Enhancing Thermal and Dynamic Mechanical Properties of Lignocellulosic Borassus Husk Fibre/Epoxy Composites through Alkali Treatment

Natural fibres from renewable resources offer a sustainable and biodegradable alternative to synthetic reinforcements. This study investigates the thermal an d mechanical properties of Borassus husk fibre/epoxy composites, fabricated via the hand layup process using untreated and alkali-treated fibres. The fibres were treated with 5% NaOH for varying durations (0.25–2 hours), and their thermal stability was as sessed through thermogravimetric analysis (TGA) following ASTM E2550. Dynamic mechanical analysis (DMA) was performed according to ASTM D5418-01 to evaluate their mechanical performance at elevated temperatures. Results indicate that alkali treatment significantly enhances the thermal stability of the composites, as evidenced by increased char content (up to 11.5%) and higher integral procedural decomposition temperature (IPDT), w ith the 0.75 -hr treated fibre/epoxy (0.75TBHFE) achieving the highest IPDT (580°C). The composites also demonstrated superior energy dissipation and mechanical stiffness compared to neat epoxy (NE) and other bio -fibres based composites. The glass transition temperature (Tg) increased from 83.9°C (NE) to 94.6°C (0.5TBHFE), outperforming compo sites reinforced with other natural fibres. Additionally, storage modulus and damping factor (tan δ) improved significantly, with 0.5TBHFE exhibiting the best balance between stiffness and damping. The total mass loss (TML) was reduced by approximately 34% compared to NE, further confirming the enhanced thermal stability. These findings suggest that alkali -treated Borassus husk fibre/epoxy composites offer excellent thermal resistance, mechanical strength and impact resistance, making them promising

for high-performance applications in the aerospace and automotive industries, which would also promote sustainable development. However, variations in properties of biofibres require further research, along with the development of an efficient supply chain for industrial- scale production.

Borassus flabellifer husk fibre, agro -waste, thermal properties, dynamic mechanical analysis, sustainability Nomenclature Subscripts IPDT IPDH q(DSC) Q Hd E' E'' E* tan δ Tg TML Integral process decomposition temperature (°C) Integral process decomposition heat flow (W/g) Heat flow (mW) Specific heat flow (W/g) Specific decomposition enthalpy (J/g) Storage modulus (MPa) Loss modulus (MPa) Shear (Complex) modulus (MPa) Damping factor Glass transition temperature (°C) Total mass loss (%) T P w t δ W Temperature (°C) Load (N) Width (mm) Thickness (mm) Phase Angle (°) Weight (mg) 1. Introduction Natural fibres from renewable resources offer a sustainable and biodegradable alternative to synthetic reinforcements. They are lightweight, cost -effective, and environmentally friendly, with excellent specific properties. Additionally, these fibres provid e superior thermal and insulating performance while requiring minimal energy for processing, making them an efficient and eco-friendly choice for various applications [1], [2]. With global temperatures and greenhouse gas emissions rising, the United Nations Environment Programme's (UNEP) latest Emissions Gap Report warns that current Paris Agreement commitments could lead to a 2.5–2.9°C temperature increase above pre-industrial levels by the end of the century, underscoring the urgent need for stronger climate action [3]. Under this agreement, European Union (EU) members have committed to making the EU the world’s first climate-neutral economy and society by 2050. As part of thi s effort, the EU has submitted its long-term carbon reduction strategy and pledged to cut emissions by at least 55% by 2030 compared to 1990 levels [4], [5] . Furthermore, EU agreed to keep global average temperature rise to well below 2°C above pre-industrial levels, with efforts to limit it to 1.5°C [6]. A range of polymer composite materials reinforced with natural fibres has been developed using modified synthetic strategies, enabling applications that extend from automotive to biomedical fields [7]-[9]. Common natural fibres include coconut, sisal, jute, ramie, banana, hemp, kenaf, flax, pineapple leaf, abaca leaf, bamboo, date palm, sugarcane fibre, and cotton. These fibres are incorporated into polymeric resins to improve the performance and properties of the final products [10]-[12]. Borassus flabellifer (Palmyra palm) husk fibre remains largely unexplored among conventional natural fibres despite its significant potential. It shares similar chemical components —cellulose, hemicellulose, and li gnin—while offering mechanical properties and thermal resistance comparable to well -known fibres such as jute, sisal, hemp, bamboo, and flax [13]-[16]. Borassus flabellifer, commonly known as the Asian Palmyra palm, is a vital crop supporting local economies across South and Southeast Asia, valued for its fruit and palm sugar production [17], [18]. Borassus flabellifer fibres are mainly extracted from the fruit of the palm tree, though they can also be obtained from the leaves and bark using mechanical or water retting methods. While the fruit, leaves, trunk, and bark have traditionally been used for household applications, the fruit shell (husk) has been treated as agricultural waste in Bangladesh [19], [20]. Unlike other natural fibers such as jute, sisal, flax, and ramie, acquiring the raw material from Borassus husk requires planting and/or preserving the Borassus flabellifer trees, rather than cutting them down. To do so, we are contributing towards net -zero carbon emission aim set by Paris agreement, 2015 [4], [5]. On top of that, it would also help to keep locals safe from ma jor natural calamities, including flood [21], thunder lightning [22], cyclone [23], riverbank erosion [24] and keeping local bio-diversity [25] in Bangladesh. Like other lignocellulosic fibres, Borassus fibres are naturally hydrophilic, meaning they absorb moisture easily. This reduces their compatibility with hydrophobic polymer matrices, making composite fabrication challenging. Additionally, the extracted fi bres often contain impurities, such as , waxes and pectin, further limiting their suitability for engineering applications [26]-[28]. To enhance compatibility and reduce hydrophilicity by removing impurities, wax, and hemicellulose, various chemical treatments can be applied, including alkali, saline, potassium permanganate, benzoylation, and acetic acid treatments. Among these, alkali treatment is the most widely used due to its cost -effectiveness, efficiency, and ease of application [26], [27]. However, a high alkali concentration and extended treatment time can lead to the excessive removal of protecti ve components (cellulose) from the material surface, significantly weakening the fiber and reducing its strength [28]-[30]. The impact of chemical treatment on the mechanical behaviour of banana fiber -reinforced polyester composites has been studied, showing that alkali -treated banana fiber composites display stronger fiber -matrix interactions, resulting in improved mechanical properties [31]. Few studies have explored the impact behavior of natural fiber-reinforced polymer composites. Jute fibers have been shown to significantly enhance fiber-matrix adhesion, thereby improving the mechanical properties of jute fiber-reinforced polypropylene (PP) composites [32]. Composites are widely used in spacecraft, military planes, commercial aircraft and unmanned aerial vehicles (UAVs), and their applications include engine parts, aeroplane coverings, and interior coatings [33]. Composites are valued for their high specific strength, impact resistance, fatigue resistance, corrosion resistance, and ability to optimize mechanical properties in high - stress areas. They are also commonly used in airplanes to reduce weight and improve fuel efficiency [1], [2], [34] -[36]. One way to meet this requirement is by using polymer matrix

that can be repeatedly heated and cooled for reuse. When combined with natural fibers such as flax, jute, date palm, hemp, or sisal, these composites become 100% recyclable [37]. Balakrishan et al [38] reported that the aircraft industry has a growing demand for lightweight materials due to rising oil and gas prices, as fuel costs account for nearly half of operating expenses, even in general aviation. Additionally, the average cost of launching a heavy-lift system into low Earth orbit is approximately €5,000–15,000 per kg. Santos et al [36] stated key material criteria for aircraft internal structural components include being non -toxic, sourced from non -problematic origins (such as avoiding deforestation for wood), and not generating hazardous waste during or after fabrication that could contribute to ozone depletion or global warming. Aircraft cabin components must also be resistant to moisture absorption while remaining lightweight to reduce fuel consumption and carbon emissions, all without compromising performance [33]. Sustainability should be prioritised by incorporating end-of-life strategies such as recyclability, biodegradability and ease of reuse or refurbishment, supporting a circular economy and reducing material waste [39]-[41]. Thermal comfort is crucial, necessitating materials that maintain a consistent temperature to prevent internal components from becoming too hot or cold. Furthermore, panels should contribute to passenger comfort by effectively reducing cabin noise levels [42]-[44]. Hexion L-285 epoxy resin (with hardener H-285) is widely used in aeronautics, including in gliders and light aircraft, due to its exceptional mechanical and thermal properties, along with a broad operating temperature range [45]. Locatelli with co-researchers [46] reported that the wing box of the Airbus A320-200 was constructed using ramie fiber-reinforced polymer, resulting in a weight reduction of up to 14% compared to 7000-series aluminum, thanks to its low density, all while maintaining structural integrity. Flax fiber -reinforced polymer composites were used for the manufacturing of the tailplane, cabin door, partition panels, tray tables, and baggage compartments [47], [48], whereas wing was manufactured from hemp, sisal and ramie-based composites [49]. Natural fiber -reinforced polymer matrix composites have achieved commercial success in semi-structural and structural applications, including in electronics, sports technology, automotive, aerospace, and plastics. By using natural fibers and bio -based resins, 100% bio- based composites with enhanced mechanical properties can be developed for more demanding structural applications [50]. Flexible and versatile materials are crucial for a range of light spacecraft applications, such as solar sails, sun shield s, radar systems, rovers, reflect arrays, solar concentrators, and antennas. As a result, polymer composites now account for approximately 80% of the components used in satellite launches. Similarly, in the automotive industry, leading companies like Mazda, Mitsubishi, Toyota, Fiat, Mercedes-Benz, BMW, and V olkswagen have adopted bio-composites to reduce carbon footprints and lower fuel costs [7], [43], [51], [52]. Thermogravimetric analysis (TGA) involves measuring the change in a sample's mass as its temperature or time is varied under controlled conditions. The experiment typically involves heating or cooling a sample in a pan within a furnace, while its mass is continuously recorded. A purge gas is used to control the sample environment, with inert gases like nitrogen commonly employed for pyrolysis to flow over the sample [53]. Researchers [54]-[65] carried out thermogravimetric analysis (TGA) was conducted on natural fiber -based composites, where char content and the derivative weight loss rate were recorded. Additionally, to assess the thermal stability of the test material, researchers used the integral proces s decomposition temperature (IPDT) [66]-[68]. Meanwhile, to estimate the specific heat capacity (Cp) in relation to endothermi c and exothermic heat flow, authors suggested integral process decomposition heat (IPDH), as reported in their previous studies [69], [70]. Dynamic mechanical analysis (DMA) is an essential and effective technique for assessing the morphology and viscoelastic properties of crystalline polymers and composite materials. It offers valuable insights into primary relaxation processes and key parameters, including dynamic/complex viscosity, storage and loss compliance, and damping factor [71]-[74]. The DMA technique offers significantly greater sensitivity in determining Tg, being up to 100 times more sensitive than the differential scanning calorimetry (DSC) method [32], [71], [73]. Gupta and Srivastava [54] carried out DMA analysis of jute fiber-reinforced epoxy at different fiber loadings showed that the epoxy with 25% (w.t) jute fiber exhibited improved storage modulus and loss modulus, along with a reduced damping factor (tanδ), compared to both neat epoxy and other composite variations. Manral with co -workers [75] found that 10% sodium bicarbonate-treated jute fibre reinforced polylactic acid (PLA) composite showed better impact properties (tanδ) while composite with 20% treated jute fibre achieved maximum storage and loss modulus values. Kumar with co-researchers [76] carried out DMA at different frequencies on alkali-treated flax fibre reinforced composites, and found that with increasing frequency, storage and loss modulus as well as glass transition temperatures, Tg, increased, wherea s damping factor (tanδ) found to be decreased, compared to neat epoxy. Ram with co-researchers [77] carried out DMA on alkali -treated Asian Palmyra sprouts fibre reinforced epoxy composites at different fibre loadings. They found that effectiveness of fibre is highest at 40% fibre loading with epoxy, and the loss modulus and damping peaks decreased with increase of fibre loading, whereas storage modulus decreased with increase in fibre loading. Most previous studies have primarily focused on composites made from fine and coarse fibers of Borassus, with limited research conducted on Borassus husk fibers. However, preliminary investigations into the properties of Borassus husk fibers have already b een reported by the authors [19], [30], [69], [70], [78] . In this study, composites were fabricated using the hand layup process, incorporating raw and alkali-treated Borassus husk fibers (treated between 0.25- hr and 2-hr) reinforced with epoxy resin. The primary objective of this paper is to investigate the thermal properties, including decomposition rates, onset decomposition temperature, integral process decomposition temperature (IPDT), integral process decomposition heat flow (IPDH), and specific dec omposition enthalpy, in accordance with ASTM E2550 standards. Additionally, dynamic mechanical analysis (DMA) was conducted to evaluate properties such as storage modulus (E ’), loss modulus (E ”), and damping factor (tan δ) following ASTM D5418-01. Other critical factors, including shear modulus (E*), phase angle (δ), glass transition temperature (Tg), and total mass loss (TML), were also assessed. 2. Materials and Methods 2.1. Raw materials Fruit shells of the Palmyra Palm (Borassus flabellifer) were collected fr om rural areas in Bogura, Bangladesh. The shells were cut into smaller pieces and cleaned thoroughly through a water-retting process. They were then sun -dried for several days before being chopped and ground into fine fibers using an electric blender, followed by sieve analysis. Epoxy laminating resin (EL2) and a compatible slow hardener were sourced from Easy Composites, UK. For alkali treatment, hydrochloric acid (HCl) and sodium hydroxide (NaOH) were procured from Sigma-Aldrich, UK. 2.2. Alkali Treatment The particles were treated with a 5% ( w.t) NaOH (alkali) solution for 0.75 hr, 1 hr and 2 h rs. The ratio of the distilled wat er to sodium hydroxide to fibre used was 19:1:1 [30], [69], [78], [79]. Then the solution with samples was neutralised with hydrochloric acid (HCl), and rinsed with ta p water to eliminate any remaining chemical residue. The optimum mechanical properties of the composite were observed at a concentration of 5% NaOH [80]-[82]. The fibres were washed and then conditioned at 80°C for 2 4 hours in a hot air oven before being stored in desiccator containers. 2.3. Composite preparation Composites were prepared using the hand lay-up method. First, 10% (w.t) fiber (either treated or untreated) was mixed with resin in a mixing pot and stirred mechanically for 10 minutes to achieve a homogeneous mixture. The mixture was then placed in a vacuum chamber at a gauge pressure of 20 bar for 20 minutes to remove any trapped moisture [30], [78]. Next, the mixture was poured into a 160 x 160 mm mould t o form a 3 mm thick board. Prior to pouring, the mould was polished with a release agent to prevent the composite from sticking during removal. The composite was left to cure at room temperature for 24 hours, then demoulded and placed in an oven at 60°C for 6 hours for post-curing, following the supplier's technical datasheet instructions. After post -curing, the sample was allowed to cool at room temperature for 24 hours before being cut to the desired dimensions for the experiments. Finally, the samples were given representative names for convenience. Figure 1 illustrates the composite preparation process, and Table 1 lists the names of the representative composites. Figure 1. Composite preparation by hand layup. Table 1. Composition of composites and representative names. Serial No Sample Description Representative Name 01 Neat Epoxy NE 02 Untreated Borassus husk fibre reinforced epoxy UBHFE 03 0.25-hr alkali-treated Borassus husk fibre reinforced epoxy 0.25TBHFE 04 0.5-hr alkali-treated Borassus husk fibre reinforced epoxy 0.5TBHFE 05 0.75-hr alkali-treated Borassus husk fibre reinforced epoxy 0.75TBHFE 06 1-hr alkali-treated Borassus husk fibre reinforced epoxy 1TBHFE 07 2-hr alkali-treated Borassus husk fibre reinforced epoxy 2TBHFE 2.4. Thermogravimetric and Differential Thermal Analysis (TGA/DTA) TGA/DTA was performed using a TA Instruments SDT -Q600 Simultaneous TGA/DTA instrument. Sample sizes ranged from 8 to 12 mg, and the heating rate was set to 20 °C/min under a nitrogen flow of 110 mL/min. Each sample was heated from 25°C to 700°C, following the ASTM E2550 standard [83]. The integral process decomposition temperature (IPDT) has been adhered to estimate the thermal stability of materials based on their components, which was proposed by Doyle [67] for polymeric materials. IPDT was determined from the equation used in previ ous study [66], [68]: 𝑰𝑷𝑫𝑻 (°𝑪) = 𝑨 × 𝑲 × (∆𝑻) + 𝑻𝟎 (4) 𝑨 = 𝑺𝟏 + 𝑺𝟐 𝑺𝟏 + 𝑺𝟐 + 𝑺𝟑 (5) 𝑲 = 𝟏 + 𝑺𝟐 𝑺𝟏 (6) ∆𝑻 (°𝑪) = 𝑻𝟏 − 𝑻𝟎 (7) Where, A is the area ratio of the complete experimental curve as found from the TGA thermogram, K is the coefficient of A, T0 is the starting temperature (˚C), and T 1 is the final temperature (˚C). S1, S2 and S3 are the areas under the curve depicted in Figure 2. Figure 2. Schematic diagram of S1, S2 and S3 areas for determining IPDT. Wang et al. [84] suggested that the bio-fibers are thermally unstable, unlike metals, due to the presence of various constituents such as wax, pectin, impurities, cellulose, hemicellulose, and lignin embedded within the material. As a result, they undergo different stages of decomposition under an inert gas flow. Following the methodology suggested by Doyle [67], integral process decomposition heat, IPDH, was proposed by the authors [70] to determine decomposition heat flow for the material. This indicates the material's ability to withst and specific heat loads during decomposition. The equations are similar to those used for IPDT [69], [70], [78] However, due to the material's thermal instability, specific heat flow (W/g) is calculated based on the changing mass of the sample rather than its initial mass. Additionally, both the starting and final temperatures of the test must remain consistent, along with a constant heating rate of 20 °C/min, to ensure reliable results. The equations are provided below: 𝑰𝑷𝑫𝑯 (𝑾/𝒈) = 𝑨 × 𝑲 × (∆𝑸) + 𝑸𝟎 (8) 𝑨 = 𝑺𝟏 + 𝑺𝟐 𝑺𝟏 + 𝑺𝟐 + 𝑺𝟑 (9) 𝑲 = 𝟏 + 𝑺𝟐 𝑺𝟏 (10) 𝑸 (𝑾 𝒈 ) = 𝒒𝑫𝑺𝑪 𝑾 (11) ∆𝑸 (𝑾 𝒈⁄ ) = 𝑸𝟏 − 𝑸𝟎 (12) Where, A is the area ratio of the complete experimental curve as found from the TGA thermogramme, K is the coefficient of A, heat flow, qDSC is the heat load (mW) sample absorbed or emitted (can be assessed from the TGA data), and W is the weight (mg) of the sample at that time. Furthermore, Q0 is the starting specific heat flow (W/g), and Q1 is the final specific heat flow (W/g). S1, S2 and S3 are the areas under the curve depicted in Figure 3. Figure 3. Schematic diagram of S1, S2 and S3 areas for determining IPDH. Additionally, specific decomposition enthalpy (Hd) has been introduced, which represents the amount of heat energy absorbed by the sample throughout the duration of the experiment, from start to end. Since bio-fibers are thermally unstable (unlike metals), the analysis considers the variable mass (weight) of the sample, rather than its initial mass, following a similar approach used for IPDH evaluation. All the data being gathered from TGA. The equations are provided below: 𝑯𝒅 = ∫ 𝑸. 𝒅𝒕 𝒕𝒇 𝒕𝒊 (13) 𝑸 (𝑾 𝒈 ) = 𝒒𝑫𝑺𝑪 𝑾 (14) Where, Hd is the specific decomposition enthalpy (J/g), heat flow, q DSC is the heat load (mW) sample absorbed or emitted (assessed from the TGA data), and W is the weight (mg) of the sample at that time. Furthermore, Q is the specific heat flow (W/g), and t i as well as t f is the stating as well as the ending time of the test [duration], respectively. 2.5. Dynamic Mechanical Analysis (DMA) Dynamic Mechanical Analysis (DMA) was conducted to assess the viscoelastic behavior of Borassus/epoxy composites, as well as neat epoxy, following the ASTM 5418-01 standard. The tests were performed using a TA Instruments DMA Q800 in dual-cantilever mode. The samples were cut into rectangular shapes with dimensions of 55 mm x 13 mm x 2.5 mm. The experiments were carried out at a frequency of 1 0 Hz with a controlled amplitude of 10 µm. The temperature was gradually increased from room temperature to 150°C using sinusoidal strain, with a heating rate of 3°C/min, under a compressed air atmosphere at 4.6 bar [30], [78]. The storage modulus [71]-[74], loss modulus [85]-[87] and damping factor (tan δ) [73], [88] can be directly obtained from DMA data. However, shear (complex) modulus that refers to

resistance to undergo deformation, can be calculated from Pythagorean theorem [89] following the diagram illustrates in Figure 4. 𝑺𝒉𝒆𝒂𝒓 𝑴𝒐𝒅𝒖𝒍𝒖𝒔, 𝑬∗ = √(𝑺𝒕𝒐𝒓𝒂𝒈𝒆 𝑴𝒐𝒅𝒖𝒍𝒖𝒔, 𝑬′)𝟐 + (𝑳𝒐𝒔𝒔 𝑴𝒐𝒅𝒖𝒍𝒖𝒔, 𝑬")𝟐 (18) Figure 4. Correlation among storage modulus, loss modulus, shear modulus and phase angle. Where, vertical axis (Y) and horizontal axis (X) represent loss modulus, E ” and storage modulus, E’ (MPa), respectively. Additionally, the resultant modulus depicts as shear modulus, E* (MPa), where ‘δ’ is the phase angle (°). Phase angle, δ, can be calculated from the following equation (Figure 4): 𝐭𝐚𝐧 𝜹 = 𝑳𝒐𝒔𝒔 𝑴𝒐𝒅𝒖𝒍𝒖𝒔, 𝑬" 𝑺𝒕𝒐𝒓𝒂𝒈𝒆 𝑴𝒐𝒅𝒖𝒍𝒖𝒔, 𝑬′ (19) 𝑷𝒉𝒂𝒔𝒆 𝒂𝒏𝒈𝒍𝒆, 𝜹 = 𝐭𝐚𝐧−𝟏( 𝑳𝒐𝒔𝒔 𝑴𝒐𝒅𝒖𝒍𝒖𝒔, 𝑬" 𝑺𝒕𝒐𝒓𝒂𝒈𝒆 𝑴𝒐𝒅𝒍𝒖𝒔, 𝑬′) (20) Total mass loss, TML (%) refers to the percentage of mass lost by the sample during the experiment under thermo-mechanical conditions. It is calculated by comparing the difference between the initial mass (before the experiment) and the fina l mass (after the experiment) of the sample [90]. In principle, low TML value indicates that the sample should be stable under designated condition, whereas high value indicates material ’s instability. TML can be calculated from the following equation: 𝑻𝑴𝑳 (%) = (𝟏 − 𝑴𝒇 𝑴𝒊 ) × 𝟏𝟎𝟎 (21) Where, Mi is the initial mass (g) and Mf is the final mass (g) of the sample. 3. Results and Discussion 3.1. Thermogravimetric Analysis (TGA) Comparative thermogravimetric analysis (TGA) of all Borassus husk fibre reinforced epoxy composites are showed in Error! Reference source n ot found.. There are three significant phases of mass loss observed due to rising temperature. According to Figure 5a, the first weight loss between 70°C and 170°C corresponds to vaporization of water molecules and/or moisture content as also observed in the case of natural fibre polymer composites. The second step of major weight loss is associated with breaking down and volatisation fundamental compositions of epoxy resin as well as Borassus husk fibre (hemicellulose, cellulose and lignin). The final step refers to the formation of residue. However, it is evident that pure epoxy composites show relatively less weight loss up to 17 0°C temperature due to its hydrophobic nature, indicating the presence of less water molecules, compared to any Borassus fibre reinforced epoxy . The onset decomposition temperature of epoxy is around 322°C, whereas it can be observed around 330°C [ Figure 5a] for Borassus fibre/epoxy composites although for treated Borassus husk fibre-based epoxy samples, negligible change in values being observed. The major mass loss (approximately 83%) was found to be from 340 – 495°C, which is due to chemical compositions of epoxy resin and husk fibre. From the TGA data, it has been found that T15% of NE was at 340°C and T75% occurred at 407°C, whereas T15% of UBHFE was at 338°C and T75% occurred at 409°C, which should be due to the presence of moisture absorbing composition, hemicellulose. Nevertheless, degradation temperatures of T 15% (340 - 345°C) as well as T 75% (411 - 414°C) for all the alkali-treated Borassus husk fibre/epoxy composites were found to be higher, and 0.75TBHFE shows the highest value, which is due to elimination of hemicellulose and moisture absorptive chemical bonds that was confirmed in authors’ previous work [69] as well as other research works [91], [92]. The final stage is char formation: The char residue of the NE found to be 6.42%, whereas in other studies it was around 9.6% [57] and 6.18% [78]. Nevertheless, all the Borassus husk fibre/epoxy samples showed higher char content (Table 2) compared to neat epoxy, where treated fibre reinforced epoxy composites have ch ar residue between 8.64% and 11.5%, whereas in authors’ previous work [78], it was found from 7.6% to 10.4% with respect to different heating rate ( 10°C/min). This is due to treated fibre has more lignin and cellulose contents, which are thermally stable compared to hemicellulose (in raw fibre). And this has been found in other studies including authors own work [69], [70], [78] . Gupta with co-researcher [54] found that the char residue found to be below 5% for jute fibre reinforced epoxy composite samples at different fibre loadings. Gheith et al [57] found the char content around 19% for 50% date palm fibre reinforced epoxy, and they suggested that afte r higher fibre loading char content increased. Kumar et al [58] carried out TGA analysis on ramie root fibre (at different loadings) reinforce polyester composites and found that the char contents between 5 – 11% with respect to different fibre loadings in composites. Sudhakara et al [79] incorporated Borassus fine, sisal, jute and coir fibres into polypropylene (PP) resin and carried out TGA analysis. They found that the char residue of Borassus fibre/polypropylene found to be 7%, whereas char contents of coir/PP, jute/PP and sisal/PP found to be 9%, 6% and 2%, respectively. Richmond and co-researchers [93] found the char content of 5.6% for the bamboo fibre reinforced epoxy composite. Saba et al [94] suggested that the higher residue content improves the flame resistan ce behaviour of materials . The char residue order for all the composites: 0.75TBHFE > 0.5TBHFE > 2TBHFE > 0.25TBHFE > UBHFE > 1TBHFE > NE. Furthermore, the derivative thermogravimetry (DTG) from Figure 5b shows the mass loss rate of the composite samples. All the samples found to be similar trend up to around 200°C, which is associated with moisture due to presence of hemicellulose and void creation during fabrication process. The highest mass loss rate found to be 1.08 %/°C at 379°C for NE. When Borassus husk fibres (raw and treated) were incorporated with epoxy resin, thermal decomposition rates and related properties being affected significantly. The mass loss rate was found to be 1.03 %/°C at 381 °C for UBHFE, which is higher than neat epoxy (NE). The maximum derivative mass loss rate of alkali-treated Borassus fibre/epoxy composites found to be ranging from 1.04 %/°C to 1.17 %/°C and corresponding temperature found to be between 343°C and 381°C, depending on different samples. When fibre was treated and incorporated with epoxy resin, the corresponding temperature of derivative mass loss rates found to be increased, which is also an indication of improved thermal stability. The fluctuation in the DTG curve was found for all sample that could be associated with sample preparation, fibre alignment in the resin and fibre content in the sample [16], [95]-[98]. Furthermore, it was found to be with increasing heating rate, char content and maximum decomposition rates changes [99], which was evident from authors’ own previous works, carried out at 10°C/min [69], [70], [78]. Integral process decomposit ion temperature (IPDT ) proposed early by Doyle [67]-[69] is a quantitative thermal analysis used to assess the thermal stability of sample containing the residual carbon yields of the resulting materials at high temperatures, whether TGA degradation is executed in a single process or multi-process [66]. This value is consistent with char content found for all samples, where IPDT of NE found to be 486.81°C in this study, and it was found to 464°C [68] and 428.9°C [78], when the experiment carried out at 10°C/min. All the alkali- treated fibre/epoxy samples found to be higher IPDT value (529 – 580°C) compared to raw fibre/epoxy (529°C) and neat epoxy value. Nevertheless, the highest value was found for 0.75TBHFE. This is due to the IPDT value for raw as well as alkali-treated Borassus husk fibre reinforced epoxy composites found to be hi gher in authors ’ previous works [69], [70] . The IPDT order for all the composites: 0.75TBHFE > 0.5TBHFE > 2TBHFE > 0.25TBHFE > UBHFE > 1TBHFE > NE. Integral process decomposition heat flow (IPDH) of NE found to be 6.72 W/g, whereas UBHFE had 7.12 W/g (Table 2). Nevertheless , including of alkali -treated fibre into epoxy resin increased the value up to 5.83 W/g. The positive value of IPDH refers to overall much more exothermic heat flow compared to endothermic one (Figure 5c). However, treated Borassus fibre/epoxy samples show lower IPDH value compared to NE and among them 0. 5TBHFE shows the lowest, 4.4 W/g. This was found in authors’ previous work, where they reported that the IPDH value of raw (untreated) Borassus husk fibre found to be -15.36 W/g [70] and values ranging from 5.3 W/g to 16 W/g for 0.25 -hr to 2 -hr alkali-treated Borassus husk fibre [30]. They also found that specific heat capacity, Cp, found to be higher with lower IPDH value and Cp was lower when IPDH value found to be higher for Borassus husk fibre [69]. The IPDH order for all the composites: 0.5TBHFE < 0.75TBHFE < 1TBHFE < 2TBHFE < 0.25TBHFE < NE < UBHFE. The specific decomposition enthalpy, Hd, refers to the heat energy (J) experience by a unit mass (g) of the sample during entire pyrolysis process. The H d value, 13102 J/g, found for the NE and 12291 J/g found for UBHFE. However, there is diverge values found for the alkali-treated Borassus husk fibre reinforced epoxy samples. For example, the highest H d value, 6673 J/g, found for the 2 TBHFE and the least ( 3500 J/g) among treated-fibre based epoxies found for 0.5TBHFE. The discrepancy found in H d values can be associated with sample preparation, collection and maturity of the source of Borassus husk fibre [82], [100], [101] . Figure 5 and Table 2 show all the data of TGA for all composites at heating rate of 20°C/min. Figure 5. TGA thermograms: a. Weight-temperature plot; b. Deri. weight loss rate- temperature plot; and c. Weight-specific heat flow plot. Table 2. TGA data from all composite samples. Samples Max. dev. Weight loss rate (%/°C) Char Residue (%) Integral process decomposition temperature, IPDT (˚ C) Integral process decomposition heat, IPDH (W/g) Specific Decomposition Enthalpy, Hd (J/g) NE 1.08 6.42 486.81 6.72 13102 UBHFE 1.03 9.05 529.11 7.12 12291 0.25TBHFE 1.17 10.26 555.88 5.83 6445 0.5TBHFE 1.11 11.13 573.27 4.39 3500 0.75TBHFE 1.08 11.47 579.69 4.62 3894 1TBHFE 1.07 8.64 525.02 5.37 6475 2TBHFE 1.04 11.02 568.60 5.72 6673 3.2. Dynamic mechanical properties 3.2.1. Storage Modulus (E’) The storage modulus (E’) measures the energy (storage) stored in a material during a single oscillation cycle. It also demonstrates temperature -dependent stiffness behaviour and load - bearing capabilities of the composite material. Figure 6 depicts the storage modulus - temperature curve, where neat epoxy along with untreated and alkali -treated Borassus husk fibre reinforced epoxy composites are presented. It has been evid ent that E’ was found to be decreased with rising temperature for all samples. Nevertheless, only untreated Borassus husk fibre reinforced epoxy (UBHFE) shows higher storage modulus loss than neat epoxy (NE). Rest of the alkali -treated husk fibre reinforced epoxies show higher storage modulus retain capability during the test, and 0.5TBHFE shows the highest capability . The outcomes agree with previous studies [78], [86], [88], [102] . Figure 6 shows that in the glassy zone, the E’ broadens due to closely packed and frozen components, resulting in a large storage modulus value below the glass transition temperature, Tg. The E’ curves show a sign ificant drop at around 55 - 110˚C, indicating a glass/rubbery state transition, depending on samples. As the temperature rises, the composites lose their tight packing structure losing inter-molecular bond strength, resulting in decreased E’ values in the rubbery zone. The dramatic fall in E’ value near the Tg suggests the material is transitioning from glass to rubber. Above Tg, untreated fibre/epoxy composite (UBHFE) has a lower storage modulus than other composites, indicating increased molecular mobility that supports the phenomenon results from increases in the molecular mobility of polymer chains above Tg. The storage modulus curves show that adding untreated fibre decreases but incorporating alkali treated fibre to epoxy significantly raises the E’ values. The inclusion of treated fibre enhanced the adhesion property between stiff husk fibre and epoxy matrix, improving interfacial bonding, which has been found in previous studies [28], [103], including authors’ own work in SEM analysis [69], [70], [78]. This can be attributed to the clear as well as rough surface found from the scanning electron microscopy (SEM) images revealed in previous studies [69], [81], [104]-[107], and hemicellulose, moisture absorbing composi tion foun d to be eliminated, confirmed through Fourier transform infrared spectroscopy (FTIR) analysis [69], [91], [104], [108]. The untreated fibre/epoxy composite (UBHFE) shows a greater decrease in storage modulus compared to all treated/epoxy samples. This is because impurities and hemicellulose (as identified in the FTIR analysis) act as barriers, preventing proper bonding with the matrix [19], [69]. This observation is further supported by the SEM results [19], [109], [110], where raw fibre surface was found to be covered with impurities , and in the fractured surface fibre pull - outs were observed in authors’ previous work [78]. In is notice able that 0. 5-hr treate d fibre/epoxy composite (0.5TBHFE) shows the highest E’ followed by that of 0.25-hr treated (0.25TBHFE) and 0.75-hr treated (0.75TBHFE) fibres reinforced epoxy samples, and 1TBHFE and 2TBHFE samples show least strength in the experiments . This can be attributed to the prolonged time of alkali treatment removes cellulose [28], [29], [69] , which deteriorates mechanical properties. At higher temperatures in the rubbery region, above 120˚C, all the alkali treated samples along with NE exhibit show more flexibility and have enhanced molecular mobility, except UBHFE; therefore, the influence of alkali treatment is evident . The findings are in good agreement with previous works, where sisal, jute, palm, banana reinforced epoxy [111], banana fibre reinforced epoxy [31], flax fibre reinforced epoxy [112], and sisal fibril reinforced epoxy [113] being used along with authors’ works [78]. Figure 6. Storage modulus-temperature plot. 3.2.2. Loss Modulus (E”) Loss modulus refers to the amount of energy released as heat during deformation or viscous reaction of materials. This property assesses the viscous behaviour of a material under stress. Figure 7 represents the loss modulus-temperature curve, where neat epoxy (NE) shows the least energy dissipation followed by all Borassus husk fibre/epoxy composites , where 1TBHFE exhibits the highest value of loss modulus. Adding Borassus husk to composites improves loss modulus, which follows a similar pattern as storage modulus [30], [78]. Nevertheless, 1 -hr treated husk fibre/epoxy shows the highest loss modulus followed by 0.25-hr and 0.75 -hr treated/epoxy composites and this has been found previously in authors own work [30]. The loss modulus curves demonstrated the highest mechanical energy dissipation, which decreased at higher temperatures due to the increased mobility of polymer chains [71], [73], [88], [114]. As the temperature rose, the polymer chains exhibited greater freedom of movement, leading to reduced energy dissipation. The E" value peak height was much larger for Borassus husk fibre/epoxy composites compared to neat epoxy (NE), indicating increased internal friction and energy dissipation [30]. The loss modulus of composites increased with the inclusion of Borassus husk fibre content, but decreased significantly during the rubbery stage. The glass transition temperature (Tg) calculated from the E” curve is provided in Table 3. The study found that Tg values derived from the loss modulus were more accurate than those obtained from damping factor [32], [71]. Thus, this is being crucial point for any materials to be suitable for engineering designs. The outcomes show good agreement with previous research works [58], [111], [115]-[117], although Shinoj et al [85] found that alkali treatment did not influence transition temperatures for oil palm fibre -based composites from the loss modulus. Figure 7. Loss modulus-temperature plot. 3.2.3. Damping factor (tan δ) The damping factor (tanδ) is the ratio of the loss modulus to the storage modulus (Eʹ/Eʺ). The damping factor may be used to assess the interlocking bonding of the fibre matrix as well as the curing behaviour of composites [54], [72] . This property is incredibly crucial for engineering applications, especially in aerospace and automotive, where material needs to sustain its integrity under the simultaneous effect of heat and mechanical load [2], [31], [71], [118]. Figure 8 illustrates the tanδ for all composites, where the untreated husk fibre/epoxy composite (UBHFE) shows the lowest value followed by neat epoxy (NE). Nonetheless, all of the husk fibre/epoxy displays a single peak, except UBHFE, indicating good interaction between fibre and matrix due to lower heterogeneity in the composite [30], [85]. For all the sam ples, up to the peak of the tanδ, damping factor increased with rising temperature, and after that, it dropped gradually with increasing temperature. Table 3 summarizes the damping factors for all the samples along with corresponding temperatures. The corresponding temperature with peak of tanδ is also considered as glass transition temperature, Tg, but this one is suggested for comparison purpose [90]. After this, material becomes soft and rubbery suggesting inter - molecular bond strength dropped drastically and material losses its load -bearing capability [56], [119], [120]. The order of damping factor (tanδ) of all composites: 0.75TBHFE > 0.5TBHFE > 1TBHFE > 0.25TBHFE > 2TBHFE > NE > UBHFE. It is noticeable that all the alkali -treated fibre/epoxy composites showed higher and enhancement in tanδ value than NE , and particularly, 0.75TBHFE and 0.5TBHFE exhibit the maximum values of 1.39 and 1.25, respectively, which found to be similar findings reported in authors’ previous works [30], [78]. Nevertheless, damping factors found to be higher than those of found in the literature for other biofibres -based composites, such as, 0.46 for jute /epoxy [54], 0.42 for woven flax reinfo rced epoxy [76], 0.86 for Borassus sprout reinforced epoxy [77], 0.43 for kenaf reinforced epoxy [86], 0.62 for date palm reinforced epoxy [57], 0.17 for ramie root reinforced polyester [58], and 0.58 for banana reinforced epoxy [31]. It is interesting to have found that after the alkali treatment, the adhesion property of Borassus husk fibre enhanced, resulting better interlocking characteristic between husk fibre and epoxy matrix that improves heat dissipation and load absorbing capacity of the treated sample, which also can be attributed to their impact and toughness, whereas, it has been found in the literature that after incorporating biofibres, such as, ramie, flax, jute, sisal, banana into polymeric resin that reduced the damping factor [56], [58], [72], [76], [77], [111], [112], [115], [121] -[123], although Richmond and co-researchers [93] found no considerable changes found in their work on bamboo fibre reinforced epoxy after 1% alkali treatment (NaOH). Untreated fibre/epoxy composite (UBHFE) results in decreased damping factor can be attributed to less matrix (volume) in composites and poor adhesion between resin and fibre as a result of fibre pulled out, which reduces vibration energy and fibre agglomeration [86], [119]. A larger peak indicates slower polymeric chain movement, resulting in increased crosslinking density for treated fibre/epoxy composites with improved interfacial interaction and energy dissipation ability [73], [74] . In contrast , neat epoxy (NE) and untreated husk fibre/epoxy (UBHFE) composites exhibit a lower d amping factor. This can be attributed to the heterogeneity of the mixture, limited ability to convert mechanical energy into heat and the thermal instability of the material [87]. This works show good agreement with previous studies including authors’ ones [30], [102], [115], [124], [125], although some found decreased value after the alkali-treatment [72]. Figure 8. Damping factor-temperature plot. 3.2.4. Glass transition temperature, Tg Tg may be calculated using numerous approaches, including the peaks of loss modulus (E") and tan δ from Figure 7 and Figure 8, respectively. Nonetheless, Tg determined by the peak E" (Figure 7) has been deemed more convincing and realistic than damping factor -derived ones [32], [71], [86]. Table 3 presents the data of Tg of all the samples, where Tg derived by E" was determined to be lower than that of tan δ curves, as evaluated by previous studies [72], [126], [127]. The data clearly indicates that incorporating untreated Borassus husk fibre into epoxy resin introduces heterogeneity. Additionally, the presence of hemicellulose and other impurities found [69] in the fibre may compromise the composite's integrity during DMA experiments [30], [78] . As a result, the composite exhibits a lower glass transition temperature (Tg), corresponding to the peak Eʺ, compared to neat epoxy. On the other hand, all the alkali-treated fibre/epoxy composites show higher values than neat epoxy because of improved ad hesion property between resin and fibre that also found in authors own works previously at different experimental conditions [30], [78]. The order of Tg values corresponding to loss modulus, E”, is provided below: 0.5TBHFE > 0.25TBHFE > 0.75TBHFE > 1TBHFE > 2TBHFE > NE > UBHFE. It has been found from the previous studies that after the alkali treatment, Borassus fibre shows enhanced thermal stability [69], [106] and better mechanical property [80], [81], [110]. 0.5-hr treated Borassus husk fibre/ epoxy (0.5TBHFE) shows the highest Tg value, 9 4.6˚C, corresponding to E”, which should be attributed to fibre intrinsic thermal stability found in author’s previous work [69], [78], compared to other samples [68], [69]. The glass transition temperature, Tg (from peak loss modulus), in this study for 0.5TBHFE found to be higher than those of found in the literature, such as, 70˚C for banana reinforced epoxy [31], 70˚ C for kenaf reinforced epoxy [86], 72.5˚ C for sisal, jute, banana, palm reinforced epoxy [111], 79˚ C for date palm reinforced epoxy [57] 79˚ C for palm sprouts reinforced epoxy [77], 74.8˚ C for woven flax reinforced epoxy [76] and 74.5˚ C for jute reinforced epoxy [54]. Nevertheless, it has also been found that Tg value was gradually decreasing for 0.75TBHFE (88.7°C), 1TBHFE (86°C) and 2TBHFE (84.6°C) with prolonged alkali-treatment, which can be associated with removal (or damage) of temperature resistant composition s, crystalline cellulose and lignin, in Borassus husk fibres [30], [78]. Table 3. Glass transition temperatures and damping factor of all composites. Samples Glass Transition Temperature, Tg (°C) Peak tanδ (Damping factor) Tg (°C) [from E”] Tg (°C) [from tan δ] NE 83.9 100.6 0.88 UBHFE 66.1 93.5 0.73 0.25TBHFE 89.8 97.2 1.05 0.5TBHFE 94.6 107.1 1.25 0.75TBHFE 88.7 100.6 1.39 1TBHFE 86.0 96.5 1.18 2TBHFE 84.6 95.0 1.00 3.2.5. Cole-Cole plot The Cole-Cole or Wicket plot provides useful insight into the connection between loss modulus (E”) and storage modulus (E’). In principle, perfect semi -circle curve means homogenous mixture between fibre and matrix, imperfect semi -circle refers to heteroge neous mixture between fibre and matrix, and irregular shaped curve represents nonhomogeneous mixture between fibre and matrix [58], [88], [114], [117]. Figure 9 shows plot for all the sample, where all the samples exhibit imperfect semi -circular shape compared to kenaf/epoxy composite [86], where it was found that with the perfect semi- circle, damping factor increased (0.43) so as Tg (70 ˚C) corresponding to loss modulus, E”. In this study, all alkali -treated Borassus fibre/epoxy show imperfect semi -circular shapes that refer to heterogeneity in adhesion resulting higher damping factor and energy ab sorbing property. Interestingly, 1TBHFE followed by 0.25TBHFE composites have greater Cole-Cole curves than the other composites, similar result reported by previous studies on flax fibre/epoxy [76] as well as date palm/epoxy [57] and they suggested that a widen curve indicates that strong interaction between fibre and matrix exists, resulting enhanced strength of the composites. In this study, NE followed by 2TBHFE showed the least curvature representing low impact properties comp ared to other alkali-treated composites , which was also found in authors’ previous work [30], [78] . A lkali treatments significantly increased fibre -matrix bonding, providing strong evidence. Figure 9. Cole-Cole plot. 3.2.6. Phase angle, Shear modulus and Total mass loss (TML)

exposed to temperature fluctuations and cyclic loading, such as vibrations, gradually dissipate internal energy, resulting in a loss of strength over time. This process can also lead to mass loss. With each vibration, intermolecular bonds weaken, causing molecules to shift from their original state to new configurations at a specific angle, known as the phase angle (δ). Under cyclic loading, polymers typically display viscous behaviour, with mol ecules shifting between positions [117], [128] . If a molecule does not undergo dislocation under applied mechanical or thermal load (loss modulus, Eʺ = 0), and only temporarily changes its shape, the phase (change) angle is 0°, indicating the material is fully elastic. In contrast, if the deformation is permanent (storage modulus, Eʹ = 0), the phase angle is 90°, signifying the material is fully plastic [87]. Materials that exhibit a combination of elastic and plastic behaviour are termed viscoelastic. For these materials, the phase angle lies between 1° and 89°, reflecting their ability to recover from plastic (permanent) deformation. This can influence the damping factor and Cole-Cole plot of any sample. Table 4 summarises all the data including phase (change) angle (δ), shear modulus (E*) and total mass loss (TML) for all samples at initial and peak loss modulus (Eʺ) conditions indicate that alkali -treated fibre/epoxy composites exhibit higher phase angles at peak Eʺ. The NE shows the least phase angle change , 17.9˚, followed by UBHFE (17.4˚), indicating its elastic nature compared to other alkali -treated f ibre/epoxy samples . The 0.25TBHFE showed the highest phase angle, 23.6˚, followed by other treated fibre/epoxy samples (Table 4). This suggests that treated fibre/epoxy composites possess superior viscoelastic properties compared to NE and UBHFE samples. Similarly, in the shear modulus, 0.75TBHFE shows the highest drop in shear modulus compared to other composite samples. This behaviour can be attributed to the high damping factors (1.39), Cole-Cole plot and loss modulus (E ”) found earlier from the DMA experiments. The outcomes in this study found to be consistence with authors ’ previous studies [30], [78]. Additionally, under the specified conditions, all the alkali-treated fibre/epoxy composites show less total mass loss, except 2-hr treated fibre/epoxy, 2TBHFE (0.58%), compared to neat epoxy, NE (50%). Nevertheless, 0.75-hr treated fibre/epoxy (0.75TBHFE) shows the lowest mass loss, 0.33%, followed by 0.5TBHFE (0.35%) . Hence, these samples should perform better in thermo-mechanical condition than NE. UBHFE found to be highest total mass loss of 1.22%, which can be attributed to the presence of moisture absorbing as well as weak composition, hemicellulose [91], [92], [129]. Table 4. Phase angles, shear modulus and TML of all composites. Samples Phase angle, δ (ͦ ) Shear Modulus, E* (MPa) Total mass loss, TML (%) Initial Phase angle, δi (ͦ ) Phase angle at E”, δg (ͦ ) Initial Shear Modulus, Ei* (MPa) Shear Modulus Eg*, at E” (MPa) NE 0.90 17.9 3190.5 979.5 0.50 UBHFE 1.44 17.4 3262.6 1225.8 1.22 0.25TBHFE 0.94 23.6 2821.9 947.8 0.44 0.5TBHFE 1.01 21.5 2975.8 936.4 0.35 0.75TBHFE 0.99 21.7 3219.0 980.8 0.33 1TBHFE 0.88 22.7 3189.9 1033.9 0.41 2TBHFE 0.94 21.4 2771.1 889.1 0.58 4. Conclusion In this study, composites were fabricated using the hand layup process, incorporating untreated (raw) and alkali-treated Borassus husk fibers as reinforcement in an epoxy resin matrix. The fibers underwent alkali treatment for varying durations, ranging from 0.25 to 2 hours. This research examines the thermal properties of the composites were analyzed following the ASTM E2550 standard. Additionally, the effects of elevated temperature on mechanical properties were assessed through dynamic mechanical analysis adhering ASTM D5418-01 standard. The

of these investigations are presented below:  TGA analysis reve aled a descent char residue (6.4 %) for NE. While incorporating untreated Borassus husk fibre into epoxy, char co ntent (9 .1%) increased , but after including alkali -treated fibres into epoxy , char contents (up to 11.5%) increased significantly, where 0.75TBHFE showed the highest value (11.5%). The gained values were found to be higher than jute/epoxy (5%), Borassus fine fibre/polypropylene (7%), jute/polypropylene (6%), sisal/polypropylene (2%), and competitive with ramie root reinforced polyester value (5 – 11%). This was due to Borassus husk fibre’s intrinsic thermal resistant property because of the presence of thermal resistant compositi ons, such as, cellulose and lignin in fibre.  The onset decomposition peak was found to be around 322 °C for NE and with the inclusion of Borassus husk fibre s (treated and untreated) into epoxy shifted the peak value to higher temperature (330°C).  The IPDT values for neat epoxy (NE) found to be around 487°C and raw Borassus husk fibre/epoxy found to be 529°C. Incorporating alkali -treated fibres into epoxy resin enhanced the IPDT value: t he highest value found to be 580°C for 0.75 TBHFE and least was for 525°C for 1TBHFE. This was due to the intrinsic thermal stability of Borassus husk fibre and after alkali treatment, it was enhanced further because of the removal of hemicellulose.  The IPDH value for UB HFE found to be 7.1 W/g and 6.7 W/g for NE. Nevertheless, after alkali-treatment, the lowest value found to be 4.4 W/g for 0.5TBHFE followed by 4.6 W/g for 0.75TBHFE.  The storage modulus increased with the incorporation of alkali-treated Borassus husk fibre in the epoxy composite (NE), surpassing that of polymer composites reinforced with other biofibres , such as sisal, flax, ramie root, jute, palm sprouts and banana. Similarly, the loss modulus values also increased with alkali-treated fibres, reaching the highest value in the 1 -hour a lkali-treated Borassus husk fibre/epoxy (1TBHFE) composite.  The glass transition temperature (Tg), corresponding to E”, was 83.9°C for neat epoxy (NE). With the addition of alkali-treated Borassus husk fibre, Tg increased significantly, reaching 94.6°C for 0.5TBHFE, the highest among the tested composites. Other alkali- treated samples also showed elevated Tg values, between 84°C and 90°C. However, the Tg dro pped to 66 °C for the untreated husk fibre/epoxy (UBHFE) composite. Furthermore, alkali-treated Borassus husk fibre/epoxy composites exhibited higher Tg values than composites reinforced with other biofibres, such as , kenaf (70°C), flax (74.7°C), jute (74.5°C), and banana (70°C). This indicates superior thermal stability, making Borassus fibre-reinforced epoxy composites more suitable for high-temperature applications.  The lowest tanδ value (0.73) was recorded for the untreated Borassus husk fibre/epoxy (UBHFE) composite. In contrast, the addition of alkali -treated fibres significantly increased the t anδ peak values. The highest values were observed in the 0. 75TBHFE (1.39) and 0.5TBHFE (1.25 ) composites, followed by 1TBHFE (1.18 ), 0.25TBHFE (1.05), and 2TBHFE (1.00), all of which surpassed NE (0.88 ). This superior damping performance indicates that alk ali-treated Borassus fibre/epoxy composites possess enhanced impact resistance compared to both neat epoxy and other bio -fibre composites.  Cole-Cole plot revealed all the samples show heterogeneity but 1 -hr alkali -treated Borassus fibre/epoxy composite (1TBHFE) reveals comparatively high curves to other samples that associated with better adhesion properties between epoxy resin and alkali- treated fibre.  Phase angle ( δ) data showed that all alkali -treated Borassus fibre/epoxy composites exhibited a greater change in phase angle from their initial state to the glass transition point, indicating their better viscoelastic nature. A similar trend was observed in the shear (complex) modulus, which can be attributed to the treated samples' enhanced toughness and impact properties.  Total mass loss (TML) is highest for UBHFE (1.22%) followed by 2TBHFE (0.58 %) composites, as well as NE (0.50%). In contrast, the lower TML values are observed in 0.75TBHFE (0.33%) and 0.5TBHFE (0.35%) composites, which is approximately 34% lower than that of neat epoxy (NE). This reduction can be attributed to the enhanced intrinsic thermal stability of the alkali-treated Borassus husk fibres. Alkali treatment enhances the thermal performance of Borassus husk fibre/epoxy composites, as evidenced by increased char content and improved integral process decomposition temperature (IPDT), particularly in the 0.75TBHFE sample. These treated composites exhibit superior energy dissipation and mechanical stiffness compared to neat epoxy (NE) and other bio-fibre composites. Their reduced total mass loss (TML), enhanced strength, and higher damping factor (tan δ) highlight their exceptional intrinsic thermal stability. Among the treated samples, the 0.5 -hour alkali -treated Borassus husk fibre/epoxy composite (0.5TBHFE) achieves an optimal balance between stiffness and damping, demonstrated by its high storage modulus (E’) and tan δ. This makes it a promising candidate for high-performance engineering applications, particularly in the aerospace and automotive industries, where mechanical strength, thermal stability, and impact resistance are critical. However, bio -fibre properties can vary significantly due to environmental conditions, geographic origin, and fibre maturity. Further research is required to improve their performance and consistency. Additionally, while Borassus flabellifer husk is locally abundant, developing an efficient collection and supply ch ain system is crucial for supporting la rge-scale industrial production.

[1] N. Mazlan, S. M. Sapuan and R. A. Ilyas, Advanced Composites in Aerospace Engineering Applications. 2022. [2] J. Silva et al , "Cork: Is it a good material for aerospace structures?" in 52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference 19th AIAA/ASME/AHS Adaptive Structures Conference 13t, 2011, . [3] UN Environment, "Nations must go further th an current paris pledges or face global warming of 2.5-2.9C," UN Environment, Kenya, Nov 20. 2023. [4] J. Dinneen, "Satellite launched to track down leaks of potent greenhouse gas," NewScientist, Mar 4. 2024. [5] B. Plumer, "Climate Change Is Speeding Toward Catastrophe. The Next Decade Is Crucial, U.N. Panel Says," NYTimes.Com Feed, 2023. Available: https://global.factiva.com/en/du/article.asp?accessionno=NYTFEED020230320ej3k002pb. [6] E. Council, "Paris agreement on climate change," Oct 17. 2023. [7] N. M. Nurazzi et al, "A review on mechanical performance of hybrid natural fiber polymer composites for structural applications," Polymers, vol. 13, (13), pp. 2170, 2021. . [8] M. M. Reddy et al, "Biobased plastics and bionanocomposites: Current status and future opportunities," Progress in Polymer Science, vol. 38, (10), pp. 1653–1689, 2013. Available: https://www.sciencedirect.com/science/article/pii/S0079670013000476. DOI: 10.1016/j.progpolymsci.2013.05.006. [9] A. S. Getme and B. Patel, "A review: Bio -fiber’s as reinforcement in composites of polylactic acid (PLA)," Materials Today: Proceedings, vol. 26, pp. 2116–2122, 2020. . [10] M. J. John and S. Thomas, "Biofibres and biocomposites," Carbohydr. Polym., vol. 71, (3), pp. 343–364, 2008. . [11] K. L. Pickering, M. A. Efendy and T. M. Le, "A review of recent developments in natural fibre composites and their mechanical performance," Composites Part A: Applied Science and Manufacturing, vol. 83, pp. 98–112, 2016. . [12] A. K. Mohanty, M. Misra and L. T. Drzal, "Sustainable bio -composites from renewable resources: opportunities and challenges in the green materials world," Journal of Polymers and the Environment, vol. 10, pp. 19–26, 2002. . [13] H. Chandekar, V. Chaudhari and S. Waigaonkar, "A review of jute fiber reinforced polymer composites," Materials Today: Proceedings, vol. 26, pp. 2079–2082, 2020. . [14] A. Karimah et al , "A review on natural fibers for development of eco -friendly bio - composite: characteristics, and utilizations," Journal of Materials Research and Technology, vol. 13, pp. 2442–2458, 2021. . [15] C. W. Nguong, S. Lee and D. Sujan, "A review on natural fibre reinforced polymer composites," International Journal of Materials and Metallurgical Engineering, vol. 7, (1), pp. 52–59, 2013. . [16] Ş Yıldızhan et al, "Bio-composite materials: a short review of recent trends, mechanical and chemical properties, and applications," European Mechanical Science, vol. 2, (3), pp. 83– 91, 2018. . [17] V. S. Ramachandran, K. Swarupanandan and C. Renuka, "A traditional irrigation system using palmyra palm (Borassus flabellifer) in Kerala, India," Palms, vol. 48, (4), pp. 175–181, 2004. . [18] K. Pipatchartlearnwong et al, "Genetic evidence of multiple invasions and a small number of founders of Asian Palmyra palm (Borassus flabellifer) in Thailand," BMC Genetics, vol. 18, (1), pp. 1–8, 2017. . [19] M. A. Rahman, M. Ndiaye and B. Weclawski, "Palmyra Palm Shell (Borassus flabellifer) Properties Part 1: Insights into Its Physical and Chemical Properties," Authorea Preprints, 2024. . DOI: 10.22541/au.173514453.33906268/v1. [20] M. Afroza Khatun et al, "Physical, mechanical, thermal and morphological analysis of date palm mat (DPM) and palmyra palm fruit (PPF) fiber reinforced high density polyethylene hybrid composites," Advanced Materials Science, vol. 4, pp. 1–6, 2019. . [21] A. A. Mamun et al , "Assessing riverbank erosion and livelihood resilience using traditional approaches in northern Bangladesh," Sustainability, vol. 14, (4), pp. 2348, 2022. . [22] R. Ramanath, "Odisha: ‘Lightning dea ths linked to palm tree felling’ ," The Times of India, India, Sep 5. 2023. [23] T. R. Krishnaveni et al, "Potential review on palmyra (Borassus Flabellifer L.)," Advances in Research, vol. 21, (9), pp. 29–40, 2020. . [24] M. Z. Khan and B. A. Al Shoumik, "Land degradation neutrality concerns in Bangladesh," Soil Security, vol. 9, pp. 100075, 2022. . [25] S. H. Patwary, "Stop extinction of babui, the weaver bird," Daily Sun, Bangladesh, Aug 22. 2019. [26] P. Jagadeesh et al, "A review on extraction, chemical treatment, characterization of natural fibers and its composites for potential applications," Polymer Composites, vol. 42, (12), pp. 6239–6264, 2021. . [27] X. Li, L. G. Tabil and S. Panigrahi, "Chemical treatments of natural fiber for use in natural fiber-reinforced composites: a review," Journal of Polymers and the Environment, vol. 15, pp. 25–33, 2007. . [28] P. Sahu and M. K. Gupta, "A review on the properties of natural fibres and its bio - composites: Effect of alkali treatment," Proceedings of the In stitution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications, vol. 234, (1), pp. 198–217, 2020. . [29] P. C. Akubue, P. K. Igbokwe and J. T. Nwabanne, "Production of kenaf fibre reinforced polyethylene composite for ballistic protection," Int.J.Sci.Eng.Res, vol. 6, (7), 2015. . [30] M. A. Rahman et al, "Effect of Alkali Treatment on Dynamic Mechanical Properties of Borassus Flabellifer Husk Fibre Reinforced Epoxy Composites," 2025. . [31] T. Murugan and B. S. Kumar, "Studies on mechanical and dynamic mechanical properties of banana fibre nonwoven composite," Materials Today: Proceedings, vol. 39, pp. 1254–1258, 2021. . [32] M. Jawaid et al, "Effect of jute fibre loading on tensile and dynamic mechanical properties of oil palm epoxy composites," Composites Part B: Engineering, vol. 45, (1), pp. 619–624, 2013. Available: https://www.sciencedirect.com/science/article/pii/S1359836812003071. DOI: 10.1016/j.compositesb.2012.04.068. [33] A. Amiri et al , "The potential of natural composite materials in structural desig n," in Sustainable Composites for Aerospace ApplicationsAnonymous 2018, . [34] A. Tiwary, R. Kumar and J. S. Chohan, "A review on characteristics of composite and advanced materials used for aerospace applications," Materials Today: Proceedings, vol. 51, pp. 865–870, 2022. . [35] J. M. Silva et al, "Exploring the use of cork based composites for aerospace applications," in Materials Science Forum, 2010, . [36] C. V. d. Santos et al, "Materials selection for sustainable executive aircraft interiors,"

Research, vol. 19, pp. 339–352, 2016. . [37] X. Zhang, Y. Chen and J. Hu, "Recent advances in the development of aerospace materials," Prog. Aerospace Sci., vol. 97, pp. 22–34, 2018. . [38] P. Balakrishnan et al, "Natural fibre and polymer matrix composites and their applications in aerospace engineering," in Advanced Composite Materials for Aerospace EngineeringAnonymous 2016, . [39] O. Boegler et al, Potential of Sustainable Materials in Wing Structural Design. 2015. [40] R. A. Ilyas et al, "Potential of natural fibre composites for transport industry: A review," in Prosiding Seminar Enau Kebangsaan, 2019, . [41] A. Żarnowska, "Sustainability Assessment of a Sustainable Innovation for the Aviation Industry: Case Study of Bio Composites for Aircraft Interiors," 2023. . [42] C. Narasimha, "Designing Bio-based Materials," . [43] M. Z. Rahman et al, "Advanced biopolymers for automobile and aviation engineering applications," Journal of Polymer Research, vol. 30, (3), pp. 106, 2023. . [44] D. Bhadra and N. R. Dhar, "Selection of the natural fiber for sustainable applications in aerospace cabin interior using fuzzy MCDM model," Materialia, vol. 21, pp. 101270, 2022. . [45] J. Njuguna and K. Pielichowski, "The role of advanced polymer materials in aerospace," Res.Gate, vol. 148, 2013. . [46] D. Locatelli, S. B. Mulani and R. K. Kapania, "Wing -box weight optimization using curvilinear spars and ribs (SpaRibs)," J. Aircr., vol. 48, (5), pp. 1671–1684, 2011. . [47] K. A. Henschel, "Biocomposites in Aviation Structures on the Example of Flax and its Hybrids," Biocomposites in Aviation Structures on the Example of Flax and its Hybrids, 2019. . [48] J. Bachmann et al , "Towards a circular economy in the aviation sec tor using eco - composites for interior and secondary structures. Results and recommendations from the EU/China project ECO-COMPASS," Aerospace, vol. 8, (5), pp. 131, 2021. . [49] O. Boegler et al, Potential of Sustainable Materials in Wing Structural Design. 2015. [50] M. C. Kuşhan, S. Gürgen and M. A. Sofuoğlu, Materials, Structures and Manufacturing for Aircraft. 2022. [51] M. Syduzzaman et al , "Plant -based natural fibre reinforced composites: A review on fabrication, properties and applications," Coatings, vol. 10, (10), pp. 973, 2020. . [52] I. Elfaleh et al, "A comprehensive review of natural fibers and their composites: an eco - friendly alternative to conventional materials," Results in Engineering, pp. 101271, 2023. . [53] K. P. Menard and N. R. Menard, "Thermomechanical Analysis," Dynamic Mechanical Analysis, pp. 69, 2020. . DOI: 10.1201/9780429190308-4. [54] M. K. Gupta and R. K. Srivastava, "Mechanical, thermal and dynamic mechanical analysis of jute fibre reinforced epoxy composite," 2017. . [55] M. J. M. Ridzuan et al , "Thermal behaviour and dynamic mechanical analysis of Pennisetum purpureum/glass-reinforced epoxy hybrid composites," Composite Structures, vol. 152, pp. 850 –859, 2016. Available: https://www.sciencedirect.com/science/article/pii/S026382231630890X. DOI: 10.1016/j.compstruct.2016.06.026. [56] K. M. Nair, S. Thomas and G. Groeninckx, "Thermal and dynamic mechanical analysis of polystyrene compo sites reinforced with short sisal fibres," Composites Sci. Technol., vol. 61, (16), pp. 2519–2529, 2001. . [57] M. H. Gheith et al, "Flexural, thermal and dynamic mechanical properties of date palm fibres reinforced epoxy composites," Journal of Materials Research and Technology, vol. 8, (1), pp. 853–860, 2019. . [58] T. VarunKumar et al, "An examining the static and dynamic mechanical characteristics of milled ramie root reinforced polyester composites," Scientific Reports, vol. 13, (1), pp. 17054, 2023. . [59] S. Olhan et al , "Mechanical, thermal, and viscoelastic behavior of sisal fibre -based structural composites for automotive applications: Experimental and FEM analysis," Composite Structures, vol. 322, pp. 117427, 2023. . [60] S. Kumar et al, "Thermogravimetric analysis of lignocellulosic leaf-based fiber-reinforced thermosets polymer composites: an overview," Biomass Conversion and Biorefinery, vol. 14, (12), pp. 12673–12698, 2024. . [61] V. S. Hiremath et al, "Thermal degradation and fire retardant behaviour of natural fibre reinforced polymeric composites -A comprehensive review," Journal of Materials Research and Technology, 2024. . [62] J. S. Neto et al, "A review on the thermal characterisation of natural and hybrid fiber composites," Polymers, vol. 13, (24), pp. 4425, 2021. . [63] N. Nurazzi et al , "Thermogravimetric analysis properties of cellulosic natural fiber polymer composites: A review on influence of chemical treatments," Polymers, vol. 13, (16), pp. 2710, 2021. . [64] M. Asyraf et al, "Thermal properties of oil palm lignocellulosic fibre reinforced polymer composites: a comprehensive review on thermogravimetry analysis," Cellulose, vol. 30, (5), pp. 2753–2790, 2023. . [65] S. Kumar et al, "Thermogravimetric analysis of lignocellulosic leaf-based fiber-reinforced thermosets polymer composites: an overview," Biomass Conversion and Biorefinery, vol. 14, (12), pp. 12673–12698, 2024. . [66] S. Park et al, "Thermal stability of imidized epoxy blends initiated by N-benzylpyrazinium hexafluoroantimonate salt," Macromolecules, vol. 34, (22), pp. 7573–7575, 2001. . [67] C. D. Doyle, "Estimating thermal stability of experimental polymers by empirical thermogravimetric analysis," Anal. Chem., vol. 33, (1), pp. 77–79, 1961. . [68] C. Chiang, R. Chang and Y. Chiu, "Thermal stability and degradation kinetics of novel organic/inorganic epoxy hybrid containing nitrogen/silicon/phosphorus by sol –gel method," Thermochimica Acta, vol. 453, (2), pp. 97 –104, 2007. Available: https://www.sciencedirect.com/science/article/pii/S0040603106005661. DOI: 10.1016/j.tca.2006.11.013. [69] M. A. Rahman et al, "Palmyra Palm Shell (Borassus flabellifer) Properties Part 3: Insights into Its Morphological, Chemical and Thermal Properties after Alkali Treatment," 2024. . DOI: 10.22541/au.173557633.34492875/v1. [70] M. A. Rahman et al, "Palmyra Palm Shell (Borassus flabellifer) Properties Part 2: Insights into Its Thermal and Mechanical Properties," Authorea Preprints, 2024. . DOI: 10.22541/au.173498231.12031245/v1. [71] N. Saba et al, "A review on dynamic mechanical properties of natural fibre rei nforced polymer composites," Constr. Build. Mater., vol. 106, pp. 149–159, 2016. . [72] S. H. Aziz and M. P. Ansell, "The effect of alkalization and fibre alignment on the mechanical and thermal properties of kenaf and hemp bast fibre composites: Part 1 –polyester resin matrix," Composites Sci. Technol., vol. 64, (9), pp. 1219–1230, 2004. . [73] N. I. N. Haris et al, "Dynamic mechanical properties of natural fiber reinforced hybrid polymer composites: a review," Journal of Materials Research and Technology, vol. 19, pp. 167–182, 2022. . [74] P. J. Herrera -Franco and A. Valadez -Gonzalez, "Mechanical properties of continuous natural fibre -reinforced polymer composites," Composites Part A: Applied Science and Manufacturing, vol. 35, (3), pp. 339–345, 2004. . [75] A. Manral and P. K. Bajpai, "Effect of chemical treatment on impact strength and dynamic thermal properties of Jute/PLA composites," Materials Today: Proceedings, vol. 34, pp. 546– 549, 2021. . [76] S. V. Kumar et al, "Mechanical, DMA and Sound Acoustic b ehaviour of Flax woven fabric reinforced Epoxy composites," Materials Research Express, vol. 7, (8), pp. 085302, 2020. . [77] A. J. K. S. Ram, M. A. Kumar and M. I. Reddy, "Dynamic mechanical analysis of Asian Palmyra Sprouts fiber reinforced epoxy composi tes," International Research Journal of Engineering and Technology (IRJET), vol. 5, (7), pp. 183–187, 2018. . [78] M. A. Rahman et al, "Optimizing Borassus Husk Fibre/Epoxy Composites: A Study on Physical, Thermal, Flexural and Dynamic Mechanical Performan ce," 2025. . DOI: 10.22541/au.174102783.30560324/v1. [79] P. Sudhakara et al, "Fabrication of Borassus fruit lignocellulose fiber/PP composites and comparison with jute, sisal and coir fibers," Carbohydr. Polym., vol. 98, (1), pp. 1002–1010, 2013. . [80] L. Boopathi, P. S. Sampath and K. Mylsamy, "Investigation of physical, chemical and mechanical properties of raw and alkali treated Borassus fruit fiber," Composites Part B: Engineering, vol. 43, (8), pp. 3044–3052, 2012. . [81] K. O. Reddy, B. R. Guduri an d A. V. Rajulu, "Structural characterization and tensile properties of borassus fruit fibers," J Appl Polym Sci, vol. 114, (1), pp. 603–611, 2009. . [82] K. Dash et al , "Compressive characterization of different chemically treated Borassus flabellifer fruit fibers," SPE Polymers, vol. 5, (2), pp. 127–135, 2024. . [83] ASTM E2550-17, "Standard Test Method for Thermal Stability by Thermogravimetry," 2017. . [84] S. Wang et al, "Research of specific heat capacities of three large seaweed biomass," Journal of Thermal Analysis and Calorimetry, vol. 115, pp. 2071–2077, 2014. . [85] S. Shinoj et al, "Dynamic mechanical properties of oil palm fibre (OPF)-linear low density polyethylene (LLDPE) biocomposites and study of fibre –matrix interactions," Biosystems Engineering, vol. 109, (2), pp. 99–107, 2011. . [86] N. Saba et al, "Dynamic mechanical properties of oil palm nano filler/kenaf/epoxy hybrid nanocomposites," Constr. Build. Mater., vol. 124, pp. 133–138, 2016. . [87] K. P. Menard and N. Menard, Dynamic Mechanical Analysis. 2020. [88] B. Rashid et al, "Dynamic mechanical analysis of treated and untreated sugar palm fibre- based phenolic composites," BioResources, vol. 12, (2), pp. 3448–3462, 2017. . [89] K. Singh, Engineering Mathematics through Applications. 2019. [90] D. ASTM, "Standard test method for glass transition temperature (DMA Tg) of polymer matrix composites by dynamic mechanical analysis (DMA)," PA, 2008. [91] M. M. Kabir et al, "Effects of chemical tre atments on hemp fibre structure," Appl. Surf. Sci., vol. 276, pp. 13–23, 2013. . [92] A. Brígida et al, "Effect of chemical treatments on properties of green coconut fiber," Carbohydr. Polym., vol. 79, (4), pp. 832–838, 2010. . [93] T. Richmond et al, "Physical and dynamic mechanical properties of continuous bamboo reinforcement/bio-based epoxy composites," Materials Research Express, vol. 9, (1), pp. 015505, 2022. . [94] N. Saba et al, "A review on flammability of epoxy polymer, cellulosic and non‐cellulosic fiber reinforced epoxy composites," Polym. Adv. Technol., vol. 27, (5), pp. 577–590, 2016. . [95] M. R. Sanjay et al , "A comprehensive review of techniques for natural fibers as reinforcement in composites: Preparation, processing and characterization," Carbohydr. Polym., vol. 207, pp. 108–121, 2019. . [96] G. Rangasamy et al, "An extensive analysis of mechanical, thermal and physical properties of jute fiber composites with different fiber orientations," Case Studies in Thermal Engineering, vol. 28, pp. 101612, 2021. . [97] P. P. Das and V. Chaudhary, "Moving towards the era of bio fibre based polymer composites," Cleaner Engineering and Technology, vol. 4, pp. 100182, 2021. . [98] M. J. John and S. Thomas, "Biofibres and biocomposites," Carbohydr. Polym., vol. 71, (3), pp. 343–364, 2008. . [99] J. Rath et al, "Heat of wood pyrolysis," Fuel, vol. 82, (1), pp. 81–91, 2003. . [100] B. N. Dukkipati, B. G. Rao and V. S. T. Putti, "A Comprehensive Examination of Polymer Composites Reinforced with Lignocellulos e Fibers from Borassus Flabellifer: A Review," 2023. . [101] A. Jerry, "A comprehensive review on the medicinal properties of Borassus flabellifer," Journal of Academia and Industrial Research, vol. 7, (7), pp. 93–97, 2018. . [102] S. Manoharan et al, "Effect of short fiber reinforcement on mechanical properties of hybrid phenolic composites," Journal of Materials, vol. 2014, (1), pp. 478549, 2014. . [103] G. P. Bernardes, M. de Prá Andrade and M. Poletto, "Effect of alkaline treatment on the thermal stabil ity, degradation kinetics, and thermodynamic parameters of pineapple crown fibres," Journal of Materials Research and Technology, vol. 23, pp. 64–76, 2023. . [104] K. O. Reddy et al , "Effect of chemical treatment and fiber loading on mechanical properties of borassus (toddy palm) fiber/epoxy composites," International Journal of Polymer Analysis and Characterization, vol. 20, (7), pp. 612–626, 2015. . [105] K. Obi Reddy et al , "Mechanical and physical characterization of sodium hydroxide treated Borassus fruit fibers," Journal of Forestry Research, vol. 23, pp. 667–674, 2012. . [106] G. R. Chilukoti et al, "Study of Alkali Treatment and Its Influence on Characteristics of Borassus Palm Fiber," Journal of Natural Fibers, vol. 19, (16), pp. 14951–14962, 2022. . [107] Y. N. Marathe et al, "Borassus powder‐reinforced poly (lactic acid) composites with improved crystallization and mechanical properties," J Appl Polym Sci, vol. 136, (18), pp. 47440, 2019. . [108] J. K. Singh, A. K. Rout and K. Kumari, "A review on Borassus flabellifer lignocellulose fiber reinforced polymer composites," Carbohydr. Polym., vol. 262, pp. 117929, 2021. . [109] K. S. Saravanya, S. Kavitha and M. Parthiban, "Thermal properties of natural fibres extracted from Palmyra sprouts," Indian Journal of Fibre & Textile Research (IJFTR), vol. 45, (4), pp. 488–494, 2021. . [110] K. Obi Reddy et al, "Tensile and structural characterization of alkali treated Borassus fruit fine fibers," Composites Part B: Engineering, vol. 44, (1), pp. 433–438, 2013. Available: https://www.sciencedirect.com/science/article/pii/S1359836812003654. DOI: 10.1016/j.compositesb.2012.04.075. [111] S. S. Kumar et al , "Stat ic and dynamic mechanical analysis of hybrid natural fibre composites for engineering applications," Biomass Conversion and Biorefinery, vol. 14, (13), pp. 14889–14901, 2024. . [112] Y. Shen et al , "Dynamic mechanical analysis on delaminated flax fiber rei nforced composites," Materials, vol. 12, (16), pp. 2559, 2019. . [113] S. Nimanpure et al, "Electrical and dynamic mechanical analysis of sisal fibril reinforced epoxy composite," IEEE Trans. Dielectr. Electr. Insul., vol. 25, (5), pp. 2020–2028, 2018. . [114] M. K. Gupta and R. Singh, "Flexural and dynamic mechanical analysis (DMA) of polylactic acid (PLA) coated sisal fibre reinforced polyester composite," Materials Today: Proceedings, vol. 5, (2), pp. 6109–6114, 2018. . [115] E. Bisanda and M. P. Ansell , "The effect of silane treatment on the mechanical and physical properties of sisal-epoxy composites," Composites Sci. Technol., vol. 41, (2), pp. 165– 178, 1991. . [116] L. A. Pothan et al, "Effect of chemical modification on the mechanical and electrical properties of banana fiber polyester composites," J. Composite Mater., vol. 41, (19), pp. 2371– 2386, 2007. . [117] A. Palanivel et al, "Dynamic mechanical analysis and crystalline analysis of hemp fiber reinforced cellulose filled epoxy composite," Polímeros, vol. 27, (4), pp. 309–319, 2017. . [118] N. Mazlan et al , "Biocomposites as Aircraft Materials," Sustainable Materials and Manufacturing Techniques in Aviation, pp. 27–53, 2024. . [119] A. A. Mohammed et al, "Effect of sugar palm fibers on the properties of blended wheat starch/polyvinyl alcohol (PVA)-based biocomposite films," Journal of Materials Research and Technology, vol. 24, pp. 1043–1055, 2023. . [120] J. R. Sarasua and J. Pouyet, "Dynamic mechanical behavior and interphase adhesion of thermoplastic (PEEK, PES) short fiber composites," J. Thermoplast. Compos. Mater., vol. 11, (1), pp. 2–21, 1998. . [121] T. Venkategowda, L. H. Manjunatha and P. R. Anilkumar, "Dynamic mechanical behavior of natural fibers reinforced polymer matrix composites–A review," Materials Today: Proceedings, vol. 54, pp. 395–401, 2022. . [122] M. K. Gupta and R. K. Srivastava, "Effect of sisal fibre loading on dynamic mechanical analysis and water absorption behaviour of jute fibre epoxy composite," Materials Today: Proceedings, vol. 2, (4-5), pp. 2909–2917, 2015. . [123] M. Z. Rahman, "Mechanical and damping performances of flax fibre composites –A review," Composites Part C: Open Access, vol. 4, pp. 100081, 2021. . [124] J. Militký and A. Jabbar, "Comparative evaluation of fiber treatments on the creep behavior of jute/green epoxy composites," Composites Part B: Engineering, vol. 80, pp. 361– 368, 2015. . [125] Y. Li, Y. Mai and L. Ye, "Effects of fibre surface treatment on fracture -mechanical properties of sisal-fibre composites," Composite Interfaces, vol. 12, (1-2), pp. 141–163, 2005. . [126] S. Deng, M. Hou and L. Ye, "Temperature-dependent elastic moduli of epoxies measured by DMA and their correlations to mechanical testing data," Polym. Test., vol. 26, (6), pp. 803– 813, 2007. . [127] A. Shalwan and B. F. Yousif, "In state of art: mechanical and tribological behaviour of polymeric composites based on natural fibres," Mater Des, vol. 48, pp. 14–24, 2013. . [128] S. Dong and R. Gauvin, "Application of dynamic mechanical ana lysis for the study of the interfacial region in carbon fiber/epoxy composite materials," Polymer Composites, vol. 14, (5), pp. 414–420, 1993. . [129] N. Sweygers et al, "Prediction of the equilibrium moisture content based on the chemical composition and crystallinity of natural fibres," Industrial Crops and Products, vol. 186, pp. 115187, 2022. .