Effect of pat/agave/coir-dust reinforcement on the mechanical and moisture properties of epoxy composites

Alrasheedi, N. H. (2026). "Effect of pat/agave/coir-dust reinforcement on the mechanical and moisture properties of epoxy composites," BioResources 21(3), 6174–6202.

Abstract

Epoxy composites were reinforced with alkali (NaOH)–treated pat (jute) fibers, untreated agave fibers, and coir dust to improve mechanical and moisture resistance properties. Alkali treatment was applied to the pat fibers. Ten formulations (PA1–PA10) were fabricated by varying fiber proportions and evaluated for tensile, flexural, impact, hardness, interlaminar shear strength (ILSS), density, water absorption, and thickness swelling. Mechanical performance strongly depended on fiber composition and interfacial bonding. Tensile strength increased from 22 MPa (neat epoxy, PA10) to 44 MPa (PA3), while flexural strength ranged from 25 to 52 MPa, with PA3 showing superior performance. The highest impact strength (0.40 J), hardness (84 Shore D), and ILSS (9 MPa) were also observed for PA3, indicating efficient stress transfer. Moisture analysis showed minimum water absorption (10%) and thickness swelling (2.3%) for PA3. Density ranged between 1.20 and 1.36 g/cm³, suggesting that performance was governed mainly by interfacial interaction. Overall, PA3 (15% treated pat and 15% agave fiber) demonstrated the best balance of strength and environmental resistance. That formulation demonstrated the most balanced combination of mechanical strength, interlaminar integrity, and environmental resistance, highlighting the effectiveness of fiber reinforcement with coir dust for green epoxy composites.

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Effect of Pat/Agave/Coir-Dust Reinforcement on the Mechanical and Moisture Properties of Epoxy Composites

Nashmi H. Alrasheedi

DOI: 10.15376/biores.21.3.6174-6202

Keywords: Mechanical characterization; Sustainable composites; Mechanical testing; Water absorption behavior; Pat; Agave; Coir dust

Contact information: Department of Mechanical Engineering, College of Engineering, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh, 11432, Kingdom of Saudi Arabia;

* Corresponding author: nhrasheedi@imamu.edu.sa

INTRODUCTION

Natural fibers and fillers have attracted considerable interest in the composite industry because of their various benefits, such as renewability, biodegradability, and cost-effectiveness (Mittal and Chaudhary 2018; Ramasubbu et al. 2024). These characteristics render them exceptionally suited for the advancement of sustainable materials that correspond with worldwide initiatives aimed at minimizing environmental effects. Jute and agave fibers are notable for their exceptional strength, broad availability, and versatility among the many natural fibers (Karuppusamy et al. 2023). Both fibers have proven to be crucial elements in the advancement of composite materials, especially in areas where they are widely grown. Nonetheless, despite their benefits, the intrinsic hydrophilic characteristics of these fibers pose a significant challenge (Bhuvaneswari et al. 2022). This characteristic restricts their compatibility with hydrophobic polymer matrices, frequently leading to inadequate interfacial bonding and diminished composite properties. Resolving this issue is essential for realizing the complete capabilities of natural fiber composites in both structural and functional applications (Kumar et al. 2022; Kar et al. 2024). Chemical treatments have proven to be effective solutions for improving the compatibility between natural fibers and polymer matrices. Among these, alkali treatment is a widely used and effective method (Mittal et al. 2016). This procedure entails subjecting the fibers to a NaOH solution, effectively eliminating impurities such as lignin, hemicellulose, and surface waxes. The elimination of these components enhances the surface smoothness of the fibers and introduces hydroxyl groups, which promote stronger interfacial bonding with the polymer matrix (Cisneros-López et al. 2017). Alongside enhancing mechanical properties, alkali treatment effectively decreases the hydrophilicity of fibers, thereby lessening their propensity to absorb moisture. The fibers are thus rendered more appropriate for applications in settings where maintaining dimensional stability is essential.

Jute fiber, which is commonly known as “golden fiber” because of its shiny and lustrous look, is among the most widely utilized natural fibers in the composite industry (Sathishkumar et al. 2014; Ayrilmis et al. 2024). This material originates from the bast or outer layer of the jute plant and consists mainly of cellulose, hemicellulose, and lignin. The material’s impressive tensile strength, reasonable elongation, and effective thermal insulation characteristics render it a compelling option for enhancing polymer composites. Jute is abundantly accessible in substantial amounts, especially in the nations of India and Bangladesh, where is widely farmed (Ibrahim et al. 2016). Similarly, agave fiber, obtained from the leaves of the agave plant, is another natural fiber with considerable potential. Known for its high stiffness, strength, and resistance to microbial degradation, agave fiber has been increasingly used in composite applications. However, like jute, its hydrophilic nature necessitates chemical modification to improve its compatibility with polymer matrices (Vigneshwaran et al. 2020). In addition to natural fibers, fillers play a vital role in composite materials. Coir dust, a byproduct of coconut processing, is an example of an effective filler that has gained attention in recent years. Coir dust particles are derived from the monocarp or husk of coconuts and are primarily composed of lignin and cellulose (Govindarajan et al. 2024; Mahalingam 2024). This filler material offers several advantages, including low cost, high availability, and good thermal stability. When incorporated into composites, coir dust particles act as a reinforcing agent, enhancing mechanical properties such as stiffness and impact resistance. Additionally, their use contributes to the value-added utilization of agricultural waste, aligning with the principles of sustainability and circular economy (Dugvekar and Dixit 2022).

The combination of various natural fibers and fillers presents a valuable strategy for creating composites with customized characteristics. Combining fibers with complementary mechanical characteristics allows for a balanced outcome of strength, stiffness, and toughness in the final composite material (Praveena et al. 2022; Goutham et al. 2023). The incorporation of fillers, such as coir dust particles, significantly improves the performance of these hybrids by enhancing dimensional stability, lowering material costs, and boosting specific mechanical properties (Gurusamy et al. 2024). Nonetheless, the success of hybridization is influenced by various elements, such as the specific fibers and fillers employed, their ratios, and the bonding at the interface between the components.

This study analyzed the effects of hybridization using chemically modified jute (pat) and agave fibers mixed with coir dust particles in epoxy composites (Dharmaratne et al. 2021). The primary objective was to evaluate the mechanical performance and water absorption properties of these hybrid composites. The mechanical qualities, such as tensile strength, compressive strength, flexural strength, hardness, and impact resistance, are critical determinants of the suitability of composites for structural applications (Kumar and Raja 2021). The behavior of water absorption provides critical insights into the environmental stability and durability of the composites, particularly in humid or wet situations. The use of chemically modified fibers into epoxy matrix has significantly improved the mechanical characteristics of composites. Alkali-treated jute and agave fibers have been found to exhibit better interfacial adhesion with the matrix, resulting in improved load transmission and mechanical performance (Chithra et al. 2024).

The incorporation of coir dust particles enhances the composite structure by effectively filling voids and serving as agents for stress transfer. The combined influence of fibers and fillers is anticipated to yield hybrid composites that exhibit enhanced properties when compared to those reinforced with only one type of fiber or filler (Badyankal et al. 2021). The absorption of water is a significant element that affects the long-term efficacy of natural fiber composites. Natural fibers that have not been treated exhibit a strong affinity for water, resulting in swelling, changes in dimensions, and a decline in mechanical properties as time progresses (Gupta and Ramkumar 2021). Chemical treatments such as alkali treatment can markedly decrease the water absorption capacity of fibers by eliminating hydrophilic components and diminishing the presence of free hydroxyl groups. The addition of coir dust particles, characterized by their lower hydrophilicity compared to untreated fibers, enhances the water resistance of the hybrid composites. Through a methodical examination of the water absorption characteristics of these materials, important understanding can be achieved regarding their appropriateness for use in humid or wet conditions (Aruchamy et al. 2025).

The possible uses of these hybrid composites are extensive and varied. In the construction sector, these materials serve as lightweight and durable options for panels, roofing, and flooring applications. In the automotive sector, there is an eco-friendly alternative to synthetic composites for both interior and exterior components (Manickaraj et al. 2024b). The advancement of these materials presents significant potential for consumer products, packaging, and various sectors where sustainability and performance are of paramount importance. While there are benefits to natural fiber composites, their broad implementation faces several obstacles. The differences in fiber properties, shaped by elements like plant species, growth conditions, and processing techniques, can result in variations in composite performance (Kumar et al. 2021). Furthermore, the affinity of natural fibers for moisture and their consequent sensitivity pose considerable challenges. Nonetheless, continuous exploration and progress in chemical treatments, hybridization techniques, and composite fabrication methods persist in tackling these challenges, facilitating the wider use of natural fiber composites (Thangavel et al. 2024).

In natural fiber composites, fiber length and alignment critically influence mechanical performance. Unlike thermoplastic extrusion, epoxy processing (hand lay-up/compression molding) preserves fiber length and orientation, enhancing stress transfer and strength (Pandiarajan et al. 2025). Although epoxy is more brittle and costly, this approach allows effective reinforcement with hybrid fibers such as pat and agave combined with coir dust, improving mechanical and moisture-related properties in high-performance green composites (Gunti et al. 2018).

This study systematically evaluated the mechanical properties and water absorption behavior of hybrid composites reinforced with chemically modified jute (pat) and agave fibers, in addition to coir dust particles. The goal was to enhance existing knowledge on sustainable composite materials and establish a basis for their use across different sectors (Praveen Kumar and Nalla Mohamed 2018). This study illustrates how chemical modification and hybridization can significantly improve composite performance, with the goal of advancing the creation of sustainable materials that align with contemporary engineering and design requirements (Thirumalaisamy et al. 2023).

EXPERIMENTAL

Fibers

The fibers used in this study were pat (jute) and agave. Pat fiber is strong, flexible, and widely available, making it suitable for composite applications. Agave fibers are stiff, durable, and resistant to microbial degradation, providing additional strength to composites (Palanisamy et al. 2022a; Manickaraj et al. 2024c). The fibers were collected from Amman Impex, Pollachi, Tamil Nadu, India. Figure 1 shows various fibers.

Fig. 1. a: Pat Fiber; b: Agave Fiber

Fig. 2. Coir dust fillers

Filler

Coir dust particles were used as a filler. Coir dust is a byproduct of coconut processing, composed of cellulose and lignin. It is an affordable, eco-friendly material that enhances the composite’s stiffness, impact resistance, and water absorption resistance (Del Campo et al. 2020). The fillers were collected from local village in Pollachi, Tamil Nadu, India. Figure 2 shows the coir dust fillers.

Matrix

The matrix material consisted of epoxy resin blended with an appropriate hardener. Epoxy resin provides outstanding mechanical properties, exceptional chemical resistance, and robust adhesion to natural fibers, rendering it highly suitable for reinforcing composites (Ighalo et al. 2021; Palanisamy et al. 2023). Epoxy resin (LY556) and hardener (HY951) were procured from Covai Seenu Company, located in Coimbatore, India.

Fiber Treatment

Alkali treatment was employed to improve the adhesion between the fiber and the matrix. The fibers were immersed in a 5% NaOH solution for 24 hours. Subsequent to the soaking operation, the fibers are subjected to washing and drying to remove excess alkali and moisture (Gurusamy et al. 2024). Alkali treatment reduces fiber hydrophilicity, improving compatibility with the hydrophobic epoxy matrix, and enhancing the mechanical performance of the composite. Figure 3 illustrates the fiber submerged in a chemical container for the purpose of chemical treatment.

Fig. 3. Fibers in chemical treatment

Composite Fabrication

The hand lay-up technique was used to fabricate the composite materials. In this process, the fibers (pat and agave) and coir dust were carefully layered in a mold, with a constant amount of epoxy resin (60%) and coir dust (10%) applied. The weight ratios of pat and agave fibers were varied to assess the impact on the composite properties (Ali et al. 2022). The following fiber weight ratios were used for composite fabrication. Table 1 shows sample ID and fiber varying percentages.

Table 1. Composite Formulations (Fiber percentage with Sample ID)

The composite formulations (PA1–PA10) were systematically designed to evaluate the effects of fiber hybridization and coir dust filler in an epoxy matrix. In PA1–PA7, epoxy content was fixed at 60% and coir dust at 10%, while the total fiber content (30%) was varied by altering the pat and agave fiber ratios to study hybridization effects. PA1–PA5 represent different hybrid combinations of pat and agave fibers, with PA3 (15% pat and 15% agave) providing equal hybridization as shown in Fig. 4. PA6 and PA7 were single-fiber composites containing only pat or only agave fiber, respectively, along with coir dust. PA8 and PA9 contained higher fiber loading (40%) of only pat or only agave fiber without coir dust, to assess the effect of filler removal and increased reinforcement. PA10 was neat epoxy (100%) and served as the control sample for baseline comparison of mechanical, physical, and moisture absorption properties.

Fig. 4. PA3 Sample

Fabrication Process

Following the arrangement of the fibers and filler within the mold, the composite specimens underwent a curing process at room temperature for a duration of 24 hours, facilitating the hardening of the epoxy resin. Following this, the specimens were subjected to post-curing at 70 °C for a period of 4 h to optimize the curing process, ensuring that the epoxy matrix had reached its maximum strength, thereby improving the final mechanical properties of the composite (Balaji et al. 2022). The dual curing process improves the adhesion between the fibers and the matrix, resulting in the formation of strong and durable composites.

Mechanical Testing

Tensile test

The tensile test was performed in accordance with ASTM D638-14 (2022) with a universal testing machine (UTM). The test evaluates tensile strength by applying a uniaxial tensile load to the specimen until it fails. Tensile strength denotes the greatest load a material can withstand prior to failure. This test yields significant data on the material’s tensile strength (Nithyanandhan et al. 2024). It is crucial for applications involving tensile or tensile forces, particularly in structural and load-bearing elements.

Flexural test

The flexural test was performed according to ASTM D790 (2017), employing a three-point bending configuration to evaluate the flexural strength of the composite (Gokul et al. 2024). A force is exerted in the center of the specimen, which is supported at both ends, resulting in bending. The flexural strength is the maximum stress that the composite can endure before failure. This test is crucial for materials utilized in applications such as beams, panels, and automobile components, where bending stresses frequently occur (Rangappa et al. 2022).

Hardness test

The Shore D hardness test was used to measure the surface hardness of the composites via ASTM D2240 (2021). This test involves using a Shore D durometer to apply a standard force to an indenter, which penetrates the surface of the material (Natrayan et al. 2024). The depth of indentation determines the material’s hardness value. Higher values indicate greater resistance to surface deformation, which is vital for applications requiring wear resistance. Materials with high Shore D hardness are generally more durable and can withstand abrasive conditions (Stevens et al. 2022).

Impact test

The Izod impact test was performed following ASTM D256 (2023) standards to assess the energy absorption capacity of the composite material under impact conditions (Azad et al. 2022). A notched specimen undergoes impact from a pendulum hammer, and the energy required to fracture the specimen is recorded. The impact strength indicates the ability of the material to absorb energy before experiencing fracture. This test is essential for evaluating the toughness of the material and its ability to withstand unforeseen pressures or impacts, which is critical for applications in the automotive, aerospace, and construction industries (Mohammed et al. 2022).

Water absorption test

The water absorption test was conducted following ASTM D570 (2022) standards, with the specimens immersed in water for a duration of 48 hours. The weight increase was recorded at each time interval to assess the material’s ability to absorb water (Manickaraj et al. 2024a). This test is critical for assessing the material’s durability under humid or wet conditions. The phenomenon of high-water absorption results in swelling, a reduction in the strength of the composite, and a deterioration of mechanical properties. Consequently, this test is critical for assessing the composite’s appropriateness for outdoor or marine applications (Oladele et al. 2020; Abhilash and Singaravelu 2022).

Thickness swelling test

Thickness swelling was determined alongside water absorption to evaluate dimensional stability. Specimen thickness was measured before and after immersion, and the percentage change was calculated. This test indicates the extent of fiber swelling and matrix softening due to moisture ingress (Alrasheedi et al. 2026). Lower thickness swelling values correspond to better structural stability in moisture-rich environments, making the composite suitable for marine, packaging, and outdoor applications.

Interlaminar shear strength test

Inter-laminar shear strength (ILSS) test was evaluated according to ASTM D2344 using a short-beam three-point bending method. The test measures the maximum shear stress sustained between layers of the composite before interlaminar failure occurs. ILSS is a critical indicator of fiber–matrix adhesion quality and resistance to delamination, which directly influences performance in structural, automotive, and aerospace components where shear loads are significant (Sathish et al. 2017).

Density

Density was determined using the Archimedes principle by measuring the mass of the specimen in air and in water. The density values were calculated to analyze material compactness, void content, and the influence of fiber and filler incorporation in the epoxy matrix (Jenish et al, 2021).

Scanning electron microscopic analysis

Scanning electron microscopic (SEM) analysis was conducted to examine the microstructural characteristics of the fracture surfaces. The micrographs provide insights into fiber–matrix adhesion, void formation, fiber pull-out, and failure mechanisms. Improved interfacial bonding, reduced porosity, and uniform fiber distribution observed in SEM images correlate with enhanced mechanical properties (Pandiarajan et al. 2025; Ravichandran et al. 2025). SEM thus validates the experimental findings and helps understand the structure–property relationship of the composites.

RESULTS AND DISCUSSION

Tensile Strength

The tensile strength results for the ten composite samples (PA1 to PA10) revealed a strong dependence on fiber composition, hybridization ratio, and filler presence, clearly demonstrating the effectiveness of controlled reinforcement in improving load-bearing capacity. Sample PA1 (5% pat and 25% agave) exhibited a tensile strength of 28 MPa. The lower pat fiber fraction limits stiffness contribution, while the higher agave content may enhance ductility but not significantly improve tensile load transfer (Ramesh et al. 2025). Increasing the pat fiber content to 10% in PA2 improved tensile strength to 34 MPa, indicating enhanced stress transfer efficiency and improved fiber–matrix interfacial bonding. The highest tensile strength of 44 MPa was observed in PA3 (15% pat and 15% agave), confirming that equal hybridization produced an optimal synergistic effect. At this ratio, the balanced distribution of fibers likely promoted a uniform stress distribution, minimized stress concentration sites, and enhanced interfacial adhesion, resulting in superior tensile performance (Abhilash and Singaravelu 2022). However, further increasing pat fiber content led to a gradual decline in strength. PA4 (20% Pat, 10% Agave) recorded 40 MPa, and PA5 (25% pat, 5% agave) showed 36 MPa. This reduction may be attributed to reduced hybrid synergy, possible fiber agglomeration, insufficient wetting at higher fiber loadings, and localized stress concentrations (Madhu et al. 2019).

The performance of single-fiber systems further supports the advantage of hybridization. PA6 (30% pat) and PA7 (30% agave) exhibited tensile strengths of 33 MPa and 31 MPa, respectively, both lower than PA3, indicating that combining fibers enhanced reinforcement efficiency. In PA8 and PA9, where fiber loading increased to 40% without coir dust filler, tensile strengths were 30 and 28 MPa. The absence of particulate filler may reduce matrix continuity and interfacial support, limiting effective stress transfer. The neat epoxy (PA10) showed the lowest tensile strength of 22 MPa, confirming the significant reinforcing role of natural fibers. Figure 5 illustrates the tensile strength variation among all formulations, clearly highlighting the superior performance of the balanced hybrid composite (PA3) compared to single-fiber and non-hybrid systems.

Fig. 5. Tensile test

The tensile strength of these composite materials was strongly influenced by the proportion of pat fiber, which provided stiffness and strength, while agave fiber added flexibility but may reduce tensile strength when used in excess (Oladele et al. 2020). The highest tensile strength was observed in PA3, where there was an optimal balance between both fibers. Samples with higher pat fiber content tended to show increased strength, but this was moderated by the amount of agave fiber, with the most favorable results occurring in PA3, which struck the best balance.

The tensile stress–strain (Fig. 6) data clearly illustrate the mechanical behavior and load-carrying capacity of the composites PA1 to PA10. All samples exhibited an initial linear increase in stress with strain, indicating elastic behavior where stress is directly proportional to strain. Among all formulations, PA3 showed the highest tensile performance, reaching a maximum stress of approximately 44 MPa at around 1.6 strain, confirming its superior strength and better load transfer capability. This indicates strong fiber–matrix bonding and effective hybrid reinforcement.

PA4 and PA5 also demonstrated high tensile strengths, reaching peak stresses of about 40 and 36 MPa respectively, but their ultimate strengths were slightly lower than PA3, suggesting that excessive dominance of one fiber slightly reduces hybrid efficiency. PA2 and PA6 exhibit moderate tensile behavior, with maximum stresses around 34 and 32 MPa, reflecting balanced but less optimized reinforcement.

PA1, PA7, PA8, and PA9 showed comparatively lower tensile strengths, indicating weaker interfacial bonding or less efficient stress transfer. The neat epoxy sample PA10 recorded the lowest tensile strength (about 22 MPa), confirming that fiber reinforcement significantly enhanced tensile performance.

Fig. 6. Tensile stress vs. strain diagram

After reaching peak stress, all samples showed a decline in stress, representing material failure and crack propagation. PA3 maintained higher stress values for a longer strain range, indicating better toughness and ductility compared to other samples. Overall, the stress–strain behavior confirms that PA3 possesses the best tensile performance, stiffness, and structural integrity among all tested composites.

Flexural Strength

The flexural strength results for the ten composite samples (PA1 to PA10) indicated a clear influence of fiber hybridization, fiber proportion, and filler presence on bending performance. Among the hybrid composites containing coir dust (PA1–PA7), a progressive improvement in flexural strength was observed with increasing pat fiber content up to an optimal ratio. Sample PA1 (5% pat and 25% agave) exhibited the lowest flexural strength of 29 MPa, which can be attributed to the limited pat fiber reinforcement and the higher proportion of agave fiber that may contribute more to flexibility than stiffness (Athith et al. 2018).

Fig. 7. Flexural test

In PA2 (10% pat and 20% agave), flexural strength increased significantly to 42 MPa, indicating improved rigidity and resistance to bending due to enhanced load transfer from matrix to fiber. The maximum flexural strength of 52 MPa was recorded for PA3 (15% pat and 15% agave), demonstrating the beneficial effect of equal hybridization. This balanced composition likely ensures uniform stress distribution under bending loads, improved interfacial bonding, and reduced stress concentration, thereby maximizing flexural performance (Agaliotis et al. 2022). Beyond this optimal ratio, a gradual decline was observed. PA4 (20% pat and 10% agave) recorded 48 MPa, while PA5 (25% pat and 5% agave) showed 44 MPa. Although increasing pat fiber enhanced stiffness, excessive dominance may reduce hybrid synergy and fiber dispersion efficiency, slightly lowering performance (Palaniappan et al. 2024a).

The single-fiber composites PA6 (30% pat) and PA7 (30% agave) exhibited flexural strengths of 41 and 39 MPa, respectively, confirming that hybrid reinforcement provided superior bending resistance compared to individual fiber systems. In PA8 and PA9, with 40% single-fiber loading and no coir dust, flexural strengths decreased to 37 and 35 MPa, suggesting reduced matrix continuity and filler support. The neat epoxy (PA10) showed the lowest value of 25 MPa, confirming the reinforcing effect of fibers. Figure 7 presents the flexural test results.

The flexural strength of these materials is largely influenced by the proportion of pat fiber, with higher pat fiber content leading to better resistance to bending and deformation (Vijay and Singaravelu 2016). PA3 exhibited the highest flexural strength due to an optimal balance between pat fiber and agave fiber, while PA1, with minimal pat fiber, showed the lowest flexural strength.

The flexural stress–strain results (Fig. 8) clearly demonstrate the bending performance and load-bearing capacity of the composites PA1 to PA10. Initially, all samples showed a steady linear increase in flexural stress with increasing strain, indicating elastic deformation under bending load. Among all formulations, PA3 exhibited the highest flexural strength, reaching a maximum of approximately 52 MPa at around 2.1 strain. It also sustained load over a wider strain range before failure, confirming superior stiffness, better fiber–matrix adhesion, and enhanced resistance to crack propagation under bending.