Modified basalt fiber / aramid nanofiber insulation paper and preparation method thereof

Abstract

The invention discloses aramid nanofiber insulation paper with a self-assembled layered structure and a preparation method thereof.The preparation method comprises the steps that firstly, a modified basalt filler with ZIF-8 on the surface is prepared through a surface in-situ growth method, and then stably existing modified basalt fiber / aramid nanofiber dispersion liquid is obtained through an in-situ coating method; and finally, carrying out vacuum filtration to form the modified basalt / aramid nanofiber insulation paper with the self-assembled layered structure. The obtained insulation paper has low thermal conductivity, high breakdown strength, excellent mechanical properties and electrical insulating properties, can be used in the fields of electronic thermal management, buildings and the like, and has extremely high use value.

Description

Technical Field

[0001] The present invention relates to the technical field of insulating composite materials, and particularly relates to a modified basalt fiber / aramid nanofiber insulating paper and a preparation method thereof. Background Art

[0002] Aramid fibers have excellent mechanical, temperature resistance, acid and alkali resistance, chemical stability and other properties. However, their surfaces are smooth and lack active groups, making it difficult to have physical or chemical interactions with themselves or other materials, seriously hindering their development and application in the fields of hybrid and composite materials. Aramid nanofibers are a new type of polymer nanofiber prepared by deprotonation of aramid fibers using a "top-down" strategy. It retains most of the properties of aramid fibers, including thermal stability and high crystallinity. At the same time, the aramid nanofibers at the nanoscale endow it with excellent mechanical and optical properties. In addition, the aramid nanofiber paper / membrane formed by hydrogen bonding between aramid nanofibers has excellent mechanical and optical properties. Moreover, the rich active groups, large aspect ratio and specific surface area on the surface of aramid nanofibers endow them with excellent characteristics of nanomaterials, such as high strength, high temperature resistance, transparency and good flexibility. The aramid nanofibers with a high aspect ratio will preferentially align in the plane due to the effect of vacuum filtration in the direction perpendicular to the plane, presenting a biomimetic hierarchical structure, which is beneficial to improving the mechanical properties and insulation properties of aramid nanofiber paper. Therefore, aramid nanofibers have great application potential in the fields of electrical insulating materials, battery separators, etc.

[0003] With the rapid development of science and technology, the research focus of electrical engineering is oriented towards high power, high integration, large capacity and high performance, etc. Especially for large power generators working in harsh environments, higher requirements are put forward for their core component, aramid insulating paper. In recent years, many researchers have been committed to the research and development of high-performance aramid insulating paper and have done a lot of work to explore methods for improving the insulation properties of aramid paper and its paper-based materials.

[0004] The patent "A meta-aramid fiber mica paper and its preparation method" with publication number CN105544285A uses aramid precipitated fibers as the bonding material and aramid short fibers as the skeleton material, inlays mica flakes therein, and firmly bonds the mica flakes together through high-temperature melting deformation, thereby improving the mechanical strength and dielectric strength of the mica paper; the patent "A preparation method of para-aramid fiber mica paper" with publication number CN105544286A uses para-aramid short fibers, para-aramid precipitated fibers and mica flakes as raw materials, modifies the short fibers with a silane coupling agent, and modifies the mica flakes with cationic starch to make them have bonding properties. The mixed slurry is dehydrated and formed, and then pressed and high-temperature calendered to obtain para-aramid mica paper, and the mechanical properties are improved by modifying the fibers and mica; the patent "Para-aramid fiber mica composite paper and its production method" with publication number 105568750A uses short aramid fibers, para-aramid precipitated fibers and mica flakes as raw materials, and obtains a para-aramid mica composite paper with a higher temperature resistance grade through dehydration forming and high-temperature calendering.

[0005] The above-mentioned existing patents introduce methods for enhancing aramid fiber paper with mica, which improve the mechanical properties or dielectric strength of aramid paper to a certain extent. However, the thermal decomposition temperature of meta-aramid fibers is relatively low, and it is difficult to reflect the high-temperature resistance performance of mica in combination with mica, making it difficult to meet the usage requirements in high-end fields. The bonding strength between para-aramid precipitated fibers and mica is relatively low. Although modification can improve the mechanical strength, it will reduce the temperature resistance performance. Without modification, it will lead to a large porosity during the composite process of precipitated fibers, short fibers and mica, reducing the electrical performance. It can be seen that the above-mentioned existing technologies all have certain defects and will greatly reduce the performance of the obtained aramid fiber paper. Summary of the Invention

[0006] To solve some problems of the existing technology, the present invention provides an aramid nanofiber insulating paper and its preparation method. Modified basalt scales with ZIF-8 grown in situ on the surface are added to the aramid nanofiber insulating paper, greatly improving the electrical and mechanical properties of the aramid nanofiber paper, and endowing it with excellent insulation and flame retardancy.

[0007] A preparation method of a modified basalt fiber / aramid nanofiber insulating paper includes the following steps:

[0008] S1: Mix PPTA fibers, KOH, deionized water and DMSO to form a mixed solution, and stir the mixed solution to obtain an ANF / DMSO solution;

[0009] S2: Modify the surface of basalt fibers by silane functionalization;

[0010] S3: In-situ growth of ZIF-8 on the surface of silane-functionalized basalt fibers to obtain modified basalt fibers;

[0011] S4: Mix the modified basalt fibers with the ANF / DMSO solution and disperse them under ultrasonic action to form a suspension, and then inject deionized water for protonation reduction to prepare a modified basalt fiber-ANF / DMSO dispersion;

[0012] S5: Wash the modified basalt fiber-ANF-DMSO dispersion obtained in S4 with deionized water, remove the DMSO solvent, then perform vacuum filtration and drying to obtain the modified basalt fiber / aramid nanofiber insulating paper.

[0013] In some embodiments of the present invention, the mixing ratio of the PPTA fibers, KOH, deionized water, and DMSO in S1 is: 1.5 - 2 g : 2.5 - 3 g : 30 - 35 ml : 500 - 600 ml.

[0014] In some embodiments of the present invention, the surface silane-functionalization modification in S2 includes the following steps: Add basalt fibers to anhydrous ethanol, stir, filter and separate, and then dry. Then, prepare an ethanol solution of an amino-silane coupling agent, use 1 - 1.5 mol / L hydrochloric acid as a catalyst, and adjust the pH of the solution to 3.5 - 5. Add the basalt fibers to it, continuously stir for 4 - 5 h, filter and separate, and dry to obtain silane-functionalized basalt fibers.

[0015] In some embodiments of the present invention, in S3, the treatment method for in-situ growth of ZIF-8 on the surface includes the following steps: Add zinc salt to a beaker containing methanol and stir evenly at a speed of 200 - 300 r / min at room temperature; then add the silane-functionalized basalt fibers to the above solution and continuously stir for 12 h to obtain a dispersion. Separately, add 2-methylimidazole to a beaker containing methanol and stir evenly at a speed of 200 - 300 r / min at room temperature. Then, mix the above solution with the dispersion and continuously stir for 1 - 2 h until it is uniform, and then let it stand for 24 h to complete the reaction. Finally, centrifuge the completely reacted solution at a speed of 3000 - 4000 r / min for 5 - 10 min, take out the precipitate and wash it with methanol, and place the product in an oven at 60 - 80 °C and dry it for 12 h until it reaches a constant weight to obtain the modified basalt fibers.

[0016] Furthermore, the molar ratio of the zinc salt to the 2-methylimidazole used is 1 : 2 - 2.5. Among them, the zinc salt can be zinc nitrate hexahydrate, zinc nitrate heptahydrate, etc.

[0017] Furthermore, the added mass of the silane-functionalized basalt fibers is 0.2 - 0.25 times the total mass of the zinc salt and 2-methylimidazole.

[0018] In some embodiments of the present invention, in S4, the added mass of the modified basalt fiber accounts for 35-50% of the mass of the finally obtained insulating paper; the ultrasonic dispersion time is 10-15 min.

[0019] In some embodiments of the present invention, in S4, the volume ratio of the suspension to deionized water is 1:2-2.2.

[0020] In some embodiments of the present invention, the specific operation of injecting deionized water in S4 is as follows: After obtaining shear force by stirring the modified basalt fiber-ANF / DMSO suspension at a rotation speed of 1500 rmp, use a disposable pump syringe to measure and inject deionized water into it.

[0021] In some embodiments of the present invention, in S5, the washing is carried out 3-5 times, and the drying conditions are vacuum drying at 105-120 °C for 3-6 min.

[0022] In the present invention, one end of the amino-silane coupling agent reacts with the hydroxyl groups on the surface of the basalt fiber, and at the same time, the amino group at the other end provides a nucleation site for the formation of ZIF-8. The complexation between zinc ions and N atoms promotes the generation of ZIF-8, and the stability of ZIF-8 on the surface of the basalt fiber is achieved through covalent interactions.

[0023] Mix the modified basalt fiber with ZIF-8 on the surface and aramid fiber to prepare insulating paper, and modify the basalt fiber by in-situ coating treatment during the protonation reduction process of aramid nanofibers. The hydrogen bond between the imidazole ring and the amide group improves the interaction force between the microfibrils in the aramid fiber, so that the obtained insulating paper has better mechanical properties and thermal stability. In addition, through the method of vacuum filtration for self-assembly, a layered structure with clear alternating arrangement of organic fibers and inorganic fibers is obtained. The modified basalt fiber acts as a physical barrier in the structure, has a microporous structure that prevents the volatilization of combustibles, and can adsorb the volatile components of the combustibles, further reducing the thermal conductivity of the insulating paper, thereby improving its breakdown strength.

[0024] However, due to the characteristics of its structure, the addition of the modified basalt fiber will also increase the micropores inside the insulating paper to a certain extent, affecting the thermal conductivity of the material. Therefore, the inventor decided through research that preferably, the added mass of the modified basalt fiber accounts for 35-50% of the mass of the finally obtained insulating paper.

[0025] The present invention also provides a modified basalt fiber / aramid nanofiber insulating paper prepared by the above preparation method.

[0026] Beneficial effects: Compared with the prior art, the present invention creatively uses the in-situ coating treatment of modified basalt fibers during the protonation reduction process of aramid nanofibers. The imidazole ring in ZIF-8 on the surface of the modified basalt fibers interacts with the amide groups in the aramid nanofibers through hydrogen bonds, thereby obtaining a homogeneous dispersion with a core-shell structure system. Through the method of vacuum filtration for self-assembly, the obtained insulating paper has a layered structure with alternating organic fibers and inorganic fibers.

[0027] The addition of the modified basalt fibers improves the interaction force between the microfibrils in the aramid nanofibers; combined with the high interconnectivity of the aramid nanofiber network and the multi-site crosslinking with the modified basalt fibers, the entire material undergoes uniform deformation, resulting in ultra-high toughness and obtaining high mechanical properties.

[0028] Moreover, the high specific surface area of the modified basalt fibers can absorb the volatile components of combustion and prevent the emergence of microporous structures caused by the volatilization of combustibles, thereby reducing the thermal conductivity of the obtained insulating paper and achieving a high breakdown strength. Specific embodiments

[0029] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation embodiments of the present invention.

[0030] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0032] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of this application are only exemplary.

[0033] Example 1

[0034] S1: Mix 1.5 g of PPTA fiber, 2.5 g of KOH, 30 ml of deionized water and 500 ml of DMSO to form a mixed solution, and stir the mixed solution to obtain an ANF / DMSO solution;

[0035] S2: Surface silane functionalization modification of basalt fiber: Add 10 g of basalt fiber to 30 ml of absolute ethanol and stir, filter by suction, separate and dry. Then prepare an ethanol solution of KH550 with a volume fraction of 2%, use 1 mol / L hydrochloric acid as a catalyst, and adjust the pH of the solution to 3.5. Add the dried basalt fiber into it, continuously stir for 4 h, filter by suction, separate and dry to obtain silane-functionalized basalt fiber;

[0036] S3: In-situ growth of ZIF-8 on the surface of silane-functionalized basalt fiber to obtain modified basalt fiber: Add 2.97 g of zinc nitrate hexahydrate to a beaker containing 200 ml of methanol and stir evenly at a speed of 200 r / min at room temperature; then add 0.9224 g of the silane-functionalized basalt fiber obtained in S2 to the above solution, and continuously stir for 12 h to obtain a dispersion. Take another 1.642 g of 2-methylimidazole and add it to a beaker containing 200 ml of methanol and stir evenly at a speed of 200 r / min at room temperature. Then mix the above solution with the dispersion and continuously stir for 2 h until uniform, and then let it stand for 24 h to complete the reaction; finally, centrifuge the completely reacted solution at a speed of 3000 r / min for 10 min, take out the precipitate and wash it with methanol, and place the product in an oven at 60 °C and dry it for 12 h to constant weight to obtain modified basalt fiber;

[0037] S4: Mix 0.305 g of modified basalt fiber with 200 ml of ANF / DMSO solution and disperse it under ultrasonic stirring for 10 min to form a suspension, and simultaneously inject 400 ml of deionized water for protonation reduction to obtain a modified basalt fiber-ANF / DMSO dispersion;

[0038] S5: Wash the modified basalt fiber-ANF-DMSO dispersion obtained in S4 three times with deionized water, remove the DMSO solvent, then perform vacuum filtration and vacuum dry at 105 °C for 6 min to obtain the modified basalt fiber / aramid nanofiber insulating paper.

[0039] Example 2

[0040] S1: Mix 2 g of PPTA fiber, 3 g of KOH, 35 ml of deionized water and 550 ml of DMSO to form a mixed solution, and stir the mixed solution to obtain an ANF / DMSO solution;

[0041] S2: Silane functional modification of the surface of basalt fibers: Add 10 g of basalt fibers to 30 ml of absolute ethanol, stir, filter with suction, separate and dry. Then prepare an ethanol solution of KH792 with a volume fraction of 3%, use 1.2 mol / L hydrochloric acid as a catalyst, and adjust the pH of the solution to 4; add the dried basalt fibers thereto, continuously stir for 4 h, filter with suction, separate and dry to obtain silane-functionalized basalt fibers;

[0042] S3: In-situ growth of ZIF-8 on the surface of silane-functionalized basalt fibers to obtain modified basalt fibers: Add 2.87 g of zinc sulfate heptahydrate to a beaker containing 200 ml of methanol and stir evenly at a rotation speed of 250 r / min at room temperature; subsequently, add 1.0939 g of the silane-functionalized basalt fibers obtained in S2 to the above solution and continuously stir for 12 h to obtain a dispersion; separately, add 1.886 g of 2-methylimidazole to a beaker containing 200 ml of methanol and stir evenly at a rotation speed of 250 r / min at room temperature. Subsequently, mix the above solution with the dispersion and continuously stir for 1.5 h until homogeneous, then let stand for 24 h to complete the reaction; finally, centrifuge the completely reacted solution at a rotation speed of 3500 r / min for 8 min, take out the precipitate and wash it with methanol, and place the product in an oven at 70 °C to dry for 12 h until constant weight to obtain modified basalt fibers;

[0043] S4: Mix 0.456 g of modified basalt fibers with 200 ml of ANF / DMSO solution and disperse them under ultrasonic stirring for 12 min to form a suspension, and simultaneously inject 420 ml of deionized water for protonation reduction to prepare a modified basalt fiber-ANF / DMSO dispersion;

[0044] S5: Wash the modified basalt fiber-ANF-DMSO dispersion obtained in S4 4 times with deionized water, remove the DMSO solvent, then perform vacuum filtration and vacuum dry at 110 °C for 4 min to obtain the modified basalt fiber / aramid nanofiber insulating paper.

[0045] Example 3

[0046] S1: Mix 3 g of PPTA fibers, 5 g of KOH, 64 ml of deionized water and 1200 ml of DMSO to form a mixed solution, stir the mixed solution to prepare an ANF / DMSO solution;

[0047] S2: Silane functional modification of the surface of basalt fibers: Add 10 g of basalt fibers to 30 ml of absolute ethanol, stir, filter with suction, separate and dry. Then prepare an ethanol solution of KH550 with a volume fraction of 5%, use 1.5 mol / L hydrochloric acid as a catalyst, and adjust the pH of the solution to 5; add the dried basalt fibers thereto, continuously stir for 5 h, filter with suction, separate and dry to obtain silane-functionalized basalt fibers;

[0048] S3: In-situ growth of ZIF-8 on the surface of silane-functionalized basalt fibers to obtain modified basalt fibers: Add 5.74 g of zinc sulfate heptahydrate to a beaker containing 300 ml of methanol and stir evenly at a speed of 300 r / min at room temperature; then add 2.46 g of the silane-functionalized basalt fibers obtained in S2 to the above solution and continuously stir for 12 h to obtain a dispersion; separately, add 4.1 g of 2-methylimidazole to a beaker containing 300 ml of methanol and stir evenly at a speed of 300 r / min at room temperature. Then mix the above solution with the dispersion and continuously stir for 2 h until uniform, and then let it stand for 24 h to complete the reaction; finally, centrifuge the completely reacted solution at a speed of 400 r / min for 10 min, take out the precipitate and wash it with methanol, and place the product in an oven at 80 °C and dry it for 12 h to constant weight to obtain the modified basalt fibers;

[0049] S4: Mix 0.475 g of the modified basalt fibers with 200 ml of ANF / DMSO solution and disperse them for 15 min under ultrasonic stirring to form a suspension, and simultaneously inject 440 ml of deionized water for protonation reduction to prepare a modified basalt fiber-ANF / DMSO dispersion;

[0050] S5: Wash the modified basalt fiber-ANF-DMSO dispersion obtained in S4 5 times with deionized water, remove the DMSO solvent, then perform vacuum filtration and vacuum dry at 120 °C for 3 min to obtain the modified basalt fiber / aramid nanofiber insulating paper.

[0051] Example 4

[0052] Similar to Example 3, except that the addition amount of the modified basalt fibers in S4 is 0.5 g.

[0053] Comparative Example 1

[0054] Similar to Example 3, except that in-situ growth of ZIF-8 on the surface of the basalt fibers is not carried out.

[0055] Comparative Example 2

[0056] Similar to Example 3, except that modified basalt is not added.

[0057] Performance Test

[0058] Thermal conductivity: Tested according to GB / T5591.2-2017;

[0059] Breakdown strength: Tested according to GB / T3333-1999;

[0060] Tensile strength: Tested according to ASTM D828-97.

[0061] The test results are shown in Table 1 as follows:

[0062] Table 1 Performance test results of the insulating papers obtained in Examples 1-4 and Comparative Examples 1-3

[0063]

[0064] It can be seen from the data in Table 1 that the addition of the modified basalt fibers greatly improves the thermal conductivity, breakdown strength and tensile strength of the aramid nanofibers. The results of Example 4 show that when the addition amount of the modified basalt fibers reaches a certain level, the performance indexes of the obtained modified basalt fiber / aramid nanofiber insulating paper are no longer optimized actively and even slightly decreased. The results of Comparative Examples 1-2 show that the modified basalt fibers with ZIF-8 grown in-situ on the surface play an important role in improving the performance of the insulating paper.

Claims

1. A preparation method of a modified basalt fiber / aramid nanofiber insulating paper, characterized in that, It includes the following steps: S1: Mix PPTA fibers, KOH, deionized water and DMSO to form a mixed solution, and stir the mixed solution to obtain an ANF / DMSO solution; S2: Perform surface silane functionalization modification on basalt fibers; S3: Conduct in-situ growth of ZIF-8 on the surface of silane-functionalized basalt fibers to obtain modified basalt fibers; S4: Mix the modified basalt fibers with the ANF / DMSO solution and disperse them under ultrasonic stirring to form a suspension, and simultaneously inject deionized water for protonation reduction to obtain a modified basalt fiber-ANF / DMSO dispersion; S5: Wash the modified basalt fiber-ANF-DMSO dispersion obtained in S4 with deionized water, remove the DMSO solvent, then perform vacuum filtration and vacuum drying to obtain the modified basalt fiber / aramid nanofiber insulating paper.

2. The preparation method of the modified basalt fiber / aramid nanofiber insulating paper according to claim 1, characterized in that, The mixing ratio of the PPTA fibers, KOH, deionized water and DMSO in S1 is: 1.5 - 2 g : 2.5 - 3 g : 30 - 35 ml : 500 - 600 ml.

3. The preparation method of the modified basalt fiber / aramid nanofiber insulating paper according to claim 1, characterized in that, The surface silane functionalization modification in S2 includes the following steps: Add basalt fibers to anhydrous ethanol and stir, filter and separate and dry, then prepare an ethanol solution of an amino silane coupling agent, use 1 - 1.5 mol / L hydrochloric acid as a catalyst, and adjust the pH of the solution to 3.5 - 5; Add the basalt fibers into it, continuously stir for 4 - 5 h, filter and separate and dry to obtain silane-functionalized basalt fibers.

4. The preparation method of the modified basalt fiber / aramid nanofiber insulating paper according to claim 1, wherein, In S3, the treatment method for in-situ growth of ZIF-8 on the surface includes the following steps: Add zinc salt to a beaker containing methanol and stir evenly at a speed of 200 - 300 r / min at room temperature; Subsequently, add the silane-functionalized basalt fibers to the above solution and continuously stir for 12 h to obtain a dispersion; Take another 2-methylimidazole and add it to a beaker containing methanol and stir evenly at a speed of 200 - 300 r / min at room temperature, then mix the above solution with the dispersion and continuously stir for 1 - 2 h until uniform, and then let it stand for 24 h to complete the reaction; Finally, centrifuge the solution after the reaction is complete at a speed of 3000 - 4000 r / min for 5 - 10 min, take out the precipitate and wash it with methanol, and place the product in an oven at 60 - 80 °C and dry it for 12 h to constant weight to obtain modified basalt fibers.

5. The preparation method of the modified basalt fiber / aramid nanofiber insulating paper according to claim 4, characterized in that, The molar ratio of the zinc salt to the 2-methylimidazole used is 1 : 2 - 2.

5.

6. The preparation method of the modified basalt fiber / aramid nanofiber insulating paper according to claim 4, characterized in that, The added mass of the silane-functionalized basalt fibers is 0.2 - 0.25 times the total mass of the zinc salt and 2-methylimidazole.

7. The preparation method of the modified basalt fiber / aramid nanofiber insulating paper according to claim 1, characterized in that, In S4, the modified basalt fibers account for 35 - 50% of the mass of the finally obtained insulating paper; the ultrasonic dispersion time is 10 - 15 min.

8. The preparation method of the modified basalt fiber / aramid nanofiber insulating paper according to claim 1, characterized in that, In S4, the volume ratio of the suspension to deionized water is 1 : 2 - 2.

2.

9. The preparation method of the modified basalt fiber / aramid nanofiber insulating paper according to claim 1, characterized in that, In S5, the washing is carried out 3 - 5 times, and the drying conditions are vacuum drying at 105 - 120 °C for 3 - 6 min.

10. A modified basalt fiber / aramid nanofiber insulating paper, characterized in that, Prepared by using the preparation method according to any one of claims 1 - 9.

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