Alkali-Engineered Tobacco Stem Particles for Polyester Composites: Enhancing Physical, Mechanical, Thermal, and Dynamic Mechanical Properties

Alkali-Engineered Tobacco Stem Particles for Polyester Composites: Enhancing Physical, Mechanical, Thermal, and Dynamic Mechanical Properties | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Alkali-Engineered Tobacco Stem Particles for Polyester Composites: Enhancing Physical, Mechanical, Thermal, and Dynamic Mechanical Properties Nasmi Herlina Sari, Sujita Sujita, Suteja Suteja, Muhammad Firdaus, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6702277/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 30 Sep, 2025 Read the published version in Discover Materials → Version 1 posted 9 You are reading this latest preprint version Abstract The increasing demand for eco-friendly materials has driven the development of sustainable biocomposites using renewable natural fibers. This study evaluates the mechanical, physical, tribological, and thermal properties of sustainable polyester biocomposites reinforced with treated tobacco stem particles (NTSPs). The NTSPs were treated with sodium hydroxide (NaOH) at concentrations of 2%, 5%, and 8% to enhance compatibility with the polyester matrix. Biocomposites containing 30% NTSPs by volume were fabricated via hot pressing at 105 °C and 75 Pa. Testing included tensile and flexural strength, thermal analysis, dynamic mechanical analysis (DMA), tribological evaluation, and scanning electron microscopy (SEM). The 8% NaOH-treated composite showed the best performance, with tensile strength of 48.53 ± 2 MPa, modulus of 2035.6 ± 77 MPa, and density of 1.22 ± 1.5 g/cm³. FTIR confirmed surface modification, while SEM revealed improved fiber–matrix bonding. The results demonstrate that treated tobacco stems particles are promising reinforcements for eco-friendly polyester composites, suitable for automotive interiors and semi-structural applications. Polyester matrix tobacco stem particles (NTSPs) Alkali treatment Sustainable composites Mechanical properties Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Introduction The escalating environmental concerns and the depletion of fossil fuel reserves have intensified the search for sustainable materials in various industries. Natural fiber-reinforced polymer composites (NFRPCs) have garnered significant attention as eco-friendly alternatives to synthetic composites due to their biodegradability, renewability, and favorable mechanical properties [ 1 – 3 ]. Among the myriad of natural fibers explored, tobacco (commonly known as tobacco) stems represent an underutilized agricultural byproduct with potential as reinforcement in polymer matrices. The utilization of tobacco stalk stem particles in composite materials not only adds value to agricultural waste but also contributes to waste management and environmental sustainability. However, the inherent hydrophilicity and surface impurities of natural fibers often lead to poor interfacial adhesion with hydrophobic polymer matrices, adversely affecting the mechanical performance of the resulting composites [ 1 , 4 – 6 ]. To address these challenges, chemical surface modification techniques, particularly alkali treatment using sodium hydroxide (NaOH), have been employed to enhance fiber-matrix compatibility [ 3 , 7 – 10 ]. Alkali treatment effectively removes non-cellulosic components such as hemicellulose and lignin from the fiber surface, increasing surface roughness and exposing reactive hydroxyl groups, thereby improving interfacial bonding [ 11 – 13 ]. Studies by Aprilia et al. [ 14 ] and Ji et al. [ 6 ] have demonstrated improved mechanical, thermal, and water absorption characteristics in various natural fiber composites following chemical surface treatments. For instance, Phoenix sp. and oil palm fibers showed enhanced performance in polymer matrices when treated with appropriate alkali conditions. Similarly, research on Sansevieria trifasciata Laurentii fibers treated with liquid smoke followed by microwave treatment reported notable improvements in tensile strength, surface morphology, and thermal characteristics, highlighting the effectiveness of such treatments in enhancing fiber properties [ 15 ]. Similar enhancements have been observed in fibers such as jute, corn husk, and Paederia foetida following NaOH treatment, which improves interfacial adhesion and mechanical strength through the removal of surface impurities and the modification of fiber morphology [ 16 ]. Pokhriyal and Rakesh [ 17 ] found that Himalayacalamus falconeri fibers treated with 2% NaOH displayed a low fibril micro angle (7.87° ± 1.50) and high cellulose content (74.9%), resulting in tensile strength of 177 MPa, Young’s modulus of 18.6 GPa, and elongation of just 1%. These characteristics highlight their potential as biodegradable reinforcements in polymer-based composites. In the context of tobacco stalk fibers, several recent studies have provided insights into their chemical composition and treatment responses. Liu et al. [ 18 ] and Sun et al. [ 19 ] explored the fractionation and structural elucidation of tobacco stalk lignin for value-added applications. Dallé et al. [ 20 ] reported the kinetic evaluation of alkaline treatment on tobacco stalks under varying conditions, establishing critical process-structure-performance correlations. Sophanodorn et al. [ 21 ] focused on the environmental management and bioethanol potential of tobacco stalks through pretreatment strategies, while He et al. [ 22 ] examined their capacity for phosphate adsorption from wastewater. Changle et al. [ 15 ] investigated the effects of different parts of tobacco stalk—xylem (TSX), husk (TSH), and core (TSC)—on the mechanical properties of TSF/polypropylene composites. They reported tensile strengths of 32.8 MPa (TSX), 25.6 MPa (TSH), and 26.4 MPa (TSC), and corresponding flexural strengths of 56.0 MPa, 46.1 MPa, and 48.7 MPa, respectively, with good reusability potential. These studies collectively underscore the versatility and untapped potential of tobacco stalks as bioresources for advanced materials and bio-based product development. However, the specific application of alkali-treated tobacco stem particles (NTP) as reinforcement in unsaturated polyester composites remains underexplored. Therefore, this study aims to fill this gap by evaluating the effects of NaOH surface treatments on NTP and assessing their potential as reinforcements in polyester matrices. Specifically, it examines the influence of NaOH treatment at varying concentrations (2%, 5%, and 8%) on the fiber's chemical composition, morphology, and interfacial bonding. The research further explores the impact of these treatments on the composites’ mechanical properties (tensile strength and modulus), thermal stability, dynamic mechanical behavior, and water absorption performance. Through this comprehensive performance evaluation, the study seeks to develop high-performance, bio-based composite materials that contribute to sustainable material design for applications such as automotive interiors, construction panels, and other semi-structural components. 2. Materials and Method 2.1 Materials Waste of tobacco steam (NTs) were collected from agricultural residues from cultivated tobacco plants in Mataram, West Nusa Tenggara, Indonesia. Sodium hydroxide (NaOH) solutions with concentrations of 2%, 5%, and 8% (w/v). Unsaturated polyester resin and a catalyst—methyl ethyl ketone peroxide (MEKP)—were supplied by PT Justus Kimia Raya, Surabaya, Indonesia. The catalyst was used at a concentration of 1.5% by volume of the polyester resin. The pure polyester resin had a density of 1.2 g/cm³ and a tensile strength of 27 MPa. The tobacco stem particles used in this study were collected as post-harvest agricultural waste from a commercial farm located in East Lombok, Indonesia. The plant species was identified as Nicotiana tabacum L . based on standard botanical characteristics and confirmed using agricultural classification guidelines. Since the plant material was sourced from cultivated agricultural waste and not collected from the wild, no voucher specimen was prepared. Nicotiana tabacum L . is not listed as an endangered or protected species under the IUCN Red List or CITES regulations. 2.2 Extraction of Tobacco Stem Particles (NTSPs) The extraction process of tobacco stem particle (NTSPs) is illustrated in Fig. 1 . Initially, the collected NTs were thoroughly washed with fresh water to remove soil, dust, and other surface contaminants. The cleaned stems were then manually chopped into smaller pieces and oven-dried at 80°C for 48 hours using a forced-air circulating oven to reduce moisture content and ensure ease of grinding. After drying, the coarse NTs particles were ground using a mechanical grinder. The resulting material was then sieved through a 100-mesh sieve to obtain a uniform powder with an average particle size of approximately 0.149 mm (149 µm). This final product is referred to hereafter as tobacco stem particles (NTSPs). 2.3 Alkali treatment of NTSPs As illustrated in detail in Fig. 2 , the untreated tobacco stem powder (NTSPs untreated) was divided into three equal portions for alkaline treatment. Each portion was soaked separately in aqueous NaOH solutions with different concentrations of 2%, 5%, and 8% (w/v), respectively for 2 hours at room temperature (± 25°C) [ 23 , 24 ]. Then, the particles were thoroughly rinsed with distilled water several times until the rinsing water reached a neutral pH (~ 7), indicating the removal of residual alkali. They were then dried in a circulating air oven at 65°C for 48 hours; to reduce the moisture content to approximately 10% and were stored in airtight containers to prevent moisture absorption and contamination. The treated samples were labeled as NTSPs-2NaOH (NTSPs after 2% NaOH treatment), NTSPs-5NaOH (NTSPs after 5% NaOH treatment), and NTSPs-8NaOH (NTSPs after 8% NaOH treatment), respectively. Table 1 provides complete physical and chemical parameters for each NTSPs (untreated and treated NaOH). Table 1 Physical and chemical properties of NTSPs-2NaOH, NTSPs-5NaOH and NTSPs-8 NaOH and NTSPs untreated. Particles codes Density (g/cm 3 ) Moisture content (%) Cellulose (%) Hemicellulose (%) Lignin (%) NTSPs untreated 0.802 ± 0.027 6.28 ± 0.22 41.01 20.23 22.76 NTSPs − 2NaOH 0.85 ± 0.011 4.12 ± 0.56 45.06 15.64 6.17 NTSPs − 5NaOH 0.9 ± 0.033 3.74 ± 0.21 52.06 9.07 4.28 NTSPs − 8NaOH 0.94 ± 0.021 3.06 ± 0.28 59.85 5.27 4.02 2.4 Fabrication of NTSPs-Based Polyester Composites NTSPs Untreated and the chemically treated particles (NTSPs-2NaOH, NTSPs-5NaOH, and NTSPs-8NaOH) were each weighed according to a predetermined composition. The NTP and polyester ratios were set at 30% and 70% (% vol.), respectively, using a catalyst MEKP (1.5% vol. polyester). All components were thoroughly mixed using a mechanical stirrer for 20 minutes; to ensure homogeneous dispersion of the NTSPs within the polyester matrix. The resulting slurry was then poured into a stainless-steel mold and subjected to hot press molding at 105°C under a pressure of 75 MPa for 60 minutes [ 25 , 26 ]. The complete fabrication procedure is illustrated in Fig. 3 . Four types of different composites were prepared, and a control composite using untreated NTSPs. Each composite type was fabricated in six replicates to ensure statistical reliability. The detailed composition and labeling of the composite samples are presented in Table 2 . Table 2 Composition and labeling of the composite NTSPs – polyester. . Composites codes Compositions NTR Composites based 30% of NTSPs untreated and 70% polyester (% vol.). TUS Composites based 30% of NTSPs-2NaOH and 70% polyester (% vol.). SJT Composites based 30% of NTSPs-5NaOH and 70% polyester (% vol.). NHS Composites based 30% of NTSPs-8NaOH and 70% polyester (% vol.). 2.5 Characterization 2.5.1 Density of composites The density of the composite samples was determined using the water displacement method based on Archimedes' principle, as described in Eq. ( 1 ). First, each composite specimen was weighed using a digital analytical balance with a precision of 0.001 g to obtain its mass ( m , in grams). The specimen was then carefully submerged in a graduated measuring cylinder filled with distilled water to measure the volume of water displaced, which corresponds to the specimen's volume ( V , in cm³). The density ( ρ , in g/cm³) was then calculated using the following equation [ 11 ]: $$\:\rho\:\:\left(\frac{g}{{cm}^{3}}\right)=\frac{m}{V}$$ 1 All measurements were conducted at room temperature (± 25°C), and each test was repeated three times to ensure accuracy and reproducibility. The average value was reported as the final density for each composite type. 2.5.2 Moisture content of composites The moisture content (MC) of the composite samples was determined using the gravimetric method, as expressed in Eq. ( 2 ). This method involves measuring the weight of the composite before and after oven drying[ 11 ]. $$\:MC\:\left(\%\right)=\:\frac{{W}_{1}-{W}_{2}}{{W}_{2}}\times\:100$$ 2 Where, W₁ is the initial weight of the composite sample before drying (in grams), and W₂ is the final weight of the composite sample after drying at 105°C for 24 hours (in grams). All measurements were performed using a precision digital balance (± 0.001 g). The samples were considered to have reached constant weight when the mass change between two consecutive measurements was less than 0.001 g. Each test was conducted in triplicate, and the average values were reported as the final moisture content. 2.5.3 Fourier Transform Infrared (FTIR) Spectroscopy The functional groups present in composites were analyzed using a Perkin Elmer Frontier FTIR spectrometer equipped with a Universal Attenuated Total Reflectance (UATR) accessory. FTIR spectra were recorded in the wavenumber range of 4000–400 cm⁻¹, with a resolution of 4 cm⁻¹. Each spectrum was obtained by averaging 32 scans per sample to ensure high signal-to-noise ratio and spectral accuracy. Prior to measurement, the background spectrum was collected and subtracted automatically to eliminate ambient interferences. 2.5.4 Tensile and Flexural Tests Tensile and flexural properties of the composite samples were evaluated using a universal testing machine (UTM), model RTG 1310 INSTRON. All tests were conducted in accordance with ASTM D3039-03 for tensile testing and ASTM D790 for flexural testing [ 11 ]. The tests were performed under controlled laboratory conditions at a temperature of 27°C and a relative humidity of 56%. The crosshead speed was maintained at 0.5 mm/min for both tensile and flexural tests. For each composite type, five specimens were tested for both mechanical properties to ensure statistical reliability. 2.5.5 Morphological Analysis by SEM The surface morphology and fracture characteristics of the composite samples after tensile testing were examined using a SEM, model JEOL JSM–S5200. Prior to imaging, the fractured surfaces were sputter-coated with a thin conductive layer of copper, approximately 25 nm thick, to prevent charging and improve image resolution. The SEM observations were performed under high vacuum conditions at an accelerating voltage of 3 kV and a beam current of 15 mA [ 11 ]. 2.5.6 Water Absorption Test The water absorption behavior of the composite samples was evaluated based on weight gain after immersion in distilled water. Prior to testing, all samples were oven-dried at 60°C for 24 hours to eliminate residual moisture. Square samples with dimensions of 20 × 20 × 3 mm³ were prepared for the test [ 27 ]. Each dried sample was weighed (denoted as W o ​) using an analytical balance with 0.001 g accuracy. The samples were then fully immersed in distilled water at room temperature for 24 hours. After immersion, samples were gently wiped with tissue paper to remove surface water and immediately reweighed to obtain the wet weight ( W t ​ ). The water absorption percentage ( W g ​ ) was calculated using Eq. ( 3 ):[ 11 ] . $$\:{W}_{g}\left(\%\right)=\frac{{W}_{t}-{W}_{0}}{{W}_{0}}\times\:100\%$$ 3 Where, W o ​ is the initial (dry) weight of the specimen (g), and W t ​ ​ is the weight after water immersion for the specified time (g). 2.5.7 Thermogravimetric Analysis (TGA/DSC) The thermal behavior and stability of the samples were investigated using Thermogravimetric Analysis (TGA). The measurements were performed using a TGA–1 instrument (Mettler Toledo, Switzerland) under a nitrogen atmosphere to prevent oxidation during thermal decomposition. Approximately 10 mg of each composite sample was placed in an alumina crucible. The analysis was conducted in ramp mode over a temperature range of 27°C to 600°C, with a constant heating rate of 20°C/min and a nitrogen flow rate of 50 mL/min [ 27 ]. 2.5.8 Dynamic Mechanical Analysis (DMA) A NETZSCH DMA 242 equipment was used to perform Dynamic Mechanical Analysis (DMA) on the composites to determine their viscoelastic properties. The analysis was conducted at temperatures ranging from 40°C to 200°C, with a constant heating rate of 10°C/min and a fixed oscillation frequency of 1Hz. The storage modulus (E′), loss modulus (E″), or damping factor (tan δ) were investigated to understand the stiffness, energy dissipation, or glass transition behaviour of the composites, respectively. ASTM D4065-01 was used to manufacture test specimens measuring 60 × 12.5 × 3 mm³. Before testing, all samples were conditioned in regulated humidity settings (25% and 95% RH) [ 1 , 28 ]. 3. Results and Discussion 3.1 Density Analysis As shown in Table 2 , the average densities of composites made from NTR, TUS, SJT, and NHS were 1.17 ± 0.02 g/cm³, 1.19 ± 0.02 g/cm³, 1.20 ± 0.02 g/cm³, and 1.22 ± 0.01 g/cm³, respectively. The composite of particles treated with 8% NaOH (NHS sample) had the highest density, whereas the TUS sample had the lowest density. The composite density increased significantly when the composite was reinforced with NTSPs-8NaOH solution, as compared to NTSPs-2NaOH (sample TUS), NTSPs-5NaOH (sample SJT), nor untreated (NTR) (see Table 1 ). This behavior is explained by the fact that higher alkali concentrations remove amorphous components including hemicellulose, lignin, and extractives more efficiently. When the NaOH content was increased (8%), the loss of these constituents increased, resulting in particles that were richer in crystalline cellulose and denser. Furthermore, the 8% NaOH treatment reduced the internal porosity of the particles caused by swelling and shrinkage of the cell walls during the washing or drying processes, which led to a more compact structure, higher interfacial integration with the matrix, denser particles, strengthening the interfacial bond, and reducing the formation of micro voids, all of which directly increased the density of the composite. These findings show that, the 8% NaOH treatment was the most successful in enhancing the internal structure of the particles and promoting integration with the matrix. When compared to other natural fiber composites such as Purun fiber-reinforced composites (0.92 g/cm³) and corn husk fiber composites (1.14 g/cm³) [ 14 , 29 ]. Table 3 Density and moisture content of NTSPs reinforced polyester composites. Samples composites Density (g/cm 3 ) Moisture content (%) NTR 1.17 ± 1.2 0.46 ± 0.17 TUS 1.19 ± 1.2 0.45 ± 0.15 SJT 1.2 ± 1.2 0.43 ± 0.16 NHS 1.22 ± 1.5 0.43 ± 0.13 3.2 Moisture content analysis Table 3 presents the moisture content of NTSPs-reinforced composites. The results indicate that the composites treated with 5%NaOH and 8% NaOH (samples SJT and NHS)—exhibited lower moisture content (0.43%) compared to the TUS and NTR samples, which showed slightly higher moisture content. According to Sari et al. [ 8 ], this trend can be attributed to the increased removal of hemicellulose and other amorphous, hydrophilic components as the concentration of NaOH rises. Hemicellulose contains abundant hydroxyl groups that readily bond with water molecules [ 30 , 31 ]. Its removal significantly reduces the water affinity of the fiber, promoting surface fibrillation and enhancing interfacial bonding with the polyester matrix [ 32 , 33 ]. 3.3 FTIR Analysis The FTIR spectra of NTSPs-based composites are shown in Fig. 4 . All spectra displayed a similar overall pattern, suggesting that the core chemical structure of the composite remains consistent across the treatments, with notable differences in peak intensities. A total of nine significant absorption bands were identified, and their respective functional group assignments are summarized in Table 4 . These bands reflect the presence and interactions of key chemical constituents in the composite materials. At a peak 3368–3374 cm⁻¹ attributed to O–H stretching vibrations associated with hydrogen bonding in hydroxyl groups and α-cellulose (cellulose Iβ). A peak 2905–2911 cm⁻¹ corresponds to C–H stretching vibrations found in cellulose and hemicellulose. At the band 1504–1510 cm⁻¹ associated with aromatic C = C stretching vibrations typical of lignin structures. At a peak 1422–1428 cm⁻¹ linked to CH₂ bending and crystalline cellulose regions. At the band 1370–1376 cm⁻¹ assigned to C–H bending vibrations, particularly from cellulose [ 34 ]. At peak 1264–1271 cm⁻¹ attributed to C–O stretching in the acetyl groups of lignin. At the band 1107–1113 cm⁻¹ indicative of C–O stretching vibrations in cellulose, hemicellulose, and lignin. At peak 894–900 cm⁻¹ corresponds to β-glycosidic linkages in cellulose, indicative of polysaccharide integrity[ 35 ]. The results confirm the retention of key chemical functionalities following alkali treatment and its composite. However, variations in peak intensity, especially in the O–H and C–H regions, suggest partial removal of hemicellulose and lignin, particularly at sample NHS (8% NaOH concentrations). This supports the hypothesis that NaOH treatment modifies the NTSPs surface and reduces hydrophilic groups, which is in agreement with the moisture content and morphological results discussed earlier. These FTIR findings validate the chemical interaction and interfacial bonding between treated NTSPs and the polyester matrix, essential for the improved performance of NTSPs -reinforced composites. Table 4 FTIR stretching frequencies and functional group of NTSPs-based polyester composites Wave number (cm ‒1 ) Assignments NTR TUS NHS SJT 3359 3368 3371 3374 Cellulose I β/O–H stretching vibrations of α‒cellulose and hydrogen bond of the hydroxyl groups 2901 2905 2908 2911 Cellulose and hemicellulose components/C‒H stretching vibration in cellulose and hemicellulose 1506 1504 1507 1510 Lignin/aromatic C = C stretching in lignin 1421 1422 1425 1428 Cellulose/CH 2 bending 1371 1371 1373 1376 Cellulose/C‒H bending 1320 1321 1323 1326 Lignin/aromatic C‒O bending 1261 1264 1268 1271 Lignin/‒CO stretching of acetyl group 1103 1107 1111 1114 Cellulose, hemicellulose, lignin/C‒O stretching vibration in cellulose 894.04 894.04 897 900 Cellulose/β‒glucosides linkage in cellulose 3.4 Tensile Strength Analysis of Composite Figure 5 a presents the tensile strength of the composite samples NTR, TUS, SJT, and NHS, with average values of 38.49 ± 3 MPa, 40.64 ± 3 MPa, 44.83 ± 3 MPa, and 48.53 ± 2 MPa, respectively. At a constant volume fraction of NTSPs, the composites' tensile strength increased more than the NTR composites after reinforcing with NaOH-treated NTSPs. The NHS sample had the maximum tensile strength (48.53 ± 2 MPa), while the TUS sample had the lowest (40.64 ± 3 MPa). Alkaline treatment with NaOH (2%-8%) effectively eliminates amorphous components from the NTSP surface, resulting in increased tensile strength values for the composites investigated. This removal increases the surface roughness of NTSP, improves interfacial adhesion, and allows the polyester matrix to wet more thoroughly, resulting in greater mechanical interlocking. Furthermore, 8% NaOH treatment greatly roughens the NTSP surface, enhancing the contact area with the matrix, as demonstrated in the NHS sample, resulting in the maximum tensile strength. However, it is important to note that excessively high NaOH concentrations can damage cellulose chains and lead to a transformation from cellulose I to the less mechanically stable cellulose II [ 36 ]. Figure 5 b shows the elongation at break for all samples. NHS recorded the highest elongation (1.73 ± 0.17%), followed by SJT (1.57 ± 0.26%), TUS (1.47 ± 0.17%), and NTR ((1.23 ± 0.2%). The improvement in elongation suggests that NaOH treatment not only enhances NTSPs -matrix adhesion but also introduces flexibility in the composite, allowing the NTSPs to deform more before failure. Next, As presented in Fig. 5 c, the elastic tensile modulus of different composite. The NHS sample had the highest modulus of elasticity among the samples, at around 2035.6 ± 77 MPa, demonstrating greater resistance to elastic deformation during tensile stress. SJT (1700 ± 91MPa), TUS 1506 ± 86 MPa), and NTR (1405 ± 86 MPa) were the next strongest. The trend indicates a noticeable increase in stiffness from NTR to NHS, most likely due to higher NaOH concentrations. This behavior is attributed to improved interfacial stress transfer between particles and matrix due to stronger bonding. A rougher NTSPs surface increases mechanical interlocking, which enhances the stiffness of the composite and allows it to resist deformation under load. In contrast, the lower modulus in the NTR sample indicates a more compliant material, which may be advantageous for applications requiring more flexibility and lower rigidity. NaOH treatment at 8% concentrations significantly improves the mechanical properties of NTSPs-based composites by enhancing fiber-matrix bonding, increasing tensile strength, elongation, and stiffness. Furthermore, in comparison with other natural fiber composites, such as coconut shell powder (16.96–22.46 MPa), composites NTSPs exhibit superior tensile performance. However, they are slightly inferior to composites Hibiscus tiliaceus with filler 30% carbon, which reach up to 54.98 ± 2.5 MPa. Although lower NaOH concentrations (as in TUS and SJT) can increase NTSPs roughness, they may not sufficiently enhance the tensile properties due to insufficient removal of impurities and weaker NTSPs strength. 3.4 Flexural Strength Analysis of Composites Figure 6 a presents the effect of NaOH treatment concentrations on the flexural strength of NTSPs -reinforced composites, namely NTR, TUS, SJT, and NHS. Overall, a significant increase in flexural strength was observed as the NaOH concentration increased from 2–8% (% vol.). The NHS sample, treated with 8% NaOH, exhibited the highest flexural strength of approximately 124 ± 14 MPa, whereas the NTR sample, showed the lowest value, approximately 102 ± 11 MPa. This trend clearly indicates that alkali treatment plays a crucial role in enhancing the mechanical performance of the composite. The enhancement in flexural strength is primarily attributed to the chemical and morphological modifications induced on the fiber surface by the alkali treatment. Furthermore, NaOH treatment increases the surface roughness of the NTSPs, thereby promoting a stronger mechanical interlocking between the NTSPs and the polyester matrix. This enhanced physical interlocking helps prevent delamination or fiber pull-out under flexural loading, thereby contributing significantly to the composite's bending resistance. However, the effectiveness of alkali treatment is highly dependent on the concentration used. At lower concentrations (2%), the chemical alteration of the NTSPs surface may be insufficient to significantly improve adhesion, resulting in weak interfacial bonding and limited load transfer capability. In contrast, the 8% NaOH treatment appears to optimize both the structural stability and rigidity of the NTSPs, leading to superior flexural performance. These findings are consistent with previous studies, which have reported that alkali concentrations in the range of 5–10% can significantly improve the mechanical properties of natural fiber-reinforced composites by enhancing fiber–matrix adhesion, as long as fiber degradation is avoided [ 36 , 37 ]. Figure 6 b depicts the flexural modulus of four distinct composite materials: NTR, TUS, SJT, and NHS. The NHS sample had the highest flexural modulus, approximately 2673 ± 77 MPa, indicating superior stiffness and strength under flexural stress. SJT (2319 ± 91 MPa), TUS (2038 ± 86 MPa), and NTR (1874 ± 86 MPa) were the next strongest. The gradual rise in flexural modulus from NTR to NHS suggests that the reinforcing NTSPs and distribution have a substantial impact on composite stiffness. The increased modulus seen in the NHS composite could be due to improved bonding between the matrix and the reinforcement, more efficient stress transfer, as well as a greater degree of fiber alignment and packing. In contrast, the NTR composite's lower modulus suggests a more flexible structure, making it potentially appropriate for applications that require better deformability but lower rigidity. 3.5 Morphology analysis by SEM Figure 7 displays the SEM micrographs of the fracture surfaces of the composite samples, which provide insight into the fiber–matrix interfacial adhesion and failure mechanisms under flexural loading. Figure 7 a shows the surface morphology of the sample NTR. Some particles are well entrenched in the polyester matrix, whereas others appear to have poor interfacial adhesion, indicating possible flaws in particle-matrix bonding. Furthermore, elongated cylindrical formations are seen, which could be agglomerated particles or residual fibrous contaminants that were not fully dispersed during production. There are no large cracks, although tiny delamination features are visible in some spots, which could indicate localized stress concentrations. These microstructural traits are anticipated to influence the composite's mechanical performance, specifically its tensile strength, flexural qualities, and durability. Figure 7 b shows the TUS sample, which reveals relatively smooth fracture regions with minimal composite breakage. The interface between the NTSPs and matrix appears loosely bonded, suggesting weak interfacial adhesion. This morphology is indicative of insufficient stress transfer across the interface, which can result in premature failure during flexural loading. Such weak bonding has been associated with poor mechanical performance in natural fiber composites, as reported by Madhu et al. [ 3 ], where low alkali concentration led to incomplete removal of hemicellulose and lignin. Figure 7 c corresponds to the SJT sample and presents a more complex fracture surface, with visible NTSPs and matrix deformation. This suggests moderate interfacial bonding, where partial load transfer occurs, but is still hindered by interfacial slippage and fiber agglomeration. The pulled-out fibers with clean surfaces indicate insufficient chemical bonding. However, some rougher fracture features imply the onset of improved fiber–matrix adhesion. These observations are in line with findings by Alao et al., [ 38 ] who emphasized the importance of alkali-induced surface roughening in promoting frictional resistance and mechanical interlocking, even if not fully optimized. While, Fig. 7 d displays SEM photo the NHS sample, which demonstrates a rougher and more irregular fracture surface with clear signs of particle breakage and strong matrix-NTSPs integration. The embedded NTSPs exhibit fewer gaps at the interface, suggesting effective interfacial adhesion due to optimal NTSPs treatment with 8% NaOH. The rough fracture surface morphology is characteristic of improved load transfer and energy absorption, indicative of ductile fracture behavior. This enhanced adhesion is attributed to the removal of surface impurities and the exposure of hydroxyl groups, which promotes better chemical bonding and mechanical interlocking [ 39 , 40 ]. The SEM analysis confirms that increasing NaOH concentration enhances NTSPs–matrix adhesion, with the NHS sample showing the most effective bonding characteristics. 3.6 TGA/DSC Analysis Figure 8 presents the thermal behavior of the composites through TGA (Fig. 8 a) and DSC (Fig. 8 b) analyses. The TGA curves (Fig. 8 a) indicate a typical three-stage thermal degradation pattern. The initial weight loss below 120°C corresponds to the evaporation of moisture and volatile compounds. The second major degradation phase, occurring between 220–360°C, is attributed to the decomposition of hemicellulose and cellulose components. Beyond 360°C, the degradation of lignin and the residual carbonaceous material becomes evident. Among the samples, the NHS sample exhibited improved thermal stability with a slower degradation rate and a lower total mass loss. The char residue of 11.923% in the NHS sample was higher than that of TUS (13.523%) and SJT (14.498%), indicating greater thermal resistance and higher structural integrity at elevated temperatures. This behavior is primarily due to the 8% NaOH treatment that effectively removed amorphous hemicellulose and surface impurities, leading to denser packing and better thermal insulation properties [ 41 ]. The DSC curves (Fig. 8 b) further support this observation by revealing thermal transitions related to composite softening and decomposition. All samples exhibit an endothermic peak between 60–120°C due to water loss and relaxation of amorphous chains. The NHS sample shows a higher peak degradation temperature (~ 370°C) compared to SJT (~ 355°C) and TUS (~ 348°C), reflecting enhanced thermal stability. This shift is indicative of stronger NTSPs–matrix adhesion, improved crystallinity, and reduced molecular mobility due to effective particles treatment. Additionally, the sharper and more defined endothermic peak in the NHS sample suggests a more uniform matrix–particles interaction, whereas broader transitions in TUS and SJT indicate heterogeneous thermal behavior. These findings align with those of Gnanasekaran et al. [ 42 ], who highlighted the role of alkaline-treated fibers in improving thermal resistance and structural performance in polymer composites. 3.7 Water absorption analysis Figure 9 illustrates the water absorption behavior of the TUS, SJT, and NHS composites over a 24-day immersion period. All samples exhibited a rapid increase in water uptake during the initial 10 days, which subsequently plateaued, indicating the approach to saturation. This two-phase absorption trend is commonly observed in natural fiber-reinforced composites due to the presence of hydrophilic hydroxyl groups in the lignocellulosic structure of the fibers [ 36 ]. The NHS composite demonstrated the lowest water absorption, reaching approximately 13.1% at equilibrium. In contrast, the SJT and TUS composites exhibited higher final absorption values, approximately 13.9% and 14.3%, respectively. The reduced water uptake in the NHS composite is attributed to the combined effect of alkali (NaOH) treatment on the NTSPs, which effectively removed hemicellulose and surface impurities while enhancing NTSPs–matrix interfacial bonding. NHS composites' water absorption resistance qualities make them a better alternative for use in humid or wet conditions requiring dimensional stability and long-term durability. A similar improvement in water resistance following pineapple leaves fiber and alkaline treatments has been reported by Gnanasekaran et al., [ 42 ], where plasma-modified pineapple leaves fiber showed superior dimensional stability in moist environments. In contrast, the higher water uptake observed in SJT and TUS samples implies a less efficient fiber treatment, resulting in higher porosity and weaker interfacial adhesion. The saturation trend also indicates that the absorption follows Fickian diffusion behavior, consistent with previous findings by Serra-parareda et al., [ 43 ], where the rate of water diffusion slows down significantly after the fiber’s accessible hydroxyl groups are fully engaged. 3.8 Dynamic mechanical analysis (DMA) Dynamic Mechanical Analysis (DMA) was performed to evaluate the viscoelastic behavior of the composite samples in relation to temperature variations. Figure 10 illustrates the storage modulus (E′), loss modulus (E″), and damping factor (tan δ) for TUS, SJT, and NHS composites. The storage modulus (E′) profile (Fig. 10 a) demonstrates a decreasing trend with increasing temperature. Among the samples, NHS exhibited the highest E′ values throughout the temperature range, indicating enhanced stiffness and superior elastic response. This improvement is attributed to better NTSPs–matrix interfacial adhesion, facilitated by the synergistic effect of NaOH treatment, which likely enhanced surface roughness and functional group availability on the NTSPs surface. This finding is consistent with the study by Serra-parareda et al. [ 43 ], where plasma-treated fibers resulted in significantly improved storage modulus in epoxy-based composites. In the loss modulus (E″) curves (Fig. 10 b), all samples display a prominent peak between − 50 and − 45°C, corresponding to the glass transition temperature (Tg) of the polyester matrix. The TUS sample showed the highest E″ peak, possibly indicating greater internal friction and energy dissipation due to poorer interfacial bonding. In contrast, the NHS sample, while exhibiting a slightly lower E″, maintained a broad and stable peak, implying effective load transfer with minimal viscous losses. The tan δ curves (Fig. 10 c) further confirm the interfacial characteristics of the composites. All samples exhibited Tg values in the range of − 47 to − 45°C, consistent with their E″ results. However, the NHS sample presented the lowest tan δ peak, which is a strong indicator of enhanced NTSPs–matrix adhesion and restricted molecular motion at the interface. This aligns with the findings of Lendvai et al. [ 1 ], who observed that lower tan δ values in treated natural fiber composites correlate with improved stress transfer efficiency and reduced damping behavior. 4. Conclusion This study investigated the influence of varying NaOH concentrations (2%, 5%, and 8%) applied for 2 hours on the surface properties of tobacco stem particles (NTSPs), and their subsequent reinforcing effect on polyester composites. Comprehensive evaluations were conducted, including mechanical properties, thermal stability, dynamic mechanical analysis (DMA), density, moisture content, and water absorption behavior. The chemical treatments resulted in the effective removal of hemicellulose and lignin components, while increasing the relative cellulose content of the NTSPs. These structural modifications directly influenced the performance of the resulting composites. The tensile strength and elastic modulus of the composites ranged from 40.64 MPa to 48.53 MPa and from 1305 MPa to 2035 MPa, respectively, demonstrating the effectiveness of NTSPs surface engineering at a fixed NTP content of 30% by volume. Among the samples, the composite reinforced with NTP treated using 8% NaOH (NHS sample) exhibited the most superior performance in terms of mechanical strength, thermal stability, and water resistance. This was further supported by changes in functional group characteristics, increased density, and reduced moisture content following chemical modification. These improvements highlight the potential of composites based NTSPs for eco-friendly structural and semi-structural applications, particularly in automotive interiors, construction panels, and packaging materials. Declarations Acknowledgements The researcher would like to thank the University of Mataram has supported the funding of this research through the Grant funding of the professor program in 2024 (No. 1235/UN18.L1/PP/2024). CRediT authorship contribution statement Nasmi Herlina Sari: Supervision, Conceptualization, Methodology, Investigation, Writing – original draft, formal analysis. Sujita, Suteja: Methodology, Investigation, Data curation. Muhammad Firdaus, Deni Wardani: Resources, Project administration, Visualization, Edi Syafri: Validation, Writing - Review & Editing. Competing interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Ethics, Consent to Participate, and Consent to Publish declarations: not applicable Ethical Statement This research complies with institutional, national, and international guidelines regarding the use of plant materials. The plant species used ( Nicotiana tabacum L .) is not endangered and was obtained from cultivated agricultural waste, ensuring that no natural populations were disturbed. Clinical trial number: not applicable Data Availability: The data that support the findings of this study are available from the corresponding author upon reasonable request. References L. Lendvai, “Lignocellulosic agro-residue/polylactic acid (PLA) biocomposites: Rapeseed straw as a sustainable filler,” Clean. Mater. , vol. 9, pp. 1–6, Sep. 2023, doi: 10.1016/j.clema.2023.100196. C. E. Okafor, L. C. Kebodi, J. Kandasamy, M. May, and I. E. Ekengwu, “Properties and performance index of natural fiber reinforced cross-ply composites made from Dioscorea alata stem fibers,” Compos. Part C Open Access , vol. 7, Mar. 2022, doi: 10.1016/j.jcomc.2021.100213. P. Madhu, M. R. Sanjay, M. Jawaid, S. Siengchin, A. Khan, and C. I. Pruncu, “A new study on effect of various chemical treatments on Agave Americana fiber for composite reinforcement: Physico-chemical, thermal, mechanical and morphological properties,” Polym. Test. , vol. 85, p. 106437, 2020, doi: 10.1016/j.polymertesting.2020.106437. F. Yudhanto, J. Jamasri, R. A. Ilyas, and P. Terzioğlu, “Effect of Microcrystalline Cellulose Filler on Mechanical and Water Absorption Properties of Ramie/Glass/Carbon Hybrid Laminated Composite,” in AIP Conference Proceedings , Dec. 2023, vol. 2865, no. 1, doi: 10.1063/5.0181999. N. H. Sari, S. Suteja, M. N. Samudra, and H. Sutanto, “Composite of Hibiscus Tiliaceus Stem Fiber/Polyester Modified with Carbon Powder: Synthesis and Characterization of Tensile Strength, Flexural Strength and Morphology Properties,” Int. J. Nanoelectron. Mater. , vol. 14, no. 3, pp. 247–258, 2021. M. Ji et al. , “Enhanced mechanical properties, water resistance, thermal stability, and biodegradation of the starch-sisal fibre composites with various fillers,” Mater. Des. , vol. 198, p. 109373, 2021, doi: 10.1016/j.matdes.2020.109373. M. Syduzzaman, S. Sultana Rumi, F. Faiza Fahmi, M. Akter, and R. Begum Dina, “Mapping the recent advancements in bast fiber reinforced biocomposites: A review on fiber modifications, mechanical properties, and their applications,” Results Mater. , vol. 20, Dec. 2023, doi: 10.1016/j.rinma.2023.100448. N. Herlina Sari, I. N. G. Wardana, Y. S. Irawan, and E. Siswanto, “Characterization of the Chemical, Physical, and Mechanical Properties of NaOH-treated Natural Cellulosic Fibers from Corn Husks,” J. Nat. Fibers , vol. 15, no. 4, pp. 545–558, 2018, doi: 10.1080/15440478.2017.1349707. S. S. Kumar, P. S. Pravat, R. Pati, and P. Kumar, “Wear and Frictional Performance of Epoxy Composites Reinforced with Natural Waste Fibers and Fillers for Engineering Applications,” Fibers Polym. , vol. 25, no. 4, pp. 1429–1442, 2024, doi: 10.1007/s12221-024-00519-2. A. Raza et al. , “A comprehensive review on material characterization and thermal properties of geopolymers: Potential of various fibers,” Case Stud. Constr. Mater. , vol. 21, no. July, p. e03519, 2024, doi: 10.1016/j.cscm.2024.e03519. N. H. Sari, Suteja, H. Anas, A. Amrullah, and M. Mahardika, “Enhanced mechanical and thermal performance of Paederia foetida fiber-magnesium/epoxy composites: A sustainable solution for automotive and aerospace industries,” Case Stud. Chem. Environ. Eng. , vol. 11, no. December 2024, p. 101077, 2025, doi: 10.1016/j.cscee.2024.101077. A. K. Trivedi, M. K. Gupta, and H. Singh, “PLA based biocomposites for sustainable products: A review,” Adv. Ind. Eng. Polym. Res. , vol. 6, no. 4, pp. 382–395, Oct. 2023, doi: 10.1016/j.aiepr.2023.02.002. A. Vinod et al. , “Extraction and Characterization of Natural Fiber from Stem of Cardiospermum Halicababum,” J. Nat. Fibers , vol. 18, no. 6, pp. 898–908, 2021, doi: 10.1080/15440478.2019.1669514. S. Aprilia, Y. Syamsuddin, A. Amin, and I. Zuwanna, “Physical , morphological , mechanical and thermal properties of polyester composites reinforced with orientation of purun fiber ( Eleocharis dulcis ) composition,” South African J. Chem. Eng. , vol. 47, no. November 2023, pp. 338–344, 2024. Z. Changle, L. Shouhai, L. Yinghua, J. Jiang, and F. Hanguang, “Effect of boron on microstructure evolution and properties of wear-resistant cast Fe – Si – Mn – Cr – B alloy,” Integr. Med. Res. , vol. 9, no. 3, pp. 5564–5576, 2020, doi: 10.1016/j.jmrt.2020.03.081. N. H. Sari, E. Syafri, Suteja, W. Fatriasari, and A. Karimah, “Comprehensive Characterization Of Novel Cellulose Fiber From Paederia Foetida and Its Modification For Sustainable Composites Application,” J. Appl. Sci. Eng. , vol. 26, no. 10, pp. 1399–1408, 2023, doi: 10.6180/jase.202310_26(10).0005. M. Pokhriyal and P. Kumar, “Mechanical and microstructural behaviour of NaOH treated Himalayacalamus falconeri fibers as biodegradable reinforcing material in polymer based composites Materials Today : Proceedings Mechanical and microstructural behaviour of NaOH treated Himalayacala,” Mater. Today Proc. , no. April, pp. 1–6, 2022, doi: 10.1016/j.matpr.2022.04.295. Z. C. Liu, Z. W. Wang, S. Gao, Y. X. Tong, and X. Le, “Isolation and Fractionation of the Tobacco Stalk Lignin for Customized Value-added Utilization,” vol. 9, no. December, pp. 1–9, 2021, doi: 10.3389/fbioe.2021.811287. D. Sun, B. Wang, H. Wang, M. Li, Q. Shi, and L. Zheng, “Industrial Crops & Products Structural elucidation of tobacco stalk lignin isolated by di ff erent integrated processes,” Ind. Crop. Prod. , vol. 140, p. 111631, 2019, doi: 10.1016/j.indcrop.2019.111631. D. Dalle et al. , “Kinetic evaluation of tobacco stalk waste exposed to alkaline surface treatment under different conditions,” Cellulose , vol. 0123456789, no. 28, pp. 2053–2073, 2021, doi: 10.1007/s10570-020-03657-x. K. Sophanodorn, Y. Unpaprom, K. Whangchai, N. Homdoung, and N. Dussadee, “Environmental management and valorization of cultivated tobacco stalks by combined pretreatment for potential bioethanol production,” Biomass Convers. Biorefinery , no. 12, pp. 1–11, 2020. H. He, N. Zhang, N. Chen, Z. Lei, K. Shimizu, and Z. Zhang, “Bioresource Technology Reports Efficient phosphate removal from wastewater by MgAl-LDHs modified hydrochar derived from tobacco stalk,” Bioresour. Technol. Reports , vol. 8, no. September, p. 100348, 2019, doi: 10.1016/j.biteb.2019.100348. A. J. Adeyi, O. Adeyi, E. O. Oke, O. A. Olalere, S. Oyelami, and A. D. Ogunsola, “Effect of varied fiber alkali treatments on the tensile strength of Ampelocissus cavicaulis reinforced polyester composites: Prediction, optimization, uncertainty and sensitivity analysis,” Adv. Ind. Eng. Polym. Res. , vol. 4, no. 1, pp. 29–40, 2021, doi: 10.1016/j.aiepr.2020.12.002. K. Sakthi vadivel and P. Govindasamy, “Mechanical and water absorption properties of Acacia Arabica bark fiber/polyester composites: Effect of alkali treatment and fiber volume fraction,” Mater. Today Proc. , vol. 46, no. xxxx, pp. 2281–2287, 2021, doi: 10.1016/j.matpr.2021.04.057. H. F. M. de Queiroz, N. V. dos Santos, J. S. S. Neto, and M. D. Banea, “Mechanical characterization of novel natural fibre-reinforced composites via a three-dimensional fibre architecture,” Compos. Sci. Technol. , vol. 261, p. 110996, Mar. 2025, doi: 10.1016/j.compscitech.2024.110996. S. S. Shifa et al. , “Influence of heat treatment and water absorption on mechanical properties of cotton-glass fiber reinforced epoxy hybrid composites: An eco-friendly approach for industrial materials,” Hybrid Adv. , vol. 5, no. February, p. 100181, 2024, doi: 10.1016/j.hybadv.2024.100181. N. Herlina, B. Anshari, E. Syafri, M. El, and A. Susan, “Exploring the impact of water soaking on the mechanical , thermal , and physical properties of Paederia foetida fiber stem biocomposites : A study in sustainable material innovation,” Case Stud. Chem. Environ. Eng. , vol. 10, no. August, p. 100977, 2024, doi: 10.1016/j.cscee.2024.100977. S. V. Sri and M. B. S. Sathees, “Optimization and Prediction of Wear Characteristics of Khas Khas Grass / Mesquite Bark Powder / Banana Fiber ‑ Reinforced Epoxy Green Hybrid Composites Using Taguchi Technique,” Fibers Polym. , vol. 25, no. 12, pp. 4845–4857, 2024, doi: 10.1007/s12221-024-00745-8. N. H. Sari and S. Suteja, “Corn husk Fibers Reinforced Polyester Composites: Tensile Strength Properties, Water Absorption Behavior, and Morphology,” IOP Conf. Ser. Mater. Sci. Eng. , vol. 722, no. 1, 2020, doi: 10.1088/1757-899X/722/1/012035. S. Sathees Kumar, “Effect of Natural Fiber Loading on Mechanical Properties and Thermal Characteristics of Hybrid Polyester Composites for Industrial and Construction Fields,” Fibers Polym. , vol. 21, no. 7, pp. 1508–1514, 2020, doi: 10.1007/s12221-020-9853-4. H. Fouad, M. Jawaid, and M. A. Azeem, “Flexural , impact and dynamic mechanical analysis of hybrid composites : Olive tree leaves powder / pineapple leaf fibre / epoxy matrix,” J. Mater. Res. Technol. , vol. 21, pp. 4241–4252, 2022, doi: 10.1016/j.jmrt.2022.11.036. A. Czajka, A. Plichta, R. Pomilovskis, A. Iuliano, T. Cygan, and J. Ryszkowska, “PLA reinforced with modified chokeberry pomace and beetroot pulp fillers . Effect of oligomeric chain extender on the properties of biocomposites,” vol. 289, no. September, 2023, doi: 10.1016/j.polymer.2023.126472. E. Kılıç, P. Fullana-i-palmer, M. Fullana, M. Delgado-aguilar, and R. Puig, “Science of the Total Environment Circularity of new composites from recycled high density polyethylene and leather waste for automotive bumpers . Testing performance and environmental impact,” Sci. Total Environ. , vol. 919, no. January, p. 170413, 2024, doi: 10.1016/j.scitotenv.2024.170413. M. Hadadi, F. Kamali, J. Mirhosseininia, M. Shahbazi, and B. Vaferi, “Experimental investigation of biopolymers influences on rheology and filtration properties of water-based drilling fluids,” Heliyon , vol. 10, no. 23, p. e40780, Dec. 2024, doi: 10.1016/j.heliyon.2024.e40780. H. Li, G. Wang, Y. Wu, N. Jiang, and K. Niu, “Functionalization of Carbon Nanotubes in Polystyrene and Properties of Their Composites: A Review,” Polymers (Basel). , vol. 16, no. 6, 2024, doi: 10.3390/polym16060770. E. Widodo and T. Dwi, “Comprehensive investigation of raw and NaOH alkalized sansevieria fiber for enhancing composite reinforcement,” Case Stud. Chem. Environ. Eng. , vol. 9, no. August 2023, p. 100546, 2024, doi: 10.1016/j.cscee.2023.100546. J. A. Cottrell, M. Ali, A. Tatari, and D. B. Martinson, “Effects of Fibre Moisture Content on the Mechanical Properties of Jute Reinforced Compressed Earth Composites,” Constr. Build. Mater. , vol. 373, Apr. 2023, doi: 10.1016/j.conbuildmat.2023.130848. P. F. Alao, R. Press, H. Kallakas, J. Ruponen, T. Poltimäe, and J. Kers, “Investigation of Efficient Alkali Treatment and the Effect of Flame Retardant on the Mechanical and Fire Performance of Frost-Retted Fiber Hemp Reinforced PLA,” Polymers (Basel). , vol. 14, pp. 1–8, 2022. S. Ovalı, “Characterization of Waste Nicotiana rustica L . ( Tobacco ) Fiber,” Polymers (Basel). , vol. 16, pp. 1–15, 2024. A. H. Birniwa et al. , “Recent Trends in Treatment and Fabrication of Plant-Based Fiber-Reinforced Epoxy Composite : A Review,” J. Compos. Sci. , vol. 7, no. 120, pp. 1–33, 2023. G. Rajeshkumar, V. Hariharan, S. Indran, M. R. Sanjay, S. Siengchin, and J. P. Maran, “Influence of Sodium Hydroxide ( NaOH ) Treatment on Mechanical Properties and Morphological Behaviour of Phoenix sp . Fiber / Epoxy Composites,” J. Polym. Environ. , no. 0123456789, 2020, doi: 10.1007/s10924-020-01921-6. S. Gnanasekaran, N. I. A. A. Nordin, M. M. . Hamidi, and J. H. Shariffuddin, “Effect of Alkaline treatment on the characteristics of pineapple leaves fibre Effect of Alkaline treatment on the characteristics of pineapple leaves fibre and PALF / PP biocomposite,” J. Mech. Eng. Sci. , vol. 15, no. 4, p. 2021, 2021, doi: 10.15282/jmes.15.4.2021.05.0671. F. Serra-parareda, F. X. Espinach, M. À. Pelach, M. Alberto, F. Vilaseca, and Q. Tarr, “Effect of NaOH Treatment on the Flexural Modulus of Hemp Core Reinforced Composites and on the Intrinsic Flexural Moduli of the Fibers,” Polymers (Basel). , vol. 12, pp. 1–21, 2020. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 30 Sep, 2025 Read the published version in Discover Materials → Version 1 posted Editorial decision: Revision requested 16 Jun, 2025 Reviews received at journal 13 Jun, 2025 Reviews received at journal 09 Jun, 2025 Reviewers agreed at journal 06 Jun, 2025 Reviewers agreed at journal 30 May, 2025 Reviewers invited by journal 30 May, 2025 Editor assigned by journal 30 May, 2025 Submission checks completed at journal 28 May, 2025 First submitted to journal 28 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6702277","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":464437399,"identity":"51835d77-10ee-4051-980e-0d52831b2765","order_by":0,"name":"Nasmi Herlina 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3","display":"","copyAsset":false,"role":"figure","size":229247,"visible":true,"origin":"","legend":"\u003cp\u003ePreparation of composite based NTSPs\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6702277/v1/4bc54aa7743e7e0dfbac15e6.png"},{"id":83784921,"identity":"7c116af8-8bc1-48bd-9b4e-c54281d3be1f","added_by":"auto","created_at":"2025-06-02 16:34:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":26380,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of composite polyester based NTSPs\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6702277/v1/44d5bd0e1a7f06ec255855da.png"},{"id":83784923,"identity":"8d5ee400-81df-4f3e-a2cd-ff7fe2eceffd","added_by":"auto","created_at":"2025-06-02 16:34:44","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":457402,"visible":true,"origin":"","legend":"\u003cp\u003e(a). Tensile strength, (b) Elongation, and (c) modulus of elasticity of composites based NTSPs.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6702277/v1/8408f2a31664a0fe24747d35.png"},{"id":83784925,"identity":"80fd8a63-fa7e-4944-a273-c5d4ded6acb4","added_by":"auto","created_at":"2025-06-02 16:34:44","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":317563,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Flexural strength, and (b) Flexural modulus of composites based NTP\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6702277/v1/b07b4306feb50b419fc851d8.png"},{"id":83784928,"identity":"404763c9-47ff-4943-8b9c-45e6d912997c","added_by":"auto","created_at":"2025-06-02 16:34:44","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":580370,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of composite samples; (a) NTR, (b) TUS, (c) SJT, and (d) NHS.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6702277/v1/04f599cd9f9c4456cd7500a2.png"},{"id":83785550,"identity":"91c0974d-7fc0-44b6-a062-65938bd69f03","added_by":"auto","created_at":"2025-06-02 16:42:44","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":132984,"visible":true,"origin":"","legend":"\u003cp\u003e(a) TGA. (b) DSC of composites based NTP treated NaOH\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6702277/v1/12af358b698817ab1e368bb7.png"},{"id":83785549,"identity":"f0cd6cd6-03bf-4dd4-af35-f683b70994e0","added_by":"auto","created_at":"2025-06-02 16:42:44","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":28347,"visible":true,"origin":"","legend":"\u003cp\u003eWater absorption of composites reinforced NTSPs treated NaOH.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6702277/v1/4e3f569c250562475a305984.png"},{"id":83784927,"identity":"b55afb11-af1c-4e07-a6a0-388290593080","added_by":"auto","created_at":"2025-06-02 16:34:44","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":190297,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Modulus storage, (b) Loss modulus, and (c) tan δ of different composites\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6702277/v1/ce565e363b4a2a7afb6796ae.png"},{"id":92884420,"identity":"8c8a6b86-4310-47e5-83c7-bce1d6e466c3","added_by":"auto","created_at":"2025-10-06 16:12:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3572855,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6702277/v1/fe452104-4b0d-4826-b06c-4817719cca8a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Alkali-Engineered Tobacco Stem Particles for Polyester Composites: Enhancing Physical, Mechanical, Thermal, and Dynamic Mechanical Properties","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe escalating environmental concerns and the depletion of fossil fuel reserves have intensified the search for sustainable materials in various industries. Natural fiber-reinforced polymer composites (NFRPCs) have garnered significant attention as eco-friendly alternatives to synthetic composites due to their biodegradability, renewability, and favorable mechanical properties [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Among the myriad of natural fibers explored, tobacco (commonly known as tobacco) stems represent an underutilized agricultural byproduct with potential as reinforcement in polymer matrices. The utilization of tobacco stalk stem particles in composite materials not only adds value to agricultural waste but also contributes to waste management and environmental sustainability. However, the inherent hydrophilicity and surface impurities of natural fibers often lead to poor interfacial adhesion with hydrophobic polymer matrices, adversely affecting the mechanical performance of the resulting composites [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. To address these challenges, chemical surface modification techniques, particularly alkali treatment using sodium hydroxide (NaOH), have been employed to enhance fiber-matrix compatibility [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAlkali treatment effectively removes non-cellulosic components such as hemicellulose and lignin from the fiber surface, increasing surface roughness and exposing reactive hydroxyl groups, thereby improving interfacial bonding [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Studies by Aprilia et al. [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] and Ji et al. [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] have demonstrated improved mechanical, thermal, and water absorption characteristics in various natural fiber composites following chemical surface treatments. For instance, Phoenix sp. and oil palm fibers showed enhanced performance in polymer matrices when treated with appropriate alkali conditions. Similarly, research on \u003cem\u003eSansevieria trifasciata Laurentii\u003c/em\u003e fibers treated with liquid smoke followed by microwave treatment reported notable improvements in tensile strength, surface morphology, and thermal characteristics, highlighting the effectiveness of such treatments in enhancing fiber properties [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Similar enhancements have been observed in fibers such as jute, corn husk, and \u003cem\u003ePaederia foetida\u003c/em\u003e following NaOH treatment, which improves interfacial adhesion and mechanical strength through the removal of surface impurities and the modification of fiber morphology [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Pokhriyal and Rakesh [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] found that \u003cem\u003eHimalayacalamus falconeri\u003c/em\u003e fibers treated with 2% NaOH displayed a low fibril micro angle (7.87\u0026deg; \u0026plusmn; 1.50) and high cellulose content (74.9%), resulting in tensile strength of 177 MPa, Young\u0026rsquo;s modulus of 18.6 GPa, and elongation of just 1%. These characteristics highlight their potential as biodegradable reinforcements in polymer-based composites.\u003c/p\u003e \u003cp\u003eIn the context of tobacco stalk fibers, several recent studies have provided insights into their chemical composition and treatment responses. Liu et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] and Sun et al. [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] explored the fractionation and structural elucidation of tobacco stalk lignin for value-added applications. Dall\u0026eacute; et al. [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] reported the kinetic evaluation of alkaline treatment on tobacco stalks under varying conditions, establishing critical process-structure-performance correlations. Sophanodorn et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] focused on the environmental management and bioethanol potential of tobacco stalks through pretreatment strategies, while He et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] examined their capacity for phosphate adsorption from wastewater. Changle et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] investigated the effects of different parts of tobacco stalk\u0026mdash;xylem (TSX), husk (TSH), and core (TSC)\u0026mdash;on the mechanical properties of TSF/polypropylene composites. They reported tensile strengths of 32.8 MPa (TSX), 25.6 MPa (TSH), and 26.4 MPa (TSC), and corresponding flexural strengths of 56.0 MPa, 46.1 MPa, and 48.7 MPa, respectively, with good reusability potential. These studies collectively underscore the versatility and untapped potential of tobacco stalks as bioresources for advanced materials and bio-based product development. However, the specific application of alkali-treated tobacco stem particles (NTP) as reinforcement in unsaturated polyester composites remains underexplored.\u003c/p\u003e \u003cp\u003eTherefore, this study aims to fill this gap by evaluating the effects of NaOH surface treatments on NTP and assessing their potential as reinforcements in polyester matrices. Specifically, it examines the influence of NaOH treatment at varying concentrations (2%, 5%, and 8%) on the fiber's chemical composition, morphology, and interfacial bonding. The research further explores the impact of these treatments on the composites\u0026rsquo; mechanical properties (tensile strength and modulus), thermal stability, dynamic mechanical behavior, and water absorption performance. Through this comprehensive performance evaluation, the study seeks to develop high-performance, bio-based composite materials that contribute to sustainable material design for applications such as automotive interiors, construction panels, and other semi-structural components.\u003c/p\u003e"},{"header":"2. Materials and Method","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eWaste of tobacco steam (NTs) were collected from agricultural residues from cultivated tobacco plants in Mataram, West Nusa Tenggara, Indonesia. Sodium hydroxide (NaOH) solutions with concentrations of 2%, 5%, and 8% (w/v). Unsaturated polyester resin and a catalyst\u0026mdash;methyl ethyl ketone peroxide (MEKP)\u0026mdash;were supplied by PT Justus Kimia Raya, Surabaya, Indonesia. The catalyst was used at a concentration of 1.5% by volume of the polyester resin. The pure polyester resin had a density of 1.2 g/cm\u0026sup3; and a tensile strength of 27 MPa.\u003c/p\u003e \u003cp\u003eThe tobacco stem particles used in this study were collected as post-harvest agricultural waste from a commercial farm located in East Lombok, Indonesia. The plant species was identified as \u003cem\u003eNicotiana tabacum L\u003c/em\u003e. based on standard botanical characteristics and confirmed using agricultural classification guidelines. Since the plant material was sourced from cultivated agricultural waste and not collected from the wild, no voucher specimen was prepared. \u003cem\u003eNicotiana tabacum L\u003c/em\u003e. is not listed as an endangered or protected species under the IUCN Red List or CITES regulations.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Extraction of Tobacco Stem Particles (NTSPs)\u003c/h2\u003e \u003cp\u003eThe extraction process of tobacco stem particle (NTSPs) is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Initially, the collected NTs were thoroughly washed with fresh water to remove soil, dust, and other surface contaminants. The cleaned stems were then manually chopped into smaller pieces and oven-dried at 80\u0026deg;C for 48 hours using a forced-air circulating oven to reduce moisture content and ensure ease of grinding. After drying, the coarse NTs particles were ground using a mechanical grinder. The resulting material was then sieved through a 100-mesh sieve to obtain a uniform powder with an average particle size of approximately 0.149 mm (149 \u0026micro;m). This final product is referred to hereafter as tobacco stem particles (NTSPs).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Alkali treatment of NTSPs\u003c/h2\u003e \u003cp\u003eAs illustrated in detail in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the untreated tobacco stem powder (NTSPs untreated) was divided into three equal portions for alkaline treatment. Each portion was soaked separately in aqueous NaOH solutions with different concentrations of 2%, 5%, and 8% (w/v), respectively for 2 hours at room temperature (\u0026plusmn;\u0026thinsp;25\u0026deg;C) [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Then, the particles were thoroughly rinsed with distilled water several times until the rinsing water reached a neutral pH (~\u0026thinsp;7), indicating the removal of residual alkali. They were then dried in a circulating air oven at 65\u0026deg;C for 48 hours; to reduce the moisture content to approximately 10% and were stored in airtight containers to prevent moisture absorption and contamination. The treated samples were labeled as NTSPs-2NaOH (NTSPs after 2% NaOH treatment), NTSPs-5NaOH (NTSPs after 5% NaOH treatment), and NTSPs-8NaOH (NTSPs after 8% NaOH treatment), respectively. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e provides complete physical and chemical parameters for each NTSPs (untreated and treated NaOH).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhysical and chemical properties of NTSPs-2NaOH, NTSPs-5NaOH and NTSPs-8 NaOH and NTSPs untreated.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParticles codes\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDensity (g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMoisture content (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCellulose (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHemicellulose (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eLignin (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNTSPs untreated\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.802\u0026thinsp;\u0026plusmn;\u0026thinsp;0.027\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e6.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e41.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e20.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e22.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNTSPs \u0026minus;\u0026thinsp;2NaOH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.011\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e4.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e45.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e15.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNTSPs \u0026minus;\u0026thinsp;5NaOH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.033\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e3.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e52.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNTSPs \u0026minus;\u0026thinsp;8NaOH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.021\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e3.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e59.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.02\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Fabrication of NTSPs-Based Polyester Composites\u003c/h2\u003e \u003cp\u003eNTSPs Untreated and the chemically treated particles (NTSPs-2NaOH, NTSPs-5NaOH, and NTSPs-8NaOH) were each weighed according to a predetermined composition. The NTP and polyester ratios were set at 30% and 70% (% vol.), respectively, using a catalyst MEKP (1.5% vol. polyester). All components were thoroughly mixed using a mechanical stirrer for 20 minutes; to ensure homogeneous dispersion of the NTSPs within the polyester matrix. The resulting slurry was then poured into a stainless-steel mold and subjected to hot press molding at 105\u0026deg;C under a pressure of 75 MPa for 60 minutes [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The complete fabrication procedure is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Four types of different composites were prepared, and a control composite using untreated NTSPs. Each composite type was fabricated in six replicates to ensure statistical reliability. The detailed composition and labeling of the composite samples are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComposition and labeling of the composite NTSPs \u0026ndash; polyester. .\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComposites\u003c/p\u003e \u003cp\u003ecodes\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCompositions\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNTR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eComposites based 30% of NTSPs untreated and 70% polyester (% vol.).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eComposites based 30% of NTSPs-2NaOH and 70% polyester (% vol.).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSJT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eComposites based 30% of NTSPs-5NaOH and 70% polyester (% vol.).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNHS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eComposites based 30% of NTSPs-8NaOH and 70% polyester (% vol.).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Characterization\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.5.1 Density of composites\u003c/h2\u003e \u003cp\u003eThe density of the composite samples was determined using the water displacement method based on Archimedes' principle, as described in Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). First, each composite specimen was weighed using a digital analytical balance with a precision of 0.001 g to obtain its mass (\u003cem\u003em\u003c/em\u003e, in grams). The specimen was then carefully submerged in a graduated measuring cylinder filled with distilled water to measure the volume of water displaced, which corresponds to the specimen's volume (\u003cem\u003eV\u003c/em\u003e, in cm\u0026sup3;). The density (\u003cem\u003eρ\u003c/em\u003e, in g/cm\u0026sup3;) was then calculated using the following equation [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\rho\\:\\:\\left(\\frac{g}{{cm}^{3}}\\right)=\\frac{m}{V}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAll measurements were conducted at room temperature (\u0026plusmn;\u0026thinsp;25\u0026deg;C), and each test was repeated three times to ensure accuracy and reproducibility. The average value was reported as the final density for each composite type.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.5.2 Moisture content of composites\u003c/h2\u003e \u003cp\u003eThe moisture content (MC) of the composite samples was determined using the gravimetric method, as expressed in Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This method involves measuring the weight of the composite before and after oven drying[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:MC\\:\\left(\\%\\right)=\\:\\frac{{W}_{1}-{W}_{2}}{{W}_{2}}\\times\\:100$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere, \u003cem\u003eW₁\u003c/em\u003e is the initial weight of the composite sample before drying (in grams), and \u003cem\u003eW₂\u003c/em\u003e is the final weight of the composite sample after drying at 105\u0026deg;C for 24 hours (in grams).\u003c/p\u003e \u003cp\u003eAll measurements were performed using a precision digital balance (\u0026plusmn;\u0026thinsp;0.001 g). The samples were considered to have reached constant weight when the mass change between two consecutive measurements was less than 0.001 g. Each test was conducted in triplicate, and the average values were reported as the final moisture content.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.5.3 Fourier Transform Infrared (FTIR) Spectroscopy\u003c/h2\u003e \u003cp\u003eThe functional groups present in composites were analyzed using a Perkin Elmer Frontier FTIR spectrometer equipped with a Universal Attenuated Total Reflectance (UATR) accessory. FTIR spectra were recorded in the wavenumber range of 4000\u0026ndash;400 cm⁻\u0026sup1;, with a resolution of 4 cm⁻\u0026sup1;. Each spectrum was obtained by averaging 32 scans per sample to ensure high signal-to-noise ratio and spectral accuracy. Prior to measurement, the background spectrum was collected and subtracted automatically to eliminate ambient interferences.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e2.5.4 Tensile and Flexural Tests\u003c/h2\u003e \u003cp\u003eTensile and flexural properties of the composite samples were evaluated using a universal testing machine (UTM), model RTG 1310 INSTRON. All tests were conducted in accordance with ASTM D3039-03 for tensile testing and ASTM D790 for flexural testing [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The tests were performed under controlled laboratory conditions at a temperature of 27\u0026deg;C and a relative humidity of 56%. The crosshead speed was maintained at 0.5 mm/min for both tensile and flexural tests. For each composite type, five specimens were tested for both mechanical properties to ensure statistical reliability.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e2.5.5 Morphological Analysis by SEM\u003c/h2\u003e \u003cp\u003eThe surface morphology and fracture characteristics of the composite samples after tensile testing were examined using a SEM, model JEOL JSM\u0026ndash;S5200. Prior to imaging, the fractured surfaces were sputter-coated with a thin conductive layer of copper, approximately 25 nm thick, to prevent charging and improve image resolution. The SEM observations were performed under high vacuum conditions at an accelerating voltage of 3 kV and a beam current of 15 mA [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e2.5.6 Water Absorption Test\u003c/h2\u003e \u003cp\u003eThe water absorption behavior of the composite samples was evaluated based on weight gain after immersion in distilled water. Prior to testing, all samples were oven-dried at 60\u0026deg;C for 24 hours to eliminate residual moisture. Square samples with dimensions of 20 \u0026times; 20 \u0026times; 3 mm\u0026sup3; were prepared for the test [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Each dried sample was weighed (denoted as \u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003eo\u003c/em\u003e\u003c/sub\u003e​) using an analytical balance with 0.001 g accuracy. The samples were then fully immersed in distilled water at room temperature for 24 hours. After immersion, samples were gently wiped with tissue paper to remove surface water and immediately reweighed to obtain the wet weight (\u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e​\u003c/em\u003e). The water absorption percentage (\u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003eg\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e​\u003c/em\u003e) was calculated using Eq.\u0026nbsp;(\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e):[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e.\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:{W}_{g}\\left(\\%\\right)=\\frac{{W}_{t}-{W}_{0}}{{W}_{0}}\\times\\:100\\%$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere, \u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003eo\u003c/em\u003e\u003c/sub\u003e​ is the initial (dry) weight of the specimen (g), and \u003cem\u003eW\u003c/em\u003e\u003csub\u003e\u003cem\u003et\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e​\u003c/em\u003e​ is the weight after water immersion for the specified time (g).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e2.5.7 Thermogravimetric Analysis (TGA/DSC)\u003c/h2\u003e \u003cp\u003eThe thermal behavior and stability of the samples were investigated using Thermogravimetric Analysis (TGA). The measurements were performed using a TGA\u0026ndash;1 instrument (Mettler Toledo, Switzerland) under a nitrogen atmosphere to prevent oxidation during thermal decomposition. Approximately 10 mg of each composite sample was placed in an alumina crucible. The analysis was conducted in ramp mode over a temperature range of 27\u0026deg;C to 600\u0026deg;C, with a constant heating rate of 20\u0026deg;C/min and a nitrogen flow rate of 50 mL/min [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e2.5.8 Dynamic Mechanical Analysis (DMA)\u003c/h2\u003e \u003cp\u003eA NETZSCH DMA 242 equipment was used to perform Dynamic Mechanical Analysis (DMA) on the composites to determine their viscoelastic properties. The analysis was conducted at temperatures ranging from 40\u0026deg;C to 200\u0026deg;C, with a constant heating rate of 10\u0026deg;C/min and a fixed oscillation frequency of 1Hz. The storage modulus (E\u0026prime;), loss modulus (E\u0026Prime;), or damping factor (tan δ) were investigated to understand the stiffness, energy dissipation, or glass transition behaviour of the composites, respectively. ASTM D4065-01 was used to manufacture test specimens measuring 60 \u0026times; 12.5 \u0026times; 3 mm\u0026sup3;. Before testing, all samples were conditioned in regulated humidity settings (25% and 95% RH) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Density Analysis\u003c/h2\u003e \u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the average densities of composites made from NTR, TUS, SJT, and NHS were 1.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 g/cm\u0026sup3;, 1.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 g/cm\u0026sup3;, 1.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 g/cm\u0026sup3;, and 1.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 g/cm\u0026sup3;, respectively. The composite of particles treated with 8% NaOH (NHS sample) had the highest density, whereas the TUS sample had the lowest density. The composite density increased significantly when the composite was reinforced with NTSPs-8NaOH solution, as compared to NTSPs-2NaOH (sample TUS), NTSPs-5NaOH (sample SJT), nor untreated (NTR) (see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This behavior is explained by the fact that higher alkali concentrations remove amorphous components including hemicellulose, lignin, and extractives more efficiently. When the NaOH content was increased (8%), the loss of these constituents increased, resulting in particles that were richer in crystalline cellulose and denser. Furthermore, the 8% NaOH treatment reduced the internal porosity of the particles caused by swelling and shrinkage of the cell walls during the washing or drying processes, which led to a more compact structure, higher interfacial integration with the matrix, denser particles, strengthening the interfacial bond, and reducing the formation of micro voids, all of which directly increased the density of the composite. These findings show that, the 8% NaOH treatment was the most successful in enhancing the internal structure of the particles and promoting integration with the matrix. When compared to other natural fiber composites such as \u003cem\u003ePurun\u003c/em\u003e fiber-reinforced composites (0.92 g/cm\u0026sup3;) and corn husk fiber composites (1.14 g/cm\u0026sup3;) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDensity and moisture content of NTSPs reinforced polyester composites.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003cp\u003ecomposites\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDensity\u003c/p\u003e \u003cp\u003e(g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMoisture content (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNTR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.17\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.46\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.19\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSJT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNHS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.22\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Moisture content analysis\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents the moisture content of NTSPs-reinforced composites. The results indicate that the composites treated with 5%NaOH and 8% NaOH (samples SJT and NHS)\u0026mdash;exhibited lower moisture content (0.43%) compared to the TUS and NTR samples, which showed slightly higher moisture content. According to Sari et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], this trend can be attributed to the increased removal of hemicellulose and other amorphous, hydrophilic components as the concentration of NaOH rises. Hemicellulose contains abundant hydroxyl groups that readily bond with water molecules [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Its removal significantly reduces the water affinity of the fiber, promoting surface fibrillation and enhancing interfacial bonding with the polyester matrix [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.3 FTIR Analysis\u003c/h2\u003e \u003cp\u003eThe FTIR spectra of NTSPs-based composites are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. All spectra displayed a similar overall pattern, suggesting that the core chemical structure of the composite remains consistent across the treatments, with notable differences in peak intensities. A total of nine significant absorption bands were identified, and their respective functional group assignments are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. These bands reflect the presence and interactions of key chemical constituents in the composite materials. At a peak 3368\u0026ndash;3374 cm⁻\u0026sup1; attributed to O\u0026ndash;H stretching vibrations associated with hydrogen bonding in hydroxyl groups and α-cellulose (cellulose Iβ). A peak 2905\u0026ndash;2911 cm⁻\u0026sup1; corresponds to C\u0026ndash;H stretching vibrations found in cellulose and hemicellulose. At the band 1504\u0026ndash;1510 cm⁻\u0026sup1; associated with aromatic C\u0026thinsp;=\u0026thinsp;C stretching vibrations typical of lignin structures. At a peak 1422\u0026ndash;1428 cm⁻\u0026sup1; linked to CH₂ bending and crystalline cellulose regions. At the band 1370\u0026ndash;1376 cm⁻\u0026sup1; assigned to C\u0026ndash;H bending vibrations, particularly from cellulose [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. At peak 1264\u0026ndash;1271 cm⁻\u0026sup1; attributed to C\u0026ndash;O stretching in the acetyl groups of lignin. At the band 1107\u0026ndash;1113 cm⁻\u0026sup1; indicative of C\u0026ndash;O stretching vibrations in cellulose, hemicellulose, and lignin. At peak 894\u0026ndash;900 cm⁻\u0026sup1; corresponds to β-glycosidic linkages in cellulose, indicative of polysaccharide integrity[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The results confirm the retention of key chemical functionalities following alkali treatment and its composite. However, variations in peak intensity, especially in the O\u0026ndash;H and C\u0026ndash;H regions, suggest partial removal of hemicellulose and lignin, particularly at sample NHS (8% NaOH concentrations). This supports the hypothesis that NaOH treatment modifies the NTSPs surface and reduces hydrophilic groups, which is in agreement with the moisture content and morphological results discussed earlier. These FTIR findings validate the chemical interaction and interfacial bonding between treated NTSPs and the polyester matrix, essential for the improved performance of NTSPs -reinforced composites.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFTIR stretching frequencies and functional group of NTSPs-based polyester composites\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eWave number (cm\u003csup\u003e‒1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eAssignments\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNTR\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTUS\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNHS\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSJT\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3359\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3368\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3371\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3374\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCellulose \u003cem\u003eI\u003c/em\u003eβ/O\u0026ndash;H stretching vibrations of α‒cellulose and hydrogen bond of the hydroxyl groups\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2901\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2905\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2908\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2911\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCellulose and hemicellulose components/C‒H stretching vibration in cellulose and hemicellulose\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1506\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1504\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1507\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1510\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLignin/aromatic C\u0026thinsp;=\u0026thinsp;C stretching in lignin\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1421\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1422\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1425\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1428\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCellulose/CH\u003csub\u003e2\u003c/sub\u003e bending\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1371\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1371\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1373\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1376\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCellulose/C‒H bending\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1320\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1321\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1323\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1326\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLignin/aromatic C‒O bending\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1261\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1264\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1268\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1271\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLignin/‒CO stretching of acetyl group\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1103\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1107\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1111\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1114\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCellulose, hemicellulose, lignin/C‒O stretching vibration in cellulose\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e894.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e894.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e897\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCellulose/β‒glucosides linkage in cellulose\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Tensile Strength Analysis of Composite\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea presents the tensile strength of the composite samples NTR, TUS, SJT, and NHS, with average values of 38.49\u0026thinsp;\u0026plusmn;\u0026thinsp;3 MPa, 40.64\u0026thinsp;\u0026plusmn;\u0026thinsp;3 MPa, 44.83\u0026thinsp;\u0026plusmn;\u0026thinsp;3 MPa, and 48.53\u0026thinsp;\u0026plusmn;\u0026thinsp;2 MPa, respectively.\u003c/p\u003e \u003cp\u003eAt a constant volume fraction of NTSPs, the composites' tensile strength increased more than the NTR composites after reinforcing with NaOH-treated NTSPs. The NHS sample had the maximum tensile strength (48.53\u0026thinsp;\u0026plusmn;\u0026thinsp;2 MPa), while the TUS sample had the lowest (40.64\u0026thinsp;\u0026plusmn;\u0026thinsp;3 MPa). Alkaline treatment with NaOH (2%-8%) effectively eliminates amorphous components from the NTSP surface, resulting in increased tensile strength values for the composites investigated. This removal increases the surface roughness of NTSP, improves interfacial adhesion, and allows the polyester matrix to wet more thoroughly, resulting in greater mechanical interlocking. Furthermore, 8% NaOH treatment greatly roughens the NTSP surface, enhancing the contact area with the matrix, as demonstrated in the NHS sample, resulting in the maximum tensile strength. However, it is important to note that excessively high NaOH concentrations can damage cellulose chains and lead to a transformation from cellulose I to the less mechanically stable cellulose II [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb shows the elongation at break for all samples. NHS recorded the highest elongation (1.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17%), followed by SJT (1.57\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26%), TUS (1.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17%), and NTR ((1.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2%). The improvement in elongation suggests that NaOH treatment not only enhances NTSPs -matrix adhesion but also introduces flexibility in the composite, allowing the NTSPs to deform more before failure. Next, As presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec, the elastic tensile modulus of different composite. The NHS sample had the highest modulus of elasticity among the samples, at around 2035.6\u0026thinsp;\u0026plusmn;\u0026thinsp;77 MPa, demonstrating greater resistance to elastic deformation during tensile stress. SJT (1700\u0026thinsp;\u0026plusmn;\u0026thinsp;91MPa), TUS 1506\u0026thinsp;\u0026plusmn;\u0026thinsp;86 MPa), and NTR (1405\u0026thinsp;\u0026plusmn;\u0026thinsp;86 MPa) were the next strongest. The trend indicates a noticeable increase in stiffness from NTR to NHS, most likely due to higher NaOH concentrations. This behavior is attributed to improved interfacial stress transfer between particles and matrix due to stronger bonding. A rougher NTSPs surface increases mechanical interlocking, which enhances the stiffness of the composite and allows it to resist deformation under load. In contrast, the lower modulus in the NTR sample indicates a more compliant material, which may be advantageous for applications requiring more flexibility and lower rigidity. NaOH treatment at 8% concentrations significantly improves the mechanical properties of NTSPs-based composites by enhancing fiber-matrix bonding, increasing tensile strength, elongation, and stiffness.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurthermore, in comparison with other natural fiber composites, such as coconut shell powder (16.96\u0026ndash;22.46 MPa), composites NTSPs exhibit superior tensile performance. However, they are slightly inferior to composites \u003cem\u003eHibiscus tiliaceus\u003c/em\u003e with filler 30% carbon, which reach up to 54.98\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5 MPa. Although lower NaOH concentrations (as in TUS and SJT) can increase NTSPs roughness, they may not sufficiently enhance the tensile properties due to insufficient removal of impurities and weaker NTSPs strength.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Flexural Strength Analysis of Composites\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea presents the effect of NaOH treatment concentrations on the flexural strength of NTSPs -reinforced composites, namely NTR, TUS, SJT, and NHS. Overall, a significant increase in flexural strength was observed as the NaOH concentration increased from 2\u0026ndash;8% (% vol.). The NHS sample, treated with 8% NaOH, exhibited the highest flexural strength of approximately 124\u0026thinsp;\u0026plusmn;\u0026thinsp;14 MPa, whereas the NTR sample, showed the lowest value, approximately 102\u0026thinsp;\u0026plusmn;\u0026thinsp;11 MPa. This trend clearly indicates that alkali treatment plays a crucial role in enhancing the mechanical performance of the composite. The enhancement in flexural strength is primarily attributed to the chemical and morphological modifications induced on the fiber surface by the alkali treatment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurthermore, NaOH treatment increases the surface roughness of the NTSPs, thereby promoting a stronger mechanical interlocking between the NTSPs and the polyester matrix. This enhanced physical interlocking helps prevent delamination or fiber pull-out under flexural loading, thereby contributing significantly to the composite's bending resistance. However, the effectiveness of alkali treatment is highly dependent on the concentration used. At lower concentrations (2%), the chemical alteration of the NTSPs surface may be insufficient to significantly improve adhesion, resulting in weak interfacial bonding and limited load transfer capability. In contrast, the 8% NaOH treatment appears to optimize both the structural stability and rigidity of the NTSPs, leading to superior flexural performance. These findings are consistent with previous studies, which have reported that alkali concentrations in the range of 5\u0026ndash;10% can significantly improve the mechanical properties of natural fiber-reinforced composites by enhancing fiber\u0026ndash;matrix adhesion, as long as fiber degradation is avoided [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb depicts the flexural modulus of four distinct composite materials: NTR, TUS, SJT, and NHS. The NHS sample had the highest flexural modulus, approximately 2673\u0026thinsp;\u0026plusmn;\u0026thinsp;77 MPa, indicating superior stiffness and strength under flexural stress. SJT (2319\u0026thinsp;\u0026plusmn;\u0026thinsp;91 MPa), TUS (2038\u0026thinsp;\u0026plusmn;\u0026thinsp;86 MPa), and NTR (1874\u0026thinsp;\u0026plusmn;\u0026thinsp;86 MPa) were the next strongest. The gradual rise in flexural modulus from NTR to NHS suggests that the reinforcing NTSPs and distribution have a substantial impact on composite stiffness. The increased modulus seen in the NHS composite could be due to improved bonding between the matrix and the reinforcement, more efficient stress transfer, as well as a greater degree of fiber alignment and packing. In contrast, the NTR composite's lower modulus suggests a more flexible structure, making it potentially appropriate for applications that require better deformability but lower rigidity.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Morphology analysis by SEM\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e displays the SEM micrographs of the fracture surfaces of the composite samples, which provide insight into the fiber\u0026ndash;matrix interfacial adhesion and failure mechanisms under flexural loading. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea shows the surface morphology of the sample NTR. Some particles are well entrenched in the polyester matrix, whereas others appear to have poor interfacial adhesion, indicating possible flaws in particle-matrix bonding. Furthermore, elongated cylindrical formations are seen, which could be agglomerated particles or residual fibrous contaminants that were not fully dispersed during production. There are no large cracks, although tiny delamination features are visible in some spots, which could indicate localized stress concentrations. These microstructural traits are anticipated to influence the composite's mechanical performance, specifically its tensile strength, flexural qualities, and durability. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb shows the TUS sample, which reveals relatively smooth fracture regions with minimal composite breakage. The interface between the NTSPs and matrix appears loosely bonded, suggesting weak interfacial adhesion. This morphology is indicative of insufficient stress transfer across the interface, which can result in premature failure during flexural loading. Such weak bonding has been associated with poor mechanical performance in natural fiber composites, as reported by Madhu et al. [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], where low alkali concentration led to incomplete removal of hemicellulose and lignin.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec corresponds to the SJT sample and presents a more complex fracture surface, with visible NTSPs and matrix deformation. This suggests moderate interfacial bonding, where partial load transfer occurs, but is still hindered by interfacial slippage and fiber agglomeration. The pulled-out fibers with clean surfaces indicate insufficient chemical bonding. However, some rougher fracture features imply the onset of improved fiber\u0026ndash;matrix adhesion. These observations are in line with findings by Alao et al., [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] who emphasized the importance of alkali-induced surface roughening in promoting frictional resistance and mechanical interlocking, even if not fully optimized.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWhile, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed displays SEM photo the NHS sample, which demonstrates a rougher and more irregular fracture surface with clear signs of particle breakage and strong matrix-NTSPs integration. The embedded NTSPs exhibit fewer gaps at the interface, suggesting effective interfacial adhesion due to optimal NTSPs treatment with 8% NaOH. The rough fracture surface morphology is characteristic of improved load transfer and energy absorption, indicative of ductile fracture behavior. This enhanced adhesion is attributed to the removal of surface impurities and the exposure of hydroxyl groups, which promotes better chemical bonding and mechanical interlocking [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. The SEM analysis confirms that increasing NaOH concentration enhances NTSPs\u0026ndash;matrix adhesion, with the NHS sample showing the most effective bonding characteristics.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e3.6 TGA/DSC Analysis\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e presents the thermal behavior of the composites through TGA (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea) and DSC (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb) analyses. The TGA curves (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea) indicate a typical three-stage thermal degradation pattern. The initial weight loss below 120\u0026deg;C corresponds to the evaporation of moisture and volatile compounds. The second major degradation phase, occurring between 220\u0026ndash;360\u0026deg;C, is attributed to the decomposition of hemicellulose and cellulose components. Beyond 360\u0026deg;C, the degradation of lignin and the residual carbonaceous material becomes evident. Among the samples, the NHS sample exhibited improved thermal stability with a slower degradation rate and a lower total mass loss. The char residue of 11.923% in the NHS sample was higher than that of TUS (13.523%) and SJT (14.498%), indicating greater thermal resistance and higher structural integrity at elevated temperatures. This behavior is primarily due to the 8% NaOH treatment that effectively removed amorphous hemicellulose and surface impurities, leading to denser packing and better thermal insulation properties [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe DSC curves (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb) further support this observation by revealing thermal transitions related to composite softening and decomposition. All samples exhibit an endothermic peak between 60\u0026ndash;120\u0026deg;C due to water loss and relaxation of amorphous chains. The NHS sample shows a higher peak degradation temperature (~\u0026thinsp;370\u0026deg;C) compared to SJT (~\u0026thinsp;355\u0026deg;C) and TUS (~\u0026thinsp;348\u0026deg;C), reflecting enhanced thermal stability. This shift is indicative of stronger NTSPs\u0026ndash;matrix adhesion, improved crystallinity, and reduced molecular mobility due to effective particles treatment. Additionally, the sharper and more defined endothermic peak in the NHS sample suggests a more uniform matrix\u0026ndash;particles interaction, whereas broader transitions in TUS and SJT indicate heterogeneous thermal behavior. These findings align with those of Gnanasekaran et al. [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], who highlighted the role of alkaline-treated fibers in improving thermal resistance and structural performance in polymer composites.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003e3.7 Water absorption analysis\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e illustrates the water absorption behavior of the TUS, SJT, and NHS composites over a 24-day immersion period. All samples exhibited a rapid increase in water uptake during the initial 10 days, which subsequently plateaued, indicating the approach to saturation. This two-phase absorption trend is commonly observed in natural fiber-reinforced composites due to the presence of hydrophilic hydroxyl groups in the lignocellulosic structure of the fibers [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The NHS composite demonstrated the lowest water absorption, reaching approximately 13.1% at equilibrium. In contrast, the SJT and TUS composites exhibited higher final absorption values, approximately 13.9% and 14.3%, respectively. The reduced water uptake in the NHS composite is attributed to the combined effect of alkali (NaOH) treatment on the NTSPs, which effectively removed hemicellulose and surface impurities while enhancing NTSPs\u0026ndash;matrix interfacial bonding. NHS composites' water absorption resistance qualities make them a better alternative for use in humid or wet conditions requiring dimensional stability and long-term durability. A similar improvement in water resistance following pineapple leaves fiber and alkaline treatments has been reported by Gnanasekaran et al., [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], where plasma-modified pineapple leaves fiber showed superior dimensional stability in moist environments.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast, the higher water uptake observed in SJT and TUS samples implies a less efficient fiber treatment, resulting in higher porosity and weaker interfacial adhesion. The saturation trend also indicates that the absorption follows Fickian diffusion behavior, consistent with previous findings by Serra-parareda et al., [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e], where the rate of water diffusion slows down significantly after the fiber\u0026rsquo;s accessible hydroxyl groups are fully engaged.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec25\" class=\"Section2\"\u003e \u003ch2\u003e3.8 Dynamic mechanical analysis (DMA)\u003c/h2\u003e \u003cp\u003eDynamic Mechanical Analysis (DMA) was performed to evaluate the viscoelastic behavior of the composite samples in relation to temperature variations. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e illustrates the storage modulus (E\u0026prime;), loss modulus (E\u0026Prime;), and damping factor (tan δ) for TUS, SJT, and NHS composites. The storage modulus (E\u0026prime;) profile (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea) demonstrates a decreasing trend with increasing temperature. Among the samples, NHS exhibited the highest E\u0026prime; values throughout the temperature range, indicating enhanced stiffness and superior elastic response. This improvement is attributed to better NTSPs\u0026ndash;matrix interfacial adhesion, facilitated by the synergistic effect of NaOH treatment, which likely enhanced surface roughness and functional group availability on the NTSPs surface. This finding is consistent with the study by Serra-parareda et al. [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e], where plasma-treated fibers resulted in significantly improved storage modulus in epoxy-based composites. In the loss modulus (E\u0026Prime;) curves (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eb), all samples display a prominent peak between \u0026minus;\u0026thinsp;50 and \u0026minus;\u0026thinsp;45\u0026deg;C, corresponding to the glass transition temperature (Tg) of the polyester matrix. The TUS sample showed the highest E\u0026Prime; peak, possibly indicating greater internal friction and energy dissipation due to poorer interfacial bonding. In contrast, the NHS sample, while exhibiting a slightly lower E\u0026Prime;, maintained a broad and stable peak, implying effective load transfer with minimal viscous losses.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe tan δ curves (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ec) further confirm the interfacial characteristics of the composites. All samples exhibited Tg values in the range of \u0026minus;\u0026thinsp;47 to \u0026minus;\u0026thinsp;45\u0026deg;C, consistent with their E\u0026Prime; results. However, the NHS sample presented the lowest tan δ peak, which is a strong indicator of enhanced NTSPs\u0026ndash;matrix adhesion and restricted molecular motion at the interface. This aligns with the findings of Lendvai et al. [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], who observed that lower tan δ values in treated natural fiber composites correlate with improved stress transfer efficiency and reduced damping behavior.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study investigated the influence of varying NaOH concentrations (2%, 5%, and 8%) applied for 2 hours on the surface properties of tobacco stem particles (NTSPs), and their subsequent reinforcing effect on polyester composites. Comprehensive evaluations were conducted, including mechanical properties, thermal stability, dynamic mechanical analysis (DMA), density, moisture content, and water absorption behavior. The chemical treatments resulted in the effective removal of hemicellulose and lignin components, while increasing the relative cellulose content of the NTSPs. These structural modifications directly influenced the performance of the resulting composites. The tensile strength and elastic modulus of the composites ranged from 40.64 MPa to 48.53 MPa and from 1305 MPa to 2035 MPa, respectively, demonstrating the effectiveness of NTSPs surface engineering at a fixed NTP content of 30% by volume. Among the samples, the composite reinforced with NTP treated using 8% NaOH (NHS sample) exhibited the most superior performance in terms of mechanical strength, thermal stability, and water resistance. This was further supported by changes in functional group characteristics, increased density, and reduced moisture content following chemical modification. These improvements highlight the potential of composites based NTSPs for eco-friendly structural and semi-structural applications, particularly in automotive interiors, construction panels, and packaging materials.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe researcher would like to thank the University of Mataram has supported the funding of this research through the Grant funding of the professor program in 2024 (No. 1235/UN18.L1/PP/2024).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNasmi Herlina Sari: Supervision, Conceptualization, Methodology, Investigation, Writing – original draft, formal analysis. Sujita, Suteja: Methodology, Investigation, Data curation. Muhammad Firdaus, Deni Wardani: Resources, Project administration, Visualization, Edi Syafri: Validation, Writing - Review \u0026amp; Editing.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics, Consent to Participate, and Consent to Publish declarations:\u0026nbsp;\u003c/strong\u003enot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research complies with institutional, national, and international guidelines regarding the use of plant materials. The plant species used (\u003cem\u003eNicotiana tabacum L\u003c/em\u003e.) is not endangered and was obtained from cultivated agricultural waste, ensuring that no natural populations were disturbed.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number:\u0026nbsp;\u003c/strong\u003enot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability:\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eL. Lendvai, \u0026ldquo;Lignocellulosic agro-residue/polylactic acid (PLA) biocomposites: Rapeseed straw as a sustainable filler,\u0026rdquo; \u003cem\u003eClean. Mater.\u003c/em\u003e, vol. 9, pp. 1\u0026ndash;6, Sep. 2023, doi: 10.1016/j.clema.2023.100196.\u003c/li\u003e\n\u003cli\u003eC. E. Okafor, L. C. Kebodi, J. Kandasamy, M. May, and I. E. Ekengwu, \u0026ldquo;Properties and performance index of natural fiber reinforced cross-ply composites made from Dioscorea alata stem fibers,\u0026rdquo; \u003cem\u003eCompos. Part C Open Access\u003c/em\u003e, vol. 7, Mar. 2022, doi: 10.1016/j.jcomc.2021.100213.\u003c/li\u003e\n\u003cli\u003eP. Madhu, M. R. Sanjay, M. Jawaid, S. Siengchin, A. Khan, and C. I. Pruncu, \u0026ldquo;A new study on effect of various chemical treatments on Agave Americana fiber for composite reinforcement: Physico-chemical, thermal, mechanical and morphological properties,\u0026rdquo; \u003cem\u003ePolym. Test.\u003c/em\u003e, vol. 85, p. 106437, 2020, doi: 10.1016/j.polymertesting.2020.106437.\u003c/li\u003e\n\u003cli\u003eF. Yudhanto, J. Jamasri, R. A. Ilyas, and P. Terzioğlu, \u0026ldquo;Effect of Microcrystalline Cellulose Filler on Mechanical and Water Absorption Properties of Ramie/Glass/Carbon Hybrid Laminated Composite,\u0026rdquo; in \u003cem\u003eAIP Conference Proceedings\u003c/em\u003e, Dec. 2023, vol. 2865, no. 1, doi: 10.1063/5.0181999.\u003c/li\u003e\n\u003cli\u003eN. H. Sari, S. Suteja, M. N. Samudra, and H. Sutanto, \u0026ldquo;Composite of Hibiscus Tiliaceus Stem Fiber/Polyester Modified with Carbon Powder: Synthesis and Characterization of Tensile Strength, Flexural Strength and Morphology Properties,\u0026rdquo; \u003cem\u003eInt. J. Nanoelectron. Mater.\u003c/em\u003e, vol. 14, no. 3, pp. 247\u0026ndash;258, 2021.\u003c/li\u003e\n\u003cli\u003eM. Ji \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Enhanced mechanical properties, water resistance, thermal stability, and biodegradation of the starch-sisal fibre composites with various fillers,\u0026rdquo; \u003cem\u003eMater. Des.\u003c/em\u003e, vol. 198, p. 109373, 2021, doi: 10.1016/j.matdes.2020.109373.\u003c/li\u003e\n\u003cli\u003eM. Syduzzaman, S. Sultana Rumi, F. Faiza Fahmi, M. Akter, and R. Begum Dina, \u0026ldquo;Mapping the recent advancements in bast fiber reinforced biocomposites: A review on fiber modifications, mechanical properties, and their applications,\u0026rdquo; \u003cem\u003eResults Mater.\u003c/em\u003e, vol. 20, Dec. 2023, doi: 10.1016/j.rinma.2023.100448.\u003c/li\u003e\n\u003cli\u003eN. Herlina Sari, I. N. G. Wardana, Y. S. Irawan, and E. Siswanto, \u0026ldquo;Characterization of the Chemical, Physical, and Mechanical Properties of NaOH-treated Natural Cellulosic Fibers from Corn Husks,\u0026rdquo; \u003cem\u003eJ. Nat. Fibers\u003c/em\u003e, vol. 15, no. 4, pp. 545\u0026ndash;558, 2018, doi: 10.1080/15440478.2017.1349707.\u003c/li\u003e\n\u003cli\u003eS. S. Kumar, P. S. Pravat, R. Pati, and P. Kumar, \u0026ldquo;Wear and Frictional Performance of Epoxy Composites Reinforced with Natural Waste Fibers and Fillers for Engineering Applications,\u0026rdquo; \u003cem\u003eFibers Polym.\u003c/em\u003e, vol. 25, no. 4, pp. 1429\u0026ndash;1442, 2024, doi: 10.1007/s12221-024-00519-2.\u003c/li\u003e\n\u003cli\u003eA. Raza \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;A comprehensive review on material characterization and thermal properties of geopolymers: Potential of various fibers,\u0026rdquo; \u003cem\u003eCase Stud. Constr. Mater.\u003c/em\u003e, vol. 21, no. July, p. e03519, 2024, doi: 10.1016/j.cscm.2024.e03519.\u003c/li\u003e\n\u003cli\u003eN. H. Sari, Suteja, H. Anas, A. Amrullah, and M. Mahardika, \u0026ldquo;Enhanced mechanical and thermal performance of Paederia foetida fiber-magnesium/epoxy composites: A sustainable solution for automotive and aerospace industries,\u0026rdquo; \u003cem\u003eCase Stud. Chem. Environ. Eng.\u003c/em\u003e, vol. 11, no. December 2024, p. 101077, 2025, doi: 10.1016/j.cscee.2024.101077.\u003c/li\u003e\n\u003cli\u003eA. K. Trivedi, M. K. Gupta, and H. Singh, \u0026ldquo;PLA based biocomposites for sustainable products: A review,\u0026rdquo; \u003cem\u003eAdv. Ind. Eng. Polym. Res.\u003c/em\u003e, vol. 6, no. 4, pp. 382\u0026ndash;395, Oct. 2023, doi: 10.1016/j.aiepr.2023.02.002.\u003c/li\u003e\n\u003cli\u003eA. Vinod \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Extraction and Characterization of Natural Fiber from Stem of Cardiospermum Halicababum,\u0026rdquo; \u003cem\u003eJ. Nat. Fibers\u003c/em\u003e, vol. 18, no. 6, pp. 898\u0026ndash;908, 2021, doi: 10.1080/15440478.2019.1669514.\u003c/li\u003e\n\u003cli\u003eS. Aprilia, Y. Syamsuddin, A. Amin, and I. Zuwanna, \u0026ldquo;Physical , morphological , mechanical and thermal properties of polyester composites reinforced with orientation of purun fiber ( Eleocharis dulcis ) composition,\u0026rdquo; \u003cem\u003eSouth African J. Chem. Eng.\u003c/em\u003e, vol. 47, no. November 2023, pp. 338\u0026ndash;344, 2024.\u003c/li\u003e\n\u003cli\u003eZ. Changle, L. Shouhai, L. Yinghua, J. Jiang, and F. Hanguang, \u0026ldquo;Effect of boron on microstructure evolution and properties of wear-resistant cast Fe \u0026ndash; Si \u0026ndash; Mn \u0026ndash; Cr \u0026ndash; B alloy,\u0026rdquo; \u003cem\u003eIntegr. Med. Res.\u003c/em\u003e, vol. 9, no. 3, pp. 5564\u0026ndash;5576, 2020, doi: 10.1016/j.jmrt.2020.03.081.\u003c/li\u003e\n\u003cli\u003eN. H. Sari, E. Syafri, Suteja, W. Fatriasari, and A. Karimah, \u0026ldquo;Comprehensive Characterization Of Novel Cellulose Fiber From Paederia Foetida and Its Modification For Sustainable Composites Application,\u0026rdquo; \u003cem\u003eJ. Appl. Sci. Eng.\u003c/em\u003e, vol. 26, no. 10, pp. 1399\u0026ndash;1408, 2023, doi: 10.6180/jase.202310_26(10).0005.\u003c/li\u003e\n\u003cli\u003eM. Pokhriyal and P. Kumar, \u0026ldquo;Mechanical and microstructural behaviour of NaOH treated Himalayacalamus falconeri fibers as biodegradable reinforcing material in polymer based composites Materials Today : Proceedings Mechanical and microstructural behaviour of NaOH treated Himalayacala,\u0026rdquo; \u003cem\u003eMater. Today Proc.\u003c/em\u003e, no. April, pp. 1\u0026ndash;6, 2022, doi: 10.1016/j.matpr.2022.04.295.\u003c/li\u003e\n\u003cli\u003eZ. C. Liu, Z. W. Wang, S. Gao, Y. X. Tong, and X. Le, \u0026ldquo;Isolation and Fractionation of the Tobacco Stalk Lignin for Customized Value-added Utilization,\u0026rdquo; vol. 9, no. December, pp. 1\u0026ndash;9, 2021, doi: 10.3389/fbioe.2021.811287.\u003c/li\u003e\n\u003cli\u003eD. Sun, B. Wang, H. Wang, M. Li, Q. Shi, and L. Zheng, \u0026ldquo;Industrial Crops \u0026amp; Products Structural elucidation of tobacco stalk lignin isolated by di ff erent integrated processes,\u0026rdquo; \u003cem\u003eInd. Crop. Prod.\u003c/em\u003e, vol. 140, p. 111631, 2019, doi: 10.1016/j.indcrop.2019.111631.\u003c/li\u003e\n\u003cli\u003eD. Dalle \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Kinetic evaluation of tobacco stalk waste exposed to alkaline surface treatment under different conditions,\u0026rdquo; \u003cem\u003eCellulose\u003c/em\u003e, vol. 0123456789, no. 28, pp. 2053\u0026ndash;2073, 2021, doi: 10.1007/s10570-020-03657-x.\u003c/li\u003e\n\u003cli\u003eK. Sophanodorn, Y. Unpaprom, K. Whangchai, N. Homdoung, and N. Dussadee, \u0026ldquo;Environmental management and valorization of cultivated tobacco stalks by combined pretreatment for potential bioethanol production,\u0026rdquo; \u003cem\u003eBiomass Convers. Biorefinery\u003c/em\u003e, no. 12, pp. 1\u0026ndash;11, 2020.\u003c/li\u003e\n\u003cli\u003eH. He, N. Zhang, N. Chen, Z. Lei, K. Shimizu, and Z. Zhang, \u0026ldquo;Bioresource Technology Reports Efficient phosphate removal from wastewater by MgAl-LDHs modified hydrochar derived from tobacco stalk,\u0026rdquo; \u003cem\u003eBioresour. Technol. Reports\u003c/em\u003e, vol. 8, no. September, p. 100348, 2019, doi: 10.1016/j.biteb.2019.100348.\u003c/li\u003e\n\u003cli\u003eA. J. Adeyi, O. Adeyi, E. O. Oke, O. A. Olalere, S. Oyelami, and A. D. Ogunsola, \u0026ldquo;Effect of varied fiber alkali treatments on the tensile strength of Ampelocissus cavicaulis reinforced polyester composites: Prediction, optimization, uncertainty and sensitivity analysis,\u0026rdquo; \u003cem\u003eAdv. Ind. Eng. Polym. Res.\u003c/em\u003e, vol. 4, no. 1, pp. 29\u0026ndash;40, 2021, doi: 10.1016/j.aiepr.2020.12.002.\u003c/li\u003e\n\u003cli\u003eK. Sakthi vadivel and P. Govindasamy, \u0026ldquo;Mechanical and water absorption properties of Acacia Arabica bark fiber/polyester composites: Effect of alkali treatment and fiber volume fraction,\u0026rdquo; \u003cem\u003eMater. Today Proc.\u003c/em\u003e, vol. 46, no. xxxx, pp. 2281\u0026ndash;2287, 2021, doi: 10.1016/j.matpr.2021.04.057.\u003c/li\u003e\n\u003cli\u003eH. F. M. de Queiroz, N. V. dos Santos, J. S. S. Neto, and M. D. Banea, \u0026ldquo;Mechanical characterization of novel natural fibre-reinforced composites via a three-dimensional fibre architecture,\u0026rdquo; \u003cem\u003eCompos. Sci. Technol.\u003c/em\u003e, vol. 261, p. 110996, Mar. 2025, doi: 10.1016/j.compscitech.2024.110996.\u003c/li\u003e\n\u003cli\u003eS. S. Shifa \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Influence of heat treatment and water absorption on mechanical properties of cotton-glass fiber reinforced epoxy hybrid composites: An eco-friendly approach for industrial materials,\u0026rdquo; \u003cem\u003eHybrid Adv.\u003c/em\u003e, vol. 5, no. February, p. 100181, 2024, doi: 10.1016/j.hybadv.2024.100181.\u003c/li\u003e\n\u003cli\u003eN. Herlina, B. Anshari, E. Syafri, M. El, and A. Susan, \u0026ldquo;Exploring the impact of water soaking on the mechanical , thermal , and physical properties of Paederia foetida fiber stem biocomposites : A study in sustainable material innovation,\u0026rdquo; \u003cem\u003eCase Stud. Chem. Environ. Eng.\u003c/em\u003e, vol. 10, no. August, p. 100977, 2024, doi: 10.1016/j.cscee.2024.100977.\u003c/li\u003e\n\u003cli\u003eS. V. Sri and M. B. S. Sathees, \u0026ldquo;Optimization and Prediction of Wear Characteristics of Khas Khas Grass / Mesquite Bark Powder / Banana Fiber ‑ Reinforced Epoxy Green Hybrid Composites Using Taguchi Technique,\u0026rdquo; \u003cem\u003eFibers Polym.\u003c/em\u003e, vol. 25, no. 12, pp. 4845\u0026ndash;4857, 2024, doi: 10.1007/s12221-024-00745-8.\u003c/li\u003e\n\u003cli\u003eN. H. Sari and S. Suteja, \u0026ldquo;Corn husk Fibers Reinforced Polyester Composites: Tensile Strength Properties, Water Absorption Behavior, and Morphology,\u0026rdquo; \u003cem\u003eIOP Conf. Ser. Mater. Sci. Eng.\u003c/em\u003e, vol. 722, no. 1, 2020, doi: 10.1088/1757-899X/722/1/012035.\u003c/li\u003e\n\u003cli\u003eS. Sathees Kumar, \u0026ldquo;Effect of Natural Fiber Loading on Mechanical Properties and Thermal Characteristics of Hybrid Polyester Composites for Industrial and Construction Fields,\u0026rdquo; \u003cem\u003eFibers Polym.\u003c/em\u003e, vol. 21, no. 7, pp. 1508\u0026ndash;1514, 2020, doi: 10.1007/s12221-020-9853-4.\u003c/li\u003e\n\u003cli\u003eH. Fouad, M. Jawaid, and M. A. Azeem, \u0026ldquo;Flexural , impact and dynamic mechanical analysis of hybrid composites : Olive tree leaves powder / pineapple leaf fibre / epoxy matrix,\u0026rdquo; \u003cem\u003eJ. Mater. Res. Technol.\u003c/em\u003e, vol. 21, pp. 4241\u0026ndash;4252, 2022, doi: 10.1016/j.jmrt.2022.11.036.\u003c/li\u003e\n\u003cli\u003eA. Czajka, A. Plichta, R. Pomilovskis, A. Iuliano, T. Cygan, and J. Ryszkowska, \u0026ldquo;PLA reinforced with modified chokeberry pomace and beetroot pulp fillers . Effect of oligomeric chain extender on the properties of biocomposites,\u0026rdquo; vol. 289, no. September, 2023, doi: 10.1016/j.polymer.2023.126472.\u003c/li\u003e\n\u003cli\u003eE. Kılı\u0026ccedil;, P. Fullana-i-palmer, M. Fullana, M. Delgado-aguilar, and R. Puig, \u0026ldquo;Science of the Total Environment Circularity of new composites from recycled high density polyethylene and leather waste for automotive bumpers . Testing performance and environmental impact,\u0026rdquo; \u003cem\u003eSci. Total Environ.\u003c/em\u003e, vol. 919, no. January, p. 170413, 2024, doi: 10.1016/j.scitotenv.2024.170413.\u003c/li\u003e\n\u003cli\u003eM. Hadadi, F. Kamali, J. Mirhosseininia, M. Shahbazi, and B. Vaferi, \u0026ldquo;Experimental investigation of biopolymers influences on rheology and filtration properties of water-based drilling fluids,\u0026rdquo; \u003cem\u003eHeliyon\u003c/em\u003e, vol. 10, no. 23, p. e40780, Dec. 2024, doi: 10.1016/j.heliyon.2024.e40780.\u003c/li\u003e\n\u003cli\u003eH. Li, G. Wang, Y. Wu, N. Jiang, and K. Niu, \u0026ldquo;Functionalization of Carbon Nanotubes in Polystyrene and Properties of Their Composites: A Review,\u0026rdquo; \u003cem\u003ePolymers (Basel).\u003c/em\u003e, vol. 16, no. 6, 2024, doi: 10.3390/polym16060770.\u003c/li\u003e\n\u003cli\u003eE. Widodo and T. Dwi, \u0026ldquo;Comprehensive investigation of raw and NaOH alkalized sansevieria fiber for enhancing composite reinforcement,\u0026rdquo; \u003cem\u003eCase Stud. Chem. Environ. Eng.\u003c/em\u003e, vol. 9, no. August 2023, p. 100546, 2024, doi: 10.1016/j.cscee.2023.100546.\u003c/li\u003e\n\u003cli\u003eJ. A. Cottrell, M. Ali, A. Tatari, and D. B. Martinson, \u0026ldquo;Effects of Fibre Moisture Content on the Mechanical Properties of Jute Reinforced Compressed Earth Composites,\u0026rdquo; \u003cem\u003eConstr. Build. Mater.\u003c/em\u003e, vol. 373, Apr. 2023, doi: 10.1016/j.conbuildmat.2023.130848.\u003c/li\u003e\n\u003cli\u003eP. F. Alao, R. Press, H. Kallakas, J. Ruponen, T. Poltim\u0026auml;e, and J. Kers, \u0026ldquo;Investigation of Efficient Alkali Treatment and the Effect of Flame Retardant on the Mechanical and Fire Performance of Frost-Retted Fiber Hemp Reinforced PLA,\u0026rdquo; \u003cem\u003ePolymers (Basel).\u003c/em\u003e, vol. 14, pp. 1\u0026ndash;8, 2022.\u003c/li\u003e\n\u003cli\u003eS. Ovalı, \u0026ldquo;Characterization of Waste Nicotiana rustica L . ( Tobacco ) Fiber,\u0026rdquo; \u003cem\u003ePolymers (Basel).\u003c/em\u003e, vol. 16, pp. 1\u0026ndash;15, 2024.\u003c/li\u003e\n\u003cli\u003eA. H. Birniwa \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Recent Trends in Treatment and Fabrication of Plant-Based Fiber-Reinforced Epoxy Composite : A Review,\u0026rdquo; \u003cem\u003eJ. Compos. Sci.\u003c/em\u003e, vol. 7, no. 120, pp. 1\u0026ndash;33, 2023.\u003c/li\u003e\n\u003cli\u003eG. Rajeshkumar, V. Hariharan, S. Indran, M. R. Sanjay, S. Siengchin, and J. P. Maran, \u0026ldquo;Influence of Sodium Hydroxide ( NaOH ) Treatment on Mechanical Properties and Morphological Behaviour of Phoenix sp . Fiber / Epoxy Composites,\u0026rdquo; \u003cem\u003eJ. Polym. Environ.\u003c/em\u003e, no. 0123456789, 2020, doi: 10.1007/s10924-020-01921-6.\u003c/li\u003e\n\u003cli\u003eS. Gnanasekaran, N. I. A. A. Nordin, M. M. . Hamidi, and J. H. Shariffuddin, \u0026ldquo;Effect of Alkaline treatment on the characteristics of pineapple leaves fibre Effect of Alkaline treatment on the characteristics of pineapple leaves fibre and PALF / PP biocomposite,\u0026rdquo; \u003cem\u003eJ. Mech. Eng. Sci.\u003c/em\u003e, vol. 15, no. 4, p. 2021, 2021, doi: 10.15282/jmes.15.4.2021.05.0671.\u003c/li\u003e\n\u003cli\u003eF. Serra-parareda, F. X. Espinach, M. \u0026Agrave;. Pelach, M. Alberto, F. Vilaseca, and Q. Tarr, \u0026ldquo;Effect of NaOH Treatment on the Flexural Modulus of Hemp Core Reinforced Composites and on the Intrinsic Flexural Moduli of the Fibers,\u0026rdquo; \u003cem\u003ePolymers (Basel).\u003c/em\u003e, vol. 12, pp. 1\u0026ndash;21, 2020.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"dime","sideBox":"Learn more about [Discover Materials](https://www.springer.com/journal/43939)","snPcode":"","submissionUrl":"","title":"Discover Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Polyester matrix, tobacco stem particles (NTSPs), Alkali treatment, Sustainable composites, Mechanical properties","lastPublishedDoi":"10.21203/rs.3.rs-6702277/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6702277/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe increasing demand for eco-friendly materials has driven the development of sustainable biocomposites using renewable natural fibers. This study evaluates the mechanical, physical, tribological, and thermal properties of sustainable polyester biocomposites reinforced with treated tobacco stem particles (NTSPs). The NTSPs were treated with sodium hydroxide (NaOH) at concentrations of 2%, 5%, and 8% to enhance compatibility with the polyester matrix. Biocomposites containing 30% NTSPs by volume were fabricated via hot pressing at 105 °C and 75 Pa. Testing included tensile and flexural strength, thermal analysis, dynamic mechanical analysis (DMA), tribological evaluation, and scanning electron microscopy (SEM). The 8% NaOH-treated composite showed the best performance, with tensile strength of 48.53 ± 2 MPa, modulus of 2035.6 ± 77 MPa, and density of 1.22 ± 1.5 g/cm³. FTIR confirmed surface modification, while SEM revealed improved fiber–matrix bonding. The results demonstrate that treated tobacco stems particles are promising reinforcements for eco-friendly polyester composites, suitable for automotive interiors and semi-structural applications.\u003c/p\u003e","manuscriptTitle":"Alkali-Engineered Tobacco Stem Particles for Polyester Composites: Enhancing Physical, Mechanical, Thermal, and Dynamic Mechanical Properties","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-02 16:34:40","doi":"10.21203/rs.3.rs-6702277/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-06-16T08:52:25+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-13T10:36:21+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-09T10:30:08+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"115714741265975150410407267381918916036","date":"2025-06-06T16:40:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"9574114403182888294038334079522260076","date":"2025-05-30T17:44:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-30T14:57:12+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-30T12:57:22+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-28T20:02:17+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Materials","date":"2025-05-28T20:01:08+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-materials","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"dime","sideBox":"Learn more about [Discover Materials](https://www.springer.com/journal/43939)","snPcode":"","submissionUrl":"","title":"Discover Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ba67609b-e687-491d-b012-a78fb32c73ca","owner":[],"postedDate":"June 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-06T16:08:37+00:00","versionOfRecord":{"articleIdentity":"rs-6702277","link":"https://doi.org/10.1007/s43939-025-00388-3","journal":{"identity":"discover-materials","isVorOnly":false,"title":"Discover Materials"},"publishedOn":"2025-09-30 15:56:59","publishedOnDateReadable":"September 30th, 2025"},"versionCreatedAt":"2025-06-02 16:34:40","video":"","vorDoi":"10.1007/s43939-025-00388-3","vorDoiUrl":"https://doi.org/10.1007/s43939-025-00388-3","workflowStages":[]},"version":"v1","identity":"rs-6702277","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6702277","identity":"rs-6702277","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}