A modified graphene for polyethylene electrofusion fittings or pipes, its preparation method and application

Abstract

The present invention relates to the field of polyethylene electrofusion pipe materials, and particularly to a modified graphene for polyethylene electrofusion fittings or pipes, a preparation method thereof and an application. The preparation method of the modified graphene comprises the following steps: using graphene oxide and 2-bromoisobutyryl bromide as reaction raw materials to carry out a substitution reaction to obtain brominated graphene; using ethylene and 3-buten-1-amine as graft monomers to carry out an ATRP reaction on the brominated graphene to obtain amino-functionalized polyethylene modified graphene; using the amino-functionalized polyethylene modified graphene and 2-bromoisobutyryl bromide as reaction raw materials to carry out a substitution reaction to obtain brominated polyethylene modified graphene; using ethylene as a graft monomer to carry out an ATRP reaction on the brominated polyethylene modified graphene to obtain the modified graphene. The above preparation method can graft polyethylene with a long-chain structure on the graphene, thereby improving the binding force between the graphene and the matrix, and further greatly enhancing the pressure resistance of the pipe.

Description

Technical Field

[0001] The present invention relates to the field of polyethylene electrofusion pipeline materials, and particularly to a modified graphene for polyethylene electrofusion fittings or pipes, a preparation method thereof, and an application thereof. Background Art

[0002] Polyethylene (PE) electrofusion fittings are pre - arranged with resistance wires inside the fittings. The heat generated when the resistance wires are electrified melts the surrounding polyethylene, fusing the outer wall of the pipe with the electrofusion fitting together. After cooling and solidification, an electrofusion joint is formed. Due to its outstanding comprehensive performance advantages, PE electrofusion fittings have been widely used in pipeline transportation and distribution fields such as natural gas and water supply and drainage. However, due to the limitations of the PE material itself, its tensile strength is limited, and it can only be applied to water supply pipes with a pressure of 1.6 MPa and below, and natural gas pipes with a pressure of 0.8 MPa and below, which greatly limits its application range. And to ensure the pressure resistance strength, the wall thickness of its products is very thick, and the material consumption is huge.

[0003] By adding graphene to the PE material, the pressure resistance strength of the pipeline can be improved. However, the compatibility between graphene and polyethylene is poor, and it is easy to appear agglomeration phenomenon, which limits the improvement of the pressure resistance strength of the PE pipeline. Patent CN201910604942.3 discloses a corrosion - resistant polyethylene communication pipe and a preparation method thereof. The communication pipe uses high - density polyethylene as the matrix material and adopts low - molecular - weight polyethylene treated by ozone oxidation to modify the filler In 2 O 3 / CNTs / graphene, so that low - molecular - weight polyethylene can be covalently grafted onto the surface of In 2 O 3 / CNTs / graphene, enabling the filler to better fuse with the high - density polyethylene matrix material and enhancing the bonding force between the two. However, the cross - linking strength that can be formed between linear polyethylene and the matrix material is limited, and it is difficult to greatly improve the pressure resistance strength of the PE pipeline. Summary of the Invention

[0004] In order to solve the technical problem of the low pressure resistance strength of the PE pipeline, the present invention provides a modified graphene for polyethylene electrofusion fittings or pipes, a preparation method thereof, and an application thereof. By using the preparation method of the modified graphene in the present invention, polyethylene with a long - branched chain structure can be grafted onto graphene, thereby improving the bonding force between graphene and the matrix, and further greatly enhancing the pressure resistance strength of the pipeline.

[0005] The specific technical solution of the present invention is as follows:

[0006] In the first aspect, the present invention provides a preparation method of a modified graphene for polyethylene electrofusion fittings or pipes, comprising the following steps:

[0007] (1) Synthesis initiator: Using graphene oxide and 2-bromoisobutyryl bromide as reaction raw materials, a substitution reaction is carried out to obtain brominated graphene;

[0008] (2) Grafting amino-functionalized polyethylene: Using ethylene and 3-buten-1-amine as graft monomers, an atom transfer radical polymerization reaction is carried out on brominated graphene to obtain amino-functionalized polyethylene modified graphene;

[0009] (3) Synthesis initiator: Using amino-functionalized polyethylene modified graphene and 2-bromoisobutyryl bromide as reaction raw materials, a substitution reaction is carried out to obtain brominated polyethylene modified graphene;

[0010] (4) Grafting polyethylene long branches: Using ethylene as a graft monomer, an atom transfer radical polymerization reaction is carried out on brominated polyethylene modified graphene to obtain modified graphene.

[0011] In the above steps, the mechanism for preparing the modified graphene is as follows: In step (1), using the hydroxyl groups in graphene oxide, a substitution reaction occurs with 2-bromoisobutyryl bromide to graft -COC(CH 3 ) 2 Br onto the graphene oxide, forming the initiating active center for atom transfer radical polymerization (ATRP) reaction; in step (2), through the ATRP reaction, ethylene and 3-buten-1-amine are grafted onto the brominated graphene in the form of a copolymer to form the polyethylene main chain, and 3-buten-1-amine can introduce amino groups on its molecular chain for subsequent grafting of long branches; in step (3), 2-bromoisobutyryl bromide undergoes a substitution reaction with the amino groups on the polyethylene main chain, thereby forming multiple initiating active centers for the ATRP reaction on the polyethylene main chain; in step (4), through the ATRP reaction, polyethylene long branches can be synthesized on the polyethylene main chain.

[0012] By using the method of the present invention, the polyethylene grafted on the graphene can have more branches. While improving the compatibility between the graphene and the matrix material of the polyethylene electrofusion fittings or pipes, enabling the modified graphene to be fully dispersed in the matrix, it can also utilize the entanglement between the branches and the matrix molecular chains to enhance the binding force between the two, enabling the graphene to better play the role of improving the mechanical properties of the fittings or pipes, thereby improving the pressure resistance of the pipeline. Moreover, if the length of the branches in the polyethylene is too short, it is difficult to entangle with the matrix molecular chains, and at the same time, it will increase the distance between the main chain and the matrix molecular chains, hindering their crosslinking, resulting in the inability to effectively improve the pressure resistance of the pipeline; while the present invention uses the method of first forming the initiating active center for the ATRP reaction on the polyethylene main chain and then synthesizing polyethylene branches through the ATRP reaction, which is convenient for controlling the branch length and can prevent it from being too short, thereby ensuring that the polyethylene branches can effectively improve the binding force between the graphene and the matrix, and further improving the pressure resistance of the pipeline.

[0013] Preferably, the specific process of step (4) includes the following steps: Under the protection of an inert gas, brominated polyethylene modified graphene, ethylene, reaction solvent D, a catalyst and a ligand are mixed, and an atom transfer radical polymerization reaction is carried out, and the product is separated to obtain modified graphene.

[0014] Furthermore, in step (4): The mass ratio of the brominated graphene, ethylene, catalyst, ligand and reaction solvent D is 1:40-50:1.5-3:3-6:150-200; The temperature of the atom transfer radical polymerization reaction is 90-110 °C, and the time is 4-6 h.

[0015] Preferably, the specific process of step (2) includes the following steps: Under the protection of an inert gas, brominated graphene, ethylene, 3-buten-1-amine, reaction solvent B, a catalyst and a ligand are mixed, and an atom transfer radical polymerization reaction is carried out, and the product is separated to obtain aminoethylated polyethylene modified graphene.

[0016] Furthermore, in step (2): The mass ratio of the brominated graphene, ethylene, 3-buten-1-amine, catalyst, ligand and reaction solvent B is 1:25-30:2.5-3:1-2:2-4:90-100.

[0017] Preferably, in step (2): The temperature of the atom transfer radical polymerization reaction is 90-110 °C. After reacting for 8-10 h, vinyl-terminated polysiloxane is added and the reaction continues for 0.5-1.5 h.

[0018] Graphene has a large specific surface area. After the long-chain polyethylene grafted on its surface forms physical entanglement with the matrix molecular chains of PE electrofusion fittings or pipes, it is easy to cause a decrease in the molecular chain movement performance of the matrix after electrofusion, which is not conducive to the mutual penetration and entanglement of the molecular chains at the interface between the fittings and the pipes. Therefore, the connection strength between the pipe and the pipe is relatively low. For this reason, in the present invention, polysiloxane is grafted onto the main chain end of the long-chain polyethylene. After electrofusion, the polysiloxane can utilize its flexible -Si-O-Si- main chain to play a lubricating role between the polyethylene-grafted modified graphene and the matrix molecular chains, and promote the movement of the matrix molecular chains after electrofusion. Therefore, it is beneficial to improve the connection strength between the fittings and the pipes.

[0019] In addition, due to the relatively poor compatibility between the polysiloxane and the matrix, therefore, in the present invention, grafting the polysiloxane onto the main chain end of the long-chain polyethylene can, while improving the connection strength between the fittings and the pipes, reduce the adverse effect of the polysiloxane on the compatibility between the polyethylene-grafted modified graphene and the matrix, and avoid the polysiloxane from causing too much hindrance to the crosslinking between the polyethylene on the graphene and the matrix molecular chains, thereby ensuring the pressure resistance of the pipeline.

[0020] Furthermore, the mass ratio of the graphene bromide to the vinyl-terminated polysiloxane is 1:10 to 15.

[0021] Preferably, the specific process of step (1) includes the following steps: mixing graphene oxide, triethylamine and reaction solvent A, dispersing evenly, adding 2-bromoisobutyryl bromide, carrying out a substitution reaction, separating the product, and obtaining graphene bromide.

[0022] Furthermore, in step (1): the mass ratio of the graphene oxide, 2-bromoisobutyryl bromide, triethylamine and reaction solvent A is 0.01:0.2 to 0.3:0.1 to 0.2:8 to 12; the temperature of the substitution reaction is 20 to 30 °C, and the time is 5 to 8 h.

[0023] Preferably, the specific process of step (3) includes the following steps: mixing amino-functionalized polyethylene modified graphene, triethylamine and reaction solvent C, dispersing evenly, adding 2-bromoisobutyryl bromide, carrying out a substitution reaction, separating the product, and obtaining graphene bromide.

[0024] Furthermore, in step (3): the mass ratio of the graphene oxide, 2-bromoisobutyryl bromide, triethylamine and reaction solvent C is 0.01:0.4 to 0.6:0.1 to 0.2:8 to 12; the temperature of the substitution reaction is 20 to 30 °C, and the time is 10 to 15 h.

[0025] In a second aspect, the present invention provides a modified graphene prepared by the above preparation method.

[0026] In a third aspect, the present invention provides the application of the modified graphene in polyethylene electrofusion fittings or pipes.

[0027] Preferably, the raw materials of the polyethylene electrofusion fittings or pipes include the following components in parts by weight: 100 parts of high-density polyethylene, 0.5 to 5 parts of the modified graphene, 0 to 3 parts of an antioxidant, and 0 to 1.5 parts of a masterbatch.

[0028] Preferably, the preparation method of the polyethylene electrofusion fittings or pipes includes the following steps:

[0029] S1: Mixing all the raw materials evenly, melting and granulating to obtain a PE mixture;

[0030] S2: Injection molding the PE mixture. When preparing polyethylene electrofusion fittings, a resistance wire connected with an electrode is buried on the inner wall of the fitting during the injection molding process; cooling and shaping to obtain a PE electrofusion fitting or pipe blank;

[0031] S3: After tempering the PE electrofusion fitting or pipe blank to release internal stress, cool it, let it stand to further release internal stress, and then perform precision machining to obtain the polyethylene electrofusion fitting or pipe.

[0032] In step S3, through tempering treatment, the modified graphene and the PE material body can be fully adjusted in the fitting to release the internal stress generated by the injection molding process; then through natural standing for further stress release, stable dimensions and good comprehensive performance can be obtained.

[0033] Further, in step S3, the temperature of the tempering treatment is 80 - 100 °C and the time is 2 - 3 h.

[0034] Further, in step S3, the standing time is 3 - 5 d.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] (1) In the preparation process of the modified graphene of the present invention, by first forming an initiating active center for ATRP reaction on the polyethylene main chain and then synthesizing polyethylene branches through ATRP reaction, polyethylene with long chain branch structure can be grafted onto the graphene, thereby effectively improving the pressure resistance of the pipeline;

[0037] (2) In the preparation process of the modified graphene of the present invention, by grafting polysiloxane at the end of the polyethylene main chain, while ensuring the pressure resistance of the pipeline, the connection strength between the fitting and the pipe can be effectively improved. Specific Embodiments

[0038] The present invention will be further described below in conjunction with embodiments.

[0039] General Embodiment

[0040] A preparation method of modified graphene for polyethylene electrofusion fittings or pipes includes the following steps:

[0041] (1) Synthesize the initiator: Using graphene oxide and 2 - bromoisobutyryl bromide as reaction raw materials, perform a substitution reaction to obtain brominated graphene;

[0042] (2) Graft amino - functionalized polyethylene: Using ethylene and 3 - butene - 1 - amine as graft monomers, perform atom transfer radical polymerization reaction on brominated graphene to obtain amino - functionalized polyethylene modified graphene;

[0043] (3) Synthesize the initiator: Using amino - functionalized polyethylene modified graphene and 2 - bromoisobutyryl bromide as reaction raw materials, perform a substitution reaction to obtain brominated polyethylene modified graphene;

[0044] (4) Grafted polyethylene long branched chains: Using ethylene as the graft monomer, atom transfer radical polymerization reaction is carried out on brominated polyethylene modified graphene to obtain modified graphene.

[0045] As a specific embodiment, the specific process of step (1) includes the following steps: Mix graphene oxide, triethylamine and reaction solvent A, and after dispersing evenly, add 2-bromoisobutyryl bromide. The mass ratio of graphene oxide, 2-bromoisobutyryl bromide, triethylamine and reaction solvent A is 0.01:0.2 - 0.3:0.1 - 0.2:8 - 12. Carry out substitution reaction at 20 - 30 °C for 5 - 8 h, separate the product to obtain brominated graphene.

[0046] As a specific embodiment, the specific process of step (2) includes the following steps: Under the protection of inert gas, mix brominated graphene, ethylene, 3-buten-1-amine, reaction solvent B, catalyst and ligand. The mass ratio of brominated graphene, ethylene, 3-buten-1-amine, catalyst, ligand and reaction solvent B is 1:25 - 30:2.5 - 3:1 - 2:2 - 4:90 - 100. Carry out atom transfer radical polymerization reaction at 90 - 110 °C for 8 - 10 h, separate the product to obtain amino-functionalized polyethylene modified graphene.

[0047] As a specific embodiment, in step (2), after carrying out atom transfer radical polymerization reaction at 90 - 110 °C for 8 - 10 h, add vinyl-terminated polysiloxane and continue to react for 0.5 - 1.5 h. The mass ratio of brominated graphene and vinyl-terminated polysiloxane is 1:10 - 15.

[0048] As a specific embodiment, the specific process of step (3) includes the following steps: Mix amino-functionalized polyethylene modified graphene, triethylamine and reaction solvent C, and after dispersing evenly, add 2-bromoisobutyryl bromide. The mass ratio of graphene oxide, 2-bromoisobutyryl bromide, triethylamine and reaction solvent C is 0.01:0.4 - 0.6:0.1 - 0.2:8 - 12. Carry out substitution reaction at 20 - 30 °C for 10 - 15 h, separate the product to obtain brominated graphene.

[0049] As a specific embodiment, the specific process of step (4) includes the following steps: Under the protection of inert gas, mix brominated polyethylene modified graphene, ethylene, reaction solvent D, catalyst and ligand. The mass ratio of brominated graphene, ethylene, catalyst, ligand and reaction solvent D is 1:40 - 50:1.5 - 3:3 - 6:150 - 200. Carry out atom transfer radical polymerization reaction at 90 - 110 °C for 4 - 6 h, separate the product to obtain modified graphene.

[0050] The application of the above-mentioned modified graphene in polyethylene electrofusion fittings or pipes.

[0051] As a specific embodiment, the raw materials of the polyethylene electrofusion fitting or pipe include the following components in parts by weight: 100 parts of high-density polyethylene, 0.5 - 5 parts of the modified graphene, 0 - 3 parts of antioxidant, and 0 - 1.5 parts of masterbatch.

[0052] As a specific embodiment, the preparation method of the polyethylene electrofusion fitting or pipe includes the following steps:

[0053] S1: After mixing all the raw materials evenly, melt granulation is carried out to obtain a PE mixture.

[0054] S2: The PE mixture is injection molded. When preparing the polyethylene electrofusion fitting, a resistance wire connected with an electrode is buried on the inner wall of the fitting during the injection molding process; after cooling and shaping, a PE electrofusion fitting or pipe blank is obtained.

[0055] S3: The PE electrofusion fitting or pipe blank is subjected to tempering treatment at 80 - 100 °C for 2 - 3 h to release internal stress, then cooled, placed for 3 - 5 d to further release internal stress, and then precision machining is carried out to obtain the polyethylene electrofusion fitting or pipe.

[0056] Preparation Example 1

[0057] The modified graphene is prepared through the following steps:

[0058] (1) By weight, 1 part of graphene oxide, 15 parts of triethylamine, and 1000 parts of toluene are made into a mixed solution. After stirring, ultrasonic dispersion is carried out for 2 h, and then 25 parts of 2-bromoisobutyryl bromide are added dropwise to the mixed solution. The reaction is carried out at room temperature (23 °C) and under ultrasonic for 8 h, followed by vacuum filtration and washing with methanol and water in sequence to obtain brominated graphene.

[0059] (2) By weight, 1 part of brominated graphene, 25 parts of ethylene, 2.5 parts of 3-buten-1-amine, 80 parts of toluene, and 20 parts of DMF are added to a reactor. After replacing the air in the reactor with nitrogen, 1.5 parts of copper chloride and 3 parts of pentamethyldiethylenetriamine (PMDETA) are added, and they are stirred and mixed. The temperature is controlled at 100 ± 2.5 °C, and after stirring and reacting for 10 h, 15 parts of vinyl-terminated poly(dimethylsiloxane) are added, and the stirring reaction continues for 1 h. Then, toluene is added for dilution, followed by vacuum filtration and washing with methanol and water in sequence to obtain amino-functionalized polyethylene modified graphene.

[0060] (3) By weight, 1 part of amino-functionalized polyethylene modified graphene, 15 parts of triethylamine, and 1000 parts of toluene are made into a mixed solution. After stirring, 50 parts of 2-bromoisobutyryl bromide are added dropwise thereto, and the stirring reaction is carried out at room temperature (23 °C) for 12 h, followed by vacuum filtration and washing with methanol and water in sequence to obtain brominated graphene.

[0061] (4) By weight, add 1 part of brominated polyethylene modified graphene, 45 parts of ethylene, and 200 parts of toluene into a reactor. After displacing the air in the reactor with nitrogen, add 1.5 parts of cuprous chloride and 3 parts of PMDETA, stir and mix, control the temperature at 100 ± 2.5 °C, stir and react for 5 h, then add toluene for dilution, perform vacuum filtration, wash successively with methanol and water, and dry to obtain modified graphene.

[0062] Preparation Example 2

[0063] The modified graphene was prepared through the following steps:

[0064] (1) By weight, make a mixed solution of 1 part of graphene oxide, 20 parts of triethylamine, and 1200 parts of toluene. After stirring, perform ultrasonic dispersion for 2 h, then dropwise add 30 parts of 2-bromoisobutyryl bromide into the mixed solution, react at room temperature (23 °C) and under ultrasonic for 5 h, perform vacuum filtration, and wash successively with methanol and water to obtain brominated graphene.

[0065] (2) By weight, add 1 part of brominated graphene, 25 parts of ethylene, 3 parts of 3-buten-1-amine, 70 parts of toluene, and 20 parts of DMF into a reactor. After displacing the air in the reactor with nitrogen, add 2 parts of cuprous chloride and 4 parts of pentamethyldiethylenetriamine (PMDETA), stir and mix, control the temperature at 95 ± 2.5 °C, stir and react for 10 h, then add 10 parts of vinyl-terminated poly(dimethylsiloxane), continue to stir and react for 1.5 h, then add toluene for dilution, perform vacuum filtration, and wash successively with methanol and water to obtain aminoethylated polyethylene modified graphene.

[0066] (3) By weight, make a mixed solution of 1 part of aminoethylated polyethylene modified graphene, 20 parts of triethylamine, and 1200 parts of toluene. After stirring, dropwise add 40 parts of 2-bromoisobutyryl bromide into it, stir and react at room temperature (23 °C) for 15 h, perform vacuum filtration, and wash successively with methanol and water to obtain brominated graphene.

[0067] (4) By weight, add 1 part of brominated polyethylene modified graphene, 40 parts of ethylene, and 150 parts of toluene into a reactor. After displacing the air in the reactor with nitrogen, add 1.5 parts of cuprous chloride and 3 parts of PMDETA, stir and mix, control the temperature at 95 ± 2.5 °C, stir and react for 4 h, then add toluene for dilution, perform vacuum filtration, wash successively with methanol and water, and dry to obtain modified graphene.

[0068] Preparation Example 3

[0069] The modified graphene was prepared through the following steps:

[0070] (1) By weight, 1 part of graphene oxide, 10 parts of triethylamine and 800 parts of toluene are made into a mixed solution. After stirring, it is ultrasonically dispersed for 2 h, and then 20 parts of 2-bromoisobutyryl bromide are added dropwise to the mixed solution. The reaction is carried out at room temperature (23 °C) and under ultrasonic for 8 h, followed by vacuum filtration and washing with methanol and water in sequence to obtain brominated graphene;

[0071] (2) By weight, 1 part of brominated graphene, 30 parts of ethylene, 3 parts of 3-buten-1-amine, 80 parts of toluene and 20 parts of DMF are added to a reactor. After replacing the air in the reactor with nitrogen, 1 part of copper chloride and 2 parts of pentamethyldiethylenetriamine (PMDETA) are added, and they are stirred and mixed. The temperature is controlled at 105 ± 2.5 °C, and after stirring and reacting for 8 h, 15 parts of vinyl-terminated poly(dimethylsiloxane) are added, and the stirring reaction is continued for 0.5 h. Then, it is diluted with toluene, followed by vacuum filtration and washing with methanol and water in sequence to obtain amino-functionalized polyethylene-modified graphene;

[0072] (3) By weight, 1 part of amino-functionalized polyethylene-modified graphene, 10 parts of triethylamine and 800 parts of toluene are made into a mixed solution. After stirring, 60 parts of 2-bromoisobutyryl bromide are added dropwise thereto, and the reaction is stirred at room temperature (23 °C) for 10 h, followed by vacuum filtration and washing with methanol and water in sequence to obtain brominated graphene;

[0073] (4) By weight, 1 part of brominated polyethylene-modified graphene, 50 parts of ethylene and 200 parts of toluene are added to a reactor. After replacing the air in the reactor with nitrogen, 3 parts of copper chloride and 6 parts of PMDETA are added, and they are stirred and mixed. The temperature is controlled at 105 ± 2.5 °C, and the stirring reaction is carried out for 6 h. Then, it is diluted with toluene, followed by vacuum filtration and washing with methanol and water in sequence, and then dried to obtain modified graphene.

[0074] Preparation Example 4

[0075] In this preparation example, polysiloxane is not grafted to the end of the polyethylene main chain. The specific preparation steps of the modified graphene are as follows:

[0076] (1) By weight, 1 part of graphene oxide, 15 parts of triethylamine and 1000 parts of toluene are made into a mixed solution. After stirring, it is ultrasonically dispersed for 2 h, and then 25 parts of 2-bromoisobutyryl bromide are added dropwise to the mixed solution. The reaction is carried out at room temperature (23 °C) and under ultrasonic for 8 h, followed by vacuum filtration and washing with methanol and water in sequence to obtain brominated graphene;

[0077] (2) By weight, add 1 part of graphene bromide, 25 parts of ethylene, 2.5 parts of 3-buten-1-amine, 80 parts of toluene, and 20 parts of DMF into a reactor. After replacing the air in the reactor with nitrogen, add 1.5 parts of cuprous chloride and 3 parts of pentamethyldiethylenetriamine (PMDETA), stir and mix, control the temperature at 100 ± 2.5 °C, stir and react for 10 h, then add toluene for dilution, perform vacuum filtration, and wash successively with methanol and water to obtain amino-functionalized polyethylene-modified graphene;

[0078] (3) By weight, make a mixture of 1 part of amino-functionalized polyethylene-modified graphene, 15 parts of triethylamine, and 1000 parts of toluene. After stirring, add 50 parts of 2-bromoisobutyryl bromide dropwise thereto, stir and react at room temperature (23 °C) for 12 h, perform vacuum filtration, and wash successively with methanol and water to obtain graphene bromide;

[0079] (4) By weight, add 1 part of graphene bromide modified with polyethylene, 45 parts of ethylene, and 200 parts of toluene into a reactor. After replacing the air in the reactor with nitrogen, add 1.5 parts of cuprous chloride and 3 parts of PMDETA, stir and mix, control the temperature at 100 ± 2.5 °C, stir and react for 5 h, then add toluene for dilution, perform vacuum filtration, and wash successively with methanol and water, and dry to obtain modified graphene.

[0080] Preparation Example 5

[0081] In this preparation example, polysiloxane is grafted in the middle of the polyethylene main chain. The specific preparation steps of the modified graphene are as follows:

[0082] (1) By weight, make a mixture of 1 part of graphene oxide, 15 parts of triethylamine, and 1000 parts of toluene. After stirring, perform ultrasonic dispersion for 2 h, and then add 25 parts of 2-bromoisobutyryl bromide dropwise to the mixture. React under ultrasonic condition at room temperature (23 °C) for 8 h, perform vacuum filtration, and wash successively with methanol and water to obtain graphene bromide;

[0083] (2) By weight, add 1 part of graphene bromide, 25 parts of ethylene, 2.5 parts of 3-buten-1-amine, 15 parts of vinyl-terminated poly(dimethylsiloxane), 80 parts of toluene, and 20 parts of DMF into a reactor. After replacing the air in the reactor with nitrogen, add 1.5 parts of cuprous chloride and 3 parts of pentamethyldiethylenetriamine (PMDETA), stir and mix, control the temperature at 100 ± 2.5 °C, stir and react for 11 h, then add toluene for dilution, perform vacuum filtration, and wash successively with methanol and water to obtain amino-functionalized polyethylene-modified graphene;

[0084] (3) By weight, 1 part of amino-functionalized polyethylene-modified graphene, 15 parts of triethylamine, and 1000 parts of toluene are made into a mixed solution. After stirring, 50 parts of 2-bromoisobutyryl bromide are added dropwise thereto, and the mixture is stirred and reacted at room temperature (23 °C) for 12 h, then vacuum filtered and washed successively with methanol and water to obtain brominated graphene;

[0085] (4) By weight, 1 part of brominated polyethylene-modified graphene, 45 parts of ethylene, and 200 parts of toluene are added to a reactor. After replacing the air in the reactor with nitrogen, 1.5 parts of copper chloride and 3 parts of PMDETA are added, and the mixture is stirred and mixed. The temperature is controlled at 100 ± 2.5 °C, and the mixture is stirred and reacted for 5 h. Then, toluene is added for dilution, and the mixture is vacuum filtered and washed successively with methanol and water, and then dried to obtain modified graphene.

[0086] Comparative Preparation Example 1

[0087] In this comparative preparation example, linear polyethylene is grafted onto the surface of graphene, and the specific preparation steps of the modified graphene are as follows:

[0088] (1) By weight, 1 part of graphene oxide, 15 parts of triethylamine, and 1000 parts of toluene are made into a mixed solution. After stirring, it is ultrasonically dispersed for 2 h, and then 25 parts of 2-bromoisobutyryl bromide are added dropwise to the mixed solution. The reaction is carried out at room temperature (23 °C) and under ultrasonic conditions for 8 h, then vacuum filtered and washed successively with methanol and water to obtain brominated graphene;

[0089] (2) By weight, 1 part of brominated graphene, 27.5 parts of ethylene, 100 parts of toluene, and 20 parts of DMF are added to a reactor. After replacing the air in the reactor with nitrogen, 1.5 parts of copper chloride and 3 parts of pentamethyldiethylenetriamine (PMDETA) are added, and the mixture is stirred and mixed. The temperature is controlled at 100 ± 2.5 °C, and the mixture is stirred and reacted for 10 h. Then, 15 parts of vinyl-terminated poly(dimethylsiloxane) are added, and the reaction is continued for 1 h. Then, toluene is added for dilution, and the mixture is vacuum filtered and washed successively with methanol and water to obtain modified graphene.

[0090] Comparative Preparation Example 2

[0091] In this comparative preparation example, short-chain branched polyethylene is grafted onto the surface of graphene, and the specific preparation steps of the modified graphene are as follows:

[0092] (1) By weight, 1 part of graphene oxide, 20 parts of triethylamine, and 1200 parts of toluene are made into a mixed solution. After stirring, it is ultrasonically dispersed for 2 h, and then 30 parts of 2-bromoisobutyryl bromide are added dropwise to the mixed solution. The reaction is carried out at room temperature (23 °C) and under ultrasonic conditions for 5 h, then vacuum filtered and washed successively with methanol and water to obtain brominated graphene;

[0093] (2) By weight, add 1 part of graphene bromide, 25 parts of ethylene, 3 parts of 3-buten-1-amine, 70 parts of toluene, and 20 parts of DMF into a reactor. After displacing the air in the reactor with nitrogen, add 2 parts of cuprous chloride and 4 parts of pentamethyldiethylenetriamine (PMDETA), stir and mix. Control the temperature at 95 ± 2.5 °C, stir and react for 10 h, then add 10 parts of vinyl-terminated poly(dimethylsiloxane), continue to stir and react for 1.5 h, then add toluene for dilution, perform vacuum filtration, and wash successively with methanol and water to obtain amino-functionalized polyethylene-modified graphene;

[0094] (3) By weight, make a mixture of 1 part of amino-functionalized polyethylene-modified graphene, 20 parts of triethylamine, and 1200 parts of toluene. After stirring, add 40 parts of 2-bromoisobutyryl bromide dropwise thereto, stir and react at room temperature (23 °C) for 15 h, perform vacuum filtration, and wash successively with methanol and water to obtain graphene bromide;

[0095] (4) By weight, add 1 part of brominated polyethylene-modified graphene, 40 parts of ethylene, and 150 parts of toluene into a reactor. After displacing the air in the reactor with nitrogen, add 1.5 parts of cuprous chloride and 3 parts of PMDETA, stir and mix. Control the temperature at 95 ± 2.5 °C, stir and react for 1 h, then add toluene for dilution, perform vacuum filtration, and wash successively with methanol and water, and dry to obtain modified graphene.

[0096] Application Examples 1 - 5 and Comparative Application Examples 1 - 2

[0097] Use the modified graphene prepared in Preparation Examples 1 - 5 and Comparative Preparation Examples 1 - 2 respectively to prepare PE electrofusion fittings and pipes. The steps are as follows:

[0098] S1: By weight, stir 100 parts of high-density polyethylene, 3 parts of modified graphene, 1.5 parts of antioxidant 168, and 1.5 parts of titanium dioxide evenly, and then use a granulator to melt and granulate to obtain PE compound;

[0099] S2: Inject the PE compound through an injection molding machine to form a shape, and embed a resistance wire connected to an electrode on the inner wall of the fitting, then cool and shape to obtain the blanks of PE electrofusion fittings and pipes;

[0100] S3: Put the blanks of PE electrofusion fittings and pipes into an oven at 90 ± 10 °C for tempering treatment for 2 - 3 h, cool, and transfer to a warehouse for storage for 3 d to complete the state adjustment;

[0101] S4: Use numerical control processing equipment to precisely process the state-adjusted blanks of PE electrofusion fittings and pipes to obtain the finished products of SDR11 series PE electrofusion fittings and pipes.

[0102] Using a PE electrofusion fitting as a connector, two sections of PE electrofusion pipes are connected by electrofusion welding (welding voltage: 39.5 V, time: 100 s) to form a PE water supply pipeline.

[0103] Application Example 6

[0104] In this application example, the modified graphene (with no polysiloxane grafted to the end of the polyethylene main chain) prepared in Preparation Example 4 is dispersed and added to the PE electrofusion fittings and pipes together with polysiloxane. The specific preparation steps for the PE electrofusion fittings and pipes are as follows:

[0105] S1: By weight, 100 parts of high-density polyethylene, 3 parts of modified graphene, 5 parts of vinyl-terminated poly(dimethylsiloxane), 1.5 parts of antioxidant 168, and 1.5 parts of titanium dioxide are stirred evenly and then melt granulated using a granulator to obtain a PE blend.

[0106] S2: The PE blend is injection molded using an injection molding machine, and a resistance wire connected to an electrode is embedded on the inner wall of the fitting. After cooling and shaping, a blank of the PE electrofusion fitting and pipe is obtained.

[0107] S3: The blanks of the PE electrofusion fittings and pipes are placed in an oven at 90 ± 10 °C for tempering for 2 - 3 h, cooled, and then stored in a warehouse for 3 d to complete the state adjustment.

[0108] S4: Using numerical control processing equipment, the state-adjusted blanks of the PE electrofusion fittings and pipes are precisely processed to obtain finished products of SDR11 series PE electrofusion fittings and pipes.

[0109] Using a PE electrofusion fitting as a connector, two sections of PE electrofusion pipes are connected by electrofusion welding (welding voltage: 39.5 V, time: 100 s) to form a PE water supply pipeline.

[0110] Test Example

[0111] Circumferential tensile tests and burst tests are conducted on the PE water supply pipelines obtained in Application Examples 1 - 6 and Comparative Application Examples 1 - 2 to detect their circumferential tensile strength and burst pressure. The test results are shown in Table 1.

[0112] PE pipe Modified graphene Circumferential tensile strength / MPa Bursting pressure / MPa Application Example 1 Preparation Example 1 86.0 9.8 Application Example 2 Preparation Example 2 85.8 9.2 Application Example 3 Preparation Example 3 84.6 9.1 Application Example 4 Preparation Example 4 71.5 8.0 Application Example 5 Preparation Example 5 64.0 7.3 Application Example 6 Preparation Example 4 73.3 8.2 Comparative Application Example 1 Comparative Preparation Example 1 69.4 7.5 Comparative Application Example 2 Comparative Preparation Example 2 62.9 6.9

[0113] In Application Examples 1 to 3, the method of the present invention is used to graft long-chain branched polyethylene onto graphene. In Comparative Application Example 1, linear polyethylene is used to graft-modify graphene. As can be seen from Table 1, the circumferential tensile strength and burst pressure of the former PE water supply pipe are significantly higher than those of the latter. This is because: in the PE water supply pipe, the long-chain branches on the modified graphene can entangle with the high-density polyethylene molecular chains, improving the bonding force between the two, so that graphene can better play the role of improving the mechanical properties of pipe fittings and pipes, and thus improve the pressure resistance of the pipe.

[0114] Compared with Application Example 2, in Comparative Application Example 2, the reaction time in step (4) is shortened, and the grafted polyethylene branches are shorter. As can be seen from Table 1, the circumferential tensile strength and burst pressure of the former PE water supply pipe are significantly higher than those of the latter. This is because: if the length of the polyethylene branches in the modified graphene is too short, the branches are difficult to entangle with the high-density polyethylene molecular chains, and at the same time, it will increase the distance between the polyethylene main chain and the high-density polyethylene molecular chains, hindering their crosslinking, resulting in the ineffective improvement of the pressure resistance of the pipe.

[0115] Compared with Application Example 1, in Application Example 4, polysiloxane is not grafted at the end of the polyethylene main chain. As can be seen from Table 1, the circumferential tensile strength and burst pressure of the former PE water supply pipe are significantly higher than those of the latter. This is because: graphene has a large specific surface area. After the long-chain branched polyethylene grafted on its surface forms physical entanglement with the high-density polyethylene molecular chains, it is not conducive to the mutual penetration and entanglement of the molecular chains at the interface between the pipe fittings and pipes, so the connection strength between the pipe and the pipe is low, which in turn affects the pressure resistance of the pipe; by grafting polysiloxane at the end of the main chain of the long-chain branched polyethylene, the flexible -Si-O-Si- main chain can play a lubricating role between the modified graphene and the high-density polyethylene molecular chains.

[0116] Compared with Application Example 1, in Application Example 6, the modified graphene and polysiloxane are dispersed and added. As can be seen from Table 1, compared with not adding polysiloxane (Application Example 4), dispersing and adding the modified graphene and polysiloxane (Application Example 6) can improve the circumferential tensile strength and burst pressure of the PE water supply pipe to a certain extent. However, it may be due to the difficulty of specifically playing a lubricating role between the modified graphene and the high-density polyethylene molecular chains, and the improvement effect of Application Example 6 on the strength of the PE water supply pipe is limited and lower than that of Application Example 1.

[0117] In Application Example 1, the polysiloxane was grafted at the end of the polyethylene main chain, while in Application Example 5, it was grafted in the middle of the polyethylene main chain. As can be seen from Table 1, the circumferential tensile strength and burst pressure of the former PE water supply pipe are significantly higher than those of the latter. The reason is as follows: The compatibility between the polysiloxane and the matrix is relatively poor. If it is grafted in the middle of the polyethylene main chain, it will result in poor compatibility between the modified graphene and high-density polyethylene, and it is not conducive to the formation of molecular chain crosslinking between the polyethylene on the modified graphene and high-density polyethylene, thus resulting in a lower pressure resistance of the pipe. However, when the polysiloxane is grafted at the end of the polyethylene main chain, it can reduce the adverse effects of the polysiloxane on the compatibility and the degree of molecular chain crosslinking between the modified graphene and high-density polyethylene.

[0118] In the present invention, the raw materials and equipment used, unless otherwise specified, are common raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.

[0119] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. Preparation method of modified graphene for polyethylene electrofusion pipe fittings or pipes, characterized in that, it includes the following steps: (1) Synthesize initiator: Using graphene oxide and 2-bromoisobutyryl bromide as reaction raw materials, carry out substitution reaction to obtain brominated graphene; (2) Graft amino-functionalized polyethylene: Using ethylene and 3-buten-1-amine as graft monomers, carry out atom transfer radical polymerization reaction on brominated graphene for 8-10 h, then add vinyl-terminated polysiloxane and continue to react for 0.5-1.5 h to obtain amino-functionalized polyethylene modified graphene; (3) Synthesize initiator: Using amino-functionalized polyethylene modified graphene and 2-bromoisobutyryl bromide as reaction raw materials, carry out substitution reaction to obtain brominated polyethylene modified graphene; (4) Graft polyethylene long branches: Using ethylene as graft monomer, carry out atom transfer radical polymerization reaction on brominated polyethylene modified graphene to obtain modified graphene.

2. The preparation method according to claim 1, characterized in that, the specific process of step (4) includes the following steps: Under the protection of inert gas, mix brominated polyethylene modified graphene, ethylene, reaction solvent D, catalyst and ligand, carry out atom transfer radical polymerization reaction, separate the product, and obtain modified graphene.

3. The preparation method according to claim 2, characterized in that, in step (4): The mass ratio of the brominated graphene, ethylene, catalyst, ligand and reaction solvent D is 1:40-50:1.5-3:3-6:150-200; the temperature of the atom transfer radical polymerization reaction is 90-110 °C, and the time is 4-6 h.

4. The preparation method according to claim 1, characterized in that, the specific process of step (2) includes the following steps: Under the protection of inert gas, mix brominated graphene, ethylene, 3-buten-1-amine, reaction solvent B, catalyst and ligand, carry out atom transfer radical polymerization reaction, separate the product, and obtain amino-functionalized polyethylene modified graphene.

5. The preparation method according to claim 1 or 4, characterized in that, in step (2): The temperature of the atom transfer radical polymerization reaction is 90-110 °C.

6. The preparation method according to claim 5, characterized in that, the mass ratio of the brominated graphene and vinyl-terminated polysiloxane is 1:10-15.

7. A modified graphene prepared by the preparation method according to any one of claims 1-6.

8. Application of the modified graphene according to claim 7 in polyethylene electrofusion pipe fittings or pipes.

9. The application according to claim 8, characterized in that, the raw materials of the polyethylene electrofusion pipe fittings or pipes include the following components in parts by weight: 100 parts of high-density polyethylene, 0.5-5 parts of the modified graphene, 0-3 parts of antioxidant, and 0-1.5 parts of masterbatch.

10. The application according to claim 9, characterized in that, the preparation method of the polyethylene electrofusion pipe fittings or pipes includes the following steps: S1: After mixing all raw materials evenly, melt and granulate to obtain PE mixed materials; S2: Inject and mold the PE compounding material. When preparing polyethylene electrofusion pipe fittings, during the injection molding process, embed a resistance wire connected with an electrode on the inner wall of the pipe fitting; cool and shape it to obtain a PE electrofusion pipe fitting or a pipe blank. S3: After performing a tempering treatment on the PE electrofusion pipe fitting or the pipe blank to release the internal stress, cool it, place it to further release the internal stress, and then perform precise machining to obtain the polyethylene electrofusion pipe fitting or the pipe.