Mechanical Properties and Microstructure of Cocos Nucifera (Coconut) Coir Fibres L.Awang1, Z.Salleh2,*, M.Y.M.Yusop3, A.A.Roslee4, Sapuan S.M,5 and M.R. Ishak6 1,2,3,4
Applied Science and Advanced Technology Section, UniKL Malaysian Institute of Marine Engineering Technology, Dataran Industri Teknologi Kejuruteraan Marin, Bandar Teknologi Maritim, Jalan Pantai Remis, 32200 Lumut, Perak, Malaysia. 5,6 Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia *Corresponding author:
[email protected] Abstract: In this research, the mechanical properties of three types of coconut (cocos nucifera) fibres were investigated specifically young coconut (YC), ripe coconut (RP) and Komeng coconut (KC). Tensile test was carried out using Universal Testing Machine with a load capacity of 5kN in accordance to ASTM D 3379 standard for single fibre tensile test. Tensile test showed that tensile strength ranges between (0.10-31.15MPa) for KC, followed by RC (0.03-16.95MPa) and YC (0.07-12.01MPa). The morphology of these three coir fibres and shell surface were also investigated using optical microscope. Keywords: Coconut, Komeng, Cocos Nucifera, Mechanical properties, Coir Fibre. 1.
INTRODUCTION
It is estimated that about 55 billion of coconuts are produced yearly around the world, yet only 15% of the husk fibres are actually recovered for use, leaving most husks abandoned. This is a waste of natural resources and causes environmental pollution [1]. Coir fibres will decompose in 20–30 years [1] and it can be regarded as an environmentally friendly material. The fibre extracted from the husk of a coconut (Cocos Nucifera), commonly known as a coir fibre and has been traditionally used in tropical regions of Asia, Africa and South America in a variety of simple items such as rugs and as filling material for mattresses and cushions. Coconut shells are abundant residues in agricultural countries. The fibres from the coconut crust nowadays are disposed as an unwanted waste. This can be seen as potential recyclable materials that can be used in polymeric matrix composite material [2,3,4]. Its fibres can be extracted from any part of the tree including the long leaf sheath, the midribs of the leaves, the bark of the stalk and the coconut crust [5]. Coir fibres are found between the husk and the outer shell of a coconut. The individual fibre cells are narrow and hollow, with thick walls composed by cellulose. They are pale when immature but later become hardened and yellowed as a layer of lignin is deposited on their walls. There are two varieties of coir. Brown coir is harvested from fully ripened coconut. It is thick, strong and has high abrasion resistance. It is typically used in mats, brushes and sacking. Mature brown fibres contain more lignin and less cellulose than fibres such as flax and cotton and are stiffer. White coir fibres are harvested from the coconuts before they are ripe. These fibres are white or light brown in colour and are smoother and finer, but also more flexible. 1
Normal coconnuts are usuually used forr a variety of N o products bbut coconuts without theeir exocarp and endocarrp are considdered as waaste. In Malaaysia, especiially in the northern n area, these typpes of coconnut are know wn as Komenng coconut. Komeng cooconuts are considered c a as having no o economic value. However, there is a potentiall of using Koomeng coconnut fibres as a new com mposite mateerial in consstruction inddustry. To date d no studyy has been conducted on o Komeng coconut fibrre. Hence, itt is importannt to perform m several expperiments onn the Komenng wledge its potential. p D During the innvestigation process, noormal coconuut coir fibrees to acknow coir fibrees will be used as referennce as its fibbres are wideely used. Thee scope of th his research is coir fibrees’ tensile strrength and microscopic m structure. 2.
M METHODO LOGY
Three types of coconut were selectted for this study nam T mely young coconut, rippe coconut and a Komeng g coconut thhat were obtained from Kampung K Serdang, Peraak. The fibrees were cleaaned, washed and dried under the suun and then cooled c to room temperaature. Figure 1 shows th he cross-secttional of alll three typees of coconuuts with andd without th heir endocarrp material and designaated as you ung coconut (YC), ripe coconut (RC C) and Kom meng coconuut (KC). In order to obttain results with w statisticcal meaning and consideering that thee natural fibrre nisotropic material m that have diverse variationns, the speciimen of thee fibres werre is an an carefully y selected affter it was gently g separaated by hand d from the hhusk. The selected fibrees were careefully examiined using optical o microoscope in ord der to ensuree that there is i no physical damage done d to the fibre. f The fib bre was thenn glued to a tab t shaped ppaper which was designeed -3 with a gaauge length of 20 x 10 m and testeed according g to ASTM D 3379 stan ndard (methood for a singgle fibre tesst). The tab shaped papeer was cut at a mid-gaugee length afteer it has beeen fixed firm mly in the jaaws of the unniversal testting machinee (UTM). Fiigure 2 show ws a specimeen safely plaaced in the jaws of the UTM. U
a) YC (bb) RC Y Fig. 1: Crooss-sectionall view of thee coconuts
(c) KC
The specimenn was tested T d with a crossshead speed d of 5mm/miin with repliication of ~330 specimenns using UT TM (Instron 3366) with a load capaacity of 5kN N. Every inddividual fibrre breaking load was recorded r andd their diam meters were measured uusing opticaal microscoppe (Leica MS M 5).
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Fig. 2: Specimen placed in the grip jaws of the Universal Testing Machine 3
RESULTS AND DISCUSSION
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Tensile Properties
Results of the tensile tests of all these coconut are presented in Table 1. The highest maximum stress of a coconut fibre recorded was 31.15MPa that belongs to KC, while the lowest maximum stress recorded was 12.01MPa which belongs to YC. Table 1: Tensile properties of YC, RC and KC specimens Standard Test/Parameter Mean Min Max. Deviation (a) Tensile of YC Strain at Break (%) 64.51 18.11 17.75 103.64 Stress at Break (MPa) 1.26 2.15 0.07 12.01 Young’s Mod. (MPa) 1177.84 455.80 644.02 2833.76 (b) Tensile of RC Strain at Break (%) 52.05 31.77 10.63 133.03 Stress at Break (MPa) 2.15 4.39 0.03 16.95 Young’s Mod. (MPa) 1418.33 2046.70 293.81 8364.40 (c) Tensile of KC Strain at Break (%) 56.57 22.95 12.61 99.67 Stress at Break (MPa) 3.10 6.35 0.10 31.15 Young’s Mod. (MPa) 1439.16 725.23 642.11 4074.23 Although the samples were cut with same length ~20mm, there was difference of more than 1MPa in mean stresses between of them. This may be due to the varying thickness of the specimen since the fibre was cut manually. For the lowest and highest value of stress at break, it was observed that KC specimen exhibit higher stress values when compared to both RC and YC. However the difference is greater when comparing values of stresses between KC and RC. It can be safely deduced that 3
KC specimen exhibit more than twice the strength RC specimen. This fact is justified since Young’s Modulus of KC specimen is much higher at 1439.16MPa as compared to 1418.33MPa for RC and 1177.84 for YC. The higher Young’s Modulus value for KC might be due to the presence of impurities such as lignin, pectin and fatty acid in the specimen. These impurities might have caused a significant increase of elongation at break point since the specimen was treated with an alkaline solution (NaOH) that might have retained the presence of the impurities[1]. Another probable cause that might have contributed to the increase in tensile strength in fibres is its moisture content. When the fibre absorb moisture and diffuse it into the cell wall, the water molecules start to form hydrogen bonding with the hydroxyl group of the fibre. This causes the cellulose chains to move apart which then resulted in the increase of the microfibril size. This changes the size of the cell, which in turn causes the fibre to swell. As the celluloses inside the fibre moved away from each other due to the swelling, large gaps are created between the cellulose chains and thus weaken the intermolecular and intramolecular bonding in the fibre. On the other hand, if the water molecules were removed, the microfibrils would shrink and decrease in size causing the cellulose chains to become closer and forming a stronger intermolecular bonding among the microfibrils as well as intramolecular bonding within the microfibrils. Fibre becomes stronger as the cellulose chains form strong bonding among themselves. The decrease in the strength of natural fibre due to the presence of moisture has also been previously reported [6]. 3.2
Optical Micrograph Example of specimen images as observed under an optical microscope is presented in Figure 3. From the images, it can be seen that the surface of coir fibre is covered with a layer of substances which may include pectin, lignin and other impurities. All specimens have rough outer surface as they are extensively covered with nodes and irregular stripes.
(a) YC coir fibre
(b) KC coir fibre
(c) RC coir fibre Fig. 3: Optical micrograph at 400 times magnification of (a) YC, (b) KC and (c) RC coir fibres. 4
Specimens were categorised according to its fibre diameter average tensile stress was then calculated. The fibre diameter for YC coir fibre specimen averages between 0.019m to 0.044m and the tensile stress is between 0.89-1.85MPa. For KC coir fibre, the fibre diameter ranges between 0.020m to 0.042m while the measured tensile stress is between 0.91– 4.37MPa. As for RC coir fibre specimen, the fibre diameter is between 0.023m to 0.044m and the measured tensile stress is between 1.30 – 2.99MPa. These are represented in Figure 4. 5.00 4.50 Average Tensile Stress (MPa)
4.00 3.50
Tensile stress at Break (Standard) (MPa)‐ RC Tensile stress at Break (Standard) (MPa)‐ YC Tensile stress at Break (Standard) (MPa)‐ KC
3.00 2.50 2.00 1.50 1.00 0.50 0.00
2.00
3.00 Fibre Diameter(x10 ‐2m)
4.00
Fig. 4: Average Tensile Stress (MPa) versus Fibre Diameter (m) From Figure 4, it can seen that KC specimen has the highest tensile stress at 4.37MPa for fibre diameter of approximately 0.034m while YC and RC specimens have an average tensile stress below 3MPa. This result supports the earlier hypothesis that the strength of coir fibres is lessened when the fibre contains high amount of dilated microfibrils that is caused by high moisture content. In this case both YC and RC specimens showed lower average tensile stress as compared to KC specimen since both YC and RC specimens has higher water content. However, it is worth to note that the average tensile stress for KC specimen is lower than RC and YC specimens for fibre diameter of 0.04m. This may be due to the irregular shape of fibre’s internal structure that can be hugely affected by the location from which the fibre was extracted [7]. The fibres can be extracted either near to or far from the endocarp. Fibres that are near the endocarp might have contained slightly higher moisture content thus lessening its tensile strength. However this can only be justified through further investigation.
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CONCLUSION Mechanical properties of coir fibres obtained from 3 types of coconuts namely young coconut (YC), ripe coconut (RC) and Komeng coconut (KC) were investigated. Early results showed that KC’s coir fibre with diameter ranging from 0.02m to 0.03m has higher tensile strength (tensile stress) compared to YC and RC of similar fibre diameter. Further investigation is needed in determining the effects of moisture content and fibre’s internal structure on tensile strength of coir fibres.
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ACKNOWLEDGEMENT The authors would like to acknowledge the Ministry of Higher Education (MoHE) for providing the research fund (FRGS/2/10/TK/UNIKL/03/2) for this project. The authors would like to also thank you the Department of Mechanical and Manufacturing, Faculty of Engineering, Universiti Putra Malaysia (UPM) for their generosity in permitting the use of testing facilities.
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