Effect Of Graphene Nanoplatelets Research Articles

Effect of graphene nanoplatelets and nano zinc oxide on gas barrier and antibacterial properties of thermoplastic nanocomposites

AbstractGraphene‐loaded thermoplastic nanocomposite films must be evaluated for antibacterial activity, mechanical, and barrier properties before being utilized as food packaging. Herein, economically feasible linear low‐density polyethylene (LLDPE)‐based flexible packaging materials were developed via the melt compounding technique at 170°C temperature by taking advantage of both graphene nanoplatelets (GNP) and nano zinc oxide (ZnO) fillers. Morphological studies reveal that in composites loaded with GNP/ZnO hybrid fillers, ZnO nanoparticles form a network‐like structure throughout the polymer matrix. Simultaneously, GNPs are uniformly dispersed. The inclusion of hybrid nanofiller considerably reduces both the oxygen transmission rate and the water vapor transmission rate (WVTR) in LLDPE nanocomposites. A maximum decrease of 36% and 67%, respectively, in both oxygen transmission rate and WVTR is observed for 3 wt% of hybrid filler loading in a thermoplastic matrix containing 1 wt% of nano ZnO. The antibacterial efficacy of the derived nanocomposite films is obvious against gram‐positive (Bacillus subtilis) and gram‐negative (Escherichia coli) bacterial strains. These nanocomposite films have the potential to be successfully utilized as flexible packaging materials owing to their improved thermal, barrier, and antibacterial effectiveness.Highlights GNP/ZnO was used as a hybrid reinforcing filler in the LLDPE matrix. ZnO nanoparticles establish a network‐like morphology. LLDPE nanocomposite films exhibited excellent antibacterial activity. Oxygen and water vapor barrier properties were significantly improved. The thermoplastic composite films could be used as food packaging materials.

Effect of graphene nano-platelets on the low-velocity-impact and compression-after-impact strength of the glass fiber epoxy composite laminates

Detecting the low-velocity impact damage on the FRP composite structures can be challenging because the visible signs on the surface may be subtle. Mitigating the effects of BVID (Barely Visible Impact Damage) is crucial in ensuring the safety and reliability of composite components, especially in industries where these materials are commonly used, such as aerospace and automotive. This article explores the experimental investigations of the impact and post-impact damage propagation under compression in the Graphene Nano-Platelets (GNPs) infused glass fiber epoxy composite laminates. A comparative study of varying the percentage of the nano-platelets (0, 0.25, 0.5, and 0.75%) in the matrix material of the composite laminate is presented. The impact tests at low energies (15 J, 20 J, and 25 J), followed by the quasi-static compression tests, are carried out as per the procedures mentioned in the ASTM D7136/D7137. The digital image correlation technique (DIC) is used to measure strains and plot the strain field on the impacted face of the specimen under compression. Damage envelopes of the impact and compression tests are studied using X-ray CT scans. Micro-level failures are observed through Scanning Electron Microscopy (SEM) to get better insights into the failure mechanism of the composite materials under impact and compression loadings. Upon completing the study, it is found that the addition of the GNP into the matrix materials not only increased the impact performance but also increased the load-carrying capacity of the laminate under compressive loading. A decrement of 2–21% in the energy absorbed in the damage formation is seen with the incorporation of GNPs into composite materials. A maximum increment of 17% in the compressive strength is observed for the composite laminates with the 0.75% GNPs. However, for a particular percentage of the GNP, the compressive strength of the laminate is reduced with an increase in impact energy compared with its virgin counterpart. From X-ray CT scans, it is seen that the laminate under the compression tests fails due to excessive ply-splitting and the delamination at the damage site created during the impact. Fiber breakage, fiber brooming, matrix cracking, fiber-matrix debonding, etc., are some of the other failure modes observed in SEM studies.

Effect of graphene nanoplatelets (GNPs) in cementitious material

Effect of graphene nanoplatelets (GNPs) in cementitious material

Fabrication and characterization of graphene‐loaded recycled poly(ethylene terephthalate) electrospun composite nanofibrous mats with improved thermal conductivity

AbstractIn this study, graphene‐loaded electrospun recycled poly(ethylene terephthalate) (rPET) nanofibrous mats were produced and characterized morphologically, spectrally, mechanically and thermally. Particularly, the effects of graphene nanoplatelets (GNP) and multilayer graphene (GML) in improving the thermal conductivity and heat dissipation abilities of rPET‐based composite nanofibers were investigated. The morphological analyzes pointed out that 1% graphene loading led to smooth nanofibers while 5 and 10% of GNP‐loading resulted in coarser nanofibers with rougher surfaces and agglomerations. The differential scanning calorimetry results pointed out that the crystallization temperature increased with increasing graphene content as a result of the pronounced nucleation effect. The thermogravimetric analysis demonstrated an improvement in the thermal stability of the composite nanofibers. The thermal conductivity coefficients increased to 25.422 W/mK‐35.842 W/mK for rPET/GNP nanofibers and up to 62.669 W/mK for rPET/GML nanofibers, compared to that of 12.753 W/mK for neat rPET nanofibers which correspond to an increase between 99 and 391%. Heat dissipation capability of the graphene‐loaded composite nanofibers was illustrated with infrared thermography data, displaying an increase in the average surface temperature of the nanofibrous mats between 2 and 19°C at 30 s of heating. The results suggest the use of the graphene‐loaded rPET composite nanofibers as textile materials for thermoregulating applications.Highlights Recycled poly(ethylene terephthalate)/graphene composite nanofibers are electrospun. Thermal conductivity of graphene‐loaded nanofibers increases by up to 391%. Graphene loading in nanofibers leads to faster and more uniform heat dissipation. Mechanical properties of composite nanofibers improve. Value‐added recycled polyester materials for thermal management are foreseen.

3D-Printed Clay Enhanced with Graphene Nanoplatelets for Sustainable and Green Construction

This paper presents a study on the effects of graphene nanoplatelets (GNPs) on the mechanical behavior of 3D-printed burnt clay, the most sustainable and green construction material, under constant printing parameters. Mixes with different nanofilament contents—0.1%, 0.2%, and 0.3% by clay weight—were printed and tested under compression and bending loadings. The results obtained on the printed samples were compared with those fabricated using the molding method. The samples’ microstructures were then analyzed using a scanning electron microscope (SEM). Energy dispersive X-ray (EDX) analysis was employed to obtain the elemental distributions. The testing results were then statistically analyzed using a t-statistical method to investigate the impact of using GNPs on the properties of 3D-printed clay. Strength test results showed that mixes containing a low GNP content, i.e., 0.1 wt.%, attained higher compressive and flexural strengths than those containing higher contents, i.e., 0.2 and 0.3wt.%. The results additionally highlighted that the efficiency of GNPs was better observed in the printed samples rather than the molded ones, indicating that the printing process contributed to a better and more uniform dispersion of GNPs in the clay matrix. The t-statistical analysis confirmed that a significant improvement in compressive strength could be obtained using a GNP content of 0.1 wt.%, regardless of the fabrication method. On the other hand, significant flexural strength improvements were observed in the printed samples at all GNP dosages. Micrographs of GNP-modified clay supported the strength results obtained in this study. In summary, this research work signified the importance of using nanofilaments in 3D printing applications in order to achieve the desired elements’ mechanical properties.

Graphene nanoplatelets reinforced Al-Cu-Mg composite fabricated using laser powder bed fusion: microstructure, mechanical properties, and wear behaviour

Aluminium-based metal matrix composites reinforced with graphene (Gr) and its derivatives have been reported as promising composites due to their superior properties such as strength, damage tolerance, fatigue resistance, and density. However, the crack and porosity susceptibility of Aluminium 2024 Alloy (AA2024) with added Gr when fabricated using additive manufacturing techniques is not sufficiently well understood. The present work addresses this knowledge gap by focusing on the effect of graphene nanoplatelets (GNPs) and scanning speed on the AA2024 composites’ wear performance and microstructural and mechanical properties of specimens fabricated using laser powder bed fusion (LPBF). The experimental findings demonstrate that up to 0.5% presence of Gr in the composite improves its crystallite size and microhardness by up to 37.6% and 45%, respectively; however, it increases the porosity and crack formation due to the high laser power requirement. Moreover, the composites’ macroscale scratch and nanoscale wear performances showed improvements by up to 50% and 56% with higher Gr concentration (0.5%), suggesting that Gr is distributed uniformly in the structure. The improved understanding of the relationship between microstructure and mechanical characteristics of the GNPs/Al2024 composites fabricated using LPBF in terms of cracking and porosity formation is another significant contribution of this work.Graphical abstract

Effect of graphene nanoplatelets on mode I fracture Toughness of epoxy adhesives under water aging conditions

ABSTRACT In this work, graphene nanoplatelets (GNP) are used to reinforce epoxy adhesives, and the effects of GNP on mode I fracture toughness of adhesive under water aging condition are studied through double cantilever beam (DCB) test. Although the GNP reinforced adhesives deliver slightly higher GIC than neat epoxy before water aging, they exhibit an exceptional 21.93% higher GIC after immersing in water for 56 d, at a GNP content of 0.25 w.t.%. According to the experimental results, the effectively dispersed GNP could significantly alleviate the degradation rate in mode I fracture toughness due to the water aging. For example, compared to the non-aging condition, the mode I fracture toughness of neat epoxy decreases by 29.19% after 56 d of water aging. In a stark contrast, the degradation rate for 0.25 w.t.% GNP reinforced adhesive is only 15.76%. In addition, it is observed that GNP greatly improves the fracture surface roughness of DCB samples, which suggests that the incorporation of GNP is able to delay the negative effect of water aging on mode I fracture toughness of adhesive by lowering the diffusion of water into the adhesive, while increasing torturous of the crack propagation path.

Development of epoxy composites with graphene nanoplatelets and micro-sized carbon foam: Morphology and thermal, mechanical and tribological properties

The effect of graphene nanoplatelets (GNPs) and carbon foam (CF) micrograins on the morphology and thermomechanical and tribological properties of epoxy composites was determined. The binary composites containing separately CF grains or GNPs and multiphase composites with CF particles and GNPs together obtained by two procedures were studied. In the first method GNPs were dispersed initially in epoxy resin and then CF particles were introduced. In the second procedure, conversely, CF particles were distributed in polymer before GNPs addition. CF simultaneously applied with GNPs strongly improves storage modulus, hardness and thermal stability of composites and reduces the friction coefficient and the wear rate compared to epoxy matrix. The composite fabricated by the first method exhibited better tribological properties, especially considering the higher wear load.

Effect of graphene nanoplatelets on fatigue performance of Glass Fiber Reinforced Composite materials based on recycled polyethylene terephthalate

Utilization of recycled polyethylene terephthalate (PET) based resins for manufacturing composites is an environment friendly and cost effective solution. This study attempts to explore the influence of graphene nanoplatelets (GPnP) addition on the fatigue performance of glass fiber reinforced composites based on recycled PET in terms of S–N Data, area of hysteresis loops during fatigue loading, fatigue life distributions, self generated temperature during fatigue loading and stiffness degradation. Incorporation of GPnP in rPET-UPR based composites brings their fatigue performance at par with virgin polyester resin based composites. Statistical analysis of fatigue life data using two parameter Weibull distribution established that GPnP addition has only marginal effect in increasing dispersion in fatigue lives.

Size-dependent thermomechanical critical loads of GPL-reinforced nanobeams

The effect of graphene nanoplatelets (GPLs) as a nanofillers’ reinforcement is studied on the thermomechanical buckling loads of a reinforced composite nanobeam. The virtual work principle is used to derive governing equations of a shear deformable model. Effective mechanical and thermal properties are computed based on the Halpin–Tsai model for various patterns of distribution. A solution procedure is developed to find thermal and mechanical buckling loads. A parametric analysis is provided to study the influence of significant parameters such as various distributions of GPLs, weight fractions of GPLs, opening angle, nonlocal parameter, and some geometric parameters of GPLs such as the number of layers on the mechanical and thermal buckling loads. Before the presentation of full numerical results, comprehensive comparisons with previous references are presented for validation. A decrease in the stiffness of reinforced curved nanobeam is observed as the opening angle increases leading to a major decrease in thermal and mechanical buckling loads. The effect of various reinforcement distributions yields the conclusion that Pattern 3 and Pattern 2 give the largest and smallest mechanical and thermal buckling loads, respectively.

The effect of graphene nanoplatelets on Physico-chemical properties of Sterculia foetida biodiesel-diesel fuel blends

Biodiesel is well known as an alternative to the CI engines owing to being renewable, environmentally friendly, biodegradable, and non-toxic with fewer emissions. Biodiesel is prepared from several types of vegetable oils, and the current study uses Sterculia foetida oil (non-edible oil). The major problem with using biodiesel blends in CI engines is emissions that rely on physicochemical properties. Hence, the current study is to evaluate the physicochemical properties of biodiesel-diesel blends with the addition of graphene nanoplatelets at different dosage levels of 25, 50, and 75 ppm. The prepared samples are expressed as SFOME20, SFOME20GNPs25, SFOME20GNPs50, and SFOME20GNPs75. The physicochemical properties are measured for prepared samples according to the ASTM standards. The inclusion of nanoplatelets improves the fuel blend properties such as density, viscosity, cetane index, flash point, fire point, cloud, and pour point. In contrast, the calorific value is a little decreased.

Effect of dispersant added graphene nanoplatelets with diesel–Sterculia foetida seed oil biodiesel blends on diesel engine: engine combustion, performance and exhaust emissions

In this experimental study, the effect of graphene nanoplatelets (GNPs) on the performance, combustion, and emissions of a diesel engine using Sterculia foetida seed oil biodiesel (SFOME20) was investigated. The novelty of the present study is the surface modification of GNPs with a lipophilic surfactant at different ratios to achieve stable dispersion of GNPs in fuel blends. The homogeneity of the nano-additives in the fuel was tested by ultraviolet spectrometry, and an optimized amount of surfactant was found. The GNPs are dispersed in SFOME20 in different compositions such as 25, 50 and 75 ppm. The experiments were performed at a constant speed under different load conditions. Significant improvements in performance were oberved: brake thermal efficiencywas increased by 8.48%, and brake-specific fuel consumption was decreased by 16.53%. Emission levels Hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx)) were reduced by 28.3%, 24.16% and 10.43%, respectively, at 50 ppm in SFOME20. Significant improvement in combustion parameters was noted in the form of reduced ignition delay (ID), decreased combustion duration, and improved peak pressure and heat release rate under full load conditions. The GNPs were found to be promising additives for biodiesel blends to improve the overall performance, combustion and emission characteristics of the engine.

A comparative study of GNPs and MWCNTs additives on dispersion behavior and strength characteristics of the adhesively bonded joints

In this research, the effects of graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) inclusion at various weight fractions (0.25, 0.5, 0.75, and 1 wt%) on the dispersion behavior and strength characteristics of adhesively bonded joints were experimentally investigated and compared. For uniform dispersion of GNPs and MWCNTs across adhesive, an extensive solution mixing technique was carefully carried out. Two types of lap joints, that is, single lap joint (SLJ) and double strap joint (DSJ) were prepared using the neat and modified adhesive. The joints were fabricated using Al 5083 as adherends. A comparison of the strength properties was made after tensile testing of the lap joints. A substantial increase in the strength properties was observed with the added GNPs and MWCNTs. However, the strength response depicted by MWCNTs was superior to GNPs. A maximum improvement of 60% and 31% in lap shear strength was observed for SLJ and DSJ, respectively. This improved response was depicted at 1 wt% of MWCNTs addition in the adhesive. Fourier-transform infrared spectroscopy (FTIR) and ultraviolet–visible spectroscopy (UV–Vis-Nir) were utilized for chemical and dispersion analysis. Digital and scanning electron microscopy techniques were utilized in close examination of the fracture surfaces at high magnifications. Finally, a comprehensive discussion on the difference in strengthening mechanism between the two nanofillers was critically discussed.

Time‐dependent properties of high‐density polyethylene with wood/graphene nanoplatelets reinforcement

AbstractThe effect of graphene nanoplatelets (GNPs) on the long‐term performance of wood fiber/high‐density polyethylene (HDPE) composite is investigated by using short‐term creep tests with an efficient, faster data analysis approach. Previously, it was shown that the addition of GNPs at 15 wt% into HDPE reduces the viscoplastic (VP) strain developed during 2 h creep by ~50%. The current study shows that 25 and 40 wt% wood content in HDPE reduce the VP strains developed during 2 h creep time by >75% with no noticeable effect of the increased wood content. However, further addition of GNPs results in more than 90% total reduction in the VP strains. The current study shows that the development of the VP strains in the hybrid composites follows Zapas model. Viscoelastic (VE) response of these composites is nonlinear and thus is described by Schapery's model. Parameters for VP and VE models are obtained from the creep experiments and were validated in a separate loading‐unloading test sequence. Results show a very good agreement between experiments and predictions for the studied materials as long as the micro‐damage is not present.

Investigation of low‐velocity impact behavior of aluminum honeycomb composite sandwiches with GNPs doped BFR laminated face‐sheets and interfacial adhesive for aircraft structures

AbstractThe low‐velocity impacts that represent the equipment drop during maintenance and production, crash and drops of luggage that may occur during transportation and bird strikes during takeoff may occur in aircraft parts where honeycomb composite structures are used. Therefore, the low‐velocity impact (LVI) resistance of aircraft components is crucial. In this study, the effect of graphene nano platelets (GNPs) on the LVI behaviors of the BFR (basalt fiber reinforcement) laminated face‐sheets and the interface adhesive between the face‐sheet and the aluminum honeycomb core for composite sandwich structures were investigated. LVI tests were applied to GNPs doped and un‐doped BFR/aluminum composite sandwich samples to determine the values of the impact forces, displacements, interaction times, and absorbed energy at two different energy levels of 10 J and 20 J. The surface damages in the impact zones of the GNPs doped and un‐doped BFR laminated top face‐sheets of the sandwich samples were investigated on a macro scale with liquid penetrant. The damage formation and development of GNPs were detected in the cross‐sectional micro‐images of the top face‐sheets. SEM analysis was accomplished to define the fracture mechanisms provided by GNPs. As a consequence of tests and damage analysis, it was reported that GNPs increase the impact resistance of BFR/aluminum honeycomb composite sandwiches and limit and reduce damage development. GNPs showed increases in force and rebound energies of approximately 16.1% and 21.1% for 10 J, and approximately 8.2% and 14.7% for 20 J, respectively.

The Dose- and Time-Dependent Cytotoxic Effect of Graphene Nanoplatelets: In Vitro and In Vivo Study.

Graphene-based nanomaterials received attention from scientists due to their unique properties: they are highly conductive, mechanically resistant and elastic. These materials can be used in different sectors of society from electronic energy storage in industry to biomedical applications. This study evaluates the influence of graphene nanoplatelets in vitro and in vivo. The toxicological influence of graphene nanoplatelets (GPs) was analyzed by cytotoxic methods, the change of cell proliferation was assessed in real-time, and the effect of GPs on a living organism was evaluated in an animal model using histopathological examination. We analyzed two types of GP administration: intratracheal and peroral. We found dose- and time-dependent cytotoxic effects of GPs in vitro; the concentration above 50 μg/mL increased the cytotoxicity significantly. The real-time analysis confirmed these data; the cells exposed to a high concentration of GPs for a longer time period resulted in a decrease in cell index which indicated lower cell viability. Histopathological examination revealed thickened alveolar septa and accumulation of GPs in the endocardium after intratracheal exposure. Peroral administration did not reveal any morphological changes. This study showed the dose- and time-dependent cytotoxic potential of graphene nanoplatelets in in vitro and in vivo models.

Effect of Graphene Nanoplatelets on Mechanical Performance of GFRP Composites

The carbonaceous nanofillers such as graphene nanoplatelets (GN) due to their unique properties have been increasingly used as nanofillers to improve the mechanical properties of FRP composites. In the present study, unidirectional glass fiber reinforced polymer (GFRP) composites and GFRP composites with graphene nanoplatelets (GN-GFRP) are fabricated using vacuum bag process and hand layup method. The percentage of GN added in GN-GFRP composites is 0.1% and 0.5% in case of hand layup method and 0.5% in case of vacuum bag process. The specimens are tested under uniaxial tension and three-point bending to study the effect of GN on the tensile and flexural performance of GFRP composites. In case of composites fabricated using hand layup method, the tensile strength of GFRP composites increased by 35.8% and 40.4% with the addition of 0.1% and 0.5% GN respectively. The tensile modulus of GN-GFRP composites with 0.5% GN decreased by 11.8% compared to GFRP composites. The flexural strength of GN-GFRP composites with 0.1% and 0.5% GN are found to have increased by 6.5% and 5.3% respectively compared to GFRP composites. The flexural modulus of GN-GFRP with 0.1% GN increased by 11% and the same for GN-GFRP with 0.5% decreased by 8.2% compared to GFRP composites. The tensile strength and modulus of GN-GFRP composites fabricated using vacuum bag process decreased by 24.4% and 7.7% respectively compared to GFRP composites. Scanning Electron Microscope (SEM) investigation reveals that poor adhesion of resin with the fibers caused delamination in GN-GFRP composites fabricated using vacuum bag process resulting in reduction of tensile properties.

Effects of graphene nanoplatelets and montmorillonite nanoclay reinforcement on dental polymethyl methacrylate

AbstractThe study aimed at developing a cytocompatible dental polymer composite with high mechanical and surface characteristics by reinforcing polymethyl methacrylate resin with graphene nanoplatelets and montmorillonite nanoclay. After ball milling the particles into the polymer samples were prepared via conventional compression molding method. Samples were tested for flexural strength, polishability, fatigue failure, wear, hardness, and cytotoxicity. The fracture mode and surface polish were tested using a field emission scanning electron microscope. Most properties displayed enhancement at the tested fraction weight in relation to the control, while some properties were downgraded. However, the tested polymer composite was cytocompatible at all concentrations. Within study limits, graphene nanoplatelets and montmorillonite nanoclay reinforced polymer brought about a positive effect to a particular degree. Establishing optimal concentration of reinforcement and alternate blending methods may boost the resultant characteristics of the resin composite.

Effect of graphene nanoplatelets on the mechanical properties and cutting performance of alumina nanocomposite ceramic tools prepared using the SPS-HF dual sintering method

Al2O3/graphene nanoplatelets (GNPs) materials were prepared using the spark plasma sintering-high-frequency (SPS-HF) dual sintering method. The mechanical properties and microstructure of the composites were observed, and the effects of the sintering process and GNPs on the composites were analyzed. Under the sintering condition of a temperature of 1350 °C, pressure of 35 MPa and holding time of 8 min, the optimal mechanical properties of Al2O3 ceramic tool materials were obtained. The addition of GNPs had a positive effect on the mechanical properties of Al2O3 materials. Results show that the SPS-HF dual-sintering method shortens sintering time significantly. Compared to Al2O3 ceramic material, the composite material with 0.5 vol% GNPs had better mechanical properties than the Al2O3 ceramic material, with its flexural strength and fracture toughness being increased by 15.3% (617 MPa) and 63.4% (6.7 MPa m1/2), respectively. The toughening mechanisms of Al2O3/GNPs ceramic nanocomposites are graphene pull-out, graphene breaking, crack deflection, and crack branching. Dry machining tests of 40Cr hardened steel were carried out using an Al2O3/GNP ceramic tool and an Al2O3 ceramic tool. Compared with the Al2O3 ceramic tool, the life of the Al2O3/GNPs ceramic tool was increased by 16.3%, the workpiece roughness was decreased by 9.2%, and the friction coefficient was reduced by 12.8%, confirming the improvement of cutting performance by adding GNPs to ceramic tool materials.

Effect of Graphene Nanoplatelets on Tribological Properties of Bacterial Cellulose/Polyolester Oil Bio-Lubricant

The demand for bio-degradable lubricants is continuously increasing due to environmental concerns. One of the methods to achieve the bio-degradability property of lubricants is by using nanoparticles from bio-resources as additives in bio-degradable oils. Among the nanomaterials are nanofibers, cellulose, and graphene nanoplatelets. They can be mixed in Polyolester (POE) oil to produce lubricants for tribological applications. In a previous study, it has been confirmed that friction and wear of the tribo-pair reduced from 5 to 10% by mixing various volume percentages of bacterial cellulose (BC) into PEO as the base lubricant. The tribological performance BC containing POE base lubricant can further be enhanced by incorporating graphene nanoplatelets. This study shows that the specific wear rate of the material decreased by 20% by adding graphene nanoplatelets in BC containing POE oil. The friction and wear improvement can be related to the formation of tribofilm on the contact interface. EDS analysis indicates that oxygen played an important role in the friction and wear performance of the POE oil-based lubricant with BC and graphene additives. The tribofilm shows significant traces of oxygen elements. The presence of graphene nanoplatelets in POE oil removed the oxygen-rich layer but could not reduce the wear rate. However, incorporating both graphene and BC in POE oil significantly improved friction and wear, although the oxygen element was still traceable on the contact interface.