- Email: [email protected]
epoxy hybrid nanocomposites
Accepted Manuscript Physical, structural and thermomechanical properties of oil palm nano filler/kenaf/ epoxy hybrid nanocomposites N. Saba, M.T. Paridah, K. Abdan, N.A. Ibrahim PII:
S0254-0584(16)30689-7
DOI:
10.1016/j.matchemphys.2016.09.026
Reference:
MAC 19172
To appear in:
Materials Chemistry and Physics
Received Date: 14 June 2016 Revised Date:
24 August 2016
Accepted Date: 10 September 2016
Please cite this article as: N. Saba, M.T. Paridah, K. Abdan, N.A. Ibrahim, Physical, structural and thermomechanical properties of oil palm nano filler/kenaf/epoxy hybrid nanocomposites, Materials Chemistry and Physics (2016), doi: 10.1016/j.matchemphys.2016.09.026. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Physical, Structural and Thermomechanical properties of oil palm nano filler/kenaf/epoxy hybrid nanocomposites
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N.Saba1*, M.T. Paridah1, K. Abdan2, N. A. Ibrahim3
Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products
Department of Biological and Agricultural Engineering, Faculty of Engineering, Universiti Putra
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(INTROP), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
Malaysia, 43400 UPM Serdang, Selangor. Malaysia 3
Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang,
Abstract
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Selangor. Malaysia
The present research study deals with the fabrication of kenaf/epoxy hybrid nanocomposites by
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the incorporation of oil palm nano filler, montmorillonite (MMT) and organically modified montmorillonite (OMMT) at 3% loading, through hand lay-up technique. Effect of adding
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different nano fillers on the physical (density), structural [X-ray diffraction (XRD)] and thermomechanical analysis (TMA) of kenaf/epoxy composites were carried out. Density results revealed that the incorporation of nano filler in the kenaf/epoxy composites increases the density which in turn increases the hardness of the hybrid nanocomposites. XRD analysis confirmed the presence of nano fillers in the structure of their respective fabricated hybrid nanocomposites. All hybrid nanocomposites displayed lower coefficient of thermal expansion (CTE) with respect to kenaf/epoxy composites. Overall results predicted that the properties improvement in nano 1
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OPEFB/kenaf/epoxy was quite comparable to MMT/kenaf/epoxy but relatively lesser to OMMT/kenaf/epoxy hybrid nanocomposites and higher with respect to kenaf/epoxy composites.
fibers and epoxy matrix by addition of nano filler.
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The improvement ascribed due to improved interfacial bonding or cross linking between kenaf
Keywords: Oil palm nano filler; Kenaf fibers; Nanocomposites; Hybrid nanocomposites; X-ray
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Diffraction; Thermomechanical properties.
*Corresponding author: Naheed Saba, E-mail: [email protected], Tel.: +603-89466960;
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Fax: +603-86471896
Introduction
Thermosets including epoxy polymers undergo crystallization to form brittle and crystalline
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structure. This drawback can be minimized by the incorporation of natural fibers and nano filler. Kenaf fiber having properties allied to jute fiber and is one of the most abundant, renewable and biodegradable lignocellulosic fiber with low density (1.3 g/cm3) used for fabricating a wide
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variety of composites products, with variety of thermosets and thermoplastics polymers [1] [2].
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Fabrication of natural fibers reinforced hybrid polymer composite materials are currently receiving higher attention from both industries and scientists owing to perfect balance between performances and manufacturing cost [3]. Research study established that hybridization of natural fiber with synthetic or with other natural fiber can improve the physical, thermal and thermomechanical properties of natural fiber polymer composites. Nanocomposites represents the most attractive, potential, indispensable and encouraging approaches in the field of future advanced engineering applications tailored by adding nano scale filler in the polymer matrix to 2
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meet the growing demands of the specific properties, for versatile practical applications [4] [5]. Polymer nanocomposites exhibit better physical and mechanical properties than conventional composites based on a polymer with micro sized filler [6]. Moreover, nanoscience and
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nanotechnology have opened up a new way of developing hybrid nanocomposites, by replacing the synthetic fibers with nano fillers (nanoclay, nanotube, graphite, nano metal oxide etc.). The hybrid nanocomposites possess improved physical, structural, mechanical, thermal and
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thermomechanical properties with respect to natural fibers reinforced polymer composites [7]. Nanoclay (MMT, OMMT) based polymer composites are formed by insertion of the
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polymer chains between the clay layers [8]. Organoclays possess layered structure produced by treatment of bentonite and MMT clay minerals with organics by replacing exchangeable cations (Ca2+, Mg2+, K+, and Na+ ) by cationic surfactants of the form (CH3)NR or (CH3)2NR2 (R- alkyl or aromatic hydrocarbon). Organoclays displays varied applications due to their specific active
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sites and high aspect ratio which allows efficient load tolerance to the polymer matrices and thus provide better strength and stiffness to the nanocomposites [9]. Replacement of inorganic cations via cation exchange to form organoclays, by the alkyl cations such as quaternary ammonium hexadecytrimethylammonium
(HDTMA),
hexadecylpyridinium
(HDP),
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cations,
tetramethylammonium and trimethylphenylammonium (TMPA), have been extensively reviewed
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by the researchers [10]. X-ray diffraction is most common, versatile, non-destructive technique that provides detailed information about crystallographic structure including polymer crystallinity, phase identification and quantification for all crystalline, semi-crystalline or amorphous polymers and polymer composites. XRD is the only technique to investigate the intercalation and exfoliation behavior of the nanoclay based nanocomposites by estimating the distance between the silicate platelets [11]. Infrared (IR) spectroscopy, especially FTIR is the
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most reliable and cost effective analytical tool for identification of polymers and assessment of the quality of composite materials, by providing distinctive “fingerprint” characteristics of the composite materials [12] [13]. TMA is one of the most sensitive and effective technique used to
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determine the dimensional changes as function of temperature or time under investigation. On heating or cooling most of the composite materials undergoes thermomechanical and dimensional changes, thus its quite essential to analyze their coefficient of linear thermal
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expansion (CTE) [14] through TMA analysis with temperature fluctuations, prior to use in high
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end applications. The CTE is defined as α, and calculated by the (Eq.1) [15]
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Where L is the sample length and ∆ T is the temperature range
CTE is the materials property as it indicates the extent to which a material expands upon heating. Higher the CTE value lower is its dimensional stability with temperature, and lower its CTE
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value higher its dimensional stability with temperature. Several research studies were reported on the hybridization of kenaf fibers with natural/synthetic
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fibers/nano filler in the literature. Some of the exclusive findings on hybridization of kenaf fibers were tabulated in Table 1.
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Table 1. Reported study on the hybridization of kenaf fibers with synthetic fibers/natural fibers/ nano filler by researchers
Kenaf/Coir fibers/MMT
Polymer Matrix Epoxy
Kenaf/Jute fibers/E-glass
Epoxy
Kenaf fibers/Wood flour/Rice hulls/Newsprint fibres Kenaf/Hemp/Flax/Glass fibers
PP PP
[19]
Kenaf fibers/MMT
Epoxy
[20]
Kenaf fibers/Pultruded jute Kenaf/Hemp fibers Kenaf/Short carbon fibers Kenaf/Glass fibers/CNTs
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References
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Reinforcements
[16]
[17]
[18]
UP
[21]
CNSL
[22]
NR
[23]
Epoxy
[24]
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Note: Cashew nut shell liquid matrix (CNSL), Polypropylene (PP), Unsaturated polyester (UP), Natural rubber (NR), Carbon nanotubes (CNTs)
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From the literature review it is evident that no study has been conducted on the hybridization of kenaf fibers reinforced epoxy composites with oil palm nano filler. Present study is the extension
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of our previous research work, involving the preparation of oil palm nano filler from wastes oil palm empty fruit bunch (OPEFB) fibers, through combined effects of cryogenizer and high energy ball milling (HEBM) technique [25]. In this study, an effort has been made to fabricate kenaf/epoxy, nano OPEFB/kenaf/epoxy, MMT/kenaf/epoxy and OMMT/kenaf/epoxy hybrid nanocomposites having 40% kenaf fibers loading in each case, by hand lay-up technique. Effect of adding oil palm nano filler to the kenaf/epoxy composites on physical, structural and thermomechanical properties were investigated through density measurements, X-ray diffraction 5
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and CTE analysis and are compared with kenaf/epoxy composites. Comparative studies were also made with MMT/kenaf/epoxy and OMMT/kenaf/epoxy hybrid nanocomposites, in order to provide open a new platform by using green nano filler in polymer nanocomposites industries
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from wastes fibers of Malaysia.
Experimental
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Materials
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The OPEFB fiber was obtained from MPOB, Bangi-Selangor, Malaysia. The kenaf non-woven mat was obtained from Innovative Pultrusion Sdn, Bhd, Malaysia. Montmorillonite (MMT) and organically modified montmorillonite (OMMT) nanoclay were procured from Zarm scientific & Supplies Sdn., Bhd, Malaysia. MMT is a hydrated sodium calcium aluminium magnesium silicate hydroxide powder, having surface area of 250m2/g with the pH 3-4. OMMT were the
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nanoclay Nanomer® I.31PS, contains 0.5-5 wt. % aminopropyltriethoxysilane, 15-35 wt. % octadecylamine with mean mesh size of 15-25µm and having bulk density 200-500 kg/m3. The epoxy resin D.E.R 331, is a clear liquid resin based on diglycidyl ether of bisphenol A (DGEBA),
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obtained from Dow Chemical Pacific Singapore, Singapore. The curing agent, epoxy hardener
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Jointmine 905-3S, is a clear and transparent color liquid, supplied by Epochemie International Pte Ltd. Singapore. Silicone spray and Teflon sheets were procured from Dow Chemical Pacific Singapore, Singapore and NR Medicare Sdn. Bhd., Selangor, Malaysia, respectively. purchased chemicals were used without any further purification.
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Fabrication of composites Procedure for the fabrication of composites were same as discussed in our previous research
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work [26][27]. Two pre-pressed kenaf non-woven mats were used in the fabrication of both kenaf/epoxy composites and different filler filled kenaf/epoxy hybrid nanocomposites through high speed mechanical stirrer followed by hand lay-up technique. Fabrication procedures for
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kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites are illustrated in
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Figure 1.
Figure 1. Fabrication procedure of kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites
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Non-woven kenaf mat roll, compressed kenaf mat, steel mold, fabricated kenaf/epoxy composites, nano OPEFB/kenaf/epoxy, MMT/kenaf/epoxy and OMMT/kenaf/epoxy hybrid
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nanocomposites are displayed in Figure 2.
Figure 2. (a) Kenaf non-woven mat roll (b) compressed kenaf mat (c) steel mold (d) kenaf/epoxy composites (e) nano OPEFB/kenaf/epoxy (f) MMT/kenaf/epoxy and (g) OMMT/kenaf/epoxy hybrid nanocomposites
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Characterization Density Density is the mass per unit volume of composite samples, calculated by using ASTM D792
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standard. Mass determination was carried out by weighing the 8 replicate hybrid nanocomposites with analytical balance (Shimadzu, Japan EPA-151-WT-12) and the volume were calculated by using digimatic micrometer Mitutoyo (Figure 3). Prior to mass and volume measurement the
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samples are oven dried at 50 o C for 24 h, and then allowed to cool in desiccators.
Figure 3. Density samples of (a) kenaf/epoxy (b) nano OPEFB/kenaf/epoxy (c) analytical
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balance and (d) digimatic micrometer Mitutoyo
X-ray diffraction (XRD)
The identification of the crystallographic structure of different nano fillers (nano OPEFB, MMT, OMMT), kenaf/epoxy composites and filler filled/kenaf/epoxy hybrid nanocomposites was achieved by powdered X-ray diffractometer (X’ Pert, Siemens XRD D5000) equipped with
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computerized data collection and analytical tools having copper anode X-ray tube. The XRD analyses of nano fillers and hybrid nanocomposite samples were conducted with Cu Kα radiation of 1.5406 Å, operating at 30kV and current 20.0 (mA). Samples were first gently consolidated in
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an aluminum holder and X-ray diffractogram of samples were analyzed using X’Pert High Score software recorded at an angular incidence of 2θ=10° to 40°, at scan rate of 2°/min. XRD
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diffractometer and XRD samples are displayed in Figure 4.
Figure 4. (a) XRD-Siemens D5000 (b) XRD samples of nano fillers and (c) filler filled kenaf/epoxy hybrid nanocomposites
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Thermomechanical analysis (TMA) TMA employs a sensitive probe in contact with the surface of composites sample. As the sample
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heated, the probe senses change in dimension. TMA was made according to ASTM D696 to investigate CTE of composites through TA Instrument Q400 under nitrogen. The samples were in dimension of 6 × 6 × 4 mm3 and the temperature was ramped from room temperature to 200°C
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at a heating rate 5°C/min. The dimensional change was then measured in the thickness direction to calculate the CTE of composites. The two replicate TMA specimens of each composites
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sample and TMA instrument are shown in Figure 5.
Figure 5. TMA samples of kenaf/epoxy, filler filled kenaf/epoxy hybrid nanocomposites and
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TMA instrument
Results and discussion Density of composites
Density of kenaf/epoxy composites and nano OPEFB/kenaf/epoxy, MMT/kenaf/epoxy and OMMT/kenaf/epoxy hybrid nanocomposites are displayed in Figure 6. From the density graph it
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is evident that density of kenaf/epoxy composites are 1.32 g/cm3, which are quite close to the density reported in the literature for the chopped 40% kenaf fibers/epoxy composites [28]. It is clearly evident from density graph that the incorporation of nano fillers (nano OPEFB, MMT,
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OMMT) considerably increase the density of kenaf/epoxy matrix, and it lies in the range of 1.375–1.42 g/cm3. The increase in density can be ascribed of relatively denser and harder phase of incorporated nano fillers as compared to kenaf/epoxy composites. Interestingly, the nano
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OPEFB/kenaf/epoxy and MMT/kenaf/epoxy displayed relatively similar density improvement. However the higher density improvements are observed in the case of OMMT/kenaf/epoxy
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hybrid nanocomposites among all composites, owing to denser OMMT nanoclay particles.
1.42 1.4
1.34 1.32 1.3 1.28
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1.26
Density (g/cm3)
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1.36
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1.38
Figure 6. Effect of loading different nano fillers on the density of kenaf/epoxy composites
The improvement in density of kenaf/epoxy composites can also be explained on account of increase in the cross linking density of epoxy chains and interfacial bonding which ultimately 12
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improves the hardness of the resulting hybrid nanocomposites, by the incorporation of nano fillers.
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X-ray diffraction (XRD)
X-ray diffraction was carried out to explore the characteristics diffraction peak of nano fillers (nano OPEFB, MMT, OMMT), kenaf/epoxy composites and filler filled kenaf/epoxy hybrid
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nanocomposites. The X-ray diffractogram of all nano fillers are displayed in Figure 7. Figure 8 illustrates the X-ray diffractogram of kenaf/epoxy composites and filler filled kenaf/epoxy hybrid
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nanocomposites.
The characteristics peak of OMMT are well observed at 2θ=19o and 23o in the Figure 7. The obtained diffractogram of OMMT nanoclay also correspond to the reported literature [29] [30]. The XRD measurements showed that 2θ had been shifted from the high angle to the low angle as
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compared with MMT to afford OMMT due to ion exchange process [31]. The presence of small reflections at 2θ=20o and 35o, and sharp reflection at 2θ=25o corresponds to characteristics peaks of MMT nanoclay [32] [13]. The two characteristics pointed peak of nano OPEFB at 2θ=25o and
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near 20o are already discussed in our previous reported study [25]. X-ray diffraction measurements shown in Figure 8, characterize the morphological structure of
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kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites. From the XRD diffractogram of MMT/kenaf/epoxy and OMMT/kenaf/epoxy hybrid nanocomposites, it is evident that no reflections are observed at low angle region (2θ=0.4–10°), indicating the formation of exfoliated nanocomposites, having interlayering space larger than that of the intercalated structure.
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Figure 7. XRD graph of incorporated nano fillers (nano OPEFB, MMT, OMMT)
Figure 8. XRD-graph of kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites 14
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The diffractogram of nano OPEFB/kenaf/epoxy hybrid nanocomposites also does not display any sharp peaks below 2θ=10o, indicating homogenous dispersion in the kenaf/epoxy
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composites. From XRD results, it could be concluded that the inter-gallery spacing of OMMT facilitates the entry of epoxy matrix molecules to enter into the galleries, as the hydrophilic clay surface changed to an organophilic surface. The statement was also in line with other reported
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literature [33]. Moreover, the characteristics peak of OMMT, are also observed near 2θ=22.5o in the OMMT/kenaf/epoxy hybrid nanocomposites. Remarkably, the intense peak at 2θ=29.3o, was
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observed for both kenaf/epoxy composites and filler filled hybrid nanocomposites in the diffractogram, signifying the presence of kenaf fibers moieties in all of them [34].
Thermomechanical analysis (TMA)
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Thermomechanical analysis of kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites were carried out to evaluate the dimensional changes or CTE, in both rubber and glassy regions as a function of temperature under a nitrogen atmosphere, are displayed in Figure
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9. The thermal expansion coefficients showed progressive diminution by adding nano filler to the kenaf/epoxy composites displaying minimal expansion of kenaf fibers in the epoxy matrix. From
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Figure 9, it is evident that each of the hybrid nanocomposites and kenaf/epoxy composites shows both contraction and expansion in dimensions with change in temperature. Marked small contraction below 100oC corresponds to the some moisture loss from kenaf fibers in all the cases. Kenaf/epoxy composites display only one contraction and one thermal expansions coefficient whereas nano OPEFB/kenaf/epoxy displayed two contractions and two thermal expansions coefficient. MMT/kenaf/epoxy displayed three contractions and two thermal expansions coefficient, whereas more than two contractions and two thermal expansions coefficient are 15
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observed for OMMT/kenaf/epoxy hybrid nanocomposites. Thus it clearly evident from TMA graph that heterogeneity are more pronounced in all filler filled/kenaf/epoxy hybrid nanocomposites with respect to kenaf/epoxy composites. Similar arguments are also reported in
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literature for the TMA of palm fiber and its ABS composites [35]. The cole-cole shapes also governed the obtained TMA graph [27]. TMA graph also revealed that CTE of all hybrid nanocomposites in the glassy and rubbery region, presented lower thermal dilatations than
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kenaf/epoxy composites. This revealed that a synergy between reinforced kenaf fibers and epoxy
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fillers (nano OPEFB, MMT, OMMT).
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matrix on the CTE of the hybrid nanocomposites get improved by the incorporation of nano
Figure 9. TMA graph of kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites
Moreover, the decrease in CTE value also corresponds to the decreased polymeric segmental motion in the free space by the addition of nano filler along with improved interfacial adhesion
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between kenaf fibers and the epoxy matrix governing better thermal and mechanical properties. Researchers reviewed that thermal expansion also involves the transmission of stress across an interface reflecting an evidence on the interfacial adhesion between the phases, thus favoring the
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higher dimensional stability by the incorporation of nano filler to the kenaf/epoxy composites [36]. TMA graph clearly shows that the CTE of the kenaf/epoxy composites shows higher dimensional stability by the addition of OMMT nanoclay in contrast to nano OPEFB filler on
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temperature fluctuations. However, the CTE value for nano OPEFB/kenaf/epoxy is quite comparable with the MMT/kenaf/epoxy hybrid nanocomposites. Thus, the addition of nano
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OPEFB filler are quite effective in controlling thermal expansion behavior of the kenaf/epoxy composites, due to larger aspect ratio of nano OPEFB filler and enhanced interfacial bonding of kenaf fibers to the epoxy matrix. Comparable arguments were found in the literature for the high
Conclusion
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density polyethylene composites reinforced with hybrid inorganic fillers [37].
In this work an attempt were made to fabricate hybrid nanocomposites by incorporating nano
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fillers to the kenaf reinforced epoxy composites by hand lay-up technique. From the density measurements, it has been found that the addition of nano OPEFB, MMT and OMMT nanoclay,
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considerably improves the density of the kenaf/epoxy composites in each case. The density of nano OPEFB/kenaf/epoxy are quite similar to the MMT/kenaf/epoxy hybrid nanocomposites, however slight lesser with respect to OMMT/kenaf/epoxy hybrid nanocomposites. XRD analysis revealed the presence of characteristics peaks of nano OPEFB, MMT and OMMT fillers in their respective hybrid nanocomposites. TMA data also indicates that kenaf/epoxy hybrid nanocomposites display more thermal contraction and thermal expansions coefficient, compared
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to kenaf/epoxy composites due to higher heterogeneity and better interfacial bonding by the homogenous and uniform dispersion of incorporated nano filler in the kenaf fibers/epoxy composites. Addition of nano OPEFB filler quite effectively controlled the thermal expansion
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behavior of the kenaf/epoxy composites. Overall we can attributed that the developed nano OPEFB/kenaf/epoxy hybrid nanocomposites displayed improved density and thermomechanical (CTE) properties compared to kenaf/epoxy composites, without adding any additional coupling
are
comparable
to
MMT/kenaf/epoxy
but
comparatively
lesser
with
respect
to
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OMMT/kenaf/epoxy hybrid nanocomposites.
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agent and kenaf fibers treatment. The enhancements in properties of nano OPEFB/kenaf/epoxy
Utilization of nano OPEFB filler thus can generate promising and innovative platform with respect to existing expensive and environmentally high impact filler, to fabricate nanocomposites and hybrid nanocomposites. Developed nano OPEFB/hybrid nanocomposites will be a promising
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alternative to steel, iron metals, iron/cobalt and iron/copper/nickel alloys that are extensively been used in diverse structural applications, as they possess high degree of dimensional stability
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with temperature variations.
Acknowledgements
The authors thankful to the Universiti Putra Malaysia-Malaysia, for supporting this research study through Putra Grant Vot No. 9420700.
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Highlights Nano OPEFB/kenaf/epoxy hybrid nanocomposites were fabricated by hand lay-up
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Effect of nano OPEFB on density & structure of kenaf/epoxy were investigated
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Thermal expansion coefficients of kenaf/epoxy and hybrid nanocomposites evaluated
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Comparative studies were made with MMT and OMMT kenaf /epoxy hybrid
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•
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nanocomposites
S0254-0584(16)30689-7
DOI:
10.1016/j.matchemphys.2016.09.026
Reference:
MAC 19172
To appear in:
Materials Chemistry and Physics
Received Date: 14 June 2016 Revised Date:
24 August 2016
Accepted Date: 10 September 2016
Please cite this article as: N. Saba, M.T. Paridah, K. Abdan, N.A. Ibrahim, Physical, structural and thermomechanical properties of oil palm nano filler/kenaf/epoxy hybrid nanocomposites, Materials Chemistry and Physics (2016), doi: 10.1016/j.matchemphys.2016.09.026. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Physical, Structural and Thermomechanical properties of oil palm nano filler/kenaf/epoxy hybrid nanocomposites
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N.Saba1*, M.T. Paridah1, K. Abdan2, N. A. Ibrahim3
Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products
Department of Biological and Agricultural Engineering, Faculty of Engineering, Universiti Putra
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(INTROP), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
Malaysia, 43400 UPM Serdang, Selangor. Malaysia 3
Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang,
Abstract
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Selangor. Malaysia
The present research study deals with the fabrication of kenaf/epoxy hybrid nanocomposites by
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the incorporation of oil palm nano filler, montmorillonite (MMT) and organically modified montmorillonite (OMMT) at 3% loading, through hand lay-up technique. Effect of adding
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different nano fillers on the physical (density), structural [X-ray diffraction (XRD)] and thermomechanical analysis (TMA) of kenaf/epoxy composites were carried out. Density results revealed that the incorporation of nano filler in the kenaf/epoxy composites increases the density which in turn increases the hardness of the hybrid nanocomposites. XRD analysis confirmed the presence of nano fillers in the structure of their respective fabricated hybrid nanocomposites. All hybrid nanocomposites displayed lower coefficient of thermal expansion (CTE) with respect to kenaf/epoxy composites. Overall results predicted that the properties improvement in nano 1
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OPEFB/kenaf/epoxy was quite comparable to MMT/kenaf/epoxy but relatively lesser to OMMT/kenaf/epoxy hybrid nanocomposites and higher with respect to kenaf/epoxy composites.
fibers and epoxy matrix by addition of nano filler.
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The improvement ascribed due to improved interfacial bonding or cross linking between kenaf
Keywords: Oil palm nano filler; Kenaf fibers; Nanocomposites; Hybrid nanocomposites; X-ray
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Diffraction; Thermomechanical properties.
*Corresponding author: Naheed Saba, E-mail: [email protected], Tel.: +603-89466960;
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Fax: +603-86471896
Introduction
Thermosets including epoxy polymers undergo crystallization to form brittle and crystalline
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structure. This drawback can be minimized by the incorporation of natural fibers and nano filler. Kenaf fiber having properties allied to jute fiber and is one of the most abundant, renewable and biodegradable lignocellulosic fiber with low density (1.3 g/cm3) used for fabricating a wide
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variety of composites products, with variety of thermosets and thermoplastics polymers [1] [2].
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Fabrication of natural fibers reinforced hybrid polymer composite materials are currently receiving higher attention from both industries and scientists owing to perfect balance between performances and manufacturing cost [3]. Research study established that hybridization of natural fiber with synthetic or with other natural fiber can improve the physical, thermal and thermomechanical properties of natural fiber polymer composites. Nanocomposites represents the most attractive, potential, indispensable and encouraging approaches in the field of future advanced engineering applications tailored by adding nano scale filler in the polymer matrix to 2
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meet the growing demands of the specific properties, for versatile practical applications [4] [5]. Polymer nanocomposites exhibit better physical and mechanical properties than conventional composites based on a polymer with micro sized filler [6]. Moreover, nanoscience and
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nanotechnology have opened up a new way of developing hybrid nanocomposites, by replacing the synthetic fibers with nano fillers (nanoclay, nanotube, graphite, nano metal oxide etc.). The hybrid nanocomposites possess improved physical, structural, mechanical, thermal and
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thermomechanical properties with respect to natural fibers reinforced polymer composites [7]. Nanoclay (MMT, OMMT) based polymer composites are formed by insertion of the
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polymer chains between the clay layers [8]. Organoclays possess layered structure produced by treatment of bentonite and MMT clay minerals with organics by replacing exchangeable cations (Ca2+, Mg2+, K+, and Na+ ) by cationic surfactants of the form (CH3)NR or (CH3)2NR2 (R- alkyl or aromatic hydrocarbon). Organoclays displays varied applications due to their specific active
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sites and high aspect ratio which allows efficient load tolerance to the polymer matrices and thus provide better strength and stiffness to the nanocomposites [9]. Replacement of inorganic cations via cation exchange to form organoclays, by the alkyl cations such as quaternary ammonium hexadecytrimethylammonium
(HDTMA),
hexadecylpyridinium
(HDP),
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cations,
tetramethylammonium and trimethylphenylammonium (TMPA), have been extensively reviewed
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by the researchers [10]. X-ray diffraction is most common, versatile, non-destructive technique that provides detailed information about crystallographic structure including polymer crystallinity, phase identification and quantification for all crystalline, semi-crystalline or amorphous polymers and polymer composites. XRD is the only technique to investigate the intercalation and exfoliation behavior of the nanoclay based nanocomposites by estimating the distance between the silicate platelets [11]. Infrared (IR) spectroscopy, especially FTIR is the
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most reliable and cost effective analytical tool for identification of polymers and assessment of the quality of composite materials, by providing distinctive “fingerprint” characteristics of the composite materials [12] [13]. TMA is one of the most sensitive and effective technique used to
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determine the dimensional changes as function of temperature or time under investigation. On heating or cooling most of the composite materials undergoes thermomechanical and dimensional changes, thus its quite essential to analyze their coefficient of linear thermal
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expansion (CTE) [14] through TMA analysis with temperature fluctuations, prior to use in high
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end applications. The CTE is defined as α, and calculated by the (Eq.1) [15]
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Where L is the sample length and ∆ T is the temperature range
CTE is the materials property as it indicates the extent to which a material expands upon heating. Higher the CTE value lower is its dimensional stability with temperature, and lower its CTE
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value higher its dimensional stability with temperature. Several research studies were reported on the hybridization of kenaf fibers with natural/synthetic
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fibers/nano filler in the literature. Some of the exclusive findings on hybridization of kenaf fibers were tabulated in Table 1.
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Table 1. Reported study on the hybridization of kenaf fibers with synthetic fibers/natural fibers/ nano filler by researchers
Kenaf/Coir fibers/MMT
Polymer Matrix Epoxy
Kenaf/Jute fibers/E-glass
Epoxy
Kenaf fibers/Wood flour/Rice hulls/Newsprint fibres Kenaf/Hemp/Flax/Glass fibers
PP PP
[19]
Kenaf fibers/MMT
Epoxy
[20]
Kenaf fibers/Pultruded jute Kenaf/Hemp fibers Kenaf/Short carbon fibers Kenaf/Glass fibers/CNTs
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References
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Reinforcements
[16]
[17]
[18]
UP
[21]
CNSL
[22]
NR
[23]
Epoxy
[24]
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Note: Cashew nut shell liquid matrix (CNSL), Polypropylene (PP), Unsaturated polyester (UP), Natural rubber (NR), Carbon nanotubes (CNTs)
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From the literature review it is evident that no study has been conducted on the hybridization of kenaf fibers reinforced epoxy composites with oil palm nano filler. Present study is the extension
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of our previous research work, involving the preparation of oil palm nano filler from wastes oil palm empty fruit bunch (OPEFB) fibers, through combined effects of cryogenizer and high energy ball milling (HEBM) technique [25]. In this study, an effort has been made to fabricate kenaf/epoxy, nano OPEFB/kenaf/epoxy, MMT/kenaf/epoxy and OMMT/kenaf/epoxy hybrid nanocomposites having 40% kenaf fibers loading in each case, by hand lay-up technique. Effect of adding oil palm nano filler to the kenaf/epoxy composites on physical, structural and thermomechanical properties were investigated through density measurements, X-ray diffraction 5
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and CTE analysis and are compared with kenaf/epoxy composites. Comparative studies were also made with MMT/kenaf/epoxy and OMMT/kenaf/epoxy hybrid nanocomposites, in order to provide open a new platform by using green nano filler in polymer nanocomposites industries
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from wastes fibers of Malaysia.
Experimental
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Materials
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The OPEFB fiber was obtained from MPOB, Bangi-Selangor, Malaysia. The kenaf non-woven mat was obtained from Innovative Pultrusion Sdn, Bhd, Malaysia. Montmorillonite (MMT) and organically modified montmorillonite (OMMT) nanoclay were procured from Zarm scientific & Supplies Sdn., Bhd, Malaysia. MMT is a hydrated sodium calcium aluminium magnesium silicate hydroxide powder, having surface area of 250m2/g with the pH 3-4. OMMT were the
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nanoclay Nanomer® I.31PS, contains 0.5-5 wt. % aminopropyltriethoxysilane, 15-35 wt. % octadecylamine with mean mesh size of 15-25µm and having bulk density 200-500 kg/m3. The epoxy resin D.E.R 331, is a clear liquid resin based on diglycidyl ether of bisphenol A (DGEBA),
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obtained from Dow Chemical Pacific Singapore, Singapore. The curing agent, epoxy hardener
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Jointmine 905-3S, is a clear and transparent color liquid, supplied by Epochemie International Pte Ltd. Singapore. Silicone spray and Teflon sheets were procured from Dow Chemical Pacific Singapore, Singapore and NR Medicare Sdn. Bhd., Selangor, Malaysia, respectively. purchased chemicals were used without any further purification.
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Fabrication of composites Procedure for the fabrication of composites were same as discussed in our previous research
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work [26][27]. Two pre-pressed kenaf non-woven mats were used in the fabrication of both kenaf/epoxy composites and different filler filled kenaf/epoxy hybrid nanocomposites through high speed mechanical stirrer followed by hand lay-up technique. Fabrication procedures for
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kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites are illustrated in
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Figure 1.
Figure 1. Fabrication procedure of kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites
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Non-woven kenaf mat roll, compressed kenaf mat, steel mold, fabricated kenaf/epoxy composites, nano OPEFB/kenaf/epoxy, MMT/kenaf/epoxy and OMMT/kenaf/epoxy hybrid
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nanocomposites are displayed in Figure 2.
Figure 2. (a) Kenaf non-woven mat roll (b) compressed kenaf mat (c) steel mold (d) kenaf/epoxy composites (e) nano OPEFB/kenaf/epoxy (f) MMT/kenaf/epoxy and (g) OMMT/kenaf/epoxy hybrid nanocomposites
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Characterization Density Density is the mass per unit volume of composite samples, calculated by using ASTM D792
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standard. Mass determination was carried out by weighing the 8 replicate hybrid nanocomposites with analytical balance (Shimadzu, Japan EPA-151-WT-12) and the volume were calculated by using digimatic micrometer Mitutoyo (Figure 3). Prior to mass and volume measurement the
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samples are oven dried at 50 o C for 24 h, and then allowed to cool in desiccators.
Figure 3. Density samples of (a) kenaf/epoxy (b) nano OPEFB/kenaf/epoxy (c) analytical
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balance and (d) digimatic micrometer Mitutoyo
X-ray diffraction (XRD)
The identification of the crystallographic structure of different nano fillers (nano OPEFB, MMT, OMMT), kenaf/epoxy composites and filler filled/kenaf/epoxy hybrid nanocomposites was achieved by powdered X-ray diffractometer (X’ Pert, Siemens XRD D5000) equipped with
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computerized data collection and analytical tools having copper anode X-ray tube. The XRD analyses of nano fillers and hybrid nanocomposite samples were conducted with Cu Kα radiation of 1.5406 Å, operating at 30kV and current 20.0 (mA). Samples were first gently consolidated in
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an aluminum holder and X-ray diffractogram of samples were analyzed using X’Pert High Score software recorded at an angular incidence of 2θ=10° to 40°, at scan rate of 2°/min. XRD
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diffractometer and XRD samples are displayed in Figure 4.
Figure 4. (a) XRD-Siemens D5000 (b) XRD samples of nano fillers and (c) filler filled kenaf/epoxy hybrid nanocomposites
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Thermomechanical analysis (TMA) TMA employs a sensitive probe in contact with the surface of composites sample. As the sample
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heated, the probe senses change in dimension. TMA was made according to ASTM D696 to investigate CTE of composites through TA Instrument Q400 under nitrogen. The samples were in dimension of 6 × 6 × 4 mm3 and the temperature was ramped from room temperature to 200°C
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at a heating rate 5°C/min. The dimensional change was then measured in the thickness direction to calculate the CTE of composites. The two replicate TMA specimens of each composites
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sample and TMA instrument are shown in Figure 5.
Figure 5. TMA samples of kenaf/epoxy, filler filled kenaf/epoxy hybrid nanocomposites and
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TMA instrument
Results and discussion Density of composites
Density of kenaf/epoxy composites and nano OPEFB/kenaf/epoxy, MMT/kenaf/epoxy and OMMT/kenaf/epoxy hybrid nanocomposites are displayed in Figure 6. From the density graph it
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is evident that density of kenaf/epoxy composites are 1.32 g/cm3, which are quite close to the density reported in the literature for the chopped 40% kenaf fibers/epoxy composites [28]. It is clearly evident from density graph that the incorporation of nano fillers (nano OPEFB, MMT,
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OMMT) considerably increase the density of kenaf/epoxy matrix, and it lies in the range of 1.375–1.42 g/cm3. The increase in density can be ascribed of relatively denser and harder phase of incorporated nano fillers as compared to kenaf/epoxy composites. Interestingly, the nano
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OPEFB/kenaf/epoxy and MMT/kenaf/epoxy displayed relatively similar density improvement. However the higher density improvements are observed in the case of OMMT/kenaf/epoxy
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hybrid nanocomposites among all composites, owing to denser OMMT nanoclay particles.
1.42 1.4
1.34 1.32 1.3 1.28
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1.26
Density (g/cm3)
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Figure 6. Effect of loading different nano fillers on the density of kenaf/epoxy composites
The improvement in density of kenaf/epoxy composites can also be explained on account of increase in the cross linking density of epoxy chains and interfacial bonding which ultimately 12
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improves the hardness of the resulting hybrid nanocomposites, by the incorporation of nano fillers.
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X-ray diffraction (XRD)
X-ray diffraction was carried out to explore the characteristics diffraction peak of nano fillers (nano OPEFB, MMT, OMMT), kenaf/epoxy composites and filler filled kenaf/epoxy hybrid
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nanocomposites. The X-ray diffractogram of all nano fillers are displayed in Figure 7. Figure 8 illustrates the X-ray diffractogram of kenaf/epoxy composites and filler filled kenaf/epoxy hybrid
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nanocomposites.
The characteristics peak of OMMT are well observed at 2θ=19o and 23o in the Figure 7. The obtained diffractogram of OMMT nanoclay also correspond to the reported literature [29] [30]. The XRD measurements showed that 2θ had been shifted from the high angle to the low angle as
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compared with MMT to afford OMMT due to ion exchange process [31]. The presence of small reflections at 2θ=20o and 35o, and sharp reflection at 2θ=25o corresponds to characteristics peaks of MMT nanoclay [32] [13]. The two characteristics pointed peak of nano OPEFB at 2θ=25o and
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near 20o are already discussed in our previous reported study [25]. X-ray diffraction measurements shown in Figure 8, characterize the morphological structure of
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kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites. From the XRD diffractogram of MMT/kenaf/epoxy and OMMT/kenaf/epoxy hybrid nanocomposites, it is evident that no reflections are observed at low angle region (2θ=0.4–10°), indicating the formation of exfoliated nanocomposites, having interlayering space larger than that of the intercalated structure.
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Figure 7. XRD graph of incorporated nano fillers (nano OPEFB, MMT, OMMT)
Figure 8. XRD-graph of kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites 14
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The diffractogram of nano OPEFB/kenaf/epoxy hybrid nanocomposites also does not display any sharp peaks below 2θ=10o, indicating homogenous dispersion in the kenaf/epoxy
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composites. From XRD results, it could be concluded that the inter-gallery spacing of OMMT facilitates the entry of epoxy matrix molecules to enter into the galleries, as the hydrophilic clay surface changed to an organophilic surface. The statement was also in line with other reported
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literature [33]. Moreover, the characteristics peak of OMMT, are also observed near 2θ=22.5o in the OMMT/kenaf/epoxy hybrid nanocomposites. Remarkably, the intense peak at 2θ=29.3o, was
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observed for both kenaf/epoxy composites and filler filled hybrid nanocomposites in the diffractogram, signifying the presence of kenaf fibers moieties in all of them [34].
Thermomechanical analysis (TMA)
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Thermomechanical analysis of kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites were carried out to evaluate the dimensional changes or CTE, in both rubber and glassy regions as a function of temperature under a nitrogen atmosphere, are displayed in Figure
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9. The thermal expansion coefficients showed progressive diminution by adding nano filler to the kenaf/epoxy composites displaying minimal expansion of kenaf fibers in the epoxy matrix. From
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Figure 9, it is evident that each of the hybrid nanocomposites and kenaf/epoxy composites shows both contraction and expansion in dimensions with change in temperature. Marked small contraction below 100oC corresponds to the some moisture loss from kenaf fibers in all the cases. Kenaf/epoxy composites display only one contraction and one thermal expansions coefficient whereas nano OPEFB/kenaf/epoxy displayed two contractions and two thermal expansions coefficient. MMT/kenaf/epoxy displayed three contractions and two thermal expansions coefficient, whereas more than two contractions and two thermal expansions coefficient are 15
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observed for OMMT/kenaf/epoxy hybrid nanocomposites. Thus it clearly evident from TMA graph that heterogeneity are more pronounced in all filler filled/kenaf/epoxy hybrid nanocomposites with respect to kenaf/epoxy composites. Similar arguments are also reported in
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literature for the TMA of palm fiber and its ABS composites [35]. The cole-cole shapes also governed the obtained TMA graph [27]. TMA graph also revealed that CTE of all hybrid nanocomposites in the glassy and rubbery region, presented lower thermal dilatations than
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kenaf/epoxy composites. This revealed that a synergy between reinforced kenaf fibers and epoxy
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fillers (nano OPEFB, MMT, OMMT).
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matrix on the CTE of the hybrid nanocomposites get improved by the incorporation of nano
Figure 9. TMA graph of kenaf/epoxy composites and filler filled kenaf/epoxy hybrid nanocomposites
Moreover, the decrease in CTE value also corresponds to the decreased polymeric segmental motion in the free space by the addition of nano filler along with improved interfacial adhesion
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between kenaf fibers and the epoxy matrix governing better thermal and mechanical properties. Researchers reviewed that thermal expansion also involves the transmission of stress across an interface reflecting an evidence on the interfacial adhesion between the phases, thus favoring the
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higher dimensional stability by the incorporation of nano filler to the kenaf/epoxy composites [36]. TMA graph clearly shows that the CTE of the kenaf/epoxy composites shows higher dimensional stability by the addition of OMMT nanoclay in contrast to nano OPEFB filler on
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temperature fluctuations. However, the CTE value for nano OPEFB/kenaf/epoxy is quite comparable with the MMT/kenaf/epoxy hybrid nanocomposites. Thus, the addition of nano
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OPEFB filler are quite effective in controlling thermal expansion behavior of the kenaf/epoxy composites, due to larger aspect ratio of nano OPEFB filler and enhanced interfacial bonding of kenaf fibers to the epoxy matrix. Comparable arguments were found in the literature for the high
Conclusion
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density polyethylene composites reinforced with hybrid inorganic fillers [37].
In this work an attempt were made to fabricate hybrid nanocomposites by incorporating nano
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fillers to the kenaf reinforced epoxy composites by hand lay-up technique. From the density measurements, it has been found that the addition of nano OPEFB, MMT and OMMT nanoclay,
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considerably improves the density of the kenaf/epoxy composites in each case. The density of nano OPEFB/kenaf/epoxy are quite similar to the MMT/kenaf/epoxy hybrid nanocomposites, however slight lesser with respect to OMMT/kenaf/epoxy hybrid nanocomposites. XRD analysis revealed the presence of characteristics peaks of nano OPEFB, MMT and OMMT fillers in their respective hybrid nanocomposites. TMA data also indicates that kenaf/epoxy hybrid nanocomposites display more thermal contraction and thermal expansions coefficient, compared
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to kenaf/epoxy composites due to higher heterogeneity and better interfacial bonding by the homogenous and uniform dispersion of incorporated nano filler in the kenaf fibers/epoxy composites. Addition of nano OPEFB filler quite effectively controlled the thermal expansion
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behavior of the kenaf/epoxy composites. Overall we can attributed that the developed nano OPEFB/kenaf/epoxy hybrid nanocomposites displayed improved density and thermomechanical (CTE) properties compared to kenaf/epoxy composites, without adding any additional coupling
are
comparable
to
MMT/kenaf/epoxy
but
comparatively
lesser
with
respect
to
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OMMT/kenaf/epoxy hybrid nanocomposites.
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agent and kenaf fibers treatment. The enhancements in properties of nano OPEFB/kenaf/epoxy
Utilization of nano OPEFB filler thus can generate promising and innovative platform with respect to existing expensive and environmentally high impact filler, to fabricate nanocomposites and hybrid nanocomposites. Developed nano OPEFB/hybrid nanocomposites will be a promising
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alternative to steel, iron metals, iron/cobalt and iron/copper/nickel alloys that are extensively been used in diverse structural applications, as they possess high degree of dimensional stability
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with temperature variations.
Acknowledgements
The authors thankful to the Universiti Putra Malaysia-Malaysia, for supporting this research study through Putra Grant Vot No. 9420700.
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Highlights Nano OPEFB/kenaf/epoxy hybrid nanocomposites were fabricated by hand lay-up
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Effect of nano OPEFB on density & structure of kenaf/epoxy were investigated
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Thermal expansion coefficients of kenaf/epoxy and hybrid nanocomposites evaluated
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Comparative studies were made with MMT and OMMT kenaf /epoxy hybrid
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nanocomposites