Aramid fiber reinforced epoxy composites for GIS insulating pull rods and methods of making

Abstract

The application belongs to the technical field of electrical insulation composite materials, and discloses an aramid fiber reinforced epoxy composite material for a GIS insulation pull rod and a preparation method thereof. In view of the problems of single interface bonding, insufficient stress dissipation and easy migration of carriers of the existing aramid / epoxy composite material, a quasi-polyrotaxane topological interlocking interface layer is constructed on the surface of aramid fiber and grafted, then fluorine-containing diisocyanate is introduced to react with beta-cyclodextrin hydroxyl to form a fluorine-containing functional structure. The interface structure can not only enhance load transfer and energy dissipation through the "ring-shaft" topological interlocking and molecular slip to improve impact resistance, but also form charge trapping sites by using the strong electronegativity of the fluorine-containing group to inhibit the migration of carriers along the interface and reduce the interface conductivity. The application realizes the synergistic improvement of mechanical properties and electrical insulation performance, and is suitable for force-bearing insulation components such as GIS insulation pull rods.

Description

Technical Field

[0001] This application belongs to the field of electrical insulation composite materials technology, and particularly relates to an aramid fiber reinforced epoxy composite material for GIS insulating tie rods, its preparation method and application. Background Technology

[0002] Aramid fiber reinforced epoxy composites are widely used in key load-bearing insulating components such as insulating tie rods in gas-insulated metal-enclosed switchgear (GIS) due to their excellent specific strength, electrical insulation properties, and structural design flexibility. For GIS insulating tie rods, during long-term operation, they not only need to withstand high-voltage electric fields but also maintain stable structural integrity and insulation reliability under closing and opening impacts, electrodynamic disturbances, and complex mechanical loads. Therefore, higher requirements are placed on the interfacial bonding strength, impact resistance, and electrical insulation properties of the material.

[0003] However, existing aramid fiber / epoxy composites still have significant shortcomings in terms of interface structure. On the one hand, the surface of aramid fibers is chemically inert, and the interfacial bonding between them and epoxy resin mainly relies on limited physical interactions or simple chemical bonds. The interface structure is simple, making it prone to stress concentration under external loads, and difficult to achieve effective stress regulation and energy dissipation. This leads to interfacial debonding and crack propagation, reducing the material's impact resistance and structural reliability. On the other hand, due to the limited cross-linking reaction in the interfacial region, the local cross-linking density is usually lower than that of the bulk resin, increasing the free volume and weakening the structural constraint in this region. The free path of electrons in the interfacial region increases accordingly, making them more likely to migrate along the interface and form continuous conductive paths under the influence of an electric field. This results in increased interfacial conductivity and reduced electrical insulation reliability of the material.

[0004] To address the aforementioned issues, existing research has attempted to improve interfacial bonding performance through methods such as plasma treatment and coupling agent grafting. However, these methods primarily focus on enhancing interfacial adhesion strength and lack structural design strategies that can simultaneously achieve mechanical enhancement and charge transport regulation in the interfacial region. This makes it difficult to meet the comprehensive performance requirements of GIS insulated tie rods under high voltage levels and complex service environments. Therefore, there is an urgent need to develop an interfacial structural design method that can balance interfacial mechanical properties and electrical insulation properties. Summary of the Invention

[0005] One objective of this invention is to provide a method for preparing aramid fiber-reinforced epoxy composite materials for GIS insulated tie rods. This application involves constructing and grafting a quasi-polyrotaxane topologically interlocked interface layer on the surface of aramid fibers, followed by the introduction of a fluorinated diisocyanate reacting with β-cyclodextrin hydroxyl groups to form a fluorinated functionalized structure. This preparation method achieves a synergistic improvement in both mechanical and electrical insulation properties, making it suitable for load-bearing insulating components such as GIS insulated tie rods.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing an aramid fiber reinforced epoxy composite material for GIS insulating tie rods, comprising the following steps: (1) Polyetheramine and β-cyclodextrin were dissolved in deionized water and self-assembled by stirring to obtain quasi-polyrotaxane. After separation and drying, the quasi-polyrotaxane solution was dissolved in an organic solvent. (2) Surface plasma treatment of aramid fibers to obtain activated aramid fibers; (3) The activated aramid fiber was fully wetted by immersing it in a quasi-polyrotaxane solution, dried, and then heat-treated at 110-130 °C for 1-2 h to obtain the modified aramid fiber with a quasi-polyrotaxane topological interlocking structure on its surface. (4) Add the modified aramid fiber to an anhydrous organic solvent, then add fluorinated diisocyanate, and heat the reaction under a protective atmosphere to allow some of the isocyanate groups in the fluorinated diisocyanate to react with the hydroxyl groups on β-cyclodextrin to form urethane bonds, and introduce fluorinated functional groups into the quasi-polyrotaxane structure; after the reaction is completed, wash and dry to obtain the modified aramid fiber with a fluorinated functionalized quasi-polyrotaxane interface structure on the surface, which is referred to as functionalized modified aramid fiber; (5) The functionalized modified aramid fibers are arranged in the mold along the axial direction of the GIS insulating tie rod, and the mixture of epoxy resin and curing components is impregnated to obtain the GIS insulating tie rod preform; then the GIS insulating tie rod preform is degassed and cured to obtain the aramid fiber reinforced epoxy composite material for GIS insulating tie rod.

[0007] As a further improvement to the preparation method of the above-mentioned aramid fiber reinforced epoxy composite material for GIS insulating tie rods: Preferably, in step (1), 1 mol of polyetheramine and 2-18 mol of β-cyclodextrin are dissolved in deionized water and stirred and assembled at room temperature for 8-16 h. After standing, filtration, washing and drying, quasi-polyrotaxane is obtained. The quasi-polyrotaxane is dissolved in an organic solvent to prepare a quasi-polyrotaxane solution with a solid content of 1-3 wt%.

[0008] Preferably, in step (1), the structural formula of the β-cyclodextrin is as follows; .

[0009] Preferably, in step (1), the polyetheramine has the following structural formula: .

[0010] Preferably, the polyetheramine is selected from one or more of polyetheramine D230, polyetheramine D400, and polyetheramine D2000.

[0011] Preferably, in step (2), the aramid fiber is a para-aramid filament.

[0012] Preferably, in step (3), the impregnated aramid fibers are dried at 30-50 °C for 0.5-1 h and at 60-80 °C for 0.5-1 h to remove the organic solvent.

[0013] Preferably, in step (4), the fluorinated diisocyanate is 4,4'-(hexafluoroisopropyl)bis(phenylisocyanate), with the following structural formula: .

[0014] Preferably, the molar ratio of β-cyclodextrin in step (1) to fluorinated diisocyanate in step (4) is 1:(1-20); the heating reaction in step (4) is carried out in nitrogen or inert gas, the reaction temperature is 70-90 °C, and the reaction time is 3-6 h.

[0015] Preferably, in step (5), the epoxy resin is selected from at least one of bisphenol A type epoxy resin, alicyclic epoxy resin, or phenolic epoxy resin; the curing component includes a curing agent and a curing accelerator; the curing agent is at least one of acid anhydride curing agents; the curing accelerator is selected from at least one of imidazole curing accelerators and tertiary amine curing accelerators; the mixed system of epoxy resin and curing component includes 100 parts by weight of epoxy resin, 30 to 100 parts by weight of curing agent, and 0.3 to 1 part by weight of curing accelerator.

[0016] Preferably, in step (5), the GIS insulating tie rod preform is subjected to staged heating and curing: the pre-curing temperature is 60-90 ℃ and the curing time is 1-2 h; the main curing temperature is 100-120 ℃ and the curing time is 2-4 h; the post-curing temperature is 140-160 ℃ and the curing time is 6-18 h.

[0017] The second objective of this invention is to provide an aramid fiber reinforced epoxy composite material for GIS insulating tie rods prepared by any of the above-described preparation methods.

[0018] The advantages of this invention compared to the prior art are as follows: (1) This invention provides a method for preparing an aramid fiber reinforced epoxy composite material for GIS insulating tie rods, the method comprising the following steps: A quasi-polyrotaxane structure is formed by supramolecular self-assembly of polyetheramine and β-cyclodextrin; β-cyclodextrin with hydrophobic cavities spontaneously intercalates on the terminal amino polyether backbone in solution to form a quasi-polyrotaxane structure.

[0019] Aramid fibers are subjected to surface plasma treatment to introduce hydroxyl or carboxyl active groups on the surface. Activated aramid fibers are immersed in a quasi-polyrotaxane solution, which allows polyetheramine axial links to be branched onto the fiber surface, thus constructing a quasi-polyrotaxane topological interlocking structure on the aramid fiber surface. A "ring-axis" structural unit with restricted molecular slippage capability is introduced into the interfacial region, which can achieve interfacial stress regulation and energy dissipation under load, thereby improving interfacial bonding strength, impact resistance and structural stability.

[0020] Then, the modified aramid fibers with a quasi-polyrotaxane topological interlocking structure on their surface were placed in an anhydrous organic solvent, and a fluorinated diisocyanate was added. The mixture was heated under an inert atmosphere to react some of the isocyanate groups in the fluorinated diisocyanate with the hydroxyl groups on β-cyclodextrin to form urethane bonds, and fluorinated functional groups were introduced into the quasi-polyrotaxane structure. The fluorinated groups were enriched in the interfacial region near the aramid fibers. The strong electronegativity of the fluorinated groups formed stable charge trapping sites, which inhibited the migration of charge carriers along the fiber / resin interface, reduced the interfacial conductivity, and thus improved the electrical insulation reliability of the material.

[0021] (2) The aramid fiber reinforced epoxy composite material for GIS insulating tie rods prepared by the present invention includes epoxy resin, curing components and aramid fibers with an interface functional layer formed on the surface. The epoxy resin and the curing component form an epoxy crosslinking network through a curing reaction; The interface functional layer is disposed between the surface of the aramid fiber and the epoxy crosslinking network, including a quasi-polyrotaxane topological interlocking structure and a fluorinated isocyanate functionalized structure; Quasi-polyrotaxane is formed by supramolecular self-assembly of polyetheramine axial chains and β-cyclodextrin cyclic molecules; quasi-polyrotaxane is grafted onto the surface of the aramid fiber through chemical bonds at both ends of its polyetheramine axial chain; Some of the isocyanate groups in the fluorinated isocyanate react with the hydroxyl groups on the β-cyclodextrin cyclic molecule to form urethane bonds, which grafts the fluorinated functional structure into the quasi-polyrotaxane structure, thereby forming a high-density functionalized curing network rich in fluorinated groups in the interfacial region near the aramid fiber. The remaining hydroxyl groups on the β-cyclodextrin cyclic molecule that did not participate in the reaction with fluorinated isocyanate undergo a ring-opening reaction with the epoxy crosslinking network during the epoxy resin curing process and are embedded in the epoxy crosslinking network; The remaining isocyanate groups in the fluorinated isocyanate react with the hydroxyl groups in the epoxy crosslinking network during the epoxy resin curing process.

[0022] The aramid fiber reinforced epoxy composite material obtained in this application achieves a synergistic improvement in mechanical properties and electrical insulation properties, and is suitable for load-bearing insulating components such as GIS insulating tie rods. Attached Figure Description

[0023] Figure 1 This is a structural model diagram of the quasi-polyrotaxane obtained in step (1) of Example 1.

[0024] Figure 2 This is a structural model diagram of the activated aramid fiber obtained in step (2) of Example 1.

[0025] Figure 3 This is a structural model diagram of the modified aramid fiber obtained in step (3) of Example 1.

[0026] Figure 4 This is a structural model diagram of the functionalized modified aramid fiber obtained in step (4) of Example 1.

[0027] Figure 5 This is a structural model diagram of the aramid fiber reinforced epoxy composite material for GIS insulating tie rods prepared in step (5) of Example 1.

[0028] Figure 6 This is a surface electron microscope image of the aramid fiber (para-aramid filament) used in Comparative Example 1.

[0029] Figure 7 This is a schematic diagram of the interfacial shear strength (IFSS) test of the aramid fiber reinforced epoxy composite material prepared in Comparative Example 1 without interfacial modification.

[0030] Figure 8 This is a schematic diagram of the fiber bundle pull-out strength (TFBT) test of the aramid fiber reinforced epoxy composite material prepared in Comparative Example 1 without interface modification.

[0031] Figure 9 This is a surface electron microscope image of the functionalized aramid fiber obtained in step (4) of Example 3.

[0032] Figure 10 This is a schematic diagram of the interfacial shear strength (IFSS) test of the aramid fiber reinforced epoxy composite material for GIS insulating tie rods prepared in Example 3, where (b) is a partial enlarged view of (a).

[0033] Figure 11 This is a schematic diagram of the fiber bundle pull-out strength (TFBT) test of the aramid fiber reinforced epoxy composite material for GIS insulating tie rod prepared in Example 3, where (a) and (b) are different positions.

[0034] Figure 12 This is a surface electron microscope image of the functionalized aramid fiber obtained in step (4) of Example 4.

[0035] Figure 13This is a schematic diagram of the interfacial shear strength (IFSS) test of the aramid fiber reinforced epoxy composite material for GIS insulating tie rods prepared in Example 4, where (b) is a partial enlarged view of (a).

[0036] Figure 14 This is a schematic diagram of the fiber bundle pull-out strength (TFBT) test of the aramid fiber reinforced epoxy composite material for GIS insulating tie rod prepared in Example 4, where (a) and (b) are different positions.

[0037] Figure 15 This is the XPS spectrum of untreated aramid fiber (para-aramid filament) in Comparative Example 1.

[0038] Figure 16 This is the XPS spectrum of the functionalized modified aramid fiber prepared in Example 1.

[0039] Figure 17 This is the XPS spectrum of the functionalized modified aramid fiber prepared in Example 2.

[0040] Figure 18 This is the XPS spectrum of the functionalized modified aramid fiber prepared in Example 3.

[0041] Figure 19 This is the XPS spectrum of the functionalized modified aramid fiber prepared in Example 4. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. 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.

[0043] Example 1 This embodiment provides a method for preparing an aramid fiber reinforced epoxy composite material for GIS insulating tie rods, comprising the following steps: (1) Preparation steps of quasi-polyrotaxane: 1 mol of polyetheramine D2000 and 9 mol of β-cyclodextrin were dissolved in deionized water and stirred at room temperature for 12 h. After standing, filtration, washing, and freeze-drying, quasi-polyrotaxane was obtained. The quasi-polyrotaxane was dissolved in dimethyl sulfoxide to prepare a quasi-polyrotaxane solution with a solid content of 2 wt%. The structural model of the quasi-polyrotaxane is shown below. Figure 1 As shown.

[0044] The structural formula of the polyetheramine is shown below, where n=33; .

[0045] The structural formula of the β-cyclodextrin is shown below; .

[0046] (2) The aramid fiber (para-aramid filament) is subjected to surface plasma treatment to introduce active groups on the surface, thereby obtaining activated aramid fiber. The structural model is as follows: Figure 2 As shown.

[0047] (3) Interface layer construction steps: Activated aramid fibers were thoroughly wetted by immersing them in a quasi-polyrotaxane solution. They were then removed and dried sequentially at 40 °C for 0.75 h and 70 °C for 0.75 h to remove the organic solvent. Finally, they were kept at 110 °C for 1 h to graft the terminal amino groups of the quasi-polyrotaxane onto the surface of the activated aramid fibers, resulting in modified aramid fibers with a quasi-polyrotaxane topological interlocking structure on their surface. The structural model is shown below. Figure 3 As shown.

[0048] (4) Fluorine functionalization steps: Modified aramid fibers were placed in an anhydrous organic solvent (anhydrous dimethyl sulfoxide), and fluorinated diisocyanate was added, wherein the molar ratio of β-cyclodextrin in step (1) to fluorinated diisocyanate in step (4) was 1:5; the reaction was carried out in a nitrogen atmosphere at 80 °C for 4 h, so that some of the isocyanate groups in the fluorinated diisocyanate reacted with the hydroxyl groups on the β-cyclodextrin to form urethane bonds; after the reaction was completed, the fibers were washed and dried to obtain modified aramid fibers with a fluorinated functionalized quasi-polyrotaxane interface structure on the surface, denoted as functionalized modified aramid fibers, and the structural model is as follows. Figure 4 As shown.

[0049] The structural formula of the fluorinated diisocyanate is shown below: .

[0050] (5) Lamination and curing steps: Functionalized modified aramid fibers are arranged along the axial direction of the GIS insulating tie rod in a mold and impregnated with a mixture of epoxy resin and curing components; the mixture is composed of 100 parts by weight of bisphenol A epoxy resin, 50 parts by weight of methyltetrahydrophthalic anhydride and 0.5 parts by weight of benzyl dimethylamine (BDMA); thus obtaining a GIS insulating tie rod preform. The GIS insulated tie rod preform was then degassed under vacuum and subsequently cured in stages: cured at 80 ℃ for 1 h, 110 ℃ for 2 h, and 150 ℃ for 12 h, to obtain an aramid fiber reinforced epoxy composite material for GIS insulated tie rods. The structural model is shown below. Figure 5 As shown.

[0051] Example 2 This embodiment is basically the same as that of embodiment 1, except that in step (1), the molar ratio of polyetheramine D2000 to β-cyclodextrin is 1:12, and the other steps and conditions are the same.

[0052] Example 3 This embodiment is basically the same as that of Embodiment 1, except that in step (1), the molar ratio of polyetheramine D2000 to β-cyclodextrin is 1:15, and the other steps and conditions are the same.

[0053] Example 4 This embodiment is basically the same as that of embodiment 1, except that in step (1), polyetheramine D400 is selected, and the other steps and conditions are the same.

[0054] Example 5 This embodiment is basically the same as that of embodiment 1, except that: in step (1), the solid content of the quasi-polyrotaxane solution is 3 wt%, and the other steps and conditions are the same.

[0055] Example 6 This embodiment is basically the same as Embodiment 1, except that the molar ratio of β-cyclodextrin in step (1) to fluorinated diisocyanate in step (4) is 1:20, and the other steps and conditions are the same.

[0056] Example 7 This embodiment provides a method for preparing an aramid fiber reinforced epoxy composite material for GIS insulating tie rods, comprising the following steps: (1) Preparation steps of quasi-polyrotaxane: 1 mol of polyetheramine D230 and 2 mol of β-cyclodextrin were dissolved in deionized water and stirred at room temperature for 8 h. After standing, filtration, washing, and freeze-drying, quasi-polyrotaxane was obtained. The quasi-polyrotaxane was dissolved in dimethyl sulfoxide to prepare a quasi-polyrotaxane solution with a solid content of 1 wt%.

[0057] The polyetheramine has the same structural formula as in Example 1, where n=2.

[0058] The structural formula of the β-cyclodextrin is the same as that in Example 1.

[0059] (2) The aramid fiber (para aramid filament) is subjected to surface plasma treatment to introduce active groups on the surface to obtain activated aramid fiber.

[0060] (3) Interface layer construction steps: The activated aramid fiber was thoroughly wetted by immersing it in a quasi-polyrotaxane solution. It was then removed and dried sequentially at 30 °C for 1 h and 60 °C for 1 h to remove the organic solvent. Finally, it was kept at 110 °C for 1 h to graft the terminal amino groups of the quasi-polyrotaxane onto the surface of the activated aramid fiber, resulting in a modified aramid fiber with a quasi-polyrotaxane topological interlocking structure on its surface.

[0061] (4) Fluorine functionalization steps: The modified aramid fiber was placed in an anhydrous organic solvent (anhydrous dimethyl sulfoxide) and a fluorinated diisocyanate was added, wherein the molar ratio of the β-cyclodextrin in step (1) to the fluorinated diisocyanate in step (4) was 1:1; the reaction was carried out in a nitrogen atmosphere at 70 °C for 6 h, so that some of the isocyanate groups in the fluorinated diisocyanate reacted with the hydroxyl groups on the β-cyclodextrin to form urethane bonds; after the reaction was completed, the fiber was washed and dried to obtain a modified aramid fiber with a fluorinated functionalized quasi-polyrotaxane interface structure on the surface, which was denoted as functionalized modified aramid fiber.

[0062] The fluorinated diisocyanate has the same structural formula as in Example 1.

[0063] (5) Lamination and curing steps: Functionalized modified aramid fibers are arranged along the axial direction of the GIS insulating tie rod in a mold and impregnated with a mixture of epoxy resin and curing components; the mixture is composed of 100 parts by weight of bisphenol A epoxy resin, 30 parts by weight of methyltetrahydrophthalic anhydride and 0.3 parts by weight of benzyl dimethylamine (BDMA); thus obtaining a GIS insulating tie rod preform. The GIS insulating tie rod preform was then degassed under vacuum and then cured in stages: cured at 60 ℃ for 2 h, 100 ℃ for 4 h, and 140 ℃ for 18 h to obtain an aramid fiber reinforced epoxy composite material for GIS insulating tie rods.

[0064] Example 8 This embodiment provides a method for preparing an aramid fiber reinforced epoxy composite material for GIS insulating tie rods, comprising the following steps: (1) Preparation steps of quasi-polyrotaxane: 1 mol of polyetheramine D400 and 18 mol of β-cyclodextrin were dissolved in deionized water and stirred at room temperature for 16 h. After standing, filtration, washing, and freeze-drying, quasi-polyrotaxane was obtained. The quasi-polyrotaxane was dissolved in dimethyl sulfoxide to prepare a quasi-polyrotaxane solution with a solid content of 3 wt%.

[0065] The polyetheramine has the same structural formula as in Example 1, where n=5.

[0066] The structural formula of the β-cyclodextrin is the same as that in Example 1.

[0067] (2) The aramid fiber (para aramid filament) is subjected to surface plasma treatment to introduce active groups on the surface to obtain activated aramid fiber.

[0068] (3) Interface layer construction steps: The activated aramid fiber was thoroughly wetted by immersing it in a quasi-polyrotaxane solution. After being removed, it was dried at 50 °C for 0.5 h and then at 80 °C for 0.5 h to remove the organic solvent. Then, it was kept at 110 °C for 1 h to graft the terminal amino groups of the quasi-polyrotaxane onto the surface of the activated aramid fiber, thus obtaining a modified aramid fiber with a quasi-polyrotaxane topological interlocking structure on its surface.

[0069] (4) Fluorine functionalization steps: The modified aramid fiber was placed in an anhydrous organic solvent (anhydrous dimethyl sulfoxide), and a fluorinated diisocyanate was added, wherein the molar ratio of the β-cyclodextrin in step (1) to the fluorinated diisocyanate in step (4) was 1:15; the reaction was carried out in a nitrogen atmosphere at 90 °C for 3 h, so that some of the isocyanate groups in the fluorinated diisocyanate reacted with the hydroxyl groups on the β-cyclodextrin to form urethane bonds; after the reaction was completed, the fiber was washed and dried to obtain a modified aramid fiber with a fluorinated functionalized quasi-polyrotaxane interface structure on the surface, which was denoted as functionalized modified aramid fiber.

[0070] The fluorinated diisocyanate has the same structural formula as in Example 1.

[0071] (5) Lamination and curing steps: Functionalized modified aramid fibers are arranged along the axial direction of the GIS insulating tie rod in a mold and impregnated with a mixture of epoxy resin and curing components; the mixture is composed of 100 parts by weight of bisphenol A epoxy resin, 100 parts by weight of methyltetrahydrophthalic anhydride and 1 part by weight of benzyl dimethylamine (BDMA); thus obtaining a GIS insulating tie rod preform. The GIS insulating tie rod preform is then degassed under vacuum and then cured in stages by heating: curing at 90 ℃ for 1 h, 120 ℃ for 2 h, and 160 ℃ for 6 h to obtain an aramid fiber reinforced epoxy composite material for GIS insulating tie rods.

[0072] Comparative Example 1 This comparative example provides an aramid fiber reinforced epoxy composite material without interface modification. Untreated aramid fibers (para-aramid filaments) were directly arranged along the axial direction of a GIS insulating tie rod in a mold and impregnated with a mixture of epoxy resin and curing components. The mixture consisted of 100 parts by weight of bisphenol A type epoxy resin, 30 parts by weight of methyltetrahydrophthalic anhydride, and 0.5 parts by weight of benzyl dimethylamine (BDMA). After vacuum degassing, the mixture was sequentially cured at 80 °C for 1 h, 110 °C for 2 h, and 150 °C for 12 h to obtain the composite material.

[0073] Comparative Example 2 The difference between this comparative example and Example 1 is that only the aramid fiber (para-aramid filament) is subjected to the plasma treatment in step (2), and the quasi-polyrotaxane interface layer construction in step (3) and the fluorine-containing functionalization treatment in step (4) are not performed. The other composite and curing conditions are the same.

[0074] Comparative Example 3 The difference between this comparative example and Example 1 is that after completing the construction of the quasi-polyrotaxane interface layer in step (3), the fluorine-containing functionalization step in step (4) is not performed, that is, no fluorine-containing diisocyanate is added, and the remaining composite and curing conditions are the same.

[0075] Performance testing (1) Figure 6 This is a surface electron microscope image of the aramid fiber (para-aramid filament) used in Comparative Example 1. Figure 9 This is a surface electron microscope image of the functionalized aramid fiber obtained in step (4) of Example 3. Figure 12 This is a surface electron microscope image of the functionalized aramid fiber obtained in step (4) of Example 4. A comparison of the above images shows that the original para-aramid filament (AF) has a relatively smooth surface, while the surface exhibits a noticeably rough structure after functionalization modification. This microscale undulation enhances the capillary adsorption and mechanical intercalation of the resin on the fiber surface, thereby facilitating the formation of interfacial bonds.

[0076] (2) The aramid fiber reinforced epoxy composite materials prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were used as test samples for performance testing. The performance testing included interface performance testing and electrical performance testing.

[0077] Interfacial shear strength (IFSS) was tested using the single-fiber micro-debonding method. An axial load was applied to a single aramid fiber embedded in the resin using a loading device, and the maximum load during interfacial debonding was measured and the interfacial shear strength was calculated. Fiber bundle pull-out strength (TFBT) was tested using the transverse fiber bundle pull-out test method. The fiber bundle was partially embedded in the epoxy resin matrix, and the interfacial failure load was recorded through tensile testing to characterize the interfacial bonding performance. Resistance testing was performed using the clamp electrode method. Electrodes were clamped at both ends of the sample with a distance of 1 cm between the electrodes, and a DC voltage of 1 kV was applied at room temperature. The test results are shown in Table 1. Figure 7 This is a schematic diagram of the interfacial shear strength (IFSS) test of the aramid fiber reinforced epoxy composite material prepared in Comparative Example 1 without interfacial modification. Figure 8 This is a schematic diagram of the fiber bundle pull-out strength (TFBT) test of the aramid fiber reinforced epoxy composite material prepared in Comparative Example 1 without interface modification. Figure 7 , 8 The surface is extremely smooth and has obvious peeling gaps, exhibiting typical interfacial brittle debonding.

[0078] Figure 10 , Figure 13 These are schematic diagrams of the interfacial shear strength (IFSS) test of the aramid fiber reinforced epoxy composite materials for GIS insulating tie rods prepared in Examples 3 and 4, respectively. Figure 11 , 14 These are schematic diagrams of fiber bundle pull-out strength (TFBT) tests of aramid fiber reinforced epoxy composite materials for GIS insulating tie rods prepared in Examples 3 and 4, respectively. Figure 10 , 11 The interface boundary between 13 and 14 is blurred, and the fiber surface is covered by thick resin tear residue. This shift from "interface peeling" to "matrix energy-dissipating damage" strongly demonstrates that the topological interlocking layer successfully diverts stress from the easily failed weak interface to the more load-bearing matrix depth.

[0079] Table 1 Performance tests of composite materials from Examples 1-6 and Comparative Examples 1-3

[0080] As shown in Table 1, in the unmodified aramid fiber reinforced epoxy composite material prepared in Comparative Example 1, there is a lack of effective interfacial bonding between the aramid fiber and the epoxy resin. Under load, the interface is prone to debonding failure, resulting in low IFSS and TFBT levels. Simultaneously, the interfacial region has limited cross-linking and a relatively loose structure, making it easier for charge carriers to migrate along the fiber / resin interface, leading to low resistance. In Comparative Example 2, after plasma treatment of the aramid fiber alone, IFSS, TFBT, and resistance were all slightly improved compared to Comparative Example 1. This is mainly because plasma treatment can introduce active groups such as hydroxyl and carboxyl groups on the fiber surface, improving the wettability and interfacial adhesion between the fiber and the epoxy resin. Simultaneously, the surface-active groups can participate in the interfacial reaction during curing, increasing the cross-linking density of the interfacial region to a certain extent, thus slightly restricting charge carrier migration along the interface, resulting in a slight increase in resistance. However, since this method only involves surface activation modification, the degree of interfacial structure control is limited, so the overall improvement is small. In Comparative Example 3, after introducing a quasi-polyrotaxane topological interlocking structure on the surface of aramid fiber, the IFSS and TFBT were significantly higher than those in Comparative Example 1 and Comparative Example 2, indicating that the "ring-axis" structure in the quasi-polyrotaxane can enhance the transfer of interfacial load and dissipate interfacial stress through restricted molecular slip. However, since Comparative Example 3 did not further introduce a fluorinated isocyanate functionalized structure, the interfacial region lacked high-density fluorinated charge trapping sites, so its resistance was not improved compared to Comparative Example 2.

[0081] In contrast, Examples 1-6 significantly improved interfacial performance and resistance by synergistically constructing quasi-polyrotaxane topologically interlocked structures and fluorinated functionalized structures in the interfacial region. Example 1 demonstrated significantly better interfacial bonding strength and resistance than the comparative example. In Examples 2 and 3, with the increase of β-cyclodextrin content, more "ring-axis" topologically interlocked structural units were formed, enhancing interfacial load transfer and stress dissipation capabilities, further improving IFSS and TFBT. Furthermore, under the condition that the molar ratio of β-cyclodextrin to fluorinated diisocyanate remained constant, the amount of fluorinated diisocyanate introduced increased synchronously with the β-cyclodextrin content, increasing the number of fluorinated functional structures and charge trapping sites in the interfacial region, thereby more effectively suppressing carrier migration along the interface, resulting in a synchronous increase in resistance. In Example 4, short-chain polyetheramine D400 was used instead of D2000. Due to the shortened axial chain length, the number of chain segments available for β-cyclodextrin grafting decreased, resulting in a reduction in the number of topologically interlocked structural units. This weakened the interfacial stress regulation and energy dissipation capabilities, thus significantly reducing IFSS and TFBT. Simultaneously, the reduced β-cyclodextrin grafting also reduced the number of hydroxyl sites that could be grafted with fluorinated diisocyanates, decreasing the number of fluorinated functional structures introduced into the interfacial region and weakening the inhibition of carrier migration, thus also leading to a decrease in resistivity. In Example 5, increasing the solid content of the quasi-polyrotaxane solution resulted in a limited increase in the actual grafting amount of quasi-polyrotaxane due to the limited number of active sites on the aramid fiber surface, and the interfacial structure change was not significant. Therefore, the overall performance was similar to that of Example 1. It is worth noting that in Example 6, adjusting the molar ratio of β-cyclodextrin to fluorinated diisocyanate to 1:20 increased the amount of fluorinated diisocyanate introduced, significantly increasing the number of fluorinated functional structures in the interfacial region. This resulted in the formation of more charge-trapping sites, thereby more effectively suppressing carrier migration along the interface and significantly improving resistance. However, excessive fluorinated diisocyanate consumed more hydroxyl groups on β-cyclodextrin, reducing the number of active groups that could further react with the epoxy resin network during subsequent curing of the functionalized aramid fiber. This decreased the chemical bonding ability between the interfacial layer and the epoxy network, thus reducing IFSS and TFBT.

[0082] (3) XPS spectra of the untreated aramid fiber (para-aramid filament) of Comparative Example 1 and the functionalized modified aramid fibers prepared in Examples 1, 2, 3, and 4 were tested respectively. The results are as follows: Figure 15 , 16 As shown in figures 17, 18, and 19. (By...) Figure 15 , 16As shown in Figures 17, 18, and 19, in the high-resolution C1s spectra, compared to the untreated aramid fiber (para-aramid filament) of Comparative Example 1, the CO component ratio at 286.5 eV of the functionalized modified aramid fibers treated with surface plasma and fluorine-containing functionalization in Examples 1, 2, 3, and 4 increases with increasing β-CD content. This increase originates from the abundant oxygen-containing carbon environment in the β-CD cyclic structure, including C-OH and COC groups, indicating that pPR molecules containing cyclodextrin units have been successfully introduced into the fiber surface.

[0083] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing an aramid fiber reinforced epoxy composite material for GIS insulating tie rods, characterized in that, The steps include the following: (1) Polyetheramine and β-cyclodextrin were dissolved in deionized water and self-assembled by stirring to obtain quasi-polyrotaxane. After separation and drying, the quasi-polyrotaxane solution was dissolved in an organic solvent. (2) Surface plasma treatment of aramid fibers to obtain activated aramid fibers; (3) The activated aramid fiber was fully wetted by immersing it in a quasi-polyrotaxane solution, dried, and then heat-treated at 110-130 °C for 1-2 h to obtain the modified aramid fiber with a quasi-polyrotaxane topological interlocking structure on its surface. (4) The modified aramid fiber is added to an anhydrous organic solvent, and then a fluorinated diisocyanate is added. The mixture is heated under a protective atmosphere and reacted. After the reaction is completed, the fiber is washed and dried to obtain a modified aramid fiber with a fluorinated functionalized quasi-polyrotaxane interface structure on its surface, which is referred to as functionalized modified aramid fiber. The fluorinated diisocyanate is 4,4'-(hexafluoroisopropyl)bis(phenylisocyanate), and its structural formula is shown below: ； (5) The functionalized modified aramid fibers are arranged in the mold along the axial direction of the GIS insulating tie rod, and the mixture of epoxy resin and curing components is impregnated to obtain the GIS insulating tie rod preform; then the GIS insulating tie rod preform is degassed and cured to obtain the aramid fiber reinforced epoxy composite material for GIS insulating tie rod.

2. The method for preparing the aramid fiber reinforced epoxy composite material for GIS insulating tie rods according to claim 1, characterized in that, In step (1), 1 mol of polyetheramine and 2-18 mol of β-cyclodextrin are dissolved in deionized water and stirred and assembled at room temperature for 8-16 h. After standing, filtration, washing and drying, quasi-polyrotaxane is obtained. The quasi-polyrotaxane is dissolved in an organic solvent to prepare a quasi-polyrotaxane solution with a solid content of 1-3 wt%.

3. The method for preparing the aramid fiber reinforced epoxy composite material for GIS insulating tie rods according to claim 1 or 2, characterized in that, The polyetheramine is selected from one or more of polyetheramine D230, polyetheramine D400, and polyetheramine D2000.

4. The method for preparing the aramid fiber reinforced epoxy composite material for GIS insulating tie rods according to claim 1, characterized in that, In step (2), the aramid fiber is a para-aramid filament.

5. The method for preparing the aramid fiber reinforced epoxy composite material for GIS insulating tie rods according to claim 1, characterized in that, In step (3), the impregnated aramid fibers are dried at 30-50 °C for 0.5-1 h and at 60-80 °C for 0.5-1 h to remove the organic solvent.

6. The method for preparing the aramid fiber reinforced epoxy composite material for GIS insulating tie rods according to claim 1, characterized in that, The molar ratio of β-cyclodextrin in step (1) to fluorinated diisocyanate in step (4) is 1:(1-20); the heating reaction in step (4) is carried out in nitrogen or inert gas, the reaction temperature is 70-90 °C, and the reaction time is 3-6 h.

7. The method for preparing the aramid fiber reinforced epoxy composite material for GIS insulating tie rods according to claim 1, characterized in that, In step (5), the epoxy resin is selected from at least one of bisphenol A type epoxy resin, alicyclic epoxy resin or phenolic type epoxy resin; the curing component includes a curing agent and a curing accelerator; the curing agent is an acid anhydride curing agent; the curing accelerator is selected from at least one of imidazole curing accelerator and tertiary amine curing accelerator; the mixed system of epoxy resin and curing component includes 100 parts by weight of epoxy resin, 30 to 100 parts by weight of curing agent and 0.3 to 1 part by weight of curing accelerator.

8. The method for preparing the aramid fiber reinforced epoxy composite material for GIS insulating tie rods according to claim 1, characterized in that, In step (5), the GIS insulated tie rod preform is subjected to staged heating and curing: the pre-curing temperature is 60-90℃ and the curing time is 1-2 h; the main curing temperature is 100-120℃ and the curing time is 2-4 h; the post-curing temperature is 140-160℃ and the curing time is 6-18 h.

9. An aramid fiber reinforced epoxy composite material for GIS insulating tie rods, prepared by the method described in any one of claims 1-8.

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