Preparation method of single-layer shell-core microcapsule type polyvinyl water tree self-repairing insulating material treated by low-temperature plasma

Abstract

The invention relates to preparation of a single-layer shell-core microcapsule type polyvinyl water tree self-repairing insulating material treated by low-temperature plasma, which is a method for fundamentally prolonging the service life of the insulating material. The invention aims to provide preparation of a single-layer shell-core microcapsule type polyvinyl water tree self-repairing insulating material treated by low-temperature plasma, and the surface characteristics of microcapsules are adjusted by regulating and controlling plasma parameters and plasma discharge time. The dispersity of the microcapsule is improved through plasma surface treatment, the microcapsule is more uniformly and comprehensively distributed in an area where water tree damage is likely to happen, the agglomeration phenomenon is reduced, and local breakdown is prevented. The high breakdown voltage characteristic is achieved, and meanwhile the good self-repairing characteristic is achieved. The microcapsule single-layer shell-core structure can react in time when the water tree is aged, so that the repair rate can be increased, and the repair speed can also be increased. According to the invention, the polyvinyl composite self-repairing material can be obtained.

Description

Technical Field

[0001] The invention belongs to the research field of insulating material self-repairing technology, and specifically relates to a preparation method of a single-layer core-shell microcapsule type polyethylene-based water tree self-repairing insulating material treated with low-temperature plasma. Background Art

[0002] During the manufacturing process of polyethylene cables, due to process limitations, micro defects such as micro cracks and holes are inevitable in their insulation layer. During the laying and operation of the cables, the combined effects of long-term electrothermal stress, chemical corrosion, overvoltage and other factors will also make the number and depth of micro defects more serious. Among them, moisture enters the insulation layer through various means and channels such as air, precipitation, land environment conditions, etc., and reaches the void defects under high field strength, thereby causing water trees. Water trees continue to grow along the direction of the electric field force and begin to branch to form water tree areas. Some of the water trees evolve into electrical trees, which eventually lead to the breakdown of the cable insulation, causing accidents such as combustion and explosion, and seriously threatening the normal operation of the power grid.

[0003] These tiny defects are often formed deep in the material structure. Existing technologies make it difficult to detect tiny defects in the insulation layer of cables during operation. Defect damage can only be detected by partial discharge after a power outage. However, there is no more effective treatment method except for overall replacement. Replacing the cable will consume a lot of manpower, material and financial resources, and will also generate a lot of waste, resulting in a waste of resources. If the insulating material itself has self-repairing capabilities, it can automatically detect and repair tiny defects in the early stages of their occurrence, which can inhibit the development of damage, effectively restore the performance of the material, and extend the service life of the material. Therefore, it is necessary to develop a polyethylene-based composite water tree microcapsule with self-repairing capabilities to fundamentally explore methods to extend the operating life of insulating materials.

[0004] Compared with traditional material modification methods such as chemical, mechanical and electrochemical methods, plasma modification methods have the advantages of mild treatment conditions, simple operation and easy control. In terms of gas-phase plasma, gas-phase chemical deposition and nano-modification technology have received widespread attention from researchers. Plasma modification technology is highly favored in material modification due to four major advantages: ① low temperature required for the reaction environment; ② high treatment efficiency; ③ wide range of applications; ④ will not destroy the properties of the material itself. Yang Guoqing et al. used CF4 / N2 plasma to synergize coupling agents to modify nano-SiO2 fillers, change their interface characteristics in the matrix, and prepare nano-SiO2 / epoxy resin composites with different mass fractions. The results show that plasma fluorination can effectively graft fluorine elements on the surface of particles, hinder the migration of carriers inside the material, and improve the electrical properties of the composite material.

[0005] When microcapsules are doped into a polyethylene matrix, they tend to aggregate in the polymer due to their high specific surface area and surface activity. The microcapsules tend to accumulate charge at the aggregated locations, causing local breakdown. In addition, the existing microcapsule-type self-healing materials have the problem of catalyst and repair liquid being separated, resulting in damage defects that can only be repaired when both the catalyst and the repair liquid are present, i.e., there are problems such as low repair efficiency and limited repair area. Therefore, this project aims to break through the bottleneck of the difficulty in co-optimization of polymer materials and microcapsules, and to produce materials with high breakdown voltage characteristics and self-healing properties, that is, to provide a method for preparing a single-layer core-shell microcapsule-type polyethylene-based water tree self-healing insulating material treated with low-temperature plasma. Multilayer core-shell microcapsules surface-modified with plasma technology can reduce the agglomeration of microcapsules, while the single-layer core-shell structure can greatly improve the repair rate while also having good dielectric properties. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies in the prior art. The present invention provides a method for preparing a single-layer core-shell microcapsule polyethylene-based water tree self-repairing insulating material treated with low-temperature plasma, which is an extension and development of the self-repairing technology of insulating materials.

[0007] The purpose of the present invention is achieved through the following technical solutions: A method for preparing a low-temperature plasma treated single-layer core-shell microcapsule type polyethylene-based water tree self-repairing insulating material, comprising the preparation of UF prepolymer, the preparation of a single-layer core-shell microcapsule water phase, the formation of a single-layer core-shell microcapsule, and the drying of the single-layer core-shell microcapsule to obtain a repaired polyethylene-based self-repairing composite medium water tree microcapsule. The surface of the microcapsule is treated by plasma to obtain the treated microcapsule, which is then melt blended, cross-linked, and vacuum dried to obtain a plasma-treated multi-layer core-shell microcapsule type polyethylene-based self-repairing composite medium. Specifically comprising the following steps: (1) Preparation of UF prepolymer: Dissolve urea in deionized water, add 37% formaldehyde solution, adjust the pH of the system to 8-9 with TEA, and then keep the reaction at 70°C for 60 minutes, and then cool to room temperature. The obtained UF prepolymer is a colorless, transparent solution with a certain viscosity. (2) Preparation of the aqueous phase of the single-layer core-shell microcapsules: In a water bath at 40° C., the emulsifier styrene-maleic anhydride copolymer, LABSA and deionized water were mixed and stirred for 30 minutes until the solution became white milky. (3) Formation of single-layer core-shell microcapsules: Sodium hydroxide solution was used to slowly increase the pH of the solution to 9-10, and ammonium chloride, resorcinol, and UF prepolymer were added dropwise in sequence. Then, citric acid was used to slowly reduce the pH of the solution to about 3.0, and the mixture was stirred and reacted at 53°C for 3 hours. (4) Drying treatment of single-layer core-shell microcapsules: After completion, the product was filtered using slow double-circle qualitative filter paper, washed three times with alcohol and deionized water respectively to remove impurities and obtain a filter cake. Finally, it was dried at 25°C for 48 hours to obtain a powdered single-layer core-shell microcapsule sample. (5) Plasma treatment of microcapsule surface: During the experiment, the microcapsules were evenly spread on the dielectric plate, and the mass flow meter was used to control the flow ratio of CF4:N2 to 25:1. After the airflow was stable, the high-frequency AC power supply was adjusted to apply 7kV and 9kHz voltages. The plasma treatment lasted for 10 minutes, and the treated microcapsules were collected and stored. Similarly, the power supply voltage amplitude, frequency, action time, atmosphere and other parameters were changed to perform plasma treatment on the microcapsule surface, and the treated microcapsules were collected, labeled and stored. (6) Melt blending: After the temperature of the torque rheometer is set to 110 °C and the speed is set to 60 rpm, LDPE is placed in the torque rheometer. After LDPE is in a molten state and the torque is stable, antioxidants, microcapsules, and DCP are added in order. The mixing time is 20 minutes in total. After completion, the uniformly mixed composite material is taken out and cut into small particles for later use. (7) Determine the shape: Make a corresponding mold according to the shape of the sample and calculate the mass of the required composite material. Set the temperature of the flat vulcanizer to 110°C, put the composite material in, heat for 15 minutes, and then increase the pressure every 5 minutes. Observe the pressure gauge in time and add pressure in time if the pressure is insufficient. (8) Cross-linking reaction: The temperature of another plate vulcanizer was set to 175°C. The above molten materials were placed in the plate vulcanizer and the pressure was increased to 15 MPa. The pressure was supplemented at any time. After heating for 35 minutes, the sample was fully cooled. (9) Vacuum drying: The temperature of the vacuum drying oven was set at 80°C, and the XLPE was vacuum dried to obtain a multilayer core-shell structure microcapsule / XLPE water tree self-healing material surface-treated by plasma technology.

[0008] In the technical solution of the present invention: the mass ratio of the urea-formaldehyde resin wall material to the repair material core material in (3) is 2:1.

[0009] In the technical solution of the present invention: the purpose of increasing the pressure in (7) is to fully shape the material so that the impurity gas in the material can be fully discharged.

[0010] In the technical solution of the present invention: the purpose of step (9) is to reduce the influence of the cross-linking byproducts and residual stress inside the sample on the test.

[0011] Compared with the prior art, the advantages of the present invention are: (1) The reaction between the repair fluid and the catalyst consumes the moisture in the insulator. The organic polymer formed after the reaction fills the micropores, thereby eliminating the water tree and restoring the insulation performance of the aged cable. Silicone resin is not easy to decompose at high temperatures, has the characteristics of high voltage resistance and good insulation performance, and has similar properties to polyethylene, and can effectively fill the voids formed by water trees. (2) The single-layer core-shell structure of the microcapsules can not only separate the repair liquid from the catalyst during the production process to ensure that the repair material does not react with water, but also ensure that the microcapsules do not come into contact with water when the microcapsule / polyethylene self-healing composite medium does not undergo water tree aging, thus avoiding ineffective reactions. (3) The single-layer core-shell microcapsules treated with plasma surface treatment can make the microcapsules in the composite medium distributed independently in the composite material, improve the dispersibility of the microcapsules, and reduce the occurrence of agglomeration. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 1 is a SEM image, in which 1 is the prepared single-layer core-shell microcapsule.

[0013] Figure 2 This is the morphology of water tree branches formed after the composite medium accelerated water tree aging experiment.

[0014] Figure 3 This is the water tree aging repair diagram of the composite medium.

[0015] Figure 4 Schematic diagram of the internal structure of single-layer core-shell microcapsules with plasma-treated microcapsule surface. DETAILED DESCRIPTION

[0016] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0017] Specific implementation method: This implementation method is a method for preparing a single-layer core-shell microcapsule polyethylene-based water tree self-repairing insulation material, which is specifically completed according to the following steps: (1) Preparation of UF prepolymer: 20 g of urea was dissolved in 60 g of deionized water, and then a 37% formaldehyde solution was added. The mixture was stirred at 300-400 rpm by magnetic force, and the pH of the system was adjusted to 8-9 with TEA. The mixture was then kept at 70° C. for 60 minutes and then cooled to room temperature. The obtained UF prepolymer was a colorless, transparent solution with a certain viscosity. (2) Preparation of the aqueous phase of the single-layer core-shell microcapsules: 1.5 g of emulsifier styrene-maleic anhydride copolymer, 20 g of catalyst LABSA and 45 g of deionized water were mixed and stirred at 40° C. for 30 minutes at a speed of 500 rpm until the solution became white milky. (3) Formation of single-layer core-shell microcapsules: Sodium hydroxide solution was used to slowly increase the pH of the solution to 9-10, and 1 g of ammonium chloride, 2 g of resorcinol, and UF prepolymer were added dropwise in sequence. Then, citric acid was used to slowly reduce the pH of the solution to about 3.0, and the mixture was stirred and reacted at 53°C for 3 hours. (4) Drying treatment of single-layer core-shell microcapsules: After the reaction is completed, the product is filtered using a slow double-circle qualitative filter paper, washed three times with alcohol and deionized water respectively to remove impurities, and a filter cake is obtained. Finally, it is dried at 25°C for 48 hours to obtain a powdered single-layer core-shell microcapsule sample. (5) Plasma treatment of microcapsule surface: During the experiment, the microcapsules were evenly spread on the dielectric plate, and the mass flow meter was used to control the flow ratio of CF4:N2 to 25:1. After the airflow was stable, the high-frequency AC power supply was adjusted to apply 7kV and 9kHz voltages. The plasma treatment lasted for 10 minutes, and the treated microcapsules were collected and stored. Similarly, the power supply voltage amplitude, frequency, action time, atmosphere and other parameters were changed to perform plasma treatment on the microcapsule surface, and the treated microcapsules were collected, labeled and stored. (6) Melt blending: After the temperature of the torque rheometer is set to 110 °C and the speed is set to 60 rpm, LDPE is placed in the torque rheometer. After LDPE is in a molten state and the torque is stable, antioxidants, microcapsules, and DCP are added in order. The mixing time is 20 minutes in total. After completion, the uniformly mixed composite material is taken out and cut into small particles for later use. (7) Determine the shape: Make a corresponding mold according to the shape of the sample and calculate the mass of the required composite material. Set the temperature of the flat vulcanizer to 110°C, put the composite material in, heat for 15 minutes, and then increase the pressure every 5 minutes. Observe the pressure gauge in time and add pressure in time if the pressure is insufficient. (8) Cross-linking reaction: The temperature of another plate vulcanizer was set to 175°C. The above molten materials were placed in the plate vulcanizer and the pressure was increased to 15 MPa. The pressure was supplemented at any time. After heating for 35 minutes, the sample was fully cooled. (9) Vacuum drying: The temperature of the vacuum drying oven is set to 80° C., and the XLPE is vacuum dried to obtain a multilayer core-shell structure microcapsule / XLPE water tree self-healing material surface-treated with plasma technology.

Claims

1. A method for preparing a single-layer core-shell microcapsule polyethylene-based water tree self-repairing insulating material treated with low-temperature plasma, characterized in that: The plasma surface treated urea-formaldehyde resin is used as the wall material, the repair liquid and the catalyst are used as the core material, the capsule core is embedded in the capsule wall, and the polymerization reaction is regulated by changing the pH value of the emulsion to obtain a single-layer core-shell microcapsule that can repair water tree damage in polyethylene cables.

2. The repair polyethylene composite medium water tree microcapsule with a single-layer shell-core structure according to claim 1, characterized in that: The structural morphology is a single-layer core-shell microcapsule, the repair liquid and the catalyst are in the same whole, and the mass ratio of the repair liquid to the catalyst is determined to be 4:

1.

3. The repair polyethylene composite medium water tree microcapsule with a single-layer core-shell structure according to claim 1, characterized in that: The outer shell is treated with plasma, the repair material core material repair liquid is dodecyltrimethoxysilane, and the catalyst is linear alkylbenzene sulfonic acid.

4. A method for preparing a single-layer core-shell microcapsule polyethylene-based water tree self-repairing insulating material treated with low-temperature plasma, characterized in that: The following steps are involved: (1) Preparation of UF prepolymer: Dissolve urea in deionized water, add 37% formaldehyde solution, and adjust the pH of the system to 8-9 with TEA. Then, keep the reaction at 70°C for 60 minutes and then cool to room temperature. The obtained UF prepolymer is a colorless, transparent solution with a certain viscosity. (2) Preparation of single-layer core-shell microcapsules: In a water bath at 40°C, the emulsifier styrene-maleic anhydride copolymer, LABSA and deionized water were mixed and stirred for 30 minutes. When the solution became white milky, the pH of the solution was slowly increased to 9-10 with sodium hydroxide solution. Ammonium chloride, resorcinol and UF prepolymer were added dropwise in sequence. Then, the pH of the solution was slowly lowered to about 3.0 with citric acid. After the reaction was completed at 53°C with stirring for 3 hours, the single-layer core-shell microcapsule sample was obtained by filtration, washing and drying. (3) Plasma treatment of microcapsule surface: During the experiment, the microcapsules were evenly spread on the dielectric plate, and the mass flow meter was used to control the flow ratio of CF4:N2 to 25:

1. After the airflow was stable, the high-frequency AC power supply was adjusted to apply 7kV and 9kHz voltages. The plasma treatment was performed for 10 min, and the treated microcapsules were collected and stored. Similarly, the power supply voltage amplitude, frequency, action time, atmosphere and other parameters were changed to perform plasma treatment on the microcapsule surface, and the treated microcapsules were collected, labeled and stored; (4) Preparation of plasma surface treated single-layer core-shell microcapsule / XLPE composite material: LDPE is placed into the torque rheometer. After LDPE is in a molten state and the torque is stable, antioxidants, microcapsules, DCP and cross-linking agents are placed in order for melt blending. A corresponding mold is made according to the shape of the sample, and the mass of the required composite material is calculated. It is pressurized using a flat vulcanizer and finally vacuum dried to obtain a plasma surface treated single-layer core-shell microcapsule / XLPE water tree self-healing material.

5. The method for preparing a low-temperature plasma treated single-layer core-shell microcapsule polyethylene-based water tree self-repairing insulating material according to claim 4, characterized in that: Plasma surface treatment improves the dispersibility of microcapsules and reduces the occurrence of agglomeration.

6. The method for preparing a low-temperature plasma treated single-layer core-shell microcapsule polyethylene-based water tree self-repairing insulating material according to claim 4, characterized in that: The single-layer core-shell structure of the microcapsule can improve both the repair rate and the repair speed.

Images