Graphene filler as well as preparation method and application thereof

Abstract

The invention discloses a graphene filler and a preparation method and application thereof, the preparation method comprises the following steps: step 1, adding graphene nanosheet powder into a mixed solution of ethanol and deionized water, and carrying out tip ultrasonic treatment to obtain a suspension; step 2, adding a silane coupling agent into the suspension, and magnetically stirring to complete a surface reaction; and then performing high-shear mixing, stripping, filtering, cleaning and drying to obtain the stripped graphene filler. According to the invention, a cheap graphene nanosheet powder material is adopted, and a graphene filler is obtained by using a liquid phase stripping process, so that the graphene nanosheet is reduced in size, thinned in thickness and improved in dispersion performance; the graphene filler and POM particles are subjected to melt blending, under the optimal filler content of 0.5 wt%, the mechanical performance of the POM / e-GNP composite material is enhanced, and the bending strength, the tensile strength and the impact strength are totally improved by 26.4%; a dry friction test on the steel ball also shows that the friction reduction and the wear rate are respectively improved by 22% and 40.6%.

Description

Technical Field

[0001] This invention relates to the field of friction materials technology, and in particular to a graphene filler, its preparation method, and its application. Background Technology

[0002] Today, many metal friction and wear components are being replaced by lightweight yet robust polymers and polymer composites due to their ease of processing, light weight, and low cost. When polymers are reinforced with nanomaterials such as alumina (Al₂O₃), molybdenum disulfide (MoS₂), carbon nanotubes (CNTs), and graphene, their performance is even more superior. However, achieving uniform dispersion of nanoparticles (especially graphene nanosheets) and strong filler-matrix interfacial bonding within a polymer matrix is ​​challenging, significantly impacting the material's mechanical and tribological properties.

[0003] Polyoxymethylene (POM), also known as polyacetal, is a widely used engineering thermoplastic with advantages such as low coefficient of friction, wear resistance, high stiffness, excellent chemical inertness, and low cost. It is also widely used in linear drive systems for height-adjustable desks as sliding components with metal mating surfaces. The dry sliding behavior and notched impact characteristics of pure POM are affected during start-up or shutdown under low-speed and heavy-load conditions, where friction increases over time, leading to friction-induced noise or thermal softening, and an uneven transfer layer on the sliding mating surfaces. Therefore, using appropriate and compatible fillers to reinforce the POM matrix to overcome these weaknesses is a primary consideration. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a graphene filler, its preparation method, and its application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first aspect is to provide a method for preparing graphene fillers, including the following steps:

[0007] Step 1: Add graphene nanosheet powder to a mixed solution of ethanol and deionized water and perform high-precision ultrasonic treatment to obtain a suspension of graphene nanosheets.

[0008] Step 2: Add the silane coupling agent to the suspension obtained in Step 1 and stir magnetically to complete the surface reaction; then mix under high shear and exfoliate at 8000-15000 rpm for 0.5-5 hours, then filter, wash and dry to obtain the exfoliated graphene filler.

[0009] Furthermore, in step one, the volume ratio of ethanol to deionized water in the ethanol and deionized water mixed solution is 7:3; the thickness of the graphene nanosheet layer in the graphene nanosheet powder is 5-100 nm.

[0010] Furthermore, in step one, the conditions for the tip ultrasonic treatment are: 12-20mm titanium probe, ice bath, power 500-1200W, vibration frequency 18-20kHz, and treatment time 2-4 hours.

[0011] Furthermore, in step two, the silane coupling agent is 3-aminopropyltriethoxysilane, and its addition amount is 0.1-1 wt% of the suspension.

[0012] Furthermore, in step two, the cleaning reagent used is ethanol, the drying temperature is 80-100℃, and the drying time is 18-24 hours.

[0013] The second aspect is to provide a graphene filler prepared by the above-described preparation method, wherein the graphene nanosheets in the graphene filler have a thickness of 0.5-1 nm.

[0014] The third aspect is to provide a composite filler, including the above-mentioned graphene filler, and one or more of polytetrafluoroethylene, carbon fiber, glass fiber, and nano-Al2O3.

[0015] Furthermore, the average particle size of the polytetrafluoroethylene is 10-15 μm; the nano-Al2O3 is spherical α-alumina with an average particle size of 10-100 nm.

[0016] The fourth aspect is to provide the application of the above-mentioned graphene filler, which is added to a polymer material to prepare a friction-reducing material; the polymer material is one or a combination of several of the following: polypropylene, low-density polyethylene, high-density polyethylene, acrylonitrile butadiene styrene, ultra-high molecular weight polyethylene, polyamide, polyoxymethylene, polyphenylene sulfide, polyether ether ketone, polyethyleneimine, polyimide, and epoxy resin.

[0017] Furthermore, the polymer material is polyoxymethylene; the amount of graphene filler added is 0.5-1 wt%.

[0018] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0019] This invention utilizes inexpensive graphene nanosheet powder material and prepares graphene filler using a liquid phase exfoliation (LPE) process, resulting in smaller and thinner graphene nanosheets with improved dispersion performance. The obtained graphene filler is melt-blended with POM particles. At an optimal e-GNP filler content of 0.5 wt%, the mechanical properties of the POM / e-GNP composite material are enhanced, with an overall increase of 26.4% in flexural, tensile, and impact strength. Dry friction tests on steel balls also show that, at the same e-GNP content, the coefficient of friction and wear rate are lowest, with friction reduction and wear rate increases of 22% and 40.6%, respectively. Notably, uniform e-GNP dispersion and strong matrix-filler interaction are crucial for uniform stress transfer under external loads and the formation of a lubricating transfer film on the sliding surface, which are key factors in improving mechanical and tribological properties. Attached Figure Description

[0020] Figure 1 The images show information on the size, shape, and degree of exfoliation of graphene before and after the liquid phase exfoliation (LPE) process, as studied by SEM and Raman spectroscopy. Specifically, a is a scanning electron microscope image of graphene nanosheets (GNPs) not treated by the method of this invention; b is a scanning electron microscope image of graphene fillers (e-GNPs) obtained by the method of this invention; c is the Raman spectrum of GNPs and e-GNPs; and d is a comparison of the degree of exfoliation between GNPs and e-GNPs.

[0021] Figure 2 The test results of tensile strength and elongation at break of Neat POM, POM / GNP, and POM / e-GNP composites are shown.

[0022] Figure 3 The fracture surface morphology after tensile testing is shown. Among them, a is a scanning electron microscope (SEM) image of the fracture surface of POM material without graphene nanosheets (Neat POM); b is a scanning electron microscope (SEM) image of the fracture surface of POM / GNP composite material; and c is a scanning electron microscope (SEM) image of the fracture surface of POM / e-GNP composite material.

[0023] Figure 4 The results of tribological property tests for Neat POM, POM / GNP, and POM / e-GNP composites are shown; where a is the dry friction coefficient; b is the friction coefficient with grease; c is the average friction coefficient; and d is the wear amount.

[0024] Figure 5 SEM images of the worn surfaces of the polymer nanocomposite material after dry friction and grease-lubricated friction tests are shown. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0026] The reagents used in the following examples are as follows: high-viscosity POM homopolymer (Delrin 100P) with a density of 1.42 g / cm³. 3 The melt flow rate is 2.5 g / 10 min (190℃ / 2.16 kg), and it was purchased from DuPont in granular form. Purity ≥90%, specific surface area 50-150 m² / g. 2 The graphene nanosheets (g / g) were supplied by Tanfeng Technology Co., Ltd., China; the layer thickness and lateral dimensions of the graphene were 3-8 nm and 10-50 μm, respectively. 3-Aminopropyltriethoxysilane or silane coupling agent (trade name KH-550) was supplied by Jinan Xingfeilong Chemical Co., Ltd. All other reagents were supplied by Sinopharm Chemical Reagent Co., Ltd. and used as is.

[0027] Example 1

[0028] This embodiment provides a method for preparing graphene filler, including the following steps:

[0029] Step 1: Place GNP powder in a 500ml beaker and add a mixture of ethanol and deionized water (ethanol to water volume ratio 7:3); immerse a 12mm diameter titanium probe-tipped ultrasonic generator (SJIA-500, Ningbo Sijia Laboratory Equipment Co., Ltd., China) in the beaker to initiate ultrasonic treatment; ultrasonic treatment is carried out in a soundproof room with an ice bath for 2 hours at 500W power and 20kHz vibration frequency to produce a uniformly dispersed suspension of monolayer and few-layer graphene.

[0030] Step two: 1 wt% of silane coupling agent (KH-550) is added dropwise to the suspension, and the mixture is stirred magnetically for 1 hour to complete the surface reaction. As the final step in the LPE process, the modified graphene dispersion is stirred using a high-shear stirrer (IKAT-25 Digital). (China) Further exfoliation was performed at 8000 rpm for 0.5 hours to produce a high concentration of graphene nanolayers. The method includes an exfoliation process generating high shear forces in a narrow gap between the rotor and stator walls, along with other hydrodynamic effects. The resulting solution with a uniform, fine GNP suspension was filtered through a 0.22 μm PTFE membrane and thoroughly washed with ethanol to remove excess reagents. It was then dried in a vacuum oven at 100 °C for 24 hours to obtain the exfoliated GNPs, i.e., the graphene filler.

[0031] Figure 1Information on the size, shape, and degree of exfoliation of graphene before and after the liquid phase exfoliation (LPE) process, as studied by SEM and Raman spectroscopy, is presented.

[0032] and Figure 1 Compared to the original graphene in a, the size of the exfoliated graphene particles becomes smaller, approximately 2-8 μm, under the influence of ultrasonic microjets, collisions, and high shear forces during the LPE process, and the number of tightly packed layers is significantly reduced to thin sheets. Figure 1 b). The aggregated graphene particles are broken down, thereby further improving their dispersibility.

[0033] In addition to visual information Figure 1 Raman spectroscopy analysis is also shown in c and 1d to further compare the quality of graphene exfoliation. This technique is one of the most promising non-destructive analytical tools for characterizing the near-surface chemical structure of carbon-based materials. Figure 1 Three significant peaks are clearly visible in c, representing the D band (1349 cm⁻¹). -1 Defects at point ) and G-band (1577cm) -1 sp at ) 2 Stretching vibrations of carbon atoms and 2D bands (2704 cm⁻¹) -1 The stacking order at I0 is considered. The D-band is attributed to disordered and amorphous carbon bonds, thus reflecting defect characteristics in carbonaceous materials. The G-band, however, reflects the crystallinity of graphene. Its intensity increases linearly with the number of graphene layers, and more carbon atoms can be detected in multilayer graphene. Furthermore, the 2D band is closely related to the band structure of the graphene layers. For example, the presence of a sharp, symmetrical 2D band can be used to identify monolayer graphene, while a broad shoulder of the peak is associated with graphene nanosheets. Therefore, the I0 band can be used to identify graphene nanosheets. D / I G and I 2D / I G The degree of peeling was assessed by the change in strength ratio. After LPE treatment, the strength of the D and G bands appeared to decrease, while a narrower and higher strength peak appeared at the 2D band, which is a sign of peeling. Figure 1 c). To clearly distinguish the changes in graphene structure during LPE, Figure 1 d gives I D / I G and I 2D / I G The change in strength ratio. It can be seen that the ID / IG ratio decreases after exfoliation, indicating that the graphene has lower dispersibility and higher crystallinity due to the grafting of silane coupling agents to the edges and surface of the graphene. And I... 2D / I G The increase is due to the hydrodynamic effects during the LPE process promoting peeling.

[0034] Example 2

[0035] This embodiment provides a method for preparing graphene filler, including the following steps:

[0036] Step 1: Place GNP powder in a 500ml beaker and add a mixture of ethanol and deionized water (ethanol to water volume ratio 7:3); immerse a 20mm diameter titanium probe-tipped ultrasonic generator (SJIA-500, Ningbo Sijia Laboratory Equipment Co., Ltd., China) in the beaker to initiate ultrasonic treatment; ultrasonic treatment is carried out in a soundproof room with an ice bath for 4 hours at 900W power and 18kHz vibration frequency to produce a uniformly dispersed suspension of monolayer and few-layer graphene.

[0037] Step two: 1 wt% of silane coupling agent (KH-550) is added dropwise to the suspension, and the mixture is stirred magnetically for 4 hours to complete the surface reaction. As the final step in the LPE process, the modified graphene dispersion is stirred using a high-shear stirrer (IKAT-25 Digital). (China) Further exfoliation was performed at 15,000 rpm for 5 hours to produce a high concentration of graphene nanolayers. The method includes an exfoliation process generating high shear forces in a narrow gap between the rotor and stator walls, along with other hydrodynamic effects. The resulting solution with a uniform, fine GNP suspension was filtered through a 0.22 μm PTFE membrane and thoroughly washed with ethanol to remove excess reagents. It was then dried in a vacuum oven at 100 °C for 24 hours to obtain the exfoliated GNPs, i.e., the graphene filler.

[0038] Application Example 1

[0039] POM / e-GNP composites and POM / GNP composites were prepared by melt blending.

[0040] 0.5 wt% graphene filler (prepared by the method in Example 1) was mixed with POM particles and dried at 80°C for 4 hours to remove absorbed moisture. Simultaneously, purchased GNP (purity ≥90%, specific surface area 50-150 m²) was also used. 2 / g of graphene nanosheets (provided by Tanfeng Technology Co., Ltd. of China) were mixed with POM particles to compare performance.

[0041] The above-mentioned mixed materials were melt-blended using a co-rotating twin-screw extruder (SHJ-20, Jiangsu Xinda Technology Co., Ltd., China), with a screw diameter of 21.7 mm and an L / D ratio of 40. Process parameters, namely the barrel temperature from the feeder to the nozzle and the rotor speed, were set at 170-190℃ and 250 rpm, respectively, to ensure proper dispersion. The molten extrudate was immediately cooled in a water bath, air-dried, and formed into 2 mm granules. All obtained composite granules were dried overnight at 80℃ and then used as test samples in a single-screw injection molding machine (MA-1200, Haitian Plastics Machinery Co., Ltd., China) at a temperature range of 180-200℃, a screw speed of 55 rpm, and an injection pressure of 65 MPa. The mold temperature was set at 80℃. A cross-sectional area of ​​10 × 4 mm was successfully prepared. 2 The samples for tensile testing (150 mm in length), bending testing (80 mm in length), and cantilever beam impact testing (80 mm in length with a 2 mm notch) were all defect-free. The friction and wear test samples were 30 × 30 × 5 mm in size. 3 It is plate-shaped.

[0042] 1.1 Mechanical Test

[0043] The tensile and flexural properties of the composite samples were determined on a universal testing machine (WDW-20D, Jinan Chengyu Testing Equipment Co., Ltd., China) according to GB / T1040 and GB / T9341 standards, respectively. The testing machine was equipped with a 20kN load cell, maintaining a displacement control of 10mm / min throughout all tests. Stress-strain curves were simultaneously plotted on a computer screen to characterize the tensile and flexural parameters. The cantilever beam impact strength of the notched specimens was measured using an XJFD-5.5 (Jinhe, China) impact testing machine according to GB / T1843. Five samples of each composition were tested to ensure the repeatability of the results, and the average value is given.

[0044] Results Reference Figure 2 , Figure 2 The tensile properties of POM reinforced with GNP and e-GNP polymers at an optimal graphene content of 0.5 wt% were plotted, with the highest tensile strength and elongation at break observed in the POM / e-GNP composite. Clearly, the toughness and ability to withstand tensile or tensile forces are enhanced in the nanocomposite compared to pure POM and the POM / GNP composite. Based on the results, we suggest that appropriate exfoliation and surface treatment, along with the optimal e-GNP content, can provide a larger interface between the two phases, thereby increasing interfacial bonding and effective stress transfer. On the other hand, aggregated GNP loading may lead to poor dispersibility and agglomeration, resulting in reduced interaction surface area and stress concentration within the matrix, thus degrading mechanical properties.

[0045] 1.2 Scanning electron microscopy analysis

[0046] Results Reference Figure 3 , Figure 3 a is a scanning electron microscope image of the fractured surface of POM material (Neat POM) without graphene nanosheets; Figure 3 b is a scanning electron microscope image of the fracture surface of the POM / GNP composite material; Figure 3 c is a scanning electron microscope image of the fracture surface of the POM / e-GNP composite material.

[0047] The fracture surfaces of pure POM, POM / GNP, and POM / e-GNP nanocomposites were studied using SEM to further analyze the effects of interfacial interactions and filler aggregates on mechanical properties. Fracture surfaces were collected from tensile tests and ultrasonically cleaned with ethanol before SEM observation. It was observed that the fracture surface of pure POM was highly discrete, exhibiting a brittle fracture mechanism, while the other nanocomposites showed pull-out and protrusion of the supporting graphene from the matrix. Specifically, tightly embedded and uniformly distributed graphene layers were detected on the fracture surface of POM / e-GNP, which are considered to effectively absorb tensile and impact forces. However, a large number of GNP aggregates were observed on the POM / GNP nanocomposites. The optimal e-GNP filler content of 0.5 wt% effectively bridged the external load transfer from the matrix and reduced stress concentration, representing significantly strong interfacial interactions and some compatibility with chemical (APTES) surface treatment. Conversely, the fracture surface of POM / GNP showed graphene aggregates, which may act as stress concentrators and lead to early fracture.

[0048] 1.3 Tribological Testing

[0049] Tribological tests were performed using a pin-disc tribometer (TRB3, Anton Paar GmbH, Austria) in a reciprocating ball-plate contact configuration, such as... Figure 5 As shown. The dry friction and grease-lubricated friction behavior of the nanocomposite material was evaluated at room temperature for a sliding duration of 1 hour. The applied load, total sliding amplitude, and linear velocity were set to 10 N, 10 mm, and 0.038 m / s, respectively. A high-precision 100Cr6 steel ball (G5, Ra0.02 μm, diameter 6 mm) was selected as the reciprocating contact surface, and the initial Hertzian contact stress under normal load was 120.7 MPa. The proposed test conditions simulate tribological phenomena, namely, that the frictional behavior of the metal / polymer contact is prone to stick-slip under such low speed and high contact pressure.

[0050] Figure 4The dry friction coefficient and grease-lubricated friction coefficient of the nanocomposite material with a steel ball are shown, along with the calculated average friction coefficient and wear rate. Based on the results, e-GNP filler reinforcement significantly reduces the COF of pure POM polymer. Figure 4 In a and 4b, we can see that the entire friction process is divided into (i) the running-in stage, where the fresh metal / polymer contact surfaces begin to slide, and the coefficient of friction continuously increases until it enters the (ii) steady-state stage and stabilizes. Adding 0.5 wt% e-GNP filler alleviates severe friction, reducing the COF to 0.29, and increasing the friction reduction by approximately 22% compared to unfilled POM. The friction curve also becomes smoother and less volatile due to optimal matrix reinforcement and stable friction film formation. Furthermore, under optimal filler load, enhanced tensile, flexural, and impact strengths help resist frictional shear forces and reduce corresponding wear surface deformation. When the metal surface slides against the nanocomposite material, fine wear fragments are generated, subsequently compacted onto the metal surface platform, and interlocked with the rough texture, completely covering the metal mating surface. Therefore, a transfer film with viscosity and toughness is a key factor in reducing friction. Compared to the blocky wear spalling of pure POM and POM / GNP composites, the wear debris generated by e-GNP-filled nanocomposites is considered to be smaller and more uniform, thus making it easier to chelate the wear debris to the metal mating surface and form a dense transfer layer. Furthermore, the anisotropic properties of graphene, its excellent intralayer load-bearing capacity due to its in-plane covalent bonds, and its easily shearable layers due to weak van der Waals forces provide optimal lubrication by suppressing direct metal / polymer contact surfaces and nanoscale load-bearing friction interfaces. However, further enhancing the original graphene filler is detrimental to tribological performance because it leads to particle agglomeration and uneven transfer films, which are easily destroyed during friction.

[0051] Figure 4 d shows the calculated wear rate of the POM-based polymer. The trend of wear performance is related to... Figure 4 The average friction coefficient values ​​shown in a are very consistent, with the POM / e-GNP reinforced material achieving 1.7 × 10⁻⁶ under dry sliding conditions. -2 mm 3 The lowest wear rate is / Nm, compared to the wear rate of pure POM of 2.9×10. -2 mm 3Compared to / Nm, wear resistance improved by approximately 40.6%. It can be seen that due to the poor thermal conductivity of pure POM, most of the frictional heat cannot dissipate at the contact interface, but rather concentrates on the rough, uneven surface, resulting in localized softening and discontinuities, leading to a higher specific wear rate. Furthermore, the minimum wear rate can be attributed to the high specific surface area of ​​the e-GNP filler, which promotes load transfer within the polymer matrix, especially at the optimal filler content with good dispersion. Conversely, the presence of agglomerated GNP particles weakens load transfer capacity and leads to a high wear rate.

[0052] Figure 5 SEM images of the worn surfaces of polymer nanocomposites after dry friction and grease-lubricated friction tests are shown to examine the wear mechanisms of the worn surfaces. In dry friction wear, wavy deformation and microcracks perpendicular to the sliding direction were detected on the worn surface of pure POM, due to severe adhesion and stick-slip motion between the friction pairs. Another aspect of these wavy and microcracks can be described by the energy dissipated in the form of frictional heat, as pure POM accumulates more energy more easily than other nanocomposites, leading to thermal softening and wrinkling deformation. Later, the wavy deformation of the POM / GNP nanocomposites decreased, but deep wear grooves and larger surface cracks appeared along the sliding direction due to composite defects. This effect can be demonstrated by a combination of severe wear and fatigue wear mechanisms caused by the roughness of the steel mating surfaces, which induces periodic stress concentration areas and cracks along the grooves. It has been reported that the deformation of the worn surface during friction is largely dependent on mechanical properties; for example, unless the tensile strength of the polymer material is greater than the frictional tensile stress, the material will tear or undergo plastic deformation. The POM / e-GNP nanocomposite exhibits significantly improved wear surface quality, with only fine and shallow scratches observed in dry friction. The large specific surface area of ​​e-GNP provides maximum coverage on the wear surface, resulting in lower interlaminar shear and preventing material damage due to wear-induced crack formation. Furthermore, the well-dispersed e-GNP filler effectively withstands loads and inhibits crack propagation by preventing large-scale blocky wear debris, thereby promoting the chemical bonding of the thin transfer film on the steel surface. On the other hand, under grease-lubricated friction tests, the wear surface is very small and smooth, especially in the POM / e-GNP nanocomposite.

[0053] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing graphene filler, characterized in that, Includes the following steps: Step 1: Add graphene nanosheet powder to a mixed solution of ethanol and deionized water and perform high-precision ultrasonic treatment to obtain a suspension of graphene nanosheets. Step 2: Add the silane coupling agent to the suspension obtained in Step 1 and stir magnetically to complete the surface reaction; then mix under high shear and exfoliate at 8000-15000 rpm for 0.5-5 hours, then filter, wash and dry to obtain the exfoliated graphene filler.

2. The method for preparing graphene filler according to claim 1, characterized in that, In step one, the volume ratio of ethanol to deionized water in the ethanol and deionized water mixed solution is 7:3; the thickness of the graphene nanosheet layer in the graphene nanosheet powder is 5-100 nm.

3. The method for preparing graphene filler according to claim 1, characterized in that, In step one, the conditions for the tip ultrasonic treatment are: 12-20mm titanium probe, ice bath, power 500-1200W, vibration frequency 18-20kHz, and treatment time 2-4 hours.

4. The method for preparing graphene filler according to claim 1, characterized in that, In step two, the silane coupling agent is 3-aminopropyltriethoxysilane, and its addition amount is 0.1-1 wt% of the suspension.

5. The method for preparing graphene filler according to claim 1, characterized in that, In step two, the cleaning reagent used is ethanol, the drying temperature is 80-100℃, and the drying time is 18-24 hours.

6. A graphene filler prepared by the preparation method according to any one of claims 1-5, characterized in that, The graphene nanosheets in the graphene filler have a thickness of 0.5-1 nm.

7. A composite filler, characterized in that, It includes the graphene filler as described in claim 6, and one or a mixture of several of polytetrafluoroethylene, carbon fiber, glass fiber, and nano-Al2O3.

8. The composite filler according to claim 7, characterized in that, The polytetrafluoroethylene has an average particle size of 10-15 μm; the nano-Al2O3 is spherical α-alumina with an average particle size of 10-100 nm.

9. The application of the graphene filler as described in claim 6, characterized in that, The graphene filler is added to a polymer material to prepare a friction-reducing material; the polymer material is one or a combination of several of the following: polypropylene, low-density polyethylene, high-density polyethylene, acrylonitrile butadiene styrene, ultra-high molecular weight polyethylene, polyamide, polyoxymethylene, polyphenylene sulfide, polyether ether ketone, polyethyleneimine, polyimide, and epoxy resin.

10. The application according to claim 9, characterized in that, The polymer material is polyoxymethylene; the amount of graphene filler added is 0.5-1 wt%.

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