A perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating and its preparation method

Abstract

This invention discloses a perfluoroalkylsilane covalently grafted molybdenum disulfide-reinforced polyamide-imide composite coating and its preparation method, belonging to the field of polymer composite coating technology. This invention utilizes a dehydration condensation reaction between hydroxylated molybdenum disulfide nanosheets and perfluoroalkylsilane to form Si-O-Mo covalent bonds, solving the core problem of weak interfacial bonding between molybdenum disulfide and the polyamide-imide matrix in traditional physical mixing, significantly improving the structural integrity and wear resistance of the composite coating. After covalent grafting with perfluoroalkylsilane, the surface of molybdenum disulfide is covered with low surface energy perfluoroalkyl chains, which not only effectively improves its dispersibility in the polyamide-imide emulsion and coating matrix, avoiding agglomeration, but also endows it with excellent hydrophobic properties, significantly reducing the risk of corrosive media penetration. The preparation method of this invention is process-controllable and highly reproducible, and the prepared composite coating possesses comprehensive properties such as long-lasting wear resistance, resistance to damp heat corrosion, and high temperature resistance, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of polymer composite coating technology, and in particular to a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating and its preparation method. Background Technology

[0002] Polyamide-imide (PAI) is a high-performance specialty engineering plastic that combines high temperature resistance, chemical corrosion resistance, and excellent mechanical strength, giving it irreplaceable advantages in aerospace and high-end equipment surface protection. However, pure polyamide-imide coatings suffer from problems such as a high coefficient of friction, limited wear life, and easy adsorption of moisture on the surface. These issues lead to performance degradation under dynamic friction or humid and corrosive environments, limiting its application in harsh service scenarios.

[0003] To improve the tribological properties of polyamide-imide coatings, existing technologies commonly employ molybdenum disulfide (MoS2) as a solid lubricant filler for composite modification. While the layered crystal structure of molybdenum disulfide can reduce friction through interlayer slip, its lack of active functional groups on its surface results in weak interfacial adhesion, easy agglomeration, and uneven dispersion due to its physical adsorption to the polyamide-imide matrix. Under frictional stress, the molybdenum disulfide filler easily detaches from the matrix, leading to a sharp decline in the coating's wear resistance. Furthermore, the strong hydrophilicity of molybdenum disulfide surface readily adsorbs moisture from the environment, accelerating coating aging and the penetration of corrosive media.

[0004] In existing technologies, surface modification of molybdenum disulfide mainly includes two categories: physical coating and covalent grafting. While physical coating is simple to operate, it suffers from weak interfacial interactions and poor stability. Traditional covalent grafting often uses silane coupling agents, but it suffers from harsh reaction conditions (requiring a high-temperature, anhydrous environment), low grafting efficiency, and poor synergy with the polyamide-imide matrix. Furthermore, this type of modified molybdenum dioxide is typically designed for solid-state or organic solvent-based polymer systems, which have limitations such as high environmental and safety risks, complex processing conditions, and high costs.

[0005] In comparison, waterborne polyamide-imide emulsion systems offer better environmental friendliness, processability, and relatively mild curing conditions, making them an important research direction for polyamide-imide coatings. However, polyamide-imide emulsion systems place higher technical demands on the compatibility and stability of molybdenum disulfide or existing molybdenum disulfide. Layered molybdenum disulfide is prone to agglomeration and sedimentation in aqueous media; although surface modification can improve dispersibility, the modification process is complex and can easily affect the lubrication properties of molybdenum disulfide. Furthermore, polyamide-imide emulsions rely on the emulsion system for stability; introducing molybdenum disulfide fillers can easily disrupt the charge balance or steric hindrance of the emulsion, leading to demulsification, layering, or sudden viscosity changes. Although polyamide-imide emulsions offer milder curing conditions and higher environmental friendliness, their cured film density and temperature resistance are generally lower than those of organic solvent-based polyamide-imides. Therefore, designing a suitable method for modifying molybdenum disulfide to achieve its combination with modified molybdenum disulfide in a polyamide-imide emulsion system, and obtaining a composite coating with excellent comprehensive performance under relatively mild processing conditions, is a technical obstacle that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of the above-mentioned deficiencies of the prior art, the purpose of this invention is to provide a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating and its preparation method. Through the covalent grafting reaction of perfluoroalkylsilane and molybdenum disulfide, a strong "filler-matrix" interaction interface is constructed. Combining the layered lubrication characteristics of molybdenum disulfide with the low surface energy advantage of the perfluoroalkyl chain, the wear resistance, hydrophobicity, and high-temperature resistance of the composite coating are synergistically optimized. It is applicable to polyamide-imide emulsion processing systems and uses a mild and environmentally friendly process to prepare the composite coating, overcoming the defects of existing molybdenum disulfide / polyamide-imide composite coatings such as weak interfacial bonding, short wear life, and poor environmental stability.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows: In a first aspect of the present invention, a method for preparing a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating is provided, comprising the following steps: (1) Hydroxylated molybdenum disulfide nanosheets were added to ethanol and dispersed to form a molybdenum disulfide dispersion; perfluoroalkylsilane was added to the molybdenum disulfide dispersion and reacted at a certain temperature; after the reaction was completed, the product was collected and purified to obtain perfluoroalkylsilane covalently grafted molybdenum disulfide filler. (2) Add perfluoroalkylsilane covalently grafted molybdenum disulfide filler to polyamide-imide emulsion, disperse and then add additives to obtain composite coating slurry; (3) The composite coating slurry is coated on the substrate surface and cured to obtain a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide imide composite coating.

[0008] Hydroxylated molybdenum disulfide nanosheets are molybdenum disulfide nanomaterials that have undergone surface chemical modification. Their core characteristic is the introduction of hydroxyl functional groups onto the surface or edges of the molybdenum disulfide sheets. This invention can be achieved using commercially available finished products or by immersing the molybdenum disulfide nanosheets in a mixture of sufficient hydrogen peroxide and ethanol.

[0009] Preferably, in step (1), the preparation steps of the hydroxylated molybdenum disulfide nanosheets include: immersing the molybdenum disulfide nanosheets in a mixed solution of hydrogen peroxide and ethanol for hydroxylation treatment, separating the solid product, and washing to obtain the hydroxylated molybdenum disulfide nanosheets.

[0010] More preferably, the concentration of hydrogen peroxide is 25 wt.%~35 wt.%, the volume ratio of hydrogen peroxide to ethanol is 1:100~5:100, and the hydroxylation treatment time is 20~40 min.

[0011] Preferably, in step (1), the concentration of the molybdenum disulfide dispersion is 10~20 mg / mL.

[0012] Preferably, in step (1), the mass ratio of the hydroxylated molybdenum disulfide nanosheets to the perfluoroalkyl silane is 1:2 to 1:5.

[0013] Preferably, in step (1), the perfluoroalkylsilane has the structure F(CF2). n CH2CH2Si(OR)3, where n is an integer selected from 4 to 8, and R is methyl or ethyl.

[0014] Preferably, in step (1), the reaction temperature is 70~80℃ and the reaction time is 8~12 h.

[0015] In this reaction step, the alkoxy group of the perfluoroalkylsilane hydrolyzes to generate silanol groups, which then undergo a dehydration condensation reaction with the hydroxyl groups on the surface of the hydroxylated molybdenum disulfide nanosheets for grafting. Those skilled in the art can choose appropriate purification and recovery methods according to actual conditions or needs. For example, centrifugation at 4000–10000 rpm for 5–15 min, separation of the precipitate, washing with ethanol 4–5 times, and vacuum drying at 60°C for 6–12 h; other suitable methods can also achieve the same effect as this step.

[0016] Preferably, in step (2), based on 100 parts by weight of the polyamide-imide emulsion, the amount of perfluoroalkylsilane covalently grafted molybdenum disulfide filler added is 1 to 20 parts, and the amount of additive added is 1 to 5 parts.

[0017] Preferably, in step (2), the polyamide-imide emulsion is a mixed system consisting of polyamide-imide, a polar organic solvent, and water; the polar organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0018] Preferably, in step (2), the additives include one or both of defoamers and dispersants.

[0019] More preferably, the defoamer includes one of BYK-161 and BYK-110; the dispersant includes one of HLD-8ks and HLD-11c.

[0020] The technical effectiveness of this invention depends on the design of the modification scheme in the emulsion system. The additives used in the above steps perform their general functions, and those skilled in the art can select them according to actual needs or conditions. BYK-161 is a type of defoamer produced by BYK Chemicals. It is a high molecular weight block copolymer solution that stabilizes pigments and prevents flocculation through steric hindrance. BYK-110 is a copolymer solution containing acidic groups produced by the same company that deflocculates pigments through steric hindrance and is specifically designed to stabilize inorganic pigments. HLD-8ks is a polymer derivative produced by Silicona that has excellent wetting and dispersing ability for both organic and inorganic pigments. HLD-11c is a nonionic polymer defoamer produced by the same company and is used in water-based coatings, printing inks, etc.

[0021] Preferably, in step (3), the coating method includes one of spraying, brushing, and dipping; the coating thickness is 10~50 μm.

[0022] Preferably, in step (3), the curing includes the following steps: first, pre-curing at 110~120℃ for 0.5~2 h, then curing at 250~300℃ for 0.5~1 h, and naturally cooling to room temperature to obtain a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating.

[0023] The coating of this invention is applicable to various types of metal substrates, such as copper alloys, aluminum alloys, or titanium alloys. Before coating, those skilled in the art can sequentially use sandpaper to polish, acetone ultrasonic cleaning, anhydrous ethanol washing, and drying to remove impurities or oxide layers from the substrate surface, thereby enhancing the adhesion between the coating and the substrate.

[0024] In a second aspect of the present invention, a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating is provided, which is prepared using the preparation method provided in the first aspect of the present invention.

[0025] Based on the above technical solutions, the design concept and principle of this invention are as follows: This invention employs perfluoroalkylsilanes to graft and modify molybdenum disulfide. The perfluoroalkylsilane molecule possesses both hydrolyzable alkoxysilane groups and low surface energy perfluoroalkyl chains. The silanol groups generated by the hydrolysis of the alkoxysilane groups can form stable Si-O-Mo covalent bonds with the hydroxyl groups on the surface of molybdenum disulfide, while the perfluoroalkyl chains impart hydrophobic properties to molybdenum disulfide. This simultaneously addresses the issues of molybdenum disulfide dispersion, interfacial adhesion, and environmental stability of the coating.

[0026] Polyamide-imide emulsions are mixed emulsion systems composed of polyamide-imide, polar solvents, and water. The perfluoroalkyl chains introduced by the modified molybdenum disulfide exhibit low polarity and low surface energy, which helps optimize distribution and promote uniform dispersion in the mixed system by utilizing polarity differences. When the two are mixed, the modified molybdenum disulfide, due to its low polarity, tends to escape the highly polar solvent phase and distribute in the medium-to-high polarity polyamide-imide resin phase, rather than agglomerating in the solvent. Due to its hydrophobic properties, it also does not dissolve in the aqueous phase of the polyamide-imide emulsion and aggregate. During curing, with solvent evaporation, if the modified molybdenum disulfide has a strong affinity for the solvent, it will migrate with the solvent during evaporation, leading to the enrichment of molybdenum disulfide filler on the coating surface or bottom, causing unevenness. However, the low compatibility of the perfluoroalkyl chains with highly polar solvents helps reduce the tendency of modified molybdenum disulfide to migrate with solvent evaporation, thereby optimizing coating quality. This method uses perfluoroalkylsilanes for covalent grafting of molybdenum disulfide. After hydrolysis of the alkoxysilane groups, Si-O-Mo covalent bonds are formed with the hydroxyl groups on the molybdenum disulfide surface. The Si-O bond energy in Si-O-Mo is approximately 460 kJ / mol, and the O-Mo bond energy is approximately 300–450 kJ / mol. In an aqueous environment, these bonds are not broken by water molecules as in physical adsorption or ionic bonds. Furthermore, they do not hydrolyze or break under humid heat corrosion or high temperatures, providing a stronger interfacial bonding force than physical adsorption.

[0027] It should be noted that existing technologies include grafting with alkoxy groups generated by hydrolysis (Kong Xiangkun, Wang Lu, Zhou Kai, et al. Surface functionalization of molybdenum disulfide and its application in phenolic resins [J]. China Powder Technology, 2020, 26(1):6.DOI:10.13732 / j.issn.1008-5548.2020.01.005.), or introducing perfluoroalkyl silane groups into molybdenum disulfide to increase hydrophobicity (K. Lv, C. Teng, M. Shi, Y. Yuan, Y. Zhu, J. Wang, Z. Kong, X. Lu). Y. Zhu (Hydrophobic and Electronic Properties of the E-MoS2 Nanosheets Induced by FAS for the CO2 Electroreduction to Syngas with a Wide Range of CO / H2 Ratios, Adv. Funct. Mater., 28, 2018, DOI: 10.1002 / adfm.201802339.). However, existing solutions are not designed for the needs of polyamide-imide emulsions, and their applications are not polyamide-imide / modified molybdenum disulfide composite coatings. The purpose of this invention in selecting perfluoroalkylsilanes, not solely based on covalent bond generation and the introduction of hydrophobic groups, is also to form a gradient interface of inorganic molybdenum disulfide-fluorosilicone-organic polyamide-imide. In the composite coating structure of this invention, the inner molybdenum disulfide layer is hard and has a high modulus, while the outer polyamide-imide layer has a lower modulus. The Si-O-Mo bonded fluorosilane flexible chain in the middle serves as a transition layer to buffer stress and avoid interfacial stress concentration and microcracks caused by abrupt changes in stiffness. Furthermore, the moderately polar Si-O-Mo bonded to the surface of the molybdenum disulfide transitions to low surface energy perfluoroalkyl chains, thus achieving compatibility with the polyamide-imide and a more thermodynamically stable match. This gradient interface macroscopically ensures uniform dispersion of the filler in the emulsion system without demulsification and is less prone to migration and aggregation during curing due to solvent detachment, resulting in long-term interface stability and the formation of a composite coating tightly bonded to the substrate.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention provides a method for preparing a polyamide-imide composite coating reinforced with perfluoroalkylsilane covalently grafted molybdenum disulfide. The method utilizes hydroxylated molybdenum disulfide nanosheets with active hydroxyl groups, which undergo a dehydration condensation reaction with perfluoroalkylsilane to form Si-O-Mo covalent bonds. This grafting is strong and stable, solving the core problem of weak interfacial bonding between molybdenum disulfide and the polyamide-imide matrix in traditional physical mixing processes. This significantly improves the structural integrity and wear resistance of the composite coating. After covalent grafting with perfluoroalkylsilane, the surface of molybdenum disulfide is covered with low surface energy perfluoroalkyl chains, which not only effectively improves its dispersibility in the polyamide-imide emulsion and coating matrix, preventing agglomeration, but also endows it with excellent hydrophobic properties, with a water contact angle exceeding 90°, significantly reducing the risk of corrosive media penetration. The preparation method of this invention is process-controllable and highly repeatable. The prepared composite coating possesses comprehensive properties such as long-lasting wear resistance, resistance to damp heat corrosion, and high temperature resistance, meeting the stringent protection requirements of aerospace, marine engineering, and precision machinery fields, and has broad application prospects.

[0029] This invention provides a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating. The composite coating forms a synergistic system of molybdenum disulfide interlayer slip lubrication and perfluoroalkyl chain low surface energy lubrication. At the same time, the covalent bond connection ensures that the filler does not fall off during friction, thereby significantly reducing the coating's friction coefficient and wear rate. Attached Figure Description

[0030] Figure 1 The image shows the elemental distribution of molybdenum disulfide after grafting with perfluoroalkylsilane using scanning electron microscopy. Among them, (a) is the original electron image, (b) is the sulfur distribution map, (c) is the molybdenum distribution map, (d) is the fluorine distribution map, and (e) is the silicon distribution map. Figure 2 Contact angle tests were performed on molybdenum disulfide before and after grafting with perfluoroalkylsilane; (a) shows the contact angle test results of the original molybdenum disulfide, and (b) shows the contact angle test results of the perfluoroalkylsilane-grafted molybdenum disulfide filler. Figure 3 For perfluoroalkyl thiols grafted with molybdenum disulfide-reinforced polyamide-imide composite coatings (C 14 H 19 F 13 O3Si-5%MoS2, C 14 H 19 F 13 Friction coefficient curves of O3Si-10%MoS2 and polyamide-imide coating (PAI); where (a) is the test result with a load of 5N and (b) is the test result with a load of 10N. Detailed Implementation

[0031] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0032] In the following embodiments: Hydrogen peroxide, concentration 30 wt.% The polyamide-imide emulsion, model PR025D, was purchased from Nantong Bolian Materials Technology Co., Ltd. It is a pale yellow liquid, with N-methylpyrrolidone and water as solvents, and a solid content of 22 wt.%. Molybdenum disulfide nanosheets were purchased from Maclean's reagents and have a purity of ≥99.5%.

[0033] Example 1 This embodiment provides a method for preparing a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating, the steps of which are as follows: (1) Take 2.0 g of molybdenum disulfide nanosheet powder and add it to a mixed solution of ethanol and hydrogen peroxide (100 mL of anhydrous ethanol and 3 mL of hydrogen peroxide). Sonicate for 30 min to perform hydroxylation treatment, centrifuge at 8000 rpm for 10 min, wash with anhydrous ethanol 3 times, and vacuum dry at 60℃ for 6 h to obtain hydroxylated molybdenum disulfide nanosheets. 1.0 g of hydroxylated molybdenum disulfide nanosheets were added to 100 mL of anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a molybdenum disulfide dispersion with a concentration of 10 mg / mL. 4.0 g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane was added and stirred in an oil bath at 70 °C for 10 h. The mixture was then centrifuged at 8000 rpm for 10 min, washed three times with anhydrous ethanol, and vacuum dried at 60 °C for 6 h to obtain a perfluoroalkylsilane covalently grafted molybdenum disulfide filler. (2) Add 5 g of perfluoroalkylsilane covalently grafted molybdenum disulfide filler prepared in step (2) to 100 g of polyamide-imide emulsion, ultrasonically disperse for 30 min, then add 2 g of additive (the mass ratio of defoamer to dispersant is 1:1), stir at high speed for 30 min to obtain a uniform composite coating slurry. (3) The aluminum alloy substrate was successively polished with 400# and 800# sandpaper, ultrasonically cleaned with acetone for 15 min, and dried at 60℃ for 1 h. The above slurry was sprayed onto the substrate surface, and then pre-cured at 120℃ for 1 h, cured at 280℃ for 1 h, and naturally cooled to room temperature to obtain a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide imide composite coating.

[0034] Example 2 This embodiment provides a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating, prepared using the method of Example 1, denoted as C. 14 H 19 F 13 O3Si-5%MoS2.

[0035] Example 3 This embodiment provides a method for preparing a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating, the steps of which are as follows: (1) Take 2.0 g of molybdenum disulfide nanosheet powder and add it to a mixed solution of ethanol and hydrogen peroxide (100 mL of anhydrous ethanol and 3 mL of hydrogen peroxide). Sonicate for 30 min to perform hydroxylation treatment, centrifuge at 8000 rpm for 10 min, wash with anhydrous ethanol 3 times, and vacuum dry at 60℃ for 6 h to obtain hydroxylated molybdenum disulfide nanosheets. 1.0 g of hydroxylated molybdenum disulfide nanosheets were added to 100 mL of anhydrous ethanol and ultrasonically dispersed for 30 min to obtain a molybdenum disulfide dispersion with a concentration of 10 mg / mL. 4.0 g of 1H,1H,2H,2H-perfluorooctyltriethoxysilane was added and stirred in an oil bath at 70 °C for 10 h. The mixture was then centrifuged at 8000 rpm for 10 min, washed three times with anhydrous ethanol, and vacuum dried at 60 °C for 6 h to obtain a perfluoroalkylsilane covalently grafted molybdenum disulfide filler. (2) Add 10 g of perfluoroalkylsilane covalently grafted molybdenum disulfide filler prepared in step (2) to 100 g of polyamide-imide emulsion, ultrasonically disperse for 30 min, then add 2 g of additive (the mass ratio of defoamer to dispersant is 1:1), stir at high speed for 30 min to obtain a uniform composite coating slurry. (3) The aluminum alloy substrate was successively polished with 400# and 800# sandpaper, ultrasonically cleaned with acetone for 15 min, and dried at 60℃ for 1 h. The above slurry was sprayed onto the substrate surface, and then pre-cured at 120℃ for 1 h, cured at 280℃ for 1 h, and naturally cooled to room temperature to obtain a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide imide composite coating.

[0036] Example 4 This embodiment provides a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating, prepared using the method of Example 1, denoted as C. 14 H 19 F 13 O3Si-10%MoS2.

[0037] Those skilled in the art can select appropriate parameters and their combinations according to actual needs or conditions under the guidance of the preferred parameter range of this invention, and can achieve the preparation process of the objective of this invention and obtain the target perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating.

[0038] Example 5 In this embodiment, the original morphology and elemental distribution of the perfluoroalkylsilane covalently grafted molybdenum disulfide filler in Example 1 were observed using scanning electron microscopy elemental surface distribution mapping. The results are as follows: Figure 1 As shown.

[0039] Figure 1(a) Obvious undulations and layered / plate-like stacking features can be observed on the material surface. This is highly consistent with the layered crystal structure of molybdenum disulfide itself, indicating that the grafting of perfluoroalkylsilane did not destroy the original lamellar morphology of the molybdenum disulfide nanosheets, thus preserving the structural basis for its subsequent solid lubrication effect in the coating. (b) The red highlighted areas are widely and uniformly distributed throughout the field of view, which corresponds to the morphological features in (a), confirming that the main framework of the sample is a molybdenum-based compound. In (c), the gray-white noise dots represent the distribution of molybdenum. Molybdenum and sulfur, as characteristic elements of molybdenum disulfide, show an overlapping mapping relationship, proving that the sample contains a large amount of uniformly distributed molybdenum disulfide. In (d), the bright spots of fluorine are densely distributed on the sample surface. Perfluoroalkylsilane contains a large number of fluorine atoms, and the presence of fluorine indicates that the target group has been introduced and is stably present on the filler surface. Silicon is the molecular framework element of perfluoroalkylsilane, and the bright spots representing silicon in (e) are also densely distributed. The distribution patterns of fluorine and silicon are highly similar, and both largely overlap with the distribution regions of molybdenum / sulfur. This indicates that perfluoroalkylsilanes are not simply physically adsorbed onto the surface of molybdenum disulfide, but are uniformly fixed onto the molybdenum disulfide sheets through covalent grafting via chemical reactions.

[0040] The above results demonstrate that the perfluoroalkylsilane covalently grafted molybdenum disulfide filler successfully retains the layered morphology of molybdenum disulfide, and the perfluoroalkylsilane molecules are uniformly covalently grafted onto the surface of molybdenum disulfide. This structural design endows molybdenum disulfide with abundant fluorinated organic functional groups, improving its dispersion stability in aqueous emulsion systems, and also imparting excellent hydrophobic and low-friction surface properties to the composite material.

[0041] Example 6 In this embodiment, raw hydroxylated molybdenum disulfide nanosheet powder and perfluoroalkylsilane covalently grafted molybdenum disulfide filler powder were respectively prepared using an infrared tablet press at 5 MPa for 2 min to prepare test samples with a diameter of 13.3 mm. Contact angle tests were then conducted, and the results are as follows: Figure 2 As shown.

[0042] Figure 2The test sample in Figure (a) exhibits a distinctly irregular shape and a small contact angle, with 81.74° on the left and 75.06° on the right. In Figure (b), the test sample maintains a regular cylindrical shape, and the contact angle is significantly increased, with 108.70° on the left and 108.86° on the right. The large difference in the two contact angle values ​​in Figure (a) (>6°) indicates a significant hysteresis in the contact angle of water droplets on the original powder tablet surface. This is usually because the hydroxylated surface is highly hydrophilic, and water droplets easily spread or locally penetrate the surface micropores, resulting in a large difference between the advance and retreat angles. In contrast, the contact angles in Figure (b) are very close (<0.2°), indicating that the grafted surface properties are more uniform, chemically inert, and the state of the water droplets on the surface is more stable.

[0043] The above results demonstrate that covalent grafting with perfluoroalkylsilane successfully transformed the surface properties of hydroxylated molybdenum disulfide nanosheets from hydrophilic to hydrophobic. This hydrophobic modification is an effective means to address the problem of easy aggregation of molybdenum disulfide in polyamide-imide emulsion systems. Due to the reduced surface energy and increased water repulsion, the grafted material exhibits significantly improved dispersion stability in aqueous media, creating a favorable interfacial foundation for the subsequent preparation of high-performance composite coatings.

[0044] Example 7 This embodiment uses an Rtec friction and wear tester to test the polyamide-imide coating and the perfluoroalkyl thiol-grafted molybdenum disulfide-reinforced polyamide-imide composite coating (C). 14 H 19 F 13 O3Si-5%MoS2, C 14 H 19 F 13 The tribological properties of O3Si-10%MoS2 were tested.

[0045] Compared with the polyamide-imide coating, the aluminum alloy substrate was successively polished with 400# and 800# sandpaper, ultrasonically cleaned with acetone for 15 min, and dried at 60℃ for 1 h. The polyamide-imide emulsion was sprayed onto the substrate surface, then pre-cured at 120℃ for 1 h, cured at 280℃ for 1 h, and naturally cooled to room temperature to obtain the polyamide-imide coating, denoted as PAI.

[0046] The test loads were set to 5 N and 10 N, the reciprocating frequency to 2 Hz, the friction stroke to 8 mm, and the test duration to 10 min. The results are as follows: Figure 3 As shown.

[0047] Figure 3The test curves (a) and (b) under different loads show that the coefficient of friction of the pure polyamide-imide coating remained at its highest level during the friction test, accompanied by drastic fluctuations, generally staying in the relatively high range of 0.35 to 0.60. This indicates that the pure polyamide-imide coating is prone to adhesion or abrasive wear during friction, resulting in high and highly unstable surface friction resistance. 14 H 19 F 13 O3Si-5%MoS2, C 14 H 19 F 13 The friction coefficient of O3Si-10%MoS2 was significantly reduced and tended to stabilize, with the curve maintaining good stability and no obvious periodic fluctuations. Compared with pure polyamide-imide coating, the friction reduction effect exceeded 30%, and the smoothness of the curve was greatly improved.

[0048] The above results demonstrate that the introduction of perfluoroalkylsilane covalently grafted molybdenum disulfide significantly improves the friction reduction and wear resistance of polyamide-imide coatings. This modification strategy successfully reduced the coefficient of friction of the coating to below 0.25 and effectively eliminated severe fluctuations during the friction process. Through the surface covalent grafting modification of this invention, polyamide-imide, as a high-load engineering plastic, can also achieve excellent self-lubricating properties, showing broad application prospects in the protection of friction pairs under harsh conditions such as aerospace and precision machinery.

[0049] Tables 1 and 2 show the control group and C, respectively. 14 H 19 F 13 Wear data of O3Si-5%MoS2 after tribological testing under a 5 N load, measured by laser confocal microscopy.

[0050] Table 1: Wear data of the comparison group

[0051] Table 2: C 14 H 19 F 13 O3Si-5%MoS2 Wear Data

[0052] The above results indicate that the average wear volume of the polyamide-imide coating in the control group is as high as 540044.28 μm. 3 This indicates that, without the addition of lubricant, the polyamide-imide coating experienced significant material loss during friction, and its surface resistance to ploughing and adhesive failure was weak. 14 H 19 F 13The average wear volume of O3Si-5%MoS2 decreased to 122467.02 μm. 3 The wear volume was reduced by approximately 77.33%, demonstrating that the addition of perfluoroalkylsilane covalently grafted molybdenum disulfide significantly enhances the coating's wear resistance. Even at low addition levels, this modified filler achieves a significant leap in the overall protective performance of the coating through a dual mechanism of reducing frictional resistance and forming a protective transfer film. This provides important guidance for developing long-life, maintenance-free, high-performance engineering coatings. The composite coating prepared by this invention significantly outperforms pure polyamide-imide coatings in terms of tribological and hydrophobic properties, exhibiting excellent overall performance and meeting the requirements for long-term protection.

[0053] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating, characterized in that, Includes the following steps: (1) Hydroxylated molybdenum disulfide nanosheets were added to ethanol and dispersed to form a molybdenum disulfide dispersion; perfluoroalkylsilane was added to the molybdenum disulfide dispersion and reacted at a certain temperature; after the reaction was completed, the product was collected and purified to obtain perfluoroalkylsilane covalently grafted molybdenum disulfide filler. (2) Add perfluoroalkylsilane covalently grafted molybdenum disulfide filler to polyamide-imide emulsion, disperse and then add additives to obtain composite coating slurry; (3) The composite coating slurry is coated on the substrate surface and cured to obtain a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide imide composite coating.

2. The method for preparing the perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating according to claim 1, characterized in that, In step (1), the preparation steps of the hydroxylated molybdenum disulfide nanosheets include: immersing the molybdenum disulfide nanosheets in a mixed solution of hydrogen peroxide and ethanol for hydroxylation treatment, separating the solid product, and washing to obtain the hydroxylated molybdenum disulfide nanosheets.

3. The method for preparing the perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating according to claim 1, characterized in that: The perfluoroalkylsilane has the structure F(CF2). n CH2CH2Si(OR)3, where n is an integer selected from 4 to 8, and R is methyl or ethyl.

4. The method for preparing the perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating according to claim 1, characterized in that: In step (1), the concentration of the molybdenum disulfide dispersion is 10~20 mg / mL; the mass ratio of the hydroxylated molybdenum disulfide nanosheets to the perfluoroalkyl silane is 1:2~1:

5.

5. The method for preparing the perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating according to claim 1, characterized in that: In step (1), the reaction temperature is 70~80℃ and the reaction time is 8~12 h.

6. The method for preparing the perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating according to claim 1, characterized in that: In step (2), based on 100 parts by weight of the polyamide-imide emulsion, the amount of perfluoroalkylsilane covalently grafted molybdenum disulfide filler added is 1 to 20 parts, and the amount of additive added is 1 to 5 parts.

7. The method for preparing the perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating according to claim 1, characterized in that: In step (2), the polyamide-imide emulsion is a mixed system consisting of polyamide-imide, a polar organic solvent, and water; the polar organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; the additives include one or two of defoamers and dispersants.

8. The method for preparing the perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating according to claim 1, characterized in that: In step (3), the coating method includes one of spraying, brushing, and dipping; the coating thickness is 10~50 μm.

9. The method for preparing the perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating according to claim 1, characterized in that, In step (3), the curing includes the following steps: first, pre-curing at 110~120℃ for 0.5~2 h, then curing at 250~300℃ for 0.5~1 h, and naturally cooling to room temperature to obtain a perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating.

10. A perfluoroalkylsilane covalently grafted molybdenum disulfide reinforced polyamide-imide composite coating, characterized in that: It is prepared by any one of the preparation methods described in claims 1 to 9.

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