Microcapsule / XLPE composite material self-repairing material based on reversible Diels-Alder reaction and preparation method of microcapsule / XLPE composite material self-repairing material

Abstract

A crosslinked polyethylene cable is widely applied to a modern power grid, but in the manufacturing and laying process, certain microdefects are inevitably caused in the cable, the cable is corroded by power frequency voltage and different substances in soil during operation, and the microdefects are eroded by water to gradually induce water branch defects. Some water branches grow along the direction of the electric field force and gradually derive into electric branches under the action of overvoltage, and finally the cable insulation layer is broken down. An existing microcapsule type self-repairing material is limited by a triggering mode, is single in function and harsh in triggering condition, cannot perform self-repairing on various defects such as mechanical damage, electric tree branches, water tree branches and micropores, and only can perform single-time repairing, namely, the problems that multiple-time repairing cannot be performed, the repairing efficiency is low and the like exist. Therefore, it is necessary to develop a microcapsule / crosslinked polyethylene composite insulating material with multiple and multiple self-repairing capabilities, and a method for fundamentally exploring and prolonging the service life of the insulating material is provided.

Description

Technical Field

[0001] The invention belongs to the research field of insulating material self-repairing technology, and specifically relates to a new microcapsule / cross-linked polyethylene water tree self-repairing material with multiple repair capabilities and a preparation method thereof. Background Art

[0002] Cross-linked polyethylene cables have been widely used in my country's urban power grids due to their reliable electrical and mechanical properties. Cross-linked polyethylene power cables have the advantages of high breakdown field strength, high allowable operating temperature, large current carrying capacity, easy laying and installation, and low transmission loss. However, during the production and manufacturing process, due to technical limitations, certain microscopic defects will be caused to the cables. In the subsequent working state, due to long-term heat, aging by power frequency voltage, and different degrees of corrosion by different substances in the soil, certain microscopic defects will also be caused, inducing water tree branches. Water tree branches continue to grow along the direction of the electric field force and begin to fork to form water tree areas. Some of the water tree branches evolve into electric tree branches, causing electric field distortion and ultimately causing the breakdown of the cable insulation.

[0003] Existing microcapsule self-healing materials are limited by the single triggering mode and function, and the harsh triggering conditions. They cannot self-repair various defects such as mechanical damage, electrical trees, water trees and micropores, and can only be repaired "once", that is, they cannot be repaired multiple times and the repair efficiency is low. Therefore, it is necessary to develop a microcapsule / cross-linked polyethylene composite insulation material with multiple self-repairing capabilities to fundamentally explore ways to extend the service life of insulation materials.

[0004] Microcapsules are a method of forming a thin protective layer around solid particles, droplets or bubbles to separate them from the surrounding environment and achieve compatibility with specific materials to complete various applications. Microcapsule self-repair technology refers to encapsulating the repair material in a specific microcapsule and incorporating the microcapsule into the repaired material. When the repaired material is damaged and reaches certain conditions, the microcapsule ruptures and the internal repair material is released to repair the defective structure, thereby restoring the material performance to a certain extent. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies of the prior art. The present invention provides a microcapsule / cross-linked polyethylene water tree self-healing material based on a reversible Diels-Alder reaction and a preparation method thereof, which is an extension and development of the insulating material microcapsule self-healing technology.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a microcapsule / cross-linked polyethylene water tree self-repairing material based on a reversible Diels-Alder reaction, including the preparation of a urea-formaldehyde resin prepolymer, the preparation of a microcapsule core material: a PDMS-F / PDMS-M / HPSi3 mixed solvent, the formation of microcapsules, and finally cooling, washing, and drying to obtain repaired cross-linked polyethylene composite insulation material electric tree and water tree microcapsules, and then melt blending, cross-linking reaction, and vacuum drying to obtain a cross-linked polyethylene composite insulation material with microcapsules having multiple self-repairing capabilities. Specifically comprising the following steps:

[0008] (1) Preparation of urea-formaldehyde resin prepolymer: Dissolve urea in deionized water and add 37% formaldehyde solution. Adjust the pH of the system to 8-9 with triethanolamine under magnetic stirring at 300-400 rpm, and then keep the reaction at 70°C for 60 minutes. Then cool to room temperature. The obtained urea-formaldehyde resin prepolymer is a colorless, transparent solution with a certain viscosity.

[0009] (2) Synthesis of hyperbranched polysiloxane containing furan rings: Using toluene as solvent, γ-glycidyloxypropyltrimethoxysilane (KH560) and furanamine were reacted under nitrogen conditions at 55°C for 8 hours. The resulting product was rotary evaporated for 0.5 hours to obtain KH560-FA. KH560-FA and γ-methacryloxypropyltrimethoxysilane (KH570) were mixed, and 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.

[0010] (3) Synthesis of organosilicon polymer containing furan functional groups: In a nitrogen ice bath, bisaminopropyl polydimethylsiloxane (NH2-PDMS-NH2) and triethylamine were added to anhydrous dichloromethane solvent in sequence. After stirring for 1 hour, dimethylaminopyridine was added. After complete dissolution, an anhydrous dichloromethane solution of 2-furoyl chloride was added dropwise. The reaction was carried out at room temperature for 48 hours. The preliminary product was filtered, washed, and dried to obtain a yellow product, namely, an organosilicon polymer containing furan functional groups (PDMS-F).

[0011] (4) Synthesis of silicone polymer containing maleimide functional group: Using glacial acetic acid as the base solvent, bisaminopropyl polydimethylsiloxane (NH2-PDMS-NH2) and maleic anhydride were fully stirred and dissolved at room temperature for 2 hours, and the temperature was raised to 140°C for reaction for 6 hours. After cooling, dichloromethane was added. After standing for 1 hour, the mixture was filtered, washed, and dried to obtain a yellow-brown liquid, namely, silicone polymer containing maleimide functional group (PDMS-M).

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

[0013] (6) Formation of microcapsules: Urea-formaldehyde resin prepolymer was added dropwise to the PDMS-F / PDMS-M / HPSi3 mixed solvent, and urea-formaldehyde resin curing agent ammonium chloride and urea-formaldehyde resin water-resistant modifier resorcinol were added, and magnetic stirring was performed for 3 minutes. Then, 1 to 2 drops of defoaming agent n-octanol were added, and the pH of the solution was slowly lowered to about 3.0 with citric acid. The rotation speed was 400 rpm during acidification. Finally, the temperature was raised to 60°C, and the rotation speed was 300 rpm for stirring and reaction for 3 hours.

[0014] (7) Microcapsule drying treatment: After the reaction is completed, the product is filtered using a slow double-circle qualitative filter paper, and washed three times with alcohol and deionized water to remove impurities to obtain a filter cake. Finally, it is dried at 30°C for 24 hours to obtain a repaired cross-linked polyethylene composite insulation material water tree microcapsule sample with a multi-shell structure.

[0015] (8) Melt blending: After the temperature of the torque rheometer is set to 110°C and the speed is set to 60 rpm, low-density polyethylene is placed in the torque rheometer. After the low-density polyethylene is in a molten state and the torque is stable, antioxidants, microcapsules, and cross-linking agents are added in order. The uniformly mixed composite material is taken out and cut into small particles for later use.

[0016] (9) Material melting: 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.

[0017] (10) Cross-linking reaction: The temperature of another flat vulcanizer was set to 175°C, and the material of (9) was placed in the press. The pressure was increased to 15 MPa and the pressure was supplemented at any time. After heating for 35 minutes, the sample was fully cooled.

[0018] (11) Vacuum drying: The temperature of the vacuum drying oven is set to 80° C. The cross-linked polyethylene is vacuum dried to obtain a microcapsule / cross-linked polyethylene water tree self-healing material with a multi-shell structure.

[0019] 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.

[0020] In the technical solution of the present invention: the purpose of increasing the pressure in (9) is to fully shape the material so that the impurity gas in the material can be fully discharged.

[0021] In the technical solution of the present invention: the purpose of step (10) is to fully graft and cross-link the cross-linking agent and the polar molecules with the low-density polyethylene.

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

[0023] Compared with the prior art, the advantages of the present 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, an in-situ polymerization method was used to obtain self-healing microcapsules for repairing the electrical water tree of the cross-linked polyethylene composite insulating material. The preparation method is simple and low in cost.

[0025] (2) The hydrolysis reaction in the core material consumes the water in the insulator, and the organic polymer generated after the reaction can fill the micropores, thereby eliminating the water tree and restoring the insulation performance of the water-tree aged cable. Silicone resin is not easy to decompose at high temperatures and has the characteristics of high pressure resistance and good insulation performance. Its performance is similar to that of cross-linked polyethylene, which effectively fills the water tree voids. Due to the electroluminescence phenomenon generated by the electric tree, under the action of the photoinitiator benzophenone, free radical polymerization is initiated in the polysiloxane, thereby solidifying and filling the voids.

[0026] (3) After the core material repairs the electrical tree or water tree, if it encounters the electrical tree or water tree again, the furan functional group in the core material and the maleamide functional group will undergo a reversible Diels-Alder reaction, thereby achieving the purpose of repeated repair. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Flow chart for the preparation of multi-repair microcapsules.

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

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

[0030] Figure 4 This is the synthesis diagram of the hydrolysis products HPSi1, HPSi2 and HPSi3.

[0031] Figure 5 This is the synthesis diagram of PDMS-F.

[0032] Figure 6This is the synthesis image of PDMS-M.

[0033] Figure 7 This is a sample image of multiple repair microcapsules.

[0034] Figure 8 This is the preparation process diagram of multi-repair microcapsule / XLPE composite material.

[0035] Fig. 9 This is a schematic diagram of the composite material produced by the present invention.

[0036] Fig.10 Dielectric properties of multi-repaired microcapsules / XLPE composites at different concentrations.

[0037] Fig.11 This is a SEM image of tree branch aging. The left side of the image is a schematic diagram of the electric-water hybrid tree branch defect without the self-repairing composite insulating material, and the right side is a schematic diagram of the self-repairing defect of the self-repairing composite insulating material. DETAILED DESCRIPTION

[0038] 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.

[0039] (1) Preparation of urea-formaldehyde resin prepolymer: 20 g of urea was dissolved in 60 g of deionized water, and then 20 g of 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 mixture was kept at 70°C for 60 minutes. The mixture was then cooled to room temperature. The obtained urea-formaldehyde resin prepolymer was a colorless, transparent solution with a certain viscosity.

[0040] (2) Synthesis of hyperbranched polysiloxane containing furan ring: KH560 (11.8 g, 0.05 mol) and furanylamine (4.85 g, 0.05 mol) were first reacted at 55 °C for 8 h under a nitrogen atmosphere with toluene (100 mL) as solvent to obtain the product. The solvent toluene was then rotary evaporated for 0.5 h to generate the product KH560-FA. KH560-FA, ethanol and H2O were hydrolyzed in a molar ratio of 1:1:1.2, stirred at 55°C, and hydrochloric acid was added to adjust the pH to 4-5. After reacting for 4 hours, the hydrolysis product HPSi1 was obtained; similarly, KH560-FA and KH570 were mixed in a 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 ratio of 1:1:1.2 to obtain the hydrolysis product HPSi3.

[0041] (3) Synthesis of organic silicon polymer containing furan functional group: With anhydrous dichloromethane (200 mL) as solvent, the reaction conditions are nitrogen atmosphere, ice bath, first add bisaminopropyl polydimethylsiloxane (NH2-PDMS-NH2) (Mn=1000, 40 g, 20 mmol) to the solvent, then add triethylamine (14 mL) and stir for 1 hour. After stirring for one hour, add dimethylaminopyridine (97.6 mg, 0.8 mmol), and after complete dissolution, add 2-furancarbonyl chloride (10.44 mg, 80 mmol) in anhydrous dichloromethane (80 mL) dropwise with a constant pressure funnel. React at room temperature for 48 hours. The crude product is 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, filtered, and the solvent is removed to obtain a yellow product, and the organic silicon polymer containing furan functional group (PDMS-F) is obtained.

[0042] (4) Synthesis of organosilicon polymer containing maleimide functional group: Bisaminopropyl polydimethylsiloxane (NH2-PDMS-NH2) (Mn=1000, 40 g, 20 mmol) and maleic anhydride (15.68 g, 160 mmol) were reacted with glacial acetic acid (200 mL) as solvent, and the mixture was fully stirred and dissolved at room temperature for 2 hours, then heated to 140°C for reaction for 6 hours, cooled and added with dichloromethane, and allowed to stand for 1 hour, then washed with saturated sodium chloride solution 3 times, and dried with anhydrous magnesium sulfate, and filtered to remove the solvent to obtain a yellow-brown liquid, thereby preparing organosilicon polymer containing maleimide functional group (PDMS-M).

[0043] (5) Synthesis of microcapsule core material: 32 g of PDMS-F, 32 g of PDMS-M and 2.5 g of HPSi3 were mixed, and 1 g of benzophenone was added. The resulting sample was called PDMS-F / PDMS-M / HPSi3 mixed solvent.

[0044] (6) Formation of microcapsules: Urea-formaldehyde resin prepolymer was added dropwise to the PDMS-F / PDMS-M / HPSi3 mixed solvent, and 1g of urea-formaldehyde resin curing agent ammonium chloride and 2g of urea-formaldehyde resin water-resistant modifier resorcinol were added, and magnetic stirring was performed for 3 minutes. Then, 1-2 drops of defoaming agent n-octanol were added, and the pH of the solution was slowly lowered to about 3.0 with citric acid. The rotation speed was 400 rpm during acidification. Finally, the temperature was raised to 60°C, and the reaction was stirred at 300 rpm for 3 hours.

[0045] (7) Microcapsule drying treatment: After the reaction is completed, the product is filtered using a slow double-circle qualitative filter paper, and washed three times with alcohol and deionized water respectively to remove impurities to obtain a filter cake. Finally, it is dried at 30°C for 24 hours to obtain a multi-repair cross-linked polyethylene composite insulation material electric water tree microcapsule sample.

[0046] (8) Melt blending: Weigh 40 g of low-density polyethylene, 0.12 g of antioxidant, 0.8 g of microcapsule, and 0.72 g of cross-linking agent. Set the temperature of the torque rheometer to 110°C and the speed to 60 rpm. Place the low-density polyethylene in the torque rheometer. Add antioxidant, microcapsule, and cross-linking agent in the order of running time of 1 min, 3 min, and 18 min. After 2 minutes, take out the uniformly mixed composite material and cut it into small particles for later use.

[0047] (9) Material melting: According to the shape of the sample, a mold with a length and width of 10 cm and a height of 200 μm was made. The mass of the required composite material was weighed to be 2.02 g. The temperature of the flat vulcanizer was set to 110°C. The composite material wrapped with an iron plate and an oily polyester film was placed in the mold. After heating for 15 minutes, the pressure was increased every 5 minutes. The pressure gauge values ​​were 0 MPa, 5 MPa, 10 MPa, and 15 MPa. The pressure gauge was observed in time and the pressure was supplemented in time if it was insufficient.

[0048] (10) Cross-linking reaction: The temperature of another flat vulcanizer was set to 175°C, and the material of (9) was placed in the press. The pressure was increased to 15 MPa and the pressure was supplemented at any time. After heating for 35 minutes, the sample was fully cooled.

[0049] (11) Vacuum drying: The temperature of the vacuum drying oven is set to 80° C. The cross-linked polyethylene is vacuum dried for 12 hours to obtain a microcapsule / cross-linked polyethylene water tree self-healing material with multiple repair effects.

Claims

1. A microcapsule / XLPE composite self-healing material based on a reversible Diels-Alder reaction and a preparation method thereof, characterized in that: Urea-formaldehyde resin is used as the wall material and PDMS-F / PDMS-M / HPSi3 mixed solvent is used as the core material. The capsule core is embedded in the capsule wall to form a microcapsule structure. The polymerization reaction is regulated by changing the pH value of the emulsion to obtain cross-linked polyethylene composite insulating material water tree microcapsules with multiple repair effects.

2. The microcapsule based on the reversible Diels-Alder reaction according to claim 1, characterized in that: The structural morphology is a single-layer microcapsule, and the mass ratio of the core material PDMS-F:PDMS-M:HPSi3 is determined to be 64:64:

5.

3. The microcapsule based on the reversible Diels-Alder reaction 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 the water tree. Due to the electroluminescence phenomenon generated by the electric tree, under the action of the photoinitiator benzophenone, free radical polymerization is initiated in the polysiloxane, thereby solidifying and filling the void.

4. A microcapsule / cross-linked polyethylene water tree self-repairing material with multiple repair effects, characterized in that: The following steps are involved: (1) Preparation of urea-formaldehyde resin prepolymer: Urea and formaldehyde solution are reacted to obtain a colorless, transparent solution with a certain viscosity. (2) Synthesis of furan ring-containing hyperbranched polysiloxane: Using toluene as solvent, γ-glycidyloxypropyltrimethoxysilane and furanamine were reacted under nitrogen conditions at 55°C for 8 hours. The product was evaporated on a rotary evaporator for 0.5 hour to obtain KH560-FA. KH560-FA and γ-methacryloxypropyltrimethoxysilane were mixed, and 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: In a nitrogen ice bath, bisaminopropyl polydimethylsiloxane (NH2-PDMS-NH2) and triethylamine were added to anhydrous dichloromethane solvent in sequence. After stirring for 1 hour, dimethylaminopyridine was added. After complete dissolution, an anhydrous dichloromethane solution of 2-furoyl chloride was added dropwise. The reaction was carried out at room temperature for 48 hours. The preliminary product was filtered, washed, and dried to obtain a yellow product, i.e., an organosilicon polymer containing furan functional groups. (4) Synthesis of silicone polymer containing maleimide functional group: Using glacial acetic acid as the base solvent, diaminopropyl polydimethylsiloxane and maleic anhydride were fully stirred and dissolved at room temperature for 2 hours, and the temperature was raised to 140°C for reaction for 6 hours. After cooling, dichloromethane was added. After standing for 1 hour, the mixture was filtered, washed and dried to obtain a yellow-brown liquid, i.e., silicone polymer containing maleimide functional group. (5) Synthesis of microcapsule core material: Samples of linear polysiloxane PDMS-F containing furan functional groups, linear polysiloxane PDMS-M containing maleimide functional groups, and hyperbranched polysiloxane HPSi3 were mixed, and a photoinitiator benzophenone was added. The resulting sample was called PDMS-F / PDMS-M / HPSi3 mixed solvent. (6) Preparation of microcapsules: Urea-formaldehyde resin prepolymer was added dropwise to the PDMS-F / PDMS-M / HPSi3 mixed solvent, and urea-formaldehyde resin curing agent ammonium chloride and urea-formaldehyde resin water-resistant modifier resorcinol were added, and magnetic stirring was performed for 3 minutes. Then, n-octanol was added dropwise, and the pH of the solution was lowered to about 3.0 with citric acid, and finally the temperature was raised to 60°C, and the mixture was stirred for 3 hours. After filtering, washing, and drying, a sample of electric water tree microcapsules with multi-repair cross-linked polyethylene composite insulation material was obtained. (7) Preparation of composite materials: Low-density polyethylene, antioxidants, microcapsules and cross-linking agents are melt-blended using a torque rheometer, and the cross-linked polyethylene composite material is made into the shape required for the test using a flat vulcanizer. Finally, it is vacuum dried to obtain a microcapsule / cross-linked polyethylene water tree self-healing material with multiple repair effects.

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

6. The method for preparing a microcapsule / cross-linked polyethylene water tree self-repairing 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 insulation properties similar to those of cross-linked polyethylene.

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