A method for preparing a pbo nanofiber membrane

Abstract

The application belongs to the field of new materials, and particularly relates to a preparation method of PBO nanofiber membrane, and specifically comprises the following steps: (1) preparing a precursor 4,6-diisopropoxy-polyhydroxyamide (ipr-PHA) solution; (2) pouring the ipr-PHA solution into deionized water, and performing precipitation, suction filtration and washing to obtain ipr-PHA polymer; (3) redissolving the ipr-PHA polymer in a solvent, and performing electrospinning to obtain an ipr-PHA nanofiber membrane; and (4) performing high-temperature heat treatment on the ipr-PHA nanofiber membrane to obtain a PBO nanofiber membrane. The above method significantly improves the solubility of PHA in an organic solvent, improves the spinnability of the PHA solution, the ipr-PHA has better thermal stability, the conversion rate of PHA to PBO is improved, and the prepared PBO nanofiber membrane has better comprehensive performance.

Description

Technical Field

[0001] This invention belongs to the field of new materials, and specifically provides a method for preparing PBO nanofiber membranes. Background Technology

[0002] Poly(p-phenylenebenzobisoxazole) (PBO) fiber is a high-performance aromatic heterocyclic organic fiber. Its rigid, all-aromatic heterocyclic structure endows it with excellent comprehensive properties, leading to its wide application in both military and civilian fields, earning it the title of "super fiber of the 21st century." However, PBO is typically used as a filament, and research on the direct electrospinning of PBO spinning solutions to prepare nanofiber membranes is limited. PBO nanofiber membranes possess excellent mechanical properties and heat resistance, along with a large specific surface area and aspect ratio, thus showing promising application prospects in many fields such as battery separators, composite reinforcement materials, flexible electrodes, high-temperature filtration, and electronic packaging.

[0003] PBO macromolecules are extremely rigid and have very weak solubility in organic solvents, making direct electrospinning very difficult. Furthermore, commonly used solvents for dissolving PBO have low volatility and are difficult to remove during the spinning process. Therefore, a two-step method for preparing PBO nanofiber membranes can be considered. The applicant's prior patent, "A Method for Preparing Poly(p-phenylenebenzodioxazole) Fibers," patent number ZL201910596905.2, uses a two-step dry spinning technique to prepare PBO filaments. First, a PBO precursor—polyhydroxyamide (PHA)—is prepared, followed by dry spinning, and then thermal cyclization to convert PHA fibers into PBO fibers. PHA has some solubility in organic solvents, so we considered using PHA for electrospinning. However, in practical applications, it was found that the solubility of PHA is still insufficient. While it can prepare micron-sized PBO filaments, it is difficult to meet the requirements for preparing nanofibers. The prepared PBO nanofibers have a relatively large diameter and poor shape, limiting its technological development.

[0004] The applicant needs to solve the problem of whether it can further improve the solubility of PHA in organic solvents and then apply it to the preparation of PBO nanofiber membranes. Summary of the Invention

[0005] To address the problems existing in the above-mentioned technologies, this invention provides a PBO nanofiber membrane and its preparation method, specifically including the following steps: (1) preparing a precursor 4,6-diisopropoxy-polyhydroxyamide (ipr-PHA) solution; (2) pouring the ipr-PHA solution into deionized water, precipitating, filtering, and washing to obtain an ipr-PHA polymer; (3) redissolving the ipr-PHA polymer in a solvent and electrospinning it to obtain an ipr-PHA nanofiber membrane; (4) subjecting the ipr-PHA nanofiber membrane to high-temperature heat treatment to obtain a PBO nanofiber membrane. This invention designs a 4,6-diisopropoxy-modified ipr-PHA polymer, which significantly improves the solubility of PHA in organic solvents, enhances the spinnability of PHA solutions, and provides better thermal stability, effectively preventing thermal cyclization of PHA before electrospinning and thus reducing its solubility. On the other hand, by controlling the solvent content in ipr-PHA nanofibers, this invention maintains a suitable solvent residue rate in the fiber matrix, effectively enhances the mobility of chain segments during thermal cyclization, reduces the cyclization barrier, and improves the conversion rate of PHA to PBO, resulting in better overall performance of the prepared PBO nanofiber membrane.

[0006] The biggest difference between this invention and the prior application is that 4,6-diaminoresorcinol is replaced with 4,6-diisopropoxy-1,3-diaminobenzene. The preparation method of 4,6-diisopropoxy-1,3-diaminobenzene is based on the literature (Fukumaru T, Saegusa Y, Fujigaya T. Macromolecules 2014, 47(6), 2088-2095). The preparation method is as follows:

[0007] A certain amount of DMF solvent was added to a reaction flask and stirred. 1,5-Difluoro-2,4-dinitrobenzene, isopropanol, and potassium carbonate were added sequentially. Under nitrogen protection, the mixture was heated to reflux and reacted for 5–10 h. The reaction solution was cooled, and a certain amount of water was added to the cooling solution to form a precipitate. The precipitate was washed and dried to obtain 4,6-diisopropoxy-1,3-dinitrobenzene. Cyclopropylethyl acetate, 4,6-diisopropoxy-1,3-dinitrobenzene, and 10% Pd / C catalyst were added to a high-pressure reactor. The mixture was purged with nitrogen three times and then with hydrogen three times. The mixture was stirred at 70–100 °C for 3–5 h. After filtration, the filtrate was cooled to room temperature, and a precipitate was formed. The precipitate was filtered and dried to obtain 4,6-diisopropoxy-1,3-diaminobenzene (ipr-DAR).

[0008] The difference between the two monomers is that the precursor ipr-PHA prepared by the polycondensation of 4,6-diisopropoxy-1,3-diaminobenzene and terephthaloyl chloride has better solubility and better spinnability in organic solvents such as tetrahydrofuran and dimethylacetamide.

[0009] When using conventional PHA solutions for electrospinning, the high viscosity of the solution extruded from the electrospinning needle can easily lead to melt fracture or needle blockage, preventing spinning. Therefore, larger diameter spinning needles are necessary. Secondly, after extrusion, the charged PHA solution, due to its poor chain segment relaxation ability, struggles to move rapidly and orient itself along the stretching direction during stretching, easily resulting in breakage. Thus, PHA solution electrospinning requires thicker needles and larger injection volumes, resulting in excessively large PHA nanofibers. This invention replaces 4,6-diisopropoxy-1,3-diaminobenzene in the prior art with 4,6-diaminoresorcinol to prepare an IPR-PHA spinning solution for electrospinning, overcoming the aforementioned technical difficulties of PHA solution electrospinning and possessing high application value.

[0010] The specific technical solution of the present invention is as follows:

[0011] A PBO nanofiber membrane and its preparation method include the following steps: (1) preparing a precursor 4,6-diisopropoxy-polyhydroxyamide (ipr-PHA) solution; (2) pouring the ipr-PHA solution into deionized water, precipitating, filtering, and washing to obtain an ipr-PHA polymer; (3) redissolving the ipr-PHA polymer in a solvent and electrospinning it to obtain an ipr-PHA nanofiber membrane; (4) subjecting the ipr-PHA nanofiber membrane to high-temperature heat treatment to obtain a PBO nanofiber membrane.

[0012] The process of the above preparation method is as follows:

[0013]

[0014] The more specific steps are as follows:

[0015] (1) Add solvent to a three-necked flask, purge with nitrogen gas, and maintain the temperature inside the flask at 10-40°C. Add 4,6-diisopropoxy-1,3-diaminobenzene (ipr-DAR), stir for 15-30 min, add terephthaloyl chloride in batches in equimolar amounts to 4,6-diisopropoxy-1,3-diaminobenzene, stir for 15-30 min, add catalyst, and react at 10-40°C for 16 hours to obtain the precursor ipr-PHA solution.

[0016] (2) Slowly pour the ipr-PHA solution into deionized water, stir at high speed, then filter with a Buchner funnel, wash the precipitate with methanol 3 to 5 times, and dry it under vacuum at 60 to 90°C for 12 hours to obtain ipr-PHA polymer.

[0017] (3) The ipr-PHA polymer is redissolved in a mixed solvent and then injected into a spinning needle for single-needle electrospinning. The spinning process parameters are set, and ipr-PHA nanofiber membranes are obtained on the collecting plate.

[0018] (4) The ipr-PHA nanofiber membrane is rapidly heated to 250°C and subjected to atmospheric pressure heat treatment for 3 to 6 hours, and then subjected to vacuum heat treatment at 300°C for 1 to 2 hours to obtain the PBO nanofiber membrane.

[0019] The solvent in step (1) is one or more of dimethylacetamide (DMAC), N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF);

[0020] In step (1), the solid content of the reactants is 13% to 18%, the catalyst is one or more of pyridine, isoquinoline or triethylamine, and the amount added is 1% to 5% of the mass of ipr-DAR;

[0021] In step (2), the stirring speed is 500-1000 r / min, the stirring time is 20-30 min, and the stirring temperature is 10-40℃;

[0022] In step (3), the mixed solvent is tetrahydrofuran (THF) and dimethylacetamide (DMAC) in a volume ratio of 9:1 to 6:4; the solid content of the ipr-PHA polymer in the spinning solution is 15% to 20%.

[0023] In step (3), the spinning temperature is 5-20℃, the extrusion speed of the spinning solution is 5-10ul / min, the diameter of the spinneret is 0.4-0.7mm, the ambient humidity is 50%-70%, the voltage is 16-20kV, and the distance between the spinneret and the receiving plate is 18-25cm. By comprehensively controlling the above process parameters, the solvent residue rate in the IPR-PHA nanofibers is maintained at 2%-5%.

[0024] In step (4), the IPR-PHA nanofiber membrane is subjected to atmospheric pressure heat treatment at 250°C. During this process, PHA is cyclically closed to generate PBO. Controlling the residual solvent in the IPR-PHA nanofiber to 2% to 5% in the previous step can improve the mobility of macromolecular chain segments during thermal cyclization, reduce the cyclization barrier, and increase the cyclization rate. Then, the residual solvent is removed under high vacuum at 300°C to achieve complete cyclization. The heat treatment vacuum range is -0.07 to -0.09 MPa.

[0025] Compared with existing technologies, the above-mentioned technical solution is characterized by the significant improvement in the solubility of PHA in solvents such as THF and DMAC through 4,6-diisopropoxy-substituted ipr-PHA, which also improves the spinnability of PHA solutions. Furthermore, ipr-PHA exhibits better thermal stability, effectively preventing thermal cyclization of PHA before electrospinning and thus reducing its solubility. On the other hand, by controlling the solvent content in ipr-PHA nanofibers, this invention maintains a suitable solvent residue rate in the fiber matrix, effectively enhancing the chain segment transport ability during thermal cyclization, lowering the cyclization barrier, and increasing the conversion rate of PHA to PBO. The resulting PBO nanofiber membrane exhibits superior overall performance. Detailed Implementation

[0026] The following detailed embodiments further illustrate the above-described content of the present invention, but should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Unless otherwise specified, the following embodiments are all implemented using conventional prior art, and all percentages are weight percentages.

[0027] Example 1:

[0028] A PBO nanofiber membrane and its preparation method, comprising the following steps:

[0029] (1) Add 100g of DMAC solvent to a three-necked flask, purge with nitrogen gas and maintain the temperature inside the flask at 10℃, add 6.63g of IPR-DAR, stir for 15min, add 7.37g of TPC in batches, stir for 15min, add 0.066g of pyridine, and react at 10℃ for 16 hours to obtain the precursor IPR-PHA solution.

[0030] (2) The ipr-PHA solution was slowly poured into deionized water and stirred at a high speed of 500 r / min for 20 min. The stirring temperature was 10℃. Then, the mixture was filtered using a Buchner funnel. The precipitate was washed three times with methanol and dried under vacuum at 60℃ for 12 h to obtain the ipr-PHA polymer.

[0031] (3) The ipr-PHA polymer was redissolved in a THF / DMAC mixed solvent with a volume ratio of 9:1. The solid content of the ipr-PHA polymer in the solution was 20%. Then it was injected into a spinning needle and electrospinned by a single needle. The spinning temperature was 20℃, the extrusion speed of the spinning solution was 5ul / min, the diameter of the spinneret was 0.4mm, the ambient humidity was 50%, the voltage was 16kV, and the distance between the spinneret and the receiving plate was 25cm. The ipr-PHA nanofiber membrane was obtained on the collecting plate. The solvent residue rate in the ipr-PHA nanofiber was 2%.

[0032] (4) The IPR-PHA nanofiber membrane is rapidly heated to 250℃ and subjected to atmospheric pressure heat treatment for 3 hours. Then, it is subjected to heat treatment at 300℃ for 1 hour under a vacuum of -0.07MPa to obtain the PBO nanofiber membrane.

[0033] Tests showed that the PBO nanofiber membrane had a single filament diameter of 300–400 nm, a strength of 98 MPa, and an elastic modulus of 1320 MPa.

[0034] Example 2:

[0035] A PBO nanofiber membrane and its preparation method, comprising the following steps:

[0036] (1) Add 100g of NMP solvent to a three-necked flask, purge with nitrogen gas and maintain the temperature inside the flask at 40℃, add 9.03g of IPR-DAR, stir for 25min, add 0.01g of TPC in batches, stir for 25min, add 0.211g of triethylamine, and react at 30℃ for 16 hours to obtain the precursor IPR-PHA solution.

[0037] (2) The ipr-PHA solution was slowly poured into deionized water and stirred at a high speed of 700 r / min for 25 min. The stirring temperature was 30℃. Then, the mixture was filtered using a Buchner funnel. The precipitate was washed with methanol four times and dried under vacuum at 80℃ for 12 h to obtain the ipr-PHA polymer.

[0038] (3) The ipr-PHA polymer was redissolved in a THF / DMAC mixed solvent with a volume ratio of 7:3. The solid content of the ipr-PHA polymer in the solution was 18%. Then it was injected into a spinning needle tube for single-needle electrospinning. The spinning temperature was 10℃, the extrusion speed of the spinning solution was 7ul / min, the diameter of the spinneret was 0.6mm, the ambient humidity was 60%, the voltage was 18kV, and the distance between the spinneret and the receiving plate was 20cm. The ipr-PHA nanofiber membrane was obtained on the collecting plate. The solvent residue rate in the ipr-PHA nanofiber was 3%.

[0039] (4) The IPR-PHA nanofiber membrane was rapidly heated to 250℃ and subjected to atmospheric pressure heat treatment for 5 hours. Then, it was subjected to heat treatment at 300℃ for 1.5 hours under a vacuum of -0.08MPa to obtain the PBO nanofiber membrane.

[0040] Tests showed that the PBO nanofiber membrane had a single filament diameter of 250–380 nm, a strength of 110 MPa, and an elastic modulus of 1500 MPa.

[0041] Example 3:

[0042] A PBO nanofiber membrane and its preparation method, comprising the following steps:

[0043] (1) Add 100g of DMF solvent to a three-necked flask, purge with nitrogen gas and maintain the temperature inside the flask at 40℃, add 10.41g of Ipr-DAR, stir for 30min, add 11.54g of TPC in batches, stir for 30min, add 0.33g of isoquinoline, and react at 40℃ for 16 hours to obtain the precursor Ipr-PHA solution.

[0044] (2) The ipr-PHA solution was slowly poured into deionized water and stirred at a high speed of 1000 r / min for 30 min. The stirring temperature was 40℃. Then, the mixture was filtered using a Buchner funnel. The precipitate was washed with methanol 5 times and dried under vacuum at 90℃ for 12 h to obtain the ipr-PHA polymer.

[0045] (3) The ipr-PHA polymer was redissolved in a THF / DMAC mixed solvent with a volume ratio of 6:4. The solid content of the ipr-PHA polymer in the solution was 15%. Then it was injected into a spinning needle and electrospinned by a single needle. The spinning temperature was 5℃, the extrusion speed of the spinning solution was 10ul / min, the diameter of the spinneret was 0.7mm, the ambient humidity was 70%, the voltage was 20kV, and the distance between the spinneret and the receiving plate was 16cm. The ipr-PHA nanofiber membrane was obtained on the collecting plate. The solvent residue rate in the ipr-PHA nanofiber was 5%.

[0046] (4) The IPR-PHA nanofiber membrane was rapidly heated to 250℃ and subjected to atmospheric pressure heat treatment for 6 hours. Then, it was subjected to heat treatment at 300℃ for 2 hours under a vacuum of -0.09MPa to obtain the PBO nanofiber membrane.

[0047] Tests showed that the PBO nanofiber membrane had a single filament diameter of 400–500 nm, a strength of 91 MPa, and an elastic modulus of 1210 MPa.

[0048] Comparative Example 1

[0049] PBO nanofiber membranes were prepared by direct electrospinning of unmodified PHA, including the following steps:

[0050] (1) Add 100g of NMP solvent to a three-necked flask, purge with nitrogen gas and maintain the temperature inside the flask at 40℃, add 6.89g of DAR, stir for 25min, add 10.01g of TPC in batches, stir for 25min, add 0.145g of pyridine, and react at 30℃ for 16 hours to obtain the precursor PHA solution.

[0051] (2) PHA solution was slowly poured into deionized water and stirred at high speed. The stirring speed was 700 r / min and the stirring time was 25 min. The stirring temperature was 30℃. Then, the mixture was filtered with a Buchner funnel. The precipitate was washed with methanol 4 times and dried under vacuum at 80℃ for 12 h to obtain PHA polymer.

[0052] (3) The PHA polymer was redissolved in a THF / DMAC mixed solvent with a volume ratio of 7:3. The solid content of the PHA polymer in the solution was 18%. Then it was injected into a spinning needle tube for single-needle electrospinning. The spinning temperature was 10℃, the extrusion speed of the spinning solution was 15ul / min, the diameter of the spinneret was 0.9mm, the ambient humidity was 60%, the voltage was 18kV, and the distance between the spinneret and the receiving plate was 20cm. A PHA nanofiber membrane was obtained on the collecting plate. The solvent residue rate in the PHA nanofiber was 3%.

[0053] (4) The PHA nanofiber membrane was rapidly heated to 250°C and subjected to atmospheric pressure heat treatment for 5 hours. Then, it was subjected to heat treatment at 300°C for 1.5 hours under a vacuum of -0.08MPa to obtain the PBO nanofiber membrane.

[0054] Electrospinning was performed directly using an unmodified PHA solution. Because the PHA solution has high viscosity and poor spinnability, a coarse needle with a diameter of at least 0.9 mm must be used during the spinning process; otherwise, the needle is prone to clogging. Furthermore, the extrusion speed of the spinning solution must be faster to prevent filament breakage. Testing showed that the PBO nanofiber membrane prepared by the above process had a single filament diameter of 700–900 nm, a strength of 14 MPa, and an elastic modulus of 310 MPa. The overall performance was far lower than that of the product obtained in the embodiments of this invention.

[0055] Comparative Example 2:

[0056] A PBO nanofiber membrane and its preparation method are disclosed. When the solvent residue rate in the IPR-PHA fibers is kept low, it can negatively impact the conversion of IPR-PHA to PBO. The preparation method includes the following steps:

[0057] (1) Add 100g of DMAC solvent to a three-necked flask, purge with nitrogen gas and maintain the temperature inside the flask at 10℃, add 6.63g of IPR-DAR, stir for 15min, add 7.37g of TPC in batches, stir for 15min, add 0.066g of pyridine, and react at 10℃ for 16 hours to obtain the precursor IPR-PHA solution.

[0058] (2) The ipr-PHA solution was slowly poured into deionized water and stirred at a high speed of 500 r / min for 20 min. The stirring temperature was 10℃. Then, the mixture was filtered using a Buchner funnel. The precipitate was washed three times with methanol and dried under vacuum at 60℃ for 12 h to obtain the ipr-PHA polymer.

[0059] (3) The ipr-PHA polymer was redissolved in a THF / DMAC mixed solvent with a volume ratio of 9:1. The solid content of the ipr-PHA polymer in the solution was 20%. Then, it was injected into a spinning needle and electrospinned by a single needle. The spinning temperature was 25°C, the extrusion speed of the spinning solution was 5 μL / min, the diameter of the spinneret was 0.4 mm, the ambient humidity was 50%, the voltage was 16 kV, and the distance between the spinneret and the receiving plate was 25 cm. The ipr-PHA nanofiber membrane was obtained on the collecting plate. The solvent residue rate in the ipr-PHA nanofiber was 0.4%.

[0060] (4) The IPR-PHA nanofiber membrane is rapidly heated to 250℃ and subjected to atmospheric pressure heat treatment for 3 hours. Then, it is subjected to heat treatment at 300℃ for 1 hour under a vacuum of -0.07MPa to obtain the PBO nanofiber membrane.

[0061] In this comparative example, the solvent residue in the IPR-PHA nanofibers was controlled to 0.4%, which is lower than the control range proposed in this invention. At a relatively low solvent residue, the IPR-PHA macromolecules have lower mobility and poorer thermal cyclization reaction ability, resulting in incomplete conversion of PHA to PBO and poor performance.

[0062] Tests showed that the PBO nanofiber membrane had a single filament diameter of 400–600 nm, a strength of 47 MPa, and an elastic modulus of 890 MPa, which were lower than the product performance obtained in the embodiments of this invention.

[0063] The above embodiments enable those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a PBO nanofiber membrane, characterized in that, Includes the following steps: (1) Add solvent to a three-necked flask, purge with nitrogen, and maintain the temperature inside the flask at 10~40℃. Add 4,6-diisopropoxy-1,3-diaminobenzene and stir for 15~30 min. Add terephthaloyl chloride in batches, equal in molar amount to 4,6-diisopropoxy-1,3-diaminobenzene, and stir for 15~30 min. Then add catalyst and react at 10~40℃ for 16 hours to obtain the precursor IPR-PHA solution. The solid content of the reactants in step (1) is 13%~18%, and the catalyst is one or more of pyridine, isoquinoline, or triethylamine. The amount added is 1%~5% of the mass of IPR-DAR. (2) Slowly pour the ipr-PHA solution into deionized water, stir at high speed, then filter it with a Buchner funnel, wash the precipitate with methanol 3 to 5 times, and dry it under vacuum at 60 to 90°C for 12 hours to obtain ipr-PHA polymer. (3) The IPR-PHA polymer is redissolved in a mixed solvent and then injected into a spinning needle for single-needle electrospinning. The spinning process parameters are set, and an IPR-PHA nanofiber membrane is obtained on the collecting plate. The solvent residue rate in the IPR-PHA nanofiber is 2%~5%. (4) The ipr-PHA nanofiber membrane is rapidly heated to 250°C and subjected to atmospheric pressure heat treatment for 3-6 hours, and then subjected to vacuum heat treatment at 300°C for 1-2 hours to obtain the PBO nanofiber membrane.

2. The method for preparing the PBO nanofiber membrane according to claim 1, characterized in that: The solvent in step (1) is one or more of dimethylacetamide, N-methylpyrrolidone, and N,N-dimethylformamide.

3. The method for preparing the PBO nanofiber membrane according to claim 1, characterized in that: In step (2), the stirring speed is 500~1000r / min, the stirring time is 20~30min, and the stirring temperature is 10~40℃.

4. The method for preparing the PBO nanofiber membrane according to claim 1, characterized in that: In step (3), the mixed solvent is tetrahydrofuran and dimethylacetamide in a volume ratio of 9:1 to 6:4; the solid content of the ipr-PHA polymer in the spinning solution is 15% to 20%.

5. The method for preparing the PBO nanofiber membrane according to claim 1, characterized in that: In step (3), the spinning temperature is 5~20℃, the extrusion speed of the spinning solution is 5~10ul / min, the diameter of the spinneret is 0.4~0.7mm, the ambient humidity is 50%~70%, the voltage is 16~20kV, and the distance between the spinneret and the receiving plate is 18~25cm.

6. The method for preparing the PBO nanofiber membrane according to claim 1, characterized in that: The heat treatment vacuum range in step (4) is -0.07 to -0.09 MPa.

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