A method for preparing a dynamic cross-linked polyethylene for electrical damage repair and applications thereof

Abstract

The application provides a preparation method and application of a dynamic cross-linking polyethylene for electric injury repair, and belongs to the field of polyethylene cable insulation materials. The method comprises the following steps: performing rotary evaporation on polyethylene particles and peroxide to obtain semi-finished product particles mixed with peroxide, and performing post-absorption to obtain cross-linkable insulation material; adding grafting monomers and reaction monomers to the cross-linkable insulation material, and performing reaction in a molten state to obtain mixed blocks; and performing hot pressing treatment on the mixed blocks to obtain a dynamic cross-linking polyethylene material. The dynamic cross-linking polyethylene material can repair the damaged area of the insulation layer after electric injury by transformation and recombination in the material, so that the electrical performance of the cable insulation material is restored. The dynamic cross-linking polyethylene material has high mechanical performance and electrical performance, and has self-repairing and recyclable properties, and can improve the reliability and service life of the cable.

Description

Technical Field

[0001] This invention relates to the field of polyethylene cable insulation materials, and more specifically to a method for preparing dynamically cross-linked polyethylene for electrical damage repair and its application. Background Technology

[0002] Cross-linked polyethylene (XLPE) is a material with a three-dimensional network structure, widely used in power cables due to its excellent mechanical properties, heat resistance, and insulation performance. However, under high-voltage environments, cables are susceptible to electrical damage, such as electrical breakdown, corona damage, and electrical treeing damage. Electrical breakdown leads to localized breakdown of the insulation material, corona discharge accelerates insulation layer deterioration, and electrical treeing damage forms dendritic cracks that gradually propagate until the cable breaks down. These phenomena severely affect the stability, reliability, and long-term serviceability of cable insulation materials.

[0003] The invention patent with publication number CN 112358631 B discloses a method for preparing dynamically covalently cross-linked polyethylene materials. This method achieves the transformation and recombination of the polymer network through a reversible exchange reaction between different borate ester groups. However, the dynamically covalently cross-linked polyethylene materials prepared by this technology do not address the self-healing performance after electrical damage and have disadvantages such as high cost and difficult operation, which are not conducive to large-scale application in the power cable industry. In addition, XLPE cables cannot be recycled after retirement and are usually disposed of by incineration or landfill, which leads to serious environmental pollution and resource waste.

[0004] Therefore, how to endow cross-linked polyethylene cable insulation materials with self-healing and recyclable properties for electrical damage has become a challenge in existing technologies. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing dynamically cross-linked polyethylene for repairing electrical damage, and its applications. This method achieves self-healing and recyclability of polyethylene while maintaining high levels of mechanical and insulation properties, and offers advantages such as simple operation and readily available raw materials. This invention has broad prospects in the production of high-performance polyethylene materials and in realizing the self-healing and recycling of polyethylene materials.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing dynamically cross-linked polyethylene for repairing electrical damage, comprising the following steps:

[0008] (1) Polyethylene particles are rotary evaporated with peroxide to obtain semi-finished particles with mixed peroxide, which are then absorbed to obtain cross-linkable insulating material;

[0009] (2) Add graft monomers and reactive monomers to the crosslinkable insulating material obtained in step (1) and react them in the molten state to obtain a mixed block material;

[0010] (3) The mixed block material obtained in step (2) is subjected to hot pressing to obtain dynamic cross-linked polyethylene material.

[0011] Preferably, in step (1), the peroxide is selected from at least one of dicumyl peroxide, bis-tert-butylperoxyisopropylbenzene, butanone peroxide, hexane peroxide, tert-butylhydrogen peroxide, and di-tert-butylperoxide.

[0012] Preferably, in step (1), the mass content of peroxide in the mixture of polyethylene particles and peroxide is 0.2% to 2.0%.

[0013] Preferably, in step (1), the post-absorption temperature is 60~80℃ and the post-absorption time is 0~48h.

[0014] Preferably, in step (2), the grafting monomer is selected from at least one of maleic anhydride, methyl acrylate and methyl methacrylate; the reaction monomer is selected from at least one of butanediol, 2-hydroxyethyl disulfide, hydroquinone and terephthalic acid.

[0015] Preferably, in step (2), the mass ratio of grafted monomer to crosslinkable insulating material is (1~10):100.

[0016] Preferably, in step (2), the molar ratio of the reaction monomer to the grafted monomer is (0.5~3):2.

[0017] Preferably, in step (2), the temperature of melt blending is 100~180℃ and the time of melt blending is 5~30min.

[0018] Preferably, in step (3), the hot pressing temperature is 120~200℃ and the hot pressing time is 6~180min.

[0019] The present invention also provides a dynamically cross-linked polyethylene material prepared by the aforementioned preparation method.

[0020] The present invention also provides the application of the dynamically cross-linked polyethylene material as an insulating material in the field of power cables.

[0021] The present invention has the following beneficial effects:

[0022] This invention provides a method for preparing dynamically cross-linked polyethylene for electrical damage repair, including the addition of reactive monomers during the reaction process. This enables the material to achieve self-healing properties after electrical damage. By controlling the ratio of grafted monomers to reactive monomers, excellent mechanical properties and electrical insulation characteristics can be maintained simultaneously. Results from the examples show that the dynamically cross-linked polyethylene material prepared by this invention exhibits good repair effects at 120℃ for 12 hours. Furthermore, the breakdown strength of the dynamically cross-linked polyethylene material prepared by this invention reaches 325.9 kV / mm, its tensile strength reaches 17.3 MPa, and its elongation at break reaches 1300%, demonstrating excellent mechanical properties and electrical insulation characteristics. The tensile strength of the sample after mechanical damage repair is approximately 94% of the initial state, and the elongation at break is approximately 100% of the initial state. The breakdown strength of the sample after corona discharge damage repair is approximately 100% of the initial state, indicating that the dynamically cross-linked polyethylene material has good self-healing properties. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 Fourier transform infrared spectra of polyethylene prepared in Examples 1-3 and Comparative Examples 1-2 of this invention;

[0025] Figure 2 The breakdown strength of the dynamically cross-linked polyethylene prepared in Example 2 and Comparative Example 1 of this invention;

[0026] Figure 3 Mechanical damage and mechanical properties after repair of dynamically cross-linked polyethylene prepared in Example 2 of this invention;

[0027] Figure 4 This is a schematic diagram of the electrical tree damage and repair of the dynamically cross-linked polyethylene prepared in Example 2 of the present invention;

[0028] Figure 5 The breakdown strength of the dynamically cross-linked polyethylene prepared in Example 2 of this invention before and after corona damage and after corona repair is shown. Detailed Implementation

[0029] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0030] This invention provides a method for preparing dynamically cross-linked polyethylene for repairing electrical damage, comprising the following steps:

[0031] (1) Polyethylene particles are rotary evaporated with peroxide to obtain semi-finished particles with mixed peroxide, which are then absorbed to obtain cross-linkable insulating material;

[0032] (2) Add graft monomers and reactive monomers to the crosslinkable insulating material obtained in step (1) and react them in the molten state to obtain a mixed block material;

[0033] (3) The mixed block material obtained in step (2) is subjected to hot pressing to obtain dynamic cross-linked polyethylene material.

[0034] Unless otherwise specified, the present invention does not have any special limitations on the source of each component, and commercially available products well known to those skilled in the art can be used.

[0035] In this invention, the peroxide is preferably selected from at least one of dicumyl peroxide, bis(tert-butylperoxide)-propylbenzene, butanone peroxide, hexane peroxide, tert-butyl hydroperoxide, and di-tert-butyl peroxide, more preferably dicumyl peroxide, tert-butyl hydroperoxide, and di-tert-butyl peroxide, and most preferably dicumyl peroxide. As an initiator, the peroxide decomposes under heating to generate free radicals, which abstract hydrogen atoms from the macromolecular chain, producing macromolecular chain free radicals. Simultaneously, due to the three-dimensional network structure of cross-linked polyethylene, the peroxide also acts as a cross-linking agent.

[0036] In this invention, the mass content of peroxide in the mixture of polyethylene particles and peroxide is preferably 0.2% to 2.0%. The amount of peroxide added needs to be controlled within a certain proportion; otherwise, it will not only affect the performance of the material but also cause waste.

[0037] In this invention, the post-absorption temperature is preferably 60~80℃, more preferably 70℃; the post-absorption time is preferably 0~48h, more preferably 3~36h, and most preferably 6~24h. By limiting the post-absorption temperature and time within the above ranges, this invention enables the reaction to proceed more fully.

[0038] In this invention, the grafting monomer is preferably selected from at least one of maleic anhydride, methyl acrylate, and methyl methacrylate, and more preferably maleic anhydride. Taking maleic anhydride as the grafting monomer as an example, under the action of peroxide, the maleic anhydride monomer is activated and can abstract a hydrogen atom from the polyethylene macromolecular chain to form polyethylene free radical and maleic anhydride free radical, respectively. The two undergo coupling termination to generate polyethylene grafted maleic anhydride.

[0039] In this invention, the reactive monomer is preferably selected from one of butanediol, 2-hydroxyethyl disulfide, hydroquinone, and terephthalic acid. The hydroxyl groups at both ends of the reactive monomer can react with maleic anhydride on the polyethylene chain, acting as crosslinking agents to form a crosslinked network structure. More preferably, it is 2-hydroxyethyl disulfide. The 2-hydroxyethyl disulfide not only has groups capable of reacting with maleic anhydride but also possesses dynamically reversible disulfide bonds, endowing the material with dual dynamic properties and further improving its self-healing efficiency.

[0040] In this invention, the preferred mass ratio of the grafted monomer to the crosslinkable insulating material is (1~10):100, and more preferably (2~8):100.

[0041] In this invention, the preferred molar ratio of the reactive monomer to the grafted monomer is (0.5~3):2, more preferably (1~2):2. Excessive addition of the reactive monomer will lead to a decrease in the material's mechanical properties (tensile strength and elongation at break) and insulation properties (breakdown strength); similarly, excessive addition of the grafted monomer will also lead to a decrease in the material's mechanical properties (tensile strength and elongation at break) and insulation properties. Conversely, the improvement in the performance of polyethylene will be limited.

[0042] In this invention, the melt blending temperature is preferably 100~180℃, more preferably 110~150℃; the melt blending time is preferably 5~30min, more preferably 6~20min.

[0043] In this invention, the hot pressing temperature is preferably 120~200℃, more preferably 120~180℃; the hot pressing time is preferably 6~180min, more preferably 6~120min.

[0044] In this invention, the rotary evaporation is preferably carried out in the evaporation flask of a rotary evaporator.

[0045] In this invention, the post-absorption is preferably carried out in a forced-air drying oven.

[0046] In this invention, the melt blending is preferably carried out in a torque rheometer.

[0047] In this invention, the hot pressing process is preferably carried out in a hot press.

[0048] This invention provides a dynamically cross-linked polyethylene material prepared by the aforementioned method. In this invention, the thickness of the material is preferably 0.03~2 mm.

[0049] The dynamically cross-linked polyethylene material prepared by this invention has self-healing properties against electrical breakdown, corona discharge, and electrical tree damage.

[0050] This invention also provides the application of the dynamically cross-linked polyethylene material in the field of power cable insulation materials. The application of the dynamically cross-linked polyethylene material in the field of power cable insulation materials is not particularly limited; any technical solution for the application of cross-linked polyethylene in the field of power cable insulation materials well-known to those skilled in the art can be used.

[0051] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0052] Example 1

[0053] A certain amount of polyethylene granules was placed in the evaporation flask of a rotary evaporator, and dicumyl peroxide was added according to the mass percentage. The mixture was rotary evaporated at 70°C for 20 min. The semi-finished granules mixed with dicumyl peroxide were then kept in a 70°C oven for 15 h to absorb the saturated material, yielding a crosslinkable insulating material. 100 parts by weight of the crosslinkable insulating material contained 1.8 parts by weight of peroxide. Then, 100 parts by weight of the crosslinkable insulating material, 4.16 parts by weight of maleic anhydride, and 3.27 parts by weight of 2-hydroxyethyl disulfide were melt-blended at 130°C for 5 min at a rotation speed of 100 rpm / min (at this point, the molar ratio of maleic anhydride to 2-hydroxyethyl disulfide was 2:1.4). The mixed lumps were naturally cooled, and finally, pre-pressed at 120°C for 6 min and hot-pressed at 150°C for 1 h in a hot press to obtain a dynamically crosslinked polyethylene material, denoted as PE-MA-HEDS1.

[0054] Example 2

[0055] The 2-hydroxyethyl disulfide in Example 1 was replaced with 4.58 parts by weight, and all other parameters were the same as in Example 1 (at this time, the molar ratio of maleic anhydride to 2-hydroxyethyl disulfide was 2:1.4), to obtain a dynamically cross-linked polyethylene material, denoted as PE-MA-HEDS2.

[0056] Example 3

[0057] The 2-hydroxyethyl disulfide in Example 1 was replaced with 5.89 parts by weight, and all other parameters were the same as in Example 1 (at this time, the molar ratio of maleic anhydride to 2-hydroxyethyl disulfide was 2:1.8), to obtain a dynamically cross-linked polyethylene material, denoted as PE-MA-HEDS3.

[0058] Comparative Example 1

[0059] Maleic anhydride and 2-hydroxyethyl disulfide were omitted in Example 1. The crosslinkable insulating material was pre-pressed at 120°C for 6 minutes and then hot-pressed at 150°C for 1 hour in a hot press to obtain crosslinked polyethylene material, denoted as XLPE.

[0060] Comparative Example 2

[0061] The 2-hydroxyethyl disulfide in Example 1 was omitted, and all other parameters were the same as in Example 1, to obtain a polyethylene-grafted maleic anhydride material, denoted as PE-MA.

[0062] Comparative Example 3

[0063] The maleic anhydride in Example 1 was replaced with 5.26 parts by weight (at this time, the molar ratio of maleic anhydride to 2-hydroxyethyl disulfide was 2:1.0), and all other parameters were the same as in Example 1, to obtain a dynamically cross-linked polyethylene material, denoted as PE-MA-HEDS4.

[0064] Compared to Example 1, Examples 2 and 3 contain more 2-hydroxyethyl disulfide, and Comparative Example 3 contains more maleic anhydride. The performance test results of the above examples and comparative examples are shown in Table 1.

[0065] Table 1 Comparison of performance of different samples

[0066]

[0067] As shown in Table 1, the molar ratio of maleic anhydride to 2-hydroxyethyl disulfide in Example 1 was 2:1.0. Example 2 contained more 2-hydroxyethyl disulfide than Example 1, indicating that more groups reacted with the maleic anhydride, allowing the reaction to proceed fully; therefore, the test data was superior to Example 1. The performance of Example 3 decreased because the introduction of excessive 2-hydroxyethyl disulfide resulted in a dynamic reaction that limited the improvement of mechanical properties.

[0068] Compared to Comparative Example 1, Example 2 exhibits higher elongation at break and breakdown strength, but lower tensile strength. This is because Comparative Example 1 has a higher degree of crosslinking, resulting in better tensile strength. Compared to Comparative Example 2, Example 2 has lower breakdown strength. This is because the introduced 2-hydroxyethyl disulfide forms a crosslinked network in the material, thus increasing the breakdown strength of Comparative Example 2. Comparative Example 3, compared to Example 1, contains excessive maleic anhydride, leading to the generation of numerous byproducts during the reaction and a decrease in its performance.

[0069] Fourier transform infrared (FTIR) spectra of the polyethylene materials prepared in Examples 1-3 and Comparative Examples 1-2 were tested. The prepared polyethylene materials were cut into 30mm × 30mm pieces and tested using a Fourier transform infrared spectrometer with a scanning range of 4000–600 cm⁻¹.-1 The result is as follows Figure 1 As shown. By Figure 1 As can be seen, compared to Comparative Example 1, the introduction of grafting groups in Comparative Example 2 can be observed, and dynamically cross-linked polyethylene was successfully prepared in Examples 1-4.

[0070] The breakdown strength of the cross-linked polyethylene prepared in Example 2 and Comparative Example 1 was tested using a pressure resistance testing device (RK2674-A; MEIRUIKE Co., Ltd., China). The results are as follows: Figure 2 As shown. (Through) Figure 2 It can be seen that the breakdown strength of the dynamically cross-linked polyethylene prepared using Example 2 is higher than that of cross-linked polyethylene, and the breakdown strength of the dynamically cross-linked polyethylene can reach 325.9 kV / mm.

[0071] To test the mechanical properties of the dynamically cross-linked polyethylene prepared in Example 2 before and after repair, the samples were cut into dumbbell shapes and then mechanically damaged. The damaged samples were then placed in a 120°C forced-air drying oven for 12 hours for repair. The mechanical properties of the samples before and after repair were tested using a MARK-10 tensile testing machine at a speed of 50 mm / min. The results are as follows: Figure 3 As shown. (Through) Figure 3 It can be seen that the tensile strength of the sample after repair is about 94% of that in the initial state, and the elongation at break is about 100% of that in the initial state, indicating that the dynamic cross-linked polyethylene has good self-healing properties in terms of mechanical damage.

[0072] This is a schematic diagram of electrical tree damage and repair in the dynamically cross-linked polyethylene prepared in Example 2. The electrical treeing experiment used steel needle electrodes on the XLPE insulating sample, with the needle tips perpendicular to the bottom edge of the sample and a spacing of 2 mm. A power frequency AC voltage was applied to the needle electrodes via a step-up transformer, and the experiment lasted 20 minutes. The entire process of electrical tree initiation and growth within the insulating sample was recorded using an optical microscope and a video acquisition module. After complete electrical tree growth, the sample was repaired in a 120°C forced-air drying oven for 12 hours. The results are as follows: Figure 4 As shown. (Through) Figure 4 It can be seen that the electrical trees of PE-MA-HEDS2 can achieve self-repair through thermal stimulation.

[0073] The breakdown strength of the dynamically cross-linked polyethylene prepared in Example 2 was tested. After corona treatment, the dynamically cross-linked polyethylene was placed in a 120°C forced-air drying oven for 12 hours for repair. Then, its breakdown strength before and after repair was tested in a withstand voltage testing device (RK2674-A; MEIRUIKE, China). The results are as follows: Figure 5 As shown. (Through) Figure 5It can be seen that the breakdown strength of the sample decreased by 16% after corona damage, and the breakdown strength of the sample after repair was about 100% of the initial state.

[0074] The above description is merely a specific embodiment 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 technical scope 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 method for preparing dynamically cross-linked polyethylene for repairing electrical damage, characterized in that, Includes the following steps: (1) Polyethylene particles are rotary evaporated with peroxide to obtain semi-finished particles with mixed peroxide, which are then absorbed to obtain cross-linkable insulating material. (2) Add graft monomers and reactive monomers to the crosslinkable insulating material obtained in step (1) and react them in the molten state to obtain a mixed block material; (3) The mixed block material obtained in step (2) is subjected to hot pressing to obtain dynamic cross-linked polyethylene material; In step (2), the grafting monomer is maleic anhydride, and the reaction monomer is 2-hydroxyethyl disulfide; the molar ratio of the reaction monomer to the grafting monomer is (0.5-3):

2. The prepared dynamic cross-linked polyethylene material simultaneously exhibits self-healing properties against electrical breakdown, corona discharge, and electrical tree damage.

2. The method for preparing dynamically cross-linked polyethylene for electrical damage repair according to claim 1, characterized in that, In step (1), the peroxide is selected from at least one of dicumyl peroxide, bis-tert-butylperoxyisopropylbenzene, butanone peroxide, hexane peroxide, tert-butylhydrogen peroxide and di-tert-butylperoxide.

3. The method for preparing dynamically cross-linked polyethylene for electrical damage repair according to claim 1, characterized in that, In step (1), the mass content of peroxide in the mixture of polyethylene particles and peroxide is 0.2% to 2.0%.

4. The method for preparing dynamically cross-linked polyethylene for electrical damage repair according to claim 1, characterized in that, In step (1), the post-absorption temperature is 60-80℃, the post-absorption time is 0-48h, and the post-absorption time is not 0.

5. The method for preparing dynamically cross-linked polyethylene for electrical damage repair according to claim 1, characterized in that, In step (2), the mass ratio of grafted monomer to crosslinkable insulating material is (1-10):

100.

6. The method for preparing dynamically cross-linked polyethylene for electrical damage repair according to claim 1, characterized in that, In step (2), the temperature of melt blending is 100-180℃ and the time of melt blending is 5-30 min.

7. The method for preparing dynamically cross-linked polyethylene for electrical damage repair according to claim 1, characterized in that, In step (3), the hot pressing temperature is 120-200℃ and the hot pressing time is 6-180min.

8. The dynamically cross-linked polyethylene material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the dynamically cross-linked polyethylene material of claim 8 as an insulating material in the field of power cables.

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