9(3): 1-10, 2016; Article no.JSRR.20385
ISSN: 2320-0227
SCIENCEDOMAIN international www.sciencedomain.org
1
2*
3
1
Department of Industrial/Production Engineering, Nnamdi Azikiwe University, Awka, Nigeria.
2
Federal College of Education (Technical), Umunze, Nigeria.
3
Department of Mechanical Engineering, Nnamdi Azikiwe University, Awka, Nigeria.
Authors’ contributions
This work was carried out in collaboration between all authors. Author MKA designed the study, wrote the protocol and wrote the first draft of the manuscript. Author CCI plotted the graphs and author CEO read proof the work and made useful corrections. All authors read and approved the final manuscript.
Article Information
DOI: 10.9734/JSRR/2016/20385
Editor(s):
(1) Mohamed Abd El-Moneim Ramadan, Pretreatment & Finishing of Cellulosic Fibres Department, Textile Research Division,
Egypt.
Reviewers:
(1) Randa M.Osman, National Research Centre, Cairo, Egypt.
(2) Danupon Tonnayopas, Prince of Songkla University, Thailand.
(3) Diene Ndiaye, University of Gaston Berger of Saint Louis, Senegal.
Complete Peer review History: http://sciencedomain.org/review-history/11904
Original Research Article
Received 25
Accepted 6 th
September 2015
Published 19 th th
July 2015
October 2015
This paper investigated the performance of coconut fibre particles as a filler material and highdensity polyethylene as matrix in polymer matrix composites (PMC). Three different particle sizes of the filler material were used in formulating the composite samples and the concentration of the filler material varied up to 40% by volume. The composite samples were prepared by injection moulding and kept at room temperature for 48 hours prior to testing in order to promote relaxation of stresses. The test specimens were prepared and tested in accordance with ASTM standards
D638, D790, D256, and D785 for tensile strength, elastic modulus, flexural strength, impact strength and Rockwell hardness respectively. At optimum condition of volume fractions and particle sizes of coconut fibre-filler, the coconut fibre reinforced HDPE (CFRP) has 28.6 MPa, 800 MPa,
_____________________________________________________________________________________________________
*Corresponding author: Email: achike4christ07@yahoo.com;

Ihueze et al.; JSRR, 9(3): 1-10, 2016; Article no.JSRR.20385
22.3 MPa, 55.0 J/m and 54.0 HR as optimum value for tensile strength, elastic modulus, flexural strength, impact strength and hardness. It can be concluded from the results obtained that the
Coconut fibre reinforced HDPE showed improved performance for applications of HDPE.
Keywords: Reinforcement combinations; coconut fibre; volume fraction; particle size; archimedes principle; optimum performance.
Most of the pressing scientific problems that are currently faced today are due to the limitations of the materials that are currently available [1].
Mulinari [2] defined composite materials as materials made from two or more constituent materials with significantly different physical or chemical properties, that when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure. The fact that composites in general can be custom tailored to suit individual requirements, have desirable properties in corrosive environment, provide higher strength to weight ratio and have lower life-cycle costs has aided in their evolution [3]. Binshan, Alrik and
Bank [4] observed that these qualities in addition to the ability to monitor the performance of the material in the field via embedded sensors give composites an edge over conventional materials.
The ability of composites to withstand tensile, compressive and impact loads without failure is a measure of their reliability [5].
To cope with the obvious limitations of polymers, for example, low stiffness and low strength, and to expand their applications in different engineering areas, different types of particulate fillers are often added to process polymer composites, which normally combine the advantages of their constituent phases [6].
Nakamura and Okubo [7] stated that reinforcement of polymers by particulates plays an important role in the improvement of mechanical properties of high performance materials.
Natural fibre composites offer environmental advantages such as reduced dependence on non-renewable energy/material sources, lower pollutant emissions, lower greenhouse gas emissions, enhanced energy recovery and end of life biodegradability of components [8]. Due to poor compatibility of natural fibres, the surface of the fibres must be treated to improve the adhesion between the fibre and matrix. Bledzki
[9] reported many methods to modify the surface of natural fibres for their use in composite materials such as acetylation, alkali and isocyanates treatments. These Treatments make the fibres more hydrophobic. It is important to indicate that the good cohesion between fibres and matrix is governed by many parameters such as the surface area, the roughness and the surface tensile of fibres.
The methodology of this research employs experimental and analytical methods to investigate tensile strength, elastic modulus, flexural strength, impact strength and hardness value of coconut fibre particles reinforced highdensity polyethylene composite at different volume fractions and particle sizes.
The researchers considered fibre surface treatment, volume fraction of fibres, and particle size of fibres as factors controlling the behavior or characteristics of HDPE matrix filled fillers.
The ASTM specified standard particle sizes are presented in Table 1. Archimedes principle was employed to determine the density of coconut fibre from where the composite samples are designed following the method of Okafor et al.
[10] and ASTM Standards for mechanical properties tests. Table 1 shows three grades of fibre particle sizes and their corresponding sieve sizes according to ASTM Standard.
It must be noted that because of high processing viscosity of thermoplastic polymers, a proper wetting of fibres is difficult. High temperatures of up to 170°C can also cause unwanted changes of the fibre surface or even destroy the fibres.
Natural fibres will only act as fillers in thermoplastic polymers without improving any quality if compatiblizers are not added.
Treatment is required to turn harvested plants into fibres suitable for composite processing. The first step is retting. After retting, hemicellulose and lignin can be removed by hydro-thermolysis or alkali reactions. The hemicellulose is
2

responsible for a great deal of the moisture absorption.
Table 1. Sieve sizes
Grade ASTM number
Sieve size
1
2
3
325
270
200
45 micron (0.045 mm)
53 micron (0.053 mm)
75 micron (0.075 mm)
Source: Annual book of ASTM Standards 2013
A certain quantity of the coconut fibre extracted was dried under sun for 5 days and further dried in an oven at 50 o
C for 1 hour without surface treatment. The remaining portion of the fibre was soaked with 4% NaOH and 2% Na
2
SO
3
solution for 24 hours. These fibres were washed with distilled water and dried under sun for days. To further remove any trace of moisture, the fibres were further dried in an oven at 50°C for one hour. The untreated coconut fibre was labeled A while the treated one was labeled B. Both grades of fibre were ground to a fine powder using electrical milling machine and then sieved unto a set of sieves arranged in descending order of fineness.
The calculation of the volume of an irregular object (such as coconut fibre) from its dimensions is a mirage by traditional method.
Such a volume can be accurately measured following Archimedes principle that the volume of water displaced is equal to the volume of the object immersed [10]. Following Archimedes
Principle, the density of fibre is expressed as:
ߩ
௙
=
ܯ
௙
(1)
ܸ
௙
2.2.1 Determination of fibre volume
Calculation of volume of coconut fibre is achieved following the derivations from rule of mixtures based on the procedures of Jones and
Barbero [11] and implementation of Archimedes principle applying equations (2) to (7) as expressed in Okafor et al. [10].
ܯ
௖
ܸ
௙
= ܯ
௙
+ ܯ
ோ
(2)
=
ܯ
௙
ߩ
௙
(3)
3
Ihueze et al.; JSRR, 9(3): 1-10, 2016; Article no.JSRR.20385
ܸ
ோ
=
ܯ
ோ
ߩ
ோ
(4)
ܸ
௖
= ܸ
௙ା
ܸ
ோ
(5)
ܸ
௙௥
=
ܸ
ܸ
௙
௖
=
ܸ
௙
ܸ
௙
+ ܸ
ோ
(6)
ܸ
ோ
=
ܸ
௙
(1 − ܸ
௙௥
)
(7)
ܸ
௙௥
Equation (7) means that once the volume of fibre is determined by Archimedes principle and the volume fraction decision is taken, then volume of resin can be calculated.
Where,
ܯ
௙
= Mass of Coconut Fibre, ܸ
௙
Coconut Fibre, ߩ
௙
= Volume of
= Density of Coconut Fibre,
ܸ
௙௥
= Volume Fraction of Fibre, ܯ
ோ
= Mass of
Resin, ܸ
ோ
= Volume of Resin, ߩ
ோ
Resin = 0.97 g/cm
3
, ܯ
௖
=
= Density of
Mass of ASTM
Specified Sample Size,
Specified Sample Size.
ܸ
௖
= Volume of ASTM
Table 2. ASTM standards for mechanical tests
S/N Mechanical ASTM Specification test standard
1 Tensile test ASTM
D638
2 Elastic
Modulus
ASTM
D638 of size
60x6x3 mm
60x6x3 mm
3 Flexural
Strength
4 Impact
Strength
ASTM
D790
ASTM
D256
80x12.5x3 mm
120x10x4 mm
5 Hardness
(Rockwell)
ASTM
D785
80x10x4 mm
Source: Annual Book of ASTM Standard 2013 [12]
By using volume fraction of fibres 5%, 10%, 15%,
20%, 30%, and 40% and applying ASTM standard specifications from Table 2 in equations
2 to 7 above, yields Tables 3 to 6 .
The aggregates were mixed thoroughly until even dispersion was achieved. Addition of 1% weight of chromium catalyst was made and stirred for 3 minutes, after which 2% weight of accelerator (Cobalt Octoate) was added and stirred for another 3 minutes before pouring the composite mixture into the hopper of the injection moulding machine where the already prepared mould is fitted. The mould was cleaned with

acetone and coated with polyvinyl alcohol (PVA) and allowed to dry before fixing it on the injection moulding machine. This was done to prevent particles of the composite sticking to the walls of the mould which may alter the dimensional accuracy of the samples produced. The procedure was repeated for all the samples produced with changes in the percentage of ground coconut fibre based on volume fraction decision and particle sizes. Barrel temperature set-points of rear zone, middle zone, and nozzle zone of the injection moulding machine was kept at 150°C, 180°C and 200°C respectively. Screw speed was set to 240 rpm and injection speed was around 1 m/s. All the samples prepared were kept at room temperature for 48 hours prior to testing to promote relaxation of stress [1]. The tensile strength, elastic modulus, flexural strength, impact strength and hardness value of each of the samples developed were determined.
Five samples in each case were tested and the average value recorded.
Ihueze et al.; JSRR, 9(3): 1-10, 2016; Article no.JSRR.20385
2.4.1 Tensile test
The tensile properties investigated in this research are tensile strength and elastic modulus using universal tensile testing machine (JJ Lloyd
London, capacity 1- 20 KN) at a crosshead speed of 10 mm/min and an applied load of 5KN.
The result of tensile strength is presented in
Table 7, Fig. 1 and elastic modulus is presented in Table 8, Fig. 2.
2.4.2 Flexural test
Flexural properties were investigated using the same universal testing machine. Three-point bending test was performed at a crosshead speed of 12 mm/min considering a beam span of
50 mm. The result of flexural test is presented in
Table 9, Fig. 3.
Table 3. Tensile test composition data
V fr
0.05
M f
(g)
0.0318
V f
(cm
3
)
0.054
V
R
(cm
3
)
1.026
M
R
(cm
3
)
0.9952
0.10
0.15
0.20
0.30
0.40
0.0636
0.0954
0.1272
0.1908
0.2544
0.108
0.162
0.216
0.324
0.432
0.972
0.918
0.864
0.756
0.648
0.9428
0.8905
0.8381
0.7333
0.6286
V fr
0.05
0.10
0.15
0.20
0.30
0.40
M f
(g)
0.0884
Table 4. Flexural test composition data
V f
(cm
3
)
0.1500
V
R
(cm
2.8500
3
)
0.1767
0.2651
0.3534
0.5301
0.7068
0.3000
0.4500
0.6000
0.9000
1.2000
2.7000
2.5500
2.4000
2.1000
1.8000
M
R
(g)
2.7645
2.6190
2.4735
2.3280
2.0370
1.7460
Table 5. Impact test composition data
V fr
0.05
0.10
0.15
0.20
0.30
0.40
M f
(g)
0.1414
0.2827
0.4241
0.5654
0.8482
1.1309
V f
(cm
3
)
0.240
0.480
0.720
0.960
1.440
1.920
V
R
(cm
3
)
4.560
4.320
4.080
3.840
3.360
2.880
M
R
(g)
4.4232
4.1904
3.9576
3.7248
3.2592
2.7936
4

0
5
10
15
20
30
40
Ihueze et al.; JSRR, 9(3): 1-10, 2016; Article no.JSRR.20385
Table 6. Hardness test composition data
V fr
0.05
0.10
0.15
0.20
0.30
0.40
M f
(g)
0.0942
0.1885
0.2827
0.3770
0.5654
0.7540
V f
(cm
3
)
0.1600
0.3200
0.4800
0.6400
0.9600
1.2800
V
R
(cm
3
)
3.0400
2.8800
2.7200
2.5600
2.2400
1.9200
M
R
(g)
2.9488
2.7936
2.6384
2.4832
2.1728
1.8624
2.4.3 Impact test
Charpy impact tester (Changteh China, model
JC-25, pendulum capacity of 4J at a test velocity of 5 m/s) was used to determine the impact strength of the specimens. V-notch depth of 2.5 mm and notch angle of 45° was cut on each of the specimens prior to testing. The energy
Fig. 2 from Table 7 shows that the addition of coconut fibre particles improved tensile yield strength but only at certain concentrations.
Improvement up to 15.5% was obtained from about 24.6 MPa to 28.4 MPa for the untreated transferred to the material can be inferred by comparing the difference in the height of the striker (hammer) before and after the fracture as indicated on the impact meter. The result of fibre and 18% was obtained from 24.6 MPa to
29.0 MPa for the treated fibre. Tensile strength did not change much with coconut fibre concentration up to 10-15%. Significant increase impact test is presented in Table 10, Fig. 4. in strength was obtained with 45 micron and 53 micron coconut fibre particles when their concentration exceeded 15% for both the untreated and treated fibre. This reflected the
2.4.4 Hardness test
Hardness of a material is defined as its resistance to permanent deformation, indentation or scratching. The hardness values of the developed samples were measured using
Rockwell Hardness Tester on M-Scale in accordance with ASTM D785. The result of
contribution made by the fibre to impart its own property to the polymer. Thus, strength increased with fibre concentration and fibre treatment. This is possible when there is good adhesion between the coconut fibre particles and the polymer matrix. In the case of coconut fibre with the smallest particle size (45 microns), increased surface area might have allowed for better fillerhardness test is presented in Table 11, Fig. 5. matrix interaction thus increasing the chances to enhance the strength.
Fig. 3 from Table 8 also shows that the tensile
The results obtained from the experiments are shown from Tables 7-11 with their corresponding graphs. elastic modulus increases with volume fraction treatment, but with decreased particle size with a maximum optimum modulus of 800 MPa
Table 7. Tensile strength of the 3 grades of untreated and treated coconut fibre filled HDPE composite samples at specified fibre volume fractions
V fr
(%)
G1U G2U
Tensile strength (MPa)
G3U G1T G2T G3T
24.6
25.4
25.8
26.1
26.6
26.2
26.0
24.6
25.0
25.2
25.6
26.0
25.8
25.6
24.6
24.7
25.0
25.4
25.6
25.4
25.2
24.6
26.0
27.2
27.8
28.6
28.4
27.6
24.6
25.5
26.2
27.4
28.2
27.8
27.4
24.8
24.4
25.0
Where, ܩ1ܷ = Untreated Grade 1 Composite Sample; ܩ2ܷ = Untreated Grade 2 Composite Sample
ܩ3ܷ = Untreated Grade 3 Composite Sample; ܩ1ܶ = Treated Grade 1 Composite Sample
ܩ2ܶ = Treated Grade 2 Composite Sample; ܩ3ܶ = Treated Grade 3 Composite Sample
24.6
24.0
25.0
25.4
5

Ihueze et al.; JSRR, 9(3): 1-10, 2016; Article no.JSRR.20385
29
28
G1U
27
G2U
26
G3U
25
G1T
24
23 G2T
0 10 20 30 40 50
G3T
V fr
(%)
0
5
10
15
20
30
40
Fig. 1. A plot of tensile strength of the 3 grades of untreated and treated coconut fibre filled
HDPE composite against fibre volume fractions
Table 8. Elastic modulus of the 3 grades of untreated and treated coconut fibre filled HDPE composite samples at specified fibre volume fractions
V fr
(%)
G1U
480
500
530
580
650
780
610
G2U
480
600
640
630
600
730
630
Elastic modulus (MPa)
G3U G1T
480
540
550
600
650
700
750
480
520
550
580
670
800
700
G2T
480
610
670
680
720
750
710
G3T
480
570
590
610
680
730
760
900
800
700
600
500
400
300
200
100
0
GIU
G2U
G3U
G1T
G2T
G3T
0 10 20 30 40 50
V fr
(%)
Fig. 2. A plot of elastic modulus of the 3 grades of untreated and treated coconut fibre against fibre volume fraction at volume fraction of 30%. This observation supports earlier study made by Pukanszkyl [14] application of small values of strain. Such small stresses are not sufficient even to break the that strength of the interaction between the filler material and the matrix influences tensile modulus of the composite. This is because modulus is a phenomenon involving very small strain values. Small stresses are produced by weak interactions at the interface. Thus, these small stresses can easily be transferred from matrix to filler thereby allowing the filler to contribute its high modulus to the composite.
Particle size also did not seem to influence the
6

0
5
10
15
20
30
40 elastic modulus. However, fluctuations in the values of modulus were observed. These fluctuations were more for highly filled HDPE composites as is obvious from the graph.
Fig. 4 from Table 9 shows that the flexural strength of HDPE filled Coconut fiber fillers increases with treatment, volume fraction, but with decreased particle size of fillers with maximum optimum value of 22.3 MPa at volume fraction of 40%. The increase becomes more pronounced when filler concentration went above
Ihueze et al.; JSRR, 9(3): 1-10, 2016; Article no.JSRR.20385 obtained from 17.4 Mpa to 21.8 Mpa for untreated coconut composite samples while an increase of 28.5% from 17.4 MPa to 22.3 MPa was obtained for the treated composite samples.
This could be attributed to the contribution of high strength coconut fibre particles, thus strength increased with increasing concentration of the filler and also with fibre treatment. This again is only possible if there is stress transfer from matrix to filler through a fairly strong interfacial bond. Further improvement in flexural strength might be obtained by increasing the filler
10%. A maximum of about 25.3% increase was concentration beyond 40%.
Table 9. Flexural Strength of the 3 grades of untreated and treated coconut fibre filled HDPE composite samples at specified fibre volume fractions
V fr
(%)
G1U
17.4
18.3
18.7
20.1
20.0
21.4
21.8
G2U
17.4
18.0
18.1
19.6
19.3
20.1
21.3
Flexural Strenght (MPa)
G3U G1T
17.4
17.3
17.4
17.8
19.0
20.6
20.8
17.4
18.4
18.8
20.8
20.6
21.8
22.3
G2T
17.4
18.0
18.5
19.6
19.5
20.0
21.6
G3T
17.4
17.3
17.5
18.2
19.0
19.8
21.0
25
20
15
G1U
G2U
G3U 10
5
G1T
G2T
0
0 10 20 30 40 50 G3T
V fr
(%)
Fig. 3. A graph of flexural strength of the 3 grades of untreated and treated coconut fibre against fibre volume fraction
Table 10. Impact strength of the 3 grades of untreated and treated coconut fibre filled HDPE composite Samples at specified fibre volume fractions
V fr
(%)
0
5
10
15
20
30
40
G1U
48.0
49.0
50.0
51.0
53.0
50.0
48.0
G2U
48.0
49.0
49.2
49.5
50.0
48.0
46.0
Impact strength (J/m)
G3U G1T
48.0
48.5
49.0
48.0
46.0
43.0
42.0
48.0
49.0
51.0
53.0
55.0
52.0
49.0
G2T
48.0
48.5
49.0
50.0
52.0
49.0
47.0
G3T
48.0
48.5
49.0
49.5
48.0
45.0
43.0
7

Ihueze et al.; JSRR, 9(3): 1-10, 2016; Article no.JSRR.20385
60
50
G1U
40
G2U
30
G3U
20
GIT
10
G2T
0
0 10 20 30 40 50
G3T
V fr
(%)
Fig. 4. A plot of impact strength of the 3 grades of untreated and treated coconut fibre against fibre volume fraction
Table 11. Hardness value (HR) of the 3 grades of untreated and treated coconut fibre filled
HDPE composite Samples at specified volume fractions
V fr
(%)
0
5
10
15
20
30
40
G1U
12.5
15.3
22.4
30.5
38.3
46.8
53.4
Hardness values (HR)/Fibre particle sizes
G2U G3U G1T G2T
12.5
14.8
20.5
26.3
32.6
40.4
47.8
12.5
14.3
18.0
24.4
30.2
37.5
43.6
12.5
15.8
23.2
32.0
46.5
52.6
54.0
12.5
15.4
21.4
28.6
36.2
44.8
48.6
G3T
12.5
15.0
19.2
26.4
32.4
40.2
42.8
60
50
G1U
40
G2U
30
G3U
20
G1T
10
G2T
0
G3T
0 10 20 30 40 50
V fr
(%)
Fig. 5. A plot of hardness values (HR) of the 3 grades of untreated and treated coconut fibre filled HDPE composite samples against fibre volume fraction
Also Fig. 5 from Table 10 depicts that impact were checked probably by generation of strength increases with fibre treatment and volume fraction but decreases with particle size of filler at maximum optimum volume fraction of
20% with a value of 55 J/m. At higher fibre concentrations and larger particle size, impact strength was found to reduce. Further reductions secondary cracks. In order to increase impact strength of the composite further, suitable surface treatment of the fibre was made which increased the strength of the chemical bond between the filler and the matrix.
8

Ihueze et al.; JSRR, 9(3): 1-10, 2016; Article no.JSRR.20385
Table 12. Comparison of experimental results with standard results
Properties
Tensile strength (MPa) 28.2 26.0 25.6 28.6 28.2 24.8 11.0-43.0 21.4
Elastic modulus (MPa) 780 730 700 800 750 730 450- 1500 909
Flexural strength (MPa) 20.0 19.3 19.0 20.6 19.5 19.0 13.8-48.3 28.2
Impact strength (J/m) 53.0 50.0 46.0 55.0 52.0 48.0 20.0-110.0 2.79
Hardness (HR) Value 53.4 47.8 43.6 54 48.6 42.8 33.0-66.0 48.7
Furthermore, Fig. 6 from Table 11 clearly shows that Hardness increases with volume fraction and fibre treatment, but decreases with particle size.
The maximum optimum value of 54.0 HR was recorded at 40% volume fraction. The hardness value of the developed composite samples increased as filler concentration increases for both untreated and treated samples. Generally,
•
Developed composites can be applied for applications requiring energy absorbtion and dissipation such as in brake bands and clutch plates
•
Developed composites can be applied for applications requiring energy absorbtion and dissipation such as autobodies. treated fibre composite specimens possess greater hardness value than the untreated samples. The increase in hardness is related to the increasing amount of hard and brittle coconut fibre particles in the polymer matrix and strong interfacial bond between the fibre and the matrix.
These hard and brittle fibre particles will continuously resist deformation due to indentation. Also the smaller the particle size, the harder the composite specimens.
The values of experimental results are compared with literature data obtained from MatWeb
(WWW.MATWEB.COM) for HDPE injection molded grade and presented in Table 12 above.
The new material of HDPE shows increased mechanical properties with volume fraction of modified coconut fibres.
It can be concluded that:
•
At optimum condition of volume fraction and particle size of coconut fibre-filler, the coconut fibre reinforced HDPE (CFRP) has
28.6 MPa, 720 MPa, 22.3 MPa, 55.0 J/m and 54.4 HR as optimum value for tensile strength, elastic modulus, flexural strength, impact strength and hardness.
•
Developed composites have shown improved
Values obtained from experiment at maximum optimum fibre volume fraction for the composite samples
HDPE-Injection molded (MatWeb)
G1U G2U G3U G1T G2T G3T Range of values
Average values mechanical properties as compared with the unreinforced highdensity polyethylene resin.
Authors have declared that no competing interests exist.
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