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Evaluation of mechanical and free vibration properties of the pineapple leaf fibre reinforced polyester composites
Construction and Building Materials 195 (2019) 423–431
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Evaluation of mechanical and free vibration properties of the pineapple leaf fibre reinforced polyester composites K. Senthilkumar a, N. Saba b, M. Chandrasekar c, M. Jawaid b,d,⇑, N. Rajini a, Othman Y. Alothman d, Suchart Siengchin e a
Centre for Composite Materials, Department of Mechanical Engineering, Kalasalingam Academy of Research and Education, 626126, India Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products, INTROP, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Department of Aerospace Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia d Department of Chemical Engineering, College of Engineering, King Saud University, Riyadh, Saudi Arabia e Department of Mechanical and Process Engineering, The Sirindhorn International ThaiGerman Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok 10800, Thailand b c
h i g h l i g h t s Development of sustainable eco-friendly composites by cost effective process. Mechanical performance of PALF/Polyester composite on the influence of fibre loading. SEM analysis showed improved stress transfer through better interfacial adhesion. Improved natural frequency and decrease in damping ratio were found for increasing fibre loading. Suitability of optimal composite for structural members in construction industry.
a r t i c l e
i n f o
Article history: Received 20 April 2018 Received in revised form 19 August 2018 Accepted 10 November 2018
Keywords: Pineapple leaf fibre Polyester Mechanical properties Compressive strength Damping factor Free vibration
a b s t r a c t Pineapple Leaf Fibre (PALF) Reinforced Polyester (PE) composites were fabricated by hand lay-up using randomly oriented PALF in PE matrix, compressed at 17 MPa by compression moulding. Effect of PALF loading in PE composites on mechanical, morphological, free vibrational and damping properties were investigated. Result analysis revealed that the tensile, compressive strength and flexural properties considerably increased with increasing PALF loading according to the rule of mixtures. Moreover, SEM images of tensile fracture samples shows relatively less fibre pull-out, fibre breakage and improved fibre/matrix adhesion due to effective stress transfer with the increased PALF loading in PE composites. Natural frequency improved while damping ratio decreased as a result of increasing the PALF loading in PALF/PE composites. Finally, a composite with 45 wt% PALF loading is found as suitable replacement for structural component in construction industries. Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction Over recent decades, reinforcement of natural fibres to produce bio-based composites for various applications has attracted great interest to overcome the continuous increasing price of petroleum and growing environmental impact due to usage of synthetic fibre reinforced polymer composites [1,2]. Many parts of plants and fruits could be a viable source of raw fibre materials for industrial use [3,4]. Nevertheless, many of the plants and fruits are being ⇑ Corresponding author at: Biocomposite Technology Laboratory, INTROP, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. E-mail addresses: [email protected], [email protected] (M. Jawaid). https://doi.org/10.1016/j.conbuildmat.2018.11.081 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.
wasted as in the absence of beneficial harvest due to lack of knowledge relating to their economic uses [5]. Besides, the various natural fibres like kenaf, hemp, flax, jute, banana and sisal, pineapple leaf fibres (PALF) currently receiving higher attention as a green reinforcement (a composite made up using natural fibre is called as green reinforcement). PALF also exhibit good mechanical properties and are environmental friendly due to their biodegradability. Research study states that it is a potential material to substitute synthetic fibre in fibre reinforced polymer composites for many structural and non-structural applications in the coming future [6]. PALF is cultivated largely in tropical countries and each plant has around 25–30 leaves that grow upto 90–150 cm in length
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and 2 cm and 5 cm in width. The PALF can be extracted either by (i) water retting and scrapping or (ii) microbial retting process. The microbial retting process was found to be more effective in producing fibres with good appearance, good strength with essential chemical composition. PALF has 70–82% of cellulose, 5–12% of lignin and 1.1% of ash [3]. Extracted fibres could be used for producing woven knitted, woven fabrics and non-woven mats. PALF applications also extended in pharmaceuticals and for animal feeds. Arib et al. [7] reported that the PALF has a higher content of cellulose and exhibited better mechanical properties with respect to other natural fibres. In other study PALF reinforced in PALF/phenolic polymer composites possess considerable tendency to transfer load effectively from the matrix to fibre, thereby resulting in improved mechanical properties [8]. Various thermoset resins like epoxy [9–11], vinyl ester [12], bisphenol [13], polyester (PE) [5,14–16], etc. have been reinforced with PALF and their mechanical properties were studied with respect to fibre orientation (continuous or discontinuous), alignments and fibres loadings. In general, introduction of PALF into the matrix improves the mechanical properties of the composites. Some of research findings where PALF are reinforced in PE and their tensile, flexural and impact properties have been investigated are shown in Table 1. Dynamic properties play a significant role in the field of construction industries, automotive components, machine supports and machine component design [17]. In the machine component design process a reduction of resonant amplitude is an important task. A modal damping accompanying with each mode of the structure has an influence on the resonant amplitude. Usually, metal matrix composites possess lesser damping than the natural fibre reinforced composites (NFRCs) [18], because the molecular mobility can be freely takes place in the case of NFRCs due to the viscoelastic nature and interfacial debonding between the fibrematrix. However, free vibration characteristics of polymer composites are rarely found or are merely absent. Natural fibres like sisal, banana, coconut sheath and jute have been used either as individual fibres or along with other natural fibres in hybrid configuration reinforced in polyester resin and their free vibration characteristics have been studied by some researchers, as shown in Table 2. From the Tables 1 and 2 it is evident that no work has been reported in literature where dynamic characteristics (natural frequency and damping) and compression properties of PALF/PE were made using the free vibration method as per the author’s knowledge. The compression and free vibration properties of PALF/PE require in depth study for understanding the behaviour of compos-
ites under applied loads in order to use it for the advance structural applications. Thus the topic of interest to this study is to reveal the influence of randomly oriented PALF loading on the tensile, flexural, compressive, free vibration, damping and morphological properties of PE composites, under varying fibre 25%, 35% and 45% loading. Further, SEM analysis of the tensile, compressive and flexural fractured specimens was observed to investigate the failure behaviour due to increase in fibre loading. 2. Experimental procedure 2.1. Materials PALF, unsaturated isophthalic polyester resin with a curing agent methyl ethyl ketone peroxide-MEKP and catalyst cobalt naphthenate used in this study were procured from India. Properties of PALF and PE resins used in this study are listed in Table 3. 2.2. Mould details and fabrication of composites Composites were fabricated by hand lay-up technique using the compression moulding process. For fabricating the composites, split type moulds made from EN90 steel were used in this work, having total three parts namely, the flat surface bottom plate, middle plate with rectangular cavity and the top mould, as depicted in Fig. 1. The various steps involved in the fabrication of composites by hand lay-up are depicted in Fig. 2. Moulds were cleaned and then polished by wax. Washed and dried PALF of 3 mm length was randomly arranged in the mould at different 25, 35 and 45% loading by weight. The resin (with 1.5 wt% of initiator) was poured onto the fibres, and the mould was closed followed by compression at 17 MPa. The setup was left undisturbed for 24 h at room temperature to allow the resin to cure. 3. Characterization 3.1. Tensile testing Fabricated PALF/PE and pure PE composites of dimensions of 120 mm 20 mm 3 mm were subjected to tensile tests according to ASTM D3039 standard, having the crosshead speed 5 mm/ min and gauge length of 50 mm. From the experimentation, the tensile properties such as strength, modulus and percentage of
Table 1 Reported studies on mechanical properties of the PALF/PE composites. Material
Observation
References
PALF/PE
Maximum tensile, flexural and impact strength observed until 30% fibre loading but drops on increasing fibre content to 40% in polymer composites Tensile strength and modulus of PALF/PE composites increased by increasing the PALF content from 0% to 30% Specific flexural stiffness improved for 2.3 times at 30 wt% of fibre content.
[5] [14] [16]
Table 2 Free vibration properties of natural fibre reinforced polymer composites. Polymer Composites
Observation
References
Sisal/PE Banana/PE Coconut sheath/PE Banana/PE Additive: Red-mud Banana/Sisal/PE Sisal/Coconut-sheath PE Banana/Jute/PE
Damping improved with the increase in fibre loading in the composite Free vibration properties improved with the addition of 3% Montmorillonite (MMT) nanoclay Lowering the particle size of red-mud, the free vibration properties increased in the composites Increase in the fibre loading, increases the natural frequency while a decrease in damping of composites is observed Natural frequencies were higher in treated hybrid composites than in the untreated ones Natural frequency increased with the addition of nanoclay until 2 wt% while damping improved with the addition of nanoclay >2 wt% Damping of Coconut sheath/PE > Banana/PE
[19] [20] [21] [22] [23] [24]
Banana/PE Coconut sheath/PE
[25]
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K. Senthilkumar et al. / Construction and Building Materials 195 (2019) 423–431 Table 3 Mechanical and physical properties of PALF and PE resin [4]. Fibre/Matrix
Density (g/cm3)
Tensile Strength (MPa)
Elongation at break (%)
Tensile modulus (MPa)
Specific strength (MPa)
Specific Modulus (MPa)
PALF PE resin
1.526 1.159
170 22.9
3 1.6
6210 580
110 19.7
4070 502
Fig. 1. Flat surface bottom plate, Middle plate, Top mould and (b) Composed mould.
Fig. 2. Fabrication steps of PALF/PE composites.
elongation were found for varying fibre loading. In ease case, the average value of 5 specimens was reported for tensile strength and tensile modulus. 3.2. Compressive testing Fabricated composites of dimensions of 60 mm 20 mm 3 mm were subjected to compressive tests as per the ASTM D3410 standard. The gauge length was set to 30 mm and a cross head speed of 1.27 mm/min was maintained throughout the tests. Compressive stress vs strain and compressive strength were recorded for all tested specimens. An average of 5 specimens was used in compressive testing. 3.3. Flexural testing Influence of PALF loading on the flexural properties of the PE composite was investigated. Flexural tests were conducted on 5 replicate specimens of pure PE and PALF/PE composites having the dimensions of 120 mm 20 mm 3 mm according to the ASTM D790 standard. The crosshead speed and gauge length was set to 1.27 mm/min and 50 mm respectively and the average values were reported.
Fig. 3. Schematic diagram of free vibration experimental setup.
produced higher frequencies were used [20]. A sharp hardened impact hammer was used for exciting the fabricated composite, while the displacement signals were acquired by an accelerometer joined at the end of the composite by wax and recorded using a data acquisition system. Two separate adaptors were used for capturing the output signal. One was attached to the impact hammer, and the other was fixed at the free end of the laminate composite. 3.5. Morphological analysis
3.4. Free vibration modal analysis Free vibration characteristics of the fabricated PALF/PE composites were studied using the Kistler model 9722A500, shown in Fig. 3. The sample dimensions of 200 mm 20 mm 3 mm which
The microstructure, morphology and failure behavior of the tensile fractured specimens of PALF/PE composites were carried out through SEM followed by micrographs with SEM 230 (USA) field emission instrument.
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4. Results and discussion
Table 4 Tensile properties of PALF/PE composites with varying PALF loading.
4.1. Tensile properties
PALF loading (wt%)
Tensile Strength (MPa)
Tensile Modulus (GPa)
Elongation at break (%)
The effect of fibre loading on the tensile stress as a function of tensile strain (%) for PALF/PE is shown in this Fig. 4a. It is evident from Figure that the elongation at break increased with the PALF loading indicating an increase in ductility of the PALF/PE composites compared to the pure PE (1.6%). Quite similar results are observed by Devi et al on PALF/PE composites [4]. The effect of PALF loading on tensile strength and modulus of PE composites are shown in Fig. 4b and in Table 4. It is evident that an increase in PALF loading led to an increase in tensile modulus. Highest tensile modulus was observed for 45 wt% fibre loading in the PALF/PE which was 25% higher compared to 25 wt% fibre loading. Moreover, the tensile strength of PALF/PE composites followed the same increasing trend as that of tensile modulus. At 45 wt% PALF loading, the tensile strength (33.13 MPa) of the composites was 7.4% and 23% higher than the 25 wt% and 35 wt% respectively. PALF contained richer cellulose (70–82%) compared to the other natural fibres [3] and as per Idicula et al. [26], the cellulose content of PALF was dependent on the tensile modulus and tensile strength. It is believed to be the reason for superior tensile modulus and tensile strengths at higher fibre loading (45 wt%) in the PE composites.
25 35 45
25.49 27.53 33.13
1.161 1.4 1.553
4.03 4.06 4.11
4.2. Compressive properties The compressive stress vs strain for different PALF loading of the PE composite are shown in Fig. 5a and the effect of fibre loading on the compressive strength is displayed in Fig. 5b. From Fig. 5a, it is evident that the stiffness increased with the addition of fibre wt% into the composite. The dependency of composite stiffness on the fibre reinforcement has been reported by many researchers [27,28]. Fig. 5b shows that the % improvement in compressive strength for the composites was approximately 16% and 41% respectively with the increase in PALF loading from 25% to 35% and 45% respectively. Increase of compressive strength with the addition of fibre weight upto 30% in the natural fibre reinforced composites has been reported in literature by researchers on Grewia-optiva/phe nol-formaldehyde composite [29], saccaharum cilliare/resorcinolformaldehyde composite [30] and agave/epoxy composite [31]. The improved compressive strength for the composites with the high fibre loading could be due to the enhanced interfacial adhe-
Fig. 5a. Compressive stress vs strain of PALF/PE.
sion between the chopped PALF and PE matrix. In another study the dependence of the compressive strength of the chopped fibre reinforced composite has been reported to be influenced by the interfacial adhesion between the fibre and matrix, fibre length (3 mm fibre length showed better compressive properties) and fibre loading [31]. Figure 8(a–c) shows the SEM images of the fractured PALF/PE specimens at different fibre loadings from the compression test. Generally, the kinking behaviour of material failure due to the compression load can be easily observed in the case of aligned composites using long fibers. But, it is not easy in the case of randomly oriented composites. However, the kinking behaviour was expected to happen in the subsurface of the laminates. In this study, SEM micrograph of compressed specimens showed only
Fig. 4. Effect of fibre loading on a) Tensile stress vs strain % and b) Tensile strength and modulus of PALF/PE.
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Fig. 6b. Flexural strength and modulus of PALF/PE.
Fig. 5b. Compressive strength vs PALF loading of PALF/PE.
the appearance of crushed fibres and fibre fraying on the top surface of randomly oriented composites which could have masked the dislocation of fibre band due to the kinking effect at the subsurface. However, the extent of kinking was lower as the fibre wt% increased in the composites. This could be the result of the high compressive strength arising from an increase in fibre wt% that resists kinking of the composites. Literature also explains that the composites kinking properties under compressive load are due to micro-buckling of the fibre [28]. 4.3. Flexural properties The flexural stress-strain for the PALF/PE composites as a function of fibre loading is shown in Fig. 6a and the effect of PALF loading on flexural properties are displayed in Fig. 6b. A considerable
Table 5 Flexural properties of PALF/PE composites with varying PALF loading. PALF loading (wt%)
Flexural Strength (MPa)
Flexural Modulus (GPa)
25 35 45
39.86 82.97 75.92
1.926 4.05 6.379
difference in flexural behaviour was observed by varying PALF loading in the pure PE. The magnitude of flexural strength is mainly depends upon the fibre wt-% for the constant fibre length. Due to the application of flexural loading, the inner layer of laminate subjected to bending effect and outer layer will be subjected to tensile behaviour. The addition of lower wt% fibre loading in composite can allow the fibres to take up both compression and shear which leads to the increase in magnitude of flexural strength. On the other hand, the addition of fibre content beyond a limit can reduce the possibility of shearing action which is the main factor for deciding the outer layer and in turn reduce the flexural strength. In general, the flexural failure or rupture of composites under investigation is due to bending stress (combination of tensile and compressive stresses) or shear stress. The flexural strength and modulus of PALF/PE composites at different PALF loading are tabulated in Table 5 and also displayed in Fig. 6b. Flexural strength increases by 108% following an increase in the fibre loading from 25 wt% to 35 wt% while the flexural strength decreases by 8.5% further by increasing the fibre loading to 45 wt %. The reduction of flexural strength at 45% PALF loading could be due to non-uniform applied stress transfer between the fibre and matrix due to higher inter-fibre interaction within the matrix and poor fibre dispersion. The dependency of flexural strength on fibre loading have also been reported for PALF/PE [5], PALF/ polypropylene [7] and PALF/epoxy [10]. The % improvement in flexural modulus for the composites was approximately 52% and 70% respectively with the increase in fibre weight from 25% and 35% to 45% respectively. Similar improvements in flexural modulus with the increasing sisal fibre loading in the case of sisal fibre/PE [32] and PALF in PALF/PE composites are reported [33]. 4.4. Morphological analysis
Fig. 6a. Flexural stress vs flexural strain of PALF/PE.
Tensile fractured specimens were exposed to SEM to investigate failure modes and to realise the physical bonding between PALF
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and PE and to interpret the observed tensile strength in each composite at different PALF loading. SEM images of fractured tensile tested specimens are shown in Fig. 7(a–f) at different fibre loading. Increased fibre distribution with respect to the increasing fibre loading could be clearly observed in Fig. 7(a, c and e). PALF/PE composites having 25 wt% PALF loading displayed highest fibre pull out and matrix cracking (Fig. 7a,b). In general the mechanical properties of the composites depend on individual fibre wt%- and matrix and fibre/matrix interfacial adhesion [34]. Less fibre pull out and enhanced bonding/ adhesion at the fibre/matrix with the increased fibre loading could be seen in Fig. 7(c–f). Thus, the increase fibre content in the composite helped to distribute the load effectively within the matrix, thereby leading to improved tensile strengths/modulus in the PALF/PE composites compared to pure PE. Fig. 9(a–c) shows the SEM images of the fractured samples from the flexural test. Less fibre pull out and enhanced fibre/matrix adhesion was observed with the increase in fibre loading identical
to the tensile failure images. Although the strength of 25 wt% composite is low, the improved interfacial bonding between fibre and matrix can be clearly seen in Fig. 9a. On the other hand, bending and the poor dispersion of short fibers shown in Fig. 9b, normally do not allow the proper load transfer. Fig. 9c shows the larger contact between the fibres due to the reduction of matrix which can resist the shearing action between the fibres and it leads to the slight decrease in flexural strength. 4.5. Free vibration properties The dynamic characteristics of a structure like natural frequency, damping and mode shapes play a significant role [35] especially in aerospace and automobile vehicles where many vibration inputs are present that could lead to resonance in these stated structures. The stiffness and damping characteristics of anisotropic polymer composites used in these applications are significantly influenced by the vibration in the structure. Accordingly for
Fig. 7(a,b). SEM tensile fractured samples of 25 wt% of PALF/PE composites.
Fig. 7(c,d). SEM tensile fractured samples 35 wt% of PALF/PE composites.
Fig. 7(e,f). SEM tensile fractured samples of 45 wt% of PALF/PE composites.
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Fig. 8. (a–c) SEM micrograph of compression fractured samples of 25, 35 and 45 wt% of PALF/PE.
Fig. 9. (a-c) SEM images of flexural fractured samples with different failure mechanisms for 25, 35 and 45 wt% composites.
each mode of vibration, a unique damping value could be obtained [36]. Moreover, the natural frequency of composites depend upon many factors namely fibre length, fibre loading, fibre orientation, fibre-matrix bonding, moment of inertia, tensile modulus, density and chemical treatment. In this study, the natural frequency and damping has been calculated by using the impact hammer technique. For this technique, a piezoelectric impact hammer was used to apply a constant force at the free end of the PALF/PE composite specimen (Fig. 3). From output response the measurements and ratio of input is obtained by using excitation force
dissipation in composite structures occurs due to matrix, interphase, broken fibres and matrix crack. Interestingly, damping mechanism of polymer composites are quite different when compared to conventional materials. Damping can be calculated by using the half-power bandwidth method [36] or graphical or mathematical approaches [35]. In the present study damping has been calculated using the half-power band width method and has been calculated based on Eq. (1) [37].
a Fast Fourier Transform (FFT) analyser. This stated ratio may be termed the Frequency Response Function (FRF). A typical curve of FRF obtained for 45 wt% PALF/PE is shown in Fig. 10. Three peaks named as Mode 1 (bending), Mode 2 (twisting) and Mode 3 (secondary bending) also termed as the mode shape are observed. Generally, energy dissipation occurs whenever the structures are subjected to damping due to the vibratory motion. The energy
where: f–Damping factor,
f ¼ Dx=2xn
ð1Þ
Dx – Bandwidth, and xn –Natural frequency of composite sample. Fig. 11 presents the first mode of natural frequency and damping of PALF/PE composites at different fibre loadings. From the plot
Fig. 10. A typical curve of frequency response function of 45 wt% PALF/PE composites.
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it is evident that an increase in the natural frequency of composites are observed with an increase in PALF loading in the order of 45 wt % > 35 wt% > 25 wt%. An increase in natural frequency with an increase in fibre loading has also been reported by other researchers on sisal/polyester and banana/polyester composites [19]. In another study, higher fibre loading of hemp in the polymer matrix was found to increase the stiffness, which influences the natural frequency of the composite [38]. Modes 2 and 3 of the natural frequency of the PALF/PE composites at different loadings are shown in Table 6. Differences in natural frequency between the different fibre loadings are likely due to the compatibility between the fibre and matrix and change in contact surface area. The randomly oriented short fibre length (3 mm) also helps to improve the good fibre/matrix interface. The highest stiffness of 45 wt% PALF/PE composites is attributed to these factors. Fig. 11 clearly reveals a decline in damping ratio with the increase in fibre loading. The PALF and PE possess elastic and viscoelastic behaviours respectively. Thus an increase in PALF loading in PE matrix is expected to change the viscoelastic behaviour of PE to elastic behaviour which contributes to a reduction in damping ratio [38]. Furthermore, the stiffness is the important factor to decide the natural frequency and damping charactertics of the composites subjected to dynamic loading. In the case of 45 wt% PALF loading, the composite exhibited higher stiffness and that has been proved from the calculated modulus value. However, the damping ratio was relatively poor compared to composites with low PALF loading. Research studies indicate that the interfacial bonding also influences the mechanical properties and damping behavior of polymer composites [39]. The strong interfacial bonding in polymer composites was highly effective in the efficient distribution of the loads from the fibre to matrix leading to higher mechanical properties but is of no help in the case of damping.
5. Conclusions Increasing demand of developing sustainable eco-friendly materials into account the PALF/PE composites were developed using cost effective method and subjected to mechanical and dynamic properties. Based on the result of analysis, following inferences have been made: A maximum increase in 23% and 25% of tensile strength and tensile modulus were found in the composite with 35 wt% PALF fibre loading compared to 25 wt%. It could happen due to the increasing region of improved interfacial adhesion between the fibre/matrix which results in an enhancement in cumulative stress transfer. Similarly, compressive stress and strain properties showed an increasing trend with an increase in fibre loading. The higher flexural strength was noticed for the PALF loading of 35 wt% but further increase in fibre loading showed a slight decrease in flexural strength. In contrast, the flexural modulus showed an increasing trend with the addition of fibre weight from 25 wt% to 45 wt%. SEM observations of fractured samples showed mechanisms like fibre pull out, improved interfacial adhesion, fibre bending, fibre crushing, poor dispersive nature of fibers and interfacial debonding which are directly responsible for affecting the mechanical performance of composites. From the free vibration experimentation, it was observed that the natural frequency of the PE composed improved with the increase in fibre loading and 45 wt% PALF/PE exhibited the highest natural frequency among the composites evaluated. Damping ratio decreased with the increasing fibre content in the PALF/PE composites and maximum damping value of 0.1939 is observed for 25 wt% PALF loading. The enhanced mechanical and dynamic characteristics of Biocomposites with 35 wt% PALF fibre loading can be a suitable replacement for Cementitious composite used in low strength structural applications. Based on these encouraging results, the authors have the future plan to study the reinforcement effect of various chemical treatments of PALF with respect to mechanical strength and stiffness. Conflict of interest None. Acknowledgements
Fig. 11. Natural frequency and damping of PALF/PE composites (Mode 1).
Table 6 Dynamic characteristics of PALF/PE composites (Mode 2 and Mode 3). PALF loading wt%
25 35 45
The authors thankful to Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Malaysia and Kalasalingam Academy of Research and Education, Tamilnadu, India” for their collaborations and financial support. The authors also extend their appreciation to International Scientific Partnership Program ISPP at King Saud University for funding this research through ISPP-0011. This research was partly supported by the King Mongkut’s University of Technology North Bangkok through the PostDoc Program (Grant No. KMUTNB-61-Post-003 and KMUTNB-62KNOW-13). References
Natural frequency (Hz)
Damping
Mode 2
Mode 3
Mode 2
Mode 3
175.78 119.63 195.31
351.56 195.31 383.90
0.0242 0.0431 0.0215
0.0121 0.0255 0.0109
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Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Evaluation of mechanical and free vibration properties of the pineapple leaf fibre reinforced polyester composites K. Senthilkumar a, N. Saba b, M. Chandrasekar c, M. Jawaid b,d,⇑, N. Rajini a, Othman Y. Alothman d, Suchart Siengchin e a
Centre for Composite Materials, Department of Mechanical Engineering, Kalasalingam Academy of Research and Education, 626126, India Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products, INTROP, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Department of Aerospace Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia d Department of Chemical Engineering, College of Engineering, King Saud University, Riyadh, Saudi Arabia e Department of Mechanical and Process Engineering, The Sirindhorn International ThaiGerman Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok 10800, Thailand b c
h i g h l i g h t s Development of sustainable eco-friendly composites by cost effective process. Mechanical performance of PALF/Polyester composite on the influence of fibre loading. SEM analysis showed improved stress transfer through better interfacial adhesion. Improved natural frequency and decrease in damping ratio were found for increasing fibre loading. Suitability of optimal composite for structural members in construction industry.
a r t i c l e
i n f o
Article history: Received 20 April 2018 Received in revised form 19 August 2018 Accepted 10 November 2018
Keywords: Pineapple leaf fibre Polyester Mechanical properties Compressive strength Damping factor Free vibration
a b s t r a c t Pineapple Leaf Fibre (PALF) Reinforced Polyester (PE) composites were fabricated by hand lay-up using randomly oriented PALF in PE matrix, compressed at 17 MPa by compression moulding. Effect of PALF loading in PE composites on mechanical, morphological, free vibrational and damping properties were investigated. Result analysis revealed that the tensile, compressive strength and flexural properties considerably increased with increasing PALF loading according to the rule of mixtures. Moreover, SEM images of tensile fracture samples shows relatively less fibre pull-out, fibre breakage and improved fibre/matrix adhesion due to effective stress transfer with the increased PALF loading in PE composites. Natural frequency improved while damping ratio decreased as a result of increasing the PALF loading in PALF/PE composites. Finally, a composite with 45 wt% PALF loading is found as suitable replacement for structural component in construction industries. Ó 2018 Elsevier Ltd. All rights reserved.
1. Introduction Over recent decades, reinforcement of natural fibres to produce bio-based composites for various applications has attracted great interest to overcome the continuous increasing price of petroleum and growing environmental impact due to usage of synthetic fibre reinforced polymer composites [1,2]. Many parts of plants and fruits could be a viable source of raw fibre materials for industrial use [3,4]. Nevertheless, many of the plants and fruits are being ⇑ Corresponding author at: Biocomposite Technology Laboratory, INTROP, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. E-mail addresses: [email protected], [email protected] (M. Jawaid). https://doi.org/10.1016/j.conbuildmat.2018.11.081 0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.
wasted as in the absence of beneficial harvest due to lack of knowledge relating to their economic uses [5]. Besides, the various natural fibres like kenaf, hemp, flax, jute, banana and sisal, pineapple leaf fibres (PALF) currently receiving higher attention as a green reinforcement (a composite made up using natural fibre is called as green reinforcement). PALF also exhibit good mechanical properties and are environmental friendly due to their biodegradability. Research study states that it is a potential material to substitute synthetic fibre in fibre reinforced polymer composites for many structural and non-structural applications in the coming future [6]. PALF is cultivated largely in tropical countries and each plant has around 25–30 leaves that grow upto 90–150 cm in length
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and 2 cm and 5 cm in width. The PALF can be extracted either by (i) water retting and scrapping or (ii) microbial retting process. The microbial retting process was found to be more effective in producing fibres with good appearance, good strength with essential chemical composition. PALF has 70–82% of cellulose, 5–12% of lignin and 1.1% of ash [3]. Extracted fibres could be used for producing woven knitted, woven fabrics and non-woven mats. PALF applications also extended in pharmaceuticals and for animal feeds. Arib et al. [7] reported that the PALF has a higher content of cellulose and exhibited better mechanical properties with respect to other natural fibres. In other study PALF reinforced in PALF/phenolic polymer composites possess considerable tendency to transfer load effectively from the matrix to fibre, thereby resulting in improved mechanical properties [8]. Various thermoset resins like epoxy [9–11], vinyl ester [12], bisphenol [13], polyester (PE) [5,14–16], etc. have been reinforced with PALF and their mechanical properties were studied with respect to fibre orientation (continuous or discontinuous), alignments and fibres loadings. In general, introduction of PALF into the matrix improves the mechanical properties of the composites. Some of research findings where PALF are reinforced in PE and their tensile, flexural and impact properties have been investigated are shown in Table 1. Dynamic properties play a significant role in the field of construction industries, automotive components, machine supports and machine component design [17]. In the machine component design process a reduction of resonant amplitude is an important task. A modal damping accompanying with each mode of the structure has an influence on the resonant amplitude. Usually, metal matrix composites possess lesser damping than the natural fibre reinforced composites (NFRCs) [18], because the molecular mobility can be freely takes place in the case of NFRCs due to the viscoelastic nature and interfacial debonding between the fibrematrix. However, free vibration characteristics of polymer composites are rarely found or are merely absent. Natural fibres like sisal, banana, coconut sheath and jute have been used either as individual fibres or along with other natural fibres in hybrid configuration reinforced in polyester resin and their free vibration characteristics have been studied by some researchers, as shown in Table 2. From the Tables 1 and 2 it is evident that no work has been reported in literature where dynamic characteristics (natural frequency and damping) and compression properties of PALF/PE were made using the free vibration method as per the author’s knowledge. The compression and free vibration properties of PALF/PE require in depth study for understanding the behaviour of compos-
ites under applied loads in order to use it for the advance structural applications. Thus the topic of interest to this study is to reveal the influence of randomly oriented PALF loading on the tensile, flexural, compressive, free vibration, damping and morphological properties of PE composites, under varying fibre 25%, 35% and 45% loading. Further, SEM analysis of the tensile, compressive and flexural fractured specimens was observed to investigate the failure behaviour due to increase in fibre loading. 2. Experimental procedure 2.1. Materials PALF, unsaturated isophthalic polyester resin with a curing agent methyl ethyl ketone peroxide-MEKP and catalyst cobalt naphthenate used in this study were procured from India. Properties of PALF and PE resins used in this study are listed in Table 3. 2.2. Mould details and fabrication of composites Composites were fabricated by hand lay-up technique using the compression moulding process. For fabricating the composites, split type moulds made from EN90 steel were used in this work, having total three parts namely, the flat surface bottom plate, middle plate with rectangular cavity and the top mould, as depicted in Fig. 1. The various steps involved in the fabrication of composites by hand lay-up are depicted in Fig. 2. Moulds were cleaned and then polished by wax. Washed and dried PALF of 3 mm length was randomly arranged in the mould at different 25, 35 and 45% loading by weight. The resin (with 1.5 wt% of initiator) was poured onto the fibres, and the mould was closed followed by compression at 17 MPa. The setup was left undisturbed for 24 h at room temperature to allow the resin to cure. 3. Characterization 3.1. Tensile testing Fabricated PALF/PE and pure PE composites of dimensions of 120 mm 20 mm 3 mm were subjected to tensile tests according to ASTM D3039 standard, having the crosshead speed 5 mm/ min and gauge length of 50 mm. From the experimentation, the tensile properties such as strength, modulus and percentage of
Table 1 Reported studies on mechanical properties of the PALF/PE composites. Material
Observation
References
PALF/PE
Maximum tensile, flexural and impact strength observed until 30% fibre loading but drops on increasing fibre content to 40% in polymer composites Tensile strength and modulus of PALF/PE composites increased by increasing the PALF content from 0% to 30% Specific flexural stiffness improved for 2.3 times at 30 wt% of fibre content.
[5] [14] [16]
Table 2 Free vibration properties of natural fibre reinforced polymer composites. Polymer Composites
Observation
References
Sisal/PE Banana/PE Coconut sheath/PE Banana/PE Additive: Red-mud Banana/Sisal/PE Sisal/Coconut-sheath PE Banana/Jute/PE
Damping improved with the increase in fibre loading in the composite Free vibration properties improved with the addition of 3% Montmorillonite (MMT) nanoclay Lowering the particle size of red-mud, the free vibration properties increased in the composites Increase in the fibre loading, increases the natural frequency while a decrease in damping of composites is observed Natural frequencies were higher in treated hybrid composites than in the untreated ones Natural frequency increased with the addition of nanoclay until 2 wt% while damping improved with the addition of nanoclay >2 wt% Damping of Coconut sheath/PE > Banana/PE
[19] [20] [21] [22] [23] [24]
Banana/PE Coconut sheath/PE
[25]
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K. Senthilkumar et al. / Construction and Building Materials 195 (2019) 423–431 Table 3 Mechanical and physical properties of PALF and PE resin [4]. Fibre/Matrix
Density (g/cm3)
Tensile Strength (MPa)
Elongation at break (%)
Tensile modulus (MPa)
Specific strength (MPa)
Specific Modulus (MPa)
PALF PE resin
1.526 1.159
170 22.9
3 1.6
6210 580
110 19.7
4070 502
Fig. 1. Flat surface bottom plate, Middle plate, Top mould and (b) Composed mould.
Fig. 2. Fabrication steps of PALF/PE composites.
elongation were found for varying fibre loading. In ease case, the average value of 5 specimens was reported for tensile strength and tensile modulus. 3.2. Compressive testing Fabricated composites of dimensions of 60 mm 20 mm 3 mm were subjected to compressive tests as per the ASTM D3410 standard. The gauge length was set to 30 mm and a cross head speed of 1.27 mm/min was maintained throughout the tests. Compressive stress vs strain and compressive strength were recorded for all tested specimens. An average of 5 specimens was used in compressive testing. 3.3. Flexural testing Influence of PALF loading on the flexural properties of the PE composite was investigated. Flexural tests were conducted on 5 replicate specimens of pure PE and PALF/PE composites having the dimensions of 120 mm 20 mm 3 mm according to the ASTM D790 standard. The crosshead speed and gauge length was set to 1.27 mm/min and 50 mm respectively and the average values were reported.
Fig. 3. Schematic diagram of free vibration experimental setup.
produced higher frequencies were used [20]. A sharp hardened impact hammer was used for exciting the fabricated composite, while the displacement signals were acquired by an accelerometer joined at the end of the composite by wax and recorded using a data acquisition system. Two separate adaptors were used for capturing the output signal. One was attached to the impact hammer, and the other was fixed at the free end of the laminate composite. 3.5. Morphological analysis
3.4. Free vibration modal analysis Free vibration characteristics of the fabricated PALF/PE composites were studied using the Kistler model 9722A500, shown in Fig. 3. The sample dimensions of 200 mm 20 mm 3 mm which
The microstructure, morphology and failure behavior of the tensile fractured specimens of PALF/PE composites were carried out through SEM followed by micrographs with SEM 230 (USA) field emission instrument.
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4. Results and discussion
Table 4 Tensile properties of PALF/PE composites with varying PALF loading.
4.1. Tensile properties
PALF loading (wt%)
Tensile Strength (MPa)
Tensile Modulus (GPa)
Elongation at break (%)
The effect of fibre loading on the tensile stress as a function of tensile strain (%) for PALF/PE is shown in this Fig. 4a. It is evident from Figure that the elongation at break increased with the PALF loading indicating an increase in ductility of the PALF/PE composites compared to the pure PE (1.6%). Quite similar results are observed by Devi et al on PALF/PE composites [4]. The effect of PALF loading on tensile strength and modulus of PE composites are shown in Fig. 4b and in Table 4. It is evident that an increase in PALF loading led to an increase in tensile modulus. Highest tensile modulus was observed for 45 wt% fibre loading in the PALF/PE which was 25% higher compared to 25 wt% fibre loading. Moreover, the tensile strength of PALF/PE composites followed the same increasing trend as that of tensile modulus. At 45 wt% PALF loading, the tensile strength (33.13 MPa) of the composites was 7.4% and 23% higher than the 25 wt% and 35 wt% respectively. PALF contained richer cellulose (70–82%) compared to the other natural fibres [3] and as per Idicula et al. [26], the cellulose content of PALF was dependent on the tensile modulus and tensile strength. It is believed to be the reason for superior tensile modulus and tensile strengths at higher fibre loading (45 wt%) in the PE composites.
25 35 45
25.49 27.53 33.13
1.161 1.4 1.553
4.03 4.06 4.11
4.2. Compressive properties The compressive stress vs strain for different PALF loading of the PE composite are shown in Fig. 5a and the effect of fibre loading on the compressive strength is displayed in Fig. 5b. From Fig. 5a, it is evident that the stiffness increased with the addition of fibre wt% into the composite. The dependency of composite stiffness on the fibre reinforcement has been reported by many researchers [27,28]. Fig. 5b shows that the % improvement in compressive strength for the composites was approximately 16% and 41% respectively with the increase in PALF loading from 25% to 35% and 45% respectively. Increase of compressive strength with the addition of fibre weight upto 30% in the natural fibre reinforced composites has been reported in literature by researchers on Grewia-optiva/phe nol-formaldehyde composite [29], saccaharum cilliare/resorcinolformaldehyde composite [30] and agave/epoxy composite [31]. The improved compressive strength for the composites with the high fibre loading could be due to the enhanced interfacial adhe-
Fig. 5a. Compressive stress vs strain of PALF/PE.
sion between the chopped PALF and PE matrix. In another study the dependence of the compressive strength of the chopped fibre reinforced composite has been reported to be influenced by the interfacial adhesion between the fibre and matrix, fibre length (3 mm fibre length showed better compressive properties) and fibre loading [31]. Figure 8(a–c) shows the SEM images of the fractured PALF/PE specimens at different fibre loadings from the compression test. Generally, the kinking behaviour of material failure due to the compression load can be easily observed in the case of aligned composites using long fibers. But, it is not easy in the case of randomly oriented composites. However, the kinking behaviour was expected to happen in the subsurface of the laminates. In this study, SEM micrograph of compressed specimens showed only
Fig. 4. Effect of fibre loading on a) Tensile stress vs strain % and b) Tensile strength and modulus of PALF/PE.
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Fig. 6b. Flexural strength and modulus of PALF/PE.
Fig. 5b. Compressive strength vs PALF loading of PALF/PE.
the appearance of crushed fibres and fibre fraying on the top surface of randomly oriented composites which could have masked the dislocation of fibre band due to the kinking effect at the subsurface. However, the extent of kinking was lower as the fibre wt% increased in the composites. This could be the result of the high compressive strength arising from an increase in fibre wt% that resists kinking of the composites. Literature also explains that the composites kinking properties under compressive load are due to micro-buckling of the fibre [28]. 4.3. Flexural properties The flexural stress-strain for the PALF/PE composites as a function of fibre loading is shown in Fig. 6a and the effect of PALF loading on flexural properties are displayed in Fig. 6b. A considerable
Table 5 Flexural properties of PALF/PE composites with varying PALF loading. PALF loading (wt%)
Flexural Strength (MPa)
Flexural Modulus (GPa)
25 35 45
39.86 82.97 75.92
1.926 4.05 6.379
difference in flexural behaviour was observed by varying PALF loading in the pure PE. The magnitude of flexural strength is mainly depends upon the fibre wt-% for the constant fibre length. Due to the application of flexural loading, the inner layer of laminate subjected to bending effect and outer layer will be subjected to tensile behaviour. The addition of lower wt% fibre loading in composite can allow the fibres to take up both compression and shear which leads to the increase in magnitude of flexural strength. On the other hand, the addition of fibre content beyond a limit can reduce the possibility of shearing action which is the main factor for deciding the outer layer and in turn reduce the flexural strength. In general, the flexural failure or rupture of composites under investigation is due to bending stress (combination of tensile and compressive stresses) or shear stress. The flexural strength and modulus of PALF/PE composites at different PALF loading are tabulated in Table 5 and also displayed in Fig. 6b. Flexural strength increases by 108% following an increase in the fibre loading from 25 wt% to 35 wt% while the flexural strength decreases by 8.5% further by increasing the fibre loading to 45 wt %. The reduction of flexural strength at 45% PALF loading could be due to non-uniform applied stress transfer between the fibre and matrix due to higher inter-fibre interaction within the matrix and poor fibre dispersion. The dependency of flexural strength on fibre loading have also been reported for PALF/PE [5], PALF/ polypropylene [7] and PALF/epoxy [10]. The % improvement in flexural modulus for the composites was approximately 52% and 70% respectively with the increase in fibre weight from 25% and 35% to 45% respectively. Similar improvements in flexural modulus with the increasing sisal fibre loading in the case of sisal fibre/PE [32] and PALF in PALF/PE composites are reported [33]. 4.4. Morphological analysis
Fig. 6a. Flexural stress vs flexural strain of PALF/PE.
Tensile fractured specimens were exposed to SEM to investigate failure modes and to realise the physical bonding between PALF
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and PE and to interpret the observed tensile strength in each composite at different PALF loading. SEM images of fractured tensile tested specimens are shown in Fig. 7(a–f) at different fibre loading. Increased fibre distribution with respect to the increasing fibre loading could be clearly observed in Fig. 7(a, c and e). PALF/PE composites having 25 wt% PALF loading displayed highest fibre pull out and matrix cracking (Fig. 7a,b). In general the mechanical properties of the composites depend on individual fibre wt%- and matrix and fibre/matrix interfacial adhesion [34]. Less fibre pull out and enhanced bonding/ adhesion at the fibre/matrix with the increased fibre loading could be seen in Fig. 7(c–f). Thus, the increase fibre content in the composite helped to distribute the load effectively within the matrix, thereby leading to improved tensile strengths/modulus in the PALF/PE composites compared to pure PE. Fig. 9(a–c) shows the SEM images of the fractured samples from the flexural test. Less fibre pull out and enhanced fibre/matrix adhesion was observed with the increase in fibre loading identical
to the tensile failure images. Although the strength of 25 wt% composite is low, the improved interfacial bonding between fibre and matrix can be clearly seen in Fig. 9a. On the other hand, bending and the poor dispersion of short fibers shown in Fig. 9b, normally do not allow the proper load transfer. Fig. 9c shows the larger contact between the fibres due to the reduction of matrix which can resist the shearing action between the fibres and it leads to the slight decrease in flexural strength. 4.5. Free vibration properties The dynamic characteristics of a structure like natural frequency, damping and mode shapes play a significant role [35] especially in aerospace and automobile vehicles where many vibration inputs are present that could lead to resonance in these stated structures. The stiffness and damping characteristics of anisotropic polymer composites used in these applications are significantly influenced by the vibration in the structure. Accordingly for
Fig. 7(a,b). SEM tensile fractured samples of 25 wt% of PALF/PE composites.
Fig. 7(c,d). SEM tensile fractured samples 35 wt% of PALF/PE composites.
Fig. 7(e,f). SEM tensile fractured samples of 45 wt% of PALF/PE composites.
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Fig. 8. (a–c) SEM micrograph of compression fractured samples of 25, 35 and 45 wt% of PALF/PE.
Fig. 9. (a-c) SEM images of flexural fractured samples with different failure mechanisms for 25, 35 and 45 wt% composites.
each mode of vibration, a unique damping value could be obtained [36]. Moreover, the natural frequency of composites depend upon many factors namely fibre length, fibre loading, fibre orientation, fibre-matrix bonding, moment of inertia, tensile modulus, density and chemical treatment. In this study, the natural frequency and damping has been calculated by using the impact hammer technique. For this technique, a piezoelectric impact hammer was used to apply a constant force at the free end of the PALF/PE composite specimen (Fig. 3). From output response the measurements and ratio of input is obtained by using excitation force
dissipation in composite structures occurs due to matrix, interphase, broken fibres and matrix crack. Interestingly, damping mechanism of polymer composites are quite different when compared to conventional materials. Damping can be calculated by using the half-power bandwidth method [36] or graphical or mathematical approaches [35]. In the present study damping has been calculated using the half-power band width method and has been calculated based on Eq. (1) [37].
a Fast Fourier Transform (FFT) analyser. This stated ratio may be termed the Frequency Response Function (FRF). A typical curve of FRF obtained for 45 wt% PALF/PE is shown in Fig. 10. Three peaks named as Mode 1 (bending), Mode 2 (twisting) and Mode 3 (secondary bending) also termed as the mode shape are observed. Generally, energy dissipation occurs whenever the structures are subjected to damping due to the vibratory motion. The energy
where: f–Damping factor,
f ¼ Dx=2xn
ð1Þ
Dx – Bandwidth, and xn –Natural frequency of composite sample. Fig. 11 presents the first mode of natural frequency and damping of PALF/PE composites at different fibre loadings. From the plot
Fig. 10. A typical curve of frequency response function of 45 wt% PALF/PE composites.
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it is evident that an increase in the natural frequency of composites are observed with an increase in PALF loading in the order of 45 wt % > 35 wt% > 25 wt%. An increase in natural frequency with an increase in fibre loading has also been reported by other researchers on sisal/polyester and banana/polyester composites [19]. In another study, higher fibre loading of hemp in the polymer matrix was found to increase the stiffness, which influences the natural frequency of the composite [38]. Modes 2 and 3 of the natural frequency of the PALF/PE composites at different loadings are shown in Table 6. Differences in natural frequency between the different fibre loadings are likely due to the compatibility between the fibre and matrix and change in contact surface area. The randomly oriented short fibre length (3 mm) also helps to improve the good fibre/matrix interface. The highest stiffness of 45 wt% PALF/PE composites is attributed to these factors. Fig. 11 clearly reveals a decline in damping ratio with the increase in fibre loading. The PALF and PE possess elastic and viscoelastic behaviours respectively. Thus an increase in PALF loading in PE matrix is expected to change the viscoelastic behaviour of PE to elastic behaviour which contributes to a reduction in damping ratio [38]. Furthermore, the stiffness is the important factor to decide the natural frequency and damping charactertics of the composites subjected to dynamic loading. In the case of 45 wt% PALF loading, the composite exhibited higher stiffness and that has been proved from the calculated modulus value. However, the damping ratio was relatively poor compared to composites with low PALF loading. Research studies indicate that the interfacial bonding also influences the mechanical properties and damping behavior of polymer composites [39]. The strong interfacial bonding in polymer composites was highly effective in the efficient distribution of the loads from the fibre to matrix leading to higher mechanical properties but is of no help in the case of damping.
5. Conclusions Increasing demand of developing sustainable eco-friendly materials into account the PALF/PE composites were developed using cost effective method and subjected to mechanical and dynamic properties. Based on the result of analysis, following inferences have been made: A maximum increase in 23% and 25% of tensile strength and tensile modulus were found in the composite with 35 wt% PALF fibre loading compared to 25 wt%. It could happen due to the increasing region of improved interfacial adhesion between the fibre/matrix which results in an enhancement in cumulative stress transfer. Similarly, compressive stress and strain properties showed an increasing trend with an increase in fibre loading. The higher flexural strength was noticed for the PALF loading of 35 wt% but further increase in fibre loading showed a slight decrease in flexural strength. In contrast, the flexural modulus showed an increasing trend with the addition of fibre weight from 25 wt% to 45 wt%. SEM observations of fractured samples showed mechanisms like fibre pull out, improved interfacial adhesion, fibre bending, fibre crushing, poor dispersive nature of fibers and interfacial debonding which are directly responsible for affecting the mechanical performance of composites. From the free vibration experimentation, it was observed that the natural frequency of the PE composed improved with the increase in fibre loading and 45 wt% PALF/PE exhibited the highest natural frequency among the composites evaluated. Damping ratio decreased with the increasing fibre content in the PALF/PE composites and maximum damping value of 0.1939 is observed for 25 wt% PALF loading. The enhanced mechanical and dynamic characteristics of Biocomposites with 35 wt% PALF fibre loading can be a suitable replacement for Cementitious composite used in low strength structural applications. Based on these encouraging results, the authors have the future plan to study the reinforcement effect of various chemical treatments of PALF with respect to mechanical strength and stiffness. Conflict of interest None. Acknowledgements
Fig. 11. Natural frequency and damping of PALF/PE composites (Mode 1).
Table 6 Dynamic characteristics of PALF/PE composites (Mode 2 and Mode 3). PALF loading wt%
25 35 45
The authors thankful to Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Malaysia and Kalasalingam Academy of Research and Education, Tamilnadu, India” for their collaborations and financial support. The authors also extend their appreciation to International Scientific Partnership Program ISPP at King Saud University for funding this research through ISPP-0011. This research was partly supported by the King Mongkut’s University of Technology North Bangkok through the PostDoc Program (Grant No. KMUTNB-61-Post-003 and KMUTNB-62KNOW-13). References
Natural frequency (Hz)
Damping
Mode 2
Mode 3
Mode 2
Mode 3
175.78 119.63 195.31
351.56 195.31 383.90
0.0242 0.0431 0.0215
0.0121 0.0255 0.0109
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