A microcapsule / XLPE composite self-repairing material based on reversible Diels-Alder reaction and a preparation method thereof

Abstract

Cross-linked polyethylene cable is widely used in modern power grid, but in the process of manufacturing and laying, there will inevitably be some micro defects in the cable, which will gradually induce water tree defects under the action of power frequency voltage and the corrosion of different substances in the soil during operation. Some water trees grow along the direction of electric field force, and under the action of overvoltage, they gradually develop into electrical trees, and eventually cause the breakdown of the cable insulation layer. The existing microcapsule type self-repairing material is limited by the trigger mode and single function, and the trigger condition is harsh, which cannot repair multiple defects such as mechanical damage, electrical tree, water tree and micro hole, and can only repair once, that is, it cannot be repaired multiple times and the repair efficiency is low. Therefore, it is necessary to develop a microcapsule / cross-linked polyethylene composite insulating material with multiple and multiple self-repairing ability, and fundamentally explore the method to prolong the service life of the insulating material.

Description

Technical Field

[0001] This invention belongs to the research field of self-healing technology for insulating materials, specifically involving a novel microcapsule / cross-linked polyethylene water tree self-healing material with multiple repair capabilities and its preparation method. Background Technology

[0002] Cross-linked polyethylene (XLPE) cables are widely used in my country's urban power grids due to their reliable electrical and mechanical properties. XLPE power cables offer advantages such as high breakdown field strength, high allowable operating temperature, large current carrying capacity, convenient laying and installation, and low transmission loss. However, during production and manufacturing, technological limitations can cause certain microscopic defects in the cables. Furthermore, during subsequent operation, prolonged exposure to heat, aging from power frequency voltage, and varying degrees of corrosion from different substances in the soil can also cause these microscopic defects, inducing water trees. Water trees grow along the direction of the electric field and begin to branch, forming water tree regions. Some of these water trees evolve into electrical trees, causing electric field distortion and ultimately leading to cable insulation breakdown.

[0003] Existing microencapsulated self-healing materials are limited by their single triggering method and function, and stringent triggering conditions. They cannot self-repair various defects such as mechanical damage, electrical trees, water trees, and micropores, and can only perform "one-time" repairs, meaning they cannot be repaired multiple times and have low repair efficiency. Therefore, it is necessary to develop a microencapsulated / cross-linked polyethylene composite insulation material with multiple self-healing capabilities to fundamentally explore methods to extend the service life of insulation materials.

[0004] Microencapsulation is a method of achieving various applications by forming a thin protective layer around solid particles, droplets, or bubbles, separating them from their surroundings, and ensuring compatibility with specific materials. Microcapsule self-healing technology involves encapsulating repair materials within specific microcapsules and incorporating these microcapsules into the material being repaired. When the material is damaged and certain conditions are met, the microcapsules rupture, releasing the internal repair material to repair the defective structure, thereby restoring some of the material's properties. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies. This invention provides a microcapsule / crosslinked polyethylene water tree self-healing material based on a reversible Diels-Alder reaction and its preparation method, which is an extension and development of the microcapsule self-healing technology for insulating materials.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a microcapsule / crosslinked polyethylene self-healing material based on a reversible Diels-Alder reaction includes the preparation of a urea-formaldehyde resin prepolymer, the preparation of a microcapsule core, the forming of the microcapsules, and finally cooling, washing, and drying to obtain microcapsules for repairing electrical and water treeing in crosslinked polyethylene composite insulation materials. The crosslinked polyethylene composite insulation material with multiple self-healing capabilities is then obtained through melt blending, crosslinking reaction, and vacuum drying. Specifically, the method includes the following steps:

[0008] (1) Preparation of urea-formaldehyde resin prepolymer: Urea was dissolved in deionized water and then a 37% formaldehyde solution was added. Under magnetic stirring at 300-400 rpm, the pH of the system was adjusted to 8-9 with triethanolamine, and then the reaction was carried out at 70°C for 60 minutes. After that, it was cooled to room temperature. The obtained urea-formaldehyde resin prepolymer was a colorless and transparent solution with a certain viscosity.

[0009] (2) Synthesis of hyperbranched polysiloxanes containing furan rings: γ-glycidoxypropyltrimethoxysilane (KH560) was reacted with furanylmethylamine at 55°C under nitrogen for 8 hours using toluene as solvent. The product was then rotary evaporated for 0.5 hours to obtain KH560-FA. KH560-FA and γ-methacryloyloxypropyltrimethoxysilane (KH570) were mixed and hydrolyzed with ethanol and H2O. Hydrochloric acid was added at 55°C to adjust the pH of the solution to 4-5. After reacting for 4 hours, the hydrolysis product HPSi3 was obtained.

[0010] (3) Synthesis of organosilicon polymers containing furan functional groups: Under nitrogen ice bath conditions, diaminopropyl polydimethylsiloxane (NH2-PDMS-NH2) and triethylamine were added to anhydrous dichloromethane solvent one after another. After stirring for 1 hour, dimethylaminopyridine was added. After complete dissolution, an anhydrous dichloromethane solution of 2-furan carboxyl chloride was added dropwise. The reaction was carried out at room temperature for 48 hours. The obtained preliminary product was filtered, washed and dried to obtain a yellow product, which is the organosilicon polymer containing furan functional groups (PDMS-F).

[0011] (4) Synthesis of organosilicon polymers containing maleimide functional groups: Using glacial acetic acid as the base solvent, diaminopropyl polydimethylsiloxane (NH2-PDMS-NH2) and maleic anhydride were thoroughly stirred and dissolved at room temperature for 2 hours, and then heated to 140℃ for 6 hours. After cooling, dichloromethane was added, and after standing for 1 hour, the mixture was filtered, washed, and dried to obtain a yellowish-brown liquid, which is the organosilicon polymer (PDMS-M) containing maleimide functional groups.

[0012] (5) Synthesis of microcapsule core material: The samples of linear polysiloxane PDMS-F containing furan functional group, linear polysiloxane PDMS-M containing maleimide functional group and hyperbranched polysiloxane HPSi3 were mixed and the photoinitiator benzophenone was added. The resulting sample is called PDMS-F / PDMS-M / HPSi3 mixed solvent.

[0013] (6) Microcapsule formation: The urea-formaldehyde resin prepolymer was added dropwise to a mixed solvent of PDMS-F / PDMS-M / HPSi3, along with ammonium chloride (urea-formaldehyde resin curing agent) and resorcinol (urea-formaldehyde resin water-resistant modifier). The mixture was magnetically stirred for 3 minutes. Then, 1-2 drops of n-octanol (defoaming agent) were added dropwise, and the pH of the solution was slowly lowered to 3.0 with citric acid at a stirring speed of 400 rpm. Finally, the temperature was raised to 60°C, and the mixture was stirred at 300 rpm for 3 hours.

[0014] (7) Drying of microcapsules: After the reaction was completed, the product was filtered using slow double-circle qualitative filter paper. The filter cake was washed three times each with alcohol and deionized water to remove impurities. Finally, the filter cake was dried at 30°C for 24 hours to obtain microcapsule samples.

[0015] (8) Melt blending: After setting the temperature of the torque rheometer to 110℃ and the rotation speed to 60rpm, put the low-density polyethylene into the torque rheometer. After the low-density polyethylene is in a molten state and the torque is stable, add the antioxidant, microcapsules and crosslinking agent in sequence. Take out the uniformly blended composite material and cut it into small particles for later use.

[0016] (9) Material melting: Make a corresponding mold according to the shape of the sample and calculate the required mass of composite material. Set the temperature of the flat vulcanizing machine to 110℃, put in the composite material, heat for 15 minutes, and then pressurize every 5 minutes. Observe the pressure gauge in time and replenish the pressure in time if the pressure is insufficient.

[0017] (10) Crosslinking reaction: The temperature of another flat vulcanizing machine is set to 175°C. The material of (9) is put in, the pressure is increased to 15MPa, and the pressure is replenished at any time. After heating for 35 minutes, the sample is cooled completely.

[0018] (11) Vacuum drying: The temperature of the vacuum drying oven is set to 80℃, and the cross-linked polyethylene is vacuum dried to obtain microcapsule / cross-linked polyethylene self-healing material.

[0019] In the technical solution of the present invention: the mass ratio of urea-formaldehyde resin wall material to repair material core material in step (6) is 2:1.

[0020] In the technical solution of this invention: the purpose of pressurizing in step (9) is to fully shape the material so that impurity gases in the material can be fully discharged.

[0021] In the technical solution of this invention, the purpose of step (10) is to fully graft and crosslink the crosslinking agent and polar molecules with low-density polyethylene.

[0022] In the technical solution of this invention, the purpose of step (11) is to reduce the influence of cross-linking byproducts and residual stress inside the sample on the test.

[0023] Compared with the prior art, the advantages of this invention are:

[0024] (1) Using urea-formaldehyde resin as the shell material of the microcapsule-type self-healing material and PDMS-F / PDMS-M / HPSi3 mixed solvent as the core material of the microcapsule-type self-healing material, the self-healing microcapsules for repairing the electro-water tree of cross-linked polyethylene composite insulation material are obtained by in-situ polymerization. The preparation is simple and low cost.

[0025] (2) The hydrolysis reaction in the core material consumes the moisture in the insulation, and the organic polymer generated after the reaction can fill the micropores, thereby eliminating water treeing and restoring the insulation performance of water-tree aged cables. Organosilicon resin is not easily decomposed at high temperatures and has high voltage resistance and good insulation performance, with properties similar to cross-linked polyethylene, effectively filling the water tree voids. Due to the electroluminescence phenomenon generated by electrical treeing, free radical polymerization is initiated in polysiloxane under the action of the photoinitiator benzophenone, thereby solidifying and filling the voids.

[0026] (3) When the core material repairs electrical or water trees, if it encounters electrical or water trees again, the furan functional groups and maleamide functional groups in the core material will undergo a reversible Diels-Alder reaction, thereby achieving the purpose of repeated repair. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating the preparation process of multi-repair microcapsules.

[0028] Figure 2 This is a reversible Diels-Alder chemical reaction formula.

[0029] Figure 3 This is a composite image of KH560-FA.

[0030] Figure 4 This is a composite image of PDMS-F.

[0031] Figure 5 This is a composite image of PDMS-M.

[0032] Figure 6 Image of a multi-repair microcapsule.

[0033] Figure 7This is a process diagram for preparing multi-repair microcapsule / XLPE composite materials.

[0034] Figure 8 This is a schematic diagram of the composite material manufactured according to the present invention.

[0035] Figure 9 To improve the dielectric properties of multi-concentration repair microcapsule / XLPE composite materials.

[0036] Figure 10 The image shows SEM images of tree branch aging. The left side of the image is a schematic diagram of tree branch defects caused by electro-hydraulic mixing without self-healing composite insulation material, while the right side is a schematic diagram of self-healing tree branch defects caused by electro-hydraulic mixing with self-healing composite insulation material. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0038] (1) Preparation of urea-formaldehyde resin prepolymer: 20g of urea was dissolved in 60g of deionized water, and then 20g of 37% formaldehyde solution was added. Under magnetic stirring at 300-400rpm, the pH of the system was adjusted to 8-9 with triethanolamine, and then the reaction was carried out at 70℃ for 60 minutes. After that, it was cooled to room temperature. The obtained urea-formaldehyde resin prepolymer was a colorless and transparent solution with a certain viscosity.

[0039] (2) Synthesis of hyperbranched polysiloxane containing furan ring: First, KH560 (11.8g, 0.05mol) and furanylamine (4.85g, 0.05mol) were reacted at 55℃ for 8h under a nitrogen atmosphere. Toluene (100mL) was used as solvent. After obtaining the product, the solvent toluene was rotary evaporated for 0.5h to generate product KH560-FA. KH560-FA, ethanol, and H2O were hydrolyzed in a molar ratio of 1:1:1.2 at 55°C with stirring. Hydrochloric acid was added to adjust the pH to 4-5, and the reaction was carried out for 4 hours to obtain the hydrolysis product HPSi1. Similarly, KH560-FA and KH570 were mixed in a molar ratio of 10:1, and the mixture was hydrolyzed with ethanol and H2O in a molar ratio of 1:1:1.2 to obtain the hydrolysis product HPSi2. KH560-FA and KH570 were mixed in a molar ratio of 10:2, and the mixture was hydrolyzed with ethanol and H2O in a molar ratio of 1:1:1.2 to obtain the hydrolysis product HPSi3.

[0040] (3) Synthesis of organosilicon polymers containing furan functional groups: Anhydrous dichloromethane (200 mL) was used as the solvent. The reaction conditions were nitrogen atmosphere and ice bath. First, diaminopropyl polydimethylsiloxane (NH2-PDMS-NH2) (Mn=1000, 40 g, 20 mmol) was added to the solvent, followed by triethylamine (14 mL) and stirring for 1 hour. After stirring for one hour, dimethylaminopyridine (97.6 mg, 0.8 mmol) was added. After complete dissolution, 2-furancarbamoyl chloride (10.44 mg, 80 mmol) in anhydrous dichloromethane (80 mL) solution was added dropwise through a constant pressure funnel. The reaction was carried out at room temperature for 48 h. The crude product was post-treated, filtered, washed three times with saturated sodium bicarbonate solution and deionized water, and then dried with anhydrous magnesium sulfate to remove the solvent to obtain the final product. After filtration and removal of the solvent, a yellow product was obtained, yielding the organosilicon polymer (PDMS-F) containing furan functional groups.

[0041] (4) Synthesis of organosilicon polymer containing maleimide functional group: Diaminopropyl polydimethylsiloxane (NH2-PDMS-NH2) (Mn=1000, 40g, 20mmol) and maleic anhydride (15.68g, 160mmol) were reacted with glacial acetic acid (200mL) as solvent. The mixture was stirred and dissolved at room temperature for 2 hours, then heated to 140℃ and reacted for 6 hours. After cooling, dichloromethane was added, and the mixture was allowed to stand for 1 hour. After washing 3 times with saturated sodium chloride solution, anhydrous magnesium sulfate was added and dried. The solvent was removed by filtration, and a yellowish-brown liquid was obtained. The organosilicon polymer containing maleimide functional group (PDMS-M) was prepared.

[0042] (5) Synthesis of microcapsule core material: 32g of PDMS-F, 32g of PDMS-M and 2.5g of HPSi3 were mixed and 1g of benzophenone was added. The resulting sample was called PDMS-F / PDMS-M / HPSi3 mixed solvent.

[0043] (6) Microcapsule formation: The urea-formaldehyde resin prepolymer was added dropwise to a mixed solvent of PDMS-F / PDMS-M / HPSi3, along with 1g of ammonium chloride (urea-formaldehyde resin curing agent) and 2g of resorcinol (urea-formaldehyde resin water-resistant modifier). The mixture was magnetically stirred for 3 minutes. Then, 1-2 drops of n-octanol (defoaming agent) were added dropwise, and the pH of the solution was slowly lowered to about 3.0 with citric acid at a stirring speed of 400 rpm. Finally, the temperature was raised to 60°C, and the mixture was stirred at 300 rpm for 3 hours.

[0044] (7) Microcapsule drying treatment: After the reaction was completed, the product was filtered using slow double-circle qualitative filter paper. The product was washed three times each with alcohol and deionized water to remove impurities and obtain a filter cake. Finally, the product was dried at 30°C for 24 hours to obtain microcapsule samples of electro-water tree microcapsules with multiple repair cross-linked polyethylene composite insulation material.

[0045] (8) Melt blending: Weigh 40g of low-density polyethylene, 0.12g of antioxidant, 0.8g of microcapsules and 0.72g of crosslinking agent. Set the temperature of the torque rheometer to 110℃ and the speed to 60rpm. Then put the low-density polyethylene into the torque rheometer and add the antioxidant, microcapsules and crosslinking agent in the order of running time 1 minute, 3 minutes and 18 minutes. After 2 minutes, take out the uniformly blended composite material and cut it into small particles for later use.

[0046] (9) Material melting: Make a mold with a length and width of 10cm and a height of 200um according to the shape of the sample. Weigh the required composite material as 2.02g. Set the temperature of the flat vulcanizing machine to 110℃. Put in the composite material wrapped in iron plate and oily polyester film. After heating for 15 minutes, pressurize once every 5 minutes. The pressure gauge readings are 0MPa, 5MPa, 10MPa and 15MPa. Observe the pressure gauge in time and replenish the pressure in time if the pressure is insufficient.

[0047] (10) Crosslinking reaction: The temperature of another flat vulcanizing machine is set to 175°C. The material of (9) is put in, the pressure is increased to 15MPa, and the pressure is replenished at any time. After heating for 35 minutes, the sample is cooled completely.

[0048] (11) Vacuum drying: The temperature of the vacuum drying oven is set to 80℃, and the cross-linked polyethylene is vacuum dried for 12 hours to obtain microcapsule / cross-linked polyethylene self-healing material with multiple repair effects.

Claims

1. A self-healing microcapsule / XLPE composite material based on a reversible Diels-Alder reaction, characterized in that: Using urea-formaldehyde resin as the wall material and an organosilicon polymer containing furan functional groups / an organosilicon polymer containing maleimide functional groups / a hyperbranched polysiloxane containing furan rings / benzophenone as the core material, the core material is embedded in the wall material to form a microcapsule structure. The polymerization reaction is controlled by adjusting the pH of the emulsion to 3.0 with citric acid to obtain self-healing microcapsules for repairing electro-water trees in cross-linked polyethylene composite insulation material.

2. The self-healing material according to claim 1, characterized in that: The structure is a single-layer microcapsule, and the core material contains an organosilicon polymer with furan functional groups: an organosilicon polymer with maleimide functional groups: a hyperbranched polysiloxane containing furan rings in a mass ratio of 64:64:

5.

3. The self-healing material according to claim 1, characterized in that: The photoinitiator is benzophenone. The hydrolysis reaction in the core material consumes the moisture in the insulator, and the organic polymer generated after the reaction can fill the micropores, thereby eliminating water treeing. Due to the electroluminescence phenomenon caused by electrical treeing, free radical polymerization is initiated in the polysiloxane under the action of the photoinitiator benzophenone, thereby solidifying and filling the voids.

4. A method for preparing a microcapsule / cross-linked polyethylene water tree self-healing material with multiple repair effects, characterized in that: Includes the following steps: (1) Preparation of urea-formaldehyde resin prepolymer: Urea and formaldehyde solution are reacted to obtain urea-formaldehyde resin prepolymer, which is a colorless and transparent solution with a certain viscosity; (2) Synthesis of hyperbranched polysiloxanes containing furan ring: γ-glycidoxypropyltrimethoxysilane was reacted with furanylmethylamine at 55°C under nitrogen for 8 hours using toluene as solvent. The product was rotary evaporated for 0.5 hours to obtain KH560-FA. KH560-FA and γ-methacryloyloxypropyltrimethoxysilane were mixed. The mixture was hydrolyzed with ethanol and H2O. Hydrochloric acid was added at 55°C to adjust the pH of the solution to 4-5. After reacting for 4 hours, the hydrolysis product HPSi3 was obtained. (3) Synthesis of organosilicon polymers containing furan functional groups: Under nitrogen ice bath conditions, diaminopropyl polydimethylsiloxane (NH2-PDMS-NH2) and triethylamine were added to anhydrous dichloromethane solvent one after another. After stirring for 1 hour, dimethylaminopyridine was added. After complete dissolution, an anhydrous dichloromethane solution of 2-furan carboxyl chloride was added dropwise. The reaction was carried out at room temperature for 48 hours. The obtained preliminary product was filtered, washed and dried to obtain a yellow product, which is an organosilicon polymer containing furan functional groups. (4) Synthesis of organosilicon polymers containing maleimide functional groups: Using glacial acetic acid as the base solvent, diaminopropyl polydimethylsiloxane and maleic anhydride were thoroughly stirred and dissolved at room temperature for 2 hours, and then heated to 140°C for 6 hours. After cooling, dichloromethane was added, and after standing for 1 hour, the mixture was filtered, washed, and dried to obtain a yellowish-brown liquid, which is the organosilicon polymer containing maleimide functional groups. (5) Synthesis of microcapsule core material: The samples of organosilicon polymer PDMS-F containing furan functional group, organosilicon polymer PDMS-M containing maleimide functional group and hyperbranched polysiloxane HPSi3 containing furan ring were mixed and photoinitiator benzophenone was added. The resulting sample is called PDMS-F / PDMS-M / HPSi3 mixed solvent. (6) Preparation of microcapsules: Urea-formaldehyde resin prepolymer was added dropwise to a mixed solvent of PDMS-F / PDMS-M / HPSi3, and urea-formaldehyde resin curing agent ammonium chloride and urea-formaldehyde resin water-resistant modifier resorcinol were added. The mixture was magnetically stirred for 3 minutes, then n-octanol was added dropwise, and then citric acid was used to lower the pH of the solution to 3.

0. Finally, the temperature was raised to 60°C and stirred for 3 hours. After filtration, washing and drying, the microcapsule sample of electro-water tree of multi-repair cross-linked polyethylene composite insulation material was obtained. (7) Preparation of composite materials: Low-density polyethylene, antioxidant, microcapsules and crosslinking agent are melt-blended using a torque rheometer, and crosslinked polyethylene composite materials are made into the required shapes for the test using a flat vulcanizing machine. Finally, vacuum drying is performed to obtain microcapsule / crosslinked polyethylene electro-water tree self-healing material with multiple repair effects.

5. The preparation method of a microcapsule / cross-linked polyethylene water tree self-healing material with multiple repair effects according to claim 4, characterized in that: When the core material repairs electrical or water trees, if it encounters electrical or water trees again, the furan and maleamide functional groups in the core material will undergo a reversible Diels-Alder reaction, thereby achieving the purpose of repeated repairs.

6. The preparation method of a microcapsule / cross-linked polyethylene water tree self-healing material with multiple repair effects according to claim 4, characterized in that: Based on the self-healing network of the polysiloxane system, the repaired material has a dielectric strength similar to that of cross-linked polyethylene.

Images