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Article

Comparative Study on Mechanical and Tribological Properties of Alkali-Treated and Untreated Sida acuta Fiber-Reinforced Composite

by
Chandra Mohan Heggade Halli Krishnappa
1,
Devaraj Sonnappa
2,
Narayana Swamy Kalavara Saddashiva Reddy
2,
Nikhil Rangaswamy
2,
Ganesh Ravi Chate
3,* and
Manjunath Patel Gowdru Chandrashekarappa
4,*
1
Department of Mechanical Engineering, SJC Institute of Technology, Visvesvaraya Technological University, Chickaballapur 562101, India
2
School of Mechanical Engineering, REVA University, Bengaluru 560064, India
3
Department of Mechanical Engineering, KLS Gogte Institute of Technology, Visvesvaraya Technological University, Belagavi 590018, India
4
Department of Mechanical Engineering, PES Institute of Technology & Management, Visvesvaraya Technological University, Belagavi 590018, India
*
Authors to whom correspondence should be addressed.
Eng 2025, 6(7), 143; https://doi.org/10.3390/eng6070143
Submission received: 8 May 2025 / Revised: 13 June 2025 / Accepted: 18 June 2025 / Published: 30 June 2025
(This article belongs to the Special Issue Fibres and Textiles: Innovations, Engineering, and Sustainability—in Memory of Professor Izabella Krucińska (1953–2023))
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Abstract

The present study focused on a comparative analysis of NaOH-treated and untreated Sida acuta fiber-reinforced composites with respect to their wear behavior and compressive strength. The Sida acuta fibers were treated with 5% NaOH, while the untreated fibers were used directly as reinforcement, both comprising 32 ± 1 wt.% of the epoxy matrix composites. The composites were further characterized based on their average density, hardness, and compressive strength. Additionally, weight loss, volume loss, and wear rate were examined under dry wear test conditions across various loads and sliding velocities. The results indicate that the alkali-treated fiber-reinforced composite exhibits superior hardness (84.3 ± 2.0) and compressive strength (99.89 ± 3.92 MPa), representing improvements of 12.57% and 13.5%, respectively, over the untreated fiber-reinforced composite. Moreover, the 5% NaOH-treated fiber-reinforced composite demonstrated lower wear rates compared to its untreated counterpart. Scanning Electron Microscopy (SEM) was employed to examine the dry wear surface morphology of both composite laminates, providing insights that support the observed test results. Overall, the developed Sida acuta composite exhibits promising properties, making it suitable for lightweight and medium-strength structural applications.

1. Introduction

The thread-like fiber material derived from plants (cellulose-based: seeds, stem, leaf, fruit, and wood), animals (protein-based: silk, hair, fur, feather, and wool), and geological (mineral-based: asbestos) processes is referred to as natural fibers [1,2]. Natural fibers are lightweight, low-cost, biodegradable, and environmentally friendly materials that are abundantly available in many countries [3,4]. The use of natural fibers supports the achievement of sustainable development goals by facilitating the introduction of environmentally friendly products into the market [5]. Natural fibers are flexible, easy to use and handle, ensure a versatile alternative to traditional materials and composites, and enable industry personnel to contribute to eco-friendly construction and sustainability goals [5,6,7]. Natural fibers serve as alternate materials to carbon and glass fibers in fiber-reinforced polymer composites, particularly in building products, packaging applications, and automotive components such as dashboards, door panels, and interior parts [8,9]. Therefore, studying various types of natural fibers and their properties plays a vital role in developing innovative products and widening their industrial applications.
In the past two decades, natural fibers (sisal, banana, cotton, flax, jute, kenaf, abaca, coir, etc.) have received global attention in the fabrication of FRP (Fiber Reinforced Polymer) composites possessing customized properties (density and strength) [10]. The abundant availability of natural fibers economically in all seasons ensures a potential alternative material to replace synthetic fibers and petrochemical products [11,12]. Unlike other natural fibers, Sida acuta fibers are biodegradable, lightweight, environmentally friendly, and grown abundantly on wasteland (forest edges and roadsides), ensuring that they are freely available in India [13]. Sida acuta fibers derived from the hard stem part of the plant are spheroidal in shape, polygonal in structure, irregular in length, and yellow [14]. Sida acuta plants and their fibers have been used to prepare ropes, toothbrushes, chewing sticks, baskets, and brooms [15,16,17]. Recently, Sida acuta fibers and their FRPs were studied to examine their physical and mechanical behavior [13,18,19], microstructural characteristics [12], moisture absorption [19,20], and so on. The surface treatment of (NaOH solution) Sida acuta fibers led to improved surface roughness and thermal stability compared to other chemically treated solutions, such as decyl, dodecyl, and ammonia [12]. The Sida acuta fiber orientation effects in FRP composites on moisture absorption and mechanical properties were investigated [19]. The composite laminate with ±45° fabric orientation exhibited a permeability of 1.15 × 10−3 mm2/s and a diffusion coefficient of 1.09 × 10−3 mm2/s, respectively. These properties were found to be 33.5% lower for a composite with a 0°/90° fabric orientation. The study also concluded that a laminate with a ±45° fiber orientation enhances the tensile strength and modulus by 17.5% and 6%, respectively, compared to a composite with 0/90° fabric orientation. The composite laminate with a ±45° fiber (fiber content of 32 wt.%) fabric orientation resulted in an in-plane shear strength equal to 7.15 MPa, respectively [13]. Sida acuta fiber fabric with an orientation of ±45° in a composite improves compression strength by 30.97%, flexural strength by 14.76%, impact strength by 18.88%, and inter-laminar strength by 33.4% compared to those with a 0°/90° fiber fabric orientation in composites [18]. Given these performance gains, studying the wear properties of Sida acuta fiber composites is crucial for their potential use in structural, automotive, and sustainable engineering applications.
In recent years, several researchers have investigated the wear performance of various types of FRP composites with varying reinforcements, particle sizes, and loading conditions. Compared to glass and carbon fibers, aramid fiber fabric as a reinforcement material exhibited better abrasive wear behavior in a polyetherimide composite [21]. The glass fiber-reinforced composite showed a decreased wear rate with a corresponding increase in normal and sliding velocity conditions [22]. The size of abrasive particles influenced the wear rate of a polyether sulfone–aramid fiber fabric composite laminate [23]. The carbon-reinforced composite laminates exhibited superior wear resistance compared to glass epoxy composites [24]. The study concluded that the coefficient of friction decreased with a reduction in load and an increase in sliding velocity. Incorporating 40% fly ash into the vinyl ester matrix significantly enhances wear resistance and reduces wear loss [25]. The wear behavior of bamboo fiber-reinforced composite laminates using a block-on-ring wear testing apparatus was investigated [26]. The results indicated that the wear volume increased with increased normal load and sliding velocity. Specimens with normal fiber orientation exhibited superior wear resistance compared to those with parallel orientation, and the outer laminate layers demonstrated enhanced wear performance. Cotton fiber with an ultrahigh-modification polyester resin composite laminate resulted in reduced wear with an increase in normal load [27]. The polyvinyl alcohol-treated bamboo-reinforced composites exhibited a reduced coefficient of friction and lower volume loss under dry wear conditions [28]. The wear behavior of sugarcane fiber-reinforced polyester composite laminate exhibited improved wear resistance compared to pure polyester resin composites [29]. The use of water as a lubricant during wear examination significantly enhanced performance, reducing wear and friction in betel nut-reinforced polyester composite laminates by ≈ 94% and 50%, respectively, compared to tests conducted without lubrication. The literature review confirmed that testing the wear and friction behavior of synthetic [30,31] and natural fiber (sugarcane [32], cotton [33], betelnut [34,35], kenaf [36], sisal [37])-reinforced composites under different tribological loading conditions to enhance the performance of mechanical parts is of industrial relevance.
Chemical treatment of both natural and synthetic fibers plays a crucial role in enhancing fiber–matrix interfacial bonding, thereby improving the overall performance of FRP composites [38]. Studies on such treatments are of significant practical relevance for developing high-performance, durable, and sustainable composite materials [6,39]. The effect of surface-treated Kenaf fiber reinforcement in poly-lactic acid composites on mechanical properties was investigated [40]. The study concluded that Silane and NaOH-treated Kenaf fibers exhibited superior properties compared to untreated Kenaf fiber-reinforced PLA (Polylactic Acid) composites. Surface treatment of carbon fiber with nitric acid increases the concentration of oxygen-containing functional groups on the fiber surface and enhances surface roughness by forming longitudinal crevices, thereby improving fiber–matrix bonding in the laminate [41]. The chemical treatment of natural fibers to improve fiber–matrix bonding in composite laminates is of practical relevance.
The literature review highlights a significant research gap in the study of the wear behavior of surface-treated Sida acuta fiber-reinforced composite laminates. Investigations involving Sida acuta as a reinforcement material, both with and without surface treatment on wear behavior, are often limited. The present study aims to examine the tribological performance of epoxy-based fiber-reinforced composites fabricated using Sida acuta fibers. Initially, the fibers were treated with a 5% NaOH solution to enhance interfacial bonding through surface modification. Subsequently, epoxy composite laminates were fabricated using both untreated and alkali-treated Sida acuta fibers via the hand lay-up technique. The composites were evaluated to determine weight loss, wear volume loss, and the wear rate under varying applied loads and sliding velocities. All tribological tests were conducted at room temperature. This study not only contributes to understanding the wear characteristics of Sida acuta-based bio-composite laminates but also offers insight into the effect of alkali surface treatment on their performance, presenting a novel, eco-friendly alternative for structural and tribological applications.

2. Experimental Methods

2.1. Materials

Composite laminates are fabricated using Sida acuta fibers in untreated and alkali-treated forms to examine the effect of chemical treatment on their performance. Purified sodium hydroxide (NaOH) pellets used for surface treatment were sourced from S D Fine-Chem Limited (SDFCL), located at TV Industrial Estate, Worli Road 248, Mumbai, India. Medium-viscosity epoxy resin (Lapox L-12) and K-6 polyamine hardener were obtained from Atul Ltd., Gujarat, India, for use as the matrix system. During laminate preparation, epoxy resin and K-6 hardener were mixed in a 10:1 ratio by weight, respectively.

2.2. Surface Treatment

Prior to surface treatment, Sida acuta fibers were dried in an air oven at 50 °C for 20 h to remove moisture and facilitate better alkali penetration during chemical modification. Subsequently, the dried fibers were treated with a 5% NaOH solution (refer to Figure 1). Approximately 30 g of Sida acuta fibers was treated with a 5% NaOH solution at room temperature for a duration of 4 h. After alkali treatment, the Sida acuta fibers were rinsed 2–3 times with warm water to remove residual NaOH, followed by immersion in a 0.1 N acetic acid solution for 3 min to neutralize the surface. Subsequently, the fibers soaked in acetic acid were rinsed with warm water to remove any residual solution from the surface and then dried at room temperature for 48 h. The procedure for fiber surface treatment and the optimal test conditions were selected based on the fiber strength, referring to past literature [19], consultation with experts, and pilot experimental studies at research laboratories.

2.3. Composite Preparation

In this study, Sida acuta fiber-reinforced epoxy composites were prepared to investigate their wear properties. Treated and untreated Sida acuta fibers were separately pre-impregnated with epoxy resin and K-6 hardener and subsequently used for fabrication of biocomposites using the hand lay-up technique. Semi-circular hollow metallic dies, comprising cope and drag parts with an inner diameter of 10 mm and a length of 250 mm, were employed in the fabrication of Sida acuta fiber-reinforced composites (refer to Figure 2). Specimens for wear and compression tests were prepared following ASTM G99 [42], with the compression test specimens maintaining an L/D ratio below 2 (refer to Figure 3). Additionally, specimens for density and hardness tests were prepared in accordance with the relevant standards. In both untreated and alkali-treated Sida acuta fiber-reinforced composites, the fibers were oriented in a single direction perpendicular to the counter face of the disk and parallel to the load direction (longitudinal orientation) with a fiber content maintained at 32 ± 1 wt.% in both composites.

2.4. Density Test

Density measurements for both NaOH-treated and untreated Sida acuta fiber-reinforced composites were carried out based on Archimedes’ principle using a Contech (CAH-100) electronic balance (Contech Instruments Ltd, Mumbai, India). The density evaluation is essential for determining the uniformity and compactness of the composite structure, providing insights into void formation and the effectiveness of fiber-matrix bonding. For the density test, three identical samples were taken from each of the alkali-treated and untreated Sida acuta fiber-reinforced composites, and the average density was calculated.

2.5. Compression Test

The compression strength test for both untreated and surface-treated Sida acuta epoxy composites was conducted using a BISS UT-01-0025 compression-testing machine (BISS, Bangalore, India) at a strain rate of 0.016 s−1. Three identical cylindrical specimens with an L/D ratio of less than 2 were selected from each composite type, and the average compressive strength and modulus were calculated.

2.6. Hardness Test

Rockwell hardness measurements for both untreated and surface-treated Sida acuta composites were conducted using a Q-250 MS computerized hardness tester (QATM, Mammelzen, Germany) with a 0.5-inch diameter carbide ball indenter, following the HR-15Y scale as per ASTM E18 [43]. The hardness value for each composite was determined by averaging the results from three specimens.

2.7. Wear Test

The wear behavior of untreated and 5% NaOH-treated fiber-reinforced composites was evaluated using a Ducom TR-20 pin-on-disc (Ducom Instruments, Bangalore, India) wear testing machine, following the ASTM G99 test standard. Figure 4 illustrates the schematic view of the wear testing setup for Sida acuta fiber-reinforced composites. A 400-grit abrasive emery paper was first cut to fit the 100 mm diameter rotating disc and fixed securely using a circular metallic holder with locking screws. To maintain uniform test conditions, the emery paper was replaced after each test set. For each test, the initial and final length and diameter of the specimen were measured using a digital Vernier caliper (least count: 0.01 mm), and the mass was measured with a digital weighing balance (least count: 0.1 mg). The specimen was then mounted on the pin-on-disc wear testing machine. Wear testing was carried out at a constant sliding diameter of 80 mm and a fixed duration of 3 min. Each alkali-treated and untreated Sida acuta composite specimen was tested under different applied loads (5, 10, and 15 N) and sliding velocities (0.83, 1.67, and 2.51 m/s) to evaluate wear performance. After each wear test, the specimens were reweighed and measured to determine the wear, weight loss, and volume loss of both alkali-treated and untreated Sida acuta epoxy composites. The wear test value for each composite was determined by averaging the results from three specimens. The corresponding results are reported in Table 1 and Table 2, respectively.

2.8. Worn Surface Morphology

Worn surfaces of untreated and NaOH-treated fiber epoxy composites were examined using a TESCAN VEGA 3 LMU SEM (TESCAN, Brno, Czech Republic) at 10 kV. Prior to imaging, the samples were gold-coated to enhance surface conductivity.

3. Results and Discussion

The prepared composite was tested for density, hardness, compression strength, and wear. The results of these tests are discussed in this section.

3.1. Density

The density of untreated and 5% NaOH-treated Sida acuta fiber-reinforced composites, each with a fiber loading of 32 ± 1 wt.%, was measured using three identical specimens from each composite laminate composition. Treated Sida acuta fiber-reinforced composites exhibited an average density of 0.846 ± 0.006 g/cc, whereas the untreated composites showed a lower average density of 0.809 ± 0.005 g/cc. The densities of both untreated and alkali-treated Sida acuta composites were approximately similar because NaOH treatment primarily removes surface impurities (non-cellulosic components like lignin, hemicellulose, and pectin) without altering the fiber volume [44]. The alkali-treated fiber improves the surface roughness and fiber–matrix adhesion, which does not substantially affect the fiber mass or resin infiltration [45]. The overall composite density showed negligible variation as the fiber loading remained constant for both treated and untreated specimens.

3.2. Rockwell Hardness

Alkali-treated fiber-reinforced composites exhibited a Rockwell hardness of 84.3 ± 2.0, while the untreated composites showed a lower value of 73.7 ± 1.3. The alkali-treated fiber-reinforced composite laminate, containing 32 ± 1 wt.% fiber, exhibited a 12.57% increase in hardness compared to the untreated fiber-reinforced composite laminate. This enhancement is primarily due to improved fiber–matrix interfacial bonding, which also contributes to greater overall composite laminate strength [45]. The Rockwell hardness of surface-treated and untreated Sida acuta fiber-reinforced composite laminates was 30% and 19.94% higher, respectively, than that of neat epoxy. The hardness of neat epoxy ranged from 57 to 60.

3.3. Compression Strength

The stress–strain curves obtained from the compression tests of treated and untreated Sida acuta fiber epoxy composites are shown in Figure 5. NaOH-treated fiber-reinforced composites exhibited an average compressive strength of 99.89 ± 3.92 MPa and a compressive modulus of 1.295 ± 0.02 GPa. In comparison, the untreated fiber-reinforced composite exhibited a compressive strength of 88.01 ± 1.14 MPa and a compressive modulus of 1.633 ± 0.05 GPa. The mechanical performance of FRP composite laminates is largely influenced by the fiber volume fraction and the strength of the fiber–matrix interfacial bonding. The average values were obtained by testing three identical samples from each composite laminate composition. The compressive strength of alkali-treated fiber-reinforced composites was 99.89 MPa, which is 13.5% higher than that of untreated fiber epoxy composites. This improvement may be attributed to enhanced bonding strength between the matrix and fiber materials. However, the compressive modulus of the treated fiber-reinforced composite was observed as 1.29 GPa, which is 20.85% lower compared to that of the untreated fiber-reinforced composite (1.63 GPa). Linearity in the stress–strain response was observed up to approximately 60 MPa at 4% strain. The subsequent deviation in the curves is due to the varying ductility characteristics of the alkali-treated and untreated fiber-reinforced composites. The alkali-treated fiber-reinforced composite exhibited lower ductility compared to the untreated fiber-reinforced composite (refer to Figure 5), a result consistent with the findings reported earlier by the authors of [19]. The mode of failure in both treated and untreated fiber-reinforced composites exhibited a barreling pattern after reaching the maximum compressive strength.

3.4. Weight Loss of the Composite

Figure 6a,b present the weight loss behavior of alkali-treated and untreated Sida acuta composites under varying normal loads at a constant sliding velocity of 2.51 m/s and under varying sliding velocities at a constant load of 15 N, respectively. The weight loss values presented in Table 1 and Table 2 represent the average of three repeated trials (n = 3) for each test condition, and the standard deviation values for alkali-treated and untreated Sida acuta composites were found to be ±0.002 g and ±0.003 g. The weight loss in both alkali-treated and untreated fiber-reinforced composites increased noticeably with increasing applied load and sliding velocity. A similar weight loss trend was reported in the literature for jute–polypropylene composites [46] and carbon–epoxy composites [7]. As shown in Figure 6a, the NaOH-treated fiber-reinforced composite exhibited a reduction in wear loss (in grams) compared to the untreated Sida acuta fiber biocomposite at a constant sliding velocity. The reduction was 0% at 5 N load, 33.33% at 10 N, and 32.45% at 15 N. At constant sliding velocities of 0.83 m/s and 1.67 m/s, both treated and untreated Sida acuta fiber-reinforced composites exhibited comparable weight loss across different applied loads, as presented in Table 1 and Table 2. Figure 6b reveals that at a constant load of 15 N, the 5% NaOH-treated fiber-reinforced composite exhibited a reduction in weight loss of 50%, 41.66%, and 33% at sliding velocities of 0.83 m/s, 1.67 m/s, and 2.51 m/s, respectively, when compared to the untreated Sida acuta fiber-reinforced composite. This study revealed a lower percentage of weight loss in the alkali-treated Sida acuta fiber-reinforced composite, which was 33.33% less than that of the untreated composite under both maximum constant load and constant sliding velocity conditions.

3.5. Volume Loss of the Composite

Figure 7a depicts the volume loss of NaOH-treated and untreated fiber-reinforced composites under various applied loads at a constant sliding velocity of 2.51 m/s. The volume loss of the alkali-treated fiber-reinforced composite decreased by 66.21%, with an increase in the applied load from 5 N to 10 N. With a further increase in the applied load from 10 N to 15 N, the volume loss of the composite laminate increased by 19.59% compared to the 10 N condition, yet remained 57.98% lower than that observed at 5 N. As shown in Figure 7a, the volume loss of the untreated fiber-reinforced composite at a 15 N load and a sliding velocity of 2.51 m/s decreased by 52.56% and 72% compared to the values observed at 5 N and 10 N loads, respectively. Both alkali-treated and untreated Sida acuta fiber-reinforced composites exhibited a minimum volume loss of approximately 11.5 mm3 at a 15 N load and a sliding velocity of 2.51 m/s, indicating lower wear under these conditions. The decrease in volume loss at higher loads is mainly due to the formation of a protective transfer layer, surface smoothing, and compaction of wear debris, all of which act to shield the composite from further wear [47]. The untreated fibers have poor adhesion with the epoxy matrix, which might be due to the presence of surface impurities, leading to higher wear through fiber–matrix separation and surface degradation under stress [44,45]. It is important to note that both composites perform similarly at higher loads (probably due to matrix densification and friction-induced stability). However, the treated composite consistently shows superior wear resistance at lower and moderate loads due to better fiber–matrix integrity.
Figure 7b shows the volume loss of untreated and treated fiber-reinforced composites at different sliding velocities (0.83, 1.67, and 2.51 m/s) under a constant load of 15 N. The volume loss of the untreated fiber-reinforced composite decreased sharply from 31.80 mm3 to 10.99 mm3 with an increase in sliding velocity. In contrast, the alkali-treated fiber-reinforced composites showed a slight increase in volume loss from 10.60 mm3 to 12.21 mm3 as the sliding velocity increased from 0.83 m/s to 2.51 m/s. The reduced volume loss observed in the NaOH-treated fiber-reinforced composite, relative to the untreated composite, is primarily due to enhanced interfacial bonding between the fiber and matrix materials. Figure 7a depicts the non-linear behavior in volume loss with increased applied load, which is attributed to the combined impact of tribological and material behavioral factors. At a moderate load of 10 N, the formation of a protective tribo-layer, surface smoothening, and compaction of wear debris contributed to reduced volume loss. The above mechanism protects the composite from further wear, which reduces the abrasive interactions. As the load further increased to 15 N, localized frictional heat tended to dominate, which could cause matrix softening and degradation of the fiber–matrix interface, particularly in untreated composites. Stresses are generally increased at higher loads, which can cause fiber pullout and initiate micro-cracks, resulting in slightly increased wear. The volume loss at 15 N was significantly lower than at 5 N due to the stable effects of densified surface layers and debris compaction. Thereby, the observed non-linearity reflects the complex interplay between mechanical compaction and thermal degradation effects under loading conditions. As presented in Table 1, the volume loss of the alkali-treated fiber-reinforced composite increased progressively with increasing sliding velocity from 0.83 to 2.51 m/s under all applied normal load conditions. Table 2 presents the measured volume loss of the untreated fiber-reinforced composite under different sliding velocities and normal load conditions for comparative analysis. The volume loss values presented in Table 1 and Table 2 represent the average of three repeated trials (n = 3) for each test condition, and the standard deviation values for alkali-treated and untreated Sida acuta composites were found to be ±0.23 mm3 and ±0.27 mm3.

3.6. Wear Rate of the Composite

Figure 8a presents the wear rate of 5% NaOH-treated and untreated Sida acuta composites under varying normal loads at a constant sliding velocity of 2.51 m/s, while Figure 8b presents the wear rate under different sliding velocities at a constant normal load of 15 N. Figure 8a depicts that wear in both alkali-treated and untreated fiber epoxy composite laminates decreases noticeably with an increase in applied load from 5 N to 15 N. Likewise, Figure 8b shows a reduction in wear with increasing sliding velocity (from 0.83 m/s to 2.51 m/s) at a constant applied load of 15 N. At a constant sliding velocity, the wear rate of the treated fiber laminate showed a significant decrease from 0.013 mm3/N·m to 0.002 mm3/N·m as the applied load increased from 5 N to 10 N, and further reduced to 0.0018 mm3/N·m at 15 N. A similar trend was observed for the untreated fiber-reinforced composite, where the wear rate reduced from 0.010 mm3/N·m to 0.001 mm3/N·m as the applied load increased. Figure 8b depicts the wear rate of the treated fiber-reinforced composite at a sliding velocity of 0.83 m/s, which is 66.57% lower compared to that of the untreated Sida acuta composite. This reduction is attributed to the increased hardness of the treated fiber-reinforced composites.
Additionally, the wear test was conducted by increasing the sliding velocity from 1.67 to 2.51 m/s under a fixed applied load of 15 N. Both composites exhibited comparable wear values under the given test conditions. In summary, the experimental results demonstrated that for each applied load condition, the wear of both alkali-treated and untreated Sida acuta fiber epoxy composite laminates decreased consistently as the sliding velocity increased from 0.83 to 2.51 m/s. Additionally, the wear rate of the 5% NaOH-treated Sida acuta composite was observed to be lower than that of the untreated fiber laminate, primarily due to the enhanced hardness resulting from the alkali treatment. The wear rate values presented in Table 1 and Table 2 represent the average of three repeated trials (n = 3) for each test condition, and the standard deviation values for alkali-treated and untreated Sida acuta composites were found to be ±0.0007 mm3/N·m, and ±0.0005 mm3/ N·m. Table 3 presents a comparative analysis of wear rate values for untreated and alkali-treated SAF (Sida Acuta Fiber) -reinforced composites under various loads and rotational speeds. Alkali treatment significantly improves wear resistance at low to moderate loads and speeds, particularly at a 1.0 kg load, where improvements exceed 70% consistently. However, at higher sliding speeds (600 rpm at 0.5 kg load) or loads (1.5 kg), the alkali treatment did not show any improvement, possibly due to increased thermal degradation or fiber–matrix debonding.

3.7. Surface Morphology of the Composite

SEM analysis was performed on the worn surfaces of 5% alkali-treated and untreated Sida acuta epoxy composite specimens tested at a sliding velocity of 2.51 m/s and a load of 15 N. Figure 9a,b and Figure 9c,d display the respective surface morphologies at 250× and 500× magnifications. Figure 9a,b reveal that the worn surface of the alkali-treated Sida acuta fiber-reinforced composite is relatively smooth, with identifiable features such as the sliding direction, wear debris, surface cracks, and pits. Figure 9c,d illustrates the worn surface of the untreated fiber epoxy composite, characterized by pronounced abrasive grooves in the sliding direction, weak fiber–matrix interfacial bonding, surface cracking, and visible wear debris. The presence of deep grooves on the worn surface of the untreated fiber laminate indicates the dominance of an abrasive wear mechanism. Therefore, the formation of deep grooves and weak interfacial bonding between the fiber and matrix in the untreated Sida acuta composite contributes to a higher wear rate compared to the treated fiber-reinforced composite under maximum sliding velocity and applied load conditions.

4. Conclusions

In the present study, Sida acuta fibers were surface-treated with a 5% NaOH solution to remove impurities and foreign particles from the fiber surface. With a fiber loading of 32 ± 1 wt.%, both alkali-treated and untreated Sida acuta fibers were individually incorporated as reinforcement in the fabrication of composites. The resulting composite laminates were evaluated for their density, hardness, compressive strength, wear rate, volume loss, and weight loss. This study includes a discussion of key characterization parameters and highlights the potential applications of Sida acuta composites in various lightweight and tribological applications.
  • The density of both untreated and alkali-treated Sida acuta composites was found to be approximately the same, with an average value of 0.827 g/cc. This occurs because the alkali treatment primarily removes the surface impurities (non-cellulosic components like lignin, hemicellulose, and pectin) without altering fiber volume.
  • An increase of 12.57% in Rockwell hardness was observed in the alkali-treated fiber epoxy composite (32 ± 1 wt.% fiber loading) compared to the untreated composite, primarily due to enhanced interfacial bonding between the fiber and matrix.
  • The average compressive strength of the treated Sida acuta composite was 99.89 ± 3.92 MPa, which is 13.5% higher than that of the untreated composite (88.01 ± 1.14 MPa), indicating improved mechanical performance due to alkali treatment.
  • The wear rate of the 5% NaOH-treated Sida acuta epoxy composite was lower compared to that of the untreated composite, likely due to the increased hardness of the treated fiber-reinforced laminate.
  • The alkali-treated SAF composite significantly improves the wear resistance at 1.0 kg load, resulting in a more than 70% increase in performance compared to the untreated SAF composite. However, at higher sliding speeds (600 rpm at 0.5 kg load) or loads (1.5 kg), the alkali treatment did not show any improvement, possibly due to increased thermal degradation or fiber–matrix debonding.
  • Finally, alkali-treated Sida acuta fiber-reinforced composites demonstrated enhanced mechanical strength and wear resistance over untreated counterparts, suggesting their suitability for lightweight structural and tribological applications in household and industrial settings.

Author Contributions

Conceptualization: C.M.H.H.K., D.S., N.R. and M.P.G.C.; methodology: C.M.H.H.K., N.R., G.R.C. and D.S.; software: C.M.H.H.K., N.R. and N.S.K.S.R.; validation: C.M.H.H.K. and D.S.; formal analysis: M.P.G.C., C.M.H.H.K. and D.S.; methodology: C.M.H.H.K., D.S. and N.S.K.S.R.; investigation D.S., N.S.K.S.R. and G.R.C.; resources: C.M.H.H.K., D.S. and N.S.K.S.R.; writing—original draft preparation: M.P.G.C., C.M.H.H.K., N.R. and G.R.C.; writing—review and editing: M.P.G.C., G.R.C. and N.R.; visualization: C.M.H.H.K.; supervision, D.S. and N.S.K.S.R.; project administration: C.M.H.H.K., D.S. and N.S.K.S.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data is contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The 5% NaOH treatment of Sida acuta fiber.
Figure 1. The 5% NaOH treatment of Sida acuta fiber.
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Figure 2. Wear test samples. (a) Untreated fiber-reinforced composites and (b) treated fiber-reinforced composites.
Figure 2. Wear test samples. (a) Untreated fiber-reinforced composites and (b) treated fiber-reinforced composites.
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Figure 3. Compression test samples. (a) Untreated fiber-reinforced composites and (b) treated fiber-reinforced composites.
Figure 3. Compression test samples. (a) Untreated fiber-reinforced composites and (b) treated fiber-reinforced composites.
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Figure 4. Schematic view of wear test experimental setup.
Figure 4. Schematic view of wear test experimental setup.
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Figure 5. Compression test stress–strain diagram of treated and untreated Sida acuta fiber-reinforced composite.
Figure 5. Compression test stress–strain diagram of treated and untreated Sida acuta fiber-reinforced composite.
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Figure 6. (a) Weight loss of Sida acuta composites at 2.51 m/s sliding velocity under varying applied loads; (b) weight loss at a constant load of 15 N under varying sliding velocities.
Figure 6. (a) Weight loss of Sida acuta composites at 2.51 m/s sliding velocity under varying applied loads; (b) weight loss at a constant load of 15 N under varying sliding velocities.
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Figure 7. (a) Volume loss of Sida acuta fiber-reinforced composites after wear testing at a sliding velocity of 2.51 m/s under various applied loads; (b) volume loss of Sida acuta fiber-reinforced composites after wear testing at a constant load of 15 N under various sliding velocities.
Figure 7. (a) Volume loss of Sida acuta fiber-reinforced composites after wear testing at a sliding velocity of 2.51 m/s under various applied loads; (b) volume loss of Sida acuta fiber-reinforced composites after wear testing at a constant load of 15 N under various sliding velocities.
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Figure 8. (a) Wear of Sida acuta fiber-reinforced composites after wear testing at a sliding velocity of 2.51 m/s under various normal loads; (b) wear of Sida acuta fiber-reinforced composites after wear testing at a constant load of 15 N under various sliding velocities.
Figure 8. (a) Wear of Sida acuta fiber-reinforced composites after wear testing at a sliding velocity of 2.51 m/s under various normal loads; (b) wear of Sida acuta fiber-reinforced composites after wear testing at a constant load of 15 N under various sliding velocities.
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Figure 9. SEM photographs of worn surfaces: (a) alkali-treated Sida acuta fiber (SAF) composite at 250× magnification; (b) alkali-treated SAF composite at 500× magnification; (c) untreated SAF composite at 250× magnification; (d) untreated SAF composite at 500× magnification.
Figure 9. SEM photographs of worn surfaces: (a) alkali-treated Sida acuta fiber (SAF) composite at 250× magnification; (b) alkali-treated SAF composite at 500× magnification; (c) untreated SAF composite at 250× magnification; (d) untreated SAF composite at 500× magnification.
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Table 1. Wear test details of alkali-treated Sida acuta composite at various applied loads and sliding velocities.
Table 1. Wear test details of alkali-treated Sida acuta composite at various applied loads and sliding velocities.
Load on Specimen
(kg’s)		Speed
(rpm)		Weight Loss
(gm’s)		Volume Loss
(mm3)		Wear Rate
(mm3/N·m)
0.52000.0220.020.026
4000.0221.590.014
6000.0129.050.013
1.02000.013.140.002
4000.018.240.003
6000.019.810.002
1.52000.0210.600.004
4000.0212.560.003
6000.0112.210.002
Table 2. Summary of wear test parameters and results for untreated Sida acuta fiber-reinforced composites at different load and velocity conditions.
Table 2. Summary of wear test parameters and results for untreated Sida acuta fiber-reinforced composites at different load and velocity conditions.
Load on Specimen
(kg’s)		Speed
(rpm)		Weight Loss
(gm’s)		Volume Loss
(mm3)		Wear Rate
(mm3/N·m)
0.52000.152.220.069
4000.0649.480.032
6000.0323.170.010
1.02000.0513.740.009
4000.0333.770.011
6000.0239.260.008
1.52000.01531.800.014
4000.01714.710.003
6000.0210.990.002
Table 3. Comparison of the percentage improvement in wear performance between treated and untreated composites across all conditions.
Table 3. Comparison of the percentage improvement in wear performance between treated and untreated composites across all conditions.
Load on Specimen
(kg’s)		Speed
(rpm)		Wear Rate of Untreated SAF Composite (mm3/N·m)Wear Rate of Alkali-Treated SAF Composite (mm3/N·m)Improvement (%)
0.52000.0690.02662.3
4000.0320.01456.3
6000.0100.013−30.0
1.02000.0090.00277.8
4000.0110.00372.7
6000.0080.00275.0
1.52000.0140.00471.4
4000.0030.0030.0
6000.0020.0020.0
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Krishnappa, C.M.H.H.; Sonnappa, D.; Saddashiva Reddy, N.S.K.; Rangaswamy, N.; Chate, G.R.; Gowdru Chandrashekarappa, M.P. Comparative Study on Mechanical and Tribological Properties of Alkali-Treated and Untreated Sida acuta Fiber-Reinforced Composite. Eng 2025, 6, 143. https://doi.org/10.3390/eng6070143

AMA Style

Krishnappa CMHH, Sonnappa D, Saddashiva Reddy NSK, Rangaswamy N, Chate GR, Gowdru Chandrashekarappa MP. Comparative Study on Mechanical and Tribological Properties of Alkali-Treated and Untreated Sida acuta Fiber-Reinforced Composite. Eng. 2025; 6(7):143. https://doi.org/10.3390/eng6070143

Chicago/Turabian Style

Krishnappa, Chandra Mohan Heggade Halli, Devaraj Sonnappa, Narayana Swamy Kalavara Saddashiva Reddy, Nikhil Rangaswamy, Ganesh Ravi Chate, and Manjunath Patel Gowdru Chandrashekarappa. 2025. "Comparative Study on Mechanical and Tribological Properties of Alkali-Treated and Untreated Sida acuta Fiber-Reinforced Composite" Eng 6, no. 7: 143. https://doi.org/10.3390/eng6070143

APA Style

Krishnappa, C. M. H. H., Sonnappa, D., Saddashiva Reddy, N. S. K., Rangaswamy, N., Chate, G. R., & Gowdru Chandrashekarappa, M. P. (2025). Comparative Study on Mechanical and Tribological Properties of Alkali-Treated and Untreated Sida acuta Fiber-Reinforced Composite. Eng, 6(7), 143. https://doi.org/10.3390/eng6070143

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