Method of making piezoelectric hollow fiber membranes with self-polarization during membrane formation and products

Abstract

The application discloses a preparation method of a piezoelectric hollow fiber membrane with self-polarization in a membrane forming process and a product, and belongs to the technical field of water treatment membranes. The application takes polyvinylidene fluoride as a base material, introduces a lamellar ferroelectric material as a structure inducer, and is supplemented with a pore inducer to form a uniformly dispersed spinning solution in an organic solvent system, and a nonsolvent phase separation synchronous induction technology is used for spinning forming. In the slit of a spinneret, the spinning solution is subjected to high-intensity fluid shear force, which promotes the regular orientation arrangement of the lamellar ferroelectric material along the flow direction. The ordered structure not only stabilizes and enriches the beta crystal form of polyvinylidene fluoride, but also guides the directional arrangement of the dipole moment in the polyvinylidene fluoride molecular chain, so that the spontaneous polarization of the beta crystal is synchronously induced in the membrane filament forming process. The method of the application can obtain the polyvinylidene fluoride hollow fiber ultrafiltration membrane with high beta crystal content and piezoelectric activity without subsequent stretching or high-voltage polarization steps.

Description

Technical Field

[0001] This invention belongs to the field of water treatment membrane technology, and particularly relates to the preparation method and product of self-polarized piezoelectric hollow fiber membranes during the film formation process. Background Technology

[0002] With the acceleration of industrialization and urbanization, water pollution has become increasingly severe, and water quality safety has become one of the core issues of widespread social concern. Among various separation methods, membrane separation technology has become a research hotspot in the field of water treatment due to its advantages such as high efficiency and energy saving, simple operation, and environmental friendliness, and has shown broad application prospects in drinking water purification, wastewater treatment, and reuse. Hollow fiber membranes, in particular, occupy an important position in membrane separation technology due to their high packing density, good mechanical strength, low manufacturing cost, and ease of modularization and automation, and are widely used in multiple levels of water treatment processes, including microfiltration, ultrafiltration, and even nanofiltration. However, membrane fouling remains a core bottleneck restricting the long-term stable operation and extended service life of hollow fiber membranes. The adsorption and deposition of pollutants on the membrane surface or within the pores not only leads to decreased flux and increased energy consumption, but also increases cleaning frequency and operating and maintenance costs.

[0003] To address the challenge of membrane fouling, researchers have conducted extensive research across multiple levels, from material modification and structural optimization to process control. For example, patent CN115920670A discloses a method for preparing an antifouling hydrophilic hollow fiber membrane. This method involves introducing nano-TiO2 seeds into a base membrane, then constructing a titanium crystal layer on the membrane surface and combining it with a hydrophilic polymer to form a functional antifouling coating. However, this method is cumbersome, and the functional layer is at risk of peeling off under long-term backwashing or strong acid / alkali cleaning conditions, resulting in insufficient stability. Another example is patent CN119588165A, which designs an antifouling hollow fiber membrane module with a specific geometry. By optimizing the surface slope of the sealing adhesive layer and the sub-aeration pipe, it utilizes the synergistic effect of gravity and airflow to promote pollutant removal. While this approach has some innovation, its antifouling performance is overly dependent on structural parameters, resulting in poor engineering adaptability. In practical applications, it is easily affected by installation errors, operational fluctuations, and other factors, making it difficult to achieve a stable and reliable antifouling effect.

[0004] Against this backdrop, developing a novel hollow fiber membrane that combines high-efficiency separation performance with sustained anti-fouling capabilities has become a key research direction. In recent years, piezoelectric materials have shown great potential in membrane fouling control due to their unique force-electric coupling characteristics. The piezoelectric effect refers to the polarization phenomenon that occurs when certain crystalline materials are deformed under external force, thereby creating a potential difference on the material surface. This potential can drive local electrochemical reactions or change the surface charge distribution, achieving electro-driven repulsion, degradation, or self-cleaning functions against pollutants.

[0005] Polyvinylidene fluoride (PVDF), as a typical piezoelectric polymer, derives its piezoelectric properties primarily from the relative content of the β-crystal form. Therefore, increasing the proportion of β-crystals in PVDF membranes and inducing their spontaneous polarization is a core strategy for constructing piezoelectrically responsive separation membranes. Although existing research has attempted to improve the β-crystal content and piezoelectric properties through post-processing methods (such as mechanical stretching and high-pressure polarization), for example, patent CN117886439A uses a stretching-polarization combined process to prepare PVDF piezoelectric ultrafiltration membranes. However, this method is energy-intensive and complex, hindering large-scale production. Another example is patent CN119926195A, which hydrothermally grows a piezoelectric phase on the ceramic membrane surface, imparting some piezoelectric activity to the membrane. However, the process involves high-temperature sintering and multi-step composite steps, resulting in a long preparation cycle, high cost, and potential vulnerabilities in the bonding strength between the substrate and functional layers. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a method for preparing a self-polarized piezoelectric hollow fiber membrane during the film formation process, thereby obtaining a self-polarized piezoelectric hollow fiber membrane of polyvinylidene fluoride.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing a self-polarizing piezoelectric hollow fiber membrane during film formation, comprising the following steps:

[0009] (1) Add an amphiphilic block copolymer, a pore-forming agent and polyvinylidene fluoride to a layered ferroelectric material solution, and then heat, stir and let stand to degas to obtain a spinning solution doped with layered ferroelectric material; the amphiphilic block copolymer is a polyoxyethylene-polyoxypropylene-polyoxyethylene copolymer.

[0010] (2) Based on the spinning solution of the doped lamellar ferroelectric material obtained in step (1), the non-solvent phase separation synchronous induction technology is used for spinning and forming, and the spontaneous polarization of β crystal is completed simultaneously during the spinning process to obtain a self-polarized piezoelectric hollow fiber membrane.

[0011] Further, the layered ferroelectric material in the solution of the layered ferroelectric material in step (1) is modified by fluorosilane grafting before use by the following method: the layered ferroelectric material is heated and refluxed in H2O2 to obtain hydroxylated layered ferroelectric material; the obtained hydroxylated layered ferroelectric material is dispersed in a mixed system of ethanol and water, and condensed by adding 1H,1H,2H,2H-perfluorodecyltrimethoxysilane solution, washed with ethanol and vacuum dried to obtain fluorosilane grafted modified layered ferroelectric material.

[0012] Further, in step (1), the layered ferroelectric material in the solution is selected from at least one of bismuth titanate, barium titanate, indium selenide, bismuth tungstate, and strontium bismuth tantalate.

[0013] Furthermore, in step (1), the proportion of layered ferroelectric material in the spinning solution doped with layered ferroelectric material is 0.5~1.5wt%, the proportion of amphiphilic block copolymer is 2wt%, the proportion of pore maker is 5wt%, and the proportion of polyvinylidene fluoride is 20wt%.

[0014] Further, the pore-forming agent mentioned in step (1) is polyethylene glycol.

[0015] Furthermore, in step (1), the temperature during heating and stirring is 40~70℃, the rotation speed is 200~400rpm, and the time is 4~5h.

[0016] Further, in step (1), the solvent of the layered ferroelectric material solution is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide and dimethylacetamide.

[0017] Furthermore, the parameters for spinning in step (2) include: the inner diameter of the spinneret is 0.3~1.4mm, the outer diameter of the spinneret is 0.5~1.8mm, the temperature of the feed tank is 60~80℃, the gas pressure of the feed tank is 0.3~0.5kPa, the distance between the spinneret and the coagulation bath is 1~3cm, the core liquid speed of the spinneret is 1.5~3mL / min, the feed outlet speed is 4~6mL / min, and the winding speed is 7~9m / min.

[0018] Furthermore, in step (2), pure water is used as the core liquid and coagulation bath during the spinning process.

[0019] The present invention also provides a self-polarized piezoelectric hollow fiber membrane, which is prepared according to the preparation method described in the above technical solution.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] This invention uses polyvinylidene fluoride (PVDF) as the matrix material and introduces layered ferroelectric materials as structure inducers, supplemented with pore-forming agents, to form a uniformly dispersed spinning solution in an organic solvent system. Non-solvent-induced phase separation (NIPS) simultaneous induction technology is then employed for spinning. At the spinneret slit, the spinning solution is subjected to high-intensity fluid shear force, causing the layered ferroelectric materials to align regularly along the flow direction. This ordered structure not only stabilizes and enriches the β-crystal form of PVDF (relative content ≥90%), but also guides the dipole moments in the PVDF molecular chains to achieve directional alignment. This simultaneously induces spontaneous polarization of the β-crystals during membrane fiber formation, effectively avoiding traditional external high-pressure polarization processes and achieving in-situ enhancement of piezoelectric properties. This invention's method eliminates the need for subsequent stretching or high-pressure polarization steps to produce PVDF hollow fiber ultrafiltration membranes with high β-crystal content and piezoelectric activity. The process is simple, energy-efficient, and easily scaled up, providing a feasible path for developing membrane materials with both high-efficiency separation and self-cleaning functions.

[0022] The self-polarized piezoelectric hollow fiber membrane prepared by this invention has a simpler manufacturing process and superior piezoelectric performance compared to traditional piezoelectric hollow fiber membranes. It outputs a 16V voltage under an air electrical signal testing device, which is about 20 times larger than the piezoelectric signal of pure PVDF membrane and about 2.5 times larger than the piezoelectric signal of traditional membranes with added spherical ferroelectric materials. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1 A schematic diagram illustrating the process of preparing a self-polarized piezoelectric hollow fiber membrane during the film formation process provided by the present invention;

[0025] Figure 2 SEM images of the self-polarized PVDF piezoelectric hollow fiber membranes prepared in Example 2 and Comparative Example 2, wherein the left image is of Example 2 and the right image is of Comparative Example 2;

[0026] Figure 3 FTIR spectra of self-polarized PVDF piezoelectric hollow fiber membranes prepared in Examples 1-3 and Comparative Example 1;

[0027] Figure 4 A schematic diagram of a device for testing piezoelectric signals in air;

[0028] Figure 5 The piezoelectric signal output results are for the self-polarized PVDF piezoelectric hollow fiber membranes prepared in Examples 1-3 and Comparative Example 1.

[0029] Figure 6The piezoelectric signal output results are for the hollow fiber membranes prepared in Examples 2, 4-5 and Comparative Example 2.

[0030] Figure 7 The pure water flux of the hollow fiber membranes prepared in Examples 1-5 and Comparative Examples 1-2;

[0031] Figure 8 The hollow fiber membranes prepared for Examples 1-5 and Comparative Examples 1-2 show the filtration fouling resistance of BSA. Detailed Implementation

[0032] 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.

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] This invention provides a method for preparing a self-polarizing piezoelectric hollow fiber membrane during film formation, comprising the following steps:

[0035] (1) Add amphiphilic block copolymer, pore-forming agent and polyvinylidene fluoride (PVDF) to the layered ferroelectric material solution, and then heat, stir and let stand to degas to obtain the spinning solution doped with layered ferroelectric material;

[0036] (2) Based on the spinning solution of the doped layered ferroelectric material obtained in step (1), the non-solvent phase separation synchronous induction technology is used for spinning and forming, and the spontaneous polarization of β crystal is completed simultaneously during the spinning process to obtain a self-polarized piezoelectric hollow fiber membrane.

[0037] In a preferred embodiment, the layered ferroelectric material in the layered ferroelectric material solution in step (1) is selected from bismuth titanate (Bi4Ti3O4). 12 At least one of barium titanate (BaTiO3), indium selenide (α-In2Se3), bismuth tungstate (Bi2WO6), and strontium bismuth tantalate (SrBi2Ta2O9), more preferably bismuth titanate (Bi4Ti3O9). 12This invention employs a sheet-like ferroelectric material with a lamellar structure as a structure inducing agent. The fluid shear force during the spinning process induces the sheet-like ferroelectric material to align regularly along the flow direction. This ordered structure not only stabilizes and strengthens the β-phase but also guides the dipole moments in the PVDF molecular chains to achieve directional alignment. This allows for the simultaneous completion of spontaneous polarization of the β-phase during the film formation process, inducing PVDF crystallization to generate a high β-phase content. This enables the film to output a larger piezoelectric signal under electromechanical coupling, thereby improving the piezoelectric properties of the film itself.

[0038] In a preferred embodiment, the layered ferroelectric material further includes a fluorosilane grafting modification step before use. The fluorosilane grafting modification process specifically involves: heating the layered ferroelectric material under reflux in H₂O₂ to obtain a hydroxylated layered ferroelectric material; dispersing the obtained hydroxylated layered ferroelectric material in a mixture of ethanol and water; adding a 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (PFHTMS) solution for condensation; washing with ethanol; and vacuum drying to obtain the fluorosilane-grafted modified layered ferroelectric material. This invention significantly improves the dispersibility and compatibility of the layered ferroelectric material in the PVDF matrix by fluorosilane grafting modification. The modified ferroelectric material can serve as a highly efficient heterogeneous nucleation site, significantly inducing the formation of a more piezoelectrically active β-phase in PVDF.

[0039] In a preferred embodiment, the solvent of the layered ferroelectric material solution in step (1) is selected from at least one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and dimethylacetamide (DMAC), and is more preferably N-methylpyrrolidone (NMP).

[0040] In a preferred embodiment, the proportion of layered ferroelectric material in the spinning solution doped with layered ferroelectric material in step (1) is 0.5~1.5wt%, more preferably 1~1.5wt%. The amount of layered ferroelectric material in the spinning solution of the present invention affects the piezoelectric properties of the self-polarized piezoelectric hollow fiber membrane. If the amount of layered ferroelectric material is too low, the induction effect is not obvious, the β phase content is low, resulting in poor piezoelectric properties of the self-polarized piezoelectric hollow fiber membrane; while if the amount of layered ferroelectric material is too high, it is easy to agglomerate, destroy the compactness and uniformity of the membrane structure, resulting in uneven distribution of internal electric field and increased defects during polarization, reducing the effective polarization degree and damaging the piezoelectric properties of the self-polarized piezoelectric hollow fiber membrane.

[0041] In a preferred embodiment, the amphiphilic block copolymer in step (1) is selected from polyoxyethylene-polyoxypropylene-polyoxyethylene copolymer (PEO-PPO-PEO); more preferably, it is Pluronic F127 produced by BASF, which is composed of ethylene oxide and propylene oxide monomers and has a molecular structure of poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) three-segment block structure.

[0042] In a preferred embodiment, in step (1), the porogen is selected from polyethylene glycol (PEG), and more preferably PEG400.

[0043] In a preferred embodiment, in step (1), the proportion of amphiphilic block copolymer in the spinning solution of the doped layered ferroelectric material is 2wt%, the proportion of pore maker is 5wt%, and the proportion of polyvinylidene fluoride is 20wt%.

[0044] In a preferred embodiment, in step (1), the temperature during heating and stirring is 40~70℃, the rotation speed is 200~400rpm, and the time is 4~5h. This invention prepares a homogeneous solution through heating and stirring to facilitate subsequent spinning.

[0045] In a preferred embodiment, in step (1), the time for static degassing is 12 hours.

[0046] In a preferred embodiment, step (2) specifically involves: placing the spinning solution doped with lamellar ferroelectric material into the feed tank of the spinning machine, opening the bottom switch to purge the air, then connecting the pipeline in sequence according to the feed tank-filter-pump head, setting the heating temperature and air pressure of the feed tank, adjusting the basic speed of the pump head to the lowest, and closing the pump head and connecting the spinneret after the spinning solution flowing out of the pipe has no obvious bubbles, adjusting the height of the spinneret and the external coagulation liquid, and then setting the core liquid speed of the spinneret and the feed inlet speed to spin the spinning solution, so that the spinning solution solidifies into a film filament in the coagulation bath, and the film filament is wound on the winding wheel after passing through the winding wheel.

[0047] In a preferred embodiment, the parameters for spinning in step (2) include: the inner diameter of the spinneret is 0.3~1.4mm, the outer diameter of the spinneret is 0.5~1.8mm, the temperature of the feed tank is 60~80℃, the gas pressure of the feed tank is 0.3~0.5kPa, the distance between the spinneret and the coagulation bath is 1~3cm, the core liquid speed of the spinneret is 1.5~3mL / min, the feed outlet speed is 4~6mL / min, and the winding speed is 7~9m / min.

[0048] In a preferred embodiment, in step (2), pure water is used as the core liquid and coagulation bath during spinning.

[0049] The present invention also provides a self-polarizing piezoelectric hollow fiber membrane, which is prepared according to the preparation method described in the above technical solution.

[0050] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0051] Example 1

[0052] A method for preparing a self-polarizing piezoelectric hollow fiber membrane during film formation, comprising the following steps:

[0053] (1) First, weigh TiO2, Bi2O3, NaCl, and KCl in a molar ratio of 3:2:2.5:2.5, mix them evenly, and calcine them at 850℃ for 2 hours. The product is washed with distilled water and ethanol until the conductivity of the supernatant is stable, and pure bismuth titanate (BiTO) is finally obtained. Then, weigh BiTO and H2O2 in a molar ratio of 1:10 (g / mL), mix and sonicate for 30 minutes, transfer to an oil bath and stir at 105℃ for 6 hours. The product is filtered, washed until neutral and dried to obtain hydroxylated BiTO (BiTO-OH). Finally, mix 19 mL of ethanol with 1 mL of deionized water, and then add 1H,1H,2H,2H-perfluoroheptadecanetrimethyloxysilane (PFHTMS) equivalent to 15% of the mass of BiTO-OH, and use 2M After adjusting the pH of the solution to 2-3 with HCl, hydrolyze it at 50℃ for 1 h, then add 0.3 g of the above BiTO-OH, and reflux at 60℃ for 2 h. The product is filtered, washed with ethanol, and dried under vacuum at 50℃ for 24 h to obtain the target fluorosilane graft product F-BiTO.

[0054] (2) Under ultrasonic treatment, the F-BiTO obtained in step (1) was fully dispersed in NMP, and then PVDF, F127 and PEG400 were added. The mixture was then heated in a water bath at 70°C and mechanically stirred at 120 rpm for 4 h to dissolve the components. After standing for 12 h to remove bubbles, a spinning solution of doped layered ferroelectric material was obtained. The proportions of F-BiTO, NMP, PVDF, F127 and PEG400 in the spinning solution were 0.5 wt%, 72.5 wt%, 20 wt%, 2 wt%, and 5 wt%, respectively.

[0055] (3) Place the spinning solution of the doped layered ferroelectric material obtained in step (2) into the feed tank of the spinning machine, open the bottom switch to purge the air, and then connect the pipeline in the order of feed tank-filter-pump head. Then set the heating temperature of the feed tank to 70℃, the air pressure inside the feed tank to 0.4kPa, and the basic speed of the pump head to the lowest. After the spinning solution flowing out of the pipe has no obvious bubbles, close the pump head and connect the spinneret (the inner diameter of the spinneret is 0.5mm and the outer diameter is 1.0mm). The distance between the spinneret and the coagulation bath is 1cm. Then set the core liquid speed of the spinneret to 2.9mL / min and the feed outlet speed to 5.2mL / min for spinning. The spinning solution is solidified into membrane fibers in the coagulation bath. After passing through the winding wheel, the membrane fibers are wound on the winding wheel. The winding wheel stretching speed is 8m / min to obtain a self-polarized PVDF piezoelectric hollow fiber membrane (denoted as PVDF / Bi). 0.5 ).

[0056] Example 2

[0057] A method for preparing a self-polarized piezoelectric hollow fiber membrane during the film formation process differs from Example 1 only in that the proportions of F-BiTO, NMP, PVDF, F127 and PEG400 in the spinning solution of step (2) are 1wt%, 72wt%, 20wt%, 2wt% and 5wt%, respectively, while the rest is the same as in Example 1. The self-polarized PVDF piezoelectric hollow fiber membrane obtained is denoted as PVDF / Bi1.

[0058] Example 3

[0059] A method for preparing a self-polarized piezoelectric hollow fiber membrane during film formation differs from Example 1 only in that the proportions of F-BiTO, NMP, PVDF, F127, and PEG400 in the spinning solution of step (2) are 1.5wt%, 71.5wt%, 20wt%, 2wt%, and 5wt%, respectively. The rest is the same as in Example 1. The resulting self-polarized PVDF piezoelectric hollow fiber membrane is denoted as PVDF / Bi. 1.5 .

[0060] Example 4

[0061] A method for preparing a self-polarized piezoelectric hollow fiber membrane during the film formation process differs from Example 1 only in that the sheet-like ferroelectric material in step (1) is commercially available bismuth tungstate (BiWO), while the rest is the same as in Example 1. The resulting self-polarized PVDF piezoelectric hollow fiber membrane is denoted as PVDF / BiWO1.

[0062] Example 5

[0063] A method for preparing a self-polarized piezoelectric hollow fiber membrane during the film formation process differs from Example 1 only in that the sheet-like ferroelectric material in step (1) is commercial indium selenide (α-In2Se3) powder, and the rest is the same as in Example 1. The self-polarized PVDF piezoelectric hollow fiber membrane obtained is denoted as PVDF / InSe1.

[0064] Comparative Example 1

[0065] A method for preparing a self-polarized PVDF piezoelectric hollow fiber membrane, comprising the following steps:

[0066] (1) NMP, PVDF, F127 and PEG400 were mixed in a ratio of 73wt%∶20wt%∶2wt%∶5wt%, and then heated in a water bath at 70℃. The mixture was dissolved by mechanical stirring at 120rpm for 4h and allowed to stand for 12h to remove bubbles, so as to obtain a uniform and stable spinning solution.

[0067] (2) Place the spinning solution obtained in step (1) into the feed tank of the spinning machine, open the bottom switch to purge the air, and then connect the pipeline in the order of feed tank-filter-pump head. Then set the heating temperature of the feed tank to 70℃, the air pressure inside the feed tank to 0.4kPa, and the basic speed of the pump head to the lowest. After the spinning solution flowing out of the pipe has no obvious bubbles, close the pump head and connect the spinneret (the inner diameter of the spinneret is 0.5mm and the outer diameter is 1.0mm). The distance between the spinneret and the coagulation bath is 1cm. Then set the core liquid speed of the spinneret to 2.9mL / min and the feed outlet speed to 5.2mL / min for spinning. The spinning solution is solidified into membrane fibers in the coagulation bath. After the membrane fibers pass through the winding wheel, they are wound on the winding wheel. The winding wheel stretching speed is 8m / min to obtain a self-polarized PVDF piezoelectric hollow fiber membrane (denoted as PVDF).

[0068] Comparative Example 2

[0069] A method for preparing a self-polarized PVDF piezoelectric hollow fiber membrane includes the following steps:

[0070] The difference between step (1) and Example 1 is that pure bismuth titanate is replaced with commercially available spherical barium titanate (BTO), otherwise the same as in Example 1;

[0071] (2) Under ultrasonic treatment, the F-BaTO obtained in step (1) was fully dispersed in NMP, and then PVDF, F127 and PEG400 were added. The mixture was then heated in a water bath at 70°C and mechanically stirred at 120 rpm for 4 h to dissolve the components. After standing for 12 h to remove bubbles, a spinning solution doped with F-BaTO was obtained. The proportions of F-BaTO, NMP, PVDF, F127 and PEG400 in the spinning solution were 1 wt%, 72 wt%, 20 wt%, 2 wt% and 5 wt%, respectively.

[0072] Step (3) is the same as in Example 1, and the resulting self-polarized PVDF piezoelectric hollow fiber membrane is denoted as PVDF / Ba1.

[0073] Figure 1 This is a schematic diagram of the process for preparing a self-polarized piezoelectric hollow fiber membrane during the film formation process provided by the present invention.

[0074] Figure 2 SEM images of the self-polarized PVDF piezoelectric hollow fiber membranes prepared in Example 2 and Comparative Example 2 are shown, with the left image representing Example 2 and the right image representing Comparative Example 2. Figure 2 As can be seen, the lamellar F-BiTO in the self-polarized PVDF piezoelectric hollow fiber membrane prepared in Example 2 exhibits significant orientation behavior under fluid shearing, and its regular arrangement provides an ordered nucleation template for the PVDF molecular chains. In Comparative Example 2, the spherical barium titanate is isotropic during the material forming process and fails to align with the fluid shear stress.

[0075] The self-polarized PVDF piezoelectric hollow fiber membranes prepared in Examples 1-3 and Comparative Example 1 were placed in an oven and dried at 60°C. Then, FTIR testing was performed to analyze their piezoelectric properties. The results are shown in [Figure 1]. Figure 3 .

[0076] Figure 3 FTIR spectra of self-polarized PVDF piezoelectric hollow fiber membranes prepared in Examples 1-3 and Comparative Example 1. Figure 3 As can be seen, in Examples 1-3 and Comparative Example 1, the α-phase (characteristic peak at 763 cm⁻¹) is clearly observed with the increase of F-BiTO content. -1 The intensity decreased significantly, and the β-phase (characteristic peak at 840 cm⁻¹) showed a significant decrease. -1 The content of β crystals first increases and then decreases with the increase of F-BiTO addition. When the addition amount is 1%, the β crystal content reaches the maximum value.

[0077] The self-polarized PVDF piezoelectric hollow fiber membranes prepared in Examples 1-5 and Comparative Examples 1-2 were placed in an oven and dried at 60°C. The dried self-polarized piezoelectric hollow fiber membranes were then subjected to electrometer testing for electrical signals in air under periodic reciprocating pressure. A schematic diagram of the testing apparatus is shown below. Figure 4 The test results are shown below. Figures 5-6 .

[0078] Figure 4 This is a schematic diagram of a device for testing piezoelectric signals in air.

[0079] Figure 5 The piezoelectric signal output results are for the self-polarized PVDF piezoelectric hollow fiber membranes prepared in Examples 1-3 and Comparative Example 1. Figure 5It can be seen that the content of lamellar ferroelectric material in the spinning solution affects the piezoelectric properties of the prepared self-polarized PVDF piezoelectric hollow fiber membrane. Under the same spinning conditions, as the content of lamellar ferroelectric material increases, the electrical signal of the piezoelectric hollow fiber membrane first increases and then decreases. When the content of lamellar ferroelectric material exceeds a certain value, it will also affect the piezoelectric signal. The self-polarized PVDF piezoelectric hollow fiber membrane prepared in Example 2 outputs a voltage of 16V under an air electrical signal testing device, which is about 20 times larger than the piezoelectric signal of the pure PVDF membrane prepared in Comparative Example 3.

[0080] Figure 6 The piezoelectric signal output results are for the self-polarized PVDF piezoelectric hollow fiber membranes prepared in Examples 2, 4-5, and Comparative Example 2. Figure 6 It can be seen that when doped with 1 wt% ferroelectric material, the shape of the ferroelectric material affects the piezoelectric properties of the prepared piezoelectric hollow fiber membrane. When the doped ferroelectric material is spherical barium titanate, its smooth shape prevents it from undergoing regular orientation and self-polarization using fluid shear force. Therefore, its piezoelectric output is significantly lower than that of the self-polarized hollow fiber membrane doped with layered bismuth titanate. The self-polarized PVDF piezoelectric hollow fiber membrane prepared in Example 2 outputs a voltage of 16V under an air electrical signal testing device, which is about 2.5 times higher than the piezoelectric signal of the membrane with added spherical ferroelectric material in Comparative Example 2. Examples 4 and 5, which also use layered ferroelectric material doping, show piezoelectric outputs of 12V and 11V respectively, which are significantly enhanced compared to the spherical ferroelectric material doping.

[0081] Pure water flux test: The encapsulated membrane module was first rinsed and degassed with pure water, then pre-compacted at 0.1 MPa for 60 minutes until the membrane structure stabilized. The permeate volume, collection time, and actual transmembrane pressure difference were then recorded. Pure water flux. (L / m) 2 The calculation method for ·h) is shown in equation (1);

[0082]

[0083] in, The volume of liquid permeated (L). Effective filtration area (m²) 2 ), The filtering time is in hours (h).

[0084] Figure 7 The pure water flux of the hollow fiber membranes prepared in Examples 1-5 and Comparative Examples 1-2 is shown. Figure 7 It can be seen that the pure water flux of the piezoelectric hollow fiber membranes prepared in Examples 1-3 of this invention is 40-60 L / m. 2Between ·h. Compared to Example 2, the pure water flux of the piezoelectric hollow fiber membrane prepared in Example 4 decreased by 2 L / m. 2 •h, the pure water flux of the piezoelectric hollow fiber membrane prepared in Example 5 decreased by 5 L / m 2 The pure water flux of the piezoelectric hollow fiber membrane prepared in Comparative Example 1 increased by 14 L / m³. 2 The pure water flux of the piezoelectric hollow fiber membrane prepared in Comparative Example 2 increased by 2 L / m². 2 This indicates that the content of the pore-forming agent has a decisive influence on the flux of the piezoelectric hollow fiber membrane, while when the proportions of pore-forming agent and filler are the same, the type of filler has no significant impact on the membrane flux.

[0085] Membrane antifouling performance determination (i.e., resistance to fouling by bovine serum albumin (BSA): At the beginning of the filtration experiment, the hollow fiber membrane sample was placed in the membrane module and pre-pressurized with deionized water at 0.1 MPa for 60 min to obtain a stable initial flux, denoted as J0. Subsequently, the filtered water was replaced with a 20 mg / L bovine serum albumin solution, the pressure was adjusted to 0.09 MPa, and the steady-state flux of the PVDF hollow fiber membrane sample was measured after filtration for 45 min, denoted as J. p Afterwards, a simple physical cleaning was performed with deionized water, and then the pure water flux of the hollow fiber membrane sample was tested again and recorded as J. c The antifouling performance of hollow fiber membranes can be measured by the total fouling resistance (Rf). t Irreversible pollution resistance (R) i ) and reversible pollution resistance (R r To evaluate, the total fouling resistance is the sum of the reversible fouling resistance and the irreversible fouling resistance, calculated according to formula (2); the reversible fouling resistance is the proportion of the membrane flux recovered through simple physical cleaning to the pure water flux before fouling, calculated according to formula (3); the irreversible fouling resistance is the proportion of the flux that is still difficult to recover after physical cleaning to the pure water flux before fouling, calculated according to formula (4).

[0086]

[0087]

[0088]

[0089] Figure 8 The filtration fouling resistance of hollow fiber membranes prepared in Examples 1-5 and Comparative Examples 1-2 to BSA. Figure 8As can be seen, the prepared hollow fiber membrane exhibits a good linear relationship between its resistance to BSA contamination and its piezoelectric output. Specifically, the total resistance to BSA contamination of the PVDF hollow fiber membrane with added lamellar ferroelectric material is significantly lower than that of the PVDF hollow fiber membrane without added lamellar ferroelectric material. Under the same conditions, the total resistance to BSA contamination of the PVDF hollow fiber membrane with added lamellar ferroelectric material is 25% lower than that of the PVDF hollow fiber membrane with added spherical ferroelectric material. Among them, the PVDF hollow fiber membrane (PVDF / Bi1) prepared under the condition of 1wt% modified bismuth titanate doping has the lowest total resistance to BSA contamination, which is only 0.4, indicating that its anti-contamination performance is significantly improved.

[0090] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a self-polarizing piezoelectric hollow fiber membrane during film formation, characterized in that, Includes the following steps: (1) An amphiphilic block copolymer, a pore-forming agent, and polyvinylidene fluoride are added to a solution of layered ferroelectric material. The solution is heated, stirred, and allowed to stand to remove bubbles, in order to obtain a spinning solution doped with layered ferroelectric material. The spinning solution doped with layered ferroelectric material contains 0.5-1.5 wt% of layered ferroelectric material, 2 wt% of amphiphilic block copolymer, 5 wt% of pore-forming agent, and 20 wt% of polyvinylidene fluoride. (2) Based on the spinning solution of the doped layered ferroelectric material obtained in step (1), the spinning solution is pushed through the spinneret by the extrusion pump. The high-intensity fluid shear force formed by the spinning solution in the narrow cavity inside the spinneret causes the layered anisotropic ferroelectric material to be regularly oriented along the flow direction, inducing the formation of polyvinylidene fluoride β crystal and the directional alignment of the dipole moment, and simultaneously completing the spontaneous polarization of β crystal. After the spinning solution flows into the coagulation bath, non-solvent phase separation and molding can be achieved to prepare a piezoelectric hollow fiber membrane.

2. The method for preparing a self-polarized piezoelectric hollow fiber membrane during film formation according to claim 1, characterized in that, Before use, the layered ferroelectric material in the solution of the layered ferroelectric material in step (1) is modified by fluorosilane grafting using the following method: The layered ferroelectric material is heated and refluxed in H2O2 to obtain hydroxylated layered ferroelectric material; The obtained hydroxylated layered ferroelectric material is dispersed in a mixed system of ethanol and water, and condensed by adding 1H,1H,2H,2H-perfluorodecyltrimethoxysilane solution. After washing with ethanol and vacuum drying, the modified layered ferroelectric material grafted with fluorosilane is obtained.

3. The method for preparing a self-polarizing piezoelectric hollow fiber membrane during film formation according to claim 1, characterized in that, The layered ferroelectric material in the solution of the layered ferroelectric material in step (1) is selected from at least one of bismuth titanate, barium titanate, indium selenide, bismuth tungstate and strontium bismuth tantalate.

4. The method for preparing a self-polarized piezoelectric hollow fiber membrane during film formation according to claim 1, characterized in that, The amphiphilic block copolymer mentioned in step (1) is a polyoxyethylene-polyoxypropylene-polyoxyethylene copolymer, and the pore-forming agent is polyethylene glycol or polyvinylpyrrolidone.

5. The method for preparing a self-polarized piezoelectric hollow fiber membrane during film formation according to claim 1, characterized in that, In step (1), the temperature during heating and stirring is 40~70℃, the rotation speed is 200~400rpm, and the time is 4~5h.

6. The method for preparing a self-polarizing piezoelectric hollow fiber membrane during film formation according to claim 1, characterized in that, In step (1), the solvent for the layered ferroelectric material solution is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and dimethylacetamide.

7. The method for preparing a self-polarized piezoelectric hollow fiber membrane during film formation according to claim 1, characterized in that, In step (2), the spinning process uses a spinneret, the temperature of the feed tank is 60~80℃, the air pressure of the feed tank is 0.3~0.5kPa, the distance between the spinneret and the coagulation bath is 1~3cm, the core liquid speed of the spinneret is 1.5~3mL / min, the feed outlet speed is 4~6mL / min, and the winding speed is 7~9m / min; pure water is used as the core liquid and the coagulation bath.

8. A self-polarizing piezoelectric hollow fiber membrane, characterized in that, The piezoelectric hollow fiber membrane, which is self-polarized during the film formation process, is prepared according to any one of claims 1 to 7.

9. The application of the self-polarized piezoelectric hollow fiber membrane according to claim 8 in the field of separation.

Images