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

Abstract

The invention discloses a preparation method of a high-temperature-resistant insulating material of multi-branched-chain aramid fiber bonded mica. The preparation method specifically comprises the following steps: step 1, preparing multi-branched-chain aramid fiber; step 2, preparing isocyanate surface modified aramid fibers according to a product obtained in the step 1; step 3, preparing isocyanate surface modified nano mica powder; step 4, synthesizing multi-branch chain alcohol resin; and 5, preparing the multi-branched-chain aramid fiber bonded mica insulating material. Through structural design of the isocyanate surface modified aramid fiber and the isocyanate surface modified nano mica powder, chemical curing is realized, and the thickness of a paper sheet of traditional aramid fiber mica can be broken through. The isocyanate surface modified aramid fiber is of a multi-branched-chain structure, so that the compatibility of the isocyanate surface modified aramid fiber in multi-branched-chain alcohol resin can be enhanced. The nano mica powder is small in particle size and is endowed with good dispersity through isocyanate surface modification. And finally, the insulating material with high temperature resistance and good mechanical property is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of insulating materials and relates to a method for preparing a high-temperature resistant insulating material of multi-branched aramid fibers bonded with mica. Background Art

[0002] Aramid fiber, primarily composed of amide bonds and aromatic benzene rings, is a synthetic fiber with excellent mechanical properties. Mica, on the other hand, boasts excellent electrical properties such as high-temperature resistance and insulation, making it a promising 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. Consequently, aramid fiber and mica have begun to be combined to create high-strength, high-temperature-resistant insulating materials. However, aramid fiber and mica are organic and inorganic materials, respectively, and significant differences in inorganic-organic solubility and dispersibility prevent their direct and effective combination. To address this organic-inorganic composite problem, existing methods prepare aramid fiber and mica into a slurry, which is then wet-formed into aramid mica paper. The aramid fiber and mica are physically bonded using a small molecule adhesive or hot-melt resin. This results in a very limited thickness when wet-formed. Furthermore, the physical bonding between the aramid fiber and mica makes it difficult to control the uniformity of their dispersion, resulting in insufficient mechanical and insulating properties. Summary of the Invention

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

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

[0005] Step 1, preparing multi-branched aramid fibers;

[0006] Step 2, preparing isocyanate surface-modified aramid according to the product obtained in step 1;

[0007] Step 3, preparing isocyanate surface-modified nano-mica powder;

[0008] Step 4, synthesizing a multi-branched alcohol resin;

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

[0010] The present invention is also characterized in that:

[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 is introduced into the mixed solution, and the reaction bottle is placed in an ice-water bath, and then terephthaloyl chloride is added three times at an average interval of 30 minutes each time. After the reaction, N,N-dimethylacetamide is added to adjust the solid content of the solution to 5.0% to obtain a polymer solution; nitrogen is continued to be introduced into the polymer solution, and spinning is performed to obtain spun fibers, and the spun fibers are stretched in a mixed solvent of 500-800 mL of N,N-dimethylacetamide and water at 70-80° C., and then dried at 120-130° C. 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 the spun fibers is as follows: using a 330*0.05 mm spinneret to spray the polymer solution into 500-800 mL of a mixed solvent of N,N-dimethylacetamide and water to obtain spun fibers.

[0014] The specific process of step 2 is:

[0015] Step 2.1: potassium hydroxide and the multi-branched aramid fiber prepared in step 1 were added to 50-100 mL of N,N-dimethylacetamide, and the mixture was stirred in an ice-water bath for 3-6 hours. After the reaction, the solution was centrifuged in a release machine at 7000 r / min for 30-60 minutes, the supernatant was collected, sodium bicarbonate was added, and stirring was continued for 30-60 minutes to obtain a mixture I;

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

[0017] Step 2.3, the mixture I obtained in step 2.1 is added dropwise to the mixture II obtained in step 2.2 for 30-60 minutes. After the addition is completed, the reaction is continued for 30-60 minutes. After the reaction is completed, 50-100 mL of anhydrous ether is added to precipitate a yellow precipitate. The precipitate is collected and washed three times with anhydrous ether, and dried at 30-45°C for 24 hours to obtain isocyanate surface-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:

[0020] Step 3.1: Add NaOH to the nano-mica powder, then add 1000-1500 mL of deionized water, place in a nano-ball mill, use 20-30 μm zirconium oxide as the milling medium, mill at a speed of 300-500 rpm, and mill for 2-4 hours. After the milling is completed, collect the mixed solution of the nano-mica powder;

[0021] Step 3.2, placing the mixed solution obtained in step 3.1 into a 7000Da dialysis bag and dialyzing it three times in 1000-1500mL deionized water, centrifuging the obtained solution to obtain wet mica powder; freeze-drying the wet nano-mica powder at -70°C for 7 days to obtain activated nano-mica powder;

[0022] In step 3.3, toluene 2,5-diisocyanate was weighed and dissolved in 1000-1500 mL of dimethyl sulfoxide solution, and stirred at room temperature for 10-20 minutes. Then, the activated nano-mica powder in step 3.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at intervals of 20-30 minutes.

[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, methyl butyl acrylate, styrene, and hydroxyethyl acrylate are added to 30-60 mL of a toluene solution, and then azobisisobutyronitrile is added and stirred evenly, and reacted at a temperature of 60-70° C. After the reaction is completed, a viscous multi-branched alcohol resin is obtained; wherein the mass ratio of methyl acrylate: methyl butyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:1-3:0.02-0.03.

[0025] The specific process of step 5 is as follows: take a multi-branched alcohol resin, isocyanate surface-modified aramid, and isocyanate surface-modified nano-mica powder, mechanically stir at -70°C and 60-80 r / min for 20-40 minutes, pour the obtained mixture into a polytetrafluoroethylene mold, wait until the temperature rises to room temperature, and then place the mold in an oven and bake at 80-100°C for 5-10 hours to obtain a multi-branched aramid fiber-bonded mica insulation material; wherein the mass ratio of the multi-branched alcohol resin: isocyanate surface-modified aramid: isocyanate surface-modified nano-mica powder is 1:2-4:2-4.

[0026] The present invention has the following beneficial effects: by constructing isocyanate-surface-modified aramid and isocyanate-surface-modified nano-mica powder, and by chemically curing the isocyanate-surface-modified aramid and the nano-mica powder with a multi-branched alcohol resin, a material with excellent high-temperature resistance, mechanical properties, and insulation properties can be obtained through polyurethane bonding. The multi-branched structure of the isocyanate-surface-modified aramid enhances its compatibility with the multi-branched alcohol resin. Furthermore, the mica is nano-mica powder, which has been surface-modified with isocyanate, imparts excellent dispersibility in toluene. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a stress-strain test curve diagram of Example 1 of the preparation method of the high-temperature resistant insulation material of multi-branched aramid fiber bonded mica of the present invention and comparative examples 1 and 3-7. DETAILED DESCRIPTION

[0028] The following describes it in detail with reference to specific implementation methods.

[0029] The preparation method of the high-temperature resistant insulating material of multi-branched aramid fiber bonded with mica of the present invention specifically comprises the following steps: Step 1, preparation of the 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 is introduced into the mixed solution, and the reaction bottle is placed in an ice-water bath, and then a certain amount of terephthaloyl chloride is added three times at an average interval of 30 minutes each time. After the reaction, N,N-dimethylacetamide is added to adjust the solid content of the solution to 5.0% (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). The polymer solution is then spun by injecting nitrogen into 500-800 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330 x 0.05 mm spinneret to produce spun fibers. The spun fibers are then stretched at 70-80°C in 500-800 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) to a stretch ratio of 110-120%, and then dried at 120-130°C for 2-4 hours to produce multi-branched aramid fibers. In the above process, the molar ratios of p-phenylenediamine: 2,5-diethoxy-1,4-phenylenediamine: 2,5-bis(hexyloxy)-1,4-phenylenediamine: lithium chloride: terephthaloyl chloride are 1:1-2:1-2:0.05-0.1:3-6.

[0030] Step 2, preparing isocyanate surface-modified aramid, the specific process is as follows: Step 2.1, taking potassium hydroxide and multi-branched aramid fiber in a certain mass ratio, adding them to 50-100 mL of N,N-dimethylacetamide, mixing, stirring in an ice-water bath for 3-6 hours, after the reaction is completed, the solution is centrifuged in a release machine at 7000 r / min for 30-60 minutes, taking the supernatant, adding a certain amount of sodium bicarbonate, and continuing to stir for 30-60 minutes to obtain mixture I.

[0031] In step 2.2, a certain amount of toluene 2,5-diisocyanate is dissolved in N,N-dimethylacetamide (50-100 mL) to obtain a mixture II.

[0032] In step 2.3, the mixture I obtained in step 2.1 is added dropwise to the mixture II obtained in step 2.2 for 30-60 minutes. After the addition is completed, the reaction is continued for 30-60 minutes. After the reaction is completed, 50-100 mL of anhydrous ether is added to precipitate a yellow precipitate. The precipitate is collected and washed three times with anhydrous ether (50-100 mL of anhydrous ether each time), and dried at 30-45° C. for 24 hours to obtain an isocyanate surface-modified aramid fiber. In the above process, the mass ratio of potassium hydroxide: multi-branched aramid fiber: sodium bicarbonate: toluene 2,5-diisocyanate is 1:3-6:1-2:2-3.

[0033] Step 3, preparing isocyanate surface-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, the ball milling medium is 20-30μm zirconium oxide, the ball milling speed is 300-500r / min, the ball milling time is 2-4h, and after the ball milling is completed, the mixed solution of nano-mica powder is collected.

[0035] In step 3.2, the mixed solution from step 3.1 was placed in a 7000Da dialysis bag and dialyzed three times in 1000-1500mL deionized water. The resulting solution was centrifuged at a speed of 10,000-12,000 rpm. The wet nano-mica powder was freeze-dried at -70°C for 7 days to obtain activated nano-mica powder.

[0036] In step 3.3, a certain amount of toluene 2,5-diisocyanate was weighed and dissolved in 1000-1500 mL of dimethyl sulfoxide solution, and stirred at room temperature for 10-20 minutes. Then, the activated nano-mica powder in step 3.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at intervals of 20-30 minutes.

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

[0038] Step 4, synthesis of a multi-branched alcohol resin, specifically involves the following steps: methyl acrylate, methyl butyl acrylate, styrene, and hydroxyethyl acrylate are added to 30-60 mL of a toluene solution, followed by addition of a certain amount of azobisisobutyronitrile, followed by stirring. The mixture is then heated to 60-70°C for reaction, yielding a viscous multi-branched alcohol resin (viscosity 8,000-15,000 cps). In the above process, the mass ratio of methyl acrylate: methyl butyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:1-3:0.02-0.03.

[0039] Step 5, preparing the multi-branched aramid fiber-bonded mica insulation material, involves the following process: A certain mass of multi-branched alcohol resin, isocyanate-surface-modified aramid, and isocyanate-surface-modified nano-mica powder are mechanically stirred at -70°C and 60-80 rpm for 20-40 minutes. The resulting mixture is then poured into a polytetrafluoroethylene mold (10 cm x 10 cm x 2 cm in length, width, and height, respectively). After the temperature reaches room temperature, the mold is placed in an oven and baked at 80-100°C for 5-10 hours. In this 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 fiber, specifically involves the following steps: 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 in a specific molar ratio. The mixed solution is then purged with nitrogen, and the reaction flask is placed in an ice-water bath. A specific amount of terephthaloyl chloride is then added in three equal portions, each separated by 30 minutes. After the reaction, N,N-dimethylacetamide is added to adjust the solids content of the solution to 5.0%. Nitrogen is continuously purged into the polymer solution, and spinning is performed by spraying the polymer solution into 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330 x 0.05 mm spinneret, yielding spun fibers. The spun fibers were then stretched at 70°C in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) to a draw ratio of 110%. The fibers were then dried at 120°C for 2 hours to yield multi-branched aramid fibers. In this process, the molar ratios of p-phenylenediamine: 2,5-diethoxy-1,4-phenylenediamine: 2,5-bis(hexyloxy)-1,4-phenylenediamine: lithium chloride: terephthaloyl chloride were 1:1:1:0.05:3. The p-phenylenediamine dosage was a constant 0.05 mol.

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

[0043] Step 2.1: Potassium hydroxide and multi-branched aramid fiber were added to 50 mL of N,N-dimethylacetamide in a specific mass ratio. The mixture was stirred in an ice-water bath for 3 hours. After the reaction, the solution was centrifuged in a mold release machine at 7000 rpm for 30 minutes. The supernatant was collected, a specific mass of sodium bicarbonate was added, and stirring was continued for 30 minutes to obtain Mixture I.

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

[0045] Step 2.3, the mixture I obtained in step 2.1 is added dropwise to the mixture II obtained in step 2.2, the addition time is 30 minutes, and the reaction is continued for 30 minutes. After the reaction is completed, 50 mL of anhydrous ether is added, and a yellow precipitate is precipitated. The precipitate is collected and washed three times with anhydrous ether (50 mL of anhydrous ether each time), and dried at 30°C for 24 hours to obtain isocyanate surface-modified aramid.

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

[0047] Step 3, preparing isocyanate surface-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, the ball milling medium is 20 μm zirconium oxide, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, collect the mixed solution of nano-mica powder.

[0049] In step 3.2, the mixed solution of step 3.1 was placed in a 7000Da dialysis bag and dialyzed three times in 1000mL of deionized water. The resulting solution was centrifuged at 10000r / min. The wet nano-mica powder was freeze-dried at -70°C for 7 days to obtain activated nano-mica powder.

[0050] In step 3.3, a certain amount of toluene 2,5-diisocyanate was weighed and dissolved in 1000 mL of dimethyl sulfoxide solution, and stirred at room temperature for 10 min. Then, the activated nano-mica powder in step 3.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at an interval of 20 min.

[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, synthesis of a multi-branched alcohol resin, specifically involves the following process: methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30 mL of a toluene solution, followed by the addition of a predetermined amount of azobisisobutyronitrile, followed by stirring. The mixture is then heated to 60°C for reaction, yielding a viscous multi-branched alcohol resin (viscosity 8,000-15,000 cps). In this 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 is a fixed value of 5 g.

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

[0054] A certain amount of multi-branched alcohol resin, isocyanate-modified aramid, and isocyanate-modified nano-mica powder were mechanically stirred at -70°C and 60 rpm for 20 minutes. The resulting mixture was poured onto a polytetrafluoroethylene mold (10 cm x 10 cm x 2 cm in length, width, and height, respectively). After the mold was heated to room temperature, it was placed in an oven and baked at 80°C for 5 hours. 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 was set at 5g.

[0055] Example 2

[0056] Step 1, preparing multi-branched aramid fibers, specifically comprises: adding p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride in a specific molar ratio to a 50 mL N-methylpyrrolidone solution, purging the mixed solution with nitrogen, and placing the reaction flask in an ice-water bath. Then, a specific amount of terephthaloyl chloride was added in three equal portions, each separated by 30 minutes. After the reaction, N,N-dimethylacetamide was added to adjust the solids content of the solution to 5.0%. Nitrogen was continued to be introduced into the polymer solution, and spinning was performed, i.e., the polymer solution was sprayed into 800 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330 x 0.05 mm spinneret, to produce spun fibers. The spun fibers were then stretched to 120% in 800 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 80°C. The fibers were then dried at 130°C for 4 hours to yield multi-branched aramid fibers. The molar ratios of p-phenylenediamine: 2,5-diethoxy-1,4-phenylenediamine: 2,5-bis(hexyloxy)-1,4-phenylenediamine: lithium chloride: terephthaloyl chloride were 1:2:2:0.1:6. The p-phenylenediamine dosage was a constant 0.05 mol.

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

[0058] In step 2.1, potassium hydroxide and multi-branched aramid fiber were added to 100 mL of N,N-dimethylacetamide in a specific mass ratio, and the mixture was stirred in an ice-water bath for 6 hours. After the reaction, the solution was centrifuged in a mold release machine at 7000 rpm for 60 minutes. The supernatant was collected, a specific mass of sodium bicarbonate was added, and stirring was continued for 60 minutes to obtain Mixture I.

[0059] Step 2.2, taking a certain amount of toluene 2,5-diisocyanate, dissolving it in N,N-dimethylacetamide (100 mL) solution to obtain mixture II;

[0060] Step 2.3, the mixture I obtained in step 2.1 was added dropwise to the mixture II obtained in step 2.2, the addition time was 60 min, and the reaction was continued for 60 min after the addition was completed. After the reaction was completed, 100 mL of anhydrous ether was added, and a yellow precipitate was precipitated. The precipitate was collected and washed three times with anhydrous ether (100 mL of anhydrous ether each time), and dried at 45 ° C for 24 h to obtain isocyanate surface-modified aramid.

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

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

[0063] In step 3.1, a certain mass of nano-mica powder (diameter to thickness ratio of 80:1) was taken, a certain amount of NaOH was added, and then 1500 mL of deionized water was added. The mixture was placed in a nano-ball mill with 30 μm zirconium oxide as the ball milling medium, the ball milling speed was 500 r / min, and the ball milling time was 4 h. After the ball milling was completed, the mixed solution of the nano-mica powder was collected.

[0064] In step 3.2, the mixed solution of step 3.1 was placed in a 7000Da dialysis bag and dialyzed three times in 1500mL of deionized water. The resulting solution was centrifuged at 12000r / min. The wet nano-mica powder was freeze-dried at -70°C for 7 days to obtain activated nano-mica powder.

[0065] In step 3.3, a certain amount of toluene 2,5-diisocyanate was weighed and dissolved in 1500 mL of dimethyl sulfoxide solution, and stirred at room temperature for 20 min. Then, the activated nano-mica powder in step 3.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at an interval of 30 min.

[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, synthesis of a multi-branched alcohol resin, specifically involves adding methyl acrylate, methyl butyl acrylate, styrene, and hydroxyethyl acrylate to 60 mL of a toluene solution, then adding a predetermined amount of azobisisobutyronitrile and stirring until uniform. The mixture is then heated to 70°C for reaction, yielding a viscous multi-branched alcohol resin (viscosity 8,000-15,000 cps). In the above process, the mass ratio of methyl acrylate: methyl butyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:3:0.03. The amount of methyl acrylate is a fixed value of 5 g.

[0068] Step 5, preparing the multi-branched aramid fiber-bonded mica insulation material, specifically involves taking a certain mass of multi-branched alcohol resin, isocyanate-surface-modified aramid, and isocyanate-surface-modified nano-mica powder, mechanically stirring at -70°C and 80 rpm for 40 minutes. The resulting mixture is poured into a polytetrafluoroethylene mold (10 cm x 10 cm x 2 cm in length, width, and height, respectively). After the temperature reaches room temperature, the mold is placed in an oven and baked at 100°C for 10 hours to produce the multi-branched aramid fiber-bonded mica insulation material. In this process, the mass ratio of multi-branched alcohol resin: isocyanate-surface-modified aramid: isocyanate-surface-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, preparing multi-branched aramid fibers, specifically comprises: adding p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride in a certain molar ratio to 40 mL of N-methylpyrrolidone solution to obtain a mixed solution. Nitrogen is then 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, each separated by 30 minutes. After the reaction, N,N-dimethylacetamide is added to adjust the solid content of the solution to 5.0%. Nitrogen is continued to be introduced into the polymer solution, and spinning is performed by spraying the polymer solution 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 spun fibers. The spun fibers were then stretched at 75°C in 650 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) to a draw ratio of 115%. The fibers were then dried at 125°C for 3 hours to yield multi-branched aramid fibers. The molar ratios of p-phenylenediamine: 2,5-diethoxy-1,4-phenylenediamine: 2,5-bis(hexyloxy)-1,4-phenylenediamine: lithium chloride: terephthaloyl chloride were 1:1.5:1.5:0.075:4.5, with the p-phenylenediamine dosage being a constant 0.05 mol.

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

[0072] In step 2.1, potassium hydroxide and multi-branched aramid fiber were added to 75 mL of N-N-dimethylacetamide in a specific mass ratio. The mixture was stirred in an ice-water bath for 4.5 hours. After the reaction, the solution was centrifuged in a mold release machine at 7000 rpm for 45 minutes. The supernatant was collected, a specific mass of sodium bicarbonate was added, and stirring was continued for 45 minutes to obtain Mixture I.

[0073] In step 2.2, a certain amount of toluene 2,5-diisocyanate was dissolved in N,N-dimethylacetamide (75 mL) to obtain a mixture II.

[0074] Step 2.3, the mixture I obtained in step 2.1 was added dropwise to the mixture II obtained in step 2.2, the addition time was 45 min, and the reaction was continued for 45 min. After the reaction was completed, 75 mL of anhydrous ether was added, and a yellow precipitate was precipitated. The precipitate was collected and washed three times with anhydrous ether (75 mL of anhydrous ether each time), and dried at 37 ° C for 24 h to obtain isocyanate surface-modified aramid.

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

[0076] Step 3, isocyanate surface modification of 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, the ball milling medium is 25 μm zirconium oxide, the ball milling speed is 400 r / min, the ball milling time is 3 h, and after the ball milling is completed, collect the mixed solution of nano-mica powder.

[0078] In step 3.2, the mixed solution of step 3.1 was placed in a 7000Da dialysis bag and dialyzed three times in 1250mL of deionized water. The resulting solution was centrifuged at a speed of 11000r / min. The wet nano-mica powder was freeze-dried at -70°C for 7 days to obtain activated nano-mica powder.

[0079] In step 3.3, a certain amount of toluene 2,5-diisocyanate was weighed and dissolved in 1250 mL of dimethyl sulfoxide solution. The mixture was stirred at room temperature for 15 min. Then, the activated nano-mica powder in step 3.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at an interval of 25 min.

[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 a fixed value. The amount of nano-mica powder used is a fixed value of 50g.

[0081] Step 4, synthesis of a multi-branched alcohol resin, specifically proceeds as follows: methyl acrylate, methyl butyl acrylate, styrene, and hydroxyethyl acrylate are added to 45 mL of a toluene solution, followed by the addition of a predetermined amount of azobisisobutyronitrile, followed by stirring. The mixture is then heated to 65°C for reaction, yielding a viscous multi-branched alcohol resin (viscosity 8,000-15,000 cps). In the above process, the mass ratio of methyl acrylate: methyl butyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:2:0.025. The amount of methyl acrylate is a fixed value of 5 g.

[0082] Step 5, preparation of the multi-branched aramid fiber-bonded mica insulation material, follows: A certain mass of multi-branched alcohol resin, isocyanate-surface-modified aramid, and isocyanate-surface-modified nano-mica powder are mechanically stirred at -70°C and 70 rpm for 30 minutes. The resulting mixture is poured into a polytetrafluoroethylene mold (10 cm x 10 cm x 2 cm in length, width, and height, respectively). After the temperature reaches room temperature, the mold is placed in an oven and baked at 90°C for 7.5 hours. In this process, the mass ratio of multi-branched alcohol resin: isocyanate-surface-modified aramid: isocyanate-surface-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 (Multi-branched aramid fiber was not modified with isocyanate, resulting in poor mechanical and insulation properties of the final material)

[0084] Step 1, preparing multi-branched aramid fibers, specifically comprises adding p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride in a specific molar ratio to a 30 mL N-methylpyrrolidone solution. Nitrogen is then introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. A specific amount of terephthaloyl chloride is then added in three equal portions, each separated by 30 minutes. After the reaction, N,N-dimethylacetamide is added to adjust the solids content of the solution to 5.0%. Nitrogen is then continuously introduced into the polymer solution, and spinning is performed by spraying the polymer solution into 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330 x 0.05 mm spinneret, thereby obtaining spun fibers. The spun fibers were then stretched at 70°C in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) to a draw ratio of 110%. The fibers were then dried at 120°C for 2 hours to yield multi-branched aramid fibers. In this process, the molar ratios of p-phenylenediamine: 2,5-diethoxy-1,4-phenylenediamine: 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride: terephthaloyl chloride were 1:1:1:0.05:3. The p-phenylenediamine dosage was a constant 0.05 mol.

[0085] Step 2, isocyanate surface modification of 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, the ball milling medium is 20 μm zirconium oxide, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, the mixed solution of nano-mica powder is collected.

[0087] In step 2.2, the mixed solution of step 2.1 was placed in a 7000Da dialysis bag and dialyzed three times in 1000mL of deionized water. The resulting solution was centrifuged at 10000r / min. The wet nano-mica powder was freeze-dried at -70°C for 7 days to obtain activated nano-mica powder.

[0088] In step 2.3, a certain amount of toluene 2,5-diisocyanate was weighed and dissolved in 1000 mL of dimethyl sulfoxide solution, and stirred at room temperature for 10 min. Then, the activated nano-mica powder in step 2.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at an interval of 20 min.

[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, synthesis of a multi-branched alcohol resin, specifically proceeds as follows: equal masses of methyl acrylate, methyl butyl acrylate, styrene, and hydroxyethyl acrylate are added to 30 mL of a toluene solution, followed by addition of a predetermined amount of azobisisobutyronitrile, stirred evenly, and the mixture is heated to 60°C for reaction. Upon completion of the reaction, a viscous multi-branched alcohol resin (viscosity 8,000-15,000 cps) is obtained. In the above process, the mass ratio of methyl acrylate: methyl butyl acrylate: styrene: hydroxyethyl acrylate: azobisisobutyronitrile is 1:1:1:1:0.02. The amount of methyl acrylate is set at 5 g.

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

[0092] A certain amount of multi-branched alcohol resin, multi-branched aramid fiber, and isocyanate-surface-modified nano-mica powder were mechanically stirred at -70°C and 60 rpm for 20 minutes. The resulting mixture was poured into a polytetrafluoroethylene mold (10 cm x 10 cm x 2 cm in length, width, and height, respectively). After the mold was heated to room temperature, it was placed in an oven and baked at 80°C for 5 hours. The mass ratio of multi-branched alcohol resin: multi-branched aramid fiber: isocyanate-surface-modified nano-mica powder was 1:2:2. The amount of multi-branched alcohol resin was set at 5g.

[0093] Comparative Example 2 (during the isocyanate surface modification of aramid fibers, the mixture II obtained in step 2 was added dropwise to the mixture I obtained in step 1, and the aramid fibers were flocculated)

[0094] Step 1, preparation of multi-branched aramid fiber, 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 in a specific molar ratio. The mixed solution was then purged with nitrogen. The reaction flask was placed in an ice-water bath. A specific amount of terephthaloyl chloride was then added in three equal portions, each separated by 30 minutes. After the reaction, N,N-dimethylacetamide was added to adjust the solids content of the solution to 5.0%. Nitrogen was continued to flow through the polymer solution, and spinning was performed by spraying the polymer solution into 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330 x 0.05 mm spinneret to produce spun fibers. The spun fibers were then stretched to 110% in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 70°C. The fibers were then dried at 120°C for 2 hours to yield multi-branched aramid fibers. In this process, the molar ratios of p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, lithium chloride, and terephthaloyl chloride were 1:1:1:0.05:3. The p-phenylenediamine dosage was a constant 0.05 mol.

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

[0097] In step 2.1, potassium hydroxide and multi-branched aramid fiber were added to 50 mL of N-N-dimethylacetamide in a specific mass ratio. The mixture was stirred in an ice-water bath for 3 hours. After the reaction, the solution was centrifuged in a mold release machine at 7000 rpm for 30 minutes. The supernatant was collected, a specific mass of sodium bicarbonate was added, and stirring was continued for 30 minutes to obtain Mixture I.

[0098] In step 2.2, a certain amount of toluene 2,5-diisocyanate was dissolved in N,N-dimethylacetamide (50 mL) to obtain a mixture II.

[0099] Step 2.3, the mixture II obtained in step 2.2 was added dropwise to the mixture I obtained in step 2.1, the addition time was 30 min, and the reaction was continued for 30 min. After the reaction was completed, 50 mL of anhydrous ether was added, and a yellow precipitate was precipitated. The precipitate was collected and washed three times with anhydrous ether (50 mL of anhydrous ether each time), and dried at 30 ° C for 24 h to obtain isocyanate surface-modified aramid.

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

[0101] Comparative Example 3 (Multi-branched aramid fiber is replaced with unbranched aramid, and the dispersion of aramid in the material becomes poor, resulting in poor mechanical and insulation properties)

[0102] Step 1, aramid fiber preparation, specifically involves the following steps: p-phenylenediamine and lithium chloride are added to a 30 mL N-methylpyrrolidone solution in a specific molar ratio. The mixed solution is then purged with nitrogen, and the reaction flask is placed in an ice-water bath. A specific amount of terephthaloyl chloride is then added in three equal portions, each separated by 30 minutes. After the reaction, N,N-dimethylacetamide is added to adjust the solids content of the solution to 5.0%. Nitrogen is continued to be introduced into the polymer solution, and spinning is performed. Using a 330 x 0.05 mm spinneret, the polymer solution is sprayed into 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) to produce spun fibers. The spun fibers are then stretched at 70°C in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) to a stretch ratio of 110%, and then dried at 120°C for 2 hours to produce aramid fibers. In the above process, the molar ratio of p-phenylenediamine: lithium chloride: terephthaloyl chloride is 1:0.05:1, wherein the amount of p-phenylenediamine used is a fixed value of 0.05 mol.

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

[0104] In step 2.1, potassium hydroxide and aramid fiber were added to 50 mL of N,N-dimethylacetamide in a specific mass ratio. The mixture was stirred in an ice-water bath for 3 hours. After the reaction, the solution was centrifuged in a mold release machine at 7000 rpm for 30 minutes. The supernatant was collected, a specific mass of sodium bicarbonate was added, and stirring was continued for 30 minutes to obtain Mixture I.

[0105] In step 2.2, a certain amount of toluene 2,5-diisocyanate was dissolved in N,N-dimethylacetamide (50 mL) to obtain a mixture II.

[0106] Step 2.3, the mixture I obtained in step 2.1 is added dropwise to the mixture II obtained in step 2.2, the addition time is 30 minutes, and the reaction is continued for 30 minutes. After the reaction is completed, 50 mL of anhydrous ether is added, and a yellow precipitate is precipitated. The precipitate is collected and washed three times with anhydrous ether (50 mL of anhydrous ether each time), and dried at 30°C for 24 hours to obtain isocyanate surface-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, wherein the amount of potassium hydroxide used is a fixed value of 10g.

[0108] Step 3, preparing isocyanate surface-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, the ball milling medium is 20 μm zirconium oxide, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, collect the mixed solution of nano-mica powder.

[0110] In step 3.2, the mixed solution of step 3.1 was placed in a 7000Da dialysis bag and dialyzed three times in 1000mL of deionized water. The resulting solution was centrifuged at 10000r / min. The wet nano-mica powder was freeze-dried at -70°C for 7 days to obtain activated nano-mica powder.

[0111] In step 3.3, a certain amount of toluene 2,5-diisocyanate was weighed and dissolved in 1000 mL of dimethyl sulfoxide solution, and stirred at room temperature for 10 min. Then, the activated nano-mica powder in step 3.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at an interval of 20 min.

[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, synthesis of a multi-branched alcohol resin, specifically involves the following process: methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30 mL of a toluene solution, followed by the addition of a predetermined amount of azobisisobutyronitrile, followed by stirring. The mixture is then heated to 60°C for reaction, yielding a viscous multi-branched alcohol resin (viscosity 8,000-15,000 cps). In this 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 is a fixed value of 5 g.

[0114] Step 5, preparation of aramid fiber-bonded mica insulation material, specifically involves the following process: A certain mass of multi-branched alcohol resin, isocyanate-surface-modified aramid, and isocyanate-surface-modified nano-mica powder are mechanically stirred at -70°C and 60 rpm for 20 minutes. The resulting mixture is then poured into a polytetrafluoroethylene mold (10 cm x 10 cm x 2 cm in length, width, and height, respectively). After the mold is heated to room temperature, it is placed in an oven and baked at 80°C for 5 hours. In this process, the mass ratio of multi-branched alcohol resin: isocyanate-surface-modified aramid: isocyanate-surface-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 (No Hydroxyethyl Acrylate Was Added to the Multi-branched Alcohol Resin, and the Multi-branched Aramid Fiber-bonded Mica Insulation Material Could Not Be Cured)

[0116] Step 1, preparing multi-branched aramid fibers, specifically comprises: adding p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride in a certain molar ratio to a 30 mL N-methylpyrrolidone solution, purging the mixed solution with nitrogen, and placing the reaction flask in an ice-water bath. Then, a certain amount of terephthaloyl chloride was added in three equal portions, each with a 30-minute interval. After the reaction, N,N-dimethylacetamide was added to adjust the solid content of the solution to 5.0%. Nitrogen was continued to be introduced into the polymer solution, and spinning was performed by spraying the polymer solution into 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330 x 0.05 mm spinneret, thereby obtaining spun fibers. The spun fibers were then stretched to 110% in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 70°C. The fibers were then dried at 120°C for 2 hours to yield multi-branched aramid fibers. In this 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 p-phenylenediamine dosage was a constant 0.05 mol.

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

[0118] In step 2.1, potassium hydroxide and multi-branched aramid fiber were added to 50 mL of N,N-dimethylacetamide in a specific mass ratio. The mixture was stirred in an ice-water bath for 3 hours. After the reaction, the solution was centrifuged in a mold release machine at 7000 rpm for 30 minutes. The supernatant was collected, a specific mass of sodium bicarbonate was added, and stirring was continued for 30 minutes to obtain Mixture I.

[0119] In step 2.2, a certain amount of toluene 2,5-diisocyanate was dissolved in N,N-dimethylacetamide (50 mL) to obtain a mixture II.

[0120] Step 2.3, the mixture I obtained in step 2.1 is added dropwise to the mixture II obtained in step 2.2, the addition time is 30 minutes, and the reaction is continued for 30 minutes. After the reaction is completed, 50 mL of anhydrous ether is added, and a yellow precipitate is precipitated. The precipitate is collected and washed three times with anhydrous ether (50 mL of anhydrous ether each time), and dried at 30°C for 24 hours to obtain isocyanate surface-modified aramid.

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

[0122] Step 3, preparing isocyanate surface-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, the ball milling medium is 20 μm zirconium oxide, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, collect the mixed solution of nano-mica powder.

[0124] In step 3.2, the mixed solution of step 3.1 was placed in a 7000Da dialysis bag and dialyzed three times in 1000mL of deionized water. The resulting solution was centrifuged at 10000r / min. The wet nano-mica powder was freeze-dried at -70°C for 7 days to obtain activated nano-mica powder.

[0125] In step 3.3, a certain amount of toluene 2,5-diisocyanate was weighed and dissolved in 1000 mL of dimethyl sulfoxide solution, and stirred at room temperature for 10 min. Then, the activated nano-mica powder in step 3.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at an interval of 20 min.

[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 a multi-branched resin, is as follows: methyl acrylate, methyl butyl acrylate, and styrene are added to 30 mL of a toluene solution, followed by the addition of a predetermined amount of azobisisobutyronitrile, followed by stirring. The mixture is then heated to 60°C for reaction, yielding a viscous multi-branched resin (viscosity 8,000-15,000 cps). In this process, the mass ratio of methyl acrylate, methyl butyl acrylate, styrene, and azobisisobutyronitrile is 1:1:1:0.02. The amount of methyl acrylate is set at 5 g.

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

[0129] A certain amount of multi-branched resin, isocyanate-modified aramid, and isocyanate-modified nano-mica powder were mechanically stirred at -70°C and 60 rpm for 20 minutes. The resulting mixture was poured into a polytetrafluoroethylene mold (10 cm x 10 cm x 2 cm in length, width, and height, respectively). After the mold was heated to room temperature, it was placed in an oven and baked at 80°C for 5 hours, but the material failed to cure. In this 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 (the multi-branched alcohol resin was replaced with an unbranched polyhydroxyethyl acrylate resin, resulting in poor thermal stability and insulation performance)

[0131] Step 1, preparation of multi-branched aramid fiber, specifically involves the following steps: 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 in a specific molar ratio. Nitrogen is then introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. A specific amount of terephthaloyl chloride is then added in three equal portions, each separated by 30 minutes. After the reaction, N,N-dimethylacetamide is added to adjust the solids content of the solution to 5.0%. Nitrogen is then continuously introduced into the polymer solution, and spinning is performed by spraying the polymer solution into 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330 x 0.05 mm spinneret, to produce spun fibers. The spun fibers were then stretched to 110% in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 70°C. The fibers were then dried at 120°C for 2 hours to yield multi-branched aramid fibers. In this 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 p-phenylenediamine dosage was a constant 0.05 mol.

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

[0133] In step 2.1, potassium hydroxide and multi-branched aramid fiber were added to 50 mL of N,N-dimethylacetamide in a specific mass ratio. The mixture was stirred in an ice-water bath for 3 hours. After the reaction, the solution was centrifuged in a mold release machine at 7000 rpm for 30 minutes. The supernatant was collected, a specific mass of sodium bicarbonate was added, and stirring was continued for 30 minutes to obtain Mixture I.

[0134] In step 2.2, a certain amount of toluene 2,5-diisocyanate was dissolved in N,N-dimethylacetamide (50 mL) to obtain a mixture II.

[0135] Step 2.3, the mixture I obtained in step 2.1 is added dropwise to the mixture II obtained in step 2.2, the addition time is 30 minutes, and the reaction is continued for 30 minutes. After the reaction is completed, 50 mL of anhydrous ether is added, and a yellow precipitate is precipitated. The precipitate is collected and washed three times with anhydrous ether (50 mL of anhydrous ether each time), and dried at 30°C for 24 hours to obtain isocyanate surface-modified aramid.

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

[0137] Step 3, preparing isocyanate surface-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, the ball milling medium is 20 μm zirconium oxide, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, collect the mixed solution of nano-mica powder.

[0139] In step 3.2, the mixed solution of step 3.1 was placed in a 7000Da dialysis bag and dialyzed three times in 1000mL of deionized water. The resulting solution was centrifuged at 10000r / min. The wet nano-mica powder was freeze-dried at -70°C for 7 days to obtain activated nano-mica powder.

[0140] In step 3.3, a certain amount of toluene 2,5-diisocyanate was weighed and dissolved in 1000 mL of dimethyl sulfoxide solution, and stirred at room temperature for 10 min. Then, the activated nano-mica powder in step 3.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at an interval of 20 min.

[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, synthesis of poly(hydroxyethyl acrylate) resin, specifically involves the following process: adding a certain mass of hydroxyethyl acrylate to 10 mL of toluene solution, then adding a certain amount of azobisisobutyronitrile, stirring evenly, and then raising the temperature to 60°C for reaction. Upon completion of the reaction, a viscous poly(hydroxyethyl acrylate) resin (viscosity 8,000-15,000 cps) is obtained. In this process, the mass ratio of hydroxyethyl acrylate to azobisisobutyronitrile is 1:0.02. The amount of hydroxyethyl acrylate is fixed at 5 g.

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

[0144] A certain amount of poly(hydroxyethyl acrylate) resin, isocyanate-modified aramid, and isocyanate-modified nano-mica powder were mechanically stirred at -70°C and 60 rpm for 20 minutes. The resulting mixture was poured into a polytetrafluoroethylene mold (10 cm x 10 cm x 2 cm in length, width, and height, respectively). After the mold was heated to room temperature, it was placed in an oven and baked at 80°C for 5 hours. The mass ratio of poly(hydroxyethyl acrylate) resin: isocyanate-modified aramid: isocyanate-modified nano-mica powder was 1:2:2. The amount of polybranched alcohol resin was set at 5g.

[0145] Comparative Example 6 (no isocyanate added to the surface-modified aramid material, poor mechanical properties of the material)

[0146] Step 1: prepare isocyanate surface-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, the ball milling medium is 20 μm zirconium oxide, the ball milling speed is 300 r / min, the ball milling time is 2 h, and after the ball milling is completed, the mixed solution of nano-mica powder is collected.

[0148] In step 1.2, the mixed solution of step 1.1 was placed in a 7000Da dialysis bag and dialyzed three times in 1000mL of deionized water. The resulting solution was centrifuged at 10000r / min. The wet nano-mica powder was freeze-dried at -70°C for 7 days to obtain activated nano-mica powder.

[0149] In step 1.3, a certain amount of toluene 2,5-diisocyanate was weighed and dissolved in 1000 mL of dimethyl sulfoxide solution. The mixture was stirred at room temperature for 10 min. Then, the activated nano-mica powder in step 1.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at an interval of 20 min.

[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, synthesis of a multi-branched alcohol resin, specifically involves the following process: methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30 mL of a toluene solution, followed by the addition of a predetermined amount of azobisisobutyronitrile, followed by stirring. The mixture is then heated to 60°C for reaction, yielding a viscous multi-branched alcohol resin (viscosity 8,000-15,000 cps). In this 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 is a fixed value of 5 g.

[0152] Step 3, preparation of mica insulation material, specifically involves the following process: A certain mass of multi-branched alcohol resin and isocyanate-surface-modified nano-mica powder are mechanically stirred at -70°C and 60 rpm for 20 minutes. The resulting mixture is then poured into a polytetrafluoroethylene mold (10 cm x 10 cm x 2 cm in length, width, and height, respectively). After the mold is heated to room temperature, it is placed in an oven and baked at 80°C for 5 hours. The mass ratio of multi-branched alcohol resin to isocyanate-surface-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 (no isocyanate surface-modified nano-mica powder is added to the material, and the thermal stability and insulation properties of the material deteriorate)

[0154] Step 1, preparation of multi-branched aramid fiber, specifically involves the following steps: adding p-phenylenediamine, 2,5-diethoxy-1,4-phenylenediamine, 2,5-bis(hexyloxy)-1,4-phenylenediamine, and lithium chloride in a specific molar ratio to a 30-50 mL N-methylpyrrolidone solution. Nitrogen is then introduced into the mixed solution, and the reaction flask is placed in an ice-water bath. A specific amount of terephthaloyl chloride is then added in three equal portions, each separated by 30 minutes. After the reaction, N,N-dimethylacetamide is added to adjust the solids content of the solution to 5.0%. Nitrogen is then continuously introduced into the polymer solution, and spinning is performed by spraying the polymer solution into 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 1:0.5) using a 330 x 0.05 mm spinneret, to produce spun fibers. The spun fibers were then stretched to 110% in 500 mL of a mixed solvent of N,N-dimethylacetamide and water (v:v = 0.2:1) at 70°C. The fibers were then dried at 120°C for 2 hours to yield multi-branched aramid fibers. In this 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 p-phenylenediamine dosage was a constant 0.05 mol.

[0155] Step 2: Preparation of isocyanate-surface-modified aramid fiber. The specific process is as follows: Step 2.1: Potassium hydroxide and multi-branched aramid fiber were added to 50 mL of N,N-dimethylacetamide in a specific mass ratio. The mixture was stirred in an ice-water bath for 3 hours. After the reaction, the solution was centrifuged in a mold release machine at 7000 rpm for 30 minutes. The supernatant was collected, a specific mass of sodium bicarbonate was added, and stirring was continued for 30 minutes to obtain Mixture I.

[0156] In step 2.2, a certain amount of toluene 2,5-diisocyanate was dissolved in N,N-dimethylacetamide (50 mL) to obtain a mixture II.

[0157] Step 2.3, the mixture I obtained in step 2.1 is added dropwise to the mixture II obtained in step 2.2, the addition time is 30 minutes, and the reaction is continued for 30 minutes. After the reaction is completed, 50 mL of anhydrous ether is added, and a yellow precipitate is precipitated. The precipitate is collected and washed three times with anhydrous ether (50 mL of anhydrous ether each time), and dried at 30°C for 24 hours to obtain isocyanate surface-modified aramid.

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

[0159] Step 3, synthesis of a multi-branched alcohol resin, specifically proceeds as follows: methyl acrylate, butyl methyl acrylate, styrene, and hydroxyethyl acrylate are added to 30 mL of a toluene solution, followed by addition of a predetermined amount of azobisisobutyronitrile, followed by stirring. The mixture is then heated to 60°C for reaction, yielding a viscous multi-branched alcohol resin (viscosity 8,000-15,000 cps). 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 is set at 5 g.

[0160] Step 4, preparation of a multi-branched aramid fiber-bonded mica insulation material, follows: A certain mass of multi-branched alcohol resin and isocyanate-surface-modified aramid are mechanically stirred at -70°C and 60 rpm for 20 minutes. The resulting mixture is poured into a polytetrafluoroethylene mold (10 cm x 10 cm x 2 cm in length, width, and height, respectively). After the mixture reaches room temperature, the mold is placed in an oven and baked at 80°C for 5 hours. The mass ratio of multi-branched alcohol resin to isocyanate-surface-modified aramid is 1:2. The amount of multi-branched alcohol resin used is a fixed value of 5 g.

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

[0162] Table 1

[0163]

[0164]

[0165] Table 2

[0166]

[0167] From Table 1 and Figure 1It can be seen that in Comparative Example 1, the multi-branched aramid fiber was not modified with isocyanate, and the aramid could not react chemically with the multi-branched alcohol resin, resulting in the inability of the aramid and the nano-mica powder to be effectively chemically bonded. The mechanical properties and insulation properties of the final material deteriorated. The thickness of the aramid-mica paper formed by the traditional wet method is usually small (≈0.2 cm), while the thickness of the materials in Examples 1-3 and Comparative Examples 1-5 can reach 0.8-1.4 cm. As shown in Table 1, the final mechanical properties and insulation properties of the insulating materials prepared in Examples 1-3 of the present invention have small errors, which shows that the preparation method proposed by the present invention has good reproducibility. In Comparative Example 2, during the isocyanate surface modification of the aramid, the mixture 2 obtained in step 2 was added dropwise to the mixture 1 obtained in step 1. From the perspective of the chemical reaction, the isocyanate surface modified aramid in the solution is always excessive during the reaction. Since toluene 2,5-diisocyanate is difunctional, each toluene 2,5-diisocyanate molecule can react with two aramid fibers, and finally the aramid fibers are flocculated. In Comparative Example 3, the multi-branched aramid fiber was replaced with unbranched aramid. Unbranched aramid has a regular structure and contains a large number of hydrogen bonds, which makes it easy for macromolecules to aggregate. Ultimately, aramid is incompatible with the multi-branched alcohol resin. This results in deterioration of the material's mechanical properties and insulation properties. In Comparative Example 4, hydroxyethyl acrylate was not added to the multi-branched alcohol resin. The polyurethane reaction of hydroxyl groups and isocyanate was lacking, and the material could not be cured. The material's mechanical properties and insulation properties were greatly reduced. In Comparative Example 5, the multi-branched alcohol resin was replaced with unbranched poly(hydroxyethyl acrylate). The isocyanate surface-modified aramid was incompatible with the unbranched poly(hydroxyethyl acrylate), resulting in poor thermal stability and poor insulation effect. As shown in Table 2, in Comparative Example 6, the material without isocyanate surface-modified aramid had the worst mechanical properties, indicating that aramid made a significant contribution to the material's mechanical properties. In Comparative Example 7, where no isocyanate-modified nano-mica powder was added, the thermal stability and insulation properties of the material deteriorated, indicating that the isocyanate-modified nano-mica powder significantly contributed to the material's insulation properties. However, the mechanical properties of Comparative Example 7 were the highest, indicating that the addition of isocyanate-modified nano-mica powder reduced the material's mechanical strength.

[0168] The present invention achieves chemical curing through the structural design of isocyanate-surface-modified aramid and isocyanate-surface-modified nano-mica powder, surpassing the paper-thinness of conventional aramid mica. The multi-branched structure of the isocyanate-surface-modified aramid enhances its compatibility with multi-branched alcohol resins. The nano-mica powder, with its small particle size and isocyanate-surface modification, imparts excellent dispersibility. The result is an insulating material with high-temperature resistance and excellent mechanical properties.

Claims

1. A method for preparing a high-temperature resistant insulating material of multi-branched aramid fiber bonded to mica, characterized by: The specific steps include: Step 1, preparing multi-branched aramid fibers; Step 2, preparing isocyanate surface-modified aramid according to the product obtained in step 1; Step 3, preparing isocyanate surface-modified nano-mica powder; Step 4, synthesizing a multi-branched alcohol resin; Step 5: Prepare multi-branched aramid fiber-bonded mica insulation material.

2. The method for preparing the high-temperature resistant insulation material of multi-branched aramid fiber bonded mica according to claim 1, characterized in that: The specific process of step 1 is: 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 is introduced into the mixed solution, and the reaction bottle is placed in an ice-water bath, and then terephthaloyl chloride is added three times at an average interval of 30 minutes each time. After the reaction, N,N-dimethylacetamide is added to adjust the solid content of the solution to 5.0% to obtain a polymer solution; nitrogen is continued to be introduced into the polymer solution, and spinning is performed to obtain spun fibers, and the spun fibers are stretched in a mixed solvent of 500-800 mL of N,N-dimethylacetamide and water at 70-80° C., and then dried at 120-130° C. for 2-4 hours to obtain multi-branched aramid fibers.

3. The method for preparing a high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 2, characterized in that: In the 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.

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

5. The method for preparing the high-temperature resistant insulation material of multi-branched aramid fiber bonded mica according to claim 3, characterized in that: The specific process of step 2 is: Step 2.1: potassium hydroxide and the multi-branched aramid fiber prepared in step 1 were added to 50-100 mL of N,N-dimethylacetamide, and the mixture was stirred in an ice-water bath for 3-6 hours. After the reaction, the solution was centrifuged in a release machine at 7000 r / min for 30-60 minutes, the supernatant was collected, sodium bicarbonate was added, and stirring was continued for 30-60 minutes to obtain a mixture I; Step 2.2, dissolving toluene 2,5-diisocyanate in 50-100 mL of N,N-dimethylacetamide solution to obtain mixture II; Step 2.3, the mixture I obtained in step 2.1 is added dropwise to the mixture II obtained in step 2.2 for 30-60 minutes. After the addition is completed, the reaction is continued for 30-60 minutes. After the reaction is completed, 50-100 mL of anhydrous ether is added to precipitate a yellow precipitate. The precipitate is collected and washed three times with anhydrous ether, and dried at 30-45°C for 24 hours to obtain isocyanate surface-modified aramid.

6. The method for preparing a high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 5, characterized in that: In the 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.

7. The method for preparing a high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 6, characterized in that: The specific process of step 3 is: Step 3.1: Add NaOH to the nano-mica powder, then add 1000-1500 mL of deionized water, place in a nano-ball mill, use 20-30 μm zirconium oxide as the milling medium, mill at a speed of 300-500 rpm, and mill for 2-4 hours. After the milling is completed, collect the mixed solution of the nano-mica powder; Step 3.2, placing the mixed solution obtained in step 3.1 into a 7000Da dialysis bag and dialyzing it three times in 1000-1500mL deionized water, centrifuging the obtained solution to obtain wet mica powder; freeze-drying the wet nano-mica powder at -70°C for 7 days to obtain activated nano-mica powder; In step 3.3, toluene 2,5-diisocyanate was weighed and dissolved in 1000-1500 mL of dimethyl sulfoxide solution, and stirred at room temperature for 10-20 minutes. Then, the activated nano-mica powder in step 3.2 was evenly divided into 5 batches and added to the dimethyl sulfoxide solution at intervals of 20-30 minutes.

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

9. The method for preparing a high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 7, characterized in that: 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 a toluene solution, and then azobisisobutyronitrile is added and stirred evenly. The mixture is reacted at a temperature of 60-70° C. to obtain a viscous multi-branched alcohol resin. The mass ratio of methyl acrylate:butyl methyl acrylate:styrene:hydroxyethyl acrylate:azobisisobutyronitrile is 1:1:1:1-3:0.02-0.

03.

10. The method for preparing a high-temperature resistant insulating material of multi-branched aramid fiber bonded mica according to claim 9, 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°C and 60-80r / min for 20-40 minutes. Pour the obtained mixture into a polytetrafluoroethylene mold, wait until the temperature rises to room temperature, and then put the mold into an oven and bake it at 80-100°C for 5-10 hours to obtain a multi-branched aramid fiber bonded mica insulation material; wherein 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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