Preparation method of high-toughness polyimide nanofiber film

Abstract

The present application relates to the technical field of polyimide film preparation, and in particular to a preparation method of high-toughness polyimide nanofiber film. The preparation method comprises a step of synthesizing polyamide acid, and further comprises a step of property regulation of a spinning solution containing the polyamide acid; the mixed solvent used for the property regulation of the spinning solution is selected from at least two of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, 1,4-dioxane, methanol, ethanol, toluene, chloroform, tetrahydrofuran, n-hexane, n-heptane and n-decane. The film prepared by the method has a breaking strength of 30 MPa and an elongation at break of 60%, various diamine and dianhydride monomers and solvent systems can be prepared by the method, and the mechanical properties are improved, the preparation process has a wide application range, and the polyimide film prepared by the method can be used for oil-water separation and has the ability of cyclic use and hot oil separation.

Description

Technical Field

[0001] This invention relates to the field of polyimide film preparation technology, and specifically to a method for preparing a high-toughness polyimide nanofiber film. Background Technology

[0002] Given the increasingly severe energy and environmental problems, the development of organic membrane materials with excellent heat resistance and controllable pore size and distribution has become a key requirement in the fields of water treatment and membrane technology. Polyimide (PI) possesses excellent mechanical properties, easy structural design, hydrolysis resistance, radiation resistance, solvent resistance, and high-temperature resistance, making it widely applicable in aerospace, electronics, and biomedicine. Meanwhile, nanofiber membranes prepared by electrospinning not only exhibit excellent structural controllability but also possess high porosity, which helps to significantly improve water treatment efficiency.

[0003] However, PI nanofiber membranes still face several challenges in their preparation and practical applications. First, obtaining electrospun membranes with uniform fiber morphology places high demands on the polyamic acid (PAA) spinning solution. PAA spinning solutions with low molecular weight or low solid content are prone to producing numerous beaded morphologies or failing to form films during electrospinning, while spinning solutions with high molecular weight and high solid content have excessive viscosity, making electrospinning difficult. Therefore, the properties of the spinning solution are crucial process parameters for preparing PI nanofiber membranes with uniform morphology and stable performance. Second, nanofiber membranes prepared by electrospinning often exhibit poor overall mechanical properties due to uneven fiber morphology and random arrangement. Furthermore, PI itself has a relatively rigid structure and strong intermolecular forces, resulting in insufficient toughness and susceptibility to damage during long-term use, limiting its stability and durability. To improve the mechanical properties of PI nanofiber membranes, researchers have explored various methods, including monomer design, crosslinking, and blending modification; however, these methods are typically costly, complex, and lack versatility. Therefore, improving the spinnability of PAA spinning solution and the mechanical properties of PI nanofiber membranes through simple, controllable, and universal process optimization has important scientific and practical significance for the design, preparation, and application of PI electrospun nanofiber membranes. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a high-toughness polyimide nanofiber film and its preparation method.

[0005] In a first aspect, the present invention provides a method for preparing a high-toughness polyimide nanofiber film. This method includes a step of synthesizing polyamic acid (PAA) and a step of regulating the properties of a spinning solution containing the polyamic acid. The mixed solvent used for regulating the properties of the spinning solution is selected from at least two of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, 1,4-dioxane, methanol, ethanol, toluene, chloroform, tetrahydrofuran, n-hexane, n-heptane, and n-decane. The present invention discovers that by regulating the composition of the solvent in the PAA spinning solution, the properties of the spinning solution are significantly affected. Without changing the solid content of the PAA spinning solution, the viscosity of the spinning solution can be increased or decreased as needed to obtain a PAA spinning solution with better spinnability. This regulation can optimize the morphology of the fibers, causing a large number of bead defects to disappear in fibers prepared from PAA spinning solutions with low solid content or low molecular weight. The uniform fiber morphology can directly promote the improvement of the mechanical properties of the nanofiber membrane.

[0006] Preferably, the method for preparing the high-toughness polyimide nanofiber film includes the following steps:

[0007] 1) Polyamic acid synthesis: Aromatic dianhydride and diamine are used as raw materials for polycondensation reaction to obtain a polyamic acid (PAA) solution with high solid content.

[0008] 2) Controlling the properties of the spinning solution: The high-solids-content polyamic acid solution is mixed with the mixed solvent and stirred to obtain a polyamic acid spinning solution.

[0009] 3) Preparation of polyamic acid nanofiber membrane: The polyamic acid spinning solution is electrospun to obtain a polyamic acid nanofiber membrane.

[0010] 4) Preparation of polyimide nanofiber membrane: The polyamic acid nanofiber membrane is thermally imidized to obtain a high-toughness polyimide (PI) nanofiber film.

[0011] Preferably, in step 2), the mixed solvent includes a first solvent and a second solvent, wherein the first solvent is selected from one or more of N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, 1,4-dioxane, methanol, ethanol, toluene, chloroform, tetrahydrofuran, n-hexane, n-heptane, and n-decane; and / or, the second solvent is N,N-dimethylformamide.

[0012] Preferably, the ratio of the first solvent to the second solvent is 10:90 to 60:40 w / w. For example, it can be 10:90, 20:80, 25:75, 30:70, 35:65, 40:60, 50:50, 60:40, etc., as well as any values ​​and ranges therein.

[0013] In some preferred embodiments provided by the present invention, the first solvent is 1,4-dioxane, the second solvent is N,N-dimethylformamide, and the suitable ratio of the two is preferably 20:80 to 50:50, for example 20:80, 30:70, 40:60, 50:50.

[0014] Further preferably, in step 1), the aromatic dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, hexafluoroisopropylphthalic anhydride, and 4,4'-biphenyl ether dianhydride, with 3,3',4,4'-biphenyltetracarboxylic acid dianhydride being a more preferred choice.

[0015] More preferably, the diamine is selected from one or more of 4,4'-diaminodiphenyl ether, m-phenylenediamine, 4,4'-diaminobiphenyl, p-phenylenediamine, and 3,4-diaminodiphenyl ether. When the diamine is selected as 4,4'-diaminodiphenyl ether, its ether bond provides a certain degree of flexibility to the molecular chain, which can further improve the toughness of the PI nanofiber membrane.

[0016] The molar ratio of the aromatic dianhydride to the diamine is preferably 0.96:1 to 1.03:1, with a more suitable ratio such as 1.01:1, to ensure an equal number of groups between the anhydride and the amino group, thereby better increasing the molecular weight of the synthesized PAA.

[0017] Preferably, the solvent of the polyamic acid solution is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; the mass fraction of the polyamic acid solution is 10-20 wt%.

[0018] Further preferably, the preparation method further includes a step of purifying the aromatic dianhydride and the diamine; the purification method of the aromatic dianhydride is selected from one or more of heating, recrystallization of acetic anhydride, and vacuum sublimation, and the purification method of the diamine is selected from one or more of recrystallization and vacuum sublimation.

[0019] Further preferably, in step 1), the polycondensation reaction is carried out in a nitrogen atmosphere, the reaction temperature is 15~30 ℃ (preferably room temperature), and the reaction time is 6~12 h.

[0020] According to a specific embodiment of the present invention, the specific steps for synthesizing polyamic acid include: dissolving diamine in N,N-dimethylformamide under nitrogen protection, mechanically stirring at room temperature, slowly adding dianhydride, the total polycondensation reaction time being 6-12 hours, the molar ratio of aromatic dianhydride to diamine being 0.96:1-1.03:1, the mass fraction of PAA solution being 10-20 wt%, and the viscosity of PAA solution being 3 × 10⁻⁶. 4 ~2×10 6 mPa·s.

[0021] Further preferably, in step 2), the mass fraction of the polyamic acid spinning solution is 10~15 wt%.

[0022] Further optimization is made in step 3), where the high-voltage electrostatic field voltage is 10~30 kV, the receiving distance is 10~20 cm, the receiving device is a flat plate, and the injection speed is 0.5~1.0 mL / h.

[0023] According to a specific embodiment of the present invention, the preparation method of the high-toughness polyamic acid nanofiber membrane is electrospinning. More preferably, the process parameters are: the high-voltage electrostatic field voltage is 10~30 kV, the receiving distance is 10~20 cm, the solution volume in the syringe is 0.5~2 mL, the receiving device is a flat plate, the injection speed is 0.5~1.0 mL / h, and the mixed solution is continuously electrospinned to obtain a fiber film with a thickness of 10~200 μm. After spinning, the fiber film is torn off with pointed tweezers and cut into any shape and size with surgical scissors.

[0024] Further preferred, in step 4), thermal imidization is carried out by a staged heating method; preferably, the temperature is increased to 70-90 ℃ at a heating rate of 3-8 ℃ / min and held for 30-50 min, then increased to 130-170 ℃ for 0.8-1.2 h and held for 1-1.2 h, then increased to 330-370 ℃ for 0.8-1.2 h and held for 1-1.2 h.

[0025] According to a specific embodiment of the present invention, the imidization method of the polyamic acid film is a staged heating thermal imidization. The specific process parameters include: heating from room temperature to 80°C at a heating rate of 5°C / min and holding for 40 min; heating from 80°C to 150°C for 1 h and holding for 1 h; heating from 150°C to 350°C for 1 h and holding for 1 h; and natural cooling. By using the above-mentioned staged heating thermal imidization, it is possible to ensure that PAA is completely imidized into PI.

[0026] In this invention, a high-strength, high-toughness, high-porosity, and uniform PI nanofiber membrane can be prepared using the above method. Compared with PI nanofiber membranes without spinning solution property control, the fiber morphology is significantly improved after control, with beads gradually decreasing and disappearing, and the fiber morphology becoming increasingly uniform. The tensile strength of the corresponding fiber membrane can be increased from 2 MPa to 30 MPa, and the elongation at break can be increased from 8% to 60%. Benefiting from its improved mechanical properties and the solvent resistance and high-temperature resistance of PI, the PI nanofiber membrane can be used as a self-supporting film for oil-water separation applications, demonstrating recyclability and hot oil separation capabilities.

[0027] Secondly, the present invention provides a high-toughness polyimide nanofiber film, which is prepared by the above-described preparation method.

[0028] Preferably, the high-toughness polyimide nanofiber film has a tensile strength of 14~30 MPa and a tensile elongation of 20~60%.

[0029] Thirdly, this invention provides the above-described preparation method or the application of the above-described high-toughness polyimide nanofiber film in oil-water separation. The high-toughness polyimide nanofiber film provided by this invention exhibits excellent properties such as good recyclability and hot oil separation when applied to oil-water separation.

[0030] The beneficial effects of this invention are at least as follows: The method for preparing high-toughness polyimide nanofiber films provided by this invention utilizes the influence of mixed solvents on the properties of the spinning solution to improve the morphology of electrospun fibers, thereby effectively enhancing the mechanical properties of PI nanofiber membranes, especially their toughness. Unlike many reported methods for improving the mechanical properties of PI, such as monomer design, crosslinking, and blending modification, this method of controlling the spinning solution does not require complex post-treatment, the process is simple and easy to implement, and it can serve as a general method, which has significant scientific value for guiding the design of electrospun membrane systems and the adjustment of process parameters. The high-toughness PI nanofiber membranes prepared by this method have demonstrated excellent separation performance, temperature resistance, and recyclability in oil-water separation applications, showing broad application prospects. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 These are scanning electron microscope images of the polyimide nanofiber membranes in Examples 1-6 and Comparative Examples 1-3 of the present invention.

[0033] Figure 2 The mechanical properties of the polyimide nanofiber membranes in Examples 2, 5 and Comparative Example 2 of this invention are shown.

[0034] Figure 3 The contact angle of the polyimide nanofiber membrane in Examples 2, 5 and Comparative Example 2 of this invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0036] Unless otherwise specified, specific techniques or conditions in the embodiments of this invention shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Devices, instruments, reagents, etc., whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels. All raw materials used in this invention are readily available in the domestic market.

[0037] In the following embodiments of the present invention, the purification of aromatic dianhydrides is carried out by vacuum sublimation, with a purity greater than 99.9%, and the purification of diamines is carried out by vacuum sublimation, with a purity greater than 99.9%.

[0038] Example 1

[0039] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The aromatic dianhydride used is 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), the diamine used is 4,4'-diaminodiphenyl ether (ODA), and the solvents are N,N-dimethylformamide (DMF) and 1,4-dioxane (Diox).

[0040] The preparation method of the high-toughness polyimide nanofiber film provided in this embodiment includes the following specific steps:

[0041] 1) Polyamic acid synthesis: First, BPDA and ODA were purified and fed in a BPDA:ODA molar ratio of 1:1 with DMF as solvent. The mixture was mechanically stirred at room temperature and polycondensed for 12 h. After the reaction was completed, the viscosity was tested to prepare a 20wt% PAA solution.

[0042] 2) Preparation of spinning solution: Weigh 20wt% PAA solution, dilute with DMF and Diox to prepare PAA spinning solution, test the viscosity, and the solid content of PAA spinning solution is 10wt%. 、 The Diox:DMF ratio is 20:80.

[0043] 3) Preparation of PAA nanofiber membrane: The prepared PAA spinning solution was transferred to a syringe for electrospinning. The positive DC voltage used was 13 kV, and the negative DC voltage was -5 kV. The solution volume in the syringe was 2 mL, and the solution injection speed was 1 mL / h. The receiving device was a flat plate with a layer of electrospinning release paper attached to its surface, i.e., no fiber orientation treatment was performed. The distance between the needle and the receiving device was 15 cm. The mixed solution was continuously electrospinned. After spinning, the fiber film could be peeled off with pointed tweezers and dried overnight at room temperature and normal pressure.

[0044] 4) Preparation of PI nanofiber membrane: The PAA nanofiber membrane was cut into appropriate sizes and subjected to thermal imidization treatment in air atmosphere by staged heating. The specific heating process parameters were as follows: starting from room temperature, the temperature was increased to 80℃ at a heating rate of 5℃ / min and held for 40 min, then increased to 150℃ for 1 h and held for 1 h, then increased to 350℃ for 1 h and held for 1 h, and finally cooled naturally to obtain the PI nanofiber membrane.

[0045] Example 2

[0046] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 1 is that the solid content of the spinning solution used is 12.5 wt%.

[0047] Example 3

[0048] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 1 is that the solid content of the spinning solution used is 15wt%.

[0049] Example 4

[0050] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 1 is that the Diox:DMF ratio used is 50:50.

[0051] Example 5

[0052] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that the Diox:DMF ratio used is 50:50.

[0053] Example 6

[0054] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 3 is that the Diox:DMF ratio used is 50:50.

[0055] Example 7

[0056] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with methanol, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and methanol (MeOH).

[0057] Example 8

[0058] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with ethanol, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and ethanol (EtOH).

[0059] Example 9

[0060] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with toluene, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and toluene (Tol).

[0061] Example 10

[0062] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with chloroform, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and chloroform (TCM).

[0063] Example 11

[0064] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with tetrahydrofuran, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and tetrahydrofuran (THF).

[0065] Example 12

[0066] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with n-hexane, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and n-hexane.

[0067] Example 13

[0068] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with n-heptane, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and n-heptane.

[0069] Example 14

[0070] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with n-decane, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and n-decane (Decane).

[0071] Example 15

[0072] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with N,N-dimethylacetamide, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc).

[0073] Example 16

[0074] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with N-methylpyrrolidone, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP).

[0075] Example 17

[0076] This embodiment provides a high-toughness polyimide nanofiber film and its preparation method. The difference from Example 2 is that Diox is replaced with dimethyl sulfoxide, and the solvent used is a mixed solvent prepared from N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO).

[0077] Comparative Example 1

[0078] The same method as in Example 1 was used, except that the spinning solution preparation step did not use a mixed solvent for dilution, and the solvent used was only N,N-dimethylformamide (DMF), and the solid content of the spinning solution was still 10 wt%.

[0079] Comparative Example 2

[0080] The difference from Comparative Example 1 is that the solid content of the spinning solution is 12.5 wt%.

[0081] Comparative Example 3

[0082] The difference from Comparative Example 1 is that the solid content of the spinning solution is 15 wt%.

[0083] Viscosity tests were conducted on the PAA spinning solutions prepared in Examples 1-17 and Comparative Examples 1-3, according to the relevant guidelines of national standard GB / T 22235-2008. Tensile strength and elongation at break were tested on the prepared high-toughness polyimide nanofiber membranes, according to the relevant guidelines of national standard GB / T 1040.3-2006, at a tensile rate of 5 mm / min. Some test results are shown in Table 1 below.

[0084] Table 1

[0085]

[0086] As shown in Table 1, the method of this invention can control the viscosity of the spinning solution. Without changing the solid content, the viscosity can be increased or decreased to a range suitable for electrospinning conditions, significantly improving the spinnability of the spinning solution and broadening the selection range of molecular weight and solid content. Simultaneously, the fiber morphology of the prepared PI nanofiber membrane is significantly improved, with the non-uniform beaded morphology reduced to the point of disappearance. This morphology improvement and solvent effect enhance the mechanical properties of the PI nanofiber membrane, such as… Figure 1 , Figure 2 As shown.

[0087] Example 18

[0088] This embodiment provides an experimental method for oil-water separation using high-toughness polyimide nanofiber membranes. The PI nanofiber membranes prepared in Examples 1-17 are sandwiched between two glass tubes to construct an oil-water separation device. The device is placed vertically, and 10 ml of an oil:water (1:1, V / V) mixture is poured in, allowing the oil to pass through the membrane under its own gravity. The oil phase passage time and the amount of water retained are recorded, and the membrane separation flux (Flux) and separation efficiency (SE) are calculated. In the oil-water mixture, the oil phase is one of dichloromethane, chlorobenzene, n-hexane, n-decane, or vegetable oil. To easily distinguish between the oil and water phases, the oil phase is stained red with Nile Red, and the water phase is stained blue with Methyl Blue.

[0089] like Figure 3 As shown, the PI nanofiber films prepared through Examples 1-17 have water contact angles of 120~129°, exhibiting strong hydrophobicity and meeting the application requirements for oil-water separation. The film separation flux can reach 10518.83 Lm. -2 h -1 The separation efficiency exceeded 95%, and no significant flux loss was observed in six cyclic separation experiments, demonstrating its recyclability. Furthermore, the membrane can separate hot oil-water mixtures at 80℃ without membrane damage or loss of separation performance, demonstrating its ability to separate hot oil. The contact angle and oil-water separation test results for partial contact angles and dichloromethane-water mixtures are shown in Table 2 below.

[0090] Table 2

[0091]

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-toughness polyimide nanofiber film, characterized in that, Includes the following steps: 1) Polyamic acid synthesis: Aromatic dianhydride and diamine are used as raw materials for polycondensation reaction to obtain a polyamic acid solution with high solid content; the mass fraction of the polyamic acid solution is 12.5 wt%. 2) Spinning solution property control: The high solids content polyamic acid solution is mixed with a mixed solvent and stirred to obtain a polyamic acid spinning solution; in step 2), the mixed solvent includes a first solvent and a second solvent, the first solvent is selected from one of n-hexane, n-heptane, and n-decane; the second solvent is N,N-dimethylformamide; the ratio of the first solvent to the second solvent is 20:80 w / w; 3) Preparation of polyamic acid nanofiber membrane: The polyamic acid spinning solution is electrospun to obtain a polyamic acid nanofiber membrane; 4) Preparation of polyimide nanofiber membrane: The polyamic acid nanofiber membrane is thermally imidized to obtain a high-toughness polyimide nanofiber film.

2. The method for preparing high-toughness polyimide nanofiber films according to claim 1, characterized in that, In step 1), the aromatic dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, hexafluoroisopropylphthalic anhydride, and 4,4'-biphenyl ether dianhydride; And / or, the diamine is selected from one or more of 4,4'-diaminodiphenyl ether, m-phenylenediamine, 4,4'-diaminobiphenyl, p-phenylenediamine, and 3,4-diaminodiphenyl ether; And / or, the molar ratio of the aromatic dianhydride to the diamine is 0.96:1 to 1.03:

1.

3. The method for preparing high-toughness polyimide nanofiber films according to claim 2, characterized in that, In step 1), the polycondensation reaction is carried out in a nitrogen atmosphere at a temperature of 15-30 °C for 6-12 h.

4. The method for preparing a high-toughness polyimide nanofiber film according to any one of claims 1-3, characterized in that, In step 3), the high voltage electrostatic field voltage is 10~30 kV, the receiving distance is 10~20 cm, the receiving device is a flat plate, and the injection speed is 0.5~1.0 mL / h.

5. The method for preparing a high-toughness polyimide nanofiber film according to any one of claims 1-3, characterized in that, In step 4), thermal imidization is carried out by a staged heating method.

6. The method for preparing a high-toughness polyimide nanofiber film according to claim 5, characterized in that, In step 4), the temperature is increased to 70-90℃ at a heating rate of 3-8℃ / min and held for 30-50 min, then increased to 130-170℃ for 0.8-1.2 h and held for 1-1.2 h, then increased to 330-370℃ for 0.8-1.2 h and held for 1-1.2 h.

7. A high-toughness polyimide nanofiber film, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The preparation method according to any one of claims 1-6 or the application of the high-toughness polyimide nanofiber film according to claim 7 in oil-water separation.

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