Lubricating additive, preparation method thereof, refrigerating machine oil and working fluid composition for refrigerating machine

Abstract

The invention relates to the technical field of lubricating materials, and discloses a lubricating additive, a preparation method of the lubricating additive, refrigerating machine oil and a working fluid composition for a refrigerating machine. The lubricating additive comprises a two-dimensional lamellar solid lubricating material and polydopamine, wherein the polydopamine is grafted on the surface of the two-dimensional lamellar solid lubricating material. According to the invention, polydopamine is grafted on the surface of a two-dimensional lamellar solid lubricating material to form a novel composite lubricating additive, and the lubricating additive provided by the invention has extremely excellent lipophilicity in lubricating base oil and can be stably dispersed for a long time; meanwhile, compared with pure base oil, the lubricating additive added into the lubricating base oil can obtain a lower friction coefficient and a lower grinding crack width, so that the lubricating performance of the lubricating base oil can be remarkably improved, the abrasion of internal parts of the compressor is effectively reduced, the working life of the compressor is prolonged, and the working condition stability of the compressor is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lubricating materials, in particular to a lubricating additive, a preparation method thereof, and a refrigeration machine oil and a working fluid composition for refrigeration machines. BACKGROUND

[0002] Inside the compressor, there are many high-speed moving parts (such as bearings, rotors, pistons, scroll plates, rollers, etc.), the friction between these parts will cause damage to the surface of the compressor parts, shorten their service life, increase the probability of safety accidents, and also cause huge energy loss. At present, the use of lubricating oil (refrigeration machine oil base oil) to lubricate the inside of the compressor is an effective method to reduce the wear of internal parts. The lubricating oil forms an oil film between these metal parts, changing the direct contact dry friction into liquid internal friction, thereby greatly reducing wear and energy loss. However, the lubricating performance of a single lubricating oil is often insufficient, and the addition of a lubricating additive can improve the lubricating performance of the lubricating oil. SUMMARY

[0003] Therefore, the purpose of the present application is to provide a lubricating additive and a preparation method thereof, so that the lubricating additive can significantly improve the lubricating performance of lubricating oil, such as refrigeration machine oil, and has excellent lipophilicity.

[0004] Another purpose of the present application is to provide a refrigeration machine oil and a working fluid composition for refrigeration machines based on the lubricating additive described in the present application.

[0005] In order to achieve all or part of the above purposes, as a first aspect of the present application, a lubricating additive is provided, comprising a two-dimensional sheet-like solid lubricating material and a polydopamine, wherein the polydopamine is grafted on the surface of the two-dimensional sheet-like solid lubricating material.

[0006] Optionally, the two-dimensional sheet-like solid lubricating material comprises one or more of graphene, molybdenum disulfide, hexagonal boron nitride, and black phosphorus.

[0007] As a second aspect of the present application, a preparation method of the lubricating additive described in the present application is provided, comprising: providing a two-dimensional sheet-like solid lubricating material; reacting the two-dimensional sheet-like solid lubricating material with dopamine hydrochloride in a buffer medium under alkaline conditions, so that dopamine is grafted and polymerized into polydopamine on the surface of the two-dimensional sheet-like solid lubricating material to obtain the lubricating additive.

[0008] Optionally, the mass ratio of the two-dimensional layered solid lubricant to dopamine hydrochloride is (1-3):(4-6). Further optionally, the two-dimensional layered solid lubricant includes one or more of graphene, molybdenum disulfide, hexagonal boron nitride, and black phosphorus; optionally, the black phosphorus is prepared by thoroughly grinding red phosphorus.

[0009] Optionally, the buffer medium comprises Tris-HCl, and the alkaline condition is 7 < pH value ≤ 9.

[0010] As a third aspect of this application, a refrigeration oil is provided, comprising a base oil and the lubricating additives described in this application or prepared by the preparation method described in this application.

[0011] Optionally, the amount of the lubricating additive added is 0.12-0.20%.

[0012] As a fourth aspect of this application, a fluid composition for a refrigeration unit is provided, comprising a refrigerant and the refrigeration oil described in this application.

[0013] This application presents a novel composite lubricant additive formed by grafting polydopamine onto the surface of a two-dimensional lamellar solid lubricant material. The lubricant additive provided by this application exhibits excellent oleophilicity in lubricating base oils and can maintain stable dispersion for a long time. At the same time, the addition of the lubricant additive of this application to lubricating base oils results in a lower coefficient of friction and wear track width compared to pure base oils, which can significantly improve the lubrication performance of the lubricating base oils, effectively reduce the wear of internal components of the compressor, and improve the working life and operating stability of the compressor. Attached Figure Description

[0014] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application. Figure 1 The images shown are scanning electron microscope (SEM) images of black phosphorus and black phosphorus-polydopamine composite material; BP represents black phosphorus, and BP-PDA represents black phosphorus-polydopamine composite material. Figure 2 The X-ray diffraction patterns of red phosphorus, black phosphorus, and black phosphorus-polydopamine composite material are shown; RP represents red phosphorus, BP represents black phosphorus, PDA represents polydopamine, and BP-PDA represents black phosphorus-polydopamine composite material. Figure 3 The image shows the dispersion stability of FW68DA lubricating base oil with three additives: polydopamine, black phosphorus, and black phosphorus-polydopamine. RP represents the red phosphorus group, BP represents the black phosphorus group, PDA represents the polydopamine group, and BP-PDA represents the black phosphorus-polydopamine composite group. Figure 4 The results show the friction coefficient of FW68DA lubricating base oil and FW68DA lubricating base oil with three additives: polydopamine, black phosphorus, and black phosphorus-polydopamine. (a) shows the friction coefficient of each group at 0.16% additive content and 10N load over time; (b) shows the average friction coefficient and wear track width of each group at 0.16% additive content and 10N load; (c) shows the average friction coefficient and wear track width of the black phosphorus-polydopamine group at different additive contents and 10N load; and (d) shows the average friction coefficient and wear track width of the black phosphorus-polydopamine group at 0.16% additive content and different loads. Pure oil indicates FW68DA lubricating base oil group, RP indicates group with added red phosphorus, BP indicates group with added black phosphorus, PDA indicates group with added polydopamine, and BP-PDA indicates group with added black phosphorus-polydopamine composite material; different letters on the bar indicate significant differences between them (p < 0.05). Figure 5 The images show a comparison of the friction characteristics of FW68DA lubricating base oil, base oil with added black phosphorus and black phosphorus-polydopamine additives; (a) is the base oil group, (b) is the BP black phosphorus group, and (c) is the BP-PDA black phosphorus-polydopamine composite material group. Detailed Implementation

[0015] This application discloses a lubricating additive and its preparation method, as well as refrigeration oil and working fluid compositions for refrigeration machines. Those skilled in the art can refer to the content herein and appropriately modify the process parameters to achieve the desired results. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this application. The products and processes described in this application have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the products and processes described herein without departing from the content, spirit, and scope of this application to realize and apply the technology of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0016] It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Moreover, the embodiments and features described in this application can be combined with each other without conflict.

[0017] Two-dimensional lamellar solid lubricants possess a unique layered structure that allows for easy slippage between layers under shear forces, thus achieving a lubricating effect. However, these materials have hydrophilic or inert surfaces, poor compatibility with non-polar mineral or synthetic oils, and difficulty in being fully wetted by oils. Furthermore, their two-dimensional lamellar structure and high specific surface area make them prone to aggregation and sedimentation. Therefore, these unique lubricants are mostly used in water-based lubrications, with limited applications in oils. Currently, surface alkyl chain modification can achieve uniform dispersion in base oils. However, over time, due to the large planar dimensions of two-dimensional lamellar solid lubricants, the van der Waals forces between them are stronger than the van der Waals forces between the two-dimensional lamellar solid lubricant and the base oil, making these dispersions more prone to aggregation and precipitation. These surface modifications and functionalization treatments cannot solve the long-term colloidal stability problem of two-dimensional lamellar solid lubricants in lubricating base oils.

[0018] In view of the above-mentioned technical defects, in the first aspect of this application, a lubricating additive is proposed, comprising a two-dimensional lamellar solid lubricating material and polydopamine, wherein the polydopamine is grafted onto the surface of the two-dimensional lamellar solid lubricating material.

[0019] Because polydopamine is distributed on the surface of the two-dimensional layered solid lubricant material, and because both polydopamine and oil molecules contain a large number of -OH and -NH groups, hydrogen bonds can form between them. This enhances the interaction between the two molecules, overcoming their own weight and the intermolecular forces, thus prolonging the dispersion stability time. Furthermore, polydopamine, through its high adhesion and elasticity, forms a protective layer at the contact interface, absorbing some of the frictional heat and mechanical energy. The composite structure formed with the two-dimensional layered solid lubricant material possesses excellent wear resistance and impact resistance, further improving the lubricating performance of the base oil, making it particularly suitable for the high-impact operating conditions in compressors.

[0020] In some embodiments of this application, the two-dimensional layered solid lubricant material includes one or more of graphene, molybdenum disulfide, hexagonal boron nitride, and black phosphorus. In other embodiments of this application, a lubricant additive is prepared by grafting polydopamine onto black phosphorus. Black phosphorus differs from other two-dimensional layered solid lubricants in that its single layer exhibits a wrinkled structure. Due to its wrinkled structure and low interlayer bonding force, black phosphorus can be curled or folded, which is more conducive to reducing friction and wear at the interface when used as a lubricant additive. Moreover, black phosphorus is unstable in air and water and is prone to oxidative degradation, causing its lubricating performance to gradually fail when used as a water-based lubricant additive. However, grafting it onto polydopamine and using it as an oil-based lubricant additive can effectively reduce its degradation.

[0021] In a second aspect of this application, a method for preparing the lubricating additive described in this application is provided, comprising: Provide two-dimensional sheet-like solid lubricating materials; The two-dimensional lamellar solid lubricant material reacts with dopamine hydrochloride in a buffer medium under alkaline conditions, causing dopamine to be grafted onto the surface of the two-dimensional lamellar solid lubricant material and polymerized into polydopamine, thereby obtaining the lubricant additive.

[0022] In some embodiments of this application, the mass ratio of the two-dimensional lamellar solid lubricant to dopamine hydrochloride is (1-3):(4-6), for example, 1:4, 1:5, 1:6, 2:4, 2:5, 2:6, 3:4, 3:5, 3:6, or any ratio between the two. In other embodiments of this application, the mass of the two-dimensional lamellar solid lubricant is 100-300 mg, for example, 100 mg, 150 mg, 200 mg, 250 mg, 300 mg, or any value between the two; the mass of the dopamine hydrochloride is 400-600 mg, for example, 400 mg, 450 mg, 500 mg, 550 mg, 600 mg, or any value between the two.

[0023] In some embodiments of this application, one of the reaction raw materials, a two-dimensional layered solid lubricant, includes one or more of graphene, molybdenum disulfide, hexagonal boron nitride, and black phosphorus. In other embodiments of this application, black phosphorus is selected to react with dopamine hydrochloride. Black phosphorus (BP) is one of the most stable allotropes of phosphorus. The formation of black phosphorus is essentially a "phase transition" process, whereby the crystal structure of other forms of phosphorus (e.g., white phosphorus, red phosphorus) is rearranged by applying high temperature and pressure, using catalysts (gold, tin, tin iodide, etc.), or ball milling, transforming them into the more stable, layered black phosphorus. Because white phosphorus is relatively reactive and toxic, for safety and ease of operation, this application uses red phosphorus as a raw material and prepares black phosphorus by thorough grinding, for example, by using a planetary ball mill to convert red phosphorus into black phosphorus through high-energy ball milling. Besides preparing black phosphorus in-house, commercially available black phosphorus products can also be selected.

[0024] In some embodiments of this application, the prepared black phosphorus may be ultrasonically treated in water to promote uniform dispersion and exfoliation of the black phosphorus particles and enhance their surface activity so as to better react with dopamine hydrochloride.

[0025] In some embodiments of this application, the buffer medium is used to maintain the relative stability of the solution pH value, ensuring that the hydrochloric acid released during the polymerization of dopamine hydrochloride to dopamine does not cause a decrease in the reaction pH value, maintaining it within a suitable range of 7 < pH ≤ 9, thus providing suitable reaction conditions for the polymerization reaction. The suitable pH value can be selected from 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, or any value between any two. The initial pH value can be adjusted by adding an alkaline substance such as sodium hydroxide, and the amount of buffer medium added can be adjusted according to the actual situation. In other embodiments of this application, the buffer medium is Tris-HCl. When the mass of the layered solid lubricating material is 100-300 mg and the mass of dopamine hydrochloride is 400-600 mg, the amount used can be referenced as 300-500 mg. In other embodiments of this application, a heating environment can be provided during the reaction to promote the reaction process, such as a constant temperature oil bath at 55-65°C.

[0026] In certain embodiments of this application, the black phosphorus-polydopamine lubricant additive prepared according to the method of this application exhibits low coefficient of friction and low wear track width in friction tests. Compared to pure lubricating base oil, the addition of 0.12-0.20% by mass of black phosphorus-polydopamine reduces the coefficient of friction by approximately 43% and the wear track width by approximately 52%, while also demonstrating significantly better lubrication performance than the control group containing only black phosphorus and only polydopamine. Moreover, it maintains dispersion stability for up to 30 days, while single black phosphorus and polydopamine exhibit obvious stratification as early as day 7.

[0027] In a third aspect of this application, based on the superior performance of the lubricating additives described in this application, a refrigeration oil is provided, comprising a base oil and the lubricating additives described in this application or the lubricating additives prepared by the preparation method described in this application.

[0028] In some embodiments of this application, the amount of the lubricating additive added is 0.12-0.20%, for example, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, or any value between the two. The amount added within this range can make the lubricating base oil with added lubricating additive have better lubrication performance, and the effect is best when the added lubricating additive is about 0.16% by mass.

[0029] In some embodiments of this application, in addition to the base oil and the lubricating additives provided in this application, the refrigeration oil may also include other additives as needed, such as one or more additives selected from anti-wear agents, acid scavengers, metal deactivators, and antifoaming agents.

[0030] The base oil includes, but is not limited to, mineral oil, POE oil, and PVE oil. POE oil is a polyol ester formed by the acidification of polyols with organic acids. The polyol is selected from one or more of pentaerythritol, dipentaerythritol, neopentyl glycol, trimethylolpropane, and trimethylolethane. The organic acid is selected from one or more of C4-C18 straight-chain or branched, saturated or unsaturated fatty acids, maleic anhydride, terephthalic acid, and adipic acid. Further, the fatty acid is selected from one or more of butyric acid, 2-methylpropionic acid, n-valeric acid, 2-methylbutyric acid, n-hexanoic acid, 2-methylheptanoic acid, 3-methylheptanoic acid, 4-methylheptanoic acid, 3-ethylhexanoic acid, n-nonanoic acid, 2-methyloctanoic acid, 3-methyloctanoic acid, 4-methyloctanoic acid, 2-ethylheptanoic acid, 3-ethylheptanoic acid, 4-ethylheptanoic acid, and 3,5,5-trimethylhexanoic acid. In some embodiments of this application, the POE oil is tested using specific FW68DA commercial oil. The PVE oil is a PVE base oil prepared from polyethylene ethers such as vinyl ethyl ether, vinyl methyl ether, and vinyl butyl ether.

[0031] The anti-wear agent is selected from one or more of phosphate esters, phosphites, organosulfur compounds, phosphorus-nitrogen complex compounds, sulfur-phosphorus-nitrogen complex compounds, and organochlorides. The metal deactivator is selected from one or more of benzotriazole derivatives and thiadiazole derivatives. The acid scavenger is selected from one or more of neodecanoic acid glycidyl ether and tert-butylphenyl glycidyl ether. The antifoaming agent is selected from one or more of silicone-type and non-silicone-type antifoaming agents. Specifically, the silicone-type antifoaming agent may be dimethyl silicone oil; the non-silicone-type antifoaming agent is selected from one or more of homopolymers or copolymers of acrylates and homopolymers or copolymers of methacrylates.

[0032] In a fourth aspect of this application, a fluid composition for refrigeration machines is provided, comprising a refrigerant and the refrigeration oil described in this application. The refrigeration oil provided in this application is typically present in refrigeration systems as a working fluid composition for refrigeration machines, formed by mixing with a refrigerant.

[0033] In some embodiments of this application, the refrigerant is selected from one or more HFO-type refrigerants, including but not limited to 1,2,3,3,3-pentafluoro-1-propylene, 1,2,3,3-tetrafluoro-1-propylene, 1,3,3,3-tetrafluoro-1-propylene, 2,3,3-trifluoro-1-propylene, 1,1,2-trifluoro-1-propylene, 1,3,3-trifluoro-1-propylene, 1,1,2,3,4-pentafluoro-2-butene, 3,3,4,4-tetrafluoro-1-butene, 1,1,1,2-tetrafluoro-2-butene, and 1,1,1,2,3,4,4,5,5,5-decafluoro-2-pentene. The content of refrigeration oil in the working fluid composition is not particularly limited; however, 1-500 parts by weight of refrigeration oil is preferred relative to 100 parts by weight of refrigerant, and more preferably 2-400 parts by weight of refrigeration oil.

[0034] In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials remain consistent to ensure comparability. Furthermore, all materials used in this application are commercially available.

[0035] The following provides a further description of a lubricating additive and its preparation method, as well as a refrigeration oil and a refrigeration working fluid composition provided in this application.

[0036] Example 1: Preparation of black phosphorus Red phosphorus (RP) was converted to black phosphorus using a planetary ball mill via high-energy ball milling. The preparation process was as follows: the ball-to-powder mass ratio was 40:1. Stainless steel balls and red phosphorus powder were placed together in a 50 mL stainless steel ball mill jar. Next, the ball mill jar was repeatedly evacuated to remove impurity gases, and argon gas at 1.2 MPa was applied. Milling was performed at 1250 r / min for 2700 min. After ball milling, the collected black phosphorus (BP) powder was stored in an argon-filled glove box.

[0037] Example 2: Preparation of polydopamine 400 mg of Tris-HCl was weighed using a high-precision balance and added to 200 mL of deionized water. The mixture was stirred thoroughly with a magnetic stirrer for 15 minutes to ensure complete homogeneity. Next, 500 mg of dopamine hydrochloride was added to the mixture and allowed to dissolve completely. After 30 minutes, the pH of the solution was adjusted to 8.5 with NaOH. Once the pH stabilized, the solution was transferred to a three-necked flask and heated in an oil bath at 60°C. The mixture was stirred at 100 rpm to promote complete polymerization of dopamine. After 12 hours of heating and stirring, the flask was cooled to room temperature. The polydopamine precipitate was obtained by centrifugation and filtration, washed repeatedly with anhydrous ethanol 3-5 times, and dried under vacuum at 50°C for 24 hours to obtain polydopamine powder.

[0038] Example 3: Preparation of a lubricating additive based on black phosphorus-polydopamine 200 mg of black phosphorus prepared in Example 1 was uniformly dispersed in 200 mL of deionized water. The solution was then transferred to a jacketed beaker, and cooling water was circulated to control the reaction temperature. Next, an ultrasonic probe was placed in the beaker, and the solution was sonicated using an ultrasonic cell disruptor for 4 hours to promote uniform dispersion and exfoliation of the black phosphorus particles and enhance their surface activity. Subsequently, 400 mg of Tris-HCl buffer and 500 mg of dopamine hydrochloride were added to the solution, and the pH of the system was adjusted to 8.5 by adding NaOH solution to ensure the reaction proceeded under suitable alkaline conditions. The reaction was carried out under continuous stirring in an oil bath at 60°C for 12 hours, allowing dopamine to polymerize on the BP surface to form stable polydopamine. After the reaction, the mixture was centrifuged, the supernatant was removed, and the mixture was repeatedly washed with deionized water to remove unreacted dopamine and byproducts. Finally, the resulting product was dried in a vacuum drying oven at 50°C for 24 hours to obtain a black phosphorus composite material with surface-grafted polydopamine (BP-PDA).

[0039] Example 4: Characterization of the black phosphorus-polydopamine lubricant additive material of this application Figure 1The images shown are microscopic feature images of the BP-PDA composite material prepared in Example 1 and Example 3. The surface morphology of the two materials was observed using SEM. Figure 1 The original BP nanosheets have a relatively smooth surface with lateral dimensions between 600-900 nm. The BP-PDA nanocomposite material has a rougher surface with more protrusions and lateral dimensions between 500-1300 nm.

[0040] Figure 2 The XRD patterns of raw material RP, BP prepared in Example 1, PDA prepared in Example 2, and BP-PDA prepared in Example 3 are shown. Figure 2 (a) It can be seen that the XRD pattern of RP shows two broad peaks at approximately 33° and 54° 2θ, corresponding to red phosphorus in an amorphous state. BP is prepared from RP by high-energy ball milling. Compared to RP, BP has sharper peaks at approximately 17.5°, 24°, and 35° 2θ, corresponding to the (020), (021), and (111) crystal planes of BP, respectively, indicating that BP has a standard orthorhombic structure. Figure 2 (b) It can be seen that PDA is in an amorphous state, while BP-PDA contains crystalline black phosphorus and amorphous polydopamine grafted onto the surface of black phosphorus.

[0041] Example 5: Dispersion Stability Test The BP, PDA, and BP-PDA composite materials prepared in the above examples were added to FW68DA lubricating base oil at a mass percentage of 0.16%, and the mixture was exfoliated and dispersed using an ultrasonic probe to obtain a lubricating oil additive system.

[0042] Figure 3 The image shows the dispersion results of BP, PDA, and BP-PDA after standing in oil for 30 days. Figure 3 It is evident that PDA prepared via self-polymerization has a large molecular weight and polydispersity, leading to rapid deposition due to intermolecular attraction, with significant deposition observed as early as day 7. Van der Waals forces exist between BP nanosheet layers, causing deposition to begin after day 7 when dispersed in oil. In contrast, the oil sample with added BP-PDA remained stable for approximately 20 days, with only slight precipitation appearing on the upper layer on day 30. The long-term stable dispersion of BP-PDA is primarily due to the PDA distribution on the BP surface. PDA contains a large number of -OH and -NH groups, as do oil molecules. This allows for hydrogen bonding between PDA and oil molecules, enhancing their interaction and overcoming the forces between PDA molecules and their own weight, thus prolonging the dispersion stability time.

[0043] Example 6: Lubrication Performance Test The BP, PDA, and BP-PDA composite materials prepared in the aforementioned examples were added to FW68DA lubricating base oil at a certain mass percentage, and then exfoliated and dispersed using an ultrasonic probe to obtain the lubricating oil additive system. The lubrication performance of each lubricating oil additive system was tested using a ball-and-disc friction and wear tester (UMT Bruker, USA).

[0044] Depend on Figure 4 (a) It can be seen that the addition of the three additives improved the lubrication performance of the lubricating oil additive system to varying degrees compared with the pure lubricating base oil. Among them, the lubricating oil sample containing BP-PDA had the lowest coefficient of friction and the most stable coefficient of friction curve.

[0045] Depend on Figure 4 (b) It can be seen that BP-PDA has the best lubrication effect. Its average coefficient of friction and wear track width are reduced by about 43% and 52% respectively compared with FW68DA lubricating base oil, and it also has significant differences compared with the BP and PDA groups (each group has 0.16% additive).

[0046] Figure 4 (c) shows the effect of different mass fractions of BP-PDA on the coefficient of friction and the width of the wear track. Different mass fractions of BP-PDA improved the frictional performance of the oil to varying degrees. Generally, the coefficient of friction initially decreased with increasing BP-PDA mass fraction. When the mass fraction exceeded 0.16%, the coefficient of friction gradually increased with further increases in BP-PDA mass fraction. Within the mass fraction range of 0.12-0.20%, the coefficient of friction showed a significant difference compared to other addition amounts, indicating better lubrication performance. This is because within a suitable mass concentration range, BP-PDA reduces friction. After reaching the optimal concentration, further increases in concentration lead to excessive additive deposition, resulting in oil film blockage and an increase in the coefficient of friction.

[0047] Figure 4 (d) shows the coefficient of friction and wear track width of BP-PDA (0.16% by mass, 200 r / min) under different loads. As the load increases, both the coefficient of friction and the wear track width increase. In summary, among the comparison of PDA, BP, and BP-PDA as oil additives, BP-PDA (0.16% by mass, 5-10 N load) exhibits the best friction-reducing and wear-resistant effects.

[0048] Figure 5 The image shows SEM images of the bottom wear tracks and corresponding upper ball wear tracks of FW68DA lubricating base oil and FW68DA lubricating base oil additive systems with added BP and BP-PDA. Figure 5(a) It can be seen that in FW68DA lubricating base oil, the wear scar width of the friction chassis is the largest, corresponding to deep grooves on the ball, and obvious adhesive wear and pits on the surface. Figure 5 (b) It can be seen that the addition of nano-BP narrows the wear track width, but the corresponding upper ball surface still has some scratches and pits, indicating severe wear. And... Figure 5 In (c), the wear scars of BP-PDA lubrication are significantly narrower, with only a few shallow and fine grooves on the upper ball surface. Compared with FW68DA lubricating base oil and BP lubrication system, its wear is significantly reduced.

[0049] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A lubricating additive, characterized in that, It includes a two-dimensional lamellar solid lubricant material and polydopamine, wherein the polydopamine is grafted onto the surface of the two-dimensional lamellar solid lubricant material.

2. The lubricating additive according to claim 1, characterized in that, The two-dimensional layered solid lubricant material includes one or more of graphene, molybdenum disulfide, hexagonal boron nitride, and black phosphorus.

3. A method for preparing the lubricating additive as described in claim 1, characterized in that, include: Provide two-dimensional sheet-like solid lubricating materials; The two-dimensional lamellar solid lubricant material reacts with dopamine hydrochloride in a buffer medium under alkaline conditions, causing dopamine to be grafted onto the surface of the two-dimensional lamellar solid lubricant material and polymerized into polydopamine, thereby obtaining the lubricant additive.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the two-dimensional layered solid lubricant to dopamine hydrochloride is (1-3):(4-6).

5. The preparation method according to claim 3 or 4, characterized in that, The two-dimensional layered solid lubricant material includes one or more of graphene, molybdenum disulfide, hexagonal boron nitride, and black phosphorus.

6. The preparation method according to claim 5, characterized in that, The black phosphorus is prepared by thoroughly grinding red phosphorus.

7. The preparation method according to claim 3, characterized in that, The buffer medium includes Tris-HCl, and the alkaline condition is 7 < pH value ≤ 9.

8. A refrigeration oil, characterized in that, It includes base oil, as well as the lubricating additives according to any one of claims 1-2 or the lubricating additives prepared by the preparation method according to any one of claims 3-7.

9. The refrigeration oil according to claim 8, characterized in that, The amount of the lubricating additive added is 0.12-0.20%.

10. A fluid composition for a refrigeration unit, characterized in that, Includes refrigerant and refrigeration oil as described in claim 8 or 9.

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