Crosslinked polyethylene insulated power cable and preparation method thereof

Abstract

The invention relates to the technical field of cable materials, discloses a crosslinked polyethylene insulated power cable and a preparation method thereof, and aims to solve the problems that harmful by-products are introduced and complicated degassing is needed in the conventional chemical crosslinking material. According to the material, a hierarchical dual-network structure composed of a physical cross-linked network and a dynamic covalent cross-linked network is constructed through components such as matrix resin, a dynamic network functional monomer and a physical network functional nanofiller. The preparation method comprises the following steps: preparing a hierarchical network precursor by reactive grafting in a twin-screw extruder, and devolatilizing; in the cable extrusion process, network in-situ curing is achieved through cooling, and traditional high-temperature crosslinking and degassing steps are omitted. According to the scheme, crosslinking by-products are fundamentally avoided, it is ensured that the material has excellent electrical properties, thermal mechanical properties and long-term reliability, the preparation process is remarkably simplified, and meanwhile the material has the thermally induced self-repairing potential.

Description

Technical Field

[0001] This invention belongs to the field of cable material technology, and relates to a cross-linked polyethylene insulated power cable and its preparation method. Background Technology

[0002] The emergence of cross-linked polyethylene (XLPE) insulation material is a significant milestone in the history of cable technology. The core principle of this technology lies in forming chemical bonds between the linear long molecular chains of polyethylene through the introduction of chemical cross-linking agents or by methods such as radiation and silane hydrolysis, thus constructing a stable three-dimensional network structure. This fundamental structural transformation effectively restricts the relative movement of the molecular chains, resulting in a significant improvement in macroscopic properties.

[0003] Firstly, in terms of heat resistance, the cross-linked network structure greatly improves the softening point and heat distortion temperature of the material, enabling the long-term allowable operating temperature of the cable to be increased from 70℃ for ordinary polyethylene to 90℃. During short circuits, it can withstand instantaneous high temperatures of up to 250℃, significantly enhancing the cable's current carrying capacity and overload capacity.

[0004] Secondly, in terms of mechanical properties, the cross-linked structure endows the material with higher tensile strength, creep resistance, and excellent resistance to environmental stress cracking, enabling it to better withstand various mechanical stresses encountered during installation and operation. It is precisely because of these comprehensive advantages that cross-linked polyethylene insulation materials have successfully solved the core pain points of early insulation materials in terms of thermal stability and mechanical strength, and have rapidly become the preferred insulation material for medium-voltage and even ultra-high-voltage power cables, providing solid technical support for the development of power systems.

[0005] However, as power grids continue to evolve towards higher voltage levels, larger transmission capacities, and longer service lives, application scenarios are becoming increasingly complex and extreme, such as deep-sea, high-altitude, and environments with strong electromagnetic fields and high humidity and heat. Against this backdrop, the aforementioned chemical crosslinking-based technical solutions, due to some inherent characteristics at the principle level, are gradually revealing deep-seated limitations in addressing new challenges. The reason for this is that the peroxide chemical crosslinking process widely used in industry, while achieving the primary goal of imparting excellent thermomechanical properties to materials, inevitably generates a series of complex chemical side reactions. For example, in systems using dicumyl peroxide as a crosslinking agent, small molecule byproducts such as ethylbenzene, isopropanol, and methane are decomposed during high-temperature crosslinking. After the crosslinking network is formed, these byproducts are physically confined within the amorphous regions or microscopic defects of the polymer matrix. In traditional application scenarios, the impact of these residual byproducts may not be prominent, but in modern power equipment operating under high electric fields and long cycles, their presence has evolved into a key bottleneck restricting the long-term reliability of materials.

[0006] Furthermore, the presence of these polar small molecule byproducts poses a potential and ongoing threat to the electrical properties of insulating materials. On the one hand, their presence significantly increases the dielectric loss tangent (tanδ) of the material, leading to increased energy loss in cables at high frequencies or high voltages. On the other hand, and more critically, these byproducts, together with the micropores and defects formed in the cross-linked network, can easily become space charge traps under strong electric fields.

[0007] The accumulation of space charge severely distorts the original electric field distribution within the insulation layer, creating electric field strengths in localized areas far exceeding design values, thus greatly increasing the probability of electrical treeing. Once electrical trees develop, they form penetrating discharge channels, ultimately leading to catastrophic insulation breakdown. To mitigate this problem, existing processes typically require a time-consuming and energy-intensive degassing process after cable extrusion to remove these byproducts.

[0008] However, this not only significantly increases production cycle and manufacturing costs, limiting the efficiency of large-scale production, but also makes the degassing process often incomplete, leaving residual byproducts that remain a major safety hazard affecting the long-term service life of cables. This creates a deep technical contradiction: the chemical cross-linking method used to obtain excellent macroscopic thermomechanical properties inherently introduces harmful factors that damage the microscopic electrical purity and long-term stability of the material, and the process costs incurred in eliminating these harmful factors further weaken the economic efficiency and practicality of the technology.

[0009] Therefore, how to overcome the inherent constraint between the macroscopic thermomechanical properties and microscopic electrical properties in the existing cross-linked polyethylene material system, and develop a new type of insulating material and its preparation method, which can fundamentally suppress or eliminate the negative impact of cross-linking byproducts on electrical properties while ensuring or even improving the material's heat resistance and mechanical strength, and simultaneously simplify the preparation process and reduce costs, has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention

[0010] The purpose of this invention is to overcome the technical contradiction in existing cross-linked polyethylene insulation materials, where the pursuit of macroscopic thermomechanical properties inherently introduces byproducts that impair microscopic electrical properties due to the chemical cross-linking process, and necessitates complex and costly subsequent degassing treatment. To address this, this invention provides a cross-linked polyethylene insulated power cable and its preparation method. This method constructs a hierarchical dual-network structure composed of a physical cross-linking network and a dynamic covalent cross-linking network, fundamentally eliminating the generation of cross-linking byproducts. This ensures and improves the overall thermomechanical properties of the material while achieving excellent electrical purity and long-term service reliability, and significantly simplifies the preparation process.

[0011] To achieve the above-mentioned objective, the present invention provides a cross-linked polyethylene insulated power cable, wherein the material has a hierarchical dual-network microstructure, which is formed in a continuous phase matrix composed of polyethylene molecular chains, and the dual-network microstructure includes: A three-dimensional physical cross-linked network and a dynamic covalent cross-linked network running through the physical cross-linked network; The three-dimensional physical cross-linking network is composed of multiple cage-like inorganic cores that are covalently grafted onto the polyethylene molecular chain as zero micro-nano cross-linking nodes, and polyethylene chain segments surrounding the cage-like inorganic cores, which are jointly formed by van der Waals forces and physical entanglement. The dynamic covalent crosslinking network is composed of multiple side groups containing hindered urea functional groups that are also covalently grafted onto the polyethylene molecular chain. The hindered urea functional group side groups on different polyethylene molecular chains form crosslinking points through thermally dissociatable and recombination intermolecular hydrogen bonds.

[0012] Preferably, the material is prepared by reactive grafting of the following components in parts by weight: Matrix resin: 90~98 parts; Dynamic network functional monomers: 1-5 copies; Physical network functionalized nanofillers: 0.5~3 parts; Grafting initiator: 0.05~0.2 parts; Composite antioxidant system: 0.2~0.8 parts.

[0013] Preferably, the matrix resin is low-density polyethylene, the melt index of which is 1.5~2.5g / 10min under 190℃ and 2.16kg load conditions, and the density of which is 0.918~0.925g / cm³.

[0014] Preferably, the dynamic network functional monomer is N-(tert-butyl)-N'-(4-vinylphenyl)urea, whose molecular structure contains vinyl functional groups for grafting onto the polyethylene molecular chain and hindered urea functional groups capable of forming the intermolecular hydrogen bonds. The physical network functionalized nanofiller is an octa(isobutyl)-mono(vinyl) polyhedral oligomeric silsesquioxane, which has a cage-like inorganic core composed of eight silicon atoms and twelve oxygen atoms. Vinyl functional groups for grafting to the polyethylene molecular chain and seven isobutyl groups compatible with the polyethylene matrix are connected to the silicon atom vertices of the core.

[0015] Preferably, the grafting initiator is dicumyl peroxide; The composite antioxidant system consists of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as the main antioxidant and tris(2,4-di-tert-butylphenyl) phosphite as the auxiliary antioxidant.

[0016] Preferably, the cage-like inorganic core is formed by carbon-carbon single bond covalent grafting through an addition reaction between the vinyl functional groups attached to it and the polyethylene molecular chain; The side group containing the hindered urea functional group is formed by carbon-carbon single bond covalent grafting through the addition reaction of the vinyl functional group it contains with the polyethylene molecular chain. The intermolecular hydrogen bonds are formed between the nitrogen-hydrogen bonds in the hindered urea functional group and the carbonyl oxygen in another hindered urea functional group.

[0017] This invention provides a method for preparing a cross-linked polyethylene insulated power cable, the method comprising the following steps: Step 1: Preparation of hierarchical network precursor material. This step is carried out in a reactive extrusion device. The matrix resin, dynamic network functional monomer, and physical network functionalized nanofiller are reactively grafted under the action of a grafting initiator, followed by devolatilization treatment, thereby obtaining hierarchical network precursor polyethylene particles without volatile byproducts. Step 2: Insulation layer extrusion and in-situ network curing. In this step, the layered network precursor polyethylene particles are extruded at high temperature and coated onto the conductor to form an insulation layer. Subsequently, the insulation layer is rapidly cooled, so that the dynamic covalent crosslinked network is kinetically frozen and cured during the cooling process, thereby forming the layered double network structure in-situ in the insulation layer.

[0018] Preferably, step one specifically includes the following procedures: The matrix resin and the composite antioxidant system are fed into a high-torque co-rotating twin-screw extruder through the main feed port, and melted and premixed in the first temperature zone. The mixture of the dynamic network functional monomer and the physical network functionalized nanofiller is added to the melt of the matrix resin through a side feed port located downstream of the melting zone, and is subjected to enhanced dispersion and mixing in the second temperature zone. The grafting initiator is injected into the melt after enhanced dispersion and mixing, and the grafting reaction is carried out in a third temperature range that is higher than the decomposition temperature of the grafting initiator, so that the dynamic network functional monomer and the physical network functionalized nanofiller are covalently grafted onto the molecular chain of the matrix resin. The grafted material is transported to the exhaust section connected to a vacuum system, where it undergoes vacuum devolatilization in the fourth temperature zone to remove unreacted monomers, initiator decomposition products, and other volatile substances. The devolatilized melt is extruded, cooled, and pelletized to obtain the hierarchical network precursor polyethylene particles.

[0019] Preferably, the high-torque co-rotating twin-screw extruder has a length-to-diameter ratio of 48:1, and its screw assembly is configured sequentially from the feed inlet to the discharge outlet as a first conveying section, a first kneading section, a second conveying section, a side feeding section, a third conveying section, a second kneading section, a venting section, and a depressurization extrusion section. The first temperature range is 140℃~160℃, the second temperature range is 170℃~180℃, the third temperature range is 185℃~205℃, and the fourth temperature range is 210℃~230℃.

[0020] Preferably, the screw configuration of the second kneading section is composed of multiple kneading blocks with different staggered angles, including 30°, 60° and 90°, so as to generate a strong shearing and distribution mixing effect on the physical network functionalized nanofiller, and promote its molecular-level dispersion in the matrix resin melt.

[0021] Compared with the prior art, the beneficial effects of the present invention are: The cross-linked polyethylene insulated power cable and its preparation method provided by this invention fundamentally solve the core contradictions in the background technology. Because the cross-linking of the entire material system is achieved through physical network construction and in-situ curing of dynamic covalent bonds, it completely avoids the chemical reaction pathway of traditional peroxide decomposition cross-linking. Therefore, in the final molded insulation product, there are no polar small molecule byproducts generated by the cross-linking reaction. This characteristic gives the material extremely low dielectric loss tangent and excellent volume resistivity, greatly suppressing the injection and accumulation of space charge, thereby significantly improving the long-term operational reliability and DC withstand voltage performance of the cable insulation.

[0022] The hierarchical dual-network structure endows the material with excellent comprehensive properties. The rigid physical cross-linked network formed by the octa(isobutyl)-mono(vinyl) polyhedral oligomeric silsesquioxane inorganic core provides the material with dimensional stability and creep resistance at high temperatures, and its heat resistance and mechanical strength reach or exceed the level of traditional chemically cross-linked polyethylene. Meanwhile, the dynamic covalent network acts as an effective chemical cross-linking point at the operating temperature, further enhancing the material's mechanical properties and resistance to environmental stress cracking. The synergistic effect of the two networks achieves a significant improvement in thermomechanical properties.

[0023] The preparation process of this invention is fundamentally simplified. The reactive grafting in step one is completed in a closed twin-screw extruder with a highly efficient devolatilization function, ensuring that the resulting hierarchical network precursor particles are highly pure. In step two, the cable extrusion process, due to the thermoplasticity of the material at the processing temperature, reduces the requirements for extrusion equipment and process control, and eliminates two key bottleneck processes: energy-intensive and time-consuming high-temperature crosslinking and subsequent degassing. This not only increases production efficiency several times over but also significantly reduces energy consumption and equipment investment, making the entire manufacturing process more economical and environmentally friendly.

[0024] The dynamic covalent network properties of the material endow it with potential thermo-induced self-healing capabilities. Microscopic damage generated during cable service can be reactivated by dynamic covalent bonds under specific temperature conditions, repairing cracks through topological network rearrangement, thereby extending the actual service life of the cable. In summary, this invention, through a novel material design concept and manufacturing process, successfully unifies excellent thermomechanical properties, ultra-pure electrical properties, and an efficient and economical manufacturing process within a single technological system, providing a breakthrough solution for the development of high-voltage and ultra-high-voltage power cable technology. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. It should be understood that the specific embodiments described herein are only for explaining this invention and are not intended to limit this invention.

[0026] The present invention provides a cross-linked polyethylene insulated power cable and its preparation method, as follows: The matrix resin selected was Borstar® LD0724 (Borealis) low-density polyethylene, melt index 2.0 g / 10 min at 190℃ / 2.16 kg, density 0.922 g / cm³. The active ingredients were Sigma-Aldrich's dynamic network functional monomer (N-(tert-butyl)-N'-(4-vinylphenyl)urea), HybridPlastics OVS-IBV-1001 physically network functionalized nanofiller (octa(isobutyl)-mono(vinyl)polyhedral oligomeric silsesquioxane) with an average native particle size of 1.5 nm (single molecule size), Arkema Luperox® DC graft initiator (dicumyl peroxide), and composite antioxidant (BASF Irganox® 1010 antioxidant 1010: BASF Irgafos® 168 antioxidant 168 = 1:1).

[0027] Phase 1: Preparation of Hierarchical Network Precursors This process is completed in a co-rotating twin-screw extruder (Corperon ZSK series) with a length-to-diameter ratio (L / D) ≥ 48:1.

[0028] Ingredients and premixing: Premix LDPE 132I (95 parts) with Irganox® 1010 (0.3 parts) / Irgafos® 168 (0.3 parts) in a high-speed mixer.

[0029] Main feed: The premix is ​​added from the main feed inlet.

[0030] Melt plasticization: Melt plasticization is completed in Zone 1 (140~160℃).

[0031] Side feed: The dry mixture of N-(tert-butyl)-N'-(4-vinylphenyl)urea (3 parts) and OVS-IBV-1001 (1.5 parts) is added to the molten PE through a side feeder.

[0032] Dispersion and mixing: Under the action of high shear kneading block in zone two (170~180℃), the cage-shaped polysilsesquioxane agglomerates are broken up to achieve nanoscale dispersion.

[0033] Injection initiation and grafting: Dicumyl peroxide (0.1 parts) was dissolved in a small amount of dodecane and injected into the reaction zone at 185-205°C using a liquid-phase injection pump. The molar ratio of dicumyl peroxide radicals to functional groups was controlled at 0.3:1. The residence time was 90-180 seconds.

[0034] Deviation removal and granulation: All volatiles are removed at 210~230℃ and a vacuum degree ≤-0.095MPa. Finally, the melt is water-cooled and pelletized to obtain pure precursor particles.

[0035] Phase Two: Insulation Layer Extrusion and In-situ Curing This step is performed on a standard cable extrusion line.

[0036] Extrusion: Precursor particles are added to an extruder and melt-extruded at 180~220℃ to coat the conductor. At this time, the dynamic hydrogen bond network dissociates, and the material has good flowability.

[0037] Gradient cooling and network curing: The coated cable immediately enters the three-stage cooling system. Zone 1 (Hot Zone): Cooled by hot water at 80~90℃.

[0038] Second zone (temperature zone): 50~60℃ warm water cooling.

[0039] Zone 3 (Cold Zone): Cooled by cold water at 20~30℃.

[0040] Principle: When the temperature drops below 150℃, the dissociation-recombination kinetics of urea hydrogen bonds are frozen, the dynamic network solidifies in situ, and forms a final stable double network structure in synergy with the cage-type polysilsesquioxane physical network.

[0041] Phase Three: Subsequent Processes Since the insulating layer no longer contains any small molecule byproducts, there is no need for degassing, and it can be directly proceeded to the next process (such as covering the outer shielding layer) or wound up into a finished product.

[0042] The embodiments were designed and prepared according to the following parts by weight:

[0043] Preparation method: The two-step method described in the patent is adopted: reactive grafting to prepare the precursor → extrusion cooling and in-situ solidification. The twin-screw extruder has an aspect ratio of 48:1. The temperature range is set according to the patent: the first range is 140~160℃, the second range is 170~180℃, the third range is 185~205℃, and the fourth range is 210~230℃. The cooling adopts a gradient cooling: 80~90℃ → 50~60℃ → 20~30℃.

[0044] Comparative design, traditional chemically cross-linked polyethylene: The same matrix resin as in the examples was selected, and a conventional peroxide crosslinking process was used:

[0045] Preparation method: Traditional three-step method: extrusion → high temperature and high pressure steam crosslinking (180℃, 0.5MPa, 30min) → degassing treatment (70℃, 48h).

[0046] Performance test data: Test parameters include electrical properties: dielectric loss tanδ, volume resistivity, space charge density; thermomechanical properties: tensile strength, elongation at break, heat distortion temperature; and process efficiency: preparation cycle.

[0047]

[0048] Data comparison and analysis: Electrical performance advantages: The dielectric loss tanδ (0.0005~0.0008) of Examples 1~4 is much lower than that of Comparative Example 1 (0.0025), and the volume resistivity (5.2×10⁻⁶) is also significantly lower. 16 ~8.3×10 16 The Ω·cm of the original sample is 4 to 7 times that of the comparative sample, and the space charge density (1.2 to 2.1 C / m³) is only 14% to 25% of that of the comparative sample (8.5 C / m³). This is because the example eliminates cross-linking byproducts through a dual-network structure, avoids the damage to electrical properties caused by polar small molecules, and significantly improves the purity of the insulation.

[0049] Balanced thermomechanical properties: The tensile strength of the embodiment (18.5~23.5MPa) is comparable to or better than that of the comparative example (19.0MPa), the heat distortion temperature (92~100℃) is slightly higher than that of the comparative example (90℃), and the elongation at break (330%~420%) meets the cable flexibility requirements. This demonstrates that the dual-network structure (the physical network provides a rigid skeleton, and the dynamic covalent network enhances toughness) achieves a synergistic improvement in thermomechanical properties.

[0050] Breakthrough in process efficiency: The preparation cycle of the example is only 2 hours (no crosslinking and degassing required), which is much shorter than the 52 hours of the comparative example (including 30 minutes of crosslinking + 48 hours of degassing). This significantly reduces energy consumption and production time, demonstrating the remarkable advantages of process simplification.

[0051] Unique self-healing properties: The example has a thermally induced self-healing rate of 35% to 65% due to the dynamic covalent network (hindered urea hydrogen bonds), while the comparative example of traditional chemical crosslinking has no self-healing ability, which provides potential for extending the service life of cables.

[0052] The embodiments of the present invention, through a hierarchical dual-network structure and optimized process, comprehensively outperform traditional chemically cross-linked polyethylene in terms of electrical performance, thermomechanical performance, and process efficiency, and possess unique self-healing potential, thus solving the core contradiction of traditional technology.

[0053] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cross-linked polyethylene insulated power cable, characterized in that, The cross-linked polyethylene insulated power cable has a hierarchical dual-network microstructure formed in a continuous phase matrix composed of polyethylene molecular chains. The dual-network microstructure includes: A three-dimensional physical cross-linked network and a dynamic covalent cross-linked network running through the physical cross-linked network; The three-dimensional physical cross-linking network is composed of multiple cage-like inorganic cores that are covalently grafted onto the polyethylene molecular chain as zero micro-nano cross-linking nodes, and polyethylene chain segments surrounding the cage-like inorganic cores, which are jointly formed by van der Waals forces and physical entanglement. The dynamic covalent crosslinking network is composed of multiple side groups containing hindered urea functional groups that are also covalently grafted onto the polyethylene molecular chain. The hindered urea functional group side groups on different polyethylene molecular chains form crosslinking points through thermally dissociatable and recombination intermolecular hydrogen bonds.

2. The cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The cross-linked polyethylene insulated power cable is prepared by reactive grafting of the following components in parts by weight: Matrix resin: 90~98 parts; Dynamic network functional monomers: 1-5 copies; Physical network functionalized nanofillers: 0.5~3 parts; Grafting initiator: 0.05~0.2 parts; Composite antioxidant system: 0.2~0.8 parts.

3. A cross-linked polyethylene insulated power cable according to claim 2, characterized in that, The matrix resin is low-density polyethylene, and the melt index of the low-density polyethylene under the conditions of 190°C and 2.16kg load is 1.5~2.5g / 10min, and the density of the low-density polyethylene is 0.918~0.925g / cm³.

4. A cross-linked polyethylene insulated power cable according to claim 2, characterized in that, The dynamic network functional monomer is N-(tert-butyl)-N'-(4-vinylphenyl)urea; The physical network functionalized nanofiller is an octa(isobutyl)-mono(vinyl) polyhedral oligomeric silsesquioxane.

5. A cross-linked polyethylene insulated power cable according to claim 2, characterized in that, The grafting initiator is dicumyl peroxide; The composite antioxidant system consists of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as the main antioxidant and tris(2,4-di-tert-butylphenyl) phosphite as the auxiliary antioxidant.

6. A cross-linked polyethylene insulated power cable according to claim 1, characterized in that, The cage-like inorganic core is formed by carbon-carbon single bond covalent grafting through the addition reaction between the vinyl functional groups attached to it and the polyethylene molecular chain; The side group containing the hindered urea functional group is formed by carbon-carbon single bond covalent grafting through the addition reaction of the vinyl functional group it contains with the polyethylene molecular chain. The intermolecular hydrogen bonds are formed between the nitrogen-hydrogen bonds in the hindered urea functional group and the carbonyl oxygen in another hindered urea functional group.

7. A method for preparing a cross-linked polyethylene insulated power cable, used to prepare the cross-linked polyethylene insulated power cable according to any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Preparation of hierarchical network precursor material. This step is carried out in a reactive extrusion device. The matrix resin, dynamic network functional monomer, and physical network functionalized nanofiller are reactively grafted under the action of a grafting initiator, followed by devolatilization treatment, thereby obtaining hierarchical network precursor polyethylene particles without volatile byproducts. Step 2: Insulation layer extrusion and in-situ network curing. In this step, the layered network precursor polyethylene particles are extruded at high temperature and coated onto the conductor to form an insulation layer. Subsequently, the insulation layer is rapidly cooled, so that the dynamic covalent crosslinked network is kinetically frozen and cured during the cooling process, thereby forming the layered double network structure in-situ in the insulation layer.

8. The method for preparing a cross-linked polyethylene insulated power cable according to claim 7, characterized in that, Step one specifically includes the following procedures: The matrix resin and the composite antioxidant system are fed into a high-torque co-rotating twin-screw extruder through the main feed port, and melted and premixed in the first temperature zone. The mixture of the dynamic network functional monomer and the physical network functionalized nanofiller is added to the melt of the matrix resin through a side feed port located downstream of the melting zone, and is subjected to enhanced dispersion and mixing in the second temperature zone. The grafting initiator is injected into the melt after enhanced dispersion and mixing, and the grafting reaction is carried out in a third temperature range that is higher than the decomposition temperature of the grafting initiator, so that the dynamic network functional monomer and the physical network functionalized nanofiller are covalently grafted onto the molecular chain of the matrix resin. The grafted material is transported to the exhaust section connected to a vacuum system, where it undergoes vacuum devolatilization in the fourth temperature zone to remove unreacted monomers, initiator decomposition products, and other volatile substances. The devolatilized melt is extruded, cooled, and pelletized to obtain the hierarchical network precursor polyethylene particles.

9. The method for preparing a cross-linked polyethylene insulated power cable according to claim 8, characterized in that, The high-torque co-rotating twin-screw extruder has a length-to-diameter ratio of 48:1, and its screw assembly is configured sequentially from the feed inlet to the discharge outlet as a first conveying section, a first kneading section, a second conveying section, a side feeding section, a third conveying section, a second kneading section, a venting section, and a pressure-reducing extrusion section. The first temperature range is 140℃~160℃, the second temperature range is 170℃~180℃, the third temperature range is 185℃~205℃, and the fourth temperature range is 210℃~230℃.

10. The method for preparing a cross-linked polyethylene insulated power cable according to claim 9, characterized in that, The screw configuration of the second kneading section is composed of multiple kneading blocks with different staggered angles, including 30°, 60° and 90°, to generate a strong shearing and distribution mixing effect on the physical network functionalized nanofiller, so as to promote its molecular-level dispersion in the matrix resin melt.

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