A high-performance aramid / PBO nano-insulating paper and its preparation method

Abstract

The present invention provides a high-performance aramid / PBO nano-insulating paper and a preparation method thereof. The method comprises the following steps: stirring PBO chopped fibers, methanesulfonic acid and trifluoroacetic acid in a closed manner at room temperature; stopping stirring when the obtained reaction solution becomes uniform and transparent to obtain a mixed solution; injecting a sodium sulfate solution into the mixed solution under stirring, and further stirring in a closed manner to obtain a dispersion; washing the dispersion solution with deionized water until neutral, and then ball milling the mixture; dispersing the obtained liquid in deionized water to obtain a ZNFs dispersion; uniformly dispersing the ZNFs dispersion solution and the aramid nanofiber dispersion solution to obtain a blended slurry; and vacuum filtering and vacuum drying the blended slurry in sequence to obtain the high-performance aramid / PBO nano-insulating paper. The method solves the problems of difficulty in achieving water dispersion of ZNFs, low paper strength, poor temperature resistance and limited corona resistance of ANFs nano-insulating paper, and fills the gap in the application of PBO fiber paper-based materials in the insulation field.

Description

Technical Field

[0001] The invention belongs to the field of polymer nanofiber insulation materials and papermaking, and particularly relates to high-performance aramid / PBO nano insulation paper and a preparation method thereof. Background Art

[0002] Commercialized aramid insulation paper is primarily made from aramid chopped fibers, aramid fibrids, or aramid pulp fibers through a wet papermaking process followed by drying. For example, in 1960, DuPont developed insulation paper using meta-aramid chopped fibers and fibrids, and achieved industrial production of Nomex insulation paper in 1967. However, aramid fibers are composed of rigid molecular chains with a smooth surface, resulting in significant interface issues. This results in low strength and susceptibility to electrical breakdown in the finished aramid paper. These issues significantly impact the application value of aramid paper in the insulation field.

[0003] With the continuous development of nanotechnology, technicians are using aramid nanofibers to enhance the insulation properties of aramid paper. Aramid nanofibers (ANFs) are derived from para-aramid fibers (PPTA), which have high strength, high modulus, and excellent heat resistance. They have a large aspect ratio and high specific surface area. They not only retain the excellent properties of aramid fibers themselves, but also bring nanoscale effects to derivative materials that cannot be achieved with macroscopic aramid fibers. Therefore, aramid nanofibers have become an ideal material for the development of nanofiber insulation paper. Insulation paper made of aramid nanofiber reinforced aramid fibers can achieve an insulation grade of H (can be used for a long time at 180°C).

[0004] However, with the rapid development of science and technology, electronic equipment is constantly shifting towards miniaturization, integration, and large capacity. The insulation system in electronic equipment is the most critical component, and high-performance insulation materials are also a key factor restricting the development of high-voltage, large-capacity transformers. Therefore, in many fields, higher requirements are placed on the insulation performance of insulation paper. Insulation paper made of aramid fiber and aramid nanofiber can no longer fully meet the application of large-capacity high-voltage motor equipment, especially under extreme conditions such as high temperature and high humidity. Therefore, it is of great significance to develop nano-paper-based insulation materials with higher performance and realize the transformation and upgrading of high-performance insulation materials.

[0005] Existing paper-based insulation materials, such as aramid paper, are primarily made by combining aramid fibrils, aramid chopped fibers, and aramid pulp fibers. However, aramid paper produced using this technology exhibits poor corona resistance and heat resistance, and cannot withstand long-term use in harsh environments such as high heat, high humidity, and strong corona. While some literature reports that the addition of mica can significantly improve the corona resistance of aramid paper, increasing the mica content significantly reduces the mechanical strength of the aramid mica paper, causing it to shed powder on the surface and become less resistant to bending, impacting its practical performance. Summary of the Invention

[0006] In response to the problems existing in the prior art, the present invention provides a high-performance aramid / PBO nano-insulating paper and a preparation method thereof, which solves the current problems of ZNFs being difficult to disperse in water, ANFs nano-insulating paper having low paper strength, poor temperature resistance, and limited corona resistance, thus filling the technical gap in the application of PBO fiber paper-based materials in the insulation field.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing high-performance aramid / PBO nano insulating paper comprises the following steps:

[0009] S1, PBO chopped fibers, methanesulfonic acid, and trifluoroacetic acid are stirred in a closed container at room temperature. Stirring is stopped when the resulting reaction solution becomes homogeneous and transparent to obtain a mixed solution. Then, sodium sulfate solution is injected into the mixed solution using a high-pressure jet pump while stirring at 1000-3000 rpm, and the mixture is stirred in a closed container for 2-6 hours to obtain a dispersion.

[0010] S2, washing the dispersion with deionized water until neutral, then ball milling, and dispersing the resulting liquid in deionized water to obtain a ZNFs dispersion with a concentration of 0.06-0.54 mg / mL;

[0011] S3, the ZNFs dispersion described in S2 and the aramid nanofiber dispersion with a concentration of 0.06-0.9 mg / mL are evenly dispersed in a mass ratio of (10-90):(10-90) to obtain a blended slurry, and the blended slurry is vacuum filtered and vacuum dried in sequence to obtain high-performance aramid / PBO nano insulating paper.

[0012] Preferably, the mass ratio of PBO chopped fibers, methanesulfonic acid and trifluoroacetic acid in S1 is 1:500:500.

[0013] Preferably, the mass percentage of the sodium sulfate solution in S1 is 1% to 30%, and the mass ratio of the sodium sulfate solution to the mixed solution is (1 to 3):1.

[0014] Preferably, the jet pressure of the high-pressure jet pump in S1 is 5-10 MPa, and the jet velocity is 0.2-1.0 mL / s.

[0015] Preferably, the washing process in S2 is performed by vacuum filtration using a G4 grade primary filter, and the filter membrane is made of polyvinylidene fluoride or polytetrafluoroethylene.

[0016] Furthermore, the pore size of the filter membrane is 0.45 to 1 μm.

[0017] Preferably, the ball milling process in S2 is carried out using a ball mill with a rotation speed of 1300-1500 rpm, wherein 8-12 alumina wear-resistant balls with a diameter of 10 mm and 8-12 alumina wear-resistant balls with a diameter of 6 mm are used.

[0018] Preferably, the aramid nanofiber dispersion described in S3 is obtained by the following process:

[0019] Para-aramid fiber, potassium hydroxide and dimethyl sulfoxide were placed in a sealed container at a ratio of 1 g:1.5 g:500 mL, stirred and reacted at 20-50 ° C for 5-8 days to obtain a reaction solution. Subsequently, deionized water with a volume twice that of the reaction solution was injected for protonation reduction reaction for 25-35 minutes. The residual dimethyl sulfoxide was removed, and deionized water was added to obtain an aramid nanofiber dispersion with a concentration of 0.06-0.9 mg / mL.

[0020] Preferably, the vacuum filtration in S3 uses a cellulose membrane with a diameter of 0.22 μm, and the vacuum drying uses a paper sheet former, with a drying temperature of 100 to 110° C. and a drying time of 6 to 10 minutes.

[0021] A high-performance aramid / PBO nano-insulating paper obtained by any one of the above methods for preparing high-performance aramid / PBO nano-insulating paper.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] The present invention provides a preparation method of high-performance aramid / PBO nano-insulating paper. The method uses methanesulfonic acid and trifluoroacetic acid to prepare water-dispersed PBO nanofibers, which solves the problems that the current PBO nanofibers can only be evenly dispersed in a strong acid system (MSA / TFA), cannot be evenly and stably dispersed in an aqueous phase system, are easily hygroscopic in the air, and cannot be stored for a long time. The aramid nanofiber dispersion liquid is blended with the PBO nanofiber dispersion liquid to form a system (ANFs / ZNFs / H2O composite system) that is uniform and stable, has an adjustable and controllable concentration, and is easy to store and transport. This expands the production methods of insulating paper and realizes two methods. The uniform dispersion and organic bonding of high-performance organic fibers in an aqueous system. PBO nanofibers, which have higher strength and temperature resistance than aramid nanofibers, act as a skeleton in paper, giving it greater tensile strength. Aramid nanofibers, on the other hand, have amide groups that facilitate the bonding of the two fibers. Furthermore, aramid nanofibers are smaller in size, acting as a filler. The resulting nanopaper also exhibits higher light transmittance, excellent mechanical strength, heat resistance, and electrical insulation properties, achieving a synergistic enhancement effect and avoiding the complex, high water consumption, and long processing time associated with preparing PBO nanopaper using a water-solvent exchange method. Existing literature indicates that PBO insulating paper can only be prepared using a time-consuming sol-gel method, requiring approximately seven days. The present invention achieves the preparation of PBO nanofibers (ZNFs) and the organic bonding of PBO nanofibers with aramid nanofibers, resulting in a simple preparation process with a short cycle time, making it suitable for large-scale industrial production.

[0024] The high-performance aramid / PBO nano-insulating paper prepared by the present invention has the advantages of tight fiber interweaving, good paper uniformity, flame retardancy, and excellent mechanical strength and compressive strength. It can more efficiently give play to the advantages of aramid nanofibers and PBO nanofibers, and can be widely used as a high-performance fiber paper-based insulation material in high-end electrical insulation fields, such as traction motors, transformers, and flexible electronic devices. It has important practical significance for promoting the development of high-performance fiber composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the mechanism of the protonation process and deprotonation reduction process of ZNFs in the present invention;

[0026] Figure 2 This is a photo of the high-performance aramid / PBO nano insulation paper obtained in Example 3 of the present invention;

[0027] Figure 3a This is a surface SEM image of the high-performance aramid / PBO nano-insulating paper obtained in Example 1 of the present invention;

[0028] Figure 3b for Figure 3aA partial enlarged view of the dotted ellipse;

[0029] Figure 4 This is a cross-sectional SEM image of the high-performance aramid / PBO nano-insulating paper obtained in Example 1 of the present invention;

[0030] Figure 5 This is a physical picture of the high-performance aramid / PBO nanofiber aqueous dispersion;

[0031] Figure 6 This is the stress-strain curve of high-performance aramid / PBO nano insulation paper;

[0032] Figure 7 This is a physical picture of the flame retardant effect of high-performance aramid / PBO nano insulation paper. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0034] Poly(p-phenylene benzobisoxazole) (PBO) fiber is a new type of composite material developed by the U.S. Air Force Materials Laboratory in the 1970s. Its tensile strength and tensile modulus are almost twice that of aramid, and its heat resistance is 100°C higher than that of para-aramid. Its limiting oxygen index (LOI) is as high as 68, which is more than 30 higher than that of aramid. Therefore, PBO fiber has broader potential application value in the insulation field. PBO fiber is an organic high-performance fiber with a similar structure to aramid fiber. Therefore, the addition of PBO fiber can not only improve the mechanical strength of aramid paper, but also improve the electrical insulation performance of aramid paper. PBO nanofibers and aramid nanofibers can both retain the properties of the original fibers while also exhibiting nanoscale effects. The prepared aramid / PBO nano-insulating paper is denser and has better performance. Therefore, PBO nanofibers can be organically combined with aramid nanofibers.

[0035] The present invention provides a method for preparing high-performance aramid / PBO nano insulating paper, comprising the following steps:

[0036] (1) Preparation of aramid nanofibers (ANFs):

[0037] Para-aramid fiber, potassium hydroxide (KOH), and dimethyl sulfoxide (DMSO) were placed in a sealed container at a ratio of 1g:1.5g:500mL and stirred at 20-50°C for 5-8 days. After the reaction, an aramid nanofiber dispersion dispersed in the KOH / DMSO system was obtained. Subsequently, deionized water twice the volume of the aramid nanofiber dispersion was injected for protonation reduction reaction for 25-35min, and 500mL of deionized water and 500mL of anhydrous ethanol (corresponding to a volume of 500mL of dimethyl sulfoxide) were alternately washed 3-6 times to remove the residual dimethyl sulfoxide in the system. A 200-500 mesh nylon filter was used for washing during the washing process. Deionized water was added to control the concentration of water-dispersed ANFs to 0.06-0.9mg / mL, thereby obtaining aramid nanofibers dispersed in the water system.

[0038] (2) Preparation of PBO nanofibers (ZNFs):

[0039] PBO short fibers with an average length of 6 mm are placed in a sealed container with methanesulfonic acid (MSA) and trifluoroacetic acid (TFA). The mass ratio of methanesulfonic acid to trifluoroacetic acid is 1:1, and the mass ratio of methanesulfonic acid to PBO short fibers is 500:1. Stirring at room temperature, after the PBO short fibers are treated with methanesulfonic acid (MSA) and trifluoroacetic acid (TFA), the fibers will dissolve in the system of these two acids. This process is accompanied by strong protonation, with the separation of the fiber cortex and the continuous reduction of the fiber size, and gradually peeling to the nanometer scale. Figure 1 As shown, the effect of methanesulfonic acid and trifluoroacetic acid on the fibers imparts positive charges to the nitrogen and oxygen atoms in the fiber chains. Because these chains are all positively charged, like charges repel each other, ultimately forming a stable PBO nanofiber / methanesulfonic acid / trifluoroacetic acid system. The fibers also maintain a well-defined nanoscale state. After 12 hours, the reaction system becomes a homogeneous, transparent, dark yellow solution, signaling the termination of the reaction. This yields a ZNF solution with a mass percentage of 0.2%. The ZNFs have been reduced in diameter from their original micrometer size (15 microns) to nanometer size (2-10 nm), with an average length of 5 μm.

[0040] (3) Deprotonation reduction of ZNFs:

[0041] Under strong stirring at 1000-3000 rpm, a sodium sulfate solution with a mass percentage of 1%-30% is injected into the ZNFs solution obtained in step (2) using a stainless steel high-pressure jet pump. The mass ratio of sodium sulfate solution to ZNFs solution is (1-3):1, the jet pressure is 5-10 MPa, and the jet speed is 0.2-1.0 mL / s. After the injection is completed, the container is sealed again and stirring is continued for 2-6 hours. At this time, the deprotonation reduction process is completed to obtain a ZNFs dispersion.

[0042] Figure 1 In the equation, Attraction refers to the mutual attraction between positively charged hydrogen ions and negatively charged (sulfate and hydroxide). In step (2), the preparation process of PBO nanofibers is mentioned. Since the final PBO nanofibers exist in the PBO nanofiber / methanesulfonic acid / trifluoroacetic acid system, that is, the PBO nanofibers are stably dispersed in two mixed acid systems, the mixed system is not electrically neutral, and the surface of the PBO nanofibers is still enriched with a lot of positive charges, which changes the molecular chain structure. In addition, the solution cannot be used directly, so the system needs to be treated to make the PBO nanofibers neutral so that it can be convenient for the subsequent preparation and use of paper. Therefore, sodium sulfate solution is used to act on the system. The sulfate ions and hydroxide ions in the sodium sulfate solution will combine with the hydrogen ions on the fiber surface, neutralizing the charge at the same time. Finally, the structure of the PBO nanofibers will be restored again. This process is called a deprotonation reduction process.

[0043] (4) Dispersion of water-dispersed ZNFs:

[0044] The ZNFs dispersion obtained in step (3) is washed with deionized water until it is neutral. The key point of this process is to remove the acid with deionized water. Whether it is neutral is tested with pH test paper. Specifically, if the methanesulfonic acid is 500g, 3L of deionized water is required. The washing process is carried out by vacuum filtration using a G4 grade primary filter. The filter membrane uses a polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.45 to 1μm and a filter membrane diameter of 90mm. The obtained dispersion is then transferred to a ball mill for treatment. The container during the treatment process uses a nylon tank, the rotation speed is 1400rpm, and the grinding balls use 10 alumina wear-resistant balls with a diameter of 10mm and 6mm, respectively. After treatment, it is dispersed in deionized water and the concentration is controlled to be 0.06 to 0.54mg / mL to obtain a water-dispersed ZNFs dispersion.

[0045] (5) Preparation of high-performance aramid / PBO nano-insulating paper:

[0046] The aramid nanofiber dispersion obtained in step (1) and the water-dispersed ZNFs dispersion obtained in step (4) are uniformly dispersed in a mass ratio of (10-90):(10-90) to obtain a blended slurry, and the total weight can be controlled to be 0.24-0.4 g. Then, vacuum filtration is performed to form a wet paper web, and the filter membrane uses a cellulose membrane with a diameter of 0.22 μm. Then, a paper sheet former is used for further vacuum drying, the drying time is 8 minutes, and the drying temperature is 105°C to obtain high-performance aramid / PBO nano insulating paper.

[0047] The basis weight of the high performance aramid / PBO nano insulation paper is 30-60 g / m2 , thermal decomposition temperature is 540~610℃, compressive strength is 40~80kV / mm, and fracture strength is 45~180MPa.

[0048] The present invention is described in further detail below in conjunction with the embodiments:

[0049] Example 1

[0050] The present embodiment provides a high-performance aramid / PBO nano insulating paper and a preparation method thereof, and the specific preparation steps are as follows:

[0051] 1.0 g of para-aramid chopped fiber, 1.5 g of potassium hydroxide (KOH) and 500 mL of dimethyl sulfoxide (DMSO) were placed in a container and stirred at 20°C for 8 days under sealed conditions to obtain an aramid nanofiber dispersion dispersed in the KOH / DMSO system; then 108 mL of the above aramid nanofiber dispersion was injected into 216 mL of deionized water for protonation reduction reaction for 30 minutes; 500 mL of deionized water and 500 mL of anhydrous ethanol were used to wash alternately 3 times to remove the dimethyl sulfoxide remaining in the system, and deionized water was added to 400 mL to obtain aramid nanofibers with a concentration of 0.54 mg / mL dispersed in the water system.

[0052] 1g of PBO chopped fibers was added to 500g of methanesulfonic acid (MSA) and 500g of trifluoroacetic acid (TFA) solvent and placed in a closed environment and stirred at room temperature. During this process, the PBO chopped fibers were strongly protonated by methanesulfonic acid and trifluoroacetic acid, and their size continued to decrease, gradually exfoliating to the nanoscale. After 12 hours, the reaction system became a uniform, transparent, dark yellow solution. The reaction was stopped to obtain a ZNFs solution with a mass percentage of 0.2%, a diameter of 2 to 10nm, and an average fiber length of 5μm.

[0053] A 1% by mass sodium sulfate solution was injected into the ZNFs solution at a stirring rate of 1000 rpm, a jet pressure of 5 MPa, and a jet velocity of 0.2 mL / s. The mass ratio of sodium sulfate solution to ZNFs solution was 1:1. After the injection, the container was resealed and stirred for 2 h. At this time, the deprotonation reduction process was completed, and a ZNFs dispersion was obtained.

[0054] The ZNFs dispersion was washed with deionized water until neutral. The washing process was carried out by vacuum filtration using a G4 grade primary filter. The filter membrane used was polyvinylidene fluoride (PVDF) with a pore size of 0.45 μm and a filter membrane diameter of 90 mm. The resulting dispersion was then transferred to a ball mill for treatment. The holding container during the treatment process was a nylon tank, the rotation speed was 1400 rpm, and the grinding balls used were 10 alumina wear-resistant balls with a diameter of 10 mm and 6 mm, 10 each. After treatment, the dispersion was dispersed in deionized water to obtain a water-dispersed ZNFs dispersion with a concentration of 0.06 mg / mL.

[0055] The water-dispersed aramid nanofiber dispersion and the water-dispersed ZNFs dispersion obtained in step (4) were evenly dispersed in a mass ratio of 90:10 to obtain a blended slurry, which was then vacuum filtered to form a wet paper web. The filter membrane used a cellulose membrane with a diameter of 0.22 μm, and then further vacuum dried using a paper sheet former. The drying time was 8 minutes and the drying temperature was 105°C to obtain high-performance aramid / PBO nano insulating paper, which was recorded as A / Z-10NP1.

[0056] Example 2

[0057] The present embodiment provides a high-performance aramid / PBO nano insulating paper and a preparation method thereof, and the specific preparation steps are as follows:

[0058] 1.0 g of para-aramid chopped fiber, 1.5 g of potassium hydroxide (KOH) and 500 mL of dimethyl sulfoxide (DMSO) were placed in a container and stirred at 50°C for 5 days under sealed conditions to obtain an aramid nanofiber dispersion dispersed in the KOH / DMSO system; then 84 mL of the above aramid nanofiber dispersion was injected into 168 mL of deionized water for protonation reduction reaction for 30 minutes; 500 mL of deionized water and 500 mL of anhydrous ethanol were used to wash alternately 6 times to remove the dimethyl sulfoxide remaining in the system, and deionized water was added to 400 mL to obtain aramid nanofibers with a concentration of 0.42 mg / mL dispersed in the water system.

[0059] 1g of PBO chopped fibers was added to 500g of methanesulfonic acid (MSA) and 500g of trifluoroacetic acid (TFA) solvent and placed in a sealed environment and stirred at room temperature. During this process, the PBO chopped fibers were strongly protonated by methanesulfonic acid and trifluoroacetic acid, and their size continued to decrease, gradually exfoliating to the nanoscale. After 12 hours, the reaction system became a uniform, transparent, dark yellow solution, indicating that the reaction was stopped to obtain a ZNFs solution with a mass percentage of 0.2%, a diameter of 2 to 10nm, and an average fiber length of 5μm.

[0060] A 15% by mass sodium sulfate solution was injected into the ZNFs solution at a stirring rate of 3000 rpm, a jet pressure of 10 MPa, and a jet velocity of 0.6 mL / s. The mass ratio of sodium sulfate solution to ZNFs solution was 3:1. After the injection, the container was resealed and stirred for 6 h. At this time, the deprotonation reduction process was completed, and a ZNFs dispersion was obtained.

[0061] The ZNFs dispersion was washed with deionized water until neutral. The washing process was carried out by vacuum filtration using a G4 grade primary filter. The filter membrane used was polytetrafluoroethylene (PTFE) with a pore size of 0.45 μm and a filter membrane diameter of 90 mm. The resulting dispersion was then transferred to a ball mill for treatment. The holding container during the treatment process was a nylon tank, the rotation speed was 1400 rpm, and the grinding balls used were 10 alumina wear-resistant balls with a diameter of 10 mm and 6 mm, 10 each. After treatment, the dispersion was dispersed in deionized water to obtain a water-dispersed ZNFs dispersion with a concentration of 0.18 mg / mL.

[0062] The water-dispersed aramid nanofiber dispersion and the water-dispersed ZNFs dispersion obtained in step (4) were evenly dispersed in a mass ratio of 70:30 to obtain a blended slurry, which was then vacuum filtered to form a wet paper web. The filter membrane used a cellulose membrane with a diameter of 0.22 μm, and then further vacuum dried using a paper sheet former. The drying time was 8 minutes and the drying temperature was 105°C to obtain high-performance aramid / PBO nano insulating paper, which was recorded as A / Z-30NP.

[0063] Example 3

[0064] The present embodiment provides a high-performance aramid / PBO nano insulating paper and a preparation method thereof, and the specific preparation steps are as follows:

[0065] 1.0 g of para-aramid chopped fiber, 1.5 g of potassium hydroxide (KOH) and 500 mL of dimethyl sulfoxide (DMSO) were placed in a container and stirred at 30°C for 7 days under sealed conditions to obtain an aramid nanofiber dispersion dispersed in the KOH / DMSO system; then 60 mL of the above aramid nanofiber dispersion was injected into 120 mL of deionized water for protonation reduction reaction for 30 minutes; 500 mL of deionized water and 500 mL of anhydrous ethanol were used to wash alternately 4 times to remove the dimethyl sulfoxide remaining in the system, and deionized water was added to 400 mL to obtain aramid nanofibers with a concentration of 0.3 mg / mL dispersed in the water system.

[0066] 1g of PBO chopped fibers was added to 500g of methanesulfonic acid (MSA) and 500g of trifluoroacetic acid (TFA) solvent and placed in a sealed environment and stirred at room temperature. During this process, the PBO chopped fibers were strongly protonated by methanesulfonic acid and trifluoroacetic acid, and their size continued to decrease, gradually exfoliating to the nanoscale. After 12 hours, the reaction system became a uniform, transparent, dark yellow solution, indicating that the reaction was stopped to obtain a ZNFs solution with a mass percentage of 0.2%, a diameter of 2 to 10nm, and an average fiber length of 5μm.

[0067] A 1% by mass sodium sulfate solution was injected into the ZNFs solution at a stirring rate of 3000 rpm, a jet pressure of 5 MPa, and a jet velocity of 1.0 mL / s. The mass ratio of sodium sulfate solution to ZNFs solution was 1:1. After the injection, the container was resealed and stirred for 4 h. At this time, the deprotonation reduction process was completed, and a ZNFs dispersion was obtained.

[0068] The ZNFs dispersion was washed with deionized water until neutral. The washing process was carried out by vacuum filtration using a G4 grade primary filter. The filter membrane used was polytetrafluoroethylene (PTFE) with a pore size of 0.45 μm and a filter membrane diameter of 90 mm. The resulting dispersion was then transferred to a ball mill for treatment. The holding container during the treatment process was a nylon tank, the rotation speed was 1400 rpm, and the grinding balls used were 10 alumina wear-resistant balls with a diameter of 10 mm and 6 mm, 10 each. After treatment, the dispersion was dispersed in deionized water to obtain a water-dispersed ZNFs dispersion with a concentration of 0.3 mg / mL.

[0069] The water-dispersed aramid nanofiber dispersion and the water-dispersed ZNFs dispersion obtained in step (4) were evenly dispersed in a mass ratio of 50:50 to obtain a blended slurry, which was then vacuum filtered to form a wet paper web. The filter membrane used a cellulose membrane with a diameter of 0.22 μm, and then further vacuum dried using a paper sheet former. The drying time was 8 minutes and the drying temperature was 105°C to obtain high-performance aramid / PBO nano insulating paper, which was recorded as A / Z-50NP.

[0070] Example 4

[0071] The present embodiment provides a high-performance aramid / PBO nano insulating paper and a preparation method thereof, and the specific preparation steps are as follows:

[0072] 1.0 g of para-aramid chopped fiber, 1.5 g of potassium hydroxide (KOH) and 500 mL of dimethyl sulfoxide (DMSO) were placed in a container and stirred at 20°C for 8 days under sealed conditions to obtain an aramid nanofiber dispersion dispersed in the KOH / DMSO system; then 12 mL of the above aramid nanofiber dispersion was injected into 24 mL of deionized water for protonation reduction reaction for 30 minutes; 500 mL of deionized water and 500 mL of anhydrous ethanol were used to wash alternately 3 times to remove the dimethyl sulfoxide remaining in the system, and deionized water was added to 400 mL to obtain aramid nanofibers with a concentration of 0.06 mg / mL dispersed in the water system.

[0073] 1g of PBO chopped fibers was added to 500g of methanesulfonic acid (MSA) and 500g of trifluoroacetic acid (TFA) solvent and placed in a sealed environment and stirred at room temperature. During this process, the PBO chopped fibers were strongly protonated by methanesulfonic acid and trifluoroacetic acid, and their size continued to decrease, gradually exfoliating to the nanoscale. After 12 hours, the reaction system became a uniform, transparent, dark yellow solution, indicating that the reaction was stopped to obtain a ZNFs solution with a mass percentage of 0.2%, a diameter of 2 to 10nm, and an average fiber length of 5μm.

[0074] A 15% by mass sodium sulfate solution was injected into the ZNFs solution at a stirring rate of 1000 rpm, a jet pressure of 5 MPa, and a jet velocity of 0.2 mL / s. The mass ratio of sodium sulfate solution to ZNFs solution was 2:1. After the injection, the container was resealed and stirred for 3 h. At this time, the deprotonation reduction process was completed, and a ZNFs dispersion was obtained.

[0075] The ZNFs dispersion was washed with deionized water until neutral. The washing process was carried out by vacuum filtration using a G4 grade primary filter. The filter membrane used was polytetrafluoroethylene (PTFE) with a pore size of 0.45 μm and a filter membrane diameter of 90 mm. The resulting dispersion was then transferred to a ball mill for treatment. The holding container during the treatment process was a nylon tank, the rotation speed was 1400 rpm, and the grinding balls used were 10 alumina wear-resistant balls with a diameter of 10 mm and 6 mm, 10 each. After treatment, the dispersion was dispersed in deionized water to obtain a water-dispersed ZNFs dispersion with a concentration of 0.54 mg / mL.

[0076] The water-dispersed aramid nanofiber dispersion and the water-dispersed ZNFs dispersion obtained in step (4) were evenly dispersed in a mass ratio of 10:90 to obtain a blended slurry, which was then vacuum filtered to form a wet paper web. The filter membrane used a cellulose membrane with a diameter of 0.22 μm, and then further vacuum dried using a paper sheet former. The drying time was 8 minutes and the drying temperature was 105°C to obtain high-performance aramid / PBO nano insulating paper, which was recorded as A / Z-90NP.

[0077] Example 5

[0078] The present embodiment provides a high-performance aramid / PBO nano insulating paper and a preparation method thereof, and the specific preparation steps are as follows:

[0079] 1.0 g of para-aramid chopped fiber, 1.5 g of potassium hydroxide (KOH) and 500 mL of dimethyl sulfoxide (DMSO) were placed in a container and stirred at 30°C for 7 days under sealed conditions to obtain an aramid nanofiber dispersion dispersed in the KOH / DMSO system; then 180 mL of the above aramid nanofiber dispersion was injected into 360 mL of deionized water for protonation reduction reaction for 30 minutes; 500 mL of deionized water and 500 mL of anhydrous ethanol were used to wash alternately 3 times to remove the dimethyl sulfoxide remaining in the system, and deionized water was added to 400 mL to obtain aramid nanofibers with a concentration of 0.9 mg / mL dispersed in the water system.

[0080] 1g of PBO chopped fibers was added to 500g of methanesulfonic acid (MSA) and 500g of trifluoroacetic acid (TFA) solvent and placed in a sealed environment and stirred at room temperature. During this process, the PBO chopped fibers were strongly protonated by methanesulfonic acid and trifluoroacetic acid, and their size continued to decrease, gradually exfoliating to the nanoscale. After 12 hours, the reaction system became a uniform, transparent, dark yellow solution, indicating that the reaction was stopped to obtain a ZNFs solution with a mass percentage of 0.2%, a diameter of 2 to 10nm, and an average fiber length of 5μm.

[0081] A 1% by mass sodium sulfate solution was injected into the ZNFs solution at a stirring rate of 3000 rpm, a jet pressure of 5 MPa, and a jet velocity of 1.0 mL / s. The mass ratio of sodium sulfate solution to ZNFs solution was 1:1. After the injection, the container was resealed and stirred for 4 h. At this time, the deprotonation reduction process was completed, and a ZNFs dispersion was obtained.

[0082] The ZNFs dispersion was washed with deionized water until neutral. The washing process was carried out by vacuum filtration using a G4 grade primary filter. The filter membrane used was polytetrafluoroethylene (PTFE) with a pore size of 0.45 μm and a filter membrane diameter of 90 mm. The resulting dispersion was then transferred to a ball mill for treatment. The holding container during the treatment process was a nylon tank, the rotation speed was 1400 rpm, and the grinding balls used were 10 alumina wear-resistant balls with a diameter of 10 mm and 6 mm, 10 each. After treatment, the dispersion was dispersed in deionized water to obtain a water-dispersed ZNFs dispersion with a concentration of 0.1 mg / mL.

[0083] The water-dispersed aramid nanofiber dispersion and the water-dispersed ZNFs dispersion obtained in step (4) were evenly dispersed in a mass ratio of 90:10 to obtain a blended slurry, which was then vacuum filtered to form a wet paper web. The filter membrane used a cellulose membrane with a diameter of 0.22 μm, and then further vacuum dried using a paper sheet former. The drying time was 8 minutes and the drying temperature was 105°C to obtain high-performance aramid / PBO nano insulating paper, which was recorded as A / Z-10NP2.

[0084] Example 6

[0085] The present embodiment provides a high-performance aramid / PBO nano insulating paper and a preparation method thereof, and the specific preparation steps are as follows:

[0086] 1.0 g of para-aramid chopped fiber, 1.5 g of potassium hydroxide (KOH) and 500 mL of dimethyl sulfoxide (DMSO) were placed in a container and stirred at 30°C for 7 days under sealed conditions to obtain an aramid nanofiber dispersion dispersed in the KOH / DMSO system; then 60 mL of the above aramid nanofiber dispersion was injected into 120 mL of deionized water for protonation reduction reaction for 30 minutes; 500 mL of deionized water and 500 mL of anhydrous ethanol were used to wash alternately 5 times to remove the dimethyl sulfoxide remaining in the system, and deionized water was added to 400 mL to obtain aramid nanofibers with a concentration of 0.3 mg / mL dispersed in the water system.

[0087] 1g of PBO chopped fibers was added to 500g of methanesulfonic acid (MSA) and 500g of trifluoroacetic acid (TFA) solvent and placed in a sealed environment and stirred at room temperature. During this process, the PBO chopped fibers were strongly protonated by methanesulfonic acid and trifluoroacetic acid, and their size continued to decrease, gradually exfoliating to the nanoscale. After 12 hours, the reaction system became a uniform, transparent, dark yellow solution, indicating that the reaction was stopped to obtain a ZNFs solution with a mass percentage of 0.2%, a diameter of 2 to 10nm, and an average fiber length of 5μm.

[0088] A 1% by mass sodium sulfate solution was injected into the ZNFs solution at a stirring rate of 2000 rpm, a jet pressure of 10 MPa, and a jet velocity of 0.4 mL / s. The mass ratio of sodium sulfate solution to ZNFs solution was 1:1. After the injection, the container was resealed and stirred for 5 h. At this time, the deprotonation reduction process was completed, and a ZNFs dispersion was obtained.

[0089] The ZNFs dispersion was washed with deionized water until neutral. The washing process was carried out by vacuum filtration using a G4 grade primary filter. The filter membrane used was polyvinylidene fluoride (PVDF) with a pore size of 0.45 μm and a filter membrane diameter of 90 mm. The resulting dispersion was then transferred to a ball mill for treatment. The holding container during the treatment process was a nylon tank, the rotation speed was 1400 rpm, and the grinding balls used were 10 alumina wear-resistant balls with a diameter of 10 mm and 6 mm, 10 each. After treatment, the dispersion was dispersed in deionized water to obtain a water-dispersed ZNFs dispersion with a concentration of 0.7 mg / mL.

[0090] The water-dispersed aramid nanofiber dispersion and the water-dispersed ZNFs dispersion obtained in step (4) were evenly dispersed in a mass ratio of 30:70 to obtain a blended slurry, which was then vacuum filtered to form a wet paper web. The filter membrane used a cellulose membrane with a diameter of 0.22 μm, and then further vacuum dried using a paper sheet former. The drying time was 8 minutes and the drying temperature was 105°C to obtain high-performance aramid / PBO nano insulating paper, which was recorded as A / Z-70NP.

[0091] The actual picture of the nanopaper prepared according to the method of Example 3 of the present invention is as follows Figure 2 As shown, it can be seen that the nanopaper is dark yellow, has a smooth surface, a thickness of 40 μm, and a diameter of 9.1 cm.

[0092] The surface SEM image of the high performance aramid / PBO nano insulation paper obtained in Example 1 of the present invention is as follows: Figure 3a As shown, the partial enlarged view of the dotted ellipse is shown in Figure 3b shown. Figure 3a The morphology shows that the paper surface is relatively flat and smooth. Figure 3b The seven short arrows on the lower right side are all aramid nanofibers (ANFs), and the long arrows in the middle are PBO nanofibers (ZNFs). ZNFs are larger and longer than ANFs, and play a skeletal support role in insulating paper. ANFs are thinner in diameter and entangled and wrapped with ZNFs to form a fiber network structure. When the paper is subjected to a tensile mechanical force, ANFs will limit the slippage and breakage of ZNFs, so the paper has excellent mechanical strength.

[0093] The cross-sectional SEM image of the high performance aramid / PBO nano insulation paper obtained in Example 1 of the present invention is as follows: Figure 4 As shown in the figure, it can be seen that the paper has an obvious layered structure after being broken, slippage occurs between the layers, and fibers are pulled out in a membrane-like state, forming a serrated structure.

[0094] The actual picture of the high-performance aramid / PBO nanofiber aqueous dispersion (i.e., the blended slurry obtained by uniformly dispersing the aramid nanofiber dispersion and the water-dispersed ZNFs dispersion) obtained in Example 1 of the present invention is as follows: Figure 5 As shown in the figure, it can be seen that the laser is used to irradiate the blended slurry, and the slurry produces the Tyndall phenomenon, and the surface of the system is well dispersed.

[0095] The stress-strain curve of the high-performance aramid / PBO nano insulation paper obtained in Example 1 of the present invention is as follows: Figure 6 As shown in the figure, it can be seen that the tensile performance test of paper prepared by ANFs alone (i.e., aramid nanofibers in a water system are directly vacuum filtered and vacuum dried) shows that the final stress reaches 112 MPa and the strain reaches 3.6%; the tensile performance test of paper prepared by ZNFs alone (i.e., water-dispersed ZNFs dispersion is directly vacuum filtered and vacuum dried) shows that the final stress reaches 51 MPa and the strain reaches 1.4%; the tensile performance test of paper prepared by compounding ANFs and ZNFs, in which ZNFs account for 10%, the final stress reaches 180 MPa and the strain reaches 7.4%, reflecting that the mechanical properties of the insulating paper prepared by compounding ANFs and ZNFs are improved.

[0096] The flame retardant effect of high performance aramid / PBO nano insulation paper obtained in Example 1 of the present invention is as follows: Figure 7 As shown in the figure, it can be seen that when the aramid / PBO nano insulation paper is placed in the outer flame of an alcohol lamp for 30 seconds, no open flame or smoke is generated by the insulation paper, indicating that the insulation paper has excellent flame retardant effect.

[0097] The nanopaper prepared by the method of Example 1 of the present invention was tested and characterized, and some of its indicators were: 1. Quantitative: 37m 2 / g; 2. Breaking strength: 180MPa; 3. Compressive strength: 80kV / mm; 4. TG 10％ : 561.5°C, indicating that the temperature at which the nanopaper loses 10% of its weight is 561.5°C. In other words, at a temperature of 561.5°C, the nanopaper loses only 10% of its weight. The high-performance aramid / PBO nano-insulating paper prepared by the present invention has high mechanical strength, excellent heat resistance, and good electrical insulation properties, and can be widely used as a high-performance insulating material in the field of high-end electrical insulation.

Claims

1. A method for preparing high-performance aramid / PBO nano-insulation paper, characterized in that: The following steps are involved: S1, PBO chopped fibers, methanesulfonic acid, and trifluoroacetic acid are stirred in a closed container at room temperature in a mass ratio of 1:500:

500. Stirring is stopped when the resulting reaction solution becomes homogeneous and transparent to obtain a mixed solution. Then, a 1% to 30% by mass sodium sulfate solution is injected into the mixed solution using a high-pressure jet pump under stirring at 1000 to 3000 rpm. The jet pressure of the high-pressure jet pump is 5 to 10 MPa, the jet speed is 0.2 to 1.0 mL / s, and the mass ratio of the sodium sulfate solution to the mixed solution is (1 to 3):

1. The mixture is then sealed and stirred for 2 to 6 hours to obtain a dispersion. S2, washing the dispersion with deionized water until neutral, using a G4 grade primary filter for vacuum filtration. The filter membrane is made of polyvinylidene fluoride or polytetrafluoroethylene with a pore size of 0.45 to 1 μm, followed by ball milling. The resulting liquid is dispersed in deionized water to obtain a ZNFs dispersion with a concentration of 0.06 to 0.54 mg / mL; S3, uniformly dispersing the ZNFs dispersion described in S2 and the aramid nanofiber dispersion with a concentration of 0.06-0.9 mg / mL in a mass ratio of (10-90):(10-90) to obtain a blended slurry, and vacuum filtering and vacuum drying the blended slurry in sequence to obtain high-performance aramid / PBO nano insulation paper; The aramid nanofiber dispersion is obtained according to the following process: Para-aramid fiber, potassium hydroxide and dimethyl sulfoxide were placed in a sealed container at a ratio of 1 g:1.5 g:500 mL, stirred and reacted at 20-50 ° C for 5-8 days to obtain a reaction solution. Subsequently, deionized water with a volume twice that of the reaction solution was injected for protonation reduction reaction for 25-35 minutes. The residual dimethyl sulfoxide was removed, and deionized water was added to obtain an aramid nanofiber dispersion with a concentration of 0.06-0.9 mg / mL.

2. The method for preparing high-performance aramid / PBO nano insulating paper according to claim 1, characterized in that: The ball milling process in S2 is carried out using a ball mill with a rotation speed of 1300-1500 rpm, wherein 8-12 alumina wear-resistant balls with a diameter of 10 mm and 8-12 alumina wear-resistant balls with a diameter of 6 mm are used.

3. The method for preparing high-performance aramid / PBO nano insulating paper according to claim 1, characterized in that: In S3, a cellulose membrane with a diameter of 0.22 μm is used for vacuum filtration, and a paper sheet former is used for vacuum drying. The drying temperature is 100 to 110° C., and the drying time is 6 to 10 minutes.

4. A high-performance aramid / PBO nano-insulating paper obtained by the preparation method of high-performance aramid / PBO nano-insulating paper according to any one of claims 1 to 3.

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