High-thermal-conductivity flame-retardant polyolefin cable insulation layer material and preparation method thereof

Abstract

The invention discloses a high-thermal-conductivity flame-retardant polyolefin cable insulating layer material and a preparation method thereof.The preparation method comprises the steps that firstly, the surface of a superfine phosphorus-containing compound is sequentially coated with polyhydroxy macromolecules and heat-conducting nanosheets, and a core-shell structure heat-conducting flame retardant is formed; then blending the modified polyolefin with an antioxidant, a compatilizer, heat-conducting nanosheets, heat-conducting nanoparticles and the like, and uniformly dispersing the mixture in an ethylene-octylene copolymer (POE) through a double-screw extruder to prepare the high-heat-conductivity flame-retardant polyolefin cable insulation layer material. The preparation process is simple and easy to control, the requirement for production equipment is low, the yield is high, and the prepared high-heat-conductivity flame-retardant polyolefin cable insulation layer material is widely applied to the field of high-current-carrying-density cables, has excellent heat conductivity and flame retardance and is suitable for being used in the field of high-current-carrying-density cables. The uniformly dispersed core-shell structure heat-conducting flame retardant, the heat-conducting nanosheets and the heat-conducting nanoparticles cooperate to form a continuous heat-conducting network, so that the heat conductivity of the POE is remarkably improved; meanwhile, when encountering high temperature, the heat-conducting network quickly transfers heat to a flame-retardant system in the heat-conducting flame retardant with the core-shell structure, so that the flame-retardant system is quickly subjected to dehydration, cross-linking and carbonization reactions, a porous expanded carbon layer is formed under the action of cracking gas, and efficient heat-insulating, oxygen-isolating and flame-retardant effects are shown. The high-thermal-conductivity flame-retardant polyolefin cable insulating layer material prepared by the invention has a wide application prospect in the field of high-current-carrying cables.

Description

Technical Field

[0001] This invention relates to the field of high thermal conductivity and flame retardant cable insulation material technology, and in particular to a high thermal conductivity and flame retardant polyolefin cable insulation material and its preparation method. Background Technology

[0002] In fields such as high-voltage power transmission, rapid charging and discharging of new energy sources, and high-power-density electronic devices (such as 5G communication base stations and data centers), the demand for high-power transmission continues to rise. To prevent cables from becoming too bulky and unusable, the conductor diameter cannot be increased indefinitely; the only option is to increase the conductor's current-carrying density. However, this brings a series of new problems. High current-carrying density causes severe heating of the cable's metallic core, while the insulation material of traditional cables has insufficient thermal conductivity, easily leading to localized overheating, which in turn causes insulation aging, efficiency reduction, and even fire accidents. Therefore, high current-carrying density places stringent requirements on the cable's heat dissipation, heat resistance, and flame retardancy.

[0003] However, there is an inherent contradiction between thermal conductivity and flame retardant modification of cable insulation materials. Thermal conductivity modification typically involves introducing high thermal conductivity fillers to construct a continuous thermally conductive network, thereby enhancing the material's thermal conductivity. Flame retardant modification, on the other hand, requires the addition of flame retardants to achieve a thermal insulation effect through the rapid formation of a charred layer, inhibiting heat transfer to the polymer matrix and thus delaying thermal degradation. When thermally conductive fillers and flame retardants are blended into the polymer matrix, they exhibit antagonistic effects. Under high-temperature conditions, the thermally conductive fillers rapidly transfer heat to the polymer matrix, accelerating its thermal degradation and reducing the flame retardant efficiency of the flame-retardant system. Simultaneously, the flame retardant disrupts the continuity of the thermally conductive network, thereby reducing the thermal conductivity of the composite material. This mutual constraint makes it difficult for materials to simultaneously possess excellent high thermal conductivity and flame retardant properties. Summary of the Invention

[0004] This invention addresses the technical bottleneck in the synergistic optimization of high thermal conductivity and flame retardancy in high current-density cable insulation materials in existing technologies. The purpose of this invention is to provide a high thermal conductivity and flame-retardant polyolefin cable insulation material and its preparation method. The thermal conductivity and flame-retardant performance of the high current-density cable insulation layer are significantly improved simultaneously, providing a reliable guarantee for the safe operation of high current-density cables.

[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows: a method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material, using ethylene-octene copolymer as the base material, and according to the mass ratio, adding 100 phr of ethylene-octene copolymer, 0.1~1.0 phr of antioxidant, 4.0~15.0 phr of compatibilizer, 15.0~30.0 phr of core-shell structure thermally conductive and flame retardant agent, 10.0~25.0 phr of organic modified thermally conductive nanosheets and 5.0~15.0 phr of thermally conductive nanoparticles into a high-speed mixer and mixing them evenly, then adding them to a twin-screw extruder, and obtaining a high thermal conductivity and flame retardant polyolefin cable insulation layer material with a thermal conductivity greater than 0.7 by melt blending extrusion through a twin-screw extruder;

[0006] Core-shell structured thermally conductive flame retardant, thermally conductive nanosheets and thermally conductive nanoparticles are uniformly dispersed in ethylene-octene copolymer, forming a three-dimensional continuous thermally conductive network composed of multi-morphological and multi-scale thermally conductive fillers, including core-shell structured thermally conductive flame retardant, thermally conductive nanosheets and thermally conductive nanoparticles.

[0007] Among them, the organic modified thermally conductive nanosheets are prepared through steps S1 and S2, and the core-shell structure thermally conductive flame retardant is prepared through steps S1, S2 and S3.

[0008] Step S1, Preparation method of organic coated flame retardant,

[0009] A solution of polyhydroxy polymer containing polyhydroxy polymers is slowly added to an aqueous dispersion of ultrafine phosphorus compounds mixed with ultrafine phosphorus compounds. The mass ratio of polyhydroxy polymers to ultrafine phosphorus compounds is 0.5~1.5:1. After stirring, the polyhydroxy polymers spontaneously coat the surface of the ultrafine phosphorus compounds. The product is collected to obtain an organic coated flame retardant.

[0010] Step S2, the preparation method of organic modified thermally conductive nanosheets, firstly, the silane coupling agent solution is slowly added to the thermally conductive nanosheet dispersion mixed with the thermally conductive nanosheets, the mass ratio of silane coupling agent to thermally conductive nanosheets is 0.1~0.5:1, then a pH adjuster is added, the silane coupling agent and the nanomaterials undergo a dehydration condensation reaction, and after the reaction is completed, the product is collected to obtain organic modified thermally conductive nanosheets;

[0011] Step S3, preparation method of core-shell structured thermally conductive flame retardant: organic coated flame retardant and organic coated flame retardant are mixed and dispersed in solvent C, and then glutaraldehyde aqueous solution is added. The mass ratio of glutaraldehyde, organic modified thermally conductive nanosheets and organic coated flame retardant is 0.005~0.03: 0.1~0.6:1. Glutaraldehyde reacts with the organic active groups on the surface of organic coated flame retardant and organic modified thermally conductive nanosheets to form covalent bonds. After the reaction is completed, the product is collected to obtain core-shell structured thermally conductive flame retardant.

[0012] Furthermore, in step S1, the organic-coated flame retardant is prepared through the following steps:

[0013] Step S1.1: The sub-step of preparing an ultrafine phosphorus-containing compound aqueous dispersion involves mixing the ultrafine phosphorus-containing compound with deionized water, mechanically stirring and ultrasonically dispersing for 5-60 minutes at a temperature of -5-30°C, uniformly dispersing the ultrafine phosphorus-containing compound in deionized water to obtain the ultrafine phosphorus-containing compound aqueous dispersion with a mass concentration of 0.5-4.0 wt%.

[0014] Step S1.2, the sub-step of preparing a polyhydroxy polymer solution, involves dissolving the polyhydroxy polymer in deionized water and stirring until homogeneous to obtain the polyhydroxy polymer solution with a mass concentration of 0.5~3.0wt%.

[0015] Step S1.3, stirring sub-step: The polyhydroxy polymer solution is slowly added dropwise to the ultrafine phosphorus-containing compound aqueous dispersion over 20-60 minutes, wherein the mass ratio of polyhydroxy polymer to ultrafine phosphorus-containing compound is 0.5-1.5:1. After the addition is complete, stirring is continued for 10-60 minutes. Under the electrostatic force between positive and negative charges, the polyhydroxy polymer spontaneously coats the surface of the ultrafine phosphorus-containing compound.

[0016] Step S1.4, Product: The product from step S1.3 is collected by centrifugation and dried to obtain an organic-coated flame retardant.

[0017] Furthermore, in step S2, the organically modified thermally conductive nanosheets are prepared through the following steps:

[0018] Step S2.1: The thermally conductive nanosheets are uniformly dispersed in solvent A by mechanical stirring and ultrasonic dispersion for 10~120 min to obtain a thermally conductive nanosheet dispersion with a mass concentration of 0.5~3.0 wt%. The reaction temperature is adjusted to 75~120℃ and mechanical stirring is continued for 10~120 min.

[0019] Step S2.2: Dissolve the silane coupling agent in solvent B to obtain a silane coupling agent solution with a mass concentration of 4.0~10.0wt%;

[0020] Step S2.3: Slowly add the silane coupling agent solution dropwise to the thermally conductive nanosheet dispersion over 15-60 min. The mass ratio of silane coupling agent to thermally conductive nanosheet is 0.1:1 to 0.5:1. At the same time, add a pH adjuster to control the pH value to 3.0-10.0. After the silane coupling agent is completely added, continue the reaction for 6-48 h. Under the action of the pH adjuster, the silane coupling agent undergoes hydrolysis to generate ~Si-OH, which then undergoes a dehydration condensation reaction with the -OH on the surface of the ultrafine phosphorus-containing compound to form a covalent bond.

[0021] Step S2.4: After the reaction is completed, the product of step S2.3 is collected by centrifugation, precipitated, washed with solvent D, and dried to obtain organic modified thermally conductive nanosheets.

[0022] Furthermore, in step S3, the core-shell structured thermally conductive flame retardant is prepared through the following steps:

[0023] Step S3.1: The organic-coated flame retardant prepared in step S1 and the organic modified thermally conductive nanosheets synthesized in step S2 are mixed and dispersed in solvent E by mechanical stirring and ultrasonic dispersion for 5-60 min to obtain a mixed dispersion with a total mass concentration of 0.5-3.0 wt%.

[0024] Step S3.2: Adjust the reaction temperature to -5~90℃ and continue mechanical stirring for 5~60 min. Slowly add a glutaraldehyde aqueous solution with a mass concentration of 1.0~10.0wt% to the above mixed dispersion over 20~60 min, while adding a pH adjuster to control the pH value to 3.0~10.0. After the glutaraldehyde aqueous solution is completely added, continue the reaction for 3~24 h. The mass ratio of glutaraldehyde, organic modified thermally conductive nanosheets and organic coated flame retardant is 0.005~0.03: 0.1~0.6:1. Under the action of the pH adjuster, glutaraldehyde reacts with the organic active groups on the organic coated flame retardant and organic modified thermally conductive nanosheets to form covalent bonds.

[0025] Step S3.3: Collect the product from step S3.2 by centrifugation, wash it with solvent F after precipitation, and dry it to obtain a core-shell structured thermally conductive flame retardant. The diameter of the core-shell structured thermally conductive flame retardant is 3~11.5μm. The core of the core-shell structured thermally conductive flame retardant is an ultrafine phosphorus-containing compound with polyhydroxy polymers coated on the surface. The core-shell layer of the core-shell structured thermally conductive flame retardant is formed by organic modified thermally conductive nanosheets coated on the outer layer of the core through the covalent cross-linking effect of glutaraldehyde.

[0026] Furthermore, the thermally conductive nanosheet is at least one of boron nitride nanosheets, molybdenum disulfide nanosheets, black phosphorus nanosheets, and silicon carbide nanosheets. The thickness of the thermally conductive nanosheet is 0.5~10nm, the diameter of the sheet is 1~5μm, and the thermal conductivity is 30~600W / (m·K).

[0027] The polyhydroxy polymer is at least one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl starch, hyaluronic acid, carboxymethyl chitosan, and polyvinyl alcohol;

[0028] The thermally conductive nanoparticles are at least one of boron nitride nanoparticles, aluminum nitride nanoparticles, silicon carbide nanoparticles, zinc oxide nanoparticles, and aluminum oxide nanoparticles. The particle size of the thermally conductive nanoparticles is 20~100nm, and the thermal conductivity is 40~400W / (m·K).

[0029] The antioxidant is at least one of antioxidant 1010, antioxidant 1076, antioxidant BHT, antioxidant 168, antioxidant 626 and antioxidant 6280;

[0030] The compatibilizer is at least one of maleic anhydride-grafted POE, maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyethylene, titanate coupling agent and aluminate coupling agent.

[0031] The ultrafine phosphorus-containing compound is at least one of ultrafine melamine polyphosphate, ultrafine ammonium polyphosphate, ultrafine aluminum hypophosphite, and ultrafine aluminum polyphosphate.

[0032] Solvent A, solvent B, solvent C, solvent D, solvent E and solvent F are at least one of diethyl ether, acetone, methanol, ethyl acetate, ethanol, isopropanol, n-propanol, deionized water, dioxane and N,N-dimethylformamide;

[0033] The silane coupling agent is , , , , and At least one of them;

[0034] The pH adjuster is at least one of the following: 1 mol / L dilute hydrochloric acid, 1 mol / L dilute acetic acid, 1 mol / L dilute sulfuric acid, 1 mol / L dilute nitric acid, 1 mol / L sodium hydroxide aqueous solution, 1 mol / L potassium hydroxide aqueous solution, 1 mol / L sodium carbonate aqueous solution, and 1 mol / L potassium carbonate aqueous solution.

[0035] Furthermore, the twin-screw extruder is arranged with nine sections sequentially from the feed inlet to the extrusion section, including the first feeding section, the second melting section, the third melting section, the fourth mixing section, the fifth mixing section, the sixth homogenizing section, the seventh homogenizing section, the eighth homogenizing section, and the ninth die section.

[0036] The temperature of the first feeding section is set to 130~160℃.

[0037] The temperatures of both the second and third melting zones are set to 150~190℃.

[0038] The temperatures of the fourth mixing section, the fifth mixing section, and the sixth homogenization section are all set to 160~200℃.

[0039] The temperatures of the homogenization sections in zones seven and eight are both set to 180~210℃.

[0040] The temperature of the die in Zone 9 is set to 170~190℃.

[0041] The screw speed of the twin-screw extruder is set to 250~500 r / min, and the feeding speed is set to 25~100 kg / h.

[0042] Furthermore, 100 phr of ethylene-octene copolymer, 0.1-0.3 phr of antioxidant, 4.0-10.00 phr of compatibilizer, 17-25 phr of core-shell structured thermally conductive flame retardant, 15-20 phr of organic modified thermally conductive nanosheets, and 8-12 phr of thermally conductive nanoparticles are added to a high-speed mixer and mixed evenly. Then, the mixture is added to a twin-screw extruder and melt-blended and extruded through the twin-screw extruder to obtain a high thermal conductivity flame retardant polyolefin cable insulation layer material with a thermal conductivity greater than 0.9.

[0043] Furthermore, in step S1, the mass ratio of the polyhydroxy polymer to the ultrafine phosphorus-containing compound is 0.5~1.2:1.

[0044] In step S2, the mass ratio of the silane coupling agent to the thermally conductive nanosheet is 0.1~0.3:1.

[0045] In step S3, the mass ratio of glutaraldehyde, the organic modified thermally conductive nanosheet, and the organic coated flame retardant is 0.005~0.03: 0.1~0.6:1.

[0046] Furthermore, the thermally conductive nanoparticles are selected from boron nitride nanoparticles with a particle size of 60-80 nm and a thermal conductivity of 300-400 W / (m·K).

[0047] In step S1, the polyhydroxy polymer is selected from hydroxypropyl methylcellulose or carboxymethyl cellulose, and the ultrafine phosphorus-containing compound is ultrafine ammonium polyphosphate or ultrafine aluminum hypophosphite; the mass ratio of the polyhydroxy polymer to the ultrafine phosphorus-containing compound is 1.0~1.2:1.

[0048] In step S2, the compatibilizer is selected from maleic anhydride-grafted POE or titanate coupling agent; the thermally conductive nanosheets are selected from boron nitride nanosheets or silicon carbide nanosheets with a sheet diameter of 1~5μm and a thermal conductivity of 400~600W / (m·K); after adding the silane coupling agent solution, a pH adjuster is added dropwise to control the pH value to be greater than 8.0.

[0049] In step S3, after adding the glutaraldehyde aqueous solution, a pH adjuster is added dropwise to control the pH value to be greater than 8.0.

[0050] The total mass concentration of the mixed dispersion of the organic modified thermally conductive nanosheets and the organic-coated flame retardant is 0.5~3.0 wt%.

[0051] The mass ratio of glutaraldehyde, the organically modified thermally conductive nanosheets, and the organically coated flame retardant is 0.005~0.01:0.1~0.3:1;

[0052] The mass ratio of organic modified thermally conductive nanosheets to organic coated flame retardant is 0.4~0.5:1;

[0053] The core-shell structured thermally conductive flame retardant has a particle size of 3~5μm.

[0054] Furthermore, a method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material is provided, which is prepared according to the aforementioned method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material.

[0055] The advantages of this invention compared to the prior art are:

[0056] 1. The high thermal conductivity and flame retardant polyolefin cable insulation material provided by the present invention, under the synergistic effect of the interfacial compatibilization of the compatibilizer and the high shear field of the twin-screw extruder, the core-shell structure thermally conductive flame retardant, thermally conductive nanosheets and thermally conductive nanoparticles are uniformly dispersed in POE, and a three-dimensional continuous thermally conductive network is constructed by the multi-morphology and multi-scale thermally conductive fillers, which significantly improves the thermal conductivity of POE.

[0057] 2. The high thermal conductivity and flame retardant polyolefin cable insulation material provided by this invention, when exposed to high temperature or open flame environment, the internal thermally conductive network quickly transfers heat to the flame retardant system inside the core-shell structure thermally conductive flame retardant, causing the flame retardant system to undergo dehydration, cross-linking and carbonization reactions, and foaming and expanding under the action of cracked gas to form a porous carbonized layer. This process destroys the original thermally conductive network while forming a porous structure with low thermal conductivity; and the layered thermally conductive nanosheets distributed in it enhance the mechanical strength, thermal stability and airtightness of the porous carbonized layer, thus having excellent heat insulation and oxygen barrier capabilities, enabling the expanded carbon layer to play a highly efficient flame retardant role.

[0058] 3. The preparation process of this invention is simple and easy to control, with low requirements for production equipment and high yield. The high thermal conductivity and flame retardant polyolefin cable insulation material prepared is widely used in the field of high current density cables.

[0059] 4. This invention utilizes electrostatic adsorption to coat the surface of ultrafine phosphorus-containing compounds with polyhydroxy polymers, and then further coats them with thermally conductive nanosheets through covalent bonding with a silane coupling agent, thus preparing a core-shell structured thermally conductive flame retardant. Subsequently, by controlling the processing technology and using a twin-screw extruder, the core-shell structured thermally conductive flame retardant, along with antioxidants, compatibilizers, thermally conductive nanosheets, and thermally conductive nanoparticles, are uniformly added to ethylene-octene copolymer (POE) to prepare a high thermal conductivity flame-retardant polyolefin cable insulation material. This significantly improves the thermal conductivity of POE. Furthermore, when the high thermal conductivity flame-retardant polyolefin cable insulation is exposed to high temperatures or open flame environments, its thermally conductive network can rapidly transfer heat to the flame-retardant system within the core-shell structured thermally conductive flame retardant. In this system, ultrafine phosphorus-containing compounds undergo thermal degradation to generate pyrophosphoric acid, which catalyzes the dehydration, cross-linking, and carbonization of polyhydroxy polymers. Simultaneously, the gas molecules generated by the pyrolysis cause the system to foam and expand, forming a porous carbon layer structure with a pore size of 5-15 μm. This expansion process disrupts the original continuous thermally conductive network of the material, while the porous carbon layer structure endows the carbon layer with excellent thermal insulation properties, effectively blocking heat transfer to the POE matrix. Notably, the introduction of layered thermally conductive nanosheets significantly enhances the mechanical strength, thermal stability, and airtightness of the carbon layer. This expanded carbon layer, which combines thermal insulation and oxygen barrier functions, exhibits highly efficient flame retardant properties. Therefore, the high thermal conductivity and flame retardant polyolefin cable insulation material provided by this invention possesses both excellent high thermal conductivity and flame retardant properties, effectively overcoming the challenge of simultaneously achieving high thermal conductivity and flame retardant properties in polymers, which is of great significance in the field of high current-density cables. Attached Figure Description

[0060] Figure 1 (a) is a SEM image of ammonium polyphosphate from Example 1(a).

[0061] Figure 1 (b) is a SEM image of the core-shell structure thermally conductive flame retardant of Example 1.

[0062] Figure 2 This is an SEM image of the brittle cross-section of the high thermal conductivity and flame retardant polyolefin cable insulation material in Example 1. Detailed Implementation

[0063] Example 1

[0064] A method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation material.

[0065] 1. Preparation of core-shell structured thermally conductive flame retardant:

[0066] 1.1 Preparation of the organic-coated flame retardant: Ultrafine ammonium polyphosphate was dispersed in deionized water at a concentration of 2.0 wt% by mechanical stirring and ultrasonic dispersion for 30 min. The reaction temperature was controlled at 10℃. Simultaneously, hydroxypropyl methylcellulose was dissolved in deionized water at a mass ratio of 1:1 to ultrafine ammonium polyphosphate, with a total mass concentration of 2.0 wt%. This hydroxypropyl methylcellulose was slowly added dropwise to the aqueous dispersion of ultrafine ammonium polyphosphate over 30 min while maintaining stirring. After the addition was complete, stirring was continued for another 30 min. The product was collected by centrifugation and dried to obtain the organic-coated flame retardant. The mass ratio of the polyhydroxy polymer to the ultrafine phosphorus-containing compound was 0.5:1-1.5:1.

[0067] 1.2 Synthesis of Organically Modified Thermally Conductive Nanosheets: Boron nitride nanosheets were uniformly dispersed in dioxane at a concentration of 1.5 wt% by mechanical stirring and ultrasonic dispersion for 60 min. The reaction temperature was adjusted to 100℃ while maintaining mechanical stirring. Dissolves in dioxane. The boron nitride nanosheets were added slowly dropwise over 30 min at a mass ratio of 0.2:1, with a total mass concentration of 8.0 wt%. Simultaneously, a 1 mol / L sodium hydroxide aqueous solution was added dropwise to maintain the pH at 8.0. After the silane coupling agent was completely added, the reaction continued for 16 h. The product was separated by centrifugation, and the precipitate was washed with ethanol and dried to obtain the organically modified thermally conductive nanosheets.

[0068] 1.3 Preparation of Core-Shell Structure Thermally Conductive Flame Retardant: The organically coated flame retardant prepared in step 1) and the organically modified thermally conductive nanosheets synthesized in step 2) were mixed and dispersed in deionized water by mechanical stirring and ultrasonic dispersion for 30 min. The mass ratio of the organically modified thermally conductive nanosheets to the organically coated flame retardant was 0.3:1, and the total mass concentration was 2.0 wt%. The reaction temperature was adjusted to 60℃ and mechanical stirring was continued. A 3.0 wt% glutaraldehyde aqueous solution was slowly added dropwise to the above mixed dispersion over 30 min. The mass ratio of glutaraldehyde to the organically coated flame retardant was 0.015:1. Simultaneously, a 1 mol / L sodium hydroxide aqueous solution was added dropwise to control the pH value at 8.5. After the glutaraldehyde aqueous solution was completely added, the reaction continued for 8 h. The product was separated by centrifugation, and the precipitate was washed with ethanol and dried to obtain the core-shell structure thermally conductive flame retardant.

[0069] Depend on Figure 1 SEM images of a show that ammonium polyphosphate is granular with a relatively smooth surface, and most particles are in the size range of 2-10 μm. Hydroxypropyl methylcellulose can spontaneously adsorb onto the surface of the ammonium polyphosphate particles through electrostatic interactions, forming an organically coated flame retardant. Subsequently, through the cross-linking effect of glutaraldehyde, the organically coated flame retardant can form covalent bonds with the organically modified thermally conductive nanosheets, resulting in a core-shell structured thermally conductive flame retardant, such as... Figure 1 As shown in b, its particle size is significantly larger than that of ammonium polyphosphate, ranging from 3 to 11.5 μm, and a large number of boron nitride nanosheets can be observed on the particle surface. SEM results show that the core-shell structured thermally conductive flame retardant has been successfully prepared. The flame retardant (core) is coated with thermally conductive nanosheets (shell), which on the one hand avoids the flame retardant from disrupting the continuity of the thermally conductive network in the polyolefin composite material; on the other hand, when the polyolefin composite material is heated, the thermally conductive network can quickly transfer heat to the flame retardant in the core, causing the flame retardant to undergo dehydration, cross-linking and carbonization reactions, rapidly forming a porous carbonized layer, and exerting a highly efficient flame-retardant protection effect.

[0070] like Figure 2 As shown, under the synergistic effect of the compatibilizer's interfacial compatibilization and the high shear field of the twin-screw extruder, additives such as core-shell thermally conductive flame retardants, thermally conductive nanosheets, and thermally conductive nanoparticles can be uniformly dispersed in POE and integrated with the POE substrate. No obvious separation of additive powder from the substrate was observed under low-temperature brittle fracture.

[0071] 2. Preparation of high thermal conductivity and flame retardant polyolefin cable insulation material:

[0072] Using ethylene-octene copolymer (POE granules) as the base material, POE granules, 0.3 phr antioxidant 1010, 10.0 phr maleic anhydride-grafted POE, 25.0 phr core-shell thermally conductive flame retardant, 15.0 phr boron nitride nanosheets, and 10.0 phr alumina nanoparticles were mixed evenly in a high-speed mixer according to the following mass ratio, and then added to a twin-screw extruder for melt blending. The parameters of the twin-screw extruder were set as follows: the temperatures of zones 1-8 were 150℃, 160℃, 170℃, 175℃, 180℃, 185℃, 190℃, and 185℃, respectively; the die temperature of zone 9 was set to 180℃; the screw speed was set to 365 r / min; and the feed rate was set to 60 kg / h.

[0073] 3. Various standard samples were prepared by injection molding, and their thermal conductivity and flame retardancy were tested. The test results are shown in Table 1 and Table 2.

[0074] This invention first coats an ultrafine phosphorus-containing compound with a polyhydroxy polymer and thermally conductive nanosheets to form a core-shell structured thermally conductive flame retardant. Then, it is blended with antioxidants, compatibilizers, thermally conductive nanosheets, and thermally conductive nanoparticles, and uniformly dispersed in ethylene-octene copolymer (POE) using a twin-screw extruder to obtain a high thermal conductivity and flame retardant polyolefin cable insulation material. The preparation process of this invention is simple, easy to control, requires less sophisticated production equipment, and has a high yield. The resulting high thermal conductivity and flame retardant polyolefin cable insulation material is widely used in high current-density cables. In this field, the high thermal conductivity and flame retardant polyolefin cable insulation material prepared by this invention possesses excellent thermal conductivity and flame retardant properties. The uniformly dispersed core-shell structured thermally conductive flame retardant, along with thermally conductive nanosheets and nanoparticles, synergistically forms a continuous thermally conductive network, significantly improving the thermal conductivity of POE. Simultaneously, when exposed to high temperatures, the thermally conductive network rapidly transfers heat to the flame-retardant system within the core-shell structured thermally conductive flame retardant, promoting rapid dehydration, cross-linking, and carbonization reactions within the flame-retardant system. Under the action of pyrolysis gas, a porous expanded carbon layer is formed, exhibiting highly efficient heat insulation, oxygen barrier, and flame retardant effects. The high thermal conductivity and flame retardant polyolefin cable insulation material prepared by this invention has broad application prospects in the field of high current-carrying cables.

[0075] Example 2

[0076] The main steps and process conditions in this embodiment are the same as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that:

[0077] In step 1.1, hydroxypropyl methylcellulose is replaced with polyvinyl alcohol, the mass ratio of polyhydroxy polymer to ultrafine phosphorus-containing compound is increased to 1.5:1, the concentration of polyhydroxy polymer solution is increased to 3.0 wt%, the dropping time of polyhydroxy polymer solution is shortened to 20 min, and the stirring time after dropping is extended to 60 min.

[0078] In step 1.2, γ-aminopropyltrimethoxysilane is replaced with 3-glycidyloxypropyltrimethoxysilane, the concentration of the silane coupling agent solution is reduced to 6.0 wt%, the mass ratio of silane coupling agent to thermally conductive nanosheets is increased to 0.4:1, the dropping time of the silane coupling agent solution is extended to 45 min, 1 mol / L sodium hydroxide aqueous solution is replaced with 1 mol / L dilute hydrochloric acid, the pH value is reduced to 4.0, and ethanol is replaced with ethyl acetate;

[0079] In step 1.3, the mechanical stirring and ultrasonic dispersion time is shortened to 10 min, the concentration of glutaraldehyde aqueous solution is reduced to 1.0 wt%, the mass ratio of glutaraldehyde to organic coated flame retardant is reduced to 0.010:1, 1 mol / L sodium hydroxide aqueous solution is replaced with 1 mol / L dilute hydrochloric acid, and the pH value is reduced to 3.0.

[0080] In step 2, the amount of compatibilizer is increased to 12.0 phr, the amount of core-shell thermally conductive flame retardant is reduced to 15 phr, the amount of thermally conductive nanosheets is increased to 25 phr, alumina nanoparticles are replaced with aluminum nitride nanoparticles, the screw speed is changed to 500 r / min, and the feeding speed is changed to 100 kg / h.

[0081] The results of the thermal conductivity and flame retardancy tests are shown in Tables 1 and 2.

[0082] Example 3

[0083] The main steps and process conditions in this embodiment are the same as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that:

[0084] In step 1.1, the reaction temperature is reduced to 0℃, hydroxypropyl methylcellulose is replaced with carboxymethyl cellulose, the dropping time of the polyhydroxy polymer solution is shortened to 25 min, and the stirring time after dropping is shortened to 20 min.

[0085] In step 1.2, boron nitride nanosheets are replaced with molybdenum disulfide nanosheets, the mechanical stirring and ultrasonic dispersion time is extended to 90 min, the concentration of the thermally conductive nanosheet dispersion is increased to 2.0 wt%, the mass ratio of silane coupling agent to thermally conductive nanosheets is reduced to 0.1:1, the 1 mol / L sodium hydroxide aqueous solution is replaced with a 1 mol / L sodium carbonate aqueous solution, and the pH value is increased to 8.5.

[0086] In step 1.3, the mass ratio of organic modified thermally conductive nanosheets to organic coated flame retardant is increased to 0.5:1, the reaction temperature is reduced to 20℃, 1 mol / L sodium hydroxide aqueous solution is replaced with 1 mol / L potassium carbonate aqueous solution, the reaction time after the glutaraldehyde aqueous solution is added is extended to 16 h, and ethanol is replaced with methanol.

[0087] In step 2, antioxidant 1010 is replaced with antioxidant 1076, the amount of antioxidant is increased to 0.5 phr, boron nitride nanosheets are replaced with molybdenum disulfide nanosheets, the amount of thermally conductive nanoparticles is reduced to 5.0 phr, the temperatures of zones 1-8 are changed to 130℃, 140℃, 150℃, 155℃, 160℃, 165℃, 170℃, and 165℃ respectively, and the die temperature of zone 9 is set to 160℃.

[0088] The results of the thermal conductivity and flame retardancy tests are shown in Tables 1 and 2.

[0089] Example 4

[0090] The main steps and process conditions in this embodiment are the same as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that:

[0091] In step 1.1, the ultrafine ammonium polyphosphate was replaced with ultrafine aluminum hypophosphite, the mechanical stirring and ultrasonic dispersion time was shortened to 10 min, and the mass ratio of polyhydroxy polymer to ultrafine phosphorus-containing compound was increased to 1.2:1.

[0092] In step 1.2, boron nitride nanosheets are replaced with silicon carbide nanosheets, dioxane is replaced with N,N-dimethylformamide, the reaction temperature is increased to 120℃, the concentration of silane coupling agent solution is reduced to 4.0wt%, the reaction time after the silane coupling agent solution is added is shortened to 8h, and ethanol is replaced with diethyl ether.

[0093] In step 1.3, the mass ratio of organic modified thermally conductive nanosheets to organic coated flame retardant is increased to 0.4:1, the total concentration of the mixed dispersion of organic modified thermally conductive nanosheets and organic coated flame retardant is reduced to 0.5wt%, the dropping time of glutaraldehyde aqueous solution is extended to 40min, and ethanol is replaced with acetone.

[0094] In step 2, maleic anhydride-grafted POE is replaced with titanate coupling agent, the amount of compatibilizer is reduced to 4.0 phr, the amount of core-shell thermally conductive flame retardant is reduced to 17 phr, the amount of thermally conductive nanosheets is increased to 20 phr, alumina nanoparticles are replaced with boron nitride nanoparticles, the screw speed is changed to 435 r / min, and the feeding speed is changed to 80 kg / h.

[0095] The results of the thermal conductivity and flame retardancy tests are shown in Tables 1 and 2.

[0096] Example 5

[0097] The main steps and process conditions in this embodiment are the same as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that:

[0098] In step 1.1, the reaction temperature is increased to 30℃, hydroxypropyl methylcellulose is replaced with hydroxyethyl cellulose, the concentration of the polyhydroxy polymer solution is reduced to 0.5wt%, and the dropping time of the polyhydroxy polymer solution is extended to 60min.

[0099] In step 1.2, dioxane is replaced with n-propanol, the reaction temperature is reduced to 90℃, the dropping time of the silane coupling agent solution is extended to 60 min, the reaction time after the silane coupling agent solution is finished is extended to 24 h, and ethanol is replaced with acetone.

[0100] In step 1.3, deionized water is replaced with isopropanol, the concentration of glutaraldehyde aqueous solution is increased to 10.0 wt%, the mass ratio of glutaraldehyde to organic coated flame retardant is increased to 0.030:1, and 1 mol / L sodium hydroxide aqueous solution is replaced with 1 mol / L potassium hydroxide aqueous solution.

[0101] In step 2, antioxidant 1010 is replaced with antioxidant BHT, maleic anhydride-grafted POE is replaced with maleic anhydride-grafted polypropylene, the amount of compatibilizer is increased to 15.0 phr, alumina nanoparticles are replaced with silicon carbide nanoparticles, the amount of thermally conductive nanoparticles is reduced to 7.0 phr, the temperatures of zones 1-8 are changed to 140℃, 150℃, 160℃, 165℃, 170℃, 175℃, 180℃, and 175℃ respectively, and the die temperature of zone 9 is set to 170℃.

[0102] The results of the thermal conductivity and flame retardancy tests are shown in Tables 1 and 2.

[0103] Example 6

[0104] The main steps and process conditions in this embodiment are the same as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that:

[0105] In step 1.1, the reaction temperature is lowered to -5℃, hydroxypropyl methylcellulose is replaced with carboxymethyl chitosan, the concentration of the polyhydroxy polymer solution is increased to 2.5wt%, and the stirring time after the polyhydroxy polymer solution is added is extended to 45min.

[0106] In step 1.2, boron nitride nanosheets are replaced with black phosphorus nanosheets, the mechanical stirring and ultrasonic dispersion time is shortened to 10 min, the concentration of the thermally conductive nanosheet dispersion is increased to 3.0 wt%, γ-aminopropyltrimethoxysilane is replaced with 3-mercaptopropyltrimethoxysilane, 1 mol / L sodium hydroxide aqueous solution is replaced with 1 mol / L dilute nitric acid, and the pH value is reduced to 3.5.

[0107] In step 1.3, the mass ratio of organic modified thermally conductive nanosheets to organic coated flame retardant is increased to 0.6:1, the mechanical stirring and ultrasonic dispersion time is extended to 40 min, deionized water is replaced with ethanol, the reaction temperature is reduced to -5℃, the pH value is increased to 10.0, and the reaction time after the glutaraldehyde aqueous solution is added is extended to 24 h.

[0108] In step 2, the amount of antioxidant is reduced to 0.1 phr, the amount of core-shell thermally conductive flame retardant is reduced to 20 phr, boron nitride nanosheets are replaced with black phosphorus nanosheets, and the amount of thermally conductive nanosheets is increased to 20 phr.

[0109] The results of the thermal conductivity and flame retardancy tests are shown in Tables 1 and 2.

[0110] Example 7

[0111] The main steps and process conditions in this embodiment are the same as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that:

[0112] In step 1.1, the ultrafine ammonium polyphosphate was replaced with ultrafine aluminum polyphosphate, the mechanical stirring and ultrasonic dispersion time was extended to 40 min, and the mass ratio of polyhydroxy polymer to ultrafine phosphorus-containing compound was reduced to 0.8:1.

[0113] In step 1.2, dioxane is replaced with ethanol, the reaction temperature is reduced to 75℃, the concentration of the silane coupling agent solution is increased to 10.0wt%, the 1mol / L sodium hydroxide aqueous solution is replaced with a 1mol / L potassium carbonate aqueous solution, the pH value is increased to 9.5, and the reaction time after the silane coupling agent solution is added is extended to 48h.

[0114] In step 1.3, the mechanical stirring and ultrasonic dispersion time is extended to 40 min, the total concentration of the mixed dispersion of organic modified thermally conductive nanosheets and organic coated flame retardant is reduced to 1.0 wt%, the concentration of glutaraldehyde aqueous solution is increased to 8.0 wt%, the dropping time of glutaraldehyde aqueous solution is extended to 60 min, 1 mol / L sodium hydroxide aqueous solution is replaced with 1 mol / L sodium carbonate aqueous solution, the reaction time after the glutaraldehyde aqueous solution is dropped is shortened to 3 h, and ethanol is replaced with diethyl ether;

[0115] In step 2, antioxidant 1010 is replaced with antioxidant 6280, maleic anhydride-grafted POE is replaced with aluminate coupling agent, the amount of compatibilizer is reduced to 6.0 phr, the amount of thermally conductive nanoparticles is increased to 12.0 phr, the temperatures of zones 1-8 are changed to 160℃, 170℃, 180℃, 190℃, 195℃, 200℃, 210℃, and 200℃ respectively, and the die temperature of zone 9 is set to 190℃.

[0116] The results of the thermal conductivity and flame retardancy tests are shown in Tables 1 and 2.

[0117] Example 8

[0118] The main steps and process conditions in this embodiment are the same as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that:

[0119] In step 1.1, hydroxypropyl methylcellulose is replaced with hydroxypropyl starch, the concentration of the polyhydroxy polymer solution is reduced to 1.5 wt%, and the dropping time of the polyhydroxy polymer solution is extended to 40 min.

[0120] In step 1.2, γ-aminopropyltrimethoxysilane is replaced with γ-aminopropyltriethoxysilane, the mass ratio of silane coupling agent to thermally conductive nanosheets is increased to 0.5:1, 1 mol / L sodium hydroxide aqueous solution is replaced with 1 mol / L potassium hydroxide aqueous solution, and the pH value is increased to 9.0.

[0121] In step 1.3, deionized water is replaced with n-propanol, the reaction temperature is reduced to 40°C, and the mass ratio of glutaraldehyde to organic coated flame retardant is reduced to 0.020:1.

[0122] In step 2, antioxidant 1010 is replaced with antioxidant 168, the amount of antioxidant is increased to 0.7 phr, the amount of core-shell thermally conductive flame retardant is increased to 30 phr, the amount of thermally conductive nanosheets is reduced to 10 phr, the screw speed is changed to 300 r / min, and the feeding speed is changed to 40 kg / h.

[0123] The results of the thermal conductivity and flame retardancy tests are shown in Tables 1 and 2.

[0124] Example 9

[0125] The main steps and process conditions in this embodiment are the same as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that:

[0126] In step 1.1, the ultrafine ammonium polyphosphate is replaced with ultrafine melamine polyphosphate, and the mechanical stirring and ultrasonic dispersion time is extended to 60 min.

[0127] In step 1.2, dioxane is replaced with isopropanol, the reaction temperature is reduced to 80℃, γ-aminopropyltrimethoxysilane is replaced with 3-glycidyloxypropyltriethoxysilane, the dropping time of the silane coupling agent solution is shortened to 15 min, 1 mol / L sodium hydroxide aqueous solution is replaced with 1 mol / L dilute acetic acid, the pH value is reduced to 3.0, the reaction time after the silane coupling agent solution is dropped is extended to 36 h, and ethanol is replaced with methanol.

[0128] In step 1.3, the mechanical stirring and ultrasonic dispersion time is extended to 60 min, the total concentration of the mixed dispersion of organic modified thermally conductive nanosheets and organic coated flame retardant is increased to 3.0 wt%, the concentration of glutaraldehyde aqueous solution is increased to 6.0 wt%, 1 mol / L sodium hydroxide aqueous solution is replaced with 1 mol / L dilute acetic acid, the pH value is reduced to 5.0, and ethanol is replaced with ethyl acetate;

[0129] In step 2, maleic anhydride-grafted POE is replaced with maleic anhydride-grafted polyethylene, the amount of compatibilizer is increased to 8.0 phr, alumina nanoparticles are replaced with zinc oxide nanoparticles, the screw speed is changed to 250 r / min, and the feeding speed is changed to 25 kg / h.

[0130] The results of the thermal conductivity and flame retardancy tests are shown in Tables 1 and 2.

[0131] Example 10

[0132] The main steps and process conditions in this embodiment are the same as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that:

[0133] In step 1.1, the reaction temperature is increased to 20℃, hydroxypropyl methylcellulose is replaced with hyaluronic acid, the mass ratio of polyhydroxy polymer to ultrafine phosphorus-containing compound is reduced to 0.5:1, the concentration of polyhydroxy polymer solution is reduced to 1.0wt%, and the stirring time after the polyhydroxy polymer solution is added is shortened to 10min.

[0134] In step 1.2, boron nitride nanosheets are replaced with silicon carbide nanosheets, the mechanical stirring and ultrasonic dispersion time is extended to 120 min, the concentration of the thermally conductive nanosheet dispersion is reduced to 0.5 wt%, γ-aminopropyltrimethoxysilane is replaced with 3-mercaptopropyltriethoxysilane, the mass ratio of silane coupling agent to thermally conductive nanosheets is increased to 0.3:1, 1 mol / L sodium hydroxide aqueous solution is replaced with 1 mol / L dilute sulfuric acid, and the pH value is reduced to 4.5.

[0135] In step 1.3, the mass ratio of organic modified thermally conductive nanosheets to organic coated flame retardant is reduced to 0.2:1, deionized water is replaced with dioxane, the reaction temperature is increased to 90℃, the dropping time of glutaraldehyde aqueous solution is shortened to 20 min, the pH value is increased to 9.0, and the reaction time after the glutaraldehyde aqueous solution is dropped is shortened to 6 h.

[0136] In step 2, antioxidant 1010 is replaced with antioxidant 626, and the antioxidant dosage is increased to 1.0 phr. Boron nitride nanosheets are replaced with silicon carbide nanosheets, and the thermally conductive nanoparticle dosage is reduced to 15.0 phr. The temperatures of zones 1-8 are set to 160℃, 170℃, 180℃, 185℃, 190℃, 195℃, 200℃, and 195℃, respectively, and the die temperature of zone 9 is set to 190℃.

[0137] The results of the thermal conductivity and flame retardancy tests are shown in Tables 1 and 2.

[0138] Comparative Example 1

[0139] To demonstrate that the present invention can impart excellent thermal conductivity and flame retardant properties to POE substrates, pure POE was used as a comparison.

[0140] Various standard samples were prepared from POE granules by injection molding, and their thermal conductivity and flame retardant properties were tested. The results are shown in Tables 1 and 2.

[0141] Comparative Example 2

[0142] To demonstrate that multi-morphological, multi-scale thermally conductive filler systems are beneficial for constructing a more continuous and complete three-dimensional thermally conductive network, only thermally conductive nanosheets were added to POE as a comparison.

[0143] POE granules, 0.3 phr antioxidant 1010, 10.0 phr maleic anhydride-grafted POE, and 30.0 phr boron nitride nanosheets were mixed evenly in a high-speed mixer, and then melt-blended in a twin-screw extruder. The twin-screw extruder parameters were set as follows: temperatures for zones 1-8 were 150℃, 160℃, 170℃, 175℃, 180℃, 185℃, 190℃, and 185℃, respectively; the die temperature for zone 9 was 180℃; the screw speed was set to 365 r / min; and the feed rate was set to 60 kg / h.

[0144] Various standard samples were prepared by injection molding, and their thermal conductivity and flame retardant properties were tested. The results are shown in Tables 1 and 2.

[0145] Comparative Example 3

[0146] To demonstrate that core-shell thermally conductive flame retardants can overcome the difficulty of simultaneously achieving thermal conductivity and flame retardancy in polymers, flame retardants and thermally conductive fillers were directly mixed and dispersed in POE as a comparison.

[0147] POE granules, 0.3 phr antioxidant 1010, 10.0 phr maleic anhydride-grafted POE, 10.0 phr ultrafine ammonium polyphosphate, 10.0 phr hydroxypropyl methylcellulose, 20.0 phr boron nitride nanosheets, and 10.0 phr alumina nanoparticles were mixed evenly in a high-speed mixer, and then added to a twin-screw extruder for melt blending. The twin-screw extruder parameters were set as follows: temperatures for zones 1-8 were 150℃, 160℃, 170℃, 175℃, 180℃, 185℃, 190℃, and 185℃ respectively; the die temperature for zone 9 was 180℃; the screw speed was set to 365 r / min; and the feed rate was set to 60 kg / h.

[0148] Various standard samples were prepared by injection molding, and their thermal conductivity and flame retardant properties were tested. The results are shown in Tables 1 and 2.

[0149] Test methods

[0150] 1. Scanning Electron Microscopy (SEM): Performed on a thermal field emission scanning electron microscope (Carl Zeiss, Germany, model: Merlin). The sample was adhered to the stage using conductive adhesive and then surface-sprayed with gold. Electron beam scanning imaging with an accelerating voltage of 5 kV was used to observe the surface morphology of the sample.

[0151] 2. Thermal conductivity test: Performed according to ASTM E1530 standard. A constant heat flux is applied to the polymer sample. After the system reaches thermal equilibrium, the steady-state temperature gradient (ΔT) and heat flux density (Q) on both sides of the sample are measured. The thermal conductivity is calculated according to Fourier's law (λ = Q×d / (A×ΔT)).

[0152] 3. Limiting Oxygen Index (LOI) Test: Performed according to ASTM D2863 standard, with a sample size of 120mm × 6.5mm × 3mm.

[0153] 4. Vertical Burning (UL-94) Test: Conducted according to ASTM 635-2003 standard, with sample size of 127mm × 12.7mm × 3.2mm.

[0154]

[0155]

[0156] As can be seen from the data in Tables 1 and 2 for Examples 1-10, core-shell structured thermally conductive flame retardants prepared by different processes using ultrafine phosphorus-containing compounds, polyhydroxy polymers, silane coupling agents, and thermally conductive nanosheets can all produce composite materials with excellent thermal conductivity and flame retardant properties when added to POE in different proportions and process conditions along with other thermally conductive fillers, antioxidants, and compatibilizers.

[0157] As shown in Table 1, the polyolefin composite material provided by this invention exhibits excellent thermal conductivity. Pure POE, due to its nonpolar molecular structure and low crystallinity, has very poor thermal conductivity, with a thermal conductivity of only 0.21 W / (m·K) (Comparative Example 1). After adding 30.0 phr of boron nitride nanosheets (Comparative Example 2), the thermal conductivity of POE can be increased to 0.52 W / (m·K). To consider flame retardant properties, a flame retardant must also be added. However, after mixing and adding thermally conductive fillers and flame retardants using conventional methods, the thermal conductivity of the resulting polyolefin composite material decreases to 0.45 W / (m·K) (Comparative Example 3). This is because the inclusion of flame retardants in conventional processing methods disrupts the continuity of the thermally conductive network, leading to a decrease in the thermal conductivity of the composite material. It is noteworthy that the polyolefin composite material provided by this invention, even with the addition of a flame retardant system, has a higher thermal conductivity than Comparative Example 2, which only added thermally conductive nanosheets. For example, the polyolefin composite material provided in Example 1 has a thermal conductivity as high as 0.77 W / (m·K). This is because in this invention, the flame-retardant system is encapsulated by thermally conductive nanosheets to form a core-shell structure thermally conductive flame retardant, which does not affect the continuity of the thermally conductive network. Under the synergistic effect of the compatibilizer's interfacial compatibilization and the high shear field of the twin-screw extruder, the core-shell structure thermally conductive flame retardant, thermally conductive nanosheets, and thermally conductive nanoparticles can be uniformly dispersed in POE. Through the synergistic construction of multi-morphological and multi-scale thermally conductive fillers, a more continuous three-dimensional thermally conductive network is formed, significantly improving the thermal conductivity of POE.

[0158] As shown in Table 2, the polyolefin composite material provided by this invention exhibits excellent flame retardant properties. Pure POE (Comparative Example 1) is highly flammable, with a limiting oxygen index (LOI) of only 18.5%, and it completely burns out in the vertical burning test, resulting in no rating. After adding a thermally conductive filler to POE (Comparative Example 2), its LOI not only did not increase but actually decreased to 16.3%. This is because under high-temperature conditions, the thermally conductive filler rapidly transfers heat to the polymer matrix, accelerating the thermal degradation of the matrix and leading to a decrease in the flame retardant properties of the system. The polyolefin composite material (Comparative Example 3), which simultaneously adds a thermally conductive filler and a flame retardant using conventional methods, only increased its LOI to 27.6%, achieving only a UL-94 V-1 rating in the vertical burning test. In contrast, the solution provided by this invention imparts excellent flame retardant properties to POE while achieving high thermal conductivity. For example, the polyolefin composite material provided in Example 6 has an LOI as high as 32.4%, achieving a UL-94 V-0 rating in the vertical burning test. This is because the polyolefin composite material provided by this invention has a thermally conductive network that can rapidly transfer heat to the flame-retardant system inside the core-shell structured thermally conductive flame retardant. The ultrafine phosphorus-containing compounds undergo thermal degradation to generate pyrophosphoric acid, catalyzing the dehydration, cross-linking, and carbonization reactions of the polyhydroxy polymers. Simultaneously, the gas molecules generated by the cracking cause the system to foam and expand, forming a stable porous carbon layer. The carbon layer expansion process disrupts the original continuous thermally conductive network of the material, and the resulting porous structure endows the carbon layer with excellent thermal insulation properties, effectively blocking heat transfer to the POE matrix. Furthermore, the layered thermally conductive nanosheets significantly enhance the mechanical strength, thermal stability, and airtightness of the carbon layer. Therefore, the expanded carbon layer can exert highly efficient thermal insulation, oxygen barrier, and flame-retardant effects.

Claims

1. A method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material, characterized in that: Using ethylene-octene copolymer as the base material, 100 phr of ethylene-octene copolymer, 0.1~1.0 phr of antioxidant, 4.0~15.0 phr of compatibilizer, 15.0~30.0 phr of core-shell structured thermally conductive flame retardant, 10.0~25.0 phr of organic modified thermally conductive nanosheets and 5.0~15.0 phr of thermally conductive nanoparticles are added to a high-speed mixer and mixed evenly. Then, the mixture is added to a twin-screw extruder and melt-blended and extruded through the twin-screw extruder to obtain a high thermal conductivity flame retardant polyolefin cable insulation layer material with a thermal conductivity greater than 0.

7. Core-shell structured thermally conductive flame retardant, thermally conductive nanosheets and thermally conductive nanoparticles are uniformly dispersed in ethylene-octene copolymer, forming a three-dimensional continuous thermally conductive network composed of multi-morphological and multi-scale thermally conductive fillers, including core-shell structured thermally conductive flame retardant, thermally conductive nanosheets and thermally conductive nanoparticles. Among them, the organic modified thermally conductive nanosheets are prepared through steps S1 and S2, and the core-shell structure thermally conductive flame retardant is prepared through steps S1, S2 and S3. Step S1, Preparation method of organic coated flame retardant, A solution of polyhydroxy polymer containing polyhydroxy polymers is slowly added to an aqueous dispersion of ultrafine phosphorus compounds mixed with ultrafine phosphorus compounds. The mass ratio of polyhydroxy polymers to ultrafine phosphorus compounds is 0.5~1.5:

1. After stirring, the polyhydroxy polymers spontaneously coat the surface of the ultrafine phosphorus compounds. The product is collected to obtain an organic coated flame retardant. Step S2, the preparation method of organic modified thermally conductive nanosheets, firstly, the silane coupling agent solution is slowly added to the thermally conductive nanosheet dispersion mixed with the thermally conductive nanosheets, the mass ratio of silane coupling agent to thermally conductive nanosheets is 0.1~0.5:1, then a pH adjuster is added, the silane coupling agent and the nanomaterials undergo a dehydration condensation reaction, and after the reaction is completed, the product is collected to obtain organic modified thermally conductive nanosheets; Step S3, preparation method of core-shell structured thermally conductive flame retardant: organic coated flame retardant and organic coated flame retardant are mixed and dispersed in solvent C, and then glutaraldehyde aqueous solution is added. The mass ratio of glutaraldehyde, organic modified thermally conductive nanosheets and organic coated flame retardant is 0.005~0.03: 0.1~0.6:

1. Glutaraldehyde reacts with the organic active groups on the surface of organic coated flame retardant and organic modified thermally conductive nanosheets to form covalent bonds. After the reaction is completed, the product is collected to obtain core-shell structured thermally conductive flame retardant.

2. The method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material according to claim 1, characterized in that: In step S1, the organic-coated flame retardant is prepared through the following steps. Step S1.1: The sub-step of preparing an ultrafine phosphorus-containing compound aqueous dispersion involves mixing the ultrafine phosphorus-containing compound with deionized water, mechanically stirring and ultrasonically dispersing for 5-60 minutes at a temperature of -5-30°C, uniformly dispersing the ultrafine phosphorus-containing compound in deionized water to obtain the ultrafine phosphorus-containing compound aqueous dispersion with a mass concentration of 0.5-4.0 wt%. Step S1.2, the sub-step of preparing a polyhydroxy polymer solution, involves dissolving the polyhydroxy polymer in deionized water and stirring until homogeneous to obtain the polyhydroxy polymer solution with a mass concentration of 0.5~3.0wt%. Step S1.3, stirring sub-step: The polyhydroxy polymer solution is slowly added dropwise to the ultrafine phosphorus-containing compound aqueous dispersion over 20-60 minutes, wherein the mass ratio of polyhydroxy polymer to ultrafine phosphorus-containing compound is 0.5-1.5:

1. After the addition is complete, stirring is continued for 10-60 minutes. Under the electrostatic force between positive and negative charges, the polyhydroxy polymer spontaneously coats the surface of the ultrafine phosphorus-containing compound. Step S1.4, Product: The product from step S1.3 is collected by centrifugation and dried to obtain an organic-coated flame retardant.

3. The method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material according to claim 2, characterized in that: In step S2, the organically modified thermally conductive nanosheets are prepared through the following steps. Step S2.1: The thermally conductive nanosheets are uniformly dispersed in solvent A by mechanical stirring and ultrasonic dispersion for 10~120 min to obtain a thermally conductive nanosheet dispersion with a mass concentration of 0.5~3.0 wt%. The reaction temperature is adjusted to 75~120℃ and mechanical stirring is continued for 10~120 min. Step S2.2: Dissolve the silane coupling agent in solvent B to obtain a silane coupling agent solution with a mass concentration of 4.0~10.0wt%; Step S2.3: Slowly add the silane coupling agent solution dropwise to the thermally conductive nanosheet dispersion over 15-60 min. The mass ratio of silane coupling agent to thermally conductive nanosheet is 0.1:1 to 0.5:

1. At the same time, add a pH adjuster to control the pH value to 3.0-10.

0. After the silane coupling agent is completely added, continue the reaction for 6-48 h. Under the action of the pH adjuster, the silane coupling agent undergoes hydrolysis to generate ~Si-OH, which then undergoes a dehydration condensation reaction with the -OH on the surface of the ultrafine phosphorus-containing compound to form a covalent bond. Step S2.4: After the reaction is completed, the product of step S2.3 is collected by centrifugation, precipitated, washed with solvent D, and dried to obtain organic modified thermally conductive nanosheets.

4. The method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material according to claim 3, characterized in that: In step S3, the core-shell structured thermally conductive flame retardant is prepared through the following steps. Step S3.1: The organic-coated flame retardant prepared in step S1 and the organic modified thermally conductive nanosheets synthesized in step S2 are mixed and dispersed in solvent E by mechanical stirring and ultrasonic dispersion for 5-60 min to obtain a mixed dispersion with a total mass concentration of 0.5-3.0 wt%. Step S3.2: Adjust the reaction temperature to -5~90℃ and continue mechanical stirring for 5~60 min. Slowly add a glutaraldehyde aqueous solution with a mass concentration of 1.0~10.0wt% to the above mixed dispersion over 20~60 min, while adding a pH adjuster to control the pH value to 3.0~10.

0. After the glutaraldehyde aqueous solution is completely added, continue the reaction for 3~24 h. The mass ratio of glutaraldehyde, organic modified thermally conductive nanosheets and organic coated flame retardant is 0.005~0.03: 0.1~0.6:

1. Under the action of the pH adjuster, glutaraldehyde reacts with the organic active groups on the organic coated flame retardant and organic modified thermally conductive nanosheets to form covalent bonds. Step S3.3: Collect the product from step S3.2 by centrifugation, wash it with solvent F after precipitation, and dry it to obtain a core-shell structured thermally conductive flame retardant. The diameter of the core-shell structured thermally conductive flame retardant is 3~11.5μm. The core of the core-shell structured thermally conductive flame retardant is an ultrafine phosphorus-containing compound with polyhydroxy polymers coated on the surface. The core-shell layer of the core-shell structured thermally conductive flame retardant is formed by organic modified thermally conductive nanosheets coated on the outer layer of the core through the covalent cross-linking effect of glutaraldehyde.

5. A method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material according to any one of claims 1-4, characterized in that: The thermally conductive nanosheet is at least one of boron nitride nanosheets, molybdenum disulfide nanosheets, black phosphorus nanosheets, and silicon carbide nanosheets. The thickness of the thermally conductive nanosheet is 0.5~10nm, the diameter of the sheet is 1~5μm, and the thermal conductivity is 30~600W / (m·K). The polyhydroxy polymer is at least one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, hydroxypropyl starch, hyaluronic acid, carboxymethyl chitosan, and polyvinyl alcohol; The thermally conductive nanoparticles are at least one of boron nitride nanoparticles, aluminum nitride nanoparticles, silicon carbide nanoparticles, zinc oxide nanoparticles, and aluminum oxide nanoparticles. The particle size of the thermally conductive nanoparticles is 20~100nm, and the thermal conductivity is 40~400W / (m·K). The antioxidant is at least one of antioxidant 1010, antioxidant 1076, antioxidant BHT, antioxidant 168, antioxidant 626 and antioxidant 6280; The compatibilizer is at least one of maleic anhydride-grafted POE, maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyethylene, titanate coupling agent and aluminate coupling agent. The ultrafine phosphorus-containing compound is at least one of ultrafine melamine polyphosphate, ultrafine ammonium polyphosphate, ultrafine aluminum hypophosphite, and ultrafine aluminum polyphosphate. Solvent A, solvent B, solvent C, solvent D, solvent E and solvent F are at least one of diethyl ether, acetone, methanol, ethyl acetate, ethanol, isopropanol, n-propanol, deionized water, dioxane and N,N-dimethylformamide; The silane coupling agent is at least one of γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropyltriethoxysilane. The pH adjuster is at least one of the following: 1 mol / L dilute hydrochloric acid, 1 mol / L dilute acetic acid, 1 mol / L dilute sulfuric acid, 1 mol / L dilute nitric acid, 1 mol / L sodium hydroxide aqueous solution, 1 mol / L potassium hydroxide aqueous solution, 1 mol / L sodium carbonate aqueous solution, and 1 mol / L potassium carbonate aqueous solution.

6. The method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material according to claim 5, characterized in that: The twin-screw extruder is configured with nine sections from the feed inlet to the extrusion section, including the first feeding section, the second melting section, the third melting section, the fourth mixing section, the fifth mixing section, the sixth homogenizing section, the seventh homogenizing section, the eighth homogenizing section, and the ninth die section. The temperature of the first feeding section is set to 130~160℃. The temperatures of both the second and third melting zones are set to 150~190℃. The temperatures of the fourth mixing section, the fifth mixing section, and the sixth homogenization section are all set to 160~200℃. The temperatures of the homogenization sections in zones seven and eight are both set to 180~210℃. The temperature of the die in Zone 9 is set to 170~190℃. The screw speed of the twin-screw extruder is set to 250~500 r / min, and the feeding speed is set to 25~100 kg / h.

7. The method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material according to claim 5, characterized in that: 100 phr of ethylene-octene copolymer, 0.1-0.3 phr of antioxidant, 4.0-10.00 phr of compatibilizer, 17-25 phr of core-shell thermally conductive flame retardant, 15-20 phr of organically modified thermally conductive nanosheets, and 8-12 phr of thermally conductive nanoparticles are added to a high-speed mixer and mixed evenly. Then, the mixture is added to a twin-screw extruder and melt-blended and extruded through the twin-screw extruder to obtain a high thermal conductivity and flame retardant polyolefin cable insulation material with a thermal conductivity greater than 0.

9.

8. The method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material according to claim 7, characterized in that: In step S1, the mass ratio of the polyhydroxy polymer to the ultrafine phosphorus-containing compound is 0.5~1.2:

1. In step S2, the mass ratio of the silane coupling agent to the thermally conductive nanosheet is 0.1~0.3:

1. In step S3, the mass ratio of glutaraldehyde, the organic modified thermally conductive nanosheet, and the organic coated flame retardant is 0.005~0.03: 0.1~0.6:

1.

9. The method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material according to claim 8, characterized in that: The thermally conductive nanoparticles are selected from boron nitride nanoparticles with a particle size of 60~80nm and a thermal conductivity of 300~400 W / (m·K). In step S1, the polyhydroxy polymer is selected from hydroxypropyl methylcellulose or carboxymethyl cellulose, and the ultrafine phosphorus-containing compound is ultrafine ammonium polyphosphate or ultrafine aluminum hypophosphite; the mass ratio of the polyhydroxy polymer to the ultrafine phosphorus-containing compound is 1.0~1.2:

1. In step S2, the compatibilizer is selected from maleic anhydride-grafted POE or titanate coupling agent; the thermally conductive nanosheets are selected from boron nitride nanosheets or silicon carbide nanosheets with a sheet diameter of 1~5μm and a thermal conductivity of 400~600W / (m·K); after adding the silane coupling agent solution, a pH adjuster is added dropwise to control the pH value to be greater than 8.

0. In step S3, after adding the glutaraldehyde aqueous solution, a pH adjuster is added dropwise to control the pH value to be greater than 8.

0. The total mass concentration of the mixed dispersion of the organic modified thermally conductive nanosheets and the organic-coated flame retardant is 0.5~3.0 wt%. The mass ratio of glutaraldehyde, the organically modified thermally conductive nanosheets, and the organically coated flame retardant is 0.005~0.01:0.1~0.3:1; The mass ratio of organic modified thermally conductive nanosheets to organic coated flame retardant is 0.4~0.5:1; The core-shell structured thermally conductive flame retardant has a particle size of 3~5μm.

10. A method for preparing a high thermal conductivity and flame retardant polyolefin cable insulation layer material, characterized in that: It is prepared by the preparation method of a high thermal conductivity and flame retardant polyolefin cable insulation layer material according to any one of claims 1 to 9.

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