Mechanical and Water Absorption Properties of Jute/Palm Leaf Fiber-Reinforced Recycled Polypropylene Hybrid Composites

Hybrid composites have proven endless bene ﬁ ts to the research communities in terms of environmental friendliness, mechanical properties, and development of new material. The present work explores the tensile, ﬂ exural, impact strengths, and water absorption properties of jute and palm leaf ﬁ ber-reinforced hybrid composites. Five types of hybrid composites were fabricated by varying jute and palm leaf ﬁ ber percentage of J100:P0, J25:P75, J50:P50, J25:P75, and J0:P100% with a constant weight ratio of polypropylene matrix. The ﬁ ndings showed that jute-palm leaf ﬁ ber-reinforced composite had positive e ﬀ ect on tensile, ﬂ exural, and impact strength. Experimental results showed that the J25:P75% (jute and palm leaf ﬁ ber) exhibited the highest tensile strength of 62.2 MPa and ﬂ exural strength of 82.26MPa due to the optimal interfacial properties between the ﬁ bers and matrix. The impact strength of composites increased as the proportion of palm leaf ﬁ ber increased. Water absorption increased with jute ﬁ ber content, reaching a maximum of 1.26% at composite J100:P0, with lower water absorption at J0:P100% composite due to the higher moisture content of jute ﬁ ber.


Introduction
There is a growing interest in the development of natural fiber composites, alternate to the existing artificial fiber composites. In recent years, the application of hybrid natural fibers as reinforcement in composite structures has received attention due to their advantages of low cost, environmental friendliness, and favorable biocompatibility over synthetic fiber composite materials [1][2][3][4][5][6]. Natural fiber-reinforced polymer composites have received more attention as a result of environmental concerns. Natural fibers including coir, banana, jute, and sisal offer an appealing and environmentally friendly alternative to glass fibers for reinforcing polymer-based composites [7].
Natural fibers are replacing synthetic fibers in mediumstrength applications due to benefits such as low cost, low density, abundant availability, environmental friendliness, nontoxicity, high flexibility, renewability, biodegradability, relative nonabrasiveness, high specific strength and stiffness, and ease of processing. Natural fibers offer several downsides in addition to these benefits, such as high moisture absorption, limited heat stability, and low impact strength. The technique of hybridization can be utilized to improve the mechanical strength of a single natural fiber-reinforced polymer composite [8][9][10].
The bulk of composites made by researchers used synthetic fibers as reinforcement, such as armed, glass fibers, silica, and carbon fibers. They did, however, provide a possible environmental problem because these fibers can become a major problem after disposal [11]. A hybrid composite is made up of two or more types of fiber, with the benefits of one type of fiber complementing the shortcomings of the other [12,13]. The use of natural fibers in a hybrid composite enables an environmentally sustainable product while still achieving the desired qualities in a balanced manner [14].
Numerous research works have been done natural fiberbased hybrid composites such as banana and palm leaf [15], palm leaf stalk fiber/jute fiber [16], banana/kenaf fiber [17], jute, pineapple leaf and glass fiber [17], banana, pineapple, and jute [18], jute/PP [19], and jute/glass fiber [20]. Gupta and Srivastava reported that PVA (polyvinyl alcohol)/starch reinforced with date palm leaf (DPL) fiber-based hybrid composite can be used for packaging applications. The thermal stability of the composite with 30% fiber is better than that of a neat PVA. The hybrid composite's biodegradation rate was lowered by including DPL fiber into the composite [9]. Polypropylene is widely used as a composite matrix because of its excellent fatigue and abrasion resistance, low density, good surface hardness, greater softening point, good strength, light weight, and electrical and chemical resistance at high temperatures [21,22].
Dhandapani and Megalingam reported that the tensile, flexural, and impact strength of sisal/palm fiber-reinforced hybrid composites increased as palm fiber content rose due to the tight link between the matrix and the fibers [23]. Jute and oil palm leaf are abundant, according to the researchers. According to a 2015 study, the palm oil sector in Malaysia generates 75.61 million tons of solid biomass waste per year, whereas the palm oil mill effluent (POME) waste created is 65.35 million tons per year [24]. Jute is an annual crop that takes 120 days to mature [8].
According to Jawaid et al., if properly constructed, hybrid composites derived from oil palm empty fruit bunches and jute could compete with synthetic composites. Automotive and aerospace have been mentioned as potential markets for oil palm-based hybrid composites in the future. Development of more appropriate, cost-effective manufacturing techniques, as well as composites with superior mechanical properties that use natural fibers as reinforcement, are ongoing problems. Nonetheless, advancements in this discipline have allowed natural fiberbased hybrid composites to be used in a variety of industries, including construction, automotive, and aerospace [25].
As previously stated, natural fiber hybrid composites have the potential to balance the limitations of one filler with the requirements of the other. The mechanical and water absorption capabilities of jute/palm leaf fiber hybrid composites with recycled polypropylene matrix were evaluated and investigated in this study.

Materials and Methods
2.1. Materials. In this study, nonhybrid and hybrid jute and palm leaf fibers were employed as reinforcement, and recycled polypropylene (PP) was used as a matrix. Jute, palm leaf fibers, and PP waste were collected from G-Seven Trading and Industry-Addis Ababa and Bahir Dar City-Ethiopia, respectively. The physical, mechanical, chemical, and thermal properties of jute and palm leaf fiber are given in Table 1 and Figures 1 and 2. 2.2. Composite Preparation. The fibers were immersed in 5% NaOH solution for 4 hours at room temperature (21-28°C). The fibers were then rinsed multiple times with distilled water before being immersed in very diluted HCl to remove the NaOH that had adhered to the surface. Finally, the fibers were rinsed multiple times with distilled water before being dried in a 60°C oven for 2 hours. This alkali treatment removed natural and artificial impurities which improves the fiber-matrix adhesion. It may also destroy the hydrogen bonding in cellulose hydroxyl groups of the fiber, thereby making them more reactive to the functional group of coupling agent, which in turn bonds to the polymer matrix.
The PP waste was crushed using gridding machine and changed to chips. The jute and palm leaf fibers were cut into 30 mm finally composite samples produced through melting, mixing, and molding process [26]. Jute and palm leaf fibers were added to the melted PP chips, mixed, and then transferred to the molding after uniform homogeneity to reduce fiber degradation due to heat. Compression molding is a closed-mold composite production method that employs matching metal molds and a 6 MPa external pressure. In this study, jute-palm leaf fiber hybrid composites were fabricated based on Table 2 weight percentage.

Characterization
3.1. Mechanical Properties of Fibers. The tensile strength and elongation of the jute and palm fibers were determined according to ES ISO 5079 standard using Tinius Olsen H1KS single-fiber strength tester as per the. The gauge length of the fibers was 50 mm, and a speed of 75 mm/min was maintained during the testing carried out at 20°C and 65 per cent relative humidity.

FTIR Analysis.
PerkinElmer FTIR instrument was used for the analysis of PP, jute, and palm leaf fibers. The spectrum version of the instrument was 10.03.06. To fix the test specimen on the instrument, a 11 N pressure force was applied. Measurement was done in the wave number region between spectral range 400-4000 cm −1 with a resolution of 2 cm −1 . To fix the test specimen on the instrument, a 12 N pressure force was applied.
3.3. Differential Scanning Calorimetry (DSC). The PerkinElmer Differential Scanning Calorimeter (DSC4000 model) was used to determine the thermal properties of the PP, jute, and palm leaf fibers. The heating rate used was 10°C/min and the samples were tested within the range from 30 to 400°C. The samples were placed in aluminum crucible and its weight was approximately 5 mg.     3 International Journal of Polymer Science absorption test, the specimens were removed from the water and cleaned to eliminate any excess moisture on the composite surface, after which they were weighted using an analytical balance at a set time interval to acquire the mass until the saturation point was reached. The mass difference is required to determine moisture absorption percentage as demonstrated in Equation (1). After that, the moisture absorption percentage was then plotted against the square root of time [8].

Moisture absorption
where M0 is the initial mass of the dry specimen and Mt is the mass of the immersed specimen after a certain period. The thermal properties of PP, jute, and palm leaf fibers using differential scanning calorimetry (DSC) have been analyzed in Figure 2. The degradation point of jute and palm leaf fibers was 340-380°C. This is the point at which a substance transforms or degrades into simpler chemical compounds. Environmentally benign and biodegradable, jute and palm leaf fibers have a degradation point. The highest degradation point is very important for manufacturing and using the technical textile products [27].    Figure 3 shows tensile strength of jute/palm leaf fiber-reinforced hybrid composites and the tensile strength increased as palm leaf fiber increases. Due to this, better tensile strength of 62.2 MPa is found for the hybrid composite J25:P75. In contrast, composite reinforced with 100% jute fiber had lower tensile strength than others. Tensile strength of hybrid composite J25:P75 is 7.6%, 5.4%, 1.2%, and 1.9% as compared to those of composites J100:P0, J75:P25, J50:P50, and J0:P100, respectively. This is because of jute fiber having low tensile strength and elongation may break first and then the load is carried by the palm leaf fiber having high strength and elongation without the failure of matrix, inducing better stress transfer from matrix to fibers and thus resulting in increased mechanical properties of hybrid composite. Another reason is that high cellulose content of palm leaf fiber also contributes to increase the mechanical properties of composite. As evident in Table 3, the statistical analysis showed that tensile strength of hybrid composite samples had significant difference with P value of 0.001 at α = 0:05. When compared to hybrid composites, nonhybrid palm leaf and jute fiber-reinforced composites had the lowest tensile strength. This is most likely due to the interfacial bond between the reinforcing fibers (jute and palm leaf) and the PP matrix, which is responsible for the composites' high strength. Because the stress is transferred from the matrix phase to the dispersion phase, the overall composite strength is increased. As seen in Table 1, the single fiber strength of jute and palm leaf fiber is comparable. However, tensile strength and elongation of composites were significant. This is because a lower amount of lignin in palm leaf fiber contributes to enhancing the mechanical properties of composites. Contrary, the reduction of tensile strength is due to the degree of compatibility at the level of the interfacial region between lignin and the matrix that is not desired [28]. Previous research has shown that the presence of lignin in a composite material lowers the material's bending mechanical properties [29,30].    MPa was recorded at composite sample reinforced with 100% jute fiber (J100:P0). As it can be seen in Figure 4, the flexural strength of hybrid composite J25:P75 is found 82.26 MPa which is 83.6%, 91.3%, 94.4%, and 98.9% more as compared to those of composites J100:P0, J75:P25, J50:P50, and J0:P100, respectively. Previous reports stated that weight percentage of palm leaf fiber shows dislocation of tightly packed fiber and matrix stickiness [23]. Nonhybrid palm leaf and jute fiber-reinforced composites demonstrated the lowest flexural strength, respectively, with compared to hybrid composites. This is because jute/palm leaf fibers with PP matrix have better interfacial characteristics. Table 3, the statistical analysis showed that hybrid composites are insignificant different in flexural strength at P value of 0.06 when α = 0:05. Figure 5 shows the impact strength of jute and palm leaf fiber-reinforced hybrid composite. Like tensile and flexural strength, impact strength increased as palm leaf fiber content increases. Composite reinforced with pure palm leaf fiber had the highest impact strength of 38.2 kJ/m 2 which is 49.8%, 57.4%, 64.7%, and 77.4% better than those of composites J100:P0, J75:P25, J50:P50, and J25:P75, respectively. On the other hand, composite sample J100:P0 had lower impact strength of 19.02 kJ/m 2 , followed by J75:P25, J50:P50, and J25:P75, respectively. Interfacial adhesion of jute/palm leaf fiber with combination of PP matrix may result in greater dispersion of components into matrices, resulting in increased impact resistance of composites, as described above.  The ANOVA result showed that the developed hybrid composite had significant difference in impact strength at F calculated (F) value of 103.594, F critical value of 2.866081, and P value of 0.001. As mentioned above, when the P value is ≤0.05, this means the composite properties are completely different and if P value is >0.05 inverse. In addition to this, when F critical < F calculated (F), it interpreted as the results are significantly difference. Figure 6 shows water absorption of hybrid jute/palm leaf fiber-reinforced composite. The percentage water absorption of composites had increased as the immersion time increases and palm leaf fiber content increases. Owing to this, composite samples J100:P0, J75:P25, J50:50, J25:P75, and J0:P100 are found 0.78%, 0.82%, 0.95%, 1.08%, and 1.26%, respectively, at 10 days. The composite J100:P0 had higher water absorption due to moisture content of fibers. As given in Table 3, the jute and palm leaf fiber moisture content was 12.03% and 8.4%, respectively, and it had significant effect on water absorption of composite. In the view of the moisture uptake, hybridization of different fibers is considered to be beneficial to the moisture sensitivity of the composites. It can be seen that the incorporation of palm leaf fiber in the hybrid composites was able to improve the resistance against moisture due to the lower moisture content of palm leaf fiber [8].

Water Absorption.
According to previous studies, including hydrophobic fibers into the jute composite increases moisture resistance and reduces water absorption into the composite [31].  Table 4 shows the comparison of mechanical properties of the present jute/palm leaf fiber-reinforced hybrid composite with different earlier published works. The tensile strength of the present hybrid composite is found to be higher by 60%, 50%, and 40% as compared to those of composites banana/sisal/epoxy, jute/ banana/epoxy, and kenaf/palm leaf/PP, respectively. Flexural strength of present hybrid composite is observed to be higher by 33.4%, 23.1%, and 23% as compared to those of composites kenaf/palm leaf/PP, banana/sisal/epoxy, and banana/jute/epoxy, respectively. Impact strength of present hybrid composite is 27.5% and 26.2% more than those of hybrid composites banana/sisal/epoxy and banana/jute/ epoxy, respectively.

Conclusion
Natural fiber hybridization in composites ensures both an environmentally friendly result and a balanced pursuit of required properties. The aim of this research work is that nonhybrid and hybrid composites were fabricated by varying jute and palm leaf fiber percentage of J100:P0, J25:P75, J50:P50, J25:P75, and J0:P100% with a constant weight ratio of polypropylene matrix. The findings revealed that the relative fiber ratio had a significant effect on composite mechanical characteristics. The favorable hybrid effect was achieved by incorporating palm leaf fiber into hybrid composites. When the percentage palm leaf fiber content was raised, the mechanical characteristics of composites improved. This phenomenon could be explained by palm leaf fiber's inherent higher strength, which results in higher mechanical strength. As a result, the incorporation of palm leaf fiber in composites improved mechanical properties and water resistance due to its high fiber strength and low moisture content compared to jute fiber. When compared to pure palm leaf and jute composite, this novel family of hybrid composite materials has unique features. Generally, tensile strength of the present hybrid composite is found to be 60%, 50%, and 40% greater than that of banana/sisal/ epoxy, jute/banana/epoxy, and kenaf/palm leaf/PP, respectively. When compared to composites kenaf/palm leaf/PP, banana/sisal/epoxy, and banana/jute/epoxy, the present hybrid composite has 33.4%, 23.1%, and 23% better flexural strength. The study concludes that the jute/palm leaf/PP hybrid composite had high tensile strength, whereas the J75:P25 composite with 50% PP matrix has improved tensile, flexural, impact, and moisture resistance. As a result, the produced lightweight and low-cost hybrid composites would be a good fit for medium-load applications such as building partition boards, automobiles, doorframes, train interior panels, and bags.

Data Availability
All data experiments can be found in the manuscript.

Conflicts of Interest
The authors declare that they have no conflicts of interest.