A high-temperature resistant PBO nanofiber paper insulating material and its preparation method

Abstract

The present invention provides a high-temperature resistant PBO nanofiber paper insulating material and a preparation method thereof. In the method, PBO short-cut fibers are added to methanesulfonic acid and trifluoroacetic acid, and then sealed and stirred for 1 to 3 days to obtain a PBO nanofiber solution; under a stirring state, a deprotonating agent is added to the PBO nanofiber solution for an electro-neutralization reaction for 3.5 to 4.5 h to obtain a suspension. After the suspension is ultrasonically treated, it is successively filtered and washed to obtain neutral PBO nanofibers; the neutral PBO nanofibers are dispersed in deionized water, magnetically stirred and then vacuum filtered to obtain a wet paper web. The wet paper web is successively dried and hot-pressed to obtain the high-temperature resistant PBO nanofiber paper insulating material. The PBO nanofiber paper insulating material of the present invention is lightweight, flame-retardant and heat-resistant, overcomes the problems of long preparation period and complex preparation process of PBO nanofiber paper materials or aerogel materials, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the fields of polymer nanofibers and papermaking, and particularly relates to a high-temperature resistant PBO nanofiber paper insulating material and a preparation method thereof. Background Art

[0002] Zylon fiber is the trade name of a fiber with the chemical name poly(p-phenylene benzobisoxazole) (PBO). The molecular structure of PBO fiber consists of alternating benzene rings and oxazole rings. Due to the strong rigidity of the molecular chain structure, its mechanical properties and heat resistance are the best among organic fibers. Its tensile strength and modulus are almost twice that of aramid fibers, its heat resistance is 100 °C higher than that of para-aramid fibers, and its limiting oxygen index is as high as 68. Due to its excellent comprehensive properties, Zylon fiber is known as the super fiber of the 21st century. Therefore, PBO fiber can replace other high-performance materials such as aramid fiber to meet the applications of advanced insulation, structural weight reduction, and composite reinforcement materials in special environments. In particular, special paper made of PBO fiber can exhibit excellent performance in the field of electrical insulation.

[0003] However, the surface inertness of PBO fiber makes it difficult to be compounded with other materials, and even the interfacial properties of the composite material are poor, which greatly limits the application range of PBO fiber. In addition, PBO fiber itself does not have hydrophilic characteristics and is difficult to be uniformly dispersed in an aqueous system, resulting in great challenges in the preparation of PBO fiber paper-based materials by traditional wet papermaking processes. Therefore, in order to enable PBO fiber to have a broader application prospect and exert its excellent performance, it is necessary to modify PBO fiber itself or develop PBO nanofibers (ZNFs) to achieve functionalization at the nanoscale.

[0004] The Chinese invention patent with the application number 201610867366.8 discloses a high-strength heat-insulating and fireproof aerogel of polybenzoxazole nanofibers and its preparation method. Among them, ZNFs are prepared by the currently commonly used protonation method, that is, PBO fibers are treated with a mixed acid solvent of methanesulfonic acid (MSA) and trifluoroacetic acid (TFA). Therefore, the protonation method is also called the mixed acid treatment method. The mixed acid treatment preparation method of poly(p-phenylene benzoxazole) nanofibers is also disclosed in a previously published paper (Nano letters, 2016, 16, 2981). Although this method is simple and easy to operate, the PBO fibers peeled to the nanoscale are mixed with the methanesulfonic acid and trifluoroacetic acid system, and it is difficult to distinguish the dissolution or separation state of the fibers in the mixed acid system, and it is not easy to separate the nanofibers from the strongly acidic solution. In addition, for the subsequent processing of ZNFs, such as preparing paper-based materials and aerogel materials, it often needs to be carried out in a solvent exchange manner, that is, the ZNFs acid solution is gelated, and then soaked in water or subjected to gradient solvent replacement multiple times until the pH reaches about 7 to obtain a hydrogel. Finally, the ZNFs paper-based materials and aerogel materials are prepared by hot pressing or freeze drying. This series of processes is often called the sol-gel-paper or sol-gel-film conversion method, but the whole process takes a lot of time, so it only stays at the laboratory preparation stage at present. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides a heat-resistant PBO nanopaper insulating material and its preparation method, which are light, flame-retardant, heat-resistant, electrically insulating, simple and feasible, overcome the problems of poor water dispersion effect of existing PBO fibers, difficulty in wet papermaking, and long preparation period and complex preparation process of PBO nanofiber (ZNFs) paper materials or aerogel materials, and have broad application prospects.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a heat-resistant PBO nanopaper insulating material, comprising the following preparation steps:

[0008] Step 1: Add PBO short-cut fibers to methanesulfonic acid and trifluoroacetic acid. The volume sum of methanesulfonic acid and trifluoroacetic acid and the mass ratio of PBO short-cut fibers is (67.34 - 1346.81) mL: 1 g. Then seal and stir for 1 - 3 days to obtain a PBO nanofiber solution;

[0009] Step 2: Under the stirring state, add the deprotonating reagent to the PBO nanofiber solution. The volume ratio of the deprotonating reagent to the PBO nanofiber solution is (1-3):(1-3). Conduct an electro-neutralization reaction between the deprotonating reagent and the PBO nanofibers for 3.5-4.5 h to obtain a suspension. After ultrasonic treatment of the suspension, perform suction filtration and washing in sequence to obtain neutral PBO nanofibers;

[0010] Step 3: Disperse the neutral PBO nanofibers into deionized water, conduct magnetic stirring and then perform negative pressure suction filtration to obtain a wet paper web. Dry and hot press the wet paper web in sequence to obtain a high-temperature resistant PBO nanofiber paper insulating material.

[0011] Preferably, the volume ratio between methanesulfonic acid and trifluoroacetic acid in Step 1 is 1:1.

[0012] Preferably, the stirring in Step 1 is carried out at a rotation speed of 1200-1500 r / min.

[0013] Preferably, the deprotonating reagent in Step 2 is deionized water, sodium sulfate solution, ethanol, isopropanol, ethyl acetate or formic acid, and the mass percentage of the sodium sulfate solution is 1%-30%.

[0014] Preferably, in Step 2, the deprotonating reagent is injected into the PBO nanofiber solution under magnetic stirring through a syringe.

[0015] Preferably, the ultrasonic treatment in Step 2 is carried out at a power of 500-800 W for 8-12 min.

[0016] Preferably, in Step 2, vacuum suction filtration is carried out using a Buchner funnel loaded with a polyvinylidene fluoride or polytetrafluoroethylene filter membrane, and then deionized water is added for washing to obtain neutral PBO nanofibers.

[0017] Preferably, in Step 3, the negative pressure suction filtration is carried out using a G4 primary filter, and a cellulose filter membrane is selected for the filter membrane to obtain a wet paper web.

[0018] Furthermore, in Step 3, the wet paper web is dried at 102-108 °C for 5-8 min and hot pressed at 5-13 MPa and 100-180 °C for 5 min-1 h to obtain a high-temperature resistant PBO nanofiber paper insulating material.

[0019] A high-temperature resistant PBO nanofiber paper insulating material is prepared by the preparation method of a high-temperature resistant PBO nanofiber paper insulating material described in any one of the above.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] The present invention provides a method for preparing a high-temperature resistant PBO nanofiber paper insulation material. Through in-situ deprotonation with a deprotonating reagent, the reconstruction of the PBO nanofiber structure is achieved. The obtained PBO nanofiber suspension has good dispersion effect and can be stably stored at room temperature, solving the problems that the surface of PBO short-cut fibers is smooth, hydrophobic, has strong inertness, few active groups, weak hydrophilicity, poor water dispersion effect, and is difficult to form paper by the wet papermaking process. In the present invention, under the action of high-speed shearing force, a deprotonating reagent is used to neutralize the hydrogen protons on the protonated nitrogen atoms and oxygen atoms in the molecular chain of PBO nanofibers after treatment with methanesulfonic acid and trifluoroacetic acid. Through high-speed shearing force, the in-situ directional precipitation of PBO nanofibers can be achieved. The obtained neutral PBO nanofiber suspension has good dispersion effect and can be stably stored at room temperature. Subsequently, the preparation of the high-temperature resistant PBO nanofiber paper insulation material can be easily realized through the vacuum-assisted filtration method and the drying and hot pressing process, which has good heat resistance and insulation properties and is expected to be applied in the fields of advanced electrical insulation, etc. Compared with another method for preparing ZNFs nanofiber paper by the sol-gel-paper conversion method, the preparation period of the present invention is greatly shortened, making the paper preparation more efficient and easier to achieve large-scale preparation.

[0022] The high-temperature resistant PBO nanofiber paper insulation material prepared by the present invention has excellent heat resistance, voltage resistance and mechanical strength. Compared with traditional PBO paper, the voltage resistance strength is increased by 2 to 3 times. In addition, the fiber slurry used for papermaking can produce a flexible thin sheet material with functions such as conductivity and heat conduction, which has a very broad application prospect in the field of electrical insulation. Brief Description of the Drawings

[0023] The accompanying drawings in the specification are used to provide a further understanding of the present invention and constitute a part of the present invention.

[0024] Figure 1 It is a scanning electron microscope image of the fracture cross-section of the high-temperature resistant PBO nanofiber paper insulation material obtained in Example 1 of the present invention.

[0025] Figure 2 It is a scanning electron microscope image of the fracture cross-section of the high-temperature resistant PBO nanofiber paper insulation material obtained in Example 2 of the present invention.

[0026] Figure 3 It is a scanning electron microscope image of the surface of the high-temperature resistant PBO nanofiber paper insulation material obtained in Example 2 of the present invention. Detailed Description of the Embodiments

[0027] The present invention will be described in detail below with reference to the embodiments. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0028] The following detailed descriptions are all descriptions of embodiments, aiming to provide further detailed explanations for the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs. The terms used in the present invention are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention.

[0029] A preparation method of a high-temperature resistant PBO nanofiber paper insulating material of the present invention first undergoes protonation, that is, treating PBO short fibers with a methane sulfonic acid and trifluoroacetic acid system to obtain PBO nanofibers (ZNFs). Secondly, a deprotonating agent is subjected to an electrical neutralization reaction with the protonated ZNFs through the action of high-speed shear force to precipitate the fibers. Finally, the fibers are washed, filtered, dried with a paper former, and hot-pressed into paper by vacuum-assisted filtration.

[0030] Specifically, it includes the following steps:

[0031] Step 1: Prepare a PBO nanofiber solution:

[0032] Mix PBO short fibers, methane sulfonic acid, and trifluoroacetic acid and seal them. The volume ratio between methane sulfonic acid and trifluoroacetic acid is 1:1. The ratio of PBO short fibers to the total of the above two mixed acids is 1 g:(67.34 - 1346.81) mL. At this time, the mass percentage of PBO short fibers is 1% - 0.05%. Stir and react at a rotation speed of 1200 - 1500 r / min for 1 - 3 d to obtain a PBO nanofiber (ZNFs) solution, and the solvent is the two mixed acids of methane sulfonic acid and trifluoroacetic acid;

[0033] Step 2: Inject a deprotonating agent (deionized water, sodium sulfate solution, ethanol, isopropanol, ethyl acetate, or formic acid, and the mass percentage of the sodium sulfate solution is 1% - 30%) into the ZNFs solution under magnetic stirring through a syringe. The volume ratio of the deprotonating agent to the ZNFs solution is (1 - 3):(1 - 3). The deprotonating agent can perform an electrical neutralization reaction with the hydrogen protons on the protonated nitrogen and oxygen atoms on the ZNFs main chain for 3.5 - 4.5 h to extract the ZNFs from the mixed acid system (methane sulfonic acid and trifluoroacetic acid) to obtain a deprotonated fiber suspension A;

[0034] Step 3: Ultrasonically treat suspension A (with a power of 500 - 800 W and a time of 8 - 12 min), then pour it into a Buchner funnel for vacuum filtration (using a water - type circulating vacuum pump connected to a negative - pressure filtration flask, with a Buchner funnel installed in the negative - pressure filtration flask for filtration. The Buchner funnel is loaded with a filter membrane, and the filter membrane is selected from polyvinylidene fluoride (PVDF) filter membrane or polytetrafluoroethylene (PTFE) filter membrane, with a filter membrane pore size of 0.45 - 1 μm) to remove methanesulfonic acid, trifluoroacetic acid, and the deprotonating reagent. Subsequently, add deionized water for washing to obtain neutral PBO nanofibers;

[0035] Step 4: Redisperse the neutral fibers obtained in Step 3 into deionized water to obtain a fiber slurry. After magnetic stirring the fiber slurry, perform negative - pressure filtration using a G4 - grade primary filter with a diameter of 90 mm (selecting a cellulose filter membrane with a filter membrane pore size of 0.22 μm and a pressure of - 0.1 MPa to obtain a wet paper web), dry at 105 °C for 5 - 8 min using a paper former (lining the lower surface of the wet paper web with the same filter membrane), and hot - press at 5 - 13 MPa and 100 - 180 °C for 5 min - 1 h using a flat vulcanizer to obtain a high - temperature - resistant PBO nanopaper insulating material.

[0036] Example 1

[0037] A preparation method of a high - temperature - resistant PBO nanopaper insulating material, wherein the high - temperature - resistant PBO nanopaper insulating material is prepared from PBO short - cut fibers as raw materials. First, through a protonation method, that is, treating PBO short - cut fibers with a methanesulfonic acid and trifluoroacetic acid system to obtain PBO nanofibers (ZNFs). Secondly, the deprotonating reagent undergoes an electrical neutralization reaction with the protonated ZNFs through the action of high - speed shear force to precipitate the fibers. Finally, use the vacuum - assisted filtration method to wash, filter, dry with a paper former, and hot - press the fibers into paper. The specific steps are as follows:

[0038] Step 1: Prepare a PBO nanofiber solution:

[0039] Add 1 g of PBO short - cut fibers to a methanesulfonic acid and trifluoroacetic acid system with a volume ratio of 1:1, control the total volume to be 673.41 mL, and stir - react at a rotation speed of 1200 r / min for 2 d to obtain a PBO nanofiber (ZNFs) solution with a mass percentage of 0.1%;

[0040] Step 2: Inject deionized water into the ZNFs solution under magnetic stirring through a syringe for 4 h for electrical neutralization. The volume ratio of deionized water to the ZNFs solution is 1:1 to obtain a suspension;

[0041] Step 3: Ultrasonically treat the suspension at a power of 500 W for 10 min, then pour it into a Buchner funnel equipped with a polyvinylidene fluoride membrane with a pore size of 1 μm and a diameter of 100 mm for vacuum filtration to remove methanesulfonic acid, trifluoroacetic acid, and the deprotonating reagent. Subsequently, add deionized water for washing to obtain neutral fibers;

[0042] Step 4: Redisperse the neutral fibers obtained in Step 3 into 500 mL of water. After magnetic stirring, perform negative pressure filtration using a G4 - grade primary filter equipped with a cellulose membrane with a pore size of 0.22 μm and a diameter of 90 mm at a pressure of -0.1 MPa. After the filtration is completed, remove the filter membrane together with the wet paper web on the filter membrane. Pad the same filter membrane on the surface of the wet paper web and then dry it using a paper former at a drying temperature of 105 °C for 5 min. The hot - pressing process is carried out using a flat vulcanizing machine at a hot - pressing temperature of 120 °C, a hot - pressing time of 10 min, and a pressure of 10 MPa to finally obtain the high - temperature - resistant PBO nanofiber paper insulation material.

[0043] Example 2

[0044] A preparation method of a high - temperature - resistant PBO nanofiber paper insulation material, wherein the high - temperature - resistant PBO nanofiber paper insulation material is prepared from PBO short - cut fibers as raw materials. First, through a protonation method, that is, treating PBO short - cut fibers with a methanesulfonic acid and trifluoroacetic acid system to obtain PBO nanofibers (ZNFs). Secondly, the deprotonating reagent undergoes electrical neutralization with the protonated ZNFs through the action of high - speed shear force to precipitate the fibers. Finally, the fibers are washed, filtered, dried using a paper former, and hot - pressed into paper by a vacuum - assisted filtration method. The specific steps are as follows:

[0045] Step 1: Prepare a PBO nanofiber solution:

[0046] Add 1 g of PBO short - cut fibers to a methanesulfonic acid and trifluoroacetic acid system with a volume ratio of 1:1, control the total volume to be 673.41 mL, and stir and react at a rotation speed of 1500 r / min for 1 d to obtain a PBO nanofiber (ZNFs) solution with a mass percentage of 0.1%;

[0047] Step 2: Inject a 1% sodium sulfate solution into the ZNFs solution under magnetic stirring for 4 h through a syringe. The volume ratio of the 1% sodium sulfate solution to the ZNFs solution is 1:1 to obtain a suspension;

[0048] Step 3: Ultrasonically treat the suspension at a power of 800 W for 10 min, then pour it into a Buchner funnel equipped with a polyvinylidene fluoride membrane with a pore size of 1 μm and a diameter of 100 mm for vacuum filtration to remove methanesulfonic acid, trifluoroacetic acid, and the deprotonating reagent. Subsequently, add deionized water for washing to obtain neutral fibers;

[0049] Step 4: Redisperse the neutral fibers obtained in Step 3 into 500 mL of water. After magnetic stirring, perform negative pressure filtration using a G4 primary filter equipped with a cellulose membrane with a pore size of 0.22 μm and a diameter of 90 mm. The pressure is -0.1 MPa. After the filtration is completed, remove the filter membrane together with the wet paper web on the filter membrane. Pad the same filter membrane on the surface of the wet paper web and then dry it using a paper former. The drying temperature is 105 °C and the drying time is 5 min. The hot pressing process is carried out using a flat vulcanizing machine. The hot pressing temperature is 120 °C, the hot pressing time is 10 min, and the pressure is 10 MPa. Finally, a high-temperature resistant PBO nanofiber paper insulation material is obtained.

[0050] Example 3

[0051] A preparation method of a high-temperature resistant PBO nanofiber paper insulation material, wherein the high-temperature resistant PBO nanofiber paper insulation material is prepared from PBO short-cut fibers as raw materials. First, through a protonation method, that is, treating PBO short-cut fibers with a methane sulfonic acid and trifluoroacetic acid system to obtain PBO nanofibers (ZNFs). Secondly, a deprotonating reagent is subjected to electrical neutralization with the protonated ZNFs through the action of high-speed shear force to precipitate the fibers. Finally, the fibers are washed, filtered, dried using a paper former, and hot pressed into paper by a vacuum-assisted filtration method. The specific steps are as follows:

[0052] Step 1: Prepare a PBO nanofiber solution:

[0053] Add 1 g of PBO short-cut fibers to a methane sulfonic acid and trifluoroacetic acid system with a volume ratio of 1:1, control the total volume to be 673.41 mL, and stir and react at a rotation speed of 1500 r / min for 1 d to obtain a PBO nanofiber (ZNFs) solution with a mass percentage of 0.1%;

[0054] Step 2: Inject a 30% sodium sulfate solution into the ZNFs solution under magnetic stirring for 4 h for electrical neutralization. The volume ratio of the 30% sodium sulfate solution to the ZNFs solution is 1:3 to obtain a suspension;

[0055] Step 3: Ultrasonically treat the suspension at a power of 800 W for 10 min and then pour it into a Buchner funnel equipped with a polyvinylidene fluoride filter membrane with a pore size of 1 μm and a diameter of 100 mm for vacuum filtration to remove methane sulfonic acid, trifluoroacetic acid, and the deprotonating reagent. Then add deionized water for washing to obtain neutral fibers;

[0056] Step 4: Redisperse the neutral fibers obtained in Step 3 in 500 mL of water. After magnetic stirring, perform negative pressure filtration using a G4 primary filter equipped with a cellulose membrane with a pore size of 0.22 μm and a diameter of 90 mm. The pressure is -0.1 MPa. After the filtration is completed, remove the filter membrane together with the wet paper web on the filter membrane. Pad the same filter membrane on the surface of the wet paper web and then dry it using a paper former. The drying temperature is 105 °C and the drying time is 8 min. The hot pressing process is carried out using a flat vulcanizing machine. The hot pressing temperature is 180 °C, the hot pressing time is 5 min, and the pressure is 13 MPa. Finally, a high-temperature resistant PBO nanofiber paper insulation material is obtained.

[0057] Example 4

[0058] A preparation method of a high-temperature resistant PBO nanofiber paper insulation material, wherein the high-temperature resistant PBO nanofiber paper insulation material is prepared from PBO short-cut fibers as raw materials. First, through a protonation method, that is, treating PBO short-cut fibers with a methanesulfonic acid and trifluoroacetic acid system to obtain PBO nanofibers (ZNFs). Secondly, a deprotonating reagent is subjected to electrical neutralization with the protonated ZNFs through the action of high-speed shear force to precipitate the fibers. Finally, the fibers are washed, filtered, dried using a paper former, and hot pressed into paper by a vacuum-assisted filtration method. The specific steps are as follows:

[0059] Step 1: Prepare a PBO nanofiber solution:

[0060] Add 1 g of PBO short-cut fibers to a methanesulfonic acid and trifluoroacetic acid system with a volume ratio of 1:1, control the total volume to be 673.41 mL, and stir and react at a rotation speed of 1500 r / min for 1 day to obtain a PBO nanofiber (ZNFs) solution with a mass percentage of 0.1%.

[0061] Step 2: Inject ethanol into the magnetically stirred ZNFs solution through a syringe for 4 h for electrical neutralization. The volume ratio of ethanol to the ZNFs solution is 2:1 to obtain a suspension.

[0062] Step 3: Ultrasonically treat the suspension at a power of 800 W for 10 min and then pour it into a Buchner funnel equipped with a polyvinylidene fluoride filter membrane with a pore size of 1 μm and a diameter of 100 mm for vacuum filtration to remove methanesulfonic acid, trifluoroacetic acid, and the deprotonating reagent. Then add deionized water for washing to obtain neutral fibers.

[0063] Step 4: Redisperse the neutral fibers obtained in Step 3 in 500 mL of water. After magnetic stirring, perform negative pressure filtration using a G4 primary filter equipped with a cellulose membrane with a pore size of 0.22 μm and a diameter of 90 mm. The pressure is -0.1 MPa. After the filtration is completed, remove the filter membrane together with the wet paper web on the filter membrane. Pad the same filter membrane on the surface of the wet paper web and then dry it using a paper former. The drying temperature is 105 °C and the drying time is 8 min. The hot pressing process is carried out using a flat vulcanizing machine. The hot pressing temperature is 100 °C, the hot pressing time is 1 h, and the pressure is 10 MPa. Finally, a high-temperature resistant PBO nanofiber paper insulation material is obtained.

[0064] Example 5

[0065] A preparation method of a high-temperature resistant PBO nanofiber paper insulation material, wherein the high-temperature resistant PBO nanofiber paper insulation material is prepared from PBO short fibers as raw materials. First, through the protonation method, that is, treating PBO short fibers with a methane sulfonic acid and trifluoroacetic acid system to obtain PBO nanofibers (ZNFs). Secondly, the deprotonating reagent is subjected to electrical neutralization with the protonated ZNFs through the action of high-speed shear force to precipitate the fibers. Finally, the fibers are washed, filtered, dried using a paper former, and hot pressed into paper by the vacuum-assisted filtration method. The specific steps are as follows:

[0066] Step 1: Prepare a PBO nanofiber solution:

[0067] Add 1 g of PBO short fibers to a methane sulfonic acid and trifluoroacetic acid system with a volume ratio of 1:1, control the total volume to be 673.41 mL, and stir and react at a rotation speed of 1500 r / min for 1 day to obtain a PBO nanofiber (ZNFs) solution with a mass percentage of 0.1%.

[0068] Step 2: Inject ethyl acetate into the magnetically stirred ZNFs solution through a syringe for 4 h for electrical neutralization. The volume ratio of ethyl acetate to the ZNFs solution is 3:1 to obtain a suspension.

[0069] Step 3: Ultrasonically treat the suspension at a power of 800 W for 10 min and then pour it into a Buchner funnel equipped with a polyvinylidene fluoride filter membrane with a pore size of 1 μm and a diameter of 100 mm for vacuum filtration to remove methane sulfonic acid, trifluoroacetic acid, and the deprotonating reagent. Then add deionized water for washing to obtain neutral fibers.

[0070] Step 4: Redisperse the neutral fibers obtained in Step 3 into 500 mL of water. After magnetic stirring, perform negative pressure filtration using a G4 primary filter equipped with a cellulose membrane with a pore size of 0.22 μm and a diameter of 90 mm. The pressure is -0.1 MPa. After the filtration is completed, remove the filter membrane together with the wet paper web on the filter membrane. Pad the same filter membrane on the surface of the wet paper web and then dry it using a paper former. The drying temperature is 105 °C and the drying time is 5 min. The hot pressing process is carried out using a flat vulcanizing machine. The hot pressing temperature is 120 °C, the hot pressing time is 10 min, and the pressure is 10 MPa. Finally, a high-temperature resistant PBO nanofiber paper insulation material is obtained.

[0071] Example 6

[0072] A preparation method of a high-temperature resistant PBO nanofiber paper insulation material, wherein the high-temperature resistant PBO nanofiber paper insulation material is prepared from PBO short-cut fibers as raw materials. First, through a protonation method, that is, treating PBO short-cut fibers with a methane sulfonic acid and trifluoroacetic acid system to obtain PBO nanofibers (ZNFs). Secondly, a deprotonating reagent is subjected to electrical neutralization with the protonated ZNFs through the action of high-speed shear force to precipitate the fibers. Finally, the fibers are washed, filtered, dried using a paper former, and hot pressed into paper by a vacuum-assisted filtration method. The specific steps are as follows:

[0073] Step 1: Prepare a PBO nanofiber solution:

[0074] Add 1 g of PBO short-cut fibers to a methane sulfonic acid and trifluoroacetic acid system with a volume ratio of 1:1, control the total volume to be 673.41 mL, and stir and react at a rotation speed of 1500 r / min for 1 d to obtain a PBO nanofiber (ZNFs) solution with a mass percentage of 0.1%.

[0075] Step 2: Inject a 1% sodium sulfate solution into the ZNFs solution under magnetic stirring for 4 h of electrical neutralization. The volume ratio of the 1% sodium sulfate solution to the ZNFs solution is 1:1 to obtain a suspension.

[0076] Step 3: Ultrasonically treat the suspension at a power of 800 W for 10 min and then pour it into a Buchner funnel equipped with a polyvinylidene fluoride filter membrane with a pore size of 1 μm and a diameter of 100 mm for vacuum filtration to remove methane sulfonic acid, trifluoroacetic acid, and the deprotonating reagent. Subsequently, add deionized water for washing to obtain neutral fibers.

[0077] Step 4: Redisperse the neutral fibers obtained in Step 3 into 500 mL of water. After magnetic stirring, perform negative pressure filtration using a G4 primary filter equipped with a cellulose membrane with a pore size of 0.22 μm and a diameter of 90 mm. The pressure is -0.1 MPa. After the filtration is completed, remove the filter membrane together with the wet paper web on the filter membrane. Pad the same filter membrane on the surface of the wet paper web and then dry it using a paper former. The drying temperature is 105 °C and the drying time is 8 min. The hot pressing process is carried out using a flat vulcanizing machine. The hot pressing temperature is 180 °C, the hot pressing time is 1 h, and the pressure is 13 MPa. Finally, a high-temperature resistant PBO nanofiber paper insulating material is obtained.

[0078] The scanning electron microscope image of the fracture cross-section of the high-temperature resistant PBO nanofiber paper insulating material obtained in Example 1 of the present invention is as Figure 1 shown. It can be seen from the figure that the PBO fibers in the PBO nanofiber paper insulating material are relatively large in size after being pulled apart, with diameters ranging from several micrometers to dozens of micrometers, and the fibers are pulled out in bundles.

[0079] The scanning electron microscope image of the fracture cross-section of the high-temperature resistant PBO nanofiber paper insulating material obtained in Example 2 of the present invention is as Figure 2 shown. It can be seen from the figure that the fracture surface of the PBO nanofiber paper exhibits a certain layered structure, and some PBO fibers are pulled out.

[0080] The scanning electron microscope image of the surface of the high-temperature resistant PBO nanofiber paper insulating material obtained in Example 2 of the present invention is as Figure 3 shown. It can be seen from the figure that the fibers on the surface of the PBO nanofiber paper insulating material are intertwined very tightly and the pores are very small.

[0081] The high-temperature resistant PBO nanofiber paper insulating material prepared in Example 2 of the present invention was tested and characterized. Some of its indicators are as follows: paper thickness: 0.018 mm, tensile strength: 43.02 MPa, tensile modulus: 3.58 GPa, withstand voltage strength: 42 kV / mm, thermal decomposition temperature: 603 °C, and the flame retardant grade in the vertical burning test can reach V0 level.

[0082] The above-described embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The embodiments in this application and the features in the embodiments can be combined arbitrarily without conflict. The protection scope of the present invention should be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, the equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A preparation method of a high-temperature resistant PBO nanofiber paper insulating material, characterized in that, It includes the following preparation steps: Step 1: Add PBO chopped fibers into methanesulfonic acid and trifluoroacetic acid. The ratio of the sum of the volumes of methanesulfonic acid and trifluoroacetic acid to the mass of PBO chopped fibers is (67.34~1346.81) mL: 1 g, and the volume ratio between methanesulfonic acid and trifluoroacetic acid is 1:

1. Then seal and stir for 1~3 days to obtain a PBO nanofiber solution; Step 2: Under the stirring state, inject a deprotonating reagent into the PBO nanofiber solution under magnetic stirring through a syringe. The deprotonating reagent is deionized water, sodium sulfate solution, ethanol, isopropanol, ethyl acetate or formic acid. The mass percentage of the sodium sulfate solution is 1%~30%. The volume ratio of the deprotonating reagent to the PBO nanofiber solution is (1~3):(1~3). The deprotonating reagent and the PBO nanofibers carry out an electro-neutralization reaction for 3.5~4.5 h to obtain a suspension. After ultrasonic treatment of the suspension, filter it by suction and wash it successively. The ultrasonic treatment is carried out at a power of 500~800 W for 8~12 min to obtain neutral PBO nanofibers; Step 3: Disperse the neutral PBO nanofibers into deionized water, stir magnetically and then filter by negative pressure to obtain a wet paper web. Dry and hot-press the wet paper web successively to obtain a high-temperature resistant PBO nanofiber paper insulating material.

2. The preparation method of a high-temperature resistant PBO nanofiber paper insulating material according to claim 1, characterized in that, The stirring described in Step 1 is carried out at a rotation speed of 1200~1500 r / min.

3. The preparation method of a high-temperature resistant PBO nanofiber paper insulating material according to claim 1, characterized in that, In Step 2, vacuum filtration is carried out using a Buchner funnel equipped with a polyvinylidene fluoride or polytetrafluoroethylene filter membrane, and then deionized water is added for washing to obtain neutral PBO nanofibers.

4. The preparation method of a high-temperature resistant PBO nanofiber paper insulating material according to claim 1, characterized in that, The negative pressure filtration in Step 3 is carried out using a G4 grade primary filter, and a cellulose filter membrane is selected as the filter membrane to obtain a wet paper web.

5. The preparation method of a high-temperature resistant PBO nanofiber paper insulating material according to claim 4, characterized in that, In Step 3, the wet paper web is successively dried at 102~108°C for 5~8 min, and hot-pressed at 5~13 MPa and 100~180°C for 5 min~1 h to obtain a high-temperature resistant PBO nanofiber paper insulating material.

6. A high-temperature resistant PBO nanofiber paper insulating material, characterized in that, It is prepared by the preparation method of a high-temperature resistant PBO nanofiber paper insulating material according to any one of claims 1~5.

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