Abstract
The utilization of natural fibers in polymer composites is increasingly popular due to their sustainability, cost-effectiveness, and favorable mechanical properties. This study introduces the novel use of Aristida hystrix fibers, processed for the first time into nano-sized particles via ball milling, to enhance dispersion and bonding within a polyester matrix. These nanoparticles were incorporated into polyester resin at various weight percentages (0 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, and 9 wt%), and composite laminates were fabricated using solvent casting and compression molding techniques. Mechanical properties were evaluated through tensile, flexural, and impact strength tests following ASTM standards. The composite containing 5 wt% nano fiber exhibited the optimum mechanical performance, with tensile strength of 30.13 MPa, flexural strength of 43.685 MPa, and impact strength of 1.87 kJ/m². At higher fiber loadings, particle agglomeration led to performance reduction. Water absorption studies indicated that increased nano fiber content resulted in higher moisture uptake, influencing long-term durability. Scanning Electron Microscopy (SEM) provided insights into fiber–matrix interfacial behavior, dispersion quality, and fracture mechanisms. Overall, this work establishes the first-time development of polyester composites reinforced with nano Aristida hystrix fibers, demonstrating their potential as a sustainable and high-performance material for lightweight structural applications in automotive, aerospace, and marine sectors.
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Enhancing Polyester Composites with Nano Aristida hystrix Fibers: Mechanical and Microstructural Insights
Pitchai Pandiarajan,a,* Padamathur Ganesan Baskaran,b Sivasubramanian Palanisamy 
,c,* Manickaraj Karuppusamy ,d Kathiresan Marimuthu,e Anish Rajan,f Mansour I. Almansour,g Quanjin Ma,h and Saleh A Al-Farraj,g
The utilization of natural fibers in polymer composites is increasingly popular due to their sustainability, cost-effectiveness, and favorable mechanical properties. This study introduces the novel use of Aristida hystrix fibers, processed for the first time into nano-sized particles via ball milling, to enhance dispersion and bonding within a polyester matrix. These nanoparticles were incorporated into polyester resin at various weight percentages (0 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, and 9 wt%), and composite laminates were fabricated using solvent casting and compression molding techniques. Mechanical properties were evaluated through tensile, flexural, and impact strength tests following ASTM standards. The composite containing 5 wt% nano fiber exhibited the optimum mechanical performance, with tensile strength of 30.13 MPa, flexural strength of 43.685 MPa, and impact strength of 1.87 kJ/m². At higher fiber loadings, particle agglomeration led to performance reduction. Water absorption studies indicated that increased nano fiber content resulted in higher moisture uptake, influencing long-term durability. Scanning Electron Microscopy (SEM) provided insights into fiber–matrix interfacial behavior, dispersion quality, and fracture mechanisms. Overall, this work establishes the first-time development of polyester composites reinforced with nano Aristida hystrix fibers, demonstrating their potential as a sustainable and high-performance material for lightweight structural applications in automotive, aerospace, and marine sectors.
DOI: 10.15376/biores.20.4.9257-9281
Keywords: Ball milling; Natural fiber; Resin; Nano; Fracture; Tensile; Flexural; Impact; Water Absorption; SEM
Contact information: a: Department of Mechanical Engineering, Theni Kammavar Sangam College of Technology, Koduvilar patti, Theni-625531, Tamilnadu, India; b: Department of Mechanical Engineering, Sri Venkateswara College of Engineering and Technology, Thirupachur, Thiruvallur District, Tamilnadu, India; c: Department of Mechanical Engineering, PTR College of Engineering and Technology, Austinpatti, Madurai – Tirumangalam Road, Madurai – 625008, Tamil Nadu. India; d: Department of Mechanical Engineering, CMS College of Engineering and Technology, Coimbatore – 641032, Tamilnadu, India; e: Department of Mechanical Engineering, Excel Engineering College (Autonomous), Namakkal – 637303, Tamilnadu, India; f: Department of Mechanical Engineering, Government Polytechnic College, Nattakom, Kottayam- 686013, Kerala, India; g: Department of Zoology, College of Science, King Saud University, P. O. Box 2455, Riyadh 11451, Saudi Arabia; h: School of Automation and Intelligent Manufacturing, Southern University of Science and Technology, Shenzhen 518055, China;
*Corresponding authors: sivaresearch948@gmail.com; pandianhero0783@gmail.com
INTRODUCTION
Natural fibers have garnered significant interest as reinforcing materials in polymer composites, outpacing synthetic fibers due to their environmental sustainability, economic efficiency, widespread availability, recyclability, low density, and high specific strength and stiffness. Moreover, natural fibers do not inflict considerable wear on processing machinery, rendering them a compelling option for composite material applications (Thakur et al. 2010, 2014; Marichelvam et al. 2023). The application of natural fiber-reinforced composite laminates has proliferated in many sectors, such as construction, aerospace, automotive, and packaging, because of its lightweight characteristics, renewability, and biodegradability (Satyanarayana et al. 2007; Malkapuram et al. 2009; Binoj et al. 2016). Nonetheless, despite their myriad advantages, natural fibers exhibit specific limitations, including moisture absorption, low thermal stability, incompatibility with polymer matrices, poor dimensional stability, and variability in mechanical properties, which can affect the overall performance of the composites (Rowell et al. 1997; Athijayamani et al. 2009; de Oliveira Braga et al. 2017; Junio et al. 2022).
In response to these constraints, many chemical and physical treatment procedures have been devised. These treatments are essential for altering the fiber surface to diminish moisture absorption and enhance interfacial adhesion with the polymer matrix. Common chemical treatments encompass alkali treatment, silane treatment, acetylation, and benzoylation, which augment fiber-matrix adhesion, hence improving the mechanical performance of the composite (Bozaci et al. 2013; Sarikanat et al. 2016; Aruchamy et al. 2025). Physical treatments, including plasma treatment, thermal treatment, and stretching, can enhance fiber surface roughness, hence augmenting mechanical interlocking between the fiber and the matrix. Nonetheless, although these treatments are efficacious, the discovery of novel procedures is essential to further improve the mechanical characteristics and durability of natural fiber composites.
Recently, the utilization of nano-sized fiber particles as reinforcing agents has surfaced as a viable approach to address the intrinsic limitations of natural fibers. Material scientists and engineers have recognized nano fiber particles as promising reinforcements because of their distinctive properties, which encompass a high surface area-to-volume ratio, elevated aspect ratio, exceptional strength, high modulus of elasticity, diminished moisture absorption, and a low coefficient of thermal expansion (Naganuma and Kagawa 2002; John and Anandjiwala 2008; Prasad et al. 2015; Thangavel et al. 2024; Manickaraj et al. 2025). The remarkable attributes of nano fiber-reinforced composites render them widely sought after for sophisticated applications in aerospace, automotive, construction, electrical, and electronic sectors, where superior performance and durability are imperative (Zhi Rong et al. 2001; Ramesh et al. 2020; Manickaraj et al. 2024b; Mylsamy et al. 2025).
The extraction of nano fiber particles from raw fibers may be accomplished using several methods, including chemical vapor deposition, electrodeposition, plasma arcing, sol-gel synthesis, and high-energy ball milling (Chirayil et al. 2014; Palanisamy et al. 2024). High-energy ball milling has been prominent among these technologies because of its simplicity, cost-effectiveness, scalability, and capacity to manufacture new materials with improved mechanical and physical qualities (Wypych and Satyanarayana 2005; Gokul et al. 2024; Aruchamy et al. 2025). This approach entails the mechanical reduction of raw fiber particles into nanoscale structures via repetitive impact and attrition pressures, assuring homogeneous particle size distribution and enhanced dispersion within the polymer matrix.
This work involves the processing of Aristida hystrix raw fiber into nanofiber particles via the high-energy ball milling technology. Aristida hystrix, a naturally occurring fiber, was chosen for its advantageous mechanical qualities, accessibility, and sustainability.
Extensive testing was performed in accordance with ASTM standards to assess the mechanical properties of these composites. Tensile strength, flexural strength, and impact resistance were evaluated to ascertain the load-bearing capacity and durability of the composite laminates. Water absorption tests were conducted to evaluate the moisture uptake characteristics of the composites, a crucial aspect in determining their long-term durability and environmental resilience. Additionally, scanning electron microscopy (SEM) was utilized to analyze the distribution of nano fiber particles inside the matrix, offering insights into fiber-matrix interactions, particle distribution, and possible failure processes.
The novelty of this research lies in the first-time development and investigation of polyester composites reinforced with nano Aristida hystrix fiber particles. Composites were fabricated with 0 to 9 wt% filler loading and evaluated for tensile, flexural, and impact strength, water absorption, and microstructural behavior (Kalimuthu et al. 2019). Particular emphasis was placed on identifying the optimum filler concentration that maximizes mechanical performance without compromising durability (Saba et al. 2014).
By integrating a novel fiber source (Aristida hystrix) with a nanoscale processing route, this research contributes to advancing the field of natural fiber composites, offering a sustainable, lightweight, and high-performance alternative for structural and engineering applications (Pandiarajan et al, 2019).
The major aim of this research is to investigate the efficacy of nano Aristida hystrix fiber particles as a reinforcing agent in polyester composites and to identify the best fiber loading that enhances mechanical performance while ensuring durability. The research is to enhance the existing knowledge on nano fiber-reinforced polymer composites, providing significant insights into the creation of high-performance and sustainable materials for structural uses (Syduzzaman et al. 2023).
Industries are increasingly pursuing lightweight and eco-friendly substitutes for traditional materials, making the incorporation of nano-sized natural fiber reinforcements into polymer matrices a feasible approach to improving mechanical qualities and overall performance. This research highlights the significance of unique material processing methods and sophisticated reinforcing strategies in producing better composite materials applicable to many engineering fields (Arasu and Manickaraj 2025; Somasundaram et al, 2025). This inquiry aims to position Aristida hystrix nano fiber-reinforced polyester composites as a viable option for next-generation composite materials, integrating sustainability with high-performance engineering solutions.
EXPERIMENTAL
Fiber Materials
The fiber used in this study was derived from the leaf of the Aristida hystrix plant, as shown in Fig. 1A. The raw fiber was sourced from Vellakulam village, located in the Virudhunagar district of Tamil Nadu, India. The selection of this fiber was based on its availability, sustainability, and potential reinforcement properties (Ravichandran et al, 2025).
Fig. 1. A. Aristida hystrix plant fiber; B. Extracted and dried macro fiber
Matrix Material
This research employed unsaturated polyester resin as the matrix material. The resin, procured from GVR Traders in Madurai, exhibited a density of 1258 kg/m³ and a viscosity of 500 cps at 25 °C. The curing process was facilitated with Methyl Ethyl Ketone Peroxide (MEKP) as the catalyst and acetone as the accelerator. Unsaturated polyester was selected due to its superior mechanical performance, ease of processing, and compatibility with natural fiber reinforcements (Karuppusamy et al. 2025).
Methods
The methodology of this study consists of three key steps: extraction of macro fiber from Aristida hystrix plant leaves, synthesis of nano fiber particles from macro fiber, and preparation of nano fiber-reinforced polyester composite laminates. These processes are detailed below (Manickaraj et al. 2025a).
Extraction of Macro Fiber
Macro fibers were manually harvested from the leaves of the Aristida hystrix plant (Fig. 1B). The fibers were carefully isolated to maintain strand integrity and then naturally dried at ambient temperature for four days to minimize moisture content. Proper drying was crucial for improving fiber–matrix adhesion during composite fabrication. The dried fibers were subsequently stored under controlled conditions to prevent reabsorption of moisture (Gurusamy et al. 2025).
Preparation of Nano Fiber Particles
The dried macro fibers were processed into nano-sized particles using a high-energy ball milling technique (Model: PM 100, Retsch, Germany). Ball milling was selected for its efficiency in reducing fiber size, achieving uniform distribution, and enhancing fiber–matrix interfacial bonding (Karuppusamy et al. 2025a). The process operated through the combined effects of impact and friction generated by tungsten carbide balls colliding with the chamber walls, as shown in Fig. 2A. The reverse rotation of the supporting disc further intensified the crushing effect, reducing the fibers to nanoscale particles. Milling parameters such as speed, time (10 h), and ball-to-fiber ratio were optimized to obtain nano-sized particles without compromising the intrinsic mechanical properties of the fiber. The resultant nano Aristida hystrix fiber (AHF) particles are shown in Fig. 2B.
Fig. 2. A. Working principle of ball; B. Nano fiber particles after 10 h of milling process
Fabrication of Nano AHF/Polyester Composites
Nano fiber particles were integrated into polyester resin at different weight percentages (0%, 1%, 3%, 5%, 7%, and 9%) to produce composite laminates using solvent casting and compression molding. These approaches guarantee consistent fiber distribution and flawless laminates. The nano Aristida hystrix fiber (AHF) particles were initially combined with acetone, serving as an accelerator, and subsequently incorporated into the polyester matrix. The mixture was sustained at 65 to 75 °C and agitated constantly with a mechanical stirrer for uniform dispersion. The mixture was thereafter put into a steel mold measuring 260 × 220 × 3 mm³ and distributed uniformly. The mold underwent compression at 12 MPa, and the resin was let to cure for 30 h at ambient temperature. The fabricated composite plates are seen in Fig. 3 (A through F). The composites were subjected to mechanical testing, including evaluations of tensile, flexural, and impact strength, in accordance with ASTM standards. Water absorption experiments were performed to evaluate moisture resistance, while SEM analysis investigated fiber dispersion and interfacial adhesion (Manickaraj et al. 2025b). The prepared composites are shown in Fig. 3.
Fig. 3. Composite plates: A. 0%; B. 1%; C. 3%; D. 5%; E. 7%; F. 9%
Mechanical Testing of Composite Laminates
The prepared composite laminates underwent various mechanical testing to investigate their mechanical properties as per ASTM standards. The testing methods were explained below.
Tensile Test (ASTM D638-14 2022)
The tensile properties, including tensile strength, tensile modulus, and elongation at break, for the different weight percentages of composite plates were assessed using the KALPAK, KIC-2, 100 C universal testing machine. The ASTM D638-14 (2022) type-I method is employed for conducting tensile testing (Farah et al. 2016; Gurusamy et al. 2024; Manickaraj et al. 2024a). The measurements of the specimens are 165 x 13 x 3 mm³. Fig 4A illustrates the testing specimens. The specimen was secured within the tensile testing machine, featuring a gauge length of 50 mm, as illustrated in Fig. 4B. The test involves applying a tensile load to the specimen until fracture occurs, conducted at a cross-head speed of 2mm/min. Three samples were analyzed to ensure precise outcomes.
Fig. 4. A. Tensile testing samples; B. Tensile testing machine
Flexural Test (ASTM D790 2017)
The flexural characteristics of nano-reinforced Aristida hystrix were evaluated by the three-point bending test technique, adhering to ASTM D790-17 (2017), with the use of a universal testing machine (Dasari et al. 2009; Kapil Dev et al. 2022). The specimen measurements for this test are 127 x 12.7 x 3.2 mm³. The specimen is positioned horizontally on two supports of the testing apparatus, with a gauge length of 63 mm, as seen in Fig. 5A. The crosshead speed is uniformly established at 2 mm/min.
Fig. 5. A. Flexural testing samples; B. Impact testing machine
Impact Test (ASTM D256 2023)
The impact test was conducted using the Izod impact setup within the impact testing apparatus, as illustrated in Fig. 5B. The ASTM D256-23 (2023) standard is utilized for conducting impact testing (Zhang et al. 2015; Melkamu et al. 2019). The dimensions of the testing specimen were 65 x 13 x 3 mm³, and featured a notch cut at a 45° angle to a depth of 2.6 mm. The impact pendulum struck the notched specimen until it fractured, allowing for the measurement of the energy absorbed by the material.
Morphological Study
The fracture surfaces of Nano AHF composites were analyzed using a scanning electron microscope (VEGA TESCAN, Brno, Czech Republic). To improve imaging quality, the samples were sputter-coated with gold, allowing clear visualization of fiber dispersion and matrix bonding at various loadings.
Water Absorption Test (ASTM D570 2022)
The research examined the water absorption properties of Nano AH fiber reinforced composite laminates, performed in compliance with ASTM Standard D570-22. The dimensions of the sample size are 20 x 20 x 2mm³, as seen in Fig. 6. The samples were subjected to an oven at 50 °C for 1 h to remove moisture content. The specimens were immersed in distilled water at room temperature for 24 h. After immersion in water, the specimens were promptly removed and weighed at regular intervals of every 2 h. To ascertain the volume of water absorbed by the specimens, they were dried using absorbent paper and then reweighed using an accurate four-digit scale. The percentage of water absorption is calculated using the following formulae,
where Ws1 is the weight (g) of the samples before immersion in water and Ws2 is the weight (g) of the samples after immersion in water.