Preparation method of high-temperature resistant insulating material of multi-branched aramid fiber bonded mica

Abstract

This invention discloses a method for preparing a high-temperature resistant insulating material composed of multi-branched aramid fibers bonded to mica, specifically including the following steps: Step 1, preparing multi-branched aramid fibers; Step 2, preparing isocyanate-modified aramid based on the product obtained in Step 1; Step 3, preparing isocyanate-modified nano-mica powder; Step 4, synthesizing multi-branched alcohol resin; Step 5, preparing the multi-branched aramid fiber-bonded mica insulating material. This invention achieves chemical curing of isocyanate-modified aramid and isocyanate-modified nano-mica powder through structural design, breaking through the limitations of traditional aramid-mica sheet thickness. The isocyanate-modified aramid has a multi-branched structure, which enhances its compatibility with multi-branched alcohol resin. The nano-mica powder has a small particle size and, through isocyanate surface modification, possesses good dispersibility. Ultimately, a high-temperature resistant insulating material with good mechanical properties is obtained.

Description

Technical Field

[0001] This invention belongs to the field of insulating materials technology, and relates to a method for preparing a high-temperature resistant insulating material of multi-branched aramid fiber bonded mica. Background Technology

[0002] Aramid fibers, primarily composed of amide bonds and aromatic benzene rings, are synthetic fibers with excellent mechanical properties. Mica, on the other hand, possesses superior electrical properties such as high-temperature resistance and insulation, and is gradually becoming a new generation of insulating materials with broad application potential. High-temperature resistant insulating materials are widely used in motors, transformers, aerospace, and high-performance electronic devices. Therefore, people have begun to use aramid fibers and mica composites to prepare high-strength, high-temperature resistant, and insulating materials. However, aramid fibers and mica belong to organic and inorganic materials, respectively, and the differences in solubility and dispersibility between inorganic and organic materials are significant, making direct and effective composites impossible. To solve the organic-inorganic composite problem, existing methods prepare aramid fibers and mica into a slurry, and then use a wet-process molding process to prepare aramid-mica paper. In this process, the bonding of aramid fibers and mica is achieved through physical bonding using small-molecule adhesives or hot-melt resins. This results in a very limited material thickness due to the wet-process molding. Furthermore, the physical bonding of aramid fibers and mica makes it impossible to control the uniformity of their dispersion, leading to insufficient mechanical and insulating properties. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a high-temperature resistant insulating material composed of multi-branched aramid fiber bonded mica, which solves the problems of insufficient mechanical and insulating properties of existing insulating materials.

[0004] The technical solution adopted in this invention is a method for preparing a high-temperature resistant insulating material of multi-branched aramid fiber bonded to mica, which specifically includes the following steps:

[0005] Step 1: Prepare multi-branched aramid fibers;

[0006] Step 2: Prepare isocyanate-modified aramid fibers based on the product obtained in Step 1;

[0007] Step 3: Prepare isocyanate-modified nano-mica powder;

[0008] Step 4: Synthesize multi-branched alcohol resin;

[0009] Step 5: Prepare multi-branched aramid fiber bonded mica insulating material.

[0010] The invention is further characterized by:

[0011] The specific process of step 1 is as follows: p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride are added to 30-50 mL of N-methylpyrrolidone solution to obtain a mixed solution. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide to obtain a polymer solution. Nitrogen gas is continued to be introduced into the polymer solution, and spinning is performed to obtain nascent fibers. The nascent fibers are stretched in a mixed solvent of N,N-dimethylacetamide and water at 70-80℃ for 500-800 mL, and then dried at 120-130℃ for 2-4 hours to obtain multi-branched aramid fibers.

[0012] In step 1, the molar ratio of p-phenylenediamine: 2,5-diethoxy-1,4-phenylenediamine: 2,5-bis(hexyloxy)-1,4-phenylenediamine: lithium chloride: terephthaloyl chloride is 1:1-2:1-2:0.05-0.1:3-6.

[0013] In step 1, the specific process of spinning to prepare nascent fibers is as follows: a polymer solution is sprayed into a mixed solvent of 500-800 mL of N,N-dimethylacetamide and water using a 330*0.05 mm spinneret to obtain nascent fibers.

[0014] The specific process of step 2 is as follows:

[0015] Step 2.1: Add potassium hydroxide and the multi-branched aramid fiber prepared in step 1 to 50-100 mL of N,N-dimethylacetamide and mix. Stir the mixture in an ice-water bath for 3-6 h. After the reaction is complete, centrifuge the solution in a release maker at 7000 r / min for 30-60 min. Take the supernatant, add sodium bicarbonate, and continue stirring for 30-60 min to obtain mixture I.

[0016] Step 2.2: Dissolve toluene 2,5-diisocyanate in 50-100 mL of N,N-dimethylacetamide solution to obtain mixture II;

[0017] Step 2.3: Add mixture I obtained in step 2.1 dropwise to mixture II obtained in step 2.2 over a period of 30-60 min. After the addition is complete, continue the reaction for another 30-60 min. After the reaction is complete, add 50-100 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether. Dry it at 30-45℃ for 24 h to obtain isocyanate-modified aramid.

[0018] In step 2, the mass ratio of potassium hydroxide: multi-branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:3-6:1-2:2-3.

[0019] The specific process of step 3 is as follows:

[0020] Step 3.1: Add NaOH to the nano mica powder, then add 1000-1500 mL of deionized water, put it into a nano ball mill, use 20-30 μm zirconium oxide as the ball milling medium, mill at a speed of 300-500 r / min, and mill for 2-4 h. After milling, collect the mixture of nano mica powder.

[0021] Step 3.2: Place the mixture obtained in step 3.1 into a 7000 Da dialysis bag and dialyze it three times in 1000-1500 mL of deionized water. Centrifuge the resulting solution to obtain wet mica powder. Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder.

[0022] Step 3.3: Weigh toluene 2,5-diisocyanate and dissolve it in 1000-1500 mL of dimethyl sulfoxide solution. Stir at room temperature for 10-20 min. Then, divide the activated nano-mica powder from step 3.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at intervals of 20-30 min.

[0023] In step 3, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:1-2:1-2.

[0024] The specific process of step 4 is as follows: Methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30-60 mL of toluene solution, and then azobisisobutyronitrile is added and stirred evenly. The mixture is then reacted at a temperature of 60-70℃. After the reaction is completed, a viscous multi-branched alcohol resin is obtained. The mass ratio of methyl acrylate: butyl methyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:1-3:0.02-0.03.

[0025] Step 5 is as follows: Take multi-branched alcohol resin, isocyanate-modified aramid, and isocyanate-modified nano-mica powder, and mechanically stir them at -70℃ and 60-80r / min for 20-40min. Pour the resulting mixture into a polytetrafluoroethylene mold. After the temperature rises to room temperature, place the mold in an oven and bake it at 80-100℃ for 5-10h to obtain multi-branched aramid fiber bonded mica insulating material. The mass ratio of multi-branched alcohol resin: isocyanate-modified aramid: isocyanate-modified nano-mica powder is 1:2-4:2-4.

[0026] The beneficial effects of this invention are as follows: This invention constructs isocyanate-modified aramid and isocyanate-modified nano-mica powder. Utilizing their chemical curing with multi-branched alcohol resins, the aramid and nano-mica powder, relying on polyurethane bonds, can yield materials with good high-temperature resistance, mechanical properties, and insulation properties. Since the isocyanate-modified aramid has a multi-branched structure, its compatibility with multi-branched alcohol resins is enhanced. Furthermore, the mica used is nano-mica powder, and through isocyanate surface modification, it is endowed with excellent dispersibility in toluene. Attached Figure Description

[0027] Figure 1 These are stress-strain test curves of Example 1 and Comparative Examples 1 and 3-7 of the preparation method of the high-temperature resistant insulating material of multi-branched aramid fiber bonded mica of the present invention. Detailed Implementation

[0028] The following detailed description is provided in conjunction with specific implementation methods.

[0029] The present invention discloses a method for preparing a high-temperature resistant insulating material of multi-branched aramid fiber bonded to mica, which specifically includes the following steps: Step 1, preparation of multi-branched aramid fiber, the specific process is as follows: p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride are added to 30-50 mL of N-methylpyrrolidone solution to obtain a mixed solution. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, a certain amount of terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide (the mass of N,N-dimethylacetamide is 5% of the total mass of p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, and 2,5-bis(hexyloxy)-1,4-phenylenediamine). Nitrogen gas was continuously introduced into the polymer solution, and spinning was carried out by spraying the polymer solution into a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330*0.05mm spinneret, to obtain nascent fibers. The nascent fibers were further stretched in a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 70-80℃, with a stretch rate of 110-120%, and then dried at 120-130℃ for 2-4 hours to obtain multi-branched aramid fibers. In the above process, the molar ratio of p-phenylenediamine:2,5-diethoxy-1,4-phenylenediamine:2,5-bis(hexyloxy)-1,4-phenylenediamine:lithium chloride:terephthaloyl chloride was 1:1-2:1-2:0.05-0.1:3-6.

[0030] Step 2, prepare isocyanate surface-modified aramid, the specific process is as follows: Step 2.1, add potassium hydroxide and multi-branched aramid fibers to 50-100mL of N,N-dimethylacetamide in a certain mass ratio, mix and stir in an ice-water bath for 3-6h. After the reaction is completed, centrifuge the solution in a release machine at 7000r / min for 30-60min, take the supernatant, add a certain mass of sodium bicarbonate, and continue stirring for 30-60min to obtain mixture I.

[0031] Step 2.2: Dissolve a certain mass of toluene 2,5-diisocyanate in N,N-dimethylacetamide (50-100 mL) solution to obtain mixture II.

[0032] Step 2.3: Add mixture I obtained in step 2.1 dropwise to mixture II obtained in step 2.2 over a period of 30-60 minutes. After the addition is complete, continue the reaction for another 30-60 minutes. After the reaction is complete, add 50-100 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether (50-100 mL each time). Dry the precipitate at 30-45℃ for 24 hours to obtain isocyanate-modified aramid fiber. In the above process, the mass ratio of potassium hydroxide: branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:3-6:1-2:2-3.

[0033] Step 3: Prepare isocyanate-modified nano-mica powder. The specific process is as follows:

[0034] Step 3.1: Take a certain mass of nano-mica powder (diameter to thickness ratio of 80:1), add a certain amount of NaOH, then add 1000-1500mL of deionized water, put it into a nano-ball mill, use 20-30um zirconium oxide as the ball milling medium, the ball milling speed is 300-500r / min, the ball milling time is 2-4h, and after the ball milling is completed, collect the mixture of nano-mica powder.

[0035] Step 3.2: Place the mixture from Step 3.1 into a 7000 Da dialysis bag and dialyze three times in 1000-1500 mL of deionized water. Centrifuge the resulting solution (10000-12000 r / min). Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder.

[0036] Step 3.3: Weigh a certain mass of toluene 2,5-diisocyanate and dissolve it in 1000-1500 mL of dimethyl sulfoxide solution. Stir at room temperature for 10-20 min. Then, divide the activated nano-mica powder from step 3.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at intervals of 20-30 min.

[0037] In the above process, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:1-2:1-2. The amount of nano-mica powder used is a fixed value of 50g.

[0038] Step 4, synthesis of multi-branched alcohol resin, the specific process is as follows: Methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30-60 mL of toluene solution. Then, a certain amount of azobisisobutyronitrile is added and stirred evenly. The temperature is raised to 60-70℃ for reaction. After the reaction is complete, a viscous multi-branched alcohol resin (viscosity 8000-15000 cps) is obtained. In the above process, the mass ratio of methyl acrylate: butyl methyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:1-3:0.02-0.03.

[0039] Step 5, preparation of multi-branched aramid fiber bonded mica insulating material, the specific process is as follows: Take a certain mass of multi-branched alcohol resin, isocyanate surface-modified aramid, and isocyanate surface-modified nano-mica powder, and mechanically stir at -70℃ and 60-80 r / min for 20-40 min. Pour the resulting mixture into a polytetrafluoroethylene mold (length x width x height are 10cm x 10cm x 2cm). After the temperature rises to room temperature, place the mold in an oven and bake at 80-100℃ for 5-10 h. In the above process, the mass ratio of multi-branched alcohol resin: isocyanate surface-modified aramid: isocyanate surface-modified nano-mica powder is 1:2-4:2-4. The amount of multi-branched alcohol resin used is a fixed value of 5g.

[0040] Example 1

[0041] Step 1, Preparation of multi-branched aramid fibers, is as follows: p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride are added to 30 mL of N-methylpyrrolidone solution according to a certain molar ratio. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, a certain amount of terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide. Nitrogen gas is continued to be introduced into the polymer solution, and spinning is performed. Specifically, a 330*0.05 mm spinneret is used to spray the polymer solution into a 500 mL mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) to obtain nascent fibers. The nascent fibers were further stretched in a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 70℃, with a stretch rate of 110%, and then dried at 120℃ for 2 hours to obtain multi-branched aramid fibers. In the above process, the molar ratio of p-phenylenediamine:2,5-diethoxy-1,4-phenylenediamine:2,5-bis(hexyloxy)-1,4-phenylenediamine:lithium chloride:terephthaloyl chloride was 1:1:1:0.05:3. The amount of p-phenylenediamine used was a constant 0.05 mol.

[0042] Step 2, preparing isocyanate-modified aramid fibers, the specific process is as follows:

[0043] Step 2.1: Potassium hydroxide and multi-branched aramid fibers were added to 50 mL of N,N-dimethylacetamide at a certain mass ratio and mixed. The mixture was stirred in an ice-water bath for 3 hours. After the reaction was completed, the solution was centrifuged at 7000 r / min for 30 minutes in a release mortise. The supernatant was collected, and a certain mass of sodium bicarbonate was added. The mixture was stirred for another 30 minutes to obtain mixture I.

[0044] Step 2.2: Dissolve a certain mass of toluene 2,5-diisocyanate in N,N-dimethylacetamide (50 mL) solution to obtain mixture II;

[0045] Step 2.3: Add mixture I obtained in step 2.1 dropwise to mixture II obtained in step 2.2 over a period of 30 minutes. After the addition is complete, continue the reaction for another 30 minutes. After the reaction is complete, add 50 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether (50 mL each time). Dry the precipitate at 30°C for 24 hours to obtain isocyanate-modified aramid.

[0046] In the above process, the mass ratio of potassium hydroxide: branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:3:1:2. The amount of potassium hydroxide used is a fixed value of 10g.

[0047] Step 3: Prepare isocyanate-modified nano-mica powder. The specific process is as follows:

[0048] Step 3.1: Take a certain mass of nano mica powder (diameter to thickness ratio of 80:1), add a certain amount of NaOH, then add 1000 mL of deionized water, put it into a nano ball mill, use 20 μm zirconium oxide as the ball milling medium, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, collect the mixture of nano mica powder.

[0049] Step 3.2: Place the mixture from Step 3.1 into a 7000 Da dialysis bag and dialyze it three times in 1000 mL of deionized water. Centrifuge the resulting solution (10000 r / min). Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder.

[0050] Step 3.3: Weigh a certain mass of toluene 2,5-diisocyanate and dissolve it in 1000 mL of dimethyl sulfoxide solution. Stir at room temperature for 10 min. Then, divide the activated nano-mica powder from step 3.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at 20 min intervals.

[0051] In the above process, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:1:1. The amount of nano-mica powder used is a fixed value of 50g.

[0052] Step 4, the synthesis of the multi-branched alcohol resin, is as follows: Methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30 mL of toluene solution. Then, a certain amount of azobisisobutyronitrile is added and stirred until homogeneous. The temperature is then raised to 60℃ for reaction. After the reaction is complete, a viscous multi-branched alcohol resin (viscosity 8000-15000 cps) is obtained. In the above process, the mass ratio of methyl acrylate: butyl methyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:1:0.02. The amount of methyl acrylate used is a fixed value of 5 g.

[0053] Step 5, Preparation of multi-branched aramid fiber bonded mica insulating material, the specific process is as follows:

[0054] A certain mass of multi-branched alcohol resin, isocyanate-modified aramid, and isocyanate-modified nano-mica powder were taken and mechanically stirred for 20 minutes at -70℃ and 60 r / min. The resulting mixture was poured into a polytetrafluoroethylene mold (10cm x 10cm x 2cm). After the temperature rose to room temperature, the mold was placed in an oven and baked at 80℃ for 5 hours. In the above process, the mass ratio of multi-branched alcohol resin: isocyanate-modified aramid: isocyanate-modified nano-mica powder was 1:2:2. The amount of multi-branched alcohol resin used was a fixed value of 5g.

[0055] Example 2

[0056] Step 1, preparation of multi-branched aramid fibers, specifically: p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride are added to 50 mL of N-methylpyrrolidone solution according to a certain molar ratio. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, a certain amount of terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide. Nitrogen gas is continued to be introduced into the polymer solution, and spinning is carried out, that is, the polymer solution is sprayed into 800 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330*0.05 mm spinneret to obtain nascent fibers. The nascent fibers were further stretched in a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 80℃ to a stretch rate of 120%, and then dried at 130℃ for 4 hours to obtain multi-branched aramid fibers. In the above process, the molar ratio of p-phenylenediamine:2,5-diethoxy-1,4-phenylenediamine:2,5-bis(hexyloxy)-1,4-phenylenediamine:lithium chloride:terephthaloyl chloride was 1:2:2:0.1:6. The amount of p-phenylenediamine used was a constant 0.05 mol.

[0057] Step 2, isocyanate surface modification of aramid, the specific process is as follows:

[0058] Step 2.1: Potassium hydroxide and multi-branched aramid fibers were added to 100 mL of N,N-dimethylacetamide at a certain mass ratio and mixed. The mixture was stirred in an ice-water bath for 6 hours. After the reaction was completed, the solution was centrifuged at 7000 r / min for 60 min in a release mortise. The supernatant was collected, and a certain mass of sodium bicarbonate was added. The mixture was stirred for another 60 min to obtain mixture I.

[0059] Step 2.2: Take a certain mass of toluene 2,5-diisocyanate and dissolve it in N,N-dimethylacetamide (100 mL) solution to obtain mixture II;

[0060] Step 2.3: Add mixture I obtained in step 2.1 dropwise to mixture II obtained in step 2.2 over a period of 60 min. After the addition is complete, continue the reaction for another 60 min. After the reaction is complete, add 100 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether (100 mL each time). Dry it at 45 °C for 24 h to obtain isocyanate-modified aramid.

[0061] In the above process, the mass ratio of potassium hydroxide: branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:6:2:3. The amount of potassium hydroxide used is a fixed 10g.

[0062] Step 3, surface modification of isocyanate with nano-mica powder, the specific process is as follows:

[0063] Step 3.1: Take a certain mass of nano mica powder (diameter to thickness ratio of 80:1), add a certain amount of NaOH, then add 1500mL of deionized water, put it into a nano ball mill, use 30μm zirconium oxide as the ball milling medium, the ball milling speed is 500r / min, the ball milling time is 4h, and after the ball milling is completed, collect the mixture of nano mica powder.

[0064] Step 3.2: Place the mixture from Step 3.1 into a 7000 Da dialysis bag and dialyze three times in 1500 mL of deionized water. Centrifuge the resulting solution (12000 r / min). Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder.

[0065] Step 3.3: Weigh a certain mass of toluene 2,5-diisocyanate and dissolve it in 1500 mL of dimethyl sulfoxide solution. Stir at room temperature for 20 min. Then, divide the activated nano-mica powder from step 3.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at 30 min intervals.

[0066] In the above process, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:2:2. The amount of nano-mica powder used is a fixed value of 50g.

[0067] Step 4, the synthesis of the multi-branched alcohol resin, specifically involves adding methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate to 60 mL of toluene solution. Then, a certain amount of azobisisobutyronitrile (AIBN) is added and stirred until homogeneous. The temperature is then raised to 70°C for reaction. After the reaction is complete, a viscous multi-branched alcohol resin (viscosity 8000-15000 cps) is obtained. In the above process, the mass ratio of methyl acrylate: butyl methyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:3:0.03. The amount of methyl acrylate used is a fixed value of 5 g.

[0068] Step 5, preparation of the multi-branched aramid fiber bonded mica insulating material, specifically: A certain mass of multi-branched alcohol resin, isocyanate-modified aramid, and isocyanate-modified nano-mica powder are taken and mechanically stirred for 40 minutes at -70℃ and 80 r / min. The resulting mixture is poured into a polytetrafluoroethylene mold (10cm x 10cm x 2cm). After the temperature rises to room temperature, the mold is placed in an oven and baked at 100℃ for 10 hours to obtain the multi-branched aramid fiber bonded mica insulating material. In the above process, the mass ratio of multi-branched alcohol resin: isocyanate-modified aramid: isocyanate-modified nano-mica powder is 1:4:4. The amount of multi-branched alcohol resin used is a fixed value of 5g.

[0069] Example 3

[0070] Step 1, preparation of multi-branched aramid fibers, specifically: p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride are added to 40 mL of N-methylpyrrolidone solution according to a certain molar ratio to obtain a mixed solution. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, a certain amount of terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide. Nitrogen gas is continued to be introduced into the polymer solution, and spinning is carried out, that is, the polymer solution is sprayed into 650 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330*0.05 mm spinneret to obtain nascent fibers. The nascent fibers were further stretched in a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 75°C to a stretch rate of 115%, and then dried at 125°C for 3 hours to obtain multi-branched aramid fibers. In the above process, the molar ratio of p-phenylenediamine:2,5-diethoxy-1,4-phenylenediamine:2,5-bis(hexyloxy)-1,4-phenylenediamine:lithium chloride:terephthaloyl chloride was 1:1.5:1.5:0.075:4.5. The amount of p-phenylenediamine used was a constant 0.05 mol.

[0071] Step 2, isocyanate surface modification of aramid, the specific process is as follows:

[0072] Step 2.1: Potassium hydroxide and multi-branched aramid fibers were added to 75 mL of N,N-dimethylacetamide at a certain mass ratio and mixed. The mixture was stirred in an ice-water bath for 4.5 h. After the reaction was completed, the solution was centrifuged at 7000 r / min for 45 min in a release mortise. The supernatant was collected, and a certain mass of sodium bicarbonate was added. The mixture was stirred for another 45 min to obtain mixture I.

[0073] Step 2.2: Take a certain mass of toluene 2,5-diisocyanate and dissolve it in N,N-dimethylacetamide (75 mL) solution to obtain mixture II.

[0074] Step 2.3: Add mixture I obtained in step 2.1 dropwise to mixture II obtained in step 2.2 over a period of 45 min. After the addition is complete, continue the reaction for another 45 min. After the reaction is complete, add 75 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether (75 mL each time). Dry it at 37 °C for 24 h to obtain isocyanate-modified aramid.

[0075] In the above process, the mass ratio of potassium hydroxide: branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:4.5:1.5:2.5. The amount of potassium hydroxide used is a fixed value of 10g.

[0076] Step 3, surface modification of isocyanate with nano-mica powder, the specific process is as follows:

[0077] Step 3.1: Take a certain mass of nano mica powder (diameter to thickness ratio of 80:1), add a certain amount of NaOH, then add 1250 mL of deionized water, put it into a nano ball mill, use 25 μm zirconium oxide as the ball milling medium, the ball milling speed is 400 r / min, and the ball milling time is 3 h. After the ball milling is completed, collect the mixture of nano mica powder.

[0078] Step 3.2: Place the mixture from Step 3.1 into a 7000 Da dialysis bag and dialyze three times in 1250 mL of deionized water. Centrifuge the resulting solution (11000 r / min). Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder.

[0079] Step 3.3: Weigh a certain mass of toluene 2,5-diisocyanate and dissolve it in 1250 mL of dimethyl sulfoxide solution. Stir at room temperature for 15 min. Then, divide the activated nano-mica powder from step 3.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at 25 min intervals.

[0080] In the above process, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:1.5:1.5. The amount of potassium hydroxide used is constant. The amount of nano-mica powder used is a constant 50g.

[0081] Step 4, the synthesis of the multi-branched alcohol resin, is as follows: Methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 45 mL of toluene solution. Then, a certain amount of azobisisobutyronitrile (AIBN) is added and stirred until homogeneous. The temperature is then raised to 65°C for reaction. After the reaction is complete, a viscous multi-branched alcohol resin (viscosity 8000-15000 cps) is obtained. In the above process, the mass ratio of methyl acrylate: butyl methyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:2:0.025. The amount of methyl acrylate used is a fixed value of 5 g.

[0082] Step 5, preparation of the multi-branched aramid fiber bonded mica insulating material, the specific process is as follows: Take a certain mass of multi-branched alcohol resin, isocyanate-modified aramid, and isocyanate-modified nano-mica powder, and mechanically stir for 30 min at -70℃ and 70 r / min. Pour the resulting mixture into a polytetrafluoroethylene mold (length x width x height are 10cm x 10cm x 2cm). After the temperature rises to room temperature, place the mold in an oven and bake at 90℃ for 7.5 h. In the above process, the mass ratio of multi-branched alcohol resin: isocyanate-modified aramid: isocyanate-modified nano-mica powder is 1:3:3. The amount of multi-branched alcohol resin used is a fixed value of 5g.

[0083] Comparative Example 1 (The multi-branched aramid fiber was not modified with isocyanate, resulting in a deterioration in the final material's mechanical and insulation properties).

[0084] Step 1, preparation of multi-branched aramid fibers, specifically: p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride are added to 30 mL of N-methylpyrrolidone solution according to a certain molar ratio. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, a certain amount of terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide. Nitrogen gas is continued to be introduced into the polymer solution, and spinning is carried out, that is, the polymer solution is sprayed into 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330*0.05 mm spinneret to obtain nascent fibers. The nascent fibers were further stretched in a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 70℃, with a stretch rate of 110%, and then dried at 120℃ for 2 hours to obtain multi-branched aramid fibers. In the above process, the molar ratio of p-phenylenediamine:2,5-diethoxy-1,4-phenylenediamine:2,5-bis(hexyloxy)-1,4-phenylenediamine, lithium chloride:terephthaloyl chloride was 1:1:1:0.05:3. The amount of p-phenylenediamine used was a constant 0.05 mol.

[0085] Step 2, surface modification of isocyanate with nano-mica powder, the specific process is as follows:

[0086] Step 2.1: Take a certain mass of nano mica powder (diameter to thickness ratio of 80:1), add a certain amount of NaOH, then add 1000 mL of deionized water, put it into a nano ball mill, use 20 μm zirconium oxide as the ball milling medium, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, collect the mixture of nano mica powder.

[0087] Step 2.2: Place the mixture from Step 2.1 into a 7000 Da dialysis bag and dialyze three times in 1000 mL of deionized water. Centrifuge the resulting solution (10000 r / min). Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder.

[0088] Step 2.3: Weigh a certain mass of toluene 2,5-diisocyanate and dissolve it in 1000 mL of dimethyl sulfoxide solution. Stir at room temperature for 10 min. Then, divide the activated nano-mica powder from step 2.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at 20 min intervals.

[0089] In the above process, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:1:1. The amount of nano-mica powder used is a fixed value of 50g.

[0090] Step 3, the synthesis of the multi-branched alcohol resin, is as follows: Equal masses of methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30 mL of toluene solution. Then, a certain amount of azobisisobutyronitrile is added and stirred until homogeneous. The temperature is raised to 60℃ for reaction. After the reaction is complete, a viscous multi-branched alcohol resin (viscosity 8000-15000 cps) is obtained. In the above process, the mass ratio of methyl acrylate: butyl methyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:1:0.02. The amount of methyl acrylate used is a fixed value of 5 g.

[0091] Step 4, preparation of multi-branched aramid fiber bonded mica insulating material, the specific process is as follows:

[0092] A certain mass of multi-branched alcohol resin, multi-branched aramid fiber, and isocyanate-modified nano-mica powder were taken and mechanically stirred for 20 minutes at -70℃ and 60 r / min. The resulting mixture was poured into a polytetrafluoroethylene mold (10cm x 10cm x 2cm). After the temperature rose to room temperature, the mold was placed in an oven and baked at 80℃ for 5 hours. In the above process, the mass ratio of multi-branched alcohol resin: multi-branched aramid fiber: isocyanate-modified nano-mica powder was 1:2:2. The amount of multi-branched alcohol resin used was a fixed value of 5g.

[0093] Comparative Example 2 (In the process of isocyanate surface modification of aramid, the mixture II obtained in step 2 is added dropwise to the mixture I obtained in step 1, and the aramid fibers flocculate)

[0094] Step 1, Preparation of multi-branched aramid fibers, the specific process is as follows:

[0095] P-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride were added to 30 mL of N-methylpyrrolidone solution at a specific molar ratio. Nitrogen gas was introduced into the mixture, and the reaction flask was placed in an ice-water bath. Then, a certain amount of terephthaloyl chloride was added in three equal portions, 30 minutes apart. After the reaction, the solid content of the solution was adjusted to 5.0% by adding N,N-dimethylacetamide. Nitrogen gas was continued to be introduced into the polymer solution, and spinning was performed by using a 330*0.05 mm spinneret to spray the polymer solution into a 500 mL mixture of N,N-dimethylacetamide and water (v:v = 1:0.5) to obtain nascent fibers. The nascent fibers were further stretched in a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 70°C to a stretch length of 110%, and then dried at 120°C for 2 hours to obtain multi-branched aramid fibers. In the above process, the molar ratio of p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, lithium chloride, and terephthaloyl chloride was 1:1:1:0.05:3. The amount of p-phenylenediamine used was a constant 0.05 mol.

[0096] Step 2, preparing isocyanate-modified aramid fibers, the specific process is as follows:

[0097] Step 2.1: Potassium hydroxide and multi-branched aramid fibers were added to 50 mL of N,N-dimethylacetamide at a certain mass ratio and mixed. The mixture was stirred in an ice-water bath for 3 hours. After the reaction was completed, the solution was centrifuged at 7000 r / min for 30 minutes in a release agent. The supernatant was collected, and a certain mass of sodium bicarbonate was added. The mixture was stirred for another 30 minutes to obtain mixture I.

[0098] Step 2.2: Take a certain mass of toluene 2,5-diisocyanate and dissolve it in N,N-dimethylacetamide (50 mL) solution to obtain mixture II.

[0099] Step 2.3: Add mixture II obtained in step 2.2 dropwise to mixture I obtained in step 2.1 over a period of 30 min. After the addition is complete, continue the reaction for another 30 min. After the reaction is complete, add 50 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether (50 mL each time). Dry it at 30 °C for 24 h to obtain isocyanate-modified aramid.

[0100] In the above process, the mass ratio of potassium hydroxide: branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:3:1:2. The amount of potassium hydroxide used is a fixed 10g.

[0101] Comparative Example 3 (Replacing branched aramid fibers with unbranched aramid fibers resulted in poorer dispersion of aramid fibers in the material, leading to decreased mechanical and insulation properties).

[0102] Step 1, Preparation of Aramid Fibers, is as follows: P-phenylenediamine and lithium chloride are added to 30 mL of N-methylpyrrolidone solution at a specific molar ratio. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, a certain amount of terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide. Nitrogen gas is continued to be introduced into the polymer solution, and spinning is performed. The polymer solution is sprayed into a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330*0.05 mm spinneret, yielding nascent fibers. The nascent fibers are further stretched at 70℃ in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) to a stretch rate of 110%. After drying at 120℃ for 2 hours, aramid fibers are obtained. In the above process, the molar ratio of p-phenylenediamine:lithium chloride:terephthaloyl chloride is 1:0.05:1. The amount of p-phenylenediamine used is a constant 0.05 mol.

[0103] Step 2, preparing isocyanate-modified aramid fibers, the specific process is as follows:

[0104] Step 2.1: Potassium hydroxide and aramid fiber were added to 50 mL of N,N-dimethylacetamide at a certain mass ratio and mixed. The mixture was stirred in an ice-water bath for 3 hours. After the reaction was completed, the solution was centrifuged at 7000 r / min for 30 minutes in a release agent. The supernatant was collected, and a certain mass of sodium bicarbonate was added. The mixture was stirred for another 30 minutes to obtain mixture I.

[0105] Step 2.2: Take a certain mass of toluene 2,5-diisocyanate and dissolve it in N,N-dimethylacetamide (50 mL) solution to obtain mixture II.

[0106] Step 2.3: Add mixture I obtained in step 2.1 dropwise to mixture II obtained in step 2.2 over a period of 30 minutes. After the addition is complete, continue the reaction for another 30 minutes. After the reaction is complete, add 50 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether (50 mL each time). Dry the precipitate at 30°C for 24 hours to obtain isocyanate-modified aramid.

[0107] In the above process, the mass ratio of potassium hydroxide: aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:3:1:2. The amount of potassium hydroxide used is a fixed value of 10g.

[0108] Step 3: Prepare isocyanate-modified nano-mica powder. The specific process is as follows:

[0109] Step 3.1: Take a certain mass of nano mica powder (diameter to thickness ratio of 80:1), add a certain amount of NaOH, then add 1000 mL of deionized water, put it into a nano ball mill, use 20 μm zirconium oxide as the ball milling medium, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, collect the mixture of nano mica powder.

[0110] Step 3.2: Place the mixture from Step 3.1 into a 7000 Da dialysis bag and dialyze three times in 1000 mL of deionized water. Centrifuge the resulting solution (10000 r / min). Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder.

[0111] Step 3.3: Weigh a certain mass of toluene 2,5-diisocyanate and dissolve it in 1000 mL of dimethyl sulfoxide solution. Stir at room temperature for 10 min. Then, divide the activated nano-mica powder from step 3.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at 20 min intervals.

[0112] In the above process, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:1:1. The amount of nano-mica powder used is a fixed value of 50g.

[0113] Step 4, the synthesis of the multi-branched alcohol resin, is as follows: Methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30 mL of toluene solution. Then, a certain amount of azobisisobutyronitrile is added and stirred until homogeneous. The temperature is then raised to 60℃ for reaction. After the reaction is complete, a viscous multi-branched alcohol resin (viscosity 8000-15000 cps) is obtained. In the above process, the mass ratio of methyl acrylate: butyl methyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:1:0.02. The amount of methyl acrylate used is a fixed value of 5 g.

[0114] Step 5, Preparation of Aramid Fiber Bonded Mica Insulating Material: The specific process is as follows: Take a certain mass of multi-branched alcohol resin, isocyanate-modified aramid, and isocyanate-modified nano-mica powder. Mechanically stir at -70℃ and 60 r / min for 20 min. Pour the resulting mixture into a polytetrafluoroethylene mold (length x width x height 10cm x 10cm x 2cm). After the temperature rises to room temperature, place the mold in an oven and bake at 80℃ for 5 h. In the above process, the mass ratio of multi-branched alcohol resin: isocyanate-modified aramid: isocyanate-modified nano-mica powder is 1:2:2. The amount of multi-branched alcohol resin used is a fixed value of 5g.

[0115] Comparative Example 4 (Without the addition of hydroxyethyl acrylate, the multi-branched aramid fiber bonded mica insulation material cannot be cured in the multi-branched alcohol resin).

[0116] Step 1, preparation of multi-branched aramid fibers, specifically: p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride are added to 30 mL of N-methylpyrrolidone solution according to a certain molar ratio. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, a certain amount of terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide. Nitrogen gas is continued to be introduced into the polymer solution, and spinning is carried out, that is, the polymer solution is sprayed into 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330*0.05 mm spinneret to obtain nascent fibers. The nascent fibers were further stretched at 70°C in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) to a length of 110%, and then dried at 120°C for 2 hours to obtain multi-branched aramid fibers. In the above process, the molar ratio of p-phenylenediamine:2,5-diethoxy-1,4-phenylenediamine:2,5-bis(hexyloxy)-1,4-phenylenediamine:lithium chloride:terephthaloyl chloride was 1:1:1:0.05:3. The amount of p-phenylenediamine used was a constant 0.05 mol.

[0117] Step 2, preparing isocyanate-modified aramid fibers, the specific process is as follows:

[0118] Step 2.1: Potassium hydroxide and multi-branched aramid fibers were added to 50 mL of N,N-dimethylacetamide at a certain mass ratio and mixed. The mixture was stirred in an ice-water bath for 3 hours. After the reaction was completed, the solution was centrifuged at 7000 r / min for 30 minutes in a release agent. The supernatant was collected, and a certain mass of sodium bicarbonate was added. The mixture was stirred for another 30 minutes to obtain mixture I.

[0119] Step 2.2: Dissolve a certain mass of toluene 2,5-diisocyanate in N,N-dimethylacetamide (50 mL) solution to obtain mixture II.

[0120] Step 2.3: Add mixture I obtained in step 2.1 dropwise to mixture II obtained in step 2.2 over a period of 30 minutes. After the addition is complete, continue the reaction for another 30 minutes. After the reaction is complete, add 50 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether (50 mL each time). Dry the precipitate at 30°C for 24 hours to obtain isocyanate-modified aramid.

[0121] In the above process, the mass ratio of potassium hydroxide: branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:3:1:2. The amount of potassium hydroxide used is a fixed value of 10g.

[0122] Step 3, preparing isocyanate-modified nano-mica powder, specifically:

[0123] Step 3.1: Take a certain mass of nano mica powder (diameter to thickness ratio of 80:1), add a certain amount of NaOH, then add 1000 mL of deionized water, put it into a nano ball mill, use 20 μm zirconium oxide as the ball milling medium, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, collect the mixture of nano mica powder.

[0124] Step 3.2: Place the mixture from Step 3.1 into a 7000 Da dialysis bag and dialyze it three times in 1000 mL of deionized water. Centrifuge the resulting solution (10000 r / min). Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder.

[0125] Step 3.3: Weigh a certain mass of toluene 2,5-diisocyanate and dissolve it in 1000 mL of dimethyl sulfoxide solution. Stir at room temperature for 10 min. Then, divide the activated nano-mica powder from step 3.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at 20 min intervals.

[0126] In the above process, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:1:1. The amount of nano-mica powder used is a fixed value of 50g.

[0127] Step 4, synthesis of the multi-branched resin, is as follows: Methyl acrylate, butyl methyl acrylate, and styrene are added to 30 mL of toluene solution. Then, a certain amount of azobisisobutyronitrile (AIBN) is added and stirred until homogeneous. The temperature is then raised to 60°C for reaction. After the reaction is complete, a viscous multi-branched resin (viscosity 8000-15000 cps) is obtained. In the above process, the mass ratio of methyl acrylate, butyl methyl acrylate, styrene, and AIBN is 1:1:1:0.02. The amount of methyl acrylate used is a fixed value of 5 g.

[0128] Step 5, Preparation of multi-branched aramid fiber bonded mica insulating material, the specific process is as follows:

[0129] A certain mass of multi-branched resin, isocyanate-modified aramid, and isocyanate-modified nano-mica powder were taken and mechanically stirred for 20 minutes at -70℃ and 60 r / min. The resulting mixture was poured into a polytetrafluoroethylene mold (length x width x height 10cm x 10cm x 2cm). After the temperature rose to room temperature, the mold was placed in an oven and baked at 80℃ for 5 hours. The material did not cure. In the above process, the mass ratio of multi-branched resin: isocyanate-modified aramid: isocyanate-modified nano-mica powder was 1:2:2. The amount of multi-branched resin used was a fixed value of 5g.

[0130] Comparative Example 5 (replacing the multi-branched alcohol resin with unbranched hydroxyethyl polyacrylate resin resulted in poor thermal stability and poor insulation performance of the material).

[0131] Step 1, Preparation of multi-branched aramid fibers, is as follows: P-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride are added to 30 mL of N-methylpyrrolidone solution according to a certain molar ratio. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, a certain amount of terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide. Nitrogen gas is continued to be introduced into the polymer solution, and spinning is performed. Specifically, a 330*0.05 mm spinneret is used to spray the polymer solution into a 500 mL mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) to obtain nascent fibers. The nascent fibers were further stretched at 70°C in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) to a length of 110%, and then dried at 120°C for 2 hours to obtain multi-branched aramid fibers. In the above process, the molar ratio of p-phenylenediamine:2,5-diethoxy-1,4-phenylenediamine:2,5-bis(hexyloxy)-1,4-phenylenediamine:lithium chloride:terephthaloyl chloride was 1:1:1:0.05:3. The amount of p-phenylenediamine used was a constant 0.05 mol.

[0132] Step 2, preparing isocyanate-modified aramid fibers, the specific process is as follows:

[0133] Step 2.1: Potassium hydroxide and multi-branched aramid fibers were added to 50 mL of N,N-dimethylacetamide at a certain mass ratio and mixed. The mixture was stirred in an ice-water bath for 3 hours. After the reaction was completed, the solution was centrifuged at 7000 r / min for 30 minutes in a release agent. The supernatant was collected, and a certain mass of sodium bicarbonate was added. The mixture was stirred for another 30 minutes to obtain mixture I.

[0134] Step 2.2: Take a certain mass of toluene 2,5-diisocyanate and dissolve it in N,N-dimethylacetamide (50 mL) solution to obtain mixture II.

[0135] Step 2.3: Add mixture I obtained in step 2.1 dropwise to mixture II obtained in step 2.2 over a period of 30 minutes. After the addition is complete, continue the reaction for another 30 minutes. After the reaction is complete, add 50 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether (50 mL each time). Dry the precipitate at 30°C for 24 hours to obtain isocyanate-modified aramid.

[0136] In the above process, the mass ratio of potassium hydroxide: branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:3:1:2. The amount of potassium hydroxide used is a fixed value of 10g.

[0137] Step 3: Prepare isocyanate-modified nano-mica powder. The specific process is as follows:

[0138] Step 3.1: Take a certain mass of nano mica powder (diameter to thickness ratio of 80:1), add a certain amount of NaOH, then add 1000 mL of deionized water, put it into a nano ball mill, use 20 μm zirconium oxide as the ball milling medium, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, collect the mixture of nano mica powder.

[0139] Step 3.2: Place the mixture from Step 3.1 into a 7000 Da dialysis bag and dialyze three times in 1000 mL of deionized water. Centrifuge the resulting solution (10000 r / min). Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder.

[0140] Step 3.3: Weigh a certain mass of toluene 2,5-diisocyanate and dissolve it in 1000 mL of dimethyl sulfoxide solution. Stir at room temperature for 10 min. Then, divide the activated nano-mica powder from step 3.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at 20 min intervals.

[0141] In the above process, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:1:1. The amount of nano-mica powder used is a fixed value of 50g.

[0142] Step 4, the synthesis of hydroxyethyl acrylate resin, is as follows: A certain mass of hydroxyethyl acrylate is added to 10 mL of toluene solution, followed by the addition of a certain amount of azobisisobutyronitrile (AIBN). After stirring until homogeneous, the temperature is raised to 60°C for reaction. After the reaction is complete, a viscous hydroxyethyl acrylate resin (viscosity 8000-15000 cps) is obtained. In the above process, the mass ratio of hydroxyethyl acrylate to AIBN is 1:0.02. The amount of hydroxyethyl acrylate used is a fixed value of 5 g.

[0143] Step 5, Preparation of multi-branched aramid fiber bonded mica insulating material, the specific process is as follows:

[0144] A certain mass of hydroxyethyl acrylate resin, isocyanate-modified aramid fiber, and isocyanate-modified nano-mica powder were taken and mechanically stirred for 20 minutes at -70℃ and 60 r / min. The resulting mixture was poured into a polytetrafluoroethylene mold (length x width x height 10cm x 10cm x 2cm). After the temperature rose to room temperature, the mold was placed in an oven and baked at 80℃ for 5 hours. In the above process, the mass ratio of hydroxyethyl acrylate resin: isocyanate-modified aramid fiber: isocyanate-modified nano-mica powder was 1:2:2. The amount of multi-branched alcohol resin used was a fixed value of 5g.

[0145] Comparative Example 6 (The material without isocyanate surface-modified aramid has poor mechanical properties)

[0146] Step 1: Prepare isocyanate-modified nano-mica powder. The specific process is as follows:

[0147] Step 1.1: Take a certain mass of nano mica powder (diameter to thickness ratio of 80:1), add a certain amount of NaOH, then add 1000 mL of deionized water, put it into a nano ball mill, use 20 μm zirconium oxide as the ball milling medium, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, collect the mixture of nano mica powder.

[0148] Step 1.2: Place the mixture from Step 1.1 into a 7000 Da dialysis bag and dialyze three times in 1000 mL of deionized water. Centrifuge the resulting solution (10000 r / min). Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder.

[0149] Step 1.3: Weigh a certain mass of toluene 2,5-diisocyanate and dissolve it in 1000 mL of dimethyl sulfoxide solution. Stir at room temperature for 10 min. Then, divide the activated nano-mica powder from step 1.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at 20 min intervals.

[0150] In the above process, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:1:1. The amount of nano-mica powder used is a fixed value of 50g.

[0151] Step 2, the synthesis of the multi-branched alcohol resin, is as follows: Methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30 mL of toluene solution. Then, a certain amount of azobisisobutyronitrile (AIBN) is added and stirred until homogeneous. The temperature is then raised to 60°C for reaction. After the reaction is complete, a viscous multi-branched alcohol resin (viscosity 8000-15000 cps) is obtained. In the above process, the mass ratio of methyl acrylate: butyl methyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:1:0.02. The amount of methyl acrylate used is a fixed value of 5 g.

[0152] Step 3, preparation of mica insulating material, the specific process is as follows: Take a certain mass of multi-branched alcohol resin and isocyanate-modified nano-mica powder, and mechanically stir for 20 min at -70℃ and 60 r / min. Pour the resulting mixture into a polytetrafluoroethylene mold (length x width x height are 10cm x 10cm x 2cm). After the temperature rises to room temperature, place the mold in an oven and bake at 80℃ for 5 h. In the above process, the mass ratio of multi-branched alcohol resin to isocyanate-modified nano-mica powder is 1:2. The amount of multi-branched alcohol resin used is a fixed value of 5g.

[0153] Comparative Example 7 (Without the addition of isocyanate-modified nano-mica powder, the thermal stability and insulation of the material deteriorated)

[0154] Step 1, Preparation of multi-branched aramid fibers, is as follows: P-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride are added to 30-50 mL of N-methylpyrrolidone solution according to a certain molar ratio. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, a certain amount of terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide. Nitrogen gas is continued to be introduced into the polymer solution, and spinning is performed. Specifically, a 330*0.05 mm spinneret is used to spray the polymer solution into a 500 mL mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) to obtain nascent fibers. The nascent fibers were further stretched at 70°C in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) to a length of 110%, and then dried at 120°C for 2 hours to obtain multi-branched aramid fibers. In the above process, the molar ratio of p-phenylenediamine:2,5-diethoxy-1,4-phenylenediamine:2,5-bis(hexyloxy)-1,4-phenylenediamine:lithium chloride:terephthaloyl chloride was 1:1:1:0.05:3. The amount of p-phenylenediamine used was a constant 0.05 mol.

[0155] Step 2, preparation of isocyanate-modified aramid fibers, the specific process is as follows: Step 2.1, potassium hydroxide and multi-branched aramid fibers are added to 50 mL of N,N-dimethylacetamide at a certain mass ratio, mixed and stirred in an ice-water bath for 3 h. After the reaction is completed, the solution is centrifuged at 7000 r / min for 30 min in a release agent. The supernatant is taken, a certain mass of sodium bicarbonate is added, and stirring is continued for 30 min to obtain mixture I.

[0156] Step 2.2: Take a certain mass of toluene 2,5-diisocyanate and dissolve it in N,N-dimethylacetamide (50 mL) solution to obtain mixture II.

[0157] Step 2.3: Add mixture I obtained in step 2.1 dropwise to mixture II obtained in step 2.2 over a period of 30 minutes. After the addition is complete, continue the reaction for another 30 minutes. After the reaction is complete, add 50 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether (50 mL each time). Dry the precipitate at 30°C for 24 hours to obtain isocyanate-modified aramid.

[0158] In the above process, the mass ratio of potassium hydroxide: branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:3:1:2. The amount of potassium hydroxide used is a fixed 10g.

[0159] Step 3, the synthesis of the multi-branched alcohol resin, is as follows: Methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30 mL of toluene solution. Then, a certain amount of azobisisobutyronitrile is added and stirred until homogeneous. The temperature is then raised to 60℃ for reaction. After the reaction is complete, a viscous multi-branched alcohol resin (viscosity 8000-15000 cps) is obtained. In the above process, the mass ratio of methyl acrylate: butyl methyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:1:0.02. The amount of methyl acrylate used is a fixed value of 5 g.

[0160] Step 4, preparation of mica insulating material bonded with multi-branched aramid fibers, is as follows: A certain mass of multi-branched alcohol resin and isocyanate-modified aramid are taken and mechanically stirred for 20 minutes at -70℃ and 60 r / min. The resulting mixture is poured into a polytetrafluoroethylene mold (length x width x height 10cm x 10cm x 2cm). After the temperature rises to room temperature, the mold is placed in an oven and baked at 80℃ for 5 hours. In the above process, the mass ratio of multi-branched alcohol resin to isocyanate-modified aramid is 1:2. The amount of multi-branched alcohol resin used is a fixed value of 5g.

[0161] Results and Discussion: Table 1 below shows the comparison results of thermal stability, mechanical properties, insulation properties, and material thickness between Examples 1-3 and Comparative Examples 1-5; Table 2 shows the comparison results of thermal stability, mechanical properties, insulation properties, and material thickness between Comparative Examples 6-7.

[0162] Table 1

[0163]

[0164]

[0165] Table 2

[0166]

[0167] From Table 1 and Figure 1As can be seen, in Comparative Example 1, the multi-branched aramid fibers were not modified with isocyanate, and the aramid could not chemically react with the multi-branched alcohol resin, resulting in the ineffective chemical bonding between the aramid and the nano-mica powder. This ultimately led to a deterioration in the mechanical and insulation properties of the material. Traditional wet-formed aramid-mica paper typically has a small thickness (≈0.2 cm), while the materials in Examples 1-3 and Comparative Examples 1-5 can reach a thickness of 0.8-1.4 cm. Table 1 shows that the insulation materials prepared in Examples 1-3 of this invention have small errors in their final mechanical and insulation properties, indicating that the preparation method proposed in this invention has good reproducibility. In Comparative Example 2, during the isocyanate surface modification of aramid, mixture 2 obtained in step 2 was added dropwise to mixture 1 obtained in step 1. From a chemical reaction perspective, the isocyanate surface-modified aramid in the solution was always in excess during the reaction. Since toluene 2,5-diisocyanate is bifunctional, each toluene 2,5-diisocyanate molecule can react with two aramid fibers, ultimately leading to flocculation of the aramid fibers. In Comparative Example 3, branched aramid fibers were replaced with unbranched aramid. Unbranched aramid, due to its regular structure and numerous hydrogen bonds, tends to aggregate easily, ultimately leading to incompatibility between aramid and branched alcohol resin. This results in deterioration of the material's mechanical and insulation properties. In Comparative Example 4, hydroxyethyl acrylate was not added to the branched alcohol resin. The lack of hydroxyl groups and isocyanate in the polyurethane reaction prevented the material from curing, significantly reducing its mechanical and insulation properties. In Comparative Example 5, the branched alcohol resin was replaced with unbranched hydroxyethyl polyacrylate. The isocyanate-modified aramid was incompatible with the unbranched hydroxyethyl polyacrylate, resulting in poor thermal stability and insulation performance. Table 2 shows that in Comparative Example 6, the material without isocyanate-modified aramid exhibited the worst mechanical properties, indicating that aramid significantly contributes to the material's mechanical properties. In Comparative Example 7, without the addition of isocyanate-modified nano-mica powder, the thermal stability and insulation properties of the material deteriorated, indicating that the isocyanate-modified nano-mica powder contributed significantly to the insulation performance of the material. However, Comparative Example 7 exhibited the greatest mechanical properties, suggesting that the introduction of isocyanate-modified nano-mica powder reduced the mechanical strength of the material.

[0168] This invention achieves chemical curing of isocyanate-modified aramid and isocyanate-modified nano-mica powder through structural design, breaking through the limitations of traditional aramid-mica paper sheets. The isocyanate-modified aramid has a multi-branched structure, which enhances its compatibility with multi-branched alcohol resins. The nano-mica powder, with its small particle size and isocyanate surface modification, possesses excellent dispersibility. The final product is an insulating material with high temperature resistance and good mechanical properties.

Claims

1. A method for preparing a high-temperature resistant insulating material of multi-branched aramid fiber bonded to mica, characterized in that: Specifically, the steps include the following: Step 1: Preparation of multi-branched aramid fibers; The specific process of Step 1 is as follows: p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride are added to 30-50 mL of N-methylpyrrolidone solution to obtain a mixed solution. Nitrogen gas is introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. Then, terephthaloyl chloride is added in three equal portions, with an interval of 30 minutes between each addition. After the reaction, the solid content of the solution is adjusted to 5.0% by adding N,N-dimethylacetamide to obtain a polymer solution. Nitrogen gas is continued to be introduced into the polymer solution, and spinning is performed to obtain nascent fibers. The nascent fibers are stretched in a mixed solvent of N,N-dimethylacetamide and water at 70-80℃ for 500-800 mL, and then dried at 120-130℃ for 2-4 hours to obtain multi-branched aramid fibers. Step 2: Prepare isocyanate-modified aramid fibers based on the product obtained in Step 1; Step 3: Prepare isocyanate-modified nano-mica powder; Step 4: Synthesize multi-branched alcohol resin; The specific process of step 4 is as follows: Methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate were added to 30-60 mL of toluene solution, followed by the addition of azobisisobutyronitrile (AIBN) and stirring until homogeneous. The mixture was then reacted at 60-70 °C. After the reaction was complete, a viscous multi-branched alcohol resin was obtained. The mass ratio of methyl acrylate: butyl methyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile was 1:1:1:1-3:0.02-0.

03. Step 5: Prepare multi-branched aramid fiber bonded mica insulating material by taking multi-branched alcohol resin, isocyanate surface-modified aramid, and isocyanate surface-modified nano mica powder.

2. The method for preparing the high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 1, characterized in that: In step 1, the molar ratio of p-phenylenediamine: 2,5-diethoxy-1,4-phenylenediamine: 2,5-bis(hexyloxy)-1,4-phenylenediamine: lithium chloride: terephthaloyl chloride is 1:1-2:1-2:0.05-0.1:3-6.

3. The method for preparing the high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 2, characterized in that: In step 1, the specific process of spinning to prepare nascent fibers is as follows: a polymer solution is sprayed into a mixed solvent of 500-800 mL of N,N-dimethylacetamide and water using a 330*0.05 mm spinneret to obtain nascent fibers.

4. The method for preparing the high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 2, characterized in that: The specific process of step 2 is as follows: Step 2.1: Add potassium hydroxide and the multi-branched aramid fiber prepared in Step 1 to 50-100 mL of N,N-dimethylacetamide and mix. Stir the mixture in an ice-water bath for 3-6 h. After the reaction is complete, centrifuge the solution in a release machine at 7000 r / min for 30-60 min. Take the supernatant, add sodium bicarbonate, and continue stirring for 30-60 min to obtain mixture I. Step 2.2: Dissolve toluene 2,5-diisocyanate in 50-100 mL of N,N-dimethylacetamide solution to obtain mixture II; Step 2.3: Add mixture I obtained in step 2.1 dropwise to mixture II obtained in step 2.2 over a period of 30-60 min. After the addition is complete, continue the reaction for another 30-60 min. After the reaction is complete, add 50-100 mL of anhydrous diethyl ether. A yellow precipitate will form. Collect the precipitate and wash it three times with anhydrous diethyl ether. Dry it at 30-45℃ for 24 h to obtain isocyanate-modified aramid.

5. The method for preparing the high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 4, characterized in that: In step 2, the mass ratio of potassium hydroxide: branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:3-6:1-2:2-3.

6. The method for preparing the high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 5, characterized in that: The specific process of step 3 is as follows: Step 3.1: Add NaOH to the nano mica powder, then add 1000-1500 mL of deionized water, put it into a nano ball mill, use 20-30 μm zirconium oxide as the ball milling medium, mill at a speed of 300-500 r / min, and mill for 2-4 h. After milling, collect the mixture of nano mica powder. Step 3.2: Place the mixture obtained in step 3.1 into a 7000 Da dialysis bag and dialyze it three times in 1000-1500 mL of deionized water. Centrifuge the resulting solution to obtain wet mica powder. Freeze-dry the wet nano-mica powder at -70℃ for 7 days to obtain activated nano-mica powder. Step 3.3: Weigh toluene 2,5-diisocyanate and dissolve it in 1000-1500 mL of dimethyl sulfoxide solution. Stir at room temperature for 10-20 min. Then, divide the activated nano-mica powder from step 3.2 into 5 equal batches and add them to the dimethyl sulfoxide solution at intervals of 20-30 min.

7. The method for preparing the high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 6, characterized in that: In step 3, the mass ratio of nano-mica powder:NaOH:toluene 2,5-diisocyanate is 1:1-2:1-2.

8. The method for preparing the high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 7, characterized in that: The specific process of step 5 is as follows: Take multi-branched alcohol resin, isocyanate surface-modified aramid, and isocyanate surface-modified nano mica powder, and mechanically stir them at -70℃ and 60-80r / min for 20-40min. Pour the resulting mixture into a polytetrafluoroethylene mold. After the temperature rises to room temperature, place the mold in an oven and bake it at 80-100℃ for 5-10h to obtain multi-branched aramid fiber bonded mica insulating material. The mass ratio of multi-branched alcohol resin: isocyanate surface-modified aramid: isocyanate surface-modified nano mica powder is 1:2-4:2-4.

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