Preparation method of polyethylene gas pipe

Abstract

The invention discloses a preparation method of a high-performance polyethylene gas pipe, and belongs to the field of polyethylene gas pipe manufacturing. A core-shell structure topological entanglement polymer directly grows on the surface of a polyvinyl base material particle through an in-situ interfacial polymerization technology, a flexible highly-branched core layer is responsible for stress dispersion, a shell layer with a reactive functional group is used for subsequent compatibilization, and then serial melting reactive extrusion is carried out, so that the core-shell structure topological entanglement polymer is obtained. The preparation method comprises the following steps: carrying out in-situ reaction on a main toughening agent POE-g-GMA and an active functional group generated after deprotection of a topological entanglement polymer to form a PE-entanglement agent-POE chemical compatibilization structure, and finally carrying out pipe extrusion molding and online microwave heat treatment to promote post-curing and chain segment rearrangement. According to the invention, the problems of interfacial compatibility and dispersity of a multiphase system are fundamentally solved, molecular-level compounding is realized, and the prepared gas pipe has ultrahigh toughness, excellent crack propagation resistance and good long-term durability.

Description

Technical Field

[0001] This invention relates to the field of polyethylene gas pipe manufacturing, specifically to a method for preparing a polyethylene gas pipe. Background Technology

[0002] Polyethylene (PE) gas pipes, especially PE100 grade pipes, are widely used in urban gas transmission due to their excellent comprehensive performance. However, as pipeline networks develop towards high pressure and large diameter, the inherent inadequacy of traditional PE pipes in terms of resistance to slow crack growth (SCG) and rapid crack propagation (RCP) has become increasingly prominent, becoming a key bottleneck restricting their safety, reliability, and service life.

[0003] To improve toughness, the industry currently relies primarily on physical blending techniques, which involve melt blending polyethylene (PE) with elastomer toughening agents (such as POE). However, this method has fundamental drawbacks. Poor interfacial compatibility between PE and non-polar elastomers leads to weak interfacial bonding, making them prone to stress concentration points and crack initiation. Simultaneously, achieving uniform nanoscale dispersion of the elastomer within the matrix is ​​difficult, resulting in agglomeration and uneven material properties. Furthermore, pre-synthesized elastomers suffer from insufficient compatibility with the matrix, leading to secondary dispersion problems and hindering the full realization of their toughening potential, often at the expense of material rigidity, strength, and processing fluidity.

[0004] Ultimately, the common bottleneck of existing technologies lies in the fact that the weak physical interface between the reinforcing component and the matrix cannot achieve efficient stress transfer, and microscopic phase separation leads to shortcomings in macroscopic performance. Traditional compatibilizer methods are inefficient and cannot achieve strong interfacial chemical bonds.

[0005] Therefore, there is an urgent need in this field for a new preparation strategy that can solve the problems of interfacial compatibility and dispersion uniformity at the molecular level, and achieve in-situ composite and chemical bonding between the reinforcing phase and the matrix, so as to prepare polyethylene gas pipes with both ultra-high toughness and long-term durability while ensuring processability. Summary of the Invention

[0006] To address the shortcomings of the existing technology, this invention provides a method for preparing a polyethylene gas pipe, which solves the problem of enhancing the interfacial compatibility and dispersion uniformity of PE and toughening agent at the molecular level, thereby improving the performance and durability of the gas pipe.

[0007] The objective of this invention is achieved through the following technical solution: preparing a topologically entangled polymer via in-situ interfacial polymerization, and using polyethylene, the topologically entangled polymer, and the main toughening agent POE-g-GMA as raw materials to prepare a gas pipe, comprising the following steps: S1 base material particle surface activation and catalyst fixation: Dry porous polyethylene carrier particles are fluidized in a fluidized bed reactor by introducing nitrogen gas. Methylaluminoxane activator solution and Pd(II)α-diimide catalyst toluene solution are sprayed sequentially through a two-fluid atomizing spray gun. After static adsorption, fluidized purging is performed to obtain catalyst@PE composite particles. S2 fluidized bed in-situ interfacial polymerization: ethylene is introduced into the reactor to replace nitrogen gas, and temperature-controlled polymerization is carried out to form a flexible core layer. Then, functional monomers are injected to carry out shell polymerization without interrupting the ethylene gas flow, introducing reactive functional groups. After depressurization, nitrogen gas is purged to obtain core-shell structured composite particles. S3 Series-type Melt Reactive Extrusion: The composite particles obtained in step S2 are melt-blended with the main toughening agent POE-g-GMA, antioxidant and processing aid in a twin-screw extruder. A tetrabutylammonium fluoride solution containing triethylamine is injected into the high-mixing zone to react, so that the functional groups react with the epoxy groups of POE-g-GMA to form a compatibilized structure. After devolatilization, pelletizing and drying, modified granules are obtained. S4 Integrated Online Molding and Post-processing: The modified granules obtained in step S3 are extruded into shape using a single-screw pipe extruder. After sizing and cooling, they undergo online microwave heat treatment to promote post-curing and chain segment rearrangement. Finally, they are cooled, allowed to stand, inspected, and packaged.

[0008] Furthermore, the synthesis of CS-EP was grafted onto the surface of polyethylene base particles, allowing the Pd(II) catalyst to be directly anchored at the activation sites of the PE100-RC base particles. Subsequently, ethylene and functional monomers were introduced, and a topologically entangled polymer layer was directly grown on the surface of the base particles. This achieved molecular-level composite of CS-EP and PE base material at the nanoscale, fundamentally solving the problems of interfacial compatibility and dispersibility.

[0009] The long-term hydrostatic strength failure of polyethylene gas pipes is essentially due to creep and slippage of molecular chains under sustained stress. The permanent physical entanglement provided by hyperbranched polymers is one of the most direct and effective mechanisms to suppress this microscopic slippage, far superior to relying solely on chemical crosslinking or elastomer toughening. Topologically entangled hyperbranched polymers both toughen and strengthen. While toughening typically leads to a decrease in modulus and strength, hyperbranched polymers significantly improve creep resistance through their entangled networks, without affecting processability. Their spherical structure can even reduce melt viscosity, avoiding the processing difficulties usually caused by adding fillers. Through catalytic system design, hyperbranched polymers with ethylene chains as the main branch can be synthesized. This has the same molecular structure as the PE matrix, exhibiting impeccable compatibility and avoiding the risk of phase separation. Its mechanism of action is purely physical entanglement, independent of any special chemical bonds that may degrade within decades, making it ideally suited for the ultra-long service life requirements of gas pipelines.

[0010] Preferably, in step S1, the nozzle orifice diameter of the dual-fluid atomizing spray gun is 0.3 mm, the atomizing gas is nitrogen, and the pressure is 0.3 MPa; in step S1, the amount of Pd(II)α-diimide catalyst solution used per 100 parts of raw material does not exceed 12 mL, corresponding to a Pd metal content of 4.8 μmol.

[0011] Preferably, in step S2, the functional monomer is (tert-butyldimethylsiloxy)-10-undecene; the preparation method of the functional monomer is as follows: reacting tert-butyldimethylchlorosilane with 10-undecene-1-ol in the presence of imidazole, and purifying to obtain a colorless liquid (tert-butyldimethylsiloxy)-10-undecene.

[0012] Furthermore, by constructing a gradient structure and precisely controlling the gas phase composition and polymerization sequence within the reactor, core-shell polymerization is continuously achieved in a single reactor, thereby forming an entangled layer with gradient changes in chemical composition and branching degree on the surface of the base material particles. This gradient structure can more efficiently transfer and disperse stress.

[0013] Preferably, in step S2, the flexible core layer formed by core-layer polymerization has a highly branched structure; the shell layer formed by shell-layer polymerization has a low degree of branching and is distributed with tert-butyldimethylsiloxy protecting groups.

[0014] Furthermore, the core layer is a highly branched structure with 35 branches per 1000C and a crystallinity of ≤15%, while the shell layer is a low-branched structure with 18 branches per 1000C.

[0015] Preferably, in step S2, the ethylene is replaced with nitrogen three times, the core polymerization time is 30 minutes, and the shell polymerization time is 50 minutes.

[0016] Preferably, in step S3, the screw element in the high-mixing zone is configured as two sets of 90° staggered kneading blocks, and tetrabutylammonium fluoride containing triethylamine is used as the solution deprotection agent.

[0017] Furthermore, the TBDMS protective base is removed within 2-3 seconds.

[0018] Preferably, in step S3, the amount of polyethylene wax used per 100 parts of raw material is 0.3 parts, and the GMA grafting rate of the main toughening agent POE-g-GMA is 1.2 wt%.

[0019] Furthermore, the amount of POE-g-GMA used per 100 parts of raw material is 4.5 parts, the side feeding rate is 4.5 kg / h, and the final melt flow rate of the modified granules (190℃ / 5 kg) is 0.35 g / 10 min.

[0020] Preferably, in step S4, the frequency of the microwave heat treatment is 2.45 GHz and the treatment temperature is 85-95℃.

[0021] Furthermore, the microwave heat treatment time is 90 seconds.

[0022] Preferably, the antioxidant is at least one of Irganox 1010 and Irgafos 168.

[0023] Furthermore, the amount of antioxidants used per 100 parts of raw material is 0.1 parts of Irganox 1010 and 0.1 parts of Irgafos 168.

[0024] A synthetic blending method for preparing polyethylene gas pipes involves constructing a core-shell hyperbranched polymer through sequential polymerization, followed by blending it with POE-g-GMA and polyethylene to prepare the gas pipe. The method includes the following steps: Preparation of topological entanglement agent CS-EP: T1 core layer polymerization: High-purity ethylene was introduced into a reactor containing anhydrous toluene, MAO (Al / Pd=500 / 1), and Pd(II)α-diimide catalyst to a pressure of 1.0 MPa, and polymerization was carried out at 25±2℃ and 600 rpm for 20 min. T2 shell polymerization: without interrupting ethylene, (tert-butyldimethylsiloxy)-10-undecene was injected within 5 min, and the temperature was raised to 50±2℃ and 1.0MPa for 40 min. After depressurization, the reaction was terminated with acidified ethanol, and the precipitate was washed and vacuum dried to obtain CS-TBDMS. T3 functional group transformation: CS-TBDMS was dissolved in anhydrous tetrahydrofuran, and tetrabutylammonium fluoride solution was added dropwise and reacted at room temperature for 6 h. The precipitate was dried to obtain CS-OH. Then, CS-OH, glycidyl methacrylate, triethylamine, and hydroquinone were dissolved in o-dichlorobenzene and reacted at 110 °C under nitrogen protection for 8 h. The precipitate was dried to obtain CS-EP (epoxide value 0.26 mmol / g). Polyethylene gas pipe preparation: E1 raw material pretreatment and premixing: Dry PE100-RC and mix it with POE-g-GMA, CS-EP, antioxidant 1010, tris(2,4-di-tert-butylphenyl) phosphite and polyethylene wax in proportion; mix at low speed for 2 minutes, then at medium speed for 3 minutes, and finally at high speed for 5 minutes, with a mixing temperature of 45-55℃. E2 melt blending and granulation: The premixed material is fed into a twin-screw extruder at a screw speed of 280 rpm and a feed rate of 25 kg / h. The vacuum degassing is set at -0.08 to -0.10 MPa. After underwater pelleting, the material is dried at 50°C until the moisture content is <0.02%. E3 pipe extrusion molding: The granules are fed into a single screw extruder with a screw speed of 45 rpm, a melt pressure of 18-22 MPa, vacuum sizing of -0.06 to -0.08 MPa, four-stage gradient cooling, and a traction speed of 1.2 m / min. E4 post-processing: pipe end cutting, stand for 24 hours, then inspect and package.

[0025] In summary, compared with the prior art, the present invention has the following advantages: 1. In this invention, polyethylene is used as the main material in gas pipes, and topologically entangled hyperbranched polymers and POE-g-GMA are used as auxiliary materials. Through the core toughening mechanism of physical topological entanglement and chemical linkage, the performance of gas pipes is improved. 2. In this invention, the topologically entangled hyperbranched polymer (CS-EP) has a large number of branches, and its molecular structure is fuzzy. Reactive groups such as epoxy groups can be attached to the ends of the branches to form chemical links with the matrix. Its three-dimensional spherical structure can generate extremely strong physical topological entanglement in the linear molecular chains of PE, which can effectively inhibit the creep and slippage of molecular chains under long-term low stress, greatly hindering the relative slippage of molecular chains and having an excellent effect on improving resistance to slow crack growth. Secondly, the entangled network can effectively prevent the rapid propagation of cracks and improve the resistance to rapid crack propagation. In addition, physical entanglement also provides creep resistance that is unmatched by traditional chemical crosslinking and does not sacrifice toughness, which greatly improves the long-term hydrostatic strength. 3. In this invention, by directly anchoring the Pd(II) catalyst to the activation sites of PE matrix particles and growing topologically entangled polymer (CS-EP) in situ on the surface, core-shell structured composite particles are formed, enabling CS-EP and PE matrix to achieve molecular-level composite at the nanoscale. This avoids the phase separation and weak interfacial bonding problems commonly found in physical blending, fundamentally solving the interfacial compatibility and dispersion problems, thereby improving the uniformity and stability of the material and reducing performance fluctuations. 4. In this invention, by precisely controlling the polymerization sequence, such as core-layer polymerization for 30 minutes to form a highly branched flexible core and shell-layer polymerization for 50 minutes to introduce a low-branched functional group shell, an entangled layer with gradient changes in chemical composition and branching degree is constructed on the surface of the base material particles. This gradient structure can more efficiently transfer and disperse external stress, such as impact or pressure, thereby significantly improving the pipe's resistance to slow crack growth (SCG) and rapid crack propagation (RCP). The core layer branching degree contains 35 branches per 1000°C, and the shell layer branching degree contains 18 branches per 1000°C, forming a double melting point peak. This structure helps to induce crazes and shear bands under stress, absorb energy, and improve toughness. 5. In this invention, a topologically entangled hyperbranched polymer with a well-defined structure and excellent performance was successfully prepared by constructing a core-shell structure through sequential polymerization to achieve functional partitioning synergy, using a protecting group strategy to achieve precise functionalization, and utilizing macromolecular monomers to control the branched structure. Through molecular design, the branches of the topologically entangled hyperbranched polymer are perfectly compatible with the PE matrix. The hyperbranched molecules have low melt viscosity and good processing fluidity, which is beneficial for processing. Moreover, the physical entanglement formed by C and D bonds is very stable and does not involve chemical bonds that are easily hydrolyzed or degraded. The best balance is achieved between high performance, processability and long-term stability, which solves the long-standing technical contradiction in the field of high-performance polyethylene pipes. 6. In this invention, a tetrabutylammonium fluoride solution containing triethylamine is injected into the high mixing zone of a twin-screw extruder. Within 2-3 seconds, the TBDMS protecting group is rapidly removed, causing the generated hydroxyl groups to undergo a ring-opening reaction with the epoxy groups of POE-g-GMA, forming a PE-topological entanglement-POE triblock compatibilized structure. The in-situ reactive compatibilization overcomes the problem of uneven dispersion of traditional compatibilizers, ensuring strong chemical bonding between the topological entanglement agent and the PE matrix and POE-g-GMA, thereby improving the overall mechanical properties of the material, such as impact strength and tensile toughness. 7. In this invention, after the pipe is extruded, online microwave heat treatment is used to further promote the post-curing of unreacted functional groups such as hydroxyl and epoxy groups, while inducing the relaxation and rearrangement of polyethylene chain segments, effectively eliminating internal stress during processing, making the crystal structure more perfect and stable, thereby improving the long-term performance of the pipe. 8. In this invention, the entire preparation process, from base material activation, in-situ polymerization, and reactive extrusion, is integrated into an online molding process, reducing intermediate steps, lowering energy consumption and pollution risks. The fluidized bed polymerization and extrusion processes are connected in series, achieving continuous production and improving efficiency. Attached Figure Description

[0026] Figure 1 This is a synthetic route diagram for the present invention; Figure 2 This is a flowchart of the step-by-step synthesis process of the present invention; Figure 3 The table shows the performance test results of this invention. Detailed Implementation

[0027] To explain in detail the technical content, structural features, objectives, and effects of the present invention, further explanation is provided below with reference to specific embodiments.

[0028] Example 1 This embodiment corresponds to the content of claims 1-9 in the claims of this invention; Raw material preparation: Polyethylene base material: PE100-RC special porous carrier particles (95.0 parts), with the following characteristics: average particle size 500μm, porosity 35%, average pore size 0.8μm, and specific surface area 120m² / g.

[0029] In-situ polymerization system: Pd(II)α-diimine catalyst (toluene solution, concentration 0.1 mmol / L); Methylaluminoxane (MAO) activator (toluene solution, concentration 1.0 mol / L); (tert-butyldimethylsiloxy)-10-undecene functional monomer (purity ≥99%) Main toughening agent: POE-g-GMA (4.5 parts, of which the GMA grafting rate is 1.2wt%). Antioxidants: Irganox 1010 (0.1 parts), Irgafos 168 (0.1 parts); Processing aid: Polyethylene wax (0.3 parts, molecular weight 2000).

[0030] Step 1: Surface activation of base material particles and fixation of catalyst (precision loading) 1. Pre-processing and loading: The porous PE100-RC masterbatch was dried at 60℃ and -0.1MPa vacuum for 6 hours to completely remove moisture and oxygen; 1.5 kg of the dried masterbatch was transferred to a fluidized bed reactor.

[0031] 2. Fluidization and activation: High-purity nitrogen gas was introduced and the gas velocity was controlled at 0.8 m / s to achieve stable piston-flow fluidization of the bed, with the bed expansion height being 1.8 times that of the static bed. 15 mL of MAO toluene solution was uniformly sprayed into the fluidized bed at a rate of 0.5 mL / min through a dual-fluid atomizing spray gun (nozzle diameter 0.3 mm, atomizing gas nitrogen, pressure 0.3 MPa). The bed temperature was maintained at 25 ± 2 °C by jacket cooling water.

[0032] 3. Catalyst anchoring: After MAO loading is completed, the mixture is allowed to stand for 15 minutes for adsorption. Then, 12 mL of Pd(II) catalyst solution (corresponding to 4.8 μmol of Pd metal) is sprayed into the reactor using the same atomization method. After loading is completed, fluidization purging is continued for 60 minutes to ensure that the toluene solvent is completely evaporated, resulting in "catalyst@PE" composite particles. The catalyst is molecularly dispersed on the particle surface and in the pores.

[0033] Step 2: In-situ interfacial polymerization in fluidized bed 1. Core-layer aggregation (constructing flexible entangled networks): High-purity ethylene is introduced into the reactor, and after replacing the nitrogen gas three times, the pressure is stabilized at 0.8±0.02 MPa. Stirring is started or fluidization is maintained. The reaction temperature is precisely controlled at 35±0.5℃ through jacket circulating water. The polymerization reaction lasts for 30 minutes. Ethylene is inserted into the active sites of the catalyst to form a highly branched (35 branches per 1000C atom) flexible core layer with a crystallinity of ≤15%.

[0034] 2. Shell polymerization (introduction of reactive functional groups): Without interrupting the ethylene gas flow, 1.8 mL of functional monomer was slowly injected into the reactor over 5 minutes using a high-temperature vaporization injection system. This system instantly vaporized the liquid monomer at 80°C and uniformly carried into the bed by the ethylene carrier gas. Simultaneously, the reaction temperature was programmed to rise to 55 ± 0.5°C. Polymerization continued at this temperature for 50 minutes. The higher temperature facilitated the insertion of functional monomer, resulting in a shell structure with low branching (18 branches per 1000 C atoms) and TBDMS protecting groups distributed at the chain ends and in the chain.

[0035] 3. Termination and Post-processing: The ethylene pressure was rapidly released to atmospheric pressure, and high-purity nitrogen was introduced to purge the reaction system for 120 minutes to completely remove unreacted monomers and possible oligomers, resulting in CS-TBDMS / PE in-situ composite particles. Samples were taken for thermal analysis, which showed that they had obvious dual melting point peaks (core layer ≈ 115℃, shell layer ≈ 122℃).

[0036] Step 3: Serial melt reactive extrusion (in-situ compatibilization) 1. Material conveying and melting: The composite granules are directly fed into a coplanar twin-screw extruder (screw diameter 40mm, L / D=40) via a fully enclosed gravity conveying system. The extruder temperature settings from the feed port to the die head are: 150℃, 170℃, 185℃, 195℃, and 190℃. In the melting zone (third zone), POE-g-GMA is accurately added at a rate of 4.5kg / h via a loss-in-weight side feeder, along with a premix of antioxidants and polyethylene wax.

[0037] 2. In-situ deprotection and reactive composting: In the sixth barrel of the extruder (set as a high-temperature mixing reaction zone at 190°C), a tetrabutylammonium fluoride solution (1.0M in THF) containing 1.0wt% triethylamine (as a deprotection reaction catalyst) is injected via a high-pressure micro-injection pump. The injection volume is 0.8% of the total polymer mass. The screw element here is configured with two sets of 90° staggered kneading blocks to ensure that the reagent and melt are vigorously mixed and fully reacted. The TBDMS protecting group is efficiently removed within 2-3 seconds, and the generated active hydroxyl group immediately undergoes a ring-opening reaction with the epoxy group on the adjacent POE-g-GMA molecular chain to form an in-situ compatibilized "PE-topological entanglement agent-POE" triblock structure.

[0038] 3. Deviation and granulation: The reacted melt enters a high-vacuum devolatilization section (-0.095 MPa) to remove byproducts and residual solvent. Finally, it is subjected to underwater pelleting, centrifugal dehydration, and fluidized bed drying at 50°C to obtain the final modified granules. The melt flow rate (190°C / 5kg) is 0.35 g / 10 min.

[0039] Step 4: Integrated online molding and post-processing 1. Pipe extrusion and shaping: Modified granules are conveyed to a series-connected single-screw pipe extruder via a vacuum feeding system, employing a low-temperature, low-shear process: extruder temperature set at 150 / 165 / 180 / 175℃, die temperature at 170℃. Screw speed is 40 rpm, and melt pressure is stabilized at 16 MPa. A laser diameter gauge and a vacuum sizing sleeve are interlocked for control, with sizing pressure at -0.07 MPa and cooling water temperature at 20±1℃, ensuring precise tolerances for the pipe's outer diameter and wall thickness.

[0040] 2. Online heat treatment and simultaneous crosslinking: After sizing and cooling, the material immediately enters an online microwave heat treatment chamber at a microwave frequency of 2.45 GHz, a power of 8 kW, a treatment temperature of 90 ± 5 °C, and a treatment time of 90 seconds. This further promotes the post-curing of incompletely reacted functional groups (hydroxyl and epoxy groups) at the interface, while inducing relaxation and rearrangement of polyethylene chain segments, partially eliminating internal stress, and making the crystalline structure more perfect and stable.

[0041] 3. Post-processing and packaging: After being cooled by spraying (water temperature gradient: 25℃→35℃→45℃) to room temperature, permanent markings are printed on the surface of the pipes using a laser marking machine. After the pipes are left to stand in a constant temperature and humidity (23℃, 50% humidity) workshop for 48 hours, dimensional inspection, hydraulic testing and full performance testing are carried out. After passing the tests, the pipes are packaged and put into storage.

[0042] Example 2 This embodiment corresponds to the content of claim 10 in the claims of this invention; 1. Preparation of topologically entangled hyperbranched polymers 1.1 Main raw materials: Ethylene (purity ≥99.95%, dehydrated and deoxygenated by molecular sieve), Pd(II)α-diimine catalyst (α-diimine palladium catalyst), methylaluminoxane (MAO, 10wt% toluene solution), tert-butyldimethylchlorosilane, 10-undecen-1-ol; 1.2 Preparation steps Step 1: Reactor preparation and catalyst loading 200 mL of anhydrous toluene, methylaluminoxane (MAO, Al / Pd=500 / 1, based on 4.0 μmol catalyst), and 4.0 μmol of Pd(II)α-diimide catalyst were added sequentially to the reactor; the reactor was sealed and connected to the high-pressure ethylene gas supply system.

[0043] tert-butyldimethylchlorosilane was reacted with 10-undecen-1-ol in the presence of imidazole, and the resulting purified liquid (tert-butyldimethylsiloxy)-10-undecene was obtained.

[0044] Step Two: Core Layer Convergence – Formation of Highly Branched Flexible Nuclei Turn on the stirrer and set the speed to 600 rpm. Introduce high-purity ethylene gas until the pressure reaches 1.0 MPa. Control the reaction temperature at 25±2℃ and let the polymerization reaction continue for 20 minutes. During this period, the reaction temperature is precisely controlled by the cooling water system to ensure that the core layer forms a highly branched, low-crystallinity flexible structure.

[0045] Step 3: Shell Polymerization – Construction of Reactive Shells Without interrupting the ethylene gas flow, 1.5 mL of (tert-butyldimethylsiloxy)-10-undecene was slowly injected over 5 min using a syringe pump. The reaction temperature was programmed to rise to 50±2℃, the ethylene pressure was maintained at 1.0 MPa, and the polymerization reaction was continued for 40 min. A shell structure with low branching degree and protective functional groups was grown on the pre-formed core.

[0046] Step 4: Reaction Termination and Primary Purification Release the ethylene pressure in the reactor, inject 100 mL of acidified ethanol (containing 5% hydrochloric acid) to terminate the reaction, continue stirring for 30 min, transfer the reaction mixture to a 2 L beaker, add 1 L of ethanol to precipitate the polymer, collect the polymer by filtration through a Buchner funnel, wash three times with 200 mL of ethanol, transfer the wet filter cake to a petri dish, and dry in a vacuum drying oven at 40 °C for 24 h to obtain the core-shell structure precursor (denoted as CS-TBDMS), with a product mass of 18.2 g.

[0047] Step 5: Functional group deprotection and transformation Add 15.0 g of CS-TBDMS and 400 mL of anhydrous tetrahydrofuran to a 1 L round-bottom flask. Stir under nitrogen protection until completely dissolved. Slowly add 30 mL of tetrabutylammonium fluoride solution and stir at room temperature for 6 h. Pour the reaction solution into 1.5 L of methanol to precipitate, filter, wash with methanol, and dry under vacuum to obtain the hydroxyl-terminated product (denoted as CS-OH).

[0048] 12.0 g of CS-OH, 8.0 g of glycidyl methacrylate, 0.5 mL of triethylamine, and 0.05 g of hydroquinone were dissolved in 250 mL of o-dichlorobenzene and reacted at 110 °C under nitrogen protection for 8 h. The product was precipitated, washed, and dried to obtain the final product CS-EP with an epoxy value of 0.26 mmol / g.

[0049] Shell functional group introduction efficiency: 83%; The ratio of core to shell structure is approximately 45:55; Overall crystallinity: 54%.

[0050] 2. Preparation of high-performance gas pipe materials 2.1 Main raw materials: Polyethylene base material: PE100-RC (92.5 parts) Main toughening agent: POE-g-GMA (5.0 parts) Topological entanglement agent: CS-EP (2.0 parts) Antioxidant main component: Antioxidant 1010 (0.1 parts) Antioxidant adjuvant: Tris(2,4-di-tert-butylphenyl) phosphite (0.1 parts) Processing aid: Polyethylene wax (0.3 parts) 2.2 Processing Equipment and Process Parameters Process steps: Step 1: Raw material pretreatment and premixing The polyethylene base material was dried in an 80℃ forced-air drying oven for 4 hours, and each component was weighed according to the formula ratio. Premixing was carried out in a high-speed mixer using a segmented feeding method: first, polyethylene base material and 1 / 2 carbon black were added, and the mixture was mixed at low speed (200 rpm) for 2 minutes; then POE-g-GMA, CS-EP, and the remaining carbon black were added, and the mixture was mixed at medium speed (800 rpm) for 3 minutes; finally, antioxidants and processing aids were added, and the mixture was mixed at high speed (1500 rpm) for 5 minutes. The total mixing time was 10 minutes, and the mixing temperature was controlled at 45-55℃ by frictional heat.

[0051] Step 2: Melt blending and granulation Twin-screw extruder temperature settings: Barrel zone 1 160℃, Barrel zone 2 175℃, Barrel zone 3 185℃, Barrel zone 4 195℃, Barrel zone 5 195℃, Die head 190℃, Screw speed 280rpm, Feed rate 25kg / h. Vacuum exhaust -0.08 to -0.10 MPa, melt pressure 3.5-4.5 MPa; underwater pelleting, cooling water temperature 35-45℃, after centrifugal dehydration, the pellets are dried in a 50℃ fluidized bed dryer to a moisture content of <0.02%.

[0052] Step 3: Pipe extrusion molding Temperature settings for the single-screw pipe extruder: feed section 150℃, compression section 175℃, metering section 190℃, die 185℃, screw speed 45rpm, melt pressure 18-22MPa, vacuum sizing -0.06 to -0.08MPa, water temperature 15±2℃, spray cooling, water temperature gradient controlled in four sections from 25℃ to 45℃, traction speed 1.2m / min, matched with the extrusion speed.

[0053] Step 4: Post-processing and testing Print markings and meter readings, cut and chamfer pipe ends, and perform dimensional and visual inspections after 24 hours of settling.

[0054] Performance tests were conducted on the gas pipes used in Examples 1 and 2 above, as well as commercially available gas pipes. The test results are shown in the table below: The embodiments of the present invention are not limited to those described above. Without departing from the spirit and scope of the present invention, those skilled in the art can make various changes and improvements to the present invention in form and detail, and these are all considered to fall within the protection scope of the present invention.

Claims

1. A method for preparing a polyethylene gas pipe, characterized in that, A topologically entangled polymer is prepared by in-situ interfacial polymerization. Gas pipes are then fabricated using polyethylene, the topologically entangled polymer, and the main toughening agent POE-g-GMA as raw materials, comprising the following steps: S1 base material particle surface activation and catalyst fixation: Dry porous polyethylene carrier particles are fluidized in a fluidized bed reactor by introducing nitrogen gas. Methylaluminoxane activator solution and Pd(II)α-diimide catalyst toluene solution are sprayed sequentially through a two-fluid atomizing spray gun. After static adsorption, fluidized purging is performed to obtain catalyst@PE composite particles. S2 fluidized bed in-situ interfacial polymerization: ethylene is introduced into the reactor to replace nitrogen gas, and temperature-controlled polymerization is carried out to form a flexible core layer. Then, functional monomers are injected to carry out shell polymerization without interrupting the ethylene gas flow, introducing reactive functional groups. After depressurization, nitrogen gas is purged to obtain core-shell structured composite particles. S3 Series-type Melt Reactive Extrusion: The composite particles obtained in step S2 are melt-blended with the main toughening agent POE-g-GMA, antioxidant and processing aid in a twin-screw extruder. A tetrabutylammonium fluoride solution containing triethylamine is injected into the high-mixing zone to react, so that the functional groups react with the epoxy groups of POE-g-GMA to form a compatibilized structure. After devolatilization, pelletizing and drying, modified granules are obtained. S4 Integrated Online Molding and Post-processing: The modified granules obtained in step S3 are extruded into shape using a single-screw pipe extruder. After sizing and cooling, they undergo online microwave heat treatment to promote post-curing and chain segment rearrangement. Finally, they are cooled, allowed to stand, inspected, and packaged.

2. The method for preparing a polyethylene gas pipe according to claim 1, characterized in that: In step S1, the nozzle orifice diameter of the dual-fluid atomizing spray gun is 0.3 mm, the atomizing gas is nitrogen, and the pressure is 0.3 MPa; in step S1, the amount of Pd(II)α-diimide catalyst solution used in every 100 parts of raw material does not exceed 12 mL, corresponding to a Pd metal content of 4.8 μmol.

3. The method for preparing a polyethylene gas pipe according to claim 1, characterized in that: In step S2, the functional monomer is (tert-butyldimethylsiloxy)-10-undecene; the preparation method of the functional monomer is as follows: tert-butyldimethylchlorosilane is reacted with 10-undecene-1-ol in the presence of imidazole, and after purification, a colorless liquid (tert-butyldimethylsiloxy)-10-undecene is obtained.

4. The method for preparing a polyethylene gas pipe according to claim 1, characterized in that: In step S2, the flexible core layer formed by core-layer polymerization has a highly branched structure; the shell layer formed by shell-layer polymerization has a low degree of branching and is distributed with tert-butyldimethylsiloxy protecting groups.

5. The method for preparing a polyethylene gas pipe according to claim 1, characterized in that: In step S2, the nitrogen gas is replaced by ethylene three times, the core polymerization time is 30 minutes, and the shell polymerization time is 50 minutes.

6. The method for preparing a polyethylene gas pipe according to claim 1, characterized in that: In step S3, the screw element in the high mixing zone is configured as two sets of 90° staggered kneading blocks, and tetrabutylammonium fluoride containing triethylamine is used as the solution deprotection agent.

7. The method for preparing a polyethylene gas pipe according to claim 1, characterized in that: In step S3, the amount of polyethylene wax used per 100 parts of raw material is 0.3 parts, and the GMA grafting rate of the main toughening agent POE-g-GMA is 1.2 wt%.

8. The method for preparing a polyethylene gas pipe according to claim 1, characterized in that: In step S4, the frequency of the microwave heat treatment is 2.45 GHz, and the treatment temperature is 85-95℃.

9. The method for preparing a polyethylene gas pipe according to claim 1, characterized in that: The antioxidant is at least one of Irganox 1010 and Irgafos 168.

10. A synthetic blending method for preparing polyethylene gas pipes, characterized in that, Gas pipes are prepared by constructing a core-shell hyperbranched polymer through sequential polymerization and then blending it with POE-g-GMA and polyethylene, including the following steps: Preparation of topological entanglement agent CS-EP: T1 core layer polymerization: High-purity ethylene was introduced into a reactor containing anhydrous toluene, MAO (Al / Pd=500 / 1), and Pd(II)α-diimide catalyst to a pressure of 1.0 MPa, and polymerization was carried out at 25±2℃ and 600 rpm for 20 min. T2 shell polymerization: without interrupting ethylene, (tert-butyldimethylsiloxy)-10-undecene was injected within 5 min, and the temperature was raised to 50±2℃ and 1.0MPa for 40 min. After depressurization, the reaction was terminated with acidified ethanol, and the precipitate was washed and vacuum dried to obtain CS-TBDMS. T3 functional group transformation: CS-TBDMS was dissolved in anhydrous tetrahydrofuran, and tetrabutylammonium fluoride solution was added dropwise and reacted at room temperature for 6 h. The precipitate was dried to obtain CS-OH. Then, CS-OH, glycidyl methacrylate, triethylamine, and hydroquinone were dissolved in o-dichlorobenzene and reacted at 110 °C under nitrogen protection for 8 h. The precipitate was dried to obtain CS-EP (epoxide value 0.26 mmol / g). Polyethylene gas pipe preparation: E1 raw material pretreatment and premixing: Dry PE100-RC and mix it with POE-g-GMA, CS-EP, antioxidant 1010, tris(2,4-di-tert-butylphenyl) phosphite and polyethylene wax in proportion; mix at low speed for 2 minutes, then at medium speed for 3 minutes, and finally at high speed for 5 minutes, with a mixing temperature of 45-55℃. E2 melt blending and granulation: The premixed material is fed into a twin-screw extruder at a screw speed of 280 rpm and a feed rate of 25 kg / h. The vacuum degassing is set at -0.08 to -0.10 MPa. After underwater pelleting, the material is dried at 50°C until the moisture content is <0.02%. E3 pipe extrusion molding: The granules are fed into a single screw extruder with a screw speed of 45 rpm, a melt pressure of 18-22 MPa, vacuum sizing of -0.06 to -0.08 MPa, four-stage gradient cooling, and a traction speed of 1.2 m / min. E4 post-processing: pipe end cutting, stand for 24 hours, then inspect and package.

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