Optimization and Characterization of Borassus Fiber-Reinforced Epoxy Composites with Caesalpinia Bonducella Seed Shell Powder Using Response Surface Methodology

Biocompatibility and degradation of naturally occurring cellulosic scaffolds made from bamboo fibers by means of surface functionalization and chemical oxidation [1]. The scaffolds exhibited desirable physicochemical characteristics and demonstrated better cellular proliferation and differentiation in laboratory settings and improved blood vessel formation and tissue restructuring in living organisms [2]. The effect of two-step densification on the inner soft portion of Borassus flabellifer wood was investigated and it rendering the wood more suited for a wide range of applications [3]. Palmyra fibers were extracted from Borassus flabellifer leaves and incorporated into cement composites at varying contents and lengths. Mechanical strength and water absorption tests were conducted to evaluate the composite performance [4]. Pure cellulose nanofibers were extracted from Palmyra fruit fiber using alkaline treatment, bleaching, and acid hydrolysis. These nanofibers were then used to reinforce starch-based biodegradable films, which were evaluated for mechanical and water absorption properties [5].

Borassus flabellifer leaf fibers were treated with NaOH using varying concentrations and durations. The effects on water absorption, tensile strength, and morphology were analyzed using SEM and FTIR [6]. Nanocellulose was extracted from Borassus flabellifer husk using TEMPO-mediated oxidation and ultrasonication. The nanocellulose was incorporated into arrowroot starch-based films with neem oil, and the films were tested for mechanical, antioxidant, and antimicrobial properties [7]. Borassus Flabellifer Petiole and Leaf Stalk fibers were combined in a vinyl ester matrix to form hybrid composites with various stacking sequences. The composites were characterized for tensile strength, impact resistance, hardness, and water absorption [8]. Turbostratic-activated carbon was extracted from Borassus flabellifer inflorescence flowers, followed by sulfonation with different sulfonating agents. The sulfonated carbon was used to coat Li-metal anodes to inhibit dendritic growth in Li-metal batteries [9]. Borassus fibers were reviewed for their potential use in polymer composites with an emphasis on alkali treatment techniques and various fabrication methods. The study also examined the mechanical, chemical, and thermal characteristics of these fibers and their composites [10]. 

Rice husk nanoparticles were blended with epoxy resin and reinforced with Borassus flabellifer leaf fiber. The erosion resistance of thecomposites was tested using an air jet test rig and analyzed using Taguchi method, ANOVA, and artificial neural networks [11]. The study evaluated the mechanical characteristics of composite materials made from Borassus flabellifer sprout fibers and polyester. Significant improvements in mechanical properties and reduced water absorption were seen in the fibers treated at a volume concentration of 35% [12]. The modified Borassus flabellifer fibers exhibited enhanced crystallinity, thermal stability, tensile strength, and reduced water absorption. The benzoyl chloride-treated fibers showed the best improvements in these properties, as confirmed by XRD, SEM, and Thermo-gravimetric analysis (TGA) [13]. The extracted microcrystalline cellulose from Borassus flabellifer flower showed a crystallinity index of 69.81%, a crystalline size of 70.73nm, and thermal stability up to 200°C. The cellulose also exhibited low surface roughness and absence of lignin and hemicellulose [14]. The study examined the tensile strength, hardness, thermal stability, and moisture absorption of epoxy composites reinforced with Borassus leaf fibers and blended with rice husk nanoparticles. The composites containing 0.45wt% of RHN demonstrated the most optimal combination of mechanical characteristics and thermal stability [15]. The palmyrah leaf base fibers had a tensile strength of 8.77 MPa, flexural strength of 147 MPa, and high hardness but reduced impact strength, indicating their viscoelastic properties. The properties underwent statistical investigation utilizing Weibull analysis [16]. 

The PLA-surface modified nano cellulose composite demonstrated a TS of 0.244 MPa, Young's modulus of 0.0030 GPa and a water contact angle of 117º. The composite demonstrated superior UV stability, biodegradability, and mechanical properties as compared to pure PLA [17]. The cellulose microfibrils (CMFs) derived from palmyra fruit peduncle waste have a crystallinity index of 78.2%, a TS of 693.3 MPa, and demonstrate remarkable thermal stabilization up to 330ºC. The findings suggest that CMFs has substantial potential as reinforcing agents in composites [18]. The Borassus Flabellifer (BF) fibers treated with alkali showed improved mechanical capabilities, lower water absorption, and excellent thermal stability. These characteristics make them ideal for use in UAV landing gear applications, surpassing other composites made from natural fibers [19]. The Caesalpinia bonducella seed extracts showed significant antibacterial activity against multiple pathogens, with phytochemical analysis confirming the presence of active constituents, suggesting their potential as natural antibiotics [20]. 

The study found that Moringa oleifera seed powder achieved an 83% reduction in nematode egg count in goats, indicating strong anthelmintic properties comparable to commercial treatments [21]. The aqueous extract of C. bonducella showed significant anti-inflammatory activity, with 75% membrane stabilization and attenuation of nitric oxide, confirming the extract's potential for anti-inflammatory applications [22]. The extract from the Bonduc nuthad a substantial impact on antioxidant levels and lipid peroxidation in rats with spleen and heart damage caused by APAP. This suggests that BNE has protective benefits in these conditions [23]. A diverse range of bioactive compounds in the ethanolic extract of Caesalpinia bonducella leaves. This discovery provides evidence for the conventional application of the plant in the treatment of several illnesses and indicates its potential in contemporary medicine [24]. The hybrid composite, including alternating Sisal and PALF, exhibited a maximum TS of 70.8 MPa. The composite, which consisted of an exterior layer made of Sisal, had remarkable fracture toughness, measuring at 3302.3 J/m², along with an amazing interlaminar shear strength (ILSS) of 16.1 MPa [25]. The composite, comprising 12wt% marble dust powder and 16 wt% coconut fiber exhibited the maximalTS (34.27 MPa), FS (37.23 MPa), and impact strength (16.32 kJ/m²). There was a little elevation in the rate of wear when the quantity of filler beyond 12 wt% [26]. The hybrid composite, composed of 2.5 wt% nano Al2O3 and 7.5wt% arecanut shell powder, exhibited the greatest values for TS (49.37 MPa), yield strength (YS) (46.89 MPa), and compressive strength (CS) (46.71 MPa) [27]. 

The incorporation of Tamarindus indica seed powder into the sugarcane fiber with epoxy resin matrix significantly improved the tensile properties of the hybridized bio-composites [28].The incorporation of fine granite powder and Tamarindus indica shell powder into the epoxy resin matrix greatly enhanced the CS of the hybridized bio-composites [29]. The composite material consisting of 35% sugarcane fiber and 15% tamarind seed powder had the highest flexural strength (36.543 MPa), flexural modulus (12.129 GPa), and compressive strength (21.32 MPa) [30]. The film composed of PLA-SMNC-ZnO nanoparticles, with a surface modified nano cellulose (SMNC) layer, demonstrated exceptional tensile strength (13.9 MPa) and Young's modulus (0.00689 GPa) as compared to films made only of PLA or PLA-SMNC. The film exhibited improved thermal stability at a temperature of 320°C, decreased water absorption, and improved resistance to UV radiation [31]. The composite with 35 wt% BF sprout fibers showed the best tensile strength (17.6 ± 0.72 MPa), flexural strength (50.2 ± 0.15 MPa), and impact strength (1.18 ± 0.21 J). The wear measurements revealed a COF of 0.52 and a SWR of 0.024 mm³/Nm, indicating a robust link between the surfaces [32]. 

This work aims to utilize the particles of Caesalpinia bonducella seed shell powder (CBSSP) for reinforcing purposes. The alkaline treatment is the most efficient technique for chemically altering natural fibers. It is commonly employed to enhance the strength of a wide variety of resins. Studies have shown that applying a sodium hydroxide solution to fibers significantly enhances interlocking, rises surface coarseness, and elevates hemi-cellulose weightage. Chemical treatment improves the inter-bonding characteristics of both the natural fiber and the matrix. So far, there has not been any prior.

3.1 SEM analysis

Figures 2(a) and 2(b) depict the morphology of the untreated and alkali-treated EV fiber, respectively, as observed under a scanning electron microscope (SEM). Figures 3(a) and 3(b) display the scanning electron microscopy (SEM) images of untreated and NaOH-treated CBSSP's correspondingly. 

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Figure 2. SEM image of (a) untreated and (b) alkali-treated BF

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Figure 3. SEM image of (a) untreated and (b) NaOH-treated CBSSPs

3.2 Density and chemical properties

In contrast to untreated CBSSPs, alkali-treated CBSSPs exhibited a higher cellulose content. Table 3 displays the density and chemical composition of Caesalpinia bonducella shell powder. The research revealed that the levels of hemicellulose, lignin, and ash in CBSSP that had been treated with alkali had decreased. Additionally, these particles established robust and enduring connections with the matrix when they were employed as reinforcement in polymer matrix composites (PMC). 

The primary factor contributing to the increased density of modified CBSSPs is the removal of non-cellulosic components from the particles during the alkalization process. The removal process can generate vacancies that particles can use to retain molecules. Table 1 displays the chemical composition of untreated and alkali-treated CBSSP. 

Table 3. Density and Chemical composition of CBSSP

3.3 FTIR analysis 

The distinct functions of the infrared (IR) peaks of both untreated and alkaline-treated CBSSP samples are illustrated in Figure 4. The wide absorption band extending from 3200 to 3500cm⁻¹ indicates that the O-H bond in CBSSP treated with NaOH was less prominent, as reflected in the results. The OH groups in fatty acids tend to consolidate when they interact with the carboxylic bonds of CBSSP.  The C-H bond's elongation is indicated by the occurrence of a peak at 2897.51cm⁻¹. Nevertheless, the peak shifted to 2884.12cm⁻¹ as a consequence of the significant extraction of hemicellulose from the particles treated with NaOH. Raw CBSSP samples exhibits an absorbing band with a peak at 1744.82cm⁻¹, which is indicative of the occurrence of the carbonyl group C=O. However, after applying alkali treatment, this band dissolved entirely because hemicellulose underwent hydrolysis, causing the C-O-C linkages among the two monomers to break. The chemically treated CBSSPs exhibited substantial removal of lignin and hemicelluloses, as evidenced by the lack of this peak.  

The raw CBSSPs exhibit a peak intensity at 1241.74cm⁻¹, which is indicative of the modulation of hemicellulose (-COO) and the elongation of lignin (C-O). The absence of this peak in the treated CBSSPs provides further evidence that the alkali treatment has effectively removed hemicellulose and lignin from the surface of the CBSSPs. The evidence that the hemicellulose and lignin components have been eradicated from the surface of the CB shell particle following chemical treatment is provided by the observation of a diminished peak at 1017.65cm⁻¹.  

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Figure 4. Evaluation of FTIR spectrum obtained from raw and alkali-treated CBSSP 

Figure 5 demonstrates the study of the FTIR spectra of untreated BF and BF that has been treated with alkali (ABF). The principal functional groups present in the fibers were identified through the examination of the spectra. The results suggested that the significant peak observed at 3329.58cm⁻¹ was caused by the elongation of OH bonds, which is evidenced by the presence of cellulose. The stretch vibration of the C-H bonds, which is induced by the occurrence of cellulose constituent’s C-H groups is the cause of the peak observed at 2918.63cm⁻¹. Furthermore, a minor absorption signal at 2849.87cm⁻¹ was used to identify the C-H symmetricalwinding of the NaOH group. In addition to an additional peak, the ABF compound exhibited stretching vibrations of the carbonyl functional group at frequencies of 161.25cm⁻¹ and 1414.98cm⁻¹. The presence of an alkyl halide functional group results in the detection of a distinctive peak at 1033cm⁻¹. The existence of biological constituents is corroborated by the presence of peaks in the FTIR spectra, as asserted by ABF.  

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Figure 5. Evaluation of FTIR spectrum for raw and alkali-treated BF 

3.4 XRD analysis 

The XRD spectra of the untreated and alkali-treated CBSSP samples are depicted in Figure 6. The intensity observed at an angle of 20.14° (2θ) was used to confirm the presence of the amorphous phase. On the other hand, the cellulose-I phase was identified by the peaks that were observed at angles of 16.58°, 18.51°, 23.12°, and 35.85°. These angles correspond to the crystallographic planes 120, 140, 210, and 005, correspondingly. Nevertheless, the contaminants present in the CBSSP samples were the cause of the residual XRD peaks. Eq. (3) has been employed to ascertain the Crystallinity Index (CI) of the CBSSP particles. The CI value increased significantly from 41.74% in the original sample to 54.08% as a consequence of the applied alkali treatment to CBSSP, which removed the disordered components. Eq. (4) was implemented to ascertain the crystallite size (CS) of the CBSSP. In comparison to untreated CBSSPs, alkali-treated CBSSPs exhibited a higher CS of 12.34nm and a lower CS of 8.79nm. The CBSSP materials exhibit enhanced chemical reactivity and moisture resistance as the concentration of the CS component increases. Consequently, while amorphous compounds can be produced from CBSSPs, granules are more effective when used as strengthening in matrix composites.  

$\mathrm{CI}=\frac{\mathrm{I}_{200}-\mathrm{I}_{\mathrm{AM}}}{\mathrm{I}_{200}} \times 100$      (3)

The CS was calculated using Scherrer's equation, which utilizes the highest CI phase (I200) at an angle of 2θ = 23 - 25°, and the intensity of the amorphous phase (IAM) at an angle of 2θ = 20 - 22°.   

$C S=\frac{k \lambda}{\beta \cos \theta}$     (4)

The variables used in this context are: K, which represents Scherrer's constant with a value of 0.89; β, which stands for FWHM; and λ, which represents the wavelength of the radiation with a value of 0.1541 nm.  

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Figure 6. The XRD spectrum of untreated and NaOH-treated CBSSP

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Figure 7. Evaluation of XRD spectrum for untreated and NaOH treated with alkali BF

Figure 7 displays the XRD patterns of the pure ethylene-vinyl fluoride (EVF) and pure alternating ethylene-vinyl fluoride (AEVF) samples. The data exhibit two distinct peaks, observed at 2ϴ = 16.73° and 2ϴ = 23.58°, which are easily discernible. The underlying semi-crystalline nature of the ABFF was evident from these two peaks. Based on the findings, it was determined that AEVF exhibited an amorphous structure due to the presence of the (1 1 0), which was accountable for the initial peak at 16.73°. (Iam). The existence of a secondary peak at an angle of 23.58°, which aligned with the (2 0 0) crystallographic plane, suggests that the fiber possessed a crystalline structure. The residual weak spectral peaks indicated the existence of contaminants in AEVF.

3.5 TGA analysis 

Evaluating the thermal properties of CBSSPs is crucial in determining their suitability as reinforcing fillers in bio-composites [36]. The process of thermal deterioration for both untreated particles and alkali-treated CBSSPs is depicted in Figure 8. The sample is primarily subjected to thermal degradation in three distinct phases. It was discovered that the early degradation temperatures of untreated CBSSP ranged from 60 to 200°C, whereas those of alkali-treated CBSSP were 90 to 220°C. Withdrawal of moisture from CBSSPs during deterioration is a hallmark of this temperature range. CBSSP and the treated CBSSP samples saw a weight decrease of approximately 10-13% within this specific temperature range. The second degradation temperature of untreated CBSSP varied from 200 to 350°C, whereas for CBSSP treated with alkali, it ranged from 240 to 380°C. Within this temperature range, the decomposition of lignin and hemicellulose, which are parts of CBSSPs, takes place. The untreated CBSSP samples experienced a weight reduction of approximately 58.48% within a certain temperature range, while the CBSSP samples treated with alkali displayed a weight reduction of 62.48%. The degradation temperature of both untreated and alkali-treated CBSSPs was found to range from 350 to 500°C, indicating the decomposition of lignin and cellulose. Lignin degradation persists until it reaches temperatures of 600°C. Figure 9 depicts the thermal efficiency of ABF and BF. The decrease in weight of the fiber commenced at a temperature of 82.18°C, which can be ascribed to the decrease in moisture content. Another slight reduction in weight was seen at approximately 160°C, which was ascribed to the breakdown of lignin. The thermal steadiness of ABF was evaluated to be approximately 260°C. Though, a following decline in quality, associated with the breakdown of hemicelluloses through heat depolymerization, was observed between temperatures of 260°C and 370°C.

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Figure 8. Comparison of weight loss in TGA analysis for untreated CBSSPs and alkali-treated CBSSP

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Figure 9. The thermal degradation performance of (a) BF and (b) ABF

3.6 Utilizing Response Surface Methodology (RSM) to conduct compositional study of the properties of the bio-composite 

The distribution of reinforcement weight in a polymer-fiber composite quickly changes its physio-mechanical characteristics. Adding more fiber reinforcement increases most physio-mechanical parameters except water absorption capacity. Table 4 shows the obtained results for different parameter mixturesby utilizing Central composite design. The length of the reinforcing fibers is a crucial factor in defining the mechanical and physical properties of polymer matrix-fiber composites. The only more important component is the weight composition of the fibers, however this is the second most important factor. According to studies, longer fiber reinforcements often have better physio-mechanical characteristics. However, it has been demonstrated that physiochemical characteristics tend to decrease after a specific length is attained, which is contingent upon the fiber type. 

Table 4. Obtained responses for design of experiments

Table 5 displays the RSM models that were created for the epoxy-Borassus fiber composite based on the response parameters that were actually used. Table 6 are the findings from the trials concerning water absorption, tensile modulus, and modified R². A regression model's sufficiency can be evaluated using the modified R² test. ANOVA was employed to assess the correctness of coefficients for the quadratic polynomial equations. The importance of each phrase is indicated by its elevated F-value and comparatively low P-value.  

The most influential elements that determined the linear connection between biomaterial loading and fiber reinforcement length were those related to tensile modulus (P ≤ 0.05). The parameters that influenced the tensile strength had a far greater impact than the individual impacts of the reinforcing weight and fiber length of the biomaterials (P ≤ 0.05). Furthermore, the linear relationship between the length of fibers and the loading of biomaterial and the individual impact of the weight of fiber reinforcement, also had a significant impact. There was a range of extremely significant to marginally significant degrees of influence on water absorption (P < 0.05). Furthermore, the model's appropriateness in accurately forecasting the experimental results is compellingly demonstrated by the high values of R² and modified R². These findings confirm that the linear model is suitable for the data in light of the particular experimental conditions [37]. However, the corrected R² values were comparatively low, indicating that there were discrepancies between the observed and predicted tensile modulus results.  

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Figure 10. The samples of a composite material made from epoxy resin, Borassus fiber and CBSSP

Table 5. RSM models for epoxy-BF fiber composite's selected response properties

Table 6. ANOVA tablefor the hybrid composite

The regression analysis results for the first-degree polynomial model and the data for TM, water absorption, and other variables, are presented in Table 6. The findings indicated that the impact energy and flexural strength were enhanced by increasing the quantity and size of fiber reinforcement. Conversely, the tensile strength and tensile modulus were both enhanced as a consequence of a decrease in the quantity and size of fiber reinforcement. Nevertheless, the biomaterials' water absorption increased as a result of their improved quality and reduced size. In general, RSM employed to examine the effects of biomaterial composition and fiber length on water absorption, TM, and TS, both individually and in conjunction. Therefore, the Epoxy and Borassus fiber composite was improved by using CCD and RSM techniques, leading to positive results. The independent variables' reactions are the source of the experimental data. Based on the study and analysis that followed, it is possible to use reaction surface plots and the linear polynomial equation to determine the water absorption and tensile modulus.

The RSM-generated contour and response surface diagrams for the tensile modulus, water absorption, impact energy, and flexural strength variables are shown in Figures 11-15. The independent factors have a considerable impact on the composite material's qualities when made with Borassus fiber and epoxy. Analysis of the fiber characteristics of the composite material yielded a tensile modulus of 275 MPa. Researchers found that reducing the reinforcing fibers' weight, composition, and length enhanced their tensile modulus. Composite materialsshowed a minimum tensile strength of 10.48 MPa, as shown by the effect of fiber properties on this property. The tensile modulus is typically found to rise in direct proportion to the reinforcing fibers' weight and length. Figure 13 shows a surface plot of the independent parameters affecting the three-dimensional flexural strength of the Epoxy-fiber composite. By investigating the impact of fiber properties, the composite achieved a minimum flexural strength of 14.31 MPa. The weight of the fiber reinforcement typically has a minimal impact. However, research has demonstrated that the flexural strength is improved by elongating the fibers. Figure 14 illustrates the correlation between fiber properties and impact energy, indicating that the composite material attained a minimum impact energy of 0.67 J. 

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Figure 11. Response plots for tensile modulus

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Figure 12. RSM plots for tensile strength

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Figure 13. RSM plots for flexural strength

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Figure 14. RSM plots for impact energy

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Figure 15. RSM plots for water absorption

The impact energy appears to have risen in proportion to the increase in weight of the reinforcing fibers, and their length and composition. Compared to the findings obtained for various fibers, this particular one exhibited consistency. Figure 15 illustrates the two-dimensional response surface of water absorption in an epoxy-Borassus fibre composite. The composite exhibited the lowest water absorption rate of 0.201%, as determined by the analysis of the fiber characteristics. Fiber reinforcements possessing reduced weight, composition, and length exhibited diminished water absorption. Consistent with previous research on various types of fibers, this study observed that the water absorption of natural fibers increases as their length and weight composition increase. This occurs due to an increase in the quantity of unbound hydroxyl (-OH) groups inside the fiber, resulting in a larger concentration of cellulose. Consequently, the fiber's capacity to absorb water is enhanced. The aforementioned properties were optimized using numerical optimization models to create the ideal Epoxy-Borassus fiber composite. This composite has a limited capacity to absorb water, a high resistance to deformation under tension, and strong resistance to bending and impact when it is reinforced with 4mm long fibers and 25% by weight of biomaterials.