Medium-high voltage flame-retardant polyethylene sheath material and preparation method thereof

Abstract

This application provides a medium- and high-voltage flame-retardant polyethylene sheath material and its preparation method. It is composed of composite polyethylene resin, composite flame retardant, compatibilizer, antioxidant, initiator, and filler. The composite polyethylene resin is prepared by mixing high-density polyethylene and linear low-density polyethylene. The composite flame retardant is composed of an organic-inorganic hybrid flame retardant, a bio-flame retardant, and a modified mesoporous silica flame retardant. The bio-flame retardant is phytic acid-modified carboxymethyl chitosan. By selecting phytic acid-modified carboxymethyl chitosan as the main component of the composite flame retardant, the flame retardancy of the sheath material can be improved while avoiding a reduction in its mechanical properties, increasing the rated operating voltage, and ensuring service life. It has the advantages of good flame retardant effect, easy wiring operation, and easy promotion and implementation.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage cable technology, specifically relating to medium and high voltage flame-retardant polyethylene sheath material and its preparation method. Background Technology

[0002] In existing technologies, high-voltage cables are mainly composed of conductive cores covered by a sheath. During use, the conductive cores generate a large amount of heat, placing high demands on the flame-retardant properties of the sheath. Current technologies typically add flame retardants to the sheath material to improve its flame-retardant performance. To achieve even higher flame-retardant performance and increase the operating voltage of the high-voltage cable, the amount of flame retardant used needs to be increased. However, adding too much flame retardant will reduce the mechanical properties of the matrix resin. While the flame-retardant performance of the cable is improved, its heat aging resistance is greatly reduced. High-voltage cables have low flexibility during wiring, making them difficult to fix in the reserved installation positions. Although the sheath has strong flame-retardant performance, it is prone to aging and cracking under prolonged high-temperature operating conditions, reducing the service life of the high-voltage cable and posing a fire risk. Therefore, improvements are urgently needed. Summary of the Invention

[0003] The first objective of this invention is to address the problem that in the prior art, high-voltage cables generate a large amount of heat during use. After adding flame retardants to prevent melting, the mechanical properties of the cables are reduced, making them more prone to cracking and reducing their service life. The invention proposes a medium- and high-voltage flame-retardant polyethylene sheath material that has little impact on the mechanical properties of the cable sheath and can enhance the flame retardant additives.

[0004] The second objective of this application is to provide a method for preparing medium- and high-pressure flame-retardant polyethylene sheathing material.

[0005] To achieve the first objective of this application, the medium- and high-pressure flame-retardant polyethylene sheath material is composed of the following components in parts by weight:

[0006]

[0007] The composite polyethylene resin is prepared by mixing high-density polyethylene and linear low-density polyethylene at a mass ratio of 2:5.

[0008] The composite flame retardant, by weight of its total mass, consists of the following components:

[0009] 4-7 parts of organic-inorganic hybrid flame retardant

[0010] 10-15 parts of bio-flame retardant

[0011] 3-6 parts of modified mesoporous silica flame retardant;

[0012] The bio-flame retardant is phytic acid-modified carboxymethyl chitosan.

[0013] In actual implementation, the composite polyethylene resin prepared by high-density polyethylene and linear low-density polyethylene has moderate crystallinity and molecular weight. Using it as a matrix resin can effectively improve its flexibility. After being made into high-voltage cable sheaths, it has excellent basic mechanical properties. During the mixing process, binding sites will be generated between molecular chains, which facilitates subsequent modification.

[0014] Preferably, the preparation method of the composite flame retardant includes the following steps:

[0015] Step 101. After mixing the organic-inorganic hybrid flame retardant, the bio-flame retardant, the modified mesoporous silica flame retardant and the ethyl acetate in a high-speed disperser until uniform, the mixture is spread out and dried to obtain the crude flame retardant.

[0016] Step 102. Add polyethylene glycol dropwise to the crude flame retardant obtained in step 101. During the dropwise addition, ultrasonically vibrate the crude modifier at 1000 Hz at room temperature. After the polyethylene glycol level covers the crude flame retardant, transfer it to a water bath at 50-60℃ and vibrate at 3000 Hz for 2-3 hours. After filtration and drying, the composite flame retardant is obtained.

[0017] Preferably, in step 102, the molecular weight of polyethylene glycol is 400-600.

[0018] In actual implementation, the surface of the composite flame retardant is modified by polyethylene glycol, so that the composite flame retardant is coated with polyethylene glycol. During the compounding process of the composite polyethylene resin, under the synergistic effect of the initiator and compatibilizer, the composite flame retardant coated with polyethylene glycol is captured. During the high-temperature compounding process, the flame retardant is uniformly dispersed in the composite polyethylene resin, and the composite flame retardant is connected between the molecular chains of the composite polyethylene resin through hydrogen bonds.

[0019] Preferably, the preparation method of the organic-inorganic hybrid flame retardant includes the following steps:

[0020] Step 201. Add potassium permanganate to the phytic acid melamine quantum dot pre-preparation solution at a mass ratio of 12:1, and stir at 200 rpm for 10 min at room temperature to obtain the pre-hybridized solution.

[0021] Step 202. Add ethyl acetate to the pre-hybridized solution obtained in step 201 at a mass ratio of 1:0.5, stir at 100 rpm for 10 min at room temperature, then transfer to a hydrothermal reactor and react at 80℃ for 24-48 h to obtain the hybridized solution.

[0022] Step 203. After adjusting the pH of the hybrid liquid obtained in step 202 to 7 with anhydrous ethanol, dry it under vacuum at 80°C for 24 hours, and then ball mill it to a particle size of 100-200 nm to obtain the organic-inorganic hybrid flame retardant.

[0023] Preferably, the preparation method of phytic acid melamine quantum dots in step 201 includes the following steps:

[0024] Step 301. Add phytic acid, melamine, and deionized water into a stirred tank in a mass ratio of 2:3:5. Gradually increase the temperature from room temperature to 60°C at a heating rate of 5°C / min. Stir at 250 rpm for 1 hour to obtain the reaction solution.

[0025] Step 302. Transfer the reaction solution prepared in step 301 to a hydrothermal reactor, heat it to 120°C at a heating rate of 10°C / min and react for 48 hours to obtain a quantum dot suspension.

[0026] Step 303. After washing and drying the quantum dot suspension prepared in step 301, ball mill it to a particle size of 50-100 nm to obtain phytic acid melamine quantum dots.

[0027] During implementation, by using organic-inorganic hybrid quantum dots as one of the composite flame retardants, the basic flame retardant requirements of high-voltage cables are guaranteed. Quantum dots have a large specific surface area and, with the cooperation of compatibilizers, have a high degree of bonding with composite polyethylene resin. Adding a small amount can have a significant flame retardant effect, reducing the impact on the mechanical properties of composite polyethylene resin. Furthermore, by hybridizing with inorganic manganese elements, its reducing properties are improved, further enhancing the flame retardant performance.

[0028] Preferably, the preparation method of the bio-flame retardant includes the following steps:

[0029] Step 401. Add phytic acid to carboxymethyl chitosan dissolved in a water bath. The mass ratio of phytic acid to carboxymethyl chitosan is 1:7.2. Stir for 1 hour in a 60°C water bath at 800 rpm to obtain solution A.

[0030] Step 402. After adding catalyst, DMPA and imidazole to solution A obtained in step 401, reflux the solution in an oil bath at 100°C for 5 hours to obtain component B.

[0031] Step 403. Transfer component B obtained in step 402 to a freeze dryer, dry at -80°C for 48 hours, remove it, wash with anhydrous ethanol until the pH value is 7, and then dry with hot air to obtain the bio-combustion promoter.

[0032] Preferably, in step 402, the catalyst is a platinum-rhodium alloy, and the mass ratio of solution A, catalyst, DMPA, and imidazole is 17:1:5:3.

[0033] In practical implementation, using bio-flame retardants as the main component of flame retardants has the following advantages: First, phytic acid-modified chitosan has high thermal stability; second, phytic acid-modified chitosan has strong compatibility with inorganic-organic hybrid flame retardants, and when combined with polyethylene glycol, it can effectively improve the dispersion degree of the mixture with polyethylene resin; third, it has low volatile gas emissions and high environmental performance, and the introduction of nitrogen during the mixing process can reduce the generation of pollutants.

[0034] Preferably, the preparation method of the modified mesoporous silica flame retardant includes the following steps:

[0035] Step 501. Add hexadecyltrimethylammonium bromide to deionized water and stir until the solution is clear. Then add H2PtCl6 dropwise and stir for 20 minutes at room temperature and 200 rpm to obtain reaction solution C. The mass ratio of hexadecyltrimethylammonium bromide, deionized water and H2PtCl6 is 1:30:7.5.

[0036] Step 502. Add tetraethyl silicate and sulfuric acid solution sequentially to the reaction solution C obtained in step 501. Stir at 500 rpm for 10 min at room temperature, then transfer to an ice-water bath and react for 24 h to obtain the modified mesoporous suspension.

[0037] Step 503. Transfer the modified mesoporous suspension obtained in step 502 to a centrifuge, centrifuge at 5000 rpm for 20 min, discard the supernatant, transfer the bottom centrifuged product to a crucible, and calcine at 600℃ for 5 h to obtain the modified mesoporous silica flame retardant.

[0038] In actual implementation, modified mesoporous silica flame retardants have high porosity and can be combined with bioflame retardants and organic-inorganic hybrid flame retardants to significantly increase the specific surface area of ​​the composite flame retardant. When combined with polyethylene glycol, it can greatly improve its dispersion in composite polyethylene resin, thus significantly improving the flame retardant performance.

[0039] To achieve the second objective of this application, the following method for preparing medium- and high-pressure flame-retardant polyethylene sheath material is adopted, comprising the following steps:

[0040] Step 601. The composite polyethylene resin, compatibilizer, antioxidant and filler are sequentially put into the first extruder and mixed and extruded at a mixing temperature of 90°C to obtain the premixed material.

[0041] Step 602. Prepare the atomizing liquid by mixing the composite flame retardant, initiator and ethyl acetate in a mass ratio of 5:2:4;

[0042] Step 603. Transfer the premixed material obtained in step 601 to the second extruder. The mixing section of the second extruder includes a first mixing section and a second mixing section connected to the first mixing section. Spray the atomized liquid obtained in step 602 into the first mixing section using N2 as the atomizing power. After mixing and extrusion, medium and high pressure flame retardant polyethylene sheath material is obtained.

[0043] Preferably, in step 603, the temperature of the extruder feeding section is 90°C, the temperature of the first mixing section is 105°C, the temperature of the second mixing section is 120°C, the temperature of the granulation section is 160°C, and the die head temperature is 145°C.

[0044] In actual implementation, some components are pre-mixed in the first extruder, and the composite flame retardant and initiator are added to the first mixing section of the second extruder. During the mixing process in the first mixing section, the composite polyethylene is chain-extended under the action of the initiator. During the chain extension process, nitrogen is sprayed onto the polyethylene chain segments, so that the composite flame retardant is embedded between the polyethylene chain segments, which greatly improves the dispersion of the flame retardant. In addition, the ratio of the introduced flexible groups and rigid groups has been screened. Therefore, after the chain extension, the composite polyethylene resin can still maintain high mechanical properties after entering the second mixing section.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] This application provides medium- and high-voltage flame-retardant polyethylene sheathing material, which is composed of composite polyethylene resin, composite flame retardant, compatibilizer, antioxidant, initiator, and filler. The composite polyethylene resin is prepared by mixing high-density polyethylene and linear low-density polyethylene. The composite flame retardant is composed of organic-inorganic hybrid flame retardant, bioflame retardant, and modified mesoporous silica flame retardant. The bioflame retardant is phytic acid-modified carboxymethyl chitosan. By selecting phytic acid-modified carboxymethyl chitosan as the main component of the composite flame retardant, the flame retardancy of the sheathing material can be improved while avoiding a reduction in the mechanical properties of the sheathing material, increasing the rated working voltage, and ensuring service life. It has the advantages of good flame retardant effect, easy wiring operation, and easy promotion and implementation.

[0047] 2. This application provides a method for preparing medium and high pressure flame-retardant polyethylene sheath material. By performing secondary extrusion on the sheath material, the dispersion degree of flame retardant in polyethylene resin is improved, and the mixing process is avoided from being contaminated by external pollutants. The dispersion degree is high, the flame retardancy is good, and it has the advantages of being easy to operate and easy to promote and implement. Detailed Implementation

[0048] The present invention will be further described below with reference to Table 1, specific embodiments 1-2 and comparative examples 1-3:

[0049] Example 1.

[0050] (1) A method for preparing a composite flame retardant, comprising the following steps:

[0051] Step 101. According to the weight parts shown in Table 1, the organic-inorganic hybrid flame retardant, the biological flame retardant, the modified mesoporous silica flame retardant and the ethyl acetate are mixed evenly in a high-speed disperser, and then spread out and dried to obtain the crude flame retardant.

[0052] Step 102. Polyethylene glycol is added dropwise to the crude flame retardant obtained in step 101. During the dropwise addition, the crude modifier is ultrasonically vibrated at 1000 Hz at room temperature. When the polyethylene glycol level covers the crude flame retardant, it is transferred to a 50°C water bath and vibrated at 3000 Hz for 2 hours. After filtration and drying, the composite flame retardant is obtained. The molecular weight of polyethylene glycol is 487.

[0053] (2) A method for preparing an organic-inorganic hybrid flame retardant, comprising the following steps:

[0054] Step 201. Add potassium permanganate to the phytic acid melamine quantum dot pre-preparation solution at a mass ratio of 12:1, and stir at 200 rpm for 10 min at room temperature to obtain the pre-hybridized solution.

[0055] Step 202. Add ethyl acetate to the pre-hybridized solution obtained in step 201 at a mass ratio of 1:0.5, stir at 100 rpm for 10 min at room temperature, then transfer to a hydrothermal reactor and react at 80°C for 24 h to obtain the hybridized solution.

[0056] Step 203. After adjusting the pH of the hybrid liquid obtained in step 202 to 7 with anhydrous ethanol, dry it under vacuum at 80°C for 24 hours, and then ball mill it to a particle size of 100 nm to obtain the organic-inorganic hybrid flame retardant.

[0057] (3) A method for preparing phytic acid melamine quantum dots, including the following steps:

[0058] Step 301. Add phytic acid, melamine, and deionized water into a stirred tank in a mass ratio of 2:3:5. Gradually increase the temperature from room temperature to 60°C at a heating rate of 5°C / min. Stir at 250 rpm for 1 hour to obtain the reaction solution.

[0059] Step 302. Transfer the reaction solution prepared in step 301 to a hydrothermal reactor, heat it to 120°C at a heating rate of 10°C / min and react for 48 hours to obtain a quantum dot suspension.

[0060] Step 303. After washing and drying the quantum dot suspension prepared in step 301, ball mill it to a particle size of 68 nm to obtain phytic acid melamine quantum dots.

[0061] (4) A method for preparing a bio-flame retardant, comprising the following steps:

[0062] Step 401. Add phytic acid to carboxymethyl chitosan dissolved in a water bath. The mass ratio of phytic acid to carboxymethyl chitosan is 1:7.2. Stir for 1 hour in a 60°C water bath at 800 rpm to obtain solution A.

[0063] Step 402. After adding catalyst, DMPA and imidazole to solution A obtained in step 401, reflux the solution in an oil bath at 100°C for 5 hours to obtain component B; wherein the catalyst is a platinum-rhodium alloy and the mass ratio of solution A, catalyst, DMPA and imidazole is 17:1:5:3.

[0064] Step 403. Transfer component B obtained in step 402 to a freeze dryer, dry at -80°C for 48 hours, remove it, wash with anhydrous ethanol until the pH value is 7, and then dry with hot air to obtain the bio-combustion promoter.

[0065] (5) A method for preparing modified mesoporous silica flame retardant, comprising the following steps:

[0066] Step 501. Add hexadecyltrimethylammonium bromide to deionized water and stir until the solution is clear. Then add H2PtCl6 dropwise and stir for 20 minutes at room temperature and 200 rpm to obtain reaction solution C. The mass ratio of hexadecyltrimethylammonium bromide, deionized water and H2PtCl6 is 1:30:7.5.

[0067] Step 502. Add tetraethyl silicate and sulfuric acid solution sequentially to the reaction solution C obtained in step 501. Stir at 500 rpm for 10 min at room temperature, then transfer to an ice-water bath and react for 24 h to obtain the modified mesoporous suspension.

[0068] Step 503. Transfer the modified mesoporous suspension obtained in step 502 to a centrifuge, centrifuge at 5000 rpm for 20 min, discard the supernatant, transfer the bottom centrifuged product to a crucible, and calcine at 600℃ for 5 h to obtain the modified mesoporous silica flame retardant.

[0069] (6) A method for preparing medium and high pressure flame-retardant polyethylene sheath material, comprising the following steps:

[0070] Step 601. The composite polyethylene resin, compatibilizer, antioxidant and filler are sequentially put into the first extruder and mixed and extruded at a mixing temperature of 90°C to obtain the premixed material.

[0071] Step 602. Prepare the atomizing liquid by mixing the composite flame retardant, initiator and ethyl acetate in a mass ratio of 5:2:4;

[0072] Step 603. Transfer the premixed material obtained in step 601 to the second extruder. The mixing section of the second extruder includes a first mixing section and a second mixing section connected to the first mixing section. Spray the atomized liquid obtained in step 602 into the first mixing section using N2 as the atomizing power. After mixing and extrusion, medium and high pressure flame retardant polyethylene sheath material is obtained.

[0073] In step 603, the temperature of the extruder feeding section is 90℃, the temperature of the first mixing section is 105℃, the temperature of the second mixing section is 120℃, the temperature of the granulation section is 160℃, and the die head temperature is 145℃.

[0074] Example 2.

[0075] (1) A method for preparing a composite flame retardant, comprising the following steps:

[0076] Step 101. According to the weight parts shown in Table 1, the organic-inorganic hybrid flame retardant, the biological flame retardant, the modified mesoporous silica flame retardant and the ethyl acetate are mixed evenly in a high-speed disperser, and then spread out and dried to obtain the crude flame retardant.

[0077] Step 102. Polyethylene glycol is added dropwise to the crude flame retardant obtained in step 101. During the dropwise addition, the crude modifier is ultrasonically vibrated at 1000 Hz at room temperature. When the polyethylene glycol level covers the crude flame retardant, it is transferred to a 60°C water bath and vibrated at 3000 Hz for 3 hours. After filtration and drying, the composite flame retardant is obtained. The molecular weight of polyethylene glycol is 487.

[0078] (2) A method for preparing an organic-inorganic hybrid flame retardant, comprising the following steps:

[0079] Step 201. Add potassium permanganate to the phytic acid melamine quantum dot pre-preparation solution at a mass ratio of 12:1, and stir at 200 rpm for 10 min at room temperature to obtain the pre-hybridized solution.

[0080] Step 202. Add ethyl acetate to the pre-hybridized solution obtained in step 201 at a mass ratio of 1:0.5, stir at 100 rpm for 10 min at room temperature, then transfer to a hydrothermal reactor and react at 80°C for 48 hours to obtain the hybridized solution.

[0081] Step 203. After adjusting the pH of the hybrid liquid obtained in step 202 to 7 with anhydrous ethanol, dry it under vacuum at 80°C for 24 hours, and then ball mill it to a particle size of 155 nm to obtain the organic-inorganic hybrid flame retardant.

[0082] (3) A method for preparing phytic acid melamine quantum dots, including the following steps:

[0083] Step 301. Add phytic acid, melamine, and deionized water into a stirred tank in a mass ratio of 2:3:5. Gradually increase the temperature from room temperature to 60°C at a heating rate of 5°C / min. Stir at 250 rpm for 1 hour to obtain the reaction solution.

[0084] Step 302. Transfer the reaction solution prepared in step 301 to a hydrothermal reactor, heat it to 120°C at a heating rate of 10°C / min and react for 48 hours to obtain a quantum dot suspension.

[0085] Step 303. After washing and drying the quantum dot suspension prepared in step 301, ball mill it to a particle size of 68 nm to obtain phytic acid melamine quantum dots.

[0086] (4) A method for preparing a bio-flame retardant, comprising the following steps:

[0087] Step 401. Add phytic acid to carboxymethyl chitosan dissolved in a water bath. The mass ratio of phytic acid to carboxymethyl chitosan is 1:7.2. Stir for 1 hour in a 60°C water bath at 800 rpm to obtain solution A.

[0088] Step 402. After adding catalyst, DMPA and imidazole to solution A obtained in step 401, reflux the solution in an oil bath at 100°C for 5 hours to obtain component B; wherein the catalyst is a platinum-rhodium alloy and the mass ratio of solution A, catalyst, DMPA and imidazole is 17:1:5:3.

[0089] Step 403. Transfer component B obtained in step 402 to a freeze dryer, dry at -80°C for 48 hours, remove it, wash with anhydrous ethanol until the pH value is 7, and then dry with hot air to obtain the bio-combustion promoter.

[0090] (5) A method for preparing modified mesoporous silica flame retardant, comprising the following steps:

[0091] Step 501. Add hexadecyltrimethylammonium bromide to deionized water and stir until the solution is clear. Then add H2PtCl6 dropwise and stir for 20 minutes at room temperature and 200 rpm to obtain reaction solution C. The mass ratio of hexadecyltrimethylammonium bromide, deionized water and H2PtCl6 is 1:30:7.5.

[0092] Step 502. Add tetraethyl silicate and sulfuric acid solution sequentially to the reaction solution C obtained in step 501. Stir at 500 rpm for 10 min at room temperature, then transfer to an ice-water bath and react for 24 h to obtain the modified mesoporous suspension.

[0093] Step 503. Transfer the modified mesoporous suspension obtained in step 502 to a centrifuge, centrifuge at 5000 rpm for 20 min, discard the supernatant, transfer the bottom centrifuged product to a crucible, and calcine at 600℃ for 5 h to obtain the modified mesoporous silica flame retardant.

[0094] (6) A method for preparing medium and high pressure flame-retardant polyethylene sheath material, comprising the following steps:

[0095] Step 601. The composite polyethylene resin, compatibilizer, antioxidant and filler are sequentially put into the first extruder and mixed and extruded at a mixing temperature of 90°C to obtain the premixed material.

[0096] Step 602. Prepare the atomizing liquid by mixing the composite flame retardant, initiator and ethyl acetate in a mass ratio of 5:2:4;

[0097] Step 603. Transfer the premixed material obtained in step 601 to the second extruder. The mixing section of the second extruder includes a first mixing section and a second mixing section connected to the first mixing section. Spray the atomized liquid obtained in step 602 into the first mixing section using N2 as the atomizing power. After mixing and extrusion, medium and high pressure flame retardant polyethylene sheath material is obtained.

[0098] In step 603, the temperature of the extruder feeding section is 90℃, the temperature of the first mixing section is 105℃, the temperature of the second mixing section is 120℃, the temperature of the granulation section is 160℃, and the die head temperature is 145℃.

[0099] Comparative Example 1.

[0100] The composite flame retardant in Example 2 was replaced with the polyphosphate ammonium salt flame retardant commonly used in high-voltage cable sheath materials in the prior art, while the rest remained unchanged.

[0101] Comparative Example 2.

[0102] The composite polyethylene resin in Example 2 was replaced with a single-component high-density polyethylene resin, while the rest remained unchanged.

[0103] Comparative Example 3.

[0104] In the preparation process of the medium- and high-pressure flame-retardant polyethylene sheath material in Example 3, the flame retardant and other components were mixed and then extruded together in an extruder, while the rest remained unchanged.

[0105] Table 1. Composition of each component in Examples 1-2 and Comparative Examples 1-3 by weight.

[0106]

[0107]

[0108] The medium- and high-voltage flame-retardant polyethylene sheathing materials prepared in Examples 1-2 and Comparative Examples 1-3 were tested according to the requirements of high-voltage cable standards QCT 1037, ISO 19642, LV216-2, IEC60840-2020, GB / T12706, and GB / T9330. The test results are shown in Table 2 below.

[0109] Table 2 shows the test results for Examples 1-2 and Comparative Examples 1-3:

[0110] Test Project Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tensile strength (MPa) 10.5 11.2 6.9 6.9 9.3 Hardness (Shore A) 71A 75A 89A 80A 73A Cable smoke test (%) 77 76.2 37.5 52.3 61.8 Thermal aging (°C*h) 200*215 200*218 200*156 200*150 200*173 Elongation at break (%) 237 240 202 210 227 Limiting oxygen index (%) 42.5 45.3 27.8 33.5 39.1

[0111] As shown in Table 2 above, this application provides a high-voltage flame-retardant polyethylene sheath material for vehicle interiors, which is composed of composite polyethylene resin, composite flame retardant, compatibilizer, antioxidant, initiator, and filler. The composite polyethylene resin is prepared by mixing high-density polyethylene and linear low-density polyethylene. The composite flame retardant is composed of organic-inorganic hybrid flame retardant, bioflame retardant, and modified mesoporous silica flame retardant. The bioflame retardant is phytic acid-modified carboxymethyl chitosan. By selecting phytic acid-modified carboxymethyl chitosan as the main component of the composite flame retardant, the flame retardancy of the sheath material can be improved while avoiding a reduction in the mechanical properties of the sheath material, increasing the rated working voltage, and ensuring service life. It has the advantages of good flame retardant effect, easy wiring operation, and easy promotion and implementation.

[0112] The composite polyethylene resin prepared by high-density polyethylene and linear low-density polyethylene has moderate crystallinity and molecular weight. Using it as a matrix resin can effectively improve its flexibility. After being made into a high-voltage cable sheath, it has excellent basic mechanical properties. During the mixing process, binding sites will be generated between molecular chains, which facilitates subsequent modification. Therefore, the mechanical properties of the sheath material in Comparative Example 1 are reduced. After the mechanical properties are reduced, the heat aging resistance is also reduced, and the flame retardant cannot function properly.

[0113] By modifying the surface of the composite flame retardant with polyethylene glycol, the composite flame retardant is coated with polyethylene glycol. During the compounding process of the composite polyethylene resin, under the synergistic effect of the initiator and compatibilizer, the composite flame retardant coated with polyethylene glycol is captured. During the high-temperature compounding process, the flame retardant is uniformly dispersed in the composite polyethylene resin, and the composite flame retardant is connected between the molecular chains of the composite polyethylene resin through hydrogen bonds.

[0114] By using organic-inorganic hybrid quantum dots as one of the composite flame retardants, the basic flame retardant requirements of high-voltage cables are guaranteed. Quantum dots have a large specific surface area and, with the cooperation of compatibilizers, have a high degree of binding with composite polyethylene resin. Adding a small amount can have a significant flame retardant effect, reducing the impact on the mechanical properties of composite polyethylene resin. Furthermore, by hybridizing with inorganic manganese elements, its reducing properties are improved, further enhancing the flame retardant performance.

[0115] In practical implementation, using bio-flame retardants as the main component of flame retardants has the following advantages: First, phytic acid-modified chitosan has high thermal stability; second, phytic acid-modified chitosan has strong compatibility with inorganic-organic hybrid flame retardants, and when combined with polyethylene glycol, it can effectively improve the dispersion degree of the mixture with polyethylene resin; third, it has low volatile gases and high environmental performance, and the introduction of nitrogen during the mixing process can reduce the generation of pollutants.

[0116] Modified mesoporous silica flame retardants have high porosity and can be combined with bioflame retardants and organic-inorganic hybrid flame retardants to significantly increase the specific surface area of ​​the composite flame retardant. When combined with polyethylene glycol, it can greatly improve its dispersion in composite polyethylene resin, thus significantly improving the flame retardant performance.

[0117] By pre-mixing some components in the first extruder, and then adding the composite flame retardant and initiator to the first mixing section of the second extruder, the composite polyethylene undergoes chain extension under the action of the initiator during the mixing process in the first mixing section. During the chain extension process, nitrogen is sprayed onto the polyethylene chain segments, allowing the composite flame retardant to be embedded between the polyethylene chain segments, greatly improving the dispersion of the flame retardant. The ratio of the introduced flexible and rigid groups was screened, so after the chain extension, the composite polyethylene resin can still maintain high mechanical properties after entering the second mixing section. As can be seen from the test results of Comparative Example 2, the amount of phosphorus-based flame retardant added is increased to improve the flame retardant performance, but polyethylene glycol has weak surface modification performance and uneven dispersion. In addition, polyethylene has low affinity with phosphorus-based flame retardants, uneven dispersion, low flame retardancy, and strong heat aging resistance.

[0118] By using secondary extrusion and adding initiators and flame retardants after atomization, the flame retardants can be embedded in the polyethylene chain segments, effectively improving dispersibility.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. Medium high voltage flame retardant polyethylene sheath material, characterized in that, consists of the following components by weight fraction: The composite polyethylene resin is prepared by mixing high-density polyethylene and linear low-density polyethylene at a mass ratio of 2:5; The composite flame retardant consists of the following components by weight fraction of its total mass: The organic-inorganic hybrid flame retardant consists of the following components by weight fraction of its total mass: The organic-inorganic hybrid flame retardant consists of the following components by weight fraction of its total mass: The preparation method of the organic-inorganic hybrid flame retardant comprises the following steps: Step 201. A pre-hybrid liquid is obtained by adding potassium permanganate to a phytic acid melamine quantum dot pre-preparation liquid at a mass ratio of 12:1, stirring at room temperature at 200 rpm for 10 min; Step 202. A hybrid liquid is obtained by adding ethyl acetate to the pre-hybrid liquid obtained in step 201 at a mass ratio of 1:0.5, stirring at room temperature at 100 rpm for 10 min, then transferring to a hydrothermal reaction kettle, and reacting at 80°C for 24-48 h; Step 203. The hybrid liquid obtained in step 202 is adjusted to a pH value of 7 with anhydrous ethanol, vacuum dried at 80°C for 24 h, and ball milled to a particle size of 100-200 nm to obtain the organic-inorganic hybrid flame retardant; The preparation method of the biological flame retardant comprises the following steps: Step 401. Phytic acid is added to carboxymethyl chitosan after dissolution in a water bath, and the mass ratio of phytic acid to carboxymethyl chitosan is 1:7.

2. Stir at 60°C water bath, 800 rpm for 1 h to obtain solution A; Step 402. Add catalyst, DMPA, and imidazole to solution A obtained in step 401, and condense under reflux at 100°C oil bath for 5 h to obtain component B; Step 403. Transfer component B obtained in step 402 to a freeze dryer, dry at -80°C for 48 h, wash with anhydrous ethanol to a pH value of 7, and then hot air dry to obtain the biological flame retardant. The preparation method of the composite flame retardant comprises the following steps: Step 101. Mix the organic-inorganic hybrid flame retardant, biological flame retardant, modified mesoporous silica flame retardant, and ethyl acetate in a high-speed dispersion machine, and then dry to obtain a crude flame retardant; Step 102. Add polyethylene glycol dropwise to the crude flame retardant obtained in step 101, and ultrasonically oscillate the crude modifier at room temperature and 1000 Hz during the addition process. After the polyethylene glycol level is above the crude flame retardant, transfer to a 50-60°C water bath and oscillate at 3000 Hz for 2-3 h, then filter and dry to obtain the composite flame retardant. In step 102, the molecular weight of the polyethylene glycol is 400-600. The preparation method of the phytic acid melamine quantum dots in step 201 comprises the following steps: ​ ​ ​ 2. The medium high voltage flame retardant polyethylene sheath material according to claim 1, characterized in that, ​ ​ ​ 3. The medium high voltage flame retardant polyethylene sheath material according to claim 2, characterized in that, ​ 4. The medium high voltage flame retardant polyethylene sheath material according to claim 1, characterized in that, ​ Step 301. Phytic acid, melamine and deionized water were sequentially added into a stirring kettle in a mass ratio of 2:3:

5. The temperature was gradually increased from room temperature to 60℃ at a rate of 5℃ / min. After stirring at 250 rpm for 1 h, a reaction solution was obtained. Step 302. The reaction solution prepared in step 301 was transferred into a hydrothermal reaction kettle. The temperature was increased to 120℃ at a rate of 10℃ / min and reacted for 48 h to obtain a quantum dot suspension.

5. The medium high voltage flame retardant polyethylene sheath material according to claim 1, characterized in that, The catalyst in step 402 is platinum-rhodium alloy, and the mass ratio of solution A, catalyst, DMPA and imidazole is 17:1:5:

3.

6. The medium high voltage flame retardant polyethylene sheath material according to claim 1, characterized in that, The preparation method of the modified mesoporous silica flame retardant comprises the following steps: Step 501. Cetyltrimethylammonium bromide was added into deionized water and stirred until the solution was clear. Then H2PtCl6 was added dropwise. After stirring at room temperature and 200 rpm for 20 min, a reaction solution C was obtained. The mass ratio of cetyltrimethylammonium bromide, deionized water and H2PtCl6 was 1:30:7.

5. Step 502. Tetraethyl orthosilicate and sulfuric acid solution were sequentially added into the reaction solution C obtained in step 501. After stirring at room temperature and 500 rpm for 10 min, the mixture was transferred into an ice water bath and reacted for 24 h to obtain a modified mesoporous suspension. Step 503. The modified mesoporous suspension obtained in step 502 was transferred into a centrifuge and centrifuged at 5000 rpm for 20 min. The supernatant was discarded, and the bottom centrifugation product was transferred into a crucible. After calcination at 600℃ for 5 h, a modified mesoporous silica flame retardant was obtained.

7. The process for the preparation of medium high voltage flame retardant polyethylene sheath material according to any one of claims 1-6, characterized in that, The preparation method comprises the following steps: Step 601. Composite polyethylene resin, compatibilizer, antioxidant and filler were sequentially added into a first extruder. After mixing and extruding at a mixing temperature of 90℃, a pre-mixed material was obtained. Step 602. Composite flame retardant, initiator and ethyl acetate were mixed in a mass ratio of 5:2:4 to prepare an atomization solution. Step 603. The pre-mixed material obtained in step 601 was transferred into a second extruder. The second extruder mixing section included a first mixing section and a second mixing section connected to the first mixing section. The atomization solution obtained in step 602 was sprayed into the first mixing section using N2 as the atomization power. After mixing and extruding, a medium-high pressure flame-retardant polyethylene sheath material was obtained.

8. The process for the preparation of medium high voltage flame retardant polyethylene sheath material according to claim 7, characterized in that, The temperature of the extruder feeding section in step 603 was 90℃, the temperature of the first mixing section was 105℃, the temperature of the second mixing section was 120℃, the temperature of the granulation section was 160℃, and the temperature of the die head was 145℃.

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