1. The crosslinked polyethylene composite material is characterized by comprising the following components in parts by mass: 100 parts of low-density polyethylene, 1.8-2 parts of cross-linking agent, 0.3-0.5 part of auxiliary cross-linking agent, 2-4 parts of nano vinyl cage polysilsesquioxane and 30-40 parts of boron nitride;

the boron nitride is composed of micron-sized boron nitride and nanometer-sized boron nitride, and the mass ratio of the micron-sized boron nitride to the nanometer-sized boron nitride is 2-6: 1.

2. The crosslinked polyethylene composite material according to claim 1, wherein the mass ratio of the boron nitride having the micron-sized particle size to the boron nitride having the nano-sized particle size is 3 to 6: 1.

3. The crosslinked polyethylene composite material according to claim 1 or 2, wherein the boron nitride having a micron-sized particle size has an average median particle size of 5 to 15 μm; the average median particle size of the boron nitride with the particle size of nanometer is 40-60 nm.

4. The crosslinked polyethylene composite of claim 1, wherein the low density polyethylene has a density<0.9230g/cm³The gel content is more than or equal to 82 percent.

5. The crosslinked polyethylene composite of claim 1, wherein the crosslinking agent is dicumyl peroxide or ethane peroxide.

6. The crosslinked polyethylene composite of claim 1, wherein the co-crosslinking agent is one of triallyl cyanurate, triallyl isocyanurate, and trimethylolpropane trimethacrylate.

7. The crosslinked polyethylene composite of claim 1, wherein the nano-vinyl cage polysilsesquioxane has a melting point of >350 ℃ and a flash point of >200 ℃.

8. The crosslinked polyethylene composite material according to claim 1, further comprising 0.2 to 0.3 parts by mass of an antioxidant.

9. A method for preparing a cross-linked polyethylene composite material as claimed in any one of claims 1 to 8, comprising the steps of:

(1) adding a silane coupling agent into an alcohol-water solution, uniformly stirring, adding dried boron nitride to obtain a mixed solution, dispersing the mixed solution by using ultrasonic waves, stirring in a water bath, and finally drying, grinding and screening to obtain surface-treated boron nitride;

(2) adding the dried low-density polyethylene, the antioxidant, the crosslinking agent, the auxiliary crosslinking agent, the nano vinyl cage polysilsesquioxane and the surface-treated boron nitride obtained in the step (1) into an internal mixer, and fully mixing to obtain a mixture;

(3) preheating the mixture obtained in the step (2) by using a vulcanizing machine to fully melt the mixture, pressurizing the vulcanizing machine to 30-50 MPa, heating to 165-185 ℃, pressing the fully melted mixture for 30-60min, keeping the pressure unchanged, cooling to room temperature, and drying to obtain the crosslinked polyethylene composite material.

10. A high voltage ac cable material comprising the crosslinked polyethylene composite of claims 1-8.

Background

In recent years, the urbanization process of China is continuously promoted, the urban power consumption demand is continuously increased, the cable transmission voltage class is developed from 110kV and 220kV to 500kV, the annual average growth rate of high-voltage cable transmission lines is up to 13%, and the cable industry development prospect is wide. Cross-linked polyethylene (XLPE) has significant advantages over oiled paper insulation for use in power cables. Currently, from 35kV medium and low voltage cables to high voltage cables above 110kV internationally, XLPE is used as main insulation. Compared with Polyethylene (PE), crosslinked polyethylene (XLPE) has a three-dimensional reticular macromolecular structure, the mechanical property and the environmental stress crack resistance of the material are obviously improved, and the long-term working temperature of the material is improved from 70 ℃ to 90 ℃. The formula of the high-voltage cable insulating material mainly comprises PE base resin, a cross-linking agent and an antioxidant. In addition, the crosslinked polyethylene insulating material is inevitably in a high-temperature environment in the production and use processes, and is easy to age under the action of heat and oxygen, so that the electrical property, the mechanical property and the thermal stability of the crosslinked polyethylene insulating material are influenced, and the service life of the cable is shortened.

The nano polymer has excellent physical and chemical properties, can improve the charge transport regulation and control capability and breakdown field strength of an insulating medium, and has become a focus of attention in the field of high-voltage insulating material research. On one hand, the nano particles can restrict the movement of the molecular chains of the surrounding polymers in the form of entanglement and the like, and have the function of pinning so as to inhibit the crack propagation process. On the other hand, the interaction between the matrix and the nano particles can change the arrangement mode of polymer molecular chains and regulate the glass transition temperature. The functionalized nanoparticles such as polyhedral oligomeric silsesquioxanes (POSS) can not only exert the nanometer effect, but also improve the dispersibility, the compatibility and the like, realize the functionalization of the nanoparticles, and further greatly improve the mechanical property, the thermal stability, the electrical property and the like of the polymer.

The heat-conducting insulating inorganic filler is mixed into the insulating matrix, and the relatively disordered low-heat-conductivity matrix is replaced by the high-heat-conductivity ordered lattice particles, so that the heat-conducting property of a composite system can be obviously improved, and the novel composite material has good insulating and heat-conducting properties. The currently commonly used inorganic heat-conducting particles mainly include nitrides such as boron nitride, aluminum nitride, silicon nitride and the like. The formation of heat conduction paths inside the matrix is a decisive factor for improving the thermal conductivity of the composite material, and the distribution state of the inorganic particles is very critical. The filling of particles with different types, particle sizes and shapes and the treatment of the particle surfaces are all used for forming effective heat conduction paths in the matrix to the maximum extent so as to improve the heat conductivity of the material.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, improve the high-voltage alternating current breakdown resistance of a crosslinked polyethylene composite material, and provide the crosslinked polyethylene composite material, a preparation method and application thereof.

In order to achieve the purpose, the invention adopts the technical scheme that: the crosslinked polyethylene composite material is characterized by comprising the following components in parts by mass: 100 parts of low-density polyethylene, 1.8-2 parts of cross-linking agent, 0.3-0.5 part of auxiliary cross-linking agent, 2-4 parts of nano vinyl cage polysilsesquioxane and 30-40 parts of boron nitride; the boron nitride is composed of micron-sized boron nitride and nanometer-sized boron nitride, and the mass ratio of the micron-sized boron nitride to the nanometer-sized boron nitride is 2-6: 1.

The crosslinked polyethylene composite material provided by the invention takes nano vinyl cage-type polysilsesquioxane and boron nitride as additives, so that the high-voltage alternating current breakdown resistance of the crosslinked polyethylene composite material can be effectively improved. Boron nitride is an insulator, and the addition of boron nitride can redistribute space charges in the crosslinked polyethylene composite material, thereby causing the electric field to be homogenized, reducing the free volume of the crosslinked polyethylene composite material, and simultaneously, the boron nitride has certain blocking effect on the injection of charges and the transmission of the injected charges. The content of boron nitride also has an influence on the breakdown field strength of the crosslinked polyethylene composite material, and when the content is higher, the boron nitride is difficult to be uniformly distributed in the low-density polyethylene, so that the breakdown performance of the composite material is influenced.

As a preferred embodiment of the crosslinked polyethylene composite material, the mass ratio of the boron nitride with the micron-sized particle size to the boron nitride with the nanometer-sized particle size is 3-6: 1, and the crosslinked polyethylene composite material prepared according to the above ratio has higher insulation breakdown field strength. More preferably, the mass ratio of the boron nitride with the grain diameter of micron scale to the boron nitride with the grain diameter of nanometer scale is 3:1, and the cross-linked polyethylene composite material prepared under the above ratio has the best insulation breakdown field strength.

As a preferred embodiment of the cross-linked polyethylene composite material according to the present invention, the boron nitride is hexagonal boron nitride with a purity > 99.1%.

As a preferred embodiment of the cross-linked polyethylene composite material, the average median particle size of the micron-sized boron nitride is 5-15 μm; the average median particle size of the boron nitride with the particle size of nanometer is 40-60 nm.

The boron nitride with different particle sizes has different distributions and different arrangement modes in the crosslinked polyethylene composite material, and has different blocking effects on the injection of charges and the transmission of injected charges.

As a preferred embodiment of the crosslinked polyethylene composite material of the present invention, the density of the low density polyethylene<0.9230g/cm³The gel content is more than or equal to 82 percent, and the melt mass flow rate of the low-density polyethylene at 190 ℃ under the load of 2.16kg is 0.9-2.1g/10 min.

As a preferred embodiment of the crosslinked polyethylene composite material according to the present invention, the crosslinking agent is dicumyl peroxide or ethane peroxide.

The invention uses dicumyl peroxide or ethane peroxide as a cross-linking agent to form a three-dimensional network structure between molecular chains of polyethylene through cross-linking, and the decomposition temperature of the dicumyl peroxide or the ethane peroxide is lower than the degradation temperature of the polyethylene, thereby avoiding the degradation condition in the polyethylene cross-linking process and effectively preventing the pre-crosslinking phenomenon of the cross-linked polyethylene.

As a preferred embodiment of the crosslinked polyethylene composite material of the present invention, the auxiliary crosslinking agent is one of triallyl cyanurate, triallyl isocyanurate, and trimethylolpropane trimethacrylate.

As a preferred embodiment of the crosslinked polyethylene composite material, the melting point of the nano vinyl cage polysilsesquioxane is more than 350 ℃, and the flash point is more than 200 ℃.

As a preferable embodiment of the crosslinked polyethylene composite material of the present invention, the crosslinked polyethylene composite material further comprises 0.2 to 0.3 parts by mass of an antioxidant.

As a preferred embodiment of the crosslinked polyethylene composite material of the present invention, the antioxidant is one of antioxidant 1010, antioxidant 1035, antioxidant 300, and antioxidant 1076.

In a second aspect, the present invention also provides a method for preparing a crosslinked polyethylene composite material, comprising the steps of:

(1) adding a silane coupling agent into an alcohol-water solution, uniformly stirring, adding dried boron nitride to obtain a mixed solution, dispersing the mixed solution by using ultrasonic waves, stirring in a water bath, and finally drying, grinding and screening to obtain surface-treated boron nitride;

(2) adding the dried low-density polyethylene, the antioxidant, the crosslinking agent, the auxiliary crosslinking agent, the nano vinyl cage polysilsesquioxane and the surface-treated boron nitride obtained in the step (1) into an internal mixer, and fully mixing;

(3) preheating the mixture obtained in the step (2) by using a vulcanizing machine to fully melt the mixture, pressurizing the vulcanizing machine to 30-50 MPa, heating to 165-185 ℃, pressing the fully melted mixture for 30-60min, keeping the pressure unchanged, cooling to room temperature, and drying to obtain the crosslinked polyethylene composite material.

The silane coupling agent can effectively enhance the compatibility of the boron nitride and the low-density polyethylene, and the silane coupling agent can react with hydroxyl on the surface of the boron nitride, so that a silane layer is covered on the surface of the boron nitride, the agglomeration of the boron nitride is effectively prevented, and the dispersibility of the boron nitride is improved. Drying at the end makes it possible to remove impurities from the crosslinked polyethylene composite.

As a preferable embodiment of the method for preparing the crosslinked polyethylene composite material according to the present invention, the volume ratio of ethanol to water in the alcohol-water solution in the step (1) is 95: 5; the mass ratio of the silane coupling agent to the boron nitride is 1: 100.

In a third aspect, the invention also provides an application of the crosslinked polyethylene composite material in a high-voltage alternating-current cable.

Compared with the prior art, the invention has the beneficial effects that: the crosslinked polyethylene composite material provided by the invention takes the nano vinyl cage type polysilsesquioxane and the boron nitride as additives, so that the high-voltage alternating current breakdown resistance of the crosslinked polyethylene composite material can be effectively improved, and the crosslinked polyethylene composite material has important significance for improving the running voltage of domestic alternating current cable materials and the safe and stable running of high-voltage alternating current cables.

Drawings

FIG. 1 is a boron nitride surface treatment process;

FIG. 2 is a Weibull distribution diagram of the AC breakdown field strength of the crosslinked polyethylene composite material obtained in examples 1-7;

FIG. 3 is a Weibull plot of the AC breakdown field strength of the crosslinked polyethylene composite obtained in example 9.

Detailed Description

To better illustrate the objects, aspects and advantages of the present invention, the present invention will be further described with reference to the following detailed description and accompanying drawings.

Example 1

The embodiment provides a crosslinked polyethylene composite material, which comprises the following components in parts by mass: 100 parts of low-density polyethylene, 1.8 parts of dicumyl peroxide, 0.4 part of triallyl cyanurate, 0.2 part of antioxidant 1010, 3 parts of nano vinyl cage polysilsesquioxane and 30 parts of boron nitride; the boron nitride is composed of micron-sized boron nitride and nanometer-sized boron nitride, and the mass ratio of the micron-sized boron nitride to the nanometer-sized boron nitride is 3: 1.

Wherein the boron nitride is hexagonal boron nitride, and the average median particle size of the boron nitride with the particle size of micron order is 10 mu m; the average median particle size of the boron nitride with the nano-scale particle size is 50nm, and the purity is 99.1%; the density of the low density polyethylene is 0.9210g/cm³The melt flow rate is 1.5g/10min, and the gel content is 86%; the melting point of the nano vinyl cage type polysilsesquioxane is 360 ℃, and the flash point of the nano vinyl cage type polysilsesquioxane is 210 ℃.

The embodiment also provides a preparation method of the crosslinked polyethylene composite material, which comprises the following steps:

(1) placing boron nitride in a drying oven, drying for 12h at 110 ℃, preparing an alcohol-water solution (the volume ratio of ethanol to water is 95ml:5ml), adding a silane coupling agent gamma-aminopropyltriethoxysilane into the alcohol-water solution for dissolving, wherein the mass of the silane coupling agent is 1% of that of the boron nitride, stirring for 20 min, and then adding the dried boron nitride into the solution. After the mixture was dispersed by ultrasonic waves for 1 hour, the mixture was stirred in a water bath at 80 ℃ for 3 hours. Placing the ultrasonically dispersed solution in a drying oven, drying for 24h at 110 ℃, carefully grinding and screening after drying to obtain surface-treated boron nitride particles, wherein the schematic diagram of the preparation process is shown in figure 1;

(2) placing low-density polyethylene, dicumyl peroxide, triallyl cyanurate, an antioxidant 1010, nano vinyl cage polysilsesquioxane and boron nitride in a drying oven, drying for 12 hours at 110 ℃, and then fully mixing in an internal mixer for 30 minutes to obtain a mixture, wherein the temperature of the internal mixer is 110 ℃, and the rotating speed of the internal mixer is 100 r/min;

(3) weighing 50g of the mixture obtained in the step (2), placing the mixture in a flat vulcanizing machine, and preheating for 15min at 120 ℃ to fully melt the mixture; and then, pressurizing to 30MPa by a flat vulcanizing machine, raising the temperature to 185 ℃, pressing for 45min, then closing a power supply of the flat vulcanizing machine, keeping the pressure unchanged, naturally cooling the sample to room temperature, then placing the sample in a vacuum drying oven at 80 ℃, and drying in vacuum for 48h to obtain the crosslinked polyethylene composite material, wherein the side length of the obtained crosslinked polyethylene composite material is 80mm multiplied by 80mm, and the thickness of the obtained crosslinked polyethylene composite material is 2 mm.

Example 2

The embodiment provides a crosslinked polyethylene composite material, which comprises the following components in parts by mass: 100 parts of low-density polyethylene, 1.9 parts of ethylene peroxide, 0.3 part of triallyl isocyanurate, 0.25 part of antioxidant 1035, 2 parts of nano vinyl cage polysilsesquioxane and 35 parts of boron nitride; the boron nitride is composed of micron-sized boron nitride and nanometer-sized boron nitride, and the mass ratio of the micron-sized boron nitride to the nanometer-sized boron nitride is 4: 1.

Wherein the boron nitride is hexagonal boron nitride, andthe average median particle size of the boron nitride with the micron-sized particle size is 5 mu m; the average median particle size of the boron nitride with the nano-scale particle size is 40nm, and the purity is 99.1%; the low density polyethylene has a density of 0.9220g/cm³The melt flow rate is 0.9g/10min, and the gel content is 84%; the melting point of the nano vinyl cage type polysilsesquioxane is 355 ℃ and the flash point is 205 ℃.

The embodiment also provides a preparation method of the crosslinked polyethylene composite material, which comprises the following steps:

(1) placing boron nitride in a drying oven, drying for 12h at 110 ℃, preparing an alcohol-water solution (the volume ratio of ethanol to water is 95ml:5ml), adding a silane coupling agent gamma-aminopropyltriethoxysilane into the alcohol-water solution for dissolving, wherein the mass of the silane coupling agent is 1% of that of the boron nitride, stirring for 20 min, and then adding the dried boron nitride into the solution. After the mixture was dispersed by ultrasonic waves for 1 hour, the mixture was stirred in a water bath at 80 ℃ for 3 hours. Drying the ultrasonically dispersed solution in a drying oven at 110 ℃ for 24h, and carefully grinding and screening after drying to obtain surface-treated boron nitride particles;

(2) placing low-density polyethylene, dicumyl peroxide, triallyl cyanurate, an antioxidant 1010, nano vinyl cage polysilsesquioxane and boron nitride in a drying oven, drying for 12 hours at 110 ℃, and then fully mixing in an internal mixer for 30 minutes to obtain a mixture, wherein the temperature of the internal mixer is 110 ℃, and the rotating speed of the internal mixer is 100 r/min;

(3) weighing 50g of the mixture obtained in the step (2), placing the mixture in a flat vulcanizing machine, and preheating for 15min at 120 ℃ to fully melt the mixture; and then, pressurizing to 40MPa by a flat vulcanizing machine, raising the temperature to 175 ℃, pressing for 30min, then closing a power supply of the flat vulcanizing machine, keeping the pressure unchanged, naturally cooling the sample to room temperature, then placing the sample in a vacuum drying oven at 80 ℃, and carrying out vacuum drying for 48h to obtain the crosslinked polyethylene composite material, wherein the side length of the obtained crosslinked polyethylene composite material is 80mm multiplied by 80mm, and the thickness of the obtained crosslinked polyethylene composite material is 2.2 mm.

Example 3

The embodiment provides a crosslinked polyethylene composite material, which comprises the following components in parts by mass: 100 parts of low-density polyethylene, 2 parts of dicumyl peroxide, 0.5 part of trimethylolpropane trimethacrylate, 0.3 part of antioxidant 300, 4 parts of nano vinyl cage polysilsesquioxane and 40 parts of boron nitride; the boron nitride is composed of micron-sized boron nitride and nanometer-sized boron nitride, and the mass ratio of the micron-sized boron nitride to the nanometer-sized boron nitride is 6: 1.

Wherein the boron nitride is hexagonal boron nitride, and the average median particle size of the boron nitride with the micron-sized particle size is 15 mu m; the average median particle size of the boron nitride with the nano-scale particle size is 60nm, and the purity is 99.1%; the low density polyethylene has a density of 0.9230g/cm³The melt flow rate is 2.1g/10min, and the gel content is 82%; the melting point of the nano vinyl cage type polysilsesquioxane is 350 ℃, and the flash point is 200 ℃.

The embodiment also provides a preparation method of the crosslinked polyethylene composite material, which comprises the following steps:

(1) placing boron nitride in a drying oven, drying for 12h at 110 ℃, preparing an alcohol-water solution (the volume ratio of ethanol to water is 95ml:5ml), adding a silane coupling agent gamma-aminopropyltriethoxysilane into the alcohol-water solution for dissolving, wherein the mass of the silane coupling agent is 1% of that of the boron nitride, stirring for 20 min, and then adding the dried boron nitride into the solution. After the mixture was dispersed by ultrasonic waves for 1 hour, the mixture was stirred in a water bath at 80 ℃ for 3 hours. Drying the ultrasonically dispersed solution in a drying oven at 110 ℃ for 24h, and carefully grinding and screening after drying to obtain surface-treated boron nitride particles;

(2) placing low-density polyethylene (LDPE), dicumyl peroxide (DCP), triallyl cyanurate, an antioxidant 1010, nano vinyl cage-type polysilsesquioxane and boron nitride in a drying oven, drying for 12h at 110 ℃, and then fully mixing in an internal mixer for 30min to obtain a mixture, wherein the temperature of the internal mixer is 110 ℃, and the rotating speed of the internal mixer is 100 r/min;

(3) weighing 50g of the mixture obtained in the step (2), placing the mixture in a flat vulcanizing machine, and preheating for 15min at 120 ℃ to fully melt the mixture; and then pressurizing to 50MPa by a flat vulcanizing machine, raising the temperature to 165 ℃, pressing for 60min, then closing a power supply of the flat vulcanizing machine, keeping the pressure unchanged, naturally cooling the sample to room temperature, then placing the sample in a vacuum drying oven at 80 ℃, and drying in vacuum for 48h to obtain the crosslinked polyethylene composite material, wherein the side length of the obtained crosslinked polyethylene composite material is 80mm multiplied by 80mm, and the thickness of the obtained crosslinked polyethylene composite material is 1.8 mm.

Example 4

The embodiment provides a crosslinked polyethylene composite material, which comprises the following components in parts by mass: 100 parts of low-density polyethylene, 1.8 parts of dicumyl peroxide, 0.4 part of triallyl cyanurate, 0.2 part of antioxidant 1076, 3 parts of nano vinyl cage polysilsesquioxane and 30 parts of boron nitride; the boron nitride is composed of micron-sized boron nitride and nanometer-sized boron nitride, and the mass ratio of the micron-sized boron nitride to the nanometer-sized boron nitride is 2: 1.

Wherein the boron nitride is hexagonal boron nitride, and the average median particle size of the boron nitride with the particle size of micron order is 10 mu m; the average median particle size of the boron nitride with the nano-scale particle size is 50nm, and the purity is 99.1%; the density of the low density polyethylene is 0.9210g/cm³The melt flow rate is 1.5g/10min, and the gel content is 86%; the melting point of the nano vinyl cage type polysilsesquioxane is 360 ℃, and the flash point of the nano vinyl cage type polysilsesquioxane is 210 ℃.

The embodiment also provides a preparation method of the crosslinked polyethylene composite material, which comprises the following steps:

(1) placing boron nitride in a drying oven, drying for 12h at 110 ℃, preparing an alcohol-water solution (the volume ratio of ethanol to water is 95ml:5ml), adding a silane coupling agent gamma-aminopropyltriethoxysilane into the alcohol-water solution for dissolving, wherein the mass of the silane coupling agent is 1% of that of the boron nitride, stirring for 20 min, and then adding the dried boron nitride into the solution. After the mixture was dispersed by ultrasonic waves for 1 hour, the mixture was stirred in a water bath at 80 ℃ for 3 hours. Drying the ultrasonically dispersed solution in a drying oven at 110 ℃ for 24h, and carefully grinding and screening after drying to obtain surface-treated boron nitride particles;

(2) placing low-density polyethylene, dicumyl peroxide, triallyl cyanurate, an antioxidant 1010, nano vinyl cage polysilsesquioxane and boron nitride in a drying oven, drying for 12 hours at 110 ℃, and then fully mixing in an internal mixer for 30 minutes to obtain a mixture, wherein the temperature of the internal mixer is 110 ℃, and the rotating speed of the internal mixer is 100 r/min;

(3) weighing 50g of the mixture obtained in the step (2), placing the mixture in a flat vulcanizing machine, and preheating for 15min at 120 ℃ to fully melt the mixture; and then pressurizing to 30MPa by a flat vulcanizing machine, raising the temperature to 185 ℃, pressing for 45min, then closing a power supply of the flat vulcanizing machine, keeping the pressure unchanged, naturally cooling the sample to room temperature, then placing the sample in a vacuum drying oven at 80 ℃, and drying in vacuum for 48h to obtain the crosslinked polyethylene composite material, wherein the side length of the obtained crosslinked polyethylene composite material is 80mm multiplied by 80mm, and the thickness of the obtained crosslinked polyethylene composite material is 2.1 mm.

Example 5

The embodiment provides a crosslinked polyethylene composite material, which comprises the following components in parts by mass: 100 parts of low-density polyethylene, 1.8 parts of dicumyl peroxide, 0.4 part of triallyl cyanurate, 0.2 part of antioxidant 1010, 1 part of nano vinyl cage polysilsesquioxane and 25 parts of boron nitride; the boron nitride is composed of micron-sized boron nitride and nanometer-sized boron nitride, and the mass ratio of the micron-sized boron nitride to the nanometer-sized boron nitride is 3: 1.

Wherein the boron nitride is hexagonal boron nitride, and the average median particle size of the boron nitride with the particle size of micron order is 10 mu m; the average median particle size of the boron nitride with the nano-scale particle size is 50nm, and the purity is 99.1%; the density of the low density polyethylene is 0.9210g/cm³The melt flow rate is 1.5g/10min, and the gel content is 86%; the melting point of the nano vinyl cage type polysilsesquioxane is 360 ℃, and the flash point of the nano vinyl cage type polysilsesquioxane is 210 ℃.

The embodiment also provides a preparation method of the crosslinked polyethylene composite material, which comprises the following steps:

(1) placing boron nitride in a drying oven, drying for 12h at 110 ℃, preparing an alcohol-water solution (the volume ratio of ethanol to water is 95ml:5ml), adding a silane coupling agent gamma-aminopropyltriethoxysilane into the alcohol-water solution for dissolving, wherein the mass of the silane coupling agent is 1% of that of the boron nitride, stirring for 20 min, and then adding the dried boron nitride into the solution. After the mixture was dispersed by ultrasonic waves for 1 hour, the mixture was stirred in a water bath at 80 ℃ for 3 hours. Placing the ultrasonically dispersed solution in a drying oven, drying for 24h at 110 ℃, carefully grinding and screening after drying to obtain surface-treated boron nitride particles, wherein the schematic diagram of the preparation process is shown in figure 1;

(2) placing low-density polyethylene, dicumyl peroxide, triallyl cyanurate, an antioxidant 1010, nano vinyl cage polysilsesquioxane and boron nitride in a drying oven, drying for 12 hours at 110 ℃, and then fully mixing in an internal mixer for 30 minutes to obtain a mixture, wherein the temperature of the internal mixer is 110 ℃, and the rotating speed of the internal mixer is 100 r/min;

(3) weighing 50g of the mixture obtained in the step (2), placing the mixture in a flat vulcanizing machine, and preheating for 15min at 120 ℃ to fully melt the mixture; and then, pressurizing to 30MPa by a flat vulcanizing machine, raising the temperature to 185 ℃, pressing for 45min, then closing a power supply of the flat vulcanizing machine, keeping the pressure unchanged, naturally cooling the sample to room temperature, then placing the sample in a vacuum drying oven at 80 ℃, and drying in vacuum for 48h to obtain the crosslinked polyethylene composite material, wherein the side length of the obtained crosslinked polyethylene composite material is 80mm multiplied by 80mm, and the thickness of the obtained crosslinked polyethylene composite material is 2 mm.

Example 6

The embodiment provides a crosslinked polyethylene composite material, which comprises the following components in parts by mass: 100 parts of low-density polyethylene, 1.8 parts of dicumyl peroxide, 0.4 part of triallyl cyanurate, 0.2 part of antioxidant 1010, 5 parts of nano vinyl cage polysilsesquioxane and 45 parts of boron nitride; the boron nitride is composed of micron-sized boron nitride and nanometer-sized boron nitride, and the mass ratio of the micron-sized boron nitride to the nanometer-sized boron nitride is 3: 1.

Wherein the boron nitride is hexagonal boron nitride, and the average median particle size of the boron nitride with the particle size of micron order is 10 mu m; the average median particle size of the boron nitride with the nano-scale particle size is 50nm, and the purity is 99.1%; the density of the low density polyethylene is 0.9210g/cm³The melt flow rate is 1.5g/10min, and the gel content is 86%; nano meterThe melting point of the vinyl cage polysilsesquioxane is 360 ℃ and the flash point is 210 ℃.

The embodiment also provides a preparation method of the crosslinked polyethylene composite material, which comprises the following steps:

(1) placing boron nitride in a drying oven, drying for 12h at 110 ℃, preparing an alcohol-water solution (the volume ratio of ethanol to water is 95ml:5ml), adding a silane coupling agent gamma-aminopropyltriethoxysilane into the alcohol-water solution for dissolving, wherein the mass of the silane coupling agent is 1% of that of the boron nitride, stirring for 20 min, and then adding the dried boron nitride into the solution. After the mixture was dispersed by ultrasonic waves for 1 hour, the mixture was stirred in a water bath at 80 ℃ for 3 hours. Placing the ultrasonically dispersed solution in a drying oven, drying for 24h at 110 ℃, carefully grinding and screening after drying to obtain surface-treated boron nitride particles, wherein the schematic diagram of the preparation process is shown in figure 1;

(2) placing low-density polyethylene, dicumyl peroxide, triallyl cyanurate, an antioxidant 1010, nano vinyl cage polysilsesquioxane and boron nitride in a drying oven, drying for 12 hours at 110 ℃, and then fully mixing in an internal mixer for 30 minutes to obtain a mixture, wherein the temperature of the internal mixer is 110 ℃, and the rotating speed of the internal mixer is 100 r/min;

(3) weighing 50g of the mixture obtained in the step (2), placing the mixture in a flat vulcanizing machine, and preheating for 15min at 120 ℃ to fully melt the mixture; and then, pressurizing to 30MPa by a flat vulcanizing machine, raising the temperature to 185 ℃, pressing for 45min, then closing a power supply of the flat vulcanizing machine, keeping the pressure unchanged, naturally cooling the sample to room temperature, then placing the sample in a vacuum drying oven at 80 ℃, and drying in vacuum for 48h to obtain the crosslinked polyethylene composite material, wherein the side length of the obtained crosslinked polyethylene composite material is 80mm multiplied by 80mm, and the thickness of the obtained crosslinked polyethylene composite material is 2 mm.

Example 7

The embodiment provides a crosslinked polyethylene composite material, which comprises the following components in parts by mass: 100 parts of low-density polyethylene, 1.8 parts of dicumyl peroxide, 0.4 part of triallyl cyanurate and 0.2 part of antioxidant 1010.

Wherein the low density polyethylene has a density of 0.9210g/cm³Melt flow rate of1.5g/10min, gel content 86%.

The embodiment also provides a preparation method of the crosslinked polyethylene composite material, which comprises the following steps:

(1) placing low-density polyethylene, dicumyl peroxide, triallyl cyanurate and an antioxidant 1010 in a drying oven, drying for 12h at 110 ℃, and then fully mixing in an internal mixer for 30min to obtain a mixture, wherein the temperature of the internal mixer is 110 ℃, and the rotating speed of the internal mixer is 100 r/min;

(2) weighing 50g of the mixture obtained in the step (1), placing the mixture in a flat vulcanizing machine, and preheating for 15min at 120 ℃ to fully melt the mixture; and then, pressurizing to 30MPa by a flat vulcanizing machine, raising the temperature to 185 ℃, pressing for 45min, then closing a power supply of the flat vulcanizing machine, keeping the pressure unchanged, naturally cooling the sample to room temperature, then placing the sample in a vacuum drying oven at 80 ℃, and drying in vacuum for 48h to obtain the crosslinked polyethylene composite material, wherein the side length of the obtained crosslinked polyethylene composite material is 80mm multiplied by 80mm, and the thickness of the obtained crosslinked polyethylene composite material is 2 mm.

Example 8

The AC breakdown field strength of the crosslinked polyethylene composite materials obtained in examples 1 to 7 was measured.

The test method comprises the following steps: the breakdown voltage of the crosslinked polyethylene composite material obtained in examples 1 to 7 was measured at a boosting rate of 1 kV/s.

The test results are shown in fig. 2.

FIG. 2 is a Weibull plot of the AC breakdown field strength of the cross-linked polyethylene composites obtained in examples 1 to 7. As can be seen from FIG. 2, under the same probability, the breakdown field strengths of the composite materials obtained in examples 1-4 are all above 49kV/mm, which are improved by 1.69 times compared with the breakdown field strength of the pure crosslinked polyethylene material in example 7, and the breakdown field strengths of examples 5 and 6 are reduced compared with those of examples 1-4 due to the changed additive content, which indicates that the technical scheme of the present invention can effectively improve the breakdown field strength of the crosslinked polyethylene.

Example 9

In this example, the influence of the mass ratio of the boron nitride with the micron-sized particle size and the boron nitride with the nanometer-sized particle size in the boron nitride on the current-carrying capacity and the insulation breakdown field strength of the high-voltage alternating-current cable of the cross-linked polyethylene composite material of the present invention is further studied. The testing method is as described in example 8, in this example, a to g test groups are provided, and the formula of each group only changes the mass ratio of the boron nitride with the particle size of micron order to the boron nitride with the particle size of nanometer order, as shown in table 1, other components and preparation methods of the crosslinked polyethylene composite material of this example are the same as those of example 1. The test results are shown in fig. 3.

TABLE 1

FIG. 2 is a Weibull plot of the AC breakdown field strength of the cross-linked polyethylene composites obtained in examples 1 to 7. As can be seen from FIG. 3, in 7 test groups, the breakdown field strengths of the composite materials in the c-f groups are the highest and are all more than 50kV/mm, and the mass ratios of the a group, the b group and the g group which are changed are not in the range of the invention, so that the breakdown field strengths are reduced compared with those in the c-f groups, which shows that the technical scheme of the invention can effectively improve the breakdown field strengths of the crosslinked polyethylene.

Finally, it should be noted that the above embodiments are intended to illustrate the technical solutions of the present invention and not to limit the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.