Aramid composite insulating paper, preparation method and application

Abstract

The present invention discloses aramid composite insulating paper, a preparation method, and applications, relating to the technical field of aramid paper. The present invention provides a method for preparing aramid composite insulating paper. The aramid composite insulating paper prepared by the present invention is prepared by combining two fiber materials, combining the advantages of aramid chopped fibers and modified cellulose, and producing a synergistic and positive effect. The present invention combines cellulose with aramid fibers for composite papermaking to produce aramid composite insulating paper, significantly reducing production costs and having broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of aramid paper, in particular to aramid composite insulating paper, a preparation method and application thereof. Background Art

[0002] Aromatic polyamide fiber, also known as aramid fiber, is a new high-tech synthetic fiber, primarily divided into para-aramid fiber (aramid 1414) and meta-aramid fiber (aramid 1313). It boasts high strength, high modulus, high-temperature resistance, electrical insulation, and lightweight properties. Aramid paper, a specialty paper-based material made primarily from aramid fiber using a wet-laid forming process, is easy to process, folds well, and is resistant to tearing. It offers enhanced mechanical and insulating properties, making it suitable as a flexible insulation material for electrical equipment. Consequently, various approaches are being adopted domestically to enhance the performance and reduce the cost of aramid composite insulation paper.

[0003] Plant cellulose has a high aspect ratio and large specific surface area. Its abundant surface hydroxyl groups can bind to a variety of substances, potentially replacing some aramid fibers and improving their performance. However, direct composites of cellulose and aramid fibers perform poorly. Furthermore, under high voltage conditions, cellulose is flammable and prone to electrical treeing, which severely impacts the mechanical and safety properties of aramid composite insulation paper.

[0004] Therefore, an aramid composite insulating paper with high mechanical strength, high resistance to electrical tree degradation and electrical breakdown, and high flame retardancy has broad application prospects. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide an aramid composite insulating paper with high mechanical strength, high resistance to electrical tree degradation and electrical breakdown, and high flame retardancy, a preparation method and application.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing aramid composite insulating paper, comprising the following steps:

[0007] (1) pretreating the meta-aramid chopped fibers to obtain a slurry suspension;

[0008] (2) After dispersing cellulose in solvent 1, acetoacetate is added to react to obtain acetoacetated cellulose;

[0009] (3) subjecting the acetoacetated cellulose to a Michael addition reaction with N-vinylcarbazole in solvent 2 to obtain modified cellulose; the grafting rate of the modified cellulose is 5% to 30%;

[0010] (4) adding the slurry suspension prepared in step (1) to the modified cellulose prepared in step (3) to obtain a mixed slurry, which is then dehydrated, formed, and papered to obtain the aramid composite insulating paper.

[0011] The aramid composite insulating paper prepared by the present invention is prepared by combining two fiber materials, combining the advantages of aramid short-cut fibers and modified cellulose, and producing a synergistic positive effect. Cellulose has a high aspect ratio and a large specific surface area, and the abundant hydroxyl groups on the surface can combine with the surface groups of the aramid fibers, thereby improving the interfacial bonding force between the fibers and giving the paper high mechanical properties. Among them, the modified cellulose prepared by the present invention grafts acetyl groups onto the cellulose, which can significantly improve the chemical reaction activity, and then chemically cross-links with N-vinylcarbazole to graft N-vinylcarbazole onto the cellulose molecules. As an organic conjugated molecule, N-vinylcarbazole has a large conjugated π bond in its molecular structure, which can better disperse space charges, inhibit space charge accumulation, increase breakdown voltage, reduce the probability of initiation of electrical dendrites, and improve mechanical properties. At the same time, the modified cellulose is more easily combined with aramid fibers, which can further improve the mechanical properties of the paper.

[0012] Preferably, the grafting rate of the modified cellulose is 10%-15%.

[0013] Preferably, in step (1), the specific method of pretreatment is: treating the meta-aramid chopped fibers with a phosphoric acid aqueous solution until they are neutral to obtain a mixed solution, and dispersing the mixed solution with sodium polyacrylate to obtain a slurry suspension;

[0014] Further preferably, the volume fraction of the phosphoric acid aqueous solution is 40%-45%, and the phosphoric acid aqueous solution treatment is carried out at 30°C-35°C for 1h-2h; the mass percentage of sodium polyacrylate in the slurry suspension is 0.1%-10%, and the decomposition is carried out at 25°C-35°C for 1h-2h.

[0015] Preferably, in step (2), the solvent 1 is at least one of ethanol, methanol, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the cellulose is at least one of bamboo pulp cellulose, bagasse pulp cellulose, bacterial cellulose, short cotton linter cellulose, and microcrystalline cellulose; and the acetoacetate is at least one of methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, butyl acetoacetate, pentyl acetoacetate, hexyl acetoacetate, heptyl acetoacetate, sec-butyl acetoacetate, isobutyl acetoacetate, isopropyl acetoacetate, isoamyl acetoacetate, n-octyl acetoacetate, and tert-butyl acetoacetate.

[0016] Preferably, in step (2), the mass percentage ratio of the cellulose to the solvent 1 is (0.1-0.5):1; the mass percentage ratio of the acetoacetate to the cellulose is (0.5-20):1; the reaction temperature is 90°C-140°C, and the reaction time is 1h-24h;

[0017] Further preferably, after the reaction of the acetoacetate and cellulose, the acetoacetated cellulose is filtered, washed and dried; further preferably, the washing solvent is one of water, ethanol and methanol, the drying temperature is 40°C-80°C, and the drying time is 1h-12h.

[0018] Preferably, in step (3), solvent 2 is at least one of ethanol, methanol, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide, and the temperature of the Michael addition reaction is 50°C-80°C, and the time is 12h-24h; further preferably, after the Michael addition reaction, the modified cellulose is filtered, washed, and dried; the washing solvent is one of water, ethanol, and methanol, the drying temperature is 80°C-100°C, and the drying time is 6h-12h.

[0019] Preferably, in step (3), the mass ratio of acetoacetated cellulose to N-vinylcarbazole is 1:(10-20). Further preferably, the mass ratio of acetoacetated cellulose to N-vinylcarbazole is 1:(12-15).

[0020] Preferably, in step (4), the mass percentage of the modified cellulose is 2%-10% of the absolute dry mass of the mixed pulp.

[0021] Preferably, in step (4), the papermaking temperature is 100° C.-260° C., the pressure is 8.0 MPa-10.0 MPa, and the time is 10 min-30 min.

[0022] In addition, the present invention provides aramid composite insulating paper prepared by the preparation method of the aramid composite insulating paper.

[0023] Furthermore, the present invention provides application of the aramid composite insulation paper in the field of transformers.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The aramid composite insulating paper prepared by the present invention is prepared by combining two fiber materials, combining the advantages of aramid short-cut fibers and modified cellulose, and producing a synergistic positive effect. Cellulose has a high aspect ratio and a large specific surface area, and the abundant hydroxyl groups on the surface can combine with the surface groups of the aramid fibers, thereby improving the interfacial bonding force between the fibers and giving the paper high mechanical properties. Among them, the modified cellulose prepared by the present invention grafts acetyl groups onto the cellulose, which can significantly improve the chemical reaction activity, and then chemically cross-links with N-vinylcarbazole to graft N-vinylcarbazole onto the cellulose molecules. As an organic conjugated molecule, N-vinylcarbazole has a large conjugated π bond in its molecular structure, which can better disperse space charges, inhibit space charge accumulation, increase breakdown voltage, reduce the probability of initiation of electrical dendrites, and improve mechanical properties. At the same time, the modified cellulose is more easily combined with aramid fibers, which can further improve the mechanical properties of the paper.

[0026] The present invention mixes cellulose with aramid fibers for composite papermaking to produce aramid composite insulation paper, which can significantly reduce production costs and has broad application prospects. DETAILED DESCRIPTION

[0027] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to specific embodiments. Its purpose is to understand the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise specified, the experimental reagents and instruments designed for the implementation and comparative examples of the present invention are all commonly used ordinary reagents and instruments, which can be obtained from commercial channels. In the implementation and comparative examples, the experimental methods used are all conventional methods unless otherwise specified; and unless otherwise specified, the raw materials used in parallel experiments are the same batch of raw materials.

[0028] The present invention provides a method for preparing aramid composite insulating paper, comprising the following steps:

[0029] (1) treating meta-aramid short fibers with a phosphoric acid aqueous solution until neutral to obtain a mixed solution, and de-escalating the mixed solution with sodium polyacrylate to obtain a slurry suspension; the volume fraction of the phosphoric acid aqueous solution is 40%-45%, and the phosphoric acid aqueous solution treatment is performed at 30°C-35°C for 1 hour-2 hours; the mass percentage of sodium polyacrylate in the slurry suspension is 0.1%-10%, and the de-escalation is performed at 25°C-35°C for 1 hour-2 hours;

[0030] (2) After dispersing cellulose in solvent 1, adding acetoacetate to react to obtain acetoacetated cellulose; the solvent 1 is at least one of ethanol, methanol, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the cellulose is at least one of bamboo pulp cellulose, bagasse pulp cellulose, bacterial cellulose, short cotton linter cellulose, and microcrystalline cellulose; the acetoacetate is at least one of methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, butyl acetoacetate, pentyl acetoacetate, hexyl acetoacetate, heptyl acetoacetate, sec-butyl acetoacetate, isobutyl acetoacetate, isopropyl acetoacetate, isopentyl acetoacetate, n-octyl acetoacetate, and tert-butyl acetoacetate;

[0031] The mass percentage ratio of the cellulose and the solvent 1 is (0.1-0.5):1; the mass percentage ratio of the acetoacetate and the cellulose is (0.5-20):1; the reaction temperature is 90°C-140°C, and the reaction time is 1h-24h; preferably, after the reaction of the acetoacetate and the cellulose, the acetoacetate is filtered, washed, and dried to obtain the acetoacetated cellulose; preferably, the washing solvent is one of water, ethanol, and methanol, the drying temperature is 40°C-80°C, and the drying time is 1h-12h;

[0032] (3) subjecting the acetoacetated cellulose to a Michael addition reaction with N-vinylcarbazole in solvent 2 to obtain modified cellulose;

[0033] The solvent 2 is at least one of ethanol, methanol, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. The temperature of the Michael addition reaction is 50°C-80°C, and the time is 12h-24h. Preferably, after the Michael addition reaction, the modified cellulose is filtered, washed, and dried. The washing solvent is one of water, ethanol, and methanol. The drying temperature is 80°C-100°C, and the drying time is 6h-12h.

[0034] The mass ratio of the acetoacetated cellulose to N-vinyl carbazole is 1:(10-20); preferably, the mass ratio of the acetoacetated cellulose to N-vinyl carbazole is 1:(12-15);

[0035] (4) adding the slurry suspension prepared in step (1) to the modified cellulose prepared in step (3) to obtain a mixed slurry, and dehydrating, forming, and papermaking to obtain the aramid composite insulating paper;

[0036] The mass percentage of the modified cellulose is 2%-10% of the absolute dry mass of the mixed pulp, the papermaking temperature is 100° C.-260° C., the pressure is 8.0 MPa-10.0 MPa, and the time is 10 min-30 min.

[0037] Examples and Comparative Examples

[0038] Raw materials: Bamboo pulp cellulose: degree of polymerization 780, cellulose content greater than 85%, Beijing North Century Cellulose Technology Development Co., Ltd.; Bagasse pulp cellulose: industrial grade (bleached), Nanning Sugar Co., Ltd. Sugar and Paper Mill; Bacterial cellulose: diameter 50-100nm, Guilin Qihong Technology Co., Ltd.

[0039] Example 1

[0040] A method for preparing aramid composite insulating paper comprises the following steps:

[0041] (1) treating meta-aramid short fibers with a phosphoric acid aqueous solution until neutral to obtain a mixed solution, and de-escalating the mixed solution with sodium polyacrylate to obtain a slurry suspension; the volume fraction of the phosphoric acid aqueous solution is 40%, and the phosphoric acid aqueous solution treatment is performed at 30° C. for 2 h; the mass percentage of sodium polyacrylate in the slurry suspension is 3%, and the de-escalation is performed at 25° C. for 2 h;

[0042] (2) After dispersing cellulose in solvent 1, adding acetoacetate to react to obtain acetoacetated cellulose; the solvent 1 is ethanol, the cellulose is bamboo pulp cellulose, and the acetoacetate is methyl acetoacetate;

[0043] The mass percentage ratio of the cellulose to the solvent 1 is 0.5:1; the mass percentage ratio of the acetoacetate to the cellulose is 5:1; the reaction temperature is 90°C and the reaction time is 24 hours; after the acetoacetate and cellulose react, the acetoacetated cellulose is filtered, washed, and dried to obtain acetoacetated cellulose; preferably, the washing solvent is water, the drying temperature is 40°C, and the drying time is 12 hours;

[0044] (3) subjecting the acetoacetated cellulose to a Michael addition reaction with N-vinylcarbazole in solvent 2 to obtain modified cellulose;

[0045] The solvent 2 is ethanol, the temperature of the Michael addition reaction is 60°C, and the time is 18 hours; after the Michael addition reaction, the modified cellulose is filtered, washed, and dried; the washing solvent is water, the drying temperature is 80°C, and the drying time is 12 hours;

[0046] The mass ratio of the acetoacetated cellulose to N-vinyl carbazole is 1:15;

[0047] (4) adding the slurry suspension prepared in step (1) to the modified cellulose prepared in step (3) to obtain a mixed slurry, and dehydrating, forming, and papermaking to obtain the aramid composite insulating paper;

[0048] The mass percentage of the modified cellulose is 5% of the absolute dry mass of the mixed slurry. The papermaking temperature is 150° C., the pressure is 10.0 MPa, and the time is 30 minutes.

[0049] Example 2

[0050] A method for preparing aramid composite insulating paper comprises the following steps:

[0051] (1) treating meta-aramid short fibers with a phosphoric acid aqueous solution until neutral to obtain a mixed solution, and de-escalating the mixed solution with sodium polyacrylate to obtain a slurry suspension; the volume fraction of the phosphoric acid aqueous solution is 45%, and the phosphoric acid aqueous solution treatment is performed at 35° C. for 1 hour; the mass percentage of sodium polyacrylate in the slurry suspension is 10%, and the de-escalation is performed at 35° C. for 1 hour;

[0052] (2) After dispersing cellulose in solvent 1, adding acetoacetate to react to obtain acetoacetated cellulose; the solvent 1 is methanol, the cellulose is bacterial cellulose, and the acetoacetate is ethyl acetoacetate;

[0053] The mass percentage ratio of the cellulose to the solvent 1 is 0.1:1; the mass percentage ratio of the acetoacetate to the cellulose is 20:1; the reaction temperature is 140°C, and the reaction time is 1 hour; after the acetoacetate and cellulose react, filtering, washing, and drying to obtain acetoacetated cellulose; preferably, the washing solvent is ethanol, the drying temperature is 80°C, and the drying time is 1 hour;

[0054] (3) subjecting the acetoacetated cellulose to a Michael addition reaction with N-vinylcarbazole in solvent 2 to obtain modified cellulose;

[0055] The solvent 2 is methanol, the temperature of the Michael addition reaction is 60°C, and the time is 18 hours; after the Michael addition reaction, the modified cellulose is filtered, washed, and dried; the washing solvent is ethanol, the drying temperature is 100°C, and the drying time is 6 hours;

[0056] The mass ratio of the acetoacetated cellulose to N-vinyl carbazole is 1:15;

[0057] (4) adding the slurry suspension prepared in step (1) to the modified cellulose prepared in step (3) to obtain a mixed slurry, and dehydrating, forming, and papermaking to obtain the aramid composite insulating paper;

[0058] The mass percentage of the modified cellulose is 5% of the absolute dry mass of the mixed slurry. The papermaking temperature is 260° C., the pressure is 8.0 MPa, and the time is 10 minutes.

[0059] Example 3

[0060] A method for preparing aramid composite insulating paper comprises the following steps:

[0061] (1) treating meta-aramid short fibers with a phosphoric acid aqueous solution until neutral to obtain a mixed solution, and de-escalating the mixed solution with sodium polyacrylate to obtain a slurry suspension; the volume fraction of the phosphoric acid aqueous solution is 40%, and the phosphoric acid aqueous solution treatment is performed at 30° C. for 2 hours; the mass percentage of sodium polyacrylate in the slurry suspension is 5%, and the de-escalation is performed at 30° C. for 1 hour;

[0062] (2) After dispersing cellulose in solvent 1, adding acetoacetate to react to obtain acetoacetated cellulose; the solvent 1 is N,N-dimethylformamide, the cellulose is bagasse pulp cellulose, and the acetoacetate is amyl ester;

[0063] The mass percentage ratio of the cellulose to the solvent 1 is 0.2:1; the mass percentage ratio of the acetoacetate to the cellulose is 10:1; the reaction temperature is 120°C, and the reaction time is 12 hours; after the acetoacetate and cellulose react, filtering, washing, and drying to obtain acetoacetated cellulose; preferably, the washing solvent is water, the drying temperature is 60°C, and the drying time is 8 hours;

[0064] (3) subjecting the acetoacetated cellulose to a Michael addition reaction with N-vinylcarbazole in solvent 2 to obtain modified cellulose;

[0065] The solvent 2 is ethanol, the temperature of the Michael addition reaction is 60°C, and the time is 18 hours; after the Michael addition reaction, the modified cellulose is filtered, washed, and dried; the washing solvent is water, the drying temperature is 80°C, and the drying time is 12 hours;

[0066] The mass ratio of the acetoacetated cellulose to N-vinyl carbazole is 1:15;

[0067] (4) adding the slurry suspension prepared in step (1) to the modified cellulose prepared in step (3) to obtain a mixed slurry, and dehydrating, forming, and papermaking to obtain the aramid composite insulating paper;

[0068] The mass percentage of the modified cellulose is 5% of the absolute dry mass of the mixed slurry. The papermaking temperature is 150° C., the pressure is 10.0 MPa, and the time is 20 minutes.

[0069] Example 4

[0070] In a single comparison with Example 3, only the temperature of the Michael addition reaction in step (3) is different, which is 50° C., and the weight parts of the remaining components and the preparation method are exactly the same.

[0071] Example 5

[0072] In a single comparison with Example 3, only the temperature of the Michael addition reaction in step (3) is different, which is 80° C., and the weight parts of the remaining components and the preparation method are exactly the same.

[0073] Example 6

[0074] In a single comparison with Example 3, only the time of the Michael addition reaction in step (3) is different, that is, the time of the Michael addition reaction is 12 hours, and the weight parts of the remaining components and the preparation method are exactly the same.

[0075] Example 7

[0076] In a single comparison with Example 3, only the time of the Michael addition reaction in step (3) is different, that is, the time of the Michael addition reaction is 24 hours, and the weight parts of the remaining components and the preparation method are exactly the same.

[0077] Example 8

[0078] In a single comparison with Example 3, only the mass ratio of the acetoacetated cellulose and N-vinyl carbazole in step (3) is different, that is, the mass ratio of acetoacetated cellulose and N-vinyl carbazole is 1:10, and the weight parts of the other components and the preparation method are exactly the same.

[0079] Example 9

[0080] In a single comparison with Example 3, only the mass ratio of the acetoacetated cellulose and N-vinyl carbazole in step (3) is different, that is, the mass ratio of acetoacetated cellulose and N-vinyl carbazole is 1:20, and the weight parts of the other components and the preparation method are exactly the same.

[0081] Example 10

[0082] In a single comparison with Example 3, only the mass percentage of the modified cellulose in step (4) is 4% of the absolute dry mass of the mixed pulp, and the weight parts of the other components and the preparation method are exactly the same.

[0083] Example 11

[0084] In a single comparison with Example 3, only the mass percentage of the modified cellulose in step (4) is 10% of the absolute dry mass of the mixed slurry, and the weight parts of the other components and the preparation method are exactly the same.

[0085] Comparative Example 1

[0086] In a single comparison with Example 3, only the temperature of the Michael addition reaction in step (3) is different, which is 40° C., and the weight parts of the remaining components and the preparation method are exactly the same.

[0087] Comparative Example 2

[0088] In a single comparison with Example 3, only the time of the Michael addition reaction in step (3) is different, that is, the time of the Michael addition reaction is 10 h, and the weight parts of the remaining components and the preparation method are exactly the same.

[0089] Comparative Example 3

[0090] In a single comparison with Example 3, only the mass ratio of the acetoacetated cellulose and N-vinyl carbazole in step (3) is different, that is, the mass ratio of acetoacetated cellulose and N-vinyl carbazole is 1:5, and the weight parts of the other components and the preparation method are exactly the same.

[0091] Comparative Example 4

[0092] In a single comparison with Example 3, only the mass percentage of the modified cellulose in step (4) is 0.5% of the absolute dry mass of the mixed slurry, and the weight parts of the other components and the preparation method are exactly the same.

[0093] Comparative Example 5

[0094] In a single comparison with Example 3, only the mass percentage of the modified cellulose in step (4) is 15% of the absolute dry mass of the mixed slurry, and the weight parts of the other components and the preparation method are exactly the same.

[0095] Performance Test-1 Test of Modified Fiber Grafting Rate

[0096] Test method: The present invention uses the content of N element to test the grafting rate, and uses elemental analysis to determine the content of C, H, O, and N elements in the product. The grafting rate ω is calculated according to the following formula:

[0097]

[0098] Among them, W N is the mass fraction of N element in the product, W′ N is the mass fraction of N element in N-vinylcarbazole, W O is the mass fraction of O element in the product, W C is the mass fraction of C element in the product, W H is the mass fraction of H element in the product.

[0099] The test results of the grafting rate of the modified fiber are shown in Table 1.

[0100] Performance test-2 Aramid composite insulation paper performance test.

[0101] Test standards: Thickness, tensile strength, and electrical strength are tested in accordance with GB / T 29627.2-2013 "Polyaramide fiberboard for electrical purposes Part 2: Test methods" and GB / T 20629.3-2019 "Non-cellulose paper for electrical purposes Part 3: Unfilled polyaramide fiber paper";

[0102] The test results are shown in Table 2.

[0103] Table 1

[0104]

[0105]

[0106] Table 2

[0107]

[0108]

[0109] As can be seen from the above table, the aramid composite insulating paper prepared in the embodiment of the present invention has a tensile strength of more than 45 MPa and an electrical strength of more than 20 kV / mm. The modified cellulose is combined with the aramid fiber, combining the advantages of aramid chopped fibers and modified cellulose, and produces a synergistic positive effect, thereby improving the tensile strength and electrical strength.

[0110] From the comparison of Example 3, Examples 4-5, and Comparative Example 1, it can be seen that the temperature of the Michael addition reaction needs to reach the reaction activation energy before the subsequent addition reaction can proceed. The temperature of the Michael addition reaction has a great influence on the grafting rate. When the temperature of the Michael addition reaction is 50°C-80°C, the grafting rate is above 10%, and the tensile strength and electrical strength of the aramid composite insulating paper finally prepared are both high.

[0111] From the comparison of Example 3, Examples 6-7 and Comparative Example 2, it can be seen that when the Michael addition reaction time is 12h-24h, the grafting rate is above 10%, and the tensile strength and electrical strength of the aramid composite insulating paper finally prepared are both high.

[0112] From the comparison of Example 3, Examples 8-9 and Comparative Example 3, it can be seen that when the mass ratio of acetoacetated cellulose to N-vinylcarbazole is 1:(10-20), the grafting rate is above 10%, and the tensile strength and electrical strength of the aramid composite insulating paper finally prepared are both high.

[0113] By comparing Example 3, Examples 10-11, and Comparative Examples 4-5, it can be seen that when the mass percentage of the modified cellulose is 2%-10% of the absolute dry mass of the mixed slurry, the grafting rate is above 10%, and the tensile strength and electrical strength of the aramid composite insulating paper finally prepared are both high. When the proportion of modified cellulose is too low, the tensile strength and electrical strength are seriously reduced. When the proportion of modified cellulose is too high, the modified cellulose content is too high. Although the high amount of grafted N-vinylcarbazole is beneficial to performance, the cellulose itself has a negative impact on tensile strength and electrical strength. Therefore, the inventors found in actual experiments that only when the mass percentage of the modified cellulose is 2%-10% of the absolute dry mass of the mixed slurry can the tensile strength and electrical strength of the prepared aramid composite insulating paper be high.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing aramid composite insulating paper, characterized in that: The following steps are involved: (1) pre-treating the meta-aramid chopped fibers to obtain a slurry suspension; (2) After dispersing cellulose in solvent 1, acetoacetate is added to react to obtain acetoacetated cellulose; (3) The acetoacetated cellulose and N-vinylcarbazole are subjected to a Michael addition reaction in solvent 2 to obtain modified cellulose; the grafting rate of the modified cellulose is 10%-30%; the temperature of the Michael addition reaction is 50°C-80°C, and the time is 12h-24h; the mass ratio of the acetoacetated cellulose to N-vinylcarbazole is 1:(10-20); (4) The slurry suspension prepared in step (1) is added to the modified cellulose prepared in step (3) to obtain a mixed slurry, which is then dehydrated, formed, and papered to obtain the aramid composite insulating paper; the mass percentage of the modified cellulose is 2%-10% of the absolute dry mass of the mixed slurry.

2. The method for preparing aramid composite insulating paper according to claim 1, wherein: In the step (1), the specific method of pretreatment is: treating the meta-aramid chopped fibers with a phosphoric acid aqueous solution until they are neutral to obtain a mixed solution, and dispersing the mixed solution with sodium polyacrylate to obtain a slurry suspension.

3. The method for preparing aramid composite insulating paper according to claim 2, wherein: The volume fraction of the phosphoric acid aqueous solution is 40%-45%, and the phosphoric acid aqueous solution treatment is carried out at 30°C-35°C for 1h-2h; the mass percentage of sodium polyacrylate in the slurry suspension is 0.1%-10%, and the decomposition is carried out at 25°C-35°C for 1h-2h.

4. The method for preparing aramid composite insulating paper according to claim 1, wherein: In the step (2), the solvent 1 is at least one of ethanol, methanol, N, N-dimethylformamide, N, N-dimethylacetamide, and dimethyl sulfoxide; the cellulose is at least one of bamboo pulp cellulose, bagasse pulp cellulose, bacterial cellulose, short cotton linter cellulose, and microcrystalline cellulose; and the acetoacetate is at least one of methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, butyl acetoacetate, pentyl acetoacetate, hexyl acetoacetate, heptyl acetoacetate, and n-octyl acetoacetate.

5. The method for preparing aramid composite insulating paper according to claim 1, wherein: In the step (2), the mass percentage ratio of the cellulose to the solvent 1 is (0.1-0.5):1; the mass percentage ratio of the acetoacetate to the cellulose is (0.5-20):1; the reaction temperature is 90°C-140°C, and the reaction time is 1h-24h.

6. The method for preparing aramid composite insulating paper according to claim 1, wherein: In the step (3), the solvent 2 is at least one of ethanol, methanol, N, N-dimethylformamide, N, N-dimethylacetamide, and dimethyl sulfoxide.

7. The method for preparing aramid composite insulating paper according to claim 1, wherein: In the step (4), the papermaking temperature is 100°C-260°C, the pressure is 8.0MPa-10.0MPa, and the time is 10min-30min.

8. Aramid composite insulating paper prepared by the method for preparing aramid composite insulating paper according to any one of claims 1 to 7.

9. Use of the aramid composite insulating paper according to claim 8 in the field of transformers.

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