An ice-melting cable inner insulation material and a method for preparing the same

Abstract

The application provides a deicing cable inner insulation material and a preparation method thereof, and belongs to the technical field of materials. Melamine-formaldehyde resin microspheres are immersed in a nano-magnesium oxide and boron nitride nanosheet water dispersion solution to obtain composite microspheres, the composite microspheres are calcined after the addition of a cobalt salt to prepare magnesium oxide / boron nitride / carbon nanotube composite microspheres, hyperbranched polysiloxane modified by a pyrene group is synthesized and grafted to obtain modified microspheres, the modified microspheres are used as functional fillers to be melt-blended and extruded with polyolefin and an initiator to obtain silane grafted polyolefin A material, polyolefin, a compatibilizer and a catalyst are melt-blended and extruded to obtain catalyst masterbatch B material, A material and B material are mixed and formed, and then wet crosslinking treatment is performed to obtain the deicing cable inner insulation material, the thermal conductivity coefficient is improved, the hardness is between that of polyolefin and that of conventional silane crosslinked material, and the deicing cable inner insulation material can be stably and high-speed extruded at 190-220 DEG C, and meanwhile, high electrical insulation and weather resistance are maintained.

Description

Technical Field

[0001] This invention relates to the field of materials technology, specifically to an internal insulation material for de-icing cables and its preparation method. Background Technology

[0002] Icing on transmission lines is one of the major natural disasters facing power systems. Under conditions of high altitude, cold weather, and micro-topography, ice formation such as rime, hoarfrost, or mixed frost easily forms on the surface of conductors. Icing on conductors leads to a sharp increase in mechanical load, deterioration of electrical performance, and increased conductor sag.

[0003] Currently, domestic and international transmission line de-icing / melting technologies are mainly divided into three categories: mechanical de-icing, chemical de-icing, and thermal de-icing. Mechanical de-icing (such as pulley scraping, electromagnetic pulse, and robotic de-icing) has drawbacks such as low operating efficiency, mechanical damage to the conductor surface, and difficulty in adapting to long spans and complex terrain. Chemical de-icing (such as spraying anti-icing coatings and spreading de-icing agents) has problems such as short effective period, environmental pollution, and corrosion of conductors and fittings. Thermal de-icing melts the ice by increasing the conductor current, and is a mature and reliable technology, mainly including short-circuit current de-icing, DC de-icing, and AC de-icing. However, traditional thermal de-icing requires shutting down the line or using external de-icing devices, which is complex to operate and has a significant impact on the power grid operation. In recent years, de-icing cable technology (such as self-heating conductors / heated cables) has received widespread attention. This technology integrates the heating conductor with the transmission conductor, and by passing current through the heating element embedded in the insulation layer, the Joule heating effect is used to raise the conductor temperature, thereby achieving continuous or intermittent de-icing without interrupting power transmission.

[0004] Unlike traditional power cables whose insulation layers only need to meet electrical insulation and mechanical protection requirements, the inner insulation layer of de-icing cables must simultaneously meet the following multiple technical requirements:

[0005] 1. High thermal conductivity. The heat generated by de-icing cables needs to be quickly transferred through the inner insulation layer to the outer conductor and the surface ice layer. If the thermal conductivity of the insulation layer is too low, heat will accumulate in the inner insulation layer, leading to localized thermal stress concentration and accelerating thermal aging of the insulation layer; de-icing efficiency will be low, and energy consumption will increase; the temperature gradient at the conductor-insulation interface will be large, generating thermal expansion mismatch stress. Therefore, the thermal conductivity of the inner insulation material needs to reach 1.0-1.5 W / (m·K), which is a significant improvement compared to conventional cable insulation materials (the thermal conductivity is usually below 0.5 W / (m·K)).

[0006] 2. Moderate Hardness and Mechanical Strength. The inner insulation layer needs sufficient hardness to maintain dimensional stability during extrusion and prevent outer diameter fluctuations due to melt expansion at the outlet or gravity sagging during high-speed extrusion. However, excessive hardness (such as reaching the hardness of polyolefin injection molding grade materials) will lead to increased screw torque in the extruder, melt fracture, and decreased interfacial compliance between the insulation layer and the heating conductor. During thermal cycling, the difference in thermal expansion coefficients will generate interfacial shear stress, causing debonding or microcracks. Therefore, an insulation material with a hardness between traditional silane cross-linked polyethylene (too soft) and polyolefin injection molding materials (too hard) is needed.

[0007] 3. Excellent extrusion processing performance. The inner insulation layer of de-icing cables is usually produced by continuous extrusion (such as single-screw or twin-screw extrusion). The material is required to have: a moderate processing temperature window (around 200℃) to avoid conductor oxidation or insulation pre-crosslinking caused by high temperature (>350℃); good melt flowability to maintain stable cross-sectional dimensions under high-speed (≥20m / min) extrusion; and compatibility with silane crosslinking process, suitable for two-step or one-step silane crosslinking production lines.

[0008] 4. Excellent electrical insulation properties and weather resistance. Despite the improved thermal conductivity, the volume resistivity still needs to be maintained at ≥10. 14 It has a dielectric loss factor of Ω·cm, low dielectric loss factor, and is resistant to tracking, ultraviolet radiation, and ozone, meeting the requirements for long-term outdoor operation.

[0009] Polyolefin insulation materials suffer from drawbacks such as high hardness, high processing temperatures (typically above 360℃), and a low thermal conductivity of only about 0.2-0.3 W / (m·K), resulting in poor heat transfer efficiency. Therefore, silane-crosslinked polyethylene (XLPE) is currently the mainstream insulation material for medium and low voltage cables. Through silane grafting and hydrolytic condensation, it forms a three-dimensional crosslinked network, exhibiting excellent electrical properties and weather resistance. Its processing temperature is moderate (approximately 200℃), making it suitable for continuous extrusion. However, when applied to de-icing cables, it suffers from low thermal conductivity (only 0.3-0.4 W / (m·K), insufficient hardness, and poor thermal cycling stability.

[0010] Therefore, it is necessary to develop a special insulation material for de-icing cables with a thermal conductivity of 1.0-1.5 W / (m·K), a hardness between that of polyolefins and conventional silane crosslinked materials, and the ability to be continuously and stably extruded at around 200℃, so as to simultaneously meet the requirements of de-icing efficiency, structural stability and industrial production. Summary of the Invention

[0011] The purpose of this invention is to propose an internal insulation material for de-icing cables and its preparation method. Addressing the problems of existing technologies, it achieves a synergistic effect of thermal conductivity of 1.0-1.5 W / (m·K), hardness between polyolefin and conventional silane crosslinked materials, and stable high-speed extrusion at 190-220℃, while maintaining high electrical insulation and weather resistance.

[0012] The technical solution of this invention is implemented as follows:

[0013] This invention provides a method for preparing the inner insulation material of a de-icing cable. Melamine-formaldehyde resin microspheres are impregnated in an aqueous dispersion of nano-magnesium oxide and boron nitride nanosheets to obtain composite microspheres. Cobalt salt is added and the mixture is calcined to prepare magnesium oxide / boron nitride / carbon nanotube composite microspheres. Hyperbranched polysiloxanes modified with pyrene groups are synthesized and grafted to obtain modified microspheres. These modified microspheres are then used as functional fillers and melt-blended with polyolefins and initiators to produce silane-grafted polyolefin material A. Simultaneously, polyolefins, compatibilizers, and catalysts are melt-blended and extruded to produce catalyst masterbatch material B. Material A and material B are mixed, molded, and then subjected to wet crosslinking treatment to obtain the inner insulation material of the de-icing cable.

[0014] As a further improvement to the present invention, the following steps are included:

[0015] S1. Formaldehyde and melamine are added to water and heated until the system is clear. Polyvinyl alcohol is added and stirred until evenly mixed. Citric acid is added and the reaction is maintained at a certain temperature. The mixture is then centrifuged, washed, and dried to obtain melamine-formaldehyde resin microspheres.

[0016] S2. Nano-magnesium oxide and boron nitride nanosheets are uniformly dispersed in water to obtain solution A; melamine-formaldehyde resin microspheres are uniformly dispersed in water to obtain solution B; solutions A and B are mixed, the pH value of the solution is adjusted, the reaction is stirred, centrifuged, and dried to obtain composite microspheres;

[0017] S3. Add the composite microspheres to ethanol, add cobalt salt, heat and stir to react, centrifuge, dry, and calcine to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres;

[0018] S4. Mix silane coupling agent KH560, silane coupling agent KH570 and diethylene glycol evenly, heat to react, and distill until the temperature of the distillate drops to 40-50℃ to obtain hyperbranched polysiloxane.

[0019] S5. Add hyperbranched polysiloxane to toluene, add 1-pyrene acetic acid and tetrabutylammonium bromide, heat and stir the reaction under an inert atmosphere, remove the solvent under reduced pressure to obtain hyperbranched polysiloxane containing pyrene groups;

[0020] S6. Carbon nanotube / magnesium oxide / boron nitride composite microspheres were added to N,N-dimethylformamide, and hyperbranched polysiloxane containing pyrene groups were added. The mixture was stirred and reacted, filtered, washed, and dried to obtain modified microspheres.

[0021] S7. Polyolefin, initiator and modified microspheres are mixed evenly and then extruded and granulated to obtain material A; polyolefin, compatibilizer and catalyst are mixed and then extruded and granulated to obtain material B; material A and material B are mixed evenly, and after extrusion, injection molding or blow molding, they are subjected to humidification crosslinking treatment in a constant temperature water bath to obtain the inner insulation material of the de-icing cable.

[0022] In the field of cable insulation materials, high thermal conductivity and electrical insulation are often a difficult contradiction to reconcile. It is well known to those skilled in the art that carbon nanotubes are excellent thermally conductive fillers, but their electrical conductivity is extremely high; even trace amounts can cause an insulating-conductive transition in the polymer matrix (the percolation threshold is typically <1 wt%). In existing technologies, using carbon nanotubes in insulation materials usually requires a large amount of insulating filler for physical isolation or the use of complex insulating coatings, but the effects are limited and the processes are cumbersome.

[0023] This invention uses melamine-formaldehyde resin microspheres as a self-sacrificing template. MgO / boron nitride nanosheets are coated onto the microsphere surface via electrostatic self-assembly. Carbon / nitrogen-containing gases generated from resin pyrolysis are then used as the carbon source, and cobalt salt catalysis is employed to grow carbon nanotubes in situ, allowing the carbon nanotubes to grow and anchor onto the microsphere surface. Subsequently, the π-π stacking effect of hyperbranched polysiloxanes containing pyrene groups is utilized to tightly coat the microspheres. Therefore, through a combined strategy of template confinement and non-covalent coating, the carbon nanotubes are strictly confined within and on the surface of the microsphere structure. The insulating organic layer of the hyperbranched polysiloxane further blocks electron tunneling between the carbon nanotubes. Thus, even with a relatively high carbon nanotube content, the material still maintains a 10... 14 It exhibits high insulation properties at the Ω·cm level while fully utilizing the ultra-high thermal conductivity of carbon nanotubes. Furthermore, melamine-formaldehyde resin is rich in nitrogen; during pyrolysis, nitrogen-containing reducing gases (NH3, CO, etc.) reduce the carbon dioxide content in the carbon nanotubes. 2+ Co nanoparticles are reduced to form a nanocatalyst. Using CO as the carbon source, carbon nanotubes are grown in situ via chemical vapor deposition. Simultaneously, nitrogen-containing gas is incorporated into the carbon nanotube lattice to form nitrogen-doped carbon nanotubes. Nitrogen doping alters the electron cloud density and polarity on the carbon nanotube surface, enhancing the electron donor / acceptor properties of its π-conjugated system. This results in stronger π-π stacking interactions with the pyrene rings, making the hyperbranched polysiloxane coating more robust and less prone to detachment under the strong shear field of melt extrusion.

[0024] Furthermore, the addition of inorganic fillers typically increases polymer melt viscosity and deteriorates processing fluidity. In this invention, the hyperbranched polysiloxane containing pyrene groups not only acts as a compatibilizer but also firmly coats the microspheres on the CNT surface through a "multi-toothed π-π anchoring" of multiple pyrene groups. Its highly branched molecular chains form numerous terminal functional groups (epoxy groups, double bonds, organosiloxane chains) around the microspheres. These flexible branches reduce the molecular chain entanglement density during melt processing, acting as a plasticizer and consequently lowering melt viscosity, thus improving the stability of high-speed extrusion.

[0025] This invention achieves a "self-lubricating" property on the originally rigid inorganic microsphere surface through flexible coating of hyperbranched polysiloxane, reducing friction with the metal wall in the extruder screw and lowering torque. At the same time, the rigid framework of magnesium oxide / boron nitride / carbon nanotubes inside the microsphere ensures the dimensional stability of the melt at the die and prevents sagging, achieving the dual effect of lubrication and stability. This breaks through the single control limitation of traditional fillers that either increase hardness and viscosity or increase toughness and reduce die size.

[0026] As a further improvement of the present invention, the mass ratio of formaldehyde, melamine, polyvinyl alcohol and citric acid in step S1 is 2-4:2-4:0.5-1:0.2-0.5, the heating temperature is 80-90℃, and the heat preservation reaction time is 10-20 min.

[0027] As a further improvement of the present invention, the mass ratio of the nano-magnesium oxide, boron nitride nanosheets, and melamine-formaldehyde resin microspheres in step S2 is 1-3:2-5:50-60, the pH value of the solution is adjusted to 4-5, and the stirring reaction time is 3-5 hours.

[0028] As a further improvement of the present invention, the mass ratio of the composite microspheres and cobalt salt in step S3 is 5-8:0.1-0.2, the cobalt salt is cobalt chloride or cobalt nitrate, the heating and stirring reaction temperature is 40-50℃ and the time is 3-5h, and the heating and calcination temperature is 850-950℃ and the time is 1-2h.

[0029] As a further improvement of the present invention, the mass ratio of silane coupling agent KH560, silane coupling agent KH570 and diethylene glycol in step S4 is 5-6:6-8:9-10, and the temperature of the heating reaction is 120-140℃.

[0030] As a further improvement of the present invention, the mass ratio of hyperbranched polysiloxane, 1-pyrene acetic acid and tetrabutylammonium bromide in step S5 is 10:1-2:0.2-0.3, and the heating and stirring reaction temperature is 90-110℃, and the time is 3-5h.

[0031] As a further improvement of the present invention, the mass ratio of the carbon nanotube / magnesium oxide / boron nitride composite microspheres and the hyperbranched polysiloxane containing pyrene groups in step S6 is 10:2-5, and the stirring reaction time is 1-3 hours.

[0032] As a further improvement of the present invention, in step S7, the extrusion granulation temperature of material A is 190-220℃, the extrusion granulation temperature of material B is 190-200℃, the wet crosslinking treatment temperature is 70-80℃, and the time is 5-10h; the polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene in a mass ratio of 2-3:1-2, the catalyst is dibutyltin dilaurate or dioctyltin dilaurate, the initiator is dicumyl peroxide or di-tert-butyl peroxide, and the compatibilizer is maleic anhydride-grafted polyolefin; in material A, the mass ratio of polyolefin, initiator, and modified microspheres is 100:0.05-0.1:5-10, and in material B, the mass ratio of polyolefin, compatibilizer, and catalyst is 100:3-5:0.01-0.05.

[0033] The present invention further protects an internal insulation material for a de-icing cable prepared by the above-described preparation method.

[0034] The present invention has the following beneficial effects:

[0035] 1. This invention uses a template method to orderly assemble nano-magnesium oxide, boron nitride nanosheets, and carbon nanotubes at the microsphere scale. The boron nitride nanosheets provide in-plane high thermal conductivity pathways, the carbon nanotubes provide ultra-high axial thermal conductivity, and the nano-magnesium oxide provides isotropic thermal conductivity supplementation and reduces interfacial thermal resistance. Confined within the same microsphere, the synergistic effect significantly improves the heat transfer efficiency between the fillers compared to the additive effect of simple physical blending. After surface modification with hyperbranched polysiloxane containing pyrene groups, the microspheres are uniformly dispersed in the polyolefin matrix, forming a secondary thermally conductive contact network between them. Ultimately, the thermal conductivity of the material reaches 1.0-1.5 W / (m·K), a significant improvement over pure polyolefin, effectively solving the problems of heat accumulation and low de-icing efficiency in the insulation layer of de-icing cables.

[0036] 2. This invention achieves precise control over material hardness by controlling the amount of modified microspheres added and the density of silane crosslinking, and by utilizing the buffering effect of the flexible segments of hyperbranched polysiloxane containing pyrene groups. The inorganic ceramic component in the modified microspheres provides the necessary rigidity and stiffness, enabling the material to resist melt outlet expansion and gravitational sag during high-speed extrusion, maintaining stable cross-sectional dimensions. Meanwhile, the organic flexible coating layer of the hyperbranched polysiloxane imparts good interfacial compliance between the microspheres and the matrix, avoiding problems such as increased screw torque, melt fracture, and thermal cycling debonding caused by excessive hardness. The final material hardness falls between that of traditional silane-crosslinked polyethylene (slightly soft) and polyolefin injection molding grade materials (too hard), perfectly meeting the continuous extrusion process requirements of the inner insulation layer of de-icing cables.

[0037] 3. This invention employs a silane grafting / wet crosslinking process, reducing the processing temperature of the polyolefin matrix to 190-220℃, far lower than the processing temperature of pure polyolefins (above 360℃). The introduction of hyperbranched polysiloxanes containing pyrene groups not only improves the compatibility between the filler and the matrix, but its highly branched molecular structure also reduces melt viscosity and improves melt flowability, enabling the material to maintain a uniform and stable outer diameter under high-speed extrusion conditions (≥20 m / min) and minimizing dimensional fluctuations. Simultaneously, the moderate processing temperature avoids the risks of conductor oxidation and insulation pre-crosslinking at high temperatures, significantly improving the stability and yield of industrial production.

[0038] 4. The most outstanding performance balance of this invention lies in the fact that, despite the introduction of highly conductive carbon nanotubes, the material still maintains a high volume resistivity. This is due to the special design of this invention, which grows carbon nanotubes in situ on the surface of MgO / boron nitride ceramic microspheres, confining them to a local area of ​​the microspheres; subsequently, by coating with an insulating layer of hyperbranched polysiloxane, direct contact between the carbon nanotubes and the matrix is ​​further prevented. Therefore, the carbon nanotubes cannot penetrate the polyolefin matrix to form a conductive permeation network, while MgO and boron nitride are themselves excellent inorganic insulating media, ultimately achieving a synergy of high thermal conductivity and high insulation, meeting the electrical safety requirements of cable insulation layers.

[0039] 5. The three-dimensional Si-O-Si network formed by silane crosslinking in this invention endows the material with excellent resistance to heat and oxygen aging; MgO and boron nitride, as inorganic ceramic fillers, possess excellent resistance to ultraviolet radiation, ozone, and electrical tracking; the organic-inorganic hybrid coating layer of hyperbranched polysiloxane containing pyrene groups further blocks the penetration of moisture and oxygen. Under the frequent "power-on heating-power-off cooling" thermal cycle conditions of the de-icing cable, the material interface shear stress is small, making it less prone to microcracks and debonding, resulting in high long-term operational reliability and good weather resistance. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a SEM image of the internal insulation material of the ice-melting cable prepared in Example 2. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Nano-sized magnesium oxide, average particle size 50 nm. Boron nitride nanosheets, 1-5 μm in diameter, 20-40 nm in thickness. High-density polyethylene, grade 8008, granules, weight average molecular weight 2.3 × 10⁻⁶. 5 g / mol, melt index 7.6 g / 10 min (230℃, 2.16 kg); linear low-density polyethylene, grade 7042, granules, weight average molecular weight 14 × 10⁻⁶ g / mol, melt index 7.6 g / 10 min (230℃, 2.16 kg); 4 g / mol, melt index is 2.6 g / 10 min (190℃, 21.6 N).

[0044] Example 1

[0045] This embodiment provides a method for preparing the inner insulation material of a de-icing cable, including the following steps:

[0046] S1. Add 2g formaldehyde solution and 2g melamine to 150mL water, heat to 80℃, stir until the system is clear, add 0.5g polyvinyl alcohol, stir and mix evenly, add 0.2g citric acid, keep warm and react for 10min, centrifuge, wash with water, dry, and obtain melamine-formaldehyde resin microspheres.

[0047] S2. Add 0.1g of nano-magnesium oxide and 0.2g of boron nitride nanosheets to 200mL of water, sonicate at 200W for 20min to disperse evenly, to obtain solution A; add 5g of melamine-formaldehyde resin microspheres to 1L of water, sonicate at 300W for 20min to disperse evenly, to obtain solution B; mix solution A and solution B, adjust the pH of the solution to 4-5, stir and react for 3h, centrifuge, and dry to obtain composite microspheres;

[0048] S3. Add 5g of composite microspheres to 200mL of ethanol, add 0.1g of cobalt chloride, heat to 40℃, stir for 5h, centrifuge, dry, heat to 850℃, calcine for 2h to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres.

[0049] S4. Mix 5g of silane coupling agent KH560, 6g of silane coupling agent KH570 and 9g of diethylene glycol evenly, heat to 120℃, stir and react, and distill at the same time. The distillation temperature is maintained at 65±2℃. After stirring and reacting for 1 hour, increase the temperature to 150℃ until the temperature of the distillate drops to 40-50℃ to obtain hyperbranched polysiloxane.

[0050] S5. Add 10g of hyperbranched polysiloxane to 100mL of toluene, add 1g of 1-pyrene acetic acid and 0.2g of tetrabutylammonium bromide, heat to 90℃ under nitrogen atmosphere, stir and react for 5h, remove solvent under reduced pressure to obtain hyperbranched polysiloxane containing pyrene groups.

[0051] S6. Add 10g of carbon nanotube / magnesium oxide / boron nitride composite microspheres to 50mL of N,N-dimethylformamide, add 2g of hyperbranched polysiloxane containing pyrene groups, stir and react for 1h, filter, wash with acetone, dry, and obtain modified microspheres.

[0052] S7. 100g of polyolefin, 0.05g of dicumyl peroxide, and 5g of modified microspheres are mixed evenly and extruded and granulated at 220℃ to obtain material A; 100g of polyolefin, 3g of maleic anhydride-grafted polyolefin, and 0.01g of dibutyltin dilaurate are mixed and extruded and granulated at 200℃ to obtain material B; materials A and B are mixed evenly, extruded, injection molded, and then subjected to a humidification crosslinking treatment in a 70℃ constant temperature water bath for 10 hours to obtain the inner insulation material for the de-icing cable. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene in a mass ratio of 3:2.

[0053] Example 2

[0054] This embodiment provides a method for preparing the inner insulation material of a de-icing cable, including the following steps:

[0055] S1. Add 4g formaldehyde solution and 4g melamine to 150mL water, heat to 90℃, stir until the system is clear, add 1g polyvinyl alcohol, stir and mix evenly, add 0.5g citric acid, keep warm and react for 20min, centrifuge, wash with water, dry, and obtain melamine-formaldehyde resin microspheres.

[0056] S2. Add 0.3g of nano-magnesium oxide and 0.5g of boron nitride nanosheets to 200mL of water, sonicate at 200W for 20min to disperse evenly, and obtain solution A; add 6g of melamine-formaldehyde resin microspheres to 1L of water, sonicate at 300W for 20min to disperse evenly, and obtain solution B; mix solution A and solution B, adjust the pH of the solution to 4-5, stir and react for 5h, centrifuge, and dry to obtain composite microspheres;

[0057] S3. Add 8g of composite microspheres to 200mL of ethanol, add 0.2g of cobalt nitrate, heat to 50℃, stir for 3h, centrifuge, dry, heat to 950℃ under nitrogen atmosphere, calcine for 1h to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres.

[0058] S4. Mix 6g of silane coupling agent KH560, 8g of silane coupling agent KH570 and 10g of diethylene glycol evenly, heat to 140℃, stir and react, and distill at the same time. The distillation temperature is maintained at 65±2℃. After stirring and reacting for 2 hours, increase the temperature to 150℃ until the temperature of the distillate drops to 40-50℃ to obtain hyperbranched polysiloxane.

[0059] S5. Add 10g of hyperbranched polysiloxane to 100mL of toluene, add 2g of 1-pyrene acetic acid and 0.3g of tetrabutylammonium bromide, heat to 110℃ under nitrogen atmosphere, stir and react for 3h, remove solvent under reduced pressure to obtain hyperbranched polysiloxane containing pyrene groups.

[0060] S6. Add 10g of carbon nanotube / magnesium oxide / boron nitride composite microspheres to 50mL of N,N-dimethylformamide, add 5g of hyperbranched polysiloxane containing pyrene groups, stir and react for 3h, filter, wash with acetone, dry, and obtain modified microspheres.

[0061] S7. 100g of polyolefin, 0.1g of di-tert-butyl peroxide, and 10g of modified microspheres were mixed evenly and then extruded and granulated at 190℃ to obtain material A. 100g of polyolefin, 5g of maleic anhydride-grafted polyolefin, and 0.05g of dioctyltin dilaurate were mixed and extruded and granulated at 190℃ to obtain material B. Materials A and B were mixed evenly, extruded, blow-molded, and then subjected to a wet crosslinking treatment in an 80℃ constant temperature water bath for 5 hours to obtain the internal insulation material for the de-icing cable. Its SEM image is shown below. Figure 1 The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene in a mass ratio of 2:1.

[0062] Example 3

[0063] This embodiment provides a method for preparing the inner insulation material of a de-icing cable, including the following steps:

[0064] S1. Add 2.6g formaldehyde solution and 2.5g melamine to 150mL water, heat to 85℃, stir until the system is clear, add 0.6g polyvinyl alcohol, stir and mix evenly, add 0.3g citric acid, keep warm and react for 15min, centrifuge, wash with water, dry, and obtain melamine-formaldehyde resin microspheres.

[0065] S2. Add 0.15g of nano-magnesium oxide and 0.3g of boron nitride nanosheets to 200mL of water, sonicate at 200W for 20min to disperse evenly, to obtain solution A; add 5.2g of melamine-formaldehyde resin microspheres to 1L of water, sonicate at 300W for 20min to disperse evenly, to obtain solution B; mix solution A and solution B, adjust the pH of the solution to 4-5, stir and react for 4h, centrifuge, and dry to obtain composite microspheres;

[0066] S3. Add 5.5g of composite microspheres to 200mL of ethanol, add 0.14g of cobalt chloride, heat to 45℃, stir and react for 4h, centrifuge, dry, heat to 900℃ under nitrogen atmosphere, and calcine for 1.5h to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres.

[0067] S4. Mix 5.2g of silane coupling agent KH560, 6.5g of silane coupling agent KH570 and 9.3g of diethylene glycol evenly, heat to 130℃, stir and react, and distill at the same time. The distillation temperature is maintained at 65±2℃. After stirring and reacting for 1.5h, the temperature is increased to 150℃ until the temperature of the distillate drops to 40-50℃ to obtain hyperbranched polysiloxane.

[0068] S5. Add 10g of hyperbranched polysiloxane to 100mL of toluene, add 1.2g of 1-pyrene acetic acid and 0.23g of tetrabutylammonium bromide, heat to 100℃ under nitrogen atmosphere, stir and react for 4h, remove solvent under reduced pressure to obtain hyperbranched polysiloxane containing pyrene groups.

[0069] S6. Add 10g of carbon nanotube / magnesium oxide / boron nitride composite microspheres to 50mL of N,N-dimethylformamide, add 2.7g of hyperbranched polysiloxane containing pyrene groups, stir and react for 2h, filter, wash with acetone, dry, and obtain modified microspheres.

[0070] S7. 100g of polyolefin, 0.06g of di-tert-butyl peroxide, and 6g of modified microspheres are mixed evenly and extruded and granulated at 220℃ to obtain material A. 100g of polyolefin, 3.5g of maleic anhydride-grafted polyolefin, and 0.02g of dibutyltin dilaurate are mixed and extruded and granulated at 200℃ to obtain material B. Materials A and B are mixed evenly, extruded, injection molded, and then subjected to a 75℃ constant temperature water bath for 7 hours for wet crosslinking treatment to obtain the inner insulation material for the de-icing cable. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene at a mass ratio of 2.2:1.6.

[0071] Example 4

[0072] This embodiment provides a method for preparing the inner insulation material of a de-icing cable, including the following steps:

[0073] S1. Add 3.4g formaldehyde solution and 3.7g melamine to 150mL water, heat to 85℃, stir until the system is clear, add 0.8g polyvinyl alcohol, stir and mix evenly, add 0.35g citric acid, keep warm and react for 15min, centrifuge, wash with water, dry, and obtain melamine-formaldehyde resin microspheres.

[0074] S2. Add 0.26g of nano-magnesium oxide and 0.42g of boron nitride nanosheets to 200mL of water, sonicate at 200W for 20min to disperse evenly, to obtain solution A; add 5.8g of melamine-formaldehyde resin microspheres to 1L of water, sonicate at 300W for 20min to disperse evenly, to obtain solution B; mix solutions A and B, adjust the pH of the solution to 4-5, stir and react for 4h, centrifuge, and dry to obtain composite microspheres;

[0075] S3. Add 7.2g of composite microspheres to 200mL of ethanol, add 0.18g of cobalt chloride, heat to 45℃, stir for 4h, centrifuge, dry, heat to 900℃ under nitrogen atmosphere, and calcine for 1.5h to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres.

[0076] S4. Mix 5.7g of silane coupling agent KH560, 7.4g of silane coupling agent KH570 and 9.8g of diethylene glycol evenly, heat to 130℃, stir and react, and distill at the same time. The distillation temperature is maintained at 65±2℃. After stirring and reacting for 1.5h, the temperature is increased to 150℃ until the temperature of the distillate drops to 40-50℃ to obtain hyperbranched polysiloxane.

[0077] S5. Add 10g of hyperbranched polysiloxane to 100mL of toluene, add 1.8g of 1-pyrene acetic acid and 0.27g of tetrabutylammonium bromide, heat to 100℃ under nitrogen atmosphere, stir and react for 4h, remove solvent under reduced pressure to obtain hyperbranched polysiloxane containing pyrene groups.

[0078] S6. Add 10g of carbon nanotube / magnesium oxide / boron nitride composite microspheres to 50mL of N,N-dimethylformamide, add 4.2g of hyperbranched polysiloxane containing pyrene groups, stir and react for 2h, filter, wash with acetone, dry, and obtain modified microspheres.

[0079] S7. 100g of polyolefin, 0.08g of dicumyl peroxide, and 8g of modified microspheres are mixed evenly and extruded and granulated at 210℃ to obtain material A; 100g of polyolefin, 4.5g of maleic anhydride-grafted polyolefin, and 0.035g of dioctyltin dilaurate are mixed and extruded and granulated at 190℃ to obtain material B; materials A and B are mixed evenly, extruded, injection molded, and then subjected to a humidification crosslinking treatment in a 75℃ constant temperature water bath for 8 hours to obtain the inner insulation material for de-icing cables. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene at a mass ratio of 2.8:1.2.

[0080] Example 5

[0081] This embodiment provides a method for preparing the inner insulation material of a de-icing cable, including the following steps:

[0082] S1. Add 3g formaldehyde solution and 3g melamine to 150mL water, heat to 85℃, stir until the system is clear, add 0.7g polyvinyl alcohol, stir and mix evenly, add 0.35g citric acid, keep warm and react for 15min, centrifuge, wash with water, dry, and obtain melamine-formaldehyde resin microspheres.

[0083] S2. Add 0.2g of nano-magnesium oxide and 0.35g of boron nitride nanosheets to 200mL of water, sonicate at 200W for 20min to disperse evenly, to obtain solution A; add 5.5g of melamine-formaldehyde resin microspheres to 1L of water, sonicate at 300W for 20min to disperse evenly, to obtain solution B; mix solution A and solution B, adjust the pH of the solution to 4-5, stir and react for 4h, centrifuge, and dry to obtain composite microspheres;

[0084] S3. Add 6g of composite microspheres to 200mL of ethanol, add 0.15g of cobalt chloride, heat to 45℃, stir and react for 4h, centrifuge, dry, heat to 900℃ under nitrogen atmosphere, and calcine for 1.5h to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres.

[0085] S4. Mix 5.5g of silane coupling agent KH560, 7g of silane coupling agent KH570 and 9.5g of diethylene glycol evenly, heat to 130℃, stir and react, and distill at the same time. The distillation temperature is maintained at 65±2℃. After stirring and reacting for 1.5h, the temperature is increased to 150℃ until the temperature of the distillate drops to 45℃ to obtain hyperbranched polysiloxane.

[0086] S5. Add 10g of hyperbranched polysiloxane to 100mL of toluene, add 1.5g of 1-pyrene acetic acid and 0.25g of tetrabutylammonium bromide, heat to 100℃ under nitrogen atmosphere, stir and react for 4h, remove solvent under reduced pressure to obtain hyperbranched polysiloxane containing pyrene groups.

[0087] S6. Add 10g of carbon nanotube / magnesium oxide / boron nitride composite microspheres to 50mL of N,N-dimethylformamide, add 3.5g of hyperbranched polysiloxane containing pyrene groups, stir and react for 2h, filter, wash with acetone, dry, and obtain modified microspheres.

[0088] S7. 100g of polyolefin, 0.075g of di-tert-butyl peroxide, and 7g of modified microspheres are mixed evenly and extruded and granulated at 200℃ to obtain material A. 100g of polyolefin, 4g of maleic anhydride-grafted polyolefin, and 0.03g of dibutyltin dilaurate are mixed and extruded and granulated at 200℃ to obtain material B. Materials A and B are mixed evenly, extruded, injection molded, and then subjected to a 75℃ constant temperature water bath for 7 hours for wet crosslinking treatment to obtain the inner insulation material for the de-icing cable. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene at a mass ratio of 2.5:1.4.

[0089] Comparative Example 1

[0090] Compared with Example 5, the only difference is that steps S1 and S3 were not performed. In step S2, 0.2g of nano-magnesium oxide and 0.35g of boron nitride nanosheets were mixed evenly to obtain a mixture.

[0091] Includes the following steps:

[0092] S1. Mix 0.2g of nano-magnesium oxide and 0.35g of boron nitride nanosheets evenly to obtain a mixture;

[0093] S2. Mix 5.5g of silane coupling agent KH560, 7g of silane coupling agent KH570 and 9.5g of diethylene glycol evenly, heat to 130℃, stir and react, and distill at the same time. The distillation temperature is maintained at 65±2℃. After stirring and reacting for 1.5h, the temperature is increased to 150℃ until the temperature of the distillate drops to 45℃ to obtain hyperbranched polysiloxane.

[0094] S3. Add 10g of hyperbranched polysiloxane to 100mL of toluene, add 1.5g of 1-pyrene acetic acid and 0.25g of tetrabutylammonium bromide, heat to 100℃ under nitrogen atmosphere, stir and react for 4h, remove the solvent under reduced pressure to obtain hyperbranched polysiloxane containing pyrene groups.

[0095] S4. Add 10g of the mixture to 50mL of N,N-dimethylformamide, add 3.5g of hyperbranched polysiloxane containing pyrene groups, stir and react for 2h, filter, wash with acetone, dry, and obtain the modified mixture;

[0096] S5. 100g of polyolefin, 0.075g of di-tert-butyl peroxide, and 7g of modified mixture are mixed evenly and then extruded and granulated at 200℃ to obtain material A. 100g of polyolefin, 4g of maleic anhydride-grafted polyolefin, and 0.03g of dibutyltin dilaurate are mixed and extruded and granulated at 200℃ to obtain material B. Materials A and B are mixed evenly, extruded, injection molded, and then subjected to a 75℃ constant temperature water bath for 7 hours for wet crosslinking treatment to obtain the inner insulation material for the de-icing cable. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene at a mass ratio of 2.5:1.4.

[0097] Comparative Example 2

[0098] The only difference from Example 5 is that boron nitride nanosheets were not added in step S2.

[0099] Includes the following steps:

[0100] S1. Add 3g formaldehyde solution and 3g melamine to 150mL water, heat to 85℃, stir until the system is clear, add 0.7g polyvinyl alcohol, stir and mix evenly, add 0.35g citric acid, keep warm and react for 15min, centrifuge, wash with water, dry, and obtain melamine-formaldehyde resin microspheres.

[0101] S2. Add 0.55g of nano-magnesium oxide to 200mL of water, sonicate at 200W for 20min to disperse evenly, and obtain solution A; add 5.5g of melamine-formaldehyde resin microspheres to 1L of water, sonicate at 300W for 20min to disperse evenly, and obtain solution B; mix solution A and solution B, adjust the pH of the solution to 4-5, stir and react for 4h, centrifuge, and dry to obtain composite microspheres;

[0102] S3. Add 6g of composite microspheres to 200mL of ethanol, add 0.15g of cobalt chloride, heat to 45℃, stir and react for 4h, centrifuge, dry, heat to 900℃ under nitrogen atmosphere, and calcine for 1.5h to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres.

[0103] S4. Mix 5.5g of silane coupling agent KH560, 7g of silane coupling agent KH570 and 9.5g of diethylene glycol evenly, heat to 130℃, stir and react, and distill at the same time. The distillation temperature is maintained at 65±2℃. After stirring and reacting for 1.5h, the temperature is increased to 150℃ until the temperature of the distillate drops to 45℃ to obtain hyperbranched polysiloxane.

[0104] S5. Add 10g of hyperbranched polysiloxane to 100mL of toluene, add 1.5g of 1-pyrene acetic acid and 0.25g of tetrabutylammonium bromide, heat to 100℃ under nitrogen atmosphere, stir and react for 4h, remove solvent under reduced pressure to obtain hyperbranched polysiloxane containing pyrene groups.

[0105] S6. Add 10g of carbon nanotube / magnesium oxide / boron nitride composite microspheres to 50mL of N,N-dimethylformamide, add 3.5g of hyperbranched polysiloxane containing pyrene groups, stir and react for 2h, filter, wash with acetone, dry, and obtain modified microspheres.

[0106] S7. 100g of polyolefin, 0.075g of di-tert-butyl peroxide, and 7g of modified microspheres are mixed evenly and extruded and granulated at 200℃ to obtain material A. 100g of polyolefin, 4g of maleic anhydride-grafted polyolefin, and 0.03g of dibutyltin dilaurate are mixed and extruded and granulated at 200℃ to obtain material B. Materials A and B are mixed evenly, extruded, injection molded, and then subjected to a 75℃ constant temperature water bath for 7 hours for wet crosslinking treatment to obtain the inner insulation material for the de-icing cable. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene at a mass ratio of 2.5:1.4.

[0107] Comparative Example 3

[0108] The only difference from Example 5 is that nano-magnesium oxide was not added in step S2.

[0109] Includes the following steps:

[0110] S1. Add 3g formaldehyde solution and 3g melamine to 150mL water, heat to 85℃, stir until the system is clear, add 0.7g polyvinyl alcohol, stir and mix evenly, add 0.35g citric acid, keep warm and react for 15min, centrifuge, wash with water, dry, and obtain melamine-formaldehyde resin microspheres.

[0111] S2. Add 0.55g of boron nitride nanosheets to 200mL of water, sonicate at 200W for 20min to disperse evenly, to obtain solution A; add 5.5g of melamine-formaldehyde resin microspheres to 1L of water, sonicate at 300W for 20min to disperse evenly, to obtain solution B; mix solution A and solution B, adjust the pH of the solution to 4-5, stir and react for 4h, centrifuge, and dry to obtain composite microspheres;

[0112] S3. Add 6g of composite microspheres to 200mL of ethanol, add 0.15g of cobalt chloride, heat to 45℃, stir and react for 4h, centrifuge, dry, heat to 900℃ under nitrogen atmosphere, and calcine for 1.5h to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres.

[0113] S4. Mix 5.5g of silane coupling agent KH560, 7g of silane coupling agent KH570 and 9.5g of diethylene glycol evenly, heat to 130℃, stir and react, and distill at the same time. The distillation temperature is maintained at 65±2℃. After stirring and reacting for 1.5h, the temperature is increased to 150℃ until the temperature of the distillate drops to 45℃ to obtain hyperbranched polysiloxane.

[0114] S5. Add 10g of hyperbranched polysiloxane to 100mL of toluene, add 1.5g of 1-pyrene acetic acid and 0.25g of tetrabutylammonium bromide, heat to 100℃ under nitrogen atmosphere, stir and react for 4h, remove solvent under reduced pressure to obtain hyperbranched polysiloxane containing pyrene groups.

[0115] S6. Add 10g of carbon nanotube / magnesium oxide / boron nitride composite microspheres to 50mL of N,N-dimethylformamide, add 3.5g of hyperbranched polysiloxane containing pyrene groups, stir and react for 2h, filter, wash with acetone, dry, and obtain modified microspheres.

[0116] S7. 100g of polyolefin, 0.075g of di-tert-butyl peroxide, and 7g of modified microspheres are mixed evenly and extruded and granulated at 200℃ to obtain material A. 100g of polyolefin, 4g of maleic anhydride-grafted polyolefin, and 0.03g of dibutyltin dilaurate are mixed and extruded and granulated at 200℃ to obtain material B. Materials A and B are mixed evenly, extruded, injection molded, and then subjected to a 75℃ constant temperature water bath for 7 hours for wet crosslinking treatment to obtain the inner insulation material for the de-icing cable. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene at a mass ratio of 2.5:1.4.

[0117] Comparative Example 4

[0118] The only difference from Example 5 is that step S5 was not performed.

[0119] Includes the following steps:

[0120] S1. Add 3g formaldehyde solution and 3g melamine to 150mL water, heat to 85℃, stir until the system is clear, add 0.7g polyvinyl alcohol, stir and mix evenly, add 0.35g citric acid, keep warm and react for 15min, centrifuge, wash with water, dry, and obtain melamine-formaldehyde resin microspheres.

[0121] S2. Add 0.2g of nano-magnesium oxide and 0.35g of boron nitride nanosheets to 200mL of water, sonicate at 200W for 20min to disperse evenly, to obtain solution A; add 5.5g of melamine-formaldehyde resin microspheres to 1L of water, sonicate at 300W for 20min to disperse evenly, to obtain solution B; mix solution A and solution B, adjust the pH of the solution to 4-5, stir and react for 4h, centrifuge, and dry to obtain composite microspheres;

[0122] S3. Add 6g of composite microspheres to 200mL of ethanol, add 0.15g of cobalt chloride, heat to 45℃, stir and react for 4h, centrifuge, dry, heat to 900℃ under nitrogen atmosphere, and calcine for 1.5h to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres.

[0123] S4. Mix 5.5g of silane coupling agent KH560, 7g of silane coupling agent KH570 and 9.5g of diethylene glycol evenly, heat to 130℃, stir and react, and distill at the same time. The distillation temperature is maintained at 65±2℃. After stirring and reacting for 1.5h, the temperature is increased to 150℃ until the temperature of the distillate drops to 45℃ to obtain hyperbranched polysiloxane.

[0124] S5. Add 10g of carbon nanotube / magnesium oxide / boron nitride composite microspheres to 50mL of N,N-dimethylformamide, add 3.5g of hyperbranched polysiloxane, stir and react for 2h, filter, wash with acetone, dry, and obtain modified microspheres.

[0125] S6. 100g of polyolefin, 0.075g of di-tert-butyl peroxide, and 7g of modified microspheres are mixed evenly and extruded and granulated at 200℃ to obtain material A. 100g of polyolefin, 4g of maleic anhydride-grafted polyolefin, and 0.03g of dibutyltin dilaurate are mixed and extruded and granulated at 200℃ to obtain material B. Materials A and B are mixed evenly, extruded, injection molded, and then subjected to a 75℃ constant temperature water bath for 7 hours for wet crosslinking treatment to obtain the inner insulation material for the de-icing cable. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene in a mass ratio of 2.5:1.4.

[0126] Comparative Example 5

[0127] The only difference from Example 5 is that steps S4, S5, and S6 were not performed.

[0128] Includes the following steps:

[0129] S1. Add 3g formaldehyde solution and 3g melamine to 150mL water, heat to 85℃, stir until the system is clear, add 0.7g polyvinyl alcohol, stir and mix evenly, add 0.35g citric acid, keep warm and react for 15min, centrifuge, wash with water, dry, and obtain melamine-formaldehyde resin microspheres.

[0130] S2. Add 0.2g of nano-magnesium oxide and 0.35g of boron nitride nanosheets to 200mL of water, sonicate at 200W for 20min to disperse evenly, to obtain solution A; add 5.5g of melamine-formaldehyde resin microspheres to 1L of water, sonicate at 300W for 20min to disperse evenly, to obtain solution B; mix solution A and solution B, adjust the pH of the solution to 4-5, stir and react for 4h, centrifuge, and dry to obtain composite microspheres;

[0131] S3. Add 6g of composite microspheres to 200mL of ethanol, add 0.15g of cobalt chloride, heat to 45℃, stir and react for 4h, centrifuge, dry, heat to 900℃ under nitrogen atmosphere, and calcine for 1.5h to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres.

[0132] S4. 100g of polyolefin, 0.075g of di-tert-butyl peroxide, and 7g of carbon nanotube / magnesium oxide / boron nitride composite microspheres are mixed evenly and extruded and granulated at 200℃ to obtain material A. 100g of polyolefin, 4g of maleic anhydride-grafted polyolefin, and 0.03g of dibutyltin dilaurate are mixed and extruded and granulated at 200℃ to obtain material B. Materials A and B are mixed evenly, extruded, injection molded, and then subjected to a 75℃ constant temperature water bath for 7 hours for wet crosslinking treatment to obtain the inner insulation material for the de-icing cable. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene at a mass ratio of 2.5:1.4.

[0133] Comparative Example 6

[0134] Compared with Example 5, the only difference is that steps S4, S5 and S6 were not performed, and the carbon nanotube / magnesium oxide / boron nitride composite microspheres were directly modified with KH560 and KH570.

[0135] Includes the following steps:

[0136] S1. Add 3g formaldehyde solution and 3g melamine to 150mL water, heat to 85℃, stir until the system is clear, add 0.7g polyvinyl alcohol, stir and mix evenly, add 0.35g citric acid, keep warm and react for 15min, centrifuge, wash with water, dry, and obtain melamine-formaldehyde resin microspheres.

[0137] S2. Add 0.2g of nano-magnesium oxide and 0.35g of boron nitride nanosheets to 200mL of water, sonicate at 200W for 20min to disperse evenly, to obtain solution A; add 5.5g of melamine-formaldehyde resin microspheres to 1L of water, sonicate at 300W for 20min to disperse evenly, to obtain solution B; mix solution A and solution B, adjust the pH of the solution to 4-5, stir and react for 4h, centrifuge, and dry to obtain composite microspheres;

[0138] S3. Add 6g of composite microspheres to 200mL of ethanol, add 0.15g of cobalt chloride, heat to 45℃, stir and react for 4h, centrifuge, dry, heat to 900℃ under nitrogen atmosphere, and calcine for 1.5h to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres.

[0139] S4. Add 0.35g of silane coupling agent KH560 and 0.97g of silane coupling agent KH570 to 200mL of ethanol, add 10g of carbon nanotube / magnesium oxide / boron nitride composite microspheres, heat to 50℃, stir and react for 2h, filter, wash with ethanol, dry, and obtain modified microspheres.

[0140] S5. 100g of polyolefin, 0.075g of di-tert-butyl peroxide, and 7g of modified microspheres are mixed evenly and extruded and granulated at 200℃ to obtain material A. 100g of polyolefin, 4g of maleic anhydride-grafted polyolefin, and 0.03g of dibutyltin dilaurate are mixed and extruded and granulated at 200℃ to obtain material B. Materials A and B are mixed evenly, extruded, injection molded, and then subjected to a 75℃ constant temperature water bath for 7 hours for wet crosslinking treatment to obtain the inner insulation material for the de-icing cable. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene at a mass ratio of 2.5:1.4.

[0141] Comparative Example 7

[0142] Compared with Example 5, the only difference is that steps S1 and S3, as well as S4, S5 and S6, were not performed. In step S2, 0.2g of nano-magnesium oxide and 0.35g of boron nitride nanosheets were mixed evenly to obtain a mixture, which was then directly added to the system.

[0143] Includes the following steps:

[0144] S1. Mix 0.2g of nano-magnesium oxide and 0.35g of boron nitride nanosheets evenly to obtain a mixture;

[0145] S2. 100g of polyolefin, 0.075g of di-tert-butyl peroxide, and 7g of a mixture are mixed evenly and then extruded and granulated at 200℃ to obtain material A. 100g of polyolefin, 4g of maleic anhydride-grafted polyolefin, and 0.03g of dibutyltin dilaurate are mixed and extruded and granulated at 200℃ to obtain material B. Materials A and B are mixed evenly, extruded, injection molded, and then subjected to a 75℃ constant temperature water bath for 7 hours for wet crosslinking treatment to obtain the inner insulation material for the de-icing cable. The polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene at a mass ratio of 2.5:1.4.

[0146] Test Example 1

[0147] The performance of the internal insulation materials of the ice-melting cables prepared in Examples 1-5 and Comparative Examples 1-7 was tested, and the results are shown in Table 1.

[0148] Table 1

[0149] Example 1 60 1.13 5.68 0.72 Example 2 64 1.42 3.14 0.54 Example 3 60 1.22 4.94 0.67 Example 4 63 1.37 3.85 0.59 Example 5 62 1.33 4.48 0.62 Comparative Example 1 66 1.17 12.48 0.71 Comparative Example 2 60 1.19 4.92 0.64 Comparative Example 3 59 1.24 5.04 0.66 Comparative Example 4 68 0.92 Does not meet insulation material requirements 1.02 Comparative Example 5 70 1.28 Does not meet insulation material requirements 1.38 Comparative Example 6 72 1.09 Does not meet insulation material requirements 1.79 Comparative Example 7 75 0.64 16.59 2.10

[0150] As can be seen from the table above, the internal insulation material of the de-icing cable prepared in Examples 1-5 of the present invention has good comprehensive performance.

[0151] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an inner insulation material for a de-icing cable, characterized in that, Melamine-formaldehyde resin microspheres were impregnated in an aqueous dispersion of nano-magnesium oxide and boron nitride nanosheets to obtain composite microspheres. After adding cobalt salt and calcining, magnesium oxide / boron nitride / carbon nanotube composite microspheres were prepared. Hyperbranched polysiloxanes modified with pyrene groups were synthesized and grafted to obtain modified microspheres. The modified microspheres were then used as functional fillers and melt-blended with polyolefins and initiators to produce silane-grafted polyolefin A material. At the same time, polyolefins, compatibilizers, and catalysts were melt-blended and extruded to produce catalyst masterbatch B material. The A material and B material were mixed and shaped and then subjected to wet crosslinking treatment to obtain the inner insulation material of de-icing cable.

2. The preparation method according to claim 1, characterized in that, Includes the following steps: S1. Formaldehyde and melamine are added to water and heated until the system is clear. Polyvinyl alcohol is added and stirred until evenly mixed. Citric acid is added and the reaction is maintained at a certain temperature. The mixture is then centrifuged, washed, and dried to obtain melamine-formaldehyde resin microspheres. S2. Nano-magnesium oxide and boron nitride nanosheets are uniformly dispersed in water to obtain solution A; melamine-formaldehyde resin microspheres are uniformly dispersed in water to obtain solution B; solutions A and B are mixed, the pH value of the solution is adjusted, the reaction is stirred, centrifuged, and dried to obtain composite microspheres; S3. Add the composite microspheres to ethanol, add cobalt salt, heat and stir to react, centrifuge, dry, and calcine to obtain carbon nanotube / magnesium oxide / boron nitride composite microspheres; S4. Mix silane coupling agent KH560, silane coupling agent KH570 and diethylene glycol evenly, heat to react, and distill until the temperature of the distillate drops to 40-50℃ to obtain hyperbranched polysiloxane. S5. Add hyperbranched polysiloxane to toluene, add 1-pyrene acetic acid and tetrabutylammonium bromide, heat and stir the reaction under an inert atmosphere, remove the solvent under reduced pressure to obtain hyperbranched polysiloxane containing pyrene groups; S6. Carbon nanotube / magnesium oxide / boron nitride composite microspheres were added to N,N-dimethylformamide, and hyperbranched polysiloxane containing pyrene groups were added. The mixture was stirred and reacted, filtered, washed, and dried to obtain modified microspheres. S7. Polyolefin, initiator and modified microspheres are mixed evenly and then extruded and granulated to obtain material A; polyolefin, compatibilizer and catalyst are mixed and then extruded and granulated to obtain material B; material A and material B are mixed evenly, and after extrusion, injection molding or blow molding, they are subjected to humidification crosslinking treatment in a constant temperature water bath to obtain the inner insulation material of the de-icing cable.

3. The preparation method according to claim 2, characterized in that, In step S1, the mass ratio of formaldehyde, melamine, polyvinyl alcohol, and citric acid is 2-4:2-4:0.5-1:0.2-0.5, the heating temperature is 80-90℃, and the heat preservation reaction time is 10-20 minutes.

4. The preparation method according to claim 2, characterized in that, In step S2, the mass ratio of nano-magnesium oxide, boron nitride nanosheets, and melamine-formaldehyde resin microspheres is 1-3:2-5:50-60, the pH of the solution is adjusted to 4-5, and the stirring reaction time is 3-5 hours.

5. The preparation method according to claim 2, characterized in that, In step S3, the mass ratio of the composite microspheres to the cobalt salt is 5-8:0.1-0.2, the cobalt salt is cobalt chloride or cobalt nitrate, the heating and stirring reaction temperature is 40-50℃ and the time is 3-5h, and the heating and calcination temperature is 850-950℃ and the time is 1-2h.

6. The preparation method according to claim 2, characterized in that, In step S4, the mass ratio of silane coupling agent KH560, silane coupling agent KH570, and diethylene glycol is 5-6:6-8:9-10, and the temperature of the heating reaction is 120-140℃.

7. The preparation method according to claim 2, characterized in that, In step S5, the mass ratio of hyperbranched polysiloxane, 1-pyrene acetic acid, and tetrabutylammonium bromide is 10:1-2:0.2-0.3, and the heating and stirring reaction is carried out at a temperature of 90-110℃ for 3-5 hours.

8. The preparation method according to claim 2, characterized in that, In step S6, the mass ratio of the carbon nanotube / magnesium oxide / boron nitride composite microspheres to the hyperbranched polysiloxane containing pyrene groups is 10:2-5, and the stirring reaction time is 1-3 hours.

9. The preparation method according to claim 2, characterized in that, In step S7, the extrusion granulation temperature of material A is 190-220℃, the extrusion granulation temperature of material B is 190-200℃, the wet crosslinking treatment temperature is 70-80℃, and the time is 5-10h; the polyolefin is a mixture of high-density polyethylene and linear low-density polyethylene in a mass ratio of 2-3:1-2; the catalyst is dibutyltin dilaurate or dioctyltin dilaurate; the initiator is dicumyl peroxide or di-tert-butyl peroxide; and the compatibilizer is maleic anhydride-grafted polyolefin; in material A, the mass ratio of polyolefin, initiator, and modified microspheres is 100:0.05-0.1:5-10; and in material B, the mass ratio of polyolefin, compatibilizer, and catalyst is 100:3-5:0.01-0.

05.

10. An internal insulation material for a de-icing cable prepared by the method according to any one of claims 1-9.

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