A high-temperature resistant perfluoropolyether grease and its preparation method

Abstract

The present invention discloses a high-temperature resistant perfluoropolyether grease and a preparation method thereof, belonging to the technical field of fluorine-containing lubricating materials. The preparation method of the high-temperature resistant perfluoropolyether grease comprises the following steps: mixing tannic acid with PTFE powder and then ball-milling to obtain tannic acid-modified PTFE powder; preparing porous molybdenum disulfide microspheres; and mixing and grinding the tannic acid-modified PTFE, porous molybdenum disulfide microspheres, and perfluoropolyether to obtain the high-temperature resistant perfluoropolyether grease. The high-temperature resistant perfluoropolyether grease prepared by the present invention has the advantages of low oil separation and low volatility, further improving the grease's high-temperature resistance. Furthermore, the inclusion of the porous molybdenum disulfide microspheres gives the grease excellent extreme pressure and anti-wear properties, as well as stability in storage and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluorine-containing lubricating materials, and in particular relates to a high-temperature resistant perfluoropolyether grease and a preparation method thereof. Background Art

[0002] With the rapid development of modern industry, a large number of mechanical equipment need to operate for long periods of time in harsh environments with high temperatures and high loads, resulting in continuously increasing requirements for grease performance. Currently, the base oils for greases are mostly mineral oils and silicone oils. Although relatively low in cost, they tend to become thinner and volatilize at high temperatures, and their anti-wear properties are poor. In contrast, greases prepared with perfluoropolyether (PFPE) as a base oil exhibit superior high-temperature resistance and oxidation stability, and are widely used in high-temperature bearing applications. To further improve the high-temperature resistance of perfluoropolyether and expand its application range, the relevant information disclosed in the prior art is as follows:

[0003] CN114045185B discloses a perfluoropolyether grease formulation that utilizes a mixture of perfluoropolyether and polytetrafluoroethylene (PTFE) powder of a specific particle size, doped with zeolites of varying particle sizes as a modifier to improve the grease's colloidal stability. While the addition of zeolites reduces the grease's oil separation to a certain extent, its colloidal stability still has significant room for improvement. Consequently, existing perfluoropolyether greases still suffer from technical issues such as poor colloidal stability at high temperatures and poor extreme pressure and anti-wear performance.

[0004] CN116082837A discloses a method for activating PTFE using a mixed solution of tert-butyl lithium and ethylenediamine. The entire experiment is protected by nitrogen. The activated PTFE is mixed with glycidyl methacrylate and subjected to a grafting reaction to introduce polar groups into the PTFE. The fillers are connected and adsorbed via covalent and hydrogen bonds, solving the problems of nanomaterial agglomeration and uneven dispersion. However, this method is complex to operate, and a strict nitrogen atmosphere must be maintained during the activation process. Furthermore, tert-butyl lithium, as a superbase, poses a high risk during use. Summary of the Invention

[0005] Based on the deficiencies of the prior art, the purpose of the present invention is to provide a high-temperature resistant perfluoropolyether grease and a preparation method thereof. The present invention uses tannic acid to modify PTFE and uses porous molybdenum disulfide microspheres in combination to prepare a high-temperature resistant perfluoropolyether grease with excellent comprehensive performance through a relatively simple process.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a high-temperature resistant perfluoropolyether grease comprises the following steps:

[0008] S1. Preparation of tannic acid-modified PTFE (TA-PTFE)

[0009] PTFE powder and tannic acid (TA) powder are mixed at a mass ratio of 1:(1.5-2.5) and ball milled. Repeated impacts within the milling media, including collision, impact, shear, and extrusion, cause the powdered PTFE to break into fragments, exposing more groups. The TA, with its polyphenolic hydroxyl structure and ester-bonded oxygen-containing groups, interacts with the O and F atoms in PTFE to form hydrogen bonds, preventing the PTFE layers from restacking due to van der Waals forces. Tannic acid-modified PTFE powder (TA-PTFE) is then obtained. Furthermore, the presence of oxygen-containing polar groups, such as phenolic hydroxyl groups and ester bonds, imparts a degree of polarity to the grease thickened with PTFE and PFPE, improving the grease's adhesion to the application site.

[0010] S2. Preparation of porous molybdenum disulfide microspheres

[0011] The present invention controls the process conditions during the synthesis of molybdenum disulfide to prepare molybdenum disulfide microspheres with a porous structure. The steps are as follows: adding a cationic modifier to a molybdate solution to obtain a mixed solution; adding a sulfur source to the mixed solution and adjusting the pH value thereof to be neutral; subjecting the obtained reaction solution to a hydrothermal reaction at a temperature of 190-220° C. to obtain a molybdenum disulfide precursor; and calcining the molybdenum disulfide precursor to obtain the molybdenum disulfide microspheres with a porous structure. Preferably, the cationic modifier is hexadecyltrimethylammonium bromide or dodecyltrimethylammonium bromide; the sulfur source is thiourea; and the calcination temperature is 500-550° C. and the calcination time is 2-3 hours. During the reaction, the cationic modifier can ionize in water to form a quaternary ammonium group with a cation. Due to the adsorption effect of positive and negative charges, molybdate is adsorbed on the surface of the cationic quaternary ammonium group, which is conducive to the subsequent reaction of molybdate with a sulfur source to form a molybdenum disulfide microsphere structure. During the subsequent calcination process, a small amount of residual thiourea decomposes, and gases such as CO2 and H2S escape, forming a porous structure in the molybdenum disulfide microspheres, thereby obtaining porous molybdenum disulfide microspheres.

[0012] S3. Heating the perfluoropolyether and stirring it until no significant resistance is achieved. Then, adding the tannic acid-modified PTFE powder and porous molybdenum disulfide microspheres to the perfluoropolyether, stirring, ultrasonicating, and finally grinding to obtain the target product. Preferably, the mass ratio of the perfluoropolyether, tannic acid-modified PTFE powder, and porous molybdenum disulfide microspheres is (50-70):(30-50):(1-3).

[0013] The present invention uses tannic acid to modify PTFE. Tannic acid (TA) is a natural polyphenol with multiple reactive groups. The typical TA molecular formula is C 76 H 52 O 46 It is composed of glucose and 5 gallic acid units connected by ester bonds. 76 H 52 O 46 The molecule contains 25 phenolic hydroxyl groups (derived from five gallic acid units, each containing three phenolic hydroxyl groups, for a total of 15; the remaining 10 hydroxyl groups are derived from glucose and ester bonds), a number that is among the highest in the world, exceeding that of most polyphenols and phenol. The presence of numerous benzene rings in the molecular structure imparts excellent structural rigidity and stability. This invention utilizes tannic acid, a polyphenolic structure and its non-toxic nature, to modify PTFE. The resulting TA-PTFE exhibits significant thickening properties with perfluoropolyether oils, enhancing the adhesion and stability of greases.

[0014] MoS2 has good lubrication and anti-wear properties and is one of the commonly used additives for grease. However, the commonly used grease MoS2 has a layered structure and a small surface area, which limits the performance of its performance. The present invention prepares a porous structure of molybdenum disulfide microspheres. Compared with layered MoS2, it has a larger specific surface area and provides more adsorption sites for perfluoropolyether. In addition, the porous structure in the molybdenum disulfide microspheres can provide a channel for perfluoropolyether molecules to enter and exit, provide a storage environment for perfluoropolyether, and ensure the hardness of the grease. When the grease provided by the present invention is applied to the use site, the perfluoropolyether will gradually seep out from the pores as the temperature rises and the pressure increases, exerting a lubricating and wear-resistant effect.

[0015] The beneficial effects of the present invention are embodied in:

[0016] (1) The present invention introduces porous molybdenum disulfide microspheres into the field of high-temperature resistant grease synthesis. Part of the perfluoropolyether is confined within the pore structure, ensuring storage stability and cone penetration. At the same time, when the grease is applied to the application area, the perfluoropolyether grease can be released through the surface pores according to the equipment temperature and pressure, thus avoiding the problem of grease failure caused by excessive release, softening, and dripping.

[0017] (2) PTFE modified with tannic acid is beneficial for increasing the adhesion of the grease; the porous molybdenum disulfide microspheres have a larger specific surface area, providing more adsorption sites for the grease. The high-temperature resistant perfluoropolyether grease prepared by the present invention has the advantages of low oil separation and volatility, and the high-temperature resistance of the grease is further improved. At the same time, the participation of the porous molybdenum disulfide microspheres makes the grease have excellent extreme pressure and anti-wear properties, as well as storage and application stability. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to the embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0019] In addition, unless otherwise specified, the preparation processes in the following examples are all conventional means in the prior art and are therefore not described in detail. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used are all commercially available.

[0020] The main raw materials used in the following examples and comparative examples are as follows:

[0021] PTFE powder was purchased from Hangzhou Sanaifu New Materials Sales Co., Ltd. with the brand name FR002A, a bulk density of 100 g / L, an average particle size of 5 μm, a melting point of 327° C., and a melt mass flow rate of 6 g / min.

[0022] PFPE base oil powder was purchased from Hunan Nonferrous Chenzhou Fluorochemical Co., Ltd., with a brand name of GB0-108 and a viscosity of 1820 mm at room temperature. 2 / s, viscosity index is 148, pour point is -12, and density is 1.78 g / mL at 100°C.

[0023] MoS2 layered materials were purchased from Shanghai Shenyu Industry and Trade Co., Ltd. with a mass fraction of 98.5% and an average particle size of 5 μm.

[0024] It should be noted that the above raw materials are only for illustrating the sources and components of the reagents used in the experiments of the present invention in order to fully disclose the information, and do not mean that the present invention cannot be achieved by using other similar reagents or reagents provided by other suppliers.

[0025] Example 1

[0026] A method for preparing a high-temperature resistant perfluoropolyether grease comprises the following steps:

[0027] S1. Preparation of TA-PTFE powder:

[0028] PTFE powder and tannic acid (TA) powder were mixed in a mass ratio of 1:2 and ball milled for 1 h at a rotation speed of 250 rpm to obtain TA-PTFE powder.

[0029] S2. Preparation of porous molybdenum disulfide microspheres:

[0030] First, 3.00 mmol of sodium molybdate dihydrate was dissolved in 20 ml of distilled water. After complete dissolution by stirring, 0.2 mmol of cetyltrimethylammonium bromide (CTAB) was added and stirred until completely dissolved. Next, 0.03 g of thiourea (CH4N2S) was dissolved in 9 ml of isopropanol and ultrasonically dispersed. After complete dissolution, the pH of the solution was adjusted to approximately 7.0 using 0.5 mol / L NaOH solution. Finally, the CH4N2S solution was slowly added dropwise to the molybdate and CTAB mixture, and stirring was continued for half an hour to obtain a mixed suspension. The mixed suspension was then transferred to an autoclave and heated in an oven at 190°C for 24 hours for a hydrothermal reaction. After cooling to room temperature, the product was washed with distilled water and ethanol multiple times and then centrifuged. The resulting black precipitate was dried in a vacuum oven at 70°C for 12 hours to obtain the MoS2 precursor. The precursor was placed in a tube furnace and calcined in an air atmosphere. The calcination temperature was set to 600°C and the calcination time was 2 hours. The obtained black powder was the porous molybdenum disulfide microspheres.

[0031] S3. Heat 50 g of PFPE in a water bath at 80°C and keep stirring until there is no obvious resistance. Mix 50 g of TA-PTFE powder and 2 g of porous molybdenum disulfide microspheres in advance and add them to the PFPE in batches and continue stirring for 1 hour. After ultrasonication for 0.5 hour, transfer the mixture to a three-roll mill and grind it for 30 minutes. After grinding, obtain the finished grease S1.

[0032] Example 2

[0033] Compared with Example 1, the difference of this embodiment is only in step S3, and the other processes are the same as those of Example 1. The process of step S3 of this embodiment is as follows:

[0034] 60 g of PFPE was heated in an 80°C water bath and stirred until no significant resistance was observed. 40 g of TA-PTFE powder and 2 g of porous molybdenum disulfide microspheres were mixed in advance and added to the PFPE in batches, followed by stirring for 1 h. After ultrasonication for 0.5 h, the mixture was transferred to a three-roll mill and ground for 30 min. The finished grease S2 was obtained after grinding.

[0035] Example 3

[0036] Compared with Example 1, the difference of this embodiment is only in step S3, and the other processes are the same as those of Example 1. The process of step S3 of this embodiment is as follows:

[0037] 70 g of PFPE was heated in an 80°C water bath and stirred until no significant resistance was observed. 30 g of TA-PTFE powder and 2 g of porous molybdenum disulfide microspheres were mixed in advance and added to the PFPE in batches, followed by stirring for 1 h. After ultrasonication for 0.5 h, the mixture was transferred to a three-roll mill and ground for 30 min. The finished grease S3 was obtained after grinding.

[0038] Comparative Example 1

[0039] 60 g of PFPE was heated in an 80°C water bath and stirred until no significant resistance was observed. TA and PTFE powders were mixed in a mass ratio of 1:2 to a total mass of 40 g without ball milling. Finally, 2 g of porous molybdenum disulfide microspheres (prepared as described in step S2 of Example 1) were added to the PFPE in batches. Stirring was continued for 1 h. After ultrasonication for 0.5 h, the mixture was transferred to a three-roll mill and ground for 30 min. Finished grease D1 was obtained.

[0040] Comparative Example 2

[0041] 60 g of PFPE (heated in an 80°C water bath and stirred until no significant resistance was observed); 40 g of TA-PTFE powder (prepared as described in step S1 in Example 1) and 2 g of MoS2 layered powder were mixed in advance and added to the PFPE in batches, followed by stirring for 1 h. After ultrasonication for 0.5 h, the mixture was transferred to a three-roll mill and ground for 30 min. Grease product D2 was obtained after grinding.

[0042] The performance tests were conducted on the products prepared in the above embodiments and comparative examples. The test results are shown in Table 1 below:

[0043] Table 1 Performance test results of the products prepared in each embodiment and comparative example

[0044]

[0045] As shown in the table above, the varying ratios of PFPE oil to TA-PTFE between the test samples affected the oil separation and volatility of the grease samples, thereby impacting grease stability. A comparison of sample S2, at the optimal ratio, with control sample D1 reveals that the physical mixing and modification of TA powder, PTFE powder, and MoS2 powder alone yielded unsatisfactory results. However, PTFE modified with TA and ball-milled, when mixed with PFPE and MoS2 powder, significantly improved the performance of the resulting product. A comparison of the test results for S2 and D2 reveals that the lack of a unique cavity structure in the layered MoS2 powder leads to a significant increase in oil separation. This increase can lead to excessive softening and dripping of the grease during actual use, preventing it from effectively adhering to friction points.

[0046] In summary, the high-temperature resistant perfluoropolyether grease provided by the present invention, which is synthesized with PFPE as the main component, TA-modified PTFE powder and porous molybdenum disulfide microspheres, has the advantages of low oil separation and low volatility, and the high-temperature resistance of the grease is further improved. At the same time, the participation of porous molybdenum disulfide microspheres enables the grease to have excellent extreme pressure and anti-wear properties, storage and application stability.

[0047] It should be noted that, in other embodiments, when the experimental process meets the following conditions, the purpose of the present invention can be achieved:

[0048] The mass ratio of PTFE powder to tannic acid powder in step S1 is preferably 1:(1.5-2.5), and can specifically be other ratios such as 1:1.5, 1:2, or 1:2.5;

[0049] The hydrothermal reaction temperature in step S2 is preferably 190-220°C, and specifically can be other temperatures such as 190°C, 210°C or 220°C;

[0050] The calcination temperature in step S2 is preferably 500-550°C, and specifically can be 500°C, 520°C, 550°C, or other temperatures; the calcination time is preferably 2-3h, and specifically can be 2h, 2.5h, or 3h;

[0051] Those skilled in the art can make appropriate selections of the above process parameters according to actual needs, and the objectives of the present invention can all be achieved.

[0052] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant perfluoropolyether grease, characterized in that: The following steps are involved: PTFE powder and tannic acid are ball-milled to obtain tannic acid-modified PTFE; Adding a cationic modifier to a molybdate solution to obtain a mixed solution; adding a sulfur source to the mixed solution and adjusting the pH thereof to be neutral; and subjecting the obtained reaction solution to a hydrothermal reaction to obtain a molybdenum disulfide precursor; The molybdenum disulfide precursor is calcined to obtain porous molybdenum disulfide microspheres; The tannic acid-modified PTFE, porous molybdenum disulfide microspheres and perfluoropolyether are mixed and ground to obtain high-temperature resistant perfluoropolyether grease.

2. The method for preparing high temperature resistant perfluoropolyether grease according to claim 1, characterized in that: The mass ratio of the PTFE powder to tannic acid is 1:(1.5-2.5).

3. The method for preparing high temperature resistant perfluoropolyether grease according to claim 1, characterized in that: The cationic modifier is hexadecyltrimethylammonium bromide or dodecyltrimethylammonium bromide.

4. The method for preparing high temperature resistant perfluoropolyether grease according to claim 1, characterized in that: The sulfur source is thiourea.

5. The method for preparing high temperature resistant perfluoropolyether grease according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 190-220°C.

6. The method for preparing high temperature resistant perfluoropolyether grease according to claim 1, characterized in that: The calcination temperature is 500-550°C.

7. The method for preparing high temperature resistant perfluoropolyether grease according to claim 1, characterized in that: The calcination time is 2-3 hours.

8. A high temperature resistant perfluoropolyether grease, characterized in that: The high-temperature resistant perfluoropolyether grease is prepared by the preparation method described in any one of claims 1 to 7; the high-temperature resistant perfluoropolyether grease comprises perfluoropolyether, tannic acid-modified PTFE and porous molybdenum disulfide microspheres.

9. The high temperature resistant perfluoropolyether grease according to claim 8, characterized in that: The mass ratio of the perfluoropolyether, tannic acid-modified PTFE and porous molybdenum disulfide microspheres is (50-70): (30-50): (1-3).

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