Insulating polypropylene composite material for power cables and method for producing the same

Abstract

The application relates to the field of high polymer materials and discloses an insulating polypropylene composite material for power cables and a preparation method thereof, which comprises the following components: polypropylene resin, modified ammonium polyphosphate, ethylene-octene copolymer and lubricant; the modified ammonium polyphosphate is made by coating ammonium polyphosphate with a copolymer formed by triazine ring derivative I, triazine ring derivative II and triazine ring derivative III; the triazine ring derivative I is made by reacting cyanuric chloride and 3-aminopropyl triethoxysilane and using 2-(trifluoromethyl) piperazine as a bridging agent; the triazine ring derivative II is made by grafting by using 3-aminopropyl triethoxysilane to aminate boron nitride nanosheet and adding cyanuric chloride; and the triazine ring derivative III is made by reacting cyanuric chloride and 3,5-di-tert-butyl-4-hydroxybenzylamine and using hydrazine dihydrochloride as a bridging agent; the modified ammonium polyphosphate is doped in the matrix, so that the composite material has good mechanical properties, aging resistance, insulation waterproofness and flame retardance.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to an insulating polypropylene composite material for power cables and its preparation method. Background Technology

[0002] As a crucial component of power transmission networks, the performance of power cables directly impacts the safety and stability of power grid operation. With the surge in demand for transmission voltage levels and capacity, the reliability of cable insulation materials under extreme conditions such as high temperatures and high electric fields faces severe challenges. Simultaneously, driven by the carbon neutrality strategy, the global energy system is accelerating its transition to low-carbon practices, placing more stringent technical standards on the eco-friendliness and recyclability of cable materials. While mainstream cross-linked polyethylene possesses excellent mechanical and electrical properties, its thermosetting characteristics make it difficult to recycle. Furthermore, the high-temperature cross-linking process in its production suffers from high energy consumption and low efficiency, and the environmental problems caused by traditional incineration or landfill disposal methods are becoming increasingly prominent. Therefore, there is an urgent need to develop new power cable insulation materials that combine recyclability and high reliability.

[0003] Thermoplastic polypropylene (PP) is considered a potential alternative to cross-linked polyethylene (XLPE) due to its advantages in heat resistance, insulation properties, and mechanical strength. PP requires no cross-linking or degassing treatment, has low production energy consumption, and is recyclable, meeting environmental protection requirements. However, PP's high rigidity and low elongation at break limit its direct application. Elastomer blending modification, as a low-cost, efficient, and easily scalable physical modification strategy, has gained widespread acceptance. Among these, polyolefin elastomers (POEs) are the most commonly used elastomers in PP copolymerization modification due to their low price and excellent electrical and mechanical properties. However, the introduction of elastomers often reduces the insulation performance of composite materials, and both PP and POEs are flammable. Furthermore, in practical applications, PP is susceptible to the effects of heat and oxygen, causing the tertiary carbon structures on its chains to oxidize into free radicals. Under the influence of oxygen and heat, a series of free radical chain reactions occur, during which the PP main chain breaks, generating carbonyl and hydroxyl groups. This leads to a significant decline in the mechanical properties of polypropylene materials. In addition, traditional intumescent flame retardant systems do not have anti-aging properties. Current technologies usually adopt the method of adding antioxidants alone, relying on the antioxidants to capture and scavenge free radicals to slow down the aging and degradation of flame-retardant polypropylene materials, thereby extending the weather resistance and service life of the materials. However, the small molecule anti-aging agents currently used have key problems such as easy precipitation and difficulty in dispersion. Moreover, ammonium polyphosphate, as one of the main components of intumescent flame retardant systems, has a weak char-forming ability, and its effect on flame-retardant polypropylene alone is not ideal. The commonly used method is to use ammonium polyphosphate in combination with char-forming agents to form an intumescent flame retardant system. However, this method still has defects such as low char-forming efficiency, poor compatibility with the matrix, and insufficient water resistance. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide an insulating polypropylene composite material for power cables and its preparation method. The method involves using a melt blending method to dope modified ammonium polyphosphate into a polypropylene resin / ethylene-octene copolymer matrix, thereby endowing the composite material with good mechanical properties, aging resistance, insulation and waterproofing properties, and flame retardant properties.

[0005] The objective of this invention can be achieved through the following technical solutions: An insulating polypropylene composite material for power cables comprises the following components in parts by weight: 75-98 parts of polypropylene resin, 2-5 parts of modified ammonium polyphosphate, 1-3 parts of ethylene-octene copolymer, and 0.5-1.5 parts of lubricant. The modified ammonium polyphosphate is prepared by coating ammonium polyphosphate with a copolymer formed between triazine ring derivative I, triazine ring derivative II and triazine ring derivative III; The triazine ring derivative I was prepared by a nucleophilic substitution reaction of cyanuric chloride and 3-aminopropyltriethoxysilane with 2-(trifluoromethyl)piperazine as a bridging agent. The triazine ring derivative II was prepared by surface grafting boron nitride nanosheets with 3-aminopropyltriethoxysilane and adding cyanuric chloride via a nucleophilic substitution reaction. The triazine ring derivative III was prepared by a nucleophilic substitution reaction between cyanuric chloride and 3,5-di-tert-butyl-4-hydroxybenzylamine to obtain an intermediate, and then by a nucleophilic substitution reaction using hydrazine dihydrochloride as a bridging agent.

[0006] Preferably, the preparation method of the modified ammonium polyphosphate includes the following steps: Triazine ring derivative I, triazine ring derivative II, triazine ring derivative III and 1,4-dioxane were added to a reactor, the temperature was raised to 45-55℃, ethylenediamine and triethylamine were slowly added dropwise, and the reaction was stirred for 1-1.5 h. Then the temperature was raised to 95-100℃, and ethylenediamine and triethylamine were slowly added dropwise. The reaction was refluxed and stirred for 4-5 h. Subsequently, ammonium polyphosphate was added, and the reaction was continued for 15-18 h. After the reaction was completed, the modified ammonium polyphosphate was prepared by filtration, washing and drying.

[0007] Preferably, the mass ratio of the triazine ring derivative I, triazine ring derivative II, triazine ring derivative III and ammonium polyphosphate is 10.2~10.9:1.8~2.2:1:25~27.

[0008] Preferably, the preparation method of the triazine ring derivative I includes the following steps: Cyanuric chloride and acetone were added to the reactor, and the temperature was controlled at 0-5℃. The mixture was stirred continuously until homogeneous. Then, a mixed solution of 3-aminopropyltriethoxysilane and acetone was slowly added dropwise, along with an aqueous solution of sodium hydroxide. The mixture was stirred for 3-5 hours. The temperature was then raised to 45-55℃, and a mixed solution of 2-(trifluoromethyl)piperazine and acetone, along with an aqueous solution of sodium hydroxide, was slowly added dropwise. The reaction was continued for 3-5 hours. After the reaction was completed, the mixture was filtered, washed, and dried to obtain triazine ring derivative I.

[0009] Preferably, the molar ratio of cyanuric chloride, 3-aminopropyltriethoxysilane and 2-(trifluoromethyl)piperazine is 2:2:1.

[0010] Preferably, the preparation method of the triazine ring derivative II includes the following steps: Nano-sized hexagonal boron nitride was dispersed in isopropanol and treated with intermittent sonication in an ultrasonic cell disruptor for 7-9 hours. After standing for 24 hours, the supernatant was washed with deionized water and dried in a freeze dryer to obtain boron nitride nanosheets. The boron nitride nanosheets were then ultrasonically dispersed in 1,4-dioxane to obtain a dispersion. The dispersion, 3-aminopropyltriethoxysilane, and deionized water were added to a reactor and stirred at 85-90°C for 5-7 hours. The temperature was then lowered to 10-15°C, cyanuric chloride was added, and triethylamine acid-binding agent was slowly added dropwise. The reaction was stirred for 4-5 hours. After the reaction was completed, the product was centrifuged, washed, and dried to prepare triazine ring derivative II.

[0011] Preferably, the mass ratio of the boron nitride nanosheets, 3-aminopropyltriethoxysilane, and cyanuric chloride is 2~3:2.2:1.8.

[0012] Preferably, the preparation method of the triazine ring derivative III includes the following steps: Cyanuric chloride, 3,5-di-tert-butyl-4-hydroxybenzylamine, and 1,4-dioxane were added to a reactor and stirred. Triethylamine was then added dropwise, and the mixture was stirred at 0-5°C for 3-5 hours to obtain an intermediate. Hydrazine dihydrochloride and sodium hydroxide were dissolved in deionized water to obtain a mixed solution. The mixed solution was then slowly added dropwise to the reactor containing the intermediate while the temperature was raised to 40-45°C. After the addition was complete, the reaction was continued for 1-2 hours. After the reaction was completed, the triazine ring derivative III was prepared by centrifugation, washing, and drying.

[0013] Preferably, the molar ratio of cyanuric chloride, 3,5-di-tert-butyl-4-hydroxybenzylamine, and hydrazine dihydrochloride is 2:2:1.

[0014] The preparation method of the insulating polypropylene composite material for power cables as described above includes the following steps: Weigh each component according to the weight parts, stir and mix the polypropylene resin, modified ammonium polyphosphate, ethylene-octene copolymer and lubricant evenly, and then melt extrude, granulate and mold the mixture through a twin-screw extruder at 180~220℃ to prepare an insulating polypropylene composite material for power cables; the lubricant is one or a combination of stearic acid, polyethylene wax and oxidized polyethylene wax.

[0015] The beneficial effects of this invention are: This invention utilizes cyanuric chloride and 3-aminopropyltriethoxysilane to undergo a nucleophilic substitution reaction, with 2-(trifluoromethyl)piperazine as a bridging agent, to prepare triazine ring derivative I via nucleophilic substitution. Simultaneously, a liquid-phase ultrasonic exfoliation method is used to prepare hydroxyl-containing boron nitride nanosheets with isopropanol as a solvent. The hydroxylated boron nitride nanosheets are then grafted onto the surface of the nanosheets with 3-aminopropyltriethoxysilane. Further addition of cyanuric chloride and a nucleophilic substitution reaction yields triazine ring derivative II. Additionally, a nucleophilic substitution reaction is conducted between cyanuric chloride and 3,5-di-tert-butyl-4-hydroxybenzylamine to obtain an intermediate. Then, using hydrazine dihydrochloride as a bridging agent, one molecule of the intermediate is grafted onto the amino groups at both ends of the hydrazine dihydrochloride via a nucleophilic substitution reaction to prepare triazine ring derivative III.

[0016] The triazine ring derivatives I, II, and III prepared in this invention each contain a chlorine atom at both ends of their molecular structures. Ethylenediamine is then used as a bridging agent among the three derivatives, and a nucleophilic substitution reaction is employed to coat ammonium polyphosphate with the resulting copolymer, thus preparing modified ammonium polyphosphate. This modification improves both the flame retardant efficiency of ammonium polyphosphate and the compatibility between ammonium polyphosphate and the polypropylene resin matrix. The resulting expanded char layer has a more uniform and dense structure. Furthermore, the modified ammonium polyphosphate is doped into the polypropylene resin / POE matrix using a melt blending method, imparting excellent flame retardant properties to the composite material. Simultaneously, the surface of the modified ammonium polyphosphate becomes rougher, increasing its water contact angle, and introducing [a certain effect] onto the surface of the modified ammonium polyphosphate. The presence of organosilicon and fluorine-containing segments enhances the hydrophobicity of the composite material. Furthermore, grafting boron nitride nanosheets with a silane coupling agent improves their dispersion in the matrix, allowing their mechanical properties to be fully realized. Additionally, the boron nitride nanosheets modified with ammonium polyphosphate have a large specific surface area, enabling the formation of numerous charge traps at the interface. These charge traps effectively hinder charge movement, enhancing the insulation of the composite material. Moreover, the introduction of hindered phenolic and hydrazine groups with anti-aging properties onto the surface of modified ammonium polyphosphate contributes to the composite material's aging resistance. Through chemical bonding, the hindered phenolic and hydrazine groups are more tightly bound to the ammonium polyphosphate, further limiting the migration of the anti-aging components within the composite material and resulting in long-lasting performance. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: A method for preparing modified ammonium polyphosphate includes the following steps: 30.7 g of triazine derivative I, 5.7 g of triazine derivative II, 3 g of triazine derivative III, and 450 mL of 1,4-dioxane were added to a reactor. The temperature was raised to 50 °C, and 0.8 g of ethylenediamine and 2.8 g of triethylamine were slowly added dropwise. The mixture was stirred for 1 h, then the temperature was raised to 100 °C, and 6 g of ethylenediamine and 10.1 g of triethylamine were slowly added dropwise. The mixture was refluxed and stirred for 4 h. Subsequently, 78.8 g of ammonium polyphosphate was added, and the reaction was continued for 16 h. After the reaction was completed, the filter cake was collected by vacuum filtration, washed three times with a 1:1 mixture of anhydrous ethanol and water, and then washed once with anhydrous ethanol. The cake was dried at 80 °C to prepare modified ammonium polyphosphate.

[0019] The preparation method of triazine ring derivative I includes the following steps: 18.4 g of cyanuric chloride and 250 mL of acetone were added to the reactor, and the temperature was controlled at 0 °C. The mixture was stirred continuously until homogeneous. Then, a mixed solution of 22.1 g of 3-aminopropyltriethoxysilane and 20 mL of acetone was slowly added dropwise, along with an aqueous solution of sodium hydroxide (4 g of sodium hydroxide dissolved in 40 mL of deionized water). The mixture was stirred for 4 h. The temperature was then raised to 50 °C, and a mixed solution of 7.7 g of 2-(trifluoromethyl)piperazine and 20 mL of acetone and an aqueous solution of sodium hydroxide (4 g of sodium hydroxide dissolved in 40 mL of deionized water) were slowly added dropwise. The mixture was stirred for another 4 h. After the reaction was completed, the filter cake was collected by suction filtration. The cake was washed twice with a mixed solution of acetone and deionized water in a volume ratio of 1:1, and then washed twice with anhydrous ethanol. The cake was dried under vacuum at 60 °C to prepare triazine ring derivative I.

[0020] The preparation method of triazine ring derivative II includes the following steps: 2g of hexagonal boron nitride nanoparticles were dispersed in 200mL of isopropanol and treated with intermittent sonication in an ultrasonic cell disruptor for 8h. After standing for 24h, the supernatant was washed with deionized water and dried in a freeze dryer to obtain boron nitride nanosheets. Subsequently, 2g of boron nitride nanosheets were ultrasonically dispersed in 200mL of 1,4-dioxane to obtain a dispersion. The dispersion, 2.2g of 3-aminopropyltriethoxysilane, and 3mL of deionized water were added to a reactor and stirred at 90℃ for 6h. Then, the temperature was lowered to 10℃, 1.8g of cyanuric chloride was added, and then 1g of triethylamine acid binder was slowly added dropwise. The reaction was stirred for 4h. After the reaction was completed, the product was centrifuged, washed, and dried to prepare triazine ring derivative II.

[0021] The preparation method of triazine ring derivative III includes the following steps: 5.5 g of cyanuric chloride, 7.1 g of 3,5-di-tert-butyl-4-hydroxybenzylamine, and 150 mL of 1,4-dioxane were added to a reactor and stirred. After mixing, 3 g of triethylamine was added dropwise, and the mixture was stirred at 0 °C for 4 h to obtain an intermediate. 1.6 g of hydrazine dihydrochloride and 1.2 g of sodium hydroxide were dissolved in 10 mL of deionized water to obtain a mixed solution. The mixed solution was then slowly added dropwise to the reactor containing the intermediate while the temperature was raised to 40 °C. After the addition was complete, the reaction was continued for 2 h. After the reaction was completed, the triazine ring derivative III was prepared by centrifugation, washing, and drying.

[0022] Example 2 An insulating polypropylene composite material for power cables, comprising the following components by weight: 77 parts polypropylene resin, 2.2 parts modified ammonium polyphosphate prepared in Example 1, 1.1 parts ethylene-octene copolymer POE3000, and 0.6 parts stearic acid lubricant.

[0023] The preparation method of the above-mentioned insulating polypropylene composite material for power cables includes the following steps: Weigh each component according to the weight parts, stir and mix the polypropylene resin, modified ammonium polyphosphate, ethylene-octene copolymer and lubricant evenly, and then melt-extrude, granulate and mold the mixture through a twin-screw extruder at 200℃ to prepare the insulating polypropylene composite material for power cables.

[0024] Example 3 An insulating polypropylene composite material for power cables, comprising the following components by weight: 85 parts polypropylene resin, 3.3 parts modified ammonium polyphosphate prepared in Example 1, 1.9 parts ethylene-octene copolymer POE3000, and 1.1 parts polyethylene wax lubricant.

[0025] The preparation method of the above-mentioned insulating polypropylene composite material for power cables is the same as that in Example 2.

[0026] Example 4 An insulating polypropylene composite material for power cables, comprising the following components by weight: 96 parts polypropylene resin, 4.5 parts modified ammonium polyphosphate prepared in Example 1, 2.7 parts ethylene-octene copolymer POE3000, and 1.3 parts oxidized polyethylene wax as a lubricant.

[0027] The preparation method of the above-mentioned insulating polypropylene composite material for power cables is the same as that in Example 2.

[0028] Comparative Example 1: A method for preparing modified ammonium polyphosphate includes the following steps: 30.7 g of triazine derivative I, 5.7 g of triazine derivative II, 3 g of triazine derivative III, and 450 mL of 1,4-dioxane were added to a reactor. The temperature was raised to 50 °C, and 0.8 g of ethylenediamine and 2.8 g of triethylamine were slowly added dropwise. The mixture was stirred for 1 h, then the temperature was raised to 100 °C, and 6 g of ethylenediamine and 10.1 g of triethylamine were slowly added dropwise. The mixture was refluxed and stirred for 4 h. Subsequently, 78.8 g of ammonium polyphosphate was added, and the reaction was continued for 16 h. After the reaction was completed, the filter cake was collected by vacuum filtration, washed three times with a 1:1 mixture of anhydrous ethanol and water, and then washed once with anhydrous ethanol. The cake was dried at 80 °C to prepare modified ammonium polyphosphate.

[0029] The preparation method of triazine ring derivative I includes the following steps: 18.4 g of cyanuric chloride and 250 mL of acetone were added to the reactor, and the temperature was controlled at 0 °C. The mixture was stirred continuously until homogeneous. Then, a mixed solution of 22.1 g of 3-aminopropyltriethoxysilane and 20 mL of acetone was slowly added dropwise, while sodium hydroxide aqueous solution (4 g of sodium hydroxide dissolved in 40 mL of deionized water) was added dropwise. The mixture was stirred and reacted for 4 h. After the reaction was completed, the filter cake was collected by vacuum filtration, washed twice with a mixed solution of acetone and deionized water in a volume ratio of 1:1, and then washed twice with anhydrous ethanol. The mixture was then dried under vacuum at 60 °C to prepare triazine ring derivative I.

[0030] The preparation methods for triazine ring derivative II and triazine ring derivative II are the same as in Example 1.

[0031] Comparative Example 2: A method for preparing modified ammonium polyphosphate includes the following steps: 30.7 g of triazine derivative I, 5.7 g of triazine derivative II, 3 g of triazine derivative III, and 450 mL of 1,4-dioxane were added to a reactor. The temperature was raised to 50 °C, and 0.8 g of ethylenediamine and 2.8 g of triethylamine were slowly added dropwise. The mixture was stirred for 1 h, then the temperature was raised to 100 °C, and 6 g of ethylenediamine and 10.1 g of triethylamine were slowly added dropwise. The mixture was refluxed and stirred for 4 h. Subsequently, 78.8 g of ammonium polyphosphate was added, and the reaction was continued for 16 h. After the reaction was completed, the filter cake was collected by vacuum filtration, washed three times with a 1:1 mixture of anhydrous ethanol and water, and then washed once with anhydrous ethanol. The cake was dried at 80 °C to prepare modified ammonium polyphosphate.

[0032] The preparation method of triazine ring derivative III includes the following steps: 5.5 g of cyanuric chloride, 7.1 g of 3,5-di-tert-butyl-4-hydroxybenzylamine and 150 mL of 1,4-dioxane were added to a reactor. After stirring and mixing, 3 g of triethylamine was added dropwise. The mixture was stirred at 0 °C for 4 h. After the reaction was completed, the triazine ring derivative III was prepared by centrifugation, washing and drying.

[0033] The preparation methods for triazine ring derivative I and triazine ring derivative II are the same as in Example 1.

[0034] Comparative Example 3: A method for preparing modified ammonium polyphosphate includes the following steps: 30.7 g of triazine derivative I, 3 g of triazine derivative III, and 450 mL of 1,4-dioxane were added to a reactor. The temperature was raised to 50 °C, and 0.8 g of ethylenediamine and 2.8 g of triethylamine were slowly added dropwise. The mixture was stirred for 1 h, then the temperature was raised to 100 °C, and 6 g of ethylenediamine and 10.1 g of triethylamine were slowly added dropwise. The mixture was refluxed and stirred for 4 h. Subsequently, 78.8 g of ammonium polyphosphate was added, and the reaction was continued for 16 h. After the reaction was completed, the filter cake was collected by vacuum filtration, washed three times with a 1:1 mixture of anhydrous ethanol and water, and then washed once with anhydrous ethanol. The cake was dried at 80 °C to prepare modified ammonium polyphosphate.

[0035] The preparation methods for triazine ring derivative I and triazine ring derivative III are the same as in Example 1.

[0036] Comparative Example 4: An insulating polypropylene composite material for power cables, comprising the following components by weight: 96 parts polypropylene resin, 4.5 parts modified ammonium polyphosphate prepared in Comparative Example 1, 2.7 parts ethylene-octene copolymer POE3000, and 1.3 parts oxidized polyethylene wax as a lubricant.

[0037] The preparation method of the above-mentioned insulating polypropylene composite material for power cables is the same as that in Example 2.

[0038] Comparative Example 5: An insulating polypropylene composite material for power cables, comprising the following components by weight: 96 parts polypropylene resin, 4.5 parts modified ammonium polyphosphate prepared in Comparative Example 2, 2.7 parts ethylene-octene copolymer POE3000, and 1.3 parts oxidized polyethylene wax as a lubricant.

[0039] The preparation method of the above-mentioned insulating polypropylene composite material for power cables is the same as that in Example 2.

[0040] Comparative Example 6: An insulating polypropylene composite material for power cables, comprising the following components by weight: 96 parts polypropylene resin, 4.5 parts modified ammonium polyphosphate prepared in Comparative Example 3, 2.7 parts ethylene-octene copolymer POE3000, and 1.3 parts oxidized polyethylene wax as a lubricant.

[0041] The preparation method of the above-mentioned insulating polypropylene composite material for power cables is the same as that in Example 2.

[0042] Comparative Example 7: An insulating polypropylene composite material for power cables, comprising the following components in parts by weight: 96 parts polypropylene resin, 4.5 parts ammonium polyphosphate, 2.7 parts ethylene-octene copolymer POE3000, and 1.3 parts oxidized polyethylene wax as a lubricant.

[0043] The preparation method of the above-mentioned insulating polypropylene composite material for power cables is the same as that in Example 2.

[0044] Performance testing The performance of the polypropylene insulating composite materials for power cables prepared in Examples 2-4 and Comparative Examples 4-7 was tested: (1) Mechanical property test: The tensile properties of the composite material were measured using a universal testing machine in accordance with GB / T 1040.1-2025 standard to evaluate the mechanical properties of the composite material. The data results are shown in Table 1.

[0045] (2) Aging resistance test: The composite material samples were subjected to thermo-oxidative aging treatment. The specific operation was as follows: The thermo-oxidative aging experiment was carried out in the aging chamber. The temperature was set to 120℃ and the air exchange rate was 50 times / h. The prepared samples were dispersed and suspended on the sample rack of the aging chamber to ensure that the samples were evenly exposed to the heat flow and oxygen environment. The samples treated for 72h and 144h were taken out respectively, and the change rate of tensile strength and elongation at break was tested to evaluate the aging resistance of the composite material. The data results are shown in Table 1.

[0046] (3) Water contact angle test: The water contact angle was tested using a PZ-200SD contact angle meter to evaluate the waterproof performance of the composite material. The data results are shown in Table 1.

[0047] (4) Volume resistivity test: A circular sample with a diameter of 100 mm and a thickness of 1 mm was prepared according to GB / T 31838.2-2019 standard. After vacuum drying at 60℃ for 12 h, the volume resistivity of the composite material was measured using a high resistance meter at a room temperature of 25℃ and a test voltage of 1000 V. The data results are shown in Table 1.

[0048] (5) Limiting oxygen index test: The test was conducted in accordance with GB / T 2406.2-2009 standard. The sample size was 80mm×10mm×4mm. The data results are shown in Table 1.

[0049] (6) Vertical burning test: The test was conducted according to the vertical burning test (UL-94). The sample size was 125mm×13mm×3.2mm. The data results are shown in Table 1.

[0050] Table 1 Sample performance test results

[0051] As can be seen from the data in Table 1, the composite materials prepared in Examples 2-4 of this invention possess good mechanical properties, aging resistance, insulation and waterproofing properties, and flame retardant properties. Specifically, in Comparative Example 4, the triazine ring derivative I introduced during the preparation process of the modified ammonium polyphosphate, without 2-(trifluoromethyl)piperazine grafting, showed a lower measured water contact angle and limiting oxygen index compared to Examples 2-4. This is because the introduction of fluorine and the piperazine group improved the waterproofing and flame retardant properties of the composite material to a certain extent. In Comparative Example 5, the triazine ring derivative III introduced during the preparation process of the modified ammonium polyphosphate, without hydrazine dihydrochloride grafting, showed significantly different measured changes in tensile strength and elongation at break compared to Examples 2-4, indicating that the introduction of the hydrazine group is beneficial to improving the aging resistance of the composite material. In Comparative Example 6, the modified ammonium polyphosphate... In the preparation process, no triazine ring derivative II was introduced. The measured tensile strength, elongation at break, and volume resistivity were significantly lower than those in Examples 2-4, indicating that the introduction of triazine ring derivative II is beneficial to improving the mechanical and insulation properties of the composite material. In Comparative Example 7, no modification treatment was performed on the ammonium polyphosphate. The measured mechanical properties, aging resistance, insulation and waterproof properties, and flame retardant properties were the most significantly lower than those in Examples 2-4. This indicates that the copolymer formed between triazine ring derivative I, triazine ring derivative II, and triazine ring derivative III significantly improved the coating modification of ammonium polyphosphate, thereby enhancing the mechanical properties, aging resistance, insulation and waterproof properties, and flame retardant properties of the composite material.

[0052] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0053] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A polypropylene composite material for insulating power cables, characterized in that, It comprises the following components by weight: 75-98 parts polypropylene resin, 2-5 parts modified ammonium polyphosphate, 1-3 parts ethylene-octene copolymer, and 0.5-1.5 parts lubricant; The modified ammonium polyphosphate is prepared by coating ammonium polyphosphate with a copolymer formed between triazine ring derivative I, triazine ring derivative II and triazine ring derivative III; The triazine ring derivative I was prepared by a nucleophilic substitution reaction of cyanuric chloride and 3-aminopropyltriethoxysilane with 2-(trifluoromethyl)piperazine as a bridging agent. The triazine ring derivative II was prepared by surface grafting boron nitride nanosheets with 3-aminopropyltriethoxysilane and adding cyanuric chloride via a nucleophilic substitution reaction. The triazine ring derivative III was prepared by a nucleophilic substitution reaction between cyanuric chloride and 3,5-di-tert-butyl-4-hydroxybenzylamine to obtain an intermediate, and then by a nucleophilic substitution reaction using hydrazine dihydrochloride as a bridging agent.

2. The insulating polypropylene composite material for power cables according to claim 1, characterized in that, The preparation method of the modified ammonium polyphosphate includes the following steps: Triazine ring derivative I, triazine ring derivative II, triazine ring derivative III and 1,4-dioxane were added to a reactor, the temperature was raised to 45-55℃, ethylenediamine and triethylamine were slowly added dropwise, and the reaction was stirred for 1-1.5 h. Then the temperature was raised to 95-100℃, and ethylenediamine and triethylamine were slowly added dropwise. The reaction was refluxed and stirred for 4-5 h. Subsequently, ammonium polyphosphate was added, and the reaction was continued for 15-18 h. After the reaction was completed, the modified ammonium polyphosphate was prepared by filtration, washing and drying.

3. The insulating polypropylene composite material for power cables according to claim 2, characterized in that, The mass ratio of the triazine ring derivative I, triazine ring derivative II, triazine ring derivative III and ammonium polyphosphate is 10.2~10.9:1.8~2.2:1:25~27.

4. The insulating polypropylene composite material for power cables according to claim 2, characterized in that, The preparation method of the triazine ring derivative I includes the following steps: Cyanuric chloride and acetone were added to the reactor, and the temperature was controlled at 0-5℃. The mixture was stirred continuously until homogeneous. Then, a mixed solution of 3-aminopropyltriethoxysilane and acetone was slowly added dropwise, along with an aqueous solution of sodium hydroxide. The mixture was stirred for 3-5 hours. The temperature was then raised to 45-55℃, and a mixed solution of 2-(trifluoromethyl)piperazine and acetone, along with an aqueous solution of sodium hydroxide, was slowly added dropwise. The reaction was continued for 3-5 hours. After the reaction was completed, the mixture was filtered, washed, and dried to obtain triazine ring derivative I.

5. The insulating polypropylene composite material for power cables according to claim 4, characterized in that, The molar ratio of cyanuric chloride, 3-aminopropyltriethoxysilane and 2-(trifluoromethyl)piperazine is 2:2:

1.

6. The insulating polypropylene composite material for power cables according to claim 2, characterized in that, The preparation method of the triazine ring derivative II includes the following steps: Nano-sized hexagonal boron nitride was dispersed in isopropanol and treated with intermittent sonication in an ultrasonic cell disruptor for 7-9 hours. After standing for 24 hours, the supernatant was washed with deionized water and dried in a freeze dryer to obtain boron nitride nanosheets. The boron nitride nanosheets were then ultrasonically dispersed in 1,4-dioxane to obtain a dispersion. The dispersion, 3-aminopropyltriethoxysilane, and deionized water were added to a reactor and stirred at 85-90°C for 5-7 hours. The temperature was then lowered to 10-15°C, cyanuric chloride was added, and triethylamine acid-binding agent was slowly added dropwise. The reaction was stirred for 4-5 hours. After the reaction was completed, the product was centrifuged, washed, and dried to prepare triazine ring derivative II.

7. The insulating polypropylene composite material for power cables according to claim 6, characterized in that, The mass ratio of the boron nitride nanosheets, 3-aminopropyltriethoxysilane, and cyanuric chloride is 2~3:2.2:1.

8.

8. The insulating polypropylene composite material for power cables according to claim 2, characterized in that, The preparation method of the triazine ring derivative III includes the following steps: Cyanuric chloride, 3,5-di-tert-butyl-4-hydroxybenzylamine, and 1,4-dioxane were added to a reactor and stirred. Triethylamine was then added dropwise, and the mixture was stirred at 0-5°C for 3-5 hours to obtain an intermediate. Hydrazine dihydrochloride and sodium hydroxide were dissolved in deionized water to obtain a mixed solution. The mixed solution was then slowly added dropwise to the reactor containing the intermediate while the temperature was raised to 40-45°C. After the addition was complete, the reaction was continued for 1-2 hours. After the reaction was completed, the triazine ring derivative III was prepared by centrifugation, washing, and drying.

9. The insulating polypropylene composite material for power cables according to claim 8, characterized in that, The molar ratio of cyanuric chloride, 3,5-di-tert-butyl-4-hydroxybenzylamine, and hydrazine dihydrochloride is 2:2:

1.

10. A method for preparing an insulating polypropylene composite material for power cables according to any one of claims 1 to 9, characterized in that, Includes the following steps: Weigh each component according to the weight parts, stir and mix the polypropylene resin, modified ammonium polyphosphate, ethylene-octene copolymer and lubricant evenly, and then melt extrude, granulate and mold the mixture through a twin-screw extruder at 180~220℃ to prepare an insulating polypropylene composite material for power cables; the lubricant is one or a combination of stearic acid, polyethylene wax and oxidized polyethylene wax.

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