Extraction of cellulose from soybean hulls for the development of polymer matrix composites with fishtail palm fibers

This study aims to extract and characterize cellulose nanocrystals (CNCs) from soybean hulls, and investigate their application as reinforcement in fishtail palm leaf stalk fiber (FPLSF) composites. CNCs were extracted through a multistep process involving alkalization, bleaching, acid hydrolysis and mechanical fibrillation. Analysis confirmed the transformation of cellulose I to cellulose II, yielding nanocrystals with 70.58% crystallinity index and thermal degradation peak at 371 °C. FTIR analysis verified removal of lignin and hemicellulose after extraction. The extracted CNCs were incorporated into FPLSF-epoxy composites at 2.5-10 wt% loading. Results showed 7.5 wt% CNCs (FT/SH4) provided optimal mechanical properties, with 51.4 MPa tensile strength, 46.09 MPa flexural strength and 36.47 kJ mm−2 impact strength. Lower CNC percentages showed significantly inferior properties due to poor fiber-matrix interfacial bonding. Overall, extracted soybean hull CNCs demonstrated good reinforcement capabilities for natural fiber composites. This provides a sustainable application route for agricultural residues and contributes to the development of high-performance biocomposites.


Introduction
Growing environmental concerns due to non-biodegradable plastic pollution necessitate the development of sustainable alternatives.Cellulose, a naturally abundant, renewable, and biodegradable biopolymer, emerges as a promising solution [1].Its derivative, nanocellulose, offers excellent properties like high crystallinity and large surface area, making it valuable for composite and biomaterial applications [2].However, current extraction methods pose challenges.Traditional mechanical processes are energy-intensive, while chemical methods often involve harsh chemicals and environmental issues.Therefore, there is a critical need for more efficient and sustainable extraction methods.
Recent studies [3][4][5][6][7][8][9][10] have demonstrated that combining chemical and mechanical techniques effectively breaks down cellulose into nano cellular forms while consuming less energy than purely mechanical approaches.In view of that, Wahib et al [11] conducted a comparison between multistep shearing followed by acid hydrolysis techniques versus soxhlet extraction for isolating CNCs from date pits.Their analysis revealed that the crystallinity index obtained through multistep shearing followed by acid hydrolysis was higher than that achieved using the soxhlet apparatus.Moreover, these methods were found to be less time-consuming and more cost-effective than the soxhlet apparatus.Specifically, the apparent crystallinity of CNCs generated via multistep shearing followed by acid hydrolysis was 69.99%, while that of CNCs obtained through the soxhlet apparatus was slightly lower at 67.79%.Similarly, Wu et al [12] reported the extraction of nanocellulose from okara using mechanical high pressure homogenization treatments at 140 MPa for three cycles, yielding nanocellulose with a diameter of about 0.23 μm and a crystallinity index of 70%.However, these pure mechanical methods would generally consume more energy and more no of cycles and high cost in processing.
Samsalee et al [13] demonstrated the possibility of preparing nanocellulose from rice husks using various methods, including high-pressure homogenization (HPH), acid hydrolysis (AH), and a combination of both (AH+HPH) treatments.After analyzing the results obtained, it was found that the AH+HPH treatment yielded higher crystallinity compared to the other methods.The resulting nanocellulose had a crystallinity index of 72% and a length ranging from 436.22 to 440.04 nm.In similar way, Kumar et al [14] used sulfuric acid hydrolysis followed by mechanical fibrillation to produced cellulose nano crystals from spruce wood.It was found that acid hydrolysis followed by mechanical fibrillation had high yield, aspect ratio (up to 48) and crystallinity index of 80.8 ± 1.7%.
Holilah et al [15] explored different inorganic acids (sulfuric acid, hydrochloric acid, phosphoric acid), organic acids (oxalic acid, citric acid, acetic acid) to isolate cellulose from industrial pepper waste (IPW).According to their report, cellulose from industrial pepper waste underwent polymorph transformation and produced spherical-shaped CNCs with an average diameter of approximately 33-67 nm when treated with inorganic acids.On the other hand, hydrolysis using organic acids resulted in rod-shaped CNCs measuring 210-321 nm in length.Likewise, Rasheed et al [16] extracted cellulose from bamboo pulp using sulfuric acid hydrolysis and found that 45 min exhibited superior characteristics such as increased degrees of crystallinity, higher yield, and Needle shaped spherical structure with size range of 200 nm-500 nm and less than diameter.Furthermore, the obtained CNCs had superior thermal stability with peak degradation temperature of 350 °C and better crystallinity index 86.96%.Also, Wu et al [17] concluded that polymorphic transformation (cellulose I into cellulose II) is significant role in extraction of nanocellulose using combination of acid hydrolysis followed by mechanical methods found that combination of these methods enhances the degree of cellulose fibrillation, leading to the production of more effective and bulk cellulose fiber compared to fibers solely produced through mechanical fibrillation.
Based on these literatures, it is understood that acid hydrolysis followed by mechanical methods like highpressure homogenization or shearing, yields nanocellulose with superior characteristics.Compared to traditional methods, this combined approach offers increased crystallinity (e.g., 72%-86.96%),improved size and shape control, and is more cost-effective and time-saving.Furthermore, despite the exploration of various plant sources for nanocellulose production, soybean hulls, a byproduct rich in cellulose, remain relatively under-investigated.This study aims to address this research gap by exploring the potential of soybean hulls as a source for nanocellulose extraction.This research hypothesizes a combined approach utilizing acid hydrolysis and mechanical shearing will effectively isolate nanocellulose with high crystallinity, suitable for reinforcement applications.

Extraction of cellulose from soybean hulls
Soybeans, a vital global crop, yield protein-rich beans used in food and diverse industrial products.Soybean hulls, constituting 8% of production, have high cellulose content, ideal for nanocellulose extraction.These byproducts, often discarded, hold untapped potential for high-value applications [18] and suitable as novel biological resources for isolating nanocellulose.India alone cultivates approximately 10.7 million hectares of soybean, with an annual production of 12.7 million tonnes [19].
The methodology involved in the extraction of nanocellulose from soybean hulls begins with the treatment of soy hulls using a 5% sodium hydroxide solution at 100 °C for 2 h, followed by thorough washing and drying as shown in figure 1. Delignification is then performed using a 35% hydrogen peroxide solution, and subsequent ball milling is employed for cellulose extraction.The obtained cellulose undergoes acid hydrolysis with 40% sulfuric acid at 55 °C for 45 min, followed by centrifugation and washes to achieve neutrality.A slurry of soybean hull cellulose is homogenized at 130 MPa, sonicated for 45 min, and the resulting nanocellulose is frozen and lyophilized to obtain dry soybean hull nanocellulose powder.
Energy dispersive x-ray diffraction (XRD) X-ray diffraction (XRD) patterns of the SBHNCs were obtained using an x-ray diffractometer (Make: D8 Advance, Bruker) operating at a Cu K α1 wavelength of 1.544 A°.The SBHNCs were exposed to the x-ray beam with the x-ray generator running at 40 kV and 40 mA.Scattered radiation was detected in the range 2θ = 10°-60°and scanning step of 0.02°per scan.The crystallinity index (CrI) was determined following the Segal method [20] using the equation (1): where I 002 is the maximum intensity value of diffraction of the 002-lattice peak for the crystalline cellulose at 2θ about 22°, while I am is the intensity value for the amorphous cellulose at 2θ about 18°.
Thermogravimetric analysis (TGA) TGA of the SBHNCs was performed using a TGA instrument (Make: Q500, TA Instruments).Approximately 5-10 mg of dried SBHNCs was placed in a platinum pan and heated from room temperature to 600 °C at a heating rate of 10 °C min −1 under nitrogen atmosphere (flow rate 60 ml min −1 ).Weight loss curves were obtained as a function of temperature.
Fourier-transform infrared spectroscopy (FTIR) FTIR spectra of the SBHNCs were acquired using an FTIR spectrometer (Make: Nicolet iS50, Thermo Scientific) equipped with a DTGS detector.The samples were pressed into KBr pellets.Spectra over the range 400 to 4000 cm −1 were collected in transmittance mode with 64 scans at a resolution of 4 cm −1 .Background correction was performed prior to each sample measurement.The FTIR spectra were baseline corrected and normalized for sample comparison.Functional groups were identified from the peak positions in the spectra.

Results and discussion on inherent properties of SBHNCs
Color value analysis It can be observed that the soybean hull nanocellulose (SBHNCs) had a bright yellowish-white color with L * , a * and b * values of 89.21, 0.13 and 8.53, respectively.This brightening effect was due to the chemical isolation processes which removed lignin and other pigmented components, leaving behind the purified cellulosic material.The positive b * value indicates some residual yellowish tones likely from small amounts of retained plant cell wall components.But overall, the high L * value and neutral a * value represent the light color expected for cellulosic nanocellulose generated from plant biomass.

XRD analysis
In the agro-residue of lignocellulosic components, both amorphous and crystalline regions are typically present.The amorphous region is primarily formed due to the presence of lignin and hemicellulose in soybean residue, while the crystalline region is a direct result of the presence of cellulose.Therefore, a multistep process followed by acid hydrolysis is employed to depolymerize hemicellulose and delignify soybean hulls.This process effectively promotes cellulose polymorphism and enhances the crystallinity of the resulting cellulose.To assess the crystalline structure and size of the novel CNCs, XRD (x-ray diffraction) analysis was conducted.The results of this analysis, depicted in figure 2 The obtained diffraction peaks are consistent with the cellulose II structure, which has also been documented in soybean straws.In general, nanocellulose typically exhibits crystallinity values ranging from 50% to 89%.The efficient depolymerization and downscaling of cellulose polymeric chains occurred as a result of hydrolysis with sulfuric acid.This process led to the formation of discrete crystals by eliminating the amorphous structure of cellulose, resulting in a crystallinity index of 70.58%.Notably, this study produced an equivalent CNCs crystallinity index comparable to those obtained from other sources such as corn cob (72.36%) [21], sugarcane bagasse (72.5%) [22], coffee silver skin (72%) [23], pinecones (70%) [24], groundnut shells (74%) [25], date seeds (70%) [26], pineapple (73%) [27], and Maize straw (75.5%) [28].The higher crystallinity index observed in the extracted cellulose after delignification is attributed to the rearrangement of the polysaccharide chain and the enhancement of hydrogen bonding.This is facilitated by the penetration of hydronium ions (H 3 O + ) into the Para crystalline region, promoting the reorganization of the polysaccharide chain and an increase in the number of effective hydrogen bonds.The hydrolytic cleavage of transverse scission of 1→4 glycosidic bonds also contribute to the liberation of high-quality cellulose.These CNCs consist of well-ordered and highly crystalline cellulose structures with minimal impurities, making them valuable for the development of biocomposites products.

TGA analysis
Thermogravimetric (TG) curves, which show changes in weight under heating, and derivative curves, which show differences in TG slope, provide insights not visible from TGA curves alone.DTG curves allow us to identify exothermic or endothermic thermal processes based on temperature differences.Figure 3 illustrates the TGA and DTG thermal properties of soybean, extracted cellulose, and nanocrystals, showcasing four distinct patterns of thermal degradation resulting in weight loss [29].Due to variances in lignin, hemicellulose, and cellulose percentages, obtained cellulose undergo degradation in multiple stages.At different temperatures, these materials break down into amorphous and crystalline phases.The aim with this study was to assess the potential applicability of nano cellulose in high-performance applications.The thermal behavior of CNCs is influenced by their chemical constituents, structure, and degree of crystallinity.The TGA curve exhibits four degradation steps that correspond to moisture content as well as hemicellulose, cellulose, and lignin degradation processes.
The degradation process of CNCs involves several stages at different temperature ranges.Initially, at temperatures below 100 °C, there is the evaporation of water and other volatile components that are loosely bound to the plant cell walls.The first phase of thermal degradation, associated with water molecules, occurs in the temperature range between 66.07 °C and 123.76 °C, resulting in a mass loss of 12.56%.This phase primarily involves the evaporation of moisture present in the fibers.In the second stage, which takes place between 123.76 °C and 251.71 °C with a mass loss of 2.14%, hemicellulose and lignin contribute to the degradation process by breaking ester and ether bonds.This stage is known as hemicellulose depolymerization and shows significant differences compared to cellulose degradation.The third stage occurs from 251.71 °C to 471.61 °C, with a substantial mass loss of 71.8%.This indicates the effective degradation of α-cellulose into cellulose II.This stage is referred to as effective delignification or polymorph conversion, during which the amorphous region undergoes disruption through processes such as dehydration, decarboxylation, depolymerization, and glycosyl linkages, resulting in significant mass loss [30].The DTG curve reveals that the maximum degradation occurs at 371.25 °C within this temperature range.This corresponding peak is compared with previous literature on soybean residue (301 °C), indicating that the soybean hulls obtained in this study had higher thermal stability [1].Generally, it's observed that the degradation temperature decreases when soybean hulls undergo chemical treatment and hydrolysis [31].This decrease can be attributed to the removal of hemicelluloses and lignin, as well as the breakage of hydrolytic cleavage of glycosidic bonds in the amorphous region.It's well-established that an increase in crystallinity enhances heat resistance, consequently leading to improved thermal stability in materials.
In the final stage, occurring between 471.63 °C and 631.73 °C, there is a mass loss rate of 9.28%, indicating the removal of lignin and wax to produce char residue.This is because lignin exhibits high thermal stability due to the cleavage of strong bonds in its aromatic structure.Lignin, which consists of aromatic rings with multiple branches, is susceptible to degradation across a broader temperature range, typically above 400 °C.The formation of char (11.28%) results from the breakdown of lignocellulosic materials, leading to the production of a solid residue.This process occurs due to the presence of various components, including lignin, hemicellulose, and stable oxides found in soybean hulls.Based on the results of FTIR and XRD tests, the lower char residues in nanocellulose indicate the effective removal of hemicellulose and lignin during the extraction process.In addition, during acid hydrolysis, amorphous regions are removed, leaving only crystalline structures from the Para crystalline region, which gives CNCs its superior thermal stability.However, the similar endothermic peak (371.25 °C) resembled the potential than that of cotton (220 °C) [32], ramie (225 °C) [6], Sansevieria ehrenbergii (223.85 °C) [33], Coccinia grandis (213.4 °C) [34], aloe vera (225 °C) [35], jackfruit peel (214.5 °C) [36], aerial root of banyan tree (230 °C) [37]and lower than that of Cymbopogon flexuosus (253.17°C) [38], Cissus quadrangularis stem (270 °C) [39], Arundo donax (275 °C) [40], Kenaf (250 °C) [41], and Furcraea foetida (320 °C) [42].The char residue of 11.34%, indicated the effective delignification of hemicellulose and lignin during bleaching followed by acid hydrolysis.

Evaluation of kinetic energy activation
The Coats-Redfern method, a model-fitting approach, was utilized to determine the kinetics of cellulose extraction and cellulose nanocrystals from soybean hull agro industrial residue.The activation energy (E a ) of the samples was estimated using the fundamental Coats-Redfern equation, as shown in equation (2).The model selection for kinetic model function (g(x)) and their corresponding correlation factor (R 2 ) were assessed based on the linear fitting approach.The thermal stability of CNCs is influenced by their physical and chemical structures including dense, chemical pretreatment, origin.Furthermore, different process and functionalities exhibit different orientations of cellulose chains and patterns of hydrogen bonding, resulting in distinct crystalline arrangements that impact thermal stability.As a result, there is an increase in activation energy for cellulose II while a slight decrease occurs for cellulose I.The calculated E a value proves crucial as it aids in predicting the thermal stability characteristics of CNCs.
Where, R -Universal gas constant (8.314J mol ⎡ ⎣ ⎤ ⎦ plotted against 100/T, E a (activation energy) and A (pre-exponential factor) can be extracted as shown in figure 4. The resulting linear relationship in the graph will have a slope of E a /R and an intercept of b .AR Ea In the context of determining the activation energy of the CNCs quantitatively, the Coats and Redfern methods are employed.These methods are specifically applied to the temperatures involved in the thermal degradation, which ranges from 251.71 °C to 471.61 °C.Using equation (2), the activation energy (E a ) calculated around to be approximately 70.12 kJ mol −1 .The obtained activation energy is better than that of the Cissus quadrangularis root (69.33 kJ mol −1 ) [39], Ficus religiosa (68.02 kJ mol −1 ) [43], and Acacia leucophloea (69.33 kJ mol −1 ) [44].It is worthy to note that as the heating rates were increased, the activation energy of FT/SH is increased.This was due to the effects of heat and mass diffusion.

Fourier transfer infrared spectroscopic (FTIR) analysis
The FTIR spectrum holds significance in providing valuable insights into the chemical composition of the extracted CNCs.By analysing characteristic peaks in the spectrum, the various functional groups present, including hydroxyl, methoxy, and cellulosic components in the soybean hulls are identified.Additionally, the chemical structure of the obtained nanocellulose is obtained.It also helps to confirm the removal of lignin and hemicellulose impurities from soybean hulls after chemical pretreatments, as depicted in figure 5.The FTIR analysis reveals that the soybean CNCs consists of cellulose, lignin, and hemicellulose components.Consequently, it contains various oxygenated functional groups such as esters, ketones, alkanes, aromatics, and alcohols.The presence of cellulose is evident through absorption bands in the 600-900 cm −1 range, which are attributed to C−H and C−O stretching peaks.The band observed at 1595.02 cm −1 corresponds to the C=O stretching of uronic ester and acetyl groups found in hemicellulose or the ester linkage of carboxylic groups from ferulic and p-coumaric acids present in lignin.Notably, the absence of the 1595.02cm −1 band in the FTIR spectra of CNCs confirms the successful removal of lignin and hemicellulose.
Distinctive peaks corresponding to cellulose can be observed at 1046.35 cm −1 and the C-H absorption bands found at 879.09 cm −1 .Additionally, stretching the OH (hydrogen-bonded) groups generate a broad absorption band with wider peaks around 3565.36 cm −1 , indicating the hydrophilic nature of the fibers.The intensity of this broader peak decreases as a result of the sequential alkali and acid treatments conducted on the soybean hull to obtain nanocellulose.This reduction in peak intensity may result from the disruption of intramolecular and intermolecular hydrogen bonds established by the majority of hydroxyl groups.Also, other minor peaks seen around 2982.04 cm −1 are associated with C-H stretching vibrations.

Fabrication of fishtail palm leaf stack fiber composites with soybean hulls nanocellulose
The characterization and analysis results indicate the successful isolation and development of nanocellulose fibers from soybean hulls.The soybean hull nanocellulose displayed typical cellulosic properties and morphology expected for nano-sized cellulose fibers.Having confirmed the suitability of the synthesized nanocellulose materials, the next phase of experimentation explored potential applications by fabricating fishtail palm leaf stack fiber biocomposites reinforced with the soybean hull nanocellulose.Natural fibers possess several advantages over synthetic fibers as composite reinforcing materials such as sustainability, low cost, and low density.The abundance and accessibility of fishtail palm leaves presents opportunity for composite development.However, natural fiber composites also have some limitations like poor moisture resistance and thermal stability.Nanocellulose materials have potential to address these challenges.This section investigates fishtail palm leaf stack fiber biocomposites integrated with the soybean hull nanocellulose fabricated in this work to analyze the impact on physicochemical and mechanical performance.The results will reveal whether the soybean hull nanocellulose can feasibly improve properties and suitability for practical applications of fishtail palm leaf stack fiber biocomposites.
Extraction of fishtail palm fiber Fishtail palms (Caryota mitis) derive their name from the distinctive shape of their leaves.They belong to the Plantae kingdom, the Arecales order, and the Arecaceae family.Caryota mitis trees exhibit clustered stems that can attain heights of up to 10 m (33 feet) and diameters of 15 cm (6 inches).The leaves of this palm species can grow to lengths of up to 3 m (10 feet), as illustrated in figure 6.The Fishtail palm leaf stalks are harvested from the Fishtail palm tree (Caryota mitis) in Coimbatore District, Tamil Nadu, India.The detailed step-by-step procedure for extracting Fishtail palm leaf stalk fibers (FPLSFs) is outlined in figure 6.Firstly, the leaves are manually removed from the leaf stalks.Subsequently, the stalks are submerged in water for a period of 3 weeks to undergo microbial degradation during the water retting process.This process aids in the removal of gum-like materials situated between the fibers and retts the stalks.After this period, the stalks are beaten with a wooden mallet to extract the fibers.Following fiber extraction, the separated fibers undergo a thorough washing and cleaning process with purified water.They are then left to dry at room temperature for 6 days to eliminate excess moisture from the fibers.Next, an alkali treatment is performed.The dried raw FPLSFs are immersed in water, and 1 g of sodium hydroxide (NaOH) pellets is added.This treatment lasts for 45 min, with the purpose of removing surface impurities and wax materials present in the fibers.Subsequently, the fibers are treated with distilled water, followed by the addition of a few drops of 0.1 N hydrochloric acid (HCl) solution for an additional 3 min.This step is aimed at eliminating any remaining impurities.Finally, the treated fibers are dried at room temperature for 2 days.
Fishtail palm leaf stalk fibers (FPLSFs) and Soybean hull nanocellulose (SBHNCs) were measured for their proportional weight ratios as listed in table 1.The fibers were uniformly arranged inside the mold prior to the application of epoxy resin.After arranging the fibers uniformly and dispersing the SBHNCs, compression was applied for 45 min at 120 °C within the mold as shown in figure 7. Subsequently, the compressed fibers were laid over a coat of epoxy resin, ensuring an even distribution of fibers.The epoxy resin mixture was poured uniformly over the fibers and compressed under a constant load of 5 kg for a curing time of 24 h.All samples have been fabricated in compliance with ASTM standards.

Tensile test
Tensile tests were conducted to determine the in-plane tensile properties of the developed FT/SH composites.It measures a material's capacity to withstand external forces that attempt to pull it apart and evaluates the material stretches before breaking.The composite samples were subjected to testing using a ZwickRoell machine (Make: ZwickRoell/Z100), operating at a constant crosshead speed of 2.1 mm min −1 .For each composite, a total of five samples were tested, and the sample dimensions adhered to ASTM D 3039 standards.The experimental setup employed for the tensile test is depicted in figure 8.

Flexural test
Flexural tests were conducted to determine the maximum stress and strain experienced by the developed FT/SH composites in ZwickRoell machine (Make: ZwickRoell/Z100) when subjected to external bending loading as shown in figure 9. To assess the flexural strength, FT/SH composite samples underwent 3-point bending tests using a ZwickRoell machine, maintaining a constant strain rate of 0.10 mm min −1 and a crosshead speed of 2.1 mm min −1 .The sample dimensions were in accordance with ASTM D 790 standards.

Impact test
Impact test is to assess the material's capacity of developed FT/SH composites to withstand sudden shock loads.The testing was conducted using a impact testing machine (Make: Coesfeld Magnus), which features a highspeed drop tower capable of reaching a maximum impactor speed of 40 m s −1 as shown in figure 10.The drop tower was released from a specific height, possessing a fixed kinetic energy upon release.For the testing procedure, the test samples were positioned in a manner similar to a simply supported beam on the resting point of the impact machine.The tests were carried out in accordance with ASTM D 256 standards.

Hardness test
The Shore D hardness testing (Make: Yuzuki) method is employed to measure the hardness of FT/SH composite materials.To conduct this test, it is essential to begin with the proper calibration of the durometer to zero, accounting for any initial misalignment or deflection.Once calibrated, position the durometer perpendicularly to the surface of the composite material at the desired test location.Apply a controlled and uniform force of 50 N to the durometer's indenter, firmly pressing it against the composite's surface, with the force magnitude typically specified in testing standards.Maintain this force for a specific dwell time, typically a 10 s, to allow the material to undergo slight deformation and reach a stable reading.Subsequently, the hardness values are recorded from the durometer's scale as shown in figure 11.A higher value signifies greater material  hardness and lower value shows its weakness.For enhanced accuracy, multiple trials are carried out at various locations on the developed FT/SH composite material and subsequently calculated the average hardness value.
Scanning electron microscopic (SEM)-surface morphology An EVO 18 Scanning Electron Microscope (SEM) analyzer (Zeiss) was employed to investigate the surface morphology of the fabricated FT/SH composites.To enhance image quality and conductivity, the samples  underwent gold plating prior to analysis.This allowed for high-resolution imaging at various magnifications, revealing crucial details regarding the fiber arrangement and the distribution of cellulose within the fibers.

Results and discussion on mechanical properties of FT/SH composites
The fabrication and testing of the fishtail palm leaf stack fiber (FPLSFs) biocomposites reinforced with varying weight fractions of soybean hull nanocellulose (SBHNCs) yielded important quantitative data on the mechanical performance.Key parameters analyzed included tensile strength, flexural strength, impact strength and hardness.These metrics provide crucial insights on the structural integrity, resilience, and load-bearing capabilities for potential real-world applications.The figure 12 visually encapsulate the major trends and findings from the experimental mechanical testing of the developed FT/SH bio-nanocomposites.The graphs allow quick visual assessment of how the different SH nanocellulose contents influenced each mechanical attribute relative to the control sample with only FPLSFs.Additionally, they highlight the weight compositions which exhibited optimal properties, which will guide selection of formulations for further evaluation or product development.The quantitative datasets empower nuanced studies, but the pictorial depiction conveys key takeaways at a glance.

Analysis on tensile strength
Figure 13 shows the measured tensile strengths of the developed FT/SH composites which comprise different weight fractions of SBHNCs.It measures the ability of the developed FT/SH composites to withstand axial loads  without breaking.In the context of FT/SH composites, tensile strength is critical because it indicates the FT/SH composite's structural integrity and its ability to bear loads.From figure 13, it is understood that the tensile strength ranges from 33.9 MPa to 51.4 MPa.The highest tensile strength, approximately 51.4 MPa, is achieved in the case of FT/SH4.This result is attributed to the effective interlocking of 7.5 wt% of SBHNCs with 32.5 wt% of FPLSFs, which is determined to be the most optimal composition for developing these composites.The  7.5 wt% concentration of SBHNCs may lead to reduced void content in the composite, which can improve the mechanical properties by providing a more uniform stress distribution.At this weight fraction, there is a balance between matrix-fiber interaction and fiber-fiber interaction [45].This balance allows for efficient stress transfer from the matrix to the fibers, enhancing the composite's mechanical strength.
The below discussion indicates the percent deviations of each sample's properties from the highest recorded values: FT/SH1 and FT/SH2: These samples have the lowest tensile strengths with deviations of approximately 34.11% and 32.73%, respectively, from the highest value (FT/SH4).This could be due to factors like inadequate fiber-matrix adhesion or poor distribution of fibers within the matrix.This indicates that the addition of 0 wt% and 2.5 wt% of SBHNCs to FPLSFs results in a more porous structure, leading to the formation of brittle composites.
FT/SH3: This sample exhibits a moderate deviation of 7.59% from FT/SH4.It suggests that FT/SH3 (addition of 5 wt% of SBHNCs to FPLSFs) has been engineered with better fiber-matrix interactions or optimized fiber dispersion, resulting in improved tensile strength.
FT/SH5: This sample shows a marginal deviation of 2.81%, indicating that its tensile strength (49.96MPa) is almost on par with FT/SH4.This reduction may be due to disruption of the crystalline structure.In contrast, higher weight fractions may increase the density and weight of the composite without a corresponding increase in strength.It could imply that FT/SH5 has been optimized for superior tensile properties, possibly by using advanced manufacturing techniques or superior fiber types.
Analysis on flexural strength Figure 14 shows the measured flexural strengths of the developed FT/SH composites which comprise different weight fractions of SBHNCs.It measures a material's ability to withstand bending forces, which is crucial for applications where the composite is subjected to bending or flexing loads.As illustrated in figure 14, range from 27.95 MPa to 46.09 MPa for the developed FT/SH composites.The highest flexural strength of 46.09 MPa is achieved with FT/SH4 containing 7.5 wt% SBHNCs and 32.5 wt% FPLSFs.This optimal flexural performance aligns with the tensile strength trends and can be attributed to strong interfacial bonding between the nano-scale SBHNC fibers and the FPLSFs.The high surface area of nanocellulose coupled with hydrogen bonding and mechanical interlocking with cellulose fibers enables uniform stress transfer without premature failure at the interface.
In contrast, FT/SH1 with only FPLSFs (no SBHNCs) recorded the lowest flexural strength of 27.95 MPa, a 39.36% reduction versus FT/SH4.This indicates poor stress transfer across the fiber-matrix interfaces, likely due to inadequate bonding.Individual fibers tend to pull out easily during bending instead of fracturing.Interestingly, adding 2.5 wt% SBHNCs (FT/SH2) only improves the flexural strength slightly to 30.722 MPa.The nanocellulose content may be insufficient to effectively bridge the micro-fibers and matrix.Hence, poor fiber-matrix interaction still dominates failure.This indicates that the addition of 0 wt% and 2.5 wt% of SBHNCs to FPLSFs results in a more porous structure, leading to the formation of brittle composites.Increasing SBHNCs to 5 wt% (FT/SH3) enhances flexural strength by 20.81% over FT/SH1, achieving 40.71MPa.This shows more nanocellulose can better reinforce interfaces and reduce stress concentrations.This improvement could be attributed to enhanced fiber orientation during compression and better fiber distribution within the composite.FT/SH5 with 10 wt% SBHNCs performs comparably to FT/SH4 in flexural loading (negligible deviation ≈0.43%).Although higher nanocellulose levels may hinder mobility and consolidation, there is adequate fiber networking to resist bending strains.This implies that FT/SH5 might have been optimized for enhanced flexural properties, possibly through controlled manufacturing processes.
Analysis on impact strength Figure 15 illustrates the impact strength values obtained through testing of the fabricated FT/SH biocomposites reinforced with varying weight percentages of soybean hull nanocellulose (SBHNCs).Impact strength measures a material's ability to resist sudden shock or impact loading, a crucial property for applications where the material may encounter dynamic forces.In this analysis, the measured highest values obtained as 36.47 kJ/mm 2 for FT/SH4, signifying its capability to withstand substantial dynamic loads or impacts.This superior performance could be attributed to excellent fiber-matrix adhesion, effective distribution of FPLSFs reinforcing fibers, and the appropriate proportion (7.5 wt% of SHCNCs) of nanocellulose mixer.In addition, uniform distribution of the cellulose fibers provides strength and support throughout the composite structure to resist localized stress concentrations during impact.The fabrication process may have induced a degree of orientation and stretching of the cellulose chains along the loading direction.This would bolster mechanical reinforcement along those aligned axes.Attractive forces at the bio-nano interfaces may promote localized crystallization, forming rigid crystalline regions for energy dissipation upon impact.
❖ FT/SH3: It demonstrates the second-highest impact strength (32.45 kJ mm −2 ) among the developed compositions, with a deviation of approximately 11.00% from FT/SH4.This suggests that FT/SH3 has been designed or engineered to have good resistance to impact, possibly through careful selection of manufacturing processes.
❖ FT/SH5: It has an impact strength deviation of 5.89% from FT/SH4.This indicates that it also possesses a reasonable ability to withstand impacts, although it falls slightly below FT/SH3 and FT/SH4.The 10 wt% SBHNCs in FT/SH5 may exceed the optimal level, aggregating into defects that concentrate destructive stresses upon impact.This overage becomes detrimental rather than reinforcing.Too much nanocellulose could restrict movement of polymer chains during fabrication, limiting mechanical interlocking between the nano and micro-scale cellulosic components.
❖ FT/SH2: It has an impact strength deviation of approximately18.26%from FT/SH4.It shows lower impact resistance compared to FT/SH3, FT/SH4, and FT/SH5, which could be attributed to variations in the material composition, fiber orientation, or manufacturing process.Issues with composite curing, drying, or pressure processing may have induced microscopic flaws that propagate cracks upon impact.Extended exposure of components to high heat during manufacturing may cause thermal depolymerization and embrittlement.
❖ FT/SH1: It has the lowest impact strength (28.36 kJ mm −2 ) with a deviation of 22.22% from FT/SH4.This indicates that FT/SH1 is less effective in resisting sudden shocks or impacts compared to the other segments.An improper cooling or contraction of the composite after processing could impart residual stresses along weak points that then fracture easily when impacted.It may require improvements in material selection or processing to enhance its impact resistance.

Analysis on hardness
Figure 16 illustrates the shore-D hardness values obtained through testing of the fabricated FT/SH biocomposites reinforced with varying weight percentages of soybean hull nanocellulose (SBHNCs).It measures a developed FT/SH composite's resistance to deformation, and it is often associated with its durability and ability to withstand wear and indentation.In this analysis, the hardness to the highest recorded value, which is FT/SH4 with a hardness of 84. 26 S d as shown in figure 16.
❖ FT/SH4: It has the highest hardness value (84.26 S d ), indicating that it is the most resistant to deformation and wear among the segments.This superior hardness can be attributed to factors such as the choice of reinforcing materials, manufacturing processes, or heat treatment methods that enhance its hardness.
❖ FT/SH3: It exhibits the second-highest hardness value (81.74 S d ) with a deviation of approximately 2.99% from FT/SH4.This suggests that FT/SH3 has been engineered to have good resistance to deformation, although it is slightly lower than FT/SH4.This could be due to specific material choices or processing techniques.Deficits in fiber-matrix adhesion allowing easier dislodging/slippage of cellulosic components under an indentation force rather than plastic deformation resistance.Presence of minute porosity from air pockets trapped during composite curing, concentrating stress and initiating premature failure under the applied indentation load.
❖ FT/SH5: It shows a minimal hardness deviation of 1.07% from FT/SH4, indicating it has similar hardness properties to FT/SH4.Slight overloading of nanocellulose leading to aggregation into weaknesses that then compress more readily upon indentation instead of withstanding the load.Subtle thermal degradation during processing generating micro-fractures and loss of molecular integrity, enabling enhanced deformability.This suggests that FT/SH5 is designed to have high hardness and durability, making it suitable for applications where wear resistance is essential.composite's morphology, fiber-matrix interactions, and the distribution of reinforcing elements, providing insights into the mechanical properties observed in the previous tests (tensile strength, flexural strength, impact strength, and hardness).
❖ FT/SH4: SEM micrographs of FT/SH4 reveal a well-defined and homogeneous microstructure.The reinforcing fibers are evenly distributed within the matrix, forming a dense and uniform network as shown in figure 17(d).This likely contributes to the high mechanical properties observed in the tensile and flexural tests.The absence of voids and defects is evident.
❖ FT/SH3: SEM images of FT/SH3 also show a uniform microstructure with well-distributed fibers as shown in figure 17(c).The interfacial bonding between fibers and the matrix appears strong, contributing to the composite's high strength.
❖ FT/SH5: FT/SH5 exhibits a microstructure similar to FT/SH4, with cluster dispersed SHCNCs in the FPLSFs fibers and a relatively uniform structure as shown in figure 17(e).This suggests good fiber-matrix adhesion and effective reinforcement.
❖ FT/SH2: SEM images of FT/SH2 reveal a somewhat less uniform microstructure compared to FT/SH4 and FT/SH3.There are minor variations in fiber distribution and orientation, which may explain the lower mechanical properties observed in the tests as shown in figure 17(b).
❖ FT/SH1: FT/SH1 exhibits a microstructure with, less homogeneity noticeable voids, and less organized fiber distribution as shown in figure 17(a).These structural irregularities may contribute to the lower mechanical properties observed in the tests.
The observations align with the mechanical property data, where FT/SH4, FT/SH3, and FT/SH5 exhibit well-structured and uniform microstructures with good fiber-matrix adhesion, leading to Superior mechanical properties.Conversely, FT/SH1 and FT/SH2 exhibit more irregular microstructures and less effective fiber distribution, correlating with lower mechanical performance.These SEM findings suggest that optimizing the microstructure and ensuring uniform fiber distribution and strong fiber-matrix bonding are crucial factors in enhancing the mechanical properties of FT/SH composites.Further investigation and optimization of manufacturing processes could lead to improved composite materials for specific applications.

Conclusion
This study successfully demonstrated the extraction of cellulose nanocrystals (CNCs) from soybean hulls, an abundant agricultural byproduct, using a combination of alkali treatment, bleaching, acid hydrolysis and mechanical shearing.The resulting SBHNCs exhibited high crystallinity (70.58%CrI), thermal stability (peak degradation at 371 °C), and morphology indicative of cellulose II crystals.FTIR analysis confirmed effective removal of lignin and hemicellulose after extraction.The SBHNCs were incorporated into fishtail palm leaf stalk fiber biocomposites at 2.5-10 wt% loading in an epoxy matrix.Enhanced mechanical properties were attained with 7.5 wt% SBHNCs, achieving 51.4 MPa tensile strength, 46.09MPa flexural strength and 36.47 kJ mm −2 impact strength.This optimal nanocellulose content balanced interfacial and intra-fiber bonding.Lower SBHNC percentages showed inferior properties due to insufficient reinforcement.To optimize the manufacturing process for more consistent results and improve the properties of FT/SH1 and FT/SH2 compositions, optimizing distribution and dispersion of the multiscale cellulosic components through techniques like high shear mixing to prevent localized clumping with standardized temperature, ramp rates, pressure and duration of the curing process.Further research is to focus on: optimizing processing conditions to maximize material properties, evaluating nanocellulose reinforcement potential across additional composite systems, analysis of interfacial bonding behaviors, long term performance assessments, examining sustainability benefits, process scale up with technoeconomic evaluation, tailoring compatibility via surface modifications, and property benchmarking against alternative agricultural waste-derived nanocelluloses.Advancing work across these research frontiers will facilitate translation of soybean hull nanocellulose from laboratory synthesis to viable industrial-scale manufacturing pathways for high-value composite products such as door panels, trunk liners, insulation boards, sporting goods, electronics cases, ducts, splints, boat hulls and ballast tanks.This will also enable sustainable agriculture waste valorization.
, indicate the successful transformation of cellulose I into cellulose II extracted from soybean hulls.The dominant peak observed at 2θ = 22.53°and 29.37°corresponds to the lattice planes (200) and (040) of crystalline cellulose polymorphism IIβ.Additionally, peaks around 2θ = 16.51 degrees correspond to the lattice planes (101) and (110) of crystalline cellulose polymorphism IIβ.The presence of these peaks aligns with the established crystalline structure of cellulose II.

Figure 12 .
Figure 12.Key findings of mechanical properties of FT/SH composites.

Table 1 .
Samples composition and designation.