Oleic acid surface modified nanoparticle modified binary mixed natural ester insulating oil as well as preparation method and application thereof

Abstract

The invention provides oleic acid surface modified nanoparticle modified binary mixed natural ester insulating oil as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, carrying out surface modification on polyhedral oligomeric silsesquioxane nanoparticles through oleic acid so as to improve the dispersion stability and compatibility of the polyhedral oligomeric silsesquioxane nanoparticles in insulating oil; and then adding the modified nanoparticles into binary mixed insulating oil composed of soybean oil-based natural ester and soybean oil methyl ester to prepare the modified insulating oil. Compared with unmodified nano particle modified oil, the modified insulating oil prepared by the invention has better performance, and nano particles are uniformly dispersed in the oil and have higher stability. The novel nano modified insulating oil developed by the invention not only keeps the intrinsic advantages of environmental protection and safety of natural ester insulating oil, but also effectively solves the problems of high viscosity, poor heat dissipation, insufficient electrical strength, nanoparticle aggregation and the like, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of insulating oil technology, specifically relating to an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, its preparation method, and its application. Background Technology

[0002] Traditional oil-immersed transformers use mineral insulating oil as their internal insulation material. However, due to the low flash point and ignition point of mineral oil, and its slow degradation, it poses numerous safety hazards such as fire and explosion. Furthermore, leaks of mineral oil can cause widespread pollution of water sources and soil. Plant-based insulating oils, such as natural ester insulating oils, as a renewable insulating medium, show great promise due to their high biodegradability, low toxicity, excellent moisture resistance, and ability to extend the lifespan of transformer solid insulation paper.

[0003] Although natural ester insulating oils offer numerous advantages as an ideal potential alternative to mineral insulating oils, such as being renewable and environmentally friendly, they also suffer from inherent technical bottlenecks, including high kinematic viscosity, relatively insufficient oxidative stability, and the need for further improvement in electrical strength. Therefore, nanofluid technology is widely used in the industry to modify basic insulating oils. However, traditional inorganic nanoparticles exhibit drawbacks in modifying natural ester insulating oils, including poor dispersion stability, poor interfacial compatibility, and a limited modification mechanism. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide an oleic acid-modified nanoparticle-modified binary mixed natural ester insulating oil, its preparation method, and its application. The oleic acid-modified nanoparticle-modified binary mixed natural ester insulating oil can solve the problems of high viscosity, poor heat dissipation, and insufficient electrical strength of traditional natural ester insulating oils, and the nanoparticles exhibit long-term stable dispersibility in the oil.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, which includes oleic acid surface-modified cage-like oligomeric silsesquioxane nanoparticles and binary mixed natural ester insulating oil.

[0007] The binary mixed natural ester insulating oil includes soybean oil-based natural ester and soybean oil methyl ester.

[0008] Preferably, the concentration of the oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles in the binary mixed natural ester insulating oil is 0.03~0.15 g / L.

[0009] Preferably, the average particle size of the oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles is 100-150 nm.

[0010] Preferably, the cage-like oligomeric silsesquioxane is selected from any one or more of aminopropyl isobutyl cage-like oligomeric silsesquioxane, isooctyl cage-like oligomeric silsesquioxane, phenyl cage-like oligomeric silsesquioxane, and vinyl cage-like oligomeric silsesquioxane.

[0011] Preferably, the volume content of soybean oil methyl ester in the binary mixed natural ester insulating oil is 5-20%.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, comprising the following steps:

[0013] S1: Provides cage-type oligomeric silsesquioxane nanoparticles with binary mixed natural ester insulating oil and oleic acid surface modification, respectively.

[0014] S2: The binary mixed natural ester insulating oil is mixed evenly with oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles to obtain the product.

[0015] Preferably, the binary mixed natural ester insulating oil is obtained by mixing soybean oil-based natural ester and soybean oil methyl ester after filtration and drying.

[0016] Preferably, the mixing is carried out under stirring conditions, and after the stirring is completed, ultrasonic dispersion is performed.

[0017] Preferably, the filtration temperature is 50~60℃ and the filtration time is 30~40 min.

[0018] Preferably, the drying is vacuum drying, and the drying temperature is 90~95℃, the pressure is 60~66 Pa, and the time is 24~48 h.

[0019] Preferably, the stirring temperature is 40~50℃, the speed is 800~900 rpm, and the time is 30~40 min.

[0020] Preferably, the ultrasonic dispersion is performed 3 to 6 times, and the duration of each ultrasonic session is not less than 20 minutes.

[0021] Preferably, the oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles are obtained by mixing activated oleic acid and cage-like oligomeric silsesquioxane in an organic solvent and undergoing an amidation reaction.

[0022] Preferably, the purity of the oleic acid is ≥99%.

[0023] Preferably, the activation is carried out under anhydrous conditions and in the presence of a condensing agent.

[0024] Preferably, the amidation reaction is carried out under an inert atmosphere with heating and reflux.

[0025] Preferably, the condensing agent is selected from any one or more of N,N'-dicyclohexylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, or carbodiimidazole.

[0026] Preferably, the organic solvent is selected from any one or more of anhydrous tetrahydrofuran, dichloromethane, toluene, or N,N-dimethylformamide.

[0027] Preferably, the temperature of the heating reflux is 65~70℃, and the time is 20~28 h.

[0028] Preferably, the process further includes a purification step after the amidation reaction is completed.

[0029] Preferably, the purification step includes filtration to remove byproducts, concentration, precipitation in a poor solvent, washing, and drying.

[0030] Preferably, the unsuitable solvent is selected from methanol or acetone.

[0031] Preferably, the drying is vacuum drying, and the drying temperature is 50~60℃, the pressure is 90~100 Pa, and the time is 12~24 h.

[0032] Preferably, the mixing in step S2 is performed by stirring and ultrasonic dispersion in sequence.

[0033] Preferably, the stirring temperature is 40~50℃, the speed is 800~900 rpm, and the time is 30~40 min.

[0034] Preferably, the ultrasonic dispersion is performed 3 to 6 times, and the duration of each ultrasonic session is not less than 20 minutes.

[0035] Preferably, after the mixing is homogenized in step S2, a drying process is also included.

[0036] Thirdly, the present invention provides an application of the above-mentioned oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil in an oil-immersed transformer.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] This invention provides an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, wherein its electrical properties are superior to those of unmodified natural ester insulating oil, and the oleic acid surface-modified nanoparticles are uniformly dispersed and have higher stability in the binary mixed natural ester insulating oil.

[0039] The novel nano-modified insulating oil developed in this invention not only retains the inherent advantages of natural ester insulating oil in terms of environmental protection and safety, but also effectively solves problems such as high viscosity, poor heat dissipation, insufficient electrical strength and nanoparticle agglomeration, and has good application prospects. Attached Figure Description

[0040] Figure 1 SEM images of cage-like oligomeric silsesquioxane particles before and after oleic acid modification;

[0041] In the images, (a) and (c) are SEM images of cage-like oligomeric silsesquioxanes without oleic acid modification at different magnifications, and (b) and (d) are SEM images of cage-like oligomeric silsesquioxane particles modified with oleic acid at different magnifications. Detailed Implementation

[0042] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0043] Part One

[0044] To address the shortcomings of existing natural ester insulating oils, such as high viscosity, poor heat dissipation, and insufficient electrical strength, as well as the poor stability of nanoparticles in oil, this invention provides an oleic acid-surface-modified nanoparticle-modified binary mixed natural ester insulating oil. This oil comprises oleic acid-surface-modified cage-like oligomeric silsesquioxane nanoparticles and a binary mixed natural ester insulating oil. The binary mixed natural ester insulating oil includes soybean oil-based natural ester and soybean oil methyl ester, wherein the volume content of soybean oil methyl ester is 5-20%, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%. This invention uses a mixture of soybean oil-based natural ester and soybean oil methyl ester. The binary mixed system combines the high flash point and high biodegradability of natural esters with the low viscosity of methyl esters, comprehensively improving fluidity, heat dissipation performance, and electrical stability, and addressing the problems of high viscosity and poor cold-start performance associated with single natural esters.

[0045] In this invention, the concentration of the oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles in the binary mixed natural ester insulating oil is 0.03~0.15 g / L, such as 0.03 g / L, 0.04 g / L, 0.05 g / L, 0.06 g / L, 0.07 g / L, 0.08 g / L, 0.09 g / L, 0.10 g / L, 0.11 g / L, 0.12 g / L, 0.13 g / L, 0.14 g / L, or 0.15 g / L, etc., preferably 0.03~0.06 g / L.

[0046] In this invention, the oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles may contain cage-like oligomeric silsesquioxane selected from any one or more of aminopropyl isobutyl cage-like oligomeric silsesquioxane, isooctyl cage-like oligomeric silsesquioxane, phenyl cage-like oligomeric silsesquioxane, or vinyl cage-like oligomeric silsesquioxane. Testing has shown that when aminopropyl isobutyl cage-like oligomeric silsesquioxane (APiB-POSS) is used, its surface amino functional groups exhibit high reactivity, enabling efficient amidation with oleic acid carboxyl groups to obtain a stable organic modification layer. Furthermore, its isobutyl side chain provides good oleophobicity and steric hindrance, resulting in superior compatibility and dispersion stability of the modified product in natural ester oils. Therefore, compared to other cage-like oligomeric silsesquioxanes, this invention further preferably uses aminopropyl isobutyl cage-like oligomeric silsesquioxane.

[0047] In some embodiments of the present invention, the oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles are obtained by mixing activated oleic acid and cage-like oligomeric silsesquioxane in an organic solvent and undergoing an amidation reaction. In other words, after activation, oleic acid is grafted onto the cage-like oligomeric silsesquioxane, which is different from the physical mixing of oleic acid and cage-like oligomeric silsesquioxane.

[0048] In this invention, the oleic acid has a purity ≥99%, and the activation is carried out under anhydrous conditions in the presence of a condensing agent selected from N,N'-dicyclohexylcarbodiimide. In some embodiments of this invention, it is preferable to dissolve oleic acid with a purity ≥99% in a solvent, such as anhydrous tetrahydrofuran, and slowly add the condensing agent under ice bath conditions (0~5°C), maintaining low temperature and stirring for 30~45 min to complete the activation reaction.

[0049] Then, according to the present invention, activated oleic acid and cage-like oligomeric silsesquioxane are mixed in an organic solvent to undergo an amidation reaction. The organic solvent is selected from anhydrous tetrahydrofuran. The amidation reaction is carried out under an inert atmosphere with heating and reflux at a temperature of 65-70°C (e.g., 65°C, 66°C, 67°C, 68°C, 69°C, or 70°C) for a time of 20-28 h (e.g., 20 h, 21 h, 22 h, 23 h, 24 h, 25 h, 26 h, 27 h, or 28 h). The duration of the amidation reaction is determined by observing the reaction system change from turbid to transparent and the appearance of the oleic acid carboxyl stretching vibration peak (approximately 1700 cm⁻¹) in the infrared spectrum. -1 The peaks of the amide bond have largely disappeared, and the characteristic peak of the amide bond (approximately 1650 cm⁻¹) has been observed. -1 The appearance of ) indicates the end of the reaction, signifying its termination.

[0050] In some preferred embodiments of the present invention, the aftermath of the amidation reaction further includes a purification step, which comprises filtration to remove byproducts, concentration, precipitation in a poor solvent, washing, and drying. The poor solvent is selected from methanol and / or acetone; the drying is vacuum drying, with a drying temperature of 50-60°C (e.g., 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, or 60°C), a pressure of 90-100 Pa (e.g., 90 Pa, 91 Pa, 92 Pa, 93 Pa, 94 Pa, 95 Pa, 96 Pa, 97 Pa, 98 Pa, 99 Pa, or 100 Pa), and a time of 12-24 h (e.g., 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, or 24 h).

[0051] In this invention, the average particle size of the oleic acid-modified cage-like oligomeric silsesquioxane finally obtained according to the above scheme is 100~150 nm, such as 100 nm, 110 nm, 120 nm, 130 nm, 140 nm or 150 nm, etc.

[0052] It should be noted that the present invention uses oleic acid to modify cage-like oligomeric silsesquioxane nanoparticles, which can significantly improve their dispersion stability and compatibility in organic systems, reduce agglomeration and improve particle surface activity. Further mixing them with binary mixed natural ester insulating oil can obtain a modified insulating oil with high breakdown strength, low dielectric loss and excellent thermal conductivity, thus achieving simultaneous improvement in the electrical properties and thermal stability of the insulating oil.

[0053] Part Two

[0054] This invention also provides a method for preparing the above-mentioned oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, comprising the following steps:

[0055] S1: Provides cage-type oligomeric silsesquioxane nanoparticles with binary mixed natural ester insulating oil and oleic acid surface modification, respectively.

[0056] S2: The binary mixed natural ester insulating oil is mixed evenly with oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles to obtain the product.

[0057] In this invention, the binary mixed natural ester insulating oil is obtained by mixing soybean oil-based natural ester and soybean oil methyl ester after filtration and drying. Preferably, the mixing is carried out under stirring conditions, and after stirring, ultrasonic dispersion is performed.

[0058] In some embodiments of the present invention, the filtration temperature is 50~60℃, such as 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃ or 60℃, etc.; the time is 30~40 min, such as 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min or 40 min, etc.

[0059] In some embodiments of the present invention, the drying is vacuum drying, the drying temperature is 90~95℃, such as 90℃, 91℃, 92℃, 93℃, 94℃ or 95℃, etc.; the pressure is 60~66 Pa, such as 60 Pa, 61 Pa, 62 Pa, 63 Pa, 64 Pa, 65 Pa or 66 Pa, etc.; the time is 24~48 h, such as 24 h, 30 h, 36 h, 42 h or 48 h, etc.

[0060] In some embodiments of the present invention, the stirring temperature is 40~50℃, such as 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, or 50℃; the speed is 800~900 rpm, such as 800 rpm, 810 rpm, 820 rpm, 830 rpm, 840 rpm, 850 rpm, 860 rpm, 870 rpm, 880 rpm, 890 rpm, or 900 rpm; and the time is 30~40 min, such as 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, or 40 min.

[0061] In some embodiments of the present invention, the number of ultrasonic dispersions is 3 to 6 times, such as 3, 4, 5 or 6 times, and the duration of a single ultrasonic dispersion is not less than 20 minutes.

[0062] The oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles can be prepared according to the above-mentioned content, and will not be repeated here.

[0063] In this invention, after obtaining oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles and binary mixed natural ester insulating oil, the binary mixed natural ester insulating oil and oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles are mixed evenly according to this invention to obtain the final product.

[0064] In some embodiments of the present invention, the above mixing is preferably performed by stirring and ultrasonic dispersion in sequence. The stirring temperature is 40-50°C, such as 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, or 50°C; the stirring speed is 800-900 rpm, such as 800 rpm, 810 rpm, 820 rpm, 830 rpm, 840 rpm, 850 rpm, 860 rpm, 870 rpm, 880 rpm, 890 rpm, or 900 rpm; and the stirring time is 30-40 min, such as 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, or 40 min.

[0065] The ultrasonic dispersion setting is the same as the ultrasonic dispersion range mentioned above, and will not be repeated here.

[0066] In some embodiments of the present invention, after the above-mentioned mixing is completed, a drying process is preferably included.

[0067] The preparation method provided by this invention is simple, convenient, easy to implement, and conducive to achieving large-scale or industrialized production.

[0068] Part Three

[0069] The present invention also provides an application of the above-mentioned oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil in an oil-immersed transformer.

[0070] In summary, this invention first modifies the surface of cage-like oligomeric silsesquioxane nanoparticles with oleic acid to improve their dispersion stability and compatibility in insulating oil. Then, the modified nanoparticles are added to a binary mixed insulating oil composed of soybean oil-based natural esters and soybean oil methyl esters at a set concentration (preferably 0.03 g / L). After stirring, ultrasonic dispersion, and vacuum drying, a modified insulating oil is obtained. The modified insulating oil of this invention exhibits the best overall performance at 0.03 g / L, showing reduced kinematic viscosity, improved thermal conductivity, reduced dielectric loss, increased volume resistivity, and improved breakdown voltage. Compared with unmodified nanoparticle-modified oil, the modified insulating oil prepared by this invention has superior performance, with more uniform dispersion and higher stability of the nanoparticles in the oil. The novel nano-modified insulating oil developed by this invention not only retains the inherent advantages of natural ester insulating oil—environmentally friendly and safe—but also effectively solves problems such as high viscosity, poor heat dissipation, insufficient electrical strength, and nanoparticle agglomeration, showing promising application prospects.

[0071] To further illustrate the present invention, the following embodiments provide a detailed description. The experimental materials used in the following embodiments of the present invention are all commercially available products.

[0072] Example 1

[0073] This embodiment provides a binary mixed natural ester insulating oil, the preparation method of which is as follows:

[0074] Soybean oil-based natural esters and soybean oil methyl esters, which meet IEC 62770 standards and have undergone filtration and vacuum drying, were mixed, with soybean oil methyl esters accounting for 10% of the mixed oil volume. Magnetic stirring was then performed at 40°C, 800 rpm, and for 30 min. After magnetic stirring, the mixed oil sample was treated with an ultrasonic disperser at 50 W for 20 min. After each dispersion, the sample was allowed to cool before being ultrasonically dispersed again, for a total of three dispersions and 60 min. Following ultrasonic dispersion, the mixed insulating oil sample was vacuum dried at 90°C / 60 Pa for 48 h. After vacuum drying, the power was turned off, and the sample was allowed to cool to room temperature before being removed, yielding the binary mixed natural ester insulating oil.

[0075] Example 2

[0076] This embodiment provides an oleic acid-surface-modified nanoparticle-modified binary mixed natural ester insulating oil, the preparation method of which is as follows:

[0077] S1: A binary mixed natural ester insulating oil is provided, referring to the method of Example 1;

[0078] S2: First, commercially available aminopropyl isobutyl cage-type oligomeric silsesquioxane (APiB-POSS) was dissolved in anhydrous tetrahydrofuran for later use. Separately, oleic acid with a purity ≥99% was dissolved in anhydrous tetrahydrofuran, and the condensing agent N,N'-dicyclohexylcarbodiimide was slowly added under ice bath conditions (0~5℃), and the mixture was stirred at low temperature for 45 min to complete the activation reaction. Subsequently, the activated oleic acid solution was slowly added dropwise to the POSS solution under nitrogen protection, the system was kept under positive nitrogen pressure, a reflux condenser was connected, and the mixture was heated under reflux at 65~70℃ for 20~28 h to allow the amino groups on the POSS molecules to undergo amidation condensation with the carboxyl groups of oleic acid. After the reaction was completed, the mixture was cooled to room temperature, and the byproduct dicyclohexylurea (DCU) was removed by filtration. The filter cake was washed with a small amount of tetrahydrofuran and the filtrates were combined. The filtrate was concentrated by rotary evaporation to a viscous state, and then slowly poured into excess methanol to precipitate the product. The precipitate was collected by vacuum filtration and washed three times with methanol to remove residual impurities and unreacted substances. Finally, the obtained wet filter cake was placed in a vacuum oven and dried at 60°C and below 100 Pa to obtain oleic acid surface-modified cage-like oligomeric silsesquioxane nanoparticles.

[0079] S3: The prepared binary mixed natural ester insulating oil was placed on a stage. Using a high-precision electronic balance, the appropriate mass of oleic acid surface-modified nanoparticles was accurately weighed. The weighed nanoparticles were slowly added to the binary mixed natural ester insulating oil at a concentration of 0.03 g / L. The oil sample beaker was then placed on a magnetic stirrer and magnetically stirred for 40 minutes. The modified oil was then transferred to an ultrasonic disperser for ultrasonic dispersion for 60 minutes. The final oil sample was transferred to a vacuum drying oven for vacuum drying. The temperature of the vacuum drying oven was set to 90℃, the pressure to 60 Pa, and the drying time to 48 h.

[0080] The vacuum drying process described above can remove air bubbles generated during the uniform dispersion process as well as moisture introduced from the external environment, thereby improving the purity and stability of the modified oil.

[0081] After vacuum drying, the dried oil sample was taken out. The nano-modified binary mixed natural ester insulating oil sample obtained at this time showed a uniform and transparent state, with no obvious particle sedimentation and bubble residue.

[0082] To verify whether oleic acid was successfully grafted onto the surface of cage-like oligomeric silsesquioxane nanoparticles, this invention used scanning electron microscopy to observe the dispersion and particle size of the surface-modified cage-like oligomeric silsesquioxane particles. The results are as follows: Figure 1 As shown. Among them, Figure 1Figures (a) and (c) show the SEM morphology of unmodified oleic acid cage-like oligomeric silsesquioxanes at different magnifications, while figures (b) and (d) show the SEM morphology of oleic acid-modified cage-like oligomeric silsesquioxane particles at different magnifications.

[0083] By comparing the four images, it is clear that the unmodified cage-like polysilsesquioxane particles exhibit obvious agglomeration characteristics, with the particles tightly adhered to each other, forming large aggregates. This indicates that they have high surface energy, strong interparticle interactions, and poor dispersibility. Looking at the morphology of individual particles, the unmodified polysilsesquioxane particles have relatively smooth surfaces and are mostly regular spherical or near-spherical structures, showing that their cage-like framework is intact and their surface lacks an organic coating layer.

[0084] Overall, after modification, the oleic acid-grafted cage-like polysilsesquioxane particles exhibited a more uniform grayscale distribution and reduced local contrast, indicating a significant reduction in agglomeration. Individual particle observation revealed a slightly blurred surface and a rougher surface texture compared to the unmodified sample. This is because the successful grafting of oleic acid molecules onto the POSS surface formed an organic long-chain coating layer. This coating layer altered the electron beam scattering characteristics, making the actually clear particle boundaries less distinct in the electron microscopy image compared to the unmodified sample. However, it effectively reduced surface energy, suppressed agglomeration, and thus significantly improved the particle dispersion in the organic system.

[0085] Example 3

[0086] This embodiment provides an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, which is prepared according to the method of Example 2. The difference from Example 2 is that the concentration of nanoparticles added is 0.06 g / L, while other parameters remain unchanged.

[0087] Example 4

[0088] This embodiment provides an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, which is prepared according to the method of Example 2. The difference from Example 2 is that the concentration of nanoparticles added is 0.09 g / L, while other parameters remain unchanged.

[0089] Example 5

[0090] This embodiment provides an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, which is prepared according to the method of Example 2. The difference between Example 2 and Example 2 is that the concentration of nanoparticles added is 0.12 g / L, while other parameters remain unchanged.

[0091] Example 6

[0092] This embodiment provides an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, which is prepared according to the method of Example 2. The difference from Example 2 is that the concentration of nanoparticles added is 0.15 g / L, while other parameters remain unchanged.

[0093] Example 7

[0094] This embodiment provides an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, which is prepared according to the method of Example 2. The difference from Example 2 is that the nanoparticles used are replaced in equal molar amounts with isooctyl cage-type oligomeric silsesquioxane (iOct–POSS) containing amino-terminal groups, while other parameters remain unchanged.

[0095] Example 8

[0096] This embodiment provides an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, which is prepared according to the method of Example 2. The difference from Example 2 is that the nanoparticles used are replaced with equimolar amounts of phenyl cage-type oligomeric silsesquioxane (Ph–POSS) containing amino-terminated groups, while other parameters remain unchanged.

[0097] Example 9

[0098] This embodiment provides an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil, which is prepared according to the method of Example 2. The difference from Example 2 is that the nanoparticles used are replaced with amino-terminated vinyl cage-type oligomeric silsesquioxanes (Vi-POSS) in equimolar amounts, while other parameters remain unchanged.

[0099] Comparative Example 1

[0100] This comparative example provides an unmodified binary mixed natural ester insulating oil with unmodified nanoparticles, and its preparation method is as follows:

[0101] S1: A binary mixed natural ester insulating oil is provided, referring to the method of Example 1;

[0102] S2: Commercially available aminopropyl isobutyl POSS (APiB-POSS) was placed in an agate cup and ground for 24 hours using a ball mill to make its average particle size about 100~150 nm, thus obtaining unmodified cage-type oligomeric silsesquioxane nanopowder.

[0103] S3: Place the prepared binary mixed natural ester insulating oil on a stage. Accurately weigh the corresponding mass of unmodified nanoparticles using a high-precision electronic balance. Slowly add the weighed nanoparticles to the binary mixed natural ester insulating oil at a concentration of 0.03 g / L. Then, place the oil sample beaker on a magnetic stirrer and stir magnetically for 40 minutes. Next, transfer the modified oil to an ultrasonic disperser for ultrasonic dispersion for 60 minutes. Transfer the final oil sample to a vacuum drying oven for vacuum drying. Set the temperature of the vacuum drying oven to 90℃, the pressure to 60Pa, and the drying time to 48 h.

[0104] Comparative Example 2

[0105] This comparative example provides an unmodified nanoparticle-modified binary mixed natural ester insulating oil, prepared according to the method of Comparative Example 1. The difference from Comparative Example 1 is that the concentration of unmodified nanoparticles added is 0.06 g / L, while other parameters remain unchanged.

[0106] Comparative Example 3

[0107] This comparative example provides an unmodified nanoparticle-modified binary mixed natural ester insulating oil, prepared according to the method of Comparative Example 1. The difference from Comparative Example 1 is that the concentration of unmodified nanoparticles added is 0.09 g / L, while other parameters remain unchanged.

[0108] Comparative Example 4

[0109] This comparative example provides an unmodified nanoparticle-modified binary mixed natural ester insulating oil, prepared according to the method of Comparative Example 1. The difference from Comparative Example 1 is that the concentration of unmodified nanoparticles added is 0.12 g / L, while other parameters remain unchanged.

[0110] Comparative Example 5

[0111] This comparative example provides an unmodified nanoparticle-modified binary mixed natural ester insulating oil, prepared according to the method of Comparative Example 1. The difference from Comparative Example 1 is that the concentration of unmodified nanoparticles added is 0.15 g / L, while other parameters remain unchanged.

[0112] Performance testing

[0113] The insulating oils prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to electrical performance tests. The test items included kinematic viscosity at 40°C, thermal conductivity, dielectric loss factor at 90°C, volume resistivity, and power frequency breakdown voltage. The test methods were as follows:

[0114] Kinematic viscosity test: This application uses a TP725 kinematic viscosity tester and follows standard GB / T 265 to test and compare the kinematic viscosity of the insulating oils prepared in the examples and comparative examples. Before starting the formal test, the oil bath temperature after power-on is set to 40°C. After the temperature rises to 40°C and stabilizes, 12 mL of the oil sample to be tested is injected into the Ubbelohde viscometer in the equipment, and then the test begins.

[0115] Thermal conductivity testing: This application uses a TC3000E thermal conductivity meter to test the thermal conductivity of the insulating oils prepared in the examples and comparative examples. The testing principle of this experimental equipment is the transient hot wire method. At the beginning of the test, 50 mL of the oil sample to be tested is poured into the container, and then the sensor is inserted into a special container to ensure that the oil sample can completely immerse the sensor. Then, thermal equilibrium detection is started. When the temperature fluctuation curve of the oil sample to be tested is less than 0.1 K / 10min and reaches a relatively stable state, the monitoring is stopped and the test begins.

[0116] Dielectric loss factor and volume resistivity testing: This application uses an A1170 fully automatic dielectric loss and resistivity meter and follows standard GB / T 5654-2007 to test and analyze the dielectric loss factor and volume resistivity of the insulating oils prepared in the examples and comparative examples at 90 ℃. Specifically, the test temperature was 90 ℃, the test frequency was 50 Hz, the electrode distance was 2 mm, the DC voltage was set to 500 V, and the voltage amplitude was set to 2 kV.

[0117] Power frequency breakdown voltage test: This application uses an intelligent withstand voltage test device to test the power frequency breakdown voltage of the insulating oils prepared in the examples and comparative examples according to standard GB / T507-2002. In the specific test process, the voltage rise rate is controlled at 2kV / s, and a breakdown operation is performed every 5 minutes, for a total of 6 repeated breakdown processes. The average value is taken as the final breakdown voltage value.

[0118] The test results are shown in Table 1:

[0119] Table 1

[0120]

[0121] As shown in Table 1, when oleic acid was used to modify APiB-POSS (Examples 2-6 and Comparative Examples 1-5), the kinematic viscosity of both groups of oil samples showed a trend of first decreasing, then increasing, and then decreasing again. When the concentration of nanoparticles was below approximately 0.09 g / L, the viscosity of the oleic acid-modified aminopropyl isobutyl cage-like oligomeric silsesquioxane nanoparticle-modified oil sample (N-OA-APiB) was slightly lower than that of the unmodified aminopropyl isobutyl cage-like oligomeric silsesquioxane nanoparticle-modified oil sample (N-APiB) at the same concentration; however, when the concentration exceeded 0.09 g / L, the viscosity of the N-OA-APiB oil sample was higher than that of the N-APiB oil sample. The overall decrease in oil viscosity after the addition of nanoparticles is mainly due to the lubricating effect of the nanoparticles, which can reduce oil friction and promote convection exchange through micro-movement in the oil, thereby improving fluidity. At low concentrations, oleic acid modification improves the dispersibility of nanoparticles, reduces the probability of aggregation, increases the number of dispersion sites, and enhances the lubrication and convection effects. At high concentrations, the number of nanoparticles increases, the spacing decreases, and the interaction force is enhanced, leading to an increase in the collision frequency and easy aggregation, which weakens the lubrication effect and increases the viscosity.

[0122] The thermal conductivity of the N-OA-APiB oil sample was generally higher than that of the N-APiB oil sample. At low concentrations (Example 2), the thermal conductivity of the N-OA-APiB oil sample reached its highest value of 0.1890 W·m. -1 ·K -1 The thermal conductivity gradually decreased with increasing concentration. This is because the introduction of nanoparticles alters the heat transfer structure of the binary oil mixture. The micro-movement of nanoparticles in the oil promotes convective heat transfer, forming an interfacial layer attached to the particle surface, reducing thermal resistance, and thus improving thermal conductivity. Compared to unmodified nanoparticles, modified nanoparticles have better dispersion stability and are more uniformly distributed in the oil, providing more heat exchange interfaces and therefore exhibiting superior thermal conductivity. As the particle concentration continues to increase, both modified and unmodified nanoparticles show varying degrees of agglomeration, hindering the heat exchange process and leading to a decrease in thermal conductivity.

[0123] The dielectric loss factor of both oil samples showed a trend of first decreasing and then increasing with increasing nanoparticle concentration, reaching its lowest value at 0.03 g / L, which was 1.362% (N-APiB) and 1.205% (N-OA-APiB), respectively. This is because the addition of nanoparticles weakens the directional polarization of molecular dipoles in the mixed oil, thereby reducing dielectric loss. As the concentration continues to increase, the nanoparticles aggregate, forming larger clusters, which weakens the interfacial effect and increases dielectric loss. Further comparison shows that at the same concentration, the dielectric loss factor of N-OA-APiB is lower than that of N-APiB. This is because oleic acid modification reduces the surface polarity of cage-like oligomeric silsesquioxane particles, weakening the polarization effect of the insulating oil; simultaneously, the modified particles are more uniformly dispersed, reducing local electric field distortion and resulting in a more balanced electric field distribution; furthermore, the oleic acid functional groups have better compatibility with the molecular structure of the insulating oil, forming a stable and compact interfacial structure, reducing interfacial charge accumulation and leakage, and further reducing dielectric loss.

[0124] With increasing nanoparticle concentration, the volume resistivity of both oil samples generally showed an upward trend. This is because the introduction of nanoparticles can create electron traps in the oil, effectively capturing free electrons and reducing electron mobility, thus increasing volume resistivity. Furthermore, the formation of an electric double layer between nanoparticles and the oil sample allows for the capture of free electrons and migrating ions over a wider area, further enhancing volume resistivity. At relatively high concentrations, a decreasing inflection point in volume resistivity occurs, specifically at 0.12 g / L for the N-APiB sample. Since the nanoparticles in the N-OA-APiB oil sample undergo surface modification, which increases uniform dispersion to some extent, the decreasing inflection point in its volume resistivity is presumably slightly delayed compared to the N-APiB oil sample. The reason for the decreasing trend in volume resistivity after increasing concentration is that excessively high nanoparticle concentrations lead to agglomeration, reducing the modification effect of the nanoparticles. Additionally, increased concentration enhances ion mobility in the oil, thus decreasing volume resistivity. Furthermore, the volume resistivity of N-APiB oil samples was higher than that of N-OA-APiB oil samples at the same concentration. This is because the organic functional groups of oleic acid have a good affinity with insulating oil molecules, forming a tighter and more stable interface between the nanoparticles and the mixed insulating oil. This optimized interface effectively prevents charge transport, improves insulation performance, and thus increases volume resistivity. Simultaneously, these organic functional groups give the nanoparticle surface a certain degree of hydrophobicity, further preventing the aggregation of polar impurities and moisture in the oil to the nanoparticle surface, reducing the number of free ions in the insulating oil, thereby increasing volume resistivity. In addition, the more uniform distribution of oleic acid-modified cage-like oligomeric silsesquioxane particles compared to pure cage-like oligomeric silsesquioxane particles effectively avoids the formation of conductive channels, increasing the resistance encountered by electrons during conduction in the mixed insulating oil, thereby increasing volume resistivity.

[0125] With increasing nanoparticle concentration, the power frequency breakdown voltage of both oil samples showed a trend of first increasing and then decreasing. At lower concentrations, the addition of nanoparticles increased the number and depth of electron traps in the oil, thereby capturing free electrons, limiting stream development, and increasing the breakdown voltage. Simultaneously, the energy and mobility of electrons decreased during the continuous capture and release process, which is beneficial for improving insulation performance. Furthermore, nanoparticles improved the thermal conductivity of the mixed oil, allowing heat generated under the electric field to be conducted more quickly, reducing bubble formation and thus lowering the risk of breakdown. At higher concentrations, collisions between particles increased, leading to a higher probability of aggregation. Aggregates weakened the surface effect and may form a "microbridge effect" in the electrode gap, resulting in enhanced local electric field and making it easier for bubbles to form in the oil, causing insulation breakdown. Comparative results showed that at the same concentration, the breakdown voltage of the N-OA-APiB oil sample was higher than that of the N-APiB oil sample. This is because oleic acid modification improves the dispersion of particles in the oil, reduces surface polarity, makes the electric field distribution more uniform, weakens polarization, and reduces electric field energy loss, thereby further improving the breakdown voltage of the insulating oil.

[0126] To further verify the effect of different substituents on the performance of oleic acid-modified cage-type oligomeric silsesquioxane-modified binary mixed natural ester insulating oil, this invention selected three POSS nanoparticles with different functionalization structures as comparative samples: oleic acid-modified isooctyl cage-type oligomeric silsesquioxane (N-OA-iOct), oleic acid-modified phenyl cage-type oligomeric silsesquioxane (N-OA-Ph), and oleic acid-modified vinyl cage-type oligomeric silsesquioxane (N-OA-Vi). The preparation methods of all three samples were the same as in Example 2, with only the type of nanoparticles differing.

[0127] As can be seen from the comparison of the data in Examples 7-9 and Example 2 in Table 1, the performance indicators of the three substituent-modified samples are all lower than those of the N-OA-APiB sample in Example 2. Among them, the N-OA-APiB modified oil sample exhibits the lowest dielectric loss factor and the highest volume resistivity, and its power frequency breakdown voltage is also significantly better than that of the N-OA-iOct, N-OA-Ph, and N-OA-Vi samples. Although the three modified samples all achieved better dispersibility and thermal conductivity than the unmodified system, their overall insulation performance still differs. In the N-OA-iOct sample, the interaction between the nonpolar isooct chain and oleic acid molecules is weak, resulting in a lower graft layer density and limited interfacial bonding force, and the dielectric loss and volume resistivity are lower than those of N-OA-APiB. In the N-OA-Ph sample, the rigidity of the phenyl substituent is relatively large, affecting the dispersion uniformity and resulting in a higher polarization loss. Although the N-OA-Vi sample has certain chemical reactivity, the stability of the organic layer formed by vinyl grafting is insufficient, which easily causes local particle agglomeration.

[0128] In summary, oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles exhibited the best performance across all insulating oil properties at a concentration of 0.03 g / L, demonstrating reduced kinematic viscosity, increased thermal conductivity, decreased dielectric loss factor, increased volume resistivity, and improved breakdown voltage. Compared to unmodified nanoparticles, oleic acid-modified nanoparticles demonstrated better dispersion stability and compatibility in insulating oil, thus achieving superior overall modification effects under the same conditions. The novel nano-modified insulating oil developed in this invention retains the inherent advantages of natural ester insulating oils—environmental friendliness and safety—while specifically addressing their technical bottlenecks such as high viscosity, poor heat dissipation, and insufficient electrical strength. Simultaneously, it ensures long-term stable dispersion of nanoparticles in the oil, meeting the development needs of insulating oils for power equipment.

[0129] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An oleic acid-surface-modified nanoparticle-modified binary mixed natural ester insulating oil, characterized in that, Including oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles and binary mixed natural ester insulating oil; The binary mixed natural ester insulating oil includes soybean oil-based natural ester and soybean oil methyl ester.

2. The oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil according to claim 1, characterized in that, The concentration of the oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles in the binary mixed natural ester insulating oil is 0.03~0.15 g / L; The average particle size of the oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles is 100-150 nm. The cage-type oligomeric silsesquioxane is selected from any one or more of aminopropyl isobutyl cage-type oligomeric silsesquioxane, isooctyl cage-type oligomeric silsesquioxane, phenyl cage-type oligomeric silsesquioxane, or vinyl cage-type oligomeric silsesquioxane.

3. The oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil according to claim 1 or 2, characterized in that, The volume content of soybean oil methyl ester in the binary mixed natural ester insulating oil is 5-20%.

4. A method for preparing an oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Provides cage-type oligomeric silsesquioxane nanoparticles with binary mixed natural ester insulating oil and oleic acid surface modification, respectively. S2: The binary mixed natural ester insulating oil is mixed evenly with oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles to obtain the product.

5. The preparation method according to claim 4, characterized in that, The binary mixed natural ester insulating oil is obtained by mixing soybean oil-based natural ester and soybean oil methyl ester after filtration and drying. The mixing is carried out under stirring conditions, and after the stirring is completed, ultrasonic dispersion is performed.

6. The preparation method according to claim 5, characterized in that, The filtration temperature is 50~60℃ and the time is 30~40 min; And / or, the drying is vacuum drying, the drying temperature is 90~95℃, the pressure is 60~66 Pa, and the time is 24~48 h; And / or, the stirring temperature is 40~50℃, the speed is 800~900 rpm, and the time is 30~40 min; And / or, the number of ultrasonic dispersions is 3 to 6 times, and the duration of a single ultrasonic session is not less than 20 minutes.

7. The preparation method according to any one of claims 4 to 6, characterized in that, The oleic acid-modified cage-like oligomeric silsesquioxane nanoparticles are obtained by mixing activated oleic acid and cage-like oligomeric silsesquioxane in an organic solvent and undergoing an amidation reaction. And / or, the purity of the oleic acid is ≥99%; And / or, the activation is carried out under anhydrous conditions and in the presence of a condensing agent; And / or, the amidation reaction refers to heating under reflux in an inert atmosphere; And / or, the process may further include a purification step after the amidation reaction is completed.

8. The preparation method according to claim 7, characterized in that, The condensing agent is selected from any one or more of N,N'-dicyclohexylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, or carbodiimidazole; And / or, the organic solvent is selected from any one or more of anhydrous tetrahydrofuran, dichloromethane, toluene, or N,N-dimethylformamide; And / or, the temperature of the heating reflux is 65~70℃, and the time is 20~28 h; And / or, the purification steps include filtration to remove byproducts, concentration, precipitation in a poor solvent, washing, and drying; And / or, the undesirable solvent is selected from methanol and / or acetone; And / or, the drying is vacuum drying, the drying temperature is 50~60℃, the pressure is 90~100 Pa, and the time is 12~24 h.

9. The preparation method according to any one of claims 4 to 8, characterized in that, The mixing process described in step S2 involves stirring and ultrasonic dispersion in sequence; And / or, the stirring temperature is 40~50℃, the speed is 800~900 rpm, and the time is 30~40 min; And / or, the number of ultrasonic dispersions is 3 to 6 times, and the duration of a single ultrasonic dispersion is not less than 20 minutes; And / or, after the mixing is completed in step S2, a drying process is also included.

10. The application of the oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil according to any one of claims 1 to 3, or the oleic acid surface-modified nanoparticle-modified binary mixed natural ester insulating oil prepared by the preparation method according to any one of claims 4 to 9, in oil-immersed transformers.

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