Self-healing polymer insulating material, preparation method and application of self-healing polymer insulating material in cable sheath

Abstract

The invention relates to the technical field of polyurethane materials, and discloses a self-healing polymer insulating material, a preparation method and application of the self-healing polymer insulating material to a cable sheath. According to the invention, a Schiff base compound modified carbon nanotube with hydroxyl and a Schiff base bond is prepared and introduced into oxime modified polyurethane, and based on two dynamic reversible covalent bonds of an oxime amino methyl ester bond and the Schiff base bond, polyurethane is endowed with self-repairing performance; meanwhile, the heat conductivity, the insulativity and the mechanical property of the polyurethane material can be optimized through the surface-modified carbon nano tubes and the nano silicon dioxide, so that the polyurethane material can be better applied to cable sheath materials.

Description

Technical Field

[0001] This invention relates to the field of polyurethane materials technology, specifically to self-healing polymer insulating materials, their preparation methods, and their application in cable sheaths. Background Technology

[0002] Polyurethane is a block copolymer whose main molecular chain contains urethane groups. Its unique molecular structure endows it with excellent flexibility, mechanical strength, and abrasion resistance, as well as advantages such as light weight, good thermal and chemical stability, and good insulation, making it a suitable sheathing material for flexible cables. To improve the stability, reliability, and service life of polyurethane, designing and manufacturing polyurethane with high mechanical strength and efficient self-healing properties is an effective method.

[0003] Currently, polymer self-healing methods are divided into exogenous self-healing and intrinsic self-healing. Intrinsic self-healing achieves its self-healing mechanism through the molecular structure of reversible chemical reactions inherent in the polymer material or through diffusion of macromolecules. This improves the mechanical properties of the material while endowing polyurethane materials with efficient self-healing properties. Based on the different forces involved, it can be mainly classified into the following three methods: dynamic covalent bond self-healing polyurethane, non-covalent supramolecular force self-healing polyurethane, and self-healing polyurethane with synergistic effects of multiple forces.

[0004] However, the activation of dynamic reversible bonds in self-healing polymers comes at the cost of mechanical properties. Therefore, the preparation of polyurethanes with excellent mechanical properties and self-healing properties is of great significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide self-healing polymer insulation materials, preparation methods, and applications in cable sheaths. This invention prepares Schiff base compounds with hydroxyl groups and Schiff base bonds to modify carbon nanotubes, and introduces them into oxime-modified polyurethane. Based on the two dynamic reversible covalent bonds of oxime methyl ester and Schiff base, the polyurethane is endowed with self-healing properties. At the same time, the surface-modified carbon nanotubes and nano-silica can optimize the thermal conductivity, insulation, and mechanical properties of polyurethane materials, making them better suited for cable sheath materials.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a self-healing polymer insulating material includes the following steps: Step (1): Mix hydroxylated carbon nanotubes and toluene, disperse by ultrasonication, add sodium ethoxide, continue ultrasonic dispersion, add 4-chloromethylstyrene, react, filter, wash, and dry to obtain styrene-based grafted carbon nanotubes. Step (2): Styrene-grafted carbon nanotubes and water are mixed, ultrasonically dispersed, and then styrene, methacrolein and azobisisobutyronitrile are added. After the reaction is completed, the mixture is filtered, washed and dried to obtain polystyrene-acrylic acid modified carbon nanotubes. Step (3): Mix 1,8-p-menthanediamine, polystyrene-acrylic acid modified carbon nanotubes and water, disperse by ultrasonication, adjust the pH value, and react. After the reaction is completed, add vanillin and continue the reaction. After the reaction is completed, purify to obtain Schiff base compound modified carbon nanotubes. Step (4): Mix and dissolve polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, N,N-dimethylformamide and catalyst dibutyltin dilaurate, and react. After the reaction is completed, polyurethane prepolymer is obtained. 1,4-Butanediol and Schiff base compounds were added to the polyurethane prepolymer and the reaction continued. After the reaction was completed, KH550 modified nano-silica was added, mixed evenly, and dried to obtain a self-healing polymer insulating material.

[0007] Preferably, in step (1), the solid-liquid ratio of hydroxylated carbon nanotubes, 4-chloromethylstyrene, sodium ethoxide, and toluene is 0.12g:6-10mL:0.8-1g:150-300mL.

[0008] Preferably, in step (1), the reaction conditions are: stirring the reaction at 25-35℃ for 3-5 hours.

[0009] Preferably, in step (1), the washing operation is as follows: washing with ethanol, toluene and tetrahydrofuran in sequence.

[0010] Preferably, in step (2), the solid-liquid ratio of styrene-grafted carbon nanotubes, styrene, methacrolein, azobisisobutyronitrile, and water is 1g:5-6mL:4-5mL:0.3g:50mL; the reaction conditions are: reaction at 60-70℃ for 8-10h in a nitrogen atmosphere.

[0011] Preferably, in step (3), the solid-liquid ratio of 1,8-p-menthanediamine, vanillin, polystyrene-acrylaldehyde modified carbon nanotubes, and water is 1g:1.8g:0.8-1g:100mL; the reaction conditions are: stirring at room temperature and pH 10 for 12-16h; and the reaction is continued at room temperature and pH 10 for 8-12h.

[0012] Preferably, in step (3), the purification operation includes: adding 0.1 mol / L hydrogen chloride aqueous solution to adjust the pH value to 7, centrifuging to collect the precipitate, adding water to wash, and drying.

[0013] Preferably, in step (4): the molar ratio of polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, and 1,4-butanediol is 4:8:2-2.5:0.5-0.8; the mass of the catalyst dibutyltin dilaurate added is 0.3% of the mass of the polyurethane prepolymer; the solid content of the polyurethane prepolymer is 30-40%; the mass of the Schiff base compound modified carbon nanotubes added is 15-20% of the mass of the self-healing polymer insulating material; and the mass of the KH550 modified nano silica added is 6-10% of the mass of the self-healing polymer insulating material.

[0014] Preferably, in step (4), the reaction conditions are: reacting for 6-12 hours in a nitrogen atmosphere at a temperature of 60-80°C; and the conditions for continued reaction are: continuing the reaction for 5-10 hours in a nitrogen atmosphere at a temperature of 60-80°C.

[0015] Preferably, a self-healing polymer insulating material is prepared using the method described above.

[0016] Preferably, the application of a self-healing polymer insulation material as described above in cable sheaths.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention prepares Schiff base compounds modified carbon nanotubes with hydroxyl groups and Schiff base bonds, and introduces them into oxime-modified polyurethane. Based on the oxime methyl ester bond and the dynamically reversible covalent Schiff base bond, the polyurethane is endowed with self-healing properties. At the same time, the surface-modified carbon nanotubes and nano-silica can optimize the thermal conductivity, insulation and mechanical properties of polyurethane materials, making them better applicable to cable sheath materials.

[0018] 2. This invention utilizes the nucleophilic substitution reaction between the hydroxyl groups on the surface of hydroxylated carbon nanotubes and the chlorine of 4-chloromethylstyrene to graft styrene groups onto the surface of the carbon nanotubes. Then, the carbon-carbon double bonds in the styrene groups are used to copolymerize with styrene and methacrolein to modify the surface of the carbon nanotubes, synthesizing polystyrene-acrylaldehyde modified carbon nanotubes. Through the Schiff base reaction between the aldehyde group and the amino group, 1,8-para-mentanediamine and vanillin are further introduced into the surface of the carbon nanotubes. The resulting Schiff base compound modified carbon nanotubes have dynamic reversible covalent bonds and phenolic hydroxyl groups, which can participate in the polymerization reaction of polyurethane as chain extenders, synergistically enhancing the self-healing properties of polyurethane by activating oxime methyl ester bonds.

[0019] 3. In this invention, Schiff base compound-modified carbon nanotubes and KH550-modified nano-silica are introduced into polyurethane. Carbon nanotubes can improve the thermal conductivity of polyurethane materials. Furthermore, due to the modification of the polymer surface of carbon nanotubes, the dispersion performance of carbon nanotubes in the polymer matrix and their interfacial bonding force with the polymer are improved, and the degree of crosslinking of polyurethane is increased, thereby improving the mechanical properties of polyurethane materials. KH550-modified nano-silica further reduces the electrical conductivity of polyurethane materials and improves their insulation performance. Attached Figure Description

[0020] Figure 1 This is a bar chart showing the thermal conductivity of the self-healing polymer insulating materials prepared in Examples 1-5 and Comparative Examples 1-2 of this invention during comprehensive performance testing. Figure 2 This is a bar chart showing the self-healing rate of the self-healing polymer insulating materials prepared in Examples 1-5 and Comparative Examples 1-2 of this invention in a comprehensive performance test. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] Example 1 This embodiment discloses a method for preparing a self-healing polymer insulating material, including the following steps: Step (1): Hydroxylated carbon nanotubes and toluene are mixed and ultrasonically dispersed for 20 min. Sodium ethoxide is added and ultrasonic dispersion is continued for 1.5 h at room temperature. 4-Chloromethylstyrene is added and the mixture is stirred at 35 °C for 3 h. After the reaction is completed, the mixture is filtered and washed successively with ethanol, toluene and tetrahydrofuran. It is then dried at 50 °C for 48 h to obtain styrene-based grafted carbon nanotubes. The solid-liquid ratio of hydroxylated carbon nanotubes, 4-chloromethylstyrene, sodium ethoxide, and toluene was 0.12 g: 6 mL: 0.8 g: 200 mL. Step (2): Styrene-grafted carbon nanotubes and water are mixed and ultrasonically dispersed for 20 min. Styrene, methacrolein and azobisisobutyronitrile are added and reacted at 70°C for 8 h in a nitrogen atmosphere. After the reaction is completed, the mixture is filtered, washed with water, and dried at 50°C for 48 h to obtain polystyrene-acrylic acid modified carbon nanotubes. The solid-liquid ratio of styrene-grafted carbon nanotubes, styrene, methacrolein, azobisisobutyronitrile, and water is 1g:6mL:4mL:0.3g:50mL. Step (3): Mix 1,8-p-menthol diamine, polystyrene-acrylic acid modified carbon nanotubes, and water, and ultrasonically disperse for 20 min. Add 0.1 mol / L sodium hydroxide aqueous solution to adjust the pH to 10. Stir and react at room temperature for 12 h. After the reaction is complete, add vanillin and continue the reaction for 12 h. After the reaction is complete, add 0.1 mol / L hydrogen chloride aqueous solution to adjust the pH to 7. Centrifuge to collect the precipitate, wash with water, and dry at 50℃ for 48 h to obtain Schiff base compound modified carbon nanotubes. The solid-liquid ratio of 1,8-p-menthanediamine, vanillin, polystyrene-acrylic acid modified carbon nanotubes, and water is 1g:1.8g:0.8g:100mL. Step (4): Polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, N,N-dimethylformamide and catalyst dibutyltin dilaurate are mixed and dissolved, and reacted at 60°C for 12 hours in a nitrogen atmosphere. After the reaction is completed, a polyurethane prepolymer with a solid content of 30% is obtained. 1,4-Butanediol and Schiff base compounds modified carbon nanotubes were added to polyurethane prepolymer and reacted at 60°C for 10 hours. After the reaction was completed, KH550 modified nano-silica was added and mixed evenly. The mixture was then dried at 70°C for 24 hours to obtain a self-healing polymer insulating material. The molar ratio of polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, and 1,4-butanediol is 4:8:2:0.8; the mass of the catalyst dibutyltin dilaurate is 0.3% of the mass of the polyurethane prepolymer; the mass of the Schiff base compound modified carbon nanotubes is 15% of the mass of the self-healing polymer insulating material; and the mass of the KH550 modified nano-silica is 6% of the mass of the self-healing polymer insulating material.

[0023] Example 2 This embodiment discloses a method for preparing a self-healing polymer insulating material, including the following steps: Step (1): Hydroxylated carbon nanotubes and toluene are mixed and ultrasonically dispersed for 20 min. Sodium ethoxide is added and ultrasonic dispersion is continued for 1.5 h at room temperature. 4-Chloromethylstyrene is added and the mixture is stirred at 35 °C for 3 h. After the reaction is completed, the mixture is filtered and washed successively with ethanol, toluene and tetrahydrofuran. It is then dried at 50 °C for 48 h to obtain styrene-based grafted carbon nanotubes. The solid-liquid ratio of hydroxylated carbon nanotubes, 4-chloromethylstyrene, sodium ethoxide, and toluene was 0.12 g: 6 mL: 0.8 g: 200 mL. Step (2): Styrene-grafted carbon nanotubes and water are mixed and ultrasonically dispersed for 20 min. Styrene, methacrolein and azobisisobutyronitrile are added and reacted at 70°C for 8 h in a nitrogen atmosphere. After the reaction is completed, the mixture is filtered, washed with water, and dried at 50°C for 48 h to obtain polystyrene-acrylic acid modified carbon nanotubes. The solid-liquid ratio of styrene-grafted carbon nanotubes, styrene, methacrolein, azobisisobutyronitrile, and water is 1g:5.8mL:4.2mL:0.3g:50mL. Step (3): Mix 1,8-p-menthol diamine, polystyrene-acrylic acid modified carbon nanotubes, and water, and ultrasonically disperse for 20 min. Add 0.1 mol / L sodium hydroxide aqueous solution to adjust the pH to 10. Stir and react at room temperature for 14 h. After the reaction is complete, add vanillin and continue the reaction for 10 h. After the reaction is complete, add 0.1 mol / L hydrogen chloride aqueous solution to adjust the pH to 7. Centrifuge to collect the precipitate, wash with water, and dry at 50℃ for 48 h to obtain Schiff base compound modified carbon nanotubes. The solid-liquid ratio of 1,8-p-menthanediamine, vanillin, polystyrene-acrylic acid modified carbon nanotubes, and water is 1g:1.8g:0.8g:100mL. Step (4): Polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, N,N-dimethylformamide and catalyst dibutyltin dilaurate are mixed and dissolved, and reacted at 60°C for 12 hours in a nitrogen atmosphere. After the reaction is completed, a polyurethane prepolymer with a solid content of 30% is obtained. 1,4-Butanediol and Schiff base compounds modified carbon nanotubes were added to polyurethane prepolymer and reacted at 60°C for 10 hours. After the reaction was completed, KH550 modified nano-silica was added and mixed evenly. The mixture was then dried at 70°C for 24 hours to obtain a self-healing polymer insulating material. The molar ratio of polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, and 1,4-butanediol is 4:8:2.1:0.7; the mass of the catalyst dibutyltin dilaurate is 0.3% of the mass of the polyurethane prepolymer; the mass of the Schiff base compound modified carbon nanotubes is 17% of the mass of the self-healing polymer insulating material; and the mass of the KH550 modified nano-silica is 7% of the mass of the self-healing polymer insulating material.

[0024] Example 3 This embodiment discloses a method for preparing a self-healing polymer insulating material, including the following steps: Step (1): Hydroxylated carbon nanotubes and toluene are mixed and ultrasonically dispersed for 20 min. Sodium ethoxide is added and ultrasonic dispersion is continued for 1.5 h at room temperature. 4-Chloromethylstyrene is added and the mixture is stirred at 35 °C for 3 h. After the reaction is completed, the mixture is filtered and washed successively with ethanol, toluene and tetrahydrofuran. It is then dried at 50 °C for 48 h to obtain styrene-based grafted carbon nanotubes. The solid-liquid ratio of hydroxylated carbon nanotubes, 4-chloromethylstyrene, sodium ethoxide, and toluene was 0.12 g: 6 mL: 0.8 g: 200 mL. Step (2): Styrene-grafted carbon nanotubes and water are mixed and ultrasonically dispersed for 20 min. Styrene, methacrolein and azobisisobutyronitrile are added and reacted at 70°C for 8 h in a nitrogen atmosphere. After the reaction is completed, the mixture is filtered, washed with water, and dried at 50°C for 48 h to obtain polystyrene-acrylic acid modified carbon nanotubes. The solid-liquid ratio of styrene-grafted carbon nanotubes, styrene, methacrolein, azobisisobutyronitrile, and water is 1g:5.5mL:4.5mL:0.3g:50mL. Step (3): Mix 1,8-p-menthol diamine, polystyrene-acrylic acid modified carbon nanotubes, and water, and ultrasonically disperse for 20 min. Add 0.1 mol / L sodium hydroxide aqueous solution to adjust the pH to 10. Stir and react at room temperature for 14 h. After the reaction is complete, add vanillin and continue the reaction for 10 h. After the reaction is complete, add 0.1 mol / L hydrogen chloride aqueous solution to adjust the pH to 7. Centrifuge to collect the precipitate, wash with water, and dry at 50℃ for 48 h to obtain Schiff base compound modified carbon nanotubes. The solid-liquid ratio of 1,8-p-menthanediamine, vanillin, polystyrene-acrylic acid modified carbon nanotubes, and water is 1g:1.8g:0.8g:100mL. Step (4): Polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, N,N-dimethylformamide and catalyst dibutyltin dilaurate are mixed and dissolved, and reacted at 60°C for 12 hours in a nitrogen atmosphere. After the reaction is completed, a polyurethane prepolymer with a solid content of 30% is obtained. 1,4-Butanediol and Schiff base compounds modified carbon nanotubes were added to polyurethane prepolymer and reacted at 60°C for 10 hours. After the reaction was completed, KH550 modified nano-silica was added and mixed evenly. The mixture was then dried at 70°C for 24 hours to obtain a self-healing polymer insulating material. The molar ratio of polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, and 1,4-butanediol is 4:8:2.3:0.65; the mass of the catalyst dibutyltin dilaurate is 0.3% of the mass of the polyurethane prepolymer; the mass of the Schiff base compound modified carbon nanotubes is 18% of the mass of the self-healing polymer insulating material; and the mass of the KH550 modified nano-silica is 8% of the mass of the self-healing polymer insulating material.

[0025] Example 4 This embodiment discloses a method for preparing a self-healing polymer insulating material, including the following steps: Step (1): Hydroxylated carbon nanotubes and toluene are mixed and ultrasonically dispersed for 20 min. Sodium ethoxide is added and ultrasonic dispersion is continued for 1.5 h at room temperature. 4-Chloromethylstyrene is added and the mixture is stirred at 35 °C for 3 h. After the reaction is completed, the mixture is filtered and washed successively with ethanol, toluene and tetrahydrofuran. It is then dried at 50 °C for 48 h to obtain styrene-based grafted carbon nanotubes. The solid-liquid ratio of hydroxylated carbon nanotubes, 4-chloromethylstyrene, sodium ethoxide, and toluene was 0.12 g: 6 mL: 0.8 g: 200 mL. Step (2): Styrene-grafted carbon nanotubes and water are mixed and ultrasonically dispersed for 20 min. Styrene, methacrolein and azobisisobutyronitrile are added and reacted at 70°C for 8 h in a nitrogen atmosphere. After the reaction is completed, the mixture is filtered, washed with water, and dried at 50°C for 48 h to obtain polystyrene-acrylic acid modified carbon nanotubes. The solid-liquid ratio of styrene-grafted carbon nanotubes, styrene, methacrolein, azobisisobutyronitrile, and water is 1g:5.2mL:4.8mL:0.3g:50mL. Step (3): Mix 1,8-p-menthol diamine, polystyrene-acrylic acid modified carbon nanotubes, and water, and ultrasonically disperse for 20 min. Add 0.1 mol / L sodium hydroxide aqueous solution to adjust the pH to 10. Stir and react at room temperature for 14 h. After the reaction is complete, add vanillin and continue the reaction for 10 h. After the reaction is complete, add 0.1 mol / L hydrogen chloride aqueous solution to adjust the pH to 7. Centrifuge to collect the precipitate, wash with water, and dry at 50℃ for 48 h to obtain Schiff base compound modified carbon nanotubes. The solid-liquid ratio of 1,8-p-menthanediamine, vanillin, polystyrene-acrylic acid modified carbon nanotubes, and water is 1g:1.8g:0.8g:100mL. Step (4): Polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, N,N-dimethylformamide and catalyst dibutyltin dilaurate are mixed and dissolved, and reacted at 60°C for 12 hours in a nitrogen atmosphere. After the reaction is completed, a polyurethane prepolymer with a solid content of 30% is obtained. 1,4-Butanediol and Schiff base compounds modified carbon nanotubes were added to polyurethane prepolymer and reacted at 60°C for 10 hours. After the reaction was completed, KH550 modified nano-silica was added and mixed evenly. The mixture was then dried at 70°C for 24 hours to obtain a self-healing polymer insulating material. The molar ratio of polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, and 1,4-butanediol is 4:8:2.4:0.6; the mass of the catalyst dibutyltin dilaurate is 0.3% of the mass of the polyurethane prepolymer; the mass of the Schiff base compound modified carbon nanotubes is 19% of the mass of the self-healing polymer insulating material; and the mass of the KH550 modified nano-silica is 9% of the mass of the self-healing polymer insulating material.

[0026] Example 5 This embodiment discloses a method for preparing a self-healing polymer insulating material, including the following steps: Step (1): Hydroxylated carbon nanotubes and toluene are mixed and ultrasonically dispersed for 20 min. Sodium ethoxide is added and ultrasonic dispersion is continued for 1.5 h at room temperature. 4-Chloromethylstyrene is added and the mixture is stirred at 35 °C for 3 h. After the reaction is completed, the mixture is filtered and washed successively with ethanol, toluene and tetrahydrofuran. It is then dried at 50 °C for 48 h to obtain styrene-based grafted carbon nanotubes. The solid-liquid ratio of hydroxylated carbon nanotubes, 4-chloromethylstyrene, sodium ethoxide, and toluene was 0.12 g: 6 mL: 0.8 g: 200 mL. Step (2): Styrene-grafted carbon nanotubes and water are mixed and ultrasonically dispersed for 20 min. Styrene, methacrolein and azobisisobutyronitrile are added and reacted at 70°C for 8 h in a nitrogen atmosphere. After the reaction is completed, the mixture is filtered, washed with water, and dried at 50°C for 48 h to obtain polystyrene-acrylic acid modified carbon nanotubes. The solid-liquid ratio of styrene-grafted carbon nanotubes, styrene, methacrolein, azobisisobutyronitrile, and water is 1g:5mL:5mL:0.3g:50mL. Step (3): Mix 1,8-p-menthol diamine, polystyrene-acrylaldehyde modified carbon nanotubes, and water, and ultrasonically disperse for 20 min. Add 0.1 mol / L sodium hydroxide aqueous solution to adjust the pH to 10. Stir and react at room temperature for 16 h. After the reaction is complete, add vanillin and continue the reaction for 8 h. After the reaction is complete, add 0.1 mol / L hydrogen chloride aqueous solution to adjust the pH to 7. Centrifuge to collect the precipitate, wash with water, and dry at 50℃ for 48 h to obtain Schiff base compound modified carbon nanotubes. The solid-liquid ratio of 1,8-p-menthanediamine, vanillin, polystyrene-acrylic acid modified carbon nanotubes, and water is 1g:1.8g:0.8g:100mL. Step (4): Polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, N,N-dimethylformamide and catalyst dibutyltin dilaurate are mixed and dissolved, and reacted at 60°C for 12 hours in a nitrogen atmosphere. After the reaction is completed, a polyurethane prepolymer with a solid content of 30% is obtained. 1,4-Butanediol and Schiff base compounds modified carbon nanotubes were added to polyurethane prepolymer and reacted at 60°C for 10 hours. After the reaction was completed, KH550 modified nano-silica was added and mixed evenly. The mixture was then dried at 70°C for 24 hours to obtain a self-healing polymer insulating material. The molar ratio of polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, and 1,4-butanediol is 4:8:2.5:0.5; the mass of the catalyst dibutyltin dilaurate is 0.3% of the mass of the polyurethane prepolymer; the mass of the Schiff base compound modified carbon nanotubes is 20% of the mass of the self-healing polymer insulating material; and the mass of the KH550 modified nano-silica is 10% of the mass of the self-healing polymer insulating material.

[0027] Comparative Example 1 This comparative example discloses a method for preparing a self-healing polymer insulating material, including the following steps: Step (1): Hydroxylated carbon nanotubes and toluene are mixed and ultrasonically dispersed for 20 min. Sodium ethoxide is added and ultrasonic dispersion is continued for 1.5 h at room temperature. 4-Chloromethylstyrene is added and the mixture is stirred at 35 °C for 3 h. After the reaction is completed, the mixture is filtered and washed successively with ethanol, toluene and tetrahydrofuran. It is then dried at 50 °C for 48 h to obtain styrene-based grafted carbon nanotubes. The solid-liquid ratio of hydroxylated carbon nanotubes, 4-chloromethylstyrene, sodium ethoxide, and toluene was 0.12 g: 6 mL: 0.8 g: 200 mL. Step (2): Polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, N,N-dimethylformamide and catalyst dibutyltin dilaurate are mixed and dissolved, and reacted at 60°C for 12 hours in a nitrogen atmosphere. After the reaction is completed, a polyurethane prepolymer with a solid content of 30% is obtained. 1,4-Butanediol was added to the polyurethane prepolymer and reacted at 60°C for 10 hours. After the reaction was completed, styrene-grafted carbon nanotubes and KH550 modified nano-silica were added and mixed evenly. The mixture was then dried at 70°C for 24 hours to obtain a self-healing polymer insulation material. The molar ratio of polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, and 1,4-butanediol is 4:8:2:0.8; the mass of the catalyst dibutyltin dilaurate is 0.3% of the mass of the polyurethane prepolymer; the mass of the styrene-based grafted carbon nanotubes is 15% of the mass of the self-healing polymer insulating material; and the mass of the KH550 modified nano-silica is 6% of the mass of the self-healing polymer insulating material.

[0028] Comparative Example 2 This comparative example discloses a method for preparing a self-healing polymer insulating material, including the following steps: Step (1): Hydroxylated carbon nanotubes and toluene are mixed and ultrasonically dispersed for 20 min. Sodium ethoxide is added and ultrasonic dispersion is continued for 1.5 h at room temperature. 4-Chloromethylstyrene is added and the mixture is stirred at 35 °C for 3 h. After the reaction is completed, the mixture is filtered and washed successively with ethanol, toluene and tetrahydrofuran. It is then dried at 50 °C for 48 h to obtain styrene-based grafted carbon nanotubes. The solid-liquid ratio of hydroxylated carbon nanotubes, 4-chloromethylstyrene, sodium ethoxide, and toluene was 0.12 g: 6 mL: 0.8 g: 200 mL. Step (2): Styrene-grafted carbon nanotubes and water are mixed and ultrasonically dispersed for 20 min. Styrene, methacrolein and azobisisobutyronitrile are added and reacted at 70°C for 8 h in a nitrogen atmosphere. After the reaction is completed, the mixture is filtered, washed with water, and dried at 50°C for 48 h to obtain polystyrene-acrylic acid modified carbon nanotubes. The solid-liquid ratio of styrene-grafted carbon nanotubes, styrene, methacrolein, azobisisobutyronitrile, and water is 1g:6mL:4mL:0.3g:50mL. Step (3): Mix 1,8-p-menthol diamine, polystyrene-acrylic acid modified carbon nanotubes, and water, and ultrasonically disperse for 20 min. Add 0.1 mol / L sodium hydroxide aqueous solution to adjust the pH to 10. Stir and react at room temperature for 12 h. After the reaction is complete, add vanillin and continue the reaction for 12 h. After the reaction is complete, add 0.1 mol / L hydrogen chloride aqueous solution to adjust the pH to 7. Centrifuge to collect the precipitate, wash with water, and dry at 50℃ for 48 h to obtain Schiff base compound modified carbon nanotubes. The solid-liquid ratio of 1,8-p-menthanediamine, vanillin, polystyrene-acrylic acid modified carbon nanotubes, and water is 1g:1.8g:0.8g:100mL. Step (4): Polycaprolactone diol, isophorone diisocyanate, N,N-dimethylformamide and catalyst dibutyltin dilaurate are mixed and dissolved, and reacted at 60°C for 12 hours in a nitrogen atmosphere. After the reaction is completed, a polyurethane prepolymer with a solid content of 30% is obtained. 1,4-Butanediol and Schiff base compounds modified carbon nanotubes were added to polyurethane prepolymer and reacted at 60°C for 10 hours. After the reaction was completed, KH550 modified nano-silica was added and mixed evenly. The mixture was then dried at 70°C for 24 hours to obtain a self-healing polymer insulating material. The molar ratio of polycaprolactone diol, isophorone diisocyanate, and 1,4-butanediol is 4:8:2.8; the mass of the catalyst dibutyltin dilaurate is 0.3% of the mass of the polyurethane prepolymer; the mass of the Schiff base compound modified carbon nanotubes is 15% of the mass of the self-healing polymer insulating material; and the mass of the KH550 modified nano-silica is 6% of the mass of the self-healing polymer insulating material.

[0029] In the above examples and comparative examples: the diameter of the hydroxylated carbon nanotubes is 30-50 nm, the length is 10-20 μm, and the hydroxyl content is 0.53 wt.%; the polycaprolactone diol is PCL2000; the preparation of KH550 modified nano silica includes the following steps: 1 g of nano silica, 90 mL of ethanol, and 30 mL of water are mixed, 0.4 g of KH550 is added, the pH value is adjusted to 5, ultrasonic dispersion is performed, and the reaction is carried out at 80 °C for 1 h. After the reaction is completed, the mixture is filtered, washed, and dried to obtain KH550 modified nano silica; the particle size of the nano silica is 50-100 nm.

[0030] Test case The comprehensive performance of the self-healing polymer insulating materials prepared in Examples 1-5 and Comparative Examples 1-2 was tested. Specific test results are shown in Table 1. Table 1 The tests for each indicator in Table 1 were conducted according to the following standards: tensile strength was determined by GB / T 1040 2006 "Determination of Tensile Properties of Plastics"; volume resistivity was tested according to GB / T 1410-2006; thermal conductivity was tested according to ASTM C518-02; the self-healing rate was tested as follows: the self-healing polymer insulating material strips prepared in Examples 1-5 and Comparative Examples 1-2 were cut in the middle, the broken edges were aligned, and the strips were heated in an oven at 130℃ for 2 hours to repair the self-healing rate. Then, the strips were placed in a vacuum oven at 80℃ for 30 hours to cure the self-healing rate. After curing, the mechanical properties were tested again, and the self-healing rate was calculated.

[0031] As can be seen from the test results in Table 1, the thermal conductivity, insulation, and mechanical properties of the self-healing polymer insulating material prepared by this invention are all improved, making it suitable for use in cable materials. This is because the Schiff base-modified carbon nanotubes possess dynamic reversible covalent bonds and phenolic hydroxyl groups, which can act as chain extenders in the polymerization reaction of polyurethane, synergistically enhancing the self-healing properties of polyurethane through oxime methyl ester bonds. Simultaneously, the carbon nanotubes improve the thermal conductivity of the polyurethane material. Furthermore, due to the modification of the polymer surface on the carbon nanotubes, the dispersion performance of the carbon nanotubes in the polymer matrix and their interfacial bonding force with the polymer are improved, increasing the crosslinking degree of polyurethane and thus enhancing the mechanical properties of the polyurethane material. KH550-modified nano-silica further reduces the electrical conductivity of the polyurethane material, improving its insulation performance.

[0032] Comparative Example 1: The styrene-grafted carbon nanotubes were not further modified, resulting in decreased dispersion of the carbon nanotubes in the polyurethane matrix. Furthermore, the lack of Schiff base bonds and oxime methyl ester bonds synergistically enhancing the self-healing properties of the polyurethane led to reduced self-healing and thermal conductivity. Comparative Example 2: The polyurethane did not contain dimethylglyoxime, thus lacking the oxime methyl ester bonds that enhance the material's self-healing properties, resulting in decreased self-healing performance.

[0033] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a self-healing polymer insulating material, characterized in that, Includes the following steps: Step (1): Mix 1,8-p-menthanediamine, polystyrene-acrylic acid modified carbon nanotubes and water, disperse by ultrasonication, adjust the pH value, and react. After the reaction is completed, add vanillin and continue the reaction. After the reaction is completed, purify to obtain Schiff base compound modified carbon nanotubes. Step (2): Mix and dissolve polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, N,N-dimethylformamide, and dibutyltin dilaurate, and react. After the reaction is complete, a polyurethane prepolymer is obtained. 1,4-Butanediol and Schiff base compounds were added to the polyurethane prepolymer and the reaction continued. After the reaction was completed, KH550 modified nano-silica was added, mixed evenly, and dried to obtain a self-healing polymer insulating material.

2. The method for preparing the self-healing polymer insulating material according to claim 1, characterized in that, In step (1), the polystyrene-acrylic acid modified carbon nanotubes are prepared by the following steps: S1. Hydroxylated carbon nanotubes and toluene are mixed and ultrasonically dispersed. Sodium ethoxide is added and ultrasonic dispersion is continued. 4-Chloromethylstyrene is added and reacted. After the reaction is completed, the mixture is filtered, washed, and dried to obtain styrene-based grafted carbon nanotubes. S2. Styrene-grafted carbon nanotubes and water are mixed and ultrasonically dispersed. Styrene, methacrolein, and azobisisobutyronitrile are added and reacted. After the reaction is completed, the mixture is filtered, washed, and dried to obtain polystyrene-acrylaldehyde modified carbon nanotubes.

3. The method for preparing the self-healing polymer insulating material according to claim 2, characterized in that, In step (1), when preparing polystyrene-acrylic aldehyde modified carbon nanotubes, the solid-liquid ratio of hydroxylated carbon nanotubes, 4-chloromethylstyrene, sodium ethoxide, and toluene in S1 is 0.12g:6-10mL:0.8-1g:150-300mL; the reaction conditions are: stirring at 25-35℃ for 3-5h.

4. The method for preparing the self-healing polymer insulating material according to claim 2, characterized in that, In step (1), when preparing polystyrene-acrylaldehyde modified carbon nanotubes, the solid-liquid ratio of styrene-grafted carbon nanotubes, styrene, methacrolein, azobisisobutyronitrile, and water in S2 is 1g:5-6mL:4-5mL:0.3g:50mL; the reaction conditions are: reaction at 60-70℃ for 8-10h in a nitrogen atmosphere.

5. The method for preparing the self-healing polymer insulating material according to claim 1, characterized in that, In step (1), the solid-liquid ratio of 1,8-p-menthanediamine, vanillin, polystyrene-acrylic acid modified carbon nanotubes, and water is 1g:1.8g:0.8-1g:100mL; the reaction conditions are: stirring at room temperature and pH 10 for 12-16h; the reaction conditions for continued reaction are: stirring at room temperature and pH 10 for 8-12h.

6. The method for preparing the self-healing polymer insulating material according to claim 1, characterized in that, In step (2): the molar ratio of polycaprolactone diol, isophorone diisocyanate, dimethylglyoxime, and 1,4-butanediol is 4:8:2-2.5:0.5-0.8; the mass of the catalyst dibutyltin dilaurate added is 0.3% of the mass of the polyurethane prepolymer; and the solid content of the polyurethane prepolymer is 30-40%.

7. The method for preparing the self-healing polymer insulating material according to claim 1, characterized in that, In step (2): the mass of Schiff base compound modified carbon nanotubes added is 15-20% of the mass of the self-healing polymer insulating material; the mass of KH550 modified nano silica added is 6-10% of the mass of the self-healing polymer insulating material.

8. The method for preparing the self-healing polymer insulating material according to claim 1, characterized in that, In step (2), the reaction conditions are: reacting for 6-12 hours in a nitrogen atmosphere at a temperature of 60-80°C; the conditions for continued reaction are: continuing the reaction for 5-10 hours in a nitrogen atmosphere at a temperature of 60-80°C.

9. A self-healing polymer insulating material prepared by the method for preparing a self-healing polymer insulating material as described in any one of claims 1-8.

10. The application of the self-healing polymer insulation material as described in claim 9 in cable sheaths.

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