High-temperature-resistant flame-retardant composite HDPE (high-density polyethylene) pipe and preparation method thereof

Abstract

The invention relates to the field of plastic pipe manufacturing, and particularly discloses a high-temperature-resistant flame-retardant composite HDPE pipe and a preparation method thereof. The high-temperature-resistant flame-retardant composite HDPE pipe is prepared from the following raw materials in parts by weight: 40 to 45 parts of polyethylene, 0.5 to 1 part of a lubricant, 6 to 7.6 parts of a filling agent, 2.4 to 4 parts of a composite flame retardant, 1 to 3 parts of a heat-stable reinforcing agent and 1.5 to 2.5 parts of a compatilizer, the composite flame retardant is prepared from decabromodiphenyl ethane, antimony trioxide and brominated polystyrene according to the ratio of (3 to 5): (1 to 2): (0.4 to 1); the filling agent is calcium carbonate. The high-temperature-resistant flame-retardant composite HDPE pipe can be used for preparing electric wires and cables, has excellent high-temperature resistance and flame retardance, and can meet the standard requirements of safety, flame retardance and high-temperature resistance in application of the electric wires and cables.

Description

Technical Field

[0001] The present application relates to the technical field of plastic pipe manufacturing, and more specifically, to a high temperature resistant flame retardant composite HDPE pipe and a preparation method thereof. Background Art

[0002] Plastic pipes are light, corrosion-resistant, and easy to process, and are widely used in the field of cable and cable protection. However, plastic materials are inherently flammable and can easily burn and release toxic gases when exposed to high temperatures or open flames. Existing plastic pipes are mainly made by adding flame retardants to the raw materials to improve their high temperature resistance and flame retardancy. Common flame retardants include halogen flame retardants, phosphorus flame retardants, nitrogen flame retardants, etc.

[0003] With respect to the above-mentioned related technologies, the inventors found that the existing flame retardants have some problems during use. For example, halogen flame retardants may produce toxic gases when burned, posing a potential threat to the environment and human health; and although phosphorus and nitrogen flame retardants are more environmentally friendly, their flame retardant efficiency is relatively low, and a higher addition amount is often required to achieve the ideal flame retardant effect, which sacrifices the physical properties of the plastic material itself to a certain extent.

[0004] With the rapid development of science and technology and modern industry, higher standards have been put forward for the high temperature resistance and flame retardancy of plastic pipes. Especially when they are used in fields such as electricity, aerospace and automobile manufacturing that need to work in high temperature environments, plastic pipes prepared by traditional flame retardant means are difficult to meet the standard requirements for high temperature resistance and flame retardancy when used in special fields. Summary of the invention

[0005] In order to improve the high temperature resistance and flame retardancy of plastic pipes and ensure the safety of plastic pipes when used for wire and cable protection, the present application provides a high temperature resistant flame retardant composite HDPE pipe and a preparation method thereof.

[0006] In the first aspect, the present application provides a high temperature resistant flame retardant composite HDPE pipe, which adopts the following technical solution: A high temperature resistant flame retardant composite HDPE pipe, wherein the raw materials include 40-45 parts of polyethylene, 0.5-1 parts of lubricant, 6-7.6 parts of filler, 2.4-4 parts of composite flame retardant, 1-3 parts of heat stable reinforcing agent and 1.5-2.5 parts of compatibilizer according to weight parts; The composite flame retardant comprises decabromodiphenylethane, antimony trioxide and brominated polystyrene in a ratio of (3-5):(1-2):(0.4-1); and the filler is calcium carbonate.

[0007] By adopting the above technical solution, the inventors found that the flame retardant effect of antimony trioxide alone is poor. Antimony trioxide is mixed with decabromodiphenylethane and brominated polystyrene as a flame retardant. Bromodiphenylethane and brominated polystyrene decompose when heated to release hydrogen halide and halogen elements. These two substances are highly active and can react with antimony trioxide to produce antimony trihalides and antimony oxyhalides, which interfere with the reaction of the combustion chain and significantly improve the flame retardancy of the material.

[0008] Antimony trihalide can react with polymers, causing them to tend to generate a carbon layer instead of combustible gas when heated. This carbon layer forms a stable barrier on the surface of the material, isolating heat and oxygen, thereby protecting the base polymer and preventing it from further thermal decomposition and combustion. The thermal decomposition of the polymer is limited, thereby further reducing the generation of combustible gas.

[0009] In addition, in the reaction process of antimony trioxide and halogen compounds, in addition to antimony trihalide and antimony oxyhalide, inert gases such as bromine gas (Br2) produced by the decomposition of hydrogen bromide (HBr) are also generated. These inert gases dilute the concentration of oxygen in the flame, reduce the oxygen supply required for combustion, and thus inhibit the combustion process.

[0010] Calcium carbonate as a filler can enhance the dimensional stability of the pipe and improve the uniformity of the overall powder dispersion.

[0011] Optionally, the calcium carbonate is talcum powder and nano-activated calcium carbonate in a mass ratio of (1-3):1.

[0012] By adopting the above technical solution, talcum powder can form a stable ceramic layer when heated. This ceramic layer can isolate heat and oxygen and reduce the burning rate of the material. Nano-activated calcium carbonate has a high specific surface area and can be more evenly dispersed in the polyethylene pipe matrix, which can promote the formation of a carbon layer and further enhance the flame retardant effect.

[0013] In addition, talcum powder has excellent thermal stability, and nano-activated calcium carbonate decomposes at high temperatures to absorb heat, which helps to lower the temperature of the material surface, reduce the thermal decomposition of polyethylene pipes and thermal expansion at high temperatures, which helps to maintain the dimensional stability of polyethylene pipes.

[0014] Optionally, the heat-stable reinforcing agent is modified carbon fiber.

[0015] By adopting the above technical solution, the modified carbon fiber has excellent high temperature resistance and mechanical properties. As a heat-stable reinforcing agent, it helps to improve the thermal stability and mechanical strength of polyethylene pipes, reduce the decline in mechanical properties of polyethylene pipes due to the addition of inorganic materials, and ensure that polyethylene pipes maintain excellent application performance at high temperatures.

[0016] Optionally, the method for preparing the modified carbon fiber comprises the following steps: S1: Cleaning and drying the carbon fiber to remove surface impurities; S2: soaking the carbon fiber treated in step S1 in a potassium salt solution of fatty alcohol ether phosphate for 1-2 hours, wherein the concentration of the potassium salt solution of fatty alcohol ether phosphate is 1.5-2.5%, filtering the carbon fiber, and drying the solution at 100-110° C. for 2-4 hours to obtain the carbon fiber.

[0017] By adopting the above technical scheme, the immersion treatment of the fatty alcohol ether phosphate potassium salt solution can effectively improve the surface properties of the carbon fiber, reduce the agglomeration of the carbon fiber, and enhance the bonding ability of the carbon fiber with the polyethylene matrix and the dispersibility in the matrix.

[0018] In addition, fatty alcohol ether phosphate introduces phosphorus-containing functional groups on the surface of carbon fibers, which may decompose at high temperatures to produce phosphoric acid or other phosphorus-containing compounds, which helps the polymer surface to quickly dehydrate and carbonize to form a carbonized layer, further hindering the spread of flames and enhancing the overall flame retardant effect.

[0019] Optionally, the lubricant is selected from any one or more combinations of calcium stearate, zinc stearate, barium stearate and paraffin.

[0020] By adopting the above technical solution, calcium stearate, zinc stearate, barium stearate and paraffin as lubricants can reduce the friction resistance of raw materials during processing, improve processing fluidity and uniformity. At the same time, they also help to demould the pipe in the mold and reduce defects and defective rates.

[0021] Optionally, the compatibilizer is selected from any one of PP-g-MAH and EAA.

[0022] By adopting the above technical solution, PP-g-MAH and EAA can improve the interface bonding between the polyethylene substrate and other additives, thereby improving the processing performance and overall mechanical properties of the polyethylene pipe.

[0023] In a second aspect, the present application provides a method for preparing a high temperature resistant flame retardant composite HDPE pipe, which adopts the following technical solution: A method for preparing a high temperature resistant flame retardant composite HDPE pipe comprises the following steps: Weigh each raw material according to its weight, heat mix all the raw materials at 100-110°C, and then cold mix at 30-40°C to obtain a blend; The blend is sent into a screw extruder for extrusion molding, and after extrusion through a die, vacuum cooling and sizing are performed to obtain the product.

[0024] By adopting the above technical solution, during the hot mixing process, due to the increase in temperature, the interaction between the raw material particles is enhanced, which helps to evenly disperse various additives and fillers in the matrix resin, and can significantly improve the processing fluidity and uniformity of the material. Cold mixing helps to further ensure that the dispersed mixture remains uniform and prevents re-agglomeration caused by temperature changes. By combining hot mixing and cold mixing and then adding them to the screw extruder for extrusion molding, the mixing cycle can be shortened, production efficiency can be improved, and the overall performance of the polyethylene pipe can be guaranteed.

[0025] Optionally, the processing technology of the screw extruder is: Feeding screw speed 40-60r / min, main screw speed 300-500r / min; The temperature of zones 1 to 3 is 190-220°C, the temperature of zones 4 to 6 is 230-250°C, and the temperature of zones 7 to 9 is 200-230°C.

[0026] In summary, this application has the following beneficial effects: 1. Since the present application adopts a mixture of antimony trioxide with decabromodiphenylethane and brominated polystyrene as a composite flame retardant, brominated diphenylethane and brominated polystyrene decompose upon heating to release hydrogen halide and halogen elements, which can react with antimony trioxide to further produce antimony trihalide, antimony oxyhalide and inert gas. Antimony trihalide can further react with polymer to promote the formation of carbon layer, effectively interfering with the reaction of the combustion chain and significantly improving the flame retardancy of the material.

[0027] 2. In this application, talcum powder and nano-activated calcium carbonate are preferably used as fillers, which can improve the dispersion uniformity between the overall raw materials, and at the same time help to maintain the size and structural stability of the polyethylene pipe at high temperature, and improve the high temperature resistance of the polyethylene pipe.

[0028] 3. This application uses modified carbon fibers that have been surface-treated with potassium salt of fatty alcohol ether phosphate. On the one hand, it can effectively improve the dispersion uniformity of carbon fibers in the polyethylene matrix, ensuring the high temperature resistance and overall mechanical properties of the polyethylene pipe. On the other hand, it introduces phosphorus-containing functional groups, which may produce phosphoric acid or other phosphorus-containing compounds at high temperatures, promoting the rapid dehydration of the polymer surface into carbon, further enhancing the flame retardant effect. DETAILED DESCRIPTION

[0029] The following examples further illustrate the present application in detail. raw material

[0030] Unless otherwise specified, the raw materials used in the examples and comparative examples of this application are all commercially available products, specifically: Polyethylene, selected from PetroChina Dushanzi, HDPE DMDA-8008H; Decabromodiphenylethane, selected from Shandong Maofa, MF-11-13; Brominated polystyrene, selected from Delun New Materials, XZ-6700; Talc, selected from Guanting, GT-123; Nano-active calcium carbonate, selected from Leifu, LF-NMG, 15000 mesh; Carbon fiber, single fiber diameter is 7-10μm, aspect ratio is 1:(50-100); Fatty alcohol ether phosphate potassium salt, selected from Jienuo Chemical, NP-10PK-80; Paraffin wax, selected from Qilin Chemical, 58#; PP-g-MAH, selected from DowDuPont, 50E806; EAA, selected from DowDuPont, A560. Preparation example of modified carbon fiber

[0031] Preparation Example 1 Modified carbon fiber and its preparation method, comprising the following steps: S1: Place the carbon fiber in a Soxhlet extractor, extract with acetone solution for 1.5 hours to remove organic impurities on the surface of the carbon fiber, then wash with deionized water for 3 times, and then dry in an oven at 80°C for 2 hours; S2: The carbon fiber treated in step S1 is immersed in a potassium salt of fatty alcohol ether phosphate solution at a solid-liquid ratio of 1:80 for 1 hour, the concentration of the potassium salt of fatty alcohol ether phosphate solution is 1.5%, and then filtered and dried in an oven at 100° C. for 4 hours to obtain the carbon fiber.

[0032] Preparation Example 2 Modified carbon fiber and its preparation method, comprising the following steps: S1: Place the carbon fiber in a Soxhlet extractor, extract with acetone solution for 1.5 hours to remove organic impurities on the surface of the carbon fiber, then wash with deionized water for 3 times, and then dry in an oven at 80°C for 2 hours; S2: The carbon fiber treated in step S1 is immersed in a potassium salt of fatty alcohol ether phosphate solution at a solid-liquid ratio of 1:80 for 1.5 hours, the concentration of the potassium salt of fatty alcohol ether phosphate solution is 2%, and then filtered and dried in an oven at 100° C. for 3 hours to obtain the carbon fiber.

[0033] Preparation Example 3 Modified carbon fiber and its preparation method, comprising the following steps: S1: Place the carbon fiber in a Soxhlet extractor, extract with acetone solution for 1.5 hours to remove organic impurities on the surface of the carbon fiber, then wash with deionized water for 3 times, and then dry in an oven at 80°C for 2 hours; S2: The carbon fiber treated in step S1 is immersed in a potassium salt of fatty alcohol ether phosphate solution at a solid-liquid ratio of 1:80 for 2 hours, wherein the concentration of the potassium salt of fatty alcohol ether phosphate solution is 2.5%. After filtering, the carbon fiber is dried in an oven at 110° C. for 2 hours to obtain the carbon fiber.

[0034] Preparation Example 4 Modified carbon fiber and its preparation method, comprising the following steps: The carbon fiber was placed in a Soxhlet extractor and extracted with acetone solution for 1.5 hours to remove organic impurities on the surface of the carbon fiber. The carbon fiber was then washed with deionized water for three times and then dried in an oven at 80°C for 2 hours. Example Example 1

[0035] A high temperature resistant flame retardant composite HDPE pipe, the raw materials and amounts are shown in Table 1, wherein the lubricant is calcium stearate, the filler is nano-activated calcium carbonate, the heat-stable reinforcing agent is the modified carbon fiber obtained in Preparation Example 1, and the compatibilizer is PP-g-MAH; Table 1

[0036] The method for preparing the high temperature resistant flame retardant composite HDPE pipe comprises the following steps: S1: Weigh each raw material according to its weight, heat-mix all the raw materials in a hot mixer at 100° C., and then cold-mix them in a cold mixer at 25° C. to obtain a blend; S2: The blend is fed into a screw extruder for extrusion molding, the speed of the feeding screw is set to 50r / min, the speed of the main screw is set to 500r / min, the temperature of the first to third zones is 190°C, the temperature of the fourth to sixth zones is 230°C, and the temperature of the seventh to ninth zones is 200°C. After extrusion through a mold, the blend is vacuum cooled and sized. Example 2

[0037] A high temperature resistant flame retardant composite HDPE pipe, which is different from Example 1 in that the raw materials and amounts are as shown in Table 1, wherein the lubricant is zinc stearate; The method for preparing the high temperature resistant flame retardant composite HDPE pipe comprises the following steps: S1: Weigh each raw material according to its weight, heat-mix all the raw materials in a hot mixer at 110° C., and then cold-mix them in a cold mixer at 35° C. to obtain a blend; S2: The blend is fed into a screw extruder for extrusion molding, the feed screw speed is set to 50r / min, the main screw speed is set to 400r / min, the temperature of the first to third zones is 200°C, the temperature of the fourth to sixth zones is 230°C, and the temperature of the seventh to ninth zones is 200°C. After extrusion through a mold, the blend is vacuum cooled and sized to obtain. Example 3

[0038] A high temperature resistant flame retardant composite HDPE pipe, which is different from Example 1 in that the raw materials and amounts are as shown in Table 1, wherein the lubricant is barium stearate and the compatibilizer is EAA; The method for preparing the high temperature resistant flame retardant composite HDPE pipe comprises the following steps: S1: Weigh each raw material according to its weight, heat-mix all the raw materials in a hot mixer at 100° C., and then cold-mix them in a cold mixer at 30° C. to obtain a blend; S2: The blend is fed into a screw extruder for extrusion molding, the feed screw speed is set to 60r / min, the main screw speed is set to 500r / min, the temperature of the first to third zones is 220°C, the temperature of the fourth to sixth zones is 250°C, and the temperature of the seventh to ninth zones is 230°C. After extrusion through a mold, vacuum cooling is performed to determine the size. Example 4

[0039] A high temperature resistant flame retardant composite HDPE pipe, which is different from Example 1 in that the raw materials and amounts are as shown in Table 1, wherein the lubricant is paraffin; The method for preparing the high temperature resistant flame retardant composite HDPE pipe comprises the following steps: S1: Weigh each raw material according to its weight, heat-mix all the raw materials in a hot mixer at 110° C., and then cold-mix them in a cold mixer at 30° C. to obtain a blend; S2: The blend is fed into a screw extruder for extrusion molding, the feed screw speed is set to 40r / min, the main screw speed is set to 300r / min, the temperature of the first to third zones is 200°C, the temperature of the fourth to sixth zones is 240°C, and the temperature of the seventh to ninth zones is 210°C. After extrusion through a mold, vacuum cooling is performed to determine the size. Example 5

[0040] A high temperature resistant flame retardant composite HDPE pipe, which is different from Example 1 in that the heat stable reinforcing agent in the raw material is the modified carbon fiber obtained in Preparation Example 2, and the other steps are the same as Example 1. Example 6

[0041] A high temperature resistant flame retardant composite HDPE pipe, which differs from Example 1 in that the heat stable reinforcing agent in the raw material is the modified carbon fiber obtained in Preparation Example 3, and the other steps are the same as Example 1. Example 7

[0042] A high temperature resistant flame retardant composite HDPE pipe, which is different from Example 1 in that the filler in the raw material is talcum powder, and the other steps are the same as Example 1. Example 8

[0043] A high temperature resistant flame retardant composite HDPE pipe, which differs from Example 1 in that the filler in the raw material is talcum powder and nano-activated calcium carbonate in a mass ratio of 1:1, and the other steps are the same as Example 1. Example 9

[0044] A high temperature resistant flame retardant composite HDPE pipe, which differs from Example 1 in that the filler in the raw material is talcum powder and nano-activated calcium carbonate in a mass ratio of 1:2, and the other steps are the same as Example 1. Example 10

[0045] A high temperature resistant flame retardant composite HDPE pipe, which differs from Example 1 in that the filler in the raw material is talcum powder and nano-activated calcium carbonate in a mass ratio of 1:3, and the other steps are the same as Example 1. Embodiment 11

[0046] A high temperature resistant flame retardant composite HDPE pipe, which is different from Example 1 in that the heat stable reinforcing agent in the raw material is the modified carbon fiber obtained in Preparation Example 4, and the other steps are the same as Example 1. Example 12

[0047] A high temperature resistant flame retardant composite HDPE pipe, which is different from Example 1 in that the heat stable reinforcing agent in the raw material is a heat stabilizer, dibutyltin dilaurate, and the other steps are the same as Example 1. Comparative Example

[0048] Comparative Example 1 A high temperature resistant flame retardant composite HDPE pipe, which differs from Example 1 in that decabromodiphenylethane and brominated polystyrene of the original composite flame retardant in the raw materials are replaced by antimony trioxide of equal mass, and other steps are the same as Example 1.

[0049] Comparative Example 2 A high temperature resistant flame retardant composite HDPE pipe, which differs from Example 1 in that antimony trioxide of the original composite flame retardant in the raw material is replaced by decabromodiphenylethane of equal mass, and other steps are the same as Example 1.

[0050] Comparative Example 3 A high temperature resistant flame retardant composite HDPE pipe, which differs from Example 1 in that decabromodiphenylethane of the original composite flame retardant in the raw material is replaced by brominated polystyrene of equal mass, and other steps are the same as Example 1.

[0051] Comparative Example 4 A high temperature resistant flame retardant composite HDPE pipe, which differs from Example 1 in that the brominated polystyrene of the original composite flame retardant in the raw material is replaced by decabromodiphenylethane of equal mass, and the other steps are the same as Example 1. Performance testing

[0052] The high temperature resistant flame retardant composite HDPE pipes obtained in Examples 1-12 and Comparative Examples 1-4 were subjected to the following relevant performance test tests, each group of tests was tested 3 times, and the average value of the test results of the 3 tests was taken as the final result, and the final result was recorded in Table 2.

[0053] 1. Combustion performance: According to the provisions of GB 8624-2012, the high temperature resistant flame retardant composite HDPE pipes obtained in Examples 1-12 and Comparative Examples 1-4 were tested for combustion growth rate index, total heat release within 600 seconds and flame tip height within 60 seconds. At the same time, the lateral spread of the flame and whether there was any burning material dripping and igniting the filter paper were observed, and the flame retardant grade of the product was judged.

[0054] 2. Mechanical properties: According to the provisions of GB / T 8804.2-2016, the tensile strength of the high temperature resistant flame retardant composite HDPE pipes obtained in Examples 1-12 and Comparative Examples 1-4 was tested.

[0055] Table 2

[0056] During the above-mentioned related performance test, the flames of the high temperature resistant flame retardant composite HDPE pipes obtained in Examples 1-12 and Comparative Examples 1-4 did not spread horizontally to the edge of the long wing of the sample, and no burning drips ignited the filter paper within 60 seconds. This shows that the above-mentioned high temperature resistant flame retardant composite HDPE pipes have basic flame retardant ability, can prevent the horizontal spread of flames, and the drips generated during combustion are not easy to ignite.

[0057] According to the performance test results in Table 2, it can be seen that the high temperature resistant flame retardant composite HDPE pipe of the present application has good high temperature resistance and combustion inhibition ability, can achieve excellent flame retardant ability without sacrificing the physical properties of the polyethylene pipe itself, and can meet the safety and flame retardant and high temperature resistance standard requirements for application in wires and cables.

[0058] It can be seen from the performance test results of Examples 1-4 and Comparative Examples 1-4 that, under the raw material ratio of the present application, the use of antimony trioxide mixed with decabromodiphenylethane and brominated polystyrene as a composite flame retardant has a more significant effect on improving the flame retardant properties of polyethylene pipes compared to a single antimony trioxide or a single organic flame retardant.

[0059] According to the performance test results of Examples 1-6 and Examples 7-10, it can be seen that talcum powder and nano-activated calcium carbonate both have good high temperature resistance. When used in conjunction, the two can further enhance the dispersion stability of the polyethylene pipe raw material, enhance the flame retardant effect, ensure that the polyethylene pipe has good mechanical properties, and maintain the stability of the material structure.

[0060] According to the performance test results of Examples 1-4 and Examples 11-12, it can be seen that compared with traditional high-temperature resistant additives, the modified carbon fiber can not only promote the polyethylene pipe to ensure good high-temperature resistance and flame retardancy, but also improve the mechanical properties of the polyethylene pipe and reduce the influence of the use of other additives such as fillers on the physical properties of the polyethylene pipe.

[0061] In Example 11, the modified carbon fiber was not soaked in a solution of potassium salt of fatty alcohol ether phosphate, and the final flame retardant properties and mechanical properties were reduced. This may be due to the decrease in the uniformity of the dispersion of the modified carbon fiber, resulting in weak binding force and dispersibility of the modified carbon fiber in the polyethylene matrix. On the other hand, it may be due to the lack of fatty alcohol ether phosphate salts, and phosphorus-containing functional groups cannot be introduced into the raw materials of the polyethylene pipe. The introduction of phosphorus-containing functional groups may decompose at high temperatures to produce phosphoric acid or other phosphorus-containing compounds, which will cause the polymer surface to quickly dehydrate and carbonize to form a carbonized layer, further hindering the spread of flames and improving the overall flame retardant effect.

[0062] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A high temperature resistant flame retardant composite HDPE pipe, characterized in that: According to weight, the raw materials include 40-45 parts of polyethylene, 0.5-1 parts of lubricant, 6-7.6 parts of filler, 2.4-4 parts of composite flame retardant, 1-3 parts of heat-stable reinforcing agent and 1.5-2.5 parts of compatibilizer; The composite flame retardant comprises decabromodiphenylethane, antimony trioxide and brominated polystyrene in a ratio of (3-5):(1-2):(0.4-1); and the filler is calcium carbonate.

2. The high temperature resistant flame retardant composite HDPE pipe according to claim 1, characterized in that: The calcium carbonate is talcum powder and nano-active calcium carbonate in a mass ratio of (1-3):

1.

3. The high temperature resistant flame retardant composite HDPE pipe according to claim 1, characterized in that: The heat-stable reinforcing agent is modified carbon fiber.

4. The high temperature resistant flame retardant composite HDPE pipe according to claim 3, characterized in that: The method for preparing the modified carbon fiber comprises the following steps: S1: Cleaning and drying the carbon fiber to remove surface impurities; S2: soaking the carbon fiber treated in step S1 in a potassium salt solution of fatty alcohol ether phosphate for 1-2 hours, wherein the concentration of the potassium salt solution of fatty alcohol ether phosphate is 1.5-2.5%, filtering the carbon fiber, and drying the solution at 100-110° C. for 2-4 hours to obtain the carbon fiber.

5. The high temperature resistant flame retardant composite HDPE pipe according to claim 1, characterized in that: The lubricant is selected from any one or more combinations of calcium stearate, zinc stearate, barium stearate and paraffin.

6. The high temperature resistant flame retardant composite HDPE pipe according to claim 1, characterized in that: The compatibilizer is selected from any one of PP-g-MAH and EAA.

7. The method for preparing a high temperature resistant flame retardant composite HDPE pipe according to any one of claims 1 to 6, characterized in that: The following steps are involved: Weigh each raw material according to its weight, heat mix all the raw materials at 100-110°C, and then cold mix at 30-40°C to obtain a blend; The blend is sent into a screw extruder for extrusion molding, and after extrusion through a die, vacuum cooling and sizing are performed to obtain the product.

8. The method for preparing the high temperature resistant flame retardant composite HDPE pipe according to claim 7, characterized in that: The processing technology of the screw extruder is: Feeding screw speed 40-60r / min, main screw speed 300-500r / min; The temperature of zones 1 to 3 is 190-220°C, the temperature of zones 4 to 6 is 230-250°C, and the temperature of zones 7 to 9 is 200-230°C.

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