A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules

Abstract

The present invention discloses a method for repairing damage to cellulose insulating paper based on mechanically enhanced microcapsules, and relates to the field of high voltage and insulation technology. The repair method of the present invention is to use cellulose insulating paper based on mechanically enhanced microcapsules for damage repair, wherein the mechanically enhanced microcapsules are mainly made of capsule walls and core materials, wherein the capsule walls include polyurethane and nano-silica, and the core materials include DCPD and Hoveyda-Grubbs catalyst. The present invention solves the problem that microcapsules in traditional insulating paper are prone to premature rupture under external stress, resulting in premature leakage of the repair agent and low repair efficiency. Using insulating paper containing the microcapsules of the present invention for damage repair can improve the efficiency and accuracy of the repair process.

Description

Technical Field

[0001] The present invention relates to the field of high voltage and insulation technology, and in particular to a method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules. Background Art

[0002] In the field of high voltage and insulation technology, cellulose insulating paper is a key insulating material used in transformers, power generation equipment, and power transmission equipment, and is widely used in various electrical equipment. However, during long-term operation, insulating paper is affected by various factors such as electric fields, thermal stress, and mechanical stress, and is prone to electrical damage such as electrical dendrites and cracks. This damage can weaken the mechanical strength of the insulating paper and reduce its dielectric properties, thereby causing partial discharge and even insulation breakdown, seriously affecting the safety and reliability of electrical equipment. Therefore, how to effectively repair electrical damage to insulating paper, improve its electrical and mechanical properties, and extend its service life has become a major technical challenge in the field of insulation technology.

[0003] In recent years, microcapsule technology has received widespread attention in the field of self-repair of materials. Microcapsules encapsulate repair agents. When external factors cause the microcapsules to rupture, the repair agents can be released and chemically react with the damaged parts, thereby achieving self-repair. However, traditional microcapsules have some limitations, especially they are prone to premature rupture under external stress, resulting in premature leakage of the repair agent and reduced repair efficiency. In addition, the mechanical properties of traditional capsule wall materials are poor and it is difficult to maintain stability under high stress environments. Therefore, improving the mechanical strength of microcapsules, avoiding premature leakage of repair agents, and ensuring that they release the repair agent accurately and efficiently when damage occurs are important directions for improving the repair effect of insulating paper. Patent document with publication number CN116574437A discloses a self-repairing insulating material for power equipment and a preparation method thereof. The insulating material is prepared by mixing self-repairing microcapsules with an aqueous polyurethane-acrylate composite emulsion, a surface modifier, and nanoparticles, stirring the mixture evenly, ultrasonically treating the mixture, and then mixing the mixture with a curing agent. The self-repairing microcapsules are made of a capsule wall and a core material. The capsule wall is a modified urea-formaldehyde resin, and the core material is hexamethylene diisocyanate or isophorone diisocyanate, which can repair cracks. However, the overall mechanical properties of the self-repairing microcapsules and the density of the capsule wall have not yet been confirmed, and it is not clear whether they can avoid premature leakage of the repair agent.

[0004] Based on the above problems, the purpose of this application is to provide a method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules. Summary of the Invention

[0005] To address the above shortcomings, the present invention provides a method for repairing cellulose insulation paper damage based on mechanically enhanced microcapsules. This method solves the problem that the microcapsules in traditional insulation paper are prone to premature rupture under external stress, resulting in premature leakage of the repair agent and low repair efficiency. The microcapsules of the present invention can effectively enhance the mechanical and electrical properties of the insulation paper. Using the cellulose insulation paper of the present invention for electrical damage repair can improve the efficiency and accuracy of the repair process. The specific technical solution is as follows:

[0006] A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules is disclosed. The method uses cellulose insulation paper based on mechanically enhanced microcapsules to repair damage. The mechanically enhanced microcapsules are mainly made of capsule walls and core materials. The capsule walls include polyurethane and nano-silica, and the core materials include DCPD (dicyclopentadiene) and a Hoveyda-Grubbs catalyst.

[0007] Preferably, the particle size of the mechanically enhanced microcapsules is 2 μm to 10 μm, and the capsule wall thickness is 200 nm to 1 μm.

[0008] Preferably, the particle size of the nano-silicon dioxide is 20 nm to 50 nm.

[0009] Preferably, it is characterized in that the preparation method of the mechanically enhanced microcapsules comprises the following steps:

[0010] (1) Nano-silica dispersion treatment: Disperse nano-silica in water or ethanol, and perform ultrasonic treatment or high-speed stirring to obtain a nano-silica suspension;

[0011] (2) Preparation of core material solution: After dissolving DCPD in an organic solvent, slowly add 0.5 to 5 mol% of the total amount of DCPD into Hoveyda-Grubbs catalyst and stir evenly to form a core material solution;

[0012] (3) Preparation of capsule wall solution: gradually adding a polyurethane precursor to the nano-silica suspension and continuously stirring to obtain a capsule wall solution; the weight ratio of the polyurethane precursor to the nano-silica suspension is 1:4-6;

[0013] (4) Emulsion preparation: adding the core material solution dropwise to the capsule wall solution to obtain a mixture, mixing the mixture with deionized water containing a surfactant (PVA), and stirring at a high speed of 1000 to 3000 rpm to obtain an emulsion;

[0014] (5) Capsule wall polymerization and microcapsule formation: adjusting the pH value of the emulsion to 7-9 and heating it to 50-70° C. to generate a polyurethane capsule wall through interfacial polymerization, and uniformly embedding nano-silica into the capsule wall to form microcapsules;

[0015] (6) Microcapsule separation and washing: filtering or centrifuging the material after the reaction in step (5), and washing the separated microcapsules;

[0016] (7) Curing and drying treatment: The washed microcapsules are dried at 60-80° C. to obtain the enhanced microcapsules.

[0017] Preferably, in step (2), the organic solvent is toluene.

[0018] Preferably, in step (3), the polyurethane precursor is prepared by mixing isocyanate and polyol in a molar ratio of 1:1 to 1.1.

[0019] Preferably, the cellulose insulation paper based on mechanically enhanced microcapsules comprises the following raw materials in weight percentage: 1-4% mechanically enhanced microcapsules, 80-90% softwood pulp, 3-7% polyamide fiber, 1-5% nanofiller, 0.5-2.5% antioxidant and 0.5-2% lubricant.

[0020] Preferably, the nanofiller is nano-alumina, the antioxidant is tocopherol, and the lubricant is dimethyl silicone oil.

[0021] Preferably, the method for preparing the mechanically enhanced microcapsule-based cellulose insulation paper comprises the following steps:

[0022] (1) Weigh each raw material according to weight percentage;

[0023] (2) soaking and dispersing the softwood pulp, cutting the polyamide fiber into 3-6 mm segments, adding the segments together into deionized water and mixing and stirring uniformly to prepare a slurry with a concentration of 5-10%, then adding the nanofiller, antioxidant and lubricant into the slurry and mixing and stirring uniformly, finally adding the mechanically enhanced microcapsules and stirring at a low speed of 50-70 rpm for 5-10 minutes to obtain a mixed slurry;

[0024] (3) The mixed slurry is evenly spread on a filter screen to form a wet paper blank, which is vacuum-absorbed and pressed, and then dried at 80 to 120° C. for 1 to 2 hours. The dried paper is subjected to high-temperature and high-pressure treatment and calendering treatment to obtain the cellulose insulating paper based on mechanically enhanced microcapsules.

[0025] Preferably, the temperature of the high temperature and high pressure treatment is 150-200°C, and the pressure is 12-15 MPa; the temperature of the calendering treatment is controlled at 100-150°C, the pressure is 10-20 MPa, and the calendering speed is controlled at 1-2 m / min.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention improves the microcapsules in cellulose insulating paper, effectively reducing premature leakage of the repair agent and ensuring accurate release of the repair agent when damage occurs. The microcapsules of the present invention can effectively enhance the mechanical and electrical properties of the insulating paper. Using the cellulose insulating paper of the present invention for damage repair can improve the efficiency and accuracy of the repair process, providing a new technical approach to solving the problem of electrical damage repair in cellulose insulating paper and having broad application prospects.

[0028] 2. The improvement of the microcapsules of the present invention specifically utilizes polyurethane as the capsule wall material and incorporates silica (SiO2) nanoparticles into the capsule wall. The polyurethane in the capsule wall has good elasticity and durability, effectively resisting external stress. The silica nanoparticles serve as a reinforcing material, with high hardness, excellent thermal stability and mechanical properties, further enhancing the tensile strength and fracture toughness of the microcapsules. The silica particles are uniformly dispersed in the polyurethane matrix. The resulting nanocomposite material not only enhances the overall mechanical properties of the microcapsules and increases their stability under high stress conditions, but also improves the density of the capsule wall, reduces the risk of premature leakage of the repair agent, and ensures the efficient execution of the repair process.

[0029] 3. When damage such as electrical treeing and cracking occurs, the microcapsules of the present invention can promptly release a repair agent, effectively performing self-repair. In particular, the use of a two-component repair agent (DCPD and a Hoveyda-Grubbs catalytic system) allows for rapid repair reactions, further improving repair efficiency. The application of these mechanically enhanced microcapsules to repair cellulose insulating paper not only effectively slows the expansion of electrical treeing and repairs cracks, but also significantly improves key performance indicators such as the dielectric constant and breakdown strength of the insulating paper, thereby enhancing the overall performance and service life of the insulating paper.

[0030] 4. The present invention reduces material waste and negative impact on substrate performance by optimizing the release mechanism of microcapsules, meets the requirements of green environmental protection and sustainable development, and reduces the cost of repair materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments.

[0032] Figure 1 : Flowchart of the method of the present invention, specifically including the steps of microcapsule and cellulose insulation paper modeling, molecular simulation to performance evaluation;

[0033] Figure 2 :Comparison of tensile strength properties of microcapsules doped with different nanomaterials:

[0034] Figure 3: Comparison of fracture toughness properties of microcapsules doped with different nanomaterials;

[0035] Figure 4 : Comparison of elastic modulus properties of microcapsules doped with different nanomaterials;

[0036] Figure 5 : Comparison of the fracture toughness of insulating paper after repair with different microcapsules (undoped microcapsules and mechanically reinforced microcapsules doped with nano-silica);

[0037] Figure 6 : Comparison of the tensile strength of insulating paper after repair with different microcapsules (undoped microcapsules and mechanically reinforced microcapsules doped with nano-silica);

[0038] Figure 7 : Comparison of dielectric constants of insulating paper after repair with different microcapsules (undoped microcapsules and mechanically reinforced microcapsules doped with nano-silica);

[0039] Figure 8 : Comparison of the breakdown strength of insulating paper after repair with different microcapsules (undoped microcapsules and mechanically reinforced microcapsules doped with nano-silica). DETAILED DESCRIPTION

[0040] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0041] Example 1

[0042] The mechanically enhanced microcapsules in this example are made of polyurethane (PU) and nano-silica (20 nm particle size) as the wall material, and DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst as the core material. The mechanically enhanced microcapsules in this example have a particle size of 2 μm and a wall thickness of 200 nm. The preparation method is as follows:

[0043] (1) Nano-silicon dioxide dispersion treatment: disperse nano-SiO2 in water and treat with ultrasonic waves to obtain nano-SiO2 suspension;

[0044] (2) Preparation of core material solution: After dissolving DCPD in toluene, slowly add 0.5 mol% of the total amount of DCPD into Hoveyda-Grubbs catalyst and stir evenly to form a core material solution;

[0045] (3) Preparation of capsule wall solution: gradually adding a polyurethane precursor to the nano-SiO2 suspension and continuously stirring to obtain a capsule wall solution; the weight ratio of the polyurethane precursor to the nano-SiO2 suspension is 1:4; the polyurethane precursor is prepared by mixing isocyanate and polyol in a molar ratio of 1:1;

[0046] (4) Emulsion preparation: adding the core material solution dropwise to the capsule wall solution to obtain a mixture, mixing the mixture with deionized water containing a surfactant (PVA), and stirring at a high speed of 1000 rpm to obtain an emulsion;

[0047] (5) Capsule wall polymerization and microcapsule formation: the pH value of the emulsion is adjusted to 7, and the temperature is raised to 50° C., a polyurethane capsule wall is generated by interfacial polymerization, and nano-SiO2 is uniformly embedded in the capsule wall to form microcapsules;

[0048] (6) Microcapsule separation and washing: filtering the material after the reaction in step (5) and washing the separated microcapsules;

[0049] (7) Curing and drying treatment: The washed microcapsules are dried at 60° C. to obtain the enhanced microcapsules.

[0050] In this embodiment, a cellulose insulation paper based on mechanically reinforced microcapsules comprises the following raw materials in weight percentage: 1% mechanically reinforced microcapsules, 90% softwood pulp, 3% polyamide fiber, 1% nano-alumina, 2.5% tocopherol, and 2.5% dimethyl silicone oil. The preparation method is as follows:

[0051] (1) Weigh each raw material according to weight percentage;

[0052] (2) soaking and dispersing the softwood pulp, cutting the polyamide fiber into 3-6 mm segments, adding the segments together into deionized water and mixing and stirring uniformly to prepare a slurry with a concentration of 5%, then adding the nano-alumina, tocopherol and dimethyl silicone oil into the slurry and mixing and stirring uniformly, finally adding the mechanically enhanced microcapsules and stirring at a low speed of 50 rpm for 10 minutes to obtain a mixed slurry;

[0053] (3) The mixed slurry is evenly spread on a filter screen to form a wet paper blank. After vacuum absorption and pressing, the wet paper blank is dried at 80°C for 1 hour. The dried paper blank is subjected to a high-temperature and high-pressure treatment and a calendering treatment to obtain the cellulose insulation paper based on mechanically enhanced microcapsules. The temperature of the high-temperature and high-pressure treatment is 150°C and the pressure is 12 MPa; the temperature of the calendering treatment is controlled at 100°C, the pressure is 10 MPa, and the calendering speed is controlled at 1 m / min.

[0054] Example 2

[0055] The mechanically enhanced microcapsules in this example are made of polyurethane (PU) and nano-silica (50 nm particle size) as the wall material, and DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst as the core material. The mechanically enhanced microcapsules in this example have a particle size of 10 μm and a wall thickness of 1 μm. The preparation method is as follows:

[0056] (1) Nano-silicon dioxide dispersion treatment: disperse nano-SiO2 in water and treat with ultrasonic waves to obtain nano-SiO2 suspension;

[0057] (2) Preparation of core material solution: After dissolving DCPD in toluene, slowly add 5 mol% of the total amount of DCPD Hoveyda-Grubbs catalyst and stir evenly to form a core material solution;

[0058] (3) Preparation of capsule wall solution: gradually adding a polyurethane precursor to the nano-SiO2 suspension and continuously stirring to obtain a capsule wall solution; the weight ratio of the polyurethane precursor to the nano-SiO2 suspension is 1:6; the polyurethane precursor is prepared by mixing isocyanate and polyol in a molar ratio of 1:1.1;

[0059] (4) Emulsion preparation: adding the core material solution dropwise to the capsule wall solution to obtain a mixture, mixing the mixture with deionized water containing a surfactant (PVA), and stirring at a high speed of 3000 rpm to obtain an emulsion;

[0060] (5) Capsule wall polymerization and microcapsule formation: the pH value of the emulsion is adjusted to 9, and the temperature is raised to 70°C. The polyurethane capsule wall is generated by interfacial polymerization, and the nano-SiO2 is uniformly embedded in the capsule wall to form microcapsules;

[0061] (6) Microcapsule separation and washing: centrifuging the material after the reaction in step (5), and washing the separated microcapsules;

[0062] (7) Curing and drying treatment: The washed microcapsules are dried at 80° C. to obtain the enhanced microcapsules.

[0063] In this embodiment, a cellulose insulation paper based on mechanically reinforced microcapsules comprises the following raw materials in percentage by weight: 4% mechanically reinforced microcapsules, 83% softwood pulp, 7% polyamide fiber, 5% nano-alumina, 0.5% tocopherol, and 0.5% dimethyl silicone oil. The preparation method is as follows:

[0064] (1) Weigh each raw material according to weight percentage;

[0065] (2) soaking and dispersing the softwood pulp, cutting the polyamide fiber into 3-6 mm segments, adding the segments together into deionized water, and mixing and stirring uniformly to prepare a slurry with a concentration of 10%, then adding the nano-alumina, tocopherol, and dimethyl silicone oil into the slurry, and mixing and stirring uniformly, and finally adding the mechanically enhanced microcapsules and stirring at a low speed of 70 rpm for 5 minutes to obtain a mixed slurry;

[0066] (3) The mixed slurry is evenly spread on a filter screen to form a wet paper blank. After vacuum absorption and pressing, the wet paper blank is dried at 120° C. for 2 hours. The dried paper blank is subjected to a high-temperature and high-pressure treatment and a calendering treatment to obtain the cellulose insulation paper based on mechanically enhanced microcapsules. The temperature of the high-temperature and high-pressure treatment is 200° C. and the pressure is 15 MPa; the temperature of the calendering treatment is controlled at 150° C. and the pressure is 20 MPa, and the calendering speed is controlled at 2 m / min.

[0067] Example 3

[0068] The mechanically enhanced microcapsules in this example are made of polyurethane (PU) and nano-silica (30 nm particle size) as the wall material, and DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst as the core material. The mechanically enhanced microcapsules in this example have a particle size of 6 μm and a wall thickness of 600 nm. The preparation method is as follows:

[0069] (1) Nano-silicon dioxide dispersion treatment: Disperse nano-SiO2 in water or ethanol, and ultrasonicate or stir at high speed to obtain nano-SiO2 suspension;

[0070] (2) Preparation of core material solution: After dissolving DCPD in toluene, slowly add 3 mol% of the total amount of DCPD Hoveyda-Grubbs catalyst and stir evenly to form a core material solution;

[0071] (3) Preparation of capsule wall solution: gradually adding a polyurethane precursor to the nano-SiO2 suspension and continuously stirring to obtain a capsule wall solution; the weight ratio of the polyurethane precursor to the nano-SiO2 suspension is 1:5; the polyurethane precursor is prepared by mixing isocyanate and polyol in a molar ratio of 1:1.1;

[0072] (4) Emulsion preparation: adding the core material solution dropwise to the capsule wall solution to obtain a mixture, mixing the mixture with deionized water containing a surfactant (PVA), and stirring at a high speed of 2000 rpm to obtain an emulsion;

[0073] (5) Capsule wall polymerization and microcapsule formation: the pH value of the emulsion is adjusted to 8, and the temperature is raised to 60° C., a polyurethane capsule wall is generated by interfacial polymerization, and nano-SiO2 is uniformly embedded in the capsule wall to form microcapsules;

[0074] (6) Microcapsule separation and washing: filtering the material after the reaction in step (5) and washing the separated microcapsules;

[0075] (7) Curing and drying treatment: The washed microcapsules are dried at 70° C. to obtain the enhanced microcapsules.

[0076] In this embodiment, a cellulose insulation paper based on mechanically reinforced microcapsules comprises the following raw materials in percentage by weight: 2% mechanically reinforced microcapsules, 88% softwood pulp, 5% polyamide fiber, 3% nano-alumina, 1% tocopherol, and 1% dimethyl silicone oil. The preparation method is as follows:

[0077] (1) Weigh each raw material according to weight percentage;

[0078] (2) soaking and dispersing the softwood pulp, cutting the polyamide fiber into 3-6 mm segments, adding the segments together into deionized water and mixing and stirring uniformly to prepare a slurry with a concentration of 7%, then adding the nanofiller, antioxidant, and lubricant into the slurry and mixing and stirring uniformly, finally adding the mechanically enhanced microcapsules and stirring at a low speed of 60 rpm for 8 minutes to obtain a mixed slurry;

[0079] (3) The mixed slurry is evenly spread on a filter screen to form a wet paper blank. After vacuum absorption and pressing, the wet paper blank is dried at 100° C. for 1.5 hours. The dried paper is subjected to a high-temperature and high-pressure treatment and calendering treatment to obtain the cellulose insulation paper based on mechanically enhanced microcapsules. The temperature of the high-temperature and high-pressure treatment is 180° C. and the pressure is 14 MPa; the temperature of the calendering treatment is controlled at 120° C. and the pressure is 15 MPa, and the calendering speed is controlled at 1.5 m / min.

[0080] Comparative Example 1

[0081] The capsule wall material of the microcapsules in this comparative example is polyurethane (PU), and the core material is DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst. Other raw materials and preparation methods are the same as those in Example 1.

[0082] Comparative Example 2

[0083] The capsule wall materials of the microcapsules in this comparative example are polyurethane (PU) and nano-aluminum oxide, and the core materials are DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst. Other raw materials and preparation methods are the same as those in Example 1.

[0084] Comparative Example 3

[0085] The capsule wall materials of the microcapsules in this comparative example are polyurethane (PU) and nano-magnesium oxide, and the core materials are DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst. Other raw materials and preparation methods are the same as those in Example 1.

[0086] Performance testing:

[0087] 1. Performance testing of the microcapsules prepared in Example 1 and the comparative examples by constructing a model

[0088] (1) Establishing a microcapsule model of Comparative Example 1: Polyurethane (PU) was selected as the capsule wall material of the microcapsule, and DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst were used as the two-component core material to establish a microcapsule model.

[0089] (2) Establishing the mechanically enhanced microcapsule model of Example 1: Polyurethane (PU) and silica nanoparticles were selected as the capsule wall materials of the microcapsule, and DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst were used as the two-component core materials to establish a mechanically enhanced microcapsule model.

[0090] (3) Establishing the microcapsule model of Comparative Example 2: Polyurethane (PU) and nano-aluminum oxide were selected as the capsule wall materials of the microcapsule, DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst were used as the two-component core materials, and a mechanically enhanced microcapsule model was established.

[0091] (4) Establishing the microcapsule model of Comparative Example 3: Polyurethane (PU) and nano-magnesium oxide were selected as the capsule wall materials of the microcapsule, DCPD (dicyclopentadiene) and Hoveyda-Grubbs catalyst were used as the two-component core materials, and a mechanically enhanced microcapsule model was established.

[0092] The tensile strength and fracture toughness of the microcapsule model were analyzed using the Structural Mechanics Module in COMSOL software, and the mechanical properties of the microcapsule models were compared with those of the microcapsule wall structures. The results are shown in Table 1.

[0093] Table 1 Improvement of mechanical properties of microcapsules doped with three nanomaterials

[0094]

[0095] The table above shows that the addition of nano-silica generally improves the material's compressive and flexural strength due to its high hardness and good wear resistance. The addition of nano-alumina significantly improves the material's strength and hardness, particularly in terms of wear resistance, maintaining strength while increasing toughness. The addition of nano-magnesium oxide generally improves the material's tensile strength, but the increase may not be as significant as with nano-silica and nano-alumina. Nano-magnesium oxide helps improve the material's toughness and reduce the risk of brittle fracture.

[0096] A comprehensive comparison of the effects of adding the three materials on the mechanical properties of microcapsules shows that nano-silica significantly improves the elastic modulus and tensile strength, while nano-aluminum oxide slightly improves the fracture toughness index, with little change in the Poisson's ratio. The addition of nano-magnesium oxide, on the other hand, does not improve mechanical properties as much as the first two. Furthermore, nano-magnesium oxide reduces the material's ability to deform laterally under stress, leading to a slight decrease in the Poisson's ratio. Nano-silicon dioxide is low-cost, easily accessible, and environmentally friendly. Nano-aluminum oxide, on the other hand, is relatively expensive. Overall, using nano-silicon dioxide is the best choice.

[0097] 2. Demonstrate the repair of insulation paper by microcapsules through model construction

[0098] (1) Establish a three-dimensional geometric model of cellulose insulating paper: Use the Structural Mechanics Module in COMSOL software to establish a three-dimensional geometric model of cellulose insulating paper and simulate its mechanical properties. Set the material parameter range as follows: the elastic modulus of cellulose is 10GPa, and the Poisson's ratio is 0.3; the elastic modulus of PU microcapsules is 1.8GPa, and the Poisson's ratio is 0.35; the elastic modulus of DCPD / Hoveyad-Grubbs repair agent is 1.5GPa, and the Poisson's ratio is 0.35. Set the lower boundary to be fixed, and apply a tensile load of 50MPa to the top. Apply the same external force to the two microcapsule models of Example 1 and Comparative Example 1, observe their deformation and rupture behavior under stress, and record mechanical properties such as tensile strength, fracture toughness and elastic modulus.

[0099] (2) Establishing a crack model and an electrical tree model for cellulose insulating paper: In COMSOL software, the AC / DC Module was used to establish a crack model and an electrical tree model for cellulose insulating paper to simulate the generation and expansion process of electrical trees. The microcapsule model of Example 1 and Comparative Example 1 was introduced, and the Electrostatics interface of the module was used to simulate the release and diffusion process of the repair agent after the mechanically enhanced microcapsules ruptured at the cracks and electrical trees. The reaction effect of the core material at the damaged area was observed to analyze the mechanism of the repair process. At the same time, the Dielectric Breakdown function was used to analyze electrical properties such as dielectric constant and breakdown strength.

[0100] (3) Record the mechanical and electrical properties of the cellulose insulation paper before and after repair. Use the Structural Mechanics Module to focus on testing its mechanical properties such as tensile strength, fracture toughness, and modulus, and use the AC / DC Module to focus on testing its electrical properties such as dielectric constant and breakdown strength. Use the Multiphysics (multi-physics field coupling) function to combine the coupling analysis of mechanical and electrical properties to evaluate the improvement effect of microcapsules on the performance of the insulation paper. At the same time, use the Electric Field (electric field) interface to observe the changes in the electric field distribution after repair, and record the electrical breakdown behavior to complete the overall evaluation of the repair effect.

[0101] Create a three-dimensional geometric model of cellulose insulation paper in the COMSOL geometry module, setting the thickness to 0.2mm, the width to 600mm, and the length to 1500mm. Select cellulose material in the "Material" module. Set the elastic modulus to 8-12GPa and the Poisson's ratio to 0.25-0.35. In the "Physics Module", select "Solid Mechanics" and set the boundary conditions. The bottom boundary is set to a fixed boundary condition and is not affected by any displacement. Apply uniform tensile stress or displacement to the upper surface (z = 0.2mm), and the tensile stress in the vertical direction can be set to 40-60MPa. It is used to simulate the tensile load on the insulation paper under actual working conditions, so as to analyze its stress and deformation under the action of the load. The measured boundaries are set as free boundaries, and no constraints or loads are applied. Left side (x = 0), right side (x = 1500mm), front side (y = 0), back side (y = 600mm): free boundaries.

[0102] Duplicate the first insulation paper model and name it "Microcrack Model." Add a microcrack feature to the geometry (use the "Cut" function to create a crack in the insulation paper with a length of 0.5 mm and a width of 0.1 mm. Represent the crack by creating a rectangle or line segment at the appropriate location in the insulation paper, ensuring that it penetrates the thickness of 0.2 mm). Ensure that the material properties are the same as the first model. In the boundary conditions, simulate electrical damage (you can set non-uniform loads or localized stress concentrations). Run the simulation and record the stress concentration and deformation in the crack area.

[0103] Use the microcapsule model in Example 1 to repair the microcracks in the insulating paper. In the "Physics" module, select the contact type (such as "Adhesion" or "Contact") to simulate the interaction between the microcapsules and the cracks. Apply boundary conditions. Fix the boundary and keep the bottom of the insulating paper fixed (z = 0). Apply a tensile load: Apply a uniform tensile stress (for example, 40-60 MPa) on the upper surface to simulate external conditions. Run the simulation and observe the stress distribution and performance recovery of the model after repair (see Tables 2 and 3 for details).

[0104] Table 2 Changes in mechanical properties of insulating paper

[0105] parameter Cellulose insulation paper (undamaged) Microcrack model Repaired insulation paper Tensile strength (MPa) 50 40 60 Fracture toughness (MPa·m^1 / 2) 1.6 1.2 1.84 Elastic modulus (GPa) 10 8 9

[0106] Table 3 Changes in electrical properties of insulating paper

[0107] parameter Cellulose insulation paper (undamaged) Microcrack model Repaired insulation paper Dielectric constant 3.5 2.5 3.2 Breakdown strength (kV / mm) 20 15 19

[0108] Microcapsules without nanosilica (Comparative Example 1) were used to repair microcracks in insulating paper. The effectiveness of nanosilica-doped and undoped microcapsules in repairing cracks in insulating paper was compared, including expected mechanical and electrical performance data. The results are shown in Tables 4 and 5.

[0109] Table 4 Comparison of mechanical properties of two microcapsule repaired insulation papers

[0110] parameter Nano-silica-doped microcapsule repair Microcapsule repair without nano-silica Tensile strength (MPa) 60 55 Fracture toughness (MPa·m^1 / 2) 1.84 1.76 Elastic modulus (GPa) 9 7

[0111] Table 5 Comparison of electrical properties of two microcapsule-repaired insulating papers

[0112] parameter Nano-silica-doped microcapsule repair Microcapsule repair without nano-silica Dielectric constant 3.2 2.8 Breakdown strength (kV / mm) 19 16

[0113] In terms of tensile strength, the nano-silica-doped microcapsules provide improved filling and adhesion, enhancing crack reinforcement and preventing brittle fracture. In terms of fracture toughness, the introduction of nano-silica increases the microcapsules' toughness, allowing the material to better disperse stress when subjected to force, enhancing its resistance to impact. In terms of elastic modulus, the doping material increases the rigidity of the polyurethane. Although the elastic modulus is higher in the intact state, it remains relatively high after repair. Analysis of the dielectric constant indicates that the structural density of the repaired material is increased, and the addition of nano-silica may have improved electrical insulation properties. The high surface area and good dispersion of nano-silica fill cracks, forming a more uniform repair layer, thereby reducing air gaps within the cracks and reducing local electric field concentration effects, resulting in a slight increase in the dielectric constant. In terms of breakdown strength, nano-silica has a relatively high dielectric constant. The doping of the microcapsules improves the insulation properties of the microcapsules, and the crack filling creates a more stable electric field distribution, thereby improving breakdown strength. At the same time, nano-silica particles have a tiny size and high surface area at the nanoscale, which makes it easier for them to distribute into microcracks when the microcapsules rupture, reducing the electric field concentration phenomenon, thereby improving the integrity and effectiveness of the repair layer. The internal structure of the repaired material is more uniform and the defects are reduced, so it can withstand higher electric field strength and improve the breakdown strength.

[0114] Nano-silica-doped microcapsules offer significant advantages in repairing insulating paper, effectively improving tensile strength, fracture toughness, and electrical properties. Compared to undoped microcapsules, the doped microcapsules demonstrate significantly higher repair efficiency across various parameters, demonstrating superior repair effectiveness.

[0115] In summary, the present invention improves the microcapsules in cellulose insulating paper, effectively reducing the premature leakage of the repair agent and ensuring that the repair agent can be accurately released when damage occurs; the microcapsules of the present invention can effectively enhance the mechanical and electrical properties of the insulating paper. Using the cellulose insulating paper of the present invention for electrical damage repair can improve the efficiency and accuracy of the repair process, providing a new technical approach to solving the problem of electrical damage repair of cellulose insulating paper and has broad application prospects.

[0116] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules, characterized in that: The damage of cellulose insulation paper is repaired by using mechanically enhanced microcapsules, wherein the mechanically enhanced microcapsules are made of capsule walls and core materials, wherein the capsule walls include polyurethane and nano-silica, and the core materials include dicyclopentadiene and Hoveyda-Grubbs catalyst; The preparation method of the mechanically enhanced microcapsules comprises the following steps: (1) Nano-silica dispersion treatment: Nano-silica is dispersed in ethanol and ultrasonically treated to obtain a nano-silica suspension; (2) Preparation of core material solution: After dissolving dicyclopentadiene in an organic solvent, slowly add 0.5 to 5 mol% of the total amount of dicyclopentadiene into the Hoveyda-Grubbs catalyst and stir evenly to form a core material solution; (3) Preparation of capsule wall solution: gradually adding a polyurethane precursor to the nano-silica suspension and continuously stirring to obtain a capsule wall solution; the weight ratio of the polyurethane precursor to the nano-silica suspension is 1:4-6; (4) Emulsion preparation: adding the core material solution dropwise to the capsule wall solution to obtain a mixture, mixing the mixture with deionized water containing a surfactant, and stirring at high speed to obtain an emulsion; (5) Capsule wall polymerization and microcapsule formation: the pH value of the emulsion is adjusted to 7-9, and the temperature is raised to 50-70°C, and a polyurethane capsule wall is generated by interfacial polymerization, and nano-silica is uniformly embedded in the capsule wall to form microcapsules; (6) Microcapsule separation and washing: filtering the material after the reaction in step (5) and washing the separated microcapsules; (7) Curing and drying treatment: The washed microcapsules are dried at 60-80°C to obtain the enhanced microcapsules.

2. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 1, characterized in that: The particle size of the mechanically enhanced microcapsules is 2µm-10µm, and the capsule wall thickness is 200nm-1µm.

3. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 1, characterized in that: The particle size of the nano-silicon dioxide is 20nm~50nm.

4. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 1, characterized in that: In step (2), the organic solvent is toluene.

5. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 1, characterized in that: In step (3), the polyurethane precursor is prepared by mixing isocyanate and polyol in a molar ratio of 1:1 to 1.

1.

6. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 1, characterized in that: The cellulose insulation paper based on mechanically reinforced microcapsules comprises the following raw materials in percentage by weight: 1-4% mechanically reinforced microcapsules, 80-90% softwood pulp, 3-7% polyamide fibers, 1-5% nanofillers, 0.5-2.5% antioxidants, and 0.5-2% lubricants.

7. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 6, characterized in that: The nano filler is nano alumina, the antioxidant is tocopherol, and the lubricant is dimethyl silicone oil.

8. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 6, characterized in that: The method for preparing the mechanically enhanced microcapsule-based cellulose insulation paper comprises the following steps: (1) Weigh each raw material according to weight percentage; (2) First, soak and disperse the softwood pulp, chop the polyamide fiber, add them together in deionized water and mix and stir them evenly to prepare a slurry with a concentration of 5-10%, then add the nanofiller, antioxidant and lubricant to the slurry and mix and stir them evenly, finally add the mechanically enhanced microcapsules and stir at a low speed of 50-70 rpm for 5-10 minutes to obtain a mixed slurry; (3) The mixed slurry is evenly spread on a filter screen to form a wet paper blank. After vacuum water absorption and pressing, the wet paper blank is dried at 80-120°C for 1-2 hours. The dried paper is subjected to high temperature and high pressure treatment and calendering treatment to obtain the cellulose insulating paper based on mechanically enhanced microcapsules.

9. The method for repairing damage to cellulose insulation paper based on mechanically enhanced microcapsules according to claim 8, characterized in that: The temperature of the high temperature and high pressure treatment is 150~200°C, and the pressure is 12~15MPa; the temperature of the calendering treatment is controlled at 100~150°C, the pressure is 10~20MPa, and the calendering speed is controlled at 1~2m / min.

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