Optimization of tribological parameters of hybrid polymer composites reinforced with kenaf fibers and recycled spent abrasive particles

ABSTRACT

Abrasive water jet machining produces large quantities of spent abrasive particles, typically discarded due to their heterogeneous composition, comprising both metallic and non-metallic components that vary with the processed material. However, these particles can be repurposed for engineering applications. This study utilized spent abrasive particles as filler materials at 2.5%, 5%, and 7.5% by weight in an epoxy resin matrix to fabricate kenaf fiber-reinforced hybrid polymer composites. The tribological properties of the composites were systematically analyzed to identify optimal conditions for minimizing wear rate and friction. Pin-on-disc wear tests were performed using a standard tribometer at sliding velocities of 1 m/s, 2 m/s, and 3 m/s, under loads of 5 N, 10 N, and 15 N, over a constant sliding distance of 800 m. Results showed a minimum wear rate of 0.0108 mm³/m and a minimum coefficient of friction of 0.0581 for composites with 7.5 wt.% filler at a 5 N load and 1 m/s sliding velocity. Worn samples were examined using scanning electron microscopy to explore the dominant wear mechanism. The inclusion of spent abrasive particles significantly improved tribological performance by enhancing wear resistance and modifying frictional behavior through improved interfacial bonding in the polymer matrix.

Keywords:
Recycle of spent abrasive particles; Polymer hybrid composites; Dry sliding wear testing; Taguchi optimization; Worn surface analysis

1. INTRODUCTION

Currently, the world is moving towards sustainability, which focuses on resolving environmental problems by reducing, recycling, and reusing engineering waste. Focusing on sustainability, various studies have been conducted on the recycling of materials [¹,²,³,⁴]. Recycling spent abrasive particles from Abrasive Water Jet Machining, such as garnet or silicon carbide, reduces waste, conserves resources, and enhances the performance of polymer composites, offering a sustainable, cost-effective solution aligned with circular economy principles. A study was conducted to review the additives in abrasive water jet machining and their performance [⁵]. But recycling and reusing of abrasive wastes is yet to be explored. Carbon, glass, asbestos, Kevlar, and other materials are employed as reinforcements for polymers, owing to their high strength and widespread availability [⁶]. Detriments of these fibers include high energy consumption, non-degradability, and high cost [⁷,⁸,⁹]. Sliding wear behaviour of micro-sized Kota stone dust reinforced epoxy composites using Taguchi method and Grey Wolf optimisation algorithm was studied and improvement in wear resistance of composites by inclusion of kota stone dust was observed [¹⁰]. Studies have been conducted on the wear and frictional performance of epoxy composites reinforced with natural waste fibers and fillers, revealing that the tribological properties of the polymer composites are significantly enhanced through the incorporation of natural fibers and waste materials [¹¹]. The thermal and mechanical properties of polymer composites exhibited notable improvements upon the incorporation of tamarind seeds, eelgrass, and adamant creeper as reinforcing agents [¹²]. Natural fiber-reinforced polymer composites have numerous applications in the building, automotive, aeronautical and marine industries. These composites have the most desirable qualities, including affordability, accessibility, low weight, and biodegradability [¹³]. The majority of research supports the idea that natural fiber reinforcement is important when preparing composites. The mechanical properties of jute-Kevlar reinforced epoxy polymer composites were systematically evaluated, revealing that the stacking sequence of the reinforcement layers significantly influences the enhancement of their mechanical performance [¹⁴]. Natural fiber-reinforced polymer composites, while initially constrained by weak mechanical strength and inadequate interfacial bonding, have seen significant advancements through the incorporation of filler inclusions, which enhance mechanical properties and expand their industrial applications, particularly due to their sustainability and improved performance [¹⁵,¹⁶,¹⁷,¹⁸,¹⁹,²⁰,²¹,²²,²³,²⁴]. Numerous studies have been steered on the various properties of natural fiber-reinforced polymer composites, and some key findings have been discussed. Studies were conducted to investigate the impact of reinforcements on the mechanical and tribological properties of polymer composites, yielding positive results [²⁵,²⁶,²⁷].

The mechanical performance of polypropylene composites reinforced with natural fibers such as flax and jute has been positively demonstrated [²⁸], while investigations into jute, hemp, and flax hybrid polymer composites further validated the beneficial effects of these reinforcements [²⁹]. The literature consistently demonstrates that incorporating fillers, such as graphite and silica fume, into composites significantly enhances mechanical properties, including wear resistance and flexural behavior, as evidenced by studies on carbon fabric-reinforced epoxy composites and high-strength concrete reinforced with natural fibers, optimizing material performance across various applications [³⁰,³¹,³²,³³,³⁴]. The mechanical behavior of glass fiber-reinforced polyamide-6 composites with varying filler loadings, graphite, polytetrafluoroethylene (PTFE), and ultra-high molecular weight polyethylene, was investigated, demonstrating that graphite fillers significantly enhance mechanical properties [³⁵]. The influence of varying matrix/fiber concentration on the mechanical properties of bi-directional carbon fiber reinforced polymer composites was investigated, revealing a significant effect of changes in the composition of the matrix and reinforcements [³⁶]. Similarly, studies on carbon fiber-reinforced polyetheretherketone (PEEK) revealed notable improvements in tribological performance, with sliding distance and temperature playing critical roles in abrasive wear under two- and three-body conditions [³⁷, ³⁸]. The wear performance of epoxy polymer composites filled with red brick dust was investigated, demonstrating a reduction in wear rate with the incorporation of the fillers [³⁹].

Studies have been conducted to investigate the tribological properties of polymers and the mechanisms that influence wear in abrasive modes [⁴⁰, ⁴¹]. In two-body abrasive wear, the harder material removes the material from softer surfaces, where the material undergoes high strain and plastic deformation. Different polymers exhibit different tribological properties. Virgin polymers have limited use in tribological applications because they cannot meet mechanical and tribological requirements. Consequently, numerous studies on polymer composites are underway. Studies have also been conducted on the tribological properties of polymer composites with reinforcements, revealing the positive effects of reinforcements [⁴², ⁴³]. Research has confirmed that polymer nanocomposites have superior mechanical, thermal insulation, optical, and other properties [⁴⁴, ⁴⁵]. The effect of nanographene filler on the sliding and abrasive wear behavior of bi-directional carbon fiber reinforced epoxy composites was studied, revealing an improvement in the wear resistance of the polymer composites [⁴⁶]. The Taguchi method, developed by Dr. Genichi Taguchi, is a statistical approach that originated in Japan. It focuses on using orthogonal array experiments to ensure a well-balanced design in which all factors are given equal importance. The Taguchi method, which employs the signal-to-noise (S/N) ratio as a performance metric, has been widely utilized for the parametric optimization of input variables to enhance response parameters [⁴⁷]. Studies using this approach have demonstrated its efficacy in evaluating and optimizing wear properties of various composites, including heat-treated pultruded kenaf fiber-reinforced polyester [⁴⁸], halloysite nanotube-reinforced silk/basalt hybrid epoxy [⁴⁹], and natural fiber polymer composites [⁵⁰], highlighting its robust application in improving material performance.

Based on the above literature review, it has been observed that, limited research exists on recycling spent abrasive particles from water jet machining as fillers in polymer composites, particularly concerning their influence on tribological performance under varied operational conditions. Hence, the present work is aimed to investigate tribological behaviour of kenaf fiber-reinforced epoxy polymer composites incorporating varying proportions (2.5%, 5%, and 7.5% by weight) of recycled spent abrasive particle fillers, with a primary objective to optimize the wear parameter using Taguchi methodology. For which, the tribological behavior was analyzed through pin-on-disc wear testing, and wear tracks were examined using scanning electron microscopy to investigate the wear mechanisms, offering insights into the performance of hybrid composites [⁵¹].

2. MATERIALS AND METHODS

2.1. Polymer matrix and reinforcement

The composite matrix was developed using epoxy resin (LY556) combined with a curing agent (HY951), reinforced with bidirectional kenaf fibers, while spent abrasive particles from an abrasive water jet machine were introduced as particulate fillers to enhance the polymer composite’s properties. Epoxy resin (LY556) and curing agent (HY951) were procured from M/s R. K. Resins and Enterprises, Coimbatore, India, and bidirectional kenaf fiber mats were purchased from Go Green Products, Chennai, India. Bi-directional woven kenaf fiber mat (0.9 mm thick, 180 g/m²) with 0°/90° fiber orientation is used as reinforcement due to their excellent compatibility with epoxy resins.

2.2. Spent abrasive fillers

The spent abrasive particles from abrasive water jet machining were found. The spent abrasive particles from abrasive collected from water jet machining, consist of commonly used abrasives such as garnet, Al₂O, B₄C, and SiC, etc., along with debris from the workpieces cut using the machine, in different shapes and sizes. To assess their potential as filler materials for polymer composites, these spent abrasives were systematically recycled and characterized using standard testing procedures. The spent abrasive particles underwent drying, sieving, and particle size analysis through laser diffraction technology using a Malvern Mastersizer 2000 (UK), which measured particle sizes ranging from 0.02 to 2000 micrometers. Scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were conducted using a VEGA3 TESCAN Scanning Electron Microscope equipped with a BRUKER Nano EDX system to evaluate the homogeneity and elemental composition of the filler material.

2.3. Hand lay-up process

The kenaf fiber-reinforced epoxy polymer composites with recycled spent abrasive particle fillers were fabricated using the hand lay-up method followed by hydraulic compression molding, wherein kenaf fiber mats (300 mm × 300 mm) were combined with an epoxy matrix comprising 20% fiber and 80% resin-hardener mixture by weight, with the matrix itself consisting of 90 wt.% epoxy resin and 10 wt.% hardener. A 500 kN capacity hydraulic compression molding machine with a 300 mm square cavity and 20 mm depth was used to mold the composites into plates with a final thickness of 3 mm. The fabrication process involved alternating layers of the resin mixture and bidirectional kenaf fiber mats to create a composite structure of four resin layers interleaved with three fiber layers. Three formulations with varying filler concentrations (2.5%, 5%, and 7.5%by weight) were prepared to evaluate the consequence of filler amount on wear behavior. To ensure uniformity, the resin, filler, and hardener mixtures were thoroughly stirred before application. The composites underwent an initial curing process at ambient temperature for 24 hours, followed by post-curing at 70°C for three hours to improve cross-linking density and enhance their mechanical performance.

2.4. Experimental details

The fabricated composite plates as shown in Figure 1(a) were sectioned into cylindrical wear test samples with a diameter and thickness of 10 mm and 3 mm respectively as shown in Figure 1(b), in accordance with the requirements for two-body abrasive wear testing. A BSM Pvt. Ltd BS6040 Model (India), a single-head laser cutting machine operating under calibrated parameters, was used for precise sample preparation. Laser-cut polymer sample discs were attached to the ends of 10 mm diameter AISI D3 Steel pin specimens using adhesives as shown in Figure 1(c) to hold firmly on the tribotester. The prepared samples were tested in compliance with the ASTM G-99 standard on a DUCOM (TR-20LE) pin-on-disc tribotester shown in Figure 1(d), using 800 grit abrasive paper applied to an AISI D3 steel disc. Wear tests were carried out with kenaf fiber-reinforced epoxy polymer samples under dry conditions with different filler additions by weight (2.5%, 5%, and 7.5%). The L27 orthogonal array experimental design with 3 Factors (Filler addition, Load and Sliding velocity) in 3 levels as provided in Table 1 is chosen for its ability to deliver a statistically efficient and balanced experimental design. Despite the fixed number of 27 experimental runs, the orthogonality of the array ensures that the main effects and interaction terms are uncoupled and statistically independent. This property facilitates the precise estimation of both main effects and two-way interactions without confounding. The operating parameters considered for the tests were a sliding velocity of 1 m/s, 2 m/s, and 3 m/s, and loads of 5, 10, and 15 N over a constant sliding distance of 800 m, ensuring complete pin-to-abrasive disc surface contact during wear testing. A combination of experiments considering the load parameters, sliding velocity, and sliding distance is provided in Table 1. The wear in micrometers and frictional forces in Newtons were acquired during the testing from the data acquisition system of the tribotester, and the same was used to determine the wear rate and co-efficient of friction, as shown in Table 1.

Figure 1
(a) As fabricated kenaf fiber-reinforced hybrid polymer composites; (b) laser-cut discs and holes; (c) wear sample - disc fixed on a steel pin; (d) pin-on-disc wear testing set-up.

Table 1
Experimental parameters and responses.

SL. NO.	FILLER ADDITION(%)	LOAD (N)	SLIDING VELOCITY (m/sec)	WEAR RATE (mm3/m)	COEFFICIENT OF FRICTION
1	2.5	5	1	0.0284	0.1008
2	2.5	5	2	0.0307	0.1673
3	2.5	5	3	0.0369	0.2053
4	2.5	10	1	0.0516	0.3961
5	2.5	10	2	0.0567	0.4474
6	2.5	10	3	0.0578	0.4884
7	2.5	15	1	0.0803	0.4345
8	2.5	15	2	0.0971	0.4570
9	2.5	15	3	0.1166	0.5780
10	5	5	1	0.0225	0.0806
11	5	5	2	0.0273	0.1422
12	5	5	3	0.0353	0.1786
13	5	10	1	0.0510	0.3169
14	5	10	2	0.0543	0.3579
15	5	10	3	0.0575	0.4103
16	5	15	1	0.0737	0.3737
17	5	15	2	0.0941	0.4342
18	5	15	3	0.1094	0.5202
19	7.5	5	1	0.0108	0.0581
20	7.5	5	2	0.0177	0.1088
21	7.5	5	3	0.0229	0.1527
22	7.5	10	1	0.0396	0.2282
23	7.5	10	2	0.0416	0.2380
24	7.5	10	3	0.0455	0.2954
25	7.5	15	1	0.0470	0.2662
26	7.5	15	2	0.0605	0.2735
27	7.5	15	3	0.0718	0.3706

3. RESULTS AND DISCUSSION

3.1. Material characterization

The particle size analysis results of the recycled spent abrasive particles revealed that the particles ranged in size from 0.1 to 40 microns (Figure 2). This size distribution makes the material ideal for integration into a polymer matrix. The particle distribution suggests that these materials can effectively serve as fillers in composite applications. Energy dispersive X-ray spectroscopy analysis of the spent abrasive particles, shown in Figure 3 shows that the composition is primarily composed of oxygen (50.18 wt.%), silicon (14.48 wt.%), aluminum (12.55 wt.%), and iron (16.76 wt.%), with smaller amounts of magnesium, calcium, and titanium. Silicon and aluminum indicate the presence of silica and alumina phases, respectively, which are recognized for their outstanding mechanical strength, hardness, and wear resistance. The iron content suggests the potential for metallic reinforcement, whereas magnesium and titanium contribute to the improved ductility and strength. The high oxygen content supports the existence of oxides, which enhance the thermal stability. This composition makes spent abrasives ideal for use as reinforcements in composite materials, as they offer enhanced stiffness, thermal resistance, and mechanical properties. Furthermore, energy-dispersive X-ray spectroscopy and elemental analysis of the kenaf-fiber-reinforced hybrid polymer composite containing 7.5 wt.% filler, as depicted in Figure 4, indicate substantial contributions from elements such as iron, silicon, and aluminum. These findings substantiate the successful incorporation of spent abrasive materials into polymer matrices.

Figure 2
Particle size distribution of the spent abrasive particles.

Figure 3
Energy dispersive X-ray spectroscopic and elemental analysis of the spent abrasive particles.

Figure 4
Energy dispersive X-ray spectroscopic and elemental analysis of the kenaf fiber reinforced polymer composite with filler addition.

3.2. Tribological analysis

The wear rate and coefficient of friction, was evaluated using the Taguchi method with the “Smaller the Better” criterion. The primary goal of this analysis was to determine the optimal operational parameters and identify the key factors influencing the performance of spent abrasive particle filler-incorporated kenaf fiber-reinforced hybrid polymer composites. The main effect plot analysis revealed that the minimum wear rate was achieved under the optimal conditions of 5 N normal load, 1 m/s sliding velocity, and 7.5 wt.% filler content (refer to Figure 5). Similarly, the minimal coefficient of friction was obtained under the same set of parameters: 5 N load, 1 m/s sliding velocity, and 7.5 wt.% filler addition (see Figure 6).

Figure 5
Main effect plot for wear rate.

Figure 6
Main effect plot for coefficient of friction.

3.3. Effect of load on wear rate and coefficient of friction

The influence of the applied load on the wear rate and coefficient of friction was observed to be more significant than compared of other parameters, such as the sliding velocity and filler percentage (Table 2 and Table 3). This is evident from the response tables (Table 2 and Table 3), which show a higher delta value of 10.36 and 10.18 for the load, ranking it first in terms of wear rate and coefficient of friction, respectively. Furthermore, both the applied load and its interaction with the filler percentage significantly affected the wear rate, as indicated by the analysis of variance (Table 4). The load contributed the most to the wear rate, accounting for 74.62% of the total variance.

Table 2
Response table for S/N ratio of wear rate.

LEVEL	FILLER ADDITION (%)	LOAD (N)	SLIDING VELOCITY (m/sec)
1	25.13	32.25	28.22
2	25.74	25.99	26.62
3	29.27	21.89	25.3
Delta	4.15	10.36	2.92
Rank	2	1	3

Table 3
Response table for S/N ratio of coefficient of friction.

LEVEL	FILLER ADDITION (%)	LOAD (N)	SLIDING VELOCITY (m/sec)
1	9.92	18.14	13.85
2	11.32	9.31	11.71
3	14.18	7.96	9.85
Delta	4.26	10.18	4.00
Rank	2	1	3

Table 4
Analysis of variance for wear rate.

SOURCE	DF	SEQ SS	ADJ SS	ADJ MS	F-VALUE	P-VALUE	CONTRIBUTION
Filler Addition (%)	2	0.0025	0.0025	0.0013	228.65	0	12.63
Load (N)	2	0.0150	0.0150	0.0075	1350.68	0	74.62
Sliding Velocity (m/sec)	2	0.0012	0.0012	0.0006	110.58	0	6.11
Filler Addition (%) *Load (N)	4	0.0007	0.0007	0.0002	31.38	0	3.47
Filler Addition (%) *Sliding Velocity (m/sec)	4	0	0	0	0.62	0.660	0.07
Load (N)* Sliding Velocity (m/sec)	4	0.0006	0.0006	0	26.03	0	2.88
Error	8	0	0	0			0.22
Total	26	0.0201					100.00

Although the analysis of variance highlighted the significance of all three parameters, the applied load emerged as the most influential factor. According to the Archard equation, the wear rate is directly proportional to the applied load, indicating that an increase in the load results in a corresponding increase in wear rate. This explains why the applied load had the most substantial effect on the wear behavior of the kenaf fiber-reinforced polymer composites.

3.4. Effect of filler composition on wear rate and coefficient of friction

The filler percentage in kenaf fiber-reinforced hybrid polymer composites also influences both the wear rate and coefficient of friction. The effect of the filler percentage on the wear rate is ranked second, with a delta value of 4.15 (Table 2). In terms of its contribution to the wear behavior, the filler percentage accounted for 12.63% of the variance. Similarly, the impact of the filler percentage on the coefficient of friction follows a comparable trend, with a delta value of 4.26 (Table 3). Though the analysis of variance (Table 5) indicates the significance of all three parameters, the filler percentage has a pronounced effect on the coefficient of friction, contributing 16.75%. Additionally, the interaction between the load and filler percentage contributes to 3.73% of the coefficient of friction. In general, the addition of a filler material to kenaf fiber-reinforced hybrid polymer composites was observed to enhance the wear resistance up to a certain threshold. This is attributed to the presence of wear-resistant nanoparticles in the filler material, which are derived from abrasive water-jet machining processes, thereby improving the ability of the composites to resist wear.

Table 5
Analysis of variance for coefficient of friction.

SOURCE	DF	SEQ SS	ADJ SS	ADJ MS	F-VALUE	P-VALUE	CONTRIBUTION
Filler Addition (%)	2	0.0939	0.0939	0.0470	562.22	0	16.75
Load (N)	2	0.3901	0.3901	0.1952	2335.2	0	69.57
Sliding Velocity (m/sec)	2	0.0503	0.0503	0.0252	301.23	0	8.97
Filler Addition (%) *Load (N)	4	0.0209	0.0209	0.0052	62.55	0	3.73
Filler Addition (%) *Sliding Velocity (m/sec)	4	0.0010	0.0010	0.0002	2.95	0.090	0.18
Load (N)* Sliding Velocity (m/sec)	4	0.0039	0.0039	0.0010	11.57	0.002	0.69
Error	8	0.0007	0.0007	0.0009			0.12
Total	26	0.5608					100.00

3.5. Effect of sliding velocity on wear rate and coefficient of friction

The sliding velocity is ranked third in terms of its effect on the wear rate, with the lowest delta value of 2.92, as indicated in the response table (Table 2). The analysis of variance (Table 4) revealed that the sliding velocity had a minimal impact, contributing only 3.47% to the wear rate. Similarly, for the coefficient of friction, the sliding velocity was ranked third with a delta value of 4.00, as shown in the response table (Table 3). Though the analysis of variance (Table 5) shows statistical significance for the sliding velocity, its contribution remains relatively small, accounting for only 8.97% of the other parameters.

3.6. Validation of results

To evaluate the tribological behavior, specifically the specific wear rate and coefficient of friction, a mathematical model was derived through general linear regression, as expressed in Eq. (1) and Eq. (2). Regression analysis yielded a coefficient of determination (R²) of 94.9% for the wear rate and 90.4% for the coefficient of friction.

(1) $$\text{Wear rate}=–0.00\text{37}+0.000\text{81 filler}+0.00\text{598 load}–0.000\text{91 sliding velocity}–0.000\text{467 filler}*\text{load}–0.000\text{278 filler}*\text{sliding velocity}+0.00\text{1}0\text{56 load}*\text{sliding velocity}$$

(2) $$\text{Coefficient of friction}=–0.0\text{7}0+0.00\text{34 filler}+0.0\text{3819 Load}+0.0\text{486 sliding velocity}–0.00\text{27}0\text{filler}*\text{Load}–0.00\text{247 filler}*\text{sliding velocity}+0.00\text{162 Load}*\text{sliding velocity}$$

Based on the derived model, the specific wear rate and coefficient of friction were calculated and compared with experimental data, as presented in Table 6. The comparison revealed an average error of 2.88% for the wear rate and 2.02% for the coefficient of friction respectively. The estimated values exhibited minimal deviation from the experimental data, demonstrating that the model had high accuracy and was in close agreement with the observed tribological behavior. Therefore, the established model can be considered to provide a reliable representation of tribological responses under the conditions studied.

Table 6
Validation of the derived model for prediction of wear rate and coefficient of friction.

SL.NO.	FILLER ADDITION (%)	LOAD (N)	SLIDING VELOCITY (m/sec)	WEAR RATE				COEFFICIENT OF FRICTION
				EXPERIMENTAL WEAR RATE (mm3/m)	PREDICTED WEAR RATE (mm3/m)	ERROR (%)	ACCURACY (%)	EXPERIMENTAL COEFFICIENT OF FRICTION	PREDICTED COEFFICIENT OF FRICTION	ERROR (%)	ACCURACY (%)
1	2.5	5	1	0.0284	0.0266	6.02	93.98	0.1008	0.1003	0.54	99.46
2	2.5	5	2	0.0307	0.0310	1.17	98.83	0.1673	0.1654	1.16	98.84
3	2.5	5	3	0.0369	0.0383	3.65	96.35	0.2053	0.2078	1.21	98.79
4	2.5	10	1	0.0516	0.0521	0.93	99.07	0.3961	0.3998	0.94	99.06
5	2.5	10	2	0.0567	0.0553	2.54	97.46	0.4474	0.4394	1.78	98.22
6	2.5	10	3	0.0578	0.0588	1.66	98.34	0.4884	0.4927	0.87	99.13
7	2.5	15	1	0.0803	0.0815	1.53	98.47	0.4345	0.4313	0.73	99.27
8	2.5	15	2	0.0971	0.0981	1.11	98.89	0.4570	0.4669	2.17	97.83
9	2.5	15	3	0.1166	0.1143	1.98	98.02	0.5780	0.5713	1.16	98.84
10	5	5	1	0.0225	0.0222	1.67	98.33	0.0806	0.0740	8.23	91.77
11	5	5	2	0.0273	0.0280	2.27	97.73	0.1422	0.1467	3.17	96.83
12	5	5	3	0.0353	0.0351	0.69	99.31	0.1786	0.1808	1.19	98.81
13	5	10	1	0.0510	0.0501	1.87	98.13	0.3169	0.3153	0.50	99.50
14	5	10	2	0.0543	0.0547	0.74	99.26	0.3579	0.3625	1.27	98.73
15	5	10	3	0.0575	0.0580	0.96	99.04	0.4103	0.4073	0.72	99.28
16	5	15	1	0.0737	0.0750	1.81	98.19	0.3737	0.3819	2.20	97.80
17	5	15	2	0.0941	0.0930	1.09	98.91	0.4342	0.4251	2.09	97.91
18	5	15	3	0.1094	0.1091	0.28	99.72	0.5202	0.5210	0.16	99.84
19	7.5	5	1	0.0108	0.0129	19.23	80.77	0.0581	0.0652	12.37	87.63
20	7.5	5	2	0.0177	0.0167	5.55	94.45	0.1088	0.1062	2.36	97.64
21	7.5	5	3	0.0229	0.0218	4.82	95.18	0.1527	0.1481	3.02	96.98
22	7.5	10	1	0.0396	0.0401	1.20	98.80	0.2282	0.2260	0.94	99.06
23	7.5	10	2	0.0416	0.0427	2.49	97.51	0.2380	0.2414	1.43	98.57
24	7.5	10	3	0.0455	0.0440	3.32	96.68	0.2954	0.2941	0.43	99.57
25	7.5	15	1	0.0470	0.0444	5.44	94.56	0.2662	0.2612	1.89	98.11
26	7.5	15	2	0.0605	0.0604	0.09	99.91	0.2735	0.2727	0.31	99.69
27	7.5	15	3	0.0718	0.0744	3.64	96.36	0.3706	0.3765	1.58	98.42
Average						2.88	97.12			2.02	97.98

3.7. Worn surface analysis

Scanning Electron Microscope images of abrasive wear surfaces of kenaf fiber-reinforced hybrid polymer composites are shown in Figure 7 and Figure 8. Figure 7 depicts the worn surface of the kenaf fiber-reinforced polymer composite with 2.5% filler addition by weight experimented at a 5N load, 1 m/s sliding velocity and 800 m sliding distance. The samples exhibited surface delamination and scaling owing to abrasive wear. Grooving was also noticed because of the low wear resistance capacity caused by less internal bonding between the fibers and the polymer matrix. Figure 8 displays the worn surface of the kenaf fiber-reinforced hybrid polymer composite with 7.5% filler addition by weight experimented at a 5 N load, 1 m/s sliding velocity, and 800 m/s sliding distance where scratching and scuffing were noticed due to abrasive wear. The resistance of kenaf fiber-reinforced hybrid polymer composites to abrasive wear was increased by the addition of filler material. The sample with 7.5 wt.% of filler inhibited the inter-laminar failure and delamination when compared to sample with 2.5 wt.% filler. The stratified arrangement of fiber and epoxy resin incorporated with a homogenously distributed filler material gives rise to inter-molar bonding between them, which results in a reduction in the wear rate.

Figure 7
Worn surface of the kenaf fiber reinforced polymer composite with 2.5% Filler addition at 5 N load, 1 m/sec sliding velocity.

Figure 8
Worn surface of the kenaf fiber reinforced polymer composite with 7.5% filler addition at 5 N load, 1 m/sec sliding velocity.

4. CONCLUSIONS

The tribological behavior of kenaf fiber-reinforced hybrid polymer composites with varying amounts of spent abrasive particles from water jet machining was experimented and the findings are as follows:

• The wear resistance of kenaf fiber-reinforced hybrid polymer composites is observed to be improved with increase in the addition of spent abrasive particles 7.5 wt.%.

• The effect of filler addtion in the wear resistance was minimal when the wear test was conducted in the combination of high-load (15 N) and high-sliding-velocity (3 m/s).

• The effect of filler addtion in the wear resistance was highly significant when the wear test was conducted in the combination of low-load (5 N) and low-sliding-velocity (1 m/s).

• The desired objectives of minimum wear rate (0.0108 mm³/m) and minimum co-efficient of friction (0.0581) was attained for the optimal parameter of 5 N Load, 1 m/s sliding velocity, 7.5 wt.% filler content.

• The established mathematical model demonstrated an accuracy of 98% in predicting tribological responses.

• The fabricated and tested, kenaf fiber-reinforced epoxy polymer composite, with spent abrasive particles as fillers, that resulted in enhanced tribological performance has significant potential across various industries that requires better tribological behaviour, including automotive, aerospace, marine, sports equipment, eco-friendly packaging, wind energy, and consumer electronics as an alternative to traditional materials.

5. BIBLIOGRAPHY

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Publication Dates

• Publication in this collection
  24 Feb 2025
• Date of issue
  2025

History

• Received
  17 Dec 2024
• Accepted
  21 Jan 2025