMER COMPOSITES—-2010

the different phases in order to reveal the presence

of either an interphase or changes in PP chain motions

due to the fiber aggregates. Huang and Liu [9] investi-

gated the properties of thermoplastic composites rein-

forced by flax fabrics. Flax yarn and PP (polypropylene)

filaments were twisted together to form a commingled

yarn in a fancy twister. Fabrics with plain and twill

weaves were woven by using the plied yarn. Composites

with five layers of identical fabric weaves were fabricated

in a heating press. They analyzed the failure mechanism

of the composite and structure of the broken end of the

composites was observed by SEM (Scanning electron

microscope). Tufail [10] reported the major problem

observed during the use of a commingled material. i.e,

de-commingling, wherein, the uniform distribution of fiber

and thermoplastic yarn gets disturbed which affects the

final quality of the composite.

In the case of short natural fiber reinforced thermoplastic

composites, most of the samples are fabricated by pre-

impregnation method, i.e, melt mixing or solution mixing

followed by conventional methods like injection molding

or compression molding using thermoplastic granules [11].

In melt mixing, the fibers are subjected to high shear and

this damage the natural fiber. In solution mixing, the use of

the organic solvent like toluene/xylene is essential and its

use is hazardous. Moreover it is very difficult to incorporate

fibers above 40% in melt mixing and in solution mixing.

In the present article, we report the fabrication of the

PP/banana fiber composites by novel commingling

method. In commingling, the polymer fiber and reinforce-

ment fiber are intermingled together. Heating and consoli-

dation of the commingled fibers involve the melting of

the dispersed polymer fibers and the subsequent formation

of a continuous polymer matrix around the reinforcement

fibers. In the present work we used short PP fibers and

short banana fibers. During compression molding, the

polypropylene fibers melt and diffuse into the banana

fibers. Thus, polypropylene act as the matrix and banana

fiber act as the reinforcement. The advantage of this

method is that reinforcement fibers are not subjected to

shear forces as in melt mixing. No solvents are required

for mixing the polymer with reinforcement fiber. More-

over percentage loading of the reinforcing fibers could be

increased up to 60%. Literature survey shows that very

limited studies have been reported on natural fiber compo-

sites prepared by using PP fiber [12–15]. No studies have

reported in literature using commingling method for the

preparation of short natural fiber/PP fiber composites.

The elastic properties of short fiber composites can be

experimentally determined or derived from a variety of

mathematical models. The advantage of a comprehensive

mathematical model is that it reduces costly and time-con-

suming experiments. The variation of the amount of fibers

in a natural fiber composite can be successfully chosen to

correlate with the mechanical properties of composite. The

amount of fiber is one of the most important factors of any

composite material since their mechanical properties are

strongly dependent on it. The volume fraction of fiber is

commonly used to estimate certain mechanical properties

of the composite material. The mechanical properties of a

composite material depend primarily on the strength and

modulus of the fiber, the strength and the chemical stabil-

ity of the matrix and the effectiveness of the bonding

between matrix and fiber in transferring stress across the

interface [16]. In this article, the modified rule of mixtures,

parallel, series and Halpin-Tsai models are applied to PP/

banana fiber composites in order to compare the experi-

mental results with the theoretical predictions

MATERIALS AND METHODS

Materials

Polypropylene fibers used as the polymer matrix with

denier 900, % elongation 26, tenacity 4.53 g/d, weight

average molecular mass 6.3 3 105 g/mol, density 0.91

were obtained from Gare Ware Ropes, India. Banana

fibers were obtained from Sheeba fibers, Poovencode,

Tamil Nadu. The banana fiber was dried in an air oven at

708C for 6 h after chopping into 6-mm length for the

preparation of the composites. The physical, mechanical

properties and chemical constituents of the banana fiber

are reported in Table 1 [17].

Preparation of PP/Banana Fiber Composites

Banana fibers and PP fibers were cut into 6- and 1-mm

length, respectively. Fibers were mixed thoroughly and

arranged in a tray measuring 150 3 150 3 3 mm3 and

pressed into a mat. Short randomly oriented fiber compos-

ite sheets were prepared by compression molding of the

above mats at 170 6 38C and a pressure of 8 kg/cm2 for

3 min. The specimens were removed after cooling the

mould at room temperature. PP/banana fiber composites

with different weight percentage of the fibers were pre-

pared in a similar manner. The schematic representation

of the preparation of the commingled composite is given

in Fig. 1.

Mechanical Properties Measurement

The tensile properties of composites were measured

using a Universal Tensile Testing Machine at a crosshead

TABLE 1. Mechanical properties, chemical constituents and physical

properties of banana fiber.

Properties Banana fiber

Tensile strength (MPa) 600–750

Tensile Modulus (GPa) 2.9–3.2

Elongation at break (%) 2–4

Cellulose content (%) 63–64

Lignin content (%) 5

Diameter of the fiber (microns) 100–125

Density (g/cm3) 1.3

DOI 10.1002/pc POLYMER COMPOSITES—-2009 817

speed of 50 mm/min and a gauge length of 50 mm. The

test specimens were rectangular in shape with dimensions

120 3 15 3 3 mm3. The load-deformation curve was

plotted to analyze the stress-strain behavior of the compo-

sites. Young’s modulus and elongation at break of the

composites was determined from the stress strain curve.

The three point flexural properties were determined by

the same machine according to ASTM D790. Charpy

impact strength (unnotched) was measured in a WinPEN

CEAST S. p. A. Italy according to ISO 179. The speci-

mens dimension were 100 3 10 3 40 mm3. The impact

energy was 2 Joules, impact velocity 2.9 m/s and the dis-

sipation energy was 0.016 J.

Hardness

Hardness of the composites was measured using Shore

D durometer.

Optical Microscopy

Olympus Magnus MSZ stereo microscope was used for

observing the impact fracture surface of PP and PP/ba-

nana fiber composites.

RESULTS AND DISCUSSION

Tensile Properties

Effect of Fiber Loading. Figure 2 shows the stress-

strain behavior of PP/banana fiber composite at different

fiber loading. The behavior of neat PP is also presented

in this figure. From the stress-strain curves, it can be

seen that neat PP is more ductile and ductility decreases

with the addition of fibers. The stress is found to

increase linearly with strain at low elongation for the

composites. A decrease in slope at the second stage of

the curve corresponds to the plastic deformation of ma-

trix and to micro-crack initiation in the matrix. Thus

gradual debonding of the fibers from the matrix occurs

during plastic deformation. The stress value is found to

be higher for 50% fiber composites and the value then

decreases for 60% fiber composites emphasizing the

maximum allowable fiber loading.

Figures 3 and 4 show the effect of fiber loading on the

tensile strength and tensile modulus of the PP/banana

fiber composites. The tensile strength and modulus is

found maximum when the fiber loading is 50%. This is

due to the reinforcement imparted by the fibers which

allows stress transfer from the matrix to the fibers. At

lower fiber loading, the matrix is not restrained by enough

fibers and highly localized strains occur in the matrix at

low stresses. As the fiber loading increases up to 50%,

FIG. 1. The schematic representation of the preparation of the com-

mingled composite.

FIG. 2. Stress–strain curve of PP/banana fiber commingled composite

with different banana fiber loading:(1) Neat PP, (2) 10%, (3) 20%, (4)

30%, (5) 40%, (6) 50%, and (7) 60%.

FIG. 3. Effect of banana fiber loading on the tensile strength of PP/ba-

nana fiber commingled composite.

818 POLYMER COMPOSITES—-2009 DOI 10.1002/pc

the stress is more evenly distributed and the stiffness of

the composite increases. It is observed that with the

increase of fiber loading from 10 to 50%, the tensile

strength and tensile modulus of the composites increases

to 42.65 and 38%, respectively. The composites contain-

ing 60% fiber loading shows a decrease in tensile proper-

ties. The deviation at higher fiber loading may be due to

the fiber packing and insufficiently rich polymer regions.

More over the possibility of fiber entanglements and

agglomeration results in the composite which leads to

decrease in stress transfer between the matrix and the

fiber. If the matrix is insufficiently available, the fibers

were no longer completely surrounded by the matrix at

higher fiber loading and voids are produced in the com-

posite. It has been reported that most of the properties of

the composites are affected by the presence of voids [18].

Houshyar et al. [18] calculated the void content of the

PP/poly(propylene-co-ethylene) (PPE) composite with 10–

60% fiber loading and reported that 10–30% samples has

voids �0. On the other hand 60% sample has a void con-

tent of 19.3%.

Elongation at break values of the composites as func-

tion of fiber loading is shown in Fig. 5. It can be revealed

from the figure that elongation at break decreases with

increase in fiber loading. This can be attributed to the fact

that the reinforcing fibers strongly restrain the deforma-

tion of the matrix polymer as demonstrated in several pre-

vious studies [19].

Flexural Properties

Flexural strength is the measure of how well a material

resists bending or what is the stiffness of the material.

Unlike tensile loading, in flexural testing all force is

applied in one direction. The stresses induced due to the

flexural load are combination of compressive and tensile

stresses. By the application of flexural force, the upper

and lower surface of the specimen under three point bend-

ing load is subjected to compression and tension and the

axi-symmetric plane is subjected to shear stress. This cre-

ates two failure modes in the materials; bending and shear

failure. The specimen fails when bending or shear stress

reaches the corresponding critical value. A schematic rep-

resentation of flexural force acting on the specimen is

given in Fig. 6. Figures 7 and 8 shows the effect of fiber

loading on the flexural strength and flexural modulus of

PP/banana fiber composites. From the figure it is clear

that flexural strength and modulus increases with fiber

loading and is maximum for 50% fiber loading and then

decreases due to the entanglement of the fibers at higher

loading as well as due to the ineffective wetting of the

fibers by the polymer. Thus the incorporation of banana

fibers (50%) into the PP matrix gave rise to a progressive

increase of the flexural strength from 36 to 56 MPa and

flexural modulus from 1.29 to 1.51 GPa.

The improvement in tensile and flexural properties is

low below the critical fiber loading because the reinforc-

ing effect of the fiber is not so good. Above the critical

fiber loading there is fiber/fiber entanglements which lead

to a decrease of properties. Here the critical fiber loading

is found to be 50%. So the properties of the composites

are found to be maximum at 50% fiber loading. The

improvement in properties will be less below and above

the critical fiber loading.

FIG. 4. Effect of banana fiber loading on the tensile modulus of PP/ba-

nana fiber commingled composite.FIG. 5. Effect of banana fiber loading on the elongation at break of

PP/banana fiber commingled composite.

FIG. 6. Schematic representation of flexural force acting on the speci-

men.


The tensile and flexural strength of the commingled

composites were compared with that of composites pre-

pared by solution mixing method. It was found that com-

posites prepared by commingling method exhibited better

mechanical properties when compared to the composites

prepared by solution mixing method (Table 2).

Impact Behavior

The impact strength becomes very important because

cracks due to sudden loads are very common in service

conditions. Forces (loads) of impact are applied so

quickly that the relaxation of the molecular structure does

not follow the process, resulting in fracture which can

involve chain breaking and or interface separation. The

impact strength of a composite depends upon many fac-

tors like toughness properties of the reinforcement, the

nature of the interfacial region, geometry of the composite

and test conditions. The nature of the interface region is

of extreme importance in determining the toughness of

the composite. If the interfacial bonding of the composite

is weak, the crack will be propagated along the fiber ma-

trix/interface causing debonding. As a result of debond-

ing, new surfaces will be produced which leads to a sig-

nificant increase in the energy absorbing capacity of the

composites. In the case of short fiber reinforced thermo-

plastic composites, the fracture is controlled by fiber pull-

out. Cracks are found to form at the fiber ends and mis-

aligned fibers are pulled through the matrix along with

some fiber fracture. In the case of short fiber reinforced

composites, fiber length is also found to be an important

parameter in controlling the impact strength, and the best

results are obtained with fibers having critical fiber length.

Inter laminar shear strength also affects the impact

strength and increases with increasing shear strength.

Impact strength can be improved by a number of ways

[20] (a) by using intrinsically tough matrices, (b) by the

application of a soft coating to the fibers that will act as

an interlayer after the composite is fabricated, (c) by

using a weak interface between fiber and the matrix.

The Fig. 9 shows the impact strength of PP and PP/ba-

nana fiber composites at different fiber loading. The

impact strength of the composite is higher than that of PP

and found to increase with increase in fiber loading upto

50% and then decreases. Cabral et al. [21] investigated

the tensile and impact properties of jute-polypropylene

composites as a function of the fiber content. They found

that tensile and impact strength sharply decreased after a

critical fiber volume fraction. They interpreted this change

in the mechanical properties in terms of a change in the

fiber dispersion homogeneity, as well as of the interfiber

contacts and the formation of interconnected paths within

the thermoplastic matrix. Li et al. [22] studied the impact

fracture toughness of saw dust/recycled PP composites.

They observed that under impact loads, neat PP and the

composites exhibited completely brittle behavior charac-

terized by an abrupt decrease of load to zero after the

maximum value. In the case of short fiber reinforced pol-

ymers with ductile matrices, such as polypropylene, the

major source of toughness derives from the matrix related

energy mechanisms such as matrix shear deformation.

The detrimental effect of the incorporation of natural

fibers to polypropylene on the impact fracture properties

can be explained by the combined effect of the matrix

embrittlement that occurs under the impact load and the

restriction to matrix yielding imposed by the natural

FIG. 8. Effect of banana fiber loading on the flexural modulus PP/ba-

nana fiber composite.FIG. 7. Effect of banana fiber loading on the flexural strength of PP/ba-

nana fiber composite.

TABLE 2. Comparison of tensile strength (T.S) and flexural strength

(F.S) of composites prepared by solution mixing method and

commingling method.

Banana fiber

loading (%)

Solution mixing method Commingling method

T.S (MPa) F.S (MPa) T.S (MPa) F.S (MPa)

10 18.0 38.0 22.0 42.0

20 21.0 42.0 24.0 45.0

30 24.0 45.0 27.5 48.0


fibers. In addition, the interfacial adhesion also influences

the material fracture behavior. If a relatively weak interfa-

cial bonding exists, fiber/matrix debonding will induce

local shear yielding of the PP matrix and the subsequent

increase of toughness. In contrast if fiber matrix debond-

ing is suppressed as a result of an excessively strong

interface, brittle fracture will occur and toughness will not

be improved.

Figure 10 shows a photomicrograph of fractured sur-

face of PP/banana fiber composite which suffered the

mechanism of fiber bridging due to the pendulum impact.

The unnotched impact test specimens show visibly dis-

tinct modes in their fractured portions. The neat

PP samples break clearly. In the case of PP/banana fiber

composite the fiber breaks and comes out of matrix. It

can be also seen that not all the fibers of a composite are

fractured during the impact test. A part of them develops

a type of bridge between the two parts of the fractured

matrix. As the crack spreads under the action of the

applied load, a part of the load is transferred to the fibers

which are elastically deformed [23].

Hardness of the Composites

Hardness provides information about material tenacity

or fragility, because it is related to the module and me-

chanical resistance of the material to the penetration of a

body [24]. In all the methods of hardness testing the

thickness of the material and the nature of substrate are

very important, because the elasticity is usually also

measured. It should be noted that hardness tests always

measure the hardness of the surface and not the inner part

of the material. The hardness property must still be eval-

uated with caution, because the surface layers of the poly-

mers can present different molecular orientations, levels

of residual tension and other different properties when

compared to the whole material [24]. Shore hardness tests

are carried out at room temperature, according to ABNT.

Shore D durometer is used to measure the hardness of

plastic composites. Results from Table 3 show that there

is a decrease of hardness due to the introduction of fibers.

These results indicate that the presence of fibers decreases

the mechanical resistance to the penetration of another

body or it can be a consequence of fiber hygroscopicity,

because water would have a plasticizing effect on the

surface.

FIG. 9. Effect of banana fiber loading on the impact strength of PP/ba-

nana fiber composite.

FIG. 10. Digital photomicrograph of the fractured surface of (a) neat

PP (b) PP/banana fiber composite, (c) Magnified view of b (Magnifica-

tion 3150). [Color figure can be viewed in the online issue, which is

available at www.interscience.wiley.com.]


Theoretical Modeling

In the literature, several theories and equations have

been developed to model the relation between the tensile

properties of the composite and the parameters such as

fiber length, fiber orientation, fiber dispersion, fiber geom-

etry and the degree of interfacial adhesion between the

fiber and the matrix [25–28]. These are (1) Modified rule

of Mixtures, (2) Series model, (3) Parallel model, (4)

Hirsch model, and (5) Halpin–Tsai model.

Modified Rule of Mixtures. The modified rule of mix-

tures [29] can be given as follows.

Tc ¼ Tmð1� VfÞ þ TfVfe ð1Þwhere Tc is the ultimate strength of the composites, Tm is

the matrix strength at the failure strain of the fiber, Tf is theultimate strength of fiber, Vf is the fiber volume fraction

and Vfe is the effective fiber volume fraction. The effective

fiber volume fraction is given in terms of the fiber volume

fraction and the ratio of real contribution as follows

Vfe ¼ Vfð1� PÞ;where P is the degradation parameter for the effective

fiber volume fraction, lying between 0 and 1. P can be

calculated from the micro geometry of the composite

components and depends only on the fiber volume frac-

tion because the micro geometry is intimately related to

the fiber volume fraction under identical manufacturing

conditions. P can be calculated from the equation

P ¼ DTcTfVf

ð2Þ

where DTc is the difference between the experimentally

measured strength and the strength predicted by the rule

of mixtures.

Parallel and Series Models. The parallel and series

models [30] are used to determine the modulus and ten-

sile strength of short fiber composites. The equations for

tensile strength are

Tc ¼ TfVf þ TmVm ðParallel modelÞ ð3Þ

Tc ¼ TmTfTmVf þ TfVm

ðSeries modelÞ ð4Þ

where Tc, Tm, Tf are the tensile strength of the composite,

matrix and fiber respectively. If modulus is the parameter

under study, notations such as Mc, Mm and Mf may be

used instead of Tc, Tm, and Tf where Mc, Mm, and Mf are

the Young’s moduli of composite, matrix and fiber,

respectively.

Hirsch Model. Hirsch Model [31] is a combination of

Parallel and Series models. The schematic representation

of Hirsch Model is shown in Fig. 11 [32]. Using this

model, the tensile strength and Young’s modulus are

determined by the equations

Tc ¼ xðTmVm þ TfVfÞ þ ð1� xÞ TmTfTmVf þ TfVm

ð5Þ

where v is a parameter which determines the stress trans-

fer between the fiber and the Matrix. In terms of the mod-

ulus, the equation is

Mc ¼ xðMmVm þMfVfÞ þ ð1� xÞ MmMf

MmVf þMfVm

ð6Þ

Halpin–Tsai Model. Several researchers used Halpin–

Tsai model [33] to determine the properties of the compo-

sites that contain discontinuous fibers oriented in the load-

ing direction. The tensile strength can be calculated using

the model as follows

Mc ¼ xðMmVm þMfVfÞ þ ð1� xÞ MmMf

MmVf þMfVm

ð7Þ

TABLE 3. Hardness of PP/banana fiber commingled composite.

Material Hardness

PP 72

PP/10% banana fiber 70




FIG. 11. A schematic representation of Hirsch Model.


Tc ¼ Tm1þ AgVf

1� gWVf

8>>:

9>>; ð8Þ

where

g ¼ ðTf=TmÞ � 1

ðTf=TmÞ þ Að9Þ

W ¼ 1þ 1� /max

/2max

8>>>:

9>>>;Vf ð10Þ

where is umax is the packing fraction of the fibers. The

value of packing fraction for different fiber arrangement

in the matrix has already reported in the literature [19].

The different arrangements of fibers in the matrix include

square packing, hexagonal packing and random packing.

In the present case, it is assumed that the fibers are ran-

domly close packed in the matrix. Therefore the value of

umax is ¼ 0.82 is substituted in the Eq. 10.The experimental and theoretical values of tensile

strength of the composite as a function of fiber loading

(10, 20, and 30%) of the composites are given in the

Fig. 12. It can be seen that, in all cases, tensile strength

increases regularly with increase in fiber loading. A good

correlation between the theoretically and experimentally

observed tensile strength was seen in model predicted by

the modified rule of mixtures. The experimental value

exactly fits with the theoretical value in the case of this

model. This model predicts the actual composite strength

because the value of q is defined to account for the

microgeometry of real composites. Series Model and Hal-

pin Tsai Model show some what agreement with

the experimental value. But the parallel and Hirsch Mod-

els agree the least with the experimental values. It can be

seen from Fig. 12 that at lower fiber loading, Parallel and

Hirsch Model show more agreement with experimental

values. This can be attributed to the fact that at lower

fiber loading, uniform stress or strain in the composite is

achieved as a result of better distribution of load through

the well-dispersed fibers in the matrix. But at higher fiber

loading, some of the fibers will be agglomerated in the

matrix. Hence the applied load will be distributed

unevenly between non-aggregated and aggregated fibers.

The Young’s modulus value of the composite samples

(10, 20, and 30%) is compared with the theoretical predic-

tions in Fig. 13. Series model is in good agreement with

the experimental value. Hirsch model (X ¼ 0.2) shows

slight positive deviation. But parallel models show still

large positive deviation from the experimental value. It

was also found that better agreement between the theoreti-

cal and experimental modulus values is observed at lower

fiber loading when compared to higher fiber loading.

The limitations of the models used in the study mainly

depend on different factors. The chance of the formation

of microvoids between the fiber and the matrix during the

preparation of the composites greatly influence the tensile

properties of the composites. The number of voids

increases with increase in fiber loading. This factor is not

accounted for any of the models used in this study. The

presence of voids, fiber-fiber interaction, and critical fiber

length, non-uniformity of the fiber and the surface irregu-

larities of the fiber may be the other reasons. More over

natural fibers can’t be produced with a definite range of

properties like glass fiber. Their characteristics properties

like tensile strength and modulus may vary considerably

from fiber to fiber.

CONCLUSIONS

In this article, novel commingling method is intro-

duced for the preparation of short natural fiber polypro-

pylene composites. Advantage of commingling method is

that it is environmentally benign. Tensile properties of

the above composites were studied as a function of fiber

FIG. 13. The experimental and theoretical value of tensile modulus of

the composites as a function of banana fiber loading.

FIG. 12. The experimental and theoretical value of tensile strength of

composites as a function of banana fiber loading.


loading. It was found that tensile properties of the com-

posite increased with fiber loading up to 50%. It was

also observed that hardness of PP is decreased by the

introduction of fibers and it decreased with the increase

in fiber loading. The experimental results of the tensile

properties of the composites were compared with the

theoretical prediction. The best correlation between the

theoretically and experimentally observed tensile strength

was seen in model predicted by the modified rule of

mixtures.

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