ANALYSIS OF MECHANICAL STRENGTH OF WEIGHT FRACTION VARIATION SUGAR PALM FIBER AS POLYPROPYLENE- ELASTOMER MATRIX REINFORCEMENT OF HYBRID COMPOSITE

Polypropylene (PP) is a commodity polymer with versatile properties, which can be further modified in various ways. Judging from its versatility, PP production is one of the largest among other commodity polymers. PP has balanced properties, good rigidity, reasonable price, low density, heat distortion temperature, transparency, and fire resistance. PP is widely used in the automotive and construction industries [1]. PP is the second most important and cost-effective thermoplastic polymer after polyethylene on the global market. Polypropylene can be produced by molecular polymerization, which is why many scientists choose PP because of its low production cycle, low cost, and good properties. As a matrix material, PP is very commonly used because it has good properties for composite fabrication [2, 3]. Composites are materials made of two or more constituent materials with different physical and chemical properties, which when combined will produce a material with different characteristics between each component. The latest materials are more in demand than traditional materials because they have advantages such as being stronger, lighter, and cheaper. Composite materials are used in various application fields such as buildings, bridges, ship hull structures, car frames, bathtubs, sinks, marble countertops, and other materials. Composites with good properties and characteristics are the result of the right mixture of fiber and matrix materials. Many of today’s composites are made of smart materials such as shape memory polymers (SMP), piezoelectric, magneto-electro-elastic (MEE), electrorheological (ER) [4–6].

Recently, more focus has been given to cellulose-based fibers as reinforcement in polymer composites due to the impact on environmental pollution caused by the use of synthetic fibers such as glass fibers to produce composite materials. Polymer matrix composites are widely used in various fields such as household appliances, vehicle industry, and others. Very different from synthetic fibers, the use of natural fibers in the manufacture of composites has many advantages such as natural fibers having high strength, light weight, being easy to obtain, environmentally friendly, and biodegradable. Various types of natural fibers are being exploited for the purpose of producing biodegradable polymer composites [7,8]. Natural fiber is a fiber that is produced from animal and vegetable sources. Natural fibers include all natural cellulose fibers (coir, cotton, flax, etc.), as well as protein-based fibers such as silk and wool. Generally, natural fibers are strongly influenced by the nature and environmental conditions of the plant. Good fiber properties are produced due to the high cellulose content and the arrangement of microfibrils in the fiber. Fibers with high cellulose content include flax and kenaf, which also have higher structural advantages [9,10]. Natural fiber composites are very popular composites in the last few decades. Natural fibers are easily found in the fields such as industry, medical implants, mining, and textiles. In industrial applications, the potential for making natural fiber composites (biocomposites) is closely related to the success of making environmentally friendly materials. Natural fiber composites have good damping properties due to their viscoelastic properties, but also have lower stiffness and strength. Therefore, increasing the strength and stiffness of natural fiber composites is important to produce good natural fiber composites [11][12][13][14][15].
The great advantages of making composites using natural fibers are lower material costs, ease of availability, sustainability, and density. There are various types of natural fibers that are trending such as sugar palm, coconut fiber, hemp, curaua, sisal, and others. Sugar palm, scientifically called (Arenga pinnata), is a fast-growing tree. Sugar palm trees are traditionally grown for their sap, which is widely used as granulated sugar and brown sugar [16]. Sugar palm trees grow a lot and can be found in Asian countries, especially Indonesia. Sugar palm fiber has the potential to be used as a reinforcement in the manufacture of composites. Sugar palm fiber has many significant advantages to consider. Sugar palm fiber is known for its low price, biodegradability, very abundant availability. In terms of properties, palm fiber has low density, good mechanical strength, and good thermal properties [17][18][19].
Therefore, in this study, natural fibers, namely sugar palm fiber (Arenga pinnata), were used as reinforcement in the manufacture of hybrid composites with a polypropylene-elastomer matrix. This study aims to analyze the mechanical strength of the sugar palm fiber weight fraction as a hybrid polypropylene-elastomer composite matrix reinforcement.

Literature review and problem statement
The paper [20] showed the effect of microwaves on the tensile strength of palm fiber mixed with 6 % NaOH-reinforced polyurethane composites. The hot press machine is used to mix palm fiber and polyurethane resin in the manufacture of composites. Temperature variations used are 70, 80, and 90 °C applied in the microwave treatment. Based on the results and discussion, the highest tensile strength was recorded at 18.42 MPa at a microwave temperature of 70 °C and 6 % alkali. The use of palm fiber as a matrix reinforcement in composite materials has various advantages. In addition to having high tensile strength, this composite from natural fibers also has good properties for various applications. Some things that have not been explored in this research are bending testing and impact testing of palm fiber.
The paper [21] presents a study on the tensile strength properties of palm fiber reinforced with high impact polystyrene composite (HIPS). Variations in fiber load used are 10, 20, 30, 40, and 50 % by weight mixed with a polymer to make composites using a hot press. Based on the results of the study, the increase in the load of short fibers on the HIPS matrix can increase the value of the modulus of elasticity and tensile strength. In this study, palm fiber as a composite material has a good modulus of elasticity and tensile strength, so that palm fiber has great potential in making composites. This study has not tested the bending of palm fiber as a composite reinforcement.
The research carried out the manufacture of composites with date fiber reinforcement (DPF) (0 %, 40 %, 50 %, and 60 %) in phenolic composites. Based on the observation, the incorporation of 50 % DPF loading increases the impact strength and modulus, while reducing the tensile strength and flexural strength. 50 % DPF composite has better thermal and mechanical properties with better interfacial bond between fiber and matrix. This material is very well used in building, wall and ceiling applications [22]. Date fiber is a natural fiber easily available as palm fiber. This research has concluded that date fiber has good mechanical and thermal properties, which is feasible as a composite that is applied to buildings.
Oil palm empty fruit bunches (OPEFB) and sugarcane fiber (SCB) attracted the attention of researchers as reinforcing materials in the manufacture of high-potential composites in the building sector. This study showed that the hybridization of OPEFB/SCB fiber composites resulted in better performance and properties than those of pure fiber composites. Based on the results, the highest tensile strength and modulus were found at 5.56 MPa and 661 MPa, where the voids and the pore area were smaller than those of pure composites. This study also discusses agricultural residues, which are alternative green product materials that function as thermal insulation and heat retention on walls [23]. Apart from the use of palm fiber, dates, there is also the use of sugarcane fiber as a reinforcing material in the manufacture of composites, which are very feasible to be applied in the building sector.
Research has been carried out on the manufacture of composites using natural fibers (flax), synthetic fibers (glass) and unsaturated polyester resins. The composite laminates made include hemp/tidy polyester, glass/tidy polyester, and hemp/glass/polyester hybrid. Based on the research results, neat glass/polyester laminates got the best mechanical performance results from other laminates [24]. By producing good mechanical strength, namely neat glass/polyester laminate, this material can be relied upon as a material in the development of composite science.
The paper [25] showed research on making composites using cowhide obtained from the leather industry, which is also polluting the environment. Leather that is not used by the industry is used by adding unsaturated polyester (UPR) as a composite material. Fiber variations are divided into (2,5,7,10,12,15, and 20 % by weight). The finished composites were tested for mechanical strength, such as tensile strength, bending strength, and also their elastic modulus. This method is very feasible in overcoming the problem of environmental pollution from leather waste. Where the polluting leather waste is used as a material for the manufacture of composites. The problem that has not been resolved is that the production of a lot of used leather leads to a lot of unsaturated polyester, which causes production costs to also increase.
The tensile strength characteristics of cobalt fillers and fiber-reinforced epoxy composites can be applied to car body parts. The percentage of fiber weight was varied, namely glass fiber (GF) and carbon fiber (CF) filled with epoxy compounds. From the results of the research, the tensile strength of GF is around 96.9 MPa and 120 MPa, while the tensile strength of CF is 194.82 MPa and 393.34 MPa. Using 0.6 % weight cobalt (Co) filler for the combination of GF and CF epoxies can strengthen the results in the strength test [26]. But there were unresolved issues related to the manufacture of composite materials from cobalt fillers and fiber-reinforced epoxy. The reason for this may be that it is very expensive, which makes relevant research impractical. Therefore, research is needed using materials that are easily available and affordable, such as materials derived from natural fibers.

The aim and objectives of the study
The aim of this study is to produce a material that has good properties and characteristics in the field of engineering, by making a polypropylene-elastomer hybrid composite material with sugar palm fiber reinforcement.
To achieve this aim, the following objectives are accomplished: -to determine the tensile strength of the weight fraction variation sugar palm fiber as polypropylene-elastomer matrix reinforcement of hybrid composite; -to determine the impact strength of the weight fraction variation sugar palm fiber as polypropylene-elastomer matrix reinforcement of hybrid composite; -to determine the bending strength of the weight fraction variation sugar palm fiber as polypropylene-elastomer matrix reinforcement of hybrid composite; -to find out the scanning electron microscopy (SEM) of the weight fraction variation sugar palm fiber as polypropylene-elastomer matrix reinforcement of hybrid composite.

1. Materials of research
In this study, natural fiber namely sugar palm fiber (Arenga pinnata) is used as a reinforcement in the manufacture of composites, because sugar palm fiber (Arenga pinnata) is cheap and easy to obtain in Indonesia, which makes it interesting to analyze as an ingredient in composite manufacture. In addition, as already mentioned, palm fiber has good properties and characteristics as a composite. The matrix used in this research is polypropylene (PP) and elastomer. The reason for using polypropylene in this study is that apart from being relatively cheap and easy to obtain, the use of PP also plays an important role in reducing environmental pollution. The variations in the weight fraction of polypropylene (PP) and elastomer composites with sugar palm fiber reinforcement in this study were 20 % (80:20), 30 % (70:30), 40 % (60:40).
The materials used in this study consisted of sugar palm fiber as reinforcement, polypropylene polymer, and elastomer as a matrix, which can be seen in Fig. 1

2. Methods of research
The procedure carried out in the following research is to first prepare the tools and materials, followed by the process of cutting the elastomer into small sizes and the process of cutting the fibers and washing the PP. After that, it was continued with the process of soaking the fibers with 5 % NaOH solution for 1 hour. After the immersion was finished, it was followed by a composite molding process with a weight fraction of 20 % (80:20), 30 % (70:30), and 40 % (60:40). The research flowchart can be seen in Fig. 4. The layout of the composite mold is shown in Fig. 5.
Hot Press is used as a method in molding a hybrid composite of polypropylene and sugar palm fiber-reinforced elastomer. The molding procedure begins by preparing a mold that has been cleaned first and then smeared with glycerin to prevent the composite from sticking to the mold. After that, the PP, elastomer matrix, and sugar palm fiber were weighed according to their variations. After the preparation is done, the mold is placed on a hot press machine and is given a pressure of 3,000 psi with a temperature of 160 °C for 2 hours until the composite is formed. The printed composite can be seen in Fig. 6.  Fig. 6 is a hybrid polypropylene-elastomer composite mold with fiber reinforcement, which is finished and ready for various mechanical tests such as tensile tests, impact tests, bending tests, and SEM photos. This composite mold is molded through a hot press machine with high pressure and temperature in order to produce a good composite mold that is ready to be tested. At the testing stage, this mold will be divided by cut to facilitate the testing process.

5.
Results of research on the analysis of mechanical strength of weight fraction variation sugar palm fiber as polypropylene-elastomer matrix reinforcement of hybrid composite
The tensile strain of each composite weight fraction (20 %, 30 %, 40 %) can be described in Table 2.  The tensile elastic modulus of each composite weight fraction (20 %, 30 %, 40 %) can be described in Table 3. Fig. 9 is a graph of the tensile elasticity modulus of each composite weight fraction (20 %, 30 %, 40 %). Bending Test Impact Test Tensile Test    MPa. The addition of the fiber weight fraction in the composite material can increase the tensile strength value. This is because the fiber is the main load reinforcement or support for a composite material so that the greater the fiber weight fraction, the greater the tensile strength that the composite can withstand. Fig. 8 shows the tensile strain value for each composite, which is similar to the tensile strength, namely the greater the percentage of fiber weight fraction, the higher the strain value. Composites with a weight fraction of 20 % (80:20) got the lowest strain value of 0.0049, while composites with a weight fraction of 30 % (70:30) got a value of 0.0061, and the highest strain value of 0.0067 was found in composites with a weight fraction of 40 % (60:40).

4. Scanning Electron Microscopy (SEM) photos
SEM photos after the tensile test on the composites of each weight fraction (20 %, 30 %, 40 %) can be seen in Fig. 14.
SEM photos after the impact test on the composites of each weight fraction (20 %, 30 %, 40 %) can be seen in Fig. 15.
SEM photos after the bending test on the composites of each weight fraction (20 %, 30 %, 40 %) can be seen in Fig. 16. . It can be seen that there is an average fracture between the fiber and the matrix and there is no pull out. This is because the fiber and the matrix have a good interfacial bond, so that when a tensile load is applied, the fiber and the matrix break at the same time [27]. While in composites with a weight fraction of 30 % (70:30) in SEM photo observations, it is clearly seen that pull outs occur. This is due to imperfect compatibility between the fiber and the matrix, so that when receiving a tensile load, the fiber and the matrix are separated from their bonds [28]. Fig. 15 shows the results of SEM composite observations with a weight fraction of 40 % (40:60) at 27 times magnification. It can be seen clearly that there is a pull out. This is due to imperfect compatibility between the fiber and the matrix. While the results of SEM observations on composites with a weight fraction of 30 % (70:30), and 20 % (80:20) with 27 times magnification show that there is an average fracture between the fiber and the matrix and no pull out occurs. This is because the fiber and the matrix have a good interfacial bond, so that when subjected to an impact load, the fiber and the matrix break at the same time. Fig. 16 shows the results of the composite SEM observation test with a weight fraction of 40 % (60:40) and 30 % (70:30) at 27 times magnification. The bond between the fiber and the matrix occurs well, so that when subjected to bending loads, the fiber and the matrix fracture at the same time as indicated by a clean fracture on the SEM photo. The composite with a weight fraction of 20 % (80:20) explains that pull out occurs in the interfacial bond between the fiber and the matrix is not perfect, so that when exposed to bending loads, the fiber and the matrix are separated from the bond.

Discussion of the results of analysis of mechanical strength of weight fraction variation sugar palm fiber as polypropylene-elastomer matrix reinforcement of hybrid composite
This study describes the test results obtained from each research objective. The highest results of the tensile strength test were obtained for the composite with a weight fraction of 40 % (60:40), which was 2.613 MPa, while the lowest tensile strength was obtained for the composite with a weight fraction of 20 % (80:20), which was 2.46 MPa as seen in Fig. 7. The addition of the fiber weight fraction in the composite can increase the tensile strength. This is because the fiber is the main load reinforcement or support for the composite material. Therefore, the higher the fiber weight fraction, the higher the tensile strength. The highest impact test results of 176495.97 kJ/mm 2 were obtained in the composite with a weight fraction of 20 % (80:20), while the composite with a weight fraction of 40 % (60:40) had the lowest impact strength of 45248.234 kJ/mm 2 as can be seen in Fig. 10. The higher the fiber weight fraction, the lower the impact strength. So the addition of the weight fraction is very important, as it causes lower impact strength in the manufacture of composite materials. For bending testing, the composite with a weight fraction of 30 % (70:30) obtained the highest bending strength of 4.8867 MPa, while the lowest bending strength was obtained in the composite with a weight fraction of 20 % (80:20), which was 1.7778 MPa as seen in Fig. 11. For SEM photo observations of the composite weight fraction of 40 % (60:20) and 20 % (80:20), it can be seen that there is an average fracture between the fiber and the matrix and there is no pull out. This is because the fiber and the matrix have a good interfacial bond, so that when a tensile load is applied, the fiber and the matrix break at the same time as seen in Fig. 14. As for the 30 % weight fraction composite (70:30) in SEM photo observations, it is clearly seen that pull outs occur. This is due to imperfect compatibility between the fiber and the matrix so that when receiving a tensile load, the fiber and the matrix are separated from their bonds as can be seen in Fig. 14. In Fig. 15, the results of SEM photo observations for composites with a weight fraction of 40 % (60:40) clearly show that there is a pull out. This is due to imperfect compatibility between the fiber and the matrix, and the results of SEM observations for composites with a weight fraction of 30 % (70:30), and 20 % (80:20) show that there is an average fracture between the fiber and the matrix and no pull out occurs. This is because the fiber and the matrix have a good interfacial bond, so that when subjected to an impact load, the fiber and the matrix break at the same time. Fig. 16 shows the results of the composite SEM observation test with a weight fraction of 40 % (60:40) and 30 % (70:30). The bond between the fiber and the matrix occurs well, so that when subjected to bending loads, the fiber and the matrix fracture at the same time as indicated by a clean fracture on the SEM photo.
The solution that can be proposed in the research for the future is to increase the use of natural fibers as reinforcement in the manufacture of composites. Besides natural fiber, there is no need to worry about availability issues. One of the natural fibers offered is palm fiber. Sugar palm fiber is a natural fiber that is very suitable to be used as a reinforcement in the manufacture of composites because it has good properties in mechanical tests such as tensile tests, bending tests, and impact tests. Sugar palm fiber as a reinforcement in the manufacture of composite materials has many advantages. In terms of material availability, sugar palm fiber is very abundant, especially in Indonesia, which causes sugar palm fiber to become a cheap and easy to obtain raw material. The recommended matrix is polypropylene (PP) plastic because besides being able to be used as a matrix in the manufacture of composites, the use of PP also helps reduce the problem of plastic wastes that can pollute the environment.
The advantages obtained in this study are the use of natural fibers, especially palm fiber compared to the use of other materials because the fibers have good tensile and bending strength as a composite material. The availability of raw materials, namely palm fiber, is very abundant, especially in Indonesia, so there is no need to worry about production problems.
The limitation of this study is the temperature on the hot press machine to print composite materials that must reach 200 °C. If the temperature is below 200 °C, the PP matrix will not be able to blend well with other matrices.
The disadvantages in this study are found in the use of elastomeric materials as a matrix, where elastomeric materials have relatively expensive prices, so the research costs required are also high. So, in the manufacture of composite materials, it is advisable to use other materials that are easily available and inexpensive as a matrix so that this can save costs in the research process.

Conclusions
1. The highest tensile strength was obtained for the composite with a weight fraction of 40 % (60:40), while the composite with a weight fraction of 20 % (80:20) had the lowest tensile strength.
2. The highest impact strength was found in composites with a weight fraction of 20 % (80:20), and the lowest impact strength was found in composites with a weight fraction of 40 % (40:60).
3. The highest bending strength was found in the composite with a weight fraction of 30 % (70:30), while the composite with a weight fraction of 20 % (80:20) obtained the lowest bending strength.
4. SEM photos after the tensile test of the composite with a weight fraction of 40 % (60:40) resulted in a photo that did not occur in the fiber and matrix pull out. While the SEM after the impact test of the composite with a weight fraction of 30 % (70:30) resulted in a photo that did not occur in the fiber pull out. For the SEM photo, the bending test of the composite with a weight fraction of 40 % (40:60) got a photo of the average fracture between the fiber and the matrix without any pull outs.