Casting light on the tribological properties of paraffin-based HDPE enriched with graphene nano-additives: an experimental investigation

The impressive mechanical properties and robust resistance to wear recorded by nano-polymeric composites have positioned them as a viable alternative in many applications. When it comes to frictional materials, high-density polyethylene (HDPE) emerges as one of the best candidate materials that can be used. However, it tribological properties need more enhancement to suite with wide variety of applications. The objective of the current study is to identify the optimal loading ratio using a comprise of paraffin oil and nano-graphene with varying loading compositions. Different experiments were carried out to assess the modulus of elasticity, hardness, and strength. Additionally, the friction coefficient and wear resistance of the proposed nanocomposite have been estimated. Surfaces topographies were analyzed to recognize the wear mechanism. The results pointed that samples containing 5% paraffin oil and 0.5 wt% have relatively better mechanical and tribological behavior compared to further compositions; where, a 38% decrease in wear and a 34% reduction in COF compared to other composite samples.


Introduction
Polymers offer a multitude of merits like cost-effectiveness, corrosion resistance, ease of manufacturing, and compatibility with biological systems.These attributes have attracted numerous research endeavors aimed at elevating and refining their properties [1][2][3].Within the biomedical field, polymers and related nanocomposites have found extensive utilization, especially in the domain of artificial joint replacements, which address the mobility challenges faced by individuals with joint injuries [4][5][6].The mechanical, physical, and tribological characteristics of polymers have been modified through the incorporation of various nanomaterials, including cellulose, gold (Au), silver (Ag), titanium dioxide (TiO 2 ), copper oxide (CuO), graphene, carbon nanotubes, and fibers.Achieving a uniform dispersion of nanoparticles can significantly augment the performance of the polymer matrix [7][8][9][10][11].In contrast to pristine polymers, composite systems exhibit unique properties that have been engineered.The procedure of substituting a deteriorated joint with an artificial counterpart, typically constructed from metal, ceramic, or polymer materials, is termed artificial joint replacement or arthroplasty.To address the challenge of minimizing friction within these artificial joints, researchers have developed and evaluated polymeric nanocomposites.These materials offer exceptional wear resistance, phase stability, and biocompatibility [12][13][14].
Due to its exceptional mechanical, physical, and frictional performance, the ultra-high molecular weight polyethylene (UHMWPE) has found extensive application.To modify the behavior of the UHMWPE, various fillers, such as particles, platelets, or fibers, have been incorporated.One promising filler for the UHMWPE matrix is multiwalled carbon nanotubes (MWCNTs) [15,16].
The adoption of a hybrid filling system combines the benefits of multiple fillers, synergistically enhancing their effectiveness.Numerous research studies have been conducted to validate this approach, aiming to elevate the behavior of the materials [17][18][19].By incorporating nanofillers composed of zirconia and hydroxyapatite, the mechanical, wear, and biological performance of the matrix were evaluated.Researchers have conducted extensive investigations into the mechanical, thermal, and tribological behavior of UHMWPE when combined with paraffin oil and carbon nanofibers (CNF) [20][21][22][23].These hybrid nanocomposites have exhibited remarkable wear resistance in both aqueous and dry conditions.They demonstrate low shear stress, self-lubricating properties, and favorable thermal characteristics.The outcomes revealed that the incorporation of nano-graphene significantly enhanced the mechanical, thermal, and tribological performance of the UHMWPE matrix, possibly due to its carbonaceous composition, which contributed to the modification and improvement of composite properties.However, highdensity polyethylene (HDPE) still has not been extensively investigated as a matrix in many research studies.In a study investigating the effects of wear mechanisms, a composite of HDPE/UHMWPE with graphene oxide was utilized.The results demonstrated a substantial reduction in both wear rate and friction coefficient, indicating a significant enhancement in the tribological behavior of HDPE/UHMWPE nanocomposites through the incorporation of graphene oxide [24,25].In a different study, an HDPE matrix was employed to have 1 wt% of nanodiamond.The authors developed an FEM of an artificial knee joint to estimate the stresses at various flexion angles [26].Furthermore, the authors blended the HDPE matrix with boron nitride nanoplatelets (h-BNNPs) and MWCNTs.The findings indicated that one effective approach for developing the thermal and mechanical behavior of HDPE involved loading the material with 0.15 wt% of h-BNNPs and 0.25 wt% of MWCNTs, respectively [27].To assess the prospective of HDPE nanocomposite as a replacement polymer for hip prostheses, researchers constructed a hip joint finite element model [28].The FEA outcomes indicated that the stresses fell within an acceptable range for HDPE containing a dispersion of 0.15 wt% of h-BNNPs and 0.25 wt% MWCNTs.In another study, the tribological and mechanical behavior of the HDPE were enhances by the incorporation of a low loading amount of Al 2 O 3 nanoparticles [29].Such improvement could be attributed to the excellent dispersion of Al 2 O 3 nanoparticles, resulting in improved capacity of the matrix structure to resist the load.Furthermore, HDPE/ MWCNT samples underwent testing to investigate the influence of MWCNT on chain structure [30].The results demonstrated notable enhancements in mechanical and wear characteristics, potentially attributed to the effective integration of MWCNTs into the HDPE matrix.Consequently, it was concluded that an HDPE matrix reinforced with a hybrid MWCNT/Al 2 O 3 combination could serve as a suitable bio-composite for artificial joints.This hybrid MWCNT/Al 2 O 3 dispersion led to reduced water absorption and cytotoxic activity, although significant increase in hardness, elongation, and tensile strength was occurred [31].The integration of nanofibers derived from rice straw (RSNFs) into (HDPE) notably boosts its tensile strength by 30%.Simultaneously, it decreases the friction coefficient and wear rate by 17.5% and 50% respectively, when compared to unadulterated HDPE [32].This highlights the potential of RSNFs as a distinctive filler for HDPE in biomaterials and offers valuable perspectives for upcoming studies.
Experiments were conducted on the mechanical performance of high-density-polyethylene (HDPE) matrix reinforced with graphite nano-plates (GNPs) and graphite nanofibers (GNFs).The results indicated that the hybrid (GNF/GNP) reinforcement exhibited superior mechanical properties compared to other types [33].The mechanical and tribological properties were scrutinized and assessed.HDPE nanocomposite of hybrid nanoparticles were Al 2 O 3 NPs and GNPs created.The findings revealed a substantial improvement in the mechanical and tribological attributes of HDPE composites due to the inclusion of nano additives.The HDPE nanocomposites exhibited the most superior performance with a loading quantity of 2.0 wt% comprising an equal proportion of hybrid nanofiller Al 2 O 3 NPs and GNPs [34].In another study, the thermal behavior of a high-density polyethylene (HDPE) matrix reinforced with 20 wt% curaua fiber was examined.Thermal stability was assessed using thermos-gravimetric and differential scanning analysis (DSC).The findings revealed that the addition of fiber reinforcement increased crystallinity [35].Likewise, the thermal behavior of an HDPE matrix reinforced with jute fiber (at concentrations of 10, 15, 30, and 45 wt%) was investigated.The study reported an increase in the thermal stability of the matrix with the addition of reinforcement [36].Paraffins and their derivatives play an essential role in more than 30 sectors, including electronics, wood products, machinery, packaging, and food.Processes involving the formation of a solid phase followed by developing a dispersed three-dimensional structure are fundamental to producing and applying goods, including these paraffin-based compounds [37].It is imperative to have a thorough understanding of the mechanisms governing structure formation in these materials, techniques to manipulate this process, and the resulting alterations in the properties of the structures that emerge to pave the way for the future development of new paraffin formulations with properties.Many different economic sectors, including food, radio electronics, agriculture, packaging, engineering, and more, use composites made of oil paraffin combined with polymers and other agents to change their distributed structure [38,39].For instance, in the cheese-making sector, polymer-paraffin composites are used to mature and store cheese [40].They are also used in viticulture and horticulture to grow grafted plants.The tribological performance of paraffin oil (PO)-impregnated low-density polyethylene (LDPE) was evaluated [41].According to the results, compared to pure LDPE, adding paraffin oil decreased friction coefficient and wear rates.
Previous studies have shown that paraffin oil is rarely used as a filler material with polyethylene.Paraffin has the benefit of enhancing the tribological properties of the matrix, but it also reduces the possibility of agglomeration in hybrid fillers.Hence, the work intends to concentrate and investigate that aspect.The main goal of the following investigation is to assess the integration of graphene nanofillers and paraffin oil into the HDPE matrix.The paraffine oil weight fraction was fixed on 5.0 wt%.On the other hand, the weight percentage of the graphene was adjustable, 0.5% to 2.0 wt%.The study examined the mechanical performance, tribological performance, and the structure of the resulting nanocomposites to assess the influence of adding these additives within the HDPE.

Materials and methods
In this investigation, High Density Polyethylene (HDPE) was chosen as the base polymer.The HDPE raw material had specific characteristics, including a density of 0.94 gm cm −13 , a tensile stress of 27 MPa, and particle sizes ranging from 40 μm to 90 μm.This HDPE material was supplied by Sigma Aldrich Co.To reinforce the HDPE matrix, additives consisting of graphene nano particles (Gr) and paraffin oil (PO) were utilized.These additives were procured from US Research Nanoparticles.Paraffin oil, at a temperature of 20 °C, had a density of 0.825 g ml −1 .The graphene used in the study exhibited properties such as 95% purity, a thickness ranging from 2-8 nm, 3-6 layers, and the surface area ranging from 500 to 1000 m 2 g −1 .Achieving homogenous distribution of additives within the HDPE resin posed a consequential challenge throughout specimen preparation.To overcome such an issue, ethanol was employed as a solvent to facilitate dispersion and prevent filler agglomeration.The process involved the following steps: • The Gr and Po were added into the ethanol solvent before agitating at 200 rpm for 10 min.
• To further improve particle dispersion, the mixture was agitated for an additional 15 min using a Dihan HG-15 apparatus from Vietnam.
• The resulting mixture was then mixed with the HDPE.
• The mixture underwent re-stirring twice: first, for ten minutes at 600 rpm using a revolving stirrer, and then for another 15 min with the Dihan HG-15 apparatus.
• To complete the process, the resin was forced into a cylindrical copper mold at a pressure of 25 MPa and elevated temperatures, reaching 200 °C.
• The high temperature during the preparation process partially evaporated the ethanol.
The weight fraction of each additive is clarified in table 1.

Experiments details
Diverse techniques are employed to evaluate the tribological, mechanical, and physical properties of HDPE samples.In particular, infrared spectroscopy is used to investigate the interaction bonds between the composite constituents.Results were obtained using the Beckman IR 4250 spectrophotometer from the USA.Infrared spectroscopy is typically characterized by transmittance (%) and wavenumbers within the range of 400-2000 cm − ¹, allowing for the identification and analysis of constituent bond frequencies.Furthermore, mechanical properties were evaluated, which included measurements of hardness, tensile stress, elastic modulus, and breaking stress percentage.These parameters helped distinguish and characterize the mechanical characteristics of the HDPE samples.The HDPE nanocomposites are subjected to various tests and analyses in accordance with ASTM standards: − Uniaxial Universal Testing: Mechanical properties of the HDPE samples are evaluated utilizing uniaxial universal machine, specifically employing the DFM-300KN machine from China.This testing followed the ASTM standard D1621.Samples of 65 mm × 15 mm were performed at 25 °C for 48 h and 50 % RH before testing, as displayed in figure 1(a).For each composition, three samples were tested, and the average value was determined by considering the differences.
− Hardness Testing: The nanocomposites hardness is assessed utilizing the Shore D Durometer equipment, following the procedures outlined in ASTM standard D2240.Five different positions were tested to ensure comprehensive hardness evaluation, and the average hardness value was determined by considering the differences.
− X-ray Diffraction (XRD): Structural characteristics and identify the HDPE nanocomposites phases are investigated using a Siemens D500 x-ray diffractometer from Germany.X-ray diffraction (XRD) analysis covered a measurement range of 0°to 70°(2θ) and was configured with a voltage of 30 kV and a current of 30 mA.
− The water relative absorption test was conducted in accordance with ASTM D750-95.To perform this test, the samples were fully immersed in distilled water for a duration of 72 h at room temperature.Both before and after the submersion, the samples were carefully weighed.This allowed for the assessment of water absorption by measuring the change in weight of the samples during the test period.
− Based on ASTM standard G99-95, a tribometer, Pin-on-Disc, is employed for precise measurement of wear and friction mechanisms.The experiment involved cylindrical samples of 8 mm × 10 mm using a stainlesssteel alloy disc and dry sliding conditions at 30°C and 60% RH.The following parameters were evaluated; friction Coefficient (COF), the friction coefficient of the specimens is measured at a speed of 0.1 m s −1 and normal loads ranging from 2 N up to10 N. The weight loss of the samples was determined at different sliding distances of 31.4,47.1, 62.8, 92.2 and 125.6 m at constant applied load of 12 N under dry sliding conditions at 30 °C and 60% RH.The weight loss (Wm, gm) is calculated by measuring the samples weight before and after testing.For each specimen individually five times were conducted, and the average reading values were used, and standard errors were calculated.The specific wear rate (WR) was calculated using the formula [42]: Where, Δm is the weight loss of the sample (gm), L is the sliding distance (m), r is the material density (gm cm −3 ), F n is the applied load (N).
The topography of the rubbed surfaces was analyzed utilizing both an optical microscope (OLYMPUS BX53M, Tokyo, Japan) and a scanning electron microscope (JCM-6000Plus; JEOL, Tokyo, Japan).These microscopic approaches are employed to investigate the surface morphology and wear patterns of the nanocomposite samples to provide deep insight into the wear mechanisms and the effects of additives on the HDPE performance.
− To assess the quality of the nanocomposite manufacturing process, the densities of the samples were computed.The densities are calculated for each nanocomposite sample, experimental and theoretical.The theoretical one is determined using the formula: Where, w , H w PO and w Gr are loading amount of HPPE resin, paraffin oil and nanographene, respectively. , It's important to note that the samples of HDPE nanocomposite showed similar functional band groups as sample O in the infrared spectra analysis.This indicated the successful incorporation of graphene (Gr) and paraffin oil (Po) into the HDPE matrix, confirming their presence and integration into the composite material.

Results
The XRD patterns of the HDPE samples were presented in figure 3.In this pattern, two distinct peaks were observed, a broad peak with high intensity at around 21.4°(2θ), and a lower-intensity peak at approximately 24.2°(2θ).These peaks correspond to specific Bragg reflection planes, the peak at 21.4°suggests the presence of the (110) crystal plane.However, the peak at 24.2°corresponds to the (200) crystal plane [47].Each HDPE sample exhibited a different XRD pattern, featuring a strong diffraction peak at 2θ of 29.2°.This prominent and sharp peak at 29.2°(2θ) is attributed to the (002) crystallographic plane of graphene (GNPs).It indicates the presence of the graphitic structure's crystallographic plane (002) within the composite material.The observation that the intensity of GNPs increases with an increased number of graphene layer stacks in HDPE nanocomposites suggests a correlation between the two [48].This may indicate that certain graphene nanosheets combine and form a more organized stacking structure during the melt mixing process.The XRD patterns of the nanocomposite samples matched the semi-crystalline structure of the pure HDPE sample.This suggests that the structural crystal characteristics of HDPE were not influenced by the presence of hybrid additives, paraffin oil, or graphene (Gr).Consequently, this indicates that there was no chemical reaction occurring between the fillers and the HDPE matrix.The agreement between the XRD outcomes for the HDPE samples and earlier research [49,50] further validates the findings and supports the conclusion that the composite material maintained the HDPE matrix's structural characteristics despite the addition of fillers.
The theoretical density results, shown in figure 4, illustrate that an increase in Gr weight fraction leads to higher density.However, it's noteworthy that the theoretical density values were higher than the experimental ones for several samples.This discrepancy may have occurred due to the presence of voids that can form  throughout the mixing process.The existence of voids can significantly impact various material properties, and their relatively low occurrence indicates that the mixing procedure was largely successful.Nevertheless, the presence of these voids can result in a reduction in the composite's overall density compared to the theoretical predictions, as they represent regions with less material density within the composite.This difference between theoretical and empirical results is an important consideration when assessing the properties of composite materials.The experimental outcomes illustrate that the calculated volume fraction of voids in the samples did not exceed 1%.This low percentage of voids suggests that the sample preparation process was appropriate and that voids were not significantly affecting the produced nano composite properties [32,51].In line with these findings, the density of the sample containing HDPE NC2 additives was improved by up to 0.63% in comparison with the pure HDPE sample.For more understanding of the cause of change in hardness, the surface of the pure HDPE and HDPE NC2 were scanned utilizing SEM as shown in figure 5.The images of the two samples, HDPE NC2 and HDPE Neat are, provide visual evidence of these differences.The surface of sample HDPE NC2 exhibits fewer voids distributed throughout it compared to the pure sample HDPE Neat, indicating higher density values for the composite material.
The strength, elastic modulus, and hardness of HDPE samples were estimated in order to determine their mechanical characteristics.The HDPE nanocomposite samples' stress-strain curve is shown in figure 6(a).It was shown that the ultimate tensile stress increased with the inclusion of Gr additives.HDPE NC4, the additives with the largest loading amount, produced the highest tensile stress of 29.3 MPa.Furthermore, when the filler loading content increased, so did the strain in the nanocomposite samples.This could be explained by the fillers narrowing the spaces between the HDPE matrix's molecules, which would have restricted mobility and plastic deformation [52].compressive yield strength and elastic modulus, respectively, the greatest loading content demonstrated the highest improvement percentage.This may suggest that the use of nanofillers besides the PO improved the HDPE matrix's ductility and strain rate [26,30].The mechanical characteristics of HDPE samples in comparison to the pure HDPE sample are tabulated in table 2.
Samples of HDPE nanocomposite was tested for wear and friction coefficient in accordance with ASTM G99-95.Figure 8 displays the variation in the friction coefficient for various loading contents of hybrid additives, PO, and Gr, with normal applied stresses.The data indicates that an increase in effective loads leads to a considerable rise in the friction coefficient for all HDPE samples.It was noted that the hybrid additives in the samples assisted in lowering contact area friction.This might be explained by graphene's and paraffin oil's respective self-lubricating properties, which had a noticeable effect on the sliding conditions.Consequently, it was determined that a progressive drop in the friction coefficient was caused by an increase in the loading content of hybrid additives [53,54].This pattern remained constant even when considering the loading of content.The HDPE NC1 sample with a loading amount of 0.5 wt.% of Gr exhibited the lowest friction coefficient, resulting in a notable improvement of approximately 35% in comparison to other samples.The observed rise in coefficient of friction can be attributable to the elevated weight fraction of the additives, as observed in the case of HDPE NC4.This increase is likely due to the enhanced likelihood of particle agglomeration inside the polymer matrix.This observation suggests that the process of agglomeration impeded the dispersion of particles and the passage of shear between different layers.Furthermore, as figure 9 illustrates, the wear rate was computed using the weight of the samples, which revealed the weight loss for each specimen.The outcomes demonstrated that the wear rate followed the same pattern in friction behavior.This graphic demonstrated how the hybrid additives strengthening of the HDPE matrix improved wear resistance.With a loading content of 0.5 weight percent, HDPE NC1's wear rate decreased under the sliding motion, overall declining 38% less than that of the sample HDPE Neat.The fact that graphene helped to generate a lubricant layer on the contact area suggests that this improvement should be taken into consideration [54,55].By adding Paraffin Oil, its viscosity is lowered, which makes it easier to process and disperse the filler evenly.The higher viscosity also helps to create smooth and protective coatings on the nanocomposite surface.In contrast, a few issues, such as particle aggregation and inadequately bonded sliding layers, emerged in the interface when nanofillers were overwhelmed.This may indicate that the presence of a high loading level over 0.5 wt.% of Gr restricted the mobility of the interior molecules, leading to plastic deformation.
SEM micrographs and optical image topography were used to study the worn surfaces in order to comprehend the deformation and damage mechanism of sliding surfaces.Using optical microscopic analysis of 2D and 3D scanned images, the topography of worn surfaces was assessed, as illustrated in Figure 10.For the pure sample, HDPE Neat, it was evident that the worn surface had layers of plastic deformation, extensive wear tracks, and plowing on the contact region.The hybrid additives were well dispersed inside the HDPE matrix, reducing particle agglomeration and successfully separating the sliding interfaces, as demonstrated by the topography photographs of the nanocomposite's samples.The surface of Sample HDPE NC1 was found to have   wear tracks, grooves, and a small, plowed area, indicating that it had lost less weight than pure HDPE.Furthermore, the sample HDPE NC2's surface showed less damage than that of the preceding sample HDPE NC1, suggesting that the increase in loading content was still positive.It was shown that Sample HDPE NC3's surface had fewer wear lines, cracks, and grooves and looked smoother overall.On the other hand, the sample HDPE NC4's surface once again displayed worn markings and a plowed region.One theory is that the reduced wear rate was caused by the additives incorporated in the HDPE matrix, which assisted in forming the selflubricating layer.While it was deemed improper to keep adding more than this limit Because of agglomeration and incoherence, this may have an impact on wear and friction performance [56].
As shown in figure 11, the SEM images were used to evaluate and investigate the matrix and nanocomposite structural mechanisms.One may investigate the appearance of cracks and furrows on Sample HDPE Neat's surface, which looked to have poor cohesion layers.Furthermore, there was less breakage and better interlayer cohesiveness in the samples augmented with hybrid additives.While the sample structure appeared better than the pure sample, the image captured for sample HDPE NC1 revealed voids and furrows on the surface.Based on SEM pictures of samples HDPE NC2 and HDPE NC3, it was found that as content loading increased, the matrix structure improved as voids and cracks decreased.This may suggest that the hybrid additives, PO and Gr, improved the matrix structure and strengthened the bonds between the layers [54].Consequently, the sample surface cracking was stopped by the matrix's integration of nanofillers.On the other hand, adding more nanofillers resulted in weaker particle dispersion and agglomeration, which produced plastic flow at the sliding area.

Conclusions
The current study investigates the influence of adding graphene nanoparticles and paraffin oil into HDPE on the mechanical and tribological behavior of the HDPE nanocomposite.Samples with varying loading amounts of graphene (0.5, 1.0, 1.5, 2.0%, and 5.0%) and paraffin oil were synthesized.Every sample underwent a group of tests and evaluations in order to ascertain the ideal loading content of nanofillers.To characterize the HDPE matrix, XRD patterns and IR spectra analyses were employed.The outcomes demonstrated that the nanofillers were added to the HDPE matrix without changing the HDPE's crystal structure.The mechanical characteristics showed virtually linear improvement as the additives loading content increased.The yield strength, modulus of elasticity, and hardness of the HDPE nanocomposites with 2 wt% of Gr and 5.0% of paraffin oil were significantly improved by approximately 17.6%, 9.2%, and 18.5%, respectively.The coefficient of friction and wear rate were measured to assess the frictional behavior of HDPE nanocomposites.The sample loading content of 0.5 wt% additives resulted in the lowest wear rate and friction coefficient, with reductions of up to 35% and 38%, respectively.The lubricating layer that kept the sliding surfaces apart and shielded them was formed in part by the graphene.Particle agglomeration, however, restricted the mobility between layers at larger loadings (2.0 wt% of graphene), which increased the fractional effect and plastic deformation.The structure of the HDPE nanocomposites matrix was disclosed by the worn surface's mechanism employing optical topography and SEM pictures.It was shown that HDPE reinforced with up to 0.5 wt% graphene exhibited a good matrix structure  with reduced voids and smoother surfaces.Consequently, the matrix's even dispersion of nanofillers aided in preventing the spread of cracks.Nevertheless, with a greater loading content of 2.0 wt% of graphene, agglomeration and weak dispersion of particles were responsible for the detection of plastic flow and plowing at the sliding area.
Gr r are the densities of components.The actual density of the samples can be obtained via Archimedes principle[43].The following formula was used to determine the samples' masses in two distinct media-air and water: r and air r are the densities of water and air, respectively.m s air -and m s water -are masses of the samples on each media.The void volume fraction can then be estimated by contrasting the density values from the experiment and theory.

Figure 2 −−−
Figure2displays the infrared (IR) spectra of the HDPE nanocomposite samples.The information obtained from these spectra was essential for gaining insights into the interactions between the added fillers, graphene (Gr) and paraffin oil (Po), and the HDPE resin.It's worth noting that the transmittance spectra of the HDPE sample exhibited characteristic bands at wave numbers of 815, 1118, 1461, 1793, 2861, and 2973 cm − ¹[44][45][46].Different bending vibration types were associated with specific band positions and peak intensities in the IR spectra.This allowed for the classification of functional bonds as single, double, or non-conjugated.Some of the key functional groups and their corresponding wave numbers identified in the analysis are as follow: − Double trans bond (-CH=CH-2): Observed at 840 cm − ¹. − Double cis bond (-CH = CH-): Observed at 680 cm − ¹. − CH-2 functional bond: Detected at 2861 cm − ¹. − CH-3 vibrational bond: Detected at wave number 1480 cm − ¹. − Functioning non-conjugated group: Revealed by the infrared signal at wave number 1820 cm − ¹. − Functional C-CH-3 single bond group: Discovered between 2850 and 2985 cm − ¹.
Figure 5(b) illustrates the hardness of the HDPE nanocomposite samples.It is obvious that as the Gr percentage increases, the hardness rises correspondingly.When compared to pure HDPE, the hardness Shore D value rose by 18.5% at the highest Gr loading fraction.
Figure 7 illustrates the change in elastic modulus and compressive yield strength as the Gr wight fraction change.With a gain of roughly 17.7% and 9.2% in

Figure 4 .
Figure 4. Theoretical and experimental densities of HDPE nanocomposite samples.

Figure 7 .
Figure 7. Elastic modulus and compressive yield strength of HDPE nanocomposite samples.

Figure 10 .
Figure 10.Optical images 2D and 3D topography of worn surfaces of HDPE nanocomposite samples.

Table 1 .
Displayed the sample labels.

Table 2 .
Mechanical properties of HDPE nanocomposite samples.