A three-layer shell core microcapsule gradient arrangement structure polyvinyl self-repairing composite medium and a preparation method thereof

Abstract

The application relates to a polyvinyl self-repairing composite material with a three-layer shell core microcapsule gradient arrangement structure and a preparation method thereof, and relates to a polyvinyl self-repairing composite medium and a preparation method thereof. The application aims to provide a polyvinyl self-repairing composite medium with a three-layer shell core microcapsule gradient arrangement structure and a preparation method thereof. The three-layer shell core microcapsule with surface modification of nano-silicon dioxide can reduce the agglomeration phenomenon of the microcapsule, and the gradient arrangement structure can control the dispersion concentration of the microcapsule in the polyvinyl matrix, improve the repair rate, and has good dielectric performance. The silicon dioxide on the surface of the three-layer shell core microcapsule can make the microcapsule and the polyvinyl matrix have better mechanical interlocking ability, make the internal structure of the material more compact, and meanwhile, the nano-silicon dioxide can make the microcapsules in the composite medium independently distributed in the composite material, improve the dispersity of the microcapsules, and reduce the agglomeration phenomenon. The gradient arrangement of the microcapsules in the polyvinyl matrix can make the microcapsules more targetedly distributed in the area of the cable prone to water tree damage, can make a faster response when water tree aging occurs, can improve the repair speed, and can improve the repair rate. The application can obtain a polyvinyl composite self-repairing material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of self-repairing of insulating materials, and particularly relates to a novel polyvinyl self-repairing composite medium with a three-shell-core microcapsule gradient arrangement structure and a preparation method thereof. BACKGROUND

[0002] Polyethylene cables have the characteristics of low cost and large transmission capacity, and as the main type of power cables in China, the long-term stable operation thereof is related to the safe operation of the entire power system. However, due to the limitation of technology, some micro defects may be caused to the cable during production and manufacturing, resulting in poor waterproof performance of most cables and some inevitable concentrated micro defects in the insulation, so that the cable is prone to water tree aging under the long-term action of electric field and moisture, and water tree aging is one of the main factors causing cable insulation aging and service life shortening. Water tree branches grow along the direction of electric field force and begin to branch to form a water tree area, and some water tree branches develop into electric tree branches to cause electric field distortion, and eventually cause the breakdown of cable insulation.

[0003] Although there is a technology for repairing water tree defects in the cable by injecting a repairing agent to react with water, this method requires the cable to be powered off, pressurized and the like, which seriously limits its use range in practical significance, and because there are differences in the diffusion rates of the molecules of the components of the repairing liquid, the initial position is prone to accumulation and blockage of the repairing liquid. Therefore, it is necessary to develop a polyethylene-based composite water tree microcapsule with self-repairing capability to fundamentally explore a method for prolonging the service life of insulating materials.

[0004] When the microcapsules are doped into the polyethylene matrix, due to the randomness, the microcapsules are not uniformly dispersed in the matrix, resulting in that the concentration of the microcapsules is too high in some areas and too low in some areas. The too high concentration of the microcapsules will reduce the mechanical strength and electrical properties of the composite medium, and the too low concentration of the microcapsules will result in that the water tree damage cannot be repaired in time, affecting the water tree repair efficiency. The purpose of the present application is to provide a polyvinyl self-repairing composite medium with a three-shell-core microcapsule gradient arrangement structure and a preparation method thereof. The three-shell-core microcapsules with surface modification by nano-silicon dioxide can reduce the agglomeration of the microcapsules, and the gradient arrangement structure can control the dispersion concentration of the microcapsules in the polyethylene matrix, thereby improving the repair rate and having good dielectric properties. SUMMARY

[0005] The present application is aimed at the deficiencies of the prior art, and provides a polyvinyl self-repairing composite medium with a three-shell-core microcapsule gradient arrangement structure and a preparation method thereof, which is an extension and development of the self-repairing technology of insulating materials.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] A three-layer shell core microcapsule gradient arrangement structure polyvinyl self-repairing composite medium and a preparation method thereof, including preparation of urea-formaldehyde resin prepolymer modified by nano-silica surface, preparation of single-layer shell core microcapsule water phase, formation of single-layer shell core microcapsule, drying treatment of single-layer shell core microcapsule, preparation of three-layer shell core microcapsule water phase, formation of three-layer shell core microcapsule, and finally cooling, washing and drying to obtain a repair polyvinyl self-repairing composite medium water tree microcapsule, and then through melt blending, cross-linking reaction, vacuum drying and multi-layer lamination, the three-layer shell core microcapsule gradient arrangement structure polyvinyl self-repairing composite medium is obtained. Specifically, the following steps are included:

[0008] (1) Preparation of urea-formaldehyde resin prepolymer modified by nano-silica surface: after mixing urea, nano-silica and formaldehyde solution, deionized water is added and stirred, under the magnetic stirring at 300-400 rpm, the pH of the system is adjusted to 8-9 by triethanolamine, and then the system is incubated at 70°C for 60 minutes. Then cool to room temperature. The obtained nano-silica surface modified urea-formaldehyde resin prepolymer is a white solution with certain viscosity;

[0009] (2) Preparation of single-layer shell core microcapsule water phase: under the conditions of mechanical stirring and 40°C water bath, the emulsifier sodium dodecyl benzene sulfonate, the catalyst straight-chain alkyl benzene sulfonic acid and deionized water are mixed and stirred for 40 minutes at a speed of 500 rpm;

[0010] (3) Formation of single-layer shell core microcapsule: the urea-formaldehyde resin prepolymer is added dropwise into the O / W emulsion, and the urea-formaldehyde resin curing agent ammonium chloride and the urea-formaldehyde resin water resistance modifier resorcinol are added, and the system is stirred for 3 minutes by magnetic stirring. Then, 1-2 drops of defoaming agent n-octanol are added, and the pH of the solution is slowly reduced to about 3.0 by citric acid, and the stirring speed is 600 rpm during acidification. Finally, the system is incubated and stirred at 60°C with a stirring speed of 500 rpm, and during the incubation, the stirring speed is reduced to 450, 400, 350 and 300, respectively, and the incubation time is 3 hours;

[0011] (4) Drying treatment of single-layer shell core microcapsule: after the above step is completed, the product is subjected to suction filtration operation by slow double-circle qualitative filter paper, and is washed with alcohol and deionized water respectively for three times to remove impurities, and a filter cake is obtained. Finally, the filter cake is dried at 25°C for 48h to obtain a powder sample of single-layer shell core microcapsule;

[0012] (5) Preparation of three-layer shell core microcapsule water phase: under the conditions of mechanical stirring and 40°C water bath, the emulsifier sodium dodecyl benzene sulfonate, the repair liquid dodecyl trimethoxysilane, the single-layer shell core microcapsule and deionized water are mixed and stirred for 30 minutes at a speed of 400 rpm;

[0013] (6) Formation of three-layer shell core microcapsules: drop the nano-silicon dioxide surface modified urea-formaldehyde resin pre-polymer into the O / W emulsion, and add urea-formaldehyde resin curing agent ammonium chloride and urea-formaldehyde resin water resistance modifier resorcinol, and magnetically stir for 3 minutes. Then, drop 1-2 drops of defoaming agent n-octanol, and then slowly reduce the pH of the solution to about 3.0 with dilute hydrochloric acid, and the rotation speed is 400 rpm during acidification. Finally, the temperature is raised to 60 DEG C, the rotation speed is 300 rpm, the reaction is stirred and heated, and the time is 3 hours;

[0014] (7) Three-layer shell core microcapsule drying treatment: after the reaction is completed, the product is subjected to suction filtration operation by using slow double circle qualitative filter paper, and is washed with alcohol and deionized water respectively for three times to remove impurities, and a filter cake is obtained. Finally, drying is carried out at 25 DEG C for 48 h to obtain a three-layer shell core repair cross-linked polyethylene water tree microcapsule sample;

[0015] (8) Melt blending: after the temperature of the torque rheometer is set to 110 DEG C and the rotation speed is set to 60 rpm, the low-density polyethylene is placed in the torque rheometer, and after the low-density polyethylene is in a molten state and the torque is stable, the antioxidant, the microcapsule and the cross-linking agent are sequentially placed, and the uniformly mixed composite material is taken out and cut into small particles for standby;

[0016] (9) Single-layer medium preparation: according to the shape of the sample, a corresponding mold is made, and the mass of the required composite material is calculated. The temperature of the flat plate vulcanizing machine is set to 110 DEG C, the composite material doped with different concentrations of microcapsules is placed, heating is carried out for 15 minutes, and pressure is increased every 5 minutes. The pressure table is observed in time, and the pressure is supplemented in time when the pressure is insufficient. The temperature of another flat plate vulcanizing machine is set to 175 DEG C, the melted material is placed, the pressure is increased to 15 MPa, and the pressure is supplemented in time. After heating for 35 minutes, the sample is cooled sufficiently; polyethylene-based composite materials doped with different concentrations of microcapsules are obtained.

[0017] (10) Microcapsule gradient arrangement composite medium preparation: the single-layer medium doped with different concentrations of microcapsules prepared in (9) is sequentially placed in the mold according to the designed gradient structure, and the sample is sufficiently cooled after hot pressing at 175 DEG C for 30 minutes using a flat plate vulcanizing machine;

[0018] (11) Vacuum drying: the temperature of the vacuum drying box is set to 80 DEG C, and the prepared composite medium is subjected to vacuum drying treatment to obtain a polyethylene-based self-repairing composite medium with a three-layer shell core microcapsule gradient arrangement structure.

[0019] In the technical scheme of the present application: (1) the particle size of the water-soluble nano-silicon dioxide is 20 nm.

[0020] In the technical scheme of the present application: (3) the mass ratio of the urea-formaldehyde resin wall material to the repair material core material is 2:1.

[0021] In the technical scheme of the present application, the purpose of the pressure increasing in (9) is to make the material fully shaped so as to fully discharge the impurity gas in the material.

[0022] In the technical scheme of the present application, the purpose of step (11) is to reduce the influence of the cross-linking byproducts and residual stress in the sample on the test.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] (1) The water in the insulator is consumed by the reaction between the repairing liquid and the catalyst, and the organic polymer generated after the reaction can fill the micropores, thereby eliminating the water trees, so that the insulation performance of the water tree aged cable can be restored. The organic silicon resin is not easy to decompose at high temperature, has high pressure resistance and good insulation performance, and has similar performance to polyethylene, effectively filling the water tree cavities;

[0025] (2) The microcapsule with a three-layer shell core structure can separate the repairing liquid and the catalyst during the manufacturing process, ensure that the repairing material does not react with water, and also ensure that the microcapsule does not contact water when the microcapsule / polyethylene-based self-repairing composite medium is water tree aged, thereby avoiding invalid reactions;

[0026] (3) The silicon dioxide on the surface of the three-layer shell core microcapsule can make the microcapsule and the polyethylene matrix have better mechanical interlocking ability, so that the internal structure of the material is more compact, and the nano silicon dioxide can make the microcapsules in the composite medium independently distributed in the composite material, thereby improving the dispersibility of the microcapsules and reducing the occurrence of agglomeration;

[0027] (4) The gradient arrangement of the microcapsules in the polyethylene matrix can make the microcapsules more targetedly distributed in the area of the cable where water tree damage is prone to occur, so that the response to water tree aging can be faster, the repair speed can be improved, and the repair rate can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The infrared spectrum is shown in the figure, wherein 1 is a polyethylene-based self-repairing composite medium prepared by the three-layer shell core microcapsule of embodiment one, 2 is a polyethylene-based self-repairing composite medium prepared by the double-layer shell core microcapsule of comparative example one, 3 is a polyethylene-based self-repairing composite medium prepared by the single-layer shell core microcapsule of comparative example two, and 4 is a polyethylene-based self-repairing composite medium prepared by pure wall material of comparative example three.

[0029] Figure 2 The SEM image is shown in the figure, wherein 1 is a three-layer shell core microcapsule prepared by embodiment one, 2 is a double-layer shell core microcapsule prepared by comparative example one, and 3 is a single-layer shell core microcapsule prepared by comparative example two.

[0030] Figure 3 To accelerate the water treeing morphology map formed after water treeing experiment, Figure 1 is a water treeing map of the composite medium prepared in Embodiment One, Figure 2 is a water treeing map of the composite medium prepared in Comparative Example One, and Figure 3 is a water treeing map of the composite medium prepared in Comparative Example Two.

[0031] Figure 4 To accelerate the water treeing morphology map formed after water treeing experiment, Figure 1 is a water treeing map of the composite medium prepared in Embodiment One, Figure 2 is a water treeing map of the composite medium prepared in Comparative Example One, and Figure 3 is a water treeing map of the composite medium prepared in Comparative Example Two.

[0032] Figure 5 To accelerate the water treeing morphology map formed after water treeing experiment, Figure 1 is a water treeing map of the composite medium prepared in Embodiment One, Figure 2 is a water treeing map of the composite medium prepared in Comparative Example One, and Figure 3 is a water treeing map of the composite medium prepared in Comparative Example Two.

[0033] Figure 6 To accelerate the water treeing morphology map formed after water treeing experiment, Figure 1 is a water treeing map of the composite medium prepared in Embodiment One, Figure 2 is a water treeing map of the composite medium prepared in Comparative Example One, and Figure 3 is a water treeing map of the composite medium prepared in Comparative Example Two. DETAILED DESCRIPTION

[0034] The application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be pointed out that, for those skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made. These all belong to the protection scope of the application.

[0035] Specific embodiment one, this embodiment one is a three-layer shell core microcapsule gradient arrangement structure of polyvinyl self-repairing composite medium and its preparation method, which is completed according to the following steps:

[0036] (1) Preparation of nano-silicon dioxide surface modified urea-formaldehyde resin prepolymer: 2g of nano-silicon dioxide and 20g of 37% formaldehyde solution were mixed and stirred, then 20g of urea dissolved in 60g of deionized water was added, under the magnetic stirring of 300~400 rpm, the pH of the system was adjusted to 8~9 with triethanolamine, then it was incubated at 70℃ for 60 minutes. Then it was cooled to room temperature. The obtained nano-silicon dioxide surface modified urea-formaldehyde resin prepolymer is a white solution with certain viscosity;

[0037] (2) Preparation of water phase of single-layer shell core microcapsule: under the conditions of mechanical stirring and 40℃ water bath, 1.5g of emulsifier sodium dodecyl benzene sulfonate, 20g of catalyst straight chain alkyl benzene sulfonic acid and 45g of deionized water were mixed and stirred for 40 minutes at a speed of 500rpm;

[0038] (3) Formation of single-shell core microcapsules: The urea-formaldehyde resin prepolymer was added dropwise to the O / W emulsion, and 1 g of urea-formaldehyde resin curing agent ammonium chloride and 2 g of urea-formaldehyde resin water resistance modifier resorcinol were added, and magnetic stirring was performed for 3 minutes. Then, 1-2 drops of antifoaming agent n-octanol were added, and the pH of the solution was slowly reduced to about 3.0 using citric acid, the stirring speed was 600 rpm during acidification, finally, the temperature was raised to 60°C, the stirring speed was 500 rpm, and the reaction was stirred for 3 hours, during which the stirring speed was reduced to 450, 400, 350, and 300;

[0039] (4) Drying treatment of single-shell core microcapsules: After the reaction was completed, the product was subjected to suction filtration using slow double-circle qualitative filter paper, and was washed with alcohol and deionized water three times respectively to remove impurities, and a filter cake was obtained. Finally, the filter cake was dried at 25°C for 48 h to obtain a powder-like single-shell core microcapsule sample;

[0040] (5) Preparation of water phase of three-shell core microcapsules: Under the conditions of mechanical stirring and a water bath at 40°C, 1.5 g of emulsifier sodium dodecylbenzenesulfonate, 16 g of repair liquid dodecyltrimethoxysilane, 4 g of single-shell core microcapsules, and 45 g of deionized water were mixed and stirred for 30 minutes at a stirring speed of 400 rpm;

[0041] (6) Formation of three-shell core microcapsules: The urea-formaldehyde resin prepolymer modified with nano-silicon dioxide was added dropwise to the O / W emulsion, and 1 g of urea-formaldehyde resin curing agent ammonium chloride and 2 g of urea-formaldehyde resin water resistance modifier resorcinol were added, and magnetic stirring was performed for 3 minutes. Then, 1-2 drops of antifoaming agent n-octanol were added, and the pH of the solution was slowly reduced to about 3.0 using dilute hydrochloric acid, the stirring speed was 400 rpm during acidification, finally, the temperature was raised to 60°C, the stirring speed was 300 rpm, and the reaction was stirred for 3 hours;

[0042] (7) Drying treatment of three-shell core microcapsules: After the reaction was completed, the product was subjected to suction filtration using slow double-circle qualitative filter paper, and was washed with alcohol and deionized water three times respectively to remove impurities, and a filter cake was obtained. Finally, the filter cake was dried at 25°C for 48 h to obtain a three-shell core repair cross-linked polyethylene water tree microcapsule sample;

[0043] (8) Melt blending: 40 g of low-density polyethylene, 0.12 g of antioxidant, and 1%, 1.5%, 2%, and 2.5% of microcapsule content based on the content of low-density polyethylene, and 0.72 g of cross-linking agent were weighed, the temperature of the torque rheometer was set to 110°C, and the stirring speed was set to 60 rpm, then the low-density polyethylene was placed in the torque rheometer, the antioxidant, the microcapsules, and the cross-linking agent were sequentially placed in the torque rheometer at running times of 1 minute, 3 minutes, and 18 minutes, and after 2 minutes, the uniformly mixed composite material was taken out and cut into small particles for standby;

[0044] (9) Single layer medium preparation: according to the shape of the sample, a mold with a length and width of 6 cm and a thickness of 1 mm is made, and the mass of the required composite material is 3.6 g. The temperature of the flat plate vulcanizing machine is set to 110°C, and the composite material wrapped in an iron plate and an oily polyester film is heated for 15 minutes. The pressure gauge value is 0MPa, 5MPa, 10MPa, 15MPa every 5 minutes, and the pressure gauge is observed in time. If the pressure is insufficient, it will be supplemented in time. The temperature of the other flat plate vulcanizing machine is set to 175°C, the melted material is put in, the pressure is increased to 15MPa, and the pressure is supplemented in time. After heating for 35 minutes, the sample is cooled sufficiently; polyvinyl composite materials doped with different concentrations of microcapsules are obtained;

[0045] (10) Preparation of microcapsule gradient arrangement composite medium: the single layer medium doped with different concentrations of microcapsules prepared in (9) is sequentially placed in the mold according to the gradient order of 1%, 1.5%, 2%, 2.5%, and then heated and pressed at 175°C for 30 minutes using a flat plate vulcanizing machine. The sample is cooled sufficiently;

[0046] (11) Vacuum drying: the temperature of the vacuum drying oven is set to 80°C, and the prepared composite medium is subjected to vacuum drying treatment to obtain a polyvinyl self-repairing composite medium with a three-layer shell-core microcapsule gradient arrangement structure.

[0047] Comparative Example 1: The difference between this comparative example and Example 1 is that in step (1) of preparing the urea-formaldehyde resin prepolymer, no nano-silicon dioxide is added.

[0048] Comparative Example 2: The difference between this comparative example and Example 1 is that only steps (1) to (4) in Example 1 are performed, and in step (1) of preparing the urea-formaldehyde resin prepolymer, no nano-silicon dioxide is added, to obtain a raw material. The other steps and parameters are the same as in Example 1.

[0049] Comparative Example 3: The difference between this comparative example and Example 1 is that only steps (1) to (4) in Example 1 are performed, and in step (1) of preparing the urea-formaldehyde resin prepolymer, no nano-silicon dioxide is added, and in step (2), no catalyst, straight-chain alkyl benzene sulfonic acid, is added, to obtain a raw material. The other steps and parameters are the same as in Example 1.

Claims

1. A method for preparing a polyethylene-based self-healing composite medium with a three-layer shell-core microcapsule gradient arrangement structure, characterized in that: The method comprises the following steps: (1) Preparation of urea-formaldehyde resin pre-polymer modified by nano-silica: mixing urea, nano-silica and formaldehyde solution, then adding deionized water and stirring, adjusting the pH value of the solution to 8-9 by using triethanolamine, and obtaining a white solution with certain viscosity; (2) Preparation of single-shell core microcapsules: mixing emulsifier sodium dodecyl benzene sulfonate, catalyst linear alkyl benzene sulfonic acid and deionized water, then adding urea-formaldehyde resin pre-polymer, ammonium chloride and resorcinol dropwise, slowly reducing the pH value of the solution to about 3 by using citric acid, heating to 60 DEG C, and completing the reaction after 3 hours of preservation and stirring, then filtering, washing and drying to obtain powder single-shell core microcapsules; (3) Preparation of three-shell core microcapsules: mixing emulsifier sodium dodecyl benzene sulfonate, repairing liquid dodecyl trimethoxysilane, single-shell core microcapsules and deionized water, then adding nano-silica modified urea-formaldehyde resin pre-polymer, ammonium chloride and resorcinol dropwise, slowly reducing the pH value of the solution to about 3 by using dilute hydrochloric acid, heating to 60 DEG C, and completing the reaction after 3 hours of preservation and stirring, then filtering, washing and drying to obtain microcapsules with three-shell core structure; (4) Preparation of polyethylene single-layer media containing different concentrations of microcapsules: using a torque rheometer to melt blend low-density polyethylene, antioxidant, three-shell core microcapsules and crosslinking agent, using a flat vulcanizing machine to prepare the polyethylene composite medium into the shape required by the test according to different doping concentrations, and finally performing vacuum drying treatment to obtain single-layer media with different microcapsule contents; (5) Preparation of microcapsule gradient arrangement structure composite medium: according to the designed different gradient structures, stacking the prepared single-layer media together through a mold, and using a flat vulcanizing machine to perform hot pressing again to obtain a polyethylene-based self-repairing composite medium with microcapsule gradient arrangement structure.

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