Halogen-free sulfur-containing eutectic solvent lubricant as well as preparation method and application thereof

Abstract

The invention provides a halogen-free sulfur-containing eutectic solvent lubricant as well as a preparation method and application thereof, and belongs to the technical field of material lubrication and tribology engineering. The halogen-free sulfur-containing eutecticevaporate solvent lubricant comprises the following components in percentage by mole: 25%-80% of a sulfur-containing hydrogen bond donor and 20%-75% of a halogen-free hydrogen bond acceptor. Based on the characteristic that the components of the eutectic solvent are adjustable, halogen-free hydrogen bond receptors (including citric acid quaternary ammonium salt, proline and polyethylene glycol) are selected, the corrosion effect of halogen on a friction interface is avoided, meanwhile, a sulfur-containing compound is used as a hydrogen bond donor, and the friction coefficient is improved. Due to introduction of sulfur, the halogen-free sulfur-containing eutectic solvent lubricant has good extreme pressure lubrication performance, an extra sulfur-containing extreme pressure additive does not need to be used, a hydrogen bond network is formed by controlling the proportion of all the components, and the halogen-free sulfur-containing eutectic solvent lubricant is obtained and has good extreme pressure lubrication and anti-wear effects in the friction process.

Description

Technical Field

[0001] This invention relates to the field of materials lubrication and tribological engineering technology, and in particular to a halogen-free sulfur-containing eutectic solvent lubricant, its preparation method, and its application. Background Technology

[0002] As a fundamental industrial material, lubricating fluids, represented by lubricating oil, lubricate, clean, and cool friction interfaces, playing a crucial role in industrial production through their widespread application in various mechanical equipment with moving parts. Lubricating fluids, through their hydrodynamic pressure effect, lubricate friction pairs by forming a fluid layer with a certain load-bearing capacity. However, under higher loads and temperatures, the fluid layer disappears, and the friction pairs come into direct contact, drastically worsening the friction condition. Therefore, in addition to base oil, lubricating oils require the addition of various sulfur, phosphorus, and nitrogen-containing additives to adsorb onto the friction interface and possess a certain level of activity. Traditional sulfur-containing extreme pressure lubricants suffer from difficulties in precisely controlling the degree of sulfurization during the sulfurization process, resulting in sulfur-containing mixtures within a certain range. In practical applications, it is difficult to precisely control the added sulfur content. Furthermore, lubricating oil production requires fractionation, purification, and refining steps, representing a high-energy-consuming and high-emission industrial process, and lubricating oil is difficult to biodegrade. These drawbacks have made the development of novel lubricating fluids a key issue in the field of lubricating materials.

[0003] Eutectic solvents (DES) are generally stable solvents formed by hydrogen bond donors and acceptors linked by hydrogen bonds. The charge delocalization between the hydrogen bond donors and acceptors lowers the melting point of the DES. Therefore, DES have the advantages of tunable composition and structure, and simple preparation. Due to the non-toxic and easily degradable raw materials and strong load-bearing capacity, DES are considered a novel type of green lubricating fluid. Currently reported DES lubricants mostly use halogenated quaternary ammonium salts such as choline chloride and tetrabutylammonium chloride as hydrogen bond acceptors. The introduction of halide ions inevitably leads to corrosion problems at the interface of the friction pair. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a halogen-free, sulfur-containing, eutectic solvent lubricant, its preparation method, and its application. The halogen-free, sulfur-containing, eutectic solvent lubricant provided by this invention can effectively protect friction pairs and has good extreme pressure lubrication and anti-wear properties.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a halogen-free sulfur-containing eutectic solvent lubricant comprising the following components in molar percentages: 25%–80% sulfur-containing hydrogen bond donors and 20%–75% halogen-free hydrogen bond acceptors, wherein the halogen-free hydrogen bond acceptors include one or more of quaternary ammonium citrate, proline, and polyethylene glycol, wherein the weight-average molecular weight of the polyethylene glycol is 400–4000.

[0007] Preferably, the weight-average molecular weight of the polyethylene glycol is 400 to 2000.

[0008] Preferably, the quaternary ammonium citrate salt includes dihydrocholine citrate and / or tricholine citrate.

[0009] Preferably, the molar percentage of the halogen-free hydrogen bond acceptor is 30% to 70%.

[0010] Preferably, the sulfur-containing hydrogen bond donor includes one or more of thioacetamide, thiourea, thiocarbamate, ammonium dithiocarbamate, cysteine, acetylcysteine, methionine, and 2-mercaptonicotinic acid.

[0011] Preferably, the molar percentage of the sulfur-containing hydrogen bond donor is 30% to 70%.

[0012] This invention also provides a method for preparing the halogen-free sulfur-containing eutectic solvent lubricant described in the above technical solution, comprising the following steps:

[0013] The sulfur-containing hydrogen bond donor and the halogen-free hydrogen bond acceptor are mixed and heated to obtain the halogen-free sulfur-containing eutectic solvent lubricant.

[0014] Preferably, the temperature of the mixed heating is 60-140°C and the time is 0.5-8 hours.

[0015] Preferably, the mixing and heating are carried out under stirring conditions, and the stirring speed is 400-700 rpm.

[0016] The present invention also provides the application of the halogen-free sulfur-containing eutectic solvent lubricant described in the above technical solution or the halogen-free sulfur-containing eutectic solvent lubricant prepared by the preparation method described in the above technical solution in the field of friction lubrication.

[0017] This invention provides a halogen-free sulfur-containing eutectic solvent lubricant comprising the following components in molar percentages: 25%–80% sulfur-containing hydrogen bond donors and 20%–75% halogen-free hydrogen bond acceptors, wherein the halogen-free hydrogen bond acceptors include one or more of quaternary ammonium citrate, proline, and polyethylene glycol, wherein the weight-average molecular weight of the polyethylene glycol is 400–4000.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] Based on the adjustable composition of eutectic solvents, this invention selects halogen-free hydrogen bond acceptors (including quaternary ammonium citrate, proline, and polyethylene glycol) to avoid the corrosive effect of halogens on the friction interface. At the same time, sulfur-containing compounds are used as hydrogen bond donors. The introduction of sulfur enables the halogen-free sulfur-containing eutectic solvent lubricant to have good extreme pressure lubrication performance without the need for additional sulfur-containing extreme pressure additives. By controlling the proportion of each component to form a hydrogen bond network, a halogen-free sulfur-containing eutectic solvent lubricant is obtained, which has good extreme pressure lubrication and anti-wear effects during friction.

[0020] Furthermore, the halogen-free hydrogen bond acceptor of this invention is processed from agricultural and forestry biological resources or has biocompatibility and degradation characteristics. The raw materials are widely available, inexpensive and readily available, which meets the requirements of green economic development. The sulfur-containing hydrogen bond donor has a well-defined molecular structure and consistent stoichiometric parameters, and the sulfur content can be precisely controlled according to the amount added. This solves the problems of performance degradation due to insufficient sulfur addition or excessive sulfur leading to excessive emissions and pollution in practical applications. While meeting the lubrication performance requirements, it also has significant advantages in environmental protection and resource conservation.

[0021] This invention also provides a method for preparing the halogen-free sulfur-containing eutectic solvent lubricant described above. This invention can prepare a stable, homogeneous, and flowable liquid-phase halogen-free sulfur-containing eutectic solvent lubricant from raw materials using a simple heating and stirring method. It does not require further purification or other post-treatment. The synthesis process is simple, economical, and environmentally friendly, and does not generate wastewater, waste gas, or waste residue, which is in line with atom economy design.

[0022] This invention also provides the application of the halogen-free sulfur-containing eutectic solvent lubricant described above in the field of friction lubrication. Examples and test results show that when the halogen-free sulfur-containing eutectic solvent lubricant provided by this invention is applied to ceramic / bearing steel friction pairs, under low load (5N) conditions, the average friction coefficient is 0.13, which contrasts sharply with the high friction coefficient (0.25) exhibited by sulfur-free eutectic solvents. Furthermore, the wear of the friction pairs is relatively slight, demonstrating a good protective effect on the friction pairs. When the halogen-free sulfur-containing eutectic solvent lubricant provided by this invention is applied to ceramic / stainless steel friction pairs, under high load (50N) conditions, the average friction coefficient is 0.12, and the lubrication state is more stable than that of sulfur-free eutectic solvents. The average friction coefficients measured when the halogen-free sulfur-containing eutectic solvent lubricant provided by this invention is applied to high load (100N) bearing steel / bearing steel friction pairs and high load (50N) bearing steel / stainless steel friction pairs are 0.07 and 0.075, respectively. The above results demonstrate the high load-bearing capacity and excellent extreme pressure lubrication and anti-wear effects of the halogen-free sulfur-containing eutectic solvent lubricant in this invention during friction. Attached Figure Description

[0023] Figure 1 Optical photographs of Dihydrocholine Citrate / Thioacetamide DES in Example 1 and Dihydrocholine Citrate / Acetamide DES in Comparative Example 1.

[0024] Figure 2 Viscosity curves of dihydrocholine citrate / thioacetamide DES in Example 1 and dihydrocholine citrate / acetamide DES in Comparative Example 1 at different shear rates.

[0025] Figure 3 Optical photographs of Proline / Thiourea DES, Proline / Thioacetamide DES, and Comparative Example 2 Proline / Urea DES;

[0026] Figure 4 Viscosity curves of proline / thiourea DES, proline / thioacetamide DES and comparative example 2 proline / urea DES at different shear rates.

[0027] Figure 5 Differential scanning calorimetry spectra of PEG400 / thiourea DES and PEG400 prepared in Examples 3, 4 and 5;

[0028] Figure 6 Differential scanning calorimetry spectra of PEG300 / thiourea DES and PEG300 prepared in comparative examples 4, 5 and 6.

[0029] Figure 7 The friction coefficient curves obtained by applying dihydrocholine citrate / thioacetamide DES in Example 1 and Comparative Example 1 to ceramic / bearing steel friction pairs under low load (5N) and high temperature (100℃) conditions are shown.

[0030] Figure 8 The friction coefficient curves obtained by applying proline / thiourea DES, proline / thioacetamide DES and comparative example 2 proline / urea DES to ceramic / stainless steel friction pairs under high load (50N) and high temperature (100℃) conditions are shown in the figure.

[0031] Figure 9 The friction coefficient curves of PEG400 / thiourea DES and PEG400 applied to bearing steel / bearing steel friction pairs in Example 4 are obtained under high load (100N) and high temperature (100℃) conditions.

[0032] Figure 10 The friction coefficient curves of PEG400 / thiourea DES and PEG400 applied to bearing steel / stainless steel friction pairs in Example 4 are obtained under high load (50N) and high temperature (100℃) conditions.

[0033] Figure 11 The wear volume of PEG400 / thiourea DES and PEG400 in Example 4 after being applied to bearing steel / bearing steel friction pairs and subjected to a 100N load is compared with the wear volume after being applied to bearing steel / stainless steel friction pairs and subjected to a 50N load. Detailed Implementation

[0034] This invention provides a halogen-free sulfur-containing eutectic solvent lubricant comprising the following components in molar percentages: 25%–80% sulfur-containing hydrogen bond donors and 20%–75% halogen-free hydrogen bond acceptors, wherein the halogen-free hydrogen bond acceptors include one or more of quaternary ammonium citrate, proline, and polyethylene glycol, wherein the weight-average molecular weight of the polyethylene glycol is 400–4000.

[0035] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0036] In this invention, the weight-average molecular weight of the polyethylene glycol (PEG) is preferably 400–2000, specifically 400, 600, 800, 1000, 1500, 2000, 3000, or 4000. This invention selects halogen-free hydrogen bond acceptors (including quaternary ammonium citrate, proline, and polyethylene glycol) to avoid the corrosive effect of halogens on the friction interface.

[0037] In this invention, the quaternary ammonium citrate salt preferably includes dihydrocholine citrate and / or tricholine citrate.

[0038] In this invention, the molar percentage of the halogen-free hydrogen bond acceptor is preferably 30% to 70%, specifically 20%, 25%, 34%, 50%, 66%, or 75%.

[0039] In this invention, the sulfur-containing hydrogen bond donor preferably includes one or more of thioacetamide, thiourea (TU), thiocarbamate, ammonium dithiocarbamate, cysteine, acetylcysteine, methionine, and 2-mercaptonicotinic acid. The introduction of sulfur in this invention endows the sulfur-containing eutectic solvent with excellent extreme pressure lubrication properties, eliminating the need for additional sulfur-containing extreme pressure additives. Furthermore, the sulfur-containing hydrogen bond donor has a well-defined molecular structure and consistent stoichiometric parameters, allowing for precise control of the sulfur content based on the amount added. This solves the problems of performance degradation due to insufficient sulfur addition or excessive sulfur leading to emissions exceeding standards and pollution in practical applications.

[0040] In this invention, the molar percentage of the sulfur-containing hydrogen bond donor is preferably 30% to 70%, specifically 25%, 34%, 50%, or 66%.

[0041] This invention forms a hydrogen bond network by controlling the ratio of the sulfur-containing hydrogen bond donor and the halogen-free hydrogen bond acceptor, thus obtaining a halogen-free sulfur-containing eutectic solvent lubricant that exhibits excellent extreme pressure lubrication and anti-wear effects during friction.

[0042] The halogen-free sulfur-containing eutectic solvent lubricant provided by this invention exhibits a homogeneous, flowable liquid phase at temperatures far below the melting points of the hydrogen bond donors and acceptors, and possesses a certain viscosity, exhibiting Newtonian fluid behavior.

[0043] In this invention, halogen-free sulfur-containing eutectic solvents obtained by using sulfur-containing hydrogen bond donors and halogen-free hydrogen bond acceptors with different molar percentage ratios exhibit different melting point temperatures (-20 to 140°C), and the ratio can be adjusted according to the usage environment to meet actual usage requirements.

[0044] This invention also provides a method for preparing the halogen-free sulfur-containing eutectic solvent lubricant described in the above technical solution, comprising the following steps:

[0045] The sulfur-containing hydrogen bond donor and the halogen-free hydrogen bond acceptor are mixed and heated to obtain the halogen-free sulfur-containing eutectic solvent lubricant.

[0046] In this invention, the temperature of the mixed heating is preferably 60 to 140°C, specifically 60, 80, 100, 120 or 140°C, and the time is preferably 0.5 to 8 hours, specifically 0.5, 1, 2, 3, 4, 5, 6, 7 or 8 hours.

[0047] In this invention, the mixing and heating is preferably carried out under water bath or oil bath conditions, more preferably oil bath, in order to avoid the influence of water vapor on the product.

[0048] In this invention, the mixing and heating are carried out under stirring conditions, and the stirring speed is preferably 400 to 700 rpm, specifically 400, 500, 600 or 700 rpm.

[0049] The present invention also provides the application of the halogen-free sulfur-containing eutectic solvent lubricant described in the above technical solution or the halogen-free sulfur-containing eutectic solvent lubricant prepared by the preparation method described in the above technical solution in the field of friction lubrication.

[0050] In this invention, the halogen-free sulfur-containing eutectic solvent lubricant can maintain good friction reduction and wear resistance on different friction pair surfaces, preferably ceramic, bearing steel and stainless steel surfaces, under high temperature (preferably 100°C) and load (preferably 100N) conditions.

[0051] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0052] The proline used in the embodiments and comparative examples of this invention is L-proline.

[0053] Example 1

[0054] Add citrate dihydrocholine and thioacetamide powder (the molar percentage ratio of citrate dihydrocholine and thioacetamide is 34%:66%) to a glass flask and mix them. Place the glass flask containing the above mixture in an oil bath and stir at 100°C for 1 hour at a stirring speed of 400 rpm to obtain a transparent, homogeneous, halogen-free, sulfur-containing eutectic solvent lubricant, denoted as citrate dihydrocholine / thioacetamide DES.

[0055] Comparative Example 1

[0056] Add citrate dihydrocholine and acetamide (34% citrate dihydrocholine and acetamide in a molar ratio of 66%) powder to a glass flask and mix them. Place the glass flask containing the mixture in an oil bath and stir at 100°C for 1 hour at a stirring speed of 400 rpm to obtain a transparent, homogeneous, viscous eutectic solvent, denoted as citrate dihydrocholine / acetamide DES.

[0057] Example 2

[0058] Proline and thiourea powder (proline to thiourea molar ratio of 34%:66%) were added to a glass flask and mixed. The two glass flasks containing the mixture were placed in an oil bath and stirred at 100°C for 1 hour at a stirring speed of 400 rpm to obtain a transparent, homogeneous, halogen-free, sulfur-containing eutectic solvent lubricant, denoted as proline / thiourea DES. Proline and thioacetamide (proline to thioacetamide molar ratio of 34%:66%) were added to another glass flask using the same procedure, and the product was denoted as proline / thioacetamide DES.

[0059] Comparative Example 2

[0060] Add proline and urea powder (proline to urea molar percentage ratio of 34%:66%) to a glass flask and mix them. Place the glass flask containing the proline and urea mixture in an oil bath and stir at 80°C for 1 hour at a stirring speed of 400 rpm to obtain a transparent, homogeneous, viscous eutectic solvent, denoted as proline / urea DES.

[0061] Example 3

[0062] PEG400 and thiourea (PEG400 to thiourea molar percentage ratio of 75%:25%) were added to a glass flask and mixed. The glass flask containing the PEG400 and thiourea mixture was placed in an oil bath and stirred at 80°C for 2 hours at a stirring speed of 400 rpm to obtain a transparent, homogeneous, halogen-free, sulfur-containing eutectic solvent lubricant, denoted as PEG400 / TU=3 / 1, or PEG400 / TU(3 / 1).

[0063] Example 4

[0064] To illustrate the performance differences of halogen-free sulfur-containing eutectic solvent lubricants prepared with halogen-free hydrogen bond acceptors and sulfur-containing hydrogen bond donors at different ratios, halogen-free sulfur-containing eutectic solvent lubricants were prepared according to the method of Example 3, except that the molar percentage ratio of polyethylene glycol PEG400 to thiourea was 66%:34%, denoted as PEG400 / TU=2 / 1, or PEG400 / TU(2 / 1).

[0065] Example 5

[0066] To illustrate the performance differences of halogen-free sulfur-containing eutectic solvent lubricants prepared with halogen-free hydrogen bond acceptors and sulfur-containing hydrogen bond donors in different ratios, halogen-free sulfur-containing eutectic solvent lubricants were prepared according to the method of Example 3, except that the molar percentage ratio of polyethylene glycol PEG400 to thiourea was 50%:50%, denoted as PEG400 / TU=1 / 1, or PEG400 / TU(1 / 1).

[0067] Comparative Example 3

[0068] Use PEG400 directly as a lubricant.

[0069] Comparative Example 4

[0070] To more fully illustrate the effect of polyethylene glycol molecular weight, a lubricant was prepared according to the method of Example 3, except that PEG400 was replaced with PEG300, denoted as PEG300 / TU = 3 / 1.

[0071] Comparative Example 5

[0072] To more fully illustrate the effect of polyethylene glycol molecular weight, a lubricant was prepared according to the method of Example 4, except that PEG400 was replaced with PEG300, denoted as PEG300 / TU = 2 / 1.

[0073] Comparative Example 6

[0074] To more fully illustrate the effect of polyethylene glycol molecular weight, a lubricant was prepared according to the method of Example 5, except that PEG400 was replaced with PEG300, denoted as PEG300 / TU = 1 / 1.

[0075] Comparative Example 7

[0076] Use PEG300 directly as a lubricant.

[0077] Performance testing

[0078] The performance of the lubricants in the above embodiments and comparative examples was tested, as follows:

[0079] Figure 1 The images show optical photographs of citrate dihydrocholine / thioacetamide DES prepared in Example 1 and Comparative Example 1, and it can be seen that both citrate dihydrocholine / thioacetamide DES and citrate dihydrocholine / acetamide DES exhibit a transparent and homogeneous liquid phase.

[0080] Viscosity measurement: The viscosity of the lubricant at different shear rates is measured using a rheometer.

[0081] Figure 2 The viscosity change curves of citrate dihydrocholine / thioacetamide DES in Example 1 and Comparative Example 1 citrate dihydrocholine / acetamide DES show that the viscosity values ​​of both are basically constant under different shear rates, which is consistent with the characteristics of Newtonian fluids. Moreover, the viscosity value of citrate dihydrocholine / thioacetamide DES is higher than that of citrate dihydrocholine / acetamide DES.

[0082] Figure 3 Optical photographs of the proline / thiourea DES, proline / thioacetamide DES, and comparative example 2 proline / urea DES prepared in Example 2. The proline / thioacetamide DES is red, while the proline / thiourea DES and proline / urea DES are both colorless, transparent, and homogeneous liquid phases.

[0083] Figure 4 The viscosity change curves of proline / thiourea DES, proline / thioacetamide DES, and comparative example 2 proline / urea DES are shown in the figure. It can be seen that the viscosity values ​​of the three are basically constant under different shear rates, which is consistent with the characteristics of Newtonian fluids. The viscosity value of proline / urea DES is between that of proline / thiourea DES and proline / thioacetamide DES.

[0084] Heat absorption and release measurement: Differential scanning calorimetry is used to measure the heat absorption and release behavior and critical transition temperatures of lubricants, such as glass transition, cold crystallization temperature and melting point.

[0085] Figure 5Differential scanning calorimetry (DSC) spectra of PEG400 / thiourea and PEG400 prepared in Examples 3, 4, and 5 show that the melting point of PEG400 is 8.65℃, the melting point of PEG400 / TU (3 / 1) is 1.05℃, the melting point of PEG400 / TU (2 / 1) is -8.90℃, and the melting point of PEG400 / TU (1 / 1) is -14.60℃. Different molar fractions of PEG400 and thiourea result in significant differences in the properties of the prepared halogen-free sulfur-containing eutectic solvents.

[0086] Figure 6 Differential scanning calorimetry (DSC) spectra of PEG300 / thiourea DES and PEG300 prepared in Comparative Examples 4, 5, and 6 show that the melting point of PEG300 is -14.4℃, while the melting points of PEG300 / TU=3 / 1, PEG300 / TU=2 / 1, and PEG300 / TU=1 / 1 are all -14.3℃. The melting points do not show a decreasing trend and do not meet the definition of a eutectic solvent, thus a halogen-free sulfur-containing eutectic solvent cannot be obtained.

[0087] Frictional testing of dihydrocholine citrate / thioacetamide DES and dihydrocholine citrate / acetamide DES under low load and high temperature conditions.

[0088] Friction tests were conducted on the lubricants used in Example 1 and Comparative Example 1 using an SRV-V friction testing machine. The test conditions were as follows: the upper sample was a zirconia ceramic ball (ZrO2, 10 mm in diameter), and the lower sample was a bearing steel disc (GCr15, hardness HRC = 60). The lower sample was heated to 100°C, a load of 5 N was applied, the frequency was 25 Hz, and the friction stroke was 1 mm. DES was dropped onto the interface of the friction pair and immersed in the contact area. The friction test was conducted continuously for 1800 s. Figure 7 It can be seen that the average coefficient of friction of dihydrocholine citrate / thioacetamide DES is 0.13, which is in stark contrast to the high coefficient of friction (0.25) exhibited by dihydrocholine citrate / acetamide DES.

[0089] Frictional testing of proline / thiourea DES, proline / thioacetamide DES and proline / urea DES under high load and high temperature conditions.

[0090] Friction tests were conducted on the lubricants used in Example 2 and Comparative Example 2 using an SRV-V friction testing machine. The test conditions were as follows: the upper sample was a zirconia ceramic ball (ZrO2, 10 mm in diameter), and the lower sample was a 304 stainless steel disc (304, hardness HRC = 35). The lower sample was heated to 100°C, a load of 50 N was applied, the frequency was 25 Hz, and the friction stroke was 1 mm. DES was dropped onto the interface of the friction pair and immersed in the contact area. The friction test was conducted continuously for 3600 s. Figure 8It can be seen that the friction coefficient of proline / urea DES is higher than 0.22 and fluctuates greatly. Under high load (50N) conditions, the average friction coefficients of proline / thiourea DES and proline / thioacetamide DES are 0.12 and 0.11, respectively, and their lubrication state is more stable than that of sulfur-free eutectic solvents.

[0091] Friction test of PEG400 / thiourea DES in bearing steel friction pair.

[0092] Friction tests were conducted on the lubricants used in Examples 3-5 and Comparative Example 3 using an SRV-V friction testing machine. The test conditions were as follows: the upper sample was a bearing steel ball (GCr15, hardness HRC=60), and the lower sample was a bearing steel disc (GCr15, hardness HRC=60). The lower sample was heated to 100°C, a load of 100 N was applied, the frequency was 25 Hz, and the friction stroke was 1 mm. The lubricant was dripped onto the interface of the friction pair and immersed in the contact area. The friction test was conducted continuously for 3600 s. Figure 9 It can be seen that the average friction coefficient of PEG400 / thiourea DES (including PEG400 / TU(3 / 1), PEG400 / TU(2 / 1) and PEG400 / TU(1 / 1)) is less than 0.07, while the friction coefficient of PEG400 is 0.185, and the friction curve fluctuates greatly.

[0093] Friction testing of PEG400 / thiourea DES in bearing steel / stainless steel friction pairs.

[0094] Friction tests were conducted on the lubricants used in Example 4 and Comparative Example 3 using an SRV-V friction testing machine. The test conditions were as follows: the upper sample was a bearing steel ball (GCr15, hardness HRC=60), and the lower sample was a 304 stainless steel disc (304, hardness HRC=35). The lower sample was heated to 100°C, a load of 50 N was applied, the frequency was 25 Hz, and the friction stroke was 1 mm. The lubricant was dripped onto the interface of the friction pair and immersed in the contact area. The friction test was conducted continuously for 3600 s. Figure 10 It can be seen that the average friction coefficient of PEG400 / TU(2 / 1)DES is 0.075 and the friction state is stable, while the friction coefficient of PEG400 is 0.2 and the lubrication state is unstable.

[0095] Figure 11The wear volumes of PEG400 / TU(2 / 1)DES prepared in Example 4 and PEG400 in Comparative Example 3 after being applied to bearing steel / bearing steel friction pairs under a load of 100N and 50N respectively are compared. It can be seen that under halogen-free sulfur-containing eutectic solvent lubrication, the wear volumes of both bearing steel / bearing steel and bearing steel / stainless steel friction pairs are reduced by more than 60% compared to PEG400, indicating a better protective effect on the friction pairs.

[0096] Table 1 shows the average friction coefficients of different halogen-free sulfur-containing eutectic solvent lubricants under different conditions. The test method is the same as the aforementioned scheme. It can be seen that the halogen-free sulfur-containing eutectic solvent lubricant of the present invention can effectively protect the friction pair and has good extreme pressure lubrication and anti-wear performance.

[0097] Table 1. Average coefficients of friction of different halogen-free sulfur-containing eutectic solvent lubricants under different conditions.

[0098]

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A halogen-free, sulfur-containing eutectic solvent lubricant, characterized in that, The components include the following molar percentages: 25%–80% sulfur-containing hydrogen bond donors and 20%–75% halogen-free hydrogen bond acceptors, wherein the halogen-free hydrogen bond acceptors include one or more of quaternary ammonium citrate, proline, and polyethylene glycol, wherein the weight-average molecular weight of the polyethylene glycol is 400–4000.

2. The halogen-free sulfur-containing eutectic solvent lubricant according to claim 1, characterized in that, The weight-average molecular weight of the polyethylene glycol is 400 to 2000.

3. The halogen-free sulfur-containing eutectic solvent lubricant according to claim 1, characterized in that, The quaternary ammonium citrate salt includes dihydrocholine citrate and / or tricholine citrate.

4. The halogen-free sulfur-containing eutectic solvent lubricant according to claim 1, characterized in that, The molar percentage of the halogen-free hydrogen bond acceptor is 30% to 70%.

5. The preparation method according to claim 1, characterized in that, The sulfur-containing hydrogen bond donors include one or more of thioacetamide, thiourea, thiocarbamate, ammonium dithiocarbamate, cysteine, acetylcysteine, methionine, and 2-mercaptonicotinic acid.

6. The halogen-free sulfur-containing eutectic solvent lubricant according to claim 1 or 5, characterized in that, The molar percentage of the sulfur-containing hydrogen bond donor is 30% to 70%.

7. The method for preparing the halogen-free sulfur-containing eutectic solvent lubricant according to any one of claims 1 to 6, characterized in that, Includes the following steps: The sulfur-containing hydrogen bond donor and the halogen-free hydrogen bond acceptor are mixed and heated to obtain the halogen-free sulfur-containing eutectic solvent lubricant.

8. The preparation method according to claim 7, characterized in that, The temperature of the mixed heating is 60–140°C, and the time is 0.5–8 hours.

9. The preparation method according to claim 7 or 8, characterized in that, The mixing and heating are carried out under stirring conditions, and the stirring speed is 400-700 rpm.

10. The application of the halogen-free sulfur-containing eutectic solvent lubricant according to any one of claims 1 to 6 or the halogen-free sulfur-containing eutectic solvent lubricant prepared by the preparation method according to any one of claims 7 to 9 in the field of friction lubrication.

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