A dynamically crosslinked polyolefin cable insulation material, its preparation method and use

Abstract

This invention discloses a dynamically cross-linked polyolefin cable insulation material, its preparation method, and its application, belonging to the field of cable joint technology. The material comprises a maleic anhydride-grafted polyolefin matrix, an alkaline catalyst, a cross-linking agent, and an elastomer. The maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polyethylene or maleic anhydride-grafted polypropylene. The cross-linking agent is trimethylolpropane tris(3-mercaptopropionate) or tetrakis(3-mercaptopropionic acid) pentaerythritol ester. A single-layer sample is obtained through melt blending, granulation, and hot pressing, and then two layers are superimposed and hot-pressed to form an integrated interface. This invention utilizes the topological reconstruction and cross-interface penetration of dynamic thioester bonds to eliminate microscopic defects at the cable joint interface, inhibit space charge accumulation, and significantly improve interface insulation performance. Simultaneously, the material is recyclable and reprocessable, making it suitable for insulation systems of power cable joints.

Description

Technical Field

[0001] This invention belongs to the field of cable joint technology, and particularly relates to a dynamic cross-linked polyolefin cable insulation material, its preparation method, and its application. Background Technology

[0002] With the rapid development of distributed energy, offshore wind power, and urban power grid transformation, the application scale of power cables continues to expand. In scenarios such as long-distance submarine cable transmission, mining mobile cables, and power grid laying in complex terrain, cable joints, as weak links in the power system, are frequently faulty due to their multi-layered structure and material interface defects. They are key components affecting the safe and stable operation of cable lines and ensuring continuous power transmission.

[0003] Currently, the industrial manufacturing of cable joints mainly employs wrapping or segmented molding processes, with cross-linked polyethylene (XLPE) or cross-linked polypropylene as the primary insulation materials. However, the manufacturing process of cable joints essentially involves constructing secondary insulation on top of the existing cable insulation. Traditional insulation systems face numerous severe challenges, most notably electrical failures caused by interfacial physical discontinuities. Specifically, cable joint manufacturing involves steps such as conductor welding and restoration, conductor shielding layer restoration, stress cone preheating, injection molding insulation, and heat vulcanization. Ultimately, the insulation material is directly applied to the surface of the conductor containing the semi-conductive layer to ensure that the joint insulation layer thickness and flexibility are consistent with the main cable insulation. Because traditional XLPE has an irreversible thermosetting three-dimensional cross-linked network, once cross-linking, curing, and crystallization are complete, the molecular chains cannot undergo cross-interfacial entanglement during joint forming. This results in only simple physical contact between the wrapping layers or at the joint interface, inevitably leaving microscopic air gaps and physical delamination. Although polypropylene has high heat resistance, its high modulus and brittleness make it prone to stress concentration and microcracks during joint wrapping, and the interfacial fusion still falls short of the requirements for integration. Therefore, under the influence of a high-voltage electric field, these interfacial defects can easily induce partial discharge, leading to a significant decrease in joint performance.

[0004] Furthermore, discontinuities at the insulation interface generate numerous deep trap energy levels, leading to severe accumulation of space charge at the joint interface. This charge accumulation induces significant local electric field distortion, causing the actual electric field strength to far exceed the design value. This accelerates the electro-aging process of the joint insulation material and can even cause surface flashover or breakdown at operating conditions far below the breakdown field strength, severely shortening the joint's service life. Existing physical modification methods (such as adding silicone grease and interface polishing) can only temporarily alleviate macroscopic gaps and cannot eliminate interface defects and interface charge accumulation at the molecular level.

[0005] Therefore, there is an urgent need to provide an integrated insulation method for cable joints that combines interface defect elimination and interface charge suppression. Summary of the Invention

[0006] This invention proposes a dynamically cross-linked polyolefin cable insulation material, its preparation method, and its application. The method utilizes a cable insulation material containing dynamic covalent bonds. By leveraging the characteristics of these dynamic covalent bonds in its molecular structure, topological reconstruction and cross-interface penetration of the interfacial molecular chains are induced during the post-joint treatment stage. This fundamentally eliminates microscopic defects in the interface region between the cable joint's body insulation and the restored insulation, suppresses electric field distortion caused by space charge, and achieves integrated joint insulation at the molecular level.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A dynamically cross-linked polyolefin cable insulation material, comprising: a maleic anhydride-grafted polyolefin matrix, an alkaline catalyst, and a cross-linking agent; The maleic anhydride-grafted polyolefin matrix includes maleic anhydride-grafted polyethylene or maleic anhydride-grafted polypropylene. The crosslinking agent includes trimethylolpropane tris(3-mercaptopropionate) (TMPMP) or pentaerythritol tetrakis(3-mercaptopropionate) (PETMP).

[0008] The dynamically cross-linked polyolefin cable insulation material provided by this invention achieves effective cross-linking of a maleic anhydride-grafted linear low-density polyethylene and polypropylene hybrid elastomer by introducing dynamic thioester bonds, thus endowing it with the ability to eliminate interfacial defects. This cross-linked network significantly improves the dielectric properties of the material. Furthermore, these dynamic covalent bonds enable the material to undergo cross-interfacial fusion, thereby eliminating interfacial defects and suppressing space charge accumulation, significantly improving the interfacial insulation performance of cable joints.

[0009] Furthermore, when the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polyethylene, it comprises the following raw materials by mass: 0.001 to 0.003 parts of alkaline catalyst, 1 part of maleic anhydride-grafted polyethylene, and 0.01 to 0.1 parts of trimethylolpropane tris(3-mercaptopropionate).

[0010] Furthermore, when the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polypropylene, the raw materials also include an elastomer; by mass parts, the raw materials include the following: 0.4 parts elastomer, 0.6 parts maleic anhydride-grafted polypropylene, 0.01~0.1 parts pentaerythritol tetrakis(3-mercaptopropionic acid) ester and 0.008 parts alkaline catalyst.

[0011] Further, the alkaline catalyst is pyridine, triethylamine, N,N-diisopropylethylamine, 1-methyl-1H-imidazolium or 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0012] Furthermore, the maleic anhydride-grafted polyethylene is low-density polyethylene (LDPE), and its maleic anhydride grafting rate is 0.1~1%.

[0013] Furthermore, the elastomer is an ethylene-octene copolymer or an ethylene-butene copolymer, i.e., a polyolefin elastomer (POE).

[0014] Furthermore, the grafting rate of the maleic anhydride-grafted polypropylene is 0.1-1%.

[0015] The present invention also provides a method for preparing the dynamically cross-linked polyolefin cable insulation material, comprising the following steps: The raw materials are weighed and mixed according to mass. After the melt blending reaction, the resulting sample is granulated and hot-pressed to obtain a single-layer dynamic cross-linked sample. Two single-layer dynamic cross-linked samples are fused together by double-layer hot pressing to form an integrated interface, thus obtaining a dynamic cross-linked polyolefin cable insulation material.

[0016] This invention is based on click chemistry principles, constructing dynamic covalent bonds through polycondensation reactions to achieve crosslinking of polyethylene and polypropylene joint insulation materials. This crosslinked polyethylene insulation material possesses excellent dual properties: it exhibits structurally stable thermosetting materials at its long-term operating temperature; however, during extrusion processing and decommissioning and recycling, it displays the plastic characteristics of thermoplastic materials.

[0017] Furthermore, when the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polyethylene, the preparation method of single-layer dynamic cross-linked polyethylene includes the following steps: under conditions of 130~190℃ and 50~70r / min, maleic anhydride-grafted polyethylene, alkaline catalyst and cross-linking agent are sequentially melt-treated, the obtained sample is extruded and granulated, and then hot-pressed at 130~190℃ and 10~15MPa for 10~30min to obtain single-layer dynamic cross-linked polyethylene.

[0018] Furthermore, when the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polypropylene, the preparation method of monolayer dynamically crosslinked polypropylene includes the following steps: under conditions of 180~190℃ and 50~70r / min, maleic anhydride-grafted polypropylene, alkaline catalyst, pentaerythritol tetrakis(3-mercaptopropionic acid) ester and elastomer are sequentially melt-treated, the obtained sample is extruded and granulated, and then hot-pressed at 190~210℃ and 10~15MPa for 10~30min to obtain monolayer dynamically crosslinked polypropylene.

[0019] Furthermore, the conditions for the double-layer superimposed hot pressing are as follows: When the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polyethylene, the hot pressing temperature is 170~190℃, the hot pressing pressure is 3~5MPa, and the hot pressing time is 3~5min. When the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polypropylene, the hot-pressing temperature is 190~210℃, the hot-pressing pressure is 3~5MPa, and the hot-pressing time is 3~5min.

[0020] This invention also provides an application of the aforementioned dynamic cross-linked polyolefin cable insulation material in AC or DC power cable joints of medium-voltage (1~35kV) or high-voltage (35~800kV) levels. Its maximum continuous operating temperature is 90℃, and the dissociation activation temperature range of its internal dynamic covalent bonds is 120~300℃.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects: The dynamically cross-linked polyolefin cable insulation material prepared by this invention achieves effective cross-linking of maleic anhydride-grafted linear low-density polyethylene and polypropylene hybrid elastomers by introducing dynamic thioester bonds, thus endowing it with the ability to eliminate interfacial defects. This cross-linking network significantly improves the dielectric properties of the material. Furthermore, compared with traditional cross-linked polyethylene and polypropylene, the dynamic covalent bonds promote cross-interfacial fusion, thereby eliminating interfacial defects and inhibiting space charge accumulation, significantly improving the interfacial insulation performance of cable joints. This material is expected to be widely used in interfacial insulation systems for power cable accessories.

[0022] The present invention provides a method for preparing recyclable cross-linked polyolefin cable insulation material, using maleic anhydride-grafted polyethylene and polypropylene, elastomers, and thiols as raw materials, which are obtained through high-temperature reaction under alkaline catalyst conditions. This method effectively overcomes the technical bottleneck caused by incomplete fusion of initial insulation and reinforcing insulation at the interface during the production of joints using traditional cross-linked polyethylene and polypropylene, fundamentally avoiding a significant decrease in joint insulation performance due to interface defects.

[0023] The preparation method provided by this invention can effectively eliminate microscopic defects at the cable joint interface, suppress space charge accumulation, and prevent the joint insulation performance from deteriorating. The resulting dynamically cross-linked polyethylene and dynamically cross-linked polypropylene materials retain their original dielectric properties while possessing recyclable processing capabilities. Because the materials of this invention combine the advantages of both thermosetting and thermoplastic materials, they are expected to be widely used in the field of high-voltage cable accessories where interface performance requirements are stringent. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The space charge density is the space charge density of the insulating materials prepared in Examples 1, 2, 1, and 2. Detailed Implementation

[0025] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0026] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0028] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0029] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0030] This invention provides a dynamically cross-linked polyolefin cable insulation material, comprising: a maleic anhydride-grafted polyolefin matrix, an alkaline catalyst, a cross-linking agent, and an elastomer; wherein the maleic anhydride-grafted polyolefin matrix comprises maleic anhydride-grafted polyethylene or maleic anhydride-grafted polypropylene; and the cross-linking agent comprises trimethylolpropane tris(3-mercaptopropionate) (TMPMP) or pentaerythritol tetrakis(3-mercaptopropionate) (PETMP).

[0031] In the following optional embodiments of the present invention, when the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polyethylene, it includes the following raw materials by mass parts: 0.001 to 0.003 parts of alkaline catalyst, 1 part of maleic anhydride-grafted polyethylene and 0.01 to 0.1 parts of trimethylolpropane tris(3-mercaptopropionate).

[0032] In the following optional embodiments of the present invention, when the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polypropylene, it comprises the following raw materials by mass parts: 0.4 parts elastomer, 0.6 parts maleic anhydride-grafted polypropylene, 0.01~0.1 parts pentaerythritol tetrakis(3-mercaptopropionic acid) ester and 0.008 parts alkaline catalyst.

[0033] In the following optional embodiments of the present invention, the alkaline catalyst is pyridine, triethylamine, N,N-diisopropylethylamine, 1-methyl-1H-imidazolium or 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0034] In the following optional embodiments of the present invention, the maleic anhydride-grafted polyethylene is low-density polyethylene (LDPE), and its maleic anhydride grafting rate is 0.1~1%.

[0035] In the following optional embodiments of the present invention, the elastomer is an ethylene-octene copolymer or an ethylene-butene copolymer, i.e., a polyolefin elastomer (POE).

[0036] In the following optional embodiments of the present invention, the grafting rate of maleic anhydride-grafted polypropylene is 0.1-1%.

[0037] This invention also provides a method for preparing a dynamically cross-linked polyolefin cable insulation material (with maleic anhydride-grafted polyethylene as the matrix), comprising the following steps: Preheat the torque rheometer to 130~190℃ (e.g., 130℃) and maintain the preheating temperature for 10~15 minutes (e.g., 10 minutes) to ensure a stable thermodynamic environment inside the equipment; adjust the rotation speed to 50~70 r / min. After stirring at 70 r / min, maleic anhydride-grafted polyethylene is added to a torque rheometer and heated for 5 min to fully melt the base material. An alkaline catalyst is added to the torque rheometer and stirred for another 5 min to ensure uniform dispersion of the catalyst in the molten maleic anhydride-grafted polyethylene matrix. Trimethylolpropane tris(3-mercaptopropionate) crosslinking agent is added to the torque rheometer and stirred for another 30 min. Through click-chemically mediated condensation, dynamic covalent bonds (thioester bonds) are introduced into the polyethylene matrix to form a dynamic crosslinking network. After the reaction, the material is removed from the torque rheometer and extruded to granulate, yielding dynamically crosslinked polyethylene granules. Using a flat vulcanizing machine, the granules are hot-pressed at 130-190℃ (e.g., 130℃) and 10-15MPa (e.g., 10MPa) for 10-30 min (e.g., 20 min) to obtain single-layer dynamically crosslinked polyethylene. Two single-layer dynamic cross-linked polyethylene sheets of the same thickness and size are stacked and hot-pressed for 3-5 minutes (e.g., 5 minutes) at a temperature of 170-190℃ (e.g., 180℃) and a pressure of 3-5MPa (e.g., 3MPa) to obtain double-layer dynamic cross-linked polyethylene.

[0038] This invention also provides a method for preparing a dynamically cross-linked polyolefin cable insulation material (with maleic anhydride-grafted polypropylene as the matrix), comprising the following steps: Preheat the torque rheometer to 180~190℃ (e.g., 190℃) and maintain the preheating temperature for 10~15min (e.g., 10min) to ensure a stable thermodynamic environment inside the equipment. Adjust the rotation speed to 50~70r / min (e.g., 60r / min), add maleic anhydride-grafted polypropylene to the torque rheometer and heat for 5min to fully melt the base material. Add pentaerythritol tetrakis(3-mercaptopropionic acid) to the torque rheometer and continue stirring for 5min. Finally, add the elastomer to the torque rheometer and continue stirring for 15min to form a dynamic crosslinked network. After the reaction is complete, remove the material from the torque rheometer and granulate it by extrusion to obtain dynamically crosslinked polypropylene granules. Use a flat vulcanizing machine to hot-press the granules at 190~210℃ (e.g., 200℃) and 10~15MPa (e.g., 10MPa) for 10~30min (e.g., 20min) to obtain single-layer dynamically crosslinked polypropylene. Two single-layer dynamic cross-linked polypropylene sheets of the same thickness and size are stacked and hot-pressed for 3-5 minutes (e.g., 5 minutes) at a temperature of 190-210℃ (e.g., 190℃) and a pressure of 3-5MPa (e.g., 3MPa) to obtain double-layer dynamic cross-linked polyethylene.

[0039] This dynamically cross-linked polyolefin cable insulation material can be recycled and reprocessed. It is obtained by reacting maleic anhydride-grafted polyethylene and polypropylene, elastomers, and thiols under alkaline catalyst conditions at high temperature. The specific steps are as follows: the dynamically cross-linked polyolefin cable insulation material is pulverized to obtain recyclable dynamically cross-linked polyethylene and polypropylene fragments; the obtained fragments are mixed with thiols and an alkaline catalyst, and then treated at 180-200℃ and 2-10MPa pressure for 10-30 minutes to reshape it.

[0040] This dynamically cross-linked polyolefin cable insulation material can be used in AC or DC power cable joints of medium voltage (1~35kV) or high voltage (35~800kV) levels. Its maximum continuous operating temperature is 90℃, and the dissociation activation temperature range of the internal dynamic covalent bonds is 120~300℃.

[0041] Unless otherwise specified, "room temperature" in this invention refers to 25±2℃.

[0042] Unless otherwise specified, the term "parts" in this invention refers to parts by weight.

[0043] All raw materials used in this invention were purchased commercially. Maleic anhydride-grafted polyethylene was purchased from Guangdong Mingyuan Plastics; trimethylolpropane tris(3-mercaptopropionate) (TMPMP) and pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) were purchased from Aladdin Biochemical Technology Co., Ltd.; the alkaline catalysts pyridine, triethylamine, N,N-diisopropylethylamine, and 1-methyl-1H-imidazol were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; maleic anhydride-grafted polypropylene was purchased from Dinghai Plastics & Chemical Co., Ltd.; and the elastomer, ENGAGE 8150, was purchased from Dow Chemical Company, USA.

[0044] The technical solution of the present invention will be further illustrated by the following embodiments.

[0045] Example 1 A dynamic cross-linked polyolefin cable insulation material, the raw materials being: 0.001 parts of alkaline catalyst (1,5,7-triazabicyclo[4.4.0]dec-5-ene), 1 part of maleic anhydride grafted polyethylene (grafting rate 1%) and 0.01 parts of trimethylolpropane tris(3-mercaptopropionate) (TMPMP) (the number of parts is an approximate value of the specific amount used, the same below).

[0046] A method for preparing a dynamically cross-linked polyolefin cable insulation material, comprising the following steps: (1) Preheat the torque rheometer to 130℃ and keep it warm for 10 min. After adjusting the speed to 70 r / min, add 40 g of maleic anhydride grafted polyethylene to the torque rheometer and heat for 5 min. Then add 0.05 g of alkaline catalyst to the torque rheometer and continue stirring for 5 min. Finally, add 0.54 g of trimethylolpropane tris(3-mercaptopropionate) crosslinking agent to the torque rheometer and continue stirring for 30 min. After the reaction is completed, take the material out of the torque rheometer and granulate it by extrusion to obtain dynamic crosslinked polyethylene granules. Use a flat vulcanizing machine to hot press the granules at 130℃ and 10 MPa pressure for 20 min to finally obtain single-layer dynamic crosslinked polyethylene. (2) Two single-layer dynamic cross-linked polyethylenes of the same thickness and size are stacked and hot-pressed for 5 minutes at a temperature of 180℃ and a pressure of 3MPa to obtain double-layer dynamic cross-linked polyethylene, i.e. dynamic cross-linked polyolefin cable insulation material.

[0047] Example 2 The raw materials are: 0.4 parts elastomer (ethylene-octene copolymer), 0.6 parts maleic anhydride-grafted polypropylene (grafting rate of 1%), 0.01 parts pentaerythritol tetrakis(3-mercaptopropionic acid) ester (PETMP), and 0.008 parts alkaline catalyst (1-methyl-1H-imidazolium).

[0048] A method for preparing a dynamically cross-linked polyolefin cable insulation material, comprising the following steps: (1) Preheat the torque rheometer to 190℃ and keep it warm for 10 min. After adjusting the speed to 60 r / min, add 18 g of maleic anhydride-grafted polypropylene to the torque rheometer and heat for 5 min. Then add 0.224 g of alkaline catalyst and 0.37 g of pentaerythritol tetrakis(3-mercaptopropionic acid) to the torque rheometer and continue stirring for 5 min. Finally, add 12 g of elastomer to the torque rheometer and continue stirring for 15 min. After the reaction is complete, take the material out of the torque rheometer and granulate it by extrusion to obtain dynamic cross-linked polypropylene granules. Use a flat vulcanizing machine to hot press the granules at 200℃ and 10 MPa pressure for 20 min to obtain single-layer dynamic cross-linked polypropylene. (2) Two single-layer dynamic cross-linked polypropylenes of the same thickness and size are stacked and hot-pressed for 5 minutes at a temperature of 190℃ and a pressure of 3MPa to obtain double-layer dynamic cross-linked polypropylene, i.e. dynamic cross-linked polyolefin cable insulation material.

[0049] Comparative Example 1 Conventional cross-linked polyethylene, purchased from Borealis GmbH, model number LS4258DCE.

[0050] Comparative Example 2 The polypropylene was purchased from Liaotong Chemical Co., Ltd., and the model number is Panjin 401.

[0051] Performance Test 1 Bilayer samples from Example 1 (dynamically cross-linked polyethylene), Example 2 (dynamically cross-linked polypropylene), Comparative Example 1 (conventional cross-linked polyethylene), and Comparative Example 2 (conventional polypropylene) were all processed into samples with the same thickness (200 micrometers). The space charge density of all bilayer samples was tested using the PEA method, and the results are as follows: Figure 1 As shown, from Figure 1 The dynamic cross-linking method effectively eliminates the space charge accumulated at the interface.

[0052] Performance Test 2 The monolayer and bilayer samples of Example 1 (dynamically cross-linked polyethylene), Example 2 (dynamically cross-linked polypropylene), Comparative Example 1 (conventional cross-linked polyethylene), and Comparative Example 2 (conventional polypropylene) were all processed into samples with the same thickness (the thickness of both monolayer and bilayer samples was 100 micrometers). Their breakdown field strength was tested, and the average breakdown field strength and shape parameter β are shown in Table 1.

[0053] Table 1 Breakdown field strength of different samples As shown in Table 1, the presence of the interface significantly reduces the breakdown characteristics of conventional cross-linked polyethylene and conventional polypropylene. For example, the breakdown field strength of conventional cross-linked polyethylene decreases from 403.3 kV / mm without the interface to 329.4 kV / mm with the interface, while the breakdown field strengths of single-layer and double-layer samples of dynamically cross-linked polyethylene and dynamically cross-linked polypropylene are similar. Furthermore, the interface also leads to a significant reduction in the shape parameter β, but the shape parameter β of single-layer and double-layer samples of dynamically cross-linked polyethylene and dynamically cross-linked polypropylene is less affected by the interface.

[0054] In summary, the dynamically cross-linked polyethylene and dynamically cross-linked polypropylene prepared in Examples 1 and 2, through the introduction of dynamic thioester bonds, endow the materials with excellent interfacial defect repair and reprocessing capabilities. These materials not only maintain excellent dielectric properties but also eliminate interfacial charge accumulation and insulation performance degradation caused by interfacial defects, showing broad engineering application prospects in the field of power cable joints or other cable accessories.

[0055] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A dynamically cross-linked polyolefin cable insulation material, characterized in that, Raw materials include: Maleic anhydride-grafted polyolefin matrix, alkaline catalyst and crosslinking agent; The maleic anhydride-grafted polyolefin matrix includes maleic anhydride-grafted polyethylene or maleic anhydride-grafted polypropylene. The crosslinking agent includes trimethylolpropane tris(3-mercaptopropionate) or pentaerythritol tetrakis(3-mercaptopropionate).

2. The dynamically cross-linked polyolefin cable insulation material according to claim 1, characterized in that, When the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polyethylene, it comprises the following raw materials by mass: 0.001 to 0.003 parts of alkaline catalyst, 1 part of maleic anhydride-grafted polyethylene, and 0.01 to 0.1 parts of trimethylolpropane tris(3-mercaptopropionate).

3. The dynamically cross-linked polyolefin cable insulation material according to claim 1, characterized in that, When the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polypropylene, the raw material also includes an elastomer; by mass parts, the raw material includes the following: 0.4 parts elastomer, 0.6 parts maleic anhydride-grafted polypropylene, 0.01~0.1 parts pentaerythritol tetrakis(3-mercaptopropionic acid) ester and 0.008 parts alkaline catalyst.

4. The dynamically cross-linked polyolefin cable insulation material according to claim 1, characterized in that, The alkaline catalyst is pyridine, triethylamine, N,N-diisopropylethylamine, 1-methyl-1H-imidazolium or 1,5,7-triazabicyclo[4.4.0]dec-5-ene; The maleic anhydride-grafted polyethylene is low-density polyethylene, and its maleic anhydride grafting rate is 0.1-1%; the maleic anhydride-grafted polypropylene has a grafting rate of 0.1-1%.

5. The dynamically cross-linked polyolefin cable insulation material according to claim 1, characterized in that, The elastomer is an ethylene-octene copolymer or an ethylene-butene copolymer.

6. A method for preparing a dynamically cross-linked polyolefin cable insulation material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: The raw materials are weighed and mixed according to mass. After the melt blending reaction, the resulting sample is granulated and hot-pressed to obtain a single-layer dynamic cross-linked sample. Two single-layer dynamic cross-linked samples are fused together by double-layer hot pressing to form an integrated interface, thus obtaining a dynamic cross-linked polyolefin cable insulation material.

7. The method for preparing the dynamically cross-linked polyolefin cable insulation material according to claim 6, characterized in that, When the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polyethylene, the preparation method of single-layer dynamic cross-linked polyethylene includes the following steps: under conditions of 130~190℃ and 50~70r / min, maleic anhydride-grafted polyethylene, alkaline catalyst and cross-linking agent are melt-treated in sequence, the obtained sample is extruded and granulated, and then hot-pressed at 130~190℃ and 10~15MPa for 10~30min to obtain single-layer dynamic cross-linked polyethylene.

8. The method for preparing the dynamically cross-linked polyolefin cable insulation material according to claim 6, characterized in that, When the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polypropylene, the preparation method of monolayer dynamically crosslinked polypropylene includes the following steps: under conditions of 180~190℃ and 50~70r / min, maleic anhydride-grafted polypropylene, alkaline catalyst, pentaerythritol tetrakis(3-mercaptopropionic acid) ester and elastomer are sequentially melt-treated, the obtained sample is extruded and granulated, and then hot-pressed at 190~210℃ and 10~15MPa for 10~30min to obtain monolayer dynamically crosslinked polypropylene.

9. The method for preparing the dynamically cross-linked polyolefin cable insulation material according to claim 6, characterized in that, The conditions for the double-layer superimposed hot pressing are: When the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polyethylene, the hot pressing temperature is 170~190℃, the hot pressing pressure is 3~5MPa, and the hot pressing time is 3~5min. When the maleic anhydride-grafted polyolefin matrix is ​​maleic anhydride-grafted polypropylene, the hot-pressing temperature is 190~210℃, the hot-pressing pressure is 3~5MPa, and the hot-pressing time is 3~5min.

10. The application of a dynamically cross-linked polyolefin cable insulation material as described in any one of claims 1 to 5 in cable joints.

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