High-temperature-resistant high-friction-reducing lubricating oil and preparation method thereof

Abstract

The application relates to the technical field of lubricating oil, and particularly discloses a high-temperature-resistant and high-friction-reducing lubricating oil and a preparation method thereof. The lubricating oil comprises the following components: 35-45 parts of poly-alpha-olefin, 10-15 parts of methyl ricinoleate, 20-30 parts of pentaerythritol tetraoleate, 15-20 parts of hydrogenated base oil, 0.1-0.2 parts of modified graphene oxide, 0.8-1.5 parts of extreme-pressure anti-wear agent, 0.5-1 part of detergent, 0.3-0.5 part of antioxidant, 0.2-0.3 part of dispersant, 0.5-0.8 part of viscosity index improver, 0.1-0.2 part of rust inhibitor and 0.01-0.05 part of antifoaming agent. The application realizes cost reduction and emission reduction by compounding multiple base oils, guaranteeing the stability of the system through multi-component synergy and replacing part of the base oil with plant-based base oil. The modified graphene oxide significantly reduces wear through physical friction reduction and chemical anti-wear synergy, quickly discharges accumulated heat and prolongs the service life at high temperature.

Description

Technical Field

[0001] This application relates to the field of lubricating oil technology, specifically to a high-temperature resistant and high-friction-reducing lubricating oil and its preparation method. Background Technology

[0002] Lubricating oil is a key lubricating medium formulated from base oil and multifunctional additives. It has multiple functions such as lubrication and friction reduction, cooling and heat dissipation, cleaning and dispersion, sealing and leak prevention, rust and corrosion prevention, and buffering and shock absorption. It is widely used in automotive power transmission systems, industrial machinery and equipment, engineering machinery, hydraulic devices and other fields. It can effectively reduce friction and wear between mechanical parts, extend the service life of equipment, and ensure the stable, efficient and safe operation of various mechanical systems. It is an indispensable material in transportation and modern industrial fields.

[0003] Lubricating oil is a complex mixture composed of multiple components. It mainly contains 80% to 95% base oil, including mineral base oil, synthetic base oil, and bio-based base oil. The remaining 5% to 20% is a compound system of various functional additives, such as detergents and dispersants, antioxidants and corrosion inhibitors, extreme pressure anti-wear agents, viscosity index improvers, pour point depressants, and antifoaming agents. Through the synergistic effect of different components, it achieves core functions such as lubrication and friction reduction, cooling and heat dissipation, cleaning and dispersion, sealing and leak prevention, rust and corrosion prevention, and buffering and shock absorption, ensuring the stable operation of mechanical systems.

[0004] Lubricating oils can be classified into four main categories: mineral oils, semi-synthetic oils, fully synthetic oils, and bio-based lubricating oils. Mineral oils are derived from petroleum refining, are inexpensive, but have an inhomogeneous molecular structure, poor high-temperature resistance, oxidation resistance, and low-temperature fluidity, and are prone to oxidation, resulting in sludge and carbon deposits. Semi-synthetic oils are a mixture of mineral and synthetic oils, offering balanced performance but failing to meet the demands of extreme operating conditions. Fully synthetic oils, while possessing excellent overall performance, suffer from high raw material costs and insufficient hydrolytic stability of some synthetic esters. Bio-based lubricating oils are environmentally friendly and biodegradable, but have weak high-temperature resistance and oxidation stability, making them unsuitable for high-load applications.

[0005] Therefore, it is of great significance to improve the high-temperature resistance and anti-wear properties of lubricating oil as much as possible while reducing pollution and achieving green environmental protection goals. Summary of the Invention

[0006] To improve the high-temperature resistance and reduce friction of lubricating oil, this application provides a lubricating oil and its preparation method.

[0007] To address the issue of lubricating oil's susceptibility to oxidation under high-temperature, heavy-load conditions, this invention employs a compounding process involving synthetic oil polyalphaolefin, plant-based base oil methyl ricinoleate, pentaerythritol tetraoleate, and hydrogenated base oil. The synthetic oil provides excellent high-temperature oxidation stability and viscosity stability. Methyl ricinoleate reduces costs and emissions, and its ester structure is compatible with the polyacrylate chains on the modified graphene surface, synergistically enhancing lubricating film strength and dispersion stability. Pentaerythritol tetraoleate acts as a lubrication-enhancing component, improving oil film strength and boundary lubrication performance. The hydrogenated base oil effectively adjusts the overall viscosity of the formulation, improves the low-temperature fluidity of the lubricating oil, and enhances the system's stability.

[0008] Graphene, with its two-dimensional layered structure, ultra-low coefficient of friction, and excellent thermal conductivity, can provide excellent protection and heat dissipation when added to lubricating oils. However, its biggest problem lies in the strong van der Waals forces between the layers, which make it difficult to disperse and prone to agglomeration and sedimentation, leading to short-term failure and even the formation of hard abrasive particles, thus exacerbating wear on the friction pair.

[0009] Therefore, this invention involves condensing and grafting graphene oxide with a silane coupling agent, followed by free radical polymerization to obtain long polyacrylate chains on its surface. The steric hindrance of the polymer molecular chains effectively prevents interactions between graphene sheets. The monomers containing long alkyl chains not only provide steric support but also enhance the compatibility of the modified graphene oxide in the oil phase through hydrophobic and oleophilic properties. Furthermore, the sulfur-containing monomers in the polymer enable the modified graphene oxide to not only provide layered friction reduction but also allow the sulfur elements on its surface to undergo tribochemical reactions with metal friction pairs, generating a lubricating film and forming a synergistic lubrication system with graphene for both physical friction reduction and chemical anti-wear. Compared to conventional grafting modification with oleic acid or alkylamines, this invention uses polymeric grafting, which not only provides greater steric hindrance and better inhibition of agglomeration but also makes the polymer chains less prone to decomposition under high-temperature conditions, thus not affecting the friction-reducing effect of graphene.

[0010] The copolymerization of sulfur-containing monomers and acrylic monomers allows long polymer chains to be grafted onto the graphene surface. This chemical bonding method can remain stable under complex working conditions such as high temperature, thereby forming a synergistic structure of graphene physical support layer and chemical reaction lubricating film at the friction interface.

[0011] When sulfur-containing monomers are polymerized and grafted onto graphene oxide by combining 2-methyl-2-acrylate-2-sulfoethyl ester and 2-(methylthio)methacryloyl ester, the sulfonate groups, due to their high polarity and strong adsorption, can quickly react with the metal surface under medium and low loads to form a robust extreme pressure film. Meanwhile, the thioether groups have good thermal stability and can continuously and gradually provide an active sulfur source under higher temperatures and extreme pressures. The molecular-level composite of the two constitutes a gradient lubrication and protection system with a wide temperature range and a wide load range.

[0012] Modified graphene oxide can not only effectively reduce direct contact between friction pairs and reduce wear, but also prevent lubricating oil from overheating and deteriorating and friction pairs from thermal deformation, significantly improve the oil film carrying capacity of lubricating oil, and prevent direct friction between metal surfaces due to oil film rupture.

[0013] In a first aspect, the present invention provides a high-temperature resistant and high-friction-reducing lubricating oil, comprising the following components: 35-45 parts of polyalphaolefin, 10-15 parts of methyl ricinoleate, 20-30 parts of pentaerythritol tetraoleate, 15-20 parts of hydrogenated base oil, 0.1-0.2 parts of modified graphene oxide, 0.8-1.5 parts of extreme pressure anti-wear agent, 0.5-1 part of detergent, 0.3-0.5 parts of antioxidant, 0.2-0.3 parts of dispersant, 0.5-0.8 parts of viscosity index improver, 0.1-0.2 parts of rust inhibitor, and 0.01-0.05 parts of antifoaming agent.

[0014] The method for preparing the modified graphene oxide includes the following steps: X1. Add graphene oxide to an ethanol aqueous solution and disperse it evenly by ultrasonication to obtain dispersion A. Mix 3-(isobutenoyloxy)propyltrimethoxysilane with an ethanol aqueous solution evenly and adjust the pH to weakly acidic with glacial acetic acid to obtain dispersion B. Add dispersion B to dispersion A, heat to 60-65℃ and stir for 18-24h. After the reaction is completed, centrifuge, wash and dry to obtain grafted graphene oxide. X2. Grafted graphene oxide was added to N,N-dimethylformamide and ultrasonically dispersed evenly. Octadecyl methacrylate and sulfur-containing monomers were added and stirred evenly. Then azobisisobutyronitrile was added. Under nitrogen protection, the mixture was heated to 70-80℃ and stirred for 2-3 hours to carry out free radical polymerization. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain modified graphene oxide.

[0015] Furthermore, the mass ratio of graphene oxide to aqueous ethanol solution is 10:150-250, and the mass ratio of 3-(isobutenoyloxy)propyltrimethoxysilane to aqueous ethanol solution is 1.5:50-150.

[0016] Furthermore, the mass ratio of the grafted graphene oxide to N,N-dimethylformamide, octadecyl methacrylate, sulfur-containing monomers, and azobisisobutyronitrile is 5:100-200:1-2:0.9-1.5:0.01-0.1.

[0017] Furthermore, the sulfur-containing monomer is one of 2-methyl-2-acrylate-2-sulfoethyl ester, 2-(methylthio)methacryloyl ethyl ester, 2-phenylthioethanolacrylic acid, or a mixture of 2-methyl-2-acrylate-2-sulfoethyl ester and 2-(methylthio)methacryloyl ethyl ester.

[0018] Furthermore, the sulfur-containing monomer is a mixture of 2-methyl-2-acrylate-2-sulfoethyl ester and 2-(methylthio)methacryloyl ester in a mass ratio of 0.8:0.4-0.5.

[0019] Furthermore, the cleaning agent is calcium sulfonate.

[0020] Furthermore, the extreme pressure anti-wear agent is zinc dialkyl dithiophosphate.

[0021] Furthermore, the antioxidant is 2,6-di-tert-butyl-p-cresol.

[0022] Furthermore, the dispersant is polyisobutylene succinimide.

[0023] Furthermore, the viscosity index improver is an ethylene-propylene copolymer.

[0024] Furthermore, the rust inhibitor is dodecenylsuccinic acid.

[0025] Furthermore, the antifoaming agent is polydimethylsiloxane.

[0026] Secondly, the present invention provides a method for preparing a high-temperature resistant and high-friction-reducing lubricating oil, comprising the following steps: S1. Polyalphaolefin, methyl ricinoleate, pentaerythritol tetraoleate and hydrogenated base oil are mixed at 60-70℃ to obtain a compound base oil. S2. Take 10% of the compound base oil and the modified graphene oxide, disperse them evenly by ultrasonication, and then mix them with the remaining compound base oil. Add extreme pressure anti-wear agent, antioxidant, detergent, dispersant, viscosity index improver, rust inhibitor, and antifoaming agent. Stir and mix evenly, filter to remove impurities, and then degas under vacuum to obtain the final product.

[0027] Compared with the prior art, the beneficial effects of this application are at least as follows: 1. In this invention, poly-α-olefins ensure oxidation stability and viscosity stability at high temperatures, methyl castor oil synergistically enhances the strength and dispersion stability of the lubricating film, pentaerythritol tetraoleate not only serves as a lubrication enhancement component but also improves boundary lubrication performance, and hydrogenated base oil effectively adjusts the viscosity of the overall formulation, improves the low-temperature fluidity of the lubricating oil, and ensures the stability of the system.

[0028] 2. This invention obtains long polyacrylate chains by condensing and grafting graphene oxide with a silane coupling agent and then free radical polymerization on its surface. This not only improves agglomeration but also enhances the compatibility with the oil phase. Furthermore, the polymer chains are less prone to decomposition under high-temperature conditions and do not affect the friction-reducing effect of graphene.

[0029] 3. The sulfur-containing monomers used in the polymerization of modified graphene oxide enable the modified graphene oxide to not only provide layered friction reduction, but also allow the sulfur elements on its surface to undergo tribochemical reactions with the metal friction pair to generate a lubricating film, forming a synergistic lubrication system with physical friction reduction and chemical anti-wear with graphene. Detailed Implementation

[0030] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0031] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0032] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0033] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0034] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0035] Graphene oxide, with sheet thickness of 1-5 nm, particle size of 0.5-2 μm, and surface hydroxyl content ≥5 mmol / g.

[0036] Polyalphaolefin, type: PAO40, viscosity at 40℃ ~400 mmHg 2 / s.

[0037] Hydrogenated base oil, API Group III, viscosity at 40℃ ~30 mm 2 / s.

[0038] 2-Methyl-2-acrylate-2-sulfoethyl ester, CAS No.: 10595-80-9.

[0039] 2-(methylthio)methacryloyl ethyl ester, CAS No.: 14216-23-0.

[0040] 2-Phenylthioethanolacrylic acid, CAS No.: 95175-38-5.

[0041] Polyisobutylene succinimide, number average molecular weight 100,000, kinematic viscosity (100℃): 150-200 mmHg 2 / s.

[0042] Ethylene-propylene copolymer, kinematic viscosity (100℃): ≥800 mm 2 / s.

[0043] Polydimethylsiloxane, viscosity at 25°C: 500 mPa s.

[0044] Example 1 A method for preparing a high-temperature resistant and high-friction-reducing lubricating oil includes the following steps: S1. Mix 40 parts of polyα-olefin, 12 parts of methyl ricinoleate, 25 parts of pentaerythritol tetraoleate, and 17.55 parts of hydrogenated base oil at 70°C to obtain a compound base oil. S2. Take 10% of the compound base oil and 0.12 parts of modified graphene oxide, disperse them evenly by ultrasonication, and then mix them with the remaining compound base oil. Add 1 part of zinc dialkyl dithiophosphate, 0.8 parts of calcium sulfonate, 0.4 parts of 2,6-di-tert-butyl-p-cresol, 0.25 parts of polyisobutylene succinimide, 0.7 parts of ethylene propylene copolymer, 0.15 parts of dodecenyl succinic acid, and 0.03 parts of polydimethylsiloxane. Stir and mix evenly, filter to remove impurities, and then degas under vacuum to obtain the final product.

[0045] The method for preparing the modified graphene oxide includes the following steps: X1. Add 10 parts of graphene oxide to 200 parts of 80% ethanol aqueous solution and disperse evenly by ultrasonication to obtain dispersion A. Mix 1.5 parts of 3-(isobutenoyloxy)propyltrimethoxysilane with 100 parts of 90% ethanol aqueous solution evenly and adjust the pH to 5 with glacial acetic acid to obtain dispersion B. Add dispersion B to dispersion A, heat to 60℃ and stir for 24 hours. After the reaction is completed, centrifuge, wash and dry to obtain grafted graphene oxide. X2. Add 5 parts of grafted graphene oxide to 150 parts of N,N-dimethylformamide and disperse evenly by ultrasonication. Add 1.5 parts of octadecyl methacrylate and 1.2 parts of 2-methyl-2-acrylate-2-sulfoethyl ester and stir evenly. Then add 0.05 parts of azobisisobutyronitrile. Under nitrogen protection, heat to 80℃ and stir for 3 hours to carry out free radical polymerization. After the reaction is completed, centrifuge, wash and dry to obtain modified graphene oxide.

[0046] Example 2 It is essentially the same as Example 1, except that 2-methyl-2-acrylate-2-sulfoethyl ester is replaced with an equal mass of 2-(methylthio)methacryloyl ester.

[0047] Example 3 It is basically the same as Example 1, except that 2-methyl-2-acrylate-2-sulfoethyl ester is replaced with an equal mass of 2-phenylthioethanolacrylic acid.

[0048] Example 4 It is basically the same as Example 2, except that the amount of modified graphene oxide is 0.1 parts.

[0049] Example 5 It is basically the same as Example 2, except that the amount of modified graphene oxide is 0.2 parts.

[0050] Example 6 The mixture is basically the same as in Example 1, except that 1.2 parts of 2-methyl-2-acrylate-2-sulfoethyl ester are replaced with a mixture of 0.8 parts of 2-methyl-2-acrylate-2-sulfoethyl ester and 0.4 parts of 2-(methylthio)methacryloyl ester.

[0051] Comparative Example 1 It is basically the same as Example 1, except that the modified graphene oxide is different; The method for preparing the modified graphene oxide includes the following steps: Ten parts of graphene oxide were added to 200 parts of 80% ethanol aqueous solution and ultrasonically dispersed to obtain dispersion A. 1.5 parts of 3-(isobutenoyloxy)propyltrimethoxysilane were mixed with 100 parts of 90% ethanol aqueous solution and the pH was adjusted to 5 with glacial acetic acid to obtain dispersion B. Dispersion B was added to dispersion A, and the mixture was heated to 60℃ and stirred for 24 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain modified graphene oxide.

[0052] Comparative Example 2 It is basically the same as Example 1, except that the modified graphene oxide is different; The method for preparing the modified graphene oxide includes the following steps: Ten parts of graphene oxide were added to 150 parts of N,N-dimethylformamide, and then 50 parts of thionyl chloride were added. After stirring and dispersing evenly, the mixture was heated to 80°C and stirred for 10 hours under nitrogen protection. After the reaction was completed, the mixture was distilled under reduced pressure until the system reached constant weight to obtain acyl-chlorinated graphene oxide. 150 parts of N,N-dimethylformamide and 6 parts of dodecanethiol were added to the acyl-chlorinated graphene oxide. After stirring and mixing, the mixture was sonicated for 20 minutes to obtain a uniform suspension. The suspension was heated to 100°C and reacted for 10 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain modified graphene oxide.

[0053] Comparative Example 3 It is basically the same as Example 1, except that the modified graphene oxide is different; The method for preparing the modified graphene oxide includes the following steps: X1. Add 10 parts of graphene oxide to 200 parts of 80% ethanol aqueous solution and disperse evenly by ultrasonication to obtain dispersion A. Mix 1.5 parts of 3-(isobutenoyloxy)propyltrimethoxysilane with 100 parts of 90% ethanol aqueous solution evenly and adjust the pH to 5 with glacial acetic acid to obtain dispersion B. Add dispersion B to dispersion A, heat to 60℃ and stir for 24 hours. After the reaction is completed, centrifuge, wash and dry to obtain grafted graphene oxide. X2. Add 1.5 parts of octadecyl methacrylate and 1.2 parts of 2-methyl-2-acrylate-2-sulfoethyl ester to 150 parts of N,N-dimethylformamide, stir evenly, then add 0.05 parts of azobisisobutyronitrile, heat to 80℃ under nitrogen protection and stir for 3 hours to carry out free radical polymerization. After the reaction is completed, centrifuge, wash and dry to obtain sulfur-containing polyacrylic acid, and mix evenly with 5 parts of grafted graphene oxide to obtain modified graphene.

[0054] Test section 1. Tribological properties of the lubricating oils prepared in the examples and comparative examples were tested. Three lower steel balls were placed in an oil box, and test oil was poured into the box to a depth of 3 mm above the top of the balls. The upper steel ball was clamped with a fixture. During the test, the three lower steel balls were fixed, while the upper steel ball rotated under the drive of a motor. The spindle speed was 1300 r / min, the test load was 400 N, and the test oil temperature was 75 °C. After the oil temperature reached the set value, it was kept at a constant temperature for 15 minutes before the test began. The friction time was 60 minutes. After the test, the three lower test balls were removed, and the wear scar diameter on each steel ball was measured from two mutually perpendicular directions, resulting in a total of 6 wear scar diameter values. The average value was taken as the final wear scar diameter. Each group of samples underwent at least 3 parallel tests, and the average value of the 3 tests was taken as the final result.

[0055] 2. Testing the extreme pressure properties of the lubricating oils prepared in the examples and comparative examples before and after high-temperature treatment. Take 50 mL of the lubricating oil sample to be tested, seal it, and place it in a 250℃ constant temperature forced-air drying oven for 200 hours. After aging, allow it to cool naturally to room temperature and shake well before use. Use a four-ball wear tester for friction and wear testing, with a spindle speed of 1450 r / min, room temperature conditions, and a single-stage load test duration of 10 s. Test the maximum non-seize load (PB) value before and after high-temperature treatment, and the minimum sintering load (PD) value before high-temperature treatment.

[0056] Table 1

[0057] Table 2

[0058] The diameter of the wear scar is an important parameter for the anti-wear performance of lubricating oil; the smaller the diameter, the better its friction-reducing effect.

[0059] The PB and PD values ​​in extreme pressure tests can reflect the critical load and maximum load-bearing capacity of the lubricating oil.

[0060] As shown in Tables 1-2, compared with the comparative example, the lubricants in the examples all exhibit better wear resistance and extreme pressure properties. The examples combine polyalphaolefin, methyl ricinoleate, pentaerythritol tetraoleate, and hydrogenated base oil. Polyalphaolefin ensures oxidation stability and viscosity stability at high temperatures, methyl ricinoleate synergistically enhances lubricating film strength and dispersion stability, pentaerythritol tetraoleate not only acts as a lubrication-enhancing component but also improves boundary lubrication performance, and the hydrogenated base oil effectively adjusts the overall viscosity of the formulation, improves the low-temperature fluidity of the lubricant, and ensures the stability of the system. Modified graphene oxide significantly reduces wear through a synergistic effect of physical friction reduction and chemical anti-wear, while rapidly dissipating accumulated heat and extending high-temperature service life.

[0061] Compared with Comparative Example 1, although Comparative Example 1 grafted graphene oxide with 3-(isobutenoyloxy)propyltrimethoxysilane, which reduced the surface polar groups and improved the internal aggregation phenomenon, the steric hindrance effect of silane was limited, and it may desorb or even decompose at high temperature. Therefore, its performance in reducing friction and maintaining stability at high temperature was not as good as that of Example 1.

[0062] Compared to Comparative Example 2, Example 1 used dodecyl mercaptan to graft and modify graphene oxide. The introduction of sulfur atoms caused the modified graphene oxide to undergo a tribochemical reaction with the metal friction pair, generating a lubricating film. However, the steric hindrance of the alkyl chain was not as good as that of the polymer chain, so its dispersion effect was poor, which directly affected the friction reduction effect. After high-temperature aging, the alkyl chain may desorb and lose its dispersibility, thus significantly reducing the extreme pressure bearing capacity.

[0063] Compared to Comparative Example 3, Example 3 synthesized a blend of sulfur-containing polyacrylic acid and grafted graphene oxide. While Comparative Example 3 showed better performance than Comparative Example 1 (which only modified with silane), it was significantly inferior to Example 1. This indicates that better lubrication and high-temperature stability can only be achieved when sulfur-containing polymer chains are chemically grafted onto the graphene framework via covalent bonds. Physically mixed modified graphene is prone to phase separation under high temperatures and other external forces, resulting in sulfur failing to produce a stable and continuous synergistic lubrication effect with graphene at the friction interface, leading to rapid performance degradation.

[0064] Compared with Examples 2 and 3, Example 1 shows that the sulfur-containing monomer 2-methyl-2-acrylate-2-sulfoethyl ester contains a highly polar sulfonate group, which can strongly adsorb onto the metal surface, resulting in the best tribochemical film formation effect and the strongest anti-wear load-bearing capacity. However, the sulfonate group has poor thermal stability and is prone to decomposition under high-temperature aerobic aging conditions at 250°C, thus reducing the extreme pressure performance after high-temperature aging. Example 3 shows that the sulfur-containing monomer 2-phenylthioethanolacrylic acid contains a rigid benzene ring, which can enhance the mechanical strength of the polymer side chains and the load-bearing capacity of the lubricating film at room temperature, thus exhibiting good extreme pressure load-bearing performance before high-temperature aging. However, after high-temperature aging, because this monomer has an acrylate structure, the thermal stability of the polymer product is lower than that of methacrylates. Simultaneously, the conjugated system of the phenylthio group can undergo cross-interfacial electronic coupling with the graphene oxide substrate, accelerating the oxidation and loss of sulfur-containing functional groups under high-temperature aerobic conditions. Therefore, the extreme pressure load-bearing capacity decreases significantly after high-temperature treatment. In Example 2, the sulfur-containing monomer 2-(methylthio)methacryloyl ester has a methacrylate structure. The α-methyl group significantly improves the thermal stability of the polymer product, and the thioether group has no additional conjugated interface effect, making it more stable at high temperatures. Therefore, even after high-temperature treatment, its extreme pressure bearing capacity can still be maintained at a good level.

[0065] Compared with Examples 4 and 5, the lubricating oil in Example 2 has better parameters, indicating that the addition amount in Example 2 is more suitable. When the amount of modified graphene oxide added is low, a continuous lubricating film that fully covers the entire surface cannot be formed. When the amount of modified graphene oxide added is high, although it can improve wear resistance, the improvement is limited and it will increase the risk of high-temperature agglomeration.

[0066] Example 6 employed a blend of two sulfur-containing monomers, exhibiting optimal performance. This was attributed to the balance between high load-bearing capacity and excellent thermal stability. The sulfonate groups, with their high polarity and strong adsorption, rapidly react with metal surfaces under low to medium loads to form a robust extreme pressure film. Meanwhile, the thioether groups, with their good thermal stability, continuously and gradually provide an active sulfur source at higher temperatures and extreme pressures, preventing sudden lubrication film failure. These two monomers are chemically grafted onto graphene to achieve a molecular-level composite, forming a gradient lubrication and protection system with a wide temperature range and broad load range, enabling the lubricating oil to balance lubricity and high-temperature stability.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A high-temperature resistant, high-friction-reducing lubricating oil, characterized in that, It comprises the following components: 35-45 parts of polyα-olefin, 10-15 parts of methyl ricinoleate, 20-30 parts of pentaerythritol tetraoleate, 15-20 parts of hydrogenated base oil, 0.1-0.2 parts of modified graphene oxide, 0.8-1.5 parts of extreme pressure anti-wear agent, 0.5-1 part of detergent, 0.3-0.5 parts of antioxidant, 0.2-0.3 parts of dispersant, 0.5-0.8 parts of viscosity index improver, 0.1-0.2 parts of rust inhibitor, and 0.01-0.05 parts of antifoaming agent; The method for preparing the modified graphene oxide includes the following steps: X1. Add graphene oxide to an ethanol aqueous solution and disperse it evenly by ultrasonication to obtain dispersion A. Mix 3-(isobutenoyloxy)propyltrimethoxysilane with an ethanol aqueous solution evenly and adjust the pH to weakly acidic with glacial acetic acid to obtain dispersion B. Add dispersion B to dispersion A, heat to 60-65℃ and stir for 18-24h. After the reaction is completed, centrifuge, wash and dry to obtain grafted graphene oxide. X2. Grafted graphene oxide was added to N,N-dimethylformamide and ultrasonically dispersed evenly. Octadecyl methacrylate and sulfur-containing monomers were added and stirred evenly. Then azobisisobutyronitrile was added. Under nitrogen protection, the temperature was raised to 70-80℃ and stirred for 2-3 hours to carry out free radical polymerization. After the reaction was completed, the mixture was centrifuged, washed and dried to obtain modified graphene oxide. The sulfur-containing monomer is one of 2-methyl-2-acrylate-2-sulfoethyl ethyl ester, 2-(methylthio)methacryloyl ethyl ester, 2-phenylthioethanolacrylic acid, or a mixture of 2-methyl-2-acrylate-2-sulfoethyl ethyl ester and 2-(methylthio)methacryloyl ethyl ester.

2. The high-temperature resistant and high-friction-reducing lubricating oil as described in claim 1, characterized in that, The mass ratio of graphene oxide to aqueous ethanol solution is 10:150-250, and the mass ratio of 3-(isobutenoyloxy)propyltrimethoxysilane to aqueous ethanol solution is 1.5:50-150.

3. The high-temperature resistant and high-friction-reducing lubricating oil as described in claim 1, characterized in that, The mass ratio of the grafted graphene oxide to N,N-dimethylformamide, octadecyl methacrylate, sulfur-containing monomers, and azobisisobutyronitrile is 5:100-200:1-2:0.9-1.5:0.01-0.

1.

4. The high-temperature resistant and high-friction-reducing lubricating oil as described in claim 1, characterized in that, The sulfur-containing monomers are 2-methyl-2-acrylate-2-sulfoethyl ester and 2-(methylthio)methacryloyl ethyl ester mixed in a mass ratio of 0.8:0.4-0.

5.

5. The high-temperature resistant and high-friction-reducing lubricating oil as described in claim 1, characterized in that, The extreme pressure anti-wear agent is zinc dialkyl dithiophosphate.

6. The high-temperature resistant and high-friction-reducing lubricating oil as described in claim 1, characterized in that, The antioxidant is 2,6-di-tert-butyl-p-cresol.

7. The high-temperature resistant and high-friction-reducing lubricating oil as described in claim 1, characterized in that, The dispersant is polyisobutylene succinimide.

8. The high-temperature resistant and high-friction-reducing lubricating oil as described in claim 1, characterized in that, The viscosity index improver is an ethylene-propylene copolymer.

9. The high-temperature resistant and high-friction-reducing lubricating oil as described in claim 1, characterized in that, The rust inhibitor is dodecenyl succinic acid.

10. The method for preparing the high-temperature resistant and high-friction-reducing lubricating oil according to any one of claims 1-9, characterized in that, Includes the following steps: S1. Mix polyα-olefin, methyl ricinoleate, pentaerythritol tetraoleate, and hydrogenated base oil at 60-70℃ to obtain a compound base oil. S2. Take 10% of the compound base oil and the modified graphene oxide, disperse them evenly by ultrasonication, and then mix them with the remaining compound base oil. Add extreme pressure anti-wear agent, antioxidant, detergent, dispersant, viscosity index improver, rust inhibitor, and antifoaming agent. Stir and mix evenly, filter to remove impurities, and then degas under vacuum to obtain the final product.

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