A low-temperature resistant polyethylene gas pipe and its preparation method

Abstract

This application relates to the field of pipeline material technology, specifically to a low-temperature resistant polyethylene gas pipe and its preparation method. The low-temperature resistant polyethylene gas pipe comprises the following raw materials: composite polyethylene resin, low-temperature toughening modifier, nanofiller, maleic anhydride-grafted polyethylene, antioxidant, ultraviolet light stabilizer, and lubricant. The preparation method is as follows: S1, the composite polyethylene resin, maleic anhydride-grafted polyethylene, and low-temperature toughening modifier are mixed evenly, then the nanofiller, antioxidant, ultraviolet light stabilizer, and lubricant are added and mixed evenly to obtain a modified polyethylene mixture; S2, the modified polyethylene mixture is melt-blended to obtain modified polyethylene granules; S3, the modified polyethylene granules are formed into pipes, cooled and solidified to obtain the low-temperature resistant polyethylene gas pipe. This low-temperature resistant polyethylene gas pipe exhibits good low-temperature drop hammer impact resistance, high simply supported beam impact strength, good low-temperature tensile properties, and excellent low-temperature toughness and weather resistance.

Description

Technical Field

[0001] This application relates to the field of pipeline materials technology, and more specifically, it relates to a low-temperature resistant polyethylene gas pipe and its preparation method. Background Technology

[0002] Polyethylene gas pipes, with their advantages of high corrosion resistance, good flexibility, convenient construction, and good sealing, have gradually replaced traditional metal pipes and are widely used in urban gas transmission and rural gas transformation projects. While conventional polyethylene gas pipes can meet the needs of normal and mildly low-temperature environments, extreme winter temperatures in regions such as Northeast my country, Northwest China, and the Qinghai-Tibet Plateau can reach -35°C or below. Existing ordinary polyethylene gas pipes have significant shortcomings in low-temperature performance, exhibiting poor low-temperature toughness and low impact strength. In extreme low-temperature environments, they are prone to molecular chain freezing and material embrittlement. Under conditions such as transportation impacts, construction bends, soil compression, and gas pressure fluctuations, pipe walls are highly susceptible to cracking and weld leaks. This not only shortens the service life of the pipes but also leads to gas leaks, pipe bursts, and other safety accidents, seriously threatening the safety of gas transmission.

[0003] Currently, conventional methods for improving the low-temperature performance of pipes in the industry mainly involve simply thickening the pipe wall, adding ordinary toughening fillers, or simple blending modification. These methods can only slightly improve the low-temperature toughness of the pipes and still have drawbacks such as limited modification effect, imbalance of overall mechanical properties of the pipes, decrease in tensile strength and pressure resistance, high production costs, and poor processability, making them unsuitable for stable use under long-term extreme low-temperature conditions. Furthermore, existing modified formulations generally suffer from uneven filler dispersion and insufficient weather resistance, making them prone to aging failure and performance degradation after long-term low-temperature service, failing to meet the long-term safe and maintenance-free use standards for gas pipelines in cold regions. Therefore, developing a polyethylene gas pipe with strong low-temperature impact resistance, excellent comprehensive mechanical properties, good aging resistance, and adaptability to extreme low-temperature environments, along with its preparation method, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] To address the technical problems mentioned in the background section, this application provides a low-temperature resistant polyethylene gas pipe and its preparation method.

[0005] In the first aspect, this application provides a low-temperature resistant polyethylene gas pipe, which adopts the following technical solution: A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 80-95 parts of composite polyethylene resin, 5-12 parts of low-temperature toughening modifier, 2-5 parts of nanofiller, 1-1.5 parts of maleic anhydride grafted polyethylene, 0.2-0.5 parts of antioxidant, 0.1-0.3 parts of ultraviolet light stabilizer, and 0.1-0.4 parts of lubricant.

[0006] Furthermore, the composite polyethylene resin is composed of high-density polyethylene, polyethylene octene co-elastomer, and chlorinated polyethylene in a mass ratio of 10-20:5-8:2-5.

[0007] Furthermore, the chlorinated polyethylene has a chlorine content of 25-38 wt% and a Mooney viscosity ML (1+4) at 120°C of 55-60.

[0008] Furthermore, the preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Add nano-silica and aminosilane coupling agent to toluene, disperse by ultrasonication, heat to reflux and react. After the reaction is complete, cool, filter, wash and dry to obtain intermediate 1. Mix intermediate 1 with toluene and mix evenly. Under nitrogen protection, add toluene diisocyanate and dibutyltin dilaurate and keep it at the temperature for reaction. Then add hydroxyl-terminated polybutadiene and stir to react to obtain active nanoparticles. Step 2: Disperse the active nanoparticles in xylene and add maleic anhydride-grafted polyolefin elastomer. An epoxy-containing unsaturated monomer and dicumyl peroxide are refluxed at 130-150℃. After the reaction is completed, the product is precipitated with anhydrous ethanol, washed, vacuum dried, pulverized and sieved to obtain a low-temperature toughening modifier.

[0009] Furthermore, in step 1, the mass ratio of toluene, nano-silica, and aminosilane coupling agent is 80-100:8-12:1-3.

[0010] Further, in step 1, the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene is 20-30:80-100:4-7:0.2-0.5:8-12.

[0011] Further, in step 1, the aminosilane coupling agent is one or more of γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and γ-aminopropyltrimethoxysilane.

[0012] Furthermore, in step 2, the mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide is 20-30:60-80:35-45:8-12:0.8-1.5.

[0013] Furthermore, in step 2, the epoxy-containing unsaturated monomer is composed of allyl glycidyl ether, glycidyl methacrylate, and epoxidized soybean oil acrylate in a mass ratio of 10-15:2-5:1-2.

[0014] Furthermore, the nanofiller is one or more of nano-calcium carbonate, nano-montmorillonite, and nano-aluminum nitride.

[0015] Furthermore, the antioxidant is one or more of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0016] Furthermore, the ultraviolet light stabilizer is one or more of light stabilizer 944, light stabilizer 622, and light stabilizer 770.

[0017] Furthermore, the lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 4-8:2-3:1-4.

[0018] Secondly, this application also provides a method for preparing a low-temperature resistant polyethylene gas pipe, employing the following technical solution: A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Mix evenly and cool to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder for melt blending, followed by plasticizing extrusion, cooling, granulation, and drying to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single screw extruder for pipe forming. After cooling and shaping in a vacuum sizing box, the pipe is left to stand to obtain a low-temperature resistant polyethylene gas pipe.

[0019] Furthermore, in step S2, the temperatures of each section of the twin-screw extruder are: Zone 1 160-170℃, Zone 2 175-185℃, Zone 3 185-195℃, and the die head 190-200℃.

[0020] Furthermore, in step S3, the barrel temperature of the single-screw extruder is: 180-190℃ for the front section, 190-200℃ for the rear section, and 200-210℃ for the die head.

[0021] Furthermore, in step S3, the vacuum degree of the vacuum sizing chamber is -0.04 to -0.06 MPa, and the sizing water temperature is 20-30℃.

[0022] In summary, this application has the following beneficial effects: This application constructs a ternary composite polyethylene resin matrix composed of high-density polyethylene, polyethylene octene co-elastomer, and chlorinated polyethylene, and combines it with a modified low-temperature toughening agent containing epoxy-containing unsaturated monomers. This synergistically optimizes the matrix structure and interfacial compatibility of polyethylene gas pipes, significantly improving the low-temperature toughness, impact resistance, and UV aging resistance of the pipe material. It effectively solves the technical problems of traditional polyethylene gas pipes being prone to low-temperature brittleness, poor deformation capacity, and rapid aging performance degradation.

[0023] This application employs a ternary composite polyethylene resin system. High-density polyethylene (HDPE) provides excellent structural strength and processing stability to the matrix, ensuring dimensional accuracy and pressure resistance after pipe molding. Polyethylene octene co-elastomer, as a flexible and toughening component, effectively disperses internal stress within the resin matrix, mitigating the problem of molecular chain freezing and hardening at low temperatures. Chlorinated polyethylene with specific chlorine content and Mooney viscosity strengthens the interfacial bonding of each resin component, compensating for the poor compatibility and low-temperature mechanical properties of single-component or two-component resin systems. The ternary composite polyethylene resin system in this application significantly improves the low-temperature deformation capacity and impact resistance of the pipe, laying a solid structural foundation for the pipe's low-temperature service stability. Meanwhile, a low-temperature toughening modifier prepared from an epoxy-containing unsaturated monomer compounded from allyl glycidyl ether, glycidyl methacrylate, and epoxidized soybean oil acrylate can form multiple cross-linking reactions with the resin matrix and active nanoparticles through the synergistic effect of the three epoxy monomers. This effectively improves the interfacial bonding effect between the low-temperature toughening modifier and the composite polyethylene resin, eliminates internal defects in the system, and uniformly transmits and disperses external force impacts. Furthermore, it can effectively inhibit the initiation and propagation of matrix cracks in low-temperature environments, significantly improving the low-temperature toughness of the pipe. Detailed Implementation

[0024] The present application will be further described in detail below with reference to the embodiments.

[0025] The high-density polyethylene (brand name: M80063S) used in the embodiments and comparative examples of this application was purchased from Shanghai Hehongcheng Plastics Technology Co., Ltd.; the polyethylene octene co-elastomer (model: 1845) was purchased from Dongguan Bailing New Materials Co., Ltd.; chlorinated polyethylene (chlorine content: 35%) and chlorinated polyethylene (chlorine content: 67%) were both purchased from Wuhan Jiyesheng Chemical Co., Ltd.; nano silica (particle size: 50nm) was purchased from Hangzhou Jiupeng New Materials Co., Ltd.; maleic anhydride grafted polyolefin elastomer (model: HH80407ONTDW) was purchased from Dongguan Shengli New Materials Co., Ltd.; allyl glycidyl ether was purchased from Wuhan Jiyesheng Chemical Co., Ltd.; glycidyl methacrylate was also purchased. Purchased from Jinan Shengda Chemical Co., Ltd.; epoxidized soybean oil acrylate purchased from Jinan Huijinchuan Chemical Co., Ltd.; polyethylene wax purchased from Foshan Jiuruixing New Material Co., Ltd.; zinc stearate purchased from Guangzhou Yinuo Chemical Technology Co., Ltd.; ethylene bis-stearamide purchased from Shandong Xuxiang Chemical Co., Ltd.; nano calcium carbonate (particle size: 50nm) purchased from Qinghe County Chaotai Metal Materials Co., Ltd.; nano montmorillonite (model: DK5) purchased from Zhejiang Fenghong New Material Co., Ltd.; nano aluminum nitride (particle size: 50nm) purchased from Hubei Xinjiecheng Chemical Technology Co., Ltd.

[0026] Examples 1-3 provide a low-temperature resistant polyethylene gas pipe and its preparation method.

[0027] Example 1 A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 80 parts of composite polyethylene resin, 5 parts of low-temperature toughening modifier, 2 parts of nanofiller, 1 part of maleic anhydride grafted polyethylene, 0.2 parts of antioxidant, 0.1 parts of ultraviolet light stabilizer, and 0.1 parts of lubricant. The composite polyethylene resin is composed of high-density polyethylene, polyethylene octene elastomer, and chlorinated polyethylene in a mass ratio of 10:5:2. The chlorine content of the chlorinated polyethylene is 35 wt%, and its Mooney viscosity ML (1+4) at 120℃ is 55-60. The nanofiller is nano-calcium carbonate, the antioxidant is antioxidant 1010, the ultraviolet light stabilizer is light stabilizer 944, and the lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 4:2:1.

[0028] The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Nano-silica and γ-aminopropyltriethoxysilane were added to toluene and ultrasonically dispersed at 100W and 40kHz at room temperature for 2 hours. The mixture was then heated to 105℃ and refluxed for 8 hours. After the reaction, it was naturally cooled to room temperature, filtered through a 200-mesh filter, washed three times with anhydrous ethanol, and dried at 60℃ for 8 hours to obtain intermediate 1. Intermediate 1 was mixed with toluene and stirred at 200rpm at room temperature for 10 minutes until homogeneous. Under nitrogen protection, formaldehyde was added... Benzene diisocyanate and dibutyltin dilaurate were heated to 75°C and reacted at a stirring speed of 200 rpm for 2 hours. Then, hydroxyl-terminated polybutadiene was added and the reaction was continued at a stirring speed of 200 rpm for another 2 hours. The mixture was then naturally cooled to room temperature to obtain active nanoparticles. The mass ratio of toluene, nano-silica, and aminosilane coupling agent was 80:8:1; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene was 20:80:4:0.2:8. Step 2: Disperse the active nanoparticles in xylene and stir at 300 rpm for 20 min at room temperature. Then add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide. Stir at 300 rpm for 20 min at room temperature and reflux at 130℃ for 4 h. After the reaction is complete, the reaction solution is obtained. It is precipitated with three times the volume of anhydrous ethanol, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ and -0.08 MPa for 12 h. After pulverizing and passing through an 80-mesh sieve, a low-temperature toughening modifier is obtained. The mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide is 20:60:35:8:0.8. The epoxy-containing unsaturated monomer is composed of allyl glycidyl ether, glycidyl methacrylate, and epoxidized soybean oil acrylate in a mass ratio of 10:2:1.

[0029] A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. Stir at 300 rpm for 20 minutes at room temperature. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Stir at 400 rpm for 20 minutes at 60°C. Cool to room temperature to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder with a screw length-to-diameter ratio of 40:1 for melt blending. The temperatures of each section of the twin-screw extruder are: 160℃ in zone 1, 175℃ in zone 2, 185℃ in zone 3, and 190℃ at the die head. The screw speed is 50 rpm and the extrusion pressure is 18 MPa. After plasticizing extrusion and cooling in a 25℃ cooling water bath, the mixture is sent to a pelletizer for hot cutting and granulation. The particle size is 2 mm. The pellets are then dried in a 70℃ hot air drying oven for 2 hours to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single-screw extruder with a screw length-to-diameter ratio of 30:1 for pipe forming. The barrel temperature of the single-screw extruder is: 180℃ in the front section, 190℃ in the rear section, and 200℃ in the die head. The screw speed is 40 rpm. The pipe is cooled and shaped in a vacuum sizing box with a vacuum degree controlled at -0.04 MPa and a sizing water temperature controlled at 20℃. After shaping, the pipe is left to stand at room temperature for 24 hours to obtain a low-temperature resistant polyethylene gas pipe.

[0030] Example 2 A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 88 parts of composite polyethylene resin, 8 parts of low-temperature toughening modifier, 4 parts of nanofiller, 1.2 parts of maleic anhydride grafted polyethylene, 0.4 parts of antioxidant, 0.2 parts of ultraviolet light stabilizer, and 0.3 parts of lubricant. The composite polyethylene resin is composed of high-density polyethylene, polyethylene octene elastomer, and chlorinated polyethylene in a mass ratio of 15:7:4. The chlorine content of the chlorinated polyethylene is 35 wt%, and its Mooney viscosity ML (1+4) at 120℃ is 55-60. The nanofiller is nano-montmorillonite, the antioxidant is antioxidant 1076, the ultraviolet light stabilizer is light stabilizer 622, and the lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 6:2.5:3.

[0031] The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Nano-silica and γ-aminopropyltriethoxysilane were added to toluene and ultrasonically dispersed at 110W and 50kHz at room temperature for 2.5h. The mixture was then heated to 108℃ and refluxed for 10h. After the reaction, it was naturally cooled to room temperature, filtered through a 200-mesh filter, washed three times with anhydrous ethanol, and dried at 70℃ for 9h to obtain intermediate 1. Intermediate 1 was mixed with toluene and stirred at 300rpm at room temperature for 15min until homogeneous. Under nitrogen protection, formaldehyde was added... Benzene diisocyanate and dibutyltin dilaurate were heated to 80°C and reacted at a stirring speed of 300 rpm for 2.5 h. Then, hydroxyl-terminated polybutadiene was added, and the reaction was continued at a stirring speed of 300 rpm for 3 h. After natural cooling to room temperature, active nanoparticles were obtained. The mass ratio of toluene, nano-silica, and aminosilane coupling agent was 90:10:2; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene was 25:90:6:0.4:10. Step 2: Disperse the active nanoparticles in xylene and stir at 400 rpm for 25 min at room temperature. Then add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide. Stir at 300 rpm for 20 min at room temperature, and then reflux at 140℃ for 5 h. After the reaction is complete, the reaction solution is precipitated with 4 times the volume of anhydrous ethanol, washed 4 times with anhydrous ethanol, and then placed at 65℃ under vacuum. The low-temperature toughening modifier was obtained by drying in a vacuum drying oven at -0.08 MPa for 14 hours and pulverizing through a 90-mesh sieve. The mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide was 25:70:40:10:1.2. The epoxy-containing unsaturated monomer was composed of allyl glycidyl ether, glycidyl methacrylate, and epoxidized soybean oil acrylate in a mass ratio of 12:4:1.5.

[0032] A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. Stir at 400 rpm at room temperature for 30 minutes. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Stir at 500 rpm at 70°C for 30 minutes. Cool to room temperature to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder with a screw length-to-diameter ratio of 44:1 for melt blending. The temperatures of each section of the twin-screw extruder are: 165℃ in zone 1, 180℃ in zone 2, 190℃ in zone 3, and 195℃ at the die head. The screw speed is 80 rpm and the extrusion pressure is 23 MPa. After plasticizing extrusion and cooling in a 30℃ cooling water bath, the mixture is fed into a pelletizer for hot cutting and granulation. The pellet size is 2.5 mm. The pellets are then dried in a 75℃ hot air drying oven for 2.5 h to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single-screw extruder with a screw length-to-diameter ratio of 32:1 for pipe forming. The barrel temperature of the single-screw extruder is: 185℃ in the front section, 195℃ in the rear section, and 205℃ in the die head. The screw speed is 60 rpm. The pipe is cooled and shaped in a vacuum sizing box with a vacuum degree controlled at -0.05 MPa and a sizing water temperature controlled at 25℃. After shaping, the pipe is left to stand at room temperature for 36 hours to obtain a low-temperature resistant polyethylene gas pipe.

[0033] Example 3 A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 95 parts of composite polyethylene resin, 12 parts of low-temperature toughening modifier, 5 parts of nanofiller, 1.5 parts of maleic anhydride grafted polyethylene, 0.5 parts of antioxidant, 0.3 parts of ultraviolet light stabilizer, and 0.4 parts of lubricant. The composite polyethylene resin is composed of high-density polyethylene, polyethylene octene elastomer, and chlorinated polyethylene in a mass ratio of 20:8:5. The chlorine content of the chlorinated polyethylene is 35 wt%, and its Mooney viscosity ML (1+4) at 120℃ is 55-60. The nanofiller is nano-aluminum nitride, the antioxidant is antioxidant 168, the ultraviolet light stabilizer is light stabilizer 770, and the lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 8:3:4.

[0034] The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Nano-silica and γ-aminopropyltriethoxysilane were added to toluene and ultrasonically dispersed at 120W and 60kHz at room temperature for 3 hours. The mixture was then heated to 110℃ and refluxed for 12 hours. After the reaction, it was naturally cooled to room temperature, filtered through a 200-mesh filter, washed three times with anhydrous ethanol, and dried at 80℃ for 10 hours to obtain intermediate 1. Intermediate 1 was mixed with toluene and stirred at 400rpm at room temperature for 20 minutes until homogeneous. Toluene was then added under nitrogen protection. Diisocyanate and dibutyltin dilaurate were heated to 85°C and reacted at a stirring speed of 400 rpm for 3 hours. Then, hydroxyl-terminated polybutadiene was added and the reaction was continued at a stirring speed of 400 rpm for 4 hours. The mixture was then naturally cooled to room temperature to obtain active nanoparticles. The mass ratio of toluene, nano-silica, and aminosilane coupling agent was 100:12:3; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene was 30:100:7:0.5:12. Step 2: Disperse the active nanoparticles in xylene. Stir at 500 rpm for 30 min at room temperature. Then add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide. Stir at 300 rpm for 20 min at room temperature. Reflux at 150°C for 6 h. After the reaction is complete, obtain the reaction solution. Precipitate with 5 times the volume of anhydrous ethanol, wash 5 times with anhydrous ethanol, and then place under vacuum at 70°C. The low-temperature toughening modifier was obtained by drying in a vacuum drying oven at -0.08 MPa for 16 hours and pulverizing it through a 100-mesh sieve. The mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer and dicumyl peroxide was 30:80:45:12:1.5. The epoxy-containing unsaturated monomer was composed of allyl glycidyl ether, glycidyl methacrylate and epoxidized soybean oil acrylate in a mass ratio of 15:5:2.

[0035] A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. Stir at 600 rpm at room temperature for 40 minutes. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Stir at 600 rpm at 80°C for 40 minutes. Cool to room temperature to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder with a screw length-to-diameter ratio of 48:1 for melt blending. The temperatures of each section of the twin-screw extruder are: 170℃ in zone 1, 185℃ in zone 2, 195℃ in zone 3, and 200℃ at the die head. The screw speed is 100 rpm and the extrusion pressure is 28 MPa. After plasticizing extrusion and cooling in a 35℃ cooling water bath, the mixture is sent to a pelletizer for hot cutting and granulation. The particle size is 3 mm. The pellets are then dried in an 80℃ hot air drying oven for 3 hours to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single-screw extruder with a screw length-to-diameter ratio of 35:1 for pipe forming. The barrel temperature of the single-screw extruder is: 190℃ in the front section, 200℃ in the rear section, and 210℃ in the die head. The screw speed is 80 rpm. The pipe is cooled and shaped in a vacuum sizing box with a vacuum degree controlled at -0.06 MPa and a sizing water temperature controlled at 30℃. After shaping, the pipe is left to stand at room temperature for 48 hours to obtain a low-temperature resistant polyethylene gas pipe.

[0036] Comparative Example 1 A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 80 parts of composite polyethylene resin, 5 parts of low-temperature toughening modifier, 2 parts of nanofiller, 1 part of maleic anhydride grafted polyethylene, 0.2 parts of antioxidant, 0.1 parts of ultraviolet light stabilizer, and 0.1 parts of lubricant. The composite polyethylene resin is composed of polyethylene octene co-elastomer and chlorinated polyethylene in a mass ratio of 5:2. The chlorine content of the chlorinated polyethylene is 35 wt%, and its Mooney viscosity ML (1+4) at 120℃ is 55-60. The nanofiller is nano-calcium carbonate, the antioxidant is antioxidant 1010, the ultraviolet light stabilizer is light stabilizer 944, and the lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 4:2:1.

[0037] The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Nano-silica and γ-aminopropyltriethoxysilane were added to toluene and ultrasonically dispersed at 100W and 40kHz at room temperature for 2 hours. The mixture was then heated to 105℃ and refluxed for 8 hours. After the reaction, it was naturally cooled to room temperature, filtered through a 200-mesh filter, washed three times with anhydrous ethanol, and dried at 60℃ for 8 hours to obtain intermediate 1. Intermediate 1 was mixed with toluene and stirred at 200rpm at room temperature for 10 minutes until homogeneous. Under nitrogen protection, formaldehyde was added... Benzene diisocyanate and dibutyltin dilaurate were heated to 75°C and reacted at a stirring speed of 200 rpm for 2 hours. Then, hydroxyl-terminated polybutadiene was added and the reaction was continued at a stirring speed of 200 rpm for another 2 hours. The mixture was then naturally cooled to room temperature to obtain active nanoparticles. The mass ratio of toluene, nano-silica, and aminosilane coupling agent was 80:8:1; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene was 20:80:4:0.2:8. Step 2: Disperse the active nanoparticles in xylene and stir at 300 rpm for 20 min at room temperature. Then add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide. Stir at 300 rpm for 20 min at room temperature and reflux at 130℃ for 4 h. After the reaction is complete, the reaction solution is obtained. It is precipitated with three times the volume of anhydrous ethanol, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ and -0.08 MPa for 12 h. After pulverizing and passing through an 80-mesh sieve, a low-temperature toughening modifier is obtained. The mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide is 20:60:35:8:0.8. The epoxy-containing unsaturated monomer is composed of allyl glycidyl ether, glycidyl methacrylate, and epoxidized soybean oil acrylate in a mass ratio of 10:2:1.

[0038] A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. Stir at 300 rpm for 20 minutes at room temperature. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Stir at 400 rpm for 20 minutes at 60°C. Cool to room temperature to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder with a screw length-to-diameter ratio of 40:1 for melt blending. The temperatures of each section of the twin-screw extruder are: 160℃ in zone 1, 175℃ in zone 2, 185℃ in zone 3, and 190℃ at the die head. The screw speed is 50 rpm and the extrusion pressure is 18 MPa. After plasticizing extrusion and cooling in a 25℃ cooling water bath, the mixture is sent to a pelletizer for hot cutting and granulation. The particle size is 2 mm. The pellets are then dried in a 70℃ hot air drying oven for 2 hours to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single-screw extruder with a screw length-to-diameter ratio of 30:1 for pipe forming. The barrel temperature of the single-screw extruder is: 180℃ in the front section, 190℃ in the rear section, and 200℃ in the die head. The screw speed is 40 rpm. The pipe is cooled and shaped in a vacuum sizing box with a vacuum degree controlled at -0.04 MPa and a sizing water temperature controlled at 20℃. After shaping, the pipe is left to stand at room temperature for 24 hours to obtain a low-temperature resistant polyethylene gas pipe.

[0039] Comparative Example 2 A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 80 parts of composite polyethylene resin, 5 parts of low-temperature toughening modifier, 2 parts of nanofiller, 1 part of maleic anhydride grafted polyethylene, 0.2 parts of antioxidant, 0.1 parts of ultraviolet light stabilizer, and 0.1 parts of lubricant. The composite polyethylene resin is composed of high-density polyethylene and chlorinated polyethylene in a mass ratio of 10:2. The chlorinated polyethylene has a chlorine content of 35 wt% and a Mooney viscosity ML (1+4) of 55-60 at 120℃. The nanofiller is nano-calcium carbonate, the antioxidant is antioxidant 1010, the ultraviolet light stabilizer is light stabilizer 944, and the lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 4:2:1.

[0040] The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Nano-silica and γ-aminopropyltriethoxysilane were added to toluene and ultrasonically dispersed at 100W and 40kHz at room temperature for 2 hours. The mixture was then heated to 105℃ and refluxed for 8 hours. After the reaction, it was naturally cooled to room temperature, filtered through a 200-mesh filter, washed three times with anhydrous ethanol, and dried at 60℃ for 8 hours to obtain intermediate 1. Intermediate 1 was mixed with toluene and stirred at 200rpm at room temperature for 10 minutes until homogeneous. Under nitrogen protection, formaldehyde was added... Benzene diisocyanate and dibutyltin dilaurate were heated to 75°C and reacted at a stirring speed of 200 rpm for 2 hours. Then, hydroxyl-terminated polybutadiene was added and the reaction was continued at a stirring speed of 200 rpm for another 2 hours. The mixture was then naturally cooled to room temperature to obtain active nanoparticles. The mass ratio of toluene, nano-silica, and aminosilane coupling agent was 80:8:1; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene was 20:80:4:0.2:8. Step 2: Disperse the active nanoparticles in xylene and stir at 300 rpm for 20 min at room temperature. Then add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide. Stir at 300 rpm for 20 min at room temperature and reflux at 130℃ for 4 h. After the reaction is complete, the reaction solution is obtained. It is precipitated with three times the volume of anhydrous ethanol, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ and -0.08 MPa for 12 h. After pulverizing and passing through an 80-mesh sieve, a low-temperature toughening modifier is obtained. The mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide is 20:60:35:8:0.8. The epoxy-containing unsaturated monomer is composed of allyl glycidyl ether, glycidyl methacrylate, and epoxidized soybean oil acrylate in a mass ratio of 10:2:1.

[0041] A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. Stir at 300 rpm for 20 minutes at room temperature. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Stir at 400 rpm for 20 minutes at 60°C. Cool to room temperature to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder with a screw length-to-diameter ratio of 40:1 for melt blending. The temperatures of each section of the twin-screw extruder are: 160℃ in zone 1, 175℃ in zone 2, 185℃ in zone 3, and 190℃ at the die head. The screw speed is 50 rpm and the extrusion pressure is 18 MPa. After plasticizing extrusion and cooling in a 25℃ cooling water bath, the mixture is sent to a pelletizer for hot cutting and granulation. The particle size is 2 mm. The pellets are then dried in a 70℃ hot air drying oven for 2 hours to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single-screw extruder with a screw length-to-diameter ratio of 30:1 for pipe forming. The barrel temperature of the single-screw extruder is: 180℃ in the front section, 190℃ in the rear section, and 200℃ in the die head. The screw speed is 40 rpm. The pipe is cooled and shaped in a vacuum sizing box with a vacuum degree controlled at -0.04 MPa and a sizing water temperature controlled at 20℃. After shaping, the pipe is left to stand at room temperature for 24 hours to obtain a low-temperature resistant polyethylene gas pipe.

[0042] Comparative Example 3 A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 80 parts of composite polyethylene resin, 5 parts of low-temperature toughening modifier, 2 parts of nanofiller, 1 part of maleic anhydride grafted polyethylene, 0.2 parts of antioxidant, 0.1 parts of ultraviolet light stabilizer, and 0.1 parts of lubricant. The composite polyethylene resin is composed of high-density polyethylene and polyethylene octene elastomer in a mass ratio of 10:5. The nanofiller is nano-calcium carbonate. The antioxidant is antioxidant 1010, the ultraviolet light stabilizer is light stabilizer 944, and the lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 4:2:1.

[0043] The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Nano-silica and γ-aminopropyltriethoxysilane were added to toluene and ultrasonically dispersed at 100W and 40kHz at room temperature for 2 hours. The mixture was then heated to 105℃ and refluxed for 8 hours. After the reaction, it was naturally cooled to room temperature, filtered through a 200-mesh filter, washed three times with anhydrous ethanol, and dried at 60℃ for 8 hours to obtain intermediate 1. Intermediate 1 was mixed with toluene and stirred at 200rpm at room temperature for 10 minutes until homogeneous. Under nitrogen protection, formaldehyde was added... Benzene diisocyanate and dibutyltin dilaurate were heated to 75°C and reacted at a stirring speed of 200 rpm for 2 hours. Then, hydroxyl-terminated polybutadiene was added and the reaction was continued at a stirring speed of 200 rpm for another 2 hours. The mixture was then naturally cooled to room temperature to obtain active nanoparticles. The mass ratio of toluene, nano-silica, and aminosilane coupling agent was 80:8:1; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene was 20:80:4:0.2:8. Step 2: Disperse the active nanoparticles in xylene and stir at 300 rpm for 20 min at room temperature. Then add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide. Stir at 300 rpm for 20 min at room temperature and reflux at 130℃ for 4 h. After the reaction is complete, the reaction solution is obtained. It is precipitated with three times the volume of anhydrous ethanol, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ and -0.08 MPa for 12 h. After pulverizing and passing through an 80-mesh sieve, a low-temperature toughening modifier is obtained. The mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide is 20:60:35:8:0.8. The epoxy-containing unsaturated monomer is composed of allyl glycidyl ether, glycidyl methacrylate, and epoxidized soybean oil acrylate in a mass ratio of 10:2:1.

[0044] A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. Stir at 300 rpm for 20 minutes at room temperature. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Stir at 400 rpm for 20 minutes at 60°C. Cool to room temperature to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder with a screw length-to-diameter ratio of 40:1 for melt blending. The temperatures of each section of the twin-screw extruder are: 160℃ in zone 1, 175℃ in zone 2, 185℃ in zone 3, and 190℃ at the die head. The screw speed is 50 rpm and the extrusion pressure is 18 MPa. After plasticizing extrusion and cooling in a 25℃ cooling water bath, the mixture is sent to a pelletizer for hot cutting and granulation. The particle size is 2 mm. The pellets are then dried in a 70℃ hot air drying oven for 2 hours to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single-screw extruder with a screw length-to-diameter ratio of 30:1 for pipe forming. The barrel temperature of the single-screw extruder is: 180℃ in the front section, 190℃ in the rear section, and 200℃ in the die head. The screw speed is 40 rpm. The pipe is cooled and shaped in a vacuum sizing box with a vacuum degree controlled at -0.04 MPa and a sizing water temperature controlled at 20℃. After shaping, the pipe is left to stand at room temperature for 24 hours to obtain a low-temperature resistant polyethylene gas pipe.

[0045] Comparative Example 4 A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 80 parts of composite polyethylene resin, 5 parts of low-temperature toughening modifier, 2 parts of nanofiller, 1 part of maleic anhydride grafted polyethylene, 0.2 parts of antioxidant, 0.1 parts of ultraviolet light stabilizer, and 0.1 parts of lubricant. The composite polyethylene resin is composed of high-density polyethylene, polyethylene octene elastomer, and chlorinated polyethylene in a mass ratio of 10:5:2. The chlorine content of the chlorinated polyethylene is 67 wt%. The nanofiller is nano-calcium carbonate. The antioxidant is antioxidant 1010. The ultraviolet light stabilizer is light stabilizer 944. The lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 4:2:1.

[0046] The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Nano-silica and γ-aminopropyltriethoxysilane were added to toluene and ultrasonically dispersed at 100W and 40kHz at room temperature for 2 hours. The mixture was then heated to 105℃ and refluxed for 8 hours. After the reaction, it was naturally cooled to room temperature, filtered through a 200-mesh filter, washed three times with anhydrous ethanol, and dried at 60℃ for 8 hours to obtain intermediate 1. Intermediate 1 was mixed with toluene and stirred at 200rpm at room temperature for 10 minutes until homogeneous. Under nitrogen protection, formaldehyde was added... Benzene diisocyanate and dibutyltin dilaurate were heated to 75°C and reacted at a stirring speed of 200 rpm for 2 hours. Then, hydroxyl-terminated polybutadiene was added and the reaction was continued at a stirring speed of 200 rpm for another 2 hours. The mixture was then naturally cooled to room temperature to obtain active nanoparticles. The mass ratio of toluene, nano-silica, and aminosilane coupling agent was 80:8:1; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene was 20:80:4:0.2:8. Step 2: Disperse the active nanoparticles in xylene and stir at 300 rpm for 20 min at room temperature. Then add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide. Stir at 300 rpm for 20 min at room temperature and reflux at 130℃ for 4 h. After the reaction is complete, the reaction solution is obtained. It is precipitated with three times the volume of anhydrous ethanol, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ and -0.08 MPa for 12 h. After pulverizing and passing through an 80-mesh sieve, a low-temperature toughening modifier is obtained. The mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide is 20:60:35:8:0.8. The epoxy-containing unsaturated monomer is composed of allyl glycidyl ether, glycidyl methacrylate, and epoxidized soybean oil acrylate in a mass ratio of 10:2:1.

[0047] A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. Stir at 300 rpm for 20 minutes at room temperature. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Stir at 400 rpm for 20 minutes at 60°C. Cool to room temperature to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder with a screw length-to-diameter ratio of 40:1 for melt blending. The temperatures of each section of the twin-screw extruder are: 160℃ in zone 1, 175℃ in zone 2, 185℃ in zone 3, and 190℃ at the die head. The screw speed is 50 rpm and the extrusion pressure is 18 MPa. After plasticizing extrusion and cooling in a 25℃ cooling water bath, the mixture is sent to a pelletizer for hot cutting and granulation. The particle size is 2 mm. The pellets are then dried in a 70℃ hot air drying oven for 2 hours to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single-screw extruder with a screw length-to-diameter ratio of 30:1 for pipe forming. The barrel temperature of the single-screw extruder is: 180℃ in the front section, 190℃ in the rear section, and 200℃ in the die head. The screw speed is 40 rpm. The pipe is cooled and shaped in a vacuum sizing box with a vacuum degree controlled at -0.04 MPa and a sizing water temperature controlled at 20℃. After shaping, the pipe is left to stand at room temperature for 24 hours to obtain a low-temperature resistant polyethylene gas pipe.

[0048] Comparative Example 5 A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 80 parts of composite polyethylene resin, 5 parts of low-temperature toughening modifier, 2 parts of nanofiller, 1 part of maleic anhydride grafted polyethylene, 0.2 parts of antioxidant, 0.1 parts of ultraviolet light stabilizer, and 0.1 parts of lubricant. The composite polyethylene resin is composed of high-density polyethylene, polyethylene octene elastomer, and chlorinated polyethylene in a mass ratio of 10:5:2. The chlorine content of the chlorinated polyethylene is 35 wt%, and its Mooney viscosity ML (1+4) at 120℃ is 55-60. The nanofiller is nano-calcium carbonate, the antioxidant is antioxidant 1010, the ultraviolet light stabilizer is light stabilizer 944, and the lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 4:2:1.

[0049] The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Nano-silica and γ-aminopropyltriethoxysilane were added to toluene and ultrasonically dispersed at 100W and 40kHz at room temperature for 2 hours. The mixture was then heated to 105℃ and refluxed for 8 hours. After the reaction, it was naturally cooled to room temperature, filtered through a 200-mesh filter, washed three times with anhydrous ethanol, and dried at 60℃ for 8 hours to obtain intermediate 1. Intermediate 1 was mixed with toluene and stirred at 200rpm at room temperature for 10 minutes until homogeneous. Under nitrogen protection, formaldehyde was added... Benzene diisocyanate and dibutyltin dilaurate were heated to 75°C and reacted at a stirring speed of 200 rpm for 2 hours. Then, hydroxyl-terminated polybutadiene was added and the reaction was continued at a stirring speed of 200 rpm for another 2 hours. The mixture was then naturally cooled to room temperature to obtain active nanoparticles. The mass ratio of toluene, nano-silica, and aminosilane coupling agent was 80:8:1; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene was 20:80:4:0.2:8. Step 2: Disperse the active nanoparticles in xylene and stir at 300 rpm for 20 min at room temperature. Then add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide. Stir at 300 rpm for 20 min at room temperature and reflux at 130℃ for 4 h. After the reaction is complete, the reaction solution is obtained. It is precipitated with 3 times the volume of anhydrous ethanol, washed 3 times with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ and -0.08 MPa for 12 h. After pulverizing and passing through an 80-mesh sieve, a low-temperature toughening modifier is obtained. The mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide is 20:60:35:8:0.8. The epoxy-containing unsaturated monomer is composed of glycidyl methacrylate and epoxidized soybean oil acrylate in a mass ratio of 2:1.

[0050] A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. Stir at 300 rpm for 20 minutes at room temperature. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Stir at 400 rpm for 20 minutes at 60°C. Cool to room temperature to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder with a screw length-to-diameter ratio of 40:1 for melt blending. The temperatures of each section of the twin-screw extruder are: 160℃ in zone 1, 175℃ in zone 2, 185℃ in zone 3, and 190℃ at the die head. The screw speed is 50 rpm and the extrusion pressure is 18 MPa. After plasticizing extrusion and cooling in a 25℃ cooling water bath, the mixture is sent to a pelletizer for hot cutting and granulation. The particle size is 2 mm. The pellets are then dried in a 70℃ hot air drying oven for 2 hours to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single-screw extruder with a screw length-to-diameter ratio of 30:1 for pipe forming. The barrel temperature of the single-screw extruder is: 180℃ in the front section, 190℃ in the rear section, and 200℃ in the die head. The screw speed is 40 rpm. The pipe is cooled and shaped in a vacuum sizing box with a vacuum degree controlled at -0.04 MPa and a sizing water temperature controlled at 20℃. After shaping, the pipe is left to stand at room temperature for 24 hours to obtain a low-temperature resistant polyethylene gas pipe.

[0051] Comparative Example 6 A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 80 parts of composite polyethylene resin, 5 parts of low-temperature toughening modifier, 2 parts of nanofiller, 1 part of maleic anhydride grafted polyethylene, 0.2 parts of antioxidant, 0.1 parts of ultraviolet light stabilizer, and 0.1 parts of lubricant. The composite polyethylene resin is composed of high-density polyethylene, polyethylene octene elastomer, and chlorinated polyethylene in a mass ratio of 10:5:2. The chlorine content of the chlorinated polyethylene is 35 wt%, and its Mooney viscosity ML (1+4) at 120℃ is 55-60. The nanofiller is nano-calcium carbonate, the antioxidant is antioxidant 1010, the ultraviolet light stabilizer is light stabilizer 944, and the lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 4:2:1.

[0052] The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Nano-silica and γ-aminopropyltriethoxysilane were added to toluene and ultrasonically dispersed at 100W and 40kHz at room temperature for 2 hours. The mixture was then heated to 105℃ and refluxed for 8 hours. After the reaction, it was naturally cooled to room temperature, filtered through a 200-mesh filter, washed three times with anhydrous ethanol, and dried at 60℃ for 8 hours to obtain intermediate 1. Intermediate 1 was mixed with toluene and stirred at 200rpm at room temperature for 10 minutes until homogeneous. Under nitrogen protection, formaldehyde was added... Benzene diisocyanate and dibutyltin dilaurate were heated to 75°C and reacted at a stirring speed of 200 rpm for 2 hours. Then, hydroxyl-terminated polybutadiene was added and the reaction was continued at a stirring speed of 200 rpm for another 2 hours. The mixture was then naturally cooled to room temperature to obtain active nanoparticles. The mass ratio of toluene, nano-silica, and aminosilane coupling agent was 80:8:1; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene was 20:80:4:0.2:8. Step 2: Disperse the active nanoparticles in xylene and stir at 300 rpm for 20 min at room temperature. Then add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide. Stir at 300 rpm for 20 min at room temperature and reflux at 130℃ for 4 h. After the reaction is complete, the reaction solution is obtained. It is precipitated with three times the volume of anhydrous ethanol, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ and -0.08 MPa for 12 h. After pulverizing and passing through an 80-mesh sieve, a low-temperature toughening modifier is obtained. The mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide is 20:60:35:8:0.8. The epoxy-containing unsaturated monomer is composed of allyl glycidyl ether and epoxidized soybean oil acrylate in a mass ratio of 10:1.

[0053] A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. Stir at 300 rpm for 20 minutes at room temperature. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Stir at 400 rpm for 20 minutes at 60°C. Cool to room temperature to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder with a screw length-to-diameter ratio of 40:1 for melt blending. The temperatures of each section of the twin-screw extruder are: 160℃ in zone 1, 175℃ in zone 2, 185℃ in zone 3, and 190℃ at the die head. The screw speed is 50 rpm and the extrusion pressure is 18 MPa. After plasticizing extrusion and cooling in a 25℃ cooling water bath, the mixture is sent to a pelletizer for hot cutting and granulation. The particle size is 2 mm. The pellets are then dried in a 70℃ hot air drying oven for 2 hours to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single-screw extruder with a screw length-to-diameter ratio of 30:1 for pipe forming. The barrel temperature of the single-screw extruder is: 180℃ in the front section, 190℃ in the rear section, and 200℃ in the die head. The screw speed is 40 rpm. The pipe is cooled and shaped in a vacuum sizing box with a vacuum degree controlled at -0.04 MPa and a sizing water temperature controlled at 20℃. After shaping, the pipe is left to stand at room temperature for 24 hours to obtain a low-temperature resistant polyethylene gas pipe.

[0054] Comparative Example 7 A low-temperature resistant polyethylene gas pipe comprises the following raw materials in parts by weight: 80 parts of composite polyethylene resin, 5 parts of low-temperature toughening modifier, 2 parts of nanofiller, 1 part of maleic anhydride grafted polyethylene, 0.2 parts of antioxidant, 0.1 parts of ultraviolet light stabilizer, and 0.1 parts of lubricant. The composite polyethylene resin is composed of high-density polyethylene, polyethylene octene elastomer, and chlorinated polyethylene in a mass ratio of 10:5:2. The chlorine content of the chlorinated polyethylene is 35 wt%, and its Mooney viscosity ML (1+4) at 120℃ is 55-60. The nanofiller is nano-calcium carbonate, the antioxidant is antioxidant 1010, the ultraviolet light stabilizer is light stabilizer 944, and the lubricant is composed of polyethylene wax, zinc stearate, and ethylene bis-stearamide in a mass ratio of 4:2:1.

[0055] The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Nano-silica and γ-aminopropyltriethoxysilane were added to toluene and ultrasonically dispersed at 100W and 40kHz at room temperature for 2 hours. The mixture was then heated to 105℃ and refluxed for 8 hours. After the reaction, it was naturally cooled to room temperature, filtered through a 200-mesh filter, washed three times with anhydrous ethanol, and dried at 60℃ for 8 hours to obtain intermediate 1. Intermediate 1 was mixed with toluene and stirred at 200rpm at room temperature for 10 minutes until homogeneous. Under nitrogen protection, formaldehyde was added... Benzene diisocyanate and dibutyltin dilaurate were heated to 75°C and reacted at a stirring speed of 200 rpm for 2 hours. Then, hydroxyl-terminated polybutadiene was added and the reaction was continued at a stirring speed of 200 rpm for another 2 hours. The mixture was then naturally cooled to room temperature to obtain active nanoparticles. The mass ratio of toluene, nano-silica, and aminosilane coupling agent was 80:8:1; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene was 20:80:4:0.2:8. Step 2: Disperse the active nanoparticles in xylene and stir at 300 rpm for 20 min at room temperature. Then add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide. Stir at 300 rpm for 20 min at room temperature and reflux at 130℃ for 4 h. After the reaction is complete, the reaction solution is obtained. It is precipitated with three times the volume of anhydrous ethanol, washed three times with anhydrous ethanol, and then dried in a vacuum drying oven at 60℃ and -0.08 MPa for 12 h. After pulverizing and passing through an 80-mesh sieve, a low-temperature toughening modifier is obtained. The mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide is 20:60:35:8:0.8. The epoxy-containing unsaturated monomer is composed of allyl glycidyl ether and glycidyl methacrylate in a mass ratio of 10:2.

[0056] A method for preparing a low-temperature resistant polyethylene gas pipe includes the following preparation steps: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. Stir at 300 rpm for 20 minutes at room temperature. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Stir at 400 rpm for 20 minutes at 60°C. Cool to room temperature to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder with a screw length-to-diameter ratio of 40:1 for melt blending. The temperatures of each section of the twin-screw extruder are: 160℃ in zone 1, 175℃ in zone 2, 185℃ in zone 3, and 190℃ at the die head. The screw speed is 50 rpm and the extrusion pressure is 18 MPa. After plasticizing extrusion and cooling in a 25℃ cooling water bath, the mixture is sent to a pelletizer for hot cutting and granulation. The particle size is 2 mm. The pellets are then dried in a 70℃ hot air drying oven for 2 hours to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single-screw extruder with a screw length-to-diameter ratio of 30:1 for pipe forming. The barrel temperature of the single-screw extruder is: 180℃ in the front section, 190℃ in the rear section, and 200℃ in the die head. The screw speed is 40 rpm. The pipe is cooled and shaped in a vacuum sizing box with a vacuum degree controlled at -0.04 MPa and a sizing water temperature controlled at 20℃. After shaping, the pipe is left to stand at room temperature for 24 hours to obtain a low-temperature resistant polyethylene gas pipe.

[0057] Performance testing The performance of the low-temperature resistant polyethylene gas pipes prepared in Examples 1-3 and Comparative Examples 1-7 of this application was tested. The specific test contents are as follows: Low-temperature simply supported beam impact strength: Referring to the national standard GB / T 1043.1-2008 "Determination of impact properties of simply supported beams of plastics - Part 1: Non-instrumental impact test", the pipe was extruded and granulated and then injection molded into a standard notched strip of 80mm×10mm×4mm. The impact strength of the sample was tested after being kept at -40℃ for 4h. Low-temperature drop hammer impact test: Referring to the national standard GB / T 15558.2-2023 "Buried polyethylene (PE) pipeline system for gas - Part 2: Pipes", a uniform nominal outer diameter DN110, SDR11 grade low-temperature resistant polyethylene gas pipe was used. The length of the pipe section cut perpendicular to the pipe axis was 200±10mm. 20 independent pipe section samples were taken from each group and kept at -20℃ for 2h. The drop hammer mass was 0.5kg and the drop height was 2m. The drop hammer impact fracture rate of the sample was recorded. Low-temperature elongation at break: Referring to the national standard GB / T 1040.1-2025 "Determination of tensile properties of plastics - Part 1: General", the wall of DN110 and SDR11 grade polyethylene gas pipes was cut into standard type I dumbbell tensile specimens with a thickness of 4 mm. All specimens were pre-cooled to -30℃ in the high and low temperature tensile testing chamber, sealed and kept at the temperature for 30 min, and then tensile testing was carried out after the temperature inside the chamber was stabilized at -30±2℃. The tensile rate was 5 mm / min, and the low-temperature elongation at break of the specimens was tested. UV aging resistance: Following the national standard GB / T 16422.3-2022 "Laboratory Light Source Exposure Test Methods for Plastics - Part 3: Fluorescent UV Lamps", a UVA-340 fluorescent UV lamp was used, with an irradiance of 0.76 W / (m²・nm) at a wavelength of 340 nm. A 12-hour cycle of 8 hours of UV irradiation followed by 4 hours of condensation was employed. During the irradiation phase, the blackboard temperature was 60±3℃; during the condensation phase, the UV lamp was turned off, and the blackboard temperature was 50±3℃. Deionized water was used as the condensing medium. A total of 500 hours of UV irradiation was accumulated, and the impact strength retention rate of the samples after UV aging was tested. The specific test results are shown in Table 1.

[0058] Table 1 Performance parameters of low-temperature resistant polyethylene gas pipes in Examples 1-3 and Comparative Examples 1-7 As shown in Table 1, the low-temperature resistant polyethylene gas pipes prepared in Examples 1-3 of this application exhibit excellent comprehensive performance. By employing a ternary composite polyethylene resin system consisting of high-density polyethylene, polyethylene octene co-elastomer, and chlorinated polyethylene, and combined with a three-component low-temperature toughening modifier derived from unsaturated monomers containing epoxy groups, the pipes achieve no cracking under -20°C drop hammer impact and an impact strength ≥19.5 kJ / m at -40°C for simply supported beams. 2 The elongation at break at -30℃ is ≥320%, and the impact strength retention rate after 500h UV aging is higher than 92%. The prepared low-temperature resistant polyethylene gas pipe has both excellent low-temperature toughness and weather resistance.

[0059] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A low-temperature resistant polyethylene gas pipe, characterized in that, The raw materials include the following parts by weight: 80-95 parts of composite polyethylene resin, 5-12 parts of low-temperature toughening modifier, 2-5 parts of nanofiller, 1-1.5 parts of maleic anhydride grafted polyethylene, 0.2-0.5 parts of antioxidant, 0.1-0.3 parts of ultraviolet light stabilizer, and 0.1-0.4 parts of lubricant.

2. The low-temperature resistant polyethylene gas pipe according to claim 1, characterized in that, The composite polyethylene resin is composed of high-density polyethylene, polyethylene octene co-elastomer, and chlorinated polyethylene in a mass ratio of 10-20:5-8:2-5.

3. The low-temperature resistant polyethylene gas pipe according to claim 2, characterized in that, The chlorinated polyethylene has a chlorine content of 25-38 wt% and a Mooney viscosity ML (1+4) at 120°C of 55-60.

4. The low-temperature resistant polyethylene gas pipe according to claim 1, characterized in that, The preparation method of the low-temperature toughening modifier includes the following preparation steps: Step 1: Add nano-silica and aminosilane coupling agent to toluene, disperse by ultrasonication, heat to reflux and react. After the reaction is complete, cool, filter, wash and dry to obtain intermediate 1. Mix intermediate 1 with toluene and mix evenly. Under nitrogen protection, add toluene diisocyanate and dibutyltin dilaurate and keep it at the temperature for reaction. Then add hydroxyl-terminated polybutadiene and stir to react to obtain active nanoparticles. Step 2: Disperse the active nanoparticles in xylene, add maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer and dicumyl peroxide, and reflux at 130-150℃. After the reaction is completed, precipitate with anhydrous ethanol, wash, vacuum dry, pulverize and sieve to obtain a low-temperature toughening modifier.

5. The low-temperature resistant polyethylene gas pipe according to claim 4, characterized in that, In step 1, the mass ratio of toluene, nano-silica, and aminosilane coupling agent is 80-100:8-12:1-3; the mass ratio of intermediate 1, toluene, toluene diisocyanate, dibutyltin dilaurate, and hydroxyl-terminated polybutadiene is 20-30:80-100:4-7:0.2-0.5:8-12.

6. The low-temperature resistant polyethylene gas pipe according to claim 4, characterized in that, In step 2, the mass ratio of active nanoparticles, xylene, maleic anhydride-grafted polyolefin elastomer, epoxy-containing unsaturated monomer, and dicumyl peroxide is 20-30:60-80:35-45:8-12:0.8-1.

5.

7. The low-temperature resistant polyethylene gas pipe according to claim 4, characterized in that, In step 2, the epoxy-containing unsaturated monomer is composed of allyl glycidyl ether, glycidyl methacrylate, and epoxidized soybean oil acrylate in a mass ratio of 10-15:2-5:1-2.

8. The low-temperature resistant polyethylene gas pipe according to claim 1, characterized in that, The lubricant is composed of polyethylene wax, zinc stearate and ethylene bis-stearamide in a mass ratio of 4-8:2-3:1-4.

9. A method for preparing a low-temperature resistant polyethylene gas pipe as described in any one of claims 1-8, characterized in that, The preparation steps include the following: S1. Add composite polyethylene resin, maleic anhydride grafted polyethylene and low temperature toughening modifier to a high-speed mixer in sequence. After mixing evenly, add nano filler, antioxidant, ultraviolet light stabilizer and lubricant. Mix evenly and cool to obtain modified polyethylene mixture. S2. The modified polyethylene mixture is fed into a twin-screw extruder for melt blending, followed by plasticizing extrusion, cooling, granulation, and drying to obtain modified polyethylene granules. S3. Modified polyethylene granules are fed into a single screw extruder for pipe forming. After cooling and shaping in a vacuum sizing box, the pipe is left to stand to obtain a low-temperature resistant polyethylene gas pipe.

10. The method for preparing a low-temperature resistant polyethylene gas pipe according to claim 9, characterized in that, In step S2, the temperatures of each section of the twin-screw extruder are: Zone 1 160-170℃, Zone 2 175-185℃, Zone 3 185-195℃, and Die head 190-200℃; in step S3, the barrel temperatures of the single-screw extruder are: Front section 180-190℃, Rear section 190-200℃, and Die head 200-210℃; in step S3, the vacuum degree of the vacuum sizing box is -0.04 to -0.06 MPa, and the sizing water temperature is 20-30℃.

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