Preparation method of super-porous polymer fiber

Abstract

The invention discloses a preparation method of an ultra-porous polymer fiber, which comprises the following steps: mixing a non-solvent and a solvent of a polymer to obtain a mixed solvent, and dissolving the polymer in the mixed solvent to form a spinning solution with certain viscosity and good spinnability; in the electrostatic spinning process by using the spinning solution, the non-solvent firstly induces fiber skin to be rapidly cured to form a fiber structure, phase separation is continuously induced in the fiber to form an ultra-porous structure, the ultra-porous polymer micro-nano fiber with three-dimensional double communicating holes in the fiber is prepared in one step, and post-treatment processes such as washing and calcining are not needed. The method can be used for simply and effectively preparing the super-porous polymer fiber, and the super-porous polymer fiber can be applied to technologies such as oil-water separation.

Description

Technical Field

[0001] This invention relates to the technical field of materials, and in particular to a method for preparing ultraporous polymer fibers. Background Technology

[0002] Porous polymer fibers are widely used in environmental, energy, catalysis, and biomedical fields due to their high efficiency in separation and filtration, excellent stability and durability, and ease of functionalization. Compared to traditional preparation processes such as wet spinning and solution spinning, which typically produce porous polymer fibers with diameters in the micrometer or millimeter range, electrospinning technology can rapidly and stably prepare micro / nanofibers, meeting the specific functionalization requirements in the context of the rapid development of nanotechnology. Currently, methods for preparing micro / nanoporous polymer fibers via electrospinning mainly include pore-forming agent methods, post-treatment methods, and phase separation methods.

[0003] Adding pore-forming agents to the spinning solution is a common preparation method. These agents can be small or large molecules, and may volatilize during spinning or be removed through post-treatment methods such as washing or calcination, thereby forming porous fibers. For example, CN 112981554 B describes the preparation of porous fiber structures by adding appropriate pore-forming agents during electrospinning using mesoporous bioactive glass and fiber-forming polymers. CN 115364825 B describes the preparation of modified polyarylene ether sulfone porous fibers with abundant pore structures obtained by electrospinning using polyethylene glycol as a pore-forming agent. CN 112877794A describes the preparation of nanofibers by electrospinning with polyethylene oxide as a pore-forming agent and adding polyvinylidene fluoride, followed by dissolving the polyethylene oxide in a water bath to obtain porous fibers. CN 105926162A describes the preparation of nanofibers by electrospinning with polyethylene glycol or polyvinylidene fluoride as a pore-forming agent and adding polyvinylidene fluoride, followed by ultrasonic oscillation and solvent washing to obtain porous nanofibers. CN 113882146 B describes a method where PBT and PS resins are blended and spun, and then the PS phase is dissolved in tetrahydrofuran solvent to obtain porous fibers. CN113242687B describes a method using polyacrylonitrile filament mat as raw material, which is activated at low temperature and then expanded at high temperature to obtain activated carbon fibers with large pores. These preparation methods are relatively complex due to the need for post-treatment processes such as washing and calcination, and they lack sufficient control over the pore structure.

[0004] In recent years, centrifugal spinning has been developed by combining electrospinning with centrifugal technology. This is a one-step method for preparing ultrafine, porous fibers. For example, CN 105714388 B adds ethyl cellulose and polyvinylpyrrolidone to a mixed solvent of ethanol and water, stirs at room temperature to obtain a homogeneous solution, and then centrifuges to obtain ultrafine, porous fibers. CN116446069B mixes titanium dioxide, polystyrene, cellulose acetate, and DMF, stirs to obtain a spinning solution, centrifuges to obtain a spinning solution, and then irradiates the fibers under ultraviolet light to obtain polystyrene / cellulose acetate / titanium dioxide fibers with a porous structure. CN 110468467 B dissolves a water-soluble hyperbranched polymer and a water-insoluble linear polymer in a common good solvent, stirs and degasssssss to obtain a spinning solution; micro / nanofibers are prepared by centrifugal spinning, then immersed in water, and dried to obtain porous fibers. However, the pore size of the pores obtained by centrifugal spinning is often large and the pore structure is relatively simple.

[0005] To obtain a more uniform and controllable pore structure, electrospinning can be integrated with polymerization, crosslinking, and sol-gel methods. For example, CN 111501200 B utilizes small-molecule volatile components generated during the condensation reaction in imidization to form a micro / nano porous structure. CN 110201552B performs a hypercrosslinking reaction on the surface of electrospun fiber membranes, preparing porous fiber membranes through Friedel-Crafts alkylation. CN 118147823 A swells and solidifies PU / PVDF electrospun membranes, making the fiber mesh denser and transforming the fiber body into porous fibers with radially permeable micropores. CN 114583384 B uses two resins for simultaneous spinning, where the functional resin has carbonyl or cyano functional groups, crosslinking and entangled with structural resins such as polymethyl methacrylate and polystyrene during spinning to form a porous structure. Although these methods improve the porosity, they often have more complex processing principles and more stringent process requirements.

[0006] Phase separation technology is a commonly used technique for preparing porous materials. In electrospinning, thermally induced phase separation and solvent-induced phase separation are relatively common. For example, CN 113046926 B utilizes the rapid stretching of the fiber during electrospinning and the rapid evaporation of low-boiling-point solvents to cause a sharp drop in fiber surface temperature, leading to thermally induced phase separation and the formation of a porous structure on the fiber surface, resulting in a silk fibroin polylactic acid porous nanofiber. CN 107447292 B uses a polystyrene solution as the core spinning solution and a polyvinylidene fluoride solution as the shell spinning solution for coaxial electrospinning, utilizing the different evaporation rates of the solvents to prepare a micro / nano spiral porous fiber. CN 115058892B utilizes the rapid evaporation characteristic of chloroform to prepare an antibacterial polylactic acid porous nanofiber that can be used as a wound dressing. However, the pores obtained by these methods are mostly only present on the fiber surface, or the pore continuity is poor, and they are mostly relatively independent pores. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a one-step method for preparing ultraporous polymer fibers. This method involves introducing a non-solvent component into the electrospinning solution. During electrospinning, the non-solvent first induces rapid solidification of the fiber skin to form a fiber structure, and then continues to induce phase separation within the fiber, thereby preparing micro / nanofibers with a three-dimensional, doubly interconnected porous structure in one step. To achieve the above-mentioned objectives and other advantages of the present invention, a method for preparing ultraporous polymer fibers is provided, comprising:

[0008] S1. Measure the non-solvent of the polymer and add it together with the solvent into the sample bottle. After stirring evenly, add the polymer and perform magnetic stirring and heating to obtain a clear, transparent and uniform polymer solution for use as a spinning solution.

[0009] S2. Draw the spinning solution into the propulsion pump, connect the positive terminal of the high voltage power supply to the spinning head needle, and connect the negative terminal to the grounded receiving device.

[0010] S3. Set the relevant spinning parameters and connect the high-voltage power supply; the non-solvent first induces the rapid solidification of the fiber skin to form a fiber structure, and then continues to induce phase separation inside the fiber to form an ultraporous structure; after a period of time, the ultraporous micro / nano polymer fibers can be collected on the receiving device. The ambient temperature for electrospinning is 20–30℃, and the ambient humidity is 40–90%. The electrospinning voltage is 8.0–15.0KV, the spinning solution flow rate is 1.0–7.0mL / h, and the receiving distance is 18–24cm.

[0011] Preferably, the difference in Hansen solubility parameter (Ra) of the polymer between the mixed solvent and the non-solvent in step S1 is 1.0 to 10.0.

[0012] Preferably, the Ra value of the polymer composed of the non-solvent and the solvent is 2.0 to 8.0.

[0013] Preferably, in step S1, the polymer mass is 0.5–5.0 g, the volume of the mixed solvent consisting of solvent and non-solvent is 10–40 mL, and the ratio of solvent to non-solvent is 9–6:1–4.

[0014] Preferably, the polymer in step S1 is polyvinylidene fluoride, polystyrene, or polycaprolactone.

[0015] Preferably, the non-solvent includes water and ethanol.

[0016] Preferably, the solvent used to dissolve the polymer includes N,N-dimethylformamide, dimethylacetamide, and chloroform.

[0017] Preferably, the diameter of the ultraporous micro / nano polymer fibers is 0.5–50 μm; the fibers have interconnected pores with an average pore diameter of 5–500 nm and a specific surface area of ​​10–20 m². 2 / g.

[0018] Ultraporous micro / nano polymer fibers can be used for filtering and separating oil-water mixtures.

[0019] The advantages of this application compared to existing technologies are as follows: By introducing a non-solvent into the electrospinning process, the non-solvent first induces rapid solidification of the fiber skin to form a fiber structure, and then continues to induce phase separation within the fiber to form an ultraporous structure. Ultraporous polymer fibers can be prepared in a one-step process by introducing a non-solvent component into the spinning solution, eliminating the need for post-treatment such as washing or calcination, and yielding micro / nanofibers with a three-dimensional, doubly interconnected porous structure within the fibers. This fiber membrane possesses both the void structure formed between electrospun nanofibers and the ultraporous structure within the nanofibers, forming a multi-level pore structure, which is beneficial for filtering and separating oil-water mixtures. This preparation method has a simple process flow, low production cost, and controllable fiber morphology. Attached Figure Description

[0020] Figure 1 The non-solvent-induced phase separation process is the method for preparing ultraporous polymer fibers according to the present invention;

[0021] Figure 2 The images show physical photos and scanning electron microscope (SEM) images of the ultraporous fiber membrane prepared by the method for preparing ultraporous polymer fibers according to the present invention.

[0022] Figure 3 Scanning electron microscope (SEM) images of the cross-sections of the ultraporous fibers in Examples 1-6 of the preparation method of ultraporous polymer fibers according to the present invention;

[0023] Figure 4Scanning electron microscope (SEM) images of the cross-sections of the ultraporous fibers in Examples 7, 8 and 2 of the preparation method of ultraporous polymer fibers according to the present invention;

[0024] Figure 5 This is a scanning electron microscope (SEM) image of the cross-section of the ultraporous fiber in Example 9 of the method for preparing ultraporous polymer fibers according to the present invention.

[0025] Figure 6 This is an example of the separation effect of ultraporous fibers on oil-water mixtures in Example 10 of the preparation method of ultraporous polymer fibers according to the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] In the following embodiments of the present invention, the polymers selected are polyvinylidene fluoride (PVDF, molecular weight 800,000) or polystyrene (PS, molecular weight 192,000), polycaprolactone (PCL, molecular weight 80,000), polyacrylic acid (PAA, molecular weight 450,000), the solvents selected are N,N-dimethylformamide (DMF) or dimethylacetamide (DMAc), and the non-solvents selected are water (H2O), ethanol (EtOH), acetone (Ac), or tetrahydrofuran (THF).

[0028] This invention involves mixing a non-solvent and a solvent, adjusting the volume ratio of the two to regulate the difference in the Hansen solubility parameter (Ra) of the polymer in the mixed solvent. The polymer is then dissolved in the mixed solvent to form a spinning solution with a certain viscosity and good spinnability, followed by electrospinning. During spinning, the non-solvent first induces rapid solidification of the fiber skin to form a fiber structure, and then continues to induce phase separation within the fiber, resulting in three-dimensional interconnected pores. As the solvent and non-solvent completely evaporate, a stable ultraporous polymer fiber with interconnected pores is finally formed, requiring no post-processing.

[0029] Example 1: Refer to Figure 1 A method for preparing and applying ultraporous polymer fibers includes the following steps:

[0030] 1.4 g of PVDF was dissolved in a mixed solvent of 7 mL DMAc and 3 mL EtOH, with Ra = 4.4. The solution was mechanically stirred at 55 °C until completely dissolved, resulting in a uniform and transparent spinning solution. The spinning solution was transferred into a syringe and connected to an 18 G needle as a uniaxial spinning head. The syringe was placed on a push pump. The positive terminal of a high-voltage power supply was connected to the spinning head needle, and the negative terminal was connected to a grounded receiving device. The spinning solution flow rate was set to 7 mL / h, the spinning voltage to 12 kV, the receiving distance to 24 cm, the ambient temperature to 25 °C, and the humidity to 55%. The syringe pump was started and the voltage was applied. After a period of time, an ultraporous micro / nano polymer fiber membrane was collected on the receiving device. The membrane was then allowed to dry naturally for testing such as SEM.

[0031] Example 2: This example provides a method for preparing porous fibers, the steps of which are the same as those in Example 1, except that the mixed solvent consists of 9 mL DMAc and 1 mL H2O, and Ra = 4.5.

[0032] Example 3: This example provides a method for preparing porous fibers, the steps of which are the same as those in Example 1, except that the mixed solvent consists of 7 mL DMF and 3 mL EtOH, with Ra = 4.6.

[0033] Example 4: This example provides a method for preparing porous fibers, the steps of which are the same as those in Example 1, except that the mixed solvent consists of 9.5 mL DMF and 0.5 mL H2O, and Ra = 3.9.

[0034] Example 5: This example provides a method for preparing porous fibers, the steps of which are the same as those in Example 1, except that the mixed solvent consists of 5.0 mL DMF and 5.0 mL Ac, and Ra = 2.0.

[0035] Example 6: This example provides a method for preparing ultraporous polymer fibers, the steps of which are as follows:

[0036] 1.4 g of PVDF was dissolved in a mixed solvent of 7 mL DMF and 3 mL EtOH, and mechanically stirred at 55 °C until completely dissolved to obtain a uniform and transparent first spinning solution. The mixed solvent of 7 mL DMF and 3 mL EtOH was used as the second spinning solution. The first and second spinning solutions were transferred into a first syringe and a second syringe, respectively. The first syringe was connected to the outer layer of a self-made coaxial spinning needle, and the second spinning solution was connected to the inner layer of the self-made coaxial spinning needle. The positive terminal of a high-voltage power supply was connected to the spinning needle, and the negative terminal was connected to a grounded receiving device. The flow rate of the outer spinning solution was set to 5 mL / h, the flow rate of the inner spinning solution to 1 mL / h, the spinning voltage to 12 kV, the receiving distance to 24 cm, the ambient temperature to 25 °C, and the humidity to 55%. The syringe pump was started and voltage was applied. After a period of time, an ultraporous micro / nano polymer fiber membrane was collected on the receiving device, and then naturally dried for SEM and other tests. This ultraporous micro / nano polymer fiber also has a hollow structure.

[0037] Example 7: This example provides a method for preparing porous fibers, the steps of which are the same as those in Example 1, except that the mixed solvent consists of 9.4 mL DMAc and 0.6 mL H2O, and Ra = 3.8.

[0038] Example 8: This example provides a method for preparing porous fibers, the steps of which are the same as those in Example 1, except that the mixed solvent consists of 9.2 mL DMAc and 0.8 mL H2O, and Ra = 3.2.

[0039] Example 9: This example provides a method for preparing ultraporous polymer core-sheath fibers, the steps of which are as follows:

[0040] 1.0 g of PCL was dissolved in 10 mL of a DMF:THF mixture of 4:6, and the solution was magnetically stirred at room temperature for 12 h to obtain a uniform and transparent first spinning solution. 1.0 g of PAA was dissolved in 10 mL of DMF, and the solution was magnetically stirred at room temperature for 12 h to obtain a second spinning solution. 2.0 g of PS was dissolved in 10 mL of a DMF:THF mixture of 6:4 (Ra = 8.2), and the solution was magnetically stirred at room temperature for 12 h to obtain a third spinning solution. The three spinning solutions were then transferred into three separate syringes. The first spinning solution was connected to the outer channel of a self-made three-stage coaxial spinning needle, the second spinning solution was connected to the middle channel, and the third spinning solution was connected to the inner channel. Connect the positive terminal of the high-voltage power supply to the spinning needle and the negative terminal to the grounded receiving device. Set the outer layer flow rate to 1 mL / h, the middle layer flow rate to 1 mL / h, and the inner layer flow rate to 2 mL / h. Set the spinning voltage to 8.2 kV, the receiving distance to 20 cm, the ambient temperature to 20 °C, and the humidity to 30%. Start the injection pump and apply the voltage. After a period of time, collect the ultraporous micro / nano polymer fiber membrane on the receiving device. Dry it at 50 °C for 24 h for SEM testing.

[0041] Example 10: This example provides an oil-water separation method based on ultraporous polymer fibers. The ultraporous polymer fibers obtained in Example 1 were used to separate an oil-in-water solution, which was prepared by adding 2 mL of water to 198 mL of soybean oil and stirring continuously at 1500 rpm for 6 hours. The filtration efficiency was greater than 99%, and the average filtration flux under gravity was 48 L·m³. 2 ·h -1 .

[0042] Results analysis: Figure 1 This refers to the non-solvent-induced phase separation phenomenon of the ultraporous polymer fiber in Example 1 during the electrospinning process. When the electrospun fiber is placed under an optical microscope for observation, the non-solvent-induced phase separation is basically completed within 30 seconds as time goes by, and the fiber solidifies to form a three-dimensional double-connected ultraporous structure.

[0043] Figure 2 a and b are, respectively, a physical image and a scanning electron microscope image of the surface of the ultraporous fiber membrane in Example 1 of the present invention. It can be seen that the diameter of the prepared ultraporous polymer fiber is 0.5-50 μm, which belongs to the micro-nano level. The fibers are tightly arranged together to form a white electrospun fiber membrane.

[0044] Figure 3 a, b, c, d, e, and f are scanning electron microscope (SEM) images of the cross-sections of the ultraporous fibers in Examples 1, 2, 3, 4, 5, and 6 of this invention, respectively. It can be seen that the fibers have interconnected pores with an average pore diameter of 5–500 nm. Because Example 6 used a coaxial spinning head and a mixed solvent as the inner spinning solution, the resulting ultraporous fibers also contain hollow structures.

[0045] Figure 4 a, b, and c are scanning electron microscope (SEM) images of the cross-sections of the ultraporous fibers in Examples 7, 8, and 2 of this invention, respectively. In image a, there are fewer double-connected pores inside the fiber; in image b, the number of double-connected pores inside the fiber gradually increases; and in image c, the fiber contains interconnected pores with an average pore diameter of 5–500 nm. The Ra values ​​corresponding to Examples 7, 8, and 2 of this invention are 3.2, 3.8, and 4.5, respectively, indicating that the number of double-connected pore structures inside the fiber gradually increases with the increase of the Ra value.

[0046] Figure 5 This is a scanning electron microscope image of the cross-section of the ultraporous fiber in Example 9 of the present invention. It can be seen that the fiber diameter is 2-5 μm and the average pore diameter is 5-500 nm. Due to the use of three-stage coaxial electrospinning and the non-solvent-induced phase separation only occurring in the inner layer solution, the fiber has a core-sheath structure. The outer layer of the fiber is tight and smooth and the inside of the fiber has three-dimensional double-connected pores.

[0047] Figure 6This is the separation effect of the ultraporous fiber on the oil-water mixture in Example 10 of the present invention. It can be seen that the solution after separation is clear and no dispersed phase can be observed under an optical microscope, indicating that the fiber membrane can achieve a good separation effect.

[0048] The parameters such as the spinning solution flow rate or the diameter of the spinning head used in this application can be adjusted to prepare ultraporous polymer nanofibers with smaller diameters.

[0049] The ultraporous polymer fibers obtained in this invention can also be used as carriers in fields such as catalysis, medicine, and energy.

[0050] The number of devices and processing scale described herein are for simplification of the invention. Applications, modifications, and variations of this invention will be readily apparent to those skilled in the art. Although embodiments of the invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for this invention, and further modifications can be readily implemented by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, this invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing ultraporous polymer fibers, characterized in that, Includes the following steps: S1. Measure the non-solvent of the polymer and add it together with the solvent into the sample bottle. After stirring evenly, add the polymer and perform magnetic stirring and heating to obtain a clear, transparent and uniform polymer solution for use as a spinning solution. S2. Draw the spinning solution into the propulsion pump, connect the positive terminal of the high voltage power supply to the spinning head needle, and connect the negative terminal to the grounded receiving device. S3. Set the spinning parameters and connect the high-voltage power supply; the non-solvent first induces the fiber skin to solidify rapidly to form a fiber structure, and then continues to induce phase separation inside the fiber to form an ultraporous structure; after a period of time, the ultraporous micro-nano polymer fiber can be collected on the receiving device.

2. The method for preparing ultraporous polymer fibers as described in claim 1, characterized in that, The difference in Hansen solubility parameter (Ra) of the polymer between the non-solvent and the solvent in step S1 is 1.0 to 10.

0.

3. The method for preparing ultraporous polymer fibers as described in claim 2, characterized in that, The Ra value of the polymer composed of the non-solvent and the solvent is 2.0 to 8.

0.

4. The method for preparing ultraporous polymer fibers as described in claim 1, characterized in that, In step S1, the polymer mass is 0.5–5.0 g, the volume of the mixed solvent consisting of solvent and non-solvent is 10–40 mL, and the ratio of solvent to non-solvent is 9–6:1–4.

5. The method for preparing ultraporous polymer fibers as described in claim 1, characterized in that, The polymer in step S1 is polyvinylidene fluoride, polystyrene, or polycaprolactone.

6. The method for preparing ultraporous polymer fibers as described in claim 1, characterized in that, The solvent used to dissolve the polymer is N,N-dimethylformamide, dimethylacetamide, or trichloromethane.

7. The method for preparing ultraporous polymer fibers as described in claim 1, characterized in that, The non-solvent is water or ethanol.

8. The method for preparing ultraporous polymer fibers as described in claim 1, characterized in that, The ultraporous micro / nano polymer fibers have a diameter of 0.5–50 μm; the fibers contain interconnected pores with an average pore diameter of 5–500 nm and a specific surface area of ​​10–20 m². 2 / g.

9. The application of the ultraporous micro / nano polymer fibers prepared according to claim 1 in the filtration and separation of oil-water mixtures.

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