Experimental investigation and analysis of mechanical properties of injection

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –

6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME

197

EXPERIMENTAL INVESTIGATION AND ANALYSIS OF MECHANICAL

PROPERTIES OF INJECTION MOLDED JUTE AND GLASS FIBERS

REINFORCED HYBRID POLYPROPYLENE COMPOSITES

Ravishankar. R1, Dr.K. Chandrashekara

2, Rudramurthy

3

1Dept. of Mechanical Engineering, Sri Jayachamarajendra College of Engg, Mysore, Karnataka

State, India, Pin: 570006 2Dept. of Mechanical Engineering, Sri Jayachamarajendra College of Engg, Mysore,

Karnataka State, India, Pin: 570006 3Dept. of Mechanical Engineering, Sri Jayachamarajendra College of Engg, Mysore,

Karnataka State, India, Pin: 570006

ABSTRACT

Preliminary studies were conducted on jute fiber reinforced polypropylene (PP) composites

to ascertain the optimum weight percent of fiber which could give maximum values for the

mechanical properties. It was found to be 40wt%. In the present investigations, effect of reinforcing

glass fibers in the optimized jute fiber reinforced PP composite is studied. The properties such as

tensile, flexural, impact and hardness with respect to randomly oriented jute and glass fiber

variations in the pp matrix are considered. Jute and glass fibers reinforced matrix composites with

different fiber contents were prepared by injection molding. Matrix content is kept as 60wt%. The

variations in jute and glass fibers by weight percentage are 40:00, 35:05, 30:10, 25:15 and 20:20. It

was found that tensile, flexural, impact and Shore-D hardness properties increased with increase in

glass fiber content. Results and discussions are made with the help of experimental data and SEM

micrographs and conclusions are presented.

Key words: Jute fiber, Glass fiber, Polypropylene, Tensile, Flexural, Impact.

1. INTRODUCTION

Fiber reinforced composites are in use in a variety of applications like, automotive interiors,

furniture, aircraft etc. Abundant use of composites in these sectors has been facilitated by

introduction of newer materials, improvement in manufacturing processes and testing methods.

Fiber-reinforced materials have higher mechanical properties and their strength-to-weight ratios are

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superior when compared with metals and their alloys. Further, fiber reinforced plastic composite

offer other advantages like non-corrosiveness, translucency, good bonding properties, and ease of

repair. Natural fibers play an important role in developing high performing fully biodegradable

‘green’ composites which could solve environmental problems. Many researchers are of the opinion

that, these fibers offer many attractive technological and environmental qualities when used as

reinforcements in polymer composites [1-7]. Natural fibers are largely divided into two categories

depending on their origin one being plant based and the other animal based. In general, plant based

fibers like jute, coir, sisal, cotton etc are lignocellulose in nature composed of cellulose,

hemicellulose and lignin. Animal based fibers like silk and wool are composed of proteins. Also

natural fibers are low cost, abundantly available, renewable and have high specific properties.

Further, they are less abrasive to machines used to fabricate them. The mechanical properties of

natural fiber composites are much lower than those of the synthetic fiber composites and they are

hydrophobic. Synthetic fibers have very good mechanical properties, moisture repellency, but these

are difficult to recycle. To take advantage of both natural and synthetic fibers, they can be combined

in the same matrix to produce hybrid composites that take full advantage of the best properties of the

constituents [8-15]. With respect to the above considerations, in the present study, investigations are

made to evaluate the mechanical properties of the jute and glass reinforced PP matrix hybrid

composite.

2. MATERIALS AND METHODS

2.1. Materials Thermoplastic polymer PP, used as matrix material is in the form of homopolymer pellets

supplied by Hindustan polymers, Bangalore, India. It has specific gravity of 0.90–0.91, melting

temperatures of 165–1710C and crystallinity of 82%. White jute fiber (Corchorus capsularis) used as

reinforcing fiber was obtained from Jute Pragna Suppliers, Bangalore, India. E-Glass fibers used as

reinforcing fibers was obtained from Concord Fiber Glass industries, Bangalore, India.

2.2. Fabrication of composites and test specimens Jute and glass fibers in the weight percent ratios of 40:00, 35:05, 30:10, 25:15 and 20:20,

were initially mixed thoroughly with PP granules. The mixtures were passed through single screw

extruder at a constant temperature of 1650C. The extruded composites were cut into pellets using

rotary cutting pellet making machine. The test specimens were prepared from the compounded

pellets using injection molding machine as per ASTM standards.

2.3. Mechanical testing Tensile, Flexural, Izod impact and Hardness tests were conducted. For each test and type of

composite, 4 specimens were used and the average values are presented.

2.3.1. Tensile test

Tensile tests were conducted according to ASTM D 638 using a Universal Testing Machine

(Make: Hounsfield, UK, Model: H 50 KM, Capacity: 50 KN, Jaw separation speed: 1 to 500

mm/min). The dimension of the dog bone shaped specimen was 175 mm x10 mm x 3.2 mm. Gauge

length was 50 mm.

2.3.2. Flexural test

Three-point static flexural tests were carried out according to ASTM D 790 using the same

testing machine mentioned above. The dimension of the specimens used was 125 mm x12.5 mm x

3.2 mm. Span length was 100 mm.



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The flexural strength (1) and modulus (2) were calculated using the following equations:

Flexural strength =3PL/2bd2

(1)

Flexural modulus; E =L3m/4bd

3 (2)

Where P is the maximum applied load, L is the length of support span, m is the slope of the tangent,

b and d are the width and thickness of the specimen respectively.

2.3.3. Izod impact test

Izod impact tests were conducted on un notched composite specimens according to ASTM D256,

using pendulum impact tester (Range: 0 to 1.5 Joules). The dimension of the specimen was 65 mm x

12.5 mm x 3.2mm.

2.3.4. Shore-D hardness

Shore-D hardness tests were conducted on specimens according to ASTM D2240 using

Durometer. (Make: Techno Instrument Company, Model: SHR – Mark III, Range: 0 to 100)

2.3.5. Scanning Electron Microscopy (SEM)

Interfacial bonding, dilation of matrix, fiber pulling or fracture between the fiber and PP matrix in

the composites were examined and analyzed using Scanning Electron Microscope. The micrographs

were taken at the magnification of 500.

3. RESULTS AND DISCUSSION

3.1. Tensile properties Variation in tensile strength with respect to addition of varying percentage by weight of glass

fiber to jute-PP composite is illustrated in the Fig.1. It could be seen that, tensile strength is

increasing with increase in percentage of glass fibers in the composite. Increase in tensile strength is

almost linear with addition of glass fiber with increment in fiber loading in steps of 5wt% up to

20wt%. Percentage increase in strength is found to be 28.67 for glass fiber loading of 20wt%. For

hybridization, addition of glass fiber with natural fiber reinforced composites, the tensile strength

increased with glass fiber loading which is in accordance with the results obtained by other

researchers [8, 9, 10, 11, 12, 13]. Reason is that, glass fiber adherence to the matrix is better when

compared to jute fiber and the interfaces between the fiber and the matrix is more (surface area of

contact). Hence, it is difficult for the prevailing forces to pull glass fibers from the matrix compared

to that of jute fiber. Also the failure of the specimen is mainly due to the fracture of the glass fiber

compared to jute fibers for which pull out of them is the main reason. The range of the tensile

strength found in the current work is 22.18–28.54 MPa.

Fig. 2 shows the variation of the tensile modulus at different glass fiber loading. Tensile

modulus is increasing with increase in glass fiber loading in accordance with the results of other

researchers [8, 9, 10, 11, 12, 13]. The percentage increase in modulus is found to be 9.1 for glass

fiber loading up to 15wt%. From 15wt% to 20wt%, increase in modulus is 15% which is significant.

This is attributed to the higher modulus of glass fiber than the jute fiber and PP matrix. Normally, the

fibers in the composite restrain the deformation of the polymer matrix, reducing the tensile strain.

During tensile loading, partially separated micro spaces are created, which obstruct stress

propagation between the fibers and matrix. As the glass fiber loading increases, the degree of

obstruction increases, which consequently increases the stiffness. Range of the tensile modulus in the

current work is found to be 1482.52–1864.66 MPa.



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3.2. Flexural properties Flexural strength of jute fiber composites at different weight percentages of glass fiber

loading in the composite are shown in Fig. 3. It increased with fiber loading. This is in accordance

with the findings of other researchers [8, 9, 10, 11, 12, 13]. It is found that the flexural strength

increased by 20.82% up to a glass fiber loading of 20wt%. This is due to the fact that some of the

glass fibers are fractured, some are pulled out of matrix and some are still adhering to the matrix. The

glass fibers in the portions of the matrix are getting aligned in the direction perpendicular to the

application of the load. These observations justify the increase in load bearing capacity of the

material. The range of the flexural strength obtained is 38.8–46.88 MPa.

Variation in flexural modulus of jute and glass fiber hybrid composites at different glass fiber

loading is shown in Fig. 4. Flexural modulus is increasing almost linearly upto 15wt% of glass fiber

loading. Percentage increase is 13.32 (from 5wt% to 15wt%). Further loading of glass fiber is

increasing the modulus significantly. This increase is 26%. Investigations of several other

researchers have shown the same trend [8, 9, 10, 11, 12, 13]. Since glass fiber is a high modulus

material compared to jute fiber and matrix, higher fiber concentration demands higher stress for the

same deformation. The range of the flexural modulus obtained is 2132.64–2687.4 MPa

3.3. Impact properties Variation of Izod impact strength with jute and glass fiber composites at different glass fiber

loadings are shown in Fig.5. Impact strength of the fiber reinforced composites depends on the

nature of the fiber, polymer and fiber–matrix interfacial bonding. It could be seen that the impact

strength is increasing with increase in percentage of glass fibers in the composite. For the synthetic

fiber addition to natural fiber reinforced composites, impact strength increase with glass fiber loading

[9, 11, 13]. There is increase in impact strength by 74.26% with increase in glass fiber loading up to

20%. Impact strength in fiber reinforced composites is caused by fiber fracture and fibers pull out.

More energy is required to fracture the composite than it is required for fiber pull out. Since the

failure of the specimen is mainly by fiber fracture and due to good interfacial adhesion between glass

fiber and the matrix, strength is increasing with increase in glass fiber content. The range of the

impact strength found in the current work is 4.43–7.72 KJ/m2.

3.4. Hardness properties In the hardness test, hardness was found to increase with increase in the quantity of glass

fiber content as observed from figure 6. For glass fiber addition to natural fiber reinforced

composites, the hardness increased with glass fiber loading [13].This is due to decrease in flexibility

and increase in stiffness of composites as glass fibers have these charecteristics. The range of the

hardness found in the current work is 72–79.

3.5. SEM morphology SEM micrograph of the tensile fractured surface of 20:20wt%, jute: glass fiber composite is

shown in Fig.7. It shows that failure of the specimen is mainly by glass fibers fracture, pull out of

some of the same (indicated by dark holes), and jute fiber pull out. Higher tensile forces are required

to fracture glass fibers and pulling them out from the matrix. Moreover, the micrographs are

indicating brittle fracture of glass fibers. One must also note that, jute fibers are not fractured but

they are pulled out of the matrix. Also, interfacial adhesion between glass fibers and matrix is

superior when compared with that of jute and matrix. The combined effect of fracture of most of the

glass fibers, pulling out of matrix of some of them and pulling of jute fibers which are embedded in

the regions where, fractured and glass fibers in the matrix are predominant, call for higher

magnitudes of forces to fracture the hybrid composite.



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SEM micrograph of cracked specimen subjected to flexural test having 20wt%:20wt%, jute:

glass fiber composite is shown in fig.8. It can be clearly seen from the micrograph that, some of the

jute fibers are within the matrix and some fibers are pulled out from the matrix. One must note that

glass fibers and jute fibers are randomly distributed in the matrix prior to the test. It is clear from the

micrograph that, both glass and jute fibers are getting axially oriented when the bending load is

applied. This calls for higher magnitude of forces. Glass fibers are either pulled out or fractured.

Further, the matrix having the fibers is getting dilated forming cleavages. Cleavages also offer

resistance to the axial orientation of fibers. Owing to these reasons, during flexural studies, the

composite material has shown increasing resistance to the prevailing loads with addition of glass

fibers.

SEM micrograph of specimen of 20wt:20wt%, jute: glass fiber composite fractured surface

subjected to impact load is shown in fig 9. It could be seen that the failure is due to predominantly

glass fibers brittle fracture and jute fiber dilation and pull out. As the percentage of glass fibers

increases in the matrix, the above said reasons confirm that higher impact energy is required to fail

the hybrid composite. Superior interfacial adhesion between glass fibers and matrix and

disorientation of jute fibers from their original orientation are some of the reasons for the hybrid

composite having higher impact strength.

Fig.1 Variation of Tensile strength with Glass fiber content

Fig. 2 Variation of Tensile modulus with Glass fiber content



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Fig. 3 Variation of Flexural strength with Glass fiber content

Fig. 4 Variation of Flexural modulus with Glass fiber content

Fig. 5 Variation of Impact Strength with Glass content



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Fig. 6 Variation of Hardness Value with Glass fiber content

Fig.7 SEM micrograph of fractured specimen of tensile test at 20wt:20wt% Jute: glass fiber



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Fig.8 SEM micrograph of cracked specimen of flexural at 20wt:20wt% Jute: glass fiber

Fig.9 SEM micrograph of fractured specimen of Impact test at 20wt:20wt% Jute: glass fiber



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4. CONCLUSION

The mechanical properties such as tensile, flexural, Impact and hardness of the jute and glass

fibers reinforced hybrid composites were studied by different weight ratios of jute and glass fibers.

Tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength and hardness

of the composite were found to be increasing with increase in glass fiber content and the values were

found to be the maximum at 20:20 percentage by weight of jute and glass. The overall increase in

strength of the hybrid composite considering tensile and flexural studies is 25.31%. Percentage

increase in impact strength is 63 which is very significant. Increase in hardness is 9.7%. These

increases in properties of the studied material could make this applicable in components of

automobiles like, dash boards, seat bases, frontal and rear bumpers, aircraft interior paneling and

furniture.

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Experimental investigation and analysis of mechanical properties of injection

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