Mechanical and Morphological Properties of 45 o /45 o Woven Kenaf Reinforced PVB-Phenolic Resin Produced Using a Hot Press Technique

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1 Mechanical and Morphological Properties of 45 o /45 o Woven Kenaf Reinforced PVB-Phenolic Resin Produced Using a Hot Press Technique Suhad D. Salman 1,3,a, Z. Leman 1,b, M.T.H. Sultan 2,c, M. R. Ishak 2,4,d and F. Cardona 2,e 1 Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Putra Malaysia, Serdang, Selangor, Malaysia 2 Aerospace Manufacturing Research Centre (AMRC), Level 7, Tower Block, Faculty of Engineering, Universiti Putra Malaysia, Serdang, Selangor, Malaysia 3 Materials Engineering Department, Faculty of Engineering, University of Mustansiriyah, Baghdad, Iraq 4 Laboratory of Bio-Composites Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, UPM Serdang, Selangor, Malaysia a suhaddawood2007@yahoo.com, b zleman@upm.edu.my, c thariq@upm.edu.my d mohdridzwan@upm.edu.my, e francisco.c@upm.edu.my Abstract Recently, the use of kenaf fiber reinforced polymer composites in the various sectors has increased widely due to their availability and readiness to be used with various manufacturing processes. In this study, tensile and flexural properties of plain woven kenaf fabric with PVB-phenolic resin at 45/-45 o orientation (WKFPH) were experimentally determined. The hot press manufacturing technique was used to prepare the specimens and eight specimens were prepared for each test, (five replications were adopted). The results show that the plain woven kenaf/pvb-phenolic composites possess good tensile and flexural strengths and they are good candidates for reinforcement material in many applications. In addition, their tensile behavior indicated that WKFPH composite offers better results than flexural strength of WKFPH composite, while the elongation at break exhibited by WKFPH composite was less. The better interfacial adhesion between the woven kenaf and the PVB-phenolic resin was clearly demonstrated through scanning electron microscopy (SEM) images. Keywords: Woven kenaf, PVB-phenolic resin, mechanical, morphological, natural-based composite. 1. Introduction The development of using natural fibers with polymer matrix composite is growing rapidly in the industrial sector to produce environmentally friendly products. Kenaf fiber reinforced polymer shows a bright future, among other natural fiber due to its availability and readiness to be used with various manufacturing processes [1]. Kenaf fiber possesses (1-10)

2 moderately high specific strength and stiffness that could be utilized as reinforcing materials in polymeric resins to make useful structural composite material [2]. Kenaf fiber is produced from the bast of stems of plants genus Hibiscus, a family of Malvaceae, species of cannibinus and requires less water to grow [3]. Woven fabrics are used in a wide variety of the consumer products as the reinforcement phase of composites due to their flexibility, formability, and high specific strength because the interlocking increases strength better than fiber matrix adhesion [4]. The use of the weave technique can add structural strength to the material because it increases both the strength and the ability of energy absorption capacity [5]. Whilst articles and even books on the overall properties of natural fiber reinforced composites have been published [6], the authors have concluded that a specific article on the overall characteristics of woven kenaf fiber at 45/-45 o orientation reinforced PVB-phenolic resin composites, has not yet been published and give value addition to enhance its use. In an experimental study, Ochi investigated the tensile and flexural strength of the unidirectional kenaf fiber composites [7] with different fiber content. Experimental results showed that the weight of composites increased linearly up to a fiber content of 50%. While Shekeil et al. [8, 9] studied the influence of fiber content on mechanical properties of kenaf bast fiber reinforced thermoplastic polyurethane composites in several studies. It was concluded that a 30% fiber loading display the best tensile strength, whilst the tensile modulus, thermal stability, hardness, and flexural strength increased with increase of fiber content, but the strain decreased. When natural reinforced polymer composite subjected to load, the fibres act as carriers of load and stress (stiffness and strength). Therefore, the orientation of natural fibres has important effects to enhance the mechanical properties in their composite materials [10]. In an experimental study, the effect of weaving patterns and random orientation on the mechanical properties of kenaf and banana fiber reinforced hybrid polyester composites by Alavudeen et al. [11]. It was reported that the plain weaving patterns composite properties were shown improved mechanical properties compared to the random type. Moreover, the maximum increase in mechanical strength was observed in the plain woven composites rather than in randomly oriented composites. In another study, Brahim and Cheikh [12] investigated the influence of fibres orientation on the mechanical properties of unidirectional Alfa/polyester composites and tested at different orientation angles 0 o, 10 o, 30 o, 45 o and 90 o. The longitudinal specimens (at 0 o orientation) showed highest tensile strength then 45 o and 90 o (transverse direction) specimens. (2-10)

3 Although kenaf fibers have very high characteristics compared to other natural fibres [13], there is no work has been done on the kenaf fibres to comprehensively understand the possibility of using such woven fibres reinforced PVB-phenolic composites especially at 45 o /-45 o orientation. Consequently, this paper aims to study the effect of orientation of kenaf fibre on tensile and flexural properties in order to draw a brief guideline for future development on using woven kenaf fibers. Furthermore, the morphological properties of tensile test samples were analysed through scanning electron microscopy (SEM) images. 2. Materials and Methods To clarify the effect of the 45 o /-45 o orientation of woven kenaf fibres/pvb-phenolic composite, tension and flexural test were carried out to define its mechanical properties. Not only fiber s strength but also physical elements about every plantation fiber must be known before it is used to reach at the maximum potential for certain usage [14, 15]. Kenaf fiber is the main fiber that's used in this study (as shown in Fig. 1). Table 1 shows the properties of plain woven kenaf that used in this study. PVB-phenolic (Polyvinyl butyral resin) is employed in a wide array of industrial and commercial applications due to their impressive performance as well as outstanding versatility. Table 1: Properties of plain woven kenaf. Characterization Woven kenaf Thickness, t (mm) 2 ± 0.2 Weight (g/m 2 ) 890 Density (g/cm 3 ) 1.2 Warp density (warp/inch) 12 Weft density (weft/inch) 12 Wavelength, λ (mm) 4.2 Inter-yarn fabric porosity (ɛ) Moisture Content (%) Water Uptake (%) Average breaking strength (MPa) Average maximum strain (%) 17.3 Fig. 1: A plain woven kenaf fabric The composite samples of WKFPH were made with 40% kenaf fiber weight content by using a hot press technique which leads to better fiber-to-resin bonding, as shown in Fig. 2. Eight specimens were fabricated for each test, five replications were considered. (3-10)

4 Fig. 2: The composite specimens by using the hot press technique Mechanical properties of WKFPH The engineering performance of any material is always evaluated in terms of its tensile and flexural properties. Tensile and flexural testing were carried out in the composite laboratory of the Mechanical Engineering Department, Universiti Putra Malaysia, according to ASTM D 3039 and ASTM D-790 standard [16, 17], to determine the ultimate tensile strength and ultimate flexural strength of the WKFPH. By using a wheel saw machine, the specimens were carefully cut and finished from the composite to the accurate size. Tensile specimens were cut to the 250 mm 25 mm 7 mm, rectangular sectional area flat strip and gage length 170 mm. The rectangular shape three-point bending specimens were prepared with dimensions of 127 mm 12.7 mm 7 mm. The distance between supports (span length) was calculated as per the standard, with a ratio of 16:1. Both tests were conducted by using a universal testing machine INSTRON 3365 with the capacity of 100 KN, and crosshead speed 2 mm/min with replication 8 times, (as shown in Fig. 3). These tests have been conducted until a specimen fracture to measure the ultimate tensile strength and ultimate flexural strength of the WKFPH, then the value of five specimen results was taken. (4-10)

5 (a) (b) Fig. 3: (a) The specimen under tensile test, (b) The specimen under flexural test Morphological observation of WKFP The failure mechanism of the tensile specimens was observed using scanning electron microscope (SEM) instrument model ZEISS SUPRA 35VP. All the fractured tensile specimens were coated with a thin layer of gold, to avoid electron charge accumulation, and subjected to a voltage of kv. 3. Results and Discussions Fig. 4 (a) shows the ultimate tensile strength while Fig. 4 (b) shows the average tensile strength and tensile modulus of WKFPH. The tensile stress curve is shown linearity in the first phase followed by non-linearity until failure. Similar trend had been reported in the study done by Khan et al. [18] on the jute fabric reinforced composites, and Yousif et al. [19] on the unidirectional kenaf/epoxy composites. All tensile specimens experienced brittle fracture with linear behavior up to fracture. The maximum tensile strength and Young s modulus of WKFPH composite in this study is MPa and MPa, respectively. Which is found to be close to the tensile strength of woven kenaf at 45 o /-45 o reinforced vinylester composites, which was 12.4 [20]. However, the present composite results showed less tensile properties compared to the previously studied kenaf/pvb-phenolic composites at 0/90 o orientation [21]. The reduction percentage of tensile strength with change angle from 0 o /90 o to 45 o /-45 o was 40%, which is highly with the agreements of the published articles [22, 10]. (5-10)

6 (a) (b) Fig. 4: (a) Tensile properties of WKFPH composites, (b) The average tensile strength and tensile Young s modulus of WKFPH composites. The similar finding was also observed in the flexural strength of WKFPH by using a 3- point flexural test, as shown in Fig. 5 (a) and (b). It is noted that the flexural stress curve is shown linearity in the first phase followed by non-linearity up to fracture, the staircase region, which lead to the sudden rupture of the specimens. The ultimate flexural strength and flexural modulus were 4.1 MPa and 35.6 MPa respectively. Similar trend had been reported in the study done by Yousif et al. [19] on the unidirectional kenaf fiber at 45 0 reinforced epoxy composites. As a result of the flexural load which leads to progressive debonding, the composite specimens weakening are occurred [23]. Therefore, the interfacial adhesion characteristics have a significant effect on the load carrying capacity of a fiber reinforced composite, especially under flexural load [24]. (a) (b) Fig. 5: (a) Flexural properties of WKFPH composites, (b) The average flexural strength and flexural Young s modulus of WKFPH composites. (6-10)

7 Generally, the increase in tensile strength and modulus of the WKFPH composites is attributed to differences in the load distribution properties. The maximum tensile strain was 20.82%, while the maximum flexural strain was 14.75%, because the flexural effect can create an interlocking structure which could result in constraints for the extension of the kenaf fiber along the directions. As researches reported, the fiber orientation is a critical factor that has an important influence on the flexural properties of the composites [25]. Besides, it is known that flexural properties of the composites are also influenced by the composition and adhesion levels of the polymers, the interfacial bonding. This is in agreement with the findings of Sukumar et al. [26] who found similar trends in the plant fibers of Kerala Morphological properties of WKFC Scanning electron microscopy (SEM) analysis was used to observe the mode of failure mechanism which occurred on the tensile composites, as shown in Figs. 9 and 10. In general, there is clear fiber degradation, breakage and debonding of some of the kenaf fibres can be seen which indicates the good interfacial adhesion of the woven kenaf fibres with the PVBphenolic resin. Furthermore, Fig. 9 shows a rich area with PVB-phenolic resin, where the resin was inside and around the bundle of the kenaf fibres. This indicates good adhesion of the some of the fibres with the matrix [27]. Due to the high degree of resin penetration, the incorporation between the fibres and resin was increased which reduced the defragment of kenaf fibre from PVB-phenolic resin, as shown in Fig. 10. Fig. 9: The SEM micrographs of the tensile failure surfaces of WKFPH. Fig. 10: The fibers orientation layers and bonding area of the WKFPH. (7-10)

8 Conclusions The kenaf fibers composite material is fabricated with PVB-phenolic resin at 45 o /-45 o orientation, to study the tensile, flexural and failure surface properties with more emphasis. The mechanical properties of the composite were found to be affected differently by the orientation fibers angle. The stress strain diagram of kenaf fiber reinforced PVB-phenolic composite at 45 o /-45 o orientation is linear. Generally, the tensile properties of the WKFPH composite are highly influenced by the kenaf fibre orientations. Forty percentage increment in the tensile strength of the PVB-phenolic composite achieved when kenaf fibres were fabricated with 0 o /90 o orientation compared to the 45 o /-45 o orientation. Furthermore, the flexural strength of WKFPH composite at 45 o /-45 o orientation was found to be less than the flexural strength of WKFPH composite at 0 o /90 o orientation, while the elongation at break exhibited by WKFPH composite was almost same. It was concluded that the WKFPH composite had higher mechanical properties in tension compared to flexural, which makes it attractive for applications that need adequate axial stiffness while having lower flexural stiffness. In addition, the WKFPH composite was made with 40% kenaf fiber weight content showed good interfacial adhesion which in turn allowed the PVB-phenolic resin to penetrate in the fibre bundles leading to good interlocking of the fibres in the matrix. Acknowledgements This work is supported by UPM under GP-IPB grant, and GP- IPS/2014/ The authors would like to express their gratitude and sincere appreciation to the Mechanical and Manufacturing Engineering Department and Aerospace Manufacturing Research Centre of the Universiti Putra Malaysia. Our appreciation and gratitude also extend to the Ministry of Higher Education & Scientific Research of Iraq and to the Material Engineering Department- College of Engineering - The University of Mustansiriyah for their scientific assistance and financial support. (8-10)

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