Electrospun porous polyimide micro-nanofiber membrane and dynamic preparation method thereof

Abstract

The application discloses a kind of electrostatic spinning porous polyimide micro-nanofiber membrane and its dynamic preparation method, the method is that binary organic amine is completely dissolved in polar aprotic solvent, according to the set adding proportion, batch addition binary organic anhydride solution, polyamide acid solution is prepared by heating and stirring and carrying out polycondensation reaction;Polyamide acid solution is chemically imidized using gradient heating method, and polyimide solution is prepared;Polar aprotic solvent and high volatility non-benign solvent are added in polyimide solution to dilute and stir, and polyimide spinning solution is prepared;Polyimide spinning solution is placed in controlled humidity environment to carry out electrospinning, and electrostatic spinning porous polyimide micro-nanofiber is obtained, and further electrostatic spinning porous polyimide micro-nanofiber membrane is obtained.The application realizes the continuous, controllable preparation of porous polyimide micro-nanofiber membrane, and provides a feasible technical path for its heat insulation protection, heat management and air filtration in extreme environment.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer fiber material preparation technology, specifically relating to an electrospun porous polyimide micro / nanofiber membrane and its dynamic preparation method. Background Technology

[0002] Polyimide is widely used in thermal insulation, separation membranes, and catalysis due to its excellent high-temperature resistance, thermal oxidation stability, and mechanical properties. Currently, polyimide micro / nanofibers with high specific surface areas are attracting increasing attention, and porous nanostructures will significantly enhance their performance in these applications. Electrospinning is currently considered an ideal method for preparing polyimide micro / nanofibers, involving the initial preparation of polyamic acid micro / nanofiber membranes, followed by thermal imidization to convert them into polyimide. Chinese invention patent application CN102251307A uses electrospinning to prepare polyimide micro / nanofiber membranes, which exhibit high porosity and high-temperature resistance, but the fibers themselves are smooth and non-porous, and their mechanical properties are insufficient.

[0003] Currently, the porous structure of polyimide nanofibers often relies on static post-processing, such as template etching and metal salt precipitation-induced structural evolution. For example, Chinese invention patent application CN104752665A first mixes soluble metal salts into a polyamic acid solution for spinning, then thermally imidizes the metal salts to convert them into metal oxide micro / nanoparticles, and finally dissolves the metal oxides by immersion in inorganic acid to form pores. However, this pore-forming method relies on multiple offline post-processing steps, resulting in a long process, complex technology, and difficulty in achieving continuous preparation. Furthermore, the pore structure control is highly dependent on the amount of metal salt added, and adding a high-quality fraction will lead to difficulties in nanofiber formation. Another example is Chinese invention patent application CN113308753A, which uses polyvinylpyrrolidone as a template to prepare composite fibers, followed by a long-term vacuum drying process to remove the polyvinylpyrrolidone, thus achieving the preparation of porous polyimide nanofibers. However, the nanofibers prepared by this method have few surface pores, and the post-processing technology makes it difficult to achieve mass production. Therefore, the dynamic and efficient construction of porous structures in electrospun polyimide nanofibers is of great significance for the industrial application of porous polyimide micro / nanofibers.

[0004] Chinese invention patent application CN105536352A discloses a method for rapidly preparing porous nanofibers by inducing phase separation of polymer solutions using water vapor. This method is mainly used for hydrophobic polymer materials such as polylactic acid (PLA). However, polyamic acid, the precursor material for polyimides, is hydrophilic and difficult to pore-form using water vapor induction. Therefore, chemical imidization of polyamic acid to prepare hydrophobic polyimide solutions has become an effective approach. However, highly volatile solvents (such as tetrahydrofuran and dichloromethane) are undesirable solvents for polyimide solutions. Their addition can easily lead to gelation of the solution, and the addition of a high proportion of non-solvents will significantly reduce the concentration of the polyimide solution, thus affecting the spinnability of the spinning solution. Solving these problems is the key and challenge for the efficient preparation of porous polyimide nanofibers. Summary of the Invention

[0005] To address the common problems in existing porous polyimide nanofiber preparation processes, such as limited polymer molecular weight, insufficient solution spinnability, and reliance on offline post-processing for porous structures, this invention provides an electrospun porous polyimide micro / nanofibers and their dynamic preparation method. This method combines stepwise polymerization with chemical imidization to construct a high-molecular-weight polyimide solution system with high chain entanglement. Furthermore, during electrospinning, a highly volatile, non-benign solvent with limited solubility for polyimide and a controlled humidity environment are synergistically introduced, enabling the simultaneous construction of surface and internal porous structures during the nanofiber forming stage. This achieves efficient and continuous preparation of porous polyimide micro / nanofibers.

[0006] To solve the above-mentioned technical problems and achieve the above-mentioned technical effects, the present invention is implemented through the following technical solution: A dynamic preparation method for electrospun porous polyimide micro / nanofiber membranes includes the following steps: Step 1: Weigh out the diamine (aromatic diamine) and the dianhydride (aromatic dianhydride) according to a certain molar ratio. Step 2: Under an inert gas environment, completely dissolve the diorganic amine (aromatic diamine) in a polar aprotic solvent to form a first mixture; Step 3: Under an inert gas environment, the dibasic organic acid anhydride (aromatic dianhydride) is dissolved in the first mixture in batches according to a set addition ratio to form the second mixture; Step 4: Under an inert gas environment, the second mixture is heated and stirred to allow the diorganic amine and the diorganic acid anhydride to undergo a polycondensation reaction in the polar aprotic solvent, thereby obtaining a polyamic acid solution. Step 5: In an inert gas environment, the polyamic acid solution is chemically imidized by gradient heating and stirring, so that the polyamic acid solution is directly dehydrated and polycondensed to obtain a polyimide solution with a certain mass fraction. Step 6: Mix the polar aprotic solvent and the highly volatile non-benign solvent in a certain mass ratio to form a mixed solvent; Step 7: Dilute the polyimide solution with the mixed solvent and stir for 2 hours to obtain a polyimide spinning solution with a certain mass fraction, forming an electrospinning precursor system with phase separation potential. Step 8: Place the polyimide spinning solution in a controlled humidity environment for electrospinning to obtain electrospun porous polyimide micro / nanofibers. Step 9: Prepare an electrospun porous polyimide micro / nanofiber membrane using the electrospun porous polyimide micro / nanofiber.

[0007] Furthermore, in step one, the molar ratio of the organic diamine to the diorganic anhydride is 1:1.02.

[0008] Furthermore, in step one, the diorganic amine is selected from one of 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)biphenyldiamine, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 1,5-diaminonaphthalene, 2,4-diaminotoluene, 4,4'-diaminodiphenyl sulfide, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

[0009] Furthermore, in step one, the dibasic organic acid anhydride is selected from one of the following: pyromellitic dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, cis-1,2,3,4-cyclobutane tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, and 3,4-dicarboxy-1,2,3,4-tetrahydronaphthalene-1,2-dianhydride.

[0010] Furthermore, in step two, the polar aprotic solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and N-ethylpyrrolidone.

[0011] Furthermore, in step three, when the dibasic organic anhydride is added in two batches, the amount added in the first batch is 30% to 60% of the total amount of the dibasic organic anhydride added, and the amount added in the second batch is 40% to 70% of the total amount of the dibasic organic anhydride added. The sum of the proportions of the two batches is 100%, and the time interval between the first batch and the second batch is 5 minutes.

[0012] Furthermore, in step four, when the dibasic organic anhydride is added in three batches, the first batch is 30% to 60% of the total amount of the dibasic organic anhydride added, the second batch is 20% to 40% of the total amount of the dibasic organic anhydride added, and the third batch is 20% to 40% of the total amount of the dibasic organic anhydride added. The sum of the proportions of the three batches is 100%. The time interval between the first batch and the second batch is 5 minutes, and the time interval between the second batch and the third batch is 2 minutes.

[0013] Furthermore, in step four, the temperature of the polycondensation reaction is 0~25℃, and the time of the polycondensation reaction is 4~10h.

[0014] Furthermore, in step five, the specific method for gradient heating and stirring is as follows: The first gradient temperature is 100~120℃, and the reaction is carried out at a constant temperature for 2~6 hours under mechanical stirring; The second gradient temperature is 180~200℃, and the reaction is carried out at a constant temperature for 8~10 hours under mechanical stirring.

[0015] Furthermore, in step six, the mass fraction of polyimide in the obtained polyimide solution is 15~20.0 wt.%.

[0016] Furthermore, in step six, the mass ratio of the highly volatile non-benign solvent to the polar aprotic solvent is 1:9 to 1:1.

[0017] Furthermore, in step six, the highly volatile non-benign solvent is selected from tetrahydrofuran and dichloromethane.

[0018] Furthermore, in step six, the polar aprotic solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and N-ethylpyrrolidone.

[0019] Furthermore, in step seven, the mass fraction of polyimide in the prepared polyimide spinning solution is 8~10 wt.%.

[0020] Furthermore, in step eight, electrospinning is performed using an electrospinning device, wherein the electrospinning voltage is 20.0~26.0kV, the spinning distance is 15.0~25.0cm, the spinning solution flow rate is 1.0~1.6mL / h, and the humidity range is 50~90%RH.

[0021] Furthermore, in step eight, the porosity of the electrospun porous polyimide micro / nanofibers obtained is 40-70%.

[0022] Based on the above dynamic preparation method, the present invention provides an electrospun porous polyimide micro / nanofiber membrane prepared by the above dynamic preparation method.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention prepares high-molecular-weight polyimide solutions through batch addition of polymerizable monomers and chemical imidization, and introduces a humidity-induced phase separation mechanism during electrospinning, enabling the dynamic and simultaneous construction of surface and internal porous structures during the fiber forming stage. This method avoids the structural damage risks associated with traditional offline secondary processing such as offline etching and template removal, resulting in polyimide micro / nanofibers with a uniform and continuous pore structure, while maintaining good structural integrity and thermal stability while increasing the material's specific surface area and permeability.

[0024] 2. This invention utilizes an electrospinning precursor system composed of a polar aprotic solvent and a highly volatile non-benign solvent. By controlling the solution composition, spinning process parameters, and environmental humidity, the porous structure is controllably constructed on the fiber surface and inside. The resulting porous polyimide micro / nanofibers not only maintain the inherent high-temperature resistance of polyimide materials but also ensure their structural stability under high-temperature conditions.

[0025] 3. This invention achieves dynamic pore-forming and continuous preparation of polyimide micro / nanofiber by controlling the proportion of highly volatile non-benign solvents and the humidity of the spinning environment in the polyimide spinning solution. This simplifies the processing flow of porous fiber materials, and the method is simple, efficient, and stable. It improves the consistency and repeatability of pore structure control, and provides reliable technical support for the application of porous polyimide fiber materials in fields such as thermal insulation, filtration and separation, and thermal management. It has good prospects for engineering promotion and industrial application.

[0026] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Specific embodiments of the present invention are given in detail below with reference to the accompanying drawings. Attached Figure Description

[0027] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 The graph shows the shear viscosity test results of the spinning solutions prepared by dianhydride in different batches in Examples 1-4 of this invention.

[0028] Figure 2 This is a surface structure diagram of the electrospun porous polyimide micro / nanofiber membrane prepared in Example 1 of the present invention, under a scanning electron microscope.

[0029] Figure 3 This is a scanning electron microscope image of the surface structure of the electrospun porous polyimide micro / nanofiber membrane prepared in Example 1 of the present invention.

[0030] Figure 4 This is a cross-sectional structure diagram of the electrospun porous polyimide micro / nanofiber membrane prepared in Example 1 of the present invention, under a scanning electron microscope.

[0031] Figure 5 The thermogravimetric decomposition curve of the electrospun porous polyimide micro / nanofiber membrane prepared in Example 1 of this invention is shown.

[0032] Figure 6 This is a yarn diagram of the electrospun porous polyimide micro / nanofiber membrane prepared in Example 1 of the present invention after being cut and twisted.

[0033] Figure 7 This is a fabric diagram of the electrospun porous polyimide micro / nanofiber yarn woven in Example 1 of the present invention.

[0034] Figure 8 The graph shows the test results of the thermal insulation performance of cotton fabric, electrospun non-porous polyimide micro / nanofiber yarn fabric, and electrospun porous polyimide micro / nanofiber yarn fabric with different stacking layers in Example 1 of the present invention.

[0035] Figure 9 The figure shows the test results of the thermal insulation performance of the single-layer electrospun porous polyimide micro / nanofiber yarn fabric in Example 1 of the present invention at different temperatures.

[0036] Figure 10 This is a surface structure diagram of the electrospun porous polyimide micro / nanofiber membrane prepared in Example 2 of the present invention, under a scanning electron microscope.

[0037] Figure 11 This is a surface structure diagram of the electrospun porous polyimide micro / nanofiber membrane prepared in Example 3 of the present invention, under a scanning electron microscope.

[0038] Figure 12 This is a surface structure diagram of the electrospun porous polyimide micro / nanofiber membrane prepared in Example 4 of the present invention, obtained under a scanning electron microscope. Detailed Implementation

[0039] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings to provide a clearer understanding of the invention's purpose, features, and advantages. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of the invention, but are merely illustrative of the essential spirit of the invention's technical solution.

[0040] In the following description, certain specific details are set forth for the purpose of illustrating various disclosed embodiments in order to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments may be practiced without one or more of these specific details. In other instances, well-known apparatuses, structures, and techniques associated with this application may not have been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0041] Unless the context requires otherwise, throughout the specification and claims, the word “comprising” and its variations, such as “including” and “having”, shall be understood to have an open, inclusive meaning, that is, to be interpreted as “including, but not limited to”.

[0042] Throughout this specification, references to "an embodiment" or "an embodiment" indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Therefore, the appearance of "in an embodiment" or "an embodiment" in various places throughout the specification does not necessarily refer to the same embodiment. Furthermore, a particular feature, structure, or characteristic may be combined in any manner in one or more embodiments.

[0043] The singular forms “a” and “the” used in this specification and the appended claims include plural references unless otherwise expressly stated herein. It should be noted that the term “or” is generally used to mean “and / or” unless otherwise expressly stated herein.

[0044] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0045] This invention provides an electrospun porous polyimide micro / nanofiber membrane and its dynamic preparation method, specifically including the following steps: Step 1: Weigh out the diamine (aromatic diamine) and the dianhydride (aromatic dianhydride) in a certain molar ratio.

[0046] Preferably, the molar ratio of the organic diamine to the diorganic anhydride is 1:1.02.

[0047] Preferably, the diorganic amine is selected from one of 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)biphenyldiamine, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 1,5-diaminonaphthalene, 2,4-diaminotoluene, 4,4'-diaminodiphenyl sulfide, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

[0048] Preferably, the dibasic organic acid anhydride is selected from one of the following: pyromellitic dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, cis-1,2,3,4-cyclobutane tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, and 3,4-dicarboxy-1,2,3,4-tetrahydronaphthalene-1,2-dianhydride.

[0049] Step 2: Under an inert gas environment, the binary organic amine is completely dissolved in a polar aprotic solvent to form a first mixture.

[0050] Preferably, the polar aprotic solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and N-ethylpyrrolidone.

[0051] Step 3: Under an inert gas environment, the binary organic acid anhydride is dissolved in the first mixture in batches according to the set addition ratio to form the second mixture.

[0052] Preferably, the dibasic organic anhydride can be added in two or three batches.

[0053] When the binary organic anhydride is added in two batches, the amount added in the first batch is 30% to 60% of the total amount of the binary organic anhydride added, and the amount added in the second batch is 40% to 70% of the total amount of the binary organic anhydride added. The sum of the proportions of the two batches is 100%, and the time interval between the first batch and the second batch is 5 minutes.

[0054] When the binary organic anhydride is added in three batches, the first batch is 30% to 60% of the total amount of the binary organic anhydride added, the second batch is 20% to 40% of the total amount of the binary organic anhydride added, and the third batch is 20% to 40% of the total amount of the binary organic anhydride added. The sum of the proportions of the three batches is 100%. The time interval between the first and second batches is 5 minutes, and the time interval between the second and third batches is 2 minutes.

[0055] This invention stabilizes the polymerization rate and chain growth process by controlling the addition ratio of dibasic organic acid anhydrides at different reaction stages. Unlike traditional one-time addition polymerization methods, this method of adding monomers in batches at different reaction stages according to a set ratio results in a smoother change in monomer concentration during the polymerization reaction. This avoids chain termination caused by a sudden increase in monomer concentration in the early stage of the reaction, prevents excessively wide molecular weight distribution, and prolongs the effective chain growth time. Through the above-mentioned stepwise polymerization method, this invention can obtain a polyamic acid solution system with a higher molecular weight and a relatively concentrated molecular weight distribution, thereby significantly improving the degree of entanglement of polymer molecular chains and providing feasibility for diluting polyimide solutions with highly volatile, non-benign solvents while ensuring spinnability.

[0056] Step 4: Under an inert gas environment, the second mixture is heated and stirred to allow the di-organic amine and the di-organic anhydride to undergo a polycondensation reaction in the polar aprotic solvent, thereby obtaining a polyamic acid solution.

[0057] Preferably, the polycondensation reaction is carried out at a temperature of 0-25°C for 4-10 hours.

[0058] Step 5: In an inert gas environment, the polyamic acid solution is chemically imidized by gradient heating and stirring, so that the polyamic acid solution is directly dehydrated and polycondensed to obtain a polyimide solution with a polyimide mass fraction of 15~20.0 wt.%.

[0059] Preferably, a dual-gradient heating and stirring method can be adopted, wherein the first gradient temperature is 100~120℃, and the reaction is carried out at a constant temperature for 2~6 hours under mechanical stirring; the second gradient temperature is 180~200℃, and the reaction is carried out at a constant temperature for 8~10 hours under mechanical stirring.

[0060] Since a high molecular weight and stable chain structure have been constructed in the polyamic acid stage of the previous step, the polyimide solution obtained in this step still exhibits good rheological properties and solution stability under high mass fraction conditions. This step effectively solves the problem in the prior art that polyimide is prone to precipitation and difficult to spin stably after the introduction of non-benign solvents, and provides the necessary material basis for the subsequent construction of a phase-separated electrospinning system.

[0061] Step 6: Mix the polar aprotic solvent and the highly volatile non-benign solvent in a certain mass ratio to form a mixed solvent.

[0062] Preferably, the mass ratio of the highly volatile non-benign solvent to the polar aprotic solvent is 1:9 to 1:1.

[0063] Preferably, the highly volatile non-benign solvent is selected from tetrahydrofuran and dichloromethane.

[0064] Preferably, the polar aprotic solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and N-ethylpyrrolidone.

[0065] Step 7: Dilute the polyimide solution with the mixed solvent and stir for 2 hours to obtain a polyimide spinning solution with a polyimide mass fraction of 8~10 wt.%, forming an electrospinning precursor system with phase separation potential.

[0066] This invention introduces a certain proportion of highly volatile, non-benign solvent into the polyimide solution to construct an electrospinning precursor system with phase separation potential. Because the polyimide solution obtained through stepwise polymerization has a high molecular weight and chain entanglement, the system can maintain stable shear rheological behavior and spinnability even under non-benign solvent dilution conditions, thereby avoiding rapid solution instability or gelation and providing material assurance for the dynamic construction of porous structures.

[0067] Step 8: Place the polyimide spinning solution in a controlled humidity environment for electrospinning to obtain the desired product. Figure 1 and Figure 2 The electrospun porous polyimide micro / nanofiber shown is an example.

[0068] Preferably, electrospinning can be performed using an electrospinning device, wherein the electrospinning voltage is 20.0~26.0kV, the spinning distance is 15.0~25.0cm, the spinning solution flow rate is 1.0~1.6mL / h, and the humidity range is 50~90%RH.

[0069] Preferably, the porosity of the electrospun porous polyimide micro / nanofibers is 40-70%.

[0070] Under the stretching effect of a high-voltage electrostatic field, the polyimide spinning solution forms micro- and nanofibers simultaneously. Meanwhile, the highly volatile, non-benign solvent preferentially evaporates and, in conjunction with ambient humidity, induces liquid-liquid and liquid-solid phase separation in the solution system. This allows for the simultaneous construction of surface and internal porous structures during the micro- and nanofiber formation process, achieving dynamic and synchronous formation of the micro- and nanofiber pore structures. By controlling the composition of the polyimide solution, the proportion of non-solvents, the electrospinning process parameters, and the ambient humidity conditions, the pore structure of the micro- and nanofibers can be controllably adjusted.

[0071] Step 9: Prepare an electrospun porous polyimide micro / nanofiber membrane using the electrospun porous polyimide micro / nanofiber.

[0072] The polyimide micro / nanofibers prepared by the above method possess continuous and intact fiber morphology and a uniformly distributed hierarchical porous structure, while maintaining the excellent high-temperature resistance and structural stability of polyimide materials. Therefore, the obtained polyimide micro / nanofibers can be further assembled into fiber membranes, yarns, or fabrics, suitable for applications such as thermal insulation, filtration, and thermal management.

[0073] The following details several specific embodiments of the present invention and their related test results.

[0074] Example 1 A dynamic preparation method for electrospun porous polyimide micro / nanofiber membranes, comprising the following steps: Step 1: In an inert gas environment, dissolve 3.2g of 2,2'-bis(trifluoromethyl)benzyldiamine in 152.9g of N-methylpyrrolidone to form the first mixture.

[0075] Step 2: Under an inert gas environment, add 4.4 g of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride to the first mixture in three batches as follows: First, add 30% of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride as the first batch to the first mixture and react for 5 minutes. Then, 40% of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride was added as the second batch to the first mixture, and the reaction was carried out for 2 minutes. Finally, the remaining 30% of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride was added to the first mixture as a third batch until it was completely dissolved to form the second mixture.

[0076] Step 3: Under an inert gas environment, the second mixture is mechanically stirred at 4°C for a total reaction time of 6 hours to obtain a polyamic acid solution.

[0077] Step 4: Under an inert gas environment, the polyamic acid solution is chemically imidized, allowing for direct dehydration and polycondensation to obtain a polyimide solution. The chemical imidization process employs a gradient temperature and stirring method: first, the solution is mechanically stirred and reacted at 120℃ for 4 hours, then the temperature is increased to 200℃ and mechanically stirred and reacted for 10 hours to obtain a polyimide solution with a mass fraction of 18 wt.%. Gel permeation chromatography results show that the obtained polyimide has a number-average molecular weight (Mn) of 158405 Da, a weight-average molecular weight (Mw) of 316859 Da, a viscosity-average molecular weight (Mυ) of 289420 Da, and a polydispersity index (PDI) of 2.00031.

[0078] Step 5: Add N-methylpyrrolidone and dichloromethane to the polyimide solution, making the mass ratio of dichloromethane to N-methylpyrrolidone 3:7. After stirring for 2 hours, a polyimide spinning solution with a mass fraction of 9 wt.% is obtained, which is the porous polyimide electrospinning precursor solution. See also Figure 1 As shown, the obtained polyimide spinning solution exhibits high shear rheological properties and high solution shear viscosity, demonstrating non-Newtonian fluid properties, which is beneficial for obtaining micro and nanofibers with uniform diameter.

[0079] Step Six: Electrospin 5 mL of porous polyimide electrospinning precursor solution was used. The needle inner diameter was 0.6 mm, silicone paper was used as the receiver, the voltage was 24 kV, the spinning solution flow rate was 1.2 mL / h, the distance between the needle and the receiver (spinning distance) was 16 cm, and the receiver rotation speed was 300 rpm. Porous polyimide micro / nanofibers were obtained on the receiver. The electrospinning humidity was 70% RH. After 4 hours of electrospinning, the following was further obtained: Figure 2 The electrospun porous polyimide micro / nanofiber membrane shown is an example.

[0080] Scanning electron microscopy results showed that the obtained electrospun porous polyimide micro / nanofiber membrane had a continuous and stable fiber structure, with an average fiber diameter of 730.49 ± 86.38 nm, a coefficient of variation of 11.83%, and a fiber porosity of 69.8%. The fiber surface [details omitted]. Figure 3 As shown, its cross-sectional structure is described in [reference needed]. Figure 4 As shown.

[0081] See Figure 5 As shown, the thermal performance analysis results indicate that the obtained electrospun porous polyimide micro / nanofiber membrane has a thermal degradation temperature as high as 600℃. (See also...) Figure 6 and Figure 7 As shown, the obtained electrospun porous polyimide micro / nanofiber membrane can be sheared and twisted to form micro / nanofiber yarn, and then woven into micro / nanofiber yarn fabric. Figure 7 ).

[0082] See Figure 8 As shown in the figure, the thermal insulation performance analysis results indicate that, compared to cotton fabric and non-porous polyimide micro / nanofiber yarn fabric of the same thickness, the obtained porous polyimide micro / nanofiber yarn fabric exhibits superior thermal insulation performance, and the thermal insulation performance increases with increasing thickness. See also... Figure 9 As shown, the obtained porous polyimide micro / nanofiber yarn fabric can maintain long-term thermal insulation stability at different temperatures.

[0083] Example 2 A dynamic preparation method for electrospun porous polyimide micro / nanofiber membranes, comprising the following steps: Step 1: In an inert gas environment, dissolve 3.2g of 2,2'-bis(trifluoromethyl)benzyldiamine in 152.9g of N-methylpyrrolidone to form the first mixture.

[0084] Step 2: Under an inert gas environment, add 4.4 g of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride to the first mixture in two batches as follows: First, add 50% of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride as the first batch to the first mixture and react for 5 minutes. Then, the remaining 50% of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride is added to the first mixture as a second batch until it is completely dissolved to form the second mixture.

[0085] Step 3: Under an inert gas environment, the second mixture is mechanically stirred at 4°C for a total reaction time of 6 hours to obtain a polyamic acid solution.

[0086] Step 4: Under an inert gas environment, the polyamic acid solution is chemically imidized, allowing for direct dehydration and polycondensation to obtain a polyimide solution. The chemical imidization process employs a gradient temperature and stirring method: first, the solution is mechanically stirred and reacted at 100℃ for 6 hours, then the temperature is increased to 180℃ and mechanically stirred and reacted for another 8 hours to obtain a polyimide solution with a mass fraction of 20 wt.%. Gel permeation chromatography results show that the obtained polyimide has a number-average molecular weight (Mn) of 39085 Da, a weight-average molecular weight (Mw) of 147973 Da, a viscosity-average molecular weight (Mυ) of 127098 Da, and a polydispersity index (PDI) of 3.78593.

[0087] Step 5: Add N-methylpyrrolidone and dichloromethane to the polyimide solution, making the mass ratio of dichloromethane to N-methylpyrrolidone 3:7. After stirring for 2 hours, a polyimide spinning solution with a mass fraction of 8 wt.% is obtained, which is the porous polyimide electrospinning precursor solution. See also Figure 1 As shown, the obtained polyimide spinning solution exhibits low shear rheological properties and low solution shear viscosity. The addition of both batches significantly reduced the molecular weight of polyimide, which is beneficial for preparing high-quality spinning solutions and provides support for the addition of non-benign solvents.

[0088] Step Six: Electrospin 5 mL of porous polyimide electrospinning precursor solution was used. The needle inner diameter was 0.6 mm, silicone paper was used as the receiver, the voltage was 26 kV, the spinning solution flow rate was 1.6 mL / h, the distance between the needle and the receiver (spinning distance) was 25 cm, and the receiver rotation speed was 300 rpm. Porous polyimide micro / nanofibers were obtained on the receiver. The electrospinning humidity was 70% RH. After 4 hours of electrospinning, the following was further obtained: Figure 10 The electrospun porous polyimide micro / nanofiber membrane shown is an example.

[0089] Scanning electron microscopy results showed that the obtained porous polyimide micro / nanofiber structure was continuous and stable, with an average fiber diameter of 567.83±154.55 nm, a coefficient of variation of 27.22%, and a fiber porosity of 55.3%.

[0090] Example 3 A dynamic preparation method for electrospun porous polyimide micro / nanofiber membranes, comprising the following steps: Step 1: In an inert gas environment, dissolve 3.2g of 2,2'-bis(trifluoromethyl)benzyldiamine in 152.9g of N-methylpyrrolidone to form the first mixture.

[0091] Step 2: Under an inert gas environment, add 4.4 g of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride to the first mixture in three batches as follows: First, add 60% of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride as the first batch to the first mixture and react for 5 minutes. Then, 20% of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride was added as the second batch to the first mixture, and the reaction was carried out for 2 minutes. Finally, the remaining 20% ​​of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride was added to the first mixture as a third batch until it was completely dissolved to form the second mixture.

[0092] Step 3: Under an inert gas environment, the second mixture is mechanically stirred at 4°C for a total reaction time of 6 hours to obtain a polyamic acid solution.

[0093] Step 4: Under an inert gas environment, the polyamic acid solution is chemically imidized, allowing for direct dehydration and polycondensation to obtain a polyimide solution. The chemical imidization process employs a gradient temperature and stirring method: first, the solution is mechanically stirred and reacted at 110℃ for 2 hours, then the temperature is increased to 200℃ and mechanically stirred and reacted for 8 hours to obtain a polyimide solution with a mass fraction of 15 wt.%. Gel permeation chromatography results show that the obtained polyimide has a number-average molecular weight (Mn) of 45157 Da, a weight-average molecular weight (Mw) of 161862 Da, a viscosity-average molecular weight (Mυ) of 140420 Da, and a polydispersity index (PDI) of 3.58443.

[0094] Step 5: Add N-methylpyrrolidone and dichloromethane to the polyimide solution, making the mass ratio of dichloromethane to N-methylpyrrolidone 1:9. After stirring for 2 hours, a polyimide spinning solution with a mass fraction of 10 wt.% is obtained, which is the porous polyimide electrospinning precursor solution. See also Figure 1 As shown, the obtained polyimide spinning solution exhibits shear rheological properties, low solution shear viscosity, and relatively low molecular weight of polyimide, which is beneficial for increasing the synthesis mass fraction of the solution and improving the stability of spinning.

[0095] Step Six: Electrospin 5 mL of porous polyimide electrospinning precursor solution was used. The needle inner diameter was 0.6 mm, silicone paper was used as the receiver, the voltage was 20 kV, the spinning solution flow rate was 1.0 mL / h, the distance between the needle and the receiver (spinning distance) was 20 cm, and the receiver rotation speed was 300 rpm. Porous polyimide micro / nanofibers were obtained on the receiver. The electrospinning humidity was 50% RH. After 4 hours of electrospinning, the following was further obtained: Figure 11 The electrospun porous polyimide micro / nanofiber membrane shown is an example.

[0096] Scanning electron microscopy results showed that the obtained porous polyimide micro / nanofiber structure was continuous and stable, with an average fiber diameter of 653.34±125.65 nm, a coefficient of variation of 26.88%, and a fiber porosity of 38.4%.

[0097] Example 4 A dynamic preparation method for electrospun porous polyimide micro / nanofiber membranes, comprising the following steps: Step 1: In an inert gas environment, dissolve 3.2g of 2,2'-bis(trifluoromethyl)benzyldiamine in 152.9g of N-methylpyrrolidone to form the first mixture.

[0098] Step 2: Under an inert gas environment, add 4.4 g of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride to the first mixture in three batches as follows: First, add 30% of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride as the first batch to the first mixture and react for 5 minutes. Then, 30% of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride was added as the second batch to the first mixture, and the reaction was carried out for 2 minutes. Finally, the remaining 40% of the total amount of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride was added to the first mixture as a third batch until it was completely dissolved to form the second mixture.

[0099] Step 3: Under an inert gas environment, the second mixture is mechanically stirred at 4°C for a total reaction time of 6 hours to obtain a polyamic acid solution.

[0100] Step 4: Under an inert gas environment, the polyamic acid solution is chemically imidized, allowing for direct dehydration and polycondensation to obtain a polyimide solution. The chemical imidization process employs a gradient temperature and stirring method: first, the solution is mechanically stirred and reacted at 120°C for 4 hours, then the temperature is increased to 180°C and mechanically stirred and reacted for 1 hour to obtain a polyimide solution with a mass fraction of 18 wt.%. Gel permeation chromatography results show that the obtained polyimide has a number-average molecular weight (Mn) of 104810 Da, a weight-average molecular weight (Mw) of 209394 Da, a viscosity-average molecular weight (Mυ) of 190088 Da, and a polydispersity index (PDI) of 1.99784.

[0101] Step 5: Add N-methylpyrrolidone and dichloromethane to the polyimide solution, making the mass ratio of dichloromethane to N-methylpyrrolidone 1:1. After stirring for 2 hours, a polyimide spinning solution with a mass fraction of 10 wt.% is obtained, which is the porous polyimide electrospinning precursor solution. See also Figure 1 As shown, the obtained polyimide spinning solution has moderate shear rheological properties, solution shear viscosity, and polyimide molecular weight, which is beneficial for preparing high-quality spinning solutions and improving spinnability.

[0102] Step Six: Electrospin 5 mL of porous polyimide electrospinning precursor solution was used. The needle inner diameter was 0.6 mm, silicone paper was used as the receiver, the voltage was 22 kV, the spinning solution flow rate was 1.4 mL / h, the distance between the needle and the receiver (spinning distance) was 20 cm, and the receiver rotation speed was 300 rpm. Porous polyimide micro / nanofibers were obtained on the receiver. The electrospinning humidity was 90% RH. After 4 hours of electrospinning, the following was further obtained: Figure 12 The electrospun porous polyimide micro / nanofiber membrane shown is an example.

[0103] Scanning electron microscopy results showed that the obtained porous polyimide micro / nanofiber structure was continuous and stable, with an average fiber diameter of 723.47±215.46 nm, a coefficient of variation of 29.78%, and a fiber porosity of 49.8%.

[0104] Comparative Example 1 A dynamic preparation method for electrospun porous polyimide micro / nanofibers, the preparation steps are the same as in Example 1, the only difference being that in step 2, 4.4 g of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride is added to the first mixture in batch.

[0105] Gel permeation chromatography results showed that the obtained polyimide had a number-average molecular weight (Mn) of 142,000 Da, a weight-average molecular weight (Mw) of 306,800 Da, a viscosity-average molecular weight (Mυ) of 269,460 Da, and a polydispersity index (PDI) of 3.98443.

[0106] Scanning electron microscopy results showed that under the condition of one batch feeding of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, the electrospun polyimide micro / nanofibers were in a continuous fiber morphology, but the fiber diameter distribution was uneven and the uniformity of the internal pore structure was poor.

[0107] The results indicate that the polyimide micro / nanofibers prepared in Comparative Example 1 have significantly lower number-average molecular weight and significantly higher polydispersity index. Furthermore, the diameter distribution of the fibers obtained by electrospinning is uneven and the internal pore structure is poorly uniform. This is because the one-time addition of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride will cause the reaction rate to be too fast in the initial stage of polymerization, resulting in uneven molecular chain growth and a wider molecular weight distribution. At the same time, the fiber pore formation process is affected by the molecular weight distribution, which reduces the uniformity of the pore structure and ultimately affects the overall performance of the fiber.

[0108] Comparative Example 2 A dynamic preparation method for electrospun porous polyimide micro / nanofibers is disclosed. The preparation steps are the same as in Example 1, except that in step 5, dichloromethane is not added to the polyimide solution before electrospinning.

[0109] Scanning electron microscopy results showed that when the polyimide solution was electrospun directly without the addition of dichloromethane, the electrospun polyimide micro / nanofibers were in a continuous fiber morphology, but the fiber surface and internal pore structure were less, with a porosity of 20.2%, which was much lower than that in Example 1.

[0110] Comparative Example 3 A dynamic preparation method for electrospun porous polyimide micro / nanofibers is disclosed. The preparation steps are the same as in Example 1, except that the electrospinning humidity is not controlled in step 6, i.e., electrospinning is performed when the ambient humidity is 32%RH.

[0111] Scanning electron microscopy results show that under an ambient humidity of 32%RH, the electrospun polyimide micro / nanofibers exhibit a continuous fiber morphology, but there are no obvious pore structures on the fiber surface or inside, indicating a high degree of fiber densification.

[0112] This invention achieves dynamic pore formation and continuous preparation of porous polyimide micro / nanofibers by organically combining a batch addition strategy of polymerizing monomers with a humidity-induced phase separation electrospinning process. This significantly simplifies the process flow, improves the uniformity and controllability of the pore structure, and provides a new technical approach for the large-scale application of porous polyimide micro / nanofiber materials.

[0113] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A dynamic preparation method for electrospun porous polyimide micro / nanofiber membranes, characterized in that, Includes the following steps: Step 1: Weigh out the di-organic amine and di-organic acid anhydride according to a certain molar ratio; Step 2: Under an inert gas environment, completely dissolve the binary organic amine in a polar aprotic solvent to form a first mixture; Step 3: Under an inert gas environment, the binary organic acid anhydride is dissolved in the first mixture in batches according to a set addition ratio to form the second mixture; Step 4: Under an inert gas environment, the second mixture is heated and stirred to allow the diorganic amine and the diorganic acid anhydride to undergo a polycondensation reaction in the polar aprotic solvent, thereby obtaining a polyamic acid solution. Step 5: In an inert gas environment, the polyamic acid solution is chemically imidized by gradient heating and stirring, so that the polyamic acid solution is directly dehydrated and polycondensed to obtain a polyimide solution with a certain mass fraction. Step 6: Mix the polar aprotic solvent and the highly volatile non-benign solvent in a certain mass ratio to form a mixed solvent; Step 7: Dilute and stir the polyimide solution using the mixed solvent to obtain a polyimide spinning solution with a certain mass fraction, forming an electrospinning precursor system with phase separation potential; Step 8: Place the polyimide spinning solution in a controlled humidity environment for electrospinning to obtain electrospun porous polyimide micro / nanofibers with a porosity of 40-70%. Step 9: Prepare an electrospun porous polyimide micro / nanofiber membrane using the electrospun porous polyimide micro / nanofiber.

2. The dynamic preparation method according to claim 1, characterized in that, In step one, the molar ratio of the organic diamine to the diorganic anhydride is 1:1.

02.

3. The dynamic preparation method according to claim 1, characterized in that, In step three, when the dibasic organic anhydride is added in two batches, the amount added in the first batch is 30% to 60% of the total amount of the dibasic organic anhydride added, and the amount added in the second batch is 40% to 70% of the total amount of the dibasic organic anhydride added. The sum of the proportions of the two batches is 100%, and the time interval between the first batch and the second batch is 5 minutes. When the binary organic anhydride is added in three batches, the first batch is 30% to 60% of the total amount of the binary organic anhydride added, the second batch is 20% to 40% of the total amount of the binary organic anhydride added, and the third batch is 20% to 40% of the total amount of the binary organic anhydride added. The sum of the proportions of the three batches is 100%. The time interval between the first and second batches is 5 minutes, and the time interval between the second and third batches is 2 minutes.

4. The dynamic preparation method according to claim 1, characterized in that, In step four, the temperature of the polycondensation reaction is 0~25℃, and the reaction time is 4~10h.

5. The dynamic preparation method according to claim 1, characterized in that, In step five, the specific method for gradient heating and stirring is as follows: The first gradient temperature is 100~120℃, and the reaction is carried out at a constant temperature for 2~6 hours under mechanical stirring; The second gradient temperature is 180~200℃, and the reaction is carried out at a constant temperature for 8~10 hours under mechanical stirring.

6. The dynamic preparation method according to claim 1, characterized in that, In step five, the mass fraction of polyimide in the obtained polyimide solution is 15~20.0 wt.%.

7. The dynamic preparation method according to claim 1, characterized in that, In step six, the mass ratio of the highly volatile non-benign solvent to the polar aprotic solvent is 1:9 to 1:

1.

8. The dynamic preparation method according to claim 1, characterized in that, In step seven, the mass fraction of polyimide in the prepared polyimide spinning solution is 8~10 wt.%.

9. The dynamic preparation method according to claim 1, characterized in that, In step eight, electrospinning is performed using an electrospinning device. The electrospinning voltage is 20.0~26.0kV, the spinning distance is 15.0~25.0cm, the spinning solution flow rate is 1.0~1.6mL / h, and the humidity range is 50~90%RH.

10. An electrospun porous polyimide micro / nanofiber membrane prepared by the dynamic preparation method according to any one of claims 1 to 9.

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