Abstract
The effect of sugar palm fiber (SPF) loading was studied relative to the mechanical properties of roselle (RF)/SPF/thermoplastic polyurethane (TPU) hybrid composites. RF/SPF/TPU hybrid composites were fabricated at different weight ratios (100:0, 75:25, 50:50, 25:75, and 0:100) by melt mixing and hot compression. The mechanical (tensile, flexural, and impact test) and morphological properties of tensile fractured samples were examined using a universal testing machine, impact machine, and scanning electron microscope. It was found that the hybridization of RF/SPF increased its impact strength corresponding to the increases in the SPF content of the composites. The tensile and flexural properties of the hybrid composites decreased due to poor interfacial bonding between the fiber and matrix. Scanning electron micrographs of the tensile fractured surface of the RF/SPF hybrid composites revealed fiber pullouts and poor adhesion bonding. In conclusion, the hybridization of SPF with RF/TPU composites enhanced its impact strength while decreasing the tensile and flexural strength.
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Mechanical Performance of Roselle/Sugar Palm Fiber Hybrid Reinforced Polyurethane Composites
A. M. Radzi,a S. M. Sapuan,b M. Jawaid,a and M. R. Mansor c
The effect of sugar palm fiber (SPF) loading was studied relative to the mechanical properties of roselle (RF)/SPF/thermoplastic polyurethane (TPU) hybrid composites. RF/SPF/TPU hybrid composites were fabricated at different weight ratios (100:0, 75:25, 50:50, 25:75, and 0:100) by melt mixing and hot compression. The mechanical (tensile, flexural, and impact test) and morphological properties of tensile fractured samples were examined using a universal testing machine, impact machine, and scanning electron microscope. It was found that the hybridization of RF/SPF increased its impact strength corresponding to the increases in the SPF content of the composites. The tensile and flexural properties of the hybrid composites decreased due to poor interfacial bonding between the fiber and matrix. Scanning electron micrographs of the tensile fractured surface of the RF/SPF hybrid composites revealed fiber pullouts and poor adhesion bonding. In conclusion, the hybridization of SPF with RF/TPU composites enhanced its impact strength while decreasing the tensile and flexural strength.
Keywords: Roselle fibers; Sugar palm fibers; Thermoplastic Polyurethane; Mechanical properties; Hybrid composites
Contact information: a: Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Product (INTROP), Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia; b: Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia; c: Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia; *Corresponding author: sapuan@upm.edu.my
INTRODUCTION
The use of petroleum-based plastic in human activities is increasing rapidly with the increase human population. Moreover, the disposal of these materials is a major issue of environmental pollution (Jumaidin et al. 2016b, 2017). Increasing awareness in society has led to numerous efforts to reduce the impact of this material on the environment (Ilyas et al. 2017; Jumaidin et al. 2017b). Environmentally friendly materials, such as natural fibers derived from renewable resources, are a promising solution for this problem (Jumaidin et al. 2016; 2017a). The application of this naturally derived material improves the properties of polymer composites (Kasim et al. 2015). Natural fiber products are widely applied in various industries such as furniture, packaging, automotive, and construction (Alamri and Low 2013; Kumar et al. 2016; Edhirej et al. 2017; Radzi et al. 2017b). The demand from industries that use natural fiber (kenaf, hemp, banana, and oil palm) sources is increasing. This material source is more friendly to the environment, low cost, easy to recycle, and biodegradable, making it a good alternative to replace the use of commercial fibers (Razali et al. 2015).
Roselle and sugar palm fibers are two natural fibers that are abundantly available in Malaysia, along with oil palm and kenaf fiber. The roselle plant grows in South Asia (Nadlene et al. 2015, 2016a), and the fibers from this plant have been used in polymer composites (Chauhan and Singh 2012; Nadlene et al. 2015a,b, 2016). The roselle tree (Hibiscus sabdariffa L.) is easy to grow and is found in tropical areas ( Razali et al. 2015; Nadlene et al.2016a). Normally, these trees are used to produce medicine, food, ropes, jute, and textiles.
The sugar palm tree (Arenga pinnata Merr.), also known as Ijuk, belongs to the ‘Palmae’ family. It is the most widely used sugar palm for the harvest of sugar and fibers. The sugar palm tree can produce traditional sugar blocks more commonly known as Enau or Gula Kabung, which are often used as sweeteners in food and sugar palm fiber. Ijuk is also utilized in products for daily use, such as for brooms, brushes, and ropes, mats, and paint brushes (Huzaifah et al. 2017).
Hybridization is a combination of more than one fiber used to reinforce a matrix to increase its mechanical properties and reduce the cost of producing the hybrid fiber reinforced matrix composites (Pandya et al. 2011; Nunna et al. 2012; Saw et al. 2012). The hybridization of natural fibers in polymer composites is another promising approach in improving the physical properties of the material. Additionally, the hybridization of natural fibers with natural or synthetic fibers can improve the thermal properties, stiffness, ductility, damping, and strength of the matrix composite (Nunna et al. 2012; Sathishkumar et al. 2014; Saba et al. 2016; Aggarwal et al. 2017). The hybridization of sugar palm fiber with seaweed waste in a thermoplastic sugar palm starch/agar matrix increases the thermal, mechanical, and biodegradation characteristics of the material (Ridhwan et al. 2017c). This finding is attributed to the similar hydrophilic nature of the natural reinforcement, which resulted in good compatibility and adhesion between them.
Roselle fiber (RF) has the advantages of good tensile strength and durability in water. RF also has a high impact on the mechanical properties when it is used as fiber reinforcement in polymer composites (Nadlene et al. 2015a,b). Therefore, the hybridization of RF with natural fiber such as SPF aims to get the best combination hybrid fibers on TPU composites. The use of SPF for hybridization is due to its good fiber strength, resistance sea water and durability to developing unique hybrid composites (Saw et al. 2012; Kasim et al. 2015; Huzaifah et al. 2017). To date, there are no studies on RF/SPF hybrid reinforced thermoplastic polyurethane (TPU) composites. The aim of this paper is to study the properties of RF/SPS hybrid reinforced TPU composites with different percentages of RF /SPF hybrid composites (100:0, 75:25, 50:50, 25:75, and 0:100). The tensile strength, flexural strength, impact strength, and morphology of RF/SPF/TPU composites were examined.
EXPERIMENTAL
Materials
RF was obtained from a roselle plantation area in Mersing, Johor, and SPF was obtained from Jempul, Negeri Sembilan, Malaysia. To produce fibers from roselle plant, it was necessary to start with a water retting process that takes 14 days after soaking with water. Tap water was used to wash the retted stem, and RF was pulled out manually to separate the fiber and stem roselle. The SPF was washed with tap water to remove impurities and dried under sunlight. Both fibers were crushed and sieved using a sieve shaker machine. The size range used, 300 to 425 µm fiber length, was fixed throughout the study. The polymer material used as a matrix in this study was TPU with a density of 1.10 g/cm3, tensile strength 9.18 Mpa, flexural strength 5.24 MPa, and impact strength 9.88 (Radzi et al. 2017b). TPU was supplied by Pultrusion Sdn. Bhd, Seremban, Malaysia.
Sample Preparation
A Brabender Plastograph internal mixer (Duisburg, Germany) was used for the pre-mixing process of the RF/SPF/TPU hybrid composites at 170 °C. A hot press machine was used to pre-heat and full press the sample into sheet form at 170 °C under the load 40 tons. The fiber was arranged randomly. Lastly, the sample in sheet form was cool-pressed. The weight percentage of the reinforcement is shown in Table 1. The TPU as a matrix was maintained at 60 wt.% according to previous work (Radzi et al. 2017a) with designation for single roselle fiber with 40 wt% (RF-T) and sugar palm fiber with 40wt% (SPF-T).
Table 1. Composition of the Materials
Tensile Testing
Tensile properties were determined using a universal testing machine (UTM; Instron model 5556, (Norwood, MA), according to the ASTM D-638 (2002). The temperature used was 23 ± 1 °C. Humidity was 50 ± 5%, and the maintained speed was 5 mm/min.
Flexural Testing
Flexural test was determined using the UTM according to ASTM D-790 (2003). There were five samples prepared for this test, and they were cut into 130 mm x 13 mm x 3 mm. The temperature was 23 ± 1 °C, the humidity was 50 ± 5% and speed was maintained at 2 mm/min.
Impact Test
The impact test was determined by using an Instron CEAST 9050 pendulum impact tester (Norwood, MA) according to ASTM D-256 (2001). 5 samples notched were cut into 60 mm x 13 mm x 3 mm.
Scanning Electron Microscopy (SEM)
Morphological studies were performed on the fractured surface of the samples strength using scanning electron microscopy (Hitachi, model S-4300N, Japan). The sample composites were gold coated to provide electrical conductivity in order to obtain good quality morphological results before their surface was examined
RESULTS AND DISCUSSION.
Tensile Properties
The tensile strength of the RF/SPF/TPU hybrid composite is shown in Fig. 1. The tensile strength and modulus of the RF/SPF/TPU hybrid composites decreased with increasing in SPF content. RS-1 showed the highest value in tensile strength compared to the other hybrid composites. The highest tensile strength value recorded was 13.4 MPa, and the lowest was 11.1 MPa. Furthermore, adding the SPF into the RF composites caused a decrease in their tensile strength and modulus. This may be due to poor adhesion, high void, fiber pullouts, incompatibility, or agglomeration, which may have led to poor load transfer between the fiber and the matrix (Rozman et al. 2001; Saw et al. 2012; Yahaya et al. 2014).
Fig. 1. Tensile strength and modulus of RF/SPF/TPU hybrid composites
Good interfacial bonding between fibers, compatibility, and matrix are an important factor for the transferring stress from the matrix to the fibers (Threepopnatkul et al. 2009; Kasim et al. 2015). Good adhesion can enhance a sample’s mechanical properties. Also, the addition of SPF was one of the factors that weakened interfacial bonding of the hybrid composites. The SPF-T showed the lowest tensile strength compared to the RF-T and other hybrid composites. It is possible that when the SPF was added into the RF composites, it decreased the properties as shown in Fig. 1, as the SPF contents may have created more stress points and an increased incapability area on the polymer composite between the fibers and the matrix. Similar results have been reported by several authors (Rozman et al. 2001; Datta 2015; Essabir et al. 2016; Radzi et al. 2017b), whose studies have shown that the creation of high-stress points and an incapability area between reinforcements and matrix caused a weakening in tensile strength.
Figure 2 shows, at 50x magnification, the fractured surface with different RF/SPF/TPU hybrid percentages of composites. The image of RF and SPF can be observed in the SEM of the fiber in Figs. 2A and 2B. Figure 2 shows the distribution of RF/SPF hybrid composites with different percentage content of hybrid fibers, and it is clear that there is poor adhesion between the hybrid fibers and the matrix when the incorporated in the composites. Figures 2A and 2B show good interfacial bonding with and without the incorporation of SPF content in the composites.