A modified graphene oxide and polyethylene modified composite pipe and preparation method

Abstract

The present application relates to the technical field of polyethylene pipes, and in particular to a modified graphene oxide and a polyethylene modified composite pipe and a preparation method thereof. The modified graphene oxide has the following preparation method: S1, respectively preparing equimolar amounts of diethanolamine solution and anhydride solution, mixing and stirring to obtain a polyamide-ester monomer; the anhydride is a mixture of phthalic anhydride and succinic anhydride; S2, using toluene as a water-carrying agent and toluenesulfonic acid as a catalyst, the polyamide-ester monomer obtained in S1 is reacted with propylene glycol to obtain a hyperbranched polyamide-ester; S3, using toluene as a water-carrying agent and toluenesulfonic acid as a catalyst, the hyperbranched polyamide-ester obtained in S2 is reacted with graphene oxide to obtain a modified graphene oxide; the modified graphene oxide has the advantages of reducing the curling rate of graphene oxide in the system and improving the mechanical properties of the polyethylene pipe.

Description

Technical Field

[0001] The present application relates to the technical field of polyethylene pipes, and in particular to a modified graphene oxide and polyethylene modified composite pipe and a preparation method thereof. Background Art

[0002] Plastic pipes include PP, PE, HDPE, etc., among which polyethylene pipes occupy a large proportion in the market. Currently, the commonly used water supply and gas pipes are PE80 and PE100 grades. However, due to the characteristics of PE particles themselves, the pipes have low strength, low impact resistance, poor low temperature resistance, and short service life. Therefore, under the premise of ensuring excellent physical properties, how to improve the mechanical properties of the pipes has become an urgent problem to be solved.

[0003] In the related art, graphene is added to improve the mechanical properties of polyethylene pipes, but graphene is very easy to agglomerate in polyethylene pipes due to strong intermolecular forces. In order to solve the problem of easy agglomeration of graphene, in related studies, graphene is replaced with graphene oxide, and small molecules are loaded on graphene oxide through chemical reactions to increase the molecular gap between graphene and reduce agglomeration. However, although this method increases the molecular gap between graphene, because graphene oxide often carries different groups and groups on both sides through reactions, and graphene oxide is an inorganic material, it has poor compatibility with the polyethylene pipe system, so that graphene oxide cannot be stretched inside the polyethylene pipe and is very easy to curl, resulting in limited ability of graphene oxide to improve the mechanical properties of polyethylene pipes. Summary of the invention

[0004] In order to reduce the curling rate of graphene oxide in the system and improve the mechanical properties of polyethylene pipes, the present application provides a modified graphene oxide and a polyethylene modified composite pipe and a preparation method.

[0005] In a first aspect, the present application provides a modified graphene oxide, using the following technical solution:

[0006] A modified graphene oxide, the preparation method of which is as follows:

[0007] S1, respectively preparing equimolar amounts of a diethanolamine solution and an acid anhydride solution, mixing them under an inert gas atmosphere, and stirring to react to obtain a polyamide-ester monomer; the acid anhydride is a mixture of phthalic anhydride and succinic anhydride, and the phthalic anhydride accounts for 20-60% of the total molar amount of the acid anhydride;

[0008] S2, in an inert gas atmosphere, using toluene as a water carrier and toluenesulfonic acid as a catalyst, the polyamide-ester monomer prepared in S1 is reacted with glycerol at a temperature of 140-160° C. to obtain a hyperbranched polyamide-ester; wherein the molar ratio of glycerol to diethanolamine is (0.8-1.2):150;

[0009] S3. Under an inert gas atmosphere, using toluene as a water-carrying agent and toluenesulfonic acid as a catalyst, the hyperbranched polyamide-ester prepared in S2 and graphene oxide are reacted at a temperature of 145-160° C. to obtain modified graphene oxide; wherein the weight ratio of the hyperbranched polyamide-ester to the graphene oxide is 300:(10-20).

[0010] By adopting the above technical scheme, due to the different number of oxidized groups contained on both sides of graphene oxide, the surface tension on both sides differs greatly. After adding the organic system, it is very easy to cause the phenomenon of rolling, so that the performance of graphene oxide is not as expected. Based on this, the inventor reduces the rolling rate of graphene oxide by modifying graphene oxide. By synthesizing hyperbranched polymers, it is then grafted on the edge of graphene oxide through esterification. Since the hyperbranched polymers are large in volume and dispersed, not only can the distance between graphene oxide molecules be increased, and its dispersibility can be improved, but also the thickness of graphene oxide can be greatly improved, and its carboxyl groups are mostly concentrated at the edges, and its edges are thicker, which can greatly reduce its rolling rate. In addition, when preparing the hyperbranched polymer, the present application adds a benzene ring structure to its molecular structure. The benzene ring structure can enable the hyperbranched polymer to partially attach its branches to the surface of graphene oxide through the action of the electron cloud. The molecular force between the polyamide segment structure and the graphene oxide further strengthens the attachment effect, and can form a stronger barrier effect between the molecules of the graphene oxide, greatly reducing the van der Waals force between the molecules, so that the hyperbranched polymer can be stretched during application and is not easy to curl.

[0011] In the second aspect, the present application provides a polyethylene modified composite pipe, which adopts the following technical solution:

[0012] A polyethylene modified composite pipe comprises the following raw materials in percentage by weight: 5-7% star-shaped SBS, 0.1-0.5% modified graphene oxide, 2-3.5% stabilizer, 1-2.5% surfactant, 3-5% flame retardant, 10-12% compatibilizer, 2-3.5% curing agent, and the balance is high-density polyethylene; the modified graphene oxide is prepared by the preparation method of the modified graphene oxide.

[0013] By adopting the above technical solution, the toughness of the simple SBS modified PE pipe is improved, but its mechanical strength is insufficient. By applying modified graphene oxide to polyethylene pipes, its mechanical properties can be improved, so that it has greater application potential. The inventors also found through experiments that the modified graphene oxide and star-shaped SBS are used as pipe raw materials together, and its mechanical properties are greatly improved compared with conventional linear SBS. This may be due to the fact that there are multiple styrene side chains in the star-shaped SBS molecule, and the side chain benzene ring of the star-shaped SBS participates in the electron cloud effect of the hyperbranched polymer, so that the graphene can be stably attached to the side chain, further reducing the curling rate, and based on the steric hindrance of the star-shaped molecular chain structure, the dispersion of the modified graphene is further improved, so that the modified graphene can achieve a more stable and dispersed state in the system based on attachment and steric hindrance, and the prepared pipe has a more uniform and excellent mechanical strength.

[0014] Preferably, the added amount of the modified graphene oxide is 0.4%.

[0015] By adopting the above technical solution, when the amount of modified graphene oxide added gradually increases, the tensile strength of the polyethylene modified composite pipe gradually increases, and its elongation at break shows a trend of first increasing and then decreasing. It is speculated that this is because the amount of modified graphene oxide added is too large, and its rigidity performance is strong, which leads to a decrease in the toughness of the polyethylene modified composite pipe. Therefore, its addition amount should not be too large.

[0016] Preferably, when preparing the modified graphene oxide, phthalic anhydride accounts for 40% of the total molar amount of the anhydride.

[0017] By adopting the above technical solution, when the amount of phthalic anhydride added is too large, the modified graphene oxide is likely to agglomerate through intermolecular conjugation. Therefore, the amount of phthalic anhydride added should not be too large.

[0018] Preferably, when preparing the modified graphene oxide, the weight ratio of the hyperbranched polyamide-ester to the graphene oxide is 300:15.

[0019] By adopting the above technical solution, when the amount of hyperbranched polymer added is certain, the more graphene oxide is added, the less sufficient the carboxyl reaction of the modified graphene oxide obtained is, the larger the surface tension on both sides is, and the rolling rate is improved to a certain extent.

[0020] Preferably, the stabilizer is dibutyltin dilaurate.

[0021] By adopting the above technical scheme, the stability of the polyethylene modified composite pipe system can be increased, the reaction can be slowed down, the chemical balance can be maintained, the surface tension of each raw material can be reduced, and the effect of preventing light, thermal decomposition or oxidative decomposition can be played.

[0022] Preferably, the surfactant is one or both of sodium dodecylbenzene sulfonate and sodium dodecyl sulfate.

[0023] By adopting the above technical solution, the addition of surfactants can wrap the particulate matter such as curing agent, flame retardant, modified graphene oxide in the system in the micelles formed by the surfactant, thereby improving their compatibility with the system, thereby improving their dispersibility, and preventing them from precipitation and deposition.

[0024] Preferably, the compatibilizer is maleic anhydride grafted high-density polyethylene.

[0025] By adopting the above technical solution, the compatibility between high-density polyethylene and star-shaped SBS can be effectively increased, so that the two are fully compatible and the reaction time is accelerated.

[0026] Preferably, the curing agent is 1250 mesh heavy calcium.

[0027] By adopting the above technical scheme, the polyethylene modified composite pipe can be made to have the characteristics of high inertness and non-easy chemical reaction. In addition, the heavy calcium itself has high whiteness, is non-toxic, odorless, and has good safety. It can also be used as an inorganic particle to improve the strength of the pipe.

[0028] In a second aspect, the present application provides a method for preparing a polyethylene modified composite pipe, which adopts the following technical solution:

[0029] A method for preparing a polyethylene modified composite pipe comprises the following steps:

[0030] S1. Preheat the star-shaped SBS to 180-190°C and preheat the high-density polyethylene to 120-150°C, then mix the two uniformly to obtain a mixture A;

[0031] S2, adding modified graphene oxide, surfactant, compatibilizer and curing agent to mixture A, performing melt blending, and controlling the temperature at 195-230° C. to obtain mixture B;

[0032] S3, adding a stabilizer and antimony trioxide to the mixture B in sequence, stirring and blending to fully disperse the additives, to obtain a mixture C;

[0033] S4, adding the mixture C into the extruder at an extrusion temperature of 200-230°C, extruding the tube embryo through the extruder die, and performing sizing treatment;

[0034] S6, cold treatment of the tube embryo;

[0035] S7, cutting the cooled tube embryo to obtain a polyethylene modified composite tube.

[0036] By adopting the above technical scheme, the preparation method of the present application is easy to operate, does not require special processes or equipment modifications, has a high pass rate for the prepared products, and is suitable for large-scale production.

[0037] In summary, the present application includes at least one of the following beneficial technical effects:

[0038] Due to the different number of oxidized groups contained on both sides of graphene oxide, the surface tensions on both sides differ greatly. After adding an organic system, it is very easy to cause a rolling phenomenon, which makes the performance of graphene oxide less than expected. Based on this, the inventor reduces the rolling rate of graphene oxide by modifying graphene oxide. By synthesizing a hyperbranched polymer, it is then grafted on the edge of graphene oxide by esterification. Since the hyperbranched polymer is large in volume and dispersed, it can not only increase the distance between graphene oxide molecules, improve its dispersibility, but also greatly improve the thickness of graphene oxide. Its carboxyl groups are mostly concentrated on the edge, and its edge is thicker, which can greatly reduce its rolling rate. And when the application prepares the hyperbranched polymer, a benzene ring structure is added to its molecular structure, and the benzene ring structure can make the hyperbranched polymer act through the electron cloud, and part of the side chain can be attached to the surface of graphene oxide, and a stronger barrier effect can be formed between the molecules of graphene oxide, which greatly reduces the van der Waals force between molecules, so that it can be stretched when applied, and is not easy to curl.

[0039] The present application further reduces the curvature of graphene through the combined effect of specific modified graphene oxide and star-shaped SBS, thereby greatly improving the mechanical strength, mechanical stability and uniformity of the pipe performance.

[0040] 3. The polyethylene modified composite pipe prepared in this application has excellent mechanical properties by adding modified graphene oxide and coordinating the dosage of each raw material in the system. Among them, the elongation at break is between 610-650%, the minimum tensile strength is 31MPa, and the maximum can reach 45MPa; and in actual use, its low temperature resistance far exceeds that of PVC-U and other water supply pipes and gas pipes, and no catalytic and brittle fracture occurs at -50°C. DETAILED DESCRIPTION

[0041] The present application is further described in detail below in conjunction with the specific contents.

[0042] raw material

[0043] The raw materials used in the preparation examples and embodiments of the present application were purchased from the market. Among them, the grade of maleic anhydride grafted high-density polyethylene is Fusabond E100, and the grafting rate is 0.5-1%; the grade of high-density polyethylene is 8008H, the melt flow rate is 8g / 10min, and the flexural elasticity is 37MPa; the processing grade of star-shaped SBS is injection molding grade, the grade is 3411; the linear SBS, the grade is 3546; the thickness of graphene oxide is about 1nm, the number of layers is 1-2, the average diameter of the flakes is 30μm, and the specific surface area is 200m 2 / g, purity>95wt%.

[0044] Preparation Example 1

[0045] A modified graphene oxide, the preparation method of which is as follows:

[0046] S1. Weigh 1.5 mol of diethanolamine, take an appropriate amount of DMAC (N,N-dimethylacetamide) and add it and stir until the diethanolamine is completely dissolved to obtain solution A;

[0047] S2, weighing 1.5 mol of anhydride, which is a mixture of phthalic anhydride and succinic anhydride, wherein the phthalic anhydride accounts for 20% of the total molar amount of the anhydride, and then adding DMAC and stirring to completely dissolve the anhydride to obtain solution B;

[0048] S3, under a nitrogen atmosphere, solution B was added dropwise to solution A at a dropping speed of 1 mL / min, and stirring was performed while dropping. After the dropping was completed, stirring was continued to react for 7 h. After the reaction was completed, the solvent and unreacted monomers were removed by distillation under reduced pressure to obtain a polyamide-ester monomer;

[0049] S4. Under nitrogen atmosphere, add the polyamide-ester prepared in S3 to an appropriate amount of DMAC until the polyamide-ester is completely dissolved, then add 550 mL of toluene as a water carrier, add 1.2 g of toluenesulfonic acid as a catalyst, and stir until dissolved to obtain solution C;

[0050] S5, weighing 0.01 mol of glycerol, adding an appropriate amount of DMAC until the glycerol is completely dissolved, and then dropping it into solution C at a dropping speed of 1 mL / min, and at the same time raising the temperature to 150° C., reflux reacting for 24 h until no liquid drips, and distilling under reduced pressure to remove the solvent and unreacted raw materials to obtain a hyperbranched polyamide-ester;

[0051] S6. Under a nitrogen atmosphere, 300 g of hyperbranched polyamide-ester was dissolved in an appropriate amount of DMAC so that the hyperbranched polyamide-ester was just completely dissolved, and then 600 mL of toluene was added as a water-carrying agent and 1.5 g of p-toluenesulfonic acid was added as a catalyst, and stirred until dissolved to obtain a solution D; 10 g of graphene oxide was dispersed in 50 g of DMAC, and after ultrasonic dispersion, the solution D was heated to 150 ° C, and then the graphene oxide dispersion was added to the solution D in 5 times. After the dropwise addition was completed, the reaction was continued to stir for 15 hours, cooled to room temperature, and then centrifuged at a speed of 2000 r / min, the supernatant was discarded, and the precipitate was washed with DMAC, then washed with ethanol, and dried to obtain modified graphene oxide.

[0052] Preparation Example 2

[0053] A modified graphene oxide, which is different from Preparation Example 1 in that the phthalic anhydride accounts for 40% of the total molar amount of anhydride, and the remaining steps are the same as Preparation Example 1.

[0054] Preparation Example 3

[0055] A modified graphene oxide, which is different from Preparation Example 1 in that the phthalic anhydride accounts for 60% of the total molar amount of anhydride, and the remaining steps are the same as Preparation Example 1.

[0056] Preparation Example 4

[0057] A modified graphene oxide, which is different from Preparation Example 2 in that the amount of graphene oxide added in S6 is 15g, and the remaining steps are the same as Preparation Example 2.

[0058] Preparation Example 5

[0059] A modified graphene oxide, which is different from Preparation Example 2 in that the amount of graphene oxide added in S6 is 20g, and the remaining steps are the same as Preparation Example 2.

[0060] Examples 1-4

[0061] A polyethylene modified composite pipe, the raw materials and the amounts of the raw materials are shown in Table 1, and the preparation method is as follows:

[0062] S1. Preheat the star-shaped SBS to 185°C and the high-density polyethylene to 135°C, and then mix the two uniformly to obtain a mixture A;

[0063] S2, adding modified graphene oxide, surfactant, compatibilizer and curing agent to mixture A, performing melt blending, and controlling the temperature at 200° C. to obtain mixture B;

[0064] S3, adding stabilizer and flame retardant to mixture B in sequence, stirring and blending to fully disperse the additives, to obtain mixture C;

[0065] S4, adding the mixture C into the extruder, the extrusion temperature is 210°C, and the tube embryo is extruded through the extruder mold for sizing treatment;

[0066] S6, cold treatment of the tube embryo;

[0067] S7, cutting the cooled tube embryo to obtain a polyethylene modified composite tube.

[0068] Among them, the modified graphene oxide comes from Preparation Example 1; the surfactant is sodium dodecyl sulfate; the stabilizer is dibutyltin dilaurate; the flame retardant is antimony trioxide; the curing agent is 1250 mesh heavy calcium; and the compatibilizer is maleic anhydride grafted high-density polyethylene.

[0069] Table 1 Raw materials and amounts of raw materials used in Examples 1-4 (g)

[0070] Example 5

[0071] A polyethylene modified composite pipe, which is different from Example 4 in that its modified graphene oxide comes from Preparation Example 2, and the remaining steps are the same as Example 4. Example 6

[0072] A polyethylene modified composite pipe, which is different from Example 4 in that its modified graphene oxide comes from Preparation Example 3, and the remaining steps are the same as Example 4. Example 7

[0073] A polyethylene modified composite pipe, which is different from Example 4 in that its modified graphene oxide comes from Preparation Example 4, and the remaining steps are the same as Example 4. Example 8

[0074] A polyethylene modified composite pipe, which is different from Example 4 in that its modified graphene oxide comes from Preparation Example 5, and the remaining steps are the same as Example 4. Example 9

[0075] A polyethylene modified composite pipe, which is different from Example 7 in that the amount of modified graphene oxide added is 0.001 kg, and the remaining steps are the same as Example 7. Example 10

[0076] A polyethylene modified composite pipe, which is different from Example 7 in that the amount of modified graphene oxide added is 0.003 kg, and the remaining steps are the same as Example 7. Embodiment 11

[0077] A polyethylene modified composite pipe, which is different from Example 7 in that the added amount of modified graphene oxide is 0.005 kg, and the remaining steps are the same as Example 7. Example 12

[0078] A polyethylene modified composite pipe, which is different from Example 7 in that linear SBS replaces star-shaped SBS in equal amounts, and the remaining steps are the same as Example 7.

[0079] Comparative Example 1

[0080] A polyethylene modified composite pipe, which is different from Example 4 in that its modified graphene oxide is replaced by unmodified graphene oxide of equal mass, and the remaining steps are the same as Example 4.

[0081] Comparative Example 2

[0082] A polyethylene modified composite pipe is different from Example 4 in that when preparing its modified graphene oxide, the amount of graphene oxide added in S6 is 25g, and the remaining steps are the same as Example 4.

[0083] Performance testing

[0084] Detection method / test method

[0085] Polyethylene modified composite pipes were prepared according to the preparation methods of Examples 1-12 and Comparative Examples 1-2, and then tested according to the following testing methods. The test results are shown in Table 2.

[0086] Tensile strength and elongation at break: Tested in accordance with the test standard of GB / T 8804-2003 "Test of tensile properties of thermoplastic pipes Part 3: Polyolefin pipes", the elongation at break standard requirement is ≥350%, and the tensile strength standard requirement is ≥16MPa;

[0087] Longitudinal shrinkage rate: tested according to the test method in GB / T6671-2001, the standard requirement is ≤3%.

[0088] Table 2 Test results of Examples 1-12 and Comparative Examples 1-2

[0089]

[0090] Through testing, the oxidation induction time of Examples 1-11 is between 1.4-1.8h, while the standard requires ≥20min.

[0091] It can be seen from Examples 1-11 and Comparative Examples 1-3, as well as the test data in Table 2, that the polyethylene modified composite pipe prepared in the present application by adding modified graphene oxide and coordinating the amounts of various raw materials in the system has excellent mechanical properties, wherein the elongation at break is between 610-650%, the tensile strength is as low as 31 MPa and as high as 45 MPa; and in actual use, its low temperature resistance far exceeds that of water supply pipes and gas pipes such as PVC-U, and no catalytic and brittle fracture occurs at -50°C.

[0092] Due to the different number of oxidized groups contained on both sides of graphene oxide, the surface tensions on both sides differ greatly. After adding the system, it is very easy to cause the phenomenon of rolling, which makes the addition effect of graphene oxide less than expected. Based on this, the inventor reduces the rolling rate of graphene oxide by modifying graphene oxide. By synthesizing hyperbranched polymers, it is then grafted on the edge of graphene oxide by esterification. Because the hyperbranched polymers are large in volume and dispersed, not only the distance between graphene oxide molecules can be increased, and its dispersibility can be improved, but also the thickness of graphene oxide can be greatly improved, and its carboxyl groups are mostly concentrated on the edge, and its edge is thicker, which can greatly reduce its rolling rate. And when the application prepares the hyperbranched polymer, a benzene ring structure is added to its molecular structure, and the benzene ring structure can make the hyperbranched polymer act through the electron cloud, and part of the side chains can be attached to the surface of graphene oxide, so that the compatibility between graphene oxide and the system is higher. After adding it to the polyethylene pipe, it can be stretched in the system, and the mechanical properties of the pipe can be greatly improved; and by controlling its amount, it can form a cross-linked structure with the maleic anhydride grafted high-density polyethylene, star-shaped SBS, etc. in the system through the effects of electron cloud, hydrogen bonding, etc., which can further improve the mechanical properties of the pipe. This can be verified by the test data of Examples 1-4 and Comparative Example 1. Combined with the test data of Examples 4-6, when the amount of phthalic anhydride added is too large, it is easy to cause the modified graphene oxide to agglomerate through intermolecular conjugation, so its addition amount should not be too large.

[0093] It can be seen from the test data of Example 4, Examples 7-8, and Comparative Example 2 that when the modified graphene oxide is prepared, when the amount of hyperbranched polymer added is constant, the more graphene oxide is added, the less sufficient the carboxyl reaction of the modified graphene oxide is, the larger the surface tension on both sides, and the curling rate is improved to a certain extent.

[0094] Through Examples 7 and 9-11, when the amount of modified graphene oxide added gradually increases, the tensile strength of the polyethylene modified composite pipe gradually increases, and its elongation at break shows a trend of first increasing and then decreasing. It is speculated that this is because the amount of modified graphene oxide added is too large, and its rigidity performance is strong, resulting in a decrease in the toughness of the polyethylene modified composite pipe.

[0095] It can be seen from the test data of Example 7 and Example 12 that the mechanical properties are greatly improved by using star-shaped SBS and modified graphene oxide together.

[0096] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A polyethylene modified composite pipe, characterized in that: The invention comprises the following raw materials in percentage by weight: 5-7% star-shaped SBS, 0.1-0.5% modified graphene oxide, 2-3.5% stabilizer, 1-2.5% surfactant, 3-5% flame retardant, 10-12% compatibilizer, 2-3.5% curing agent, and the balance is high-density polyethylene; the preparation method of the modified graphene oxide is as follows: S1, respectively preparing equimolar amounts of a diethanolamine solution and an acid anhydride solution, mixing them under an inert gas atmosphere, and stirring to react to obtain a polyamide-ester monomer; the acid anhydride is a mixture of phthalic anhydride and succinic anhydride, and the phthalic anhydride accounts for 20-60% of the total molar amount of the acid anhydride; S2, in an inert gas atmosphere, using toluene as a water carrier and toluenesulfonic acid as a catalyst, the polyamide-ester monomer prepared in S1 is reacted with glycerol at a temperature of 140-160° C. to obtain a hyperbranched polyamide-ester; wherein the molar ratio of glycerol to diethanolamine is (0.8-1.2):150; S3, under an inert gas atmosphere, using toluene as a water-carrying agent and toluenesulfonic acid as a catalyst, the hyperbranched polyamide-ester prepared in S2 and graphene oxide are reacted at a temperature of 145-160° C. to obtain modified graphene oxide; wherein the weight ratio of the hyperbranched polyamide-ester to the graphene oxide is 300:(10-20); When the modified graphene oxide is prepared, phthalic anhydride accounts for 40% of the total molar amount of the anhydride; When the modified graphene oxide is prepared, the weight ratio of the hyperbranched polyamide-ester to the graphene oxide is 300:

15.

2. A polyethylene modified composite pipe according to claim 1, characterized in that: The added amount of the modified graphene oxide is 0.4%.

3. The polyethylene modified composite pipe according to claim 1, characterized in that: The stabilizer is dibutyltin dilaurate.

4. The polyethylene modified composite pipe according to claim 1, characterized in that: The surfactant is one or both of sodium dodecylbenzene sulfonate and sodium dodecyl sulfate.

5. The polyethylene modified composite pipe according to claim 1, characterized in that: The compatibilizer is maleic anhydride grafted high-density polyethylene.

6. The polyethylene modified composite pipe according to claim 1, characterized in that: The curing agent is 1250 mesh heavy calcium.

7. A method for preparing the polyethylene modified composite pipe according to any one of claims 1 to 6, characterized in that: It includes the following steps: S1. Preheat the star-shaped SBS to 180-190°C and preheat the high-density polyethylene to 120-150°C, then mix the two uniformly to obtain a mixture A; S2, adding modified graphene oxide, surfactant, compatibilizer and curing agent to mixture A, performing melt blending, and controlling the temperature at 195-230° C. to obtain mixture B; S3, adding stabilizer and flame retardant to mixture B in sequence, stirring and blending to fully disperse the additives, to obtain mixture C; S4, adding the mixture C into the extruder at an extrusion temperature of 200-230°C, extruding the tube embryo through the extruder die, and performing sizing treatment; S6, cold treatment of the tube embryo; S7, cutting the cooled tube embryo to obtain a polyethylene modified composite tube.

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