Environment-friendly polyolefin cable insulating material and preparation and repair method thereof

Abstract

The invention discloses an environment-friendly polyolefin cable insulating material and a preparation and repair method thereof, and belongs to the technical field of new electrical materials, the environment-friendly polyolefin cable insulating material comprises the following raw materials by weight: 0.001-0.015 part of a basic catalyst, 1 part of maleic anhydride grafted polyethylene and 0.01-0.15 part of a polythiol cross-linking agent; then based on click chemistry, through condensation polymerization, the environment-friendly crosslinked polyethylene cable insulation material is prepared by adopting dynamic covalent bonds. The preparation method provided by the invention can effectively avoid the generation of a large number of byproducts, and the prepared crosslinked polyethylene keeps the dielectric property of the crosslinked polyethylene and the recoverability of linear low-density polyethylene at the same time, and the cable insulating material has the advantages of thermosetting and thermoplastic materials. The material is expected to be widely applied to a power cable insulation system.

Description

Technical Field

[0001] The invention belongs to the technical field of new electrical materials, and in particular relates to an environmentally friendly polyolefin cable insulation material and a preparation and repair method thereof. Background Art

[0002] High-voltage power cables are an important part of modern power grids that integrate renewable energy. The most common insulation material for extruded high-voltage cables is cross-linked polyethylene, which is based on low-density polyethylene and cross-linked at high temperature by peroxide. However, cross-linked polyethylene is a thermosetting plastic that is insoluble and infusible. It cannot be recycled after retirement, which leads to environmental pollution and waste of resources. In addition, peroxide cross-linking produces a large amount of by-products, such as water and methanol, which are harmful to health and cause premature aging of the dielectric during use. The above factors have promoted the development of thermoplastic cable insulation.

[0003] Low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), etc. have been used for medium and high voltage power cable insulation due to their simple processing technology, no generation of cross-linked by-products, excellent insulation performance, and good toughness. However, due to its melting temperature of about 130°C, it is not conducive to the operation of power cables under high temperature conditions. Although in the past few decades, researchers have modified polyethylene by copolymerization, blending, nano-doping and other means, and its dielectric properties have been improved, the improvement of the thermal properties of LDPE and LLDPE is not obvious. High-density polyethylene (HDPE) and polypropylene (PP) have similar dielectric properties and excellent thermal stability to LDPE and LLDPE. However, taking PP as an example, PP cannot be used for cable insulation because it is brittle and has low toughness. In order to solve this problem, elastomers are usually introduced into PP. However, the introduction of elastomers limits the operation of PP cables at high temperatures, resulting in problems such as cable eccentricity.

[0004] Therefore, there is an urgent need to provide a novel, environmentally friendly cross-linked polyolefin cable insulation material and a preparation method thereof. Summary of the invention

[0005] In view of the above technical problems, the present invention proposes an environmentally friendly polyolefin cable insulation material and a preparation and repair method thereof.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] An environmentally friendly polyolefin cable insulation material, the raw materials of which include, by weight:

[0009] 0.001-0.015 parts of alkaline catalyst, 1 part of maleic anhydride grafted polyethylene, 0.01-0.15 parts of polythiol crosslinking agent.

[0010] Preferably, the maleic anhydride grafted polyethylene used as the base material is a linear low-density polyethylene with a grafting rate of 1% to 10%.

[0011] Preferably, the polythiol includes one or more of trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptopropionate) or pentaerythritol tetrakis(3-mercaptobutyrate).

[0012] Preferably, the alkaline catalyst is one or more of pyridine, triethylamine, N,N-diisopropylethylamine, 1-methyl-1H-imidazole, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0013] Preferably, the environmentally friendly polyolefin cable insulation material is applied to AC and DC voltage types, the voltage levels are medium voltage cables and high voltage cables, its normal operating temperature is lower than 90°C, and the dissociation temperature of dynamic covalent bonds is 120-300°C.

[0014] Preferably, the environmentally friendly polyolefin cable insulation material can be recycled and reprocessed, and the specific steps are:

[0015] crushing the environmentally friendly polyolefin cable insulation material to obtain recyclable cross-linked polyethylene fragments;

[0016] The recyclable cross-linked polyethylene fragments are treated at 100-150° C. and 2-5 MPa pressure for 30-50 minutes and reshaped.

[0017] The second technical solution of the present invention:

[0018] The method for preparing the above-mentioned environmentally friendly polyolefin cable insulation material comprises the following steps:

[0019] The environmentally friendly polyolefin cable insulation material can be obtained by mixing the raw materials according to the dosage ratio, performing high-temperature reaction, extruding and then pressing into sheets.

[0020] Beneficial effects: The present invention is based on click chemistry and adopts dynamic covalent bond cross-linking polyethylene cable insulation material through polycondensation reaction. The cross-linked polyethylene insulation material is a thermosetting material at long-term working temperature and a thermoplastic material during extrusion processing and decommissioning and recycling. That is, an insulation material with the comprehensive advantages of thermoplasticity and thermoplasticity is obtained through the preparation method of the present invention.

[0021] Preferably, the high temperature reaction is carried out in a hybrid rheometer, and the hybrid rheometer needs to be preheated before the reaction.

[0022] Preferably, the preheating condition is: preheating at 150-160°C for 10-15 minutes.

[0023] Preferably, the conditions during the high temperature reaction are:

[0024] At 130-160°C, mix and react at a speed of 50-100 r / min for 10-30 min.

[0025] The third technical solution of the present invention:

[0026] The above-mentioned method for repairing the environmentally friendly polyolefin cable insulation material comprises the following steps:

[0027] The cross-linked polyolefin cable insulation material damaged by electrical breakdown is treated at 100-150°C and 1-5MPa pressure for 20-30 minutes.

[0028] Compared with the prior art, the present invention has the following advantages and technical effects:

[0029] The recyclable (environmentally friendly) cross-linked polyolefin cable insulation material prepared by the present invention realizes the cross-linking of low-density linear polyethylene grafted with maleic anhydride and its reprocessing performance by introducing dynamic thioester bonds. The cross-linked network improves the dielectric properties of the material, especially the improvement of the withstand voltage strength. Secondly, compared with the traditional insoluble and infusible cross-linked polyethylene, the dynamic covalent bond gives the material remodeling and recyclability. The material has the advantages of both thermosetting and thermoplastic materials, and is expected to be widely used in power cable insulation systems.

[0030] The preparation method of the recyclable cross-linked polyolefin cable insulation material provided by the present invention can be obtained by high temperature reaction with polyethylene grafted with maleic anhydride and mercaptan as raw materials under the catalytic condition of alkaline catalyst. Traditional cross-linked polyethylene is obtained by peroxide cross-linking, but peroxide cross-linking will produce a large number of by-products such as water, methane, etc., which need to be removed through cumbersome degassing and other operations. The preparation method provided by the present invention can effectively avoid the generation of a large number of by-products, and the prepared cross-linked polyethylene simultaneously maintains the dielectric properties of the cross-linked polyethylene and the recyclability of the linear low-density polyethylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0032] Figure 1 This is a schematic diagram of the change of the dielectric constant and loss tangent value of the recyclable cross-linked polyethylene at room temperature with frequency obtained in Example 1 of the present invention;

[0033] Figure 2This is a schematic diagram of the change of dielectric constant with frequency at room temperature of the recyclable cross-linked polyethylene prepared in Example 1 of the present invention before and after the electrical breakdown damage is repaired;

[0034] Figure 3 This is a Weibull distribution diagram of the breakdown field strength of the recyclable cross-linked polyethylene crushed and hot-pressed in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0036] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0037] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0038] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0039] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0040] The invention discloses a method for preparing recyclable cross-linked polyethylene, comprising the following steps:

[0041] S1: The raw materials include, by weight: 0.001-0.015 parts of alkaline catalyst, 1 part of maleic anhydride grafted polyethylene base material, and 0.01-0.15 parts of polythiol crosslinking agent;

[0042] S2: Mix and react the above raw materials at high temperature and extrude them, and then press them into sheets on a flat vulcanizing machine to obtain green, environmentally friendly and recyclable cross-linked polyethylene high-voltage cable insulation material.

[0043] The preparation method of recyclable cross-linked polyethylene disclosed in the present invention can be obtained by high temperature reaction with polyethylene grafted with maleic anhydride and mercaptan as raw materials under the catalytic condition of alkaline catalyst. Traditional cross-linked polyethylene is obtained by peroxide cross-linking, but peroxide cross-linking will produce a large number of by-products such as water, methane, etc., which need to be removed through cumbersome experimental operations such as degassing. The above-mentioned preparation method provided by the present invention effectively avoids the generation of a large number of by-products, and finally maintains the dielectric properties of cross-linked polyethylene and the recyclability of linear low-density polyethylene.

[0044] In a preferred embodiment, the basic catalyst is any one of pyridine, triethylamine, N,N-diisopropylethylamine, and 1-methyl-1H-imidazole.

[0045] The maleic anhydride grafted polyethylene is a linear low-density polyethylene with a grafting rate of 1% to 10%;

[0046] The thiol is a polythiol, specifically any one of trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptopropionate) or pentaerythritol tetrakis(3-mercaptobutyrate);

[0047] In a preferred embodiment, the high temperature mixing reaction process uses a mixing rheometer to perform the high temperature reaction. Specifically, in order to make the reaction more complete, a mixing rheometer with a faster rotation speed is used to perform the high temperature reaction.

[0048] In a preferred embodiment, when using the hybrid rheometer, the instrument is first preheated at 150-160° C. for 10-15 minutes. The preheating process is for sufficient mixing reaction in the next step.

[0049] In a preferred embodiment, the monomers are fully mixed and reacted at a high temperature of 130-160° C. using a mixing rheometer at a speed of 50-100 r / min for 10-30 min. In order to avoid thermal oxidative aging caused by setting the temperature too high, the speed is limited to 50-100 r / min to ensure sufficient mixing reaction.

[0050] The "parts" described in the present invention, unless otherwise specified, refer to parts by mass.

[0051] The raw materials used in the present invention are all purchased from the market. Maleic anhydride grafted polyethylene was purchased from Ningbo Yuntao Plastics, trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionic acid) ester or pentaerythritol tetra(3-mercaptobutyric acid) ester, and 1-methyl-1H-imidazole were purchased from Aladdin Biochemical Technology Co., Ltd., and pyridine, triethylamine, and N,N-diisopropylethylamine were purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0052] The technical solution of the present invention is further illustrated by the following embodiments.

[0053] Example 1

[0054] In this embodiment, maleic anhydride grafted polyethylene with a grafting rate of 1% is used as the matrix, trimethylolpropane tris(3-mercaptopropionate) is used as the polythiol, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene is used as the catalyst.

[0055] The preparation method of recyclable cross-linked polyethylene (environmentally friendly polyolefin cable insulation material) comprises the following steps:

[0056] Use a rotational rheometer, preheat at 150°C for 10 minutes; adjust the speed to 70r / min, add 30g of maleic anhydride grafted polyethylene with a grafting rate of 1%, and preheat for 5 minutes; then add 0.04g of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, and continue stirring for 5 minutes; finally, add 0.40g of trimethylolpropane tris(3-mercaptopropionate) and stir for 30 minutes to obtain a recyclable cross-linked polyethylene material.

[0057] Furthermore, the material was hot-pressed at 120° C. and 3 MPa for 20 min using a flat vulcanizer to obtain a recyclable cross-linked polyethylene sheet.

[0058] In this embodiment, the structural formula of the prepared recyclable cross-linked polyethylene is:

[0059]

[0060] Example 2

[0061] In this embodiment, maleic anhydride grafted polyethylene with a grafting rate of 1% is used as the matrix, pentaerythritol tetrakis(3-mercaptopropionate) is used as the polythiol, and 1-methyl-1H-imidazole is used as the catalyst.

[0062] The method for preparing recyclable cross-linked polyethylene comprises the following steps:

[0063] Use a rotational rheometer, preheat at 155°C for 10 minutes; adjust the speed to 80r / min, add 30g of maleic anhydride grafted polyethylene with a grafting rate of 1%, and preheat for 6 minutes; then add 0.04g of 1-methyl-1H-imidazole, and continue stirring for 5 minutes; finally, add 0.37g of pentaerythritol tetrakis(3-mercaptopropionic acid) and stir for 25 minutes to obtain a recyclable cross-linked polyethylene material.

[0064] Furthermore, the material was hot-pressed at 150° C. and 3 MPa for 20 min using a flat vulcanizer to obtain a recyclable cross-linked polyethylene sheet.

[0065] In this embodiment, the structural formula of the prepared recyclable cross-linked polyethylene is:

[0066]

[0067] Example 3

[0068] In this embodiment, maleic anhydride grafted polyethylene with a grafting rate of 2% is used as the matrix, pentaerythritol tetrakis(3-mercaptopropionate) is used as the polythiol, and triethylamine is used as the catalyst.

[0069] The method for preparing recyclable cross-linked polyethylene comprises the following steps:

[0070] Use a rotational rheometer, preheat at 160°C for 10 minutes; adjust the speed to 100 r / min, add 30g of maleic anhydride grafted polyethylene with a grafting rate of 2%, and preheat for 7 minutes; then add 0.07g of triethylamine and continue stirring for 5 minutes; finally, add 0.73g of pentaerythritol tetrakis(3-mercaptopropionic acid) and stir for 30 minutes to obtain a recyclable cross-linked polyethylene material.

[0071] Furthermore, the material was hot-pressed at 130° C. and 5 MPa for 30 min using a flat vulcanizer to obtain a recyclable cross-linked polyethylene sheet.

[0072] Example 4

[0073] In this embodiment, maleic anhydride grafted polyethylene with a grafting rate of 5% is used as the matrix, pentaerythritol tetrakis(3-mercaptopropionate) is used as the polythiol, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene is used as the catalyst.

[0074] The method for preparing recyclable cross-linked polyethylene comprises the following steps:

[0075] Use a rotational rheometer, preheat at 150°C for 10 minutes; adjust the speed to 70r / min, add 30g of maleic anhydride grafted polyethylene with a grafting rate of 5%, and preheat for 7 minutes; then add 0.18g of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, and continue stirring for 5 minutes; finally, add 1.83g of pentaerythritol tetrakis(3-mercaptopropionic acid) ester and stir for 20 minutes to obtain a recyclable cross-linked polyethylene material.

[0076] Furthermore, the material was hot-pressed at 150° C. and 2 MPa for 20 min using a flat vulcanizer to obtain a recyclable cross-linked polyethylene sheet.

[0077] Example 5

[0078] In this embodiment, maleic anhydride grafted polyethylene with a grafting rate of 10% is used as the matrix, pentaerythritol tetrakis(3-mercaptopropionate) is used as the polythiol, and N,N-diisopropylethylamine is used as the catalyst.

[0079] The method for preparing recyclable cross-linked polyethylene comprises the following steps:

[0080] Use a rotational rheometer, preheat at 160°C for 10 minutes; adjust the speed to 80r / min, add 30g of maleic anhydride grafted polyethylene with a grafting rate of 10%, and preheat for 7 minutes; then add 0.36g of N,N-diisopropylethylamine, and continue stirring for 5 minutes; finally, add 3.66g of pentaerythritol tetrakis(3-mercaptopropionic acid) and stir for 30 minutes to obtain a recyclable cross-linked polyethylene material.

[0081] Furthermore, the material was hot-pressed at 120° C. and 5 MPa for 25 min using a flat vulcanizer to obtain a recyclable cross-linked polyethylene sheet.

[0082] Example 6

[0083] In this embodiment, maleic anhydride grafted polyethylene with a grafting rate of 5% is used as the matrix, trimethylolpropane tris(3-mercaptopropionate) is used as the polythiol, and N,N-diisopropylethylamine is used as the catalyst.

[0084] The method for preparing recyclable cross-linked polyethylene comprises the following steps:

[0085] Use a rotational rheometer, preheat at 150°C for 10 minutes; adjust the speed to 70r / min, add 30g of maleic anhydride grafted polyethylene with a grafting rate of 5%, and preheat for 5 minutes; then add 0.20g of N,N-diisopropylethylamine, and continue stirring for 5 minutes; finally, add 1.99g of trimethylolpropane tris(3-mercaptopropionate) and stir for 20 minutes to obtain a recyclable cross-linked polyethylene material.

[0086] Furthermore, the material was hot-pressed at 130° C. and 4 MPa for 20 min using a flat vulcanizer to obtain a recyclable cross-linked polyethylene sheet.

[0087] Example 7

[0088] In this embodiment, maleic anhydride grafted polyethylene with a grafting rate of 10% is used as the matrix, trimethylolpropane tris(3-mercaptopropionate) is used as the polythiol, and 1-methyl-1H-imidazole is used as the catalyst.

[0089] The method for preparing the recyclable cross-linked polyethylene comprises the following steps:

[0090] Use a rotational rheometer, preheat at 155°C for 8 minutes; adjust the speed to 80r / min, add 30g of maleic anhydride grafted polyethylene with a grafting rate of 10%, and preheat for 5 minutes; then add 0.40g of 1-methyl-1H-imidazole and continue stirring for 5 minutes; finally, add 3.99g of trimethylolpropane tris(3-mercaptopropionate) and stir for 30 minutes to obtain a recyclable cross-linked polyethylene material.

[0091] Furthermore, the material was hot-pressed at 120° C. and 3 MPa for 30 min using a flat vulcanizer to obtain a recyclable cross-linked polyethylene sheet.

[0092] The recyclable cross-linked polyethylene prepared by the present invention includes thioester bonds, and utilizes the dynamic properties of the thioester bonds to achieve material damage repair and reprocessing performance. It has excellent dielectric properties, so that the material has the advantages of both thermosetting and thermoplastic materials, and is expected to be widely used in power cable insulation systems.

[0093] In addition, the present invention also discloses a damage repair method for recyclable cross-linked polyethylene prepared by the above preparation method, which specifically comprises the following steps: treating the electrically damaged cross-linked polyethylene sample at 100-150°C and 1-5MPa pressure for 20-30 minutes.

[0094] Taking the recyclable cross-linked polyethylene prepared in Example 1 (the recyclable cross-linked polyethylene sheet obtained by the hot pressing step, the same below) as an example, the dielectric properties of the recyclable cross-linked polyethylene were tested by a broadband dielectric spectrum test system. The dielectric constant and loss tangent value of the recyclable cross-linked polyethylene at room temperature vary with frequency, as shown in FIG. Figure 1 The breakdown resistance of recyclable cross-linked polyethylene was measured by DC breakdown equipment, and its breakdown field strength Weibull distribution is shown in Figure 3 As shown. Figure 1 and Figure 3 The dielectric constant of the recyclable cross-linked polyethylene prepared in Example 1 is about 2.3 to 2.4, and the loss tangent value can reach 10 -3It is comparable to traditional commercial cross-linked polyethylene, and the DC breakdown field strength is as high as 366.3 kV / mm, thus proving that the recyclable cross-linked polyethylene material prepared in Example 1 has excellent dielectric properties and breakdown resistance.

[0095] Taking the recyclable cross-linked polyethylene prepared in Example 1 as an example, a ball-ball electrode with a diameter of 25 mm was used to perform a high-voltage DC breakdown test on the recyclable cross-linked polyethylene to obtain recyclable cross-linked polyethylene with electrical breakdown damage. After the recyclable cross-linked polyethylene with electrical breakdown damage was treated at 150° C. and 3 MPa pressure for 30 min, the breakdown repair effect was observed using an optical microscope. Figure 2 As shown in the figure, the breakdown voids were observed to disappear almost completely, and the dielectric constant and loss tangent of the samples at room temperature remained almost consistent with the frequency before and after repair. This proves that recyclable cross-linked polyethylene has excellent electrical breakdown damage repair performance.

[0096] In addition, the recyclable cross-linked polyethylene prepared by the above preparation method can be crushed and hot-pressed to achieve recycling and reprocessing of the recyclable cross-linked polyethylene.

[0097] Specifically, the present invention further discloses a method for recycling and reprocessing recyclable cross-linked polyethylene prepared based on the preparation method of recyclable cross-linked polyethylene, which specifically comprises the following steps:

[0098] crushing the recyclable cross-linked polyethylene to obtain recyclable cross-linked polyethylene powder;

[0099] The recyclable cross-linked polyethylene powder is treated at 100-150° C. and 2-5 MPa pressure for 30-50 min and reshaped.

[0100] Taking the recyclable cross-linked polyethylene prepared in Example 1 as an example, the recyclable cross-linked polyethylene is shredded, and then an appropriate amount of sample is taken and placed in a hot pressing mold, and the thickness of the prepared sample is ensured to be about 0.2 mm. The reshaped recyclable cross-linked polyethylene is obtained by hot pressing at a temperature of 150°C and a pressure of 5 MPa for 30 minutes. The same crushing and hot pressing conditions are cycled twice, and a DC breakdown test is performed on the reshaped recyclable cross-linked polyethylene obtained each time. The breakdown field strength of the recyclable cross-linked polyethylene after shredding and hot pressing twice is shown in Table 1 (1 (first generation) is the direct breakdown test data, and 2 generations refer to one shredding and hot pressing).

[0101] Table 1 Breakdown field strength of recyclable cross-linked polyethylene after shredding and hot pressing twice

[0102] Cycle times <![CDATA[α [Breakdown field strength E b (kV / mm)]]]> Shape parameter β 1(first generation) 366.3 13.9 2 325.2 13.3

[0103] like Figure 3As shown, the Weibull distribution of the DC breakdown field strength of the recyclable cross-linked polyethylene obtained in Example 1 after shearing and hot pressing twice, according to the Weibull distribution, the first-generation breakdown field strength is 366.3 kV / mm, the first-generation breakdown field strength is 325.2 kV / mm, and the reshaping efficiency is as high as 89%, indicating that the recyclable cross-linked polyethylene has excellent recycling and reprocessing performance.

[0104] The performance of the recyclable cross-linked polyethylene prepared in Examples 2-7 is comparable to that in Example 1.

[0105] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. An environmentally friendly polyolefin cable insulation material, characterized in that: The raw materials include, by weight: 0.001-0.015 parts of alkaline catalyst, 1 part of maleic anhydride grafted polyethylene and 0.01-0.15 parts of polythiol crosslinking agent.

2. The environmentally friendly polyolefin cable insulation material according to claim 1, characterized in that: The maleic anhydride grafted polyethylene is a linear low-density polyethylene with a grafting rate of 1% to 10%.

3. The environmentally friendly polyolefin cable insulation material according to claim 1, characterized in that: The polythiol crosslinking agent includes one or more of trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptopropionate) or pentaerythritol tetrakis(3-mercaptobutyrate).

4. The environmentally friendly polyolefin cable insulation material according to claim 1, characterized in that: The alkaline catalyst is one or more of pyridine, triethylamine, N,N-diisopropylethylamine, 1-methyl-1H-imidazole or 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

5. An environmentally friendly polyolefin cable insulation material according to any one of claims 1 to 4, characterized in that: The environmentally friendly polyolefin cable insulation material is applied to voltage types of alternating current and direct current, and voltage levels of medium voltage cables and high voltage cables.

6. An environmentally friendly polyolefin cable insulation material according to any one of claims 1 to 4, characterized in that: The environmentally friendly polyolefin cable insulation material can be recycled and reprocessed, and the specific steps are as follows: The environmentally friendly polyolefin cable insulation material is crushed, and then treated at 100-150° C. and 2-5 MPa pressure for 30-50 minutes to be reshaped.

7. A method for preparing an environmentally friendly polyolefin cable insulation material, characterized in that: The following steps are involved: The environmentally friendly polyolefin cable insulation material can be obtained by mixing the raw materials described in any one of claims 1 to 6 according to the dosage ratio, subjecting them to high-temperature reaction, extruding and then pressing into sheets.

8. The method for preparing an environmentally friendly polyolefin cable insulation material according to claim 7, characterized in that: The high temperature reaction is carried out in a hybrid rheometer, and the hybrid rheometer needs to be preheated before the reaction; The preheating conditions are: preheating at 150-160° C. for 10-15 minutes.

9. The method for preparing an environmentally friendly polyolefin cable insulation material according to claim 7, characterized in that: The conditions in the high temperature reaction process are: Mix and react at 130-160°C at a speed of 50-100 r / min for 10-30 min.

10. A method for repairing an environmentally friendly polyolefin cable insulation material, characterized in that: The following steps are involved: The environmentally friendly polyolefin cable insulation material according to any one of claims 1 to 6 which has been damaged by electrical breakdown is treated at 100 to 150° C. and 1 to 5 MPa pressure for 20 to 30 minutes.

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