Effect of plant-based fillers on the mechanical,thermal,water absorption and morphological properties of hybrid composites

Abstract

Incorporation of filler materials in polymer composites have gained due to their superior qualities such as improved properties. The objective of the work is to study the effect of plant-based fillers, such as Rice Husk (RH), Wheat Husk (WH), and Wood Dust (WD) on the mechanical and morphological properties of Jute(J)/Glass(G)/Epoxy composites. Five layers with same stacking sequence of G/J/G/J/G were occupied in the sample. Fiber and matrix ratio were maintained as 30/70 (wt.%). Three different (1%, 3%, and 5%) wt.% of natural fillers were incorporated to investigate the effects on characterization of ten different samples (RH1, RH3, RH5, WH1, WH3, WH5, WD1, WD3, WD5, and NF). In case of mechanical characterization, WH3 exhibited the highest tensile strength of 70.25 MPa, RH3 showed the best result with the value of flexural strength of 160.04 MPa, WD3 showed strongest impact resistance, measuring at 12.293 J/cm², and RH5 provided better hardness of 76 HRB. In case of thermal characterization, WH3 sample losses its weight considerably in a faster than other samples, the maximum decompositions rate has been recorded at the temperature of 443 °C for the WD5 sample, and WD5 showed the best exothermic phenomenon. In FT-IR analysis, it was found that the RH5 sample showed less transmittance than all other samples. All WH samples provided better water absorption capability than others. SEM analysis showed that the fiber diameter was found around 20 µm and showed that filler materials were dispersed though some voids are observed due to agglomeration of the particles.

Keywords

rice husk wheat husk wood dust jute/glass fiber characterization

Highlights

• Plant-based fillers improve mechanical traits of hybrid epoxy composites.

• WH3 sample showed highest tensile strength among all composite variants.

• RH3 and WD3 exhibited best flexural strength and impact resistance, respectively.

• WD5 sample demonstrated superior thermal stability and exothermic behavior.

• SEM and FTIR confirmed filler dispersion, despite minor agglomeration issues.

1. Introduction

Composite materials are now widely used in engineering application because they provide a combination of light weight and high strength. In 2024 the global market value of composites crossed 120 billion dollars, with much of the growth linked to their use in cars, aircraft, and construction.¹ One important development is the move towards hybrid composites, where two or more reinforcements are added to the same matrix. This approach can improve properties beyond what a single reinforcement can achieve. For instance, combining flax and sisal fibers increased tensile strength by about 30% and more than doubled flexural strength compared with single-fiber composites.² Besides, it was found that the hybrid rattan/bamboo fiber composite (RBFC) exhibited approximately 29% and 17% higher flexural strength, and 29% and 78% higher impact strength compared with the bamboo fiber composite (BFC) and rattan fiber composite (RFC), respectively, demonstrating clear hybridization benefits in load-bearing performance.^3,4

Despite the remarkable mechanical performance of composites reinforced with synthetic fillers such as glass fiber, carbon fiber, metal oxides filler,⁵ and mineral powders, these materials pose several challenges.⁶ Their relatively high density negates the lightweight benefits of polymer matrices, and they are costly, frequently making up as much as 70% of overall production costs. In addition, they come from non-renewable resources, which causes problems for the environment and the economy. As a result, scientists are increasingly looking at natural and bio-based fillers as potential alternatives. When compared to their synthetic counterparts, life-cycle assessments have shown that bio-based composites can lower environmental impact by up to 40%.^7,8

Plant-derived byproducts and agricultural leftovers have become viable natural filler sources for polymer composites. Renewability, biodegradability, low density, affordability, and a small environmental impact have drawn interest in materials such rice husk, jute, banana fiber, kenaf, teak wood dust, tamarind shell powder, and cashew nutshells.^9,10 When correctly distributed and connected with polymer matrices, these agro-waste fillers have the ability to provide mechanical reinforcement in addition to aiding in waste management and resource efficiency.

Several studies have shown that almond shell filler (ASF) in jute composites improves tensile, flexural, impact, and shear strength, with the optimum performance achieved at 3 wt.% due to enhanced bonding and reduced void formation.¹¹ Similarly, the addition of nano clay in jute/E-glass composites also gave higher tensile, flexural, and impact strength, with specific formulations achieving peak performance.¹² Cashew nutshell filler between 10 and 30 vol% improved both strength and thermal stability, although excessive addition acted as a degradation barrier.¹³ Surface modification techniques have also been employed to improve fiber–matrix adhesion. Sodium bicarbonate treatment of Phoenix sp. Fibers, for example, resulted in higher tensile and flexural strengths,¹⁴ while the incorporation of small quantities of graphene in kenaf/glass/epoxy composites further improved mechanical performance.¹⁵

Among various agricultural fillers, rice husk (RH) has been extensively investigated due to its abundance and silica-rich structure. Studies indicate that RH can enhance tensile and flexural properties in hybrid composites, though it may reduce impact strength owing to its brittleness.^16,17 Rice husk-derived silicon carbide has improved erosion resistance and shear strength in jute-epoxy systems.^18,19 In epoxy-polyurethane matrices, rice husk and jute together increased electrical resistivity but reduced mechanical strength.²⁰ Chemical treatments have been applied to improve water resistance, though they can also reduce overall strength.²¹ An optimal filler content of approximately 10% rice husk has been reported as the most effective content for balancing tensile and flexural performance.²²

Wood dust (WD) fillers, particularly those from Rosewood and Padauk species, have shown significant potential in enhancing the mechanical and thermal characteristics of jute/epoxy composites. Padauk dust was found to provide better mechanical reinforcement, whereas Rosewood dust improved thermal stability.²³ In polyester-based composites, WD increased both tensile and flexural strength,²⁴ while approximately 30 wt.% loading was identified as optimal for construction-oriented jute composites.²⁵ Moreover, WD has been effectively utilized in polyurethane shoe soles²⁶ and hybrid systems with jute, banana fiber, and eggshell filler, where improvements in strength and water resistance were observed.²⁷ Optimization studies further revealed that 10 wt.% WD content yields the best overall mechanical performance.²⁸

Although wheat husk (WH) has been less extensively studied, recent investigations suggest that its incorporation into epoxy–polyurethane hybrid composites can enhance electrical and moisture resistance. However, compared with pure jute composites, WH-filled systems tend to exhibit slightly lower tensile and flexural strengths.²⁰

Although several studies have explored the incorporation of agricultural by-products such as rice husk, wood dust, and wheat husk into polymer composites, most previous works have focused either on a single filler type or limited mechanical characterization.^29–32 The majority of these investigations emphasized tensile and flexural behavior but often overlooked comprehensive evaluations of thermal stability, morphological characteristics. Furthermore, variations in filler particle size, distribution, and surface chemistry were rarely correlated with their influence on both strength and durability. In many cases, the dispersion of fillers within the matrix was not optimized, leading to inconsistent interfacial bonding and unpredictable property trends.

The novelty of the present study lies in its systematic and comparative assessment of the morphological, mechanical (tensile, flexural, impact, and hardness), and thermal (TGA, DSC) behaviors of jute/glass fiber–reinforced epoxy composites incorporated with three distinct agricultural fillers such as rice husk, wheat husk, and wood dust at different weight ratios (1%, 3%, and 5%). The results aim to show which filler provides the most balanced performance and to support the development of stronger and more sustainable composites.

2. Materials and methods

2.1. Materials

The reinforcing (jute and E-glass fibers) and matrix (resin) ingredients were the two primary composite components utilized in this work. The epoxy resin and hardener were obtained from a local supplier. Jute fiber mat with fiber orientation of (0°/90°) was collected from the local market. For composite fabrication, the mat size of 305 mm × 305 mm. Was cut from the yarn. Glass fiber mat was collected from the local vendor and was prepared for the same size as jute fiber. Typical properties of jute fiber are listed in Table 1.

Table 1.

Properties of collected jute fiber.

Properties	Jute fiber
Density (kg/m³)	1400
Diameter (µm)	25.2
Tensile strength (MPa)	393–773
Tensile modulus (GPa)	10–30
% Elongation	1.5–1.8

Rice Husk (RH), Wheat Husk (WH), and Wood Dust (WD), all of the plant-based filler materials have been collected from the local market (Figure 1).

Jute Fiber, Glass Fiber, Epoxy, Hardner, and plant-based fillers components were utilized in the investigation to prepare the hybrid composite. Table 2 shows the properties of resin and hardener.

Table 2.

Properties of epoxy resin and hardener.

Properties	Hardener	Epoxy resin
Appearance	Clear liquid	Clear liquid
Tensile modulus (GPa)	–	0.3–0.6
Density kg/m³	1200-1250	1150-1200
Tensile strength (MPa)	–	83–93
Viscosity at 25^○C (mPa.s)	50–100	10,000–12,000

Natural fiber and the fillers were chemically treated with 10% NaOH and cleaned with pressured water to get rid of any undesired organic elements that were on the surface. The ingredients were then let to dry in the sun for eight hours to get rid of any remaining moisture.

2.2. Fabrication of composites

In this study a mold was made of stainless steel in dimensions 410 mm × 410 mm. Adequate mold preparations were completed prior to the lay-up procedure commencing. Using an abrasive paper, the base plate was scrubbed to remove rust. After cleaning the surface with acetone and lint-free towels to get rid of any oil, grease, or grime, it was let to dry. Following drying, a mold release spray and a mold release sheet were applied to the top to bottom of the wooden mold to facilitate the rapid and simple removal of the composite material.

The weight percentage ratio of reinforcement to polymer matrix was kept at 30:70. Five layers of fiber mats with uniform stacking sequence of Glass/Jute/Glass/Jute/Glass (G/J/G/J/G) were considered in preparing samples. As the primary focus of this study is to find out the influence of natural fillers on the characterization of Jute/Glass hybrid composite, thus the stacking sequence didn’t alter throughout the fabrication procedure. The ratio of resin to hardener was kept at 10:1. Required amount of pre-treated filler materials were blended with the matrix. Firm stirring with a glass rod was occupied for around 15 minutes in a room temperature for proper mix-up of matrix and filler. Based on the types and the mixing proportions of filler materials, total 10 numbers of samples have been fabricated in this study. Samples are listed in Table 3.

Table 3.

Samples with various proportions of fillers.

Sample no.	Matrix (wt.%)	Fiber (wt.%)	Filler material (wt.%)		Sample name
1	70	29	Rice Husk (RH)	1	RH1
2	70	27		3	RH3
3	70	25		5	RH5
4	70	29	Wheat Husk (WH)	1	WH1
5	70	27		3	WH3
6	70	25		5	WH5
7	70	29	Wood Dust (WD)	1	WD1
8	70	27		3	WD3
9	70	25		5	WD5
10	70	30	No filler		NF

At normal temperature, an epoxy-based system typically takes 24 to 48 hours to cure. The generated composite portion was removed and subjected to additional processing after the mold was opened after curing. Following construction, the composite specimen was exposed to sunshine for a number of hours in order to eliminate any remaining moisture. The composites’ extraneous edges were removed by a grinding machine.

2.3. Specimen preparation

In this study, various types of mechanical characteristics of the composite materials were investigated, such as, tensile strength, flexural strength, impact strength, hardness. Thermal properties as well as the water absorption characteristics were investigated as well. To find out the bonding between the matrix and fiber, morphological analysis was conducted. To conduct the tests, specimens were prepared as per the ASTM standard using a CNC machine. For each test, three specimens were prepared. ASTM standard has flexibility in the thickness of the specimens. All specimens are prepared according to the ASTM standards as shown in Table 4.

Table 4.

ASTM standard for different investigations.

Tests name	Standards
Tensile test	ASTM D3039
Flexural test	ASTM D7264
Impact test	ASTM D256
Hardness test	ASTM D785
Water absorption test	ASTM D570
TGA	Granule sample
FTIR	Granule sample
SEM	Granule sample
XRD	Granule sample

3. Data reductions

3.1. Tensile properties

Testing was conducted using a UH-F1000 universal testing machine, which has a 400 kN maximum load rating. A gauge length of 127 mm and a crosshead speed of 3 mm/min were kept constant. The composite material’s maximum tensile strength was determined using the load at the breakpoint, and the associated deflections were noted. Both the initial and ultimate lengths are measured with precision. The gauge section’s elongation was measured in relation to the applied force while tension was applied.

3.2. Flexural properties

The same universal testing machine (UTM) was used to test the produced samples by applying a three-point bending force. The strain rate used for the bending was 0.5 mm/min. The two supports were kept at a spacing of 60 mm apart. The relationship between the deflection and the maximum bending moment in the critical section can be roughly divided into three segments to make the analysis easier to understand. This is comparable to the first turning point, which occurs when the critical section cracks, and the second turning point, which is the yield of the outermost tensile reinforcing steels.

3.3. Impact properties

The Charpy impact test was performed in this investigation using the composites’ V-notch specimens. Impact strength is determined by calculating the amount of kinetic energy lost when a simple pendulum with a specific weight strikes the specimens. When exposed to a high strain rate, a material’s impact strength is determined by the quantity of energy absorbed in relation to its cross-sectional area.

3.4. Hardness

By applying indentation loads normal to the diameter and length of the fibers, the hardness characteristics of the composites are investigated. The Rockwell test uses the L scale to measure the depth of penetration of an indenter under a force of 187.5 kgf in order to estimate the hardness of the material. According to the tester’s standard L-scale, the maximum force applied was 187.5 kg, and the ball indenter’s diameter was 2.5 mm. All of the samples underwent testing at room temperature. Ten seconds after the indenter firmly touched the specimen, all of the readings were obtained. To ensure precise reading, smooth emery paper was used to massage all of the sample surfaces.

3.5. Thermogravimetric analysis

In this study, Hitachi STA300 thermal analyzer was used to conduct the TGA test. The thermos-gravimetric analysis technique (TG) examines the changes in mass experienced by a substance in response to alterations in temperature. Here the TGA was conducted with increasing temperature by 5°C in every step from room temperature to 600°C. The mass in the percentage of the sample which remained in the crucible was observed in every step of the temperature. The TGA curves were plotted by Percentage of material that remained versus Temperature.

3.6. Fourier transform infrared spectroscopy

Fourier transform infrared spectroscopy (FTIR) is a widely employed method for the identification of functional groups in various materials, including gases, liquids, and solids, by the utilization of infrared light beams. Perkin-Elmer UTAR Two spectrometer was used in this study to conduct the experiment.

3.7. Scanning electron spectroscopy

Morphological analysis of the composite specimens was conducted using Scanning Electron Microscopy (SEM) images. The surface of the samples containing various filler material with different proportions underwent morphological examination using the Sigma 300 (Carl Zeiss) apparatus. The specimen was cut into small pieces measuring 2 mm² to 3 mm² approximately prior to analysis.

3.8. X-ray diffraction

XRD analysis was conducted using Panalytical EMP 3, Netherlands equipment. Operating voltage of 45 kV and current 40 mA with Cu Kα. Radiation (l = 1.5406 Å) was maintained. The 2θ range of 10-80° for scanning was considered.

3.9. Water absorption

The water absorption behavior of the fabricated composites was evaluated by immersing the test samples in distilled water for 24 hours. Prior to immersion, the samples were dried in an electric oven at 40°C for 2 hours to minimize initial moisture content and subsequently allowed to equilibrate at room temperature until reaching a steady state. After drying, the initial weights of the samples were recorded for subsequent calculations. The samples were then immersed in water at room temperature for 24 hours, and the weight gain was measured to determine water absorption. The weights of the samples after drying were noted for further calculation. The rate of water absorption of a specific sample is depending highly on time. At the initial stage of water absorption, the samples gain a higher amount of water, and the rates decreased with time. Therefore, the slopes of water absorption curves remain very high at the initial stage. Hence the curve of the percentage of water absorption versus square root of time is plotted.

4. Experimental results and discussion

4.1. Mechanical characterization

4.1.1. Tensile properties

Figure 2 illustrates the tensile properties of jute/glass fiber-reinforced epoxy composites with varying nanofiller incorporations. At 1 wt.% filler content, all composites exhibited lower tensile properties compared to the neat fiber (NF) sample, with WH1 showing the lowest strength of 41.59 MPa. This reduction may be attributed to poor interfacial bonding and inadequate dispersion of filler particles at low concentrations, where fillers may act as stress concentrators and initiate microcracks rather than reinforcing the matrix effectively.¹⁶

Among the three different filler loadings, the 3 wt.% samples consistently exhibited superior tensile performance. Compared with the NF sample, tensile strength improved by 11.08% for RH3, 11.5% for WH3, and 10.4% for WD3, with WH3 achieving the highest tensile strength of 70.25 MPa. This enhancement is likely due to the fibrous and rough surface morphology of wheat husk, which facilitates better mechanical interlocking and stress transfer between the filler and the epoxy matrix.^33,34 In contrast, RH and WD fillers are more granular in nature, offering less surface area for bonding. Additionally, the high ash/silica content in RH may reduce the number of effective bonding sites, while the high lignin content in WD can increase brittleness, thereby limiting reinforcement efficiency.

At 5 wt.% filler incorporation, a decline in tensile strength was observed across all composites compared with their 3 wt.% counterparts. This reduction can be explained by filler agglomeration and poor dispersion at higher loadings, which introduce stress concentrators and weak interfacial zones. Furthermore, excessive filler disrupts the continuity of the polymer matrix, hindering uniform load distribution and reducing overall mechanical performance.^23,25

These findings suggest that an optimum filler content of 3 wt.% provides the most effective balance between filler-matrix interaction and dispersion, thereby enhancing the tensile strength of the biocomposites.

4.1.2. Flexural properties

Figure 3 illustrates the flexural strength of prepared samples. The trend in flexural performance revealed that composites with 3 wt.% filler incorporation exhibited superior flexural strength compared to both 1 wt.% and 5 wt.% filler-loaded samples, consistent with the trend observed in tensile testing. This behavior indicates the presence of an optimum filler loading, beyond which further filler addition does not contribute positively to flexural performance. At 3 wt.% loading, the fillers are more uniformly dispersed within the epoxy matrix, enabling effective stress transfer and enhanced resistance against bending-induced deformation. Among all groups, only the 3 wt.% filler-loaded composites outperformed the neat fiber (NF) sample. Specifically, RH3 and WH3 showed flexural strength improvements of 11.29% and 10.54%, respectively, over the NF sample, with RH3 achieving the maximum value of 160.04 MPa. Interestingly, although RH3 performed relatively poorly in tensile properties, it demonstrated the best flexural performance among the 3 wt.% composites.

This enhancement can be attributed to the higher silica content present in rice husk compared with wheat husk and wood dust.^16,35 The silica contributes to increased surface roughness, rigidity, and stiffness, thereby reinforcing the epoxy matrix under bending stress. During flexural deformation, silica-rich fillers provide resistance against crack propagation and bending-induced strain, resulting in improved flexural strength. Consequently, the presence of rigid inorganic phases in RH composites likely enhances their ability to withstand bending loads more effectively than WH and WD fillers. However, at higher filler loading (5 wt.%), excess filler particles may lead to agglomeration and poor interfacial bonding with the epoxy matrix. Such agglomerates can act as stress concentration sites, promoting microcrack initiation under bending loads and ultimately reducing flexural strength. Similar reductions in flexural performance beyond an optimum filler content have been reported in related polymer composite systems.

These findings suggest that filler type and content critically influence the flexural performance of the composites, with rice husk at 3 wt.% providing the most effective reinforcement under flexural loading conditions.

4.1.3. Impact properties

The average impact strengths of the natural fiber composites with and without fillers are presented in Figure 4. The results revealed that the addition of 1 wt.% wood dust led to a noticeable reduction in impact strength compared with the neat fiber (NF) sample, suggesting that insufficient filler content may act as stress concentrators, thereby reducing energy absorption capability. In contrast, the incorporation of 3 wt.% wood dust enhanced impact performance by approximately 8.85%, achieving the highest impact strength of 122.93 kJ/m² among all tested composites. This improvement can be attributed to the more effective dispersion and interaction of wood dust at the optimum loading, which allows for better energy dissipation during crack initiation and propagation.

However, composites with rice husk incorporation exhibited a reduction in impact resistance across all loadings. This may be explained by the higher silica content in rice husk, which increases stiffness and brittleness, thereby lowering the material’s ability to absorb and dissipate impact energy effectively.³⁶

These results highlight that filler type and content play a critical role in impact performance, with 3 wt.% wood dust offering the most effective balance between toughness and energy absorption in the studied composites.

4.1.4. Hardness

Figure 5 displays the composite specimens’ Rockwell hardness values. The findings clearly show that in all composite systems, hardness improved when filler material was added. Rice husk (RH)-reinforced composites showed the greatest hardness values among the fillers that were examined.

This improvement can be explained by the fact that rice husk has a higher silica concentration than wood dust and wheat husk.^16,35 The inorganic, hard, and brittle material silica gives the composite stiffness and abrasion resistance. Furthermore, silica and lignin are heavily concentrated in the outer layer of rice husk, creating a tough protective coating that is resistant to wear and mechanical indentation. The superior hardness performance of the RH-filled composites therefore showed how silica-rich fillers might improve surface resistance to localized deformation.

These results imply that the hardness characteristics of natural fiber-reinforced epoxy composites are greatly influenced by the filler chemistry, namely the inclusion of inorganic phases like silica.

4.2. Thermal properties

4.2.1. Thermogravimetric analysis

Thermogravimetric analysis (TGA) of the composites was carried out under a nitrogen atmosphere with a heating rate of 10 °C/min up to 600 °C. The weight loss profiles of the samples are presented in Figure 6(a). The thermal decomposition of natural fiber–based composites is strongly influenced by several factors, including particle size, morphology, heating rate, temperature range, and the purity of the inert environment; hence, slight variations were observed across the samples.

All composites displayed a similar general trend of mass loss, with an initial weight reduction of up to ∼10% below 230 °C, which is primarily attributed to the evaporation of moisture and volatile compounds. A major decomposition stage occurred between 400 °C and 430 °C, corresponding to the degradation of the epoxy matrix along with cellulose and hemicellulose components. Beyond this stage, a continuous mass loss was recorded, reflecting the biodegradable nature of the filler materials. Among the tested specimens, the neat epoxy composite exhibited the earliest onset of sharp decomposition, while WH3 showed a comparatively faster weight loss progression, suggesting lower thermal stability.

Differential Thermogravimetric (DTG) curves (Figure 6(b)) provided clearer distinctions among the composites, with inflection points corresponding to maximum decomposition rates. The maximum degradation rate was observed at 443 °C for the WD5 sample, indicating improved stability compared with other systems. Three distinct decomposition zones were evident in the DTG curves: 280–320 °C (dehydration of fibers), 350–370 °C (hemicellulose decomposition), and 440–480 °C (α-cellulose decomposition). These findings confirm that the incorporation of fillers affects both the onset and rate of thermal degradation, with wood dust at higher loading (5 wt.%) imparting enhanced thermal resistance relative to rice husk and wheat husk counterparts.³⁷

Overall, the TGA and DTG analyses highlight that filler type and loading significantly influence the thermal stability of the composites, with wood dust showing the most promising behavior at higher loadings due to its higher char-forming tendency and compatibility with the epoxy matrix.

4.2.2. Differential scanning calorimetry (DSC) analysis

In Figure 7, the samples’ DSC thermograms are displayed. Exothermic responses, which are linked to chemical processes like crystallization, cross-linking of the epoxy matrix, and the thermal breakdown of organic components like cellulose, hemicellulose, and lignin from the jute fibers and plant-based fillers, were seen in all specimens.³⁸

The sample with 5 weight percent wood dust (WD5) showed the highest exothermic peak intensity among the composites, suggesting a higher release of heat during the cross-linking and breakdown processes. Wood dust’s increased cellulose and lignin content, which adds more flammable organic matter, is the cause of this behavior. On the other hand, the composite that contained 5 weight percent rice husk (RH5) showed the least amount of exothermic intensity. Rice husk’s comparatively higher silica content than wood dust explains the decreased heat flow in RH-filled samples. By improving thermal stability and acting as an inorganic barrier, silica lessens the magnitude of exothermic processes.

These findings imply that the filler mix has a significant impact on the composites’ thermal behavior. While rice husk, with its silica-rich structure, confers greater thermal stability but decreases exothermic reaction, wood dust, with its higher organic portion, increases exothermic reactivity.³⁹ These differences demonstrate how filler chemistry can be used to customize the thermal performance of natural fiber/epoxy composites.

4.2.3. Fourier transformation infrared spectroscopy (FT-IR)

In this study, the molecular structure of the prepared Jute/Glass/Epoxy composites with filler materials were thoroughly examined using FT-IR spectroscopy. Figure 8 showed that the range of the examination was 4000-500 cm^-1. All the chemically treated specimens exhibited the same curve shape, indicating the presence of hemicelluloses, cellulose, and lignin. The presence of a wide transmission band in the range of 3500-3100 cm^-1 indicating the existence of this characteristic in the pure blend is ascribed to the stretching of the hydroxyl groups (O-H) from the cellulose and hemicellulose of natural fiber and plant-based filler materials. Again a wavelength of 2926 cm^-1 refers to the symmetric C-H bond for the aliphatic groups in jute fiber, plant-based fillers and epoxy resin. The transmission drop at 1750 cm^-1 is typically assigned to hydrogen-bonded C=O indicates hemicellulose presence.

The band observed at 1508 cm^-1 is attributed to the aromatic ring vibrations especially from epoxy resin. C–O stretching vibrations of bonds found at 1235 cm^-1 indicates the presence of ether groups from epoxy or ester groups from lignin suggest the crosslinking between epoxy and fiber, while the band at 1133 cm^-1 is associated with the stretching vibrations of C-O-C and C-O-H linkages. The epoxy ring deformation was observed at 826 cm^-1. The peak found at 558 cm^-1 belongs to the M-O stretching, i.e., inorganics presence in the composites, such as, silica in RH and glass fiber. The shift of peaks (increase and decrease) between the bands indicates the intense synergy among these functional groups in the polymer blend and the plant-based fillers along with the natural fiber.

Among all samples, highest transmittance is found for the NF sample. This is expected as filler loaded samples absorbs more infrared radiation due to the changes in the samples composition, density and bonding interactions. It was found that the RH5 sample showed less transmittance than all other samples. This phenomenon exists due to the possibility of the presence of higher percentage of silica in RH5 sample which causes greater infrared absorption and scattering characteristics.⁴⁰

4.3. Water absorption characteristics

Figure 9 presents the water absorption values for all samples. It was observed that composites containing wheat husk exhibited the highest water absorption capacity. This can be attributed to the higher cellulose and hemicellulose content of wheat husk compared to rice husk and wood dust, which provides abundant hydroxyl groups capable of forming hydrogen bonds with water molecules, thereby enhancing absorption. Additionally, the microstructure of wheat husk is more porous and fibrous, facilitating greater water penetration into the composite matrix. In all cases, an increase in filler content correlated with higher water absorption, indicating that the hydrophilic nature of the natural fillers plays a significant role in governing the moisture uptake of the composites.³⁴

4.4. XRD characterization

Figure 10 depicts the XRD pattern for all biocomposites samples. The XRD patterns of the RH, WH, and WD biocomposites (10–45°, 2θ) reveal broad amorphous halos with cellulose I reflections near 16–18° (110) and ∼22° (200). The crystallinity index (CI) was found to increase in RH1 and WH1 relative to their higher-loading counterparts, while WD3 showed the highest CI among the WD series. This indicates that optimized fiber treatment and composition enhance ordering within cellulose microfibrils. Bragg’s law analysis confirmed slight reductions in d-spacing of the (200) plane, reflecting closer chain packing and improved hydrogen bonding. Broader peaks in RH5 and WD5 signify reduced crystallite size and higher microstrain, consistent with matrix intrusion and partial disruption of ordered regions. In contrast, NF samples exhibited dominant amorphous character with minimal crystalline definition. These variations demonstrate that fiber treatment and composition govern crystallinity, crystallite size, and interfacial bonding, which directly correlate with mechanical strength, thermal stability, and long-term durability of the composites.^41,42

4.5. Morphological analysis

Figure 11 illustrates the micro photograph of the filler material. Three different ranges have been considered to capture the images. Wood dust was examined and it was found that the filler material was in micro size in dimension with varying diameter. The morphology of the samples are shown in Figure 12. Different magnifications were used to examine the samples. It was found that the fiber diameter was around 20 µm. Filler materials were dispersed within the matrix though some voids are observed due to agglomeration of the particles. In case of wheat husk samples, husks are got stacked around the fiber rather proper dispersing on the matrix.

5. Conclusion

In this study, glass and jute fibers reinforced epoxy composites were fabricated using the hand lay-up technique with a five-layer G/J/G/J/G stacking sequence, incorporating plant-based fillers (rice husk, wheat husk, and wood dust) at 1%, 3%, and 5% weight ratios to evaluate their mechanical, thermal, physical and morphological properties.

Tensile, flexural, and impact tests demonstrated that 3 wt.% filler incorporation provided optimal performance. WH3 exhibited the highest tensile strength (70.25 MPa), while RH3 achieved the maximum flexural strength (160.04 MPa). WH3 and WD3 showed superior impact resistance compared to lower (1 wt.%) and higher (5 wt.%) filler loadings. Hardness was highest in RH5 (Rockwell 76), with WD-filled composites showing comparable values, indicating that rice husk and wood dust are more effective than wheat husk in enhancing surface hardness.

TGA and DTG analyses revealed that composites experienced limited weight loss up to 230 °C, with significant decomposition between 400–430 °C corresponding to the matrix and filler degradation. Maximum decomposition occurred at 443 °C for 5 wt.% WD. DSC showed exothermic behavior for all samples, with 5 wt.% WD giving the highest value.

FTIR confirmed the presence of key functional groups from cellulose, hemicellulose, lignin, epoxy, and fillers, demonstrating strong interfacial interactions. XRD analysis indicated that filler type and loading influenced crystallinity, chain packing, and hydrogen bonding, with optimized compositions enhancing composite performance.

The water absorption study revealed that composites containing wheat husk exhibited the highest absorption due to their higher cellulose and hemicellulose content and porous microstructure, which facilitated hydrogen bonding and water penetration; additionally, water absorption increased with filler content across all samples, indicating that filler type and loading significantly influence the hydrophilic behavior of the composites.

Scanning Electron Microscopic (SEM) analysis confirmed that the filler particles were mostly in the microscale range, with fibers measuring around 20 µm in diameter; while fillers were generally dispersed within the epoxy matrix, some voids and agglomerations were observed, and wheat husk in particular tended to stack around the fibers rather than dispersing uniformly, indicating that filler morphology and dispersion play a crucial role in the overall composite quality and performance.

Overall, incorporating 3 wt.% plant-based fillers, particularly wheat husk and wood dust, into glass/jute fiber epoxy composites significantly enhanced mechanical, thermal, and water absorption properties, while maintaining structural integrity, demonstrating their potential for high-performance, sustainable bio composites.

Footnotes

ORCID iD

M.S. Rabbi

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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