Ferroelectric polymer nanofiber membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of functional nano materials, in particular to a ferroelectric polymer nanofiber membrane and a preparation method and application thereof.The preparation method comprises the steps that hexamethylene adipamide and formic acid are mixed to obtain a PA solution, and a polyamide electrospun membrane substrate is obtained through electrostatic spinning; the preparation method comprises the following steps: dissolving a ferroelectric polymer in N, N-dimethylacetamide to obtain a ferroelectric polymer solution; dropwise adding the ferroelectric polymer solution to the surface of a polyamide electrospinning membrane substrate, standing, forming a liquid membrane on the surface, adding water, immersing the polyamide electrospinning membrane substrate, carrying out vacuum filtration, and drying to obtain a ferroelectric polymer nanofiber membrane; the ferroelectric polymer comprises polyvinylidene fluoride or a polyvinylidene fluoride derivative. According to the prepared ferroelectric polymer nanofiber membrane, under the condition that the airflow speed is 0.45 m / s, the PM0.3 filtering efficiency is larger than or equal to 99.999%, the resistance is smaller than or equal to 250 Pa, and low air resistance and long-term stability are kept while efficient filtering is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional nanomaterials, in particular to a ferroelectric polymer nanofiber membrane and a preparation method and application thereof. BACKGROUND

[0002] With the vigorous development of high-precision manufacturing, aerospace and other high-end industries, and the upgrading of demand in the fields of medicine, health and health management, the requirements for air cleanliness in production and living environment are becoming increasingly demanding. Air filtration is an important means to improve indoor air quality, protect precision devices and ensure production and life.

[0003] Traditional fiber filter materials rely on mechanical effects such as interception, inertia and diffusion to capture fine particles, and high energy consumption is inevitable when achieving high-precision filtration. Therefore, it is urgent to develop ultra-high efficiency air filtration materials and technologies for super-clean rooms to meet the needs of high-end industry development and energy saving.

[0004] Giving fibers electrostatic effect is an important measure to overcome the inherent contradiction between high efficiency and low resistance of mechanical filter materials, especially for particles with a particle size of <0.3 µm (PM0.3). Scholars have developed various electrostatically enhanced filtration strategies, including electret fiber filter materials with semi-permanent charge storage performance, conductive fiber filter materials stimulated by high-voltage electric field, and polarized fiber filter materials in combination with fine particle pre-charging. However, the charge of pre-electret fibers will continuously decay due to factors such as time, high temperature and humidity, and particle deposition. Conductive / polarized fibers with online charging of high-voltage electric field will also cause poor electrical performance due to particle deposition, and will increase the energy consumption of filtration and cause potential ozone pollution problems. They all have the problem of unstable dust holding filtration performance, which seriously restricts their application in the field of high-precision filtration.

[0005] With the continuous development of material science theory and preparation technology, piezoelectric materials have achieved a leap in performance, and their unique and excellent electromechanical coupling characteristics provide a new idea for breaking through the development bottleneck of traditional electrostatically enhanced filtration technology. Piezoelectric effect refers to the phenomenon that non-centrosymmetric dielectric materials produce polarization charge on their surface when subjected to external stress or strain, or undergo mechanical deformation when an external electric field is applied. When used for fine particle filtration, the inherent interaction between airflow and fibers and the positive piezoelectric effect can be used to enhance particle capture, solving the problems of high energy consumption and unstable dust holding filtration performance of electrostatically enhanced filter materials for ultra-high efficiency filtration. SUMMARY

[0006] The purpose of the present application is to provide a ferroelectric polymer nanofiber membrane and a preparation method and application thereof. The problems of high efficiency and low resistance being difficult to balance and poor stability of existing high-efficiency air filtration materials are solved.

[0007] To achieve the above objectives, the present invention provides a method for preparing ferroelectric polymer nanofiber membranes, comprising the following preparation steps: S1. Mix hexamethylene adipamide with formic acid to obtain PA solution, and obtain polyamide electrospun film substrate by electrospinning. S2. Dissolve the ferroelectric polymer in N,N-dimethylacetamide to obtain a ferroelectric polymer solution; S3. The ferroelectric polymer solution is dropped onto the surface of the polyamide electrospun membrane substrate, left to stand, and after a liquid film forms on the surface, water is added to immerse the polyamide electrospun membrane substrate. The substrate is then vacuum filtered and dried to obtain a ferroelectric polymer nanofiber membrane. The ferroelectric polymers in S2 include polyvinylidene fluoride or polyvinylidene fluoride derivatives.

[0008] In this invention, the mass concentration of PA solution in S1 is 13%-15%, the humidity of electrospinning is 35%-45%, the electrospinning rate is 0.3-0.5 mL / h, the electrospinning temperature is 23-27℃, the electrospinning time is 3-7 h, the electrospinning voltage is 30 kV, and the distance from the nozzle to the collecting plate in electrospinning is 20 cm.

[0009] In this invention, the length of the polyamide electrospun film substrate obtained in S1 is preferably 8-12 cm, the width is preferably 8-12 cm, the thickness is preferably 50-80 µm, and the pore size is 3.0-5.0 µm.

[0010] In this invention, in step S2, the ferroelectric polymer is dissolved in N,N-dimethylacetamide and stirred to obtain a ferroelectric polymer solution. The stirring temperature is 18-30°C and the stirring time is 6-8 hours.

[0011] In this invention, the polyvinylidene fluoride derivative includes polyvinylidene fluoride binary copolymer, polyvinylidene fluoride terpolymer or polyvinylidene fluoride tetropolymer, and the weight-average molecular weight of the ferroelectric polymer is preferably 580,000.

[0012] In this invention, polyvinylidene fluoride binary copolymers include poly(vinylidene fluoride-trifluoroethylene) copolymers (P(VDF-TrFE)); polyvinylidene fluoride terpolymers include poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) copolymers (P(VDF-TrFE-CFE)); and polyvinylidene fluoride tetrpolymers include poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene-fluoroalkyl acrylate) copolymers (P(VDF-TrFE-CFE-FA)).

[0013] In this invention, in the poly(vinylidene fluoride-trifluoroethylene) copolymer, the molar ratio of polyvinylidene fluoride to trifluoroethylene is 55-65:35-45; in the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) copolymer, the molar ratio of polyvinylidene fluoride, trifluoroethylene, and chlorofluoroethylene is 60-65:25-30:5-10; and in the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene-fluoroalkyl acrylate) copolymer, the molar ratio of polyvinylidene fluoride, trifluoroethylene, chlorofluoroethylene, and fluoroalkyl acrylate is 60-65:25-30:5-8:1-3.

[0014] In this invention, the mass concentration of the ferroelectric polymer solution in S2 is 1%-5%.

[0015] In this invention, the settling time in S3 is 30-40s, the vacuum degree of vacuum filtration is 4-10kPa, and the vacuum filtration time is 30-60s.

[0016] In this invention, the drying temperature in S3 is 50-70℃, and the drying time is 2-3 hours.

[0017] The present invention also provides a ferroelectric polymer nanofiber membrane prepared by the above-described method for preparing a ferroelectric polymer nanofiber membrane.

[0018] The present invention also provides the application of the above-mentioned ferroelectric polymer nanofiber membrane in the field of air filtration.

[0019] The present invention has the following beneficial effects: This invention provides a method for preparing a ferroelectric polymer nanofiber membrane, comprising the following preparation steps: S1, mixing adipamide and formic acid to obtain a PA solution, and then electrospinning to obtain a polyamide electrospun membrane substrate; S2, dissolving a ferroelectric polymer in N,N-dimethylacetamide to obtain a ferroelectric polymer solution; S3, adding the ferroelectric polymer solution dropwise to the surface of the polyamide electrospun membrane substrate, allowing it to stand, and after a liquid film forms on the surface, adding water to immerse the polyamide electrospun membrane substrate, vacuum filtering, and drying to obtain a ferroelectric polymer nanofiber membrane; wherein the ferroelectric polymer in S2 includes polyvinylidene fluoride or a polyvinylidene fluoride derivative.

[0020] This invention selects polyamide as the membrane substrate. Polyamide has good hydrophilicity and chemical stability, which can effectively support the spreading and network formation of ferroelectric polymers while ensuring the mechanical strength of the substrate. Polyvinylidene fluoride (PVDF) or PVDF derivatives are selected as the ferroelectric polymer. Utilizing its wind-driven piezoelectric properties, electrostatic adsorption forces are continuously generated through the inherent interaction between airflow and fibers, achieving highly efficient capture of PM0.3 (as small as 300 nm). Under an airflow velocity of 0.45 m / s, the filtration efficiency is ≥99.999%, and the resistance is ≤250 Pa.

[0021] In the static setting process of this invention in S3, the ferroelectric polymer solution, driven by inertial flow, overcomes viscous resistance and rapidly spreads on the surface of the polyamide electrospun film substrate to form an ultrathin liquid film with a thickness of 200-350 nm. During the spreading process, the contact angle rapidly decreases from the initial 20-25 degrees to 0 degrees, achieving super-spreading.

[0022] In this invention, water is added to S3 as a non-solvent, which rapidly diffuses into the liquid membrane, breaking the interaction between the ferroelectric polymer and N,N-dimethylacetamide, causing the liquid membrane to undergo a transient phase transformation, and finally forming a continuous interconnected ferroelectric polymer network structure. This results in a piezoelectric coefficient of 30-106 pC / N for the ferroelectric polymer nanofiber membrane, further realizing synergistic filtration of piezoelectric effect and physical interception.

[0023] This invention achieves precise and controllable preparation process of ferroelectric polymer nanofiber membrane by adjusting the mass concentration of the ferroelectric polymer solution and the parameters of vacuum filtration in S3. This avoids the problem of uneven pore size caused by random deposition of fibers in traditional electrospinning. At the same time, it is compatible with a variety of polyvinylidene fluoride derivatives, improving the material compatibility and process repeatability of large-scale production of filter membranes.

[0024] This invention further specifies that the mass concentration of the PA solution in S1 is 13%-15%, the humidity of the electrospinning is 35%-45%, the electrospinning rate is 0.3-0.5 mL / h, the electrospinning temperature is 23-27℃, and the electrospinning time is 3-7 h. Through precise control of the PA solution mass concentration and the above electrospinning parameters, the resulting polyamide electrospun membrane substrate has a three-dimensional porous network structure with good pore connectivity. This provides sufficient space for the ferroelectric polymer solution to spread while preventing liquid film accumulation due to excessively small pores and loss of the ferroelectric polymer solution due to excessively large pores, thus providing a uniform supporting environment for subsequent film formation.

[0025] This invention further defines polyvinylidene fluoride (PVDF) binary copolymers as poly(vinylidene fluoride-trifluoroethylene) copolymers; PVDF terpolymers as poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) copolymers; and PVDF tetrpolymers as poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene-fluoroalkyl acrylate) copolymers. By controlling the steric hindrance effect of the comonomers, this invention can further induce the formation of the β phase, suppress the proportion of inactive phases (such as the α phase), and improve piezoelectric properties.

[0026] The ferroelectric polymer nanofiber membrane prepared by the method of the present invention has a two-dimensional network structure with an internal fiber diameter of 20-25 nm, a pore size of 90-150 nm between fibers, a β phase ratio of 65%-72%, and a porosity of 45%-60%.

[0027] The ferroelectric polymer nanofiber membrane prepared by the method of this invention has a high β phase ratio and excellent piezoelectric properties. The nanofibers have uniform diameters and achieve high-efficiency filtration of PM0.3 while maintaining low air resistance and long-term stability.

[0028] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0029] Figure 1 This is a SEM image of the polyamide electrospun film substrate prepared in Example 1 of the present invention; Figure 2 This is a SEM image of the ferroelectric polymer nanofiber membrane prepared in Example 1 of this invention; Figure 3 The β-phase ratio and crystallinity of the ferroelectric polymer nanofiber membranes prepared in Examples 1 and 2 of this invention; Figure 4 The graph shows the automated filtration test results of the ferroelectric polymer nanofiber membranes prepared in Examples 1 and 2 of this invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0031] Example 1 A method for preparing a ferroelectric polymer nanofiber membrane includes the following preparation steps: S1. Mix hexamethylene adipamide with formic acid to obtain a PA solution with a mass concentration of 14%. Then, through electrospinning (the parameters for electrospinning are: spinning rate 0.5 mL / h, voltage 30 kV, distance from nozzle to collector plate 20 cm, humidity 40%, temperature 25℃, time 5 h), a polyamide electrospun film substrate is obtained. S2. Polyvinylidene fluoride (weight average molecular weight 580,000) was dissolved in N,N-dimethylacetamide and stirred at 25°C for 7 hours to obtain a ferroelectric polymer solution with a mass concentration of 2% (viscosity 5.5 mPa·s, surface tension 48 mN / m). S3. 250µL of ferroelectric polymer solution was dropped onto the surface of a polyamide electrospun membrane substrate (10cm long, 10cm wide, and 65µm thick). After standing for 30s, a liquid film with a thickness of 300nm was formed on the surface. Water was then added to immerse the polyamide electrospun membrane substrate. The substrate was then vacuum filtered for 30s under a pressure of 5kPa and subsequently dried at 60℃ for 2h to obtain a ferroelectric polymer nanofiber membrane, denoted as PVDF homopolymer membrane.

[0032] Example 2 A method for preparing a ferroelectric polymer nanofiber membrane includes the following preparation steps: S1. Hexamethylene adipamide and formic acid were mixed to obtain a PA solution with a mass concentration of 14%. The solution was then electrospun (electrospinning parameters: spinning rate 0.5 mL / h, voltage 30 kV, nozzle-to-collector distance 20 cm, humidity 40%, temperature 25 °C, time 5 h) to obtain a polyamide electrospun film substrate (thickness 65 µm, pore size 1.3 µm). S2. Poly(vinylidene fluoride-trifluoroethylene) copolymer (molar ratio of vinylidene fluoride to trifluoroethylene copolymer is 60:40, weight average molecular weight is 580,000) is dissolved in N,N-dimethylacetamide and stirred at 25°C for 7 h to obtain a ferroelectric polymer solution with a mass concentration of 2% (viscosity is 5.5 mPa·s, surface tension is 48 mN / m). S3. 250µL of ferroelectric polymer solution was dropped onto the surface of a polyamide electrospun membrane substrate (10cm long, 10cm wide, and 65µm thick). After standing for 30s, a liquid film with a thickness of 300nm was formed on the surface. Water was then added to immerse the polyamide electrospun membrane substrate. The substrate was then vacuum filtered for 30s under a pressure of 5kPa and subsequently dried at 60℃ for 2h to obtain a ferroelectric polymer nanofiber membrane, denoted as P(VDF-TrFE) binary copolymer membrane.

[0033] Characterization and detection: The polyamide electrospun film substrate prepared in Example 1 was observed using an electron scanning microscope, and the results are as follows: Figure 1 As shown. From Figure 1 As can be seen, the polyamide electrospun membrane substrate exhibits a three-dimensional porous network structure. The substrate fiber diameter is uniformly distributed within the range of 2.0-3.0 µm, and the pore size formed between the fibers is 3.0-5.0 µm, with good pore connectivity. This provides sufficient support space for the subsequent superspreading of the ferroelectric polymer solution (S2 step), avoiding uneven liquid film spreading due to excessively small substrate pores or loss of ferroelectric polymer due to excessively large pores.

[0034] The ferroelectric polymer nanofiber membrane prepared in Example 1 was observed using a scanning electron microscope, and the results are as follows: Figure 2 As shown. From Figure 2As can be seen, the ferroelectric polymer nanofiber membrane prepared in Example 1 has a two-dimensional continuous interconnected network structure, with the internal fiber diameter concentrated in 20-25 nm and the through-pore size formed between the fibers being 90-150 nm.

[0035] Performance testing: The piezoelectric coefficients of the ferroelectric polymer nanofiber membranes prepared in Examples 1 and 2 were tested using piezoelectric microscopy. Local pressure was applied to several different locations on the ferroelectric polymer nanofiber membrane using an AFM probe, and the piezoelectric charges generated on the surface were detected to obtain the piezoelectric coefficients. The results show that the piezoelectric coefficients of the ferroelectric polymer nanofiber membranes provided by this invention are in the range of 30-106 pC / N.

[0036] The β-phase ratio and crystallinity of the ferroelectric polymer nanofiber membranes prepared in Examples 1 and 2 were tested, and the results are as follows: Figure 3 As shown. From Figure 3 It can be seen that the ferroelectric polymer nanofiber membrane provided by the present invention has a high β phase content, which is 65%-72%.

[0037] The ferroelectric polymer nanofiber membranes obtained in Examples 1 and 2 were respectively fabricated into 100 cm⁻¹ membranes. 2 The filter membrane (area) was tested for its filtration performance using an automated filtration tester (TSI 8130) at an airflow velocity of 0.45 m / s. The results are as follows: Figure 4 As shown. From Figure 4 It can be seen that the resistance of the ferroelectric polymer nanofiber membrane obtained in Example 1 is 235 Pa, and the resistance of the ferroelectric polymer nanofiber membrane obtained in Example 2 is 247 Pa, slightly higher than that of Example 1. The resistance of both is ≤250 Pa. Furthermore, the filtration efficiency of the ferroelectric polymer nanofiber membranes obtained in Examples 1 and 2 both reached 99.999%, exhibiting low resistance and high filtration efficiency, thus resolving the contradiction of "high efficiency inevitably leading to high resistance" in traditional filter materials.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a ferroelectric polymer nanofiber membrane, characterized in that, The preparation steps include the following: S1. Mix hexamethylene adipamide with formic acid to obtain PA solution, and obtain polyamide electrospun film substrate by electrospinning. S2. Dissolve the ferroelectric polymer in N,N-dimethylacetamide to obtain a ferroelectric polymer solution; S3. The ferroelectric polymer solution is dropped onto the surface of the polyamide electrospun membrane substrate, left to stand, and after a liquid film forms on the surface, water is added to immerse the polyamide electrospun membrane substrate. The substrate is then vacuum filtered and dried to obtain a ferroelectric polymer nanofiber membrane. The ferroelectric polymers in S2 include polyvinylidene fluoride or polyvinylidene fluoride derivatives.

2. The method for preparing a ferroelectric polymer nanofiber membrane according to claim 1, characterized in that, The mass concentration of PA solution in S1 is 13%-15%, the humidity of electrospinning is 35%-45%, the electrospinning rate is 0.3-0.5 mL / h, the electrospinning temperature is 23-27℃, and the electrospinning time is 3-7 h.

3. The method for preparing a ferroelectric polymer nanofiber membrane according to claim 1, characterized in that, Polyvinylidene fluoride derivatives include polyvinylidene fluoride binary copolymers, polyvinylidene fluoride terpolymers, or polyvinylidene fluoride tetrocopolymers.

4. The method for preparing a ferroelectric polymer nanofiber membrane according to claim 3, characterized in that, Polyvinylidene fluoride binary copolymers include poly(vinylidene fluoride-trifluoroethylene) copolymers; polyvinylidene fluoride terpolymers include poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) copolymers; polyvinylidene fluoride tetrpolymers include poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene-fluoroalkyl acrylate) copolymers.

5. The method for preparing a ferroelectric polymer nanofiber membrane according to claim 4, characterized in that, In poly(vinylidene fluoride-trifluoroethylene) copolymers, the molar ratio of polyvinylidene fluoride to trifluoroethylene is 55-65:35-45; in poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) copolymers, the molar ratio of polyvinylidene fluoride, trifluoroethylene, and chlorofluoroethylene is 60-65:25-30:5-10; in poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene-fluoroalkyl acrylate) copolymers, the molar ratio of polyvinylidene fluoride, trifluoroethylene, chlorofluoroethylene, and fluoroalkyl acrylate is 60-65:25-30:5-8:1-3.

6. The method for preparing a ferroelectric polymer nanofiber membrane according to claim 1, characterized in that, The mass concentration of the ferroelectric polymer solution in S2 is 1%-5%.

7. The method for preparing a ferroelectric polymer nanofiber membrane according to claim 1, characterized in that, The settling time in S3 is 30-40 seconds, the vacuum degree of vacuum filtration is 4-10 kPa, and the vacuum filtration time is 30-60 seconds.

8. The method for preparing a ferroelectric polymer nanofiber membrane according to claim 1, characterized in that, The drying temperature in S3 is 50-70℃, and the drying time is 2-3 hours.

9. A ferroelectric polymer nanofiber membrane prepared by the method for preparing a ferroelectric polymer nanofiber membrane according to any one of claims 1-8.

10. The application of the ferroelectric polymer nanofiber membrane according to claim 9 in the field of air filtration.

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