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Mechanical property improvement of oil palm empty fruit bunch composites by hybridization using ramie fibers on epoxy–CNT matrices

  • Praswasti Pembangun Dyah Kencana Wulan EMAIL logo and Yogi Yolanda
Published/Copyright: June 9, 2023
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Science and Engineering of Composite Materials
From the journal Science and Engineering of Composite Materials Volume 30 Issue 1

Abstract

Oil palm empty fruit bunches (OPEFBs) can be transformed into composite boards with higher selling value when their cellulose is used as a fiber. Manufacturing composites with hybridization techniques can improve their properties. This study combined OPEFBs and ramie fibers in an epoxy–carbon nanotube (CNT) matrix. The proportion of OPEFBs and ramie fibers was varied (3:7, 5:5, and 7:3), with a total fiber content of 10% by volume and a matrix of 90% by volume. Alkali treatment using NaOH solution was applied to the fiber to remove impurities from the surface. CNTs were functionalized using nitric acid followed by hydrogen peroxide to improve compatibility. Surface treatment was conducted on fibers and CNTs to increase the bonds between these components in the composite material. The hybridization of OPEFBs/ramie fibers improved the tensile strength in the 3:7TR, 5:5TR, and 7:3TR composites by 127, 37, and 12%, respectively, compared to the 10T composite. The flexural strength of the 5:5TR hybrid composite increased by 120%, and that of the 3:7TR and 7:3TR composites increased by 83% against the 10R composite. The 3:7TR hybrid composite showed the best mechanical properties.

Keywords: hybridization; oil palm empty fruit bunch fiber; ramie fiber; carbon nanotube; epoxy

1 Introduction

Indonesia is one of the largest producers of palm oil in the world. The area of oil palm plantations in Indonesia in 2022 is 15.38 million ha, with a production of 48.23 million tons [1]. Solid waste produced from 35 to 40% of the total fresh fruit bunches is processed as empty fruit bunches, fibers, fruit shells, ashes, and palm oil cakes. Empty palm fruit bunches are not yet massively utilized. If allowed to accumulate, they will cause waste problems [2]. This huge amount of waste could become a source of income if it can be used to make goods with a higher selling value, increasing the economic value of oil palm empty fruit bunch (OPEFB) waste. OPEFB, shown in Figure 1, consists of a set of fibers readily available cheaply. These fibers can also be used for valuable products, such as fuels, fertilizers, and composites. OPEFB waste is lignocellulosic biomass that can be utilized in fiber composite boards [3]. For environmental reasons, it is better to use agricultural waste than virgin natural fibers. Most agricultural wastes are cheap, light, biodegradable, and environmentally friendly and are obtained from renewable sources [4].

Figure 1 OPEFB.
Figure 1

OPEFB.

A composite is a combination of two or more materials where the final assembly has better properties than the properties of each component [5]. This combination is mixed with adhesives, such as epoxy, that have high-strength bonds [6]. Composite materials commonly contain reinforcements or fibers, matrix, and fillers and are widely used in various industrial fields, including aviation, aerospace, automotive, and marine [7,8]. Developing composite boards based on natural fiber is an alternative to the wood needed for construction or furniture. The advantages of these composite products are lower production costs, abundant raw materials, flexibility in the manufacturing process, and better properties, such as high density, low air content, and stability. However, polymer wood composites have weaknesses: their mechanical properties are not as good as solid wood. Enhancing the strength of the composite can be done using nanotechnology. Carbon nanotubes (CNTs) are the most studied nanomaterials because they have excellent mechanical strength and electronic properties.

Several researchers have researched the addition of CNTs to natural fibers. Wulan [9] studied the effect of OPEFB fiber shape on the mechanical strength of composites with added CNTs. The composite was formed into chopped strands, fiber mats, and woven roving using the hand lay-up method. The composite made from woven OPEFB/CNT and epoxy resin had the highest bending strength, up to 32.41%, compared to the composite made without CNTs. However, the process used to mold composite forms still causes voids, resulting in a decrease in the strength of the material [10]. In 2021, Wulan conducted research on adding CNTs to sugarcane bagasse composites. Adding 0.5% by weight CNTs to bagasse fiber increased the flexural strength by up to 150% compared to composites without CNTs [11]. In contrast, Adin has studied the effect of adding aluminum, mica, and ceramic particles to jute epoxy composite on the tensile and bending properties of the resulting composites [12]. The tensile and bending failure loads increased.

Hybridization with other natural fibers can reinforce each component. Many studies have been carried out on hybrid composites based on natural fibers, such as banana and palm leaf [13], banana/pineapple/jute [14], and jute/glass fiber [15]. Hanan et al. [16] studied hybrid composites' mechanical and morphological properties on OPEFB/kenaf fiber with epoxy resin. The proportions of OPEFB and kenaf fibers were varied (7:3, 5:5, and 3:7) with 50% by weight of total fiber and 50% epoxy resin. Composites were printed using the hand lay-up method and pressed by a hot press. The 3:7 composition of OPEFB and kenaf fiber gave tensile strength and flexural strength of 55.7 MPa and 115.8 MPa, respectively. Adding kenaf fiber to OPEFB also reduced the void content in the composite to 4.2% because the density of kenaf fiber is higher than that of OPEFB.

This study fabricates a composite by utilizing OPEFB waste and adding other natural fibers to improve the properties and morphology of the composite to produce a good quality material for furniture or construction. Some hybrid composites have already been developed using a mixture of natural or added glass fibers. However, ramie fibers have not been studied. This study combines ramie fibers with OPEFBs because of their high cellulose content and high density [17]. The composite was made by hybridizing OPEFBs and ramie fibers by adding CNT and epoxy resin using the hand lay-up method. This hybrid composite is expected to have an optimal fiber composition and increased mechanical strength. Thus, it can be developed into a composite board and provide business opportunities for the furniture industry to be more creative, innovative, and environmentally friendly.

2 Experimental section

2.1 Materials

OPEFBs were obtained from the local waste industry in Bangka Belitung, Indonesia, and ramie was obtained from the Sleman District of Yogyakarta, Indonesia. Both fibers were then treated with NaOH solution. The 98%-purity MWCNT used in this research was obtained from Timesnano and then treated with mild acids HNO3 and H2O2 30% v/v (Sigma-Aldrich, USA). The silane-coupling agent was 99%-purity γ-glycidoxypropyltrimethoxysilane (GPTMS; KBM-403) obtained from Shin-Etsu. Epoxy resin DGBA (diglycidylether bisphenol A) was used as the matrix with hardener cycloaliphatic amine.

2.2 Procedures

The OPEFBs and ramie fibers were alkali-treated using NaOH solution to remove lignin and reduce the pectin content. OPEFB fibers (100 g) were put into an NaOH solution (10 g NaOH/1,000 ml) and heated to 100°C for 2 h. Next, 100 g of ramie fibers were soaked in 1,000 ml of the same NaOH solution at room temperature for 2 h. After the alkali treatment, the OPEFBs and ramie fibers were treated using GPTMS at 10% by volume and dissolved in 500 ml of 95% ethanol. The solution was stirred using a magnetic stirrer for 1 h. After stirring, the OPEFB and ramie fibers were separately immersed into the GPTMS–ethanol solution for 24 h. The treated fibers were washed with distilled water and dried in an oven at 100°C for 3 h.

Next, 2 g of CNT was mixed into 500 ml of 3M HNO3 solution. Then, the mixture was stirred using a magnetic stirrer at 60°C for 15 min. After stirring, the mixture was sonicated using an ultrasonicator for 2 h to produce a more even dispersion. The CNTs were then filtered using a vacuum filter and dried in an oven for 4 h. The functionalization was continued by replacing the HNO3 solution with 500 ml of 30% H2O2 solution and repeating the process. After functionalization, the CNT surface was treated using GPTMS to produce a covalent bond between the coupling agent and the CNT surface. The treatment used 10% v/v GPTMS in 500 ml of 95% ethanol. The resulting fibers and CNTs were analyzed using a Shimadzu IR Prestige-21 Fourier transform infrared (FTIR) spectrometer to characterize the chemical structure of the fibers and CNTs.

The CNT concentration was adjusted to 0.5% of the matrix by weight. Then, the CNTs were mixed with acetone and sonicated for 30 min for even dispersion. The CNTs were dispersed in an epoxy resin, ignited at a temperature of 70°C, and stirred using a magnetic stirrer until the acetone evaporated. The composite was molded using the hand lay-up technique on an iron mold measuring 130 mm × 13 mm × 3 mm. The mold is coated with mold-release wax so that the resin does not stick to it, making removing the composite from the mold easier.

The morphology of the fractured surfaces of the composites was analyzed using a scanning electron microscopy (SEM) instrument, JEOL JSM-IT 200. Mechanical properties’ tests were performed to quantify the performance of the hybrid composite and compare it with that of the pure fiber. The mechanical tests were tensile tests with a 5 mm/min crosshead speed and flexural tests with a 10 mm/min crosshead speed using a Shimadzu AGS-X Series universal testing machine. The water absorption and thickness swelling were measured according to ASTM D1037; the density and void content were determined according to ASTM D2734. All tests were conducted at room temperature.

The water absorption was calculated as follows:

(1) Water absorption ( % ) = W o – W d W d × 100 ,

where W o is the weight of specimens after immersion in distilled water and W d is the weight of specimens before immersion in distilled water.

The thickness swelling test was calculated as follows:

(2) Thickness swelling ( % ) = T o – T d T d × 100 ,

where T o is the thickness of specimens after immersion in distilled water and T d is the thickness of specimens before immersion in distilled water.

The density of the samples was calculated using the following equation:

(3) Density , ρ = Mass ( m ) Volume ( V ) ,

where m is the mass of the composite board in grams and V is the volume of the composite board in cm3.

The void content was determined from the theoretical and experimental density of the composites by applying the following equation:

(4) Void content ( % ) = ρ theoritical − ρ experimental ρ theoritical ,

where ρ theoretical was calculated as follows:

(5) ρ theoretical = 100 / R D + r d ,

where R is the matrix weight fraction, r is the fiber weight fraction, D is the matrix density, and d is the fiber density.

3 Results and discussion

3.1 FTIR spectra of OPEFB fibers

In Figure 2, the FTIR spectra of the OPEFB fiber before modification show peaks at 3268.91, 2915.18, 1539.95, and 1237.46 cm−1, which are assigned to the hydroxyl (–OH) group of cellulose, C–H (a structure found in cellulose), the carbonyl group (C═O) of hemicellulose, and the C═C aromatics associated with lignin, respectively. After the modification of the OPEFB fiber, the –OH peak shifted to 3323.57 cm−1 due to the influence of alkali treatment. The increase in the –OH peak proves that alkali treatment activated the –OH group, making the fiber with a higher concentration of –OH bonds [11]. The carbonyl group peak shifted from 1539.95 to 1599.01 cm−1 because of reduced hemicellulose on the fiber surface after alkali treatment [18]. The C═C peak was still visible between 1,200 and 1,300 cm−1, showing that the alkali treatment was less than optimal because it only reduced the lignin [19].

Figure 2 Fourier transform infrared (FTIR) spectra of OPEFB fiber before and after modification.
Figure 2

Fourier transform infrared (FTIR) spectra of OPEFB fiber before and after modification.

In Figure 2, hydroxyl and silane groups formed in the fiber and alkoxy groups, indicated by the presence of Si–O–Si and Si–O–C bonds between 740 and 940 cm−1. In the literature, the most intense peak in the GPTMS spectrum occurred between 780 and 1,200 cm−1 due to C–O, Si–O, and Si–C tension [20].

3.2 FTIR spectrum of ramie fibers

Figure 3 shows the FTIR spectrum of ramie fibers, which exhibited peaks at 3275.84, 2894.16, 1624.01, and 1237.46 cm−1, which can be attributed to the hydroxyl group of cellulose, the C–H vibration of cellulose, the carbonyl (C═O) of hemicellulose, and the C═C aromatic vibration of lignin, respectively. After modification, the −OH peak decreased in intensity. It shifted to 3378.82 cm−1, and the intensities of the carbonyl peak of hemicellulose at 1626.55 cm−1 and the C═C peak of the aromatic ring of lignin at 1254.83 cm−1 decreased.

Figure 3 FTIR spectra of ramie fibers before and after modification.
Figure 3

FTIR spectra of ramie fibers before and after modification.

The research of Sepe et al. on the surface treatment of ramie fibers using a silane-coupling agent of the GPTMS type showed that Si–O–C has a peak at 833 cm−1 [20]. The peak reductions of C═O and C═C showed that the hemicellulose and lignin contents were reduced by alkali treatment. The chemical changes between the hydroxyl and silane groups on the fiber and alkoxy groups on the coupling agent were indicated by the presence of Si–O–C and Si–O–Si bonds. Si–O–Si bonds form due to the bonds between the coupling agents; Si–O–C bonds form due to chemical reactions between the coupling agents and the fibers [21]. Si–O–C bonds will allow it to react with the polymer matrix, increasing the interface between the fiber and the matrix [22].

3.3 CNT functionalization

The FTIR spectra of CNTs before and after the functionalization process were collected, as shown in Figure 4. In the pre-functionalization CNTs, the hydroxyl group (–OH) vibration appeared at 3366.85 cm−1 and the carbonyl group (C═O) appeared at 2024.72 cm−1. FTIR analysis showed the success of the functionalization process with an increase in the intensity of the hydroxyl peak at 3278.82 cm−1 and the carbonyl peak at 2021.20 cm−1, as well as increased interaction between the matrix and CNTs and an increase in the solubility of CNTs [23,24].

Figure 4 FTIR spectra of CNTs before and after the mild acid oxidation process.
Figure 4

FTIR spectra of CNTs before and after the mild acid oxidation process.

After functionalization, the CNTs were treated using GPTMS to produce a covalent bond between the coupling agent and the CNT surface. The presence of Si–O–Si and Si–O–C bonds showed the success of treating the CNT surface with the silane-coupling agent [25]. Figure 5 shows the success of this surface treatment, namely the formation of Si–O–Si and Si–O–C bonds between 900 and 1,000 cm−1. The Si–O–Si bonds are due to the silanol group formed in GPTMS and air in ethanol. The silanol group will react quickly with an −OH on the surface of the functionalized CNT to form Si–O–C [26]. Le et al. reported the same reaction in 2013, who said that surface treatment's success for CNTs formed an Si–O peak at 1,073 cm−1 [24]. Based on the research conducted by Nie and Hubert in 2012, CNTs treated with silane can increase the dispersion of the matrix [27].

Figure 5 FTIR spectra of CNTs before and after surface treatment.
Figure 5

FTIR spectra of CNTs before and after surface treatment.

3.4 Density and void content

The compactness and density of the material were measured. Compact composites can withstand a stronger load due to the strong composite particles. The density and void content of the composites are shown in Table 1.

Table 1

Density and void content of composites

No Sample Composition Density (g/cm3) Void content (%)
1 3:7TR 30:70 OPEFB:ramie 1.1011 7.37
2 5:5TR 50:50 OPEFB:ramie 1.0905 8.35
3 7:3TR 70:30 OPEFB:ramie 1.0802 9.57
4 10T 100 OPEFB 0.8134 32.92
5 10R 100 ramie 1.0592 10.50

SNI standard composite broad >0.4 g/cm3.

Table 1 shows that the 10T composite has a density of 0.8134 g/cm3 with a void content of 32.92%, while the 10R composite has a density of 1.0592 g/cm3 and a void content of 10.05%. The combination of ramie fibers into OPEFB fibers with a composition of 30:70 OPEFB:ramie (3:7TR) had the highest density, 1.1011 g/cm3, and the smallest void content, 7.37%, compared to other hybrid composites. The reduced void content of the composite is due to the high level of interfacial bonding between the fiber of the hybrid composite and the epoxy matrix due to an enhanced synergistic effect [28]. The different densities of each composite were mainly due to the empty space in the composite. The void content indicates the presence of air trapped in the composite, causing low density. The lower the density of the composite, the higher the void content [29].

3.5 Water absorption

Figure 6 shows the water absorption of the composites for up to 48 h of immersion. A small void content will generally cause the composite to absorb less water. The small void content of the 3:7TR hybrid composite caused this composite to have the lowest absorption capacity [16], which was 5.32% after 48 h. The 5:5TR and 7:3TR hybrid composites had slightly higher water absorption levels than the 3:7TR hybrid composites, 5.39, and 5.49%, respectively. The 10T composite, which had the most significant void content, contained many microchannels that allowed air to pass through the pores on the surface of the composite, giving it the highest absorption capacity, 8.27%. The higher the void content in the composite, the higher the absorption capacity. Material density influences water absorption. This is indicated by the low density of the 10T composite, which has a large void content. The cavities present form microchannels that allow air to pass through the pores on the fiber surface [30]. Incoming water is then absorbed by the –OH group, which causes an increase in water absorption in the fiber [31].

Figure 6 Water absorption of OPEFB/ramie hybrid composites.
Figure 6

Water absorption of OPEFB/ramie hybrid composites.

3.6 Thickness swelling

In Figure 7, the swelling of the 10T composite was 5.26%, while that of the 10R composite was 4.09% between 24 and 48 h of immersion. The 10T composite showed poor interfacial adhesion between the fibers and the matrix, which caused a large amount of air to diffuse into the composite [32]. Adding ramie fibers to the OPEFB fibers in the 3:7TR hybrid composite reduced the highest thickness swelling by 37% compared to the 10T composite after 48 h of immersion (3.30%).

Figure 7 Thickness swelling of OPEFB/ramie hybrid composite.
Figure 7

Thickness swelling of OPEFB/ramie hybrid composite.

Meanwhile, the thickness swelling of the 5:5TR and 7:3TR hybrid composites was reduced by 36 and 27% compared to that of the 10T composite to 3.35 and 3.78%, respectively. The compact fiber structure of the ramie fiber had a higher density and smaller void content than the OPEFB fiber, thereby increasing the interfacial adhesion and decreasing its ability to absorb water [33]. The layer thickness is affected by exposure to temperature and changes in humidity, which cause the formation of microcracks [32]. The swelling of the composite induced stress in the interfacial region, which leads to microcracking in the matrix surrounding the fibers. Air molecules the fibers absorb form hydrogen bonds, weakening the interfacial adhesion and debonding the fibers [34].

3.7 SEM

The SEM results for the 10T composite shown in Figure 8(a) indicate that there are still many voids compared to the 10R composite (Figure 8(b)) due to the weak interfacial interaction between the fibers and the matrix [16].

Figure 8 SEM images of tensile fractures of (a) 10T OPEFB composite and (b) 10R ramie composite.
Figure 8

SEM images of tensile fractures of (a) 10T OPEFB composite and (b) 10R ramie composite.

These voids affect the density of the composite where the void content of 32.92% in the 10T composite decreases the density, i.e., 0.8134 g/cm3. Meanwhile, the SEM image of the 10R composite shown in Figure 8(b) shows a more even distribution of fibers and a good interface, which contribute to effective stress transfer from the matrix and increase the strength of the composite [16].

The SEM image of the tensile fracture of the 3:7TR hybrid composite (Figure 9(a)) showed improvements: the voids seen in the hybrid composite were reduced due to good adhesion between the fibers and the matrix. The epoxy matrix appears to cover and absorb into the fibers. This improved the interface between the fiber and the matrix, increasing the synergistic effect and reducing the void content in the composite [28]. The low void content in the 3:7TR composite (7.37%) increases the density (1.1011 g/cm3) due to the better density between the fiber and the matrix. The reduction of voids is due to the silane-coupling agent, which changes the hydrophilic properties to hydrophobic properties. This treatment forms Si–O–C bonds between the coupling agent and the fiber, increasing the interaction between the fibers and the matrix and the adhesion of the interface [28].

Figure 9 SEM results of the hybrid composite tensile fractures of (a) 3:7TR, (b) 5:5TR, and (c) 7:3TR.
Figure 9

SEM results of the hybrid composite tensile fractures of (a) 3:7TR, (b) 5:5TR, and (c) 7:3TR.

The SEM image of the tensile fracture of the 5:5TR hybrid composite in Figure 9(b) shows a microcrack in the polymer matrix formed because of the loading on the hybrid composite. The compressive strength causes weak interface interactions between the fiber and the epoxy matrix [16]. In addition, microcracks also provide a pathway for the entry of water vapor and oxygen, which causes overall material degradation and affect the durability of the composite material [35]. Fiber pull-out and fiber breakage from the matrix were also seen in the tensile fractures of 5:5TR (Figure 9(b)) and 7:3TR (Figure 9(c)). This generally resulted in poor adhesion to fibers and matrices, lowering their mechanical strength [36].

Based on Figure 9(a)–(c), adding ramie fiber to OPEFB fibers in hybrid composites reduced the void content because ramie fibers have strong mechanical properties and high density compared to OPEFB fibers [17]. The addition of CNTs to each composite also improved surface homogeneity by minimizing the composite’s fiber pull-out and fiber breakage due to micromechanical interlocking between the CNT, fiber, and matrix. This indicates good adhesion and interfacial bonding, which produce good tensile strength [36].

3.8 Tensile properties

Figure 10 shows that the 10T composite has a tensile strength of 10.22 MPa, which is smaller than the 10R composite, which has a tensile strength of 17.09 MPa. This difference in strength is due to the low density of the 10T composite than that of the 10R composite [37]. The void content of the composite causes the low density. Voids can affect mechanical strength, including shear, flexural, tensile, and compressive strengths [16]. The 3:7TR hybrid composite shows the highest increase (127%) in tensile strength to 23.25 MPa compared to the 10T composite, followed by the 5:5TR hybrid composite, which showed a 37% increase to 14.02 MPa, and the 7:3TR hybrid composite, which showed a 12% increase to 11.52 MPa, compared to the 10T composite.

Figure 10 Tensile strength of OPEFB/ramie composites.
Figure 10

Tensile strength of OPEFB/ramie composites.

Adding ramie fibers to the OPEFB/ramie hybrid composite increased the tensile strength because ramie fibers had a higher tensile strength than OPEFB fibers; they could withstand loads until deformed [31]. The increased tensile strength indicated a good distribution of fibers in the polymer matrix and an even distribution of fibers in the composite. The low interfacial bonding of OPEFB to the epoxy matrix gave OPEFB a low tensile strength [38]. Surface treatment using a silane-coupling agent improved the bonding between the matrix and the fiber. Jappes and Siwa also reported that surface modification increases the tensile strength of composites by up to 85% [39]. Modifying the fiber surface from hydrophilic to hydrophobic allows it to bind to the active groups of the polymer to prevent air from entering the fiber and the matrix [40]. Increased moisture content can form microcracks and large cavities in the composite, reducing the elastic modulus and strength. In general, swelling in composites induces stresses in the interfacial region that cause microcracks in the matrix surrounding the fibers. Water molecules absorbed by the fibers form many hydrogen bonds, which weaken the interfacial adhesion and debond the fibers [34]. As shown in Figure 7, the hydrophilicity of natural fibers implies that the fibers exhibit high water absorption, which could be caused by the failure of parts of the composites produced in wet conditions. The swelling or delamination of the fibers on the composite surface causes this.

In general, moisture diffusion in composites depends on factors such as fiber volume fraction, voids, matrix viscosity, humidity, and temperature. However, when the water absorption of the pure ramie composite and the OPEFB/hybrid ramie composite was compared, a reduction in overall water absorption for the pure OPEFB composite was observed. With hybridization, the resistance to water absorption is greatly increased, as shown in Figure 7. Jawaid and Abdul Khalil investigating the tensile and flexural strength of hybrid composites made from OPEFB with fiber-reinforced epoxy, showed that the tensile and flexural properties of the hybrid composites were higher than those of the pure empty palm oil bunch composites but lower than those of woven jute composites.

The findings of this study agree with previous research showing that the mechanical and physical properties of natural fiber–reinforced thermoset polymer composites are influenced by several factors, including (i) composite parameters such as fiber source, reinforcement type, lamination sequence, amount of reinforcement, the woven fiber content in the polymer, fiber orientation, and coating order of woven fibers; and (ii) fabrication process parameters, including processing technique, processing temperature, and pressure level [41].

3.9 Flexural properties

Based on the flexural test shown in Figure 11, the highest flexural strength measured for the 10T composite is 25.38 MPa. Meanwhile, the lowest flexural strength, 9.15 MPa, was measured for the 10R composite. This showed that the OPEFB fiber with epoxy resin has better flexibility than the ramie fiber. In Figure 10, the flexural strength of the OPEFB/ramie hybrid composite decreased compared to that of the OPEFB fiber composite but increased compared to that of the ramie fiber composite. The flexural strength of the 5:5TR hybrid composite increased the most (120%), to 20.26 MPa, followed by those of the 3:7TR hybrid composite and 7:3TR hybrid composite, which increased by 83% to 16.76 and 16.97 MPa, respectively, compared to that of the 10R composite. Thus, composite hybridization can compensate for the weakness of the ramie fiber using OPEFB fiber to improve flexural strength and maximize mechanical strength [16].

Figure 11 Flexural test results of OPEFB/ramie composites.
Figure 11

Flexural test results of OPEFB/ramie composites.

4 Conclusion

This research investigated the effect of hybridization of OPEFB/ramie-reinforced epoxy composites on their mechanical properties. The results showed that the mechanical properties of OPEFB/ramie hybrids, especially void content, water absorption, thickness swelling, tensile strength, and flexural strength degradation, increased after the specimens were soaked in water for 48 h. SEM analysis showed that the hybridization of the OPEFB/ramie composite improved its surface morphology by reducing the void content. OPEFB has poorer mechanical properties than ramie, so hybridizing these fibers with other fibers with better mechanical properties (such as ramie fiber) is an option to improve the performance of OPEFB fibers. Hybridization can produce better results than modifying natural fibers with coupling agents. The sequence of composites with differing proportions (10T, 7:3TR, 5:5TR, 3:7TR) showed the maximum mechanical strength compared to other hybrid composites. The proper hybrid ratio variation sequence is an important factor in determining the quality of hybrid composite materials. The use of hybrid natural fibers in this study has shown satisfactory results because they meet the composite board standards based on SNI 03-2105-2006. Thus, hybrid composite materials can be developed into composite boards by molding composites using vacuum bag molding. However, the use of woven natural fiber–reinforced polymer composites is not recommended for outdoor applications because the tensile strength of the composites decreases when exposed to water. From the results of this study, hybrid composites can be used for non-structural and industrial applications, such as the manufacture of indoor components in the automotive and furniture industries.

Acknowledgements

The author would like to thank the Directorate of Research and Community Service – Universitas Indonesia for research funding through The Hibah Publikasi Terindeks Internasional (PUTI) Pascasarjana Tahun Anggaran 2022-2023, with the Contract Number, Nomor: NKB-334/UN2.RST/HKP.05.00/2022.

  1. Author contributions: Praswasti PDK Wulan: Conceptualization; Formal analysis; Funding acquisition; Methodology; Resources; Supervision; Validation; Visualization; Roles/Writing – original draft; Writing – review & editing. Yogi Yolanda: Data curation; Investigation; Project administration; Software.

  2. Conflict of interest: Authors state no conflict of interest.

  3. Data availability statement: The authors confirm that the data supporting the findings of this study are available within the article. Raw data that supported the findings of this study are available from the corresponding author, upon reasonable request. A data availability statement tells the reader where the research data associated with a paper is available, and under what conditions the data can be accessed.

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Received: 2023-01-31
Revised: 2023-03-28
Accepted: 2023-03-30
Published Online: 2023-06-09

© 2023 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/secm-2022-0198
Keywords for this article
hybridization; oil palm empty fruit bunch fiber; ramie fiber; carbon nanotube; epoxy
Creative Commons
BY 4.0

Articles in the same Issue

  1. Regular Articles
  2. Effects of cellulose nanofibers on flexural behavior of carbon-fiber-reinforced polymer composites with delamination
  3. Damage mechanisms of bismaleimide matrix composites under transverse loading via quasi-static indentation
  4. Experimental study on hydraulic fracture behavior of concrete with wedge-splitting testing
  5. The assessment of color adjustment potentials for monoshade universal composites
  6. Metakaolin-based geopolymers filled with volcanic fly ashes: FT-IR, thermal characterization, and antibacterial property
  7. The effect of temperature on the tensile properties and failure mechanisms of two-dimensional braided composites
  8. The influence of preparation of nano-ZrO2/α-Al2O3 gradient coating on the corrosion resistance of 316L stainless steel substrate
  9. A numerical study on the spatial orientation of aligning fibrous particles in composites considering the wall effect
  10. A simulative study on the effect of friction coefficient and angle on failure behaviors of GLARE subjected to low-velocity impact
  11. Impact resistance capacity and degradation law of epoxy-coated steel strand under the impact load
  12. Analytical solutions of coupled functionally graded conical shells of revolution
  13. The influence of water vapor on the structural response of asphalt pavement
  14. A non-invasive method of glucose monitoring using FR4 material based microwave antenna sensor
  15. Chloride ion transport and service life prediction of aeolian sand concrete under dry–wet cycles
  16. Micro-damage analysis and numerical simulation of composite solid propellant based on in situ tensile test
  17. Experimental study on the influence of high-frequency vibratory mixing on concrete performance
  18. Effects of microstructure characteristics on the transverse moisture diffusivity of unidirectional composite
  19. Gradient-distributed ZTAp-VCp/Fe45 as new anti-wear composite material and its bonding properties during composite casting
  20. Experimental evaluation of velocity sensitivity for conglomerate reservoir rock in Karamay oil field
  21. Mechanical and tribological properties of C/C–SiC ceramic composites with different preforms
  22. Mechanical property improvement of oil palm empty fruit bunch composites by hybridization using ramie fibers on epoxy–CNT matrices
  23. Research and analysis on low-velocity impact of composite materials
  24. Optimizing curing agent ratios for high-performance thermosetting phthalonitrile-based glass fibers
  25. Method for deriving twisting process parameters of large package E-glass yarn by measuring physical properties of bobbin yarn
  26. A probability characteristic of crack intersecting with embedded microcapsules in capsule-based self-healing materials
  27. An investigation into the effect of cross-ply on energy storage and vibration characteristics of carbon fiber lattice sandwich structure bionic prosthetic foot
  28. Preparation and application of corona noise-suppressing anti-shedding materials for UHV transmission lines
  29. XRD analysis determined crystal cage occupying number n of carbon anion substituted mayenite-type cage compound C12A7: nC
  30. Optimizing bending strength of laminated bamboo using confined bamboo with softwoods
  31. Hydrogels loaded with atenolol drug metal–organic framework showing biological activity
  32. Creep analysis of the flax fiber-reinforced polymer composites based on the time–temperature superposition principle
  33. A novel 3D woven carbon fiber composite with super interlayer performance hybridized by CNT tape and copper wire simultaneously
  34. Effect of aggregate characteristics on properties of cemented sand and gravel
  35. An integrated structure of air spring for ships and its strength characteristics
  36. Modeling and dynamic analysis of functionally graded porous spherical shell based on Chebyshev–Ritz approach
  37. Failure analysis of sandwich beams under three-point bending based on theoretical and numerical models
  38. Study and prediction analysis on road performance of basalt fiber permeable concrete
  39. Prediction of the rubberized concrete behavior: A comparison of gene expression programming and response surface method
  40. Study on properties of recycled mixed polyester/nylon/spandex modified by hydrogenated petroleum resin
  41. Effect of particle size distribution on microstructure and chloride permeability of blended cement with supplementary cementitious materials
  42. In situ ligand synthesis affording a new Co(ii) MOF for photocatalytic application
  43. Fracture research of adhesive-bonded joints for GFRP laminates under mixed-mode loading condition
  44. Influence of temperature and humidity coupling on rutting deformation of asphalt pavement
  45. Review Articles
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  47. Durability and microstructure study on concrete made with sewage sludge ash: A review (Part Ⅱ)
  48. Mechanical performance of concrete made with sewage sludge ash: A review (Part Ⅰ)
  49. Durability and microstructure analysis of concrete made with volcanic ash: A review (Part II)
  50. Communication
  51. Calculation of specific surface area for tight rock characterization through high-pressure mercury intrusion
  52. Special Issue: MDA 2022
  53. Vibration response of functionally graded material sandwich plates with elliptical cutouts and geometric imperfections under the mixed boundary conditions
  54. Analysis of material removal process when scratching unidirectional fibers reinforced polyester composites
  55. Tailoring the optical and UV reflectivity of CFRP-epoxy composites: Approaches and selected results
  56. Fiber orientation in continuous fiber-reinforced thermoplastics/metal hybrid joining via multi-pin arrays
  57. Development of Mg-based metal matrix biomedical composites for acicular cruciate ligament fixation by reinforcing with rare earth oxide and hydroxyapatite – A mechanical, corrosion, and microstructural perspective
  58. Special Issue: CACMSE
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